To improve the efficiency of solar energy conversion into electricity or chemical fuels, it is essential to understand the charge carrier losses within the devices. In this context, the first part of my talk will be focused on understanding the photogenerated electron losses in dye-sensitized photoelectrochemical solar cells (DSCs) and the path we pursued to block this unwanted reaction. In DSCs, electron recombination from photoanode (electron donor) to the redox species (electron acceptor) is a dominant parasitic process, that affects the conversion efficiency. In order to suppress this reaction, we implemented a strategy of separating the electron donor from the acceptor using oxide quantum tunneling layers (QTLs), which in according to Marcus theory should exhibit an exponential decrease in the charge transfer. However, during the course of the research we discovered that only certain oxide QTLs blocked the recombination, while others promoted the back electron transfer. Using various electro-optical spectroscopic techniques we understood this ambiguity, and our scientific findings is shown to have a significant implication on many photoelectrochemical systems.
In the latter part of the talk, I will present our recent research in developing photoconductive metal-organic coordination frameworks (MOFs) for sunlight harvesting applications. MOFs can be synthesized from a vast majority of organic linkers and metal cations, available in the scientific literature. Although they offer excellent tunability in synthesis, most of the existing MOFs show poor electronic conductivity because of orbital mismatch and/or possesses redox inactive components. To effectively utilize the library of linkers and metal cations, it is important to address the issue of conductivity. We circumvent this problem by utilizing thiol and pyrazine linkers, unlike conventional carboxylic acids. The resulting MOFs shows tunable (photo)conducting properties and also exhibit photovoltaic effect.