Enhancing Heterogeneous Nucleation on Buried Interface for Efficient Antisolvent-Free Inverted Flexible Perovskite Photovoltaics.

Self-assembled molecules (SAMs) significantly boost the power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs), yet their hydrophobicity impedes uniform large-area perovskite film deposition, especially on flexible plastic conductive substrates. Herein, we propose an interface ionic engineering strategy to address this issue. Specifically, a multifunctional N-(4-Cyanophenyl)guanidine hydrochloride (NCGCl) salt with multiple hydrophilic functional groups is employed to modify the SAM layer to overcome the perovskite solution spreading problem. We demonstrate that the nitrile and guanidinium groups in NCGCl strongly interact with perovskite components, facilitating heterogeneous nucleation and defect passivation. Moreover, the π-π* stacking between the benzene rings in NCGCl and SAMs further strengthens the substrate-perovskite interface bridging. Consequently, the antisolvent-free processed PSCs on rigid and flexible substrates demonstrate champion PCEs of 26.89% (certified 26.64%) and 25.29%, respectively. We also fabricate 5 cm × 5 cm flexible mini-modules, showing an impressive PCE of 22.28%, along with outstanding mechanical bending stability.