Tuning terminal aromatics of electron acceptors to achieve high-efficiency organic solar cells

Herein, two new electron acceptors, BTTPC and BTTPC-Br, are developed through extending the conjugation of terminal electron accepting moieties with thiophene and bromine units. Such a structural design effectively improves the hole transfer of exciton dynamics in blends, revealing that BTTPC-Br and BTTPC based blends, in the presence of a smaller energetic offset as a driving force, exhibit faster hole transfer from acceptors to the polymeric donor interface, 4 times (BTTPC-Br) and 1.5 times (BTTPC) faster than 0.44 picoseconds of unmodified Y5. As a result, organic solar cells (OSCs) based on the BTTPC-Br acceptor, outperforming those of BTTPC:PBDB-T and Y5:PBDB-T, reach a power conversion efficiency of 15.22%, which is so far one of the highest among the single junction OSCs made with PBDB-T polymer donor.