Influence of the Percolation Network Geometry on Electron Transport in Dye-Sensitized Titanium Dioxide Solar Cells

Abstract

Percolation theory is applied to understand the influence of network geometry on the electron transport dynamics in dye-sensitized nanocrystalline TiO2 solar cells, and the predicted results are compared with those measured by transient photocurrent. The porosity of the films was varied experimentally from 52 to 71%. Electron transport was modeled using simulated mesoporous TiO2 films, consisting of a random nanoparticle network, and the random-walk approach. The electron transport pathway through the network was correlated with the film porosity and the coordination numbers of the particles in the film. The experimental measurements and random-walk simulations were in quantitative agreement with percolation theory, which predicts a power-law dependence of the electron diffusion coefficient D on the film porosity as described by the relation: D ∝ |P − Pc|μ. The critical porosity Pc (percolation threshold) and the conductivity exponent μ were found to be 0.76 ± 0.01 and 0.82 ± 0.05, respectively. The frac...