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

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 a larger conjugation length, smaller reorganization energy, closer molecular packing, bathochromic absorption spectra and elevated energy levels. In particular, IP4F exhibits a 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 for 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 their ID4F counterparts (8.98%). Moreover, the IP4F-based multi-component OSCs achieve a PCE of 19.6%, which is also higher than that of their ID4F counterparts (17.7%).