Theoretical exploration of diverse electron-deficient core and terminal groups in A–DA′D–A type non-fullerene acceptors for organic solar cells

Abstract

Molecular engineering for non-fullerene acceptors (NFAs) with advanced power conversion efficiencies (PCEs), particularly from the aspects of theoretical analysis, has been a hot topic in the community of bulk heterojunction organic solar cells (BHJ OSCs) in recent years. In this context, taking NFAs Y6, Y10 and Y11 as research objects, the influence of molecular engineering of the terminal group (A) and the electron-deficient core (A′) group on the performance of NFAs and donor/acceptor (D/A) interfaces was theoretically explored by using density functional theory (DFT), time-dependent DFT (TD-DFT) and Marcus charge transfer theory. It was found that the introduction of fluorine into the terminal group and benzotriazole (BTZ) into the electron-deficient core group improved the molecular polarity index (MPI), the electrostatic potential (ESP), the optical absorption properties, the first excited-state lifetime (τ), the hole and electron delocalization index (HDI, EDI), the electron transfer rate (K_e) and the electron mobility (μ_e) of the investigated NFAs, and reduced the charge recombination rate (K_CR) and enhanced the charge separation rate (K_CS) of the investigated D/A interfaces, thus leading to a higher PCE. More importantly, the designed J11/Y6, J11/Y11 and PM6/Y10 interfaces have superior K_CS/K_CR values to the experimental interfaces. Our investigation provides a theoretical guideline for a molecular design strategy of advanced OSC devices.