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Dye-sensitized solar cells (DSCs) can be regarded as third-generation photovoltaic devices which have low fabrication costs and high photovoltaic performance. The efficiency of DSCs is influenced by the electron transport within the TiO 2 -dye-electrolyte system and can be improved by modifying the TiO 2 electrode with Nb doping. DSCs with Nb-doped and undoped TiO 2 electrodes were fabricated and investigated. The Nb-doped TiO 2 layers were prepared by a sol-gel method followed by hydrothermal treatment with an Nb content ranging from 0.7 to 3.5 mol%. The obtained layers were characterized using XRD, SEM, TEM, and low temperature PL measurements. Electrical impedance spectroscopy was used to study the electronic transport at the TiO 2 -electrolyte interface. The electron lifetime, was found to increase from 8 ms for DSCs with undoped TiO 2 layers to 26 ms for cells based on TiO 2 electrodes doped with 2.7 mol% of Nb. The increase in the electron lifetime correlates with a rise in the short circuit current (J sc ). Nb doping concentrations lower than 1.7 mol% increase the resistance at the TiO 2 -electrolyte interface and consequently increase the value of the open circuit voltage (V oc ). Doping with 1.7 mol% of Nb increases the both J sc and V oc values and significantly improves the device efficiency.

Photostudies of the bis(2,9-dimethyl-1, lO-phenanthroline)copper(I) ion, Cu(dmp)2+, in solution in the presence of several different Co(III) complexes are described. Upon irradiating into the low-lying metal-to-ligand charge-transfer band of Cu(dmp)2+ a reduction of Co(III) is observed in each case, and the yield of Co(II) is markedly dependent on the nature of the Co(III) center. The results are consistent with a model in which the electron-transfer reactions occur by bimolecular processes involving a thermally equilibrated metal-to-ligand charge-transfer excited state of the copper complex. The wavelength dependence of the quantum yield for the redox process is presented for the case of the trozis-bis(iminodiacetato)cobaltate(III) complex, and somewhat smaller quantum yields are observed upon irradiating into a higher energy band of the copper complex.

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