Dye-sensitized solar cells based on (D−π−A)3L2 phenothiazine dyes containing auxiliary donors and flexible linkers with different length of carbon chain

Four (D−π−A)₃L₂ phenothiazine dyes (PTZTB1−4) and a reported reference dye (R−SB) with a mono D−π−A chain were utilized as photosensitizers for dye-sensitized solar cells. In the skeleton of the dyes PTZTB1−4, three D−π−A chains (D−π−A)₃ were connected by flexible linker of n-hexyl or n-dodecyl group (L₂) to build the (D−π−A)₃L₂ configuration. The effect of both the auxiliary donors and linkers with different length of carbon chains upon the photophysical, electrochemical as well as photovoltaic properties of the (D−π−A)₃L₂ dyes were further investigated. Results reveal that the dyes PTZTB3−4 containing the auxiliary donor of 4-octyloxyphenyl group show a higher molar extinction coefficient, a broader IPCE response region, and a higher HOMO value than those of PTZTB1−2 and R−SB. Among all of the devices, the cells based on PTZTB2 and PTZTB4 exhibit a higher open circuit voltage due to that the charge recombination is blocked significantly by the n-dodecyl linkers. Meanwhile, a maximal power conversion efficiency of 6.66% is achieved by the device fabricated with PTZTB3. Besides, it is noteworthy that the (D−π−A)₃L₂ dyes possess a superior adsorbed stability on TiO₂ interface than that of the reference dye as a result of the three anchors in a molecule of the former.