Organic double D–π–A sensitizers based on 2,2′-(2,2 diphenylethene-1,1-diyl)dithiophene: π-conjugation fragment effect on the photovoltaic properties

The development of new dye sensitizers to further reveal the influence of changes in structural components on the photovoltaic performance is of great significance to dye-sensitized solar cells (DSSCs). The propeller-shaped 2,2′-(2,2-diphenylethene-1,1-diyl)dithiophene (DPDT) unit was introduced to construct sensitizers for the first time. Three DPDT-bridged double D–π–A organic sensitizers (A6, A8, A9) were prepared by altering the π-conjugation fragment. The photophysical, electrochemical and photovoltaic properties of the sensitizers were systematically investigated to assess the role of the terminal fragment of dyes in DSSCs. The results show that, compared to the mono-anchoring congener AZ6, the di-anchoring sensitizer A6 displayed a comparable power conversion efficiency (PCE = 8.21%) and a higher short-circuit current density (JSC). Replacement of the terminal thiophene with a phenyl ring (A9) can effectively increase the photovoltage by 70 mV with an efficiency of 8.14%, which is 1.5 times higher than that of A8 (5.36%) with 2-cyanoacrylic acid at the meta-position of the phenyl ring. These results indicate that the terminal fragments of sensitizers have a significant effect on the photovoltaic performance.