Enhancing photovoltaic properties of organic solar cells through core alteration of methyl-substituted bithiophene-based small molecule acceptors†

In organic solar cells (OSCs), acceptors have emerged as a significant class of photoactive materials. On account of the already reported compound PTT-FBTz, five D₁–π–D₂–π–D₁ type acceptors (C1–C5) have been designed using methyl-substituted bithiophene as the common terminal unit (D₁) and five different core units (π–D₂–π). Both density functional theory (DFT) and its counterpart, time-dependent density functional theory (TD-DFT) approaches, were utilized to thoroughly examine the influence of core engineering on optoelectronic as well as photovoltaic properties. The results suggest that alteration of the core unit enhanced the designed acceptor molecules’ performance. Besides, the electron-accepting nature of the designed compounds is confirmed from the calculated reorganization energy (λ) values. Additionally, it is clear from the designed compounds’ absorption properties that compound C5 has higher λ_max values in both phases. Based on the D/A complex properties, the designed A1/C1–C5 complexes, can boost the separation of charge carriers at the donor/acceptor junction. Besides, due to their photovoltaic performance, complex A1/C5 achieving a PCE of 24.65%, stands out as the most favorable option for OSC fabrication.