Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Patent
1997-04-01
1999-08-03
Patel, Vip
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
313500, 313501, 313509, H01J 162
Patent
active
059329653
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns electroluminescent devices and a way of fabricating these, in particular devices which have conjugated polymers as emitting layers.
Electroluminescent devices of the type which this invention concerns, have frequently been reported. As examples of this one can mention PCT/WO 90/13148, PCT/WO 9203490, PCT/WO 92/03491, PCT/WO 93/14177, PCT/WO 94/03030, PCT/WO 94/03031 and U.S. Ser. No. 317,169. These devices have been developed to a considerable extent and new useful fields of application have been found, since the report made by J H Burroughes et al, Nature 347, 539-541 (1991). Thus, different researchers have described improvements which have resulted in that these devices emit light of any color throughout the entire visible spectrum G. Grem et al., Advanced Materials 4, 36-37 (1992); D Braun et al., Applied Physics letters 58, 1982-1984 (1991); and C Zhang et al., Journal of Electronic Materials 22, 413-17 (1993). N. C. Greenham et al. have reported on high quantum efficiency devices in Nature 365, 628-630 (1993), while Goran Gustafsson et al. have reported on the possibility of fabricating large area and flexible light emitting devices.
Conjugated polymers, being organic macromolecules, have offered new possibilities, which earlier have not been obtainable. One advantage of using conjugated polymers as materials in light emitting devices is that the layers can be processed and constructed using solvents, see the PCT publications mentioned above and A. Assadi et al., Applied Physics Letters 53, 1995 (1998) and Ji H. Burroughes et al., Nature 335, 137 (1988). Another advantage is that small chemical modifications of the polymers results in a tunability of the band gap (the color of the emitted light) B. H. Xui, Macromolecules 26, 4457 (1993) and R. E. Gill et. al. Advanced Materials 6, 132 (1994).
If one would like to fabricate devices, each of which consists of more than one emitting layer or which consists of one or more barrier layers, one has, to prevent the already existing layers from being damaged during the fabrication of the next layer placed on top thereof, needed to add different layers from different solvents which not destroy the underlying layer/layers. This problem is particularly obvious, if one would like to fabricate devices each of which consists of layers with thicknesses in the range of 20-100 nm. This restriction of the fabrication procedure is sometimes unfortunate, since it limits the freedom of choice when combining different types of conjugated polymers for the different layers.
SUMMARY OF THE INVENTION
One purpose with this invention is thus to provide a new type of electroluminescent device and a way to fabricate such a device without restricting the type of solvents when choosing the different layers of the device. Another purpose with this invention is to fabricate multilayer light emitting devices which offer more freedom of choice to combine different polymers to achieve emission of any color. A further purpose with this invention is that in such a device and in such a way of fabrication it will be possible in an intermediate step to treat one or several specific layer or layers without affecting the other layers.
The chains of conjugated polymers are randomly oriented in the bulk material. Through orientation of the chains it is possible to achieve an anisotropic structure with strong anistropic properties, almost one dimensional properties. This possibility to achieve anisotropic properties has been studied through the investigation of photoluminescence of oriented polymer films D. D. C. Bradeley et al., "Infrared characterization of Oriented Poly(phenylenevinylene)", Polymer 27, 1709 (1986) and T. W. Hagler et al., Physical Review B 44, 8652 (1991) and through the study of conductivity of electrons. All of these studies have been done on thick polymer layers, which because of their thickness, are unsuitable for or at least show disadvantages to use in electroluminescent devices or in light emitting diodes of a kind
REFERENCES:
patent: 5217650 (1993-06-01), Theophilou et al.
patent: 5317169 (1994-05-01), Nakano et al.
Dialog Information Service, file 351, Derwent WPI, Dialog accession No. 009592042, WPI accession No. 93-285588/36, Sumitomo chem Co. Ltd: "Organic electroluminescenceelement used for planar light source-consisting of luminous layer contg. conjugated system copylymer composed of at least two repeat units contg. sryryl gps.", & JP 5202355, A, 930810, 9336 (Basic), Aug. 10, 1993.
STN International, File CA, vol. 120, No. 16, Apr. 18, 1994, (Columbus Ohio, US), Yamamoto Takakazu et al: "Polymer light-emitting diodes with single- and double-layer structures using poly (2,3-diphenylguinoxaline-5, 8-diyl)", abstract No. 193495, & Jpn. J. Appl. Phys., Part 2 (1994), 33 (28), L250-L253.
Dyreklev et al., "Aligned Polymer Chain Field Effect Transistors", Solid State Communications, vol. 82, No. 52, pp. 317-320, 1992.
Berggren Rolf Magnus
Dyreklev Tord Peter
Inganas Olle W
Forskarpatent i Linkoping AB
Patel Vip
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