A qualitative study of SnSe thin film solar cells using SCAPS 1D and comparison with experimental results: A pathway towards 22.69% efficiency

We simulated a tin selenide (SnSe) based solar cell device in a standard planar substrate configuration (glass/ Mo/SnSe/CdS/i-ZnO/AZO/Al) using a Solar Cell Capacitance Simulator (SCAPS-1D) software to elucidate a path to higher power conversion efficiency (PCE). A baseline model for the device was simulated and established using the experimental results of our recent study on a 2.51% device. A stepwise fitting procedure observed a higher effective density of states in SnSe, along with a band offset of -0.11 eV for conduction between SnSe and CdS; these factors are responsible for limiting the open-circuit voltage (VOC). We optimized the buffer and absorber layer parameters to improve the working capabilities to achieve higher efficiency by improving VOC. In particular, the effects of carrier concentration, absorber-buffer interface recombination, absorber thickness, buffer layer thickness, and defect densities were studied and analyzed in detail via simulation. Interestingly, optimal absorber and buffer layer thicknesses of 1.2 mu m and 60 nm were obtained for the baseline and simulated devices. Finally, a NiO back-surface field (BSF) layer was introduced, and its performance was evaluated. Significant improvements in VOC and fill factor (FF) were observed with implementing the NiO BSF layer at the SnSe/CdS interface. The optimal device without a BSF layer exhibited a maximum efficiency of 13.79% with a VOC of 0.590 V; a short-circuit current density (JSC) of 36.28 mA cm-2, and an FF of 64.33%. Finally, the highest PCE of 22.69% with a VOC of 0.818 V, JSC of 33.65 mA cm-2, and FF of 82.41% was observed after applying the BSF layer.