The donors are key components of organic solar cells
(OSCs) and
play crucial roles in their photovoltaic performance. Herein, we designed
two new donors (BTR-γ-Cl and BTR-γ-F) by finely optimizing
small molecule donors (BTR-Cl and BTR-F) with a high performance.
The optoelectronic properties of the four donors and their interfacial
properties with the well-known acceptor Y6 were studied by density
functional theory and time-dependent density functional theory. Our
calculations show that the studied four donors have large hole mobility
and strong interactions with Y6, where the BTR-γ-Cl/Y6 has the
largest binding energy. Importantly, the proportion of charge transfer
(CT) states increases at the BTR-γ-Cl/Y6 (50%) and BTR-γ-F/Y6
(45%) interfaces. The newly designed donors are more likely to achieve
CT states through intermolecular electric field (IEF) and hot exciton
mechanisms than the parent molecules; meanwhile, donors containing
Cl atoms are more inclined to produce CT states through the direct
excitation mechanism than those containing F atoms. Our results not
only provided two promising donors but also shed light on the halogenation
effects on donors in OSCs, which might be important to design efficient
photovoltaic materials.