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.

Electrostatic Imaging

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 COLOR Digital 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

V V

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

Overview

Inorganic LED’s

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

Polymeric OLEDS

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

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

Example

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

Battery Applications

Li LiI

PVP-I CT complex

Li+

Photo-detectors

Luminescence for Mine-Sniffing

Organic Semiconducting Lasers

Organic Switches

E-ink