Charge transport model for disordered materials: Application to sensitizedTiO2

Abstract

We propose a simple model of charge transport that predicts the conducting properties of disordered materials. The transport of charge is assumed to occur by trapping and detrapping of electrons in localized states and diffusion via a conduction-band level. The input is an arbitrary density of localized states (DOLS) and the output, bulk mobilities, and conductivities as a function of the field and the density of carriers. The code can be applied to any kind of carrier (electrons, holes, or ions) and includes trap-filling effects. This leads to predictions of density-dependent mobilities—a determining factor in the conducting properties of amorphous insulators and sensitized semiconductors. Using this model, we have studied the photoconductor ${\mathrm{TiO}}_2$ by comparing the predicted conductivity for different DOLS with experimental data in steady-state conditions. Our simulations show that the presence of a few deep traps determines the observed superlinear dependence of the conductivity on the number density of carriers.