Metal Oxides for Dye-Sensitized Solar Cells

The incessant demand for energy forces us to seek it from sustainable resources; and concerns on environment demands that resources should be clean as well. Metal oxide semiconductors, which are stable and environment friendly materials, are used in photovoltaics either as photoelectrode in dye solar cells (DSCs) or to build metal oxide p-n junctions. Progress made in utilization of metal oxides for photoelectrode in DSC is reviewed in this article. Basic operational principle and factors that control the photoconversion efficiency of DSC are briefly outlined. The d-block binary metal oxides viz. TiO2, ZnO, and Nb2O5 are the best candidates as photoelectrode due to the dissimilarity in orbitals constituting their conduction band and valence band. This dissimilarity decreases the probability of charge recombination and enhances the carrier lifetime in these materials. Ternary metal oxide such as Zn2SnO4 could also be a promising material for photovoltaic application. Various morphologies such as nanoparticles, nanowires, nanotubes, and nanofibers have been explored to enhance the energy conversion efficiency of DSCs. The TiO2 served as a model system to study the properties and factors that control the photoconversion efficiency of DSCs; therefore, such discussion is limited to TiO2 in this article. The electron transport occurs through nanocrystalline TiO2 through trapping and detrapping events; however, exact nature of these trap states are not thoroughly quantified. Research efforts are required not only to quantify the trap states in mesoporous metal oxides but new mesoporous architectures also to increase the conversion efficiency of metal oxide-based photovoltaics.