Acceptor molecules with different central and terminal units for P3HT based solar cells: effects of the molecular structures on their properties

The design strategy of acceptor materials matched with poly(3-hexylthiophene) (P3HT) is highly desired for the development of low-cost organic solar cells (OSCs). Herein, we introduced strong electron-donating central units and weak electron-withdrawing end groups to construct the acceptors with high HOMO and LUMO, modulated the molecular symmetry and conjugation length by changing the structures of central units, and synthesized six acceptor molecules, namely, TDTC-O2F, TTDTC-O2F, TTTDTC-O2F, TDTC-ThBr, TTDTC-ThBr and TTTDTC-ThBr. The high LUMO energy level of the acceptors endowed the P3HT based OSCs with relatively high Voc values. Molecular symmetry, conjugation length of central units and the terminal structure jointly affect the molecular crystallinity and miscibility of the blends. Owing to the proper film morphology, the P3HT:TTDTC-ThBr based devices achieved the champion power conversion efficiency of 6.15%.