Competitive-binding buried interlayer for year-round reproducible perovskite solar cells

Homogenizing the upper surface through posttreatment has made great progress in perovskite solar cells. In contrast to the exposed surface, there are no practical remedies if imperfections form randomly at the hidden buried interface after perovskite film generation. Here, we reveal a severe distribution of residual lead iodide, voids, and grain-surface concavities at the buried interface, which severely trap carriers in inactive regions. To address these challenges, we introduce a potassium dihydrogen phosphate competitive-binding interlayer that systematically reduces residual solvents at the buried interface through strong chemical interactions. Homogenized buried interface along with facilitated perovskite film quality and charge extraction have been achieved, enabling year-round improvements in photovoltaic performance and reproducibility. The resultant devices achieve a champion power conversion efficiency (PCE) of 26.3% (certified at 25.8%) for a 0.07–square centimeter device and 25.17% for a 1.028–square centimeter device. The device also demonstrates exceptional stability, maintaining 97% of its initial PCE after 1000 hours of continuous maximum power point tracking.