Exploration of the effect of different terminal acceptors to improve the efficacy of pyrrolopyrazine-based compounds for organic solar cells: a quantum chemical approach

In organic photovoltaic (OPV) cells, the acceptor is one of the most crucial components of the photoactive layer. Herein, pyrrolopyrazine-based non-fullerene compounds (TDCD1–TDCD6) were designed by modifying the reference compound (TDCR) with strongly electron-withdrawing acceptors to improve the performance of organic solar cells (OSCs). The density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were used to perform various analyses which include the frontier molecular orbitals (FMOs), absorption properties (λ_max), density of states (DOS), transition density matrix (TDM), hole–electron and open-circuit voltage (V_oc). The results of FMOs disclosed that all derivatives showed reduced energy gaps (1.850–2.830 eV) as compared to TDCR (2.933 eV). Similarly, higher absorption values (502.221–787.351 nm) were obtained for derivatives than TDCR (482.050 nm) due to the presence of strong terminal acceptors. Moreover, the calculations such as TDM and DOS confirmed the efficient charge transfer from the HOMO to LUMO. Particularly, the most suitable results were obtained for TDCD4 molecule, i.e., least energy gap (1.850 eV), maximum absorption (787.351 nm) and minimal binding energy (0.275 eV) due to presence of the nitro (–NO₂) group in the modified acceptor. In the photovoltaic properties, especially the V_oc values were obtained ranging from 1.767 to 2.164 V. Overall, these derivatives are considered suitable materials for the photovoltaic applications.