Solution-Processed Low-Cost Approaches for High-Efficiency Organic Light Emitting Diodes Substrates
- Author(s): Tong, Kwing Shing Michael
- Advisor(s): Pei, Qibing
- et al.
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.