Single Electrochromic Devices Research Articles

Synthesis and characterization of novel P3HT-CuO composites for their application in electrochromic devices

Novel poly(3-hexylthiophene-2,5-diyl) (P3HT)-copper oxide (CuO) composites were synthesized. The influence of the synthesis method (in-situ oxidation and simple mixing) and CuO concentration (3, 5, and 8 wt% CuO) on the properties of the composite was investigated. CuO was synthesized using the chemical bath technique. P3HT, CuO and P3HT-CuO composites were characterized by FT-IR, UV-Vis, XRD, FESEM and cyclic voltammetry. With the incorporation of CuO in P3HT it was possible to increase the absorbance using the synthesis method by simple mixture, however, by the in-situ method the absorbance was reduced. Likewise, with the incorporation of CuO in P3HT in both methods, the charge storage in the polymeric films increased. The composites showed enhanced electrochromic properties, which depend on the CuO concentration in the composites. The obtained composites were tested in single electrochromic devices using the ITO/(P3HT or COMPOSITE)/ELECTROLYTE/ITO configuration. It is shown that with the incorporation of CuO in P3HT the optical contrast can be increased, depending on both the synthesis method and the CuO concentration in the composites.

Color Palette Tactic for Multicolor Electrochromics Enabled by Electrolyte Thermochromic Engineering

AbstractElectrochromism is a reversible color change triggered by the external electrical field, which can be utilized in smart windows, displays, etc. The ability to display multiple colors in a single electrochromic device is highly beneficial for the versatile applications of the electrochromic technique. Yet, achieving the ability to adopt multiple colors in one electrochromic device has proven to be a challenging task by merely using the conventional chemical structure engineering of the electrochromic materials. In this study, a thermochromic electrolyte is introduced. A multicolor electrochromic prototype device is produced by integrating the thermochromic engineered electrolyte together with electrochromic material in which both can independently contribute to the coloring of the device. This “color palette” strategy gives an additional degree of freedom and extensive flexibility to the design of multicolor electrochromic devices. It introduces a new pathway for producing multicolor electrochromic devices and removes a bottleneck imposed by conventional strategies merely depending on the electrochromic material structure engineering. Moreover, it inspires further development of electrolytes, that share the responsibility of tuning the optical properties of electrochromic devices together with the electrochromic materials, thereby accelerating and diversifying the applications of electrochromics in industry.

Toward Full‐Color Tunable Chiroptical Electrothermochromic Devices Based on a Supramolecular Chiral Photonic Material

AbstractTraditional electrochromic devices change the color of electrochromic materials by mainly transforming the absorption band of the materials electrically, which leads to low schedulable color selection and color performance of such materials after electrochromism. Although the addition of an interference‐enhanced nanocavity can improve this issue, achieving full‐color controllability on a single electrochromic device is still a huge challenge. This study first demonstrates a near‐full‐color tunable chiroptical electrothermochromic device using a supramolecular chiral photonic material called ferroelectric liquid crystal (FLC)‐doped cholesteric liquid crystal (CLC) (FLC‐CLC). Experimental results show that the pitch of the CLC can be elongated significantly by doping a low concentration of FLC (≈4 wt%) such that the photonic bandgap (PBG) redshifts from blue to the shortwave near‐infrared region at near room temperature. Based on this fascinating feature, the PBG of the FLC‐CLC can be tuned electrically over the entire visible region with high color performance at near room temperature in a low‐voltage range (≤3 V) via the efficient electrothermal effect of the indium‐tin‐oxide‐coated substrate of the sample. Two potential low‐voltage tunable applications based on electrothermochromic FLC‐CLC materials, namely, a broadband tunable laser and a near‐full‐color tunable coaxial microfibric textile, are demonstrated in the study.

Comparison of Machine Learning Models on Performance of Single- and Dual-Type Electrochromic Devices.

This study shows that the model fitting based on machine learning (ML) from experimental data can successfully predict the electrochromic characteristics of single- and dual-type flexible electrochromic devices (ECDs) by using tungsten trioxide (WO3) and WO3/vanadium pentoxide (V2O5), respectively. Seven different regression methods were used for experimental observations, which belong to single and dual ECDs where 80% percent was used as training data and the remaining was taken as testing data. Among the seven different regression methods, K-nearest neighbor (KNN) achieves the best results with higher coefficient of determination (R2) score and lower root-mean-squared error (RMSE) for the bleaching state of ECDs. Furthermore, higher R2 score and lower RMSE for the coloration state of ECDs were achieved with Gaussian process regressor. The robustness result of the ML modeling demonstrates the reliability of prediction outcomes. These results can be proposed as promising models for different energy-saving flexible electronic systems.

Colorless-to-Black Electrochromism from Binary Electrochromes toward Multifunctional Displays.

Cyclohexane-1,2,4,5-tetracarboxylic diimide with a nonconjugated core has been incorporated to bridge two conventional triphenylamine units. The obtained monomer has successfully hypsochromically shifted the maximum absorption wavelength by 10 nm in comparison to the one with a pyromellitic diimide bridge. Consequently, a colorless electrochromic (EC) polymer poly(bis(N,N-diphenyl-4-aminophenyl)cyclohexane-1,2,4,5-tetracarboxylic diimide) (PTPA-HDI) was electropolymerized on indium tin oxide (ITO)-coated glass. The morphology, absorption, and spectroelectrochemistry properties of polymer PTPA-HDI films electropolymerized by different scan cycles have been systematically investigated. It is found that comprehensive properties, such as color contrast and initial transparence, can be achieved for the polymer film electropolymerized by 15 scan cycles. Moreover, to realize colorless-to-black electrochromism, an asymmetric viologen derivative 1-(4-cyanophenyl)-1'-hexyl-4,4'-bipyridinium dihexafluorophosphate (HVCN) has been designed and straightforward synthesized. With the introduction of a cyanophenyl group and a hexyl chain on the two pyridinium units, colorless-to-green electrochromism can be realized for this processible viologen derivative. The absorption band at 495 nm of colorated PTPA-HDI compensates well for the valley in the absorption spectrum of colorated HVCN. Therefore, different types of colorless-to-black electrochromic devices (ECDs) are fabricated using polymer PTPA-HDI-deposited ITO electrode and HVCN-based gel electrolyte. Such a supporting electrolyte-free ECD with binary electrochromes exhibits fast coloration, high color contrast, and excellent reversibility. Furthermore, an encryption ECD is demonstrated by switching a black two-dimensional code. In addition, an autodigital display is integrated on a smart window and hence different functions can be realized in a single ECD. Overall, this study may facilitate the understanding of the EC behaviors of binary electrochromes and present a new path to design multifunctional displays.

Study of dual electrochromic devices based on polyaniline and poly (3-hexylthiophene) thin films

Polyaniline (PANI) and poly (3-hexylthiophene) (P3HT) are conducting polymers exhibiting electrochromic properties. In this work both polymers were studied in single and dual electrochromic devices (ECDs). PANI and P3HT are complementary electrochromic polymers, both films in its redox process in a dual device are clarified and obscured at the same time. This color change provided a significant difference in optical transmittance in a dual ECD. Both polymers were synthesized by chemical method. The effect of deposit method of P3HT films in the single and dual ECDs was studied. A viscous polymeric electrolyte (PE) of polymethyl methacrylate and lithium perchlorate dissolved in ethylene and propylene carbonates was used in ECDs. The architectural design of single and dual device was GLASS/ITO/PANI or P3HT/PE/ITO/GLASS and GLASS/ITO/PANI/PE/P3HT/ITO/GLASS, respectively. The electrochromic devices were constructed under environmental conditions. Transmittance spectra of colored and bleached states, and kinetic optical transmittance curves at 550 nm of single and dual ECDs were obtained. Dual P3HT-PANI-based ECDs exhibited a faster rate of transmittance change, higher stability and higher transmittance change compared with the single devices. The difference in transmittance depended of the deposit technique of the films. An optical contrast of 57 % was obtained at 550 nm.

Comparative study of optical kinetics in single and dual poly3-methylthiophene-based solid electrochromic devices

An electrochemically deposited poly3-methylthiophene (P3MT) thin film has been used as the primary electrochromic element in a solid two-electrode electrochromic device (ECD) with a viscous polymeric electrolyte (PE) of polymethyl methacrylate and lithium perchlorate co-dissolved in ethylene and propylene carbonates. The counter-electrode of the ECD was a transparent conductive (indium-tin oxide, ITO) glass (single ECD) or a polyaniline (PANI)-coated ITO glass (dual ECD). Dual P3MT-PANI-based ECDs exhibit a lower optical switch potential (less than 0.5 V) and a faster color change speed (around 1 s) compared with the single devices, independent on the lithium salt concentration and the viscosity of the polymeric electrolyte. Electrochemical impedance spectra of both types of ECDs were analyzed at zero bias. It indicates that the use of the secondary electroactive element leads to a lower counter-ion diffusion resistance as well as to a larger counter-ion storage capacity in the electrochromic element/polymeric electrolyte interfaces. Consequently, the oxidation–reduction potential is lower, and the charge transfer process is faster in the dual devices than those in the single ones.