A 19% efficient and stable organic photovoltaic device enabled by a guest nonfullerene acceptor with fibril-like morphology

A nonfullerene acceptor, isoIDITC, capable of exhibiting fibril-like morphology, is utilized as a third component in organic photovoltaic devices (OPVs). A power conversion efficiency (PCE) of 19% is achieved in ternary PM6:BTP-eC9:isoIDITC bulk-heterojunction (BHJ) devices. Analyses reveal the formation of an alloy model (BTP-eC9:isoIDTIC) and a well-defined fibril-like network and enhanced crystallization of BHJ in the ternary blend. Slightly increased carrier mobilities, longer carrier lifetimes, and suppressed trap-assisted/bimolecular recombination are observed in the ternary BHJ-based devices compared to the binary PM6:BTP-eC9 BHJ cells. Moreover, because of the high surface energy (gamma) and low glass-transition temperature (T-g) of BTP-eC9, the acceptor and donor tend to migrate toward the hole and electron collecting electrodes, respectively, during aging tests. Crucially, isoIDTIC with low gamma and high T-g has a low diffusion coefficient and can suppress demixing in vertical stratification of the BHJ, resulting in an increase in T-80 lifetime from 101 hours to 254 hours. Our results highlight the utilization of the nonfullerene acceptor with fibril-like morphology and high T-g as an important third component toward high-performance and stable ternary OPVs.