CdCl ₂ Treatment for Cu ₂ ZnSn(S,Se) ₄ : A Method to Enhance the Solar Cell Performance

Unlike other thin‐film absorbers, CZTSSe can be efficiently produced using nonvacuum techniques, which enable precise control over the stoichiometry of the absorber layer from the precursor solution stage. Despite extensive research over the past two decades, CZTSSe has not surpassed an efficiency of 15%, primarily due to a significant V oc deficit. To address this challenge, researchers typically pursue either alloying the absorber with additional elements to tune the band gap or doping the absorber with impurities to boost carrier concentration. This study presents a straightforward approach for improving performance by either narrowing the band gap or doping the absorber by processing, for the first time, the CZTSSe by CdCl 2 treatment, which can be applied to any fabrication process. Depending on the stage of the fabrication process at which it is carried out, the same practical CdCl 2 treatment can introduce Cd into the CZTSSe matrix as an alloying or doping agent.