Influence of TiO2 nanoparticle size on the electron transport in dye-sensitized solar cells

In this article, nanoporous electrode films are prepared from different sized anatase TiO2 nanoparticles, of which the average diameter is 13.4, 16.1, 17.5 nm, then made to dye-sensitized solar cells (DSC). The average thickness of three different films is about 11.5 mu m. The electron diffusion and recombination processes in DSC are investigated by Intensity modulated photocurrent spectroscopy (IMPS) and Intensity-modulated photovoltage spectroscopy (IMVS). The values of the diffusion coefficient (D) and the electron lifetime (tau(n)) have been obtained. It has been found that D increases and tau(n) decreases with the increase of the particle size. The increase of D is attributed to the decrease of the film surface area, and the decrease of tau(n) is interpreted with the frequency of hopping between traps in films. The value of D and rn of photoinjected electrons also have been measured under different orders of magnitude of illumination intensity that ranging from 1 x 10(15) cm(-2)s(-1) to 3 x 10(16) cm(-2)s(-1). D increases with the increase of light intensity, whereas tau decreases. The diffusion length (L-n) is calculated by L-n = (D tau(n))(1/2). As a consequence, L is only weakly intensity dependent, which varies less than 0.1 mu m over orders of magnitude of illumination intensity. The conclusions were accordance with the results reported in previous literature.