Tuning property through controlled crystallinity of Cu2ZnSnS4 as photovoltaic film by sodium doping

Cu 2 ZnSnS 4 (CZTS) is a promising candidate material for photovoltaic applications, sodium doping is crucial for improving the crystalline quality and performance of CZTS thin films. This study systematically investigated the effects of sodium dopant type, such as NaCl, NaHCO 3 , and NaOH, doping concentration at specific levels of 0, 3, 6, 9, and 12 at.%, and doping method, including precursor solution doping and post-deposition doping, on the microstructure and optical properties of CZTS thin films. Research findings indicate that NaHCO 3 serves as the optimal sodium source, effectively promoting grain growth while suppressing secondary phase formation. The film with 6 at.% doping concentration achieves optimal properties, including a maximum grain size of 57 nm and a near-ideal stoichiometry with Cu/Zn and S/Zn ratios of 2.38 and 4.90, alongside significantly enhanced surface compactness. The sodium doping in the precursor solution enhances crystallinity but tends to introduce secondary phases, whereas post-doping of the precursor film better preserves phase purity and elemental stability, albeit with a slight decrease in crystallinity.