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

Abstract

Formamidinium lead iodide (FAPbI3) 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 CdI2) to FAPbI3 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 FAPbI3 solar cells show a champion efficiency of 22.7% for 0.049 cm2 and 16.4% for cm2-scale pixels, which, to the best of the knowledge, are among the highest for air-ambient fully blade-coated pure FAPbI3 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 FAPbI3 performance solar cells.