Dissertations / Theses on the topic 'CIGS solar cells'

This thesis studies the effects of Na diffusion in Cu(In,Ga)Se2 (CIGS) solar cells,caused by electrical Potential Induced Degradation (PID) and how to prevent it. Thiswas done by subjecting CIGS solar cells a temperature of 850C and an electrical biasfrom the backside of the glass substrate to the Mo back contact of the CIGS cell.When the bias was negative at the back contact the Na diffused in to the CIGS(degradation) and when it was positive the ions diffused out again (recovery). TheCIGS samples were electrically characterized with IV- and EQE-measurements duringthese conditions and compositional depth profiling was used to track the Nadistribution.This study showed that during degradation Na seemed to accumulate in the interfacesbetween the different layers in the CIGS cell. The buffer and window layers arestrongly affected by Na diffusion. Zn(O,S) buffer layer showed a clear difference inrecovery behavior compared to CdS buffer layer. The introduction of an Al2O3barrier layer between the CIGS and Mo back contact increased the degradation timefrom 50 h to 160 h. During this study it was also found that in some cases the CIGSsolar cells efficiency could be improved by degrading the cells and then recoveringthem, in the best case from 13% average energy efficiency to 15% efficiency.

An advancement of the two stage growth recipe for the fabrication of CIGS solar cells was developed. The developed advancement was inconsistent in producing samples of similar stoichiometry. This was a huge barrier for up scaling the process as the behavior of devices would be different due to variation in stoichiometry. Samples with reproducible stoichiometry were obtained once the heating rate of elements, selenium in particular was better understood. This is mainly attributed to the exponential increase of selenium flux after its evaporation temperature. Monitoring the selenium flux was vital in getting constant selenium fluxes. Few changes to the growth recipe were induced to optimize the amount of selenium being used. Depositions were done using constant selenium to metal flux ratio of 5. Elemental tradeoffs were observed as a result of the growth recipe change. These tradeoffs are in favor of the two stage growth recipe. The solar cells were fabricated on a soda lime glass substrate with a molybdenum back contact. Improper sample cleaning and storage were found to affect the deposition outcome of the molybdenum back contact. This also had a cascading effect on the absorber layer. Residual precipitates during deposition of CdS were avoided by increasing the spinner speed which increased the reaction rate. This is attributed to the growth of CdS either by cluster-by-cluster growth or by ion-by-ion growth. SEM, EDS were some important tools used to characterize the devices. EDS in particular, was used extensively at different stages throughout the growth process to ensure that we were heading in the right direction. Current-voltage (I-V) measurements were done to study the solar cell performance under light and dark.

The current trend concerning the thinning of solar cell devices is mainly motivated by economic aspects, such as the cost of the used rare-earth elements, and by the requirements of emergent technologies. The introduction of ultra-thin absorber layers results in a reduction of used materials and thus contributes to a more cost-effective and time-efficient production process.However, the use of absorber layers with thicknesses below 500nm gives rise to multiple apprehensions, including concerns regarding light management and the absorber’s quality.Therefore, this experimental work presents a novel solar cell architecture that aims to tackle the issues of optical and electrical losses associated with ultra-thin absorber layers. To that end, a Hafnium Oxide (H f O2) rear side passivation layer was introduced in-between the copper indium gallium (di)selenide Cu(In, Ga)Se2, CIGS-based absorber layer and the Molybdenum (Mo) back contact. Then, the proposed Potassium Fluoride (KF) alkali treatment successfully established point contacts on the ALD-deposited oxide layer, resulting in a passivation effect with minimum current blockage.The established cell architecture showed significant improvements regarding both open circuit voltage (Open-Circuit Voltage (Voc)) and efficiency when compared to unpassivated reference devices. The used solar cell simulator (SCAPS) attributes the observed improvements to a reduced minority carrier recombination velocity at the rear side of the device. Moreover, the provided photoluminescence (PL) results report a higher peak intensity and lifetime for passivated devices.Furthermore, the overlay of the given external quantum efficiency (EQE) spectra with the performed simulations show that the HfO2 passivation layer improves the optical reflection from the rear contact over a wavelength interval ranging from 500 to 1100 nm, resulting in a short circuit current (Jsc) improvement. An increased quantum efficiency observed throughout almost the entire measurement range, confirms that the enhance in Jsc is also due to electronic effects.Here, a produced solar cell device including a 3nm-thick HfO2 rear passivation layer and a 500nm-thick 3-stage CIGS absorber, achieved a conversion efficiency of 9.8%.Further, the approach of combining an innovative rear surface passivation layer with a fluoride-based alkali treatment resulted in the development and successful characterisation of a 1-stage, 8.6% efficient solar cell. Such result, mainly due to a short circuit current (Jsc) enhancement, supports the introduction of more straightforward production steps, which allows a more cost-effective and time-efficient production process. The produced device consisted of a 500nm-thick CIGS absorber, rear passivated with an ultra-thin (2nm) HfO2 layer combined with a 0.6M KF treatment.
Den nuvarande trenden när det gäller solcellsanordningar huvudsakligen motiveras av ekonomiska aspekter, såsom kostnaden för att använda sällsynta jordartsmetaller, och av kraven i ny teknik. Införandet av ultratunna absorptionsskikt resulterar i en minskning av använda material och bidrar därmed till en mer kostnadseffektiv och tidseffektiv produktionsprocess.Användningen av absorptionsskikt med tjocklekar under 500 nm ger emellertid upphov till flera bekymmer, beträffande ljushantering och absorptorkvalitet.Därför presenterar detta experimentella arbete en ny solcellarkitektur som syftar till att ta itu med frågorna om optiska och elektriska förluster förknippade med ultratunna absorberlager. För detta ändamål infördes ett Hafnium Oxide (H f O2) bakre sidopassiveringsskikt mellan kopparindiumgallium (di) selenid Cu(In, Ga)Se2, CIGSbaserat absorberande skikt och Molybdenum (Mo) kontakt. Sedan upprättade den föreslagna kaliumfluorid (KF) alkali-behandlingen framgångsrikt punktkontakter på det ALD-avsatta oxidskiktet, vilket resulterade i en passiveringseffekt med minimal strömblockering.Den etablerade cellarkitektur visade signifikanta förbättringar avseende både öppna kretsspänningen (Voc) och effektivitet i jämförelse med opassiverad referensanordningar. Den använda solcellsimulatorn (SCAPS) tillskriver de observerade förbättringarna till en minskad minoritetsbärares rekombinationshastighet på enhetens baksida. Dessutom de tillhandahålls fotoluminescens (PL) resultat rapporterar en högre toppintensitet och livslängd för passive enheter.Dessutom visar överläggningen av det givna externa kvantitetseffektivitetsspektrumet (EQE) med de utförda simuleringarna att passiveringsskiktet HfO2 förbättrar den optiska reflektionen från den bakre kontakten över ett våglängdsintervall från 500 till 1100 nm, vilket resulterar i i en kortslutningsström (Jsc) förbättring. En ökad kvantverkningsgrad observerats i nästan hela mätområdet, bekräftar att öka i Jsc är också på grund av elektroniska effekter.Här, en producerad solcellsanordning innefattande en 3 nm-tjock HfO2 bakre passiveringsskikt och ett 500 nm-tjock 3-stegs CIGS absorber, uppnått en omvandlingseffektivitet på 9.8%.Vidare resulterade tillvägagångssättet att kombinera ett innovativt bakre ytpassiveringsskikt med en fluoridbaserad alkalibehandling i utvecklingen och framgångsrik karaktärisering av en 1-stegs, 8.6% effektivitet solcell. Ett sådant resultat, främst på grund av en kortslutningsström (Jsc) förbättring, stöder införandet av mer enkla produktionssteg, vilket möjliggör en mer kostnadseffektiv och tidseffektiv produktionsprocess. Den framställda anordningen bestod av ett 500 nm-tjock CIGS absorber, bakre passiverad med en ultra-tunn (2 nm) HfO2-skikt kombineras med en 0.6M KF behandling.

It is widely known that the element sodium plays a vital role in providing highefficiency CIGS solar cells and that when cells are built on sodium free substrates theyneed an alternative (a substitute) sodium source. In this study a molybdenum-sodiumcompound has been deposited, investigated and evaluated as an alternative backcontact layer containing sodium. The compound had a 5 at % sodium concentrationand it was manufactured by an Austrian company called Plansee. The aim of the studywas to create an equivalent back contact in the sense of sodium delivery, conductivityand adhesion compared to a normal molybdenum back contact on a soda lime glass. The experimental part of the study started with the construction of complete cells,which were fabricated and measured. This work took place at the ÅngströmLaboratory, Uppsala University, Sweden. The characteristics of the layer and the cellswere analyzed by current voltage measurements, quantum efficiency measurementsand secondary ion mass spectrometry analysis. Cell manufacturing involved sputtering,co evaporation and chemical deposition processes. Results show that the molybdenum-sodium compound increases the efficiency of acell built on a sodium-free substrate. Efficiencies reached 8 % for cells without sodiumin the molybdenum and these cells produced 67 % efficiency and 80 % open circuitvoltage of the reference value. Cells with sodium in the back contact layer produced90 % of the efficiency and 95% of the open circuit voltage relative to the references.The best cell with the molybdenum-sodium compound reached an efficiency of 13.3%. This implies that the new back contact layer acts as a sodium source but the cellshave 1-2 % lower efficiency than the reference cells built on soda lime glass. Othercharacteristics of the layer as conductivity and adhesion show no significant differenceto an ordinary molybdenum back contact. Measurements also indicate that the sodium is probably located inside themolybdenum grains and just a small amount is found at the boundaries and in betweenthe grains. Sodium inside the molybdenum grains is difficult to extract and thereforenot enough sodium will diffuse into the CIGS layer. The conclusions drawn from this study are that the molybdenum-sodium compoundhelps to increase the efficiency of a CIGS solar cell built on a sodium-free substrate,but it does not deliver enough sodium to constitute a substitute sodium source.

In this thesis, a novel method of reducing the rear surface recombination in copper indium gallium (di) selenide (CIGS) thin film solar cells, using atomic layer deposited (ALD) Al2O3, has been evaluated via qualitative opto-electrical characterization. The idea stems from the silicon (Si) industry, where rear surface passivation layers are used to boost the open-circuit voltage and, hence, the cell efficiency. To enable a qualitative assessment of the passivation effect, Al/Al2O3/CIGS metal-oxide-semiconductor (MOS) devices with 3-50 nm oxide thickness, some post-deposition treated (i.e. annealed), have been fabricated. Room temperature capacitance-voltage (CV) measurements on the MOS devices indicated a negative fixed charge density (Qf) within the Al2O3 layer, resulting in a reduced CIGS surface recombination due to field effect passivation. After annealing the Al2O3 passivation layers, the field effect passivation appeared to increase due to a more negative Qf. After annealing have also indications of a lower density of interface traps been seen, possibly due to a stronger or activated chemical passivation. Additionally, the feasibility of using ALD Al2O3 to passivate the surface of CIGS absorber layers has also been demonstrated by room temperature photoluminescence (PL) measurements, where the PL intensity was about 20 times stronger for a structure passivated with 25 nm Al2O3 compared to an unpassivated structure. The strong PL intensity for all passivated devices suggests that both the chemical and field effect passivation were active, also for the passivated as-deposited CIGS absorbers.

Thin-film solar cells based around the absorber material CuIn_1-xGa_xSe₂ (CIGS) are studied with respect to their stability characteristics, and different ways of modelling device operation are investigated. Two ways of modelling spatial inhomogeneities are detailed, one fully numerical and one hybrid model. In the numerical model, thin-film solar cells with randomized parameter variations are simulated showing how the voltage decreases with increasing material inhomogeneities.

With the hybrid model, an analytical model for the p-n junction action is used as a boundary condition to a numerical model of the steady state electrical conduction in the front contact layers. This also allows for input of inhomogeneous material parameters, but on a macroscopic scale. The simpler approach, compared to the numerical model, enables simulations of complete cells. Effects of material inhomogeneities, shunt defects and grid geometry are simulated.

The stability of CIGS solar cells with varying absorber thickness, varying buffer layer material and CIGS from two different deposition systems are subjected to damp heat treatment. During this accelerated ageing test the cells are monitored using characterization methods including J-V, QE, C-V and J(V)_T. The degradation studies show that the typical V_OC decrease experienced by CIGS cells subjected to damp heat is most likely an effect in the bulk of the absorber material.

When cells encapsulated with EVA are subjected to the same damp heat treatment, the effect on the voltage is considerably reduced. In this situation the EVA is saturated with moisture, representing a worst case scenario for a module in operation. Consequently, real-life modules will not suffer extensively from the V_OC degradation effect, common in unprotected CIGS devices.

Thin film solar cells, such as Cu(In,Ga)Se2, have a large potential for cost reductions, due to their reduced material consumption. However, the lack in commercial success of thin film solar cells can be explained by lower efficiency compared to wafer-based solar cells. In this work, we have investigated the aluminum oxide as a passivation layer to reduce recombination losses in Cu(In,Ga)Se2 solar cells to increase their efficiency. Aluminum oxides have been deposited using spatial atomic layer deposition. Blistering caused by post-deposition annealing of thick enough alumina layer was suggested to make randomly arranged point contacts to provide an electrical conduction path through the device. Techniques such as current-voltage measurement, photoluminescence and external quantum efficiency were performed to measure the effectiveness of aluminum oxide as a passivation layer. Very high photoluminescence intensity was obtained for alumina layer between Cu(In,Ga)Se2/CdS hetero-junction after a heat treatment, which shows a reduction of defects at the absorber/buffer layers of the device.

High efficiency CuIn1-xGaxSe2-ySy (CIGSS)/CdS thin-film solar cells were prepared by optimizing the Mo back contact layer and optimizing the parameters for preparing CIGSS absorber layer using diethylselenide as selenium source. The Mo film was sputter deposited on 2.5 cm x 10 cm soda-lime glass using DC magnetron sputtering for studying the adhesion and chemical reactivity with selenium and sulfur containing gas at maximum film growth temperature. Mo being a refractory material develops stresses, nature of which depends on the deposition power and argon pressure. It was found that the deposition sequence with two tensile stressed layers deposited at 200W and 5 x 10-3 Torr argon pressure when sandwiched between three compressively stressed layers deposited at 300 W power and 0.3 x 10-3 Torr argon pressure had the best adhesion, limited reactivity and compact nature. An organo-metallic compound, diethylselenide (DESe) was developed as selenium precursor to prepare CIGSS absorber layers. Metallic precursors Cu-In-Ga layers were annealing in the conventional furnace in the temperature range of 475oC to 515 oC and in the presence of a dilute DESe atmosphere. The films were grown in an indium rich regime. Systematic approaches lead to the optimization of each step involved in the preparation of the absorber layer. Initial experiments were focused on obtaining the range of maximum temperatures required for the growth of the film. The following experiments included optimization of soaking time at maximum temperature, quantity of metallic precursor, and amount of sodium in terms of NaF layer thickness required for selenization. The absorber surface was coated with a 50 to 60 nm thick layer of CdS as hetero-junction partner by chemical bath deposition. A window bi-layer of i:ZnO/ZnO:Al was deposited by RF magnetron sputtering. The thickness of i:ZnO was increased to reduce the shunt resistance to improve open circuit voltage. The cells were completed by depositing a Cr/Ag front contact by thermal evaporation. Efficiencies greater than 13% was achieved on glass substrates. The performance of the cells was co-related with the material properties.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering

With solar photovoltaic plants getting larger and larger, the balance in the system is getting important. Balance of the system is necessary to get the maximum power from the system by arranging its components in an optimal way. With PV systems having high DC voltages of up to 600V in USA and 1000V in Europe, the high voltage stress induced in the system is a lot. One of the effects created due to an imbalance in the system is the Potential Induced Degradation. Previous researchers have found out that the Potential Induced Degradation (PID) is due to the voltage imbalance in the string (a schematic arrangement of solar modules in a system) which is influenced by the environmental factors. The objective of the project is to characterize the electrical properties of different available CIGS solar cell types and to correlate other reliabilty tests with PID test to find out if PID has any correlation with the other degradation mechanisms. Thus 8 samples were requested from two different manufacturers of different CIGS solar cells which were tested and results were compared and analysed. Therefore it was found out some compostional structure prove stable against the PID. But changing the combinaton of the compounds have a difference. Some relational pattern of degradation with the Stability test was evident. Few of the previous finding were again confirmed with a new path of approach for the further researches.

In this master thesis, electrical characterization of thin film CuInxGa(1−x)Se2 solar cells produced by Midsummer AB were performed with the aim of determining the dominant recombination path of these cells. Current-Voltage (IV), Quantum Effinciency (QE), temperature dependent IV (IVT) and Drive-Level Capacitance Profiling (DLCP) was used with the objective to investigate the dominant recombination path as well as provide some insight of the solar cells in order to create a baseline model using the modelling software SCAPS (Solar cell CAPacitance Simulator). The IV produced mostly consistent results with slight variation, most likely due to non uniformity of equipment. The QE showed consistent results between all cells indicating a stable process for the sample preparation. Using IVT measurements were taken from a temperature of 115K −300K in order to obtain the activation energy for the dominant recombination path. By comparing it with the band gap energy from the QE measurement, it was found that the dominant recombination path is in either the space charge region or in the bulk of the CIGS and not at the hetero interface. DLCP measurement were made at both low temperature and at room temperature and revealed that the cells had a similar doping as other comparable cells at 7×1016cm−3 . The initial baseline model created in SCAPS show a good agreement with the measured IV and currently indicates a spike in the band alignment, supporting the results for the IVT measurement.

Thesis (M.S.)--University of Toledo, 2007.
Typescript. "Submitted as partial fulfillment of the requirements for the Masters of Science Degree in Physics." "A thesis entitled"--at head of title. Bibliography: leaves 99-102.

The improvement of low cost, efficient photovoltaic devices is a leading technological challenge in the recent decade. There is a need to develop scalable and high-throughput manufacturing techniques that could reduce costs and improve manufacturing of chalcogenide solar cells. Copper, indium, gallium, and selenium (CIGS) Thin films polycrystalline heterojunction solar cells appear to be most appropriate with to cost and ease of manufacture. Currently Cu (In,Ga) (Se, S)2 materials hold the highest record cell efficiency of 22.3% in laboratory scale for thin films solar cells and the efficiency still be boosted by improving the different layers of the photovoltaic devices. CIGS chalcogenide absorber layers has been a leading candidate material in photovoltaic devices for thin films solar cells and space applications due to its unique optical-electronic properties as well as its radiation resistance. In the present work, thin films of Cu (In, Ga) (Se, S)2 were deposited at room temperature on glass substrates coated with ITO and Mo by electrodeposition techniques. The obtained polycrystalline thin films were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) analysis. Thin films of Cu (In, Ga) (Se, S)2 grown by electrodeposition were subsequently processed into several sets of conditions including vacuum heat treatment, heat treatment in the presence of selenium or sulfur, heat treatment in nitrous gas atmosphere (N2H2) at different temperature and processing times. To improve the composition and the crystalline structure of the thin layers and to optimize the electro-optical properties a heat treatment of the thin films was developed in two stages after the electrodeposition. It was observed that the first annealing step (heating treatment at 450 °C in a selenium atmosphere 40 minutes) produced an appreciable improvement in the crystalline structure in the thin layer composition. In a second stage a sulfurization of the CuGaSe2 films was performed at 400 °C for 10 min in the presence of molecular sulfur and under the forming gas atmosphere. The effect of sulfurization was the complete conversion of selenium to sulfur and, therefore, the transformation of CuGaSe2 into CuGaS2. The formation of CuGaS2 thin films was evidenced by the by the displacement of the diffraction peaks of the CuGaSe2 towards higher angles to which makes the X-Ray diffraction 18 pattern which makes it coincide with the diffraction pattern of the CuGaSe2 films, and by the shift towards the blue (higher energies) of the optical gap. The optical gap found for the CuGaSe2 layer was 1.66 eV, while the optical gap for the CuGaS2 was raised up to 2.2 eV. CdS thin films have been widely used as buffer layer in CIGS solar cells. However, when alloyed with Zn, ZnCdS can still improve its performance as buffer layer. ZnCdS can be used as buffer and as window material in photoconductive devices and in heterojunction thin film solar cells due the possibility to tune the bandgap with the content of Zn. The band spacing of this ternary material can be from 2.42 to 3.50 eV, depending on the Cd/Zn ratio.
La obtención de dispositivos fotovoltaicos más eficientes y de bajo coste es uno de los desafíos tecnológicos más importantes de las últimas décadas. Existe la necesidad de desarrollar técnicas de fabricación escalables y de alto rendimiento que puedan reducir los costos y mejorar la fabricación de células solares de capa fina. Las células solares de heterounión de capas finas de seleniuro (o sulfuro) de cobre, indio y galio (CIGS) parecen estar bien adaptadas lograr este reto debido a su bajo costo, facilidad de fabricación y elevado rendimiento de los dispositivos. En la actualidad, Cu(In, Ga)Se2 ostenta el record de eficiencia de células solares con 22,3% a escala de laboratorio y esta eficiencia todavía puede ser acrecentada si se mejoran las diferentes capas de los dispositivos fotovoltaicos. Además, las capas absorbedoras de calcogenuros CIGS son un material candidato importante en dispositivos fotovoltaicos para capas delgadas celdas solares para aplicaciones espaciales debido a sus propiedades electrónicas, así como a su resistencia a la radiación. En el presente trabajo, las películas delgadas de Cu(In, Ga)(Se, S)2 se depositaron a temperatura ambiente sobre sustratos de vidrio recubiertos con ITO y Mo mediante técnicas electroquímicas. Las películas finas policristalinas obtenidas se caracterizaron por espectroscopia óptica UV-Vis, difracción de rayos X (XRD), microscopía electrónica de barrido (SEM), microscopía de fuerza atómica (AFM), microscopía electrónica de transmisión (TEM) y espectroscopia de energía dispersiva (EDS). Las películas finas de Cu(In, Ga)(Se, S)2 crecidas por electrodeposición se procesaron posteriormente en varios conjuntos de condiciones que incluían tratamiento térmico en vacío, tratamiento térmico en presencia de selenio o de azufre, tratamiento térmico en atmósfera gas nidrón (N2H2) a diferentes temperaturas y tiempos de procesado. Para mejorar la composición y la estructura cristalina de las capas finas y para optimizar las propiedades electro-ópticas se desarrolló un tratamiento térmico de las películas finas en dos etapas posterior a la electrodeposición. Se observó que la primera etapa de recocido (tratamiento térmico a 450 ºC en una atmósfera de selenio durante 40 minutos) producía una mejora apreciable en la estructura cristalina y en la composición de la capa fina. 20 En una segunda etapa se realizó una sulfuración de las películas de CuGaSe2 se realizó a 400 °C durante 10 min en presencia de azufre molecular y bajo la atmósfera reductora de gas nidrón. El efecto de la sulfuración fue la completa conversión del selenio en azufre y, por tanto, la transformación de CuGaSe2 en CuGaS2. La formación de películas delgadas de CuGaS2 se evidenció por el desplazamiento de los picos de difracción de las capas de CuGaSe2 hacia ángulos más altos hasta lo que hace que el patrón de difracción de rayos X lo que hace que coincida con el patrón de difracción del CuGaS2 y por el desplazamiento hacia el azul (energías más altas) del gap óptico. El gap óptico encontrado para las capas de CuGaSe2 era de 1,66 eV, mientras que el gap óptico para las capas de CuGaS2 se elevó hasta 2,2 eV. Las películas delgadas de CdS se han utilizado ampliamente como capa tampón en células solares CIGS. Sin embargo, cuando se alea con Zn, para formar el ternario ZnCdS, todavía puede mejorar su rendimiento como capa buffer. ZnCdS puede utilizarse como tampón y como ventana óptica en dispositivos fotoconductores y en células solares de capa fina de heterounión debido a la posibilidad de ajustar el bandgap con el contenido de Zn.
L'obtenció de dispositius fotovoltaics més eficients i més barats és un dels reptes tecnològics més importants de les últimes dècades. Hi ha la necessitat de desenvolupar tècniques de fabricació que siguen escalables i d'alt rendiment i que permeten reduir els costos de fabricació i millorar el rendiment de les cèl·lules solars de capa fina. Les cèl·lules solars de heterounió de capes fines de seleniur (o sulfur) de coure, indi i gal·li (CIGS) semblen estar ben adaptades per assolir aquest repte degut a del seu baix cost, facilitat de fabricació i elevat rendiment dels dispositius. En l'actualitat, el Cu(In, Ga)Se2 ostenta el rècord d'eficiència de cèl·lules solars amb 22,3% a escala de laboratori i aquesta eficiència encara pot ser augmentada si es milloren les característiques de les diferents capes dels dispositius fotovoltaics. Les capes absorbidores de calcogenurs CIGS són un candidat important per dispositius fotovoltaics per a pel·lícules primes en cel·les solars i aplicacions espacialles degut a les seues propietats electròniques així com a la seua resistència a la radiació. En el present treball, les pel·lícules primes de Cu(In, Ga)(Se, S)2 es van dipositar a temperatura ambient sobre substrats de vidre recoberts amb ITO i Mo mitjançant tècniques electroquímiques. Les pel·lícules fines policristal·lines obtingudes es van caracteritzar per espectroscòpia òptica UV-Vis, difracció de raigs X (XRD), microscòpia electrònica de rastreig (SEM), microscòpia de força atòmica (AFM), microscòpia electrònica de transmissió (TEM) i espectroscòpia d'energia dispersiva (EDS). Les pel·lícules fines de Cu(In, Ga)(Se, S)2 crescudes per electrodeposició es van processar posteriorment en diversos conjunts de condicions que incloïen tractament tèrmic en buit, tractament tèrmic en presència de seleni o de sofre, tractament tèrmic en atmosfera reductora de gas nidró (N2H2) a diferents temperatures i temps de processat. Per millorar la composició i l'estructura cristal·lina de les capes fines i per optimitzar les propietats electro-òptiques es va desenvolupar un tractament tèrmic de les pel·lícules fines en dues etapes posterior a la electrodeposició. Es va observar que la primera etapa de recuit (tractament tèrmic a 450 º C en una atmosfera de seleni durant 40 minuts) produïa una millora apreciable en l'estructura cristal·lina i en la composició de la capa fina. 24 En una segona etapa es va dur a terme una sulfuració de les pel·lícules de CuGaSe2 que es va realitzar a 400 °C durant 10 min en presència de sofre molecular i sota l'atmosfera reductora de gas nidró. L'efecte de la sulfuració va ser la completa conversió seleni en sofre i, per tant, la transformació de CuGaSe2 a CuGaS2. La formació de pel·lícules primes de CuGaS2 es va evidenciar pel desplaçament dels pics de difracció de les capes de CuGaSe2 cap angles més alts fins el que fa que el patró de difracció de raigs X el que fa que coincideixi amb el patró de difracció del CuGaS2 i pel desplaçament cap al blau (energies més altes) del gap òptic. El gap òptic trobat per a les capes de CuGaSe2 era de 1,66 eV, mentre que el gap òptic per a les capes de CuGaS2 es va elevar fins a 2,2 eV. Les pel·lícules primes de CdS s'han utilitzat àmpliament com a capa amortidora en cèl·lules solars de CIGS. No obstant això, quan s'alea amb Zn per formar ZnCdS encara pot millorar el seu rendiment com a capa d'amortiment. ZnCdS pot utilitzar-se com capa tampó i com a finestra òptica en dispositius fotoconductors i en cèl·lules solars de pel·lícula fina d'heterounió degut a la possibilitat d'ajustar el seu bandgap que depoen del contingut de Zn.
Ullah, S. (2017). THIN FILM SOLAR CELLS BASED ON COPPER-INDIUMGALIUM SELENIDE (CIGS) MATERIALS DEPOSITED BY ELECTROCHEMICAL TECHNIQUES [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86290
TESIS

Devices with ZnCdS/ZnS heterojunction partner layer have shown better blue photon response due to higher band gap of these compounds as compared to devices with CdS heterojunction partner layer. CdS heterojunction partner layer has shown high photovoltaic conversion efficiencies with CIGS absorber layer while efficiencies are lower with CuIn1-xGaxS2 (CIGS2). A negative conduction band offset has been observed for CdS/CIGS2 as compared to near flat conduction band alignment in case of CdS/CIGS devices, which results in higher interface dominated recombination. Moreover, it has been predicted that optimum band offsets for higher efficiency solar cells may be achieved for cells with alternative heterojunction partner such as ZnS. With varying ratio of Zn/ (Zn+Cd) in ZnxCd1-xS a range of bandgap energies can be obtained and thus an optimum band offset can be engineered. For reducing interface dominated recombination better lattice match between absorber and heterojunction partners is desirable. Although CdS has better lattice match with CuIn1-xGaxS2 absorber layer, same is not true for CuIn1-xGaxS2 absorber layers. Utilizing ZnxCd1-xS as heterojunction partner provides a range of lattice constant (between aZnS= ~5.4 Ǻ and aCdS= ~5.7 Ǻ) depending on Zn/(Zn+Cd). Therefore better lattice match can be obtained between heterojunction partner and absorber layer. Better lattice match will lead to lower interface dominated recombination, hence higher open circuit voltages. In the present study chemical bath deposition parameters are near optimized for high efficiency CIGS2 Solar cells. Effect of various chemical bath deposition parameters on device performance was studied and attempts were made to optimize the deposition parameters in order to improve the device performance.In/(In+Ga) ratio in absorber layer is varied to obtain good lattice match and optimum band alignment. Solar cells with conversion efficiencies comparable to conventional CdS/CIGS2 has been obtained with ZnxCd1-xS /CIGS2. High short current as well as higher open circuit voltages were obtained with ZnxCd1-xS as alternative heterojunction partner for CIGS2 solar cells as compared to SLG/Mo/CIGS2/ CdS / i-ZnO/ZnO:Al.
M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE

CIGS thin film solar cells usually include a thin layer of intrinsic zinc oxide (i-ZnO) deposited on a CdS buffer layer by sputtering. However an interest has grown in using chemical vapor deposition (CVD) instead. Hence, the aim of this thesis was to study how well CVD i-ZnO performs on a CdS buffer layer in a CIGS solar cell and how the properties of the layer can be controlled when using a hot-wall CVD reactor with diethylzinc and water as precursors. The process was characterized through depositions on glass substrates and was then successfully implemented in solar cell devices. The main influences of temperature, thickness and precursor flows on resistivity, optical band gap and film structure were mapped out. The analysis methods used included X-ray diffraction (XRD), X-ray fluorescence (XRF), four point probe resistivity measurements, mechanical profilometry and absorption spectrophotometry. In addition, the solar cell devices were characterized using external quantum efficiency (EQE) and current-voltage (IV) measurements. It was found that the CVD process was sensitive to the condition of the CdS surface, which resulted in a large distribution of shunted cells when grown on aged CdS. Unexpected trends in open-circuit voltage and fill factor were found. Both these factors increased when the growth temperature was decreased, resulting in higher conversion efficiencies. Compared to i-ZnO deposited by an in-house baseline sputtering process, the CVD process resulted in cells with higher short-circuit current due to higher EQE in the short-wavelength region. It was shown that the CVD process used is capable of producing solar cell devices whose performances contest those of cells manufactured with sputtered i-ZnO.

The buffer layer in Cu(In,Ga)Se2 solar cells can improve cell performance. In this work we make CdS buffer layer by chemical bath deposition (CBD) without ammonia. CBD without ammonia were sought out since ammonia is a volatile compound. Different recipes for making CdS were tested; only one of the tested recipes actually produced something that is worth further investigating. This recipe used sodium citrate, an innocuous compound instead of ammonia. The best performance was 0.15 % off from the reference.This is almost as good as the used baseline process. However the worst almost completely killed the solar cells. Cell performance dropped by more than absolute 10 %. This demonstrates that chemical bath deposition can have profound effects on the solar cell performance. When trying to improve the best cells only detrimental effects showed up. This might show that, a part in the recipe used, NaOH has detrimental effects on solar cells. Ammonia free chemical bath deposition is possible, however so far it has not produced as good results as the reference. The difference is however very small, which makes it worth further investigating with moreand better solar cell material.

Copper Indium Gallium DiSelenide absorber layers are fabricated using a two stage manufacturing friendly process. The first step involves the sequential deposition of Copper and Gallium and co-deposition of indium and selenium at 275oC. This is followed by the second stage where the substrate is annealed in the presence of Selenium and a thin layer of copper is deposited to neutralize the excess Indium and Gallium on the surface to form the CIGS absorber layer. The top copper thickness as well as the time of deposition was varied to study the effect of Copper on the performance of the cells. Another recipe was developed for the precursor formation, where Gallium was co-evaporated with Indium and Selenium. A large bandgap shift was seen with this recipe and the open circuit voltage was increased. The performance of CIGS/CdS/ZnO solar cells thus fabricated was characterized using techniques like I-V, C-V, Spectral Response and EDS/SEM. Cells with open circuit voltages of 420-450 mV, short circuit currents of 33-38 mA/cm², fill factors of 58-62% and efficiencies of 9-11% were routinely fabricated.

Present PhD thesis is the experimental and theoretical analysis of thin layer ultrashort pulsed laser ablation processes for photovoltaic devices. Experimental work was supported by modeling and simulation of energy coupling and dissipation inside the layers. The absorbed laser energy was transformed to localized transient heating inside the structure. Selectiveness of the ablation process was defined by optical and mechanical properties of the materials, and selection of the laser wavelength facilitated control of the structuring process. The 1064 nm wavelength was found optimal for the CIGS solar cell scribing in terms of quality and process speed. It is very positive result for industrial applications as the cost and the system complexity are decreased. The solar cell efficiency test revealed minor degradation in photo-electrical efficiency after the laser scribing was applied to the solar cell samples. Lock-in thermography measurements did not revealed any internal shunt formation during laser scribing with picosecond pulse duration. Picosecond lasers with fundamental harmonics and high repetition rates can be used to accomplish efficient and fast scribing process which is able to fit the demands for industrial solar cell scribing applications.
Disertacijos darbo tikslas buvo, modeliuojant bei vykdant eksperimentus, suprasti plonų sluoksnių, naudojamų Saulės elementuose, abliacijos procesus ultratrumpais impulsais, siekiant juos pritaikyti integruotų jungčių fotovoltiniuose moduliuose formavimui. Eksperimento rezultatams pagrysti buvo vykdomas lazerio spinduliuotės sklidimo bei pasiskirstymo plonasluoksnėje Saulės elemento struktūroje modeliavimas. Sugerta lazerio energija lokaliai užkaitiną medžiagą. Kadangi lazerinio proceso selektyvumas priklauso nuo medžiagos optinių savybių, todėl yra itin svarbu parinkti tinkamą lazerio spinduliuotės bangos ilgį, norint sukaupti spinduliuotę reikiamame plonasluoksnės struktūros sluoksnyje. Nustatyta, kad fundamentinė pikosekundinio lazerio spinduliuotė (1064 nm) yra optimaliausia P3 tipo rėžio formavimui CIGS Saulės elemente. Pramonės taikymams tai yra itin svarbu, nes tokiu atveju mažėja industrinės lazerinės sistemos sudėtingumas bei kaina. Saulės elementų efektyvumo tyrimai parodė nežymų fotoelektrinio efektyvumo sumažėjimą po lazerinio apdirbimo ultra trumpais impulsais, tačiau nebuvo užfiksuota defektų generacijos lazeriais paveiktose kanalo kraštų zonose. Disertacijoje pasiūlyti ir išbandyti pluošto formavimo ir lygiagretaus sluoksnių raižymo metodai, didinantys proceso našumą ir raižymo kokybę. Pikosekundiniai, didelio impulsų pasikartojimo dažnio lazeriai gali būti panaudoti didelės spartos bei aukštos kokybės Saulės elementų raižymo procesuose.

Untersuchungsgegenstand dieser Arbeit ist die Degradation flexibler Dünnschichtsolarzellen auf Basis von Cu(In,Ga)Se2 Absorbern. Zur beschleunigten Alterung unter Laborbedingungen wurden unverkapselte Solarzellen in Klimaschränken Wärme und Feuchte ausgesetzt. Die Auswirkungen von Wärme und Feuchte auf die Solarzellen wurden zunächst durch Messung von Strom–Spannungs–Kennlinien (IV) und Kapazitäts–Spannungs–Charakteristiken (CV) erschlossen. Mittels in–situ Messungen der IV–Kennlinien der Solarzellen unter Wärme und Feuchte konnte die Degradationskinetik untersucht werden. Es gelang zwei Phasen der Alterung, eine anfängliche Verbesserung und die eigentliche Degradation, zu unterscheiden. Außerdem war es dadurch möglich Degradationsraten zu bestimmen. Die Untersuchung der Stabilität der Flächenkontakte erfolgte im Schichtverbund der Solarzelle und separat. Dann wurde der Einfluss von Natrium, einem Bestandteil der Cu(In,Ga)Se2 Solarzellen, untersucht. Schichtzusammensetzung, Elementprofile und Oberflächenbeschaffenheit wurden mittels Laser–induzierter Plasmaspektroskopie (LIBS), Sekundärionen–Massenspektrometrie (SIMS), Rasterelektronenmikroskopie (SEM) und 3D–Lasermikroskopie gemessen. Die Rolle von Natrium für den Degradationsprozess konnte für zwei unterschiedliche Methoden der Natriumeinbringung in den Absorber (Ko–Verdampfung, Nachbehandlung) beschrieben werden. Schließlich wurde mittels Elektrolumineszenz (EL), Thermographie (DLIT) und der Messung Lichtstrahl–induzierter Ströme (LBIC) die Degradation ortsaufgelöst untersucht und Inhomogenitäten detektiert. Aus spannungsabhängigen Elektrolumineszenzaufnahmen gelang es Serienwiderstandskarten zu errechnen. Die Kombination der genannten Messmethoden erlaubte eine Identifizierung dominanter Degradationsprozesse in den flexiblen Cu(In,Ga)Se2 Solarzellen unter Wärme und Feuchte. Unter anderen wurde die Degradation der Grenzfläche zwischen Absorber und Rückkontakt diskutiert. Die Degradationskinetik konnte beschrieben, Solarzelllebensdauern abgeschätzt, die für die Wärme–Feuchte–Stabilität nachteilige Wirkung von Natrium identifiziert und laterale Inhomogenitäten des Degradationsprozesses aufgezeigt werden. Aus der Diskussion der Ergebnisse wurden Vorschläge zur Verbesserung der Wärme–Feuchte–Stabilität abgeleitet.

En quelques années, l'efficacité des cellules solaires à base de Cu(In,Ga)Se2 (CIGS) est passée de 20% à 22.6%. La rapidité de ce développement montre que le CIGS est un matériaux idéal pour les technologies solaires en couches minces. Pourtant, le coût de production cette technologie doit encore être abaissé pour une meilleure compétitivité. La fabrication d'un module avec une couche CIGS plus fine permettrait d'augmenter la production d'une usine et de réduire sa consommation en métaux. Ce travail de thèse vise à réduire l'épaisseur du CIGS d'un standard de 2.0-2.5 µm à une épaisseur inférieure à 500 nm sans altérer les performances des cellules. Cependant, comme rapporté dans la littérature, nous avons observé une diminution des rendements, ce que nous avons analysé en détail en comparant simulations et caractérisations d'échantillons. Celle-ci est causée à la fois par une faible absorption de la lumière dans la couche de CIGS et par un impact important du contact arrière (fortes recombinaisons et faible réflectivité). Pour dépasser ces limites, nous démontrons à la fois théoriquement et expérimentalement que le contact arrière en molybdène peut être remplacé par un oxyde transparent conducteur couplé à un miroir métallique. Nous obtenons de cette manière de meilleurs rendements de cellules. Pour atteindre ce résultat, une optimisation du dépôt de CIGS a été nécessaire. De plus, nous prouvons qu'une couche d'oxyde perforée, insérée entre le CIGS et le contact arrière, limite les recombinaisons des porteurs de charges et réduit l'influence des courants parallèles. Au final, nous avons fabriqué une cellule avec un rendement de 10.7% sur SnO2:F passivé par Al2O3
In the past three years, record efficiency of Cu(In,Ga)Se2 (CIGS) based solar cells has improved from 20% up to 22.6%. These results show that CIGS absorber is ideal for thin-film solar cells, even if this technology could be more competitive with a lower manufacture cost. The fabrication of devices with thinner CIGS absorbers is a way to increase the throughput of a factory and to reduce material consumption. This PhD thesis aims to develop cells with a CIGS thickness below 500 nm instead of the conventional 2.0-2.5 µm. However, as reported in the literature, we observed a decrease in cell performance. We carefully analyzed this effect by the comparison between simulations and sample characterizations: it is attributed, on one hand, to a lack of light absorption in the CIGS layer and, on the other hand, to an increased impact of the back-contact (high recombination and low reflectivity). To resolve these problems, we demonstrated theoretically and experimentally that the use of an alternative back-contact, other than molybdenum, such as a transparent conducting oxide coupled with a light reflector, improves the cell efficiency. To achieve this result, an optimization of the CIGS deposition was necessary. Moreover, we proved that a porous oxide layer inserted between the CIGS and the back-contact limits the charge-carrier recombination and removes some parasitic resistance. Finally, an efficiency of 10.7% was achieved for a 480-nm-thick CIGS solar cell with a SnO2:F back-contact passivated with a porous Al2O3 layer

Cu(In,Ga)Se2 (CIGS) is a semiconductor material and the basis of the promising thin-film photovoltaic technology with the same name. The CIGS film has a typical thickness of 1-2 mm, and solar cells based on CIGS technology has recently reached efficiencies of 23.3%. Ultra-thin CIGS solar cells use sub-micrometer thick films that require significantly less material and can be manufactured in a shorter amount oftime than films with typical thicknesses. With decreasing thickness, both electrical and optical losses get more significant and lower the overall performance. Electrical losses can be decreased by increasing the overall film quality and by utilising a graded bandgap throughout the CIGS layer. The band gap can be changed by varying the[Ga]/([Ga]+[In]) (GGI) ratio. Higher overall film quality and a higher band-gap towards the back of the absorber are expected to increase the performance. In this work, sputtered CIGS solar cells were made with different CIGS layer thicknesses, that ranged between 550-950 nm. Increased heat during deposition was examined and shown to increase the film quality and performance for all thicknesses. Two different ways of doping CIGS with Na was examined and it was found that higher Na content lead to an increasing predominance of the (112) plane. The bandgap was graded by varying the GGI composition throughout the CIGS layer and depth profiles were made with Glow-Discharge Optical Emission Spectroscopy (GDOES). It was found that a sputtered CuGaSe2 (CGS)layer below the CIGS-layer lead to a steep increase of the GGI near the back contact. When CGS made up 10% of the total CIGS layer thickness, a significant increase in performance was observed for all thicknesses. CIGS-absorbers with a less graded region with low GGI, making up 30% or 60% of the total CIGS layer thickness were made. A decrease in GGI in that region, was shown to increase the current but lower the voltage. No substantial increase in total performance compared to a fully graded CIGS layer was seen regardless of layer thickness. For further work the optical losses needs to be addressed and work on increasing the optical path in the CIGS layer needs to be done.

One of the natural tendencies of photovoltaic technologies is the systematic reduction of the thickness of the solar cells in order to reduce the cost, to save rare or toxic elements or to limit recombination. So far, crystalline thin-film (GaAs) and poly-crystalline (CIGS) technology are reaching optimum conversion efficiency for thicknesses around 1 or 2 microns. Typically, this thickness range does not require new solutions of optical trappings as it is the case for amorphous silicon. However, if we want to reduce these thicknesses by a factor of 10 or even 100 to study new concepts of collections and conversions (GaAs or GaSb) or reduce the use of indium (CIGS), new needs for efficient light absorption are necessary for these technologies. This manuscript is focused on the design, simulation and realization of innovative nanophotonic solutions for future ultra-thin crystalline solar cells.As a first step, we were engaged in an approach at odds with the usual design of solar cells to trap light in a ultra-thin (≤100 nm) layer of material (GaAs, GaSb and CIGS). We propose an array of metal nanostructure placed in front of the cell, transferred on a metal mirror in order to obtain a high, multi-resonant absorption independent of the angle of incidence and polarization. Numerical analysis of the resonant mechanisms involved was conducted as well as the fabrication and optical characterization of demonstrators. The results of this study are motivating for future work on the ultra-thin devices, involving new concepts of collection (ballistic transport) or conversion (hot carrier solar cells).On the other hand, we studied the possibility of integrating a rear gold nanostructured back contact (200-400 nm) in thin CIGS solar cells to potentially increase the current of short circuit and open circuit voltage. We have proposed an innovative process to achieve this structure and the optical trapping for CIGS solar cells. Numerical study, manufacture of demonstrators and first measurements are presented.

CdTe and Cu(In,Ga)Se2 (CIGS) thin film solar cells are fabricated, electrically characterized and modelled in this thesis. We start from the fabrication of CdTe thin film devices where the R.F. magnetron sputtering system is used to deposit the CdS/CdTe based solar cells. The chlorine post-growth treatment is modified in order to uniformly cover the cell surface and reduce the probability of pinholes and shunting pathways creation which, in turn, reduces the series resistance. The deionized water etching is proposed, for the first time, as the simplest solution to optimize the effect of shunt resistance, stability and metal-semiconductor inter-diffusion at the back contact. In continue, oxygen incorporation is proposed while CdTe layer deposition. This technique has been rarely examined through R.F sputtering deposition of such devices. The above experiments are characterized electrically and optically by current-voltage characterization, scanning electron microscopy, x-ray diffraction and optical spectroscopy. Furthermore, for the first time, the degradation rate of CdTe devices over time is numerically simulated through AMPS and SCAPS simulators. It is proposed that the instability of electrical parameters is coupled with the material properties and external stresses (bias, temperature and illumination). Then, CIGS materials are simulated and characterized by several techniques such as surface photovoltage spectroscopy is used (as a novel idea) to extract the band gap of graded band gap CIGS layers, surface or bulk defect states. The surface roughness is scanned by atomic force microscopy on nanometre scale to obtain the surface topography of the film. The modified equivalent circuits are proposed and the band gap graded profiles are simulated by AMPS simulator and several graded profiles are examined in order to optimize their thickness, grading strength and electrical parameters. Furthermore, the transport mechanisms and Auger generation phenomenon are modelled in CIGS devices.

The sun provides us with a surplus of energy convertible to electricity using solar cells. This thesis focuses on solar cells based on chalcopyrite (CIGSe) as well as kesterite (CZTS(e)) absorber layers. These materials yield record efficiencies of 20.4 % and 11.1 %, respectively. Especially for CZTS(e), the absorber layers often do not consist of one single desired phase but can exhibit areas with deviating material properties, referred to as secondary phases. Furthermore, several material layers are required for a working solar cell, each exhibiting interfaces. Even though secondary phases and interfaces represent a very small fraction of the solar cell they can have a profound influence on the over-all electrical solar cell characteristics. As such, it is crucial to understand how secondary phases and interfaces influence the local electrical characteristics. Characterising secondary phases and interfaces is challenging due to their small sample volume and relatively small differences in composition amongst others. This is where electronmicroscopy, especially transmission electron microscopy, offers valuable insight to material properties on the microscopic scale. The main challenge is, however, to link these material properties to the corresponding electrical characteristics of a solar cell. This thesis uses electron beam induced current imaging and introduces a new method for JV characterisation of solar cells on the micron scale. Combining microscopic structural and electrical characterisation techniques allowed identifying and characterising local defects found in the absorber layer of CIGS solar cells after thermal treatment. Furthermore, CZTSe solar cells in this thesis exhibited a low photo-current density which is traced to the formation of a current blocking ZnSe secondary phase at the front contact interface. The electron microscopy work has contributed to an understanding of the chemical stability of CZTS and has shown the need for an optimised back contact interface in order to avoid chemical decomposition reactions and formation of detrimental secondary phases. With this additional knowledge, a comprehensive picture of the material properties from the macroscopic down to the microscopic level can be attained throughout all required material layers.

A novel 2SSS (2 Step Solid Selenization) CIGS (Cu, In, Ga, Se) thin film solar cell recipe was developed which can be a replacement to the conventional co-deposition process usually employed for large-scale manufacturing. The co-deposition procedure is faced with multiple problems such as selenium incorporation, effective gallium incorporation in the absorber. It is a 2-step proprietary procedure with better control over growth mechanisms and material utilization for the absorber layer for the CIGS thin film solar cells. It makes use of solid selenium source as preferred by manufacturers. Each step of the 2-step procedure was dealt with separately for stoichiometric analysis and interesting trade-offs between materials such as gallium, indium and selenium was found. Solar cells with this proprietary absorber were fabricated on soda lime glass substrates. Results of the solar cells made with the 2SSS process matched with that of the co-deposition process with the quantum efficiencies near 80% of the co-deposition cells. These experiments are going to serve as the test bed for the pilot line that is intended to be installed at USF's research campus soon. The finished solar cells were characterized. The scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were some of the important tools during the analysis of stoichiometry and structural properties. The device performances were measured with the help of current-voltage (I-V) testing and quantum efficiency (QE) measurements.

The increasing demand of renewable energy is the big driving force for the research and development of more efficient solar energy conversion solutions. Solar cells, which use the photovoltaic effect to convert the photon energy to electrical current, are an important solar energy conversion technique. One solar cell technology is thin-film solar cells. Thin-film solar cells use an absorption layer with a direct band gap. A direct band gap has the advantage that the photons will penetrate less deep until a photoexcitation occur compared to semiconductors with an indirect band gap (e.g. silicon). For this reason the thin-film solar cells can be made very thin.CIGS is a common thin-film solar cell absorber material containing copper (Cu), indium (In), gallium (Ga) and selenium (Se). One objective of this work has been to determine element concentrations of CIGS absorption layers from sample measurements. The GGI ratio determines the band gap, which is an important factor for optimising the efficiency of the solar cell.1 The copper vacancy is the main acceptor dopant in CIGS. The Cu concentration has shown to be important for the efficiency and for other properties of the absorber [2].The measuring technique used in this work has been photoelectron spectroscopy (PES). PES produces a spectrum showing distinct peaks corresponding to electron binding energy levels for specific element subshells. Measurements with different photon energies have been performed on samples with and without post deposition treatment (PDT). A great deal of the effort has been to calculate relative element concentrations based on the PES peak intensities. Two important parameters when performing the calculations are the photoionization cross section (including the angular dependence of the cross section) and the inelastic mean free path of the photoelectrons.The results show that the GGI and the corresponding band gap will be almost the same with and without PDT except for close to the surface where PDT lowers the GGI.The calculations showed that the copper concentration is lowest at the surface. Moreover, PDT with RbF results in lower copper concentration closer to the junction.The results show a discrepancy of the GGI and CGI ratios when using the angular dependent cross sections in [10] and [11] compared to using the cross sections in [6] and [7].
Det ökande behovet av förnybar energi gör att forskning och utveckling av solenergilösningar är av största vikt. Solceller, vilka utnyttjar den fotovoltaiska effekten, är den vanligaste tekniken för omvandling av solenergi till elektricitet. Tunnfilmssolceller är en typ av solceller vars absorbent har ett direkt bandgap, till skillnad från kisel som har ett indirekt bandgap. Fördelen med ett direkt bandgap är att det ljusabsorberande materialet kan göras mycket tunt.En vanlig tunnfilmssolcell är CIGS. Det är en komposit bestående av koppar (Cu), indium (In), gallium (Ga) och selen (Se). Ett syfte med detta självständiga arbete har varit att beräkna koncentrationerna av de ingående ämnena i halvledarskiktet av CIGS. GGI-kvoten bestämmer bandgapet, vilket är en viktig faktor för solcellens verkningsgrad. Kopparvakansen är den huvudsakliga halvledaracceptorn i CIGS. Kopparkoncentrationen har visat sig vara viktig för bl.a. solcellens verkningsgrad [2].Mättekniken som används i detta arbete kallas fotoelektronspektroskopi (PES). PES-mätningar ger ett spektrum där spektrallinjerna representerar olika nivåer av elektroners bindningsenergi för olika grundämnen. Mätningar med olika fotonenergier, på prover med och utan ytbehandling (PDT), har utförts. En stor del av arbetet har varit att beräkna relativa koncentrationer av de olika grundämnena från spektrallinjerna i spektrumet. Viktiga parametrar som man behöver ta hänsyn till i uträkningarna är sannolikheten för en fotoemissionsprocess hos fotonerna, vinkelberoendet och den fria medelväglängden hos fotoelektronerna.Resultaten visar att GGI-kvot och bandgap blir nästan detsamma med eller utan PDT, förutom närmast ytan där PDT minskar GGI-kvoten.Resultaten visar också att kopparkoncentrationen är lägst på ytan och att PDT med RbF minskar kopparkoncentrationen närmast ytan.Resultaten visar att det blir skillnader mellan GGI- och CGI-kvoterna beroende på om beräkningarna baserats på vinkelberoende träffytor enligt [10] och [11] eller baserats på träffytor enligt [6] och [7].

The buffer layer is a crucial component in thin film solar cells. Defects at the interface between absorber and buffer layer lead to high recombination rate and the band structure at the interface highly affects the performance of the solar cell. In this thesis a method to synthesize thin films containing cadmium, zinc and sulfur, CdZnS, by chemical bath deposition has been developed and evaluated. A higher current from the device is expected when replacing the common buffer layer cadmium sulfide, CdS, with the more transparent CdZnS. It is also possible that the alternative buffer provides a more favorable energy band alignment at the interface with the absorber Copper-Zinc-Tin-Sulfide (CZTS). The deposition process was developed by studying depositions on glass. Increasing [Zn2+]/[Cd2+] initially led to films with higher band gap (Eg). By varying deposition time the time before colloidal growth became dominant was observed. Addition of triethanolamine showed that triethanolamine binds stronger to zinc ions than to cadmium ions. Two recipes that led to Eg=2.63 eV were evaluated as buffer layer in Copper-Indium-Gallium-Selenide (CIGSe) and CZTS solar cells. The short circuit current of the devices increased in general with the CdZnS buffers compared to CdS. The best CZTS cell with a CdZnS buffer layer had 7.7 % efficiency compared to the 7.5 % reference. For future research it is recommended that the effect of thickness variation and deposition temperature is evaluated and that additional material characterization is performed in order to further understand and develop the deposition method.

Two identified setbacks for CIGS based devices in order to obtain higher efficiency are parasitic absorption in the window layer structure and losses in open-circuit voltage due to bad interfaces. This study investigated how the performance of the solar cell is affected by depositing intrinsic ZnO (i-ZnO) and ZnMgO with atomic layer deposition (ALD) instead of the conventional sputtering. No significant improvement in fill factor was obtained by the use of ALD compared to sputtering, leading to the conclusion that pinholes in the sputtered film are not a detrimental factor for the cell. As the thickness of the i-layer increased, an increase in FF was observed for the ALD-deposited i-layer, whereas a decrease was observed for the sputtered i-layer. The open-circuit voltage was considered constant between the two series with only small fluctuations, indicating that the defect chemistry of the i-ZnO/CdS interface was not improved with the use of ALD. In this study it is shown that a gain in short-circuit current can be obtained for CIGS solar cells in the high energy region of the spectrum by reducing the thickness of the i-ZnO, as well as alloying the ZnO with Mg. When compared with a baseline layer sample with a sputtered i-layer thickness of around 90 nm, the estimated gain in short-circuit current density without a loss in fill factor was 0.14 and 0.20 mA/cm2 for ALD and sputtering, respectively. For the series with a ZnMgO i-layer, the highest estimated gain was 0.17 mA/cm2. This was observed for the sample with a 4:1 (Zn:Mg) pulse ratio, whereas higher Mg contents yielded a too high band gap that resulted in an electron blocking barrier.

This project will be a part of the LODESTAR experiment. LODESTAR is one of the experiments scheduled to fly on the REXUS/BEXUS 26 high altitude balloon flight. The primary objective of the experiment is to investigate the effects of cosmic radiation on CIGS solar cells. The objective of this project is to build a mechanical design that can fulfill all requirements set by the ESA user manual. The mechanical design will first be drawn in mechanical CAD, where the drawing will be constructed from the ESA requirements. Later the design will be simulated in order to choose appropriate materials and a design that can withstand all simulations. Lastly the design will be built according to the drawings and tested according to the simulations. The mechanical design withstood all the simulations and verification tests with no visual deformation, except for the simulation and verification of the drop test. Both the drop simulation and verification test resulted in deformation in one of the aluminium plates. Since this mechanical design is constructed to be used only once, small deformations is within the margin of error. The deformation resulted by the simulation and verification of the drop test matched with a high precision. This is a good confirmation of the results of the drop test. In conclusion, the executed tests gave very promising results. Therefor the design constructed fits all the requirements to travel with solar panels in stratospheric conditions.
LODESTAR -BEXUS Project

博士
國立臺灣大學
電子工程學研究所
104
Cu(Ga, In)Se2 (CIGS) thin film transistors and the inhomogeneity effects on CIGS solar modules are investigated. CIGS is one of the best candidate materials for thin film solar cell due to its strong light absorption as well as its relatively high mobility. It also has the advantage to reduce production cost for photovoltaics devices, and nowadays, the fabrication of CIGS solar cell is mature and commercial. But some problems like uniformity, morphology, and yield still affect the quality of CIGS solar cell and reduce its market in the competition with other kinds of solar cell like Si based solar cell, CdTe solar cell and CZTS solar cell. Besides the application in thin film solar cell, CIGS also has the potential to have a role in other fields, like light sensor, telecommunication, and thin film transistor (TFT). By solving the problems occurred in the fabrication of CIGS solar cell and achieving its application in other fields will promote the value of CIGS. In the first part of this dissertation, CIGS TFT is investigated. The fabricated CIGS TFT achieves a saturation mobility of ~1.8 cm2/V-s, and the on-off ratio over 3 orders of magnitude for the first time. We use a special ring pattern to simplify the fabrication process and avoided the problems occurred in the traditional TFTs. In the structure of CIGS TFT, Al2O3 is deposited by atomic layer deposition (ALD) on CIGS film as the dielectric layer. With the help of Al2O3 layer, the on current is high due to its high dielectric constant, and moreover, the channel can be passivated by Al2O3 layer, so that defects on the interface of CIGS/Al2O3 decrease, and eventually increase the saturation mobility. We also have applied thin-down process on the CIGS thin film, which was prepared for solar cell fabrication, to meet the required conditions for CIGS TFT. The characteristics of CIGS TFT are investigated consequently, and the improvement of saturation mobility after thin down process is found. This might be due to the different qualities of different layers in CIGS thin film, and is justified by the measurements of photoluminescence (PL) and X-ray diffraction (XRD). Moreover, the performances of CIGS TFTs with different content in CIGS films are investigated. TFT with high Cu/(Ga+In) ratio tends to have both high carrier concentration and saturation mobility. Sodium atoms might play important roles in these properties. In the second part of this dissertation, the inhomogeneity effects on CIGS solar modules are investigated. We firstly demonstrate the impact of residual strain on the CIGS solar module with Ga content fluctuation using first principle calculations. The simulation results show that the inhomogeneity effect is magnified by residual strain due to the enhanced band gap fluctuations. Then the 3D simulation results of CIGS solar cells are obtained with the residual strain effect incorporated. The parameters used in the model for the simulation are the same to those used in the commercial CIGS solar cell. A module consists of 3 cells in series, while each cell is divided into 3 sections. Intracell inhomo, intercell inhomo, and combined intracell+intercell inhomo are considered within a module, and the effects of both Ga content and thickness fluctuation are investigated. Among these three distributions, intracell+intercell inhomo is closest to the real distribution of inhomogeneity in the fabrication of CIGS solar module. In reality, Ga content fluctuation is serious and thickness fluctuation can be well controlled. The simulation results show that in terms of Ga content fluctuation, Intracell fluctuation causes VOC degradation, and intercell fluctuation causes JSC and fill factor degradations, and in terms of thickness fluctuation, VOC remains the same due to the constant Ga content, JSC is degraded due to the increase of excess carrier recombination, and the tendency of fill factor degradation is similar to Ga content fluctuation.

博士
國立臺灣大學
電子工程學研究所
101
In the first part of this dissertation, IH MOSFET is investigated. Short-channel controllability by insulating halo (IH) is investigated using the NFET strained-Si technology. By embedding SiO2/Si3N4 insulators in the halo regions, the increase of halo implant concentration reduces the S/D depths, and improves short channel effects such as drain induced barrier lowering. With Ioff similar to the control device at the same gate length by adjusting the threshold voltage, the channel doping can be reduced, and the channel mobility increases due to the decrease of vertical electric field. Moreover, insulating halos reduce the STI compressive stress in the channel and yield high electron mobility enhancement. The device performance is optimized based on simulation design. Up to 23% Ion improvement was experimentally achieved by optimal insulating halo insertion. 7% lower junction capacitance and 8% ring oscillator speed improvement is demonstrated when IH is adopted in NFET alone. Moreover, device reliability is carefully examined and is not adversely impacted by IH insertion. In the second part of this dissertation, CIGS solar cell is investigated. With Al2O3 passivation on the surface of Cu(In,Ga)Se2, the integrated photoluminescence intensity can achieve two order of magnitude enhancement due to the reduction of surface recombination velocity. The Photoluminescence intensity increases with increasing Al2O3 thickness from 5nm to 50nm. The capacitance-voltage measurement indicates negative fixed charges in the film. Based on the first principles calculations, the deposition of Al2O3 can only reduce about 35% of interface defect density as compared to the unpassivated Cu(In,Ga)Se2. Therefore, the passivation effect is mainly caused by field effect where the surface carrier concentration is reduced by Coulomb repulsion. Next, how film inhomogeneity would affect the CIGS solar cell performance is investigated. Inhomogeneity taken places both within a cell and between cells (module) are considered. The variations of lifetime, doping concentration, and Ga fraction of CIGS cells and modules are investigated by simulation. Ga fraction variation is found to have a significant impact on cell performance, where else lifetime and doping concentration variation on cell performance is mild. The Ga variation causes the open circuit voltage (Voc) variation across a single cell, and the smallest Voc dominated the net Voc. The module efficiency is degraded more significant by the Ga variation than cell due to the additional degradation of the fill factor. Appendix A: Since the direct bandgap emission of Germanium (Ge) has a higher energy than the fundamental bandgap and its reabsorption nature, the emission intensity of direct bandgap depends on the depth where emission occurrs. For vertical current flow, the carrier profile in electroluminescence distributes deeper than in photoluminescence due to electric field, and leads to relatively weaker direct bandgap emission. A lateral current flow can confine carrier distribution near the surface thus relatively stronger direct bandgap emission is observed.

碩士
國立清華大學
材料科學工程學系
99
摘要 本研究採用CIGS四元靶材進行物理性濺鍍製備銅銦鎵硒薄膜，再使用離子蝕刻技術直接於銅銦鎵硒薄膜(CIGS thin film)表面製備大面積規則銅銦鎵硒奈米尖錐陣列(CIGS NTs)以增加接觸面面積進而提高光電轉換效率。藉由調整蝕刻時間可以控制銅銦鎵硒奈米尖錐陣列的長度從120 nm到320 nm，另外，控制氬離子入射角進面控制銅銦鎵硒奈米尖錐陣列的夾角從最大90 度(垂直)到15度。所製備之銅銦鎵硒奈米尖錐陣列之密度更可大於4.5 × 1013/cm2。藉由穿透式電子顯微鏡(TEM)的分析可得知此銅銦鎵硒奈米尖錐陣列為單晶結構。由反射光譜可知，銅銦鎵硒奈米尖錐陣列對於紫外光到近紅外光波段的光具有全反射性質，亦即反射率全小於1%。藉由探討銅銦鎵硒奈米尖錐陣列相對於各種製程條件的成長狀況，釐清離子式蝕刻製備奈米結構形成原因。更進一步藉由量測銅銦鎵硒奈米尖錐陣列之亮/暗電流-電壓和外部量子效應之表現以了解此奈米結構之光電轉換效率。

碩士
國立高雄大學
應用物理學系碩士班
102
A procedure is using the basic equations of semiconductors, we calculate the space distribution of minority carrier density and current density in each layer quasi-neutral region of solar cells devices with full solar spectrum. First, we study the characteristics of single-junction solar cell with CuInGaSe2 materials that thickness is 0.5 of the solar cell conversion of efficiency is obtained 11.79%. Second, double-junction CIGS/CIGS tandem solar cells are simulated with top layer thickness of about 2.85μm, and substrate thickness of about 2.5μm. These solar cells are shown to have the maximum efficiency of about 38.5%. Thirdly, calculation of triple-junction CIGS/CIGS/Si tandem solar cells, with top layer thickness of about 2.5μm, the middle layer thickness of 1.4μm, and the substrate thickness of about 600μm is shown to have the best conversion efficiency of about 31.3%.

碩士
國防大學中正理工學院
材料科學碩士班
99
Thin-film CIGS solar cells have the highest energy conversion efficiency among second-generation solar cells. In addition, they can be manufactured by the roll to roll process and therefore flexible modules can be fabricated. They are very promising thin film solar cells. 　　In order to increase the output voltage of solar modules, sub-cells must be connected in series, so laser patterning processes are very important. In this study, we use three Nd:YVO4 lasers with different parameters to scribe the absorption layer of CIGS solar cells. The patterns of laser scribing were characterized using optical microscope, scanning electron microscope Alpha-Step Profilometer, and 3D surface Profilometer. The effects of laser scribing processing variables we studies by comparing the scrbe results. Finally, the processing parameters were optimized.

碩士
國立高雄應用科技大學
光電與通訊工程研究所
101
In this thesis, we successfully completed the simulation of V-shaped and Multi-slope band gap structures with the AMPS-1D numerical simulation software, and we obtained the higher efficiencies than other previous studys. According to the significant influence of the front grading on solar cells' open voltage and the correlation between the back grading and the back carrier recombination, we first began the optimization of the energy gap’s engineering from the front and back grading individually. Subsequently, we combined the best conditions of the front and back grading to form a spoon-shaped structure, and then obtained the efficiency of 19.28%. For the unoptimized V-shaped structure in the literature, we optimized its turning point's band gap and position on the CIGS bulk part, and obtained the efficiency of 19.95%. Consequently, the V-shaped structure was evolved into the multi-slope structure having the efficiency of 20.285%, which is 1% higher than that of the spoon-shaped structure. The proposed band gap structures provide researchers a process direction on the energy gap engineering.

碩士
國立屏東科技大學
車輛工程系所
101
The flow filed, heat conduction, and heat radiation effects on a vacuum-based manufacturing process of the CIGS thin film photovoltaic cells inside a chamber are investigated in this research. Due to the non-uniform thickness of the CIGS films on some substrates after the deposition, the computational fluid dynamics approach is used to investigate the selenization process. The purpose of using computational fluid dynamics is to study the temperature effect and the flow filed inside the chamber during the selenization, and to provide some possible modifications to improve the manufacturing efficiency. The computed temperature shows a good agreement with the experimental data and the error is about 15%.The time dependent temperature variations inside the chamber are similar to the experimental measurement. The results demonstrate the possibility of using computational fluid dynamics to improve the manufacturing process of the CIGS cells.

碩士
國立中央大學
電機工程研究所
98
In this study, we investigate the impact of In2Se3 buffer of CIGS solar cells which was used to replace the CdS buffer to avoid the toxic issue. The structure of the CIGS solar cells is Mo/CIGS/In2Se3/ZnO/ZnO:Al/Ni/Al. The metal contact Ni/Al was deposited by electron beam evaporator. The other films were deposited by RF-sputtering. Our group has successfully fabricated the CIGS solar cells with In2Se3 buffer layer. The RF power was kept at 100 W to deposit the back contact Mo for 30 minutes and the substrate temperature was 100 ℃.The RF power was kept at 50 W to deposit the absorption layer CIGS for 35 minutes. The RF power was kept at 70 W to deposit the buffer layer In2Se3 for 3 minutes. The RF power was kept at 50 W to deposit the transparent conducting ZnO film for 15 minutes. The RF power was kept at 50 W to deposit the transparent conducting ZnO:Al for 30 minutes. The fabricated cell of 0.021 cm2 active area demonstrates an efficiency of 0.235 % with VOC = 280 mV, JSC = 2 mA/cm2, FF = 41 % under AM 1.5 illumination.

碩士
國立東華大學
電機工程學系
97
Some device properties of effects upon the performance of copper indium gallium diselenide solar cells are analyed by means of the device simulation tool of AMPS-1D (Analysis of Microelectronic and Photonic Structures). First, the modeling and material parameters of all layers in CIGS solar cells are established. The effects of doping density and thickness of various CdS buffer layer, bandgap energy of high-recombination interface, thickness of Cd-doping surface layer, and hole density, thickness, and electron and hole mobility of CIGS absorber on the CIGS solar cells. We also investigate how the material parameters affect the performance of CIGS solar cells. High-efficiency CIGS solar cells employ the CdS buffers layer typically. However, the use of cadmium is not accepted from the viewpoint of environmental safety. Cd-free buffer layers such as ZnS are the attractive alternative. CIGS solar cells with the ZnS buffer layers have higher quantum efficiency at short wavelengths, but Voc and FF are lower. The various electron affinity, thickness and doping density of ZnS buffer layer of CIGS solar cells are simulated by the device simulation tool of AMPS-1D. With the simulation results, the high-efficiency CIGS solar cells with the ZnS buffer could be achieved by applying the proper band alignment.

碩士
國立臺北科技大學
光電工程系研究所
99
Copper Indium Gallium Diselenide (CIGS) is the direct band gap semiconductor material with band gap ranging from 0.9 ~ 1.7 eV. Its advantage is possessed of the higher absorption coefficient and adjusted the conductivity type by different stoichiometry. Therefore, CIGS is regarded as the most suitable absorption layer for high efficiency solar cells. The research use reactive magnetron sputtering system to grows CIGS-based thin film solar cell. The structure is IZO / ZnO / InN / CIGS / Mo. By exploring the better parameters of each films to product CIGS solar cells. The films were analyzed by scanning electron microscope, X-ray diffraction and Raman spectroscopy, respectively. The experimental analysis shows that Mo and CIGS have a good ohmic contact. In the XRD pattern, it can be observed that high temperature annealing can effectively increase the chalcopyrite crystal quality of CIGS films. The diffraction peaks of the chalcopyrite at 26.7o,44.3 o and 52.5 o. Then IZO transmittance is about 90 %.We fabricated the CIGS -based thin film solar cell successfully. Using current-voltage measurement to get fill factor(F.F.)=0.257, open circuit voltage(Voc) =0.1 V, short circuit current(Isc) =0.00824 mA/cm2 and η=0.00847% in our device.

Ma, Xuhang = 柔性襯底銅銦鎵硒太陽能電池製備工藝 / 馬續航.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2013.
Includes bibliographical references (leaves 88-91).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstracts also in Chinese.
Ma, Xuhang = Rou xing chen di tong yin jia xi tai yang neng dian chi zhi bei gong yi / Ma Xuhang.

碩士
國立彰化師範大學
機電工程學系
100
This study the low-temperature selenization process effect of CIGS (Cu(In,Ga)Se2) absorbed layer crystallization. Used the Polyimide (PI) and Stainless steel (SS) substrate respectively. The absorbed layer structure is Substrate/Mo/In/CuGa which In process used the sputtering and evaporation respectively. The Mo electrode material had pure Mo and Mo:Na. The experimental results of polyimide substrate that selenization annealed at 673 K low-temperature conform a single chalcopyrite phase. However, the surface will the island structure and small grain selenization annealed obtained less than 20 min and greater than 40 min could formation of through the duration of second phase by InSex. Evaporation In could improve the absorption layer of the surface of the island structure th reduce the surface roughness and crystal quality. Use of Mo:Na added sodium elements and low-temperature selenization on CIGS absorber layer. Observed the no obvious crystal is no obvious groweh. On polyimide substrates at 673 K/40 min. but the stainless steel substrate selenization at 823 K/30 min of the high-temperature had more visible crystal growth phenomena.

碩士
清雲科技大學
電子工程所
99
Chalcopyrite Cu(In,Ga)Se2 is a direct bandgap, whose energy bandgap(Eg) can be adjusted between 1.04 and 1.68 eV by varying the In/Ga ratio. Its high optical absorption coefficient as well as good thermal and electrical stability make it a suitable for thin film solar cells. In this study, layer-by-layer electrodeposition process to absorber layer for CIGS thin film solar cells. The film thickness and surface morphology, atomic percentage, crystal structure, and optical properties were characterized by SEM, XRF, ICP, XRD, and UV-vis analysis. In addition, a cadmium sulfide buffer layer was deposited by chemical bath deposition (CBD) onto glass and/or CIGS absorber layer. The thickness and structure were examined by SEM and XRD, and the processing parameters such as the temperature, pH and deposition time were optimized. Finally, an AZO layer was sputtered as the top electrode, and the current-voltage curve of the device was measured. The results showed that a flat and dense CIGS absorber layer can be obtained by two-layer electrodeposition (CuGa/InSe or InSe/CuGa) with a current density of 0.16 ASD followed by thermal annealing. The atomic percentage ratio was close to the ideal composition (Cu:In:Ga:Se= 25:17.5:7.5:50), and XRD analysis showed a chalcopyrite structure. For the CdS buffer layer, the required thickness can be obtained by CBD at 75oC and pH 9.5 for 5 min. XRD analysis indicated that temperature has no effect on the microstructure. Only the pH and deposition time are the key conditions for the film thickness and structure. Keywords: CIGS, Electrodeposition, Thin film solar cells.