Engineering Buried Interface by A Conductive Polymer to Mediate Carrier Behavior for Efficient Solar-driven Water Splitting on Si-based Photocathode

Abstract

Photoelectrochemical (PEC) water splitting is regarded as a promising route to produce sustainable hydrogen fuel using sunlight and water as sole inputs. To date, buried interfaces have remained challenging for photocarrier extraction/injection in Si-based PEC photocathodes, thereby affecting the overall efficiency of photoelectrochemical devices.Herein, a series of conductive polymers were introduced as an interlayer in a Si/CdS hybrid photocathode and investigated how to mediate the photocarriers. According to the analysis, the conductive polymers induced an energy-level shift and modified the work function of the Si. Inspired by these findings, the direct deposition of a conductive polymer interlayer by a simple process is a promising tactic for engineering buried interface. It is found that polythiophene formed an energetically more favorable interface and boost photocathode's efficiency, which achieved an applied bias photon-to-current efficiency (ABPE) of 4.05% with a photocurrent of 30.8 mA/cm 2 at 0 VRHE for the optimized Si/PTH/CdS/Co-P photocathode, even exceeding the reported Si/CdS photocathode. In addition, a bias-free system of Si/PTh/CdS/Co-P||Ti/TiO2/CdS/ZnSe could be successfully constructed to realize an unassisted PEC tandem system with an approximate photocurrent density of 0.53 mA/cm 2 and maintain good stability. This finding highlight that the strategically incorporated conductive polymer framework effectively mediates carrier extraction/injection through tune energy level and then promotes interfacial charge carrier transfer, offering a new paradigm in guiding the design of efficient solar water-splitting device.