Design and Synthesis of a New Non‐Fullerene Acceptor for High‐Performance Photomultiplication‐Type Organic Photodiodes

Photomultiplication‐type organic photodiodes (PM‐OPDs) rely on acceptor molecules for both charge separation and efficient gain generation. Herein, a new non‐fullerene acceptor is designed and synthesized by introducing thienylenevinylene (TV) groups into the conventional 2,2ʹ‐[[6,6,12,12‐tetrakis(4‐hexylphenyl)‐6,12‐dihydrodithieno[2,3‐d:2ʹ,3ʹ‐dʹ]‐s‐indaceno[1,2‐b:5,6‐bʹ]dithiophene‐2,8‐diyl]bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile] (ITIC) structure. The resulting TV‐ITIC acceptor possesses not only extended π‐conjugation length, which leads to lower energy bandgap as well as deeper lowest unoccupied molecular orbital (LUMO) level, but also enhanced hydrophobic characteristics, owing to the increased volumetric portion of the aliphatic chain, which improves the miscibility with the donor polymer semiconductor, poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). Moreover, pristine TV‐ITIC films consist of intrinsically well‐ordered anisotropic crystallites, which are confirmed by 2D grazing incidence X‐ray diffraction (2D‐GIXD) analysis. All of these photophysical properties are beneficial for efficient exciton separation, electron trapping, and charge injection abilities of PM‐OPDs compared to those obtained with conventional ITIC. Because of such synergetic contributions of TV‐ITIC to the photomultiplication mechanism, the resulting optimized PM‐OPD exhibits a high external quantum efficiency (>74,000%) and a large specific detectivity (>1012 Jones). By introducing thienylenevinylene (TV) groups into the conventional ITIC, a new TV‐ITIC, with an extended π‐conjugation and thus deeper LUMO level, is synthesized. This new molecule enables elongated trap lifetime and enhanced charge separation efficiency as well as improved intermolecular miscibility with polymer matrix. Such synergetic contributions of TV‐ITIC enable the efficient photoconductive gain mechanism and thus high‐performance photomultiplication‐type organic photodiodes.