Thermochromic Research Articles

Thermal performance of thermochromic smart windows in different indoor environments

Thermochromic (TC) smart windows can passively respond to the exterior and interior temperature, which further adjust their indoor thermal environments due to the varied photo-thermal parameters. This study investigated the thermal performances of practical TC windows in a room with/without air-conditioning or with stratified temperature distribution through a validated 3D CFD model. The application of TC windows could decrease the window, indoor ambient and floor temperatures, and also improve their temperature uniformity. The upper interior window could be 3.13 °C higher than the bottom in a room without air-conditioning, which could be reduced to 2.48 °C if the TC window was utilized. The uniformity improvement could be more significant for indoor environments with apparent air temperature differences, especially for the air-conditioning case. It is suggested that the indoor air temperature and its uniformity may affect the temperature and uniformity of the TC window surface in turn, specifically its phase transition time.

Thermochromic properties and surface chemical states of reactive magnetron sputtered vanadium oxide thin films at various deposition pressures

Vanadium oxide thin films were prepared using reactive magnetron sputtering method, varying the deposition pressures from 4 to 10 mTorr while maintaining the other sputtering parameters constant. Our investigations revealed sensitive dependence of deposition pressure, chemical states of the V and O atoms, crystal phases, and thermochromic (TC) optical modulation. Specifically, the film deposited at 8 mTorr displayed distinct TC characteristics with a prevalent monoclinic m-VO2 phase according to X-ray diffraction (XRD), supported by X-ray photoelectron spectroscopy (XPS). Optical transmittance modulation and electrical property measurements revealed a metal–insulator transition (MIT), confirming the intimate connection between TC characteristics and presence of the m-VO2 phase. Films deposited at pressures lower or higher than 8 mTorr exhibited typical semiconductor behavior without TC characteristics, further supported by in situ XRD, where (110) plane shifted to lower angle upon heating above τC. Chemical state analysis by XPS revealed a clear correlation between V−O peaks and the presence of a VO2 phase, with the film deposited at 8 mTorr displaying relatively large peak fitted area indicative of the VO2 phase. These findings highlight the critical and sensitive dependence of the deposition conditions in tailoring the properties of vanadium oxide thin films and provide valuable insights for potential applications in chromogenic films.

Advancing Thermochromic Glass Durability: Reinforcing Thermosensitive Hydrogels with Enhanced Adhesion Techniques

The growing use of glass in architecture has driven research into reducing its energy consumption. Thermochromic (TC) glass technology shows promise for enhancing building energy efficiency by regulating solar heat dynamically. Although TC glass helps reduce heat radiation, additional solutions like Low-E or vacuum glass are needed to control heat convection and conduction. Low-E glass, while effective in lowering heat transfer, may increase surface temperature. Thermo-sensitive hydrogels, known for their light-scattering properties at high temperatures, have been explored to complement TC glass. However, their stability at elevated temperatures remains a challenge, especially for applications requiring durability under varying weather conditions. This study proposes enhancing the adhesion between hydrogel and glass by introducing silica–oxygen bonds. As a result, TC glass demonstrates stable performance over 100 cycles within temperature ranges from 85 °C to 30 °C in summer and 40 °C to −20 °C in winter. Furthermore, by incorporating ethylene glycol, the freezing point of TC glass is reduced to −26 °C, rendering it suitable for use in colder regions. The implementation of TC glass effectively addresses the dual requirements of summer shading and winter heating in areas with both cold winters and hot summers, significantly reducing building energy consumption. This study contributes substantially to developing advanced intelligent building materials, paving the way for more sustainable architectural designs.

Fabrication of pressure visual fiber based on liquid metal control thermochromic pigments

AbstractIn this study, pressure visual fibers (PVF) with a core‐shell structure were prepared using a coaxial wet spinning process. The fiber composite shell consists of a luminescent material (as a light source) and a thermochromic pigment (as a filter light source) mixed with a polyacrylonitrile (PAN) matrix. The fiber core layer, on the other hand, was made of gallium‐indium alloy liquid metal. In operation, the filter light source is activated by joule heat drive (resulting in the fading of the thermochromic pigment), and the PVF releases phosphorescence upon exposure to ultraviolet light. When a certain pressure is applied to the fiber shell, the liquid metal in the core layer is squeezed, resulting in a local cross‐sectional area reduction, an increase in local joule thermal power, and thus local discoloration. This localized compression, in combination with a small rated current and the presence of an ultraviolet light source, converts the mechanical force (strain and compression) into an optical response. The excellent electrical conductivity of the liquid metal, combined with its compatibility with the soft matrix, makes it a promising candidate for applications in smart textiles and flexible sensing.Highlights The technology of visual fiber controlled by current is presented. The bendability and controllability of visual composites are improved. The composite fiber can be visualized when stressed.

Color morphing surfaces with effective chemical shielding

Color morphing refers to color change in response to an environmental stimulus. Photochromic materials allow color morphing in response to light, but almost all photochromic materials suffer from degradation when exposed to moist/humid environments or harsh chemical environments. One way of overcoming this challenge is by imparting chemical shielding to the color morphing materials via superomniphobicity. However, simultaneously imparting color morphing and superomniphobicity, both surface properties, requires a rational design. In this work, we systematically design color morphing surfaces with superomniphobicity through an appropriate combination of a photochromic dye, a low surface energy material, and a polymer in a suitable solvent (for one-pot synthesis), applied through spray coating (for the desired texture). We also investigate the influence of polymer polarity and material composition on color morphing kinetics and superomniphobicity. Our color morphing surfaces with effective chemical shielding can be designed with a wide variety of photochromic and thermochromic pigments and applied on a wide variety of substrates. We envision that such surfaces will have a wide range of applications including camouflage soldier fabrics/apparel for chem-bio warfare, color morphing soft robots, rewritable color patterns, optical data storage, and ophthalmic sun screening.

Biodegradable thermochromic polylactic acid (PLA) sensor

Abstract This study investigates the development of polylactic acid (PLA) by incorporating thermochromic black pigments (TCB) at varying concentrations of 0, 0.5, 1, 2 and 3 wt% through the process of melt blending. The color transition and reversion behaviors of the resulting specimens were examined at different temperatures (−10, 10, 30, 35 and 50 °C) using colorimetric analysis. Additionally, mechanical properties, thermal characteristic and thermal stability were assessed through tensile testing, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The study revealed that an increase in TCB concentrations led to a reduction in lightness (L*). Higher pigment content enhanced thermochromic properties, resulting in more pronounced color changes. The total color difference (ΔE) remained reproducible over five cycles of heating and freezing, and this reproducibility persisted after thermal aging. Tensile strength and elongation at break exhibited improvement with increasing pigment content. Glass transition temperature (Tg) and melting temperature (Tm) of the thermochromic samples showed minimal reduction compared to that of neat PLA, which is 64.2 °C. Crystallinity degree (Xc) increased slightly by 0.2–0.92 %. The thermal stability of the PLA matrix was only marginally affected by the presence of thermochromic pigments.

Thermochromic Nanocellulose Films for Temperature-Adaptive Passive Cooling.

Energy efficiency in habitation spaces is a pivotal topic for maintaining energy sufficiency, cutting climate impact, and facilitating economic savings; thus, there is a critical need for solutions aimed at tackling this problem. One viable approach involves complementing active cooling methods with powerless or passive cooling ones. Moreover, considerable scope remains for the development of passive radiative cooling solutions based on sustainable materials. Cellulose, characterized by its abundance, renewability, and biodegradability, emerges as a promising material for this purpose due to its notable radiative cooling potential exploiting the mid-infrared (MIR) atmospheric transmission window (8-13 μm). In this work, we propose the utilization of thermochromic (TC) materials in conjunction with cellulose nanofibrils (CNF) to confer temperature-dependent adaptivity to hybrid CNF films. We employ a concept where high reflection, coupled with MIR emission in the heated state, facilitates cooling, while high visible light absorption in the cold state allows heating, thus enabling adaptive thermal regulation. CNF films were doped with black-to-leuco TC particles, and a thin silver layer was optionally applied to the films. The films exhibited a rapid transition (within 1 s) in their optical properties at ∼22 °C, becoming transparent above the transition temperature. Visible range transmittance of all samples ranged from 60 to 90%, with pronounced absorption in the 8-13 μm range. The cooling potential of the films was measured at 1-4 °C without any Ag layer and ∼10 °C with a Ag layer. In outdoor field testing, a peak cooling value of 12 °C was achieved during bright sunshine, which is comparable to a commercial solar film. A simulation model was also built based on the experimental results. The concept presented in this study extends beyond applications as standalone films but has applicability also in glass coatings. Overall, this work opens the door for a novel application opportunity for green cellulose-based materials.

Bubble Sensors for Temperature Measurements through a Colorimetric Approach.

This paper introduces an innovative sensor utilizing bubbles coated with thermochromic paint, aiming to facilitate temperature measurements in challenging-to-reach locations without the requirement of an external power source. The research conducted is innovative in terms of both methodology and application. The characterization of the thermochromic properties of paints was, in fact, performed using spectroradiometric measurements by selecting a temperature range useful for applications in various fields including preventive conservation. The study encompasses two main objectives: (1) analyzing the color characteristics of thermochromic paint and plastic resin that forms the bubbles, and (2) assessing a temperature sensor comprising a thermochromic paint-coated bubble subjected to temperature variations. The thermochromic paint exhibits reversible color modifications in response to temperature changes, making it an ideal candidate for applications of this nature. The color characterization phase involves measurements using a spectroradiometer to compare the spectral reflectance factor (SRF%) of the colored plastic resin spread on canvas with that of the inflated bubbles. The sensor characterization entails evaluating color changes of the thermochromic paint on the bubble surface with varying temperatures. Experimental results indicate that the combination of a red (R) bubble and blue (B) thermochromic paint produces quantifiable color variations suitable for the proposed applications, whereas the alternative combination under examination, namely a blue bubble and red thermochromic paint, yields less accurate results. Considering that for both thermochromic paints the color change temperature is 35 °C, it is possible to see how, for B bubble with R thermochromic paint, the chromatic coordinates change value: C* = 3.14 ± 0.14 and h = 289.54 ± 11.58 at room temperature, while C* = 2.96 ± 0.12 and h = 304.20 ± 12.17 at 35 °C. The same is true for R bubble with B thermochromic paint where C* = 25.31 ± 1.01 and h* = 285.05 ± 11.40 at room temperature, while C* = 20.87 ± 0.85 and h = 288.37 ± 11.53 at 35 °C. The study demonstrates the potential of the approach and suggests further investigations into reproducibility and expanded color combinations. The results provide a promising basis for future improvements in temperature monitoring with thermochromic bubble sensors.

Reversible thermochromic fibers with excellent elasticity and hydrophobicity for wearable temperature sensors.

Color-changing fibers, which can intuitively convey information to the human eye, can be used to facilely add functionality to various types of clothing. However, they are often expensive and complex, and can suffer from low durability. Therefore, in this study, we developed highly elastic and hydrophobic thermochromic fibers as wearable temperature sensors using a simple method that does not require an electric current. A thermochromic pigment was embedded inside and outside hydrophobic silica aerogel particles, following which the thermochromic aerogel was fixed to highly elastic spandex fibers using polydimethylsiloxane as a flexible binder. In particular, multi-strand spandex fibers were used instead of single strands, resulting in the thermochromic aerogels penetrating the inside of the strands upon their expansion by solvent swelling. During drying, the thermochromic aerogel adhered more tightly to the fibers by compressing the strands. The thermochromic fiber was purple at room temperature (25 °C), but exhibited a two-stage color change to blue and then white as the temperature increased to 37 °C. In addition, even after 100 cycles of tension-contraction at 200%, the thermochromic aerogel did not detach and was strongly attached to the fiber. Additionally, it was confirmed that color change due to temperature was stable even after exposure to 1 wt% NaCl (artificial sweat) and 0.1 wt% detergent solutions. The developed thermochromic fiber therefore exhibited excellent elasticity and hydrophobicity, and is expected to be widely utilized as an economical wearable temperature sensor as it does not require electrical devices.

Transition Temperature of Color Change in Thermochromic Systems and Its Description Using Sigmoidal Models

Background: Symmetric sigmoidal models with four parameters based on an idealized S/Z-shaped curve are commonly used to analyze the optical parameters of thermochromic materials. However, our experimental findings show that this approach leads to systematic errors involving the incorrect estimation of the transition temperature or the possibility of a virtual indication of the hysteresis nature of a reversible thermochromic change. For this reason, we sought to find a five-parameter model that would appropriately avoid this problem. Methods: Two commercial thermochromic pigments were used for the test and applied to a textile substrate at different concentrations. The optical properties were measured using reflectance spectrophotometry and then converted to Kubelka–Munk function values and colorimetric coordinates. The following statistics were used to assess the quality of the selected sigmoidal models: coefficient of determination, R2; adjusted coefficient of determination, AR2; root mean square error, RMSE; and Akaike Information Criterion, AIC. Results: The four-parameter models were compared with each other and with the five-parameter models using nested F-tests based on residual variance to obtain a statistical measure of superior performance. For all thermochromic color change data examined, the five-parameter models resulted in significantly better fitting. It could be shown that the five-parameter model showed significantly higher accuracy and precision in determining the transition temperature, like non-sigmoidal quantification methods. Conclusions: We concluded that the asymmetric five-parameter model is a valuable extension of the symmetric model in the investigation of thermochromic color changes, providing better parameter estimates and a new approach to investigating the mechanisms contributing to the asymmetry of the thermochromic curve.

A fully printed sensor with optical readout for real-time flow monitoring

In recent years, there has been a growing interest in the development of flexible thermal flow sensing devices due to their wide-ranging applications. In this study, we present the fabrication of a screen-printed flow sensor with optical readout on a 125 μm polyethylene terephthalate substrate in a three-layer configuration. The device comprises electrodes made from a commercial silver (Ag) ink, a heating area using a commercial carbon ink, and a thermochromic (TC) layer employing a commercial ink with a standard activation temperature of 31 °C. We designed a specialized experimental setup to evaluate the performance of the optical flow sensor under static and dynamic conditions. To analyze the device’s thermal response and performance across various flow conditions, we utilized a combination of electrical measurements and infrared (IR)-optical imaging techniques. The all-printed device operates on the basis of a thermodynamic cycle frequency, which activates the TC ink, causing it to blink at a frequency related to the flow passing over the sensor. The results of our preliminary testing are highly promising, as the sensor successfully demonstrated a clear relationship between flow and optical duty cycle. This innovative device offers a contactless, low-cost, easy-to-use flow detection method and holds significant potential for various practical applications.

Experimental investigation on performance of composite thermochromic and ice-melting coatings for dynamic pavement temperature control

As the main type of urban roads, the surface temperature of asphalt pavement can reach 70 °C in summer because high heat absorption, causing pavement disease and aggravating the heat island effect. Solar reflective coating is an effective way to tackle the problem in summer but may bring certain negative effects in winter. In this paper, a kind of composite coating containing thermochromic (TCM) materials and snow melting and ice suppression (SMIS) functional fillers was developed. The reflective properties, thermal behavior and road performance of the pavement coatings were investigated. The results showed that the optimal TiO2 contents in TCM-black coating for pavement was 3 wt% to make full use of optical variation range. Long-term solar radiation destroyed the structure of thermochromic microcapsules and caused degradation of color and visible reflectance of TCM coatings, which could be alleviated by ultraviolet absorbers and light stabilizers. The optimal double-layer coating structure with TCM on the top and SMIS at the bottom could achieve cooling effect of 9 °C, pavement icing temperature of −5 °C and faster ice melting rate. The skid and temperature change resistance with the coatings also met requirements. This study provides a reference for developing novel pavement materials with balanced cooling effect and ice suppression capacity for mitigating heat island effect, improving driving safety, and ensuring the optimal service state and longer service life of pavement at the same time.

A Color-Changing Biomimetic Material Closely Resembling the Spectral Characteristics of Vegetation Foliage.

Multispectral/hyperspectral technologies can easily detect man-made objects in vegetation by subtle spectral differences between the object and vegetation, and powerful reconnaissance increases the demand for camouflage materials closely resembling vegetation spectra. However, previous biomimetic materials have only presented static colors that cannotchange color, and camouflage in multiple bands is difficult to achieve. To address this challenge, inspiration is drawn from the color change of foliage, and a color-change model is proposed with active and static pigments embedded in a matrix medium. The color of a composite material is dominated by the colored active pigment, which conceals the color of the static pigments and the color is revealed when the active pigment fades. A color-changing biomimetic material (CCBM) is developed with a solution casting method by adopting microcapsuled thermochromic pigments and chrome titanate yellow pigments as fillers in a base film with polyvinyl alcohol and lithium chloride. A Kubelka-Munk four-flux model is constructed to optimize the component proportions of the CCBM. The material has a reversible color change, closely resembles the foliage spectrum in UV-vis-NIR ranges, and imitates the thermal behavior of natural foliage in the mid-infrared regime. These results provide a novel approach to multispectral and hyperspectral camouflage.

Two-dimensional VO2 nanosheet converted from MXene for flexible thermochromic smart windows

Vanadium dioxide (VO2) has attracted considerable attentions owing to its unique phase-transition based thermochromic (TC) feature, which make it promising for energy-saving smart windows. For large-scale integration to ubiquitous applications, it is highly desirable to develop a simple and efficient casting technique of a reliable VO2 thin film with enhanced TC performance. However, a significant challenge lies in achieving consistent TC performance when casting VO2 thin film on diverse non-planar surfaces. Herein, we report the fabrication of two-dimensional (2D) monoclinic-phase VO2 nanosheet through the oxidation of single-layer V2CTx nanosheet. Benefitting from the high packing density of the 2D morphology, uniform thin film composed solely of VO2 nanosheet can be directly casted on various surfaces. Moreover, the tightly bound nanosheets ensure remarkable phase-transition and significantly reduced optical scattering. As a result, the VO2 nanosheet thin film exhibited excellent TC performance, including NIR switching of 62.2 %, luminous transmittance of 45.7 %, and solar modulation efficiency of 16.9 %. The VO2 nanosheet was further integrated into flexible and large-area TC smart window, demonstrating great promise for practical applications in thermal management. This study highlights the significance of the 2D morphology of VO2 in enhancing TC performance and phase-transition, offering valuable insights for future advancements in optoelectronic applications.

Thermochromic Conductive Fibers with Modifiable Solar Absorption for Personal Thermal Management and Temperature Visualization.

Thermal management textiles provide an energy-efficient strategy for personal thermal comfort by regulating heat flow between the human body and the environment. However, textiles with a single heating or cooling mode cannot realize temperature regulation under dynamic weather. Furthermore, monocolor textiles do not satisfy aesthetic requirements in a garment. Here, we develop a thermochromic (TC) conductive fiber with a coaxial structure composed of a conductive core and thermochromic shell. The TC conductive fiber-woven fabric has the ability of low-energy dynamic thermal management by combining Joule heating and modulation of solar absorption. Compared with commercial white fabrics, TC conductive fabrics exhibit a maximum temperature drop of 2.5 K, while the temperature of colored commercial fabrics is 7.5-16 K higher than that of commercial white fabrics in the hot. In the cold, the combination of Joule heating and the photothermal effect can provide desired thermal comfort for humans. Meanwhile, heat obtained from solar absorption brings the temperature of a fabric to a predetermined level, which saves energy of 625 W/m2 compared to a conductive-fiber-based textile. In addition, TC conductive fabrics with trichromatic evolution provide a sensitive and instant temperature visualization capable of identification of invisible and intense infrared radiation. These results provide another path to expand potential applications of wearable, flexible electronics.

Stability Aspects of UV-Curable Prints on Pressure-Sensitive Labels Facestock Made from Agro-Industrial By-Products

During its life cycle, packaging comes into contact with various substances and even those it protects. Thus, for example, oil, water, and alcohol, if spilled on the packaging, can damage its functionality. In addition to exposure to chemicals, graphic products (packaging) can be exposed to moisture and UV radiation, which can negatively affect their stability during transport, storage, and handling. The choice of printing substrate can directly affect the stability of prints against different degrading influences. This paper explores the stability of thermochromic (TC) and conventional offset printing inks printed on environmentally friendly printing substrates intended for packaging applications (labelling). Results have confirmed that used printing substrates and printing inks give prints good rub resistance, but somewhat lower stability in terms of ethanol, water, and UV radiation. The choice of printing substrate can directly affect the stability of prints against different degrading influences. The resistance of prints to oil cannot be clearly defined since the samples were altered with the coloration of the oil. It can only be stated that oil reduced the functionality of the TC prints given that the samples were colored by the oil itself.

Ideal thermochromic smart window in a south-facing office room of China considering daylighting and energy performance

ABSTRACT Thermochromic (TC) smart window which allows modulating the transmission of solar heat energy and sunlight in response to environmental conditions has great potential for improving the building energy and daylighting performance simultaneously. In this study, the multi-objective optimization method is used to determine the ideal optical properties of TC windows. Parametric assessment is firstly conducted to investigate the influence of several crucial parameters. Multi-objective optimization is then carried out by applying Non-dominated Sort Genetic Algorithm-III, maximizing daylight availability and building energy efficiency. Finally, the decision-making of the Pareto frontier is performed to achieve the ideal TC windows in 32 representative cities in different climatic zones of China. Results demonstrate that increasing the luminous transmittance at low-temperature and decreasing luminous transmittance modulation ability are beneficial to daylighting and energy performance. Lower solar transmittance at low-temperature contributes to building energy savings in Beijing, Shanghai, Guangzhou and Kunming, except for Harbin. Higher solar transmittance modulation ability is desired for building energy efficiency. The optimum value for the transition temperature is in the range of 23.67–38.85°C. The building energy consumption can be reduced by 13.01%, and the desired daylighting hours can be improved by 8.90%, relative to the clear double-glazed windows.

Electricity trigger chameleon core-shell fiber via liquid metal drive thermochromic polyacrylonitrile

The discovery of color-controlled fiber holds profound importance for the development of flexible wearable devices and soft display equipment. In this study, a kind of electrically triggered chameleon fiber (ETF) was fabricated. Liquid metal was used as the conductive core structure, and red, blue and yellow thermochromic pigments were mixed into a polyacrylonitrile solution with dimethyl sulfoxide as solvent to form the thermochromic matrix shell structure. By coaxial wet spinning, reversible, ETF with a core-shell structure was prepared. We utilized joule heating to drive the thermochromic pigments change the conjugate plating by adjusting the color. ETF has therefore ideal electrochromism properties. This smart fiber appearing as a dark purple fiber at room temperature and can change color when the current is adjusted. The color expressive of ETFs changed from dark purple (0.2 A) to green (0.6 A), then to yellow (1 A), and finally to white (1.2 A). When the current was turned off, the fibers were able to return to their original color due to the conjugated structure transformation of the three thermochromic pigments. Moreover, ETFs demonstrated good thermal stability, tolerating temperatures of up to 200 ℃. This work offers a simple and cost-effective method for developing soft display equipment.

Improvement of the thermal efficiency of organic roof-coatings through design aimed at increasing the durability of thermochromic pigments

This work aims to improve the thermal efficiency of roof-coatings, by appropriate design of the samples. The pigments that provide thermochromic features to organic coatings, in fact, are susceptible to rapid physical-chemical degradation when exposed to atmospheric agents. Consequently, the study evaluated the effect of an additional top-layer with the task of increasing the durability and thermochromic efficiency of the pigments. The thermochromic pigment was analyzed by colorimetric analysis, infrared spectroscopy and optical and scanning electron microscope observations, while their thermochromic efficiency was evaluated exposing them to several thermal cycles. The protective properties of the coatings were assessed by electrochemical measurements, while their durability was investigated by different accelerated degradation tests. Finally, the thermal properties of the coatings were studied as a function of the degradation of the sample, to evaluate their thermochromic efficiency over time. This work demonstrates that the durability of the pigment, and consequently the thermochromic features of the coating, can be improved by applying an additional protective layer to the sample. Thus, this type of sample can be employed as roof-coating, with high long-term thermochromic efficiency.

Development of testing procedures for assessing the thermal and optical performance of thermochromic coatings for buildings

In climates where cooling and heating demands are balanced, thermochromic (TC) building coatings represent a promising solution to reduce the overall energy consumption for space conditioning. The main TC type proposed for building application, based on leuco dye, is however affected by photodegradation and there is an increasing research interest towards more durable TC solutions. This study suggests outdoor and laboratory measurement procedures to characterize the performance of TC building coatings. In an outdoor experimental campaign, roof and façade components with leuco dye-based TC coating were tested for 13 consecutive days. Moreover, spectrophotometric measurements were carried out to: i) characterize the solar, light and near-infrared reflectance and color properties of TC panels in pristine conditions and at different aging stages in the colored/colorless phases; and ii) assess the switching process under transient thermal conditions with the newly developed procedure. In the outdoor monitoring campaign, a maximum surface temperature difference between TC panels (colorless phase) and reference ones of ∼35 °C was found. Moreover, a 0.1 reduction in solar reflectance of TC panel in the colorless phase was reported after 3 days of outdoor exposition due to photodegradation, and the hysteresis of the TC panels undergoing the switching process was measured.