Photovoltaic and Optical Characterization of Organic Heterocyclic 6,6′-Dibromoindigotin Crystal Under Changing Solvent Polarity by DFT Analysis

The photovoltaic and optical properties of 6,6′-dibromoindigotin (DBI) crystal under changing solvent polarity are investigated through DFT analysis. It includes geometry optimization, global reactivity, UV–vis analysis, open circuit voltage (V_oc), FMOs, and NBO analysis. The highest HOMO-LUMO gap (E_gap) value is found for the gaseous phase (1.82 eV), while the lowest E_gap is found for dichloro methane (1.64 eV), and intermediate values with the other solvents. The molecule has a high IP of 2.48 eV, low EA of 0.74 eV, moderate polarity, and hardness (η). The maximum absorption wavelengths (λ_max) of the compound in different solvents are dichloromethane and DMSO (373 nm), chloroform (372 nm), methanol and water (371 nm), toluene (367 nm), and gaseous (356 nm). Their V_oc range is 0.2–0.28 eV. Among all, chloroform demonstrates the highest performance with a fill factor (FF) of 0.8630, normalized open circuit (Nor. V_oc) of 31.69 eV, and J_sc of 26.47 mA cm⁻². Toluene also shows promising results with an FF of 0.8060, Nor. V_oc of 19.71 eV, and J_sc of 21.19 mA cm⁻². Water, although not as effective as other solvents, still exhibits respectable values with an FF of 0.8315, Nor. V_oc of 23.96 eV, and J_sc of 24.63 mA cm⁻².