Effect of the linkage location in double branched organic dyes on the photovoltaic performance of DSSCs

Two novel double branched D-pi-A organic dyes (DB dyes) are synthesized to investigate the influence of the linkage location in DB dyes on the performance of dye-sensitized solar cells (DSSCs), where phenothiazine is introduced as a donor, thiophene-benzotriazole unit as the pi-bridge and cyanoacrylic acid as the electron-acceptor. The photophysical, electrochemical and photovoltaic properties of the dyes are systematically investigated. The results show that the location of the linkage unit has a small effect on the physical and electrochemical properties of the dyes. However, when the dyes are applied in DSSCs, an obvious decline of short-circuit current (J(sc)) and open-circuit voltage (V-oc) is found by moving the linkage unit from the donor part to the pi-bridge part. The DSSC based on the dye DB-D with the linkage unit in the donor obtains an overall power conversion efficiency of 6.13%, which is about 68% higher than that (3.65%) of the DSSC based on the dye DB-B with the linkage unit in the pi-bridge. The DB-B based device exhibits a lower efficiency due to its serious aggregation and short electron lifetime. The results indicate that the linkage location of the dyes has a big effect on the performance of the DSSCs.