Study of operational characteristics of electrochromic coatings based on tungsten trioxide

Abstract

Every year, more than 35 million m² of residential premises are put into operation in the Russian Federation. Thanks to the development of new thermal insulation materials, it is possible to slow down the growth of energy consumption for heating. However, window openings, through which up to 50% of thermal radiant energy is spent, remain the main cause of heat loss. The solution to this problem is the use of electrochromic devices. Devices made on the basis of submicron coatings of tungsten oxide (WO₃) are considered to be especially promising. They can operate effectively in both the visible and infrared ranges of the spectrum. This article is devoted to the study of the influence of technological modes of manufacturing submicron coatings of WO₃ on the performance of electrochromic devices. As part of the study, electro-optical and cyclic tests of a number of electrochromic devices were carried out. The following technological parameters were varied: annealing temperature (from 150 °C to 450 °C) and heating rate during annealing (from 2.5 °C/min to 10.0 °C/min). As a result, it was found that the largest working optical range is observed in the samples in which the WO₃ coatings were in the amorphous state and annealed in the temperature range from 200 °C to 350 °C. In the visible region of the spectrum (λ = 680 nm), these samples had a contrast of 55%, and in the near infrared (λ = 840 nm) - 80%. However, the longest service life (1653 operating cycles) was observed in the samples in which the WO₃ annealing temperature was 350 °C, and the heating rate was 2.5 °C/min. The obtained results are explained by the fact that at high heating rates (from 5.0 °C/min to 10.0 °C/min), microdefects of the coatings are formed, which, in turn, reduce the service life of electrochromic devices. At annealing temperatures of the electrochromic material above 418 °C, amorphous WO₃ transforms into the crystalline phase, which leads to a decrease in the coating thickness, deterioration of the electro-optical characteristics by an average of 1.3 times and a reduction in the service life of the devices by 1.5 times. The lowest contrast was observed in samples of electrochromic devices in which the WO₃ coatings were annealed at 150 °C. Thus, quasi-optimal temperature ranges for the manufacture of WO₃ coatings (annealing temperature of 350 °C and heating rate of 2.5 °C/min) are determined, at which electrochromic devices have the largest working optical range and service life. Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.