Tunable Optical Constants of Aluminum Tungsten Bronzes in Electrochromic Tungsten Oxide Thin Films

Aluminum tungsten bronze (AlxWO3) as the core layer for optical modulation is of great significance to electrochromic (EC) devices. Compared with other EC properties, there remains a vacancy in the study of optical constants of AlxWO3. Herein, the tunable optical constants of AlxWO3 layers under varying potentials are investigated via a spectroscopic ellipsometer. Our findings indicate that in terms of optical constants, the AlxWO3 layer exhibits greater modulation over a more extensive voltage range and has better modulation ability than HxWO3 and LixWO3. With the generation of AlxWO3, the WO3 thin films exhibit a 2.12% increase in thickness and a 0.26 eV decrease in the optical band from the bleached to the fully colored state. The large optical constant modulation capability of aluminum–tungsten bronze enables it to achieve comparable modulation capability to that in a lithium-ion system but at lower applied voltage conditions. Furthermore, the expanded modulation range further enhances its potential applications in electronic, optical, and other devices. These results are expected to offer great assistance in understanding the coloration principle and the design of novel EC devices.