Grain boundary cracks patching and defect dual passivation with ammonium formate for high-efficiency triple-cation perovskite solar cells

Triple-cation perovskite solar cells exhibit better long-term stability as compared to FAPbI3 devices but also have more ions and vacancies defects in film. Herein, ammonium formate (NH4HCO2) is introduced and forms a stable NH4HCO2-PbI2 adduct onto the surface of perovskite to patch grain boundary cracks and passivate interfacial defects. The density functional theory calculation results indicate that there is a strong interface interaction between perovskite and NH4HCO2, and the defects are well anchored by forming Pb··COOH bond and I··NH4 bond. The density of states proves that surface trap states by the I vacancy is also effectively eliminated, which is consistent with the experimental results. As a result, the optimized devices achieve a power conversion efficiency of 24.62% and exhibit remarkable long-term stability in air. This work provides a simple defect multiple passivation strategy to prepare perovskite solar cells with high efficiency and stability. Triple-cation perovskite solar cells are more stable than formamidinium lead iodide but possess more defects. Here, grain boundary cracks and passivate interfacial defects are patched using ammonium formate which forms a stable adduct on the perovskite surface.