Revealing Interaction of Fluorinated Propylamine Hydrochloride with Precursor and Defect States of Perovskite Films Toward Efficient Flexible Solar Cells

Abstract The trap state at the surfaces and grain boundaries of perovskite is one of the major obstacles to the further commercialization of flexible perovskite solar cells (FPSCs). Herein, two innovative multifunctional fluorinated propylamine salt 2,2,3,3,3‐pentafluoropropylamine hydrochloride (PFPACl) and 3,3,3‐triflupropylamine hydrochloride (TFPACl) are in situ introduced onto the photo absorbing layer to improve the performance of the FPSCs. The nuclear magnetic resonance (NMR) spectroscopy indicates strong interactions of both PFPACl and TFPACl with the perovskite precursor components. For the first time, the structures of the supramolecular complexes formed by two additives with FAI are deduced from NOESY NMR data, thus pointing to the importance of the preorganization of the perovskite components in solution before film casting. The experiments and density functional theory（DFT) calculations reveal that PFPACl is likely dissociated more into the form of R‐NH ₃ ⁺ ‐Cl ⁻ due to the higher electronegativity of the fluoroalkyl tail. Therefore, PFPA ⁺ binds more strongly to V _FA defects than TFPA ⁺ , and anion Cl ⁻ has strong enough interaction with V _FAI and uncoordinated Pb ²⁺ , leading to homogeneous coverage of PFPACl on the entire surface of the perovskite films and better energy alignment with the hole transport layer. Consequently, PFPACl‐treated FPSCs achieved a relatively high PCE of 23.59% with excellent mechanical robustness and operational stability.