Cadmium‐Doping Slows Trap Emptying in Ambient‐Air Blade‐Coated Formamidinium Lead Iodide Perovskite Solar Cells

Abstract

Abstract Formamidinium lead iodide (FAPbI 3 ) in its α‐phase is among the most desirable perovskite compositions for solar cells. However, because of its transition into the yellow δ‐phase at room temperature, it is a challenge to process it in ambient air by scalable fabrication methods. Here the introduction of a trace amount of cadmium (in the form of CdI 2 ) to FAPbI 3 is reported and found that it enhances the stability of the perovskite's black α‐phase polymorph, inhibits non‐radiative recombination events, leads to pin‐hole free compact surface morphology, and improves band energy alignment. The 0.6% Cd‐doped FAPbI 3 solar cells show a champion efficiency of 22.7% for 0.049 cm 2 and 16.4% for cm 2 ‐scale pixels, which, to the best of the knowledge, are among the highest for air‐ambient fully blade‐coated pure FAPbI 3 solar cells with an n‐i‐p architecture. Transient absorption microscopy measurements reveal that Cd doping reduces the number of trapped charges and increases their lifetimes, promoting charge accumulation and a higher photovoltage. The study sheds light on the potential of cadmium as a homovalent dopant for the stabilization and performance enhancement of FAPbI 3 performance solar cells.