Designing efficient A-D-A1-D-A-type non-fullerene acceptors with enhanced fill factor via noncovalently conformational locking

Abstract Achieving high fill factor (FF) is a great challenge for non-fullerene organic solar cells (NF-OSCs) since the FF can be influenced by many factors. Herein, two A-D-A1-D-A-type non-fullerene acceptors (NFAs) PZ-dIDTC6 and PD-dIDTC6, consisting of indacenodithiophene (IDT) dimers bridged with weak electron withdrawing pyrazine (PZ) or pyridine (PD) unit, were designed and synthesized. Relative to the PD-dIDTC6, PZ-bridged PZ-dIDTC6 showed a wider absorption range in the 500–800 nm with lower optical band gap of 1.57 eV (~50 nm red-shifted than PD-dIDTC6), due to the more planar conformation caused by noncovalently conformational locking. Furthermore, the PM6:PZ-dIDTC6 film shown higher and balanced mobility (1.33 × 10−4 cm2 V−1 s−1 for hole and 1.88 × 10−4 cm2 V−1 s−1 for electron), which contributed to the high FF of devices. OSCs based on PM6:PZ-dIDTC6 exhibited a power conversion efficiency (PCE) of 10.91% with a FF of 0.75, while the PM6:PD-dIDTC6 device yielded a PCE of 7.78% with a FF of 0.56. This work demonstrates that noncovalently conformational locking is propitious to improve the FF of devices.