A series of new porphyrin dyes (XW42-XW44) containing oligo(ethylene glycol) units have been designed and synthesized. Two triethylene glycol units were introduced into the phenothiazine moiety of XW42, whereas diethylene glycol (DEG) and ethylene glycol chains were introduced to afford XW43 and XW44, respectively. Interestingly, the efficiencies of the DSSCs were clearly dependent on the chain lengths. Among the three dyes, XW42 and XW43 exhibited relatively high open-circuit voltages of 751 and 750 mV, respectively, and XW43 exhibited the highest efficiency of 10.32 % owing to the presence of the DEG chains with suitable lengths and excellent ability to trap Li+ . Furthermore, through a combined coadsorption and cosensitization approach, the efficiencies were dramatically enhanced. As a result, a highest efficiency of 12.10 % was obtained for the XW43+chenodeoxycholic acid+PT-C6 (a metal-free organic dye) system, which ranks among the highest efficiencies of cells based on the traditional iodine electrolyte.
Keywords: coadsorption; cosensitization; dye-sensitized solar cells; ethylene glycol; porphyrins.
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