Enhanced Photoelectrochemical Response of the ZnO/V₂O₅ Heterojunction Via Improved Visible-Light Absorption and Charge Carrier Separation

Abstract

Planar ZnO/V 2 O 5 heterojunctions show excellent photocurrent density and are easy to prepare using a simple physical vapor deposition technique. First, ZnO thin-film photo-electrodes were prepared by radio frequency sputtering, and then their thickness was optimized for improved photoelectrochemical (PEC) response, resulting in an optimum photocurrent density value of ∼0.7 mA/cm 2 at 0.61 V vs Ag/AgCl for ZnO thin films deposited for 15 min. Thereafter, ZnO/V 2 O 5 heterojunctions were fabricated by depositing V 2 O 5 thin films for different deposition durations of 10, 20, and 30 min onto ZnO thin-film samples which were already optimized to further improve the PEC performance. The structural, optical, and morphological properties of pristine and heterojunction thin-film samples were investigated by X-ray diffraction, Raman spectroscopy, UV−visible spectroscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques. The maximum photocurrent density value of 1.56 mA/cm 2 at 0.61 V vs Ag/AgCl was obtained for ZnO/V 2 O 5 heterojunction photoanodes, where the top V 2 O 5 layer was deposited by RF magnetron sputtering process which occurred for 20 min. The ZnO/ V 2 O 5 heterojunction photocurrent density was nearly twice as compared with that of the pristine ZnO photo-electrode. This improved PEC response of the ZnO/V 2 O 5 heterojunction was due to enhanced visible-light absorption and the formation of a staggered n−n heterojunction, which facilitated the separation of electron−hole pairs at the photo-anode/electrolyte junction.