Improving the Performance of Perovskite Solar Cells via a Novel Additive of N,1‐Fluoroformamidinium Iodide with Electron‐Withdrawing Fluorine Group

Abstract Additives are widely adopted for efficient perovskite solar cells (PSCs), and proper additive design contributes a lot to PSCs’ various breakthroughs. Herein, a novel additive of N,1‐fluoroformamidinium iodide (F‐FAI), whose cation replaces one amino group in guanidinium (GA⁺) with electron‐withdrawing fluorine group, is synthesized and applied as the additive for PSCs. The electron‐withdrawing effect of fluorine promotes the molecular polarity of N,1‐fluoroformamidine (F‐FA), enhancing the interaction of N,1‐fluoroformamidinium (F‐FA⁺) with MAPbI₃. Compared with the nonpolar GA⁺, F‐FA⁺ improves the crystallinity, passivates the defect, and downshifts the Fermi level of MAPbI₃ more significantly. The charge transfer and built‐in field in printable triple mesoscopic PSCs are therefore enhanced. Moreover, charge transport in MAPbI₃ is also promoted by F‐FAI. With these benefits, a power conversion efficiency of 17.01% for printable triple mesoscopic PSCs with improved open‐circuit voltage and fill factor is obtained with the addition of F‐FAI, superior to the efficiency of 15.24% for those devices with guanidinium iodide additives.