High‐Performance Reflective Electrochromic Device by Integrating White Reflector and High Optical Density Electrochromic System

Abstract

white color. To improve these optical characteristics, a wide aperture ratio and high reflection with excellent light blocking approach are highly essential.Previously, several approaches (electrophoretic, electrowetting, cholesteric liquid crystal, and electrochromic device (ECD)) have been reported as the most possible solution for reflective display applications. In particular, electrophoretic [13][14][15] and electrowetting [16][17][18] can control the intensity of reflected light by changing an area of the absorber inside the pixel. Despite paper-level readability and fast response time, their driving mechanism decreases the ACR owing to less amount of available light by limited aperture ratio. On the other hand, cholesteric liquid crystal [19][20][21] and ECD [22][23][24] can control the intensity of light via mana ging the absorbance according to the state of the transparent molecules in the complete pixel area. Although cholesteric liquid crystal has merits in terms of realizing full color and good optical control ability, it utilizes polarizer that can cause substantial optical loss. [25] Besides, only filtered light can pass through the polarizer and that consequently leads to a poor reflectivity in the white state. In contrast, ECD can easily control the reflection of light by altering the absorbance property according to the redox state of the electrochromic (EC) dye. Moreover, ECD does not require the use of a polarizer, thus, theoretically almost complete ambient light can be utilized without any optical loss. This device also possesses a high aperture ratio, high transmittance, and excellent light shutter effect. Therefore, ECD is the most favorable candidate for reflective display applications.In this paper, we demonstrate an efficient reflective ECD with a very high ACR and excellent driving stability. The fabricated reflective ECD by incorporating micro-porous titanium dioxide (TiO 2 )-based white reflector film and well-optimized EC composition revealed not only a deep black state (1.7 V) and white state (0.0 V) due to the good optical density of the EC dye but also excellent reflectivity of about 58.5% at 550 nm. Prior to the fabrication of reflective ECD, EC composition was optimized by selecting suitable proton donor, solvent, and supporting polymer to attain good coloration property, low driving voltage, and high optical density with the faster response time.This paper reports an efficient reflective electrochromic device (ECD) by integrating a highly reflective micro-porous titanium dioxide-based white reflector film and an optimized transparent to black convertible electrochromic (EC) system. This reflective ECD can reflect almost 58.5% of light in the white state and 4.7% in the dark black state at 550 nm. Similarly, it also exhibits a very high ambient contrast ratio of 38:1 under office ambient light condition and good driving stability of about 83% in the white state (0 V) and 98% in the black state (1.7 V) after 10 000 driving cycles. In addition, the EC system is optimized by select...

An optically efficient full-color reflective display with an electrochromic device and color production units

“…The schematic of full-color reflective displays consisting of a reflective ECD and color display units (CF and TCECF) is shown in Figure 1. Recently, we reported a reflective ECD [25] with a titanium-dioxide-(TiO 2 )based white reflector and simultaneously utilized a highperformance black ECD to display the basic optical information (black and white) using reflected ambient light. This reflective ECD showed high reflectance (58.5%) in the white state owing to the excellent reflection property of the TiO 2 white reflector, which reflects most of the ambient light (95.5%) in the visible wavelength range (400-700 nm) with negligible optical loss (4.5%).…”

“…To fabricate the reflective ECD, ITO glasses were sequentially cleaned in acetone and isopropyl alcohol for 10 min using an ultrasonic washer, and then rinsed using deion-ized water followed by drying using nitrogen gas. Initially, a white reflector was deposited on the bottom electrode of the reflective ECD using the previous method [25]. Then a 70-μm-thick spacer film (ROLLPACK, vacuum sealer rolls) was attached to the cleaned ITO glass with an active area of 3 × 3 cm 2 .…”

Rejuvenation of Electrochromic Devices

“…Recently, considerable efforts have been made to improve the cyclic stability of the ECDs. [16,17] Simultaneously, it is imperative to focus on the possibility of rejuvenating degraded ECDs, given the inevitable existence of ion trapping.…”

A black energy-saving electrochromic device based on a dye copolymer–metal complex

“…As one of the most important parts of optical model and display technology, bistable black electrochromic devices can adjust the intensity and spectrum of the entire visible region of solar light and has been expected by many research groups. In recent years, organic molecules 23 or polymers, [24][25][26] metal oxides 27,28 and hybrid materials 29,30 have been used to fabricate electrochromic black devices. The related reaction mechanisms can be attributed to color-mixing, 31,32 electrodeposition, [33][34][35] the designing of new materials, etc.…”