Influence of molecular orientation on photovoltaic performance in double donor with fullerene and non-fullerene acceptor-based heterojunctions

Benzodithiophene (BDT) and fullerene (C60)/non-fullerene (Y6) are donor and acceptor molecules, respectively, and are often used in organic photovoltaic (OPV) devices. In the present study, we employed density functional theory (DFT) and time-dependent DFT (TD-DFT) methodologies to explore various system orientations, focusing on structural characteristics, optoelectronic properties, and charge transfer dynamics. Our results reveal that systems with face-on-configurations exhibit deeper highest-occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies. Non-fullerene based complexes (A4 to A6) exhibit greater negative ΔG_CT values compared to the fullerene based systems (A1 to A3). Systems with a face-on orientation molecule show higher charge transfer rates than those with an edge-on orientation. Notably, A1 and A4 have a faster charge transfer rate among fullerene and non-fullerene-based systems. Thus, these results suggest that the face-on-orientation alignment of C60 and Y6 with α and β BDT units can significantly enhance the efficiency and stability of OPVs.