| Dye-Sensitized Nanocrystalline Photovoltaic Solar Cells are very prospective cleaning devices for the conversion of solar energy into electricity. They have simple structures, low costs and could be manufactured easily. They are inert to the change of light intensity and environment temperature, having high incident photon-to-current conversion efficiency and light stability, and no pollutions. So they have attracted intense attentions since appeared in 1991. How to get higher incident photon-to-current conversion efficiency and prolong the lifetime of the solar cells has been the focus in the past years.In order to solve the backward electron transfer problem, 9 kinds of rhenium(I) bipyridyl photosensitive dyes with different electron donating groups on the p or m-position of the pyridine rings, 2 kinds of rhenium(I) bipyridyl and 2 kinds of ruthenium(â…¡) tris-bipyridyl photosensitive dyes with two tyrosine ethyl ester groups on the bipyridyl rings were designed and synthesized. Their redox potentials, luminescence intensities, lifetimes, quantum yields, time-resolved absorbances, transient absorbances and kinetics decay were studied by use of cyclic voltammetry, photoluminescence analysis and nanosecond laser flash photolysis.It demonstrated that by introducing electron-donating group on the pyridine ring, the electron density on the Re could be increased which would result in partly "supplying" electron and diminishing backward electron transfer on the one hand; and the oxidation potentials of Re(â…¡/I) could be reduced which would result in decreasing the backward electron transfer driving force on the other hand. As the p-substituted group becomes more electron donating from H to CH3, OH, or NH2, the luminescence intensities, lifetimes, quantum yields, time-resolved absorbances, transient absorbances of the dyes decreased.The tyrosine Z and tyrosine D inPSâ…¡ were mimicked by introducing two tyrosine groups on the bipyridyl rings of rhenium(I) bipyridyl and ruthenium(â…¡) tris-bipyridyl photosensitive dyes through amide bonds. By irradiation of sunlight, the excited state molecule injected electron into the conduction band of the nanostructured TiO2 and formed the oxidation state of Re(â…¡) or Ru(â…¢) on the semi-conductor surface. Then the tyrosine group could transfer electron to Re(â…¡) or Ru(â…¢) and reduce it to the ground state of Re(I) or Ru(â…¡), forming the tyrosine radical and avoiding the backward electron encountered with the oxidation states of dyes. The reduced tyrosine could obtain electron from electrolyte such as I/I3 and the cycle completed with a result of preventing backward electron transfer efficiently. As the tyrosine groups being introduced, the oxidation potentials of Re(â…¡/I) decreased, the ground state and the excited state properties of the rhenium(I) bipyridyl dyes changed little; the oxidation potentials of Ru(â…¢/â…¡) decreased slightly; the luminescence intensities, lifetimes,quantum yields, time-resolved absorbances and transient absorbances of the ruthenium(â…¡)tris-bipyridyl dyes increased obviously.In order to study the factors that might influence the lifetime of the solar cells, the electrospray ionization mass spectrometry (ESI-MS) was utilized for first time to detect the relative stability of the ligands and the dyes by alternating different in-source CID (in-source Collision Induced Dissociation) fragmentations to dissociate the coordinated ligands. The results showed that the bipyridyl ligands are more stable than the pyridine ligands, the dissociation of the pyridine ligands in the rhenium(I) bipyridyl dyes and the lose of the neutral minor molecule of the substituted groups on the bipyridyl ligands in the ruthenium(â…¡) tris-bipyridyl dyes are the main reasons influencing the stability of the dyes and the lifetime of the solar cells. As the substituted group on the pyridine ligand becomes more electron donating from H to CH3, OH, NH2, or CH2-PTZ, the stability of the ligand and the dyes increased; and the stability of the m-subst...
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