Achieving 20.11% Efficiency Ternary Organic Solar Cells Based on a Novel Low‐Crystallinity Non‐Fused Ring Electron Acceptor

The ternary strategy is crucial for breaking through the efficiency bottleneck of organic solar cells (OSCs). To date, high‐performance ternary devices predominantly depend on structurally complex fused‐ring electron acceptors. However, research on non‐fused ring electron acceptors with commercial potential as the third component remains relatively limited. In this study, a medium bandgap NFREA, named BTDTP, is designed and synthesized based on a strongly electron‐deficient bithiazole core and incorporated into the classical D18:L8‐BO system to construct ternary OSCs. The key intermediate, DTP‐CHO, is prepared through a direct C‐H arylation, further simplifying the synthetic process. The bithiazole group endows BTDTP with complementary absorption and cascaded energy levels with a host binary system. Interestingly, BTDTP exhibits relatively weak intermolecular interactions and molecular crystallinity, along with good compatibility with L8‐BO, forming BTDTP:L8‐BO alloyed states and thus regulating the aggregation behavior of D18 and L8‐BO. The resulting ternary blend shows an optimized multi‐scale morphology with favorable phase separation and more ordered molecular packing, facilitating exciton dissociation and charge transport. Consequently, the D18:L8‐BO:BTDTP device achieves an impressive efficiency of 20.11%, among the highest values for NFREA‐based ternary OSCs. This research expands the design strategies for NFREAs and provides a valuable guideline for developing cost‐efficient ternary OSCs.