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Highly polarized polymer-based light-emitting diodes fabricated by using very thin photoaligned polyimide layers
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10.1063/1.3445774
/content/aip/journal/jap/107/11/10.1063/1.3445774
http://aip.metastore.ingenta.com/content/aip/journal/jap/107/11/10.1063/1.3445774

Figures

Image of FIG. 1.
FIG. 1.

Molecular structure of (a) Azo-PAA and (b) Azo-PI used in this study.

Image of FIG. 2.
FIG. 2.

Device structure of polarized PLEDs.

Image of FIG. 3.
FIG. 3.

(a) Current-voltage and (b) brightness-voltage characteristics of the polarized PLEDs with different thicknesses of the photoaligned Azo-PI film. Filled squares: 0 nm, filled circles: 1.6 nm, filled triangles: 2.8 nm, open squares: 4.0 nm, and open circles: 11.0 nm.

Image of FIG. 4.
FIG. 4.

Azo-PI photoalignment layer thickness dependence of the maximum current efficiency (filled squares) and the polarization ratio at 434 nm (filled circles). Here, and , respectively, are the perpendicular and parallel components of the EL intensity with respect to the polarization direction of the LP-L. The solid and dotted curves are guides for the eye.

Image of FIG. 5.
FIG. 5.

Polarized EL spectra of the polarized PLED with a 2.8 nm-thick photoaligned Azo-PI film, which were taken with a spectral resolution of 12 nm under a constant current density condition of . The EL spectra are not corrected for the spectral sensitivity of the spectrograph system. The inset is the polarized PL spectra of the 30 nm-thick PFO layer formed on a 2.7 nm-thick photoaligned Azo-PI film, which was formed on a quartz glass substrate. Here, and , respectively, are the perpendicular and parallel components of the EL (PL) intensity with respect to the polarization direction of the LP-L.

Image of FIG. 6.
FIG. 6.

tapping-mode AFM images of (a) a bare ITO electrode and [(b)–(e)] the photoaligned Azo-PI films with different thicknesses that were formed on ITO electrodes, and (f) surface roughness determined from two different AFM images with a scan area of . To facilitate comparison, the same Z-scale magnification was used for all the AFM images. The polarization direction of the LP-L used in the photoalignment treatment is the Y-axis in the AFM image.

Image of FIG. 7.
FIG. 7.

(a) Current-voltage and (b) brightness-voltage characteristics of the polarized PLEDs with different thicknesses of the PFO layer. Filled squares: 22 nm, filled circles: 30 nm, filled triangles: 44 nm, filled diamonds: 65 nm, open squares: 83 nm, open circles: 101 nm, and open triangles: 146 nm.

Image of FIG. 8.
FIG. 8.

Polarized EL spectra of the devices with different thicknesses of the PFO layer: (a) 22 nm, (b) 65 nm, (c) 101 nm, and (d) 146 nm. These spectra were taken with a spectral resolution of 3 nm and corrected for the spectral sensitivity of the spectrograph system. The definitions of and are the same as those in Fig. 4. To facilitate comparison, the spectral intensity of each device is normalized by setting the maximum intensity of to unity.

Image of FIG. 9.
FIG. 9.

PFO layer thickness dependence of (a) the intensity ratio of the 434 nm peak to the 460 nm peak in the spectra and the polarization ratios of (b) the 434 nm peak and (c) the 460 nm peak. The definitions of and are the same as those in Fig. 4. The filled squares are the experimental data points. The dotted, broken, and solid curves are the calculated results for cases (i), (ii), and (iii), respectively; (i) the emission zone is across the PFO layer, (ii) the 80 nm-thick emission zone is located near the Azo-PI/PFO interface, and (iii) the 80 nm-thick emission zone is located near the PFO/TPBI interface.

Image of FIG. 10.
FIG. 10.

Layered structure assumed in our calculation. An oscillating dipole polarized parallel to the surface plane is placed at distance z from the PFO/TPBI interface.

Image of FIG. 11.
FIG. 11.

PFO layer thickness dependence of the maximum current efficiency (filled squares) and the polarization ratio (filled circles) for the integrated intensity from 400 to 600 nm. The definitions of and are the same as those in Fig. 4. The solid and dotted curves are guides for the eye.

Tables

Generic image for table
Table I.

Refractive indices of each layer used in our calculation.

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/content/aip/journal/jap/107/11/10.1063/1.3445774
2010-06-09
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Highly polarized polymer-based light-emitting diodes fabricated by using very thin photoaligned polyimide layers
http://aip.metastore.ingenta.com/content/aip/journal/jap/107/11/10.1063/1.3445774
10.1063/1.3445774
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