Efficient and stable DSSC sensitizers based on substituted dihydroindolo[2,3-b] carbazole donors with high molar extinction coefficients

Four novel metal-free organic sensitizers based on 5,7-dihexyl-6,12-diphenyl-5,7-dihydroindolo[2,3-b]-carbazole (DDC) donors have been synthesized. Their optical/electrochemical properties, dye-sensitized solar cell (DSSCs) performances and photo-stability upon successive irradiation for 30 min have been investigated. The optical data indicates that all these dyes showed a high molar extinction coefficient (5.6-6.3 x 10(4) M-1 cm(-1)). Under standard global AM 1.5 solar light condition, the DDC4 sensitized cell gave a short circuit photocurrent density (J(sc)) of 14.81 mA cm(-2), an open circuit voltage (V-oc) of 0.688 V, and a fill factor (FF) of 0.69, corresponding to an overall efficiency (eta) of 7.03%. The benzothiadiazole units and thieno[3,2-b]thiophene (TT) in the pi spacer were found to increase the photo-stability of the corresponding dyes and these dyes based on this donor are promising candidates for the further application in DSSCs.