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Optical simulation and optimization of light extraction efficiency for organic light emitting diodes
Description
Current organic light emitting diodes (OLEDs) suffer from the low light extraction efficiency. In this thesis, novel OLED structures including photonic crystal, Fabry-Perot resonance cavity and hyperbolic metamaterials were numerically simulated and theoretically investigated. Finite-difference time-domain (FDTD) method was employed to numerically simulate the light extraction efficiency of various 3D OLED structures. With photonic crystal structures, a maximum of 30% extraction efficiency is achieved. A higher external quantum efficiency of 35% is derived after applying Fabry-Perot resonance cavity into OLEDs. Furthermore, different factors such as material properties, layer thicknesses and dipole polarizations and locations have been studied. Moreover, an upper limit for the light extraction efficiency of 80% is reached theoretically with perfect reflector and single dipole polarization and location. To elucidate the physical mechanism, transfer matrix method is introduced to calculate the spectral-hemispherical reflectance of the multilayer OLED structures. In addition, an attempt of using hyperbolic metamaterial in OLED has been made and resulted in 27% external quantum efficiency, due to the similar mechanism of wave interference as Fabry-Perot structure. The simulation and optimization methods and findings would facilitate the design of next generation, high-efficiency OLED devices.
ContributorsSu, Hang (Author) / Wang, Liping (Thesis advisor) / Li, Jian (Committee member) / Huang, Huei-Ping (Committee member) / Arizona State University (Publisher)
Created2016
Description
This dissertation describes work on three projects concerning the design and implementation of instrumentation used to study potential organic electronic devices. The first section describes the conducting atomic force microscope (CAFM) in the study of the mechanical and electronic interactions between DNA bases and nucleosides. Previous STM data suggested that an STM tip could recognize single base pairs through an electronic interaction after a functionalized tip made contact with a self assembled monolayer then was retracted. The conducting AFM was employed in order to understand the mechanical interactions of such a system and how they were affecting electrical responses. The results from the conducting AFM showed that the scanning probe system was measuring multiple base-pair interactions, and thus did not have single base resolution. Further, results showed that the conductance between a single base-nucleoside pair is below the detection limit of a potential commercial sequencing device. The second section describes the modifications of a scanning probe microscope in order to study the conductance of single organic molecules under illumination. Modifications to the scanning probe microscope are described as are the control and data analysis software for an experiment testing the single molecule conductance of an organic molecule under illumination. This instrument was then tested using a novel charge-separation molecule, which is being considered for its potential photovoltaic properties. The experiments showed that the instrumentation is capable of detecting differences in conductance upon laser illumination of the molecule on a transparent conductive surface. The third section describes measurements using the illuminated CAFM, as well as the design and construction of an illuminated mercury drop electrode apparatus. Both instruments were tested by attempting to observe photovoltaic behavior in a novel self-organized film of the charge-separation molecules mentioned in the previous paragraph. Results and calculations show that the conducting AFM is not a useful tool in the examination of these organic photovoltaics, while the mercury drop apparatus measured photovoltaic effects in the film. Although photovoltaic effects were measurable with the mercury drop electrode, it was found that the film exhibited very low photon-to-electron conversion efficiency (IPCE).
ContributorsKibel, Ashley Ann (Author) / Lindsay, Stuart M (Thesis advisor) / Chamberlin, Ralph (Committee member) / Moore, Thomas (Committee member) / Ozkan, Sefika (Committee member) / Sankey, Otto (Committee member) / Arizona State University (Publisher)
Created2010