A “belt” strategy for promoting the 3D network packing of fully non-fused ring acceptors in organic solar cells

Fully non-fused ring acceptor (NFRA) materials have higher structural diversity than their fused ring counterparts, which have the potential to further promote the performance of organic solar cells and reduce the materials cost. However, owing to their non-fused structural nature, it is difficult for NFRAs to achieve the desirable fully planar state during film formation, which ultimately impedes the device performance. To date, the lack of efficient control over the molecular conformation in both solution and solid states remains a major challenge in the material design of NFRAs. Here, we propose a novel “belt” strategy for construction of a high performance NFRA, which is based on installing a bulky cyclic side chain for more efficient tailoring of the molecular conformation. The molecule with a cyclic “belt” (CSO4TIC) shows a more desirable 3D network packing structure and conformation stability as compared with the molecule with conventional linear side chains (LSO4TIC). Notably, the device based on CSO4TIC achieved a power conversion efficiency of 14.22%, placing it among the top efficiencies reported to date for NFRAs. It is believed that this is the pioneering instance of incorporating a cyclic “belt” into NFRA materials, providing a new route towards low cost and high performance organic photovoltaic materials design.