Functional Materials and Advanced Manufacturing

11 Electrochromics for Smart Windows

of protons (H

+

) and electrons (e

−

) in WO

3

can be described by the highly simplied

electrochemical reaction:

˝

˙

WO

3

+ H

+

+ e

−

ˆ

ˇ

˘

[

HWO

3

]

colored

bleached

The band gap of WO

3

can vary from 2.4 eV (cubic structure) to 3.12 eV (orthorhom-

bic) leading to a high transparency of WO

3

[85]. The reduction of W

6+

ions in W

5+

is

associated with the creation of localized states under the conduction band. The elec-

tronic transfer of these to the conduction band can then be ensured by the absorption

of a low energy photon, corresponding to a red absorption band (≈1,4 eV) and which

confers on the mat ...