Side-Chain Effects on Energy-Level Modulation and Device Performance of Organic Semiconductor Acceptors in Organic Solar Cells.

Two new non-fullerene acceptors, IDTC and IDTO, were designed and synthesized for the application in organic solar cells (OSCs). Compared with IDTC, the introduction of electron-donating alkoxy groups of IDTO leads to a higher LUMO level with a slightly blue-shifted absorption. Using the polymer PBDB-T as donor and the two small molecules as acceptors in the conventional device structure, the IDTC-based OSC exhibits a power conversion efficiency (PCE) of 9.35% with an open-circuit voltage (V) of 0.917 V, a short-circuit current density (J) of 16.56 mA cm, and a fill factor (FF) of 61.61%. For the OSC based on IDTO, a higher PCE of 10.02% with a V of 0.943 V, a J of 16.25 mA cm, and an FF of 65.41% are obtained. The more balanced μ/μ, evident aggregation, and phase separation contribute to the higher FF for the device based on IDTO. The increased J for the device based on PBDB-T:IDTC can be attributed to the red-shifted and stronger absorption of the PBDB-T:IDTC blend film. These results indicate fine-tuning the electronic energy and absorption of non-fullerene acceptors is feasible to improve the performance of OSCs.