Electrical transport and optical properties were investigated in porous thin films consisting of In2O3:Sn (indium tin oxide, ITO) nanoparticles with an initial crystallite size of 16 nm and a narrow size distribution. Temperature dependent resistivity was measured in the 77<t<300 K temperature interval for samples annealed at a temperature in the 573tA1073 K range. Samples annealed at 573t A923 K exhibited a semiconducting behavior with a negative temperature coefficient of the resistivity (TCR). These data were successfully fitted to a fluctuation induced tunneling model, indicating that the samples comprised large conducting clusters of nanoparticles separated by insulating barriers. Samples annealed at tA = 1073 K displayed a metallic behavior with no signs of insulating barriers; then the TCR was positive at t> 130 K and negative at t<130 K. Effects of annealing on the ITO nanoparticles were investigated by analyzing the spectral optical reflectance and transmittance using effective medium theory and accounting for ionized impurity scattering. Annealing was found to increase both charge carrier concentration and mobility. The ITO nanoparticles were found to have a resistivity as low as 2 × 10-4 cm, which is comparable to the resistivity of dense high quality In2O3:Sn films. Particulate samples with a luminous transmittance exceeding 90% and a resistivity of 10-2 cm were obtained

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Effective medium theory was used to model optical properties in the 0.3 – 30 μm wavelength range for films comprised of nanoparticles of a transparent conducting oxide that are connected in a percolating network characterized by a filling factor f. The model is based on charge carrier density ne and resistivity ρ of the particles, and it enables analyses of these microscopic parameters upon posttreatment of the film. The theory was used to interpret data on spin coated layers consisting of nanoparticles of indium tin oxide (i.e., In2O3:Sn) with f close to the percolation limit. It showed that the as-deposited film contained nanoparticles with ne as large as ∼5×1020 cm−3 and ρ≈5×10−4 Ω cm. The model also provided important data on f, ne, and ρ after heat treatment of the film.