Charge recombination and transport in dye sensitised TiO/sub 2/ photovoltaic devices

Iodide Electron Transfer Kinetics in Dye-Sensitized Nanocrystalline TiO2 Films

“…The model has been applied to the rereduction kinetics of ruthenium complexes on nanocrystalline TiO 2 and ZnO films in various redox inactive electrolytes, and the behavior predicted by eqs 4 and 5 has been observed in all cases. 9,35,36 We note that this nonlinear dependence of the recombination half-time upon electron density, which we observe experimentally, cannot be explained by alternative second-order, homogeneous models for nongeminate charge recombination. 16 In the current context, the model must be modified in two respects: (i) the rereduction of D + by I -(eq 2) must be allowed, and (ii) the optical absorbance of the products of this alternative reaction at the probe wavelength must be included.…”

“…The model predicts that the kinetics should follow a “stretched exponential” in the limit where the electron density outnumbers the dye cation density [D + ]. Here, τ is a constant and α = T / T 0 where T is 298 K. The effective half-life of the cation, t 50% , then varies with electron density per cation, n , like The model has been applied to the rereduction kinetics of ruthenium complexes on nanocrystalline TiO 2 and ZnO films in various redox inactive electrolytes, and the behavior predicted by eqs 4 and 5 has been observed in all cases. ,, We note that this nonlinear dependence of the recombination half-time upon electron density, which we observe experimentally, cannot be explained by alternative second-order, homogeneous models for nongeminate charge recombination …”

Dependence of TiO2 Nanoparticle Preparation Methods and Annealing Temperature on the Efficiency of Dye-Sensitized Solar Cells

“…Electron Lifetime in Nanopor ous Films. It has been reported that the electron lifetime in DSC is in millisecond to second order, and is related to the inverse power of the light intensity. ,,, The experimental results of the electron lifetime have been studied with two different models. The relationship between lifetime and light intensity can be expressed from trapping models as where I is light intensity and β is a slope, or as where k is a constant and n is the small perturbation of electron density, based on the second-order reaction with I - /I 3 - redox couples. , Equation 5 is equivalent with τ = I -1/2 , in terms of the incident light intensity.…”

“…The basic transport mechanism of electrons has been described with diffusion on the basis of the assumption of the absence of a large electric field gradient in the film. − Diffusion coefficients of electrons in a nanoporous TiO 2 film have been reported by several groups. The measured values are much lower than those in a bulk crystal, ,− , and show light intensity dependence. ,, The observations have been explained by models based on the electrons diffusing in the conduction band having charge traps.…”

“…The measured values are much lower than those in a bulk crystal, ,− , and show light intensity dependence. ,, The observations have been explained by models based on the electrons diffusing in the conduction band having charge traps. In the model, the electrons spend a large fraction of their transit time at the intraband trap sites. − ,− The origin of trap sites has not been well-understood, but it has been assumed that they could be formed by titanium oxide amorphous layers, oxygen defects, boundaries between particles, and chemical surroundings . Particle synthesis method and annealing temperature are expected to change the trap site distribution and density, and consequently, affect the electron transport properties.…”