Multiple‐Asymmetric Molecular Engineering Enables Regioregular Selenium‐Substituted Acceptor with High Efficiency and Ultra‐low Energy Loss in Binary Organic Solar Cells

Asymmetric molecular engineering is utilized for developing efficient small molecular acceptors (SMAs), whereas adopting multiple asymmetric strategies at the terminals, side chains, and cores of efficient SMAs remains a challenge, and effects on reducing energy loss (E_loss) have been rarely investigation. Herein, four regioregular multiple-asymmetric SMAs (DASe-4F, DASe-4Cl, TASe-2Cl2F, and TASe-2F2Cl) are constructed by delicately manipulating the number and position of F and Cl on end groups. Triple-asymmetric TASe-2F2Cl not only exhibits a unique and most compact 3D network crystal stacking structure but also possesses excellent crystallinity and electron mobility in neat film. Surprisingly, the PM1:TASe-2F2Cl-based binary organic solar cells (OSCs) yield a champion power conversion efficiencies (PCEs) of 19.32%, surpassing the PCE of 18.27%, 17.25%, and 16.30% for DASe-4F, DASe-4Cl, and TASe-2Cl2F-based devices, which attributed to the optimized blend morphology with proper phase separation and more ordered intermolecular stacking and excellent charge transport. Notably, the champion PCE of 19.32% with ultralow nonradiative recombination energy loss (ΔE₃) of 0.179 eV marks a record-breaking result for selenium-containing SMAs in binary OSCs. Our innovative multiple-asymmetric molecular engineering of precisely modulating the number and position of fluorinated/chlorinated end groups is an effective strategy for obtaining highly-efficient and minimal ΔE₃ of selenium-substituted SMAs-based binary OSCs simultaneously.