Three-Arm Star-Shaped Acceptor Enables Organic Solar Cell over 18% Efficiency

Quasi-macromolecules (QMs) have achieved both highly efficient and stable devices along with a low batch-to-batch variation, which favors the commercialization of organic solar cells (OSCs). However, understanding of the relationship between molecular structure design for QMs and their photovoltaic properties is still limited. In this work, we reported a three-arm star-shaped QM acceptor TBT with a benzo[1,2-b:3,4-b′:5,6-b″] trithiophene (BTT) unit as the electron-donating central core and three A–DA′D–A type acceptors as the electron-deficient conjugated arms. Meanwhile, DBT with conventionally linear molecular skeletons was also synthesized for comparison. TBT exhibits an optical bandgap (1.42 eV) and energy levels similar to those of DBT, but with better light-absorption capability, an alleviated tendency to aggregate, and different packing behavior. When blended with PM6, TBT-based OSC achieved a higher power conversion efficiency of 18.04% than its DBT (16.53%) counterpart, which is one of the highest value afforded by star-shaped acceptors in binary OSCs so far. Moreover, the PM6:TBT delivered a relatively low nonradiative recombination energy loss of 0.188 eV. This work provides a feasible strategy for obtaining excellent QMs and highlights the potential of star-shaped acceptors for high-performance OSCs.