Multifunctional Regioisomeric Passivation Strategy for Fabricating Self-Driving, High Detectivity All-Inorganic Perovskite Photodetectors

The fluorination of the aromatic multifunctional Lewis base passivation strategy has been demonstrated recently as an effective approach to markedly enhance the performance of perovskite photovoltaic devices. However, the regulation mechanisms of the passivation efficiency by varying the functional group position of fluorine (F) in the regioisomers have received little attention and inadequate research. Herein, a pair of bifluorine-substituted aminobenzoic acid regioisomers [3-amino-2,6-difluorobenzoic acid (13-FABA) and 4-amino-3,5-difluorobenzoic acid (14-FABA)] were employed to investigate the passivation effects of Lewis bases dependent on behaviors of the ortho/meta-substituted position of fluorine. The density functional theory calculation on electron cloud density, interaction energy, and the basicity of Lewis bases combined with experimental evidence reveal that the ortho-effect induced by fluorine substitution weakens the passivating effect of 13-FABA Lewis base and induces its molecular propensity to form internal salts, accelerating the degradation and deterioration of the device performance. Conversely, 14-FABA with meta-connected fluorine atoms exhibit superior efficacy in suppressing defects and enhancing hydrophobicity. Eventually, the 14-FABA-modified photodetectors (PDs) achieved a high detectivity of 1.69 × 10¹³ Jones, the comparatively lower dark current density of 2.2 × 10^–10 A/cm² among all-inorganic perovskite PD systems. Our work has not only clarified the fundamental mechanisms of the F-substituted position effects of Lewis base on suppressing defects but also provided a promising passivation strategy for perovskite films via designing the regioisomeric atoms in a multifunctional Lewis base molecule.