Controlled conduction band offset in Sb2Se3 solar cell through introduction of (Zn,Sn)O buffer layer to improve photovoltaic performance: A simulation study

Enhancing the performance of antimony selenide (Sb2Se3) solar cells is significantly influenced by the optimization of the absorber/buffer junction. A wider bandgap buffer layer is suggested as a substitute for the traditional CdS buffer layer, for achieving this purpose. To enhance the short-circuit current density (Jsc) and mitigate parasitic absorption of Sb2Se3 cells, this study introduces zinc tin oxide (Zn,Sn)O as a substitute buffer layer instead of the narrow-bandgap and toxic CdS material. This study focuses on the simulation and numerical analysis of Sb2Se3 solar cells with (Zn,Sn)O buffer layer using the SCAPS (Solar Cell Capacitance Simulator) software. The photovoltaic performance was evaluated by investigating the impact of different fractions of x = Sn/(Zn + Sn) in the Zn1-xSnxO layer. The reduction of interface recombination and improvement of open-circuit voltage (Voc) can be attained by optimizing the band alignment through the Zn1-xSnxO layer. The most favorable interface between the Sb2Se3 and Zn1-xSnxO layers is attained when x = 0.2. In a traditional Sb2Se3/TiO2/CdS cell, the interface between the absorber and buffer layers has a -0.4 eV conduction band offset (CBO). The utilization of a Zn0.8Sn0.2O buffer layer causes an upward shift of the conduction band and a reduction of the negative CBO to -0.16 eV. Consequently, due to the wider gap between the conduction band of the Zn0.8Sn0.2O and the valence band of the Sb2Se3, interface recombination is reduced. According to the simulation results, the efficiency of the simulated Sb2Se3/TiO2/Zn0.8Sn0.2O cell is increased to 14.6%, representing a significant improvement compared to the conventional Sb2Se3/TiO2/CdS cell.