Defect Density Control Using an Intrinsic Layer to Enhance Conversion Efficiency in an Optimized SnS Solar Cell

We report a modification to the structure of an SnS/CdS solar cell to address the issue of its low experimental efficiency. The proposed structure primarily aims to control bulk recombination via passivation of the absorber bulk defect density and control of interfacial recombination via insertion of an intrinsic layer at the absorber–buffer interface. The device structure design is simulated with an SnS absorber, CdS buffer layer, and intrinsic layer with low hole density of ~ 10¹² cm^-3. The simulation approach matches the defect model to the experimental efficiency of the SnS/CdS structure to benchmark the parameters under varying conditions of bulk defect density, asymmetric carrier mobility, illumination, and temperature. The results confirm that the bulk recombination and fill factor losses are the major efficiency-limiting factors. Subsequent passivation of the bulk defect density in the absorber layer enhances J_SC and the efficiency by controlling the bulk recombination. Insertion of an intrinsic layer at the SnS–CdS interface in the next level of simulation improves the fill factor. This approach enhances the fill factor to 62% from 54% for the benchmarked experimental cell. A substantial improvement is found in the open-circuit voltage (V_OC) to 0.89 V from its experimental value of ~ 0.32 V. The two-tier optimization proposed in this work yields a fivefold higher efficiency of ~ 15.69% for the simulated optimal device structure when compared with the value of 3.16% reported experimentally and benchmarked initially herein to modify the device structure.