Materials Chemistry for Organic Electronics and Photonics

Prof. Dong-Yu Kim

Photonics Polymer LaboratoryDept. of Materials Science and Engineering

Gwangju Institute of Science and Technology

kimdy@gist.ac.kr, MSE 701

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Syllabus : Organic Materials for Organic Electronics and Photonics

Weekly Course Schedule

Calendar Desciption *Remarks

1st week Introduction of organic electronics and photonics Quiz 50%

2nd week Fundamentals of organic molecules

3rd week Organic semiconductors

4th week Conjugated polymers

5th week Charge transport in organic semiconductors

6th week Organic Light-Emitting Diodes : Introduction

7th week Organic Light-Emitting Diodes : Hole and electron transporting materials

8th week Organic Light-Emitting Diodes : Light emitting materials

9th week Mid-term Exam Mid-termExam 20%

10th week Organic photovoltaics : Introduction

11th week Organic photovoltaics : Donor and acceptor materials

12th week Organic photovoltaics : Interface and electrode materials

13th week Organic transistors : Introduction

14th week Organic transistors : P-channeland N-channel materials

15th week Organic transistors : Gate dielectrics and electrode materials

16th week Final Exam Final Exam 30%

Introduction of Organic Electronics and Photonics

Prof. Dong-Yu Kim

Photonics Polymer LaboratoryDept. of Materials Science and Engineering

Gwangju Institute of Science and Technology

kimdy@gist.ac.kr, MSE 701

John BardeenWalter Brattain

William Shockley(BELL Labs)

1947 – the 1st transistor(Ge point contact) 1948 – the 1st junction

transistor (Ge)

IBM Archive©

The Silicon Age (1947 onwards)

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• The basic ingredient for all high technology devices and products

• The advantages– fast– relatively dependable– versatile– technology is in place – they work!

• The disadvantages– costly– very difficult to process (UHV equipment and photolithography)– some compound SCs have horrible environmental profile (e.g. GaAs)– limited stock of some– delicate & no mechanical flexibility

Inorganic Semiconductors

5

• The 2000 Nobel Prize for Chemistry was awarded for the discovery of metal-like electrical conductivity in iodine-doped polyacetylene

• Prior to this discovery (Shirakawa, Heeger, MacDairmid), it was thought that organic polymers could not conduct electricity in the solid state

• The “Soft Age” was born

A revolution in functional materials for high technology ?

The Soft Age (1977 to …. ?)

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7

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Organic Materials

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• Explosion in “functional” soft-solids research (small molecule and large molecule organic electronics)

• Wild predictions of high tech and low tech applications – soft-solid related material benefits plus electrical (semiconducting) functionality

• IBM, Lucent, Philips, Seiko Epson, HP all have major organic electronics programs

A thin film conductingpolymer transistor and“soft-circuitry” – arraysof these transistors on

a flexible polymer sheetLight emitting polymerdisplays – thin, flexiblescreens with 180˚ view

plastic memorysmart textilesbiosensors

electronic inkorganic solar cells

Plastic Logic©

1,888 Transistors!

The Soft Age (1977 to …. ?)

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12

Printed Electronics Markets

Printed electronics will be much bigger than the silicon chip market

Market forecast by component type for 2008 to 2018 in US $ billions, for printed and potentially printed electronics including organic, inorganic and composites

Source IDTechEx

Roadmap, Nikkei Electronics, March, 2007

Printed Electronics Technology Roadmap

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Development of Novel Conjugated Polymers

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Organic Polymer-Based LEDs from Cambridge Group (1990)“PPV derived electroluminescent

device that emits yellow-green light "

Richard FriendCavendish laboratory

Andrew Holmes Cambridge University, UK

Nature1990, 347, 539-541

Organic Polymer-Based LEDs

Poly [(2-methoxy-5-(2'-ethyl hexyloxy)-1,4-phenylene) vinylene (2.2 eV)

Red shifted from PPV emission soluble because of long side groups; useful for flexible displays

MEH-PPV : Soluble PPVs from Santa Barbara (A. J. Heeger) Group (1991)

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A polymer needs to show fluorescence

and to conduct electricity

to be a light emitting polymer

Light Emitting Polymers Convert Electric power into

visible light

Light-Emitting Polymers

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OLED do not have a backlight unlike liquid crystal display (LCD).

OLED create light by the following process: A battery or power supply sends a voltage through the OLED. An electrical current flows from the cathode to the organic layer and anode. As explained earlier, the anode removes electrons and adds electron holes in the conductive layer. Between the organic layers is where electrons fill the holes and give off energy in the form of photon light.

Organic Light-Emitting Diodes (OLEDs)

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Organic Light-Emitting Diodes (OLEDs)

Flexible Display Research Trend

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Flexible Display Applications

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Electrochromic Display

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Electrophoretic Display

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E-Ink Flexible Display

Solar CellLight energy (photons) Electrical energy

-0.5 -0.4 -0.3 -0.2 -0.1 0.0-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Cur

rent

(mA

)

Voltage (V)•

•

VOC

ISC

Pmax

32

33

Radiant power at Earth’s surface~ 100000 TW

Electricity consumption ~2 TW~ 80% from fossil fuels & nuclear, ~0.05% from PVAt 10% power conversion efficiency, solar resource can meet demand with 0.02% of Earth surface areaPV is the only technology to convert solar power directly into electricity

The Solar Energy Resource

3.7 GW installed by end 2005

Present PV system costs:– 7 - 20 Euro/Wp off-grid applications.– 4 - 8 Euro/Wp grid-connected.– Module 2 – 4 Euro / Wp

Aim for:– 1 - 2 Euro/Wp for power generation– 4 - 10 Euro/Wp for smaller applications.

Cost of Si based system falling through economies of scaleTo accelerate cost reductions, need technological innovations

PV Market Growth

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Photovoltaic Efficiencies Compared

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Strategies to cost reduction

Use less photovoltaic material ?

Use cheaper photovoltaic materials and

fabrication process ?More work

per photon ?

Organic thin film materialsPrinting Technology

Molecular PV materials

Multijunction or “tandem” structuresExtracting more work

per photon

Concentration of sunlightLight trapping

Strategies to Cost Reduction

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C60 CP

Bulk Heterojunction OPVs

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Operation Principle of Fullerene Organic Photovoltaics

OPV benefits from the opportunities of renewable energies butoffers distinct competitive advantages

Pros & Cons of Photovoltaics

Organic Photovoltaics (OPVs)

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Organic Photovoltaics (OPVs) : Applications

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Source: Cristophe Brabec Konarka

Module Stack for Organic Photovoltaics (OPVs)

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Voltage

Cur

rent

den

sity

J

Silicon

Best h 24%

Organic solar cellBest h ~4-5%

400 500 600 700 800 900 1000 1100 1200 13000

1

Irrad

ianc

e /W

m-2nm

-1

W avelength / nm

Electronacceptor

Electrondonor

Maximum eVoc

Key Challenges for Organic Photovoltaics (OPVs)

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Organic Thin-Film Transistors (OTFTs)

• Organic transistors are transistors that use organic molecules rather than silicon for their active material. This active material can be composed of a wide variety of molecules.

• Advantages– compatibility with plastic substances– lower temperature manufacturing (60-120° C)– lower-cost deposition processes such as spin-

coating, printing, evaporation– less need to worry about dangling bonds

makes for simpler processing

• Disadvantages– lower mobility and switching speeds

compared to silicon wafers– usually do not operate under inversion mode

(more on this later)

P3HT

[ Organic FET ]

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Organic Thin-Film Transistors (OTFTs) Applications

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Organic Thin-Film Transistors (OTFTs) Applications

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RFID for Item Level Tagging

Organic Thin-Film Transistor (OTFT)Basic Element of Organic Integrated Circuit

Ring OscillatorInverter

P-Channel & N-Channel OTFTs

Printed RFID Tags

O O

SS

O O

O O

SS

O O+

O O

Sn

SO3-

n

HSO3

m

1. Conductor (Electrodes)

2. Semiconductor (Active Layers)

3. Insulator (Gate Dielectrics)

Materials for OTFTs

Colloidal ink of Au Nanoparticles (NP)

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Small molecules (SMs) SMs, polymers

Reproducibility of properties

Monocrystalline Polycrystalline Amorphous solids

Luminescent property

Environmentalstability

Mechanicalstability

Electrical properties (mobility)

moderate very high, low very high

low moderate high

moderate high, moderate high

polymers

very low low, moderate high

very good good, moderate moderate to poor

pBTTT

Organic Semiconductors for OTFTs

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μ = 0.6 cm2/Vs

μ = 0.1 cm2/Vs

μ = 0.007 cm2/Vs

μ = 0.01 cm2/Vs

μ = 1-5 cm2/Vs

μ = 15-20 cm2/Vs

μ = 0.1-1 cm2/Vs

• Significant progress in performance / reliability in recent years, but mobility still limited to 0.1 – 1 cm2/Vs.

n-channelp-channel

0.03 - 0.05 cm2V-1S-1

(1998, Vacuum Deposition)

~ 6 cm2V-1S-1

(in Vacuum)

0.01 - 0.05 cm2V-1S-1

Relatively low field-effect mobility and air stability compared to p-channel materials

Organic Semiconductors for OTFTs

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Printed transistor

Progress in OTFTs

Organic semiconductors come in 2 “flavors”

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Organic Memory : Advantages and Applications

• Large area fabrication with extremely low cost

• Light-weight and flexibility

• High capacity with bottom-up stacking

• Capable ubiquitous componentsthat are printed onto plastic, glass or metal foils

: Inexpensive data storage media

: Disposable, mobile, flexible and low-duty applications.

Ex.) RFID tag, smart card, e-paper, OLED driving circuit, etc.

□ Advantages

□ Applications

ITRS 2005 – Emerging Research Devices

Technology Performance Evaluation(Polymer Memory)

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Organic Memory: Research Approaches

OFET-Type Memory

[R.C.G. Naber, Nature Mater., 2005, 4, 243.]

- Ferroelectric polymer insulator- Polarizable gate dielectrics

Electrical Bistable Device

[Y. Yang, Appl. Phys. Lett. 2002, 80, 2997.]

AIDCN (2-amino-4, 5-imidazoledicarbonitrile)

- Electrical Biatability of Organic Semiconductor layer or MetalNano-particles, etc.

Hybrid Memory

[S. Möller, Nature, 2003, 426, 13.]

- In Combination of Inorganic andOrganic Materials

© www.wag.caltech.edu

© http://www.unibas.ch/phys-meso

Organic Materials to Nanotechnology : Scale without size

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Graphite

Chris Ewels (www.ewels.info)

Conductivity:

Electrical Resistivity (ohm.m)perpendicular to c-axisparallel to c-axisnatural

9.8x10-6

4.1x10-5

1.2x10-6

Single-layer graphene transistor

Organic Materials to Nanotechnology : Graphene

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Roll-up ofGraphite mesh

www.surf.nuqe.nagoya-u.ac.jp/.../ nanotubes.html

Organic Materials to Nanotechnology : Cabon Nanotube

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