Highly transparent to truly black electrochromic devices based on an ambipolar system of polyamides and viologen

Abstract

A novel electrochromic device (ECD) based on an electroactive ambipolar system was constructed and designed through an absorption-complementary approach. The system consisted of electroactive polyamides (PAs) with N,N,N′,N′-tetraphenyl-pphenylenediamine (TPPA) and tetraphenylbenzidine (TPB) units in the backbone and heptyl viologen (HV) in the supporting electrolyte. Each of the electrochromic materials (ECMs), including TPPA-PA, TPB-PA and HV, provided one of the three primary colors that merged into a black color. Because of the suitable counter electrode materials used in this study, the overall operating voltage was effectively reduced; thus, the electrochemical stability and lifetime of the ECD were greatly enhanced. Furthermore, the whole system was completely transparent in its neutral or bleaching state, and the transmittance was reduced to only 6% in the colored state in both the visible and near-infrared (NIR) regions. The ECD demonstrated a high L* change (ΔL*) of 81 and a significant transmittance change (ΔT) of 60% in the visible region. Thus, through the excellent combination of the electrochromic and ambipolar characteristics of the system, a genuine 'highly transparent to truly black' ECD was successfully fabricated, implying the great potential of this device as a shutter in transparent displays and related devices.

High‐Performance Electrochromic Optical Shutter Based on Fluoran Dye for Visibility Enhancement of Augmented Reality Display

“…The LCD utilizing dye‐doped cholesteric LC (chLC) and electrowetting devices have excellent optical properties and fast response time but too high driving voltage limits the application to portable devices like OST‐HMD . On the other hand, reported ECDs using various electrochromic materials have very low driving voltage suitable for the portable devices . Among reported electrochromic materials, fluoran dye exhibits superior characteristics than viologen and polymer materials in all evaluation items.…”

“…An ECD can provide maximum aperture ratio and great control over the tuning of light absorption property due to mutable transparency of electrochromic materials as a function of oxidation–reduction states . Normally, ECDs are categorized according to the electrochromic materials like inorganic and organic . Former results show that the inorganic ECD suffers from a low optical density at colored mode (metal‐oxide‐based ECD) and a slow response time and relatively low transparency in bleached mode (metal‐based ECD) .…”

“…As a result, these types of ECDs are not perfectly ideal candidate as an optical shutter for OST‐HMD applications. While the organic materials especially viologen and polymer based ECDs are extensively investigated but still could not fully gratify the basic optimal requirements for optical shutter. Normally, fluoran derivatives, which are mainly used as thermochromic dyes, are highly applicable in ECD for optical shutter because those are highly transparent in colorless state, intensively absorb light of a wide wavelength in colored state, and also have an electrochromic characteristic.…”

Bioinspired Stimuli‐Responsive Color‐Changing Systems

“…An EC device based on electroactive polyamides, with N , N , N ′, N ′‐tetraphenyl‐ p ‐phenylenediamine and tetraphenylbenzidine units in the backbone, has been produced, in which heptyl viologen (HV) is used as the supporting electrolyte. The device is completely transparent in the bleached state and turns to completely black in the redox state with the working voltage of <2 V …”

Multifunctional electrochromic energy storage devices by chemical cross-linking: impact of a WO3·H2O nanoparticle-embedded chitosan thin film on amorphous WO3 films

“…The EC energy storage performance (optical modulation, coloration efficiency (CE), switching speed, long-cycling stability, specific capacitance, and rate capability) of multifunctional devices is believed to be attributed to the electrochemical double-behavior of electrons and cations on active materials. In this case, the optical modulation, CE, and specific capacitance are mainly related to the degree of insertion/extraction of electrons and cations into/from the active materials in response to the applied voltage and the degree of the switching speed, and the rate capability is directly determined by the ion diffusivity and electron conductivity on active materials 8,9 . Among the active materials of multifunctional devices classified as inorganic materials (transition metal oxides, Prussian blue-based materials, etc.)…”