Investigation of Defect‐Tolerant Perovskite Solar Cells with Long‐Term Stability via Controlling the Self‐Doping Effect

Abstract Although there have been significant advances in the stability of perovskite solar cells through encapsulation techniques to remove extrinsic degradation factors, such as moisture and oxygen, irreversible photo‐degradation originating from intrinsic defects is still challenging and remains elusive. Herein, the photo‐aging mechanism due to intrinsic defects is investigated in nitrogen‐filled conditions, excluding extrinsic degradation factors. Devices with similar power conversion efficiencies (PCE) of 21%, but with different Fermi levels in the perovskite films, via controlling the self‐doping effect, have been investigated. Opto‐electronic investigations and depth profiles of the elemental constituents show that after photo‐aging, strain relaxation in the perovskite lattice and a Fermi level shift towards conduction band edge are observed, implying the formation of new defect states in Pb‐rich devices. Furthermore, thermal admittance spectroscopy measurement of the devices suggests that the formation of the deep‐traps in the perovskite leads to irreversible degradation. Thin‐film solar cells that are relatively Pb‐deficient (FA‐rich) exhibit improved long‐term stability, retaining over 90% of their initial PCE during 500 h of continuous 1‐Sun illumination. This study suggests passivation of the Pb‐I related antisite defects near the grain boundaries and the interface is crucial for the fabrication of solar cells with enhanced long‐term stability.