Effects of different anchoring groups in phenothiazinyl-benzothiadiazolyl dyes for dye-sensitized solar cells

In this work, we synthesize two new dyes with phenothiazine (PTZ) as pi-bridge, benzothiadiazole (BTD) as acceptor moiety, and rhodanine-3-acetic acid (-RA) / cyanoacrylic acid (-CA) as anchoring group. In combination with a previously reported one with anchoring group of carboxylic acid (-CH), the effects of the three anchoring groups on material properties and the performance of dye-sensitized solar cells (DSSCs) are investigated. It is found that in terms of anchoring group for DSSC dye, the moiety features of electron-pulling ability, the spatial stretching, as well as its conjugation to the main molecular axis should be considered simultaneously. When attached over a para-phenyl group to a phenothiazinyl-benzothiadiazolyl dye, among the three commonly used anchoring groups of -RA, -CA and -CH, the last one is the best, with which the CBPTZ-BTD1 based DSSC exhibits the highest power conversion efficiency of 6.69%, mainly due to the highest dye loading, open-circuit voltage, and rather high fill factor.