Insight into the Effect of Selenization Temperature for Highly Efficient Ni-Doped Cu₂ZnSn(S,Se)₄ Solar Cells

Cu₂Ni₀·₀₅Zn₀·₉₅Sn(S,Se)₄ (CNZTSSe) films were synthesized on Mo-coated glass substrates by the simple sol-gel means combined with the selenization process, and CNZTSSe-based solar cells were successfully prepared. The effects of selenization temperature on the performance and the photoelectric conversion efficiency (PCE) of the solar cells were systematically studied. The results show that the crystallinity of films increases as the selenization temperature raises based on nickel (Ni) doping. When the selenization temperature reached 540 °C, CNZTSSe films with a large grain size and a smooth surface can be obtained. The Se doping level gradually increased, and Se occupied the S position in the lattice as the selenization temperature was increased so that the optical band gap (Eg) of the CNZTSSe film could be adjusted in the range of 1.14 to 1.06 eV. In addition, the Ni doping can inhibit the deep level defect of Sn_Zn and the defect cluster [2Cu_Zn + Sn_Zn]. It reduces the carrier recombination path. Finally, at the optimal selenization temperature of 540 °C, the open circuit voltage (V_oc) of the prepared device reached 344 mV and the PCE reached 5.16%.