Academic literature on the topic 'Graphene ; Dye-sensitized solar cells ; Catalysts'

Semiconductor nanostructures have attracted considerable research interest due to their unique physical and chemical properties at nanoscale which open new frontiers for applications in electronics and sensing. Zinc oxide nanostructures with a wide range of applications, especially in optoelectronic devices and bio sensing, have been the focus of research over the past few decades. However ZnO nanostructures have failed to penetrate the market as they were expected to, a few years ago. The two main reasons widely recognized as bottleneck for ZnO nanostructures are (1) Synthesis technique which is fast, economical, and environmentally benign which would allow the growth on arbitrary substrates and (2) Difficulty in producing stable p-type doping. The main objective of this research work is to address these two bottlenecks and find a solution that is inexpensive, environmentally benign and CMOS compatible. To achieve this, we developed a Sonochemical method to synthesize 1D ZnO Nanorods, core-shell nanorods, 2D nanowalls and nanoflakes on arbitrary substrates which is a rapid, inexpensive, CMOS compatible and environmentally benign method and allows us to grow ZnO nanostructures on any arbitrary substrate at ambient conditions while most other popular methods used are either very slow or involve extreme conditions such as high temperatures and low pressure. A stable, reproducible p-type doping in ZnO is one of the most sought out application in the field of optoelectronics. Here in this project, we doped ZnO nanostructures using sonochemical method to achieve a stable and reproducible doping in ZnO. We have fabricated a homogeneous ZnO radial p-n junction by growing a p-type shell around an n-type core in a controlled way using the sonochemical synthesis method to realize ZnO homogeneous core-shell radial p-n junction for UV detection. ZnO has a wide range of applications from sensing to energy harvesting. In this work, we demonstrate the successful fabrication of an electrochemical immunosensor using ZnO nanoflakes to detect Cortisol and compare their performance with that of ZnO nanorods. We have explored the use of ZnO nanorods in energy harvesting in the form of Dye Sensitized Solar Cells (DSSC) and Perovskite Solar Cells.

碩士<br>國立臺灣大學<br>化學研究所<br>106<br>A huge amount of fossil fuels, such as coal, petroleum, and gas, has been consumed in order to meet the high demand of energy in the world. However, the combustion of these fossil fuels results in not only detrimentally environmental pollution, but also the rapid reduction of fossil resources on the Earth. Recently, several kinds of renewable energy, e.g., fuel cells, wind power, and solar energy, have drawn tremendous attention in academic studies and industrial applications. Among them, solar energy is the most attractive renewable energy; in particular, dye-sensitized solar cells (DSSCs) have the advantages of simple fabrication processes, low cost, flexibility, and semi-transparency. However, if a DSSC possesses low power conversion efficiency and utilizes noble metals, e.g., platinum (Pt) or ruthenium (Ru), as a counter electrode (CE), these disadvantages would hinder this DSSC from wide applications. Therefore, it is an urgent challenge to develop a noble metal-free CE with high power conversion efficiency in DSSCs. Graphene has high carrier mobility, high electrical conductivity, high mechanical strength and flexiblility. In this study, we took advantage of the unique chracteristics of graphene to fabricate high-performance DSSCs by employing different graphene-based CEs, such as graphene hollow nanoballs (GHBs), nitrogen-doped graphene hollow nanoballs (N-GHBs), sulfur-doped graphene hollow nanoballs (S-GHBs), and nitrogen/sulfur-codoped graphene hollow nanoballs (N,S-GHBs). First, we synthesized GHBs on silicon wafers (Si) or carbon cloth (CC) substrates with a chemical vapor deposition (CVD) method. A nitrogen or sulfur precursor, or both, was incorporated in the CVD rection to from N-GHBs, S-GHBs, and N,S-GHBs, respectively. Second, the as-synthesized doped GHBs were used as metal-free CEs to investigate their power conversion efficiencies in DSSCs. The highly curved GHBs could avoid the self-assembly restacking of planar graphene sheets and provide high surface area. In addition, the heteroatomic incorporation in GHBs can reduce the charge-transfer resistance and enhance the catalytic activity of GHBs. We found that pristine GHB (with ∆EP of 698 mV) and heteroatom-doped GHBs (∆EP of 530 mV for N-GHBs and ∆EP of 498 mV for S-GHBs) have different catalytic activities on the I-/I3- reduction reaction and the N,S-GHBs (∆EP of 459 mV) shows the best catalytic performance due to the synergistic effect of electronic and geometric changes. Consequently, the power conversion efficiency of a DSSC with N,S-GHBs as a CE reaches to 9.02 %, comparable to that (8.90 %) of a standard sputtered Pt CE-based cell.

博士<br>國立臺北科技大學<br>光電工程系研究所<br>104<br>This work aims to improve the conversion efficiency of dye- sensitized solar cells (DSSCs) by introducing a new material, graphene, in to the DSSCs structure. Graphene is a potential material for many applications due to their high electron mobility, outstanding optical properties, and thermal, chemical, and mechanical stability. Therefore, this study changes several parameters, structures, and methods to optimize and compare with the traditional DSSCs . There are three major respects about with or without graphene, (1) the method of plating or sputtering, and the structure of (2) graphene/TiO2 and Graphene/ZnO Nanoparticles DSSCs (3) or TiO2/graphene/TiO2 in DSSCs solar cells. Finally, this research knows that the method of sputtering is much better than plating, the conversion efficiency of solar energy with graphene/TiO2 was increased from 1.62 % to 3.72 %, and the conversion efficiency with TiO2/graphene/TiO2 sandwich structure was increased from 1.38 % to 3.93 %. It means that the new material, graphene, works in enhancing the conversion efficiency of DSSCs .

碩士<br>國立中興大學<br>化學工程學系所<br>101<br>In this study, graphene oxide (GO)/polyaniline(PANI) nanocomposites have been used for electrode and electrolyte in dye sensitized solar cells (DSSCs).. In the fisrt part: GO/PANI nanocomposite thin film was coated on a FTO glass by in situ polymerization and and self-assembly process for counter electrode of DSSC. SEM images confirmed the formation of the composite film GO/PANI with higher surface area on the FTO coated substrate. High electro-catalytic ability and low charge transfer resistance of GO/PANI counter electrode were characterized through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The short-circuit current density (Jsc) and power-conversion efficiency (η) of the DSSC based on the GO/PANI counter electrode are about 14.94 mAcm-2 and 6.55%, which is comparable to the the cell with conventional Pt counter electrode . In the second part: the photovoltaic (PV) properties of the DSSCs were enhanced by incorporating the GO/PANI nanocomposite into the PEO gel electrolyte. The GO/PANI nanocomposite materials serve simultaneously both as the extended electron transfer materials and as catalysts for the electrochemical reduction of I3-. Because of a higher catalytic activitiy and a higher diffusion coefficient of I3- , the incorporation of GO/PANI nanocomposite into the gel electrolyte is favorable for the reduction of the charge transfer resistances of DSSC. G40P has the best catalytic activitiy as compared to those of the PANI and GO/PANI nanocomposites (G2P and G4P). Therefore, better PV efficiency (5.63%) was observed for the DSSC incorporating GO/PANI nanocomposite G40P.

碩士<br>國立臺北科技大學<br>有機高分子研究所<br>102<br>The effects of zinc oxide doped graphene working electrode of dye-sensitized solar cells were investigated in this study. The control variables included the dispersion of graphene, the size of graphene, the amount of functional groups of grapheme, and the graphene content and thinckness of the Graphene/zinc oxide composite films. During graphene doping zinc oxide process, the graphene dipped in the mixed acid ( nitric acid : sulfuric acid = 3 : 1 ) was treated in ultrasonic bath at 60 ℃ for 2 hours. The treated graphene was cleaned with deionized water until neutral. After drying in an oven, we ground the treated graphene to powder. The powder, the treated graphene, zinc oxide nanoparticles and t-BuOH solution were mixed into the paste. The working electrode films were prepared by the doctor-blade method. The fabrication of the Graphene/zinc oxide composite films were carried out by a furnace at 150 ℃ for 1 hour. After acidification, the surface of graphene contains carboxyl and hydroxyl functional groups could improve the dispersion of graphene in a polar solvent to reduce aggregation. Besides, the functional groups of graphene linking with zinc oxide could enhance the transport of electrons. The graphene has high electron mobility due to the planar mesh structure, therefore it could effectively transmit electrons injected from the zinc oxide. The dye-sensitized solar cells with the Graphene/zinc oxide composite films were improved the short circuit current density from 6.71 mA/cm2 to 9.20 mA/cm2, and the corresponding photoelectric conversion efficiency were enhanced from 3.06 % to 3.67 %. The enhancement ratio was achieved to 20 %.

碩士<br>國立東華大學<br>材料科學與工程學系<br>105<br>Graphene(GR) has good photoelectric properties, including a large specific surface area, high charge-carrier mobility, high conductance, and fast electron transfer. In this thesis, different proportion of graphene is added to the TiO2 working electrodes of dye-sensitized solar cells (DSSCs). The working electrode of the studied DSSCs comprises two-layer stacking architecture. We use screen printing method to produce a light-scattering layer. The light-scattering layer is composed of the large particles TiO2-P200 nano powder and small particles of TiO2-P25 nano powder. An appropriate content of graphene in a working electrode is favorable to more uniform dispersion of TiO2 nanoparticles, leading to the increased amount of dye adsorption and absorbance of visible light. The graphene/TiO2 film forms a good electron transport path and then the time of electron transport is shortened. Furthermore, the interfacial charge transfer is accelerated and the electron lifetime is lowered. Consequently, the performance of the studied DSSC is thus enhanced.From the experimental results that GR / TiO2 working electrode with the scattering layer, get the best component conversion efficiency of 8.81 %, an open circuit of 0.74 V, a short-current density of 18.09 mA/cm2, a fill factor of 0.66.

碩士<br>國立雲林科技大學<br>化學工程與材料工程系<br>104<br>Recently, nano-sized TiO2 powders have been used as a working electrode for dye-sensitized solar cells ( DSSCs ) due to a higher efficiency than any other metal-oxide semiconductor. The major bottleneck is the transport of photogenerated electrons across the TiO2 nanoparticle network, which competes with the charge recombination. To suppress the recombination and improve the transport, we incorporate the three-dimensional structure of graphene aerogel into TiO2 nanostructure photoanode to form graphene aerogel bridges in DSSCs. Graphene aerogel has high specific surface area, high porosity, rapid acceptance and transfer electronic properties. So that graphene aerogel can enhance the charge transport rate to prevent the charge recombination. In addition, we incorporate the Ag/graphene aerogel into TiO2 nanostructure photoanode and hope that Ag/graphene aerogel can enhanced photocurrent of dye-sensitized solar cells. The enhancement effect is believed to be based on localized surface plasmon resonance of the Ag nanoparticles. In the present study, we used Hummer’s method and photodeposition technique to synthesize graphene coupled with Ag nanoparticles followed by self-assembly reaction to form porous structure. The morphology of the Ag/graphene aerogel characterized with HRTEM. Raman spectroscopy show that the material had surface enhance raman scattering( SERS ) property, and the signals of SERS were raised by increasing the silver loading. The part of DSSCs research was used Linear Sweep Voltammetry ( LSV ) to find that incorporation Ag/graphene aerogel could increasing photocurrent yield. Electrochemical impedance spectroscopy ( EIS ) show that it could reduce electron transit time and extend electron life time to improve cell efficiency.