Bandgap Tunable Perovskite for Si-Based Triple Junction Tandem Solar Cell: Numerical Analysis-Aided Experimental Investigation

Halide perovskites are promising in the development of multijunction solar cells with enhanced power conversion efficiency (PCE) compared to that of single-junction solar cells. Besides the optimal design limitation for mitigating optical and electrical losses, amalgamating different perovskite absorber layers with optimized bandgap and thickness for a multijunction cell is a topic of concern. Herein, we demonstrate a facile and cost-effective technique called a double-sided sandwich evaporation technique for fabricating a pure and mixed-halide-based perovskite absorbing layer. By tuning the halide ratio and B-site doping, we successfully fabricated MAPbIxBr3–x, MAPbIxCl3–x, and MAPbxSn1–xI3, formulating a triple-junction tandem solar cell. The solar cell configuration MAPbIxBr3–x (1.96 eV)/MAPbIxCl3–x (1.593 eV)/Si (1.12 eV) exhibited a higher PCE of 25.84% as compared with the original bandgap combination of MAPbIxBr3–x (1.96 eV)/MAPbxSn1–xI3 (1.31 eV)/Si (1.12 eV), showing a PCE of 24.62%. Moreover, theoretical insight for the optimal perovskite thickness was gained using SETFOS by taking into account the reflection of the bottom cell, so the thickness of the top layers could be reduced. The result shows that in the thinner upper and middle perovskite cells, the light absorption ratio of each subcell can be effectively distributed, resulting in a triple-junction tandem solar cell with a PCE of 26.40%.