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Cu 2 ZnSnS 4 nanocrystals (NCs) were synthesized via a low-cost one-pot method. The recipe was optimized by using photoelectrochemical measurements of NC films in contact with a methyl viologen solution. Non-stoichiometric copper-rich and zinc-poor starting molar ratios provided the best overall photovoltaic effect.Other analytical techniques were used to further identify the NC composition, topography and crystallinity. The oxidation states were found to be 1+, 2+, 4+ and 22 for copper, zinc, tin and sulphur, respectively.

Copper indium disulphide (CIS) nanocrystals (NCs) were prepared using a one-pot synthesis. The stoichiometry was optimized based on its current density as measured by photoelectrochemical (PEC) experiments at interfaces between NC films deposited on ITO and 0.1 M methyl viologen dichloride (MV(2+)) solution. This method also offers insight into the kinetics of the photoreaction. A copper poor sulphur rich starting ratio was found to produce a copper-rich, indium-poor and slightly sulphur rich material. Further NC characterization was performed with SEM and TEM to investigate the morphology and crystallinity of the 30-70 nm NCs. The oxidation states of the individual elements were determined to be I, III, and 2- for Cu, In and S, respectively. Characteristics of optimal as-prepared NCs were found to be compatible among high functioning absorbing layers.

This work reports a synergistic study of a noble metal (NM)/semiconductor hybrid structure featuring a mono/ bimetallic PdPt/TiO 2 heterostructure prepared by a facile anodization-hydrothermal process. The electronic interaction between TiO 2 nanotubes (NTs) and mono/bimetallic PdPt nanoparticles (NPs), as well as the bimetallic PdPt interplay, has been thoroughly investigated by various X-ray techniques. Particularly, X-ray absorption near edge structure (XANES) at the Ti L 3,2 -edge and O K-edge was employed to understand the NM sensitization effect on the local structure of the TiO 2 host. Meantime, d-charge redistribution within Pd and Pt upon alloying and loading on TiO 2 NTs was disclosed at the Pt L 3 -edge and Pd L 3 -edge XANES, respectively. Consistent results were given from their corresponding X-ray photoemission spectroscopy (XPS) analysis. In addition, extended X-ray absorption fine structure (EXAFS) at the Pt L 3 -edge and Pd K-edge was also performed to unravel the atomic distribution and intermetallic interaction of Pd and Pt upon alloying. Finally, the synergy within the mono/bimetallic PdPt/TiO 2 heterostructure was examined by size, compostion, and structure of the as-attached NM NPs assisted with photoresponse performance analysis.

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For the first time, kesterite Cu2ZnSnS4 (CZTS) thin films were efficiently obtained by electrophoretic deposition (EPD) of CZTS nanocrystal (NC) dispersion in an environmentally-friendly solvent, isopropanol. By regulating the applied potential, deposition time, and NC suspension concentration, the EPD process was successfully optimized. Photoelectrochemical measurements (PECMs) were carried out to test the EPD film performance, where the photocurrent density generated from the reduction of methyl viologen (MV2+) was evaluated. EPD films showed a photocurrent three times higher than those obtained by dropcasting at the same concentration. X-ray diffraction and Raman spectroscopy confirmed the formation of a single phase Cu2ZnSnS4 kesterite structure, without impurities. Intensity modulated photocurrent spectroscopy was used to determine the hole-electron recombination and product separation kinetics in the photoprocesses. Lastly, UV-visible spectroscopy determined the bandgap as 1.45 eV, which is an ideal value for single junction solar cell devices. The EPD approach can be combined with our optimized one-pot synthesis of CZTS NCs, which avoids annealing steps after the deposition. Based on these findings, EPD is anticipated to become one of the most promising routes toward fabrication of solar cell devices.

Solar cell performance is most affected by the quality of the light absorber layer. For thin-film devices, this becomes a two-fold problem of maintaining a low-cost design with well-ordered nanocrystal (NC) structure. The use of CuZnSnS (CZTS) NCs as the light absorber films forms an ideal low-cost design, but the quaternary structure makes it difficult to maintain a well-ordered layer without the use of high-temperature treatments. There is little understanding of how CZTS NC structures affect the photoconversion efficiency, the charge-carriers, and therefore the performance of the device manufactured from it. To examine these relationships, the measured photoresponse from the photo-generation of charge-carrier electron-hole pairs was compared against the crystal structure, as short-range and long-range crystal orders for the films. The photoresponse simplifies the electronic properties into three basic steps that can be associated with changes in energy levels within the band structure. These changes result in the formation of barriers to charge-carrier flow. The extent of these barriers was determined using synchrotron-based X-ray absorbance fine structure to probe the individual metal centers in the film, and comparing these to molecular simulations of the ideal extended x-ray absorbance fine structure scattering. This allowed for the quantification of bond lengths, and thus an interpretation of the distortions in the crystal lattice. The various characteristics of the photoresponse were then correlated to the crystallographic order and used to gain physical insight into barriers to charge-carriers in the bulk and surface regions of CZTS films.

The importance of renewable resources is becoming more and more influential on research due to the depletion of fossil fuels. Cost-effective ways of harvesting solar energy should also be at the forefront of these investigations. CuZnSnS (CZTS) solar cells are well within the frame of these goals, and a thorough understanding of how they are made and processed synthetically is crucial. The CZTS/CdS heterojunction was examined using photoelectrochemistry and synchrotron radiation (SR) spectroscopy. These tools provided physical insights into this interface that was formed by the electrophoretic deposition of CZTS nanocrystals and chemical bath deposition (CBD) of CdS for the respective films. It was discovered that CBD induced a change in the local and long range environment of the Zn in the CZTS lattice, which was detrimental to the photoresponse. X-ray absorption near-edge structures and extended X-ray absorption fine structures (EXAFSs) of the junction showed that this change was at an atomic level and was associated with the coordination of oxygen to zinc. This was confirmed through FEFF fitting of the EXAFS and through IR spectroscopy. It was found that this change in both photoresponse and the Zn coordination can be reversed with the use of low temperature annealing. Investigating CZTS through SR techniques provides detailed structural information of minor changes from the zinc perspective.