Investigation of High efficiency Organic Lighting Emitting Devices
Date Issued
2014
Date
2014
Author(s)
Huang, Yi-Hsiang
Abstract
With the consciousness of energy conservation and innovation of portable devices, organic light emitting devices having power-saving, self-emissive, short response time and flexible characteristics are promising for the next-generation displays. In this dissertation, we proposed high-efficiency organic light emitting device structures utilizing the low refractive index and conducting property of the conducting polymer PEDOT:PSS. Devices were fabricated and measured for comparison with simulation results. Agreement of simulation and experiment results confirms the effectiveness of the designs. Firstly, we replaced ITO with the high-conductive conducting polymer PEDOT:PSS as the transparent anode to implement ITO-free organic light-emitting devices. The lower refractive index of PEDOT:PSS can reduce the index mismatch between the anode and the substrate, thus reducing the waveguide mode and increasing the overall sum of radiation- and substrate-mode ratios (60.1% for PEDOT device vs. 51.3% of ITO device). The experimental results demonstrated an overall EQE ~44.1% and a luminous efficiency up to 183.2 lm/W. Furthermore, PEDOT:PSS is also commonly used as the hole-injection layer in OLEDs. In our study, by judicious combination of the low-index PEDOT:PSS and high-index ITO in OLEDs to induce appropriate microcavity effects, simulation shows that very high optical coupling efficiencies of >35% and >58% to air and to substrate, respectively, can be obtained. Experiments have demonstrated an EQE of 33.7% for green phosphorescent OLEDs and even higher EQE of 54.3% by adopting the external out-coupling lens, unlocking the full potential of conducting polymers for high-efficiency OLEDs.
Subjects
OLEDs
high efficiency
outcoupling
conducting polymers
transparent electrodes
SDGs
Type
thesis