Ability To Fine-Tune the Electronic Properties and Open-Circuit Voltage of Phenoxy-Boron Subphthalocyanines through Meta-Fluorination of the Axial Substituent

Abstract

Six different boron subphthalocyanines with fluorophenoxy axial substituents were synthesized to explore and fine-tune the HOMO and LUMO energy levels based on past observations of the unique levels of pentafluorophenoxy-boron subphthalocyanine (F5BsubPc). Electrochemistry reduction potentials, ionization energies from ultraviolet photoelectron spectroscopy (UPS) measurements, and energy levels calculated using semiempirical methods reveal finely variable values between phenoxy-BsubPc (PhO-BsubPc), without any fluorine atoms, and F5BsubPc, with all five fluorines. There is no trend between the number of fluorines on the phenoxy group and the electronic properties, but there is an influence of meta fluorine(s) altering the redox potentials and ionization energy, leading us to categorize the fluorophenoxy-BsubPcs into two “buckets”: with and without meta fluorines. We then applied the fluorophenoxy-BsubPcs as electron acceptors in planar heterojunction organic photovoltaic devices. The categorization of these “buckets” was confirmed by the fine change in open-circuit voltage between 1.15 and 1.21 V, which is an exceptionally high value. This level of fine-tuning of properties and device metrics is a unique handle enabled by the phenoxy axial substituent of BsubPcs.