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 (γ) and low glass-transition temperature (Tg) 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 γ and high Tg has a low diffusion coefficient and can suppress demixing in vertical stratification of the BHJ, resulting in an increase in T80 lifetime from 101 hours to 254 hours. Our results highlight the utilization of the nonfullerene acceptor with fibril-like morphology and high Tg as an important third component toward high-performance and stable ternary OPVs.