Tailoring Defect Passivation for Efficient and Stable Perovskite Solar Cells via an Ionic Liquid Additive

As a shining star in the photovoltaic community, perovskite solar cells (PSCs) have been making significant progress in recent years. However, poor long-term operation stability caused by various defects seriously restricts their commercialization process. In this work, a multifunctional ionic liquid passivator, 1-aminoethyl-3-methylimidazolium tetrafluoroborate (AMFB), is incorporated to passivate A(+), B2+, and X- defects in the perovskite absorber and enhance device stability further. It is found that AMFB can cooperate with undercoordinated Pb2+ and from hydrogen bonds with organic cations and I- ions, leading to a sufficiently passivated perovskite film. Besides, the more suitable energy arrangement and hydrophobicity of the resultant interface contribute to more facilitated carrier transport and durable stability of devices. As a result, the champion power conversion efficiency (PCE) of optimized devices significantly increases from 22.16 to 24.41% with negligible hysteresis, and the large-area devices also boost from 19.86 to 23.24%. Surprisingly, the unpackaged AMFB devices demonstrate excellent robustness against moisture and thermal stresses, maintaining over 90% of their initial PCE after 1500 h of continuous heating at 85 degrees C and 500 h of aging in moisture air with relative humidity of 70 +/- 5%. This work provides an effective and feasible method for improving the performance of PSCs and facilitating their commercialization process.