Tunable Optical\nConstants of Aluminum Tungsten Bronzes\nin Electrochromic Tungsten Oxide Thin Films

Abstract

Aluminum tungsten bronze (Al_<i>x</i>WO₃) as the core layer for optical\nmodulation is of great\nsignificance\nto electrochromic (EC) devices. Compared with other EC properties,\nthere remains a vacancy in the study of optical constants of Al_<i>x</i>WO₃. Herein, the tunable optical\nconstants of Al_<i>x</i>WO₃ layers\nunder varying potentials are investigated via a spectroscopic ellipsometer.\nOur findings indicate that in terms of optical constants, the Al_<i>x</i>WO₃ layer exhibits greater modulation\nover a more extensive voltage range and has better modulation ability\nthan H_<i>x</i>WO₃ and Li_<i>x</i>WO₃. With the generation of Al_<i>x</i>WO₃, the WO₃ thin films exhibit\na 2.12% increase in thickness and a 0.26 eV decrease in the optical\nband from the bleached to the fully colored state. The large optical\nconstant modulation capability of aluminum–tungsten bronze\nenables it to achieve comparable modulation capability to that in\na lithium-ion system but at lower applied voltage conditions. Furthermore,\nthe expanded modulation range further enhances its potential applications\nin electronic, optical, and other devices. These results are expected\nto offer great assistance in understanding the coloration principle\nand the design of novel EC devices.