A thorough study on electrochromic properties of metal doped tungsten trioxide film prepared by a facile solution process

Review on recent progress in WO3-based electrochromic films: preparation methods and performance enhancement strategies

Transition metal oxides have drawn tremendous interest due to their unique physical and chemical properties. As one of the most promising electrochromic (EC) materials, tungsten trioxide (WO₃) has attracted great attention due to its exceptional EC characteristics. This review summarizes the background and general concept of EC devices, and key criteria for evaluation of WO₃-based EC materials. Special focus is placed on preparation techniques and performance enhancement of WO₃ EC films. Specifically, four methods - nanostructuring, regulating crystallinity, fabricating hybrid films, and preparing multilayer composite structures - have been developed to enhance the EC performance of WO₃ films. Finally, we offer some important recommendations and perspectives on potential research directions for further study.

Effects of Ti-doping amount and annealing temperature on electrochromic performance of sol-gel derived WO3

Fine control of structural and morphological features in electrochromic materials is of paramount importance for realizing practical electrochromic devices (ECDs), which can dynamically adjust indoor light and temperature of buildings. To this end, herein we investigate impacts of two variants such as Ti-doping amount and the annealing temperature on physical and chemical properties of sol–gel derived electrochromic WO₃ films. We use a wide range of titanium coupling agents (TCAs) as Ti-dopants ranging from 0 wt% to 20 wt% and vary the annealing temperature between 200 °C and 400 °C with 50 °C interval. Both variants greatly influence the physical properties of the resulting WO₃ films, resulting in different crystallinities and morphologies. Through complementary analytical techniques, we find that the WO₃ film featuring an amorphous phase with nano-porous morphology enhances the electrochemical and electrochromic performances. The specific TCA used in this study helps stabilize the amorphous WO₃ structure and generate the nano-pores during the following thermal treatment via its thermal decomposition. As a result, the WO₃ film having an optimal 8 wt% TCA annealed at 300 °C shows a high optical density of 73.78% in visible light (400–780 nm), rapid switching speed (t_c = 5.12 s and t_b = 4.74 s), and high coloration efficiency of 52.58 cm² C⁻¹ along with a superior cyclic stability. Thus, understanding a structure–property relationship is of paramount importance in engineering the advanced electrochromic WO₃ for use in practical ECDs and other optoelectronic applications.

Fine-control of structural properties of WO₃. Faster and balanced charge transfer kinetics. Higher coloration efficiency.

Enhanced electrochromic switches and tunable green fluorescence based on terbium ion doped WO3 films

Multifunctional WO₃-based materials have been increasingly attracting attention due to their unique physical and electrochemical nature. In this work, the luminescent species, terbium (Tb) ions, were first successfully doped into WO₃ films by a hydrothermal method to incorporate their electrochromic and photoluminescent functions. The amorphous state and porous net structure are introduced, which can be attributed to the inhibited orientation growth caused by the occupation of Tb ions in the WO₃ lattice. Here, the optimal 13% Tb-WO₃ film exhibits enhanced electrochromic properties: a high transmittance modulation of 66.71%; a fast response speed of less than 10 s; an improved CE value of 48.33 cm² C^-1 at 680 nm; and cycling stability over 600 cycles without obvious degradation, arising from its larger active surface area. Meanwhile, its green-colored emission could be realized under 260 nm UV light and is electro-switchable upon applying voltage.

Tungsten Trioxide Doped with CdSe Quantum Dots for Smart Windows

Nanocrystal quantum dots (QDs) provide tunable optoelectronic properties on the basis of their dimension. CdSe QDs, which are size-dependent colloidal nanocrystals, are used for efficient electrochromic devices owing to their unique properties in modulating quantum confinement, resulting in enhanced electron insertion during the electrochromic process. Incorporating a well-known metal oxide electrochromic material such as WO₃ into CdSe QDs enhances the redox process. Herein, we propose a facile method for producing and optimizing CdSe QDs doped in WO₃. The fabrication of the electrochromic film involves a solution and annealing process. Moreover, the effect of the QD size to optimize the electrochromic layer is studied. As a result, the coloration efficiency of WO₃ and optimized CdSe QD-WO₃ are obtained as 68.6 and 112.3 cm²/C, respectively. Thus, size-tunable nanocrystal QDs combined with a metal oxide yield high-performance electrochromic devices and are promising candidates for producing smart windows.