Large-Grain Double Cation Perovskites with 18 μs Lifetime and High Luminescence Yield for Efficient Inverted Perovskite Solar Cells

Recent advancements in perovskite solar cell performance were achieved by stabilizing the alpha-phase of FAPbI(3) in nip-type architectures. However, these advancements could not be directly translated to pin-type devices. Here, we fabricated a high-quality double cation perovskite (MA(0.07)FA(0.93)PbI(3)) with low bandgap energy (1.54 eV) using a two-step approach on a standard polymer (PTAA). The perovskite films exhibit large grains (similar to 1 mu m), high external photoluminescence quantum yields of 20%, and outstanding Shockley-Read-Hall carrier lifetimes of 18.2 mu s without further passivation. The exceptional optoelectronic quality of the neat material was translated into efficient pin-type cells (up to 22.5%) with improved stability under illumination. The low-gap cells stand out by their high fill factor (similar to 83%) due to reduced charge transport losses and short-circuit currents >24 mA cm(-2). Using intensity-dependent quasi-Fermi level splitting measurements, we quantify an implied efficiency of 28.4% in the neat material, which can be realized by minimizing interfacial recombination and optical losses.