Towards high efficiency Cd-Free Sb₂Se₃ solar cells by the band alignment optimization

In this paper, we investigated the effect of Zn_1-yMg_yO/ZnO_1-xS_x double buffer layers on the antimony selenide (Sb₂Se₃) solar cells performance. Our results show that the magnesium and sulfur concentrations in proposed double buffer layers have a significant effect on the band alignment optimization at the junctions. The flexibility with Zn_1-yMg_yO/ZnO_1-xS_x double buffer layers ranging from 0 to 25% magnesium and 10%–70% sulfur allows an optimal conduction band offset (CBO) for Sb₂Se₃ solar cells. An improved open-circuit voltage (V_oc) was observed in the Sb₂Se₃ solar cell with Zn_0.93Mg_0.07O/ZnO_0.4S_0.6 proposed double buffer layers due to appropriate CBO values at the junction interfaces. The short-circuit current density (J_sc) values increased as the sulfur concentration in the ZnO_1-xS_x buffer layer increased from 0 to 0.7 (x value), which could be related to the increase in the optical band gap of the ZnO_1-xS_x layer. The results demonstrated that under small positive offset conditions (spike-like), the carrier recombination rate at the interface is reduced, and consequently, the Sb₂Se₃ solar cell performance is improved. A Sb₂Se₃ solar cell with the optimum CBO amount (+0.3 eV) represented a conversion efficiency of 15.46%, which exhibited a 68% enhancement in comparison to the traditional CdS/Sb₂Se₃ solar cell.