Exploring the influence of end-capped moieties on the photovoltaic properties of thiazolo [5,4-d] thiazole based compounds: DFT/TD-DFT approaches

Non-fullerene acceptors-based organic solar cells (NFA-OSCs) with unfused central cores retain significant optoelectronic features in recent years. Herein, eight new derivatives (TCTD1–TCTD8) were designed from TCTR reference to enlighten their photovoltaic and optoelectronic properties. The structural modulation of TCTR is performed at its both terminal ends with different unique benzothiophene based acceptors. Following this, the DFT/TD-DFT methods were accomplished to perform various analyses such as frontier molecular orbitals (FMOs), density of states (DOS), UV–Vis spectra, transition density matrix (TDM), binding energy (E_b), open circuit voltage (V_oc) and hole-electron investigations. The findings of FMOs and UV–Vis revealed that the newly designed compounds showed comparable band gaps (2.13–2.32 eV) with bathochromic shifts in both the chloroform solvent (702.30–753.06 nm) and gas phase (655.72–695.84 nm) as compared to TCTR (2.29 eV, 715.26 and 668.52 nm, respectively). The TDM, DOS and hole-electron plots represented the good charge transfer (CT) and exciton dissociation in all the derivatives. Their V_oc was calculated via the donor polymer (PBDB-T) and significant results were obtained (1.34–1.67 V). Among all the afore-mentioned derivatives, TCTD7 exhibited the least band gap (2.13 eV), highest λ_max (753.06 and 695.84 nm in chloroform solvent and gas, accordingly) and E_b (0.49 eV) values. These results illustrated the greater rate of exciton dissociation which led towards efficient photovoltaic response in the compound (TCTD7). The theoretical study marked the unique properties of newly designed unfused NFAs which aid the experimentalists in their utilization for synthesizing efficient photovoltaic materials.