TAILIEUCHUNG - Organic Light Emitting Diode Part 5

Tham khảo tài liệu 'organic light emitting diode part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 4 Nanocomposites for Organic Light Emiting Diodes Nguyen Nang Dinh University of Engineering and Technology Vietnam National University Hanoi Vietnam 1. Introduction Recently both the theoretical and experimental researches on conducting polymers and polymer-based devices have strongly been increasing Salafsky 1999 Huynh 2002 Petrella et al. 2004 Burlakov et al. 2005 due to their potential application in optoelectronics organic light emiting diode OLED displays solar flexible cells etc. Similar to inorganic semiconductors from the point of energy bandgap conducting polymers also have a bandgap - the gap between the highest occupied molecular orbital HOMO and the lowest unoccupied molecular orbital LUMO . When sufficient energy is applied to a conducting polymer or a semiconductor it becomes conducting excitation of electrons from the HOMO level valence band into the LUMO level conduction band . This excitation process leaves holes in the valence band and thus creates electron-hole-pairs EHPs . When these EHPs are in intimate contact . the electrons and holes have not dissociated they are termed excitons . In presence of an external electric field the electron and the hole will migrate in opposite directions in the conduction and valence bands respectively Figure 1 . ---------lumo ------- ----- LTIMO w ---- ----HOMO -------o----- HOMO Fig. 1. Formation of electron-hole pair induced by an excitation from an external energy source Klabunde 2001 On the other hand inorganic semiconductors when reduce to the nanometer regime possess characteristics between the classic bulk and molecular descreptions exhibiting properties of quantum confinement. These materials are reflected to as nanoparticles or nanocrystals or 74 Organic Light Emitting Diode quantum dot . Thus adding metallic semiconducting and dielectric nanocrystals into polymer matrices enables enhance the efficiency and service duration of the devices. The inorganic additives usually have nanoparticle form. .

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