Porphyrins containing a tetraphenylethylene-substituted phenothiazine donor for fabricating efficient dye sensitized solar cells with high photovoltages

With the aim to enhance the photovoltages and efficiencies of dye sensitized solar cells (DSSCs) based on porphyrin dyes, a dialkoxy-substituted highly twisted tetraphenylethylene (TPE) moiety has been introduced into the donor unit of a porphyrin dye to suppress dye aggregation and charge recombination. Thus, based on our previously reported porphyrin dye XW43, a dialkoxy-TPE moiety has been introduced into the phenothiazine donor to afford XW71. Compared with the diethyleneglycol substituent in XW43, the bulkier dialkoxy-TPE unit in XW71 is more beneficial for suppressing charge recombination. The alkoxy chains on the TPE moieties in XW71 are extended outward from the molecule and folded toward the porphyrin macrocycle, respectively, favorable for suppressing dye aggregation and charge recombination. As a result, the V-OC was dramatically improved from 0.750 V (XW43) to 0.765 V (XW71). On this basis, the substituents surrounding the porphyrin macrocycle have been optimized to further improve the V-OC and the efficiencies. Thus, XW72 and XW73 have been synthesized by replacing the dodecyloxy moieties on the meso-phenyl substituents of XW71 with two diethyleneglycol (DEG) chains and double straps, respectively. As a result, XW72 and XW73 exhibit a gradually improved V-OC of 0.772 V and 0.777 V, respectively, and a high power conversion efficiency (PCE) of 11.0% has been achieved for XW73. Upon coadsorption and cosensitization, the efficiency can be further enhanced to an outstanding value of 12.3% for the XW73 + CDCA + XC3 system.

Automated summary

By introducing a dialkoxy-TPE moiety into the donor unit of a porphyrin dye, the photovoltages and efficiencies of dye sensitized solar cells were significantly enhanced. The optimization of substituents surrounding the porphyrin macrocycle played a crucial role in improving V-OC and efficiencies.