Cation optimization for perovskite solar devices

Hybrid lead halide perovskites will potentially lead the future energy scenario if highly efficient cells have long-term stability. Here we combine state-of-the art mixed-cation formulations containing formamidinium (FA) and methylammonium (MA), with optimal guanidinium (Gua)/Cs ratios, enabling the realization of cells providing stability at their maximum efficiency. The photovoltaic stability of nonencapsulated cells containing Cs x (FAMAGua) 1− x ( x = 0.1; x = 0.2; x = 0.3) stored in the dark under air conditions for 4000 h (a), and devices under continuous light soaking at MPP tracking (b).