Inkohärente Lichtquellen. Christian Wenning - PDF

Christian Wenning Content I. i. Origin of PLEDs ii. Operational Principle II. III. Luminescent Polymers i. Luminescent Polymers ii. White PLED Device Fabrication Processes i. Spin-Coating ii. Ink-Jet Printing

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Christian Wenning Content I. i. Origin of PLEDs ii. Operational Principle II. III. Luminescent Polymers i. Luminescent Polymers ii. White PLED Device Fabrication Processes i. Spin-Coating ii. Ink-Jet Printing IV. Conclusion V. Outlook VI. References Christian Wenning 2 Subcategory of OLEDs OLEDs are based upon electroluminescence Ability to convert electric energy into photons The first efficient OLED was build by Tang and Van Syke in 1987 Three years later, in 1990 the first OLED was invented that used an polymeric emitter layer The origin of Christian Wenning 3 An emitting layer is placed between a metal cathode and a transparent anode e - are transferred into LUMO by cathode h + are pushed into HOMO by anode Recombination under radiation of photons Poor efficiency and lifetime dv Metal Cathode Emitting Polymer Transparent Anode Photons Christian Wenning 4 Charge transport is a key factor in PLED performance Significantly higher hole conductivity than electron conductivity in conjugated polymers Formation of excitons close the the cathode Excitons close to the cathode tend to relaxate nonradiatively via energy transfer Christian Wenning 5 Introduction of hole and electron transfer layers Shifting the recombination zone away from cathode Less energy transfer to the cathode Better efficiency Christian Wenning 6 Nearly any semiconducting polymer with a fitting energy distance between HOMO and LUMO Most popular is PPV and its derivatives Conjugated π-electrons By combination of two or more phosphors, the color can be controlled Resulting in multilayered or in single layer setups Christian Wenning 7 Idea: A copolymer consisting of blue, red and green phosphors Very good CRI(~90) Poor power efficiency (max. 16 lm/w) Stability problems Christian Wenning 8 Christian Wenning 9 Christian Wenning 10 Christian Wenning 11 Advantages: Bright, homogeneously shining LEDs Great variability in emission wavelength Great color rendering index Nearly no limit in screen size No dependency in viewing angle By using polymer substrates flexible displays can be build up No backlight is needed, in contrast to LCD Ink-Jet fabrication is a promising technique (30 panels/h) Christian Wenning 12 Disadvantages: Display pixels have to be encapsulated from air to inhibit degradation by Oxygen Poor lifetime in general is the biggest issue Additionally different color phosphors have different durability Color shift (blue is degraded faster) Not suitable for dimmable white lighting (color shift while voltage is decreased) Christian Wenning 13 Till nowadays, no commercial breakthrough BUT: When durability is improved, PLED displays will be a strong competitor to LCD Application, mainly in multimedia devices and large area lighting Christian Wenning 14 1. White polymeric light-emitting diodes with high color rendering index - Xiaodi Niu, Liang Ma, Bing Yao, Junqiao Ding, Guoli Tu, Zhiyuan Xie, and Lixiang Wang in Appl. Phys. Lett. 89, (2006) 2. Device Physics of White Polymer Light-Emitting Diodes - Herman T. Nicolai, André Hof, and Paul W. M. Blom in Advanced Functional Materials, Kunststoffchemie für Ingenieure Wolfgang Kaiser 4. Organische Leuchtdioden aus Polymeren und niedermolekularen Verbindungen für großflächige OLED-Anzeigen - Anis Kammoun 5. Achieving High-Efficiency Polymer White-Light-Emitting Devices - J. Huang, G. Li, E. Wu, Q. Xu, Y. Yang in Advanced Materials Volume 18, Issue 1, pages , January, 2006 Christian Wenning 15
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