Tuning the Energy Levels of ZnO/ZnS Core/Shell Nanowires To Design an efficient Nanowire-Based Dye-Sensitized Solar Cell

By using the self-consistent charge density functional tight binding method we studied the electronic structure of ZnO/ZnS core/shell nanowire as a function of both core radius and shell thickness. By studying the band energy alignment, band structure, density of states, and band edge wave functions we envisage the efficacy of this particular nano heterostructure in dye sensitized solar cell. The strong localization of valence band maximum and conduction band minimum in ZnS shell and ZnO core, respectively, irrespective of core radius and shell thickness clearly indicates the spatial charge separation in this system. This spatial charge separation decreases the charge recombination rate thereby increasing the chance of better photovoltaic performance. We also investigated the electronic structure of anthraquinone (AQ) acid dye molecule-ZnO/ZnS nanowire composite system. We demonstrated that whether the composite system will form type I or type II band alignment that very much depends on the thickness of the ZnS shell and the nature of the functional group (electron withdrawing or electron donating) attached to AQ acid molecule.