A new CsPbI2Br/CuZnSnSSe/Si tandem solar cell with higher than 32% efficiency

To avoid Shockley-Queisser limit in single p-n junctions, tandem solar cells were proposed. A new tandem cell is simulated here using the 1-dimensional SCAPS. The new cell combines two reported single solar cells together, aiming at achieving high performance by optimizing various layer characteristics. The bottom sub-cell is Mo/Si(p)/CZTSSe(p)/CdS(n)/ZnO(i)/ZnO(Al), where ZnO is an electrodeposited transparent-conductor oxide, with high UV transmittance, ZnO(i) is intrinsic layer, CZTSSe/Si is bi-absorber layer of p-CuZnSnSSe and p-Si, Mo is back contact. The optimized sub-cell exhibits a high fill factor of 85.18% with overall efficiency 20%. Based on literature, a perovskite CsPbI2Br layer is included in the top sub-cell Cu2O(HTL)/CsPbI2Br)/TiO2(ETL), where Cu2O is a hole-transport layer and TiO2 is electron-transport layer. The top sub-cell layers have been carefully selected for best alignment. Matching and optimizing various parameters in the two sub-cells is a simulation challenge. Therefore, layers in the two sub-cells have been studied separately, keeping in mind the proper combinations between various layers. With optimized layer thicknesses and band gaps, together with proper alignment of band edges, the proposed tandem solar cell exhibits high characteristics of 80% fill factor and higher than 32% overall efficiency.