Aqueous Selenium Ion Engineering: A Universal Strategy to Reverse Gradient Limitations in Sb ₂ (S,Se) ₃ Photovoltaics for Enhanced Carrier Dynamics and Performance

Abstract Antimony selenosulfide (Sb₂(S,Se)₃) is a promising earth‐abundant photovoltaic material owing to its excellent optical and electrical properties. Currently, solution‐processed Sb₂(S,Se)₃ photovoltaics face a critical selenium paradox: uncontrolled gradient formation induces band misalignment while creating sulfur vacancies ( V _S ) and antimony antisites (Sb _S/Se ). Here, an ambient aqueous selenide ion treatment (ASIT) acting as atomic‐scale “ionic scalpel” is pioneered that surgically reconstructs selenium distribution. Through room‐temperature ionic diffusion, this liquid‐phase ion engineering achieves dual breakthroughs: 1) Gradient reversal via surface and bulk selenium enrichment flattening valence band offset from 0.12 to 0.03 eV and establishing ideal Type‐II band alignment, 2) Autogenous deep‐level defects healing via Se−V _S /Sb _S bond reconfiguration. Significantly, time‐resolved photoluminescence (TRPL) characterization unveils, for the first time, the ultrafast charge‐transfer dynamics at the heterointerface of CdS/Sb₂(S,Se)₃ films fabricated via the ASIT strategy. Ultimately, the resultant Sb₂(S,Se)₃ solar cell shatters performance ceiling with a 10.38% efficiency and record open‐circuit voltage of 0.694 V, showing 57% carrier lifetime enhancement. The water‐based process compatibility with roll‐to‐roll manufacturing positions ASIT as a game‐changer for scalable production of gradient‐engineered absorbers beyond antimony‐based systems.