Uniform ZnO nanorod/Cu2O core–shell structured solar cells by bottom-up RF magnetron sputtering

Abstract

Cu₂O is a good candidate material for use as a p-type absorber in solar cells. Here, uniform ZnO nanorod (NR)–Cu₂O core–shell structures are fabricated and their diode performances are studied. ZnO NRs are grown on fluorine-doped tin oxide (FTO) glass using a hydrothermal method. Cu₂O is then deposited on the ZnO NRs using bottom-up RF magnetron sputtering. The crystal structures of the deposited ZnO NRs and Cu₂O are characterized using X-ray diffraction. From secondary electron microscopy analysis, the uniform core–shell structure and its size are identified. UV-vis spectroscopy measurements show that the optical bandgap of the Cu₂O in this structure is 2.3 eV. The diode characteristics of the fabricated nanostructures depend on the thickness of Cu₂O; 2.7 μm-thick Cu₂O on ZnO NRs shows diode properties. Lastly, we propose a band alignment model based on X-ray photoelectron spectroscopy analysis and demonstrate a possible approach for fabricating Cu_xO–ZnO nanohybrids for further improvements to device efficiency, highlighting a need for interfacial band offset medication for oxide heterojunction solar cells.