High-performance and low-energy loss organic solar cells with non-fused ring acceptor by alkyl chain engineering

Non-fused ring electron acceptors are attractive for organic solar cell (OSC) due to synthetic simplicity and availability of diverse building blocks. However, it is challenging to afford both high-performance and low-energy loss (Eloss) OSC based on the non-fused ring electron acceptors. Herein, two simple electron acceptors, BDC-4F-C6 and BDC-4F-C8 with non-fused backbones are designed and synthesized by comprising a 5,7-bis(2-ethylhexyl)-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione core, doubly endcapped by fluorinated 1,1-dicyanomethylene-3-indanone terminals through 4H-cyclopenta[1,2-b:5,4-b′]dithiophene bridge. The effects of bridge alkyl side chain length on physicochemical properties and on optoelectronic properties are systematically investigated. Compared with the BDC-4F-C6, BDC-4F-C8 shows a blue-shifted absorption and an elevated LUMO level, which is beneficial for boosting Voc. As a result, a decent power conversion efficiency of 12.53% with a remarkable low Eloss of 0.51 eV has been achieved for BDC-4F-C8-based OSCs. It is worth pointing out that Eloss of 0.51 eV is the lowest ever reported among highly efficient OSCs based on non-fused ring electron acceptors. Our work demonstrates the effectiveness of side chain engineering of non-fused ring electron acceptors for achieving higher PCE and lower Eloss, holding a bright future on the further improvement of the PCE for high-performance OSCs.