Inorganic narrow bandgap CsPb0.4Sn0.6I2.4Br0.6 perovskite solar cells with exceptional efficiency

The instability of organic/inorganic hybrid perovskite solar cells (PSCs) has motivated the development of the inorganic halide PSCs. However, the representative inorganic CsPbI3 still suffers from phase instability in ambient air and an unfavorable wide bandgap (1.75 eV), thereby limiting its efficiency. In this study, a binary metal composition of Pb:Sn = 4:6 in CsPb1-xSnxI3 is found to stabilize the cubic CsPbI3 phase and reduce its bandgap. Based on the parental CsPb0.4Sn0.6I3, compositional engineering is further conducted for CsPb0.4Sn0.6I3 Br-y(y) perovskites. After introducing a suitable Br content (y = 0.6), there are remarkable improvements in the crystalline quality and a denser morphology in the perovskite films. Furthermore, in the novel inorganic CsPb(0.4)ASn(0.6)I(2.4)Br(0.6) perovskite, trap-assisted recombination is effectively suppressed, with a desirable narrow bandgap of 1.35 eV. As a result, the corresponding PSC delivered an unprecedented efficiency of 12.34%, which is the highest among the inorganic Sn-rich (Sn > 50%) PSCs reported to date. Additionally, the unencapsulated PSC demonstrates impressive long-term air stability, which exceeds the performance of 100% Pb-based inorganic CsPbI3 and/or CsPbI2Br PSCs reported. This near-infrared absorbing (similar to 930 nm) inorganic PSC with exceptional efficiency, durability and Pb-reduction generates a promising route for further progress of perovskite-based photovoltaics.