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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2018)

An affordable and high-performing solution for organic light emitting diode (OLED) substrates has been sought after in the global lighting market with demand in mechanical flexibility, color tunability, high efficiency, and high throughput, low-cost manufacturing. One potential solution that has gained an increasing amount of attention is through the development and implementation of silver nanowire electrodes. This work makes several key contributions towards enabling the use of silver nanowires (AgNWs) through the development of solution-processed low-cost approaches to fabricate flexible substrates using polymers and nanoparticles to obtain improvements in optical outcoupling enhancement and color quality. First, a novel method for patterning silver nanowires was developed to screen-print features with up to 50 μm resolution at ~ 40,000 S cm-1 conductivity. The printed patterns were used to fabricate OLED substrates with a sheet resistance of 5 ohm sq-1 at 89% transmittance, and the fabricated OLEDs showed a 1.6X efficiency enhancement in comparison to OLEDs fabricated on the ITO/glass reference electrodes. Second, an integrated nanocomposite substrate of AgNW anode, a high index polymer layer for microcavity tuning, and a light scattering layer consist of barium strontium titanate nanoparticles and methacrylate polymer matrix for light outcoupling was developed through optimization of the layer thicknesses and particle concentrations to obtain WOLED devices that yielded a power efficacy (PE) of 107 lm W-1 and an external quantum efficiency (EQE) of 49% at 1,000 cd m-2, which corresponds to an enhancement factor of ~ 2.76 in comparison to the control devices fabricated on ITO/glass substrates. Lastly, color rendering OLED substrates were fabricated with a color conversion layer consists of FBtF dye to improve the CRI of the WOLED to 83 while maintaining device performance of 85.83 cd A-1 current efficiency, 82.96 lm W-1 power efficacy, and 48.6% EQE. The process development of the substrate architectures in this study has demonstrated the advantageous of AgNW-polymer nanocomposite electrodes in efficiency enhancement and mechanical compliance through low-cost solution-based fabrication methods and have paved the way for potential adaptation in large-scale manufacturing of this technology for commercial lighting applications.

    Cover page: Solution-Processed Low-Cost Approaches for High-Efficiency Organic Light Emitting Diodes Substrates
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    Light-emitting electrochemical cells (LECs) with the thermally activated delayed fluorescence(TADF) host and phosphorescent guests were fabricated using solution process. It is demonstrated for the first time that TADF, a well-known phenomenon that helps to increase electroluminescence efficiency by harvesting excitons from triplet states, is used as a host in LECs. Devices with green, yellow, red and warm white emissions were fabricated, with the best devices showing more than 7000 cd/m2 stable emission and a peak efficiency over 7 cd/A. Under high voltage stress, a burst of extremely high luminance of over 30,000 cd/m2 was observed. All these LEC devices are extremely simple with only one active layer. Thus, our results could pave way to produce low- cost light source with high luminance, using TADF molecules.
      Cover page: Multi-Colored Light-Emitting Electrochemical Cells Based on Thermal Activated Delayed Fluorescence Host
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2017)
      Solid-state refrigeration offers potential advantages over traditional cooling systems, but few devices offer high specific cooling power with a high coefficient of performance (COP) and the ability to be applied directly to surfaces. We developed a cooling device with a high intrinsic thermodynamic efficiency using a flexible electrocaloric (EC) polymer film and an electrostatic actuation mechanism. Reversible electrostatic forces reduce parasitic power consumption and allow efficient heat transfer through good thermal contacts with the heat source or heat sink. The EC device produced a specific cooling power of 2.8 watts per gram and a COP of 13. The new cooling device is more efficient and compact than existing surface-conformable solid-state cooling technologies, opening a path to using the technology for a variety of practical applications.
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