Rapid annealing obtained ITO films with both extremely low infrared emissivity and high visible light transmission for energy-efficient window applications

Abstract

Energy-efficient windows are essential for modern buildings, because they can greatly save the energy consumed for heating and cooling. The functionality of energy-efficient windows is realized through coating the glass with a transparent conductive film (TCF), which possesses both low infrared emissivity and high visible light transmission. However, fabricating high quality TCFs with sufficient properties for energy-efficient window applications is still very challenging. Under this context, we had tried to optimize the properties of indium tin oxide (ITO) films, that is one of the most widely used TCFs, through a combination of room temperature sputtering and post-annealing. Particularly, we had thoroughly investigated how the microstructure, morphology, and optoelectronic properties of ITO films changed after post-annealing. Our findings show that ITO films annealed using rapid annealing (RA) at high temperatures exhibit superior crystallinity, smoother surfaces and enhanced optoelectronic properties compared to those annealed using conventional thermal annealing (CTA). Notably, among all the ITO films prepared under different conditions, the one annealed at 700 °C through RA shows the lowest infrared emissivity of 0.14, and highest figure of merit value of 128.34, that is obtained with an average visible light transmittance of 86.42% and a resistivity of 1.94 × 10−4 Ω⸱cm. This indicates that ITO films prepared via RA are promising candidates for use in energy-efficient window applications. Furthermore, the adherence of the infrared emissivity and resistivity results to the Hagen-Rubens theory, particularly as the resistivity is low, confirms the reliability of our experiments and highlights the excellent conductivity of ITO films fabricated in this study.