Modified phthalocyanines for efficient near-IR sensitization of nanostructured TiO2 electrode
A zinc phthalocyanine with tyrosine substituents (ZnPcTyr), modified for efficient far-red/near-IR performance in dye-sensitized nanostructured TiO2 solar cells, and its ref., glycine-substituted zinc phthalocyanine (ZnPcGly), were synthesized and characterized. The compds. were studied spectroscopically, electrochem., and photoelectrochem. Incorporating tyrosine groups into phthalocyanine makes the dye ethanol-sol. and reduces surface aggregation as a result of steric effects. The performance of a solar cell based on ZnPcTyr is much better than that based on ZnPcGly. Addn. of 3α,7α-dihydroxy-5β-cholic acid (cheno) and 4-tert-butylpyridine (TBP) to the dye soln. when prepg. a dye-sensitized TiO2 electrode diminishes significantly the surface aggregation and, therefore, improves the performance of solar cells based on these phthalocyanines. The highest monochromatic incident photo-to-current conversion efficiency (IPCE) of ∼24% at 690 nm and an overall conversion efficiency (η) of 0.54% were achieved for a cell based on a ZnPcTyr-sensitized TiO2 electrode. Addn. of TBP in the electrolyte decreases the IPCE and η considerably, although it increases the open-circuit photovoltage. Time-resolved transient absorption measurements of interfacial electron-transfer kinetics in a ZnPcTyr-sensitized nanostructured TiO2 thin film show that electron injection from the excited state of the dye into the conduction band of TiO2 is completed in ∼500 fs and that more than half of the injected electrons recombines with the oxidized dye mols. in ∼300 ps. In addn. to surface aggregation, the very fast electron recombination is most likely responsible for the low performance of the solar cell based on ZnPcTyr.
Record created on 2015-07-06, modified on 2016-10-02