Band alignment of Pb-Sn mixed triple cation perovskites for inverted solar cells with negligible hysteresis

Substituting the toxic lead (Pb) in Pb halide perovskites by less harmful Sn is an attractive approach towards obtaining environment-friendly perovskite solar cells. However, complete substitution of Pb by Sn undermines the stability of perovskite materials and devices. Therefore, partial substitution of Pb by Sn has attracted much interest to balance environmental considerations and device performance. Here, we exploit the Sn ratio to optimize the band alignment in Pb-Sn mixed perovskite solar cells with an inverted structure. The band edge properties of Pb-Sn mixed triple cation perovskites (Cs/MA/FAPb_1-xSn_xX₃, X = Cl, Br, I) for efficient inverted solar cells are studied via simulation and experiment. The optimized solar cell with x = 0.336 shows the highest power conversion efficiency of 16.10% along with negligible hysteresis. We demonstrate that the devices are stable and maintain 93% of the initial PCE under ambient conditions for 30 days. These results suggest that bandgap engineering is a feasible approach to balance the efficiency and stability of Pb-Sn mixed PSCs.