Exploration of promising photovoltaic properties of bisisoindigo-based heterocyclic chromophores for organic solar cells: A DFT/TD-DFT study

In the current study, a series of A₁–π–A₂–π–A₁ type bisisoindigo-based organic compounds (BTIND1–BTIND9) were designed via the structural tailoring of the reference compound (BTINR) at terminal acceptors for the organic solar cells (OSCs). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches were utilized to estimate the influence of end-capped engineering over their photovoltaic properties of BTIND1–BTIND9. After their structural optimization, various analyses like, open circuit voltage (V_oc), absorption spectra (λ_max), frontier molecular orbitals (FMOs), density of states (DOS), binding energy (E_b) and transition density matrix (TDM) were performed at the B3LYP/6-311G(d,p) level. The band gaps range of the engineered molecules was observed as 1.776–1.649 eV, lesser than the BTINR reference (1.812 eV). Their TDM and DOS details further revealed electronic charge transfer in the designed derivatives. The higher λ_max values were found in the visible and near-infrared regions i.e., 666.904–701.149 nm in the chloroform solvent and 661.778–895.581 nm in the gaseous phase. Furthermore, their open-circuit voltage (V_oc) was determined with PTB7 donor polymer and showed significant values. Among all, BTIND5, BTIND7 and BTIND8 compounds were investigated with remarkable photovoltaic properties. These chromophores possessed least energy gaps (1.649, 1.668 and 1.664 eV) and bathochromic shifts (698.070, 699.646 and 701.149 nm) with least binding energies and prominent V_oc results. The above-mentioned outcomes demonstrate that the end-capped modification of bisisoindigo-based molecule is an effective strategy to obtain highly efficient OSCs.