Polarization-induced saw-tooth-like potential distribution in zincblende-wurtzite superlattice for efficient charge separation

Abstract

Hydrogen production from solar water splitting over semiconductors shows great potential in solving the urgent energy and environmental issues, but its energy conversion efficiency is always restricted by the insufficient utilization of photogenerated charge carriers. Introducing built-in electric fields is a promising strategy for achieving efficient charge utilization in photocatalysts. However, the representative examples of built-in electric fields reported to date all have their own insurmountable shortcomings. Herein, we demonstrated that the zincblende-wurtzite (ZB-WZ) superlattice structure which widely spreads in II-VI and III-V group semiconductors is a promising candidate for the sufficient utilization of photogenerated charge carriers. We developed the ZB-WZ superlattice structures in a model semiconductor photocatalyst, Cd1−xZnxS, by employing the oriented-attachment growth mechanism, and realized highly efficient photocatalytic hydrogen production under visible light irradiation with an excellent apparent quantum yield of 48.7% at 425nm. Then the huge impact of the ZB-WZ superlattice structure on the photocatalytic performance was proved by the strong reciprocal relationships between the percentage of the nanocrystals with superlattice structures and the photoluminescence intensity, as well as that between the photoluminescence intensity and the photocatalytic activity. Moreover, theoretical simulation demonstrated that the spatial separation and alternate accumulation of electrons and holes around ZB/WZ interfaces is dominated by the polarization-induced saw-tooth potential distribution in the ZB-WZ superlattice rather than the staggered band alignment, and the intensities of built-in electric fields in adjacent ZB and WZ segments can be tuned by changing the specific configuration of the ZB-WZ superlattice. These findings open a new pathway for the development of novel and efficient semiconductor photocatalysts by tuning the superlattice structure with atomic precision, which will greatly benefit the solar water splitting area.