Browsing by Author "Liang, Hsun"

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Efficiency improvement of organic bifunctional devices by applying omnidirectional antireflection nanopillars
(2014)
Ho, Yu-Hsuan
;
Liang, Hsun
;
Liu, Shun-Wei
;
Tian, Wei-Cheng
;
Chen, Fang-Chung
OLED/OPV tandem devices have attracted great interest due to their various functions in green technology and potential sensing applications. Here we report a novel concept to improve the luminous efficiency and energy conversion efficiency of tandem bifunctional devices by integrating antireflection structures consisting of irregular nanopillars as the capping layer. The nanopillars were made on flexible polycarbonate substrates by using a nanoimprint method with an anodized aluminum oxide template. The average reflectivity of the patterned polycarbonate substrate at visible wavelengths was reduced to 3.3%. With the antireflection structures, the luminous intensity for bifunctional devices was improved by 41.9% compared to a device with a flat capping layer. The power conversion efficiency was improved from 0.48% to 0.61%, a 27.0% enhancement at normal incidence.
Tunable microcavities in organic light-emitting diodes by way of low-refractive-index polymer doping
(2014-12-01)
Ling, An-Kai
;
Lin, Chun-Hao
;
Liang, Hsun
;
Chen, Fang-Chung
;
光電工程學系
A method for enhancing the light out-coupling efficiency of organic light-emitting devices (OLEDs) has been demonstrated by blending a low-refractive-index polymer, poly(2,2,3,3,3-pentafluoropropyl methacrylate) (PPFPMA), into the emission layer. The resonant wavelength of the weak microcavity devices blueshifted accompanied with a decrease in refractive indices of the light-emitting layers after the addition of PPFPMA. Stronger directed emission toward the surface normal was obtained when the resonant wavelength became closer to the peak wavelength of intrinsic emission spectrum of the organic emitters. The luminous efficiency of the devices was enhanced by more than 20%. The results suggest that the microcavity properties of the OLEDs can be tunable through blending low-refractive-index materials. (C) 2014 Elsevier B.V. All rights reserved.