Sulfur-regulated composition in CuInS₂ films for efficient solar cells

Abstract A systematic investigation is conducted to determine the role of thiourea in regulating crystallization and defect formation in solution-processed CuInS 2 solar cells. By modulating the Cu:In:S stoichiometry (1:1:6–1:1:10), sulfur content is found to critically influence material properties. The optimal stoichiometry (1:1:8) balances the defects density, stabilizes the chalcopyrite phase, and suppresses deleterious secondary phases, yielding a peak efficiency of 5.16% ( V oc = 0.68 V, J sc = 11.91 mA cm −2 , FF = 63.52%). Excessive thiourea (1:1:10) induces defects (In Cu ) and (In i ), degrading device performance. These findings establish a dual mechanism for thiourea’s role in solar cell performance: regulating defects concentration and crystal phase composition, providing a theoretical guide for solution-processed CuInS 2 devices.