Controlling Photons in Organic Light Emitting Diodes
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| Publicado en: | ProQuest Dissertations and Theses (2025) |
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| Acceso en línea: | Citation/Abstract Full Text - PDF |
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| Resumen: | In the nearly 40 years since the demonstration of the first organic light emitting diode (OLED), organic devices have come to make up a 55 billion dollar display industry with increasing demand for organic photovoltaics (OPVs) in energy generation applications that require unique form factors, including transparency and flexibility. Both device systems are constrained by key application requirements: high efficiency and reliable operational lifetime. We will investigate ways to address these key requirements through the control of photons in OPVs and OLEDs.We begin by leveraging the reciprocal relationship between OLEDs and OPVs to investigate the emissive internal quantum efficiency (IQE), i.e. emission from the charge transfer (CT) state, when operating an OPV in the dark under forward bias. We relate the degradation of the CT state emission to open circuit voltage through a semi-empirical factor, m, derived from the detailed balance of photon emission and absorption. We apply this relationship to quantify the reliability of archetype OPV structures. We find that the region of degradation within the device can be determined by m, with m=1 corresponding to degradation within the bulk heterojunction for DBP:C70 devices and m>1 corresponding to degradation outside of the bulk heterojunction for PCE-10:BT-CIC devices.Though phosphorescent OLEDs can achieve high IQE approaching 100%, their practical external efficiency is limited by light trapped within the device. In an archetypal structure, approximately 80% of photons generated in an OLED are trapped within the device in waveguided substrate or organic modes, or coupled to plasmonic modes at metal/organic interfaces. In this work, we investigate methods for extracting photons from both modes. First, we apply sub-electrode microlens arrays (SEMLA) to deep-stacked white OLEDs (WOLEDs). We demonstrate a 1.9× enhancement in external quantum efficiency for devices with waveguided modes extracted using SEMLA and substrate modes extracted using an external microlens array (MLA). While the SEMLA effectively couples organic waveguided modes to substrate modes, the MLA only couples ~60% of light from the substrate. We then discuss methods for improving MLA substrate mode outcoupling using low-index coatings.Surface plasmon polariton (SPP) modes, which couple light to the metal cathode surface within the device, are typically lossy modes. We demonstrate that by strongly coupling the SPP to excitons in the adjacent transport layer, forming a plasmon-exciton-polariton (PEP), the outcoupling efficiency of plasmonic modes can be increased from a 1.2×enhancement with outcoupled SPP modes to a 1.4×enhancement with outcoupled PEP modes using the same nanoparticle outcoupling scheme. We then present two WOLED architectures utilizing stacked and side-by-side red, green, and blue emitters. We demonstrate, in side-by-side devices, color-tunability in the 1960 color space from (u,v) = (0.33,0.36) to (0.12,0.32) through the use of a micro-scale peel-off patterning method. In the stacked devices, we demonstrate color stability over the course of device aging to 70% of the initial luminance by enhancing the lifetime of the blue emitter using the PEP-enhanced Purcell effect. These two architectures, which are compatible with the outcoupling schemes studied in this work, provide pathways toward achieving highly efficient, long-lived WOLED lighting.We conclude by presenting an outlook for the field of organic electronics as well as two new questions: 1) a design for maximizing OLED external efficiency using currently available technologies and 2) a pathway for using OLED outcoupling structures to increase OPV IQE, and thus operational power conversion efficiency. |
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| ISBN: | 9798291567760 |
| Fuente: | ProQuest Dissertations & Theses Global |