Solution-Processed Multistacked Tin-Doped Indium Oxide Nanoparticle Conductors for Cost-Effective Thin Film Heaters

Tin-doped indium oxide (ITO) nanoparticle (NP) films were fabricated as a cost-effective and highly transparent electrode for high-performance thin film heaters (TFHs), using a solution coating process on glass substrate. The electrical and optical properties of the ITO NP films depended on the number of spin coatings and post-annealing with various conditions (temperature, time, and ambient gas). The optimized three layer ITO NP films annealed at 600 degrees C under ambient N-2 showed a low sheet resistance of 14 Omega/sq and a high optical transmittance of 88% in the visible wavelength region of (400-800) nm. Cross-sectional TEM images showed the ITO nanoparticles to be evenly dispersed in the thin film with good crystallinity and well-defined elliptical shape in the range of 10 to 25 nm. X-ray diffraction analysis confirmed that heat treatment increased the size of the ITO NPs. The KPFM result exhibited that as the heat treatment duration increased, the surface roughness of the ITO NP films reduced. X-ray photoelectron spectroscopy surface analysis showed a relatively higher area ratio of oxygen vacancies and a more stable Sn state in the chemical states of the O 1s and Sn 3d(5/2) spectra than those of typical ITO films deposited by a magnetron sputtering after heat treatment. Due to the thermal stability and uniformity of the ITO NP film, ITO NP-based TFHs showed a stable time-temperature profile and uniform IR imagery. Therefore, solution-processed ITO NPs films can be applied to a promising low-cost transparent electrode in the next-generation smart window for buildings and automobiles.