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US 5,807,627 AGranted
Electroluminescent devices
AssigneeCambridge Display Technologies
InventorsRichard Henry Friend, Andrew Bruce Holmes, Donal Donat Conor Bradley, Paul Leslie Burn, Arno Kraft, Adam Richard Brown, Jeremy Henley Burroughes, Neil Clement Greenham
Life of this patent
Estimating the term…
Abstract
An electroluminescent device has at least two active semiconductive conjugated polymer light emitting layers arranged between a cathode and an anode. The layers are arranged so that at least part of at least two layers lie in an emission zone of the device.
Claims20
An electroluminescent device comprising:
- a first charge carrier injecting layer for injecting positive charge carriers;
- a first layer of a semiconductive conjugated polymer having a band gap selected such that when it is excited radiation at a first wavelength is emitted;
- a second layer of a semiconductive conjugated polymer having a band gap selected such that when it is excited radiation at a second wavelength is emitted;
- a second charge carrier injecting layer for injecting negative charge carriers;
- and
- means to enable an electric field to be applied across the said layers wherein at least a part of each of the first and second semiconductive conjugated polymer layers is located in an emission zone of the device, the difference between the band gap of the first and second semiconductive conjugated polymer layers being sufficiently small that it does not permit a large build-up of space-charge at an interface between the polymer layers, whereby said emission zone extends for a distance of at least 50 nm over a capture region of the device wherein positive and negative charge carriers combine with one another to form excitons and has a width characteristic of the distance over which said excitons migrate before decaying radiatively, such that on application of an electric field to the device both of said first and second polymer layers are caused to emit radiation at their respective wavelengths.
3 more elements
A method of making an electroluminescent device comprising the following steps:
- providing a first charge carrier injecting layer for injecting positive charge carriers;
- depositing on said charge carrier injecting layer a first layer of a soluble polymer in a solution of a first solvent and to a first predetermined thickness;
- drying said first layer;
- depositing on said first layer a second layer of a polymer to a second predetermined thickness, said second layer of polymer being deposited in the form of a precursor in a solution of a second solvent which is different than the first solvent, the first layer of polymer being insoluble in the second solvent;
- drying said second layer;
- heat treating the device so that the precursor is converted to its polymer;
- depositing a second charge carrier injecting layer for injecting negative charge carriers;
- wherein the polymer of the first layer emits radiation at a first wavelength when it is excited, and the polymer of the second layer emits radiation at a second wavelength when it is excited;
- and
- wherein the first and second predetermined thicknesses are selected so that at least a part of each of the first and second polymer layers is located in an emission zone of the device.
7 more elements
Dependencies are inferred from the claim text.