Dynamic Photocurrent Response of CuO-Nanoarray-Based Photoelectrodes: Heterostructure and Small Electric Field Effects

CuO nanoarrays were synthesized by using a hydrothermal method, and TiO2 nanocrystals were deposited on the surface of CuO nanoarrays to form bulk heterostructure photoelectrodes. The current-time curve revealed that TiO2 nanocrystals can enhance the photocurrent of CuO nanoarrays, resulting from the higher charge separation efficiency and transfer rate. In addition, the effects of small biases (–0.1 and 0.1 V) on the photocurrent and photogenerated charge dynamics in the aforementioned photoelectrodes were evaluated. A small bias was found to not influence the macroscopic dynamical process during charging and discharging of the CuO photoelectrode, but it was more correlated with the microscopic dynamics. Additionally, the built-in electric field in the CuO nanoarray/TiO2 heterojunction could be affected by a small external bias, thereby influencing the charge separation and charge diffusion concentration, which, subsequently, influenced the charge diffusion length, L. In contrast, L in the pristine CuO nanoarray was not improved under a small reverse bias, because the small reverse bias could not efficiently improve the diffusion concentration owing to the lack of a built-in electric field to dissociate electron-hole pairs. These kinetic mechanisms are helpful in understanding the photoelectric conversion process in heterogeneous photoelectrodes.