DFT study of benzothiadiazole based small molecules for high efficiency organic photovoltaics

This study employs density functional theory (DFT) and time-dependent DFT (TD-DFT) to design and evaluate eight novel non-fullerene acceptors (NFAs) (G1-G8) for organic solar cells (OSCs). The molecules were engineered through strategic terminal group modification of a reference indacenodithiophene (IDT)-benzothidiazole (BT) based structure. All designed systems exhibit substantially reduced bandgaps (1.73-2.00 eV) and redshifted absorption profiles (λ_max = 688-803 nm) compared to the reference molecule (REF), leading to enhanced light-harvesting capabilities (LHE = 0.988-0.998). Marcus charge transfer theory calculations revealed high hole hopping rates (K_h ≈ 10¹⁵ s⁻¹) and low reorganization energies (λ_h = 0.0031-0.0052 eV), indicating excellent charge transport properties. The comprehensive computational analysis projects outstanding photovoltaic performance with open-circuit voltage (V_OC = 1.13-1.66 V), fill factor (FF = 0.8927-0.9205), and estimated power conversion efficiency (PCE = 22.8-37.0%) across the series. Among the designed systems, G7 demonstrates exceptional promise due to its optimal bandgap (1.73 eV), outstanding light-harvesting efficiency (LHE = 0.998), and the highest estimated short-circuit current (J_SC = 31.2 mA/cm²), while G5 achieves the highest PCE (37.0%) through balanced photovoltaic parameters. The results establish terminal acceptor engineering as a highly effective strategy for developing high-performance organic photovoltaic materials, with G7 and G5 representing prime targets for experimental validation.