From C60Ph5Cl to C60Ph6: complete phenylation of C60 derivative renders superior organic photovoltaic performance

Abstract

Fully phenylated C₆₀Ph₆ has never been synthesized in the past two decades largely due to steric effect and poor thermodynamic stability of the initial intermediate towards its isostructural penta-phenyl adduct (C₆₀Ph₅X) that has one central site intact. Herein, we report a kinetic management strategy using nitrobenzene that can efficiently alleviate the steric effect in the substitution reaction of C₆₀Cl₆ to synthesize C₆₀Ph₆. As revealed by X-ray crystallography, the molecule of C₆₀Ph₆, in stark contrast to its isostructural C₆₀Ph₅Cl with the last chlorine intact, shows a favorable geometrical structure and molecular stacking for electron transport. Furthermore, C₆₀Ph₆ shows high LUMO energy of −3.51 eV (0.4 eV higher than that of [6,6]-phenyl-C₆₁-butyric acid methyl ester, PCBM), which is promising high open-circuit voltage for organic solar cells. The merits of both molecular packing and electrochemical property of C₆₀Ph₆ lead to high open-circuit voltage of 1.04 V for the OSC device based on poly(3-hexylthiophene) (P3HT). The present C₆₀Ph₆ exemplifies a novel class of electronic acceptors with fully aromatized groups on a fullerene cage.