Effect of the thin Ga2O3 layer in n+-ZnO/n-Ga2O3/p-Cu2O heterojunction solar cells

Abstract The influence of inserting a Ga2O3 thin film as an n-type semiconductor layer on the obtainable photovoltaic properties in Cu2O-based heterojunction solar cells was investigated with a transparent conductive Al-doped ZnO (AZO) thin film/n-Ga2O3 thin film/p-Cu2O sheet structure. It was found that this Ga2O3 thin film can greatly improve the performance of Cu2O-based heterojunction solar cells fabricated using polycrystalline Cu2O sheets that had been prepared by a thermal oxidization of copper sheets. The obtained photovoltaic properties in the AZO/Ga2O3/Cu2O heterojunction solar cells were strongly dependent on the deposition conditions of the Ga2O3 films. The external quantum efficiency obtained in AZO/Ga2O3/Cu2O heterojunction solar cells was found to be greater at wavelengths below approximately 500 nm than that obtained in AZO/Cu2O heterojunction solar cells (i.e., prepared without a Ga2O3 layer) at equivalent wavelengths. This improvement of photovoltaic properties is mainly attributed to a decrease in the level of defects at the interface between the Ga2O3 thin film and the Cu2O sheet. Conversion efficiencies over 5% were obtained in AZO/Ga2O3/Cu2O heterojunction solar cells fabricated using an n-Ga2O3 thin-film layer prepared with a thickness of 40–80 nm at an O2 gas pressure of approximately 1.7 Pa by a pulsed laser deposition.