Note: Descriptions are shown in the official language in which they were submitted.
CA 02268739 1999-04-07
ELECTROCHROMIC LAYER SYSTEM
IN PARTICULAR FOR MOTORCAR MIRRORS
TECHNICAL FIELD
The invention relates to an electrochromic layer system, in particular for
motorcar mirrors.
BACKGROUND OF THE INVENTION
There are known motorcar mirrors, which can be dipped and comprise an
electrochromic layer system, wherein the electrochromic substances are formed
as gels
or liquids. The electrochromic substances are collected inside a layer
structure having
electrode layers, further reaction layers of a mirror layer, if necessary, and
a final glass.
The motorcar mirror having such a layer structure includes a sensor
arrangement for
radiation impinging upon the mirror, and depending on the signals of one or
more
sensors the electrochromic layer is triggered via the electrodes such that the
transmission of the layer is controlled depending on the brightness.
With these well-known mirrors and layer structures, respectively, the
electrochromic liquid or gel-like layer has to be sealed outwards, whereby the
manufacturing effort is increased. Moreover, it is extremely difficult with
the curved
mirrors to constantly maintain the distance between the limiting surfaces of
the
electrochromic layer and thus the curvature thereof. If the distance of the
limiting
surfaces and its curvature, respectively, change to each other, the optical
features
deteriorate.
SUMMARY OF THE INVENTION
The subject invention is an electrochromic layer system for motorcar mirrors
comprising a first transparent, electrically conductive layer serving as an
electrode,
which is deposited upon a glass carrier, a electrochromic layer, a second
electrically
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conductive layer serving as a backplate electrode and a reflecting layer. The
system is
characterized by the electrochromic layer (3, 4, 5) comprising an oxidation-
reduction
layer (3) deposited on the electrode.
Hence the invention is based on the object, to provide an electrochromic layer
structure, in particular for motorcar mirrors, which is less expensive in its
structure and
comprise good optics.
As a result of forming the electrochromic layer as an oxidation-reduction
layer
directly deposited upon the electrode, on the one hand, and as an organic
polymer layer
having a conjugate double bond system, on the other hand, layer thicknesses
may be
exactly observed, in particular with curved substrates as well, such that the
optics of the
mirror are not impaired. Moreover, manufacturingthe mirror is simpler, since
the layer
structure does not have to be sealed.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the present invention will be readily appreciated as the
same becomes better understood by reference to the following detailed
description
when considered in connection with the accompanying drawings wherein:
Figure 1 is a cross-sectional view of an electrochromic layer system according
to the preferred embodiment.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to Figure 1, an electrochromic mirror is generally shown at 10 and
comprises a first layer, or substrate, 1 formed as a glass, upon which the
subsequent
layers are deposited. A transparent, electrically conductive coating, or
electrode layer
2 is directly deposited onto the substrate 1 by cathode sputtering, for
example, which
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includes a possibly less electric surface resistance. The electrode 2 is
composed of
indium tin oxide, for example. An oxidation-reduction (redox) layer 3 of
tungsten
oxide, i.e. Wo3, is directly deposited as a dry film upon the electrode 2 by
high-vacuum
sputtering, which has electrochromic characteristic features by virtue of
oxidation-reduction reactions. The tungsten oxide comprises a spectral
distribution
with respect to the transmission, which is similar to V ( ) curve. The layer
thickness of
the tungsten oxide layer 3 may be adapted to the desired deepening grade. It
is about
between 100 and 1000 Angstrom units.
Instead of tungsten oxide, other metal oxides such as nickel oxide, cobalt
oxide,
indium oxide and others may be used, wherein the choice depends on the desired
spectral distribution,
For controlling the oxidation-reductionreactions, a catalyst layer 4 is
deposited
upon the tungsten oxide layer 3 by vacuum evaporation, sputtering or the like,
which
layer comprises metals such as platinum, rhodium, palladium or the like. A
storage
layer 5 is deposited upon the catalyst layer 4, which for example is comprises
a polymer
such as polypropyleneor polymethylmethacrylate(PMMA) and which for example may
be formed as a microporous or nanoporous film. This storage layer 5 serves for
the
storage of protons, that means of ions being required for the oxidation-
reduction
reaction (for example H+ or Li+), which are brought in as water for example in
a
preparatory treatment step or as lithium salt.
Another electrically conductive layer 6, or backplate electrode is deposited
upon
the storage layer 5, which may simultaneously serve as a reflecting mirror
layer,
wherein in this case it is composed of chromium. However, it is also
conceivable that
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such backplate electrode 6 to be made translucent and a separate mirror layer
may be
arranged thereover. Finally, a cover layer 7 in form of a protection film is
drawn, and
added to the electrode layer 6 to protect the entire structure against
corrosion.
In another embodiment, in a first step the backplate electrode 6 may be
cathodic
sputtered upon a glass substrate such that a mirror is formed and
subsequentlythe layers
1 to 5 and the mirror are combined to a composite structure.
Light radiation impinging upon the layer system is transmitted through the
layers 1 to 5 and reflected on the mirror layer 6 and again transmitted
through the layers
5 to 1. When no current is applied to the electrode 2 and the backplate
electrode 6, the
electrochromic layer composed of the tungsten oxide layer 3, catalyst layer 4
and
storage layer 5 has its inherent maximum degree of transmission.
With applying a voltage to the electrodes 2 and 6, an ionic current between
the
storage layer 5 and the tungsten oxide layer 3 takes place, i.e., the moisture
stored inside
the storage layer 5, e.g. water, decomposes into H+ and OH- radicals, and an
oxidation
reaction and reduction reaction, respectively, takes place depending on the
direction of
the applied voltage. The catalyst layer 4 allows the hydrogen to diffuse more
easily into
the oxide layer and thus serves for reducing the activation barrier and
accelerates the
reaction and enables the use of a lower voltage. The colour and the degree of
transmission, respectively, change by virtue of the electrochromic reaction
such that the
mirror is "deepened" and returns again in the original condition during a
subsequent
direction variation of the applied voltage.
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In the explained embodiment comprising tungsten oxide, deepening is nearly
possible within the entire visible range of wave lengths, i.e. the bell cure
shaped spectral
distribution becomes flattened in the "dark" condition.
In another embodiment, the electrochromic layer is realized by an organic
polymer layer having a conjugate double bond system, i.e. the tungsten oxide
layer 3
and the catalyst layer 4 (if available) is substituted by such an organic
polymer layer.
The organic polymer layer, which can be dopened for changing the electron
structure such that the reaction is supported, in a dipping method, for
example, is
deposited upon the transparent electrode layer 2 according to the figure.
The storage layer used in the first embodiment may be maintained in connection
with the organic polymer layer. Further structure with respect to the
backplate electrode
and reflecting layer is as described above.
The dopened organic materials as active substance have a similar
electrochemical reaction behavior with respect to the oxidation and reduction,
wherein
a change in the course of the curve is achieved within the visible spectral
range as
described above. The organic polymer can be selected from
polyparaphenylene,methyl
substituted conductor-type polyparaphenylene, polythiophene, parahexaphenyl
and
polyindenefluorene. Hence, according to the desired spectral features, the
organic
polymer layer may be composed of a combination of two or more materials and
several
layers of such materials can be provided, respectively.
The invention has been described in an illustrative manner, and it is to be
understood that the terminology which has been used is intended to be in the
nature of
words of description rather than of limitation.
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Obviously, many modifications and variations of the present invention are
possible in light of the above teachings. It is, therefore, to be understood
that within the
scope of the appended claims, the invention may be practiced other than as
specifically
described.
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