DFT study of benzothiadiazole based small molecules for high efficiency organic photovoltaics
Abdul Ghaffar, Afifa Yousuf, Muhammad Zahid Qureshi, Dr. Muhammad Asghar Ali, Muhammad Nadeem Arshad
Abstract
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 (λmax = 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 (Kh ≈ 10¹⁵ s⁻¹) and low reorganization energies (λh = 0.0031–0.0052 eV), indicating excellent charge transport properties. The comprehensive computational analysis projects outstanding photovoltaic performance with open-circuit voltage (VOC = 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 (JSC = 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.