1. Field of the Invention
The present invention relates to an electrochromic layers and an electrochromic device and to processes of producing same. Additional aspects and other features of the present invention will be set forth in part in the description that follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. The description is to be regarded as illustrative in nature, and not as restrictive.
2. Discussion of the Background
Generally speaking, electrochromic materials exhibit a reversible change in absorbance, reflection or transmission of electromagnetic radiation (e.g., any one or more of ultraviolet, visible, infrared, microwave, etc.). This change in absorbance can be induced by an electrochemical oxidation-reduction reaction. Examples of electrochromic materials include transition metal oxides (e.g., tungsten oxide), viologens (1,1′-disubstituted-4,4′-bipyridinium salts), inorganic transition metal complexes (e.g., iron(III) hexacyanoferrate(II)) and conjugated conducting polymers (e.g., polythiophenes, polyalkylenedioxythiophenes, polypyrroles, polyalkylenedioxypyrroles, polycarbazoles and polyanilines). Conjugated conducting polymers are preferred electrochromic materials because the exhibit improved physicochemical properties with respect to color tunability through structural modification, electrochromic contrast, electrochromic efficiency, electrochromic stability, switching speed and processability.
An electrochromic device (ECD) is typically generally designed to modulate absorbed, reflected and/or transmitted incident electromagnetic radiation through the application of an electric field across an electrochromic material present within the device. An example of an ECD is an electrochemical cell that includes two electrodes, an electrolyte and one or more electrochromic materials that undergo a change, for example, an electrochemical oxidation-reduction reaction, upon application of external voltage that modulates the electromagnetic radiation. One typical construction of an ECD is a sandwich structure in which an electrochromic material is deposited onto two transparent electrodes (e.g., glass substrates covered with a transparent conductive oxide) that are separated by an electrolyte (e.g., gel electrolyte, solid electrolyte and/or ionic liquid) disposed therebetween.
To achieve high contrast values upon reversible switching of the electrochromic material between a colored (absorptive) state and a bleached (transmissive) state, two complementary electrochromic materials are sometimes utilized, for example a cathodic electrochromic polymer and an anodic electrochromic polymer. The cathodic electrochromic polymer usually has a low optical bandgap (determined by the onset of the π-π* transition of the polymer in the neutral state) and is colored in the neutral state, becoming transmissive upon oxidation. The anodic electrochromic polymer usually has a high optical bandgap and is transmissive in the neutral state, becoming colored upon oxidation. Therefore, when both polymers are sandwiched together in an ECD and an external voltage is applied, the ECD switches between dark and light, e.g., between a colored state and a transmissive state, with the colored state being the combined colors of both polymers.
Conventional electrochromic devices suffer from various drawbacks including rapid delamination of the electrochromic materials from the surface of the transparent electrodes, thereby rendering the ECD unusable. In addition, it is difficult to obtain a uniform thickness of the electrochromic materials deposited on the surface of the transparent electrodes by conventional methods, thereby resulting in undesirable heterogeneity in the color intensity exhibited by conventional electrochromic devices.
Accordingly, there remains a critical need for an ECD that exhibits a uniform color intensity and does not suffer from rapid delamination of the electrochromic materials from the surface of the transparent electrodes, and a process of producing the ECD by adhering the electrochromic materials in a uniform thickness to the surface of the transparent electrodes.