Introduction to Organic Electronics, 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/ Source: Apple VD 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 OLEDs Rechargeable Organic lasers battery Organic Electronics Photodetector Anti-static coating 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: Kodak group published the first efficient organic light emitting device (OLED) Results on the first organic transistor where published. 1990’s: Friend group (Cambridge University) published the first results on polymer light emitting diodes. 2000: Noble price in chemistry for the “discovering and development of conductive polymers” (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) • Molecules and polymers can be tailored for specific electronic or optical properties • Compatible with inorganic semiconductors Existing problems: • Low carrier mobility • Electronic and optical stability of the materials • Processing is incompatible with classical processing in semiconductor 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 diode (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 Color 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 780nm X = k ⋅ S λ ⋅r λ ⋅ x λ dλ S ∫ () ()S () 380nm Y S 780nm Y = k ⋅ S λ ⋅r λ ⋅ y λ dλ S ∫ () ()S () 380nm YS 780nm X Z = k ⋅ S λ ⋅r λ ⋅ z λ dλ S S ∫ () ()S () Z ZS 380nm X S(λ): spectrum of the light source, Representation of colors 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 molecule devices) Electro luminescence requires several steps, including the injection of charges (electrons 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 layer with an energy gap suitable for yielding visible light output. Solution: 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 electron 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 dielectric 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 thin film 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