Characterization of spectral selectivity of tin-doped In2O3 thin films using spectroscopic ellipsometry

Abstract

Transparent conductive oxide (TCO) films on cover glass are one of the key materials for solar thermal collector. Currently, the benefit of using TCO single layer is limited due to its insufficient optical selectivity. The objective of this paper is to increase the spectral selectivity of ITO film with different thickness by whole solar spectrum antireflection treatment. The sputter-deposited ITO thin films on glass substrate are characterized by variable-angle spectroscopic ellipsometry in the spectral range of 300nm to 2500nm. Based on suitable dielectric function models such as Drude, Gaussian, and Tauc–Lorentz, the theoretical spectra for the transmittance and reflectance of ITO film with different thickness in the spectral range from 300nm to 50μm are calculated. Also, the multi-layered AR coatings for ITO film with different thickness in the broad solar spectrum are designed using optical software. For ITO film with thickness from 40 to 120nm, an increase of the solar transmittance more than 6% is achieved, without compromise in the infrared emissivity. Following such AR designs, ITO three-layer AR coating (glass/Al2O3/ITO (120nm)/SiO2) was fabricated. The solar transmittance has been improved from 79.1% without any AR coatings to 84.7% with a three-layer AR coating, and the IR emissivity remains about 0.2 unchanged.