Home > Research > 연구분야 > Hybrid materials for OLED
1.
Alternative
transparent electrodes based on metal and polymer hybrids
Ø Simultaneously
Enhanced Light Outcoupling Efficiency and Electrical Properties of ITO-Free
Organic Light-Emitting Diodes Using High Refractive Index Polymer and Silver
Nanowires
We
develop the internal light outcoupling system (HRLOC) based on the high
refractive index polyimide (PI) and metal oxide nanoparticles for organic
light-emitting diodes (OLEDs) with silver nanowires (AgNWs). The spontaneously
formed nano-bump structures, high refractive index, and light scattering
properties of HRLOC significantly enhance the light extraction efficiency of
OLEDs. Not only do the outcoupling structures improve the light extraction
efficiency, but remarkably enhance the electrical properties of OLEDs. HRLOC
leads to the regular and smooth formation of AgNWs, resulting in the
improvement of the electrical properties of devices by preventing electrical
shorts and leakage currents. The power efficiency of the AgNW-based OLEDs with
PI is improved by a factor of 1.31 compared to the reference device with indium
tin oxide (ITO) transparent electrode. The efficiency is further improved by
incorporating TiO2 NPs into the PI matrix by a factor of 1.69. In addition, the
outcoupling structures are solution processable, thermally stable, and can be
scaled up to 200×200 mm2 for large-area applications. We believe that the light
outcoupling structures developed here have great potential for efficient,
low-cost, and flexible ITO-free OLEDs.
Figure. AFM topography images of (a) AgNW, (b) PI/AgNW, and (c) HRLOC/AgNW.
Ref. : ACS Appl. Mater. Interfaces 2018,
10, 985−991
Ø Copper-Mesh/Conductive
Polymer Hybrid Transparent Electrodes for ITO-Free Organic Light-Emitting
Diodes
We
report on highly transparent conductive electrodes based on copper (Cu)-mesh
structures combined with conductive polymer films. The hybrid transparent
electrodes show outstanding optical and electrical properties (transmittance of
81.7 % at a wavelength of 550 nm, sheet resistance of 100.7 ohm/sq). The
effective current collecting property of metal mesh structures as well as the
excellent current spreading property of the conducting polymer enables the high
performance of the hybrid transparent electrodes. Organic light-emitting diodes
(OLEDs) employing the hybrid transparent electrodes results in 2.0-fold
enhanced current and power efficiencies, compared to the control polymer
electrodes-based OLED without current collecting metal mesh structures. The
results present that Cu-mesh structures combined with conductive polymer films
can be a promising transparent conductive electrode for highly efficient low-cost,
flexible indium tin oxide-free OLEDs.
Figure
1. SEM imags of (a) PEDOT:PSS, (b) Cu-M, and (c) Cu-M/PEDOT:PSS transparent
electrodes.
Figure 2. Schematic illustrations of OLEDs
(a) with PEDOT:PSS and (b) with Cu-M/PEDOT:PSS transparent electrodes.
2. Preparation
and characterization of polymer hybrid films for high internal light extraction
in OLEDs
Ø Outcoupling-Enhanced Organic
Light-Emitting Diodes Using Simple Phase-Separated Polymer Film
A high-performance external light outcoupling films for organic light-emitting diodes (OLEDs) are developed as novel phase-separated polymers (PSP) which are spontaneously formed from a homogeneous solution of poly(amic acid) and polyimide. The phase separation during the spin-coating process leads to complex morphologies of film with random microdent and nanobump patterns by a self-assembly of polymers. The PSP film is utilized on the backside of a glass substrate in green OLEDs as a light outcoupling film, leading to the considerable enhancement of light outcoupling efficiency. Both current efficiency and the power efficiency of OLEDs with the PSP film are improved by a factor of 1.45 and 1.53, respectively, in comparison with that of the reference device.
Figure 1. Schematic illustration for phase separated patterns: a) spin-coating of binary polymer mixture solution on the glass substrate, b) arrangement of two-phase during evaporation of the solvent, c, d) proposed mechanism of phase-separated structure model (nucleation, growth and spinodal decomposition processing), e) theoretical thin-film formation, and f) real thin-film formation
Figure 3. AFM images of micro/nanopatterns on the glass
substrates were formed by phase separation. (a: images of microdent (5 µm X
5µm), b: images of nanobumps inside and outside of microdent in dimension (1µm
X 1µm))
Ø Enhancement of Light Extraction from Organic Light-Emitting
Diodes by SiO2 Nanoparticle-Embedded Phase Separated PAA/PI Polymer Blends
Using the phase separation of a binary immiscible polymer blend of poly(amic acid) and polyimide in combination with SiO2 nanoparticles, we have designed random nanopore and nanopillar patterns by a simple spin-coating technique. The spontaneously formed pattern structure enhances the external quantum efficiency of conventional green OLEDs up to a highest factor of 1.42. This enhancement is mainly attributed to reduction of the total internal reflection at the interface of glass and air by the polymer hybrid layer on the backside of OLED devices. This work provides a new and practical approach to the development of efficient external outcoupling structures for OLEDs.