Hammer throw-liked hybrid cyclic and alkyl chains: A new side chain engineering for over 18 % efficiency organic solar cells

Side chain engineering has been commonly recognized to be a simple and effective strategy in designing organic photovoltaic materials and increasing power conversion efficiencies. Different from recent traditional side chain modulation, this work presented the design and synthesis of a family of fresh hybrid side chain by combining the relatively rigid cyclic and flexible alkyl chain. To be specific, cyclopentane, cyclohexane and cycloheptane were introduced to the tail of the alkyl side chain, through which novel polymer donors D18-C6Cp, D18-C6Ch and D18-C6Chp were prepared based on the excellent skeleton of D18. In comparison with simplex cyclic or branched chain, hybrid side chains with preferential conformations were capable of impacting the self-assembling characteristics and facilitating the interpenetrating networks of blend films, thereby contributing to high-efficiency charge transport, lower energy loss, and inhibited charge recombination. Strikingly, the D18-C6Ch:L8-Bo-based single junction OPV cells reveal a prominent FF of 78.7 %, and a Voc of 0.91 V with the maximum PCE up to 18.2 %. This work exhibits an effective hybrid side chain engineering to synergistically tune the self-assembly properties and finally improve organic photovoltaic performance, which would be a broad potential in developing novel materials in the field of organic optoelectronics.