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Interface Engineering of Imidazolium Ionic Liquid toward Efficient and Stable CsPbBr3 Perovskite Solar Cells.

The defects passivation of perovskite films is a efficacious way to further boost the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). In this work, ionic liquids (ILs) of 1-butyl-2, 3-dimethylimidazolium chloride ([BMMIm]Cl) is used as a modification layer in perovskite film in carbon-based CsPbBr3 PSCs without hole-transporting material (HTM) for passivating the surface defects. The preliminary results demonstrate the [BMMIm]Cl modifier passivates the surface defects of perovskite film and reduces the valence band of perovskite close to the work function of carbon electrode, which causes a remarkably inhibited non-radiative and radiative charge recombination, improved energy level matching and decreased energy loss. After optimization, a champion efficiency of 9.92% with a Voc as high as 1.61 V is achieved for the [BMMIm]Cl tailored carbon-based CsPbBr3 PSC without HTL, which is improved by 61.3% in comparison with 6.15% for the control device. Furthermore, the encapsulation-free PSC presents good long-term stability after storage in air atmosphere with 70% RH at 20 °C or 0% RH at 80 °C as well as under continuous illumination conditions for 30 days. The significantly improved PCE and stability in high humidity or temperature suggest that the perovskite passivation by ILs is an effective strategy for fabricating high PCE and stability PSCs.