Electrodeposition of p-type cuprous oxide layers on n-type zinc oxide layers with different electrical resistivities

The development of metal oxide semiconductor-based absorber layers consisting of earth abundant elements is currently in the early stages of research. Cuprous oxide (Cu₂O) is a representative p-type oxide material with an appropriate band gap for this application. To produce all-oxide photovoltaic cells, the authors grew Cu₂O films on top of n-type Zinc oxide (ZnO) layers by electrodeposition. Prior to the electrodeposition of Cu₂O, the underlying ZnO layers were deposited by atomic layer deposition at different temperatures. The resulting films had different electrical conductivities. For the low conductivity ZnO grown at 100 °C, the Cu₂O layer was coated with a highly (111) preferred orientation leading to low electrical resistivity. Consequently, these Cu₂O/ZnO heterojunction solar cells showed relatively high conversion efficiencies despite the low conductivity of the ZnO. Conversely, the Cu₂O deposited on the highly conductive ZnO film (grown at 150 °C) exhibited extremely low photocurrent, which was attributed to low crystallinity and poor electrical properties.