Conducting color switching device

Fig. 16. Structure-color correlation table of Pt(II) complexes (left). The SEM image of a bottom-contact FET device with nanosheets as semiconducting materials is shown (center). Transient conductivity measurement of the EET device (right). The transient channel current was recorded with a light switching on and off every 5 s in a 90-s period. Reproduced with the permission of Wiley-VCH (258).

As naturally abundant and low-cost semiconductor, NiO is widely used in electrochromic windows [20], batteries [21], supercapacitors [22], and sensors [23], While all these applications benefit from an interconnected, three-dimensional NiO nanostructure that combines a high specific surface area with a good electric conductivity, the performance enhancement becomes vividly evident as an increased coloration contrast and improved switching behavior when applied in electrochromic devices. NiO nanomaterials recently employed in electrochromic studies include nanocomposites [24], inverse opals [25], macroporous [26] and mesoporous films [27-29],... 

Figure 2.21 Electrochromic switching behavior of glass/FTO/WO /ion-conductive-polymer-membrane/Niji jO/PANI/FTO/glass device (a) cychc voltammograms after the 50th and 300th cycles between -0.8 and +1.7 V at scan rate 20 m V/s (b) chronocoulometry curves and optical transmittance changes at X = 480 nm measured after 201 switches between -1.7 and +1.0 V and (c) the in situ optical spectra for bleached and colored states measured after 201 switches between -1.7 and +1.0 V and corresponding coloration efficiency. Reprinted with permission from [233]. Copyright (2012) Elsevier.

To improve performance, many PEDT derivatives used either alone or in combination have been proposed. While the electro-optical properties of WO3 are fixed, the colors and hue of conducting polymers may be altered by modification of the monomers. For example, Reynolds has studied the electrochromic properties of a multitude of EDT derivatives [100,109], and recently reported an all-polymer electrochromic device based on two different PEDT derivatives [110]. Depending on their chemical structure, the various PEDT derivatives exhibit different colors upon switching from the oxidized to the reduced state. For example, poly(tetradecylethylenedioxythiophene) (C14-EDT) is similar in switching to PEDT from transparent to blue, but it has an enhanced optical contrast. 

The absorptive/transmissive-type ECD operates with a reversible switching of the electrochromic materials between a colored state and a bleached state. Both working electrode and counter electrode are transparent so that light can pass through the device [4,5,15,250]. For flexible devices, ITO, SWNT, or PEDOT/PSS deposited onto a plastic such as poly(ethylene terepthalate) (PET) have been used [258,259]. When deposited in the doped form and dried, PEDOT/PSS films, to a thickness of 300 nm, are relatively transmissive in the visible region ( 75% T), have a relatively low resistivity (500 fi/D), and adhere to the plastic substrate in most common electrolyte solutions. The polymer films were demonstrated to be useable over the operating range of the device with no loss in conductivity or transmissivity. 

The challenge that remains for conducting polymer electrochromic applications is clearly in the domain of device scale-up. The application of these materials to large area devices, such as windows, requires uniform real-time switching of the polymer oxidation state to access different color regions. Although this has been demonstrated for small-scale devices, it is difficult at larger scales. 

Electrochromic devices may have liquid electrolytes, which make for rapid switching and sharper color changes due to greater conductivity and ion mobility. However, liquid electrolytes also give rise to faster degradation, due to the physical transport of ions involved, and problems with physical containment and operating tempera-... 

Another interesting application that uses the dynamic properties of conducting polymers is electrochromic devices. - For example, polythiophene and polyaniline undergo distinct color changes when an electrical potential is applied. Thin films of polythiophene can be switched from red (oxidized)... 

---