Electrochromic efficiency

Electrochromic properties of polymers, which include their hue, color saturation, contrast or luminance change, cycle life, and electrochromic efficiency, can be controlled by structural modification and/or electrochemical switching conditions. Influence over many material properties that include solubility, thermal and environmental stability, oxidation potential, and conductivity can also be achieved through structural modification. 

Electrochromic efficiency, expressed as C cm, is the ratio of the variation of optical density to the injected charge as a function of unit area, and it is a wavelength-dependent quantity. The electrical power needed to operate an electrochromatic device is related to electrochromic efficiency, an important parameter to discriminate among electrochromic materials for large-area devices. 

The best performing is pMeT. Switching it between 2.5 and 4 V vs Li shows an electrochromic efficiency at 530 nm of 240mC cm, a very high value. Its electrochromic response time is also satisfactory, the transmittance... 

Table 8,1 Morphology and electrochromic efficiency for proton insertion in aqueous electrolytes of some cathodic ECMs. Data obtained from ref [15]...

As expected from equation [8.13], the lithiated nickel oxide electrode becomes transparent during the cathodic cycle (Li" insertion) and coloured in the following anodic cycle (Li" extraction). It is interesting to note that the electrochromic efficiency of lithiated nickel oxide is 0.04mCcm" at 633 nm (25), i.e. of the same order as that of tungsten oxide. 

Finally, the electrochromic efficiencies of differently prepared samples of anodic ECMs are summarized in Table 8.2. 

Coloration efficiency (electrochromic efficiency). This is the amount of electronic charge (2d) which is necessary to produce an optical density change (AOD). The coloration efficiency (/ ) of an electrochromic material can be defined at the absorbing wavelength and is given by... 

Polythiophenes with P-alkyl substituents including more than three carbon atoms are commonly soluble in organic solvents. Recently, electrochromic polymers such as poly(thiophene-3-acetic acid) and its copolymer with polythiophene were prepared. The electrochromic properties of these materials were studied by observing a color change from red to black during the potential sweep with a stability for 264 cycles, establishing a high electrochromic efficiency of up to 242 cm C at 750 nm [65],... 

---