Dissertations / Theses on the topic 'Perovskites solar cell'

Dès à présent, le monde est face à des enjeux majeurs : augmentation de la production d'énergie, réduction des impacts de la production et de la consommation d'énergie sur l'environnement. La transition vers des énergies durables a déjà commencé. Le photovoltaïque a sa place parmi les énergies renouvelables qui permettront de relever ce défi. Ce travail de thèse porte sur les pérovskites hybrides halogénées et plus particulièrement leur utilisation dans des cellules solaires. En effet très récemment, ces matériaux ont attiré l'attention de la communauté scientifique en raison de leurs propriétés optoélectroniques remarquables : bande interdite directe, forte absorption de la lumière, longueurs importantes de diffusion des porteurs, propriétés optoélectroniques accordables mais aussi une fabrication aisée et à bas coût. En quelques années, le rendement a connu une augmentation spectaculaire de 3,8 % en 2009 à 22,7 % en 2017. Ainsi, ces derniers résultats placent les cellules pérovskites comme des concurrents potentiels face aux cellules solaires à base de silicium cristallin qui représentent aujourd'hui 90 % des cellules en service. Dans la conception des cellules solaires à base de pérovskite, la couche de pérovskite est généralement intercalée entre deux couches de transporteurs de charges : les couches de transporteurs d'électron et de trou (ETM et HTM, respectivement). La qualité de ces couches est essentielle pour obtenir de hauts rendements. Dans ce travail, les propriétés optoélectroniques des pérovskites halogénées sont étudiées ainsi que plusieurs couches de transport de charge
In the future, the world has to face up to major challenges: increasing the energy production, reducing the environmental impact, moving towards sustainability in energy, etc. Renewable energies such as photovoltaics can meet these challenges. This thesis concerns hybrid halide perovskite materials and their use in solar cells. These materials have recently attracted a lot of attention owing to their direct bandgaps, strong light absorption, large carrier diffusion lengths, tunable optoelectronic properties, and their facile and low-cost fabrication In few years, their energy conversion efficiency has rapidly increased from 3.8 % in 2009 to 22.7 % in 2017, hence approaching efficiencies of crystalline silicon based-devices which represent 90% of commercial photovoltaic cells. In the design of perovskite cells, the perovskite photoabsorber is generally sandwiched by two interfacial layers that yield selective charge collections: the hole and electron transport layers (HTM and ETM). Good quality and adapted interfacial layers are required to obtained high efficiency cells. In this thesis, both the perovskite material and the interfacial layers are investigated

Hybrid lead halide perovskites, AMX 3 compounds in which A = CH 3 NH 3 (MA), CH(NH 2 ) 2(FA), Cs; M = Pb,Sn; X = I, Br, Cl, display remarkable performance in solution-processed optoelectronic devices, including > 22% efficient thin film photovoltaic cells. These compounds represent the first class of materials discovered to exhibit properties associated with high performance compound semiconductors, while being formed at or near room temperature using simple solution chemistry techniques. This thesis is focused on the synthesis, structural characterisation and phase behaviour of MAPbI 3 , FAPbI 3 , A-site solid solutions and novel organic metal halide framework materials. The complete atomic structure and phase behaviour of methylammonium lead iodide is elucidated for the first time, including hydrogen positions, using high flux, constant wave-length neutron powder diffraction. At 100 K an orthorhombic phase, space group Pnma, is observed, with the methylammonium cations ordered as the C–N bond direction alternates in adjacent inorganic cages. Above 165 K a first order phase transition to tetragonal, I4/mcm, occurs with the unlocking of cation rotation, which is disordered primarily in the ab plane. Above 327 K a cubic phase, space group Pm3m, is formed, with the cations isotropically disordered on the timescale of the crystallographic experiment. The high temperature phase of formamidinium lead iodide, α-FAPbI 3 is shown for the first time to be cubic, (Pm3m), at room temperature using time-of-flight, high resolution neutron powder diffraction. Polymorphism and the low temperature phase behaviour of FAPbI 3 have been further investigated using reactor and spallation neutron sources with high resolution in temperature. A tetragonal phase, P4/mbm, is confirmed in the temperature range 140-285 K.The composition, structural and optical parameters of ’A’ site solid solutions (MA/FA)PbI 3 have been investigated by single crystal X-ray diffraction, UV-vis spectroscopy and 1 H solution NMR. A composition-dependent transition in the crystal class from tetragonal to cubic(or pseudo-cubic) at room temperature is identified and correlated to trends in the optical absorption. Novel hybrid materials with inorganic frameworks of varying dimensionality from 0D to 2D, including imidazolium lead iodide and piperazinium lead iodide, have been synthesised using various templating organic cations and their atomic structures solved by single crystal X-ray diffraction.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 68-72).
Perovskite is an emerging material for photovoltaic application that has reached 22.7% efficiency to date. Despite its excellent properties such as defect tolerance and long carrier lifetime, the high-performing perovskite material, methylammonium lead iodide (MAPI), which has 3D structure, is still unstable. Recent studies have hinted at the possibility of shifting focus from 3D to lower dimensional perovskite structures because lower dimensional structures are more environmentally stable for a longer period than the 3D analogues. We propose a detailed study where PbI₂ is used as the backbone and A-site cations are alloyed with various combinations: methylammonium, dimethylammonium, iso-propylammonium, and t-butylammonium. We measure the perovskite solar cell devices' performance and characterize the solar absorber to understand the optoelectronic properties. It is shown that the addition of large A-site cations change the structures into lower dimension, which increases the bandgap and decreases device performance properties such as efficiency, open-circuit voltage, and short-circuit current. Hence, there is a trade-off between having more stable perovskite and high-performance cell in using large A-site organic cations.
by Noor Titan Putri Hartono.
S.M.

Ce travail de thèse a pour sujet la conception des cellules solaires photovoltaïques à base de pérovskite hybride par le biais de la technologie d’impression jet d’encre. Les deux premiers chapitres font la présentation du contexte de la thèse, à savoir l’alimentation d’un réseau autonome de capteurs, et passent en revue les aspects scientifiques des technologies jet d’encre et photovoltaïque de nouvelle génération. Le troisième chapitre présente la mise au point d’une cellule photovoltaïque à l’état de l’art et son évolution vers une architecture imprimable à basse température de recuit. La problématique de la stabilité des cellules photovoltaïques à pérovskite est aussi abordée. La dernière partie présente les différents aspects et problématiques de l’impression par jet d’encre des trois couches internes d’une cellule solaire pérovskite. Au terme de ce travail la possibilité d’imprimer des cellules solaires pérovskites avec des rendements supérieurs à 10 % a été démontrée, le tout en condition ambiante et à basse température
This thesis is about the design of photovoltaic solar cells based on hybrid perovskite using inkjet printing technology. The first two chapters present the context of the thesis, namely the powering of an autonomous sensor network, and review the scientific aspects of inkjet and photovoltaic technologies. The third chapter presents the development of a state-of-the-art photovoltaic cell and its evolution towards a printable architecture at low annealing temperatures. The problem of the stability of photovoltaic cells with perovskite is also discussed. The last part presents the different aspects and problems of the inkjet printing of the three inner layers of a perovskite solar cell. At the end of this work the possibility of printing perovskite solar cells with efficiencies higher than 10% has been demonstrated, all in ambient conditions and at low temperature

In the last 10 years, the research interest has been drawn towards the hybrid organic-inorganic halide perovskites, an innovative material characterized by remarkable optoelectronic properties and by its simplicity of fabrication; hybrid halide perovskites are currently being employed as active material in solar cells, X-ray photodetectors and light emitting devices. The following thesis presents the characterization of two perovskite-based materials. The first is a methylammonium lead iodide (MAPbI3) thin film solar cell, which has been fabricated and characterized at the University of Konstanz (Germany), with the aim to optimize the deposition procedure. The second material is a methylammonium lead bromide (MAPbBr3) single crystal that have been characterized at the University of Bologna with surface photovoltage and photocurrent spectroscopies, as a function of the deposited dose of X-rays in order to monitor the induced effects of radiation. After the exposure to X-rays, the exciton binding energy, calculated from the surface photovoltage spectra, has been found to increase by 20 meV with respect to the not irradiated sample. A similar result has been found with the photocurrent spectroscopy. The reasons for the increase in binding energy is discussed and attributed to a change in polarizability of the single crystal. The recovery of the crystals has been registered as well and has shown that the material is able to return to the initial condition after just few hours from the last X-ray's deposition.

This thesis details the development of a novel photovoltaic device based on organometal halide perovskites. The initial focus of this thesis begins with the study of lighttrapping strategies in solid-state dye-sensitised solar cells (detailed in chapter 3). While I report enhancement in device performance through the application of near and far-field light-trapping techniques, I find that improvements remain step-wise due to fundamental limitations currently employed in dye-sensitised solar cell technology— notably, the available light-sensitising materials. I found a promising yet under researched family of materials in the methyl ammonium tri-halide plumbate perovskite (detailed in chapter 4). The perovskite light-sensitiser was applied to the traditional mesoscopic sensitised solar cell device architecture as a replacement to conventional dye yielding world-record breaking photo-conversion e!ciencies for solid-state sensitised solar cells as high as 8.5%. The system was further developed leading to the conception of a novel device architecture, termed the mesoporous superstructured solar cell (MSSC), this new architecture replaces the conventional mesoporous titanium dioxide semiconductor with a porous insulating oxide in aluminium oxide, resulting in very low fundamental losses evidenced through high photo-generated open-circuit voltages of over 1.1 V. This development has delivered striking photo-conversion ef- ficiencies of 10.9% (detailed in chapter 6).

To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.

Ces onze dernières années ont vu apparaitre les pérovskites organiques inorganiques hybrides (HOIPs) comme un passionnant domaine de recherche pour leur application potentielle dans les technologies du photovoltaïque (PV) en raison de leurs exceptionnelles propriétés optoélectroniques et de leur facilité de mise en oeuvre. Cependant, les matériaux HOIPs ont plusieurs inconvénients dont leur manque de stabilité en conditions opérationnelles. Améliorer celle-ci est l'un des plus grands défis à relever avant commercialisation. La formule générale est (A1,A2,A3,A4)Pb(X1,X2)3, où les sites A occupés par une distribution de 1 à 4 cations métalliques/organiques et les sites X par celle d’anions halogénures. Les défauts lacunaires natifs sont considérés comme une cause possible de dégradation des cellules solaires HOIPs. L'objectif de ce travail est de comprendre le rôle des défauts dans la stabilité à long terme des matériaux PV HOIPs. A cette fin, des défauts primaires ont été introduits de manière contrôlée par irradiation avec des électrons de haute énergie (1MeV) dans des lots de couches et cellules solaires (SCs) à base de divers composés HOIPs. Il s'agit notamment du prototype PV HOIPs, MAPbI3 (A1PbX13), et de nouveaux composés mixtes d’halogénures à triple ou quadruple cations, (CsMAFA)Pb(I1-xBrx)3 (A3PbX23) ou (GACsMAFA)Pb(I1-yBry)3 (A4PbX23). Les couches sont fabriquées selon la même procédure que les couches actives SCs et, ensuite, traitées dans des conditions similaires. Pour A1PbX13/A3PbX23, la structure SC est de type p-i-n avec des couches organiques pour le transport des trous et des électrons (HTL/ETL). Les couches sont déposées sur le substrat verre/ITO/HTL (PEDOT:PSS) sans ou avec couche supérieure ETL (PCBM). Pour A4PbX23, la structure SC est de type n-i-p avec des couches ETL inorganiques (TiO2) et HTL organiques (Spiro-OMeTAD). Les couches sont directement déposées sur du verre.La spectroscopie d'annihilation de positons donne une évidence directe de l'existence de défauts lacunaires natifs et induits par irradiation dans chaque composé. Les spectres d’absorbance en fonction de l’énergie montrent que le vieillissement naturel et après irradiation génère différentes populations de défauts dans chaque composé. De plus, celles-ci pour A1PbX13 et A3PbX23 diffèrent selon l'absence ou la présence de la couche supérieure ETL. Les populations de défauts évoluent pendant au moins 3 mois. Le vieillissement modifie (i) la bande interdite, (ii) les queues de bande de conduction/valence et (iii) l'absorption optique via des niveaux électroniques profonds. Les effets d’illumination sous laser varient aussi en fonction du vieillissement. L’asymétrie des pics de photoluminescence (PL) dans chaque composé sous illumination laser continue reflète une superposition de raies d’émission gaussiennes à énergie, FWHM et hauteur évoluant avec le temps d'illumination. Les transitions d'émission impliquent des niveaux électroniques localisés peu profonds dans A3PbX23/A4PbX23 et résonnants dans A1PbX13. De tels effets durent au moins 3 mois dans A4PbX23. Ces niveaux électroniques sont attribués à des populations de défauts spécifiquement induits par illumination. Le vieillissement naturel et après irradiation donne des spectres PL à décroissance temporelle résolue en une ou deux exponentielles. Le nombre et la durée de vie sont fortement influencés par l’irradiation initiale et la composition. Une amélioration frappante du fonctionnement PV pour le type SC p-i-n est induite par le vieillissement dû à l'irradiation. Le rendement quantique externe et les performances PVs ont des valeurs plus élevées pour l’état irradié que de référence durant 6 à 12 mois de vieillissement. Cela prouve que l'ingénierie des défauts par irradiation d'électrons à haute énergie a le potentiel de fournir des voies de traitement innovantes pour améliorer la stabilité à long terme des performances photovoltaïques HOIPs
During the last eleven years, Hybrid Organic Inorganic Perovskites (HOIPs) materials have emerged as an exciting topic of research for potential application in solar cell technologies due to their outstanding optoelectronic properties and processing advantages. However, HOIPs materials suffer from several drawbacks with, in peculiar, their lack of stability under operational conditions (light, bias, environment…). To improve this stability is one of the biggest challenges to be addressed before commercialization. The general formula for HOIPs is (A1,A2,A3,A4)Pb(X1,X2)3, where the A sites can be occupied by a distribution of 1 to 4 metallic/organic cations and X sites with halide anions. The role of native vacancy defects has been questioned as a possible cause for HOIPs solar cells degradation. The aim of this work is to understand the defect role in long term stability of HOIPs materials for photovoltaics. For this reason, primary defects were introduced in a controlled way via high energy electron irradiation (1MeV) in sets of layers and solar cells (SCs) fabricated using various HOIPs compounds. Those include the photovoltaic HOIPs prototype, MAPbI3 (A1PbX13), and emergent triple or quadruple cation mixed halide HOIPs, (CsMAFA)Pb(I1-xBrx)3 (A3PbX23) or (GACsMAFA)Pb(I1-yBry)3 (A4PbX23). The HOIPs layers are fabricated according to the same procedure as the HOIPs active SC layers and, subsequently, treated in similar conditions. For A1PbX13 and A3PbX23, the solar cells are of the p-i-n structure with organic hole and electron transport layer (HTL/ETL). The HOIPs layers are deposited on the glass/ITO/HTL (PEDOT:PSS) substrate without or with the top ETL layer (PCBM). For A4PbX23, the solar cells are of the n-i-p type with inorganic ETL (TiO2) and organic HTL (Spiro-OMeTAD) layers. The layers are directly deposited on glass without the ETL layer.Positron Annihilation Spectroscopy (PAS) gives direct evidence for native vacancy-type defects and irradiation induced ones in layers of each HOIP compound. The energy dependence of absorbance shows that natural and after irradiation ageing generates different defect populations in each HOIP compound. These populations strikingly also differ depending on the absence or presence of the top ETL layer for the A1PbX13 and A3PbX23 compounds. The defect populations evolve over ageing duration as long as 3 months. The prominent effects of ageing include (i) band gap modification, (ii) tailing of conduction/valence band extrema and (iii) optical absorption via deep subgap electronic levels. Illumination effects under laser also vary with ageing for each HOIP compound. Asymmetric photoluminescence (PL) peaks in each compound under continuous laser illumination reflect that radiative emission involves Gaussian emission rays with energy, FWHM and height evolving with illumination time. The emission transitions involve shallow localized electronic levels in A3PbX23 and A4PbX23 and resonant ones in A1PbX13. These electronic levels are attributed to specifically illumination-induced defect populations. Natural and after irradiation ageing result in PL decay lifetime spectra resolved into one or two exponential decay components. The decay components number and lifetime are strongly affected by the initial production of irradiation defects and HOIPs composition. Such effects last over 3 months at least in A4PbX23. The p-i-n solar cells exhibit most striking irradiation ageing induced photovoltaics performance. The External Quantum Efficiency (EQE versus photon energy) and the photovoltaic performance (I-V under illumination) of the irradiated solar cells have higher values than those in the reference SCs after 6 to 12 months of ageing. This gives evidence that defect engineering via high energy electron irradiation has a potential for providing innovative processing pathways to enhance the long-term stability of HOIPs photovoltaic performance

[ES] El objetivo principal de esta tesis es contribuir al avance de nuevas técnicas de elaboración con bajo coste, utilizando materiales tipo de cobre, indio, galio y selenio CIGS y Perovskita para aplicaciones en energía solar fotovoltaica. CIGS parecen ser adecuadas ya que son de bajo costo de producción y se han reportado eficiencias de conversión del 23,35%. Por otro lado, las perovskitas híbridas de haluros de plomo orgánicos-inorgánicos han aparecido como nuevos materiales excepcionales para celdas solares, especialmente porque la eficiencia de las celdas solares basadas en perovskita ha aumentado del 3.8% al 22.7% en menos de un lustro. Este trabajo se ha dedicado a experimentar sobre la elaboración y caracterización de CIGS y los perovskitas de metilamonio de yoduro de plomo de (MAPbI3) y formamidinio de yoduro de plomo (FAPbI3), que se utilizo tanto en la aplicación a las células solares de perovskitas y en las células Tándem CIGS-perovskita. Las películas se caracterizaron por difracción de rayos X, espectroscopía Raman, microscopía electrónica de barrido, análisis de espectroscopía de energía dispersiva, microscopía de fuerza atómica, transmisión electrónica microscopía, fotoluminiscencia y espectroscopia UV-Vis. En las capas de CIGS depositadas por electrodeposición se investigó el efecto de diferentes parámetros, También investigamos en detalle el efecto del contacto posterior en las propiedades estructurales y ópticas de CIGS. Constatamos que el tipo de contacto posterior tiene un efecto significativo en el rendimiento posterior de las películas delgadas CIGS. Además, estudiamos la técnica de espray pirólisis para producir películas CIGS. Se estudió el proceso de recocido, que es el factor clave para mejorar el rendimiento de las células solares. Se elaboraron diferentes películas delgadas constituidas de nuestro dispositivo CdZnS/CdS/CIGS/Mo eso utilizó una capa conductora transparente de CdZnS para minimizar la alineación de la interfaz. Por otro lado, se analizó el proceso de cristalización y la estabilidad de las capas MAPbI3. Las capas de MAPbI3 se trataron añadiendo antisolvente a diferentes velocidades. Durante el tratamiento se producen intercambios complejos que influencian muchas propiedades fisicoquímicas. Se investigaron las propiedades ópticas y eléctricas de las películas de MAPbI3. Para mejorar la estabilidad de MAPbI3, se incorporó tetrabutilamonio (TBA), observando una mejora en la formación de la estructura perovskita que crece en la dirección preferente (110). La fase cristalina de MAPbI3 dopada con TBA presenta mejor cristalinidad, gran tamaño de grano, morfología superficial sin poros lo que es adecuado para la fabricación de dispositivos optoelectrónicas con mayor rendimiento. Además, hemos identificado el impacto de TBA en las propiedades foto físicas de MAPbI3. En las muestras de TBA:MAPbI3 aumenta la intensidad de la fotoluminiscencia al reducir la densidad de los estados de trampa y la absorción óptica muestra un cambio significativo hacia longitudes de onda más largas y la banda prohibida óptica varió de 1.8 a 1.52 eV. Finalmente, las muestras dopadas con 5% TBA mejoraron su estabilidad y se encontró que después de 15 días la estabilidad permanecía excelente en una humedad de ~ 60%. Por otra parte, investigamos el efecto de guanidinio (GA) sobre las propiedades estructurales y ópticas de FAPbI3. La relación entre la fase a de perovskita deseable y la fase indeseable y se ha estudiado en función del contenido de GA. Se comprobó que el dopaje con GA es eficaz en el control de la relación de fases a/y y luego en la estabilización de la fase a. Los resultados muestran que añadiendo una cantidad adecuada del 10% GA conduce a una mejora de película de perovskita que se evidencia en la homogeneidad de la fase a estable, granos de mayor tamaño y capas libres de poros. Además, 10% GA:FaPbI3 demostraron una excelente estabilidad después de ser envejecidas durante 15 días en un ambiente con humedad relativa del 60%.
[EN] The thesis work presented is part of the work in the Laboratory of New Materials for Photovoltaic Energy in the main target to use low cost techniques for elaboration of Perovskite and Copper, indium, gallium, and selenium CIGS materials for photovoltaic application. Organic-inorganic lead halides perovskites have currently and exceptionally appeared as new materials for low cost thin film solar cells specially that the efficiency of perovskite based solar cell have jumped from 3.8% to 22.7% in short time.in other hand, CIGS solar cells record 23.35% efficiency and still can be boosted. Here, we report the elaboration and characterization of CIGS as well as methylammonium lead iodide perovskites MAPbI3 and formamidinuim iodide lead iodide perovskites FAPbI3 absorbers for perovskite-based solar cells and Tandem Perovskites/ CIGS. The thin films prepared were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis, atomic force microscopy (AFM), transmission electron microscopy (TEM), Photoluminescence analysis (PL) and UV-Vis spectroscopy. The first stage was devoted for the effect of different parameters on the growth of CIGS by electrodeposition and we investigate the impact of different back contact in structural and optical proprieties. In a second stage, we report the growth of CIGS films by spray pyrolysis, we studied the effect of experimental parameter also the annealing process which is the key factor for improving the performance of solar cells,subsequently we elaborated different films constituted CdZnS/CdS/CIGS/Mo solar cells, the approach is to change the toxic ZnO by using a transparent, conductive CdZnS layer. In other hand, MAPbI3 film was investigated in order to optimize the chemical composition and to study the crystallization process also to get sight about the stability of perovskite materials to meet the requirement of their application as an active layer in perovskite solar cell. For this purpose. the MAPbI3 film surface was treated by adding diethyl ether antisolvent with different rates. during the treatment complex exchanges are appearing at the same time under the influence of quite a lot of physicochemical properties. A whole understanding of this topic is critically important for improving solar cell performance. MAPbI3 doped by the tetrabutylammonium TBA is boosting the formation of perovskite structure, leading to a higher orientation along the (110) and shows better crystallinity, large grain size, pinhole-free, which is suitable for the manufacturing of the optoelectronic devices with higher performance. Also, we have identified the impact of TBA in the photo-physical properties, we have noticed that the TBA improve the photoluminescence emission by reducing the density of trap states and the optical absorption indicates a significant shift to the lower wavelength and optical bandgap varied from 1.8 to 1.52 eV. Finally, the stability was explored for 5% TBA, it found that after 15 days the stability remained excellent in relative humidity of ~60%. These results would be helpful for realizing stable and high performance MAPbI3-based devices. Furthermore, we inspect the effect of monovalent cation substitution of Guanidinium (GA) on the structural and optical properties of FAPbI3 thin films perovskites. The ratio between the desirable a-phase and the undesirable y yellow phase is studied as a function of GA content. GA doping is shown to be efficient in the control of a/y phases ratio and then in the stabilization of the a-FaPbI3 phase. We qualitatively evaluate the impact of 10% of guanidinium on the phase composition and microstructure of films. The results show that an adequate amount of 10% GA:FaPbI3 leads to a homogeneous perovskite film with stable a phase, large grains, and free pinholes. 10% GA: FaPbI3 films demonstrate excellent stability after aging for 15 days in relative humidity of~60%.
[CA] L'objectiu principal d'aquesta tesi és contribuir a l'avanç de noves tècniques d'elaboració de baix cost, fent servir materials d'aliatges del tipus de coure, indi, gal·li i seleni (CIGS) i perovskites, per a aplicacions en energia solar fotovoltaica. El CIGS sembla ser adequat ja que són de baix cost de producció i s'han reportat eficiències de conversió del 23,35%. D'altra banda, les perovskites híbrides d'halurs de plom orgànics-inorgànics han aparegut com a nous materials excepcionals per cel·les solars, especialment perquè l'eficiència de les cel·les solars basades en perovskites ha augmentat del 3.8% al 22.7% en menys d'un lustre. En el present treball, reportem l'elaboració i caracterització de CIGS y de perovskitas de iodur de plom de metilamoni (MAPbI3) i de iodur de plom de formamidini (FaPbI3) per a les cèl·lules solars de CIGS i tàndem Perovskites/CIGS. En les capes de CIGS dipositades per electrodeposició es va investigar l'efecte dels diferents paràmetres sobre el procés d'electrodeposició, així com l'efecte del contacte posterior sobre les propietats estructurals i òptiques del CIGS. Ens trobem que el tipus de contacte posterior té un efecte significatiu en la posterior interpretació de pel·lícules primes CIGS. A més, vam estudiar la tècnica de polvorització de la piròlisi per produir pel·lícules de CIGS. Es va estudiar el procés de recuit, que és el factor clau per millorar el rendiment de les cèl·lules solars. Es van produir diferents pel·lícules fines formades pel nostre dispositiu CdZnS/CdS/CIGS/Mo que utilitzaven una capa conductiva CdZnS transparent per minimitzar l'alineació de la interfície. D'altra banda, es van investigar perovskites MAPbI3, amb la finalitat d'optimitzar la composició química i estudiar el procés de cristal·lització també per a conèixer l'estabilitat dels materials de perovskita. la cristal·lització s'aconsegueix alentint la solubilitat en una solució saturada mitjançant l'addició d'una quantitat diferent de l'antisolvent d'èter dietílic. Durant el tractament apareixen al mateix temps intercanvis complexos sota la influència de moltes propietats fisicoquímiques. Una comprensió completa d'aquest tema és de vital importància per a millorar el rendiment. Amb l'objectiu principal d'augmentar l'estabilitat de MAPbI3, el tetrabutilamoni (TBA) es pot incorporar a MAPbI3, impulsant la formació de l'estructura de perovskita, la qual cosa porta a una major orientació al llarg de (110). MAPbI3 dopades amb TBA presenten una millora de la cristalinitat, major grandària, la qual cosa és adequada per a la fabricació de dispositius optoelectròniques de major rendiment. A més, hem identificat l'impacte de TBA en les propietats foto físiques de MAPbI3. Hem notat que el dopatge amb TBA millora tant l'emissió de la fotoluminiscència en reduir la densitat dels estats de trampes com l'absorció òptica on apareix un canvi significatiu de la banda òptica prohibida cap a longituds d'ona més llargues que significa disminuir l'energia del gap, que va variar de 1.8 a 1.52 eV. Finalment, es va explorar l'estabilitat per les perovsquites dopades amb 5%TBA. Es va trobar que després de 15 dies l'estabilitat romania excel·lent en un humitat de 60%. A més, hem estudiat FAPbI3 com un dels materials de perovskita més atractius. Hem investigat l'efecte de la substitució de guanidini (GA) sobre les propietats estructurals i òptiques de FAPbI3. La relació entre la fase a de perovskita desitjable i la fase indesitjable y es va estudiar en funció del contingut de GA. Es mostra que el dopatge amb GA és eficaç en el control de la relació de fases a /y i després en l'estabilització de la fase a-FaPbI3. Els resultats mostren que una quantitat adequada de 10% GA condueix a una pel·lícula homogènia amb fase a estable, grans grans lliures de porus i forats. Les pel·lícules de 10% GA:FaPbI3 demostraren una excel·lent estabilitat després de l'envelliment durant 15 dies en un ambient humit (humitat relativa de 60%).
Bouich, A. (2020). Study and Characterization of Hybrid Perovskites and Copper-Indium-Gallium Selenide thin films for Tandem Solar Cells [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/160621
TESIS

Perovskite solar cells (PSC) performance has risen rapidly the last few years with the current record having power conversion efficiency (PCE) of 22.1 %. This has attracted a lot of attention towards this alternative solar cell that can be manufactured with less energy and toxic material than traditional silicon solar cells. The purpose of this thesis is to reproduce high performance PSC from known recipe by Zhang et al. with potential of PCE reaching above 18 %. The thesis covers the theory regarding how a PSC operates, how they are measured and which parameters are important for a high performance PSC. The thesis includes a detailed manuscript on how to manufacture high performance PSC layer by layer and how to characterize the performance of the cells by IV-measurements. Furthermore, it includes scanning electron microscopy (SEM), by which the cells surface layers and cross-section could be evaluated. The result shows that it is possible to reproduce the PSC from literature and achieve a PCE of 18.8 %. However, the cells PCE decrease by 15 % during 2 hours of constant illumination, due to lack of stability. The manufactured PSC was used to power two catalysts that splits water into O2 and H2 and managed to reach a solar to hydrogen conversion efficiency (STHCE) of 13 %.

Depuis 5 ans, les pérovskites hybrides organiques-inorganiques sont apparues comme une nouvelle classe de semiconducteurs possédant des propriétés optoélectroniques très intéressantes pour les dispositifs photovoltaïques et émetteurs de lumière. Cette thèse porte sur une étude expérimentale de spectroscopie optique, qui s’inscrit dans le champ d’exploration des propriétés optiques et des effets excitoniques des pérovskites hybrides CH3NH3PbX3 avec X = I ou Br. Nous avons étudié les propriétés optiques de couches minces déposées par spin-coating et de monocristaux élaborés en solution. Les couches minces présentent une structure granulaire et une densité élevée de défauts qui induisent une grande variabilité des propriétés optiques. L’étude des monocristaux nous a permis de mettre en évidence les propriétés intrinsèques du matériau : émission d’excitons libres, couplage électron-phonon, dynamique de recombinaison des porteurs de charge. De plus, nous avons exploré l’impact de la transition de phase orthorhombique-tétragonale sur les propriétés optiques de CH3NH3PbI3. Enfin, nous avons quantifié l’effet de la réabsorption sur les propriétés d’émission des pérovskites hybrides. L’estimation précise de cet effet est particulièrement importante pour l’interprétation des propriétés optiques des pérovskites hybrides et explique la grande hétérogénéité des résultats dans la littérature
In the last five years, hybrid organic-inorganic perovskites have emerged as a novel class of semiconductors owing to their interesting electronic and optical properties for photovoltaic and light-emitting devices. This thesis reports an experimental study using optical spectroscopy to explore the optical properties and excitonic effects of hybrid perovskites such as CH3NH3PbX3 with X = I or Br.We studied the optical properties of spin-coated thin films and solution processed single crystals. Thin films present a granular structure and a high density of defects which induce a great variability of the optical properties. The study of single crystals allows us to highlight the intrinsic properties of material: free exciton emission, electron-phonon coupling and charge carriers recombination dynamics. Besides, we have investigated the impact of the orthorhombic-tetragonal phase transition on the optical properties of CH3NH3PbI3. Finally, we have quantified the effect of reabsorption on the emission properties of hybrid perovskites. The accurate estimate of this effect is particularly important for the interpretation of the optical properties of hybrid perovskites and explains the great heterogeneity of the results in the literature

En aquesta tesi es planteja fabricar una cel·la solar nano-estructurada de perovskita utilitzant alúmina nano-porosa anoditzada (NAA en les seves sigles en anglès) com a suport. Es va escollir la perovskita perquè les cel·les solars d'aquest material han assolit una eficiència molt similar a les cel·les existents de silici. A més a més, són barates i fàcils de preparar. El fet que la cel·la estigui nano-estructurada aportarà estabilitat davant la radiació, la temperatura i la humitat, sent aquest el principal problema d'aquests dispositius. Els nano-porus de la NAA tenen una forma cilíndrica molt ben definida on la grandària es pot controlar fàcilment sent tots els nano-porus iguals, el qual permetrà un major control sobre l'homogeneïtat del material infiltrat. Per tant l'objectiu de la tesi és aplicar la tecnologia de NAA a les cel·les solars de perovskita (CSP). Per això, primer va tenir lloc un procés de familiarització amb la fabricació i caracterització de NAA, així com dels CPSs d'alta eficiència, mitjançant mètodes estàndards coneguts. Un cop es va aconseguir la fabricació de NAA amb diferents mides de porus, la capa barrera d'alúmina que existeix entre l'alumini i el fons del porus va haver de ser eliminada, per poder aprofitar l'alumini (base de la NAA) com a contacte elèctric. Pel qual es va investigar i desenvolupar un nou mètode, ja que els mètodes existents no són adequats per eliminar la capa de barrera de gruixos superiors als 200 nm. Finalment es va estudiar la infiltració dels materials que formen una CSP en els nano-porus, mitjançant mètodes simples de deposició. Es va obtenir una cel·la solar nano-estructurada de perovskita utilitzant com a suport NAA, dels quals resultats d'eficiència són humils, pel fet que l'estructura plantejada en aquest treball és totalment innovadora. Fet que obre un ampli camí per futurs treballs.
En esta tesis se plantea fabricar una celda solar nano-estructurada de perovskita utilizando alúmina nano-porosa anodizada (NAA de sus siglas en inglés) como soporte. Se eligió la perovskita ya que las celdas solares de este material han alcanzado una eficiencia muy similar a las celdas existentes de silicio. Además, son baratas y fáciles de preparar. El hecho de que la celda este nano-estructurada aportará estabilidad frente a la radiación, temperatura y humedad, siendo este el principal problema de estos dispositivos. Los nano-poros de la NAA tienen una forma cilíndrica muy bien definida cuyo tamaño se puede controlar fácilmente siendo todos los nano-poros iguales, lo cual permitirá un mayor control sobre la homogeneidad del material infiltrado. Por lo que el objetivo de esta tesis es aplicar la tecnología de NAA a las celdas solares de perovskita (CSP). Para ello primero tuvo lugar el proceso de familiarización con la fabricación y caracterización de NAA, así como de CSPs de alta eficiencia, mediante métodos estándar conocidos. Una vez se consiguió la fabricación de NAA con diferentes tamaños de poro, la capa barrera de alúmina que existe entre el aluminio y el fondo del poro tuvo que ser eliminada, para poder aprovechar el aluminio (base de la NAA) como contacto eléctrico. Para lo cual se investigó y desarrolló un nuevo método, ya que los métodos existentes no son adecuados para eliminar capa de barrera de espesores superiores a los 200 nm. Finalmente se estudió la infiltración de los materiales que forman una CSP en los nano-poros, mediante métodos simples de deposición. Se obtuvo una celda solar nano-estructurada de perovskita utilizando como soporte NAA, cuyos resultados de eficiencia son humildes, debido a que la estructura planteada en este trabajo es totalmente novedosa. Lo cual abre un amplio camino para futuros trabajos.
In this thesis, the nanostructured perovskite solar cell manufacture using nanoporous anodic alumina (NAA) as a scaffold is proposed. The perovskite was chosen since the solar cells made with this material have achieved very similar efficiency to silicon cells. Also, they are cheap and easy to prepare. The fact that the cell will be nanostructured will provide stability against radiation, temperature and humidity, this being the main problem of these devices. The NAA nanopores have a very well defined cylindrical shape, whose size can be easily controlled, all nanopores being ident, which will allow greater control over the homogeneity of the infiltrated material. Therefore, this thesis aims to apply NAA technology to perovskite solar cells (PSCs). First, the familiarization process with the manufacture and characterization of NAA, as well as of high-efficiency PSCs, through known standard methods were carried out. Once the manufacture of NAA with different pore sizes was achieved, the alumina barrier layer that exists between the aluminium and the bottom of the nanopores had to be removed, to take advantage of the aluminium (base of the NAA) as an electrical contact. For which a new method was investigated and developed since existing methods are not suitable for removing barrier layer thicknesses greater than 200 nm. Finally, the infiltration of the materials that form a PSC within the nanopores was studied, utilizing simple deposition methods. A full working nanostructured perovskite solar cell was obtained using NAA as a scaffold, whose efficiency results are modest because the structure proposed in this work is novel. Which opens a wide path for future work.

L'energia fotovoltaica s'ha convertit en una de les alternatives més populars com a font d'energia renovable. Es basa en la transformació directa de radiació solar en electricitat. Es troba disponible a escala global i a més no necessita de cap transformador per convertir l'energia mecànica en energia elèctrica, el que fa que sigui fàcil d'implementar. Avui en dia, el material més utilitzat per a aplicacions fotovoltaiques segueix sent el silici. En canvi, el desenvolupament de noves tecnologies, més barates, fàcils de processar i que a més poden utilitzar-se en substrats flexibles, ha sorgit com a alternativa al silici. De totes elles, les perovskita basades en halurs de plom s'han convertit en una de les millors opcions per a la comunitat científica a causa de les excel·lents propietats fotovoltaiques que presenta. Tot i que les eficiències dels dispositius preparats amb perovskita han arribat al 25%, un valor que es troba molt proper al seu màxim teòric, els processos que tenen lloc en aquests dispositius encara no són del tot coneguts. En aquesta tesi es tracta d'obtenir informació sobre els processos dels transportadors de càrrega, des de com es generen fins a la recombinació, tant en les interfícies com a l'interior del propi material. Per això, s'han utilitzat diferents tècniques de caracterització avançades com el fotovoltatge transitori (TPV), la fotocorrent transitòria (TPC), l'extracció de càrrega (CE) i l’espectroscòpia d'absorció transitòria en l'escala del femtosegon (FSTA), obtenint importants conclusions sobre pèrdues i processos que afecten la recombinació de transportadors de càrrega que porten a pitjors eficiències
La energía fotovoltaica se ha convertido en una de las alternativas más populares como fuente de energía renovable. Se basa en la transformación directa de radiación solar en electricidad. Se encuentra disponible a escala global y además no precisa de ningún transformador para convertir la energía mecánica en energía eléctrica, lo que hace que sea fácil de implementar. Hoy en día, el material más utilizado para aplicaciones fotovoltaicas sigue siendo el silicio. En cambio, el desarrollo de nuevas tecnologías, más baratas, fáciles de procesar y que además pueden utilizarse en sustratos flexibles, ha surgido como alternativa al silicio. De todas ellas, las perovskitas basadas en haluros de plomo se han convertido en una de las mejores opciones para la comunidad científica debido a las excelentes propiedades fotovoltaicas que presenta. Aunque las eficiencias de los dispositivos preparados con perovskitas han alcanzado el 25%, un valor que se encuentra muy cercano a su máximo teórico, los procesos que tienen lugar en estos dispositivos aún no son del todo conocidos. En esta tesis se trata de obtener información acerca de los procesos de los transportadores de carga, desde cómo se generan hasta la recombinación, tanto en las interfaces como en el interior del propio material. Para ello, se han utilizado distintas técnicas de caracterización avanzadas como el fotovoltaje transitorio (TPV), fotocorriente transitoria (TPC), la extracción de carga (CE) y la espectrocopía de absorción transitoria en la escala del femtosegundo (fsTA), obteniendo importantes conclusiones sobre pérdidas
Photovoltaics have become one of the most popular renewable source of energy. Photovoltaic technologies transform sunlight into electricity, and they are also available worldwide, and they do not depend on the conversion of motive power, making this technology quite easy to implement. Nowadays, silicon is still the most used material for photovoltaics. Anyway, new photovoltaic technologies have emerged as alternatives to silicon, as they are cheaper, easier to process, and, they are possible to use on flexible substrates. Among them, lead halide perovskites have become one of the most popular choice in the scientific community, due to the great properties that this material presents. While efficiencies have risen above 25%, which is close to their maximum theoretical limit, there is still debate about the processes happening in the device. In this thesis, we try to gain insight into charge carrier processes from their generation to their recombination at both perovskite interfaces, and also in the bulk of the material. Using advanced characterization techniques, such as transient photovoltage (TPV), transient photocurrent (TPC), charge extraction (CE), and femtosecond transient absorption spectroscopy (fsTA) we obtained important findings about charge carrier losses, and artifacts affecting charge carrier recombination in functional devices that lead to lower power conversion efficiencies.

A range of electrical characterization techniques previously used for DSSC have been transferred to the study of planar perovskite devices. These include impedance spectroscopy (EIS), intensity modulated photovoltage spectroscopy (IMVS) and open-circuit voltage decay measurements (OCVD). An investigation into the observed response from these measurements has been carried out in order to gain a deeper understanding of device operation. Multiple processes with time constants on the microsecond, millisecond and second timescale were observed. The complimentary frequency and time domain techniques have been employed, showing excellent agreement between the two types of measurement. The high frequency (microsecond) process was found to be purely electronic in nature, which was linked to recombination. The geometric capacitance was shown to dominate this response, with accumulation of charge in the planar perovskite layer not observed. The lower frequency (millisecond and second timescale) processes were found to be linked to the coupling between recombination and the movement of ions. The low frequency EIS and IMVS measurements revealed that the recombination resistance was frequency dependent. The rate of change of the recombination resistance was found to be linked to the diffusion of ionic species. Activation energies for these processes were obtained (EA=0.55-0.66 eV) and shown to be in good agreement to computationally calculated values from literature for iodide vacancy migration. The same slow processes were also studied in the time domain using open-circuit photovoltage rise and decay measurements from well-defined equilibrium conditions. Comparable activation energies were also found using these techniques. The vacancy defect concentration was calculated to be 3x1019 cm-3, which is high enough for ionic double layers at the contacts to completely screen the built-in voltage across the perovskite at equilibrium in the dark. The slow dynamic processes observed under illumination or applied bias are therefore due to the rearrangement of ions in response to a changing electric field. As this rearrangement occurs, the rate of recombination is altered.

Aquesta tesis inclou el treball fet en ICIQ sobre fabricació, caracterització, i modelització de cel·les solars de perovskita híbrida. Agafades des de la recerca en altres tipus de cel·les solars, les eines de anàlisi, les metodologies i, més important, la seva interpretació han sigut analitzades i adaptades a aquest nou tipus de dispositiu. Llavors, aquestes tècniques han sigut utilitzades per analitzar i entendre la influència de quatre diferents i nous transportadors de forats electrònics sobre el voltatge de cel·les de perovskita. Un altre estudi ha investigat la acumulació dels electrons en les cel·les per mig de petits canvis en el gruix de cada capa i analitzant les mostres per mig de les mateixes tècniques. Des de la meva estada internacional en els grups de Dr. Piers Barnes i Prof. Jenny Nelson en Imperial College London un altre estudi ha sigut complert sobre la complexa interpretació dels resultats de espectroscòpia de impedància en presència de ions mobles en les cel·les de perovskita. També està exposat tot el programari lliure que ha sigut desenvolupat per la adquisició i processament de dades i per la modelització deriva-difusió de cel·les solars de perovskita. Una versió actualitzada de aquesta tesis es pot trobar en https://github.com/ilario/documents_in_latex-PhD_thesis/
Esta tesis incluye el trabajo hecho en ICIQ sobre fabricación, caracterización, y modelización de celdas solares de perovskita hibrida. Provenientes desde la investigación en otros tipos de celdas solares, las herramientas de análisis, las metodologías, y, aún más importante, su interpretación han sido analizadas y adaptadas a este nuevo tipo de dispositivo. Entonces, estas técnicas han sido utilizadas para analizar y entender la influencia de cuatros diferentes y novedosos transportadores de huecos electrónicos sobre el voltaje de celdas de perovskita. Otro estudio ha investigado la acumulación de electrones en las celdas utilizando pequeños cambios en el grosor de cada capa y analizando las muestras con las mismas técnicas. Desde mi estancia internacional en los grupos del Dr. Piers Barnes y de la Prof. Jenny Nelson en Imperial College London otro estudio ha sido llevado al cabo sobre la complexa interpretación de los resultados de espectroscopia de impedancia en presencia de iones móviles en las celdas de perovskita. Además, se expone todos los programas libres que han sido desarrollados para la adquisición y procesamiento de datos y para la modelización deriva-difusión de celdas solares de perovskita. Una versión actualizada de esta tesis se puede encontrar en https://github.com/ilario/documents_in_latex-PhD_thesis/
This thesis includes the work done in ICIQ about fabrication, characterization, and modelling of hybrid perovskite solar cells. Coming from other kind of solar cells, the analysis tools, the methods, and, most importantly, their interpretation have been analysed and adapted to this new kind of device. Then, these techniques has been employed for analysing and understanding the influence of four different and novel hole transport materials on perovskite solar cells voltage. Another study focussed on the electrons accumulation in devices employing small variations in each stacked layer thickness and analysing the samples using the same techniques. From by international stay in Dr. Piers Barnes and Prof. Jenny Nelson groups in Imperial College London another study was originated exploring the complex interpretation of impedance spectroscopy results when applied on perovskite solar cells with mobile ions. Finally, all the free software that has been developed for data acquisition and processing and for drift-diffusion modelling of perovskite solar cells have been exposed. An updated version of this thesis can be found on https://github.com/ilario/documents_in_latex-PhD_thesis/

Metal-halide perovskites show great promise as solution-processable semiconductors for efficient solar cells and LEDs. In particular, the diffusion range of photogenerated carriers is unexpectedly long and the luminescence yield is remarkably high. While much effort has been made to improve device performance, the barriers to improving charge transport and recombination properties remain unidentified. I first explore charge transport by investigating a back-contact architecture for measurement. In collaboration with the Snaith group at Oxford, we develop a new architecture to isolate charge carriers. We prepare thin films of perovskite semiconductors over laterally-separated electron- and hole-selective materials of SnOₓ and NiOₓ, respectively. Upon illumination, electrons (holes) generated over SnOₓ (NiOₓ) rapidly transfer to the buried collection electrode, leaving holes (electrons) to diffuse laterally as majority carriers in the perovskite layer. We characterise charge transport parameters of electrons and holes, separately, and demonstrate that grain boundaries do not prevent charge transport. Our results show that the low mobilities found in applied-field techniques do not reflect charge diffusivity in perovskite solar cells at operating conditions. We then use the back-contact architecture to investigate recombination under large excess of one charge carrier type. Recombination velocities under these conditions are found to be below 2 cm s⁻¹, approaching values of high quality silicon and an order of magnitude lower than under common bipolar conditions. Similarly, diffusion lengths of electrons and holes exceed 12 μm, an order of magnitude higher than reported in perovskite devices to date. We report back-contact solar cells with short-circuit currents as high as 18.4 mA cm⁻², giving 70% external charge-collection efficiency. We then explore the behaviour of charge carriers in continuously illuminated metal-halide perovskite devices. We show that continuous illumination of perovskite devices gives rise to a segregated charge carrier population, and we find that the distance photo-induced charges travel increases significantly under these conditions. Finally, we examine intermittancy in the photoluminescence intensity of metal-halide perovskite films.

This thesis focuses on the study of hybrid perovskites properties for the purposes of photovoltaic applications. During the almost four years PhD project that has lead to this thesis the record photovoltaic efficiency for this technology has in- creased from 10.9% to 22.1%. Such a significant pace of development can be com- pared with few other materials. It is for this reason that hybrid perovsites have at- tracted impressive research efforts. We approached the study of such unique ma- terials using computational ab-initio techniques, and in particular Density Func- tional Theory. We considered different materials, but most of the attention was concentrated on MAPI (CH 3 NH 3 PbI 3 ). The results are divided in three chapters, each exploring a different material prop- erty. The first chapter reports the electronic structure of the material bulk, sur- faces, and other electronic-related properties such as the rotation barrier for the organic component and the Berry phase polarization. The second chapter focuses on the vibrational properties primary employing the harmonic approximation but also extends to the quasi-harmonic approximation. The outcome of these calculations permitted us to calculate theoretical IR and Ra- man spectra which are in good agreement with different experimental measure- ments. The quasi-harmonic approximation was used to calculate temperature dependent properties, such as the Grüneisen parameter, the thermal dependence of heat capacity and the thermal volumetric expansion. The third and last chapter reviews the thermodynamic properties of binary halide compounds. The cobination of ab-initio calculations with the generalised quasi- chemical approximation has allowed to study the stability of mixed composition perovskites. The results certified a set of stable structures that could stand at the base of observed phenomena of photo-degradation of hybrid perovskite based devices. All three chapters have been written to understand the chemical and physical behaviour of hybrid perovskites and to extended and contribute to the under- standing of experimental work.

Les perovskites organiques-inorganiques en halogénures de plomb sont des matériaux très prometteurs pour la prochaine génération de cellules solaires avec des avantages intrinsèques tels que leur faible coût de fabrication (grande disponibilité des matériaux de base et leur mise en œuvre à basse température) et leur bon rendement de conversion photovoltaïque. Cependant, les cellules solaires pérovskites sont encore instables et montrent des effets d'hystérésis courant-tension délétères. Dans cette thèse, des résultats de l’analyse physique de couches minces de pérovskite à base de CH3NH3PbI3-xClx et de cellules solaires ont été présentés. Les caractéristiques de transport électrique et les processus de vieillissement ont été étudiés avec différentes approches.Dans une première étape, la synthèse du matériau pérovskite a été optimisée en contrôlant les conditions de dépôt des films en une seule étape telles que la vitesse de rotation (6000 rpm) de la tournette et la température de recuit des films (80 °C). Dans un second temps, des cellules solaires perovskites à base de CH3NH3PbI3-xClx ont été fabriquées en utilisant la structure planaire inversée et caractérisées optiquement et électriquement.Grace à l’utilisation de la spectroscopie optique à décharge luminescente (GDOES), un déplacement des ions halogénures a été observé expérimentalement et de façon directe sous l’application d’une tension électrique. Une longueur de diffusion ionique de 140 nm et un rapport de 65% d'ions mobiles ont été déduits. Il est montré que l'hystérésis courant-tension dans l'obscurité est fortement affectée par la migration des ions halogénures provoquant un écrantage substantiel du champ électrique appliqué. Nous avons donc trouvé sous obscurité un décalage de la tension à courant nul jusque 0,25 V et un courant de fuite jusque 0,1 mA / cm2 en fonction des conditions de mesure. Grâce aux courbes courant-tension en fonction de la température, nous avons déterminé la température de transition de la conductivité ions/électrons à 260K et analysé les résultats expérimentaux en utilisant l'équation de Nernst- Einstein donnant une énergie d'activation de 0.253 eV pour les ions mobiles.Enfin, le processus de vieillissement de la cellule solaire a été étudié avec des mesures optiques et électriques. Nous avons déduit que le processus de vieillissement apparaît d'abord à la surface des cristaux de pérovskite ainsi qu’aux joints de grains. Les mesures GDOES nous indiquent que les caractéristiques électriques des cellules pérovskites sont perdues par une corrosion progressive de l'électrode supérieure en argent causée par la diffusion des ions iodures
Organic-inorganic lead halide perovskites are very promising materials for the next generation of solar cells with intrinsic advantages such as a low-cost material due to the availability of source materials and low-temperature solution processing as well as a high power conversion efficiency of the sunlight. However, perovskite solar cells are still unstable and show deleterious current-voltage hysteresis effects. Inthis thesis, analyses of CH3NH3PbI3-xClx based perovskite thin films and solar cells are presented. The electrical transport characteristics and the ageing processes are investigated using different approaches.The synthesis of the halide perovskite materials is optimized in a first step by controlling the deposition conditions such as annealing temperature (80°C) and spinning rate (6000 rpm) in the one step-spin-casted process. CH3NH3PbI3-xClx based perovskite solar cells are then fabricated in the inverted planar structure and characterized optically and electrically in a second step.Direct experimental evidence of the motion of the halide ions under an applied voltage has been observed using glow discharge optical emission spectroscopy (GDOES). Ionic diffusion length of 140 nm and ratio of mobile iodide ions of 65 % have been deduced. It is shown that the current-voltage hysteresis in the dark is strongly affected by the halide migration which causes a substantial screening of the applied electric field. Thus we have found a shift of voltage at zero current (< 0.25 V) and a leakage current (< 0.1 mA/cm2) in the dark versus measurement condition. Through the current-voltage curves as a function of temperature we have identified the freezing temperature of the mobile iodides at 260K. Using the Nernst-Einstein equation we have deduced a value of 0.253 eV for the activation energy of the mobile ions.Finally, the ageing process of the solar cell has been investigated with optical and electrical measurements. We deduced that the ageing process appear at first at the perovskite grain surface and boundaries. The electrical characteristics are degraded through a deterioration of the silver top-electrode due to the diffusion of iodides toward the silver as shown by GDOES analysis

En aquesta tesi, l'estudi optoelectrònica i fabricació de diferents solució de processament de semiconductors inorgànics com ara PBS Quantum Dots i cèl·lules solars perovskita s'han fabricat. Al llarg d'aquesta tesi mesuraments optoelectrònics com fotoinducidas càrrega Extracció (PICE), fotoinducidas transitòria fotovoltaje (PIT-PV), fotoinducidas transitòria fotocorriente (PIT-PC) Laser transitòria Espectroscòpia d'Absorció (L-TAS) s'han realitzat a les cèl·lules solars eficients per tal de estudiar els diferents processos elèctrics interns presents en el dispositiu sota condicions de treball. Usant aquestes tècniques, el desdoblament dels nivells de Fermi s'han trobat per ser l'origen de la tensió en PBS QD cèl·lules solars (Capítol 2). A més, en el capítol 4.1 d'un estudi optoelectrònic intensiva s'ha realitzat a les cèl·lules solars perovskita mesoporosos, on es van descobrir decaïments biexponenciales de TPV i càrrega diferencial es va proposar manera tan adequada per obtenir la càrrega generada en el dispositiu. D'altra banda, els dispositius van ser fabricats utilitzant diferents polímers com HTM, i els resultats proporcionats van confirmar que la regeneració va ser superior al 90%, i que PIT-PV realitzat en condicions de foscor corresponen a la recombinació entre els orificis de la HTM i els electrons en el TiO2, com presentat en el capítol 4.2. A més, els resultats presentats en el capítol 4.3 mostrar que una capa de Al2O3 monoatòmic alentir el recombinació en el dispositiu d'augment de la tensió del dispositiu.
En esta tesis, el estudio optoelectrónico y la fabricación de diferentes solución de procesado de semiconductores inorgánicos tales como PbS Quantum Dots y células solares de perovskita se han fabricado. A lo largo de esta tesis medidas optoelectrónicos como fotoinducidas carga Extracción (PICE), fotoinducidas transitoria fotovoltaje (PIT-PV), fotoinducidas transitoria fotocorriente (PIT-PC) Laser transitoria Espectroscopia de Absorción (L-TAS) se han realizado a las células solares eficientes con el fin de estudiar los diferentes procesos eléctricos internos presentes en el dispositivo bajo condiciones de trabajo. Usando estas técnicas, el desdoblamiento de los niveles de Fermi ha sido encontrado como el origen de la tensión en PbS QD células solares (Capítulo 2). Además, en el capítulo 4.1 de un estudio optoelectrónico intensiva se ha realizado a las células solares perovskita mesoporosos, donde se descubrieron decaimientos biexponenciales de TPV y carga diferencial se propuso manera tan adecuada para obtener la carga generada en el dispositivo. Por otra parte, los dispositivos fueron fabricados utilizando diferentes polímeros como HTM, y los resultados proporcionados confirmaron que la regeneración fue superior al 90%, y que PIT-PV realizado en condiciones de oscuridad corresponden a la recombinación entre los huecos de la HTM y los electrones en el TiO2, como presentado en el capítulo 4.2. También, los resultados presentados en el capítulo 4.3 mostraron que una capa de Al2O3 monoatómico ralentiza la recombinación en el dispositivo de aumento de la tensión del dispositivo.
In this thesis, the optoelectronic study and fabrication of different solution processed inorganic semiconductor such as PbS Quantum Dots and perovskite solar cells have been fabricated. Along this thesis optoelectronic measurements such as PhotoInduced Charge Extraction (PICE), PhotoInduced Transient PhotoVoltage (PIT-PV), PhotoInduced Transient PhotoCurrent (PIT-PC) Laser Transient Absorption Spectroscopy (L-TAS) have been performed to efficient solar cells in order to study the different inner electrical processes present in the device under working conditions. Using these techniques, the splitting of Fermi levels have found to be the origin of the voltage in PbS QD solar cells (Chapter 2). Besides, in chapter 4.1 an intensive optoelectronic study has been performed to mesoporous perovskite solar cells, where biexponential decays of TPV were discovered and Differential Charging was proposed as suitable way to obtain the charge generated in the device. Moreover, devices were fabricated using different polymers as HTM, and results provided confirmed that the regeneration was over 90%, and that PIT-PV performed in dark conditions correspond to the recombination between the holes in the HTM and the electrons in the TiO2, as presented in chapter 4.2. Also, results presented in chapter 4.3 showed that a monoatomic layer of Al2O3 slow down the recombination in the device increasing the device voltage..

This thesis presents a study of hybrid solar cells, specifically looking at various methods which can be employed in order to increase the power conversion efficiency of these devices. The experiments and results contained herein also present a very accurate picture of how rapidly the field of hybrid solar cells has progressed within the past three years. Chapters 1 and 2 present the background and motivation for the investigations undertaken, as well as the relevant theory underpinning solar cell operation. Chapter 2 also gives a brief review of the literature pertinent to the main types of devices investigated in this thesis; dye-sensitised solar cells, semiconductor sensitized solar cells and perovskite solar cells. Descriptions of the synthetic procedures, as well as the details of device fabrication and any measurement techniques used are outlined in Chapter 3. The first set of experimental results is presented in Chapter 4. This chapter outlines the synthesis of mesoporous single crystals (MSCs) of anatase TiO₂ as well as an investigation of its electronic properties. Having shown that this material has superior electronic properties to the conventionally used nanoparticle films, they were then integrated into low temperature processed dye-sensitised solar cells and achieved power conversion efficiencies of > 3%, exhibiting electron transport rates which were orders of magnitude higher than those obtained for the high temperature processed control films. Chapter 5 further investigates the use of MSCs in photovoltaic devices, this time utilising a more strongly absorbing inorganic sensitiser, Sb₂S₃. Utilising the readily tunable pore size of MSCs, these Sb₂S₃ devices showed an increase in voltage and fill factor which can be attributed to a decrease in recombination within these devices. This chapter also presents the use of Sb₂S₃ in the meso-superstructured configuration. This device architecture showed consistently higher voltages suggesting that in this architecture, charge transport occurs through the absorber and not the mesoporous scaffold. Chapters 6 and 7 focus on the use of hybrid organic-inorganic perovskites in photovoltaic devices. In Chapter 6 the mixed halide, lead-based perovskite, CH₃NH₃PbI_3-xCl_x is employed in a planar heterojunction device architecture. The effects of Lewis base passivation on this material are investigated by determining the photoluminescence (PL) lifetimes and quantum efficiencies of treated and untreated films. It is found that passivating films of this material using Lewis bases causes an increase in the PLQE at low fluences as well as increasing the PL lifetime. By globally fitting these results to a model the trap densities are extracted and it is found that using these surface treatments decreases the trap density of the perovskite films. Finally, these treatments are used in complete solar cells resulting in increased power conversion efficiencies and an improvement in the stabilised power output of the devices. Chapter 7 describes the materials synthesis and characterisation of the tin-based perovskite CH₃NH₃SnI₃ and presents the first operational, lead-free perovskite solar cell. The work presented in this thesis describes significant advances in the field of hybrid solar cells, specifically with regards to improvements made to the nanostructured electrode, and the development and implementation of more highly absorbing sensitizers. The improvements discussed here will prove to be quite important in the drive towards exploiting solar power as a clean, affordable source of energy.

The aim of the work presented in this thesis is to study the opto-electronic properties of semi-conducting perovskite materials when being used in unconventional solar cell device configurations. Being a young technology, perovskites as solar cell materials have seen an unparalleled rise in the research community which has driven the fastest performance inflation to power conversion efficiencies competing with the ones of long established single crystalline technologies. The ability to process perovskites inexpensively makes them the new hope in the fight against climate change. Herein device architectures were developed with a special focus on potential commercial applications. Initially the work in this thesis has been motivated by the interest in crystal growth and morphology of perovskite thin-films, which has led to the study of confined crystal growth within microstructures. Controlling the crystal domain geometry enabled the fabrication of enhanced semi-transparent devices. More efforts were directed into the improvement of specifically neutral colour semi-transparent devices, which could be improved via a simple treatment of selectively attaching shunt-blocking layers. Furthermore, a back-contacted perovskite device design was introduced, which allows not only for the fabrication of a new type of perovskite solar cell, but also represent a great material testing platform to study perovskite and electrode characteristics. This led to the discovery of charge transport distances, that exceed those of other thin-film devices. Finally, perovskite-on-silicon tandem solar cell designs were analysed through a rigorous optical model to estimate the expected real world energy yield from such systems. Important implications include the fact that two terminal tandem solar cells come close to four-terminal configurations and can overall compete, in relative terms, well with established single junction silicon cells.

Over the last 4 years, perovskite solar cells emerged as an attractive, highly efficient, and low-cost alternative to established, conventional photovoltaic technologies. The power conversion efficiency of these devices recorded an unprecedented rise, currently exceeding certified values of 20%. This thesis covers a number of technological advancements which lead to improved photovoltaic performance, as well as vital insight into some more fundamental aspects of the perovskite device operation. The focus of this body of work is primarily directed towards the electric contact in the PV stack which is responsible for electron collection. The motivation of the study presented here is given in Chapter 1, and includes a brief summary of the current energy landscape. Chapter 2 introduces the theoretical background of photovoltaic technology, starting from the basics of semiconductor physics, through to the principles of solar cell operation, as well as some characteristic properties of the perovskite materials. Details of the experimental methods used in this study are reported in Chapter 3. Chapter 4 reports the development of a low temperature process (sub-150 °C) for the manufacture of perovskite solar cells. Dispersions of pre-synthesised, highly crystalline TiO2 nanoparticles were used as an electron selective contact, which eliminated the high temperature sintering step. Chapters 5, 6 and 7, report the interface modification of an n-type contact, resulting in a substantially improved device operation and suppression of hysteresis phenomenon which is characteristic of perovskite photovoltaics. Fullerene-based materials have been found to make excellent electronic contact with halide perovskite materials, and are shown to be far superior to commonly used metal oxides. The facilitated electron collection allows enhancements in the photovoltaic performance of these devices. Furthermore, the organic layers used in this study can be processed at low temperatures. Finally, the development of transparent conductive electrodes based on silver nanowires is presented in Chapter 8. The fabricated electrodes exhibit low sheet resistance, high degree of transparency, and can be processed at low temperatures, allowing them to be compatible with processing on flexible substrates and multi-junction architectures. The application of silver nanowires in different perovskite solar cell architectures is also reported.

Perovskite solar cells are a very promising photovoltaic technology which was first reported in 2009 and developed very rapidly. The crystallisation within perovskite films is highly dependent on processing environments, such as temperature, humidity, atmosphere, even light, which makes the fabrication of perovskite solar cells rather lab-dependent and poorly reproducible. One strategy to overcome this problem is to develop a controlled synthesis of perovskite nanocrystals which can then be ordered into films in a separatestep. In this thesis, optimisation of planar perovskite solar cells is carried out by the engineering of perovskite film fabrication methods. Different deposition methods along with different process factors such as solvents, temperature and precursor recipes are compared. One step spin-coating method with the recipe of MAI:PbCl2=3:1 gives the best PCE of 12.1 ± 0.7 % in air with controlled humidity of < 35%, showing high reliability and reproducibility. Doping of TiO2 layers with Zn2+, Sn4+ and Nb5+ ions are carried out to investigate the impacts of doping ions in different valence states on the electron-transporting properties of TiO2 ETLs. The different doping ions shift the flat band potential differently. Zn2+ largely negatively shifts the flat band potential, whereas Nb5+ positively shifts and Sn4+ barely changes the flat band potential of TiO2. the Zn-doping of the TiO2 ETL decreases the performance of the cells. However, when a thin layer of Zn-doped TiO2 is deposited on top of the pristine TiO2 layer as interlayer, the cell efficiency is slightly improved. Following the cell optimisation, to achieve better control over the crystallisation process, a facile flow reactor is developed for the synthesis of MAPbX3 perovskite nanocrystals at low temperature, which are further used for perovskite solar cells. The nanocrystals show narrow size distribution, good emissive properties and high stability. The bandgap of the nanocrystals was easily tuned between 485-745 nm by changing the halide composition. The photoluminescence of the MAPbI3 NCs in the first supernatant can also be tuned by changing the process parameters such as temperature, residence time and ligand concentration. However the impacts are more complex in the second supernatant in toluene with the appearance of multiple peaks in the PL spectra. It could be resultedfrom the formation of smaller NCs due to the reprecipitation of the incompletely removed reactants when added into toluene, or the fragmentation of the NCs upon dispersion into toluene, but better understanding is still needed. In the last part of the thesis, the synthesised MAPbI3 nanocrystals are investigated in perovskite solar cell applications. They have been applied as interlayers at the perovskite HTM interface, where they improved the stability of the devices towards moisture. The nanocrystals and their bulk by-products are also used as active light-absorbing layers for perovskite solar cells, delivering the best PCEs of 0.51% and 1.2% respectively, and notably showing outstanding water resistance. Further improvements in the cell performance could potentially be achieved by the removal of the insulating long chain ligands using effective ligand exchange treatments.

The work documented in this thesis concerns the control and modification of semiconducting perovskite thin films for their use in perovksite solar cells (PSCs). PSCs are a promising new thin-film technology, offering both high solar to electricity conversion efficiencies and cheap fabrication costs. Herein, the boundaries of perovskite solar cell research are pushed further by tackling several challenges important to the field. Initially, this work focuses on understanding why the best PSCs made so far have been mesostructured devices, with the perovskite infiltrated into a scaffold. It is shown that this can be seen as simply a fabrication aid; without the scaffold, thin films easily dewet from the substrate. By understanding the crucial parameters important in carefully controlling this dewetting, it is minimised, and it is shown that scaffold-free planar heterojunction devices with high efficiencies can be fabricated. This work leads on to the next section; the development of semi-transparent perovskite solar cells. In their present state, PSCs cannot compete with silicon as stand-alone modules. Here, the morphological control has been leveraged to realise a different embodiment – semi-transparent perovskite devices for use in building-integrated photovoltaics. Competitive efficiency and transparency are demonstrated. Moreover, a hybrid self-tinting power-generating window concept is fabricated, by combining the photovoltaic and electrochromic technologies. In the third section of the thesis, the limitations of the most studied perovskite material, methylammonium lead halide, are addressed: its overly wide bandgap and thermal instability. To address these, the chemical constituents of the perovksite are altered, and the development of more efficient and more stable materials are reported. These are likely to be important for perovskite modules to pass international certification requirements for commercialisation. Finally, an in-depth study on the effect of ambient moisture, relevant for considering scale-up and the fabrication environment needed, is carried out. It is shown that the presence of some moisture during film fabrication allows a reduction of defect states in the perovskite material, enhancing device performance and film quality.

The aim of this thesis is to develop a deeper understanding and the technology in the nascent field of solid-state organic-inorganic perovskite solar cells. In recent years, perovskite materials have emerged as a low-cost, thin-film technology with efficiencies exceeding 16% challenging the quasi-paradigm that high efficiency photovoltaics must come at high costs. This thesis investigates perovskite solar cells in more detail with a focus on incorporating plasmonic nanostructures and perovskite film formation. Chapter 1 motivates the present work further followed by Chapter 2 which offers a brief background for solar cell fabrication and characterisation, perovskites in general, perovskite solar cells in specific, and plasmonics. Chapter 3 presents the field of plasmonics including simulation methods for various core-shell nanostructures such as gold-silica and silver-titania nanoparticles. The following Chapters 4 and 5 analyze plasmonic core-shell metal-dielectric nanoparticles embedded in perovskite solar cells. It is shown that using gold@silica or silver@titania NPs results in enhanced photocurrent and thus increased efficiency. After photoluminescence studies, this effect was attributed to an unexpected phenomenon in solar cells in which a lowered exciton binding energy generates a higher fraction of free charge. Embedding thermally unstable silver NPs required a low-temperature fabrication method which would not melt the Ag NPs. This work offers a new general direction for temperature sensitive elements. In Chapters 6 and 7, perovskite film formation is studied. Chapter 6 shows the existence of a previously unknown crystalline precursor state and an improved surface coverage by introducing a ramped annealing procedure. Based on this, Chapter 7 investigates different perovskite annealing protocols. The main finding was that an additional 130°C flash annealing step changed the film crystallinity dramatically and yielded a higher orientation of the perovskite crystals. The according solar cells showed an increased photocurrent attributed to a decrease in charge carrier recombination at the grain boundaries. Chapter 8 presents on-going work showing noteworthy first results for silica scaffolds, and layered, 2D perovskite structures for application in solar cells.

In the present work, anomalous distortions occurring in the current-voltage characteristic of perovskite solar cells (PSCs), usually called J-V curve hysteresis, are studied by several methods. This includes dynamic direct current (DC) mode J-V experiments and impedance spectroscopy (IS) analyses in dark and under illumination. The J-V curves of PSCs were measured under different conditions showing capacitive hysteretic currents. This is related with low frequency excess capacitance in the IS spectra. These two features are correlated with the response of mobile ions in space charge regions close to the interfaces. The large values of capacitance under illumination in the sub-Hz regime were explained in terms of mobile ions space charges and chemical capacitances assuming a proportionality between the number of ionized/activated mobile ions and the concentration of charge carriers and photon fluence.
En el presente trabajo se estudian por varios métodos las distorsiones anómalas en la característica de corriente-voltaje de las celdas solares de perovskita (PSC), típicamente llamada histéresis de J-V. Esto incluye experimentos dinámicos de J-V en modo de corriente continua (DC) y análisis de espectroscopía de impedancia (IS) en oscuridad y bajo iluminación. Las curvas J-V en oscuridad de las PSCs exhiben corrientes capacitivas, relacionadas con un exceso de capacitancia de baja frecuencia en los espectros de IS. Estas dos características están correlacionadas con la respuesta de iones móviles en regiones espaciales de carga hacia las interfaces. Los grandes valores de capacitancia bajo iluminación a frecuencias por debajo de las unidades de Hz se explicaron en términos de regiones de cargas espaciales de iones móviles y capacitancias químicas, suponiendo una proporcionalidad entre el número de iones móviles ionizados/activados y la concentración de portadores de carga y flujo de fotones.

Historically, the interfaces and charge transportation layers dictate the performance in heterojunction solar cells. This thesis addresses the interface behaviours and the interfacial layers within perovskite solar cells (PSCs), and provides insights and practicable solutions to facilitate the realisation of efficient PSCs. To achieve efficient charge collection with interlayer fabricated with low-temperature processes, a graphene-TiO₂ nanocomposite is demonstrated; By investigating the carrier transport, we found the insertion of graphene improved the electron collection efficiency with its high surface area and ballistic carrier conduction properties, and in conjunction with pre-synthesised TiO₂, we have successfully circumvented the need for high-temperature annealing, enabling the whole device to be fabricated at under 150 °C. While the anomalous hysteresis behaviour which is widely observed in regular PSCs structure is a significant problem, the quest of stable PSCs seems to be answered by the use of inverted PSCs structures. We show a detailed development of inverted PSCs which are deconstructed layer by layer. Numerous approaches have been tailored to improve interfaces, and energy levels between layers, leading to an efficient and hysteresis-free perovskite solar cells. Lastly, an in-depth study of impurity doping is investigated using Al³⁺. The doping with small metal ions in the perovskite precursor has been found to influenced the crystallisation and optoelectronic properties of the perovskite crystals. Here, for the first time, the correlation between reduced structural crystal defects is clearly linked to enhanced photovoltaic properties, with the best performance for the lowest electronic disorder in the CH₃NH₃PbI₃ crystal.

Solar cells based on organohalide perovskites (PSCs) have made rapid progress in recent years and are a promising emerging technology. An important next evolutionary step for PSCs is their up-scaling to commercially relevant dimensions. The main challenges in scaling PSCs to be compatible with current c-Si cells are related to the limited conductivity of the transparent electrode, and the processing of a uniform and defect-free organohalide perovskite layer over large areas. In this work we present a generic and simple approach to realizing efficient solution-processed, monolithic solar cells based on methylammonium lead iodide (CH₃NH₃PbI₃). Our devices have an aperture area of 25 cm² without relying on an interconnected strip design, therefore reducing the complexity of the fabrication process and enhancing compatibility with the c-Si cell geometry. We utilize simple aluminum grid lines to increase the conductivity of the transparent electrode. These grid lines were exposed to an UV-ozone plasma to grow a thin aluminum oxide layer. This dramatically improves the wetting and film forming of the organohalide perovskite junction on top of the lines, reducing the probability of short circuits between the grid and the top electrode. The best devices employing these modified grids achieved power conversion efficiencies of up to 6.8%.

Over the last five years hybrid organic-inorganic metal halide perovskites have attracted strong interest in the solar cell community as a result of their high power conversion efficiency and the solid opportunity to realise a low-cost as well as industry-scalable technology. Nevertheless, several aspects of this novel class of materials still need to be explored and the level of our understanding is rapidly and constantly evolving, from month to month. This dissertation reports investigations of perovskite solar cells with a particular focus on their local chemical composition. The analytical characterisation of such devices is very challenging due to the intrinsic instability of the organic component in the nanostructured compounds building up the cell. STEM-EDX (Scanning Transmission Electron Microscopy - Energy Dispersive X-ray spectroscopy) was employed to resolve at the nanoscale the morphology and the elemental composition of the devices. Firstly, a powerful procedure, involving FIB (Focus Ion Beam) sample preparation, the acquisition of STEM-EDX maps and the application of cutting edge post-processing data techniques based on multivariate analysis was developed and tested. The application of this method has drastically improved the quality of the signal that can be extracted from perovskite thin films before the onset of beam-induced transformations. Morphology, composition and interfaces in devices deposited by using different methodologies and external conditions were then explored in detail by combining multiple complementary advanced characterisation tools. The observed variations in the nanostructure of the cells were related to different photovoltaic performance, providing instructive indications for the synthesis and fabrication routes of the devices. Finally, the main degradation processes that affect perovskite solar cells were probed. STEM-EDX was used in conjunction with the application of in situ heating, leading to the direct observation of elemental species migration within the device, reported here for the first time with nanometric spatial resolution. Further analyses, involving a set of experiments aimed to study the effects of air exposure and light soaking on the cells, were designed and performed, providing evidence of the main pathways leading to the drastic drop in the device performance.

Les énergies renouvelables peuvent à la fois répondre au besoin croissant en énergie tout en répondant à la nécessité de décarboniser l’énergie. La ressource énergétique solaire est quasi infinie (la terre reçoit plus d’énergie solaire en une heure qu’elle en consomme en un an) mais reste pourtant peu exploitée. Les cellules solaires hybrides à base de perovskite connaissent depuis les années 2000 un essor sans précédent dans le monde de la recherche en technologies solaires. Elles appartiennent à la catégorie des films minces, et nécessitent donc bien moins de matière première que les cellules au silicium, pour le moment largement majoritaires sur le marché. Cependant, elles n’absorbent pas au-delà de 800 nm, et tout l’infra-rouge est donc non converti par ce type de cellules solaires. Ce doctorat a pour but d’augmenter l’absorption dans l’infrarouge et donc le rendement de la cellule solaire. Pour cela, on y place des particules appelées nanoparticules d’upconversion, qui convertissent un rayonnement infrarouge en visible. Il s’agit d’un phénomène d’absorption simultané de deux photons. Cet effet ayant un rendement assez faible, il convient de le booster par l’insertion de nanoparticules métalliques afin de pouvoir bénéficier de l’augmentation de l’intensité du champ électromagnétique dans leur voisinage proche (effet dit plasmonique). En combinant les deux types de particules on parvient à augmenter l’absorption des particules à upconversion, et en les plaçant tous deux dans une cellule solaire, on augmente donc son rendement
Renewable energies represent nowadays one of the keys that can tackle at the same time energy supply needs and a sustainable environmental behavior. Photovoltaic devices convert the energy of sunlight into electricity, and solar energy remains one of the most common renewable energy sources. In the search for cost-effective solar cells, the recently discovered solution-processable hybrid organic-inorganic perovskites are considered as one of the most important candidates. They belong to the category of thin-film technologies and require much less and as abundant resource than Si. One limiting parameter of such photovoltaic devices is however the absorption of low-energy photons (wavelength over 800 nm, the near-infrared range). In order to address this specific loss of sub bandgap photons’ absorption, this PhD thesis aims to develop plasmonic-enhanced upconversion approaches to extend the spectral sensitivity of organo-metal halide perovskite solar cells to the near-IR spectrum. Near-infrared-to-visible up-conversion fluorescent materials can be used to widen the part of the spectrum used for electric current generation. Two low-energy photons are added up in order to give a higher energy photon. However, this effect has a rather small efficiency. This effect being quite inefficient, the idea is to combine those particles with metallic nanoparticles, that have the property to enhance electromagnetic field intensity at a certain wavelength (this is called plasmonic effect). By combining both types of particles, we thus enhance the activity of up-conversion materials (higher emission). Once implemented in a perovskite solar cell, this increases its efficiency

Lead halide perovskite solar cells (PSCs) are considered the fastest growing photovoltaic technology, reaching an outstanding certified power conversion efficiency of 24.2% in just 10 years. The best performing PSCs are based on polycrystalline films, where the presence of grain boundaries and ultra-fast crystallization limit the further development of their performance by increasing the bulk and surface defects. Compared to their polycrystalline counterparts, single crystals of lead halide perovskites have been shown to possess much lower trap-state densities and diffusion lengths exceeding 100𝜇m. In this thesis, using a solution space-limited inverse temperature crystallization method, twenty-microns thick single crystals of MAPbI3 are grown directly on the charge selective contact to construct highly reproducible p-i-n inverted type solar cells with fill factors(FF) as high as 84.3% and power conversion efficiencies (PCEs) exceeding 21% under 1 sun illumination (AM 1.5G). A key requisite for high PCEs is avoiding surface hydration, in which moisture attacks the perovskite/transporting layer interface and causes a significant decrease in short-circuit current. These solar cells set a record for single crystal PSCs, and highlight the potential of single crystal PSCs in furthering perovskite photovoltaic technology.

碩士
東海大學
化學系
107
Inorganic-organic perovskite solar cell are one of the most significant materials because of its high absorption and power conversion efficiency and belongs to the direct bandgap, that can make the solar cell thin and can be high efficiency. At present, many types of perovskite solar cells have been developed, and many different electron transport layers, perovskite layers and hole transport layers have been exchanged or replaced. However high efficient perovskite solar cells still uses high temperature sintered TiO2 as the electron transport layer,3D perovskite as the perovskite layer and Spiro-OMeTAD as the hole transport layer. However, since TiO2 needed this structure is too high sintering temperature(550 oC), and therefore increase the difficulty and cost of fabrication of the device, and the 3D perovskite is closely stacked, resulting decreased stability and have more hysteresis-free. In our research, we using different low-temperture to be our electron transport layer, and added urea into 2D perovskite(BA2(MA)2Pb3I10) .The efficiency of ‘ITO/SnO2/CPTA/BA2(MA)2Pb3I10/Spiro-OMeTAD/Au’ was 7.9 % under AM 1.5 sunlight.

abstract: A Fundamental study of bulk, layered, and monolayers bromide lead perovskites structural, optical, and electrical properties have been studied as thickness changes. X-Ray Diffraction (XRD) and Raman spectroscopy measures the structural parameter showing how the difference in the thicknesses changes the crystal structures through observing changes in average lattice constant, atomic spacing, and lattice vibrations. Optical and electrical properties have also been studied mainly focusing on the thickness effect on different properties where the Photoluminescence (PL) and exciton binding energies show energy shift as thickness of the material changes. Temperature dependent PL has shown different characteristics when comparing methylammonium lead bromide (MAPbBr3) to butylammonium lead bromide (BA2PbBr4) and comparing the two layered n=1 materials butylammonium lead bromide (BA2PbBr4) to butylammonium lead iodide (BA2PbI4). Time-resolved spectroscopy displays different lifetimes as thickness of bromide-based perovskite changes. Finally, thickness dependence (starting from monolayers) Kelvin Probe Force Microscopy (KPFM) of the layered materials BA2PbBr4, Butylammonium(methylammonium)lead bromide (BA2MAPb2Br7), and molybdenum sulfide (MoS2) were studied showing an exponential relation between the thickness of the materials and their surface potentials.
Dissertation/Thesis
Masters Thesis Electrical Engineering 2019

Ink-based semiconductors that come to mind today include conjugated molecules and polymers, colloidal quantum dots, metal halide hybrid perovskites, and transition metal oxides. These materials form an ink (solution/ suspension/ sol-gel) that can be applied and dried in ambient air to form high-quality films for optoelectronic devices. In this study, we will introduce the current understanding of ink-based lead and lead-free hybrid perovskite and perovskite-inspired thin films. Examples will be presented through time-resolved studies of the solidification to link the solid-state microstructure and device figures of merit to the ink’s formulation, drying, and solidification process. The perovskite crystallization kinetics characterized in situ during the solution process indicates an essential role by the inclusion of Cs+ and K+ alkali metal cations in perovskite inks. The film and device characterizations indicate the functions of mixed cation and halides in determining the optoelectronic properties. The further sophisticated design of perovskite inks enables significantly optimized charge dynamics, including exciton separation, inter-grain charge transfer, trap density, charge mobility, and charge collection efficiency. The considerably improved optoelectronic properties lead to higher charge collection efficiency and, therefore, better open-circuit voltage and fill factor for the Cs+-containing 3D perovskite devices in contrast to the control FAPbI3 one. Recent developments in ink formulation and processing that enable scalable ambient fabrication of high-quality perovskite semiconductor films will also be presented. These findings raise the possibility of developing more controlled perovskites for systematically addressing both charge dynamics and degradation mechanisms in concert for the timely commercialization of perovskite solar cells.

碩士
國立臺灣科技大學
化學工程系
103
Due to own the tunable band gap, high absorption coefficient (1.54x104 cm-1), low non-radiation carrier recombination and long carrier diffusion length, organic-inorganic hybrid perovskite materials received significant attention by many researchers in recent. There are many researchers used organic-inorganic hybrid perovskite materials as light-harvesting materials for solar cells. However, the perovskite materials is not stable in the ambient because it is very sensitive for the humidity and oxygen. Therefore, the performance of perovskite solar cells often affected by the deposition method, annealing temperature… 　　In this study, perovskite solar cells were fabricated inside the glove box under low humidity and oxygen content. For the structure of perovskite solar cells, titanium dioxide (TiO2) nanoparticles were used to construct the mesoporous structural layer. Perovskite light harvesting materials were coated on the TiO2 structural layer via two steps process. Firstly, PbI2, CH3NH3I and hole transport medium (HTM) were coated sequentially via spin coating. Then the metal electrode was deposited by thermal evaporation. From this study, we could observe that the coating method would affect the morphologies of perovskite material and influence the performance of solar cells. 　　In this study, the performance of perovskite solar cell fabricated by the optimal conditions can achieve Jsc=21.3 mA/cm2, Voc=0.99 V, FF=0.69, PCE=14.42 %.

博士
國立臺灣大學
化學研究所
106
Initially, we investigated the degradation of perovskite solar cells under operating situations through in situ X-ray diffraction and in situ X-ray absorption spectroscopies, which revealed that lead hydroxide iodide (PbIOH), a new phase that has not previously been identified as the degradation product of perovskite solar cells, was formed as an end decomposition product inside the cell. The formation of PbIOH could break the interface inside and be the key reason behind the problem of reduced cell life. In second part, we replaced the lead perovskite in carbon-electrode based solar cell with tin perovskite. In third part, we use a zwitterion additive to improve the film morphology of tin perovskite active layer by retarding nucleation process, and the efficiency of corresponding solar cells with 4 cm2 area can achieve 2.1%. In addition, the additive also significantly enhances the stability of device. The final part is about tin perovskite quantum material. We have successfully prepared tin perovskite nanoplate which demonstrates excellent quantum yield of 6.4%, narrow full width at half maximum (FWHM) of 37 nm, and wide tunability window.

碩士
中原大學
化學研究所
104
Solar cell research and development from 1954 to the first generation is now in its third generation dye-sensitized solar cell, however, due to the low absorption coefficient of the organic dye and the absorbance spectrum narrow, can not effectively get solar energy, so that the photoelectric conversion efficiency can not go beyond the first generation of conventional silicon solar cells. To compensate for the dye absorption spectrum of sunlight defects, particularly a quantum dot solar cells can be improved photovoltaic characteristics such problems. However, quantum dot solar cells with quantum dots using different materials, for example thirty-five (III-V) family of quantum dot solar cells will be connected to the surface of the electron hole easy to complex, resulting in decreased conductive element; or metal sulfide materials have chemical instability and other issues to be improved. To overcome these problems the quantum dot material, perovskite type lead halide sensitized material i.e. propose to do to resolve the policy. And then opened a new type of perovskite solar cells. In this paper, the development and application of the dye-sensitized solar cells and solar cell perovskite do for discussion.

碩士
國立成功大學
航空太空工程學系
105
The paper presents study of replacing the Pb element in the perovskite and using solvent engineering to fabricate perovskite solar cells. By replacing the Pb element to different metals to fabricate the solar cells, not only the mixture can have the advantages of each element, but also can enhance the performance of the perovskite solar cells liftime. Finally, we fabricated the inverted perovskite solar cells with the efficiency of 9.64%(CuBr2),10.56%(CuCl2),10.04%(CuI) by using the Cu metal. After 200 hours, the solar cells with 0.05M CuBr shows only approximately 5% drop in efficiency, whereas the base cell shows drop in efficiency around 50%. It appears that mixed perovskite solar cells with doubled metal cations can much improve the lifetime Key Words: mix perovskite、metal cation、perovskite solar cell、stability

碩士
國立宜蘭大學
化學工程與材料工程學系碩士班
105
The purpose of this thesis is to investigate the different process perovskite film for the perovskite solar cells (PSCs). The first part of this thesis was pervosktie materials of different halogen. In this stage, PSCs was made form TiO2 electron transport layer, CH3NH3PbI(3-x)Clx or CH3NH3PbI3 perovskite layer by One-step process, Sprio-OMeTAD hole transport layer and Ag electrode. In the same time, change heating temperature to preparation perovskite layer. First, CH3NH3PbI(3-x)Clx perovskite layer heat adjusted from 150℃ to 240℃.When heating temperature was 210℃, the current density was 10.98 mA/cm2 and efficiency obtained 4.67%. Second, CH3NH3PbI3 perovskite layer heat adjusted from 100℃ to 140℃. When heating temperature was 120℃, the current density was 13.88 mA/cm2 and efficiency obtained was 6.16%. In prove CH3NH3PbI3 pervosktie materials was better than CH3NH3PbI(3-x)Clx perovskite materials The second part of this thesis was mainly forcused on the One-Step process perovskite layer and Two-Step Process perovskite layer. In this stage, perovskite solar cells was made form TiO2 electron transport layer, CH3NH3PbI3 perovskite layer, Sprio-OMeTAD hole transport layer and Ag electrode. Two step process perovskite solar cells the current density increased form 10.98 mA/cm2 to 13.88 mA/cm2.The efficiency obatained was 8.06%. Make sure the Two-step process PSCs was better than One-step process PSCs. The third part of this thesis was the optimum condition PSCs. In this stage, PSCs was made form TiO2 electron transport layer, CH3NH3PbI3 perovskite layer by Two-step process, Sprio-OMeTAD hole transport layer and Ag electrode. In the same time, investigate effects PSCs of the diffirent PbI2 Volume. When use 80μL PbI2, the optimum condition PSCs attained current density of 20.87 mA/cm2 and the efficiency to a best value of 12.21%.

碩士
國立臺灣大學
光電工程學研究所
106
In the first part of this thesis, We synthesize TiO2 nanoparticles and fabricate low-temperature Perovskite solar cells in conventional structure using drop-casting solution process. Device performance was sequentially improved by several testing, including concentration, layer number, spin rate and the annealing temperature of TiO2 nanoparticles which serve as electron transporting layer (ETL) in perovskite solar cell. Annealing temperature and spin rate of Perovskite layer are also discussed in this part by analyzing the Scanning electron microscopy(SEM) figure of Perovskite of different temperature and measuring thickness of Perovskite at different spin rates, respectively. It proves that the drop-casting process, a fast and simple process, is beneficial for complete crystallization of Perovskite . We also discuss the difference between low-temp.(<150℃) TiO2 process and high-temp.( 550℃) sintering TiO2 by using AFM to measure the morphology of different TiO2 film and discussing its impact on the device performance. Finally the power conversion efficiency of the low-temperature Perovskite solar cells in this study has reached 13.42%, with a fill factor (F.F) of 66.45%. In the second part, we fabricated perovskite solar cell on flexible substrate. We found out that with the increase of TiO2 layer, the coverage of TiO2 increases, which is proved by AFM figure of different layer TiO2. Our best cell with tri-layer TiO2 has reached a power conversion efficiency of 6.67% . We also tested the bending stability of our flexible devices. After 500 bending cycles with radius of curvature set at 2.5mm, 91% of the original efficiency has remained. In order order to increase the conductivity of ITO on PEN substrate, we use Pedot between ITO and TiO2 and discuss the effect of Pedot.

碩士
中華科技大學
機電光工程研究所碩士班
103
With global warming and energy crisis ,many plans of renewable energy are invesigated to replace traditional fossil fuel. But all of they are still high cost, so I would like to find a low-cost way to fabricate solar cell which can be made on large-scale.Organometal halide perovskites have attracted many researcher as a promising light-harvesting material for high-efficiency in the short six years. Here we fabricate ZnO nanorod incorporating into Pero-vskite absorber layer, and control the growth time of nanorod to investigate the variation of conversion efficiency. We have power conversion efficiency of 7.76% when the ZnO nanorod grow 75 minutes, better than the PCE of 4.16% when grow 55 minutes.(as measured under simulated full sunlight),and with a good short-circuit current density Jsc of 20.08 mA/cm2 .This demonstrates that ZnO nanorod is a good charge collector in perovskite solar cell.