Regulating Hetero‐Nucleation Enabling Over 14% Efficient Kesterite Solar Cells

Abstract Developing well‐crystallized light‐absorbing layers remains a formidable challenge in the progression of kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells. A critical aspect of optimizing CZTSSe lies in accurately governing the high‐temperature selenization reaction. This process is intricate and demanding, with underlying mechanisms requiring further comprehension. This study introduces a precursor microstructure‐guided hetero‐nucleation regulation strategy for high‐quality CZTSSe absorbers and well‐performing solar cells. The alcoholysis of 2‐methoxyethanol (MOE) and the generation of high gas‐producing micelles by adding hydrogen chloride (HCl) as a proton additive into the precursor solution are successfully suppressed. This tailored modification of solution components reduces the emission of volatiles during baking, yielding a compact and dense precursor microstructure. The reduced‐roughness surface nurtures the formation of larger CZTSSe nuclei, accelerating the ensuing Ostwald ripening process. Ultimately, CZTSSe absorbers with enhanced crystallinity and diminished defects are fabricated, attaining an impressive 14.01% active‐area power conversion efficiency. The findings elucidate the influence of precursor microstructure on the selenization reaction process, paving a route for fabricating high‐quality kesterite CZTSSe films and high‐efficiency solar cells.