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than LCDs. However, TLCDs do not have memory and cannot retain information placed in it

indefinitely without some current supply. To get a complete RGB-color three different

organic materials that emit the colors red, blue and green are needed. One of the drawbacks of

the technology is that the brightness of the organic materials used decreases with time, with

the color blue lasting the least.

Figure 2.7: Cross-section of TOLED

2.4.5.1 Kodak: Transparent Organic Light-Emitting Diode (TOLED)

The technology generally referred to as OLED, which was pioneered at Kodak [35]. OLED

does not require any backlight due to its self-luminousness property thus consumes very less

power because OLED’s pixel, which is the source of light itself glows at low voltage. The

OLED technology’s benefit includes high contrast, more than 160 degrees viewing angle, full

color and relatively fast response time. The main drawback of OLED technology is that it is

not bistable.

2.4.6 Electrochromic

Electrochromic display technology is based on the chemical reaction, oxidation and reduction,

which occur during electrolyses. When certain polymer materials are part of an electrolyte

they have the ability to change color when deposited on an electrode if a voltage is applied.

The same principle is used to achieve an electrochromic display, the paper is coated on both

sides with conductive polymers, and then a potential difference is induced between both sides

by applying a voltage which in turn leads to a redox reaction. Thus the deposited color is seen

as an image by the observer. This technology is bistable i.e. the image is retained indefinitely.

2.4.6.1 Aveso E-paper

Aveso uses an electrochromic display technology invented by scientist at the Dow Chemical

Company [41]. The technology employs the electrochromic principle of oxidation-reduction

(redox) that has been twitched to be reversible. To get a display effect a redox material is used

to create a PH gradient when a voltage is applied. The change in PH levels causes a special

dye to respond shielding an image with high contrast. Bistability and paper like readability is

realised by separating the function of the redox material and the dye [41].

2.4.6.2 Acreo AB PAELLA: Electrochromic-Paper (EC Paper)

Acreo AB is a Swedish based company, research into its PAELLA technology started in 1999

it involves the incorporation of electronic materials into well established paper conversion

techniques like inkjet printing, screen printing, offset printing and lamination. To achieve the

electrochromic effect and to enable voltage capability on the paper a special polymer material

is applied on the surface of the paper. "Electro Chromic-paper (EC-paper) display cells are

built up from the combination of a conducting polymer coated paper, a printed electrochromic

polymer film, a printed electrolyte pattern and a protective seal layer” [33]. The technology is

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Amazon Kindle D00111 Manuale Utente Pagina 12