TiO2 passivation layers with laser derived p-n heterojunctions enable boosted photoelectrochemical performance of α-Fe2O3 photoanodes

Abstract

Addressing the carrier loss at the semiconductor-liquid junction of metal oxides is of significance for developing high-performance photoelectrodes for viable solar hydrogen generation, while one of the critical challenges remains in pursuing the top passivation layer with pronounced carrier extraction capability. In the present work, we propose and experimentally verify that artificial engineering of the passivation layer via laser embedding of p-n heterointerfaces leads to significantly improved carrier transfer. By virtue of the advantage of generating nanocrystals in any desired solvents via the technology of laser synthesis and processing of colloids (LSPC), p-type CdTe nanocrystals are successfully embedded in a thin layer of TiO2, which is adopted as an efficient passivation layer to address the excessive surface defects and the slow carrier transfer at α-Fe2O3 photoanodes. The embedded p-n heterointerfaces not only provide an effective built-in electric field that accelerates carrier transport in TiO2 via boosting polaron hopping but also activate hole transfer by shifting up the valence band in TiO2. Such vivid embedding is demonstrated to generate a 12-fold increase for the lifetime of photogenerated electrons, and a 3.9-fold increase for the ηinj at 1.23 VRHE, leading to a 4.4-fold increase in the photocurrent density at 1.23 VRHE. We thus believe the present work provides a universal alternative for regulating the chemical/physical features of semiconductor-liquid junctions at metal oxides.