Molecular modelling of fused heterocycle-based asymmetric non-fullerene acceptors for efficient organic solar cells

Heterocycle substitution plays a key role in designing an ultra-narrower bandgap (ultra-NBG) small molecule-based (SM) non-fullerene acceptors (NFAs) for organic solar cells (OSCs). The NFAs molecules have great significance because of their ability to improve efficiency, narrow band gap, better charge separation, higher absorption spectra, and overall device performance. However, the impact of heterocycles such as benzoselenadiazole (BSe) on optoelectronics characteristics is still unclear. Herein, seven asymmetric NFAs based on BSe electron-deficient fused-ring core were designed from the reference (R) BTP-Se. All seven NFAs exhibited a strong absorption phenomenon from visible to near-infrared (NIR) region, corresponding to the ultra-NBG and lower excitation energy (Ex). These designed asymmetric materials (BTP1-BTP7) along with R are fully characterized theoretically with various advanced quantum chemical techniques. The optical and optoelectronics features were explored with density functional theory (DFT) and time-dependent (TD-DFT) simulations. The in-depth calculations related to density of state (DOS), transition density of state (TDM), open-circuit voltage, fill factor, and reorganization energy of electrons and holes are performed intensively. BTP3 has an optical band gap narrow of 1.76 eV and an outstanding absorption maximum of 906.85 nm. For charge transfer, a donor:acceptor complex study of BTP3:PBDBT is carried-out. We hope that this may provide a favourable strategy for building highly efficient near infrared (NIR)-based OSCs.