The First OLEDs - Revision history

Cmditradmin: /* The First (“Heroic”) Experiments to Generate Light From Organic Materials:Top and Bottom Electrodes/Rectifying Junctions */

2009-07-23T22:05:34Z

The First (“Heroic”) Experiments to Generate Light From Organic Materials:Top and Bottom Electrodes/Rectifying Junctions

← Older revision		Revision as of 15:05, 23 July 2009
Line 22:		Line 22:

	See Dresner <ref>J. Dresner, RCA Rev. 30, 322 (1969)</ref>		See Dresner <ref>J. Dresner, RCA Rev. 30, 322 (1969)</ref>
			See Pope 1963 <ref>Electroluminescence in organic crystals M. Pope ert al J. Chem. Phys.38, 2042 (1963)</ref>

	==How is Light Generated?==		==How is Light Generated?==

Smhunter at 16:55, 15 July 2009

2009-07-15T16:55:45Z

← Older revision		Revision as of 09:55, 15 July 2009
Line 13:		Line 13:
	See Helfrich <ref>W.Helfrich & W.G. Sneider Phys. Rev. Lett. 14(7), 229 (1965)</ref>		See Helfrich <ref>W.Helfrich & W.G. Sneider Phys. Rev. Lett. 14(7), 229 (1965)</ref>

	Scientists used fine slices of highly purified anthracene (C<~~sub14~~>H<~~sub10~~>), approximately 5mm thick, connect them to electrodes, and apply 100-1000 volts. If the system did not short there would be faint blue light emission. Often there would be a lightning bolt-like discharge and graphite was produced instead of light. The high voltages were needed to overcome the internal resistance to charge migration (Rs) in the organic solid. The relatively large thickness of these slices was an experimental necessity – pin-hole-free ultrathin film deposition technology was not yet available for organic materials. Emission was seen occurring near the cathode, suggesting that charge recombination occurred closer to this electrode than the center of the device.		Scientists used fine slices of highly purified anthracene (C<sub>14</sub>H<sub>10</sub>), approximately 5mm thick, connect them to electrodes, and apply 100-1000 volts. If the system did not short there would be faint blue light emission. Often there would be a lightning bolt-like discharge and graphite was produced instead of light. The high voltages were needed to overcome the internal resistance to charge migration (Rs) in the organic solid. The relatively large thickness of these slices was an experimental necessity – pin-hole-free ultrathin film deposition technology was not yet available for organic materials. Emission was seen occurring near the cathode, suggesting that charge recombination occurred closer to this electrode than the center of the device.

	<embed_document width="55%" height="400">http://depts.washington.edu/cmditr/media/OLED4_firstexperiments.pdf</embed_document>		<embed_document width="55%" height="400">http://depts.washington.edu/cmditr/media/OLED4_firstexperiments.pdf</embed_document>

	Subsequent experiments used thinner slices of anthracene (50 microns) with a semitransparent gold electrode and a silver paste cathode. Lower drive voltages were required, and light emission through the semitransparent anode was observed. Despite the relatively high external quantum efficiency of these devices, it was clear that substantial materials development would be necessary before real display devices would be realized. The cited review by Dresner shows a substantial understanding of the physics of these light emitting organic thin films, which extrapolates directly to our understanding of OLEDs today.		Subsequent experiments used thinner slices of anthracene (50 microns) with a semitransparent gold electrode and a silver paste cathode. Lower drive voltages were required, and light emission through the semitransparent anode was observed. Despite the relatively high external quantum efficiency of these devices, it was clear that substantial materials development would be necessary before real display devices would be realized. The cited review by Dresner shows a substantial understanding of the physics of these light emitting organic thin films, which extrapolates directly to our understanding of OLEDs today.

			In these early devices, the rate of transport of the positive cation radical (or hole state) and the transport of the electron rich state were not equal, causing the recombination to occur near one of the contact electrodes. This phenomenon is now known to inhibit device efficiency.

	See Dresner <ref>J. Dresner, RCA Rev. 30, 322 (1969)</ref>		See Dresner <ref>J. Dresner, RCA Rev. 30, 322 (1969)</ref>
Line 27:		Line 29:
	*An electron transfer between the reduced donor and the oxidized acceptor takes place.		*An electron transfer between the reduced donor and the oxidized acceptor takes place.
	*Enough excess free energy is generated to create the emissive state of anthracene, thus light is emitted.		*Enough excess free energy is generated to create the emissive state of anthracene, thus light is emitted.

	In these early devices, the rate of transport of the positive cation radical (or hole state) and the transport of the electron rich state were not equal, causing the recombination to occur near one of the contact electrodes. This phenomenon is now known to inhibit device effiency.


	==The First Practical OLEDs==		==The First Practical OLEDs==
	[[Image:OLED4_heterojunction.jpg\|thumb\|400px]]		[[Image:OLED4_heterojunction.jpg\|thumb\|400px]]
	The first practical OLEDs were built in the late 1980’s by Ching Tang and Andy Van Slyke at Kodak. This was a ~~revolution~~ for ~~the technology~~.		The first practical OLEDs were built in the late 1980’s by Ching Tang and Andy Van Slyke at Kodak.

			C.W. Tang and coworkers at Kodak used spin casting and sublimation deposition of the organic components of the device, with patterned electrodes on the top and bottom. This was an important technological advance over slicing single-crystal anthracene as thin as possible with a razor knife. Vapor depositing molecules in a vacuum system on top of a transparent conductor enabled the layers to be much thinner, and have almost none of the pinholes that cause shorts. Transparent conducting oxide (TCO) thin films on glass served as the anode and allowed light to be emitted in a usable fashion for displays.

	C.W. Tang and coworkers at Kodak used spin casting and sublimation deposition of the organic components of the device, with patterned electrodes on the top and bottom. This was an important technological advance over slicing single-crystal anthracene as thin as possible with a razor knife. Vapor depositing molecules in a vacuum system on top of a transparent conductor enabled the layers to be much thinner, and have almost none of the pinholes that cause shorts. Transparent conducting oxide (TCO) thin films on glass served as the anode and allowed light to be emitted in a usable fashion for displays. The keys to successful development of these first devices was control of organic film deposition to create a pin-hole free film (with high RP) which was thin enough to yield a lower series resistance than the first anthracene devices, ~~providing for~~ light emission with drive voltages under 50 volts. ~~The hole transparent layer was a spin coated polymer. This~~ produced about 15 candelas per square meter~~, which is a~~ dim but visible light. (A typical CRT computer screen operates with 100-200 candelas per square meter.)		The keys to successful development of these first devices was control of organic film deposition to create a pin-hole free film (with high RP) which was thin enough to yield a lower series resistance than the first anthracene devices, producing light emission with drive voltages under 50 volts. These devices produced about 15 candelas per square meter: dim but visible light. (A typical CRT computer screen operates with 100-200 candelas per square meter.)

	==Anatomy of Early OLEDs==		==Anatomy of Early OLEDs==
	*The '''base''' of the device was a glass or plastic substrate.		*The '''base''' of the device was a glass or plastic substrate.
	*A '''transparent conductor''' such as indium tin oxide (ITO).		*A '''transparent conductor''' such as indium tin oxide (ITO).
	*A 50 nm '''hole transport layer''' (HTL) of an easily oxidized ~~material~~ such as triarylamine or poly vinyl carbazol.		*A 50 nm '''hole transport layer''' (HTL) of an easily oxidized spin-coated polymer such as triarylamine or poly vinyl carbazol.
	*A 50 nm '''electron transport layer''' (ETL) of aluminum tris quinalate.		*A 50 nm '''electron transport layer''' (ETL) of aluminum tris quinalate.
	*A '''cathode''' made from a metal such as aluminum, magnesium-silver alloy or even calcium.		*A '''cathode''' made from a metal such as aluminum, magnesium-silver alloy or even calcium.
Line 46:		Line 47:
	See Tang C.W. <ref>Tang and S.A. VanSlyke Appl. Phys. Lett. 51, 913(1987)</ref>		See Tang C.W. <ref>Tang and S.A. VanSlyke Appl. Phys. Lett. 51, 913(1987)</ref>
	<ref>C.W. Tang, U.S. Patent # 4,356,429 (1980)</ref>		<ref>C.W. Tang, U.S. Patent # 4,356,429 (1980)</ref>


	*Vacuum deposition enabled thin electron transport layer
	*Hole transport layer was spin-coated polymer: 10 – 20 V, 15cd/m<sup>2</sup> brightness
	*All vacuum device: 10 – 20 V, 100 cd/m<sup>2</sup> using Alq<sub>3</sub> emission layer

	== References ==		== References ==

Smhunter at 21:39, 25 June 2009

2009-06-25T21:39:11Z

← Older revision		Revision as of 14:39, 25 June 2009
Line 7:		Line 7:
	</table>		</table>

	~~The first OLEDs were green as seen in this early example from the University of Arizona. The image on the right is so bright that is appears white.~~
	==The First (“Heroic”) Experiments to Generate Light From Organic Materials:Top and Bottom Electrodes/Rectifying Junctions==		==The First (“Heroic”) Experiments to Generate Light From Organic Materials:Top and Bottom Electrodes/Rectifying Junctions==

	The first experiments to generate light from organic materials ~~can be traced back to~~ the late 1950s and early 1960’s at places like RCA. These studies were driven by the hypothesis that ~~these~~ materials would act as efficient light sources and would also serve as organic photoconductors.		The first experiments to generate light from organic materials were conducted in the late 1950s and early 1960’s at places like RCA. These studies were driven by the hypothesis that organic materials would act as efficient light sources and would also serve as organic photoconductors.

	See Helfrich <ref>W.Helfrich & W.G. Sneider Phys. Rev. Lett. 14(7), 229 (1965)</ref>		See Helfrich <ref>W.Helfrich & W.G. Sneider Phys. Rev. Lett. 14(7), 229 (1965)</ref>

	~~People would take~~ highly purified anthracene ~~and cut it very fine~~, approximately 5mm thick~~. They would~~ connect ~~these~~ to electrodes and apply ~~between~~ 100 ~~and~~ 1000 volts. If the system did not short there would be light emission. Often there would be a lightning bolt like discharge and ~~you produce~~ graphite instead of light. The high voltages were needed to overcome the internal resistance to charge migration in the organic solid ~~(RS)~~. The relatively large thickness of these slices was an experimental necessity – pin-hole-free ultrathin film deposition technology was not yet available for organic materials. Emission was seen occurring near the cathode, suggesting that charge recombination occurred closer to this electrode than the center of the ~~“device”~~.		Scientists used fine slices of highly purified anthracene (C<sub14>H<sub10>), approximately 5mm thick, connect them to electrodes, and apply 100-1000 volts. If the system did not short there would be faint blue light emission. Often there would be a lightning bolt-like discharge and graphite was produced instead of light. The high voltages were needed to overcome the internal resistance to charge migration (Rs) in the organic solid. The relatively large thickness of these slices was an experimental necessity – pin-hole-free ultrathin film deposition technology was not yet available for organic materials. Emission was seen occurring near the cathode, suggesting that charge recombination occurred closer to this electrode than the center of the device.

			<embed_document width="55%" height="400">http://depts.washington.edu/cmditr/media/OLED4_firstexperiments.pdf</embed_document>

	~~<embed_document width="55%" height="400">http://depts~~.~~washington~~.~~edu/cmditr/media/OLED4_firstexperiments~~.~~pdf</embed_document>~~		Subsequent experiments used thinner slices of anthracene (50 microns) with a semitransparent gold electrode and a silver paste cathode. Lower drive voltages were required, and light emission through the semitransparent anode was observed. Despite the relatively high external quantum efficiency of these devices, it was clear that substantial materials development would be necessary before real display devices would be realized. The cited review by Dresner shows a substantial understanding of the physics of these light emitting organic thin films, which extrapolates directly to our understanding of OLEDs today.

	~~Next they brought the thickness down to 50 microns and used a semitransparent gold electrode~~.		See Dresner <ref>J. Dresner, RCA Rev. 30, 322 (1969)</ref>
	How is light generated? At the anode there is the removal of an electron to create a cation radical state. At the cathode is the addition of an electron to create the anion radical state. These charges need to hop through the organic crystal in order to meet each other somewhere near the center of the device. They undergo an electron transfer between this reduced donor and the oxidized receptor. There is enough excess free energy generated to create the emissive state of anthracene. The key piece is that in the early devices the rate of transport of the positive cation radical or hole state and the transport of the electron rich state where not equal so the recombination occurred near one of the contacting electrodes. This proves to be a real problem for the efficiency of the device.

	~~The next step in~~ the ~~evolution of the OLED was to use much thinner slices of anthracene~~, ~~with~~ a ~~semi-transparent gold anode and a silver paste~~ cathode. ~~Lower drive voltages were required~~, and ~~light emission through~~ the ~~anode was observed~~. ~~Despite~~ the ~~relatively high external quantum efficiency of these devices, it was clear that substantial materials development would be necessary before real display devices would be realized~~. ~~The cited review by Dresner shows a substantial understanding of~~ the ~~physics~~ of ~~these~~ light ~~emitting organic thin films, which extrapolates directly to our understanding of OLEDs today~~.		==How is Light Generated?==
			*Electrons are removed at the anode, creating a cation radical state.
			*Electrons are added at the cathode, creating the anion radical state.
			*These charges move through the organic crystal, and meet each other near the center of the device.
			*An electron transfer between the reduced donor and the oxidized acceptor takes place.
			*Enough excess free energy is generated to create the emissive state of anthracene, thus light is emitted.

	==The First ~~“Practical” Organic Light Emitting Diodes~~==		In these early devices, the rate of transport of the positive cation radical (or hole state) and the transport of the electron rich state were not equal, causing the recombination to occur near one of the contact electrodes. This phenomenon is now known to inhibit device effiency.


			==The First Practical OLEDs==
	[[Image:OLED4_heterojunction.jpg\|thumb\|400px]]		[[Image:OLED4_heterojunction.jpg\|thumb\|400px]]
	The first practical OLEDs ~~was~~ built in the late 1980’s by Ching Tang and Andy Van Slyke at Kodak. This was a revolution for the technology.		The first practical OLEDs were built in the late 1980’s by Ching Tang and Andy Van Slyke at Kodak. This was a revolution for the technology.

	C.W. Tang and coworkers at Kodak saw an opportunity to create the first organic light emitting diodes by using spin casting and sublimation deposition of the organic components of the device, with patterned electrodes top and bottom. Each organic layer was ca. 50 nm thick, the Mg:Ag top cathode was of comparable thickness. Transparent conducting oxide (TCO) thin films on glass served as the anode and provided for light to be emitted in a useable fashion for displays. The keys to successful development of these first devices was control of organic film deposition to create a pin-hole free film (high RP) which was thin enough to yield a lower series resistance than the first anthracene devices, providing for light emission with drive voltages under 50 volts.

	~~They started with a glass or plastic substrate with a transparent conductor such as indium tin oxide which can be highly doped~~ and ~~be highly conductive yet maintain transparency in~~ the ~~visible wavelength region.~~		C.W. Tang and coworkers at Kodak used spin casting and sublimation deposition of the organic components of the device, with patterned electrodes on the top and bottom. This was an important technological advance over slicing single-crystal anthracene as thin as possible with a razor knife. Vapor depositing molecules in a vacuum system on top of a transparent conductor enabled the layers to be much thinner, and have almost none of the pinholes that cause shorts. Transparent conducting oxide (TCO) thin films on glass served as the anode and allowed light to be emitted in a usable fashion for displays. The keys to successful development of these first devices was control of organic film deposition to create a pin-hole free film (with high RP) which was thin enough to yield a lower series resistance than the first anthracene devices, providing for light emission with drive voltages under 50 volts. The hole transparent layer was a spin coated polymer. This produced about 15 candelas per square meter, which is a dim but visible light. (A typical CRT computer screen operates with 100-200 candelas per square meter.)
	~~They deposited a hole transport layer typically some tri arylamine or in~~ the ~~early versions a polymer called poly vinyl carbazol; something that is easily oxidized at this transparent conductor.~~

	~~Next we add an electron transport layer~~ and ~~the total thickness has been reduced down to 100 nm~~. This was a technological advance ~~because you were no longer having to slice~~ single crystal anthracene ~~really~~ thin with a razor knife ~~instead you are vapor~~ depositing molecules in a vacuum system on top of ~~this~~ transparent conductor. ~~This also solved another problem~~. ~~When you deposit two successive layers there are fewer~~ pin ~~holes that create~~ a ~~dead short circuit between~~ the ~~anode and cathode~~.

	~~Finally~~ the ~~top electrode is something like aluminum, magnesium, silver alloy~~ or ~~even an electropositive metal~~ such as ~~calcium~~. ~~The~~ hole ~~transparent~~ layer ~~was a spin coated polymer~~. ~~This produced about 15 candelas per square meter~~. A ~~typical CRT computer screen operates with 100-200 candelas per square meter. So this was~~ a ~~dim but visible light. Aluminum tris quinalate was used~~ as ~~both the electron transport and emissive layer~~.		==Anatomy of Early OLEDs==
			*The '''base''' of the device was a glass or plastic substrate.
			*A '''transparent conductor''' such as indium tin oxide (ITO).
			*A 50 nm '''hole transport layer''' (HTL) of an easily oxidized material such as triarylamine or poly vinyl carbazol.
			*A 50 nm '''electron transport layer''' (ETL) of aluminum tris quinalate.
			*A '''cathode''' made from a metal such as aluminum, magnesium-silver alloy or even calcium.

	See Tang C.W. <ref>Tang and S.A. VanSlyke Appl. Phys. Lett. 51, 913(1987)</ref>		See Tang C.W. <ref>Tang and S.A. VanSlyke Appl. Phys. Lett. 51, 913(1987)</ref>
Line 42:		Line 49:

	*Vacuum deposition enabled thin electron transport layer		*Vacuum deposition enabled thin electron transport layer
	*Hole transport layer was spin-coated polymer: 10 – 20 V, 15cd/m2 brightness		*Hole transport layer was spin-coated polymer: 10 – 20 V, 15cd/m<sup>2</sup> brightness
	*All vacuum device: 10 – 20 V, 100 cd/m2 using ~~Alq3~~ emission layer		*All vacuum device: 10 – 20 V, 100 cd/m<sup>2</sup> using Alq<sub>3</sub> emission layer

	== References ==		== References ==

Smhunter: The first OLEDs moved to The First OLEDs

2009-06-25T20:36:54Z

The first OLEDs moved to The First OLEDs

← Older revision	Revision as of 13:36, 25 June 2009
(No difference)

Cmditradmin: Undo revision 2809 by Cmditradmin (Talk)

2009-06-23T15:22:55Z

Undo revision 2809 by Cmditradmin (Talk)

@@ Line 1: / Line 1: @@
-[[Main_Page#Organic_Light_Emitting_Diodes_-_OLED|Return to OLED Menu]] | [[Organic/Organic Heterojunctions in OLEDs|Next Topic]]
+<table id="toc" style="width: 100%">
 The first OLEDs were green as seen in this early example from the University of Arizona. The image on the right is so bright that is appears white.
@@ Line 43: / Line 49: @@
 <references/>
 [[category:organic LED]]

Cmditradmin: Reverted edits by Cmditradmin (Talk); changed back to last version by 128.95.39.42

2009-06-23T15:21:32Z

Reverted edits by Cmditradmin (Talk); changed back to last version by 128.95.39.42

@@ Line 1: / Line 1: @@
-<table id="toc" style="width: 100%">
+[[Main_Page#Organic_Light_Emitting_Diodes_-_OLED|Return to OLED Menu]] | [[Organic/Organic Heterojunctions in OLEDs|Next Topic]]
 The first OLEDs were green as seen in this early example from the University of Arizona. The image on the right is so bright that is appears white.
@@ Line 49: / Line 43: @@
 <references/>
 [[category:organic LED]]

Cmditradmin at 15:20, 23 June 2009

2009-06-23T15:20:52Z

← Older revision		Revision as of 08:20, 23 June 2009
Line 6:		Line 6:
	</tr>		</tr>
	</table>		</table>


	~~[[Main_Page#Organic_Light_Emitting_Diodes_-_OLED\|Return to OLED Menu]] \| [[Organic/Organic Heterojunctions in OLEDs\|Next Topic]]~~

	The first OLEDs were green as seen in this early example from the University of Arizona. The image on the right is so bright that is appears white.		The first OLEDs were green as seen in this early example from the University of Arizona. The image on the right is so bright that is appears white.

Cmditradmin at 22:47, 1 June 2009

2009-06-01T22:47:59Z

← Older revision		Revision as of 15:47, 1 June 2009
Line 52:		Line 52:
	<references/>		<references/>
	[[category:organic LED]]		[[category:organic LED]]

			<table id="toc" style="width: 100%">
			<tr>
			<td style="text-align: left; width: 33%">[[What is a Light Emitting Diode?\|Previous Topic]]</td>
			<td style="text-align: center; width: 33%">[[Main_Page#Organic_Light_Emitting_Diodes\|Return to OLED Menu]]</td>
			<td style="text-align: right; width: 33%">[[Organic/Organic Heterojunctions in OLEDs\|Next Topic]]</td>
			</tr>
			</table>

Cmditradmin at 22:42, 1 June 2009

2009-06-01T22:42:02Z

← Older revision		Revision as of 15:42, 1 June 2009
Line 1:		Line 1:
			<table id="toc" style="width: 100%">
			<tr>
			<td style="text-align: left; width: 33%">[[What is a Light Emitting Diode?\|Previous Topic]]</td>
			<td style="text-align: center; width: 33%">[[Main_Page#Organic_Light_Emitting_Diodes\|Return to OLED Menu]]</td>
			<td style="text-align: right; width: 33%">[[Organic/Organic Heterojunctions in OLEDs\|Next Topic]]</td>
			</tr>
			</table>


	[[Main_Page#Organic_Light_Emitting_Diodes_-_OLED\|Return to OLED Menu]] \| [[Organic/Organic Heterojunctions in OLEDs\|Next Topic]]		[[Main_Page#Organic_Light_Emitting_Diodes_-_OLED\|Return to OLED Menu]] \| [[Organic/Organic Heterojunctions in OLEDs\|Next Topic]]

128.95.39.42: /* The First “Practical” Organic Light Emitting Diodes */

2009-05-04T23:19:56Z

The First “Practical” Organic Light Emitting Diodes

← Older revision		Revision as of 16:19, 4 May 2009
Line 31:		Line 31:
	Finally the top electrode is something like aluminum, magnesium, silver alloy or even an electropositive metal such as calcium. The hole transparent layer was a spin coated polymer. This produced about 15 candelas per square meter. A typical CRT computer screen operates with 100-200 candelas per square meter. So this was a dim but visible light. Aluminum tris quinalate was used as both the electron transport and emissive layer.		Finally the top electrode is something like aluminum, magnesium, silver alloy or even an electropositive metal such as calcium. The hole transparent layer was a spin coated polymer. This produced about 15 candelas per square meter. A typical CRT computer screen operates with 100-200 candelas per square meter. So this was a dim but visible light. Aluminum tris quinalate was used as both the electron transport and emissive layer.

	See C.W. Tang and S.A. VanSlyke Appl. Phys. Lett. 51, 913(1987)		See Tang C.W. <ref>Tang and S.A. VanSlyke Appl. Phys. Lett. 51, 913(1987)</ref>
	C.W. Tang, U.S. Patent # 4,356,429 (1980)		<ref>C.W. Tang, U.S. Patent # 4,356,429 (1980)</ref>