Heterovalent Ga3+ doping in solution-processed Cu2ZnSn(S,Se)4 solar cells for better optoelectronic performance

Additional elements in Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers present a viable strategy to improve the performance of thin film solar cells. In this study, heterovalent cation doping by partially substituting metal cations with Ga3+ is explored by constructing a sandwich-like configuration. We demonstrated that a low doping level of Ga3+ can be successfully incorporated into the host lattice of CZTSSe to form a homogeneous Cu2ZnSn(Ga) (S,Se)4 (CZTGSSe) alloy material. Characterization was performed using SEM, EDS, XRD, Raman spectroscopy, and XPS, which showed that the material fabricated by this heterovalent cation doping method expressed high phase purity, appropriate valence components, and suitable optical bandgap, which are vital for high performance solar cells. As a result, the champion device achieves stabilized efficiency as high as 10.80%, improved by nearly 28% compared with only 8.43% for the reference device.