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Lecture VII. Applications Electrostatic Imaging and Xerographic materials Organic Light-emitting diodes ) OLEDS and Active Matrix OLEDS (AMOLEDS) for Display and Lighting
Solar Cells Field-effect transistors Batteries Photo-detectors Luminescence for Land-mine Sniffing Lasers Switches E-Ink
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Inorganic Vs. Organic Material Properties
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Limitations At Early Stage Organic materials have often proved to be
unstable. Making reliable electrical contacts to organic
thin films is difficult. When exposed to air, water, or ultraviolet light,
their electronic properties can degrade rapidly. The low carrier mobilities characteristic of
organic materials obviates their use in high-frequency (greater than 10 MHz) applications.
These shortcomings are compounded by the difficulty of both purifying and doping the materials.
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Electrostatic Imaging
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Chester Carlson
History of Xerography
The first xerographic image 10-22-1938, Astoria, NY.
slide #2
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History of Xerography 1906: Haloid Corp.
founded
1900 1910 1920 1930 1940 1950
1938: 1st xerographic image
1949: 1st copier - Model A
1950 1960 1970 1980 1990 2000
1959: Xerox 914, 1st plain paper automatic copier - 7 1/2 copies/min
1964: LDX (long distance xerography) - 1st fax
1973: Xerox 6500 - 1st color copier
1977: Xerox 9700 - 1st laser printer
1988: Xerox 5090 - 135 copies/min
1997: Docutech digital printer (180 copies/min)
1997: Docucolor 70 - 70 color prints/min
Today Xerox has 91,400 employees (50,200 in US) and $18.2 billion in revenues
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What is Xerography?
Creation of a visible image using surface charge pattern on a
“photoconductor”.
Visible images consist of fine charged particles called
toners”.
slide #5
Xero-graphy = Dry-Writing (Greek)
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Xerographic Prints are composed of toners
5-10 microns COLOR Digital prints are halftones
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Inside a xerographic printer
Photoreceptor
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Charging Subsystem (Corotron):
Electrons
Positive Ions
Free ions are attracted to wire; Free electrons are repelled. Counter-charges build up on grounded surfaces.
Rapidly moving electrons and ions collide with air molecules, ionizing them and creating a corona.
Electrons continue to follow Electric Field lines to Photoreceptor until uniform charge builds up
HV Power Supply (-)
HV Power Supply (-)
HV Power Supply (-)
slide #10
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Transfer to paper
• Electric field moves particles from photoreceptor to paper or transparency
• Detachment field must overcome toner adhesion to photoreceptor
Apply E Field
Paper
Paper
Photoreceptor
Photoreceptor
slide #18
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Additives control adhesion
Changing type type of additive modifies adhesion
Atomic Force Microscopy results
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Electrical Field Detachment of Fine Particles
E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc., 10th Int. Cong. on Non-Impact Printing, 142-146
slide #19
Measure Many Particle Adhesion
Donor Receiver V
transparent conductive electrodes
V V
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Fusing Subsystem
• Permanently affix the image to the final substrate – paper of various roughness
– transparency (plastic)
• Apply heat and/or pressure
Hot Roll Fuser:
Pressure Roll
Heat Roll
Paper
slide #21
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Cleaning and Erase Subsystems
• Removes unwanted residual toner and charge from photoreceptor before next imaging cycle – Physical agitation removes toner (blade or brush)
– Light neutralizes charge by making entire photoreceptor conductive
slide #22
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Physics of the Photo-discharge of the Corona Charge
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Future of Xerography
• Color: Wide gamut, offset quality
• High Image Quality: High resolution, continuous tone
• High Speed: Full color at 200 pages per min, and higher
• Higher reliability: No paper jams
• Lower cost: Xerography vs. inkjet
slide #25
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Reference
The physics of
XEROGRAPHY:
Howard Mizes Xerox Corporation
Wilson Center for Research & Technology Webster, New York
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Organic Light-emitting diodes (OLEDS) and Active Matrix OLEDS (AMOLEDS) for Display and Lighting
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Inorganic Vs. Organic LEDs
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Why Organic LED?
Vibrant colors
High contrast
Wide viewing angles from all directions
Low power consumption
Low operating voltages
Wide operating temperature range
A thin and lightweight form factor
Cost-effective manufacturability , etc
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Organic LED Energy Diagram
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A full color, 13-inch diagonal small-molecular-weight OLED display with 2mm thickness.
Flexible internet display screen
S. R. Forrest in Nature428, 911 (2004)
Applications — Full color OLED display
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Samsung large OLED displays
KODAK OLED displays
http://www.kodak.com/eknec/PageQuerier.jhtml?pq-path=1473/1481/1491&pq-locale=en_US
Applications — Full color OLED display
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OLED Device Physics and Chemistry
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EIL, ETL: n-type materials
Alq3, PBD
HIL, HTL: p-type materials
NPB, TPD
EML:
Fluorescent dye
DCM2
Phosphorescent dye
PtOEP, Ir(ppy)3
Small molecular OLEDs — Materials
Alq3 PBD
NPB TPB
DCM2
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Cathode
Organic Layer
Anode
Substrate
Single layer device
Small molecular OLEDs — Structure
Cathode
Hole transport layer
Anode
Substrate
Electron transport layer
P-n junction device
Electron transport layer
Hole transport layer
Anode
Substrate
Emissive layer
Electron Injection layer
Cathode
Hole Injection layer
Multiple layers device
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Electron transport layer
Hole transport layer
Anode
Substrate
Emissive layer
Electron Injection layer
Cathode
Hole Injection layer
HOMO — Ev
LUMO — Ec
Transparent substrate
ITO HIL HTL EML ETL EIL Cathode
h+
e-
h+ h+
e- e- Light
Electrons injected from cathode
Holes injected from anode
Transport and radiative recombination of electron hole pairs at emissive layer
Small molecular OLEDs — Device operation principle
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Anode:
Indium-tin-oxide (ITO): 4.5-5.1 eV
Au: 5.1 eV
Pt: 5.7 eV
Cathode:
Ca: 2.9 eV
Mg: 3.7 eV
Al: 4.3 eV
Ag: 4.3 eV
Mg : Al alloys
Ca : Al Alloys
Small molecular OLEDs — Electrodes
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Substrate
Small molecules
Vacuum
Heater
Cathode
Hole transport layer
Anode
Substrate
Electron transport layer
Small molecular OLEDs — Device preparation
Growth:
~10-5-10-7 Torr
Room temperature
~20 Å- 2000 Å
Thermal vacuum evaporation
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Cathode
Emissive polymer
Anode
Substrate
Cathode
Conducting polymer
Anode
Substrate
Emissive polymer
Polymer OLEDs — Structure and Operation
http://www.ewh.ieee.org/soc/cpmt/presentations/cpmt0401a.pdf
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Conducting polymers:
PANI:PSS
PDOT:PSS
Emissive polymers:
R-PPV
PFO
Polymer OLEDs — Materials
PANI
PDOT PSS
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Polymer OLEDs — Fabrication
Spin coating
Ink jet printing
Screen printing
Web coating
Substrate
Ink jet printing
Substrate
Polymer film
Spin coating
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Organic Solar Cells
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Self-Organized Discotic Liquid Crystals for High-Efficiency Organic
Photovoltaics
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Organic Field Effect transistors
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Organic Thin Film Transistors (OTFTs)
Organic material Organic material
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An Example of an I-V of OTFTs
Lg = 20 µm W = 220 µm 400 nm SiO2
50 nm organic
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Battery Applications
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Li LiI
PVP-I CT complex
Li+
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Luminescence for Mine-Sniffing
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Organic Semiconducting Lasers
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Organic Switches