End-capped group manipulation of fluorene-based small molecule acceptors for efficient organic solar cells

Acceptor-π-donor-π-acceptor (A-π-D-π-A) type small molecule acceptors have made significant progress in organic solar cells (OSCs). To achieve high performance acceptors, three novel acceptors (s4-s6) are designed and investigated based on small molecule acceptors (s1-s3) via introduction of different end-capped groups. The quantum chemistry and Marcus theory approaches are used to calculate the electronic structures and crucial parameters dramatically related to the short-circuit current density (J_SC), involving the absorption spectrum, electron-hole correlation, driving force, and electron mobility. Compared with s1-s3, s4-s6 not only yield greater red-shift and stronger and broader absorption spectra, but also exhibit much higher electron mobility, easier exciton dissociation abilities, and much better electron transfer efficiencies in active layer. Our results will offer theoretical guidelines for further design and synthesis of acceptors to enhance the performance of OSCs.