Published on April 15, 2014
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
Inorganic Vs. Organic Material Properties
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.
Chester Carlson History of Xerography The first xerographic image 10-22-1938, Astoria, NY. slide #2
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
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)
Xerographic Prints are composed of toners 5-10 microns COLORDigital prints are halftones
Inside a xerographic printer Photoreceptor
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
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
Additives control adhesion Changing type type of additive modifies adhesion Atomic Force Microscopy results
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 VV
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
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
Physics of the Photo-discharge of the Corona Charge
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
Reference The physics of XEROGRAPHY: Howard Mizes Xerox Corporation Wilson Center for Research & Technology Webster, New York
Organic Light-emitting diodes (OLEDS) and Active Matrix OLEDS (AMOLEDS) for Display and Lighting
Inorganic Vs. Organic LEDs
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
Organic LED Energy Diagram
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
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
OLED Device Physics and Chemistry
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
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
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
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
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
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.pd
Conducting polymers: PANI:PSS PDOT:PSS Emissive polymers: R-PPV PFO Polymer OLEDs — Materials PANI PDOT PSS
Polymer OLEDs — Fabrication Spin coating Ink jet printing Screen printing Web coating Substrate Ink jet printing Substrate Polymer film Spin coating
Organic Solar Cells
Self-Organized Discotic Liquid Crystals for High-Efficiency Organic Photovoltaics
Organic Field Effect transistors
Organic Thin Film Transistors (OTFTs) Organic material Organic material
An Example of an I-V of OTFTs Lg = 20 µm W = 220 µm 400 nm SiO2 50 nm organic
Li LiI PVP-I CT complex Li+
Luminescence for Mine-Sniffing
Organic Semiconducting Lasers
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