This invention relates to an electrochromic device. In particular, it relates to an electrochromic device in which the components are built up on a single substrate which need not be transparent. Such devices are often referred to as monolithic devices.
Electrochromic systems are based on color changes that are caused by electrochemical reactions in various types of metal oxides or organic or inorganic compounds. Electrochromic devices are well known in the art. A typical electrochromic device architecture is the sandwich type architecture, which in its simplest form consists of two glass substrates on the outside and between them a counter and working electrode, an electrochromic material and an electrolyte which allows for the passage of ions. Such a device is disclosed in e.g. EP-A-1244168; Bach, U. et al, Adv. Mater. 2002, 14,No. 11, June 5and Cummins et al, J. Phys. Chem B 2000, 104, 11449-11459. One disadvantage of the sandwich type-architecture is that the electrochromic layer is typically viewed through a transparent substrate, such as glass which is covered with a transparent conducting layer. Transmission values for such conducting transparent substrates, e.g. glass or plastic coated with an electrically conducting material, are typically in the region of 70-90%. In reflective display applications, the light must pass through this layer twice when being diffusely reflected. This results in transmission losses of 19-51%, thereby limiting the maximum diffuse reflectance in the “off” state of the device to 49-81%.
WO-A-97/16838 discloses a monolithic device for solar cell applications. This device has a “classic” monolithic architecture, i.e. the working electrode layer is deposited directly onto a transparent conducting supporting substrate and is therefore the bottom layer of the device.
WO-A-01/97237 also discloses a monolithic device having a “classic” monolithic architecture where the working electrode (photoelectrode) is deposited directly onto a transparent conducting supporting substrate.
A major disadvantage of the existing monolithic devices is that they only allow deposition of electrochromic coatings onto transparent substrates, thus limiting their applications. Furthermore, pixels must be viewed through at least two layers of material, thereby adversely affecting the reflectance of the conventional devices.
It is an object of the present invention to avoid or minimize the disadvantages of the prior art.