Modulating band alignment at the 3D metal/semiconductor interface of liquid metal-embraced semiconductor photoelectrodes for water splitting

Abstract

The transfer of photogenerated charges from semiconductors as photoabsorbers to conductive substrates as current collectors is closely correlated with the interface band alignment, particularly for an emerging class of photoelectrodes possessing the three dimensional (3D) interface that semiconductors are embraced by low-melting-point (LMP) metals (i.e., Field’s metals). Herein, the interface band alignment is modulated to promote the transfer of photogenerated charges by taking advantage of the composition-dependent work function (WF) of liquid metal as the current collector. It is found that embracing ZnO particles by indium tin (IT) alloy leads to the Ohmic contact, while embracing ZnO particles by bismuth indium tin (BIT) alloy leads to the Schottky contact. Consequently, the photocurrent density of the resulting IT-embraced ZnO (IT/ZnO) photoelectrode with superior charge collection and separation ability for photoelectrochemical water splitting is increased by 19% from 0.52 mA cm⁻² of BIT-embraced ZnO (BIT/ZnO) to 0.62 mA cm⁻², ranging on the top of the representative ZnO photoelectrodes. In contrast, the photoelectrodes of WO₃, TiO₂, and Cu₂O embraced with IT or BIT have the same contact type and nearly identical performance. This work demonstrates the potential of changing the metal/semiconductor contact type to enhance the performance of LMP metal-embraced semiconductor photoelectrodes by choosing liquid metals with different WFs, paving a way to build efficient photoelectrodes.