Photovoltaic Effect of Structure Compatibility Utilizing a Same Electron-Accepting Unit on a Polymer Donor and Nonfused Nonfullerene Acceptor

The advance of nonfullerene acceptors (NFAs) has accelerated the improvement of photovoltaic performance of organic solar cells (OSCs). However, most NFAs are suggested as a multisynthesized planar molecular backbone structure containing fused conjugated rings. Therefore, nonfused NFAs (n-FNFAs) have recently been extensively studied and reported as an alternative strategy of fused-NFAs (FNFAs) by providing synthetic simplicity and fine-tuning optical properties and energy levels. In addition, the highly planar and fused NFAs have strong self -aggregation behaviors and reduced mixing properties between the polymer donor and FNFAs. To obtain excellent morphology and intermixing behavior, a same-accepting strategy on both of the polymer donor and n-FNFAs is adopted. In this study, three acceptors are designed and synthesized, BDD-IC4F, BTO4-IC4F, and TPD-IC4F, using a similar A-D-A '-D-A skeleton composed of two accepting center units linking cyclopentathiophene bridges that assure noncovalent conformational geometry. By inserting the A ' unit in the center, a full width at half-maximum of that material exhibits a broad absorption spectrum as above 200 nm in the near-infrared region and small band gaps. Among the three n-FNFAs, the optimized PM6:BDD-IC4F device achieved the best photovoltaic performance with smooth film morphology and well-miscible crystalline behavior between PM6 and BDD-IC4F. The effect of the same-accepting strategy improves formation of the intermixed blend domain and structure compatibility leading to efficient carrier transport and mobility. More importantly, these results demonstrate the possibility of nonfused acceptors for low-cost and high-efficient OSCs.