Highly efficient stereoscopic phenothiazine dyes with different anchors for dye-sensitized solar cells

In this work, three D-A-pi-A stereoscopic phenothiazine dyes JA0, JA6 and JA7 were prepared and applied in dye-sensitized solar cells. Spirobifluorene and long carbon chain units were introduced onto the donors of phenothiazine dyes to construct stereoscopic structures, this strategy can effectively suppress dye charge recombination by decreasing back reaction of the injected electrons with triiodide species in the electrolyte, the results show that the V-oc values of the DSSCs based on JA0 and JA6 were both over 800 mV. To improve the spectral responsiveness of these dyes, the strongly electron-withdrawing benzothiadiazole unit (BTD) was introduced, and the spectral response of JA6 reached about 770 nm. In addition, it is very important for sensitizers to have suitable anchors, this determines the efficiency of charge injection and the degree of bonding between the sensitizer and semiconductor surface. In order to further improve the performance of DSSCs, carboxylic acid, cyanoacrylic acid and pyridine are all used as anchors in this work, and we investigated the optical properties, electrochemical properties, and photovoltaic performance of these dyes to analyze the influence of different anchors on dyes. The results show that cyanoacrylic acid is the best anchor for this series of dyes, which is very helpful to improve the light-harvesting ability of dyes; the DSSC based on JA6 with a cyanoacrylic acid anchor exhibited the highest PCE of 7.34%. In contrast, the PCE of the DSSC based on JA7 with a pyridine anchor was only 3.05%, this should be mainly due to its poor dye adsorption properties.