Reduced bandgap and enhanced p-type electrical conduction in Ag-alloyed Cu2O thin films

Abstract

The photovoltaic absorber Cu2O has attracted much interest in recent years because it is a nontoxic, earth-abundant, and low-cost p-type semiconductor. To date, Cu2O-based solar cells have achieved a power conversion efficiency of ∼8%. However, this value is still far below its theoretical power conversion efficiency of ∼20%. Further improvement in the photovoltaic properties is believed, at least in part, to be limited by its poor p-type electrical conductivity and its relatively wide bandgap (∼2.17 eV). Herein, we studied the electrical and optical properties of Ag alloyed-Cu2O thin films. We demonstrated that the bandgaps of Cu2O can be decreased by Ag-alloying, which is confirmed by density functional theory calculations indicating that the bandgap reduction is due to the downshift of the conduction band minimum in Cu2O, while the valence band edge of Cu2O remains unchanged. Additionally, we found that p-type carrier concentrations are dramatically enhanced in Ag alloyed-Cu2O thin films. Such interesting behavior may be due to the reduced activation energy for hole transport caused by Ag-alloying. This work suggests that Ag incorporation may be a promising and practical method to improve the photovoltaic performance of high efficiency Cu2O-based solar energy conversion.