Vinylene- and ethynylene-bridged perylene diimide dimers as nonfullerene acceptors for polymer solar cells

Vinylene ( V )- and ethynylene ( E )-bridged perylene diimide dimers ( PDI-V and PDI-E ) were designed, synthesized and used as nonfullerene acceptors for polymer solar cells. Our researches revealed that the linkage between two PDI units has a great impact on the molecular geometry, the optical properties, the blend film morphology, the molecular packing orientation, and the photovoltaic performance. Computational calculations via density functional theory (DFT) showed that PDI-E and PDI-V possessed planar and twisted geometric structures, respectively. TEM investigations showed that PTB7-Th : PDI-V based blend film exhibited a uniform morphology with small domain size and PTB7-Th : PDI-E based one showed apparent phase separation with large domain size. GIWAXS results revealed that the PDI-V can influence PTB7-Th to take on a face-on orientation, which is beneficial for vertical charge transport to increase J sc . A PCE of 4.51% with a V oc of 0.76 V, a J sc of 10.03 mA cm −2 , and an FF of 0.59 was obtained for PSCs based on PTB7-Th : PDI-V , which is almost two times higher than that of PTB7-Th : PDI-E based devices, which showed a PCE of 2.66%, a V oc of 0.66 V, a J sc of 7.33 mA cm −2 , and an FF of 0.55. These results help to gain deeper insight into the design of new nonfullerene small molecular acceptors for high efficiency PSCs.