Unveiling the Dual Impact of CuI Layer and Se Content in Sb2(S, Se)3 Photocathodes for Solar Water Splitting

Sb2(S, Se)3 is a promising photocathode for photoelectrochemical (PEC) conversion of solar energy to hydrogen due to its excellent optoelectronic properties, stability, and low toxicity. For such applications, a p–i–n device architecture is favorable for efficient charge separation, with the p‐type layer improving hole extraction while the n‐type layer facilitates electron injection into the electrolyte for hydrogen evolution reaction. However, the lack of suitable p‐type layers for depositing a uniform layer of Sb2(S, Se)3 photocathode constrains the device architectures for PEC water splitting. In this work, various p‐type materials (e.g., NiO, CuS, and CuI) are investigated. Photocathodes fabricated on CuI demonstrate superior performance due to improved hole extraction and uniform growth of Sb2(S, Se)3 absorber layer. The Se/S ratio is adjusted to further fine‐tune the photocathode's absorption, influencing the efficiency of charge carriers’ injection and separation. The overall PEC performance reaches the maximum value when Se/S = 20%, achieving up to 4.2 mA cm−2 with stable photocurrents sustained for 120 min under standard illumination conditions, achieving the highest‐reported photocurrent among S‐rich‐solution‐processed Sb2(S, Se)3 photocathodes. In this work, new avenues are opened for the design of p–i–n Sb2(S, Se)3 PEC devices.