Development of Efficient White OLEDs Based on Blue Fluorescent and Yellow Exciplex Emissions
Students Name: Pyrih Orest Volodymyrovych
Qualification Level: magister
Speciality: Electronic Equipment and Devices
Institute: Institute of Telecommunications, Radioelectronics and Electronic Engineering
Mode of Study: full
Academic Year: 2021-2022 н.р.
Language of Defence: ukrainian
Abstract: The master’s thesis is devoted to the development of efficient white OLEDs based on blue fluorescent and yellow exciplex emissions. The work belongs to a promising field of solid-state electronics - organic electronics, which is based on electrophysical effects in organic semiconductor materials. Today, organic light-emitting structures, solar panels, transistors, sensors, etc. have been created. These include organic light emitting structures (OSVS). Some OSVS have been used in the commercial production of portable and widescreen high-resolution displays or ultra-thin lighting elements of any shape and area. However, in terms of efficiency, they are inferior to their counterparts based on inorganic materials. In addition, for their widespread use, it is necessary to create three basic colors (red, green, and blue) OSVS, the color coordinates of which are close to international television standards. There are also problems with the creation of lighting elements based on white OSVS and ultraviolet spectrum to meet household needs, medicine, agriculture and more. The main OSVS has three layers, including the cathode, the light emitting layer and the anode. In order to increase its efficiency, improving the injection and establishing the balance of charge carriers, introducing additional layers into its structure, performing such functions as injection, transfer and blocking of charge carriers in the OSVS, thus creating a new multilayer nanostructure. according to the nature of the light-emitting layer, there are luminescent and phosphorescent OSVS. The efficiency of fluorescent OSVS is low due to the low quantum yield of electroluminescence of organic fluorescent materials due to the use of singlet radiation recombination, and the upper limit does not exceed 25%. Although the radiation transition from the triplet state is prohibited in pure organic materials, this process can be achieved in phosphorescent OSVS by increasing spin-orbit interactions in organometallic complexes based on rare earth metals (Ir, Pt, Os). The cost of organometallic complexes significantly eliminates the competitiveness of phosphorescent OSVS based on them. In addition, the relatively long lifetime at the triplet level of organometallic complexes usually leads to quenching of electroluminescence due to triplet-triplet annihilation. Therefore, to increase efficiency, it is necessary to study the process of energy transfer from singlet to triplet. The efficiency of fluorescent OSVS is low due to the low quantum yield of electroluminescence of organic fluorescent materials due to the use of singlet radiation recombination, and the upper limit does not exceed 25%. Although the radiation transition from the triplet state is prohibited in pure organic materials, this process can be achieved in phosphorescent OSVS by increasing spin-orbit interactions in organometallic complexes based on rare earth metals (Ir, Pt, Os). The cost of organometallic complexes significantly eliminates the competitiveness of phosphorescent OSVS based on them. In addition, the relatively long lifetime at the triplet level of organometallic complexes usually leads to quenching of electroluminescence due to triplet-triplet annihilation. Therefore, to increase efficiency, it is necessary to study the process of energy transfer from singlet to triplet. Carbazole, triphenyl, fluorene and other derivatives for OSVC are still being studied. Among the existing organic materials used in OSVS, carbazole derivatives have satisfactory semiconductor properties, have fluorescence in the visible region of the spectrum, have thermal and electrochemical stability characteristics. Carbazole derivatives allow to obtain luminescence in the near ultraviolet and visible spectra. Therefore, the search for and development of new materials for luminescence or additional layers, structural modification, development of new multilayer nanolevel luminescent structures based on visible light and ultraviolet spectra of carbazole derivatives for information display elements and lighting is one of the most common. The object of the study is white OLED based on blue fluorescent and yellow exciplex radiation. The subject of research - organic light-emitting structures. The aim of the study: to develop effective white OLED based on blue fluorescent and yellow exciplex radiation. As a result of this master’s thesis, effective white OLEDs based on blue fluorescent and yellow exciplex radiation were developed. Optical modeling of 2- and 3-stack devices and their structures was performed. The angular dependences of the 2nd and 3rd WOLED stacks were investigated.