Built-in electric field induced efficient interfacial charge separation via the intimate interface of CdS-based all-sulfide binary heterojunction for enhanced photoelectrochemical performance

Cadmium sulfide (CdS), as a prospective photoelectrochemical (PEC) photoanode material, has been restrained in hydrogen production owing to the severe recombination of charge carrier and the inherent photocorrosion. Herein, a thin shell consisted of cuprous sulfide (Cu2S) nanoparticles was formed on CdS nanorods arrays to overcome the shortages. An all-sulfide heterojunction not only establishes close interface and p-n junction between two semiconductors, but also possesses additional S atom channel for charge carrier migration, all beneficial for the efficient separation of photogenerated electrons/holes. In consequence, the transient photocurrent density of CdS/Cu2S reaches to 4.95 mA/cm2 under simulated sunlight with zero bias-potential, 1.4-fold of the pristine CdS. The excellent PEC performance results from the type-II band alignment and built-in electric field in heterojunction. Additionally, by the density functional theory, the calculated work function and band structure of CdS/Cu2S heterojunction gave strong evidences for the type-II charge transfer mechanism, and the established built-in electric field between p-n junction accelerated transfer and separation of photogenerated charge carriers.