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

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 MAPbI 3 . Compared with the nonpolar GA + , F-FA + improves the crystallinity, passivates the defect, and downshifts the Fermi level of MAPbI 3 more significantly. The charge transfer and built-in field in printable triple mesoscopic PSCs are therefore enhanced. Moreover, charge transport in MAPbI 3 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.