Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1997-04-17
2000-09-12
Yamnitzky, Marie
Stock material or miscellaneous articles
Composite
Of inorganic material
428917, 4284111, 313502, 313504, 313506, 257 40, 257103, 427 66, 315291, H05B 3314
Patent
active
061175676
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The use of conjugated polymers in electroluminescent polymer diodes has been demonstrated by the group of prof. Richard Friend in Cambridge (J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burns, and A. B. Holmes, Light-emitting diodes based on conjugated polymers, Nature, 347(6293), (1990) 539-41.) and received intense interest from a wide range of scientific and industrial groups in the U.S.; polymer diodes, Appl. Phys. Lett., 58(18), (1991) 1982-4, D. Braun, A. J. Heeger, and H. Kroemer, Improved efficiency in semiconducting polymer light-emitting diodes, Journal of Electronic Materials, 20(11), (1991) 945-8.), blue-light-emitting device using poly(p-phenylene), Advanced Materials, 4(1), (1992) 36-7.G. Grem and G. Leising, Electroluminescence of wide-bandgap chemically tunable cyclic conjugated polymers, Synt. Metals, 57(1), (1993) 4105-4110.) of light-emitting-diodes and solar-cells based on poly-phenylene-vinylene, Synt. Metals, 57(1), (1993) 4186-4191.) chain length and carrier confinement layer on characteristics of poly(3-alkylthiophene) electroluminescent diodes, Solid State Commun., 80(8), (1991) 605-8, Y. Ohmori, M. Uchida, K. Muro, and K. Yoshino, Visible-light electroluminescent diodes utilizing poly(3-alkylthiophene), Japanese Journal of Applied Physics, Part 2, 30(11B), (1991) L1938-40., Y. Ohmori, M. Uchida, K. Muro, and K. Yoshino, Blue electroluminescent diodes utilizing poly(alkylfluorene), Japanese Journal of Applied Physics, Part, 30(11B), (1991) L1941-3.
These devices are prepared by sandwiching a thin film (0.05-1 .mu.m) of a conjugated polymer in between two electrode materials. The polymer is characterized by a bandgap between approximately 1.5-4 eV, and the cathode injects electrons into the lowest unoccupied molecular orbitals (LUMO) of the polymers, while the cathode injects holes into the highest occupied molecular orbitals (HOMO) of the polymer. These opposite charges meet, recombine and electroluminescence is observed in the form of photon emission. Details in these processes are described in available literature ((R. H. Friend, J. H. Burroughes, and D. D. C. Bradley, Electroluminescent Devices, Patent Application PCT/GB90/00584, (1990) )(I.Parker: Carrier Injection and Device Characteristics in Polymer Light Emitting diodes, J.Appl.Phys 75 (1994) 1666.)).
A problem that has not yet received an effective solution is that of obtaining different colours from one individual polymer LED.
Many materials have today been shown to give electroluminescence in polymer LEDs, among which are found the main groups of (substituted) poly(paraphenylene vinylene) and (substituted) polyparaphenylenes. Using different substituents on these polymers, it is possible to obtain light with colours all the way from blue to green, yellow, orange and red. The colour of the polymer LED is given from the chemical and electronic structure of the polymer, and cannot be changed except by changing the polymer in the LED. Among these main chain polymers, with the various substituents, there is no one which covers the full range of the visible spectrum. There is therefore no way of forming a full colour polymer LED using these materials.
Another means of forming a polymer LED is to use a nonconjugated prepolymer and to convert this into different forms, capable of giving emission at different wavelength. The conversion occurs by thermal or chemical methods, or combinations thereof. It is therefore possible to pattern the prepolymer in such a way as to prepare pixels of different colours adjacent to each other. (P. L. Burn, A. B. Holmes, A. Kraft, D. D. C. Bradley, A. R. Brown, and R. H. Friend, Synthesis of a segmented conjugated polymer chain giving a blue-shifted electroluminescence and improved efficiency., J. Chem. Soc., Chem. Commun., (1992) 32., P. L. Burn, A. B. Holmes, A. Kraft, D. D. C. Bradley, A. R. Brown, R. H. Friend, and R. W. Gymer, Chemical tuning of electroluminescent copolymers to improve emission efficiencies and allow
REFERENCES:
patent: 5425125 (1995-06-01), Holmes et al.
patent: 5537000 (1996-07-01), Alivisatos et al.
patent: 5670791 (1997-09-01), Halls et al.
Berggren et al: "Light emitting diodes with variables colours from polymer blends", Nature, vol. 372, Dec. 1994, pp. 444-446.
Andersson Mats R.
Berggren Rolf M.
Granstrom Arne M.
Gustafsson Bengt G.
Hjertberg Ulf T.
Forskarpatent i Linkoping AB
Yamnitzky Marie
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