Supramolecular Complex Engineering Enables Stable and High Performance α-FAPbI 3 Based Perovskite Solar Cells

Excess PbI2 management is critical to the performance and stability of perovskite solar cells (PSCs). However, typical post treatment method remains the nature of instability induced by the photolysis of PbI2. Herein, by forming robust self-assembled supramolecules ([BMIM]PbI2X5 and [BMIM]PbX3) with 1-butyl-3-methylimidazolium based ionic liquids ([BMIM]X), we report a novel “Ionic Liquid assisted Supramolecular Complex engineering” (ILaSC) approach to effectively modulate the unreacted PbI2. The formation process and mechanism of supramolecules are elucidated. With effective Pb interstitial defects passivation and tensile strain relaxation simultaneously, the ILaSC approach achieves significant enhancements in both PCE (from 21.9% to 23.5%) and device stability (retaining 95% of the initial PCE after 4080 h in ambient dry-air storage, and 80% after 1400 h continuous light illumination). The generality of the supramolecular complex engineering methodology in broader ionic salt systems is further demonstrated, representing a new direction towards highly stable and efficient PSCs.