Molecular Engineering of Carbazole Dyes for Efficient Dye-Sensitized Solar Cells

Abstract

Organic sensitizers have been recently improved and reached high efficiencies in the range of 8-9% in the performance of dye sensitized solar cells (DSSCs). In particular, carbazole based dyes (MK dyes) and bis-fluorenylamine based dyes (JK dyes) have shown to have high efficiencies and long-term stability in DSSCs preformance. Koumura et al. has recently reported that the existence of long alkyl chains on the oligothiophene linkage of MK dye molecules can increase the electron lifetime and the open-circuit voltage by suppressing the aggregation of the dyes and electron recombination. However, for MK dyes, there is a problem to be addressed in terms of relatively low short-circuit current density compared with other efficient organic dyes. The low short-circuit current density (10-14 mAcm) in MK dyes based DSSCs is originated from weak light harvesting ability in the long wavelength region (650-750 nm) due to the weak donor ability of carbazole. While bis-fluorenylamine based JK dyes have shown to have high short-circuit current density (> 14 mAcm) in DSSCs performance. This high current density can be due to the strong donor ability of amine and absorption in the long wavelength region compared to MK dyes. Therefore, we envision that the combination of the oligothiophene linkage with long alkyl chains and carbazolefunctionalized amine donor in organic dyes will be highly desirable. Moreover, there is no report on the DSSC performance base on this kind of dyes until now. These facts prompted us to develop new organic dyes containing carbazole and thiophene linker with long alkyl chain. Herein, we describe the results of our investigation on the preparation,