Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Patent
1996-04-22
1998-10-13
Patel, Nimeshkumar
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
313504, 313507, H01J 162, H01J 6304
Patent
active
058216901
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to electroluminescent devices and in particular electroluminescent devices in which the light emitting layer is a semiconductive conjugated polymer.
BACKGROUND TO THE INVENTION
Electroluminescent devices using a layer of semiconductive conjugated polymer as the light emitting layer are described in the Applicant's earlier International Application Publication No. PCT/WO90/13148. In that application, an electroluminescent device and a method of making it are described in which a layer of semiconductive conjugated polymer is placed between first and second contact layers which serve to inject into the polymer layer charge carriers of opposite types when an electric field is applied between them. These charge carriers combine in the polymer layer to form charge carrier pairs which then decay radiatively. In the radiative decay, radiation lying in the visible range is emitted.
The Applicant's earlier International Application Publication No. PCT/WO92/03490 describes a way in which the semiconductive conjugated polymer layer can be "tuned" to provide radiation in a range of selected wavelengths. This is done by controlling the semiconductor bandgap of the semiconductive layer. Thus, it is known that light of different colours can be produced using different semiconductive polymer layers. One of the main polymers of interest is poly(p-phenylenevinylene) (PPV) which emits a green light when excited. Excitation is used herein to denote the injection of charge carriers of opposite types into the polymer layer. Another polymer, poly(methylethylhexyloxy-p-phenylenevinylene) (MEH-PPV) emits a red-orange light. Furthermore, the Applicant's earlier British Patent Application No. 9226475.3 describes a class of conjugated polymers capable of emitting blue light.
Reference is also made to our earlier British Application No. 9311992.3 (Page White & Farrer Ref. 73745) which defines a class of nitrile substituted conjugated polymers suitable for use in electroluminescent devices.
The contents of the above-referenced Applications are incorporated herein by reference.
With the devices described in the above-referenced Applications, the colour of the emitted radiation is more or less fixed and is dependent on the choice of semiconductive conjugated polymer in the device. Once the device has been fabricated the colour of emitted radiation is either fixed or is subject to a slight variation if the operating characteristics of the device can be controlled to vary the brightness of the device. Any colour variation associated with a variation in brightness is however small and, being coupled to a variation in brightness, is not independent. Thus, there has not hithertofore been available an electroluminescent device using semiconductive conjugated polymers in which the colour of the emitted light can be controlled after fabrication of the device.
In the electroluminescent devices described in the above-referenced Applications, there is a single pair of contact layers arranged on either side of the polymer layer and which cooperate to inject charge carriers of opposite types into the polymer layer of the device. The polymer layer is sometimes referred to herein as the "active layer". The active layer of the device may be one substance or a plurality of different substances but is nevertheless subject to the electric field applied across the contact layers to cause the charge carriers to be injected into the active layer.
SUMMARY OF THE INVENTION
According to the present invention there is provided an electroluminescent device comprising: a first emitter comprising a layer of a polymer selected so that radiation of a first wavelength is emitted when charge carriers of opposite types are injected into the first emitter; first electrode means arranged to inject charge carriers into said first emitter; a second emitter comprising a layer of a polymer arranged in viewing overlap with said first emitter and selected so that radiation of a second wavelength is emitted when charge ca
REFERENCES:
patent: 4908603 (1990-03-01), Yamaue et al.
patent: 5247190 (1993-09-01), Friend et al.
patent: 5399502 (1995-03-01), Friend et al.
patent: 5514878 (1996-05-01), Holmes et al.
Applied Physics Letters., vol. 61, No. 26, 28 Dec. 1992, New York US pp. 3092-3094 D. Braun et al. `Nanosecond ransient electroluminescence from polymer light-emitting diodes` see the whole document.
Thin Solid Films, vol. 216, No. 1, 28 Aug. 1992, Lausanne CH pp. 96-98, D. Braun and A.J. Heeger, `Electroluminescence from light-emitting diodes fabricated from conducting polymers` see whole document.
Burn Paul Leslie
Friend Richard Henry
Holmes Andrew Bruce
Martens Josef Herbert Ferdinand
Pichler Karl
Cambridge Display Technology Limited
Haynes Mack
Patel Nimeshkumar
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