Alkyl Fluoride Modification-Enhanced Intermolecular Interactions of Phenoxazine-Based Hole-Transporting Materials for Efficient and Stable Inverted Perovskite Solar Cells

Abstract

Delicate regulation of halogens in conjugated molecules has emerged as a major strategy to modulate the aggregation of organic semiconductor materials for considerable enhancement of photovoltaic performance. Herein, three donor–π–donor hole-transporting materials, B₆P₆-F, B₆P₆-Cl, and B₆P₆-Br, containing 4,8-bis(hexyloxy)benzo[1,2-b:4,5-b′]dithiophene as a π-conjugated linker and 10-(6-fluorohexyl)-10H-phenoxazine, 10-(6-chlorohexyl)-10H-phenoxazine, and 10-(6-bromohexyl)-10H-phenoxazine respectively, as donor units, are reported. Differential scanning calorimetry curves, atomic force microscopy, and contact angle measurements with perovskite precursors collectively reveal that the halogenated alkyl chains attached to the donor units influence molecular packing patterns and subsequently alter the surface and interface properties of the resulting films. Analysis of Fourier-transform infrared absorption spectra implies that distinctive aggregation properties of B₆P₆-F may originate from its intermolecular F···π interactions. Benefiting from the F···π interactions and favorable self-assembly, the inverted PSCs based on B₆P₆-F exhibit a decent power conversion efficiency of 20.85%, outperforming that of B₆P₆-Cl and B₆P₆-Br. Further analysis of steady-state/transient photoluminescence spectra, electrochemical impedance spectroscopy, light intensity-dependent short-circuit photocurrent, and open-circuit voltage (V_oc) indicates that the distinct assembly of B₆P₆-F, facilitated by intermolecular F···π interactions, enhances efficient interfacial charge transport and extraction while suppressing unfavorable charge recombination, thereby increasing V_oc and fill factor.