Coloring ionic trapping states in WO3 and Nb2O5 electrochromic materials

Multicolored inorganic electrochromic materials: status, challenge, and prospects

Against the backdrop of advocacy for green and low-carbon development, electrochromism has attracted academic and industrial attention as an intelligent and energy-saving applied technology due to its optical switching behavior and its special principles of operation. Inorganic electrochromic materials, represented by transition metal oxides, are considered candidates for the next generation of large-scale electrochromic applied technologies due to their excellent stability. However, the limited color diversity and low color purity of these materials greatly restrict their development. Starting from the multicolor properties of inorganic electrochromic materials, this review systematically elaborates on recent progress in the aspects of the intrinsic multicolor of electrochromic materials, and structural multicolor based on the interaction between light and microstructure. Finally, the challenges and opportunities of inorganic electrochromic technology in the field of multicolor are discussed.

Towards two-dimensional color tunability of all-solid-state electrochromic devices using carbon dots

Electrochromic devices (ECDs) that display multicolor patterns have gradually attracted widespread attention. Considering the complexity in the integration of various electrochromic materials and multi-electrode configurations, the design of multicolor patterned ECDs based on simple approaches is still a big challenge. Herein, it is demonstrated vivid ECDs with broadened color hues via introducing carbon dots (CDs) into the ion electrolyte layer. Benefiting from the synergistic effect of electrodes and electrolytes, the resultant ECDs presented a rich color change. Significantly, the fabricated ECDs can still maintain a stable and reversible color change even in high temperature environments where operating temperatures are constantly changing from RT to 70°C. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of intelligent and portable electronics.

Nd-Nb Co-doped SnO2/α-WO3 Electrochromic Materials: Enhanced Stability and Switching Properties

The fabrication of Nd-Nb co-doped SnO2/α-WO3 electrochromic (EC) materials for smart window applications is presented in the present paper. Nb is a good dopant candidate for ECs owing to its ability to introduce active sites on the surface of α-WO3 without causing much lattice strain due to the similar ionic radius of Nb5+ and W6+. These active sites introduce more channels for charge insertion or removal during redox reactions, improving the overall EC performance. However, Nb suffers from prolonged utilization due to the Li+ ions trapped within the ECs. By coupling Nd with Nb, the co-dopants would transfer their excess electrons to SnO2, improving the electronic conductivity and easing the insertion and extraction of Li+ cations from the ECs. The enhanced Nd-Nb co-doped SnO2/α-WO3 exhibited excellent visible light transmission (90% transmittance), high near-infrared (NIR) contrast (60% NIR modulation), rapid switching time (∼1 s), and excellent stability (>65% of NIR modulation was retained after repeated electrochemical cycles). The mechanism of enhanced EC performance was also investigated. The novel combination of Nd-Nb co-doped SnO2/α-WO3 presented in this work demonstrates an excellent candidate material for smart window applications to be used in green buildings.

Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement

Combined frequency-resolved techniques are suitable to study electrochromic (EC) materials. We present an experimental setup for simultaneous electrochemical and color impedance studies of EC systems in transmission mode and estimate its frequency-dependent uncertainty by measuring the background noise. We define the frequency-dependent variables that are relevant to the combined measurement scheme, and a special emphasis is given to the complex optical capacitance and the complex differential coloration efficiency, which provide the relation between the electrical and optical responses. Results of a test measurement on amorphous WO₃ with LED light sources of peak wavelengths of 470, 530, and 810 nm are shown and discussed. In this case, the amplitude of the complex differential coloration efficiency presented a monotonous increase down to about 0.3 Hz and was close to a constant value for lower frequencies. We study the effect of the excitation voltage amplitude on the linearity of the electrical and optical responses for the case of amorphous WO₃ at 2.6 V vs Li/Li⁺, where a trade-off should be made between the signal-to-noise ratio (SNR) of the optical signal and the linearity of the system. For the studied case, it was possible to increase the upper accessible frequency of the combined techniques (defined in this work as the upper threshold of the frequency region for which the SNR of the optical signal is greater than 5) from 11.2 Hz to 125.9 Hz while remaining in the linear regime with a tolerance of less than 5%.

Phase transition kinetics of LiNi0.5Mn1.5O4 analyzed by temperature-controlled operando X-ray absorption spectroscopy

Charge–discharge reaction scheme of LiNi_0.5Mn_1.5O₄ at high and low temperatures.

Electrochromic properties of TiO2 nanotubes coated with electrodeposited MoO3

Despite a favourable morphology, anodized and ordered TiO2 nanotubes are incapable of showing electrochromic properties in comparison to many other metal oxide counterparts. To tackle this issue, MoO3 of ~5 to 15 nm thickness was electrodeposited onto TiO2 nanotube arrays. A homogenous MoO3 coating was obtained and the crystal phase of the electrodeposited coating was determined to be α-MoO3. The electronic and optical augmentations of the MoO3 coated TiO2 platforms were evaluated through electrochromic measurements. The MoO3/TiO2 system showed a 4-fold increase in optical density over bare TiO2 when the thickness of the MoO3 coating was optimised. The enhancement was ascribed to (a) the α-MoO3 coating reducing the bandgap of the composite material, which shifted the band edge of the TiO2 platform, and subsequently increased the charge carrier transfer of the overall system and (b) the layered morphology of α-MoO3 that increased the intercalation probability and also provided direct pathways for charge carrier transfer.