Improving Electron Transport in a Double-Cable Conjugated Polymer via Parallel Perylenetriimide Design

Double-cable conjugated polymer can be applied to single component organic solar cells (SCOSCs), which have great potential to improve the stability and to simplify the fabrication procedure compared to two component organic solar cells. However, SCOSCs always show low power conversion efficiencies (PCEs), which is mainly due to the difficulty to tune the nanophase separation in double-cable polymers for charge transport. Herein, we are able to find a way to improve the electron transport in double-cable polymers. The idea starts by introducing a parallel and large benzo[ghi]perylenetriimide into the side chains, different from the conventional perylene bisimide (PBI) side units in double-cable polymers. The new electron-deficient side units were found to lower the crystallinity of conjugated backbone and enhance the contact region between different acceptors. This could help in electron transport in the new double-cable polymers, as confirmed by space charge limited current measurement. Therefore, the new double-cable polymer provided a high PCE of 4.34% in SCOSCs compared to 1.92% based on the polymer with PBI side units. Our results demonstrate that by rationally designing electron deficient side units, the electron transport in double-cable polymers can be optimized toward efficient SCOSCs.