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Handbook of Polymer Synthesis Second Edition Episode 14

Tham khảo tài liệu 'handbook of polymer synthesis second edition episode 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 14 Polymers for Organic Light Emitting Devices Diodes OLEDs O. Nuyken E. Bacher M. Rojahn V. Wiederhirn and R. Weberskirch Technische Universitat Munchen Garching Germany K. Meerholz Universitat Zu Koln Koln Germany I. INTRODUCTION Facing the 21st century the development of new techniques that are able to display data faster more detailed and in mobile applications is one of the prospering scientific fields. One approach for lightweight flexible power-efficient full-color displays are organic light emitting diodes OLEDs . Such devices with their low driving voltage bright color and high repetition rate e.g. for video-application are ideal for usage in miniature displays as well as in large area screen 1-3 . The basic principle of these devices are electroluminescent semiconducting organic materials packed between two electrodes. After charge injection from the electrodes into the organic layer and charge migration within this layer electrons and deficient electrons so called holes can recombine to form an excited singlet state. Light emission of the latter is then a result of relaxation processes 4-6 . To achieve high electroluminescence efficiencies the materials have to fulfill several specific requirements including low injection barriers at the interface between electrodes and organic material balanced electron- and hole-density and mobility and high luminescence efficiency. Furthermore the recombination zone should be located away from the metal cathode to prevent annihilation of the exited state. Since no material known to date is able to meet all these criteria modern OLEDs consist besides the transparent substrate e.g. glass PET anode most commonly indium tin oxide ITO and metal cathode e.g. Mg-Ag-alloy of several organic layers for charge injection transport and or emission 7 8 the principal set-up is shown in Scheme 1 . Metal cathode Ca Mg Al Electron transport layer ETL Emitting layer EmL Hole transport layer HTL ITO Indium-tin-oxide Transparent .