Introduction to Organic , Fall 2005, Dr. Dietmar Knipp

Introduction to Organic Electronics (Nanomolecular Science Seminar I) Information: (Course Number 420411 ) Fall 2005 Information: http://www.faculty.iu- Introduction http://www.faculty.iu- bremen.de/course/c30 bremen.de/course/c42 Instructor: Dr. Dietmar Knipp 0331a/ 0411/

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Source h e h eee h h h e h ee h he h h Drain Ref.: Apple

Gate

Dielectric Neutral substrate VG

10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 101 Critical dimension (m)

Introduction 1 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Organic electronics and its application areas

Sensors

Displays

Rechargeable Organic lasers battery Organic Electronics Anti-static Organic TFTs

Molecular Solar cells electronics

Introduction XCLi-09/02 2 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

A little bit of history in organic electronics 1950’s: Work on crystalline organics materials starts. (At that time organic crystal where considered to be an alternative to silicon) 1970’s: Organic photoconductors (xerography) 1980’s: Organic non-linear optical materials 1987: group published the first efficient organic light emitting device (OLED) Results on the first organic where published. 1990’s: Friend group (Cambridge University) published the first results on light emitting . 2000: Noble price in chemistry for the “discovering and development of conductive ” (Heeger, MacDiarmid and Shirakawa) 2000’s: Organic solar cells with efficiencies of >5% were realized.

Introduction 3 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Introduction 4 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Advantages and Disadvantages of organic electronic materials

Attractive due to: • Technology is compatible with Large area processes (low cost) • Low temperature processing (low cost) • and polymers can be tailored for specific electronic or optical properties • Compatible with inorganic

Existing problems: • Low carrier mobility • Electronic and optical stability of the materials • Processing is incompatible with classical processing in industry.

Introduction 5 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Applications for Organic electronics: Displays Demand on Displays: • Low cost • Large area • Low power consumption • Low weight • Flexible displays

Active pixel addressing of the display is needed •Organic TFTs are of interest for pixel electronic

Ref.: Samsung

Introduction 6 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Comparison of different display technologies The ideal display!

Introduction 7 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Liquid Crystal Display

The plane of the polarized light is rotated by the liquid crystals when a voltage is applied.

Introduction 8 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Polymer-Dispersed Liquid Crystals Displays

Preparation of Polymer-dispersed liquid crystals: Encapsulation (emulsification) and phase separation; the latter process has become the primary method of manufacture. Each method produces PDLCs with different properties and characteristics. Among the factors influencing the properties of the PDLC material are the size and morphology (shape) of the droplets, the types of polymer and liquid crystal used, and cooling and heating rates in production.

E

Introduction 9 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Application of OLEDS and PLEDS

OLEDS: organic light emitting (small molecules) PLEDS: polymer light emitting diode (polymers)

Introduction 10 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Comparison of light emitting diode technologies

Ref.: J. M. Shaw and P. F. Seidler, IBM

Introduction 11 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Color Vision and perception

hc E = E − E = hf = 2 1 λ

Photon energy

The interaction of light and matter in the form of absorption and emission requires a transition from one discrete energy level to another energy level. The frequency and the wavelength of the emitted or absorbed photon is related to the difference in energy E, between the two energetic states, where h is the Planck constant h=6.626 x 10-34J, f is the frequency and λ is wavelength of the absorbed or emitted light.

Introduction 12 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Color Vision and Color perception

• A color is defined by the capabilities of the human eye. The human color perception has to be considered when designing a display. •The human color perception is non linear (in the physical sense).

Ref.: V.Bulović, Organic Opto-Electronics, MIT

Introduction 13 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Color Vision and Color perception λ λ 780nm λ λ X = k ⋅ S()⋅r ()⋅ x d () S ∫λ S 380nm λ Y S 780nm() ()λ () Y = k ⋅ S ⋅r ⋅ y λd S ∫ S 380nm ()λ () () YS 780nm λ λ X Z = k ⋅ S ⋅r ⋅ z dλ S S ∫ S Z ZS 380nm X S(λ): spectrum of the light source, Representation of in the R(λ): reflection of an object, XYZ color space. x(λ),y(λ),z(λ): color matching functions, representing the sensitivity of the human eye

Each color can be described as a vector!

Introduction 14 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Color Vision and Color perception

Dimensions of the color space: hue, chroma, value 200 Hue levels 20 Saturation levels 500 Chroma levels

Introduction Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Status of Active Matrix Organic Light Emitting Device (AMOLED) Displays

NTSC Green Mapping of the RGB (0.21,0.71) color space and the Kodak Green color space of the (0.30,0.63) display. (Gamut

Sony Green mapping) (0.26,0.65) Kodak Red (0.65,0.34)

NTSC Red (0.67,0.33) Kodak Blue (0.15,0.17)

Sony Red (0.66,0.34) NTSC Blue (0.14,0.08) Sony Blue color coordinate (0.16,0.06)

Introduction 16 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Organic light emitting diodes (small devices) Electro luminescence requires several steps, including the injection of charges ( and holes) in the device, the transport of the charges in the films, confinement of charges, and radiative recombination of charge carriers inside an organic with an energy gap suitable for yielding visible light output. : Separately optimize the individual steps by using a multilayer light-emitting devices (LEDs).

The simplest possible organic LED consists of hetero-interface between a hole-conducting material (TPD) and an

conducting material (Alq3). The light emission takes place at the interface between Alq and TPD. 3 Ref.: V.Bulović, Organic Opto-Electronics, MIT

Introduction 17 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Organic light emitting diodes (small molecule devices)

Optimized device strucutre:

Copper phthalocyanine (CuPc) as the buffer and hole-injection layer,

NPB as the hole transport layer

Alq3 as the electron transport and emitting layer.

Schematic energy-level diagram and chemical structures of the organic materials used for the OLEDs. Ref.: Riess group, IBM Zuerich

Introduction 18 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Organic light emitting diodes (small molecule devices)

Electroluminescence in doped organic films

Introduction 19 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

An exciton is a bound electron hole pair ( Coulomb correlated electron/hole pair). When constant of the material is very small, the Coulomb interaction between electron and hole become very strong and the excitons tend to be much smaller, of the same order as the unit cell, so the electron and hole sit on the same molecule. This is a Frenkel exciton, named after J. Frenkel. The probability of the hole disappearing (the electron occupying the hole) is limited by the difficulty of losing the excess energy, and as a result excitons can have a relatively long lifetime.

Introduction 20 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Polymer light emitting diodes (polymer devices)

Ref.: H. Antonidias, Osram

Introduction 21 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Polymer light emitting diodes (polymer devices)

Device structure:

PEDOT:PSS as the hole transport layer

PPV derivate as the electron transport and emitting layer.

Ref.: R. Friend, Cambridge

Introduction 22 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Polymer light emitting diodes (polymer devices)

Ref.: H. Antonidias, Osram

Introduction 23 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Passive versus Active Matrix Display Addressing

LT p-Si TFT substrate

Gate Advantages of passive OEL matrix displays:

Common line G Matrixed Pixels B R Line by Line scanning Advantages of active Discrete drivers TFT matrix displays: Low Cost Drain Each pixel has pixel switch Selected pixel stays on until next refresh cycle Disadvantages Integrated drivers High brightness; High current Disadvantages: Pixel cross-talk High cost High quality TFTs required Low area fill factor

Introduction 24 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Overview of transistor technologies

Carrier Mobility CMOS technology CPU, memory products 103 Low Cost ICs, drivers 2 crystalline 10 LCD displays silicon 101 poly silicon Displays,smart cards 100 Amorphous rf information tags ? -1 silicon 10 Small E paper, E ink molecules 10-2 Hybrid materials polymers cm2/Vs

Introduction Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Overview of thin film transistor technologies Materials, Devices and Applications

Performance Carrier CMOS Mobility 50.000-500.000 vs. 103 $/m2 Cost AMLCD 102 crystalline 5.000-10.000 silicon $/m2 101 poly Solar cells silicon 100 100-400 $/m2 Amorphous -1 silicon 10 newsprint Small 0.1 $/m2 molecules 10-2 Hybrid materials polymers cm2/Vs

Introduction Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Organic thin film Performance

Silicon wafers CPU 102 poly silicon Low cost ICs ] -1

s 0 -1 10 a-Si:H Displays, V

2 smart cards cm [ 10-2 E-paper, rf tags Organic/inorganic hybrid Mobilitiy -4 10 Thiophene oligomers 10-6 1986 1988 1990 1992 1994 1996 1998 2000 2002

Time [years]

Introduction Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Introduction 28 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Transfer characteristic of an pentacene TFT

6 • Transistors exhibit a VD=-20V 10-5 pronounced subthreshold A]

⋅√ 5 region. 3 VD=-1V • Variation of the onset of the 4 10-7 drain current from run to run. • The shift of the onset voltage 3 -9 is caused by unintentional 10 doping. 2 • Onset of the drain current is V V Drain current [A] TH Onset -11 typically positive. VD=-20V 10 Square root drain current [10 drain Square root 1 • Threshold voltage is typically negative. 0 10-13 -30 -25 -20 -15 -10 -5 0 5 10 15 gate voltage [V]

Introduction Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Summary

Organic semiconductors are of interest for a variety of applications like: Anti Static , photo conductors Most of the research in organic electronics is driven by the display industry. The goal is to develop low cost, low weight, low power consumption, large area and flexible displays. In order to enter the market organic and polymeric displays have to compete against liquid crystal displays. The performance of liquid crystal displays has be drastically improved and the cost has been drastically reduced for LCD displays. Reflective displays (for example based on Polymer-Dispersed Liquid Crystals or electronic ink) are in interesting alternative to LCD if it comes to very large areas or low power consumption. Organic and polymeric Light Emitting Displays are closest to applications in the field of organic electronics.

Introduction 30 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

Summary II

In polymer LEDs a PPV derivate is used as the electron transport and emitting layer. In organic LEDs Alq3 is used as the electron transport and emitting layer. The performance of the organic and polymeric LEDs in terms of optical output power is close to the optical output of inorganic LEDs. The optical spectrum of an LED has to be tailored towards the optical spectrum of the human eye, which is represented by a “Standard Observer (CIE Color standard)”. Organic transistor are an emerging and new field of research. Typical applications are: displays, smart cards and radio frequency information tags (RFID tags). Small molecule based transistors exhibit the highest performance of organic and polymeric transistors. The performance is comparable to the transistors (standard transistors in display industry). Most organic transistors are hole conducting devices.

Introduction 31 Introduction to Organic Electronics, Fall 2005, Dr. Dietmar Knipp

References

Pope and Swenburg, Electronic Processes in organic crystals and polymers, 2 nd Ed., Oxford Organic molecular crystals, E.A. Sininsh EA and V. Capek.

http://researchweb.watson.ibm.com/journal/rd45-1.html (Special Issue of IBM journal on organic electronics)

http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6- 973Organic-OptoelectronicsSpring2003/CourseHome/ (Organic optoelectronic lecture MIT)

http://hackman.mit.edu/6976/overview.html (Seminar on Flat Panel Displays)

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