An asymmetrical A-DAD-A-type acceptor simultaneously enhances voltage and current for efficient organic solar cells

The asymmetrical molecule is a promising class of fused-ring electron acceptor (FREA) for use in organic solar cells (OSCs). Hence, two molecules were synthesized to compare the differences between A-D-A (acceptor-donor-acceptor)-type and A-DAD-A (acceptor-donor-acceptor-donor-acceptor)-type asymmetrical acceptors, namedITIC-?Cl-2FandBTIC-?Cl-2F, respectively.BTIC-?Cl-2Fexhibits larger dipole moments (µ) and a red-shifted absorption, which would be beneficial in obtaining a greater short-circuit current (J). After they were fabricated as OSC devices, an extremely large increase inJwas achieved inBTIC-?Cl-2F-based devices without a decrease in the open circuit voltage (V); one important reason for this phenomenon is that the introduction of nitrogen atoms in the core ofBTIC-?Cl-2Fcan effectively increase the HOMO energy level but with little change in the LUMO energy level. Consequently, devices based onBTIC-?Cl-2Fachieve a champion power conversion efficiency (PCE) of 15.43%, which is the highest value reported to date for asymmetrical acceptor-based OSCs. The more obvious fibrillar network and more homogeneous morphology ofBTIC-?Cl-2Fleads to faster electron and hole mobilities, which is consistent with higherJand fill factor (FF). This suggests that A-DAD-A-type symmetry breaking is a promising strategy that can be used for designing high-performance asymmetrical FREAs.