Reducing energy loss of fused-ring electron acceptor by pyrrole extension

Abstract

We design and synthesize a novel fused hexacyclic electron acceptor IP4F, by extending the core of fused pentacyclic electron acceptor ID4F using a new pyrrole-extension strategy. Relative to ID4F, IP4F exhibits larger conjugation length, smaller reorganization energy, closer molecular packing, bathochromic absorption spectra and elevated energy levels. In particular, IP4F exhibits narrower bandgap but higher photoluminescence quantum yield, longer exciton lifetime and slower non-radiative recombination rate than ID4F, challenging the energy-gap law. The broader absorption spectrum of IP4F is beneficial to enhancing photocurrent, while reduced radiative and non-radiative recombination losses contribute to smaller energy loss and higher open-circuit voltage in the IP4F-based devices. When blended with PM6, the IP4F-based binary organic solar cells (OSCs) exhibit a power conversion efficiency (PCE) of 14.3%, which is higher than that of the ID4F counterpart (8.98%). Moreover, the IP4F-based multi-component OSCs achieve a PCE of 19.6%, which is also higher than that of the ID4F counterpart (17.7%).