Asymmetric non-fullerene acceptors with an imide-containing end group for high-performance organic solar cells

Abstract

Non-fullerene acceptors (NFAs) with asymmetric structures can improve the photovoltaic performance of organic solar cells (OSCs) with their merits of larger dipole moments, higher permittivity, and stronger intermolecular interactions. Our recently developed novel end group, imide-containing 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IIC), has shown significant potential in the design of high-performance NFAs due to its strong electron-withdrawing ability and adjustable N-position substitution groups. Here, for the first time, we introduce IIC into the molecular design of asymmetric NFAs and prepared two novel NFAs (BTP-IIC-2Cl and BTP-IIC-BO-2Cl). The asymmetric end groups resulted in a larger dipole moment, and alkylchains on thiophene β-sites of BTP affected the energy levels and optical band gaps (E_g) between the two derivatives. The BTP-IIC-2Cl-based solar cells achieved a higher power conversion efficiency (PCE) of 17.12% than BTP-IIC-BO-2Cl-based solar cells (16.50%). The OSCs incorporated with BTP-IIC-2Cl had higher short-circuit current (J_sc) due to broader absorption, more balanced charge carrier transport and highly ordered packing in the PM6:BTP-IIC-2Cl thin film. In comparison to the device based on BTP-IIC-2Cl, the BTP-IIC-BO-2Cl based device had reduced radiative and non-radiative recombination losses, and its lower PCE was attributed to the reduced J_sc. Our results demonstrate the efficacy of the imide-containing IC end group as a promising building block for the design of asymmetric NFAs for high-performance OSCs.