Utilizing 3,4-ethylenedioxythiophene (EDOT)-bridged non-fullerene acceptors for efficient organic solar cells

A rational design of efficient low-band-gap non-fullerene acceptors (NFAs) for high-performance organic solar cells (OSCs) remains challenging; the main constraint being the decrease in the energy level of the lowest unoccupied molecular orbitals (LUMOs) as the bandgap of A-D-A-type NFAs decrease. Therefore, the short current density (J(sc)) and open-circuit voltage (V-oc) result in a trade-off relationship, making it difficult to obtain efficient OSCs. Herein, three NFAs (IFL-ED-4F, IDT-ED-4F, and IDTT-ED-2F) were synthesized to address the above-mentioned issue by introducing 3,4-ethylenedioxythiophene (EDOT) as a pi-bridge. These NFAs exhibit relatively low bandgaps (1.67, 1.42, and 1.49 eV, respectively) and upshifted LUMO levels (-3.88,-3.84, and -3.81 eV, respectively) compared with most reported low-band-gap NFAs. Consequently, the photovoltaic devices based on IDT-ED-4F blended with a PBDB-T donor polymer showed the best power conversion efficiency (PCE) of 10.4% with a high J(sc) of 22.1 mA cm(-2) and V-oc of 0.884 V among the examined NFAs. In contrast, IDTT-ED-4F, which was designed with an asymmetric structure of the D-pi-A type, showed the lowest efficiency of 1.5% owing to the poor morphology and charge transport properties of the binary blend. However, when this was introduced as the third component of the PM6:BTP-BO-4Cl, complementary absorption and cascade energy-level alignment between the two substances could be achieved. Surprisingly, the IDTT-ED-4F-based ternary blend device not only improved the J(sc) and V-oc, but also achieved a PCE of 15.2%, which is approximately 5.3% higher than that of the reference device with a minimized energy loss of 0.488 eV. In addition, the universality of IDTT-ED-2F as a third component was effectively demonstrated in other photoactive systems, specifically, PM6:BTP-eC9 and PTB7-Th:IEICO-4F. This work facilitates a better understanding of the structure-property relationship for utilizing efficient EDOT-bridged NFAs in high-performance OSC applications. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.