Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1998-10-06
2001-03-27
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S506000, C313S503000, C428S690000, C257S010000
Reexamination Certificate
active
06208074
ABSTRACT:
The present invention relates to an electroluminescent device comprising a layer of electroluminescent semiconductive organic material arranged between a first electrode, constituted by a material having the property of injecting electrons into the said layer of electroluminescent material, and a second electrode constituted by a material having the property of injecting holes into this layer.
BACKGROUND OF THE INVENTION
Devices of this kind are already known, in which the semiconductive organic material consists either of a monomer organic substance, constituted by fluorescent molecules, such as anthracene, perylene, and coronene, or by molecules of an organic dye, or of a conjugated organic polymer such as poly-(p-phenylene-vinylene).
In these devices, the electrode which emits electrons is, for example, constituted by a layer of a metal chosen from among aluminium, magnesium, and calcium, or by a layer of metallic alloy, such as an alloy of magnesium and silver, and the electrode which emits holes is constituted, for example, by a layer of a metal such as gold or by a layer of tin oxide (SnO
2
) or mixed indium and tin oxide (ITO).
Such a device is described in the international patent application published under number WO 90/13148.
Such electroluminescent devices can be used in particular as light-emitting diodes in display elements, as well as for the manufacture of flat screens for portable computers or television sets.
These devices feature the advantage of easily allowing for the manufacture of large display surfaces, as well as allowing for an adjustment of the emitted light wavelength, therefore the emission colour, by selecting in an appropriate manner the semiconductive organic material which constitutes the electroluminescent layer from among the large number of known materials, which are suitable for this purpose, as well as the multiple combinations or modifications of these materials which are available to specialists.
In addition to this, these devices, in general, have a light emission efficiency which is quite acceptable, within the current state of the art, and which seems to be susceptible to improvements in the future within the capability of persons skilled in the art.
According to the prior state of the art relating to devices of this kind, the hole-injecting electrode has been provided in the form of a transparent layer, constituted, for example, by a mixed indium and tin oxide, the electron-injecting electrode itself being opaque or reflective. Devices of this type can emit light on only one face. According to one of the variants of the device described in application WO 90/13148, it is however mentioned that at least one of the charge-injecting contact layers, if these layers are of gold or aluminium and do not exceed a certain thickness, is transparent or semitransparent. It is not however specified which of these layers is transparent or semitransparent.
In addition to this, the devices currently known feature the disadvantage that they have a too short lifetime in regard of the envisaged industrial applications. More specifically, the best known devices of this type, in which the electroluminescent organic material layer is constituted by a monomer organic substance, only allow for a maximum period of use of the order of a thousand hours, in continuous operation, while the best known devices, in which the electroluminescent organic material layer consists of a conjugated polymer, do not in general resist a period of continuous operation greater than about a hundred hours.
SUMMARY OF THE INVENTION
The aim of the invention is to provide a device of the above-mentioned kind which is capable of emitting light on both its faces, i.e. an electroluminescent device in which both the electrodes located on either side of the electroluminescent material layer are transparent or translucent.
A further aim of the invention is to allow for the improvement of the device lifetime.
To this end, the device according to the invention is characterised in that the said first electrode is in the form of a transparent or translucent layer of a type n semiconductor material, chosen from among the mineral oxides and nitrides.
Favourably, the material constituting the electron-emitting electrode is chosen from among gallium nitride GaN, binary alloys of gallium nitride and indium nitride, of the general formula Ga
x
In
(1−x)
N, ternary alloys of gallium nitride, indium nitride, and aluminium nitride, of the general formula Ga
x
Al
y
In
(1−x−y)
N, and mixtures of at least two of these compounds and alloys, where x and y each represent a number between 0 and 1, the total of x+y being at the most equal to 1, the n-conductivity characteristic of the said material resulting possibly from stoichiometric defects or from doping by at least one element chosen from among groups 4a and 6a of the periodic classification table.
As the doping element, use may be made in particular of one of the following elements: Si, Sn, S, Se, and Te.
The above-mentioned type n semiconductor material, in particular gallium nitride and its alloys, may be used in any appropriate form, in particular in monocrystalline, polycrystalline, nanocrystalline, or amorphous form, or even in the form of a superimposition of layers of this type having different compositions, therefore different values of x or y, or different type of doping.
Use may also be made, as the material constituting the electron-emitting electrode, of a material chosen from among titanium oxides TiO
x
, whatever their oxygen stoichiometry may be and particularly in the sub-stoichiometric anatase and rutile phases TiO
2−y
, as well as mixtures of at least one titanium oxide with at least one other mineral oxide, particularly the multiphase materials such as the Maneli phases or the multiphase mixtures of several oxides accompanying titanium oxide.
The electron-injecting character of such materials may possibly result from the existence of stoichiometric defects or from doping by at least one element such as, for example, H, Li, Ca, Al, Cs.
The above-mentioned titanium oxides may be used in any appropriate form, and in particular in monocrystalline, polycrystalline, nanocrystalline, or amorphous form.
As the electroluminescent semiconductive organic material constituting the electroluminescent layer, use may be made of any appropriate material, in particular those constituted by the substances already used for this purpose in accordance with the prior art, in particular, conjugated polymers, such as poly(p-phenylene-vinylene), commonly designated by the abbreviation PPV, or poly p-phenylene, PPP, or polythiophene, PT, those in which the phenyl or thiophene rings carrie one or more substitutents such as an alkyl group, an alkoxy group, a halogen, or a nitro group, as well as conjugated polymers such as poly(4,4′-diphenylene-diphenylvinylene), commonly designated by the abbreviation PDPV; poly (1,4-phenylene-1-phenylinyene); poly(1,4-phenylene-diphenyvinylene); polymers of the type poly(3-alkylthiophene) or poly(3-alkylpyrrole), polymers of the type poly(2,5-dialkoxy-p-phenylenevinylene), or copolymers or mixtures of such conjugated polymers.
The use of conjugated polymers deriving from known polymers, such as those mentioned above, by grafting onto the polymer chain ends groups having the property of strengthening the adherence of the electroluminescent conjugated polymer onto the surface of the electrodes, in particular the electron-emitting electrode, and, more particularly, onto a layer of gallium nitride or titanium oxide, is particularly advantageous.
For example, use may be made of polymers deriving from poly(phenylene) of which the chain ends have one of the following formulae:
Use may equally be made, as the electroluminescent organic material constituting the electroluminescent layer, of a monomer substance, of an organic pigment or dye, this substance or this pigment or dye being possibly chosen in particular from among those appropriate for use in the electroluminescent devices of the prior art.
Ilegems Marc
Schär Michel
Zuppiroli Libero
Browning Clifford W.
DPR-Ecublens
Patel Nimeshkumar D.
Williams Joseph
Woodard Emhardt Naughton Moriarty & McNett
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