Doping the n-layer of transparent Cu₂O/ZnO nanostructures synthesized via electrodeposition and chemical bath deposition for solar cell applications

Abstract

This study focuses on the controllable synthesis of Cu₂O/ZnO heterojunctions to enhance charge carrier separation and promote directional transport, by optimizing n-type ZnO bandgap engineering and interfacial grain alignment for photovoltaic applications. For this purpose, undoped ZnO/Cu₂O, Mg–Al co-doped ZnO (MAZO) and n-layer Cu₂O/MAZO heterojunctions were prepared using two distinct methods: single-step ED (electrodeposition) and a combined process of ED-CBD (chemical bath deposition). Mott–Schottky electrochemical impedance measurements revealed n-type conductivity in the ZnO and MAZO thin films. The surfaces morphology of the heterojunctions prepared by ED exhibited cubic-shaped particles, whereas those prepared by the combined ED-CBD method exhibited pyramidal-shaped structures. X-Ray Diffraction (XRD) analysis revealed that the grown ZnO layers crystallized in a hexagonal structure, whereas the Cu₂O layers exhibited a cubic crystal structure. The bandgap of undoped ZnO layers was measured to be 3.3 eV, which increased to 3.5 eV and 3.4 eV for MAZO thin films prepared via ED and CBD, respectively. The strong absorption edge observed in Cu₂O layer in visible region indicate their suitability as an absorber layer in solar cell structures. The best photoresponse was obtained with a current density of 0.315 mA cm⁻² for the n-MAZO layer prepared by CBD deposition, which is considerable compared with similar structures reported in recent literature. These results highlight the potential of MAZO layers for optoelectronic applications; however, further optimization of the current density and interfacial charge transfer is still required to improve device efficiency.