Ionic liquid-mediated reconstruction of perovskite surface for highly efficient photovoltaics

To achieve efficient harvesting of light energy, perovskite photovoltaics require a surface passivation process of the perovskite layer. In this study, 1-butylmethylimidazolium hexafluorophosphate ionic liquid was adopted as a surface modifier to passivate a perovskite layer through post-treatment. Results revealed that the ionic liquid effectively reduces surface traps by inducing simultaneous interactions from both cation and anion components. Consequently, the surface treatment with the ionic liquid provided a ~ 15% improvement in the efficiency of the perovskite photovoltaics. However, the formation of perovskite-ionic liquid complex, leading to inefficient charge transport and extraction, was observed when an excess amount of the ionic liquid was used owing to the penetration of the ionic liquid into the photo-active layer. These observations suggest that the ionic liquid should be selectively exposed to the perovskite surface to optimize the efficiency of perovskite photovoltaics treated with ionic liquids.