Interface stoichiometry control in ZnO/Cu_2O photovoltaic devices
Cu_2O is a potential earth-abundant alternative to established thin photovoltaic materials (CIGS, CdTe, etc.) because of its low cost, high availability, and inexpensive processing, but Cu_2O has seen limited development as a photovoltaic device material owing to challenges in measurement and control of interface stoichiometry and doping. We report measurements of Cu_2O interface stoichiometry and the effect of interface composition on heterojunction device performance. ZnO/Cu_2O interface stoichiometry was varied by adjusting the ZnO window layer deposition conditions and stoichiometry was measured by X-ray photoelectron spectroscopy. Current-voltage characteristics of ZnO/Cu_2O heterojunctions indicate open circuit voltages of Voc ~ 530 mV for devices where the Cu_2O layer is stoichiometric at the interface and Voc ~ 100 mV for devices where Cu_2O is nonstoichiometric at the interface.