Potassium Salt Coordination Induced Ion Migration Inhibition and Defect Passivation for High-Efficiency Perovskite Solar Cells

The disordered distribution of trap states and ion migration limit the commercial application of perovskite solar cells (PSCs). Herein, we apply an oxamic acid potassium salt (OAPS) as a bifunctional additive of perovskite film. The Lewis base group C=O of OAPS can interact with the uncoordinated Pb2+ caused by the I site substitution by Pb and the dangling bonds of the perovskite, which is beneficial to reduce the nonradiative recombination loss. In addition, the countercation K+ of OAPS is confirmed to occupy the perovskite lattice interstitial sites and result in lattice expansion, inhibiting the formation of iodide Frenkel defects and I- ion migration. As a result, the synergistic effect achieves enhanced power conversion efficiency (PCE) from 19.98 to 23.02%, with a fill factor reaching up to 81.90% and suppressed current-voltage hysteresis. The device also presents improved stability, maintaining 93% of the initial PCE after 2000 h of storage.