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

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.

Automated summary

Investigations were conducted on the photo-aging mechanism caused by intrinsic defects, excluding extrinsic degradation factors, and it was found that new defect states were formed in Pb-rich devices. The study also revealed that relatively lead-deficient thin-film solar cells exhibit improved long-term stability, emphasizing the importance of passivating Pb-I related antisite defects near the grain boundaries and interface.