Synthesis and Application of Polyimide Materials for Organic Light-Emitting Diodes (OLEDs) Device

Abstract

Polyimide (PI), multi-characteristics materials, is one of the most high-performance polymers, which is the promising materials for high-tech field. PI has been applied for OLEDs device in many international reports in various features: flexible substrates, extracting light out-coupling, Hole/Electron transporting layers and so on. In this dissertation, PI is reported applying to OLEDs devices in some ways: - Formation of nanopore and nanopillar patterned polymer films from mixed PAA-PI solutions by phase separation method. - Outcoupling-enhanced organic light-emitting diodes (OLEDs) using simple phase-separated polymer films. - Enhancement of light extraction from organic light-emitting diodes by SiO2 nanoparticle-embedded phase separated PAA/PI polymer blends. - Preparation of various morphological films at nanoscale by phase separation method from novel polyimide. The phase separation phenomena were applied to make the random nanopore and nanopillar in polyimide film from mixed PAA-PI solution using the simple spin-coating technique. This thin, transparent film was used as an external light extraction layer, which attaching outside of the OLEDs device was expected to enhance the light out-coupling compared to conventional green OLEDs. Besides, adding the SiO2 nanoparticle into phase-separated PAA-PI polymer blends also resulted in patterned layer improving light extraction from OLEDs device. Also, the novel carbazole-based poly(amic acid) and Polyimide were synthesized and prepared to get various morphologies at the nanoscale owing phase separation phenomena. The measurements were used in this dissertation: proton nuclear magnetic resonance (1H-NMR) spectra; Ultraviolet-visible spectroscopy (UV-Vis) spectra; Fourier-transform infrared spectroscopy (FT-IR) spectra; Thermogravimetric analysis (TGA); Atomic force microscope (AFM) topography images; Field emission scanning electron microscopes (FE-SEM) images; Refractive index (RI); luminance current density–voltage (L-J–V) characteristics. In conclusion, we demonstrated a simple, low-cost, and efficient technique to make nanopore or nanopillar patterns films which had excellent flexibility and high refractive index. And we have also designed the high-quality external light outcoupling film successfully for OLEDs by applying these patterns. In summary, OLEDs has the enhancement of the current efficiency, and the power efficiency compared with the reference one by factors of 1.45 and 1.53, respectively. Also, combination of SiO2 nanoparticles and phase-separated patterns film OLEDs also can enhance factors of current efficiency and power efficiency by 1.35 and 1.42 time, respectively, higher than conventional OLEDs devices.