Density functional theory analysis for the limitations of fluoranthene-fused imide based small molecule acceptor materials in photovoltaic performance

Abstract

Recently, the bulk-heterojunction (BHJ) organic photovoltaic cells (OPVs) have attracted more attention owing to their potentials in low-weight, cost-effective, semi-transparent, colorful, and flexible. As one of the most promising candidates non-fullerene small molecule acceptors (SMA) in BHJ OPVs, fluoranthene-fused imide (FFI) derivatives can effectively regulate energy level and absorption by functional modification of active sites on its backbone. Nevertheless, it is still a challenge to design molecules based on FFI materials to achieve significant improvements in optoelectronic performance. Therefore, the key to this work is to explore the influence of introducing functional substituents at different active sites of FFIs on the photoelectric properties. By introducing different number of substituent groups with different electron-withdrawing and electron-donating capacities at FFI backbones active sites, could lead to construct “D-A-D” structures. By density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, we demonstrated that constructing “D-A-D” structure in FFI derivatives wouldn’t impact apparently on charge transfer process, because the nearly vertical dihedral angles exhibit in these geometrical configurations between between “D units” and “A units”. This has become a main factor limiting the performance improvement of FFI-based SMAs with “D-A-D” structures. On the contrary, it would be an effective approach to control the number of electron-withdrawing groups reasonably at FFI backbone in order to design more excellent performance for FFIs.