Reducing Residual PbI ₂ Through Chemical Polishing Strategy to Improve the Performance of Perovskite Solar Cells

Residual PbI 2 in perovskites induces deep‐level defects, limiting enhancement of perovskite solar cell performance. Herein, 2‐ethyl‐4‐oxo‐4,5‐dihydrothieno[3,2‐d]‐pyrimidine‐6‐carboxylate (EDC) was used in a chemical polishing strategy to modify the interface between the hole transport layer and the perovskite layer. Images from scanning electron microscopy show that after EDC modification, there is reduced residual PbI 2 in the perovskite film, concurrently with the formation of large‐sized grains. It is observed from ultraviolet–visible (UV–vis) absorption spectrum that the Urbach energy decreases after modification, suggesting that grain boundaries exhibit greater order and a reduced defect density. Consequently, the hysteresis index of EDC‐chemically polished devices decreased from 8.27% to 2.44%, and the power conversion efficiency increased from 20.5% to 22.17%. Furthermore, EDC‐modified PSCs demonstrated exceptional stability, retaining 83% of their initial conversion efficiency after 2000 h of operation under nitrogen atmosphere. After 160 h of outdoor aging at 75°C, these devices maintained 71.3% of their initial efficiency. This work proposes a viable strategy for reducing residual PbI 2 in perovskites to achieve highly efficient and stable perovskite solar cells.