Unraveling the Structure–Property–Performance Relationships of Fused-Ring Nonfullerene Acceptors: Toward a C-Shaped <i>ortho</i>-Benzodipyrrole-Based Acceptor for Highly Efficient Organic Photovoltaics
Yung‐Jing Xue, Ze‐Yu Lai, Hancheng Lu, Jun-Cheng Hong, Chia‐Lin Tsai, Ching-Li Huang, Kuo‐Hsiu Huang, Chia‐Fang Lu, Yu‐Ying Lai, Chain‐Shu Hsu, Jhih‐Min Lin, Je‐Wei Chang, Su‐Ying Chien, Gene‐Hsiang Lee, U‐Ser Jeng, Yen‐Ju Cheng
Abstract
The high-performance Y6-based nonfullerene acceptors (NFAs) feature a C-shaped A-DA’D-A-type molecular architecture with a central electron-deficient thiadiazole (Tz) A’ unit. In this work, we designed and synthesized a new A-D-A-type NFA, termed CB16, having a C-shaped ortho -benzodipyrrole-based skeleton of Y6 but with the Tz unit eliminated. When processed with nonhalogenated xylene without using any additives, the binary PM6:CB16 devices display a remarkable power conversion efficiency (PCE) of 18.32% with a high open-circuit voltage ( V oc ) of 0.92 V, surpassing the performance of the corresponding Y6-based devices. In contrast, similarly synthesized SB16, featuring an S-shaped para -benzodipyrrole-based skeleton, yields a low PCE of 0.15% due to the strong side-chain aggregation of SB16. The C-shaped A-D N B N D-A skeleton in CB16 and the Y6-series NFAs constitutes the essential structural foundation for achieving exceptional device performance. The central Tz moiety or other A’ units can be employed to finely adjust intermolecular interactions. The single-crystal X-ray structure reveals that ortho -benzodipyrrole-embedded A-D N B N D-A plays an important role in the formation of a 3D elliptical network packing for efficient charge transport. Solution structures of the PM6:NFAs detected by small- and wide-angle X-ray scattering (SWAXS) indicate that removing the Tz unit in the C-shaped skeleton could reduce the self-packing of CB16, thereby enhancing the complexing and networking with PM6 in the spin-coating solution and the subsequent device film. Elucidating the structure–property–performance relationships of A-DA’D-A-type NFAs in this work paves the way for the future development of structurally simplified A-D-A-type NFAs.