Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-09-15
2004-05-04
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S504000, C313S506000
Reexamination Certificate
active
06730416
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to organic light emitting diodes and, more particularly, to thermally stable, nominally amorphous films for use as emitting layers or charge transport layers in organic light emitting diodes (OLED's). Such films are prepared from dyes that are modified to result in ionic salt analogues.
BACKGROUND OF THE INVENTION
Organic light emitting diodes (OLED's) have attracted broad attention due to their potential for use in display technologies. A few prototype displays have been demonstrated but their widespread use has not occurred because of problems associated with their operational stability and durability.
The degradation of OLED devices has been attributed to chemical changes of the organic layers, such as oxidation, and also to physical changes such as crystallization. Many potentially useful emitting or charge-transporting materials form polycrystalline films when deposited by physical vapor deposition. Such films contain grain boundaries that can act as luminescence quenching sites. To avoid such a problem, deposition of amorphous (glassy state) thin films seems to be a good alternative approach for device fabrication. However, most nonpolymeric organic dye glasses are thermally unstable and crystallize when subjected to driving voltages in a device, causing device failure.
In traditional OLED devices, the emitting organic dye molecules (D) are generally neutral molecules which interact through weak van der Waals interactions. Because of the weak nature of these interactions, heating of the initially amorphous films (for example joule heating when the device is driven, or even heating during deposition) easily causes rearrangement of the molecules, leading to crystallization and grain growth.
The film crystallization problem has been identified by many researchers in the OLED device field. Efforts to synthesize amorphous dyes have been mainly focused on dissolving them in thermally stable amorphous polymers. A second approach is aimed at synthesizing large, symmetric, rigid and dense molecules that will be more heat-resistive (see Naito et al., J. Physical Chemistry, Vol 101, p. 2350 (1997)). An alternative approach is based on the introduction of spiro centers into defined low molecular weight structures (see Salbeck et al., Synthetic Metals, Vol. 91, p. 209 (1997)).
SUMMARY OF THE INVENTION
The invention modifies dyes so as to form ionic salt derivatives. Such derivatives are used as emitting or charge transport layers in organic light emitting diodes (OLED's). The modification involves attachment of ionizable substituents during initial synthesis, followed by formation of an ionic salt. An improvement of the OLED's durability and performance results from use of such ionic dye salts, since the evaporated films are nominally amorphous, thermally stable and resist further crystallization. Preliminary devices built using a test compound exhibit superior efficiency.
REFERENCES:
patent: 3849657 (1974-11-01), Hamblen et al.
patent: 5783292 (1998-07-01), Tokito et al.
patent: 5871579 (1999-02-01), Liang et al.
patent: 5882548 (1999-03-01), Liang et al.
patent: 6150536 (2000-11-01), Chondroudis et al.
patent: 6160267 (2000-12-01), Kunugi et al.
patent: 6194090 (2001-02-01), Okada
patent: 6210817 (2001-04-01), Igarashi
patent: 6215245 (2001-04-01), Mori
patent: 0 910 100 (1999-04-01), None
patent: 2-250881 (1990-10-01), None
patent: 04-320484 (1992-11-01), None
patent: 06-271843 (1994-09-01), None
patent: 07-086634 (1995-03-01), None
patent: 08-231536 (1996-09-01), None
patent: 10-511718 (1998-11-01), None
patent: 11-102783 (1999-04-01), None
patent: 11-149-82 (1999-06-01), None
patent: 11-193359 (1999-07-01), None
patent: 11-204266 (1999-07-01), None
patent: 11279426 (1999-10-01), None
patent: 11283750 (1999-10-01), None
patent: 11-514142 (1999-11-01), None
patent: WO 91/03142 (1991-03-01), None
patent: WO 98/03042 (1998-01-01), None
patent: WO 00/11105 (2000-03-01), None
Karasz et al. “Tunable Electroluminescence from Ionomers Doped with Cationic Lumophores”, Electrochimica Acta, vol. 43, Nos. 10-11, pp. 1623-1628, 1998.
“The Use of ionic salt dyes as amorphous, thermally stable emitting layers in organic light-emitting diodes,” Applied Physics Letters, vol. 76, No. 1, Jan. 2000, K. Chondroudis and D.B. Mitizi.
Braun et al. “Electroluminescence and electrical transport in Poly (3-Octylthiophene Diodes”, p. 564-568, 1992 American Institute of Physics.
Advanced Materials, 1997, vol. 9, No. 9, Tetsuya Noda et al., “A Novel Family of Amorphous Molecular Materials Containing an Oligothiophene Moiety as Color-Tunable Emitting Materials for Organic Electroluminescent Devices”.
Elsevier, Synthetic Metals 91 (1997), pp. 209-215, J. Salbeck et al., “Low Molecular Organic Glasses for Blue Electroluminescence”.
Elsevier, Thin Solid Films 273 (1996), pp. 202-208, Eun-Mi Han et al., “Crystallization of Organic Thin Films for Electroluminescent Devices”.
J. Phys. Chem., vol. A, No. 101, pp. 2350-2357, Katsuyuki Naito et al., “Molecular Design, Syntheses, and Physical Properties of Nonpolymeric Amorphous Dyes for Electron Transport”.
Chondroudis Konstantinos
Mitzi David B.
Garrett Dawn
Kelly Cynthia H.
Morris Daniel P.
Ohlandt Greeley Ruggiero & Perle L.L.P.
LandOfFree
Ionic salt dyes as amorphous, thermally stable emitting and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ionic salt dyes as amorphous, thermally stable emitting and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ionic salt dyes as amorphous, thermally stable emitting and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3260769