Multicolor Electrochromics: Rainbow-Like Devices

Abstract

Stimuli-responsive reversible coloration-change materials represent a highly demanded type of smart systems useful for a wide variety of applications, with a significant growing interest in multicolor abilities. In particular, electrochromic materials have received a great deal of attention due to their versatility and broad range of industrial uses. However, most of the existing electrochromic technologies provide a single coloration, while achieving multiple colors based on simple approaches remains a challenge. The present article reports on PVA gel-based electrochromic devices, containing a single viologen, providing a colorless and two different well-defined colored states. The successful fabrication of a device, based on two viologens (multi-EC gel) with a simple architecture (glass/TCO/multi-EC gel/TCO/glass), with five different multiswitchable colors based on four-zoned electrodes (rainbow-like ECD) is also demonstrated. This novel easy-to-make multichromic system represents a significant breakthrough toward the generation of full-color devices, expanding the potential of electrochromic technology.

Flexible and Tailorable Alkylviologen/Cellulose Nanocrystals Composite Films for Sustainable Applications in Electrochromic Devices

“…It is worth mentioning that the four viologen molecules show different colors at their radical‐cation states. Such a difference provide us some inspiration for preparing variously colored electrochromic materials by a choice of viologen molecule with different substituent groups …”

“…Such a difference provide us some inspiration for preparing variously colored electrochromic materials by a choice of viologen molecule with different substituent groups. [43] 2.3. Structure and Morphology of Viologen/KCl/CNCs Films Figure 3a presents a SEM image of surface morphology of pure CNCs film.…”

Viologens and Their Application as Functional Materials

“…[17] Thee lectrochromes were ac ombination of ethyl viologen dibromide and p-cyanophenyl viologen dichloride. [18] Similarly,p otassium ferrocyanide and ferricyanide salts wereemployed as redox mediators, exhibiting faster switching times of the device. Due to the lack of research of the second reduction of many viologen species, the authors initially evaluated both reductions of a mono-electrochromic device using p-cyanophenyl viologen.…”

“…Their device consisted of a poly(vinyl alcohol)‐borax gel as polyelectrolyte, which has previously shown high‐performance results in ECDs . The electrochromes were a combination of ethyl viologen dibromide and p ‐cyanophenyl viologen dichloride . Similarly, potassium ferrocyanide and ferricyanide salts were employed as redox mediators, exhibiting faster switching times of the device.…”

“…[b],[c] Switching times: time required for 90 % of the total transmittance change to occur at the maximum contrast wavelength for the colored ( t c ) and bleached steps ( t b ). [d] Color efficiency …”