A Transparent, High-Performance, and Stable Sb2S3 Photoanode Enabled by Heterojunction Engineering with Conjugated Polycarbazole Frameworks for Unbiased Photoelectrochemical Overall Water Splitting Devices

Developing low-cost, high-performance, and durable photoanodes is essential in solar-driven photoelectrochemical (PEC) energy conversion. Sb2S3 is a low-bandgap (approximate to 1.7 eV) n-type semiconductor with a maximum theoretical solar conversion efficiency of approximate to 28% for PEC water splitting. However, bulk Sb2S3 exhibits opaque characteristics and suffers from severe photocorrosion, and thus the use of Sb2S3 as a photoanode material remains underexploited. This study describes the design and fabrication of a transparent Sb2S3-based photoanode by conformably depositing a thin layer of conjugated polycarbazole frameworks (CPF-TCzB) onto the Sb2S3 film. This structural design creates a type-II heterojunction between the CPF-TCzB and the Sb2S3 with a suitable band-edge energy offset, thereby, greatly enhancing the charge separation efficiency. The CPF-TCzB/Sb2S3 hybrid photoanode exhibits a remarkable photocurrent density of 10.1 mA cm(-2) at 1.23 V vs reversible hydrogen electrode. Moreover, the thin CPF-TCzB overlayer effectively inhibits photocorrosion of the Sb2S3 and enables long-term operation for at least 100 h with approximate to 10% loss in photocurrent density. Furthermore, a standalone unbiased PEC tandem device comprising a CPF-TCzB/Sb2S3 photoanode and a back-illuminated Si photocathode can achieve a record solar-to-hydrogen conversion efficiency of 5.21%, representing the most efficient PEC water splitting device of its kind.