EP2361232A1

EP2361232A1 - Glass substrate with an electrode, especially a substrate intended for an organic light-emitting diode device

Info

Publication number: EP2361232A1
Application number: EP09760195A
Authority: EP
Inventors: Arnaud Huignard; Julien Sellier; Guillaume Lecamp
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2008-10-24
Filing date: 2009-10-22
Publication date: 2011-08-31
Also published as: FR2937798A1; KR20110073615A; US20110266562A1; EA201170603A1; CN102203025A; JP2012506607A; FR2937798B1; WO2010046604A1

Abstract

Glass substrate (1) having a first face (10) and an opposed second face (11), said substrate being provided on its second face with an electrode (2) formed from at least one electrically conducting layer, characterized in that it has, over its entire second face and with a thickness e extending towards the interior of the substrate in the direction of the first face (10), a variation of the refractive index of the glass obtained by an ion exchange treatment, the refractive index on the surface being higher than that of the glass located away from the thickness.

Description

GLASS SUBSTRATE WITH ELECTRODE PARTICULARLY FOR ORGANIC ELECTROLUMINESCENT DIODE DEVICE

The invention relates to a glass substrate provided on one of its faces with an electrode.

The invention will be more particularly described for a structure serving as a support for an organic light-emitting diode device, called "OLED" for "Organic Light Emitting Diodes" in English.

The OLED comprises a material or a stack of organic electroluminescent materials, and is framed by two electrodes, one of the electrodes the anode being constituted by that associated with the glass substrate and the other electrode, the cathode, being arranged on organic materials opposite the anode.

OLED is a device that emits light by electroluminescence using the recombination energy of holes injected from the anode and electrons injected from the cathode. In the case of its use in an emissive device whose emission is only one side, the cathode is not transparent, and the emitted photons cross against the transparent anode and the glass substrate support of OLED to provide light outside the device.

An OLED usually finds its application in a display screen or more recently in a lighting device.

An OLED has a low light extraction efficiency: the ratio between the light that actually leaves the glass substrate and that emitted by the electroluminescent materials is relatively low, of the order of 0.25. This phenomenon is explained on the one hand by the fact that a certain quantity of photons remains trapped in guided modes between the cathode and the anode, and on the other hand by the reflection of light within the glass substrate because of the index difference between the glass of the substrate (n = 1, 5) and the air outside the device (n = 1).

It is therefore sought solutions to improve the efficiency of an OLED, namely to increase the extraction gain while providing a light that is white, that is to say, emitting in some or all wavelengths of the spectrum visible.

The solutions usually proposed concern the glass substrate, that is to say at the level of the glass-air interface, we will speak of geometrical optics solutions because most often using geometrical optics, or at the level of the glass-anode interface we will talk about diffractive optics solutions because they usually use diffractive optics.

It is known as a diffractive optical solution to provide the glass-anode interface with a periodic projection structure which constitutes a diffraction grating. Document US 2004/0227462 shows a diffractive optical solution. For this purpose it discloses an OLED whose transparent substrate, support of the anode and the organic layer, is textured. The surface of the substrate thus has an alternation of excrescences and recesses whose profile is followed by the anode and the organic layer deposited on it.

However, if such a solution is effective for extracting monochromatic light, that is to say in a given direction of space, it is not as efficient for polychromatic light as white light for an application of lighting. i

In addition, in this document US 2004/0227462, the profile of the substrate is obtained by applying a photoresist mask on the surface of the substrate whose pattern corresponds to the desired one of the growths, then by etching the surface through the mask. Such a method is not easy to implement industrially on large substrate surfaces, and is above all too expensive, especially for lighting applications.

Document WO 05/081334 proposes another diffractive optical solution which consists in covering a flat glass substrate with a textured polymer layer obtained by embossing, the electrode and the organic layer being then deposited following the profile of the polymer layer. . The corrugations of the layer, which may be periodic or not, have magnitudes such that the distance separating an apex from a corrugation background is between 0.5 μm and 200 μm.

However, with such a solution, however, numerous electrical failures of the OLEDS have been observed.

The purpose of the invention is therefore to provide a mineral glass substrate provided on one of its faces with a transparent electrode, the substrate being intended to constitute the support of a light emitting device, in particular an OLED, which is of simple design, reliable and allows to improve over existing solutions, the extraction of light emitted by said device and to provide a white light.

According to the invention, the glass substrate has a first face and a second opposite face, the second face being provided with an electrode which is formed of at least one electrically conductive layer. It has at its entire second face, and a thickness e extending inwardly of the substrate towards the first face, a variation of the refractive index of the glass obtained by an exchange treatment ionic, the refractive index at the surface being greater than that of the glass located outside the thickness e (ie a thickness greater than the thickness e starting from the free surface of the substrate, on the side of the exchanged face).

This index variation is obtained by ion exchange. Ion exchange in glass is the ability of certain glass ions, especially alkaline ions, to be able to exchange with other ions with different properties, such as polarizability. These other ions are reported on the surface of the glass and thus form in the glass near its surface an ionic pattern whose refractive index is distinct from that of the glass.

The surface of the glass remains sufficiently flat to avoid generating electrical contact between the anode and the cathode, which would then deteriorate the OLED.

Advantageously, the refractive index varies according to the thickness e to the surface of the second face to tend or be equal to the refractive index of the electrode. A variation in the index between the surface of the glass and the electrode directly in contact with the glass, which is equal to 0.4 or even 0.3, is thus preferred.

The variation of the refractive index according to the thickness e can correspond to a profile passing from the value of the index of the glass established below the thickness e (outside the thickness e) to another value d 'index, in a direct way without intermediate value.

According to a preferred variant, the variation of the refractive index of the substrate corresponds to an index gradient, that is to say a variation corresponding to a profile passing through several index values. The profile is preferably (globally) linear. Such a profile is obtained by selecting in known manner the glass in particular its diffusion properties, for example the interdiffusion coefficient between silver and sodium. The index variation is greater than or equal to 0.05, preferably at least 0.08, or even at least 0.1.

The substrate advantageously has a refractive index which varies from the thickness of the glass to the surface to tend or be equal to the refractive index of the electrode.

Thus, when the glass substrate provided with its electrode serves as a support for an OLED, the photons emitted from the OLED and passing through the electrode and then meeting the glass substrate are much less deviated from their trajectory due to a break in the index. less pronounced between the electrode and the glass. An index gradient is defined as a gradual change in the index of the medium. This medium avoids too much reflection of the light that passes through it.

According to one characteristic, a variation of index in the thickness of the glass, advantageously between 1 and 100 μm, preferably between 1 μm and 10 μm, and in particular between 1 μm and 5 μm, is sufficient to direct the light into the substrate at an angle of incidence adapted to optimally ensure the photon output of the substrate.

Ion exchange is the exchange of certain ions of the glass by ions selected from, in combination or not, barium, cesium, and preferably silver or thallium. These ions are chosen for their high polarizability in comparison with the ions they replace, which gives rise to a strong variation in the refractive index of the exchanged zone of the glass.

The use of silver or thallium ions as a doping ion makes it possible to create zones having a sufficiently high refractive index with respect to that of the glass to respond according to the invention to the particular application of electroluminescent devices. Ion exchange is obtained by known techniques. The surface of the glass substrate to be treated in a bath of molten salts of the exchange ions, for example silver nitrate (AgNOs), is placed at a high temperature between 200 and 550 ^° C., and for a sufficient duration corresponding to the desired exchange depth.

It is advantageous to subject the substrate in contact with the bath to an electric field which is mainly a function of the conductivity of the glass substrate and its thickness, and preferably varies between 10 and 100 V. In this case, the substrate can then undergo another heat treatment, advantageously at a temperature between the exchange temperature and the glass transition temperature of the glass, in order to diffuse the ions exchanged in a direction normal to the face of the substrate provided with the electrode, so as to obtain a linear profile index gradient.

The light transmission of the substrate of the invention may be greater than or equal to 80%.

The glass substrate may be extraclear. Reference WO04 / 025334 may be referred to for the composition of an extraclear glass. In particular, it is possible to choose a silicosodocalcic glass with less than 0.05% Fe III or Fe ₂ O ₃ . For example, Saint-Gobain's Diamant glass, Saint-Gobain's Albarino glass (textured or smooth), Pilkington's Optiwhite glass, Schott's B270 glass.

The glass substrate may advantageously have the following composition: SiO ₂ 67.0 - 73.0%, preferably 70.0 - 72.0%

Al ₂ O ₃ 0 - 3.0%, preferably 0.4 - 2.0% CaO 7.0 - 13.0%, preferably 8.0 - 11.0%

MgO 0 - 6.0%, preferably 3.0 - 5.0% Na ₂ O 12.0 - 16.0%, preferably 13.0 - 15.0%

K ₂ O 0 - 4.0%

TiO ₂ 0 - 0.1% Total iron (expressed as Fe ₂ O ₃ ) 0 - 0.03%, preferably 0.005 - 0.01%

Redox (FeO / total iron) 0.02 - 0.4%, preferably 0.02 - 0.2%

Sb ₂ O ₃ 0 - 0.3%

CeO ₂ 0 - 1, 5%

SO ₃ 0 - 0.8%, preferably 0.2 - 0.6%

The glass substrate according to the invention is preferably used as a support in a light emitting device, in particular an electroluminescent diode (OLED) device comprising an organic layer disposed between two electrodes, one of the electrodes being constituted by the electrode of the glass substrate of the invention.

Such a light-emitting diode device is for example designed for display screens or lighting devices.

The invention will now be described by way of purely illustrative and non-limiting examples of the scope of the invention, and from the attached drawings, in which:

- Figure 1 illustrates a sectional view of a glass substrate according to the invention; FIG. 2 schematically illustrates, according to a first embodiment, the device for implementing the ion exchange process for obtaining a substrate whose refractive index is variable in its thickness;

FIG. 3 schematically illustrates, according to a second embodiment, the device for implementing the ion exchange process. for obtaining a substrate whose refractive index is variable in its thickness;

FIG. 4 is a sectional view of an OLED provided with the substrate of FIG.

The figures are not scaled for easy reading.

FIG. 1 represents a glass substrate 1 having a thickness in particular between 0.7 and 10 mm, comprising in its larger extensions a first face 10 and a second opposite face 11.

The substrate is provided on its second face 11 with an electrode 2 which consists of at least one thin layer of electrically conductive mathehau (x), this layer preferably being transparent for the use of the substrate as a means light transmission.

According to the invention, the substrate 1 has from its second face 11 to a depth e and over its entire surface a glass thickness whose refractive index is modified relative to that of the rest of the body of the substrate.

The thickness e is advantageously between 1 and 100 μm, preferably between 1 μm and 10 μm, and in particular between 1 μm and 5 μm. The refractive index of glass, which is usually 1.5, is varied by a variation of greater than or equal to 0.05, and preferably of at least 0.08 or even more than 0.1.

The substrate keeps a significant light transmission of at least 80%. The light transmission is measured in a known manner in accordance with ISO 23539: 2005. The index variation is advantageously gradual. It preferably constitutes a linear profile index gradient.

This variation of refractive index is obtained according to the invention by ion exchange treatment. Some glass ions, in particular alkaline ions, are exchanged by ions such as silver, thallium, barium, cesium.

Two techniques in the ion exchange process are proposed.

The first technique illustrated in FIG. 2 is carried out by immersing the face 11 of the substrate in a bath 3 containing the material whose ions are to be exchanged. For example, for a silver ion exchange, the bath contains silver nitrate (AgNOs).

The immersion of the substrate may be complete with a protective layer, of the type Al, Ti, Al 2 O 3, coating the opposite face to be treated and which is removed after the bath, for example by polishing.

The immersion of the substrate may be rather partial and preferably the entire thickness of the substrate flush with the opposite face to be treated.

The diffusion depth of the Ag ⁺ silver ions in the glass as a replacement for Na ⁺ sodium ions is a function of the time during which the substrate is left in the bath.

After removing the substrate from the bath, it is cooled to room temperature and thoroughly rinsed with water to avoid residual traces of silver nitrate.

This technique advantageously produces a quasi-linear profile of the index gradient. The second technique consists of an exchange carried out under an electric field with a possible additional step of heat treatment.

FIG. 3 illustrates the device for implementing the ion exchange method assisted by an electric field.

The device comprises two compartments 5 and 6 applied opposite one another, forming respective reservoirs. The compartments are attached to the substrate 1 by means of an adhesive 7 which also acts as a seal with respect to the contents of the tanks. One of the compartments contains a bath 50 AgNOs while the other compartment is filled with a mixture of KNO ₃ (or LiNO ₃ ) and NaNO ₃ .

A platinum electrode 8 and, respectively, a platinum electrode 9 are immersed in each bath 50 and 60 respectively, these electrodes being connected to a voltage generator 80.

When an electric field is applied between the electrodes 8 and 9, the alkali ions of the glass are moved to the bath 60 and are gradually replaced by the Ag ⁺ ions contained in the bath 50 (direction of migration indicated by the arrows).

As a variant of the AgNO ₃ bath, a layer of metallic silver may be deposited. It is deposited by magnetron, CVD, inkjet or silkscreen. An electrode layer is also deposited on the opposite side. The electric field is then applied between the silver layer and the metal layer. After the exchange, the electrode layer is removed by polishing or chemical bonding.

The electric field applied between the metal layer or the bath, and the electrode, therefore generates the ion exchange. Ion exchange is carried out at a temperature of between 250 and 350 ^° C. The exchange depth is a function of the intensity of the field, the time during which the substrate is subjected to this field and the temperature at which the exchange is carried out. The field is between 10 and 100 V.

This technique leads to a variation of index whose profile is similar to a step, by moving clearly from the value of the index of the glass to a second value with no variation spread between these two values. For example, it is chosen to carry out such an ionic exchange with a preferably extraclear glass, of 2 mm, at a temperature of 300 ^° C., with a duration of 10 h under a field of 10 V / min. We obtain a variation of stair type index and amplitude 0.1.

By supplementing with a heat treatment of the substrate, the profile of the index variation advantageously becomes progressive. This is to heat the substrate in an oven at a temperature between the ion exchange temperature and the glass transition temperature of the glass. The temperature and the duration of the treatment depend on the required index gradient.

Some glass compositions will be preferred so that the ion exchange does not induce yellowing of the glass and therefore an unfortunate decrease in light transmission.

For example, a glass composition is as follows: SiO ₂ 67.0 - 73.0%, preferably 70.0 - 72.0%

AI ₂ O ₃ 0 - 3.0%, preferably 0.4 - 2.0%

CaO 7.0 - 13.0%, preferably 8.0 - 11.0%

MgO 0 - 6.0%, preferably 3.0 - 5.0%

Na ₂ O 12.0 - 16.0%, preferably 13.0 - 15.0% K ₂ O 0 - 4.0%

TiO ₂ 0 - 0.1% Total iron (expressed as Fe ₂ O ₃ ) 0 - 0.03%, preferably 0.005 - 0.01% Redox (FeO / total iron) 0.02 - 0.4%, preferably 0.02 - 0.2 %

Sb ₂ O ₃ 0 - 0.3%

CeO ₂ 0 - 1, 5% SO ₃ 0 - 0.8%, preferably 0.2 - 0.6%

The ion exchange process thus makes it possible to easily treat large areas, to be reproducible industrially. It allows to act directly and in a simple manner on the glass without the need to proceed to intermediate and / or complementary steps such as deposition of layers, etching.

In addition, the unmodified surface state of the glass substrate provides a deposit of the cover electrode 2 under easy, usual conditions and in conventional thicknesses.

The electrode 2 is formed of a stack of layers of electrically conductive materials. It consists, for example, of a layer of ITO (Indium Tin Oxide) with a refractive index of about 1.9 or of a dielectric (s) / Ag / dielectric stack (s), generally with a first dielectric direct contact with glass having an index of 2.

According to the invention, the variation of the refractive index gradient is such that at depth in the glass, it corresponds to that of the glass (n = 1.5), whereas at the surface, it is more important and approaches the refractive index of the first layer of the stack of the electrode, close to 2.

FIG. 4 shows an OLED 7 comprising the substrate of the invention having the variation of refractive index and provided with the electrode 2.

The OLED thus comprises successively, the substrate 1 with variation of index serving as a support for the OLED, a first electroconductive coating transparent which consists of the electrode 2, a layer 70 of organic material (s) known per se, and a second electroconductive coating 71 which forms a second electrode and preferably and in known manner, facing of the organic layer 70, a reflecting surface for returning the light emitted by the organic layer to the opposite direction, that of the transparent substrate.

Comparative examples of OLEDs have been made in order to show the interest of the invention.

The examples all have the same constituent elements of the OLED (transparent electrode, layer of organic materials, second electrode, support glass substrate). The support or base glass substrate is a standard glass substrate, of the ALBARINO® type marketed by SAINT-GOBAIN GLASS FRANCE, with 5 cm by 5 cm and 2.1 mm thick sides.

When this base substrate is not treated, it corresponds to a reference substrate (reference example) for comparative tests which has a refractive index of 1, 52.

Example 1 relates to a base substrate which has undergone an ion exchange with silver according to the first technique, having been immersed in a silver nitrate bath (AgNOs), for twenty-one hours and at a temperature 345 ° C.

Example 2 relates to a base substrate which has undergone an ion exchange with thallium according to the first technique, having been immersed in a thallium nitrate bath (TINO3) for three hours and at a temperature of 400 ^° C. The table below summarizes the values obtained for each of the examples, as regards the refraction index of the substrate, the index gradient obtained with respect to an untreated reference substrate, the ion exchange thickness in the substrate. , and the gain in extraction obtained when the substrate of each example is integrated in an OLED having the same characteristics for the elements other than the substrate.

To calculate the extraction efficiency, the external quantum efficiency is first calculated, which corresponds to the ratio between the light optical power coming out of the OLED and the electric power injected into the OLED device. Then, considering an internal quantum yield of 25% for the OLED, the external quantum yield is divided by this internal quantum yield, here 0.25, to obtain the extraction efficiency.

The substrates of Examples 1 and 2 of the invention thus show a relative gain in light extraction efficiency of more than 19% compared to an untreated substrate. The relative gain in extraction efficiency is the ratio between the difference in efficiency of the example of the invention and the reference example, and the efficiency of the reference example. It has also been demonstrated that this gain obtained is obtained without degradation of the other properties of the OLED, in particular the colorimetric variation as a function of the angle of observation of the light.

Claims

A glass substrate (1) having a first face (10) and a second opposite face (11) and provided on its second face with an electrode

(2) which is formed of at least one electrically conductive layer, characterized in that it has at its entire second face and a thickness e extending inwardly of the substrate towards the first face (10), a variation of the refractive index of the glass obtained by an ion exchange treatment, the refractive index at the surface being greater than that of the glass located outside the thickness e.

2. Substrate according to claim 1, characterized in that the refractive index varies according to the thickness e to the surface of the second face, to tend or be equal to the refractive index of the electrode (2) .

3. Substrate according to one of claims 1 or 2, characterized in that the variation of the refractive index according to the thickness e corresponds to a profile passing from the value of the index of the glass established below the thickness e at another index value, in a direct manner without intermediate value or by several index values, the profile being preferably linear.

4. Substrate according to any one of the preceding claims, characterized in that the index variation is greater than or equal to 0.05, preferably at least 0.08, or even at least 0.1.

5. Substrate according to any one of the preceding claims, characterized in that the index variation thickness e is advantageously between 1 and 100 μm, preferably between 1 μm and 10 μm, and in particular between 1 μm and 5 μm.

6. Substrate according to any one of the preceding claims, characterized in that the index variation is obtained by an ion exchange treatment of glass with silver ions and / or thallium, and / or cesium and / or barium.

7. Substrate according to any one of the preceding claims, characterized in that its light transmission is greater than or equal to 80%.

8. Substrate according to any one of the preceding claims, characterized in that the glass substrate has the following composition: SiO ₂ 67.0 - 73.0%, preferably 70.0 - 72.0% Al ₂ O ₃ 0 3.0%, preferably 0.4 - 2.0% CaO 7.0 - 13.0%, preferably 8.0 - 11.0%

MgO 0 - 6.0%, preferably 3.0 - 5.0%

Na ₂ O 12.0 - 16.0%, preferably 13.0 - 15.0%

K ₂ O 0 - 4.0%

Redox (FeO / total iron) 0.02 - 0.4%, preferably 0.02 - 0.2%

Sb ₂ O ₃ 0 - 0.3%

CeO ₂ 0 - 1, 5%

SO ₃ 0 - 0.8%, preferably 0.2 - 0.6%.

9. Substrate according to any one of the preceding claims, characterized in that it is used as a support in a light emitting device, in particular an organic electroluminescent diode device, the electrode (2) of the substrate constituting one of the electrodes of the device.

10. Substrate according to any one of the preceding claims, characterized in that it is used in a display screen or in a lighting device.