14.2% Efficient Kesterite Solar Cells From Dimethyl Sulfoxide Solution via Li + Cd Co‐Doping

Kesterite Cu ₂ ZnSn (S,Se) ₄ (CZTSSe) solar cells, as an emerging class of inorganic photovoltaics, offer promising application prospects owing to their earth‐abundant and environmentally benign constituent elements, as well as a high theoretical power conversion efficiency. However, the relatively low majority carrier concentration, detrimental band tailing induced by bulk Cu–Zn disorder defects, and severe interface recombination limit further improvement in device efficiency. In a dimethyl sulfoxide (DMSO) solution system, extrinsic cation doping with Li ⁺ and Cd ²⁺ was introduced to optimize both bulk and interfacial properties of the CZTSSe absorber. The results show that the co‐incorporation of Li and Cd into the absorber significantly improves its crystallinity, reduces defect density, and suppresses band tailing states, while simultaneously enhancing the hole carrier concentration of CZTSSe. Furthermore, Li + Cd co‐doping results in more favorable conduction band offset (CBO) at CZTSSe/CdS heterojunction interface compared to the control group, which effectively reduces carrier recombination and enhances carrier collection efficiency, achieving a power conversion efficiency of 14.2% for the champion device.