Browsing by Subject "Electroluminescence"
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Item On the properties and design of organic light-emitting devices(2014-01) Erickson, Nicholas CarterOrganic light-emitting devices (OLEDs) are attractive for use in next-generation display and lighting technologies. In display applications, OLEDs offer a wide emission color gamut, compatibility with flexible substrates, and high power efficiencies. In lighting applications, OLEDs offer attractive features such as broadband emission, high-performance, and potential compatibility with low-cost manufacturing methods. Despite recent demonstrations of near unity internal quantum efficiencies (photons out per electron in), OLED adoption lags conventional technologies, particularly in large-area displays and general lighting applications. This thesis seeks to understand the optical and electronic properties of OLED materials and device architectures which lead to not only high peak efficiency, but also reduced device complexity, high efficiency under high excitation, and optimal white-light emission. This is accomplished through the careful manipulation of organic thin film compositions fabricated via vacuum thermal evaporation, and the introduction of a novel device architecture, the graded-emissive layer (G-EML). This device architecture offers a unique platform to study the electronic properties of varying compositions of organic semiconductors and the resulting device performance. This thesis also introduces an experimental technique to measure the spatial overlap of electrons and holes within an OLED's emissive layer. This overlap is an important parameter which is affected by the choice of materials and device design, and greatly impacts the operation of the OLED at high excitation densities. Using the G-EML device architecture, OLEDs with improved efficiency characteristics are demonstrated, achieving simultaneously high brightness and high efficiency.Item Realizing efficient electroluminescence from silicon nanocrystals(2013-11) Cheng, Kai-YuanColloidal semiconductor nanocrystals (NCs) have received considerable attention for optoelectronic applications due to their high photoluminescence efficiency and broad spectral tunability. The solution processibility of semiconductor NCs permits the integration into hybrid light-emitting devices that use organic semiconductors as charge transport layers. These devices offer the potential for low-cost manufacture through wet-coating processes in the future. While electroluminescence (EL) from group II-VI and III-V NCs has been well studied, emission from group IV NCs including silicon (Si) has not been characterized as extensively. This work focuses on solving the challenges to realizing efficient EL from hybrid nanocrystal-organic light-emitting devices (NC-OLEDs) containing organic semiconductors and SiNCs that are chemically passivated with ligands. Starting from the macroscopic point of view, this work first aims to understand the relationship between the surface morphology of SiNCs and device performance using a traditional hybrid nanocrystal-organic device design. The inherent bottlenecks of these conventional devices are discussed as they relate specifically to EL from SiNCs. Consequently, new device architecture is proposed, separately optimizing each functional layer within the hybrid device structure, concluding with the establishment of design rules for device engineering. Furthermore, efforts are made to address the significant open question of how surface passivation impacts device performance. Such discussion provides another consideration at NC surface during the hybrid-device design. Finally, an overview for the future research direction will be discussed.