Efficient solar cells based on cosensitizing porphyrin dyes containing a wrapped donor, a wrapped π-framework and a substituted benzothiadiazole unit

Abstract

Three new porphyrin dyes XW45 − XW47 have been synthesized employing a dialkoxy-wrapped phenothiazine donor, a tetraalkoxy-wrapped porphyrin π-framework, a benzothiadiazole (BTD)-based auxiliary acceptor, and an anchoring benzoic acid group. On the basis of our previously reported dye XW36 , XW45 was synthesized by introducing a BTD unit to broaden the absorption spectrum, further introducing a hexyl-substituent into the BTD unit afforded XW46 , and an additional fluorine atom was introduced to the carboxyphenyl acceptor to afford XW47 . As expected, the BTD unit obviously broadens and red-shifts the absorption threshold of XW45 − XW47 to ca . 750 nm. Dye-sensitized solar cells (DSSCs) were fabricated based on a cobalt electrolyte using chenodeoxycholic acid (CDCA) as the coadsorbent. Under full sun illumination, XW45 exhibits an efficiency of 9.73%, which is slightly lower than that of 10.19% obtained for the reference dye SM315 . By contrast, XW46 and XW47 show higher efficiencies than SM315 owing to the improved anti-aggregation ability associated with the hexyl group on the BTD unit and better ICT effect induced by the fluorine atom on the carboxyphenyl unit. Thus, XW47 exhibits the highest efficiency of 10.41% among the porphyrin dyes. Furthermore, PT-C6 was used as the cosensitizer to improve the light harvesting ability and efficiencies of the cells due to its broad absorption within 350–560 nm. Thus, high efficiencies of 10.32%, 11.38% and 10.90% were achieved for the cosensitized solar cells based on XW45 – XW47 , respectively, owing to the obviously enhanced photocurrent density ( J SC). In addition, under 30% full sun illumination, XW46 + PT-C6 exhibits a high efficiency of 13.08%. These results give an effective method for building high performance DSSCs through the cosensitization of porphyrin dyes containing a wrapped donor, a wrapped porphyrin framework and a properly substituted auxiliary benzothiadiazole unit.