Novel rod-shaped organic sensitizers for liquid and quasi-solid-state dye-sensitized solar cells

Two novel D-pi-A dyes (FD and SD) have been synthesized for dye-sensitized solar cells (DSSCs). The two rod-shaped molecules with an identical pi-spacer di(1-benzothieno)[3,2-b: 2',3'-d] pyrrole and with a different donor group 5,11-dihydroindolo[3,2-b] carbazole for FD or 11,12-dihydroindolo[2,3-a] carbazole for SD have been investigated. Compared to FD, the sensitizer SD not only showed a broader absorption spectrum extended to infrared region which was conducive to enhancing the light-trapping capability and thus to increase the photocurrent of the device fabricated with SD, but also exhibited better inhibition of dye aggregation resulting in a higher photovoltage. With the co-adsorption of chenodeoxycholic acid (CDCA), the photovoltaic performance of DSSCs based on the two dyes has dropped significantly. The results indicate that the aggregation of the two dyes FD and SD can be controlled by linking multiple branched alkyl chains in the structure. Finally, FD and SD-based cells without CDCA achieved power conversion efficiencies (PCE) of 7.20% and 7.47%, respectively, in liquid DSSCs. Correspondingly, FD and SD displayed PCE values of 5.77% and 6.67% in quasi-solid-state DSSCs, respectively, under standard global 1.5 solar conditions. (c) 2018 Elsevier Ltd. All rights reserved.