Multicolor Bipolar Modulation of Titanium–Chromium Oxide Electrochromic Coatings

Electrochromic (EC) materials offer wide-ranging commercial applications, including smart windows, electrochromic mirrors, and programmable static displays. While many conventional electrochromic applications require the encapsulation of the EC materials and other components inside a sealed cell, there are cases where the color appearance of the object's surface needs to be durable in atmospheric or aquatic environments. Among the current fabrication methods for EC materials, atomic layer deposition (ALD) remains less explored. In this work, we fill these gaps by employing ALD to grow a (Ti,Cr)Ox film as a new subset of EC coatings that operates in direct contact with aqueous solutions. The protective and bipolar coloration properties of the (Ti,Cr)Ox are achieved by the ALD alloying of TiO2 and CrOx nanocrystals. Intrinsic EC performance showed excellent cycle stability of more than 2000 cycles in aqueous electrolytes of high salinity and high corrosion resistance in pH = 0 acid. Furthermore, multicolor modulation has been achieved via a Fabry–Perot optical cavity design. Microstructural and spectroscopic characterizations combined with finite-difference time-domain (FDTD) modeling allow us to correlate the optical appearance with coating electronic and microstructures. This work showed that this ALD-grown ternary EC coating can also act as a surface protection layer and has unique advantages over other EC materials to achieve balanced performance among color tunability, coloration efficiency, and cycle stability.