Browsing by Author "Horng, SF"

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Color-tunable multilayer light-emitting diodes based on conjugated polymers
(2004-02-16)
Huang, CC
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Meng, HF
;
Ho, GK
;
Chen, CH
;
Hsu, CS
Wide-range low-voltage continuous color tuning is achieved in multilayer light-emitting diodes based exclusively on the commonly used high-efficiency electroluminescent conjugated polymers. There are three layers for red, green, and blue emission, and one extra layer for electron blocking. The color of the emitted photon depends on the position of the electron-hole recombination. Due to the stronger field dependence of the electron mobility relative to the hole mobility, the recombination zone is pushed away from the cathode and concentrated in different emissive layers as the voltage increases. (C) 2004 American Institute of Physics.
Comment on "Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes" - Reply
(2004-02-06)
Lin, LC
;
Meng, HF
;
Shy, JT
;
Horng, SF
;
Yu, LS
Comment on "Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes" - Reply
(2003-11-21)
Lin, LC
;
Meng, HF
;
Shy, JT
;
Horng, SF
;
Yu, LS
Efficient white light emission in conjugated polymer homojunctions
(2004-11-15)
Ho, GK
;
Meng, HF
;
Lin, SC
;
Horng, SF
;
Hsu, CS
We study polymer light-emitting diodes with a homojunction, i.e., junction between two layers with the same host material. One layer is poly (9,9-dioctylfluorene-2,7-diyl) (PFO) host blended with a small amount of poly (2-methoxy-5 (2'-ethyl-hexyloxy)-1,4-phenylene vinylene), another layer is either pure PFO or PFO host blended with green-emitting polyfluorene copolymers. Such homojunction devices are solution processed and show efficient white light emission. The peak luminance 3000 cd/m(2) is reached at 10 V with Internationale de L'Eclairage (CIE) coordinate (0.34, 0.34). (C) 2004 American Institute of Physics.
General method to solution-process multilayer polymer light-emitting diodes
(2006-04-17)
Tseng, SR
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Lin, SC
;
Meng, HF
;
Liao, HH
;
Yeh, CH
An intermediate liquid buffer layer is introduced to overcome the dissolution problem of solution-processed multilayer conjugated polymer light-emitting diodes. This method can be applied to arbitrary combinations of polymers with no restriction on solvents. As an example, a hole-blocking layer is successfully spin coated on the common p-type emissive polymer layers. One green- and two blue-emitting polymers are chosen as the emissive layers. The electron-hole balance and efficiency are significantly improved by the addition of hole-blocking layer. The electroluminescence efficiency can be increased up to nine times, while the luminance up to seven times. In particular, 1.5 cd/A is obtained for deep blue emission from poly(9,9-dioctyl-fluorene) with 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene spin coated as the hole-blocking material. (c) 2006 American Institute of Physics.
Giant anisotropy of carrier mobility in electroluminescent conjugated polymer
(2006-01-09)
Meng, HF
;
Chen, BL
;
Tzeng, KC
;
Horng, SF
;
物理研究所
The horizontal and vertical hole mobility of amorphous spin-coated electroluminescent conjugated films are studied. It is found that the horizontal mobility is about four orders of magnitude larger than the vertical mobility. The horizontal mobility increases daily with the aging of the polymer solution from which the film is spun. Low temperature and photoluminescence study reveal that the giant mobility anisotropy is a result of the alignment of the aggregates, formed during aging, by the centrifugal force of the spin.
One-polymer active pixel
(2004-01-26)
Tzeng, KL
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Meng, HF
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Tzeng, MF
;
Chen, YS
;
Liu, CH
A metal-oxide field-effect transistor (MOSFET) based on an electroluminescent conjugated polymer is fabricated on a glass substrate. It is found that the mobility horizontal to the substrate is two to three orders of magnitude larger than the mobility vertical to the substrate. The high horizontal mobility is attributed to the in-plane chain alignment in amorphous spin-coated films. We demonstrate an active pixel in which the light-emitting diode and the driving MOSFET share the same active polymer. (C) 2004 American Institute of Physics.
Polymer hot-carrier transistor
(2005-12-19)
Chao, YC
;
Yang, SL
;
Meng, HF
;
Horng, SF
;
物理研究所
Metal-base hot-carrier transistor with conjugated polymer emitter and collector is demonstrated. The device is fabricated by multiple spin coating with the metal base sandwiched between two polymers. A thin insulating layer of LiF is inserted between the emitter and base to enhance the hot carrier kinetic energy and reduce mutual dissolution. Using poly(9-vinylcarbazole) as the emitter, Al as the base, and poly(3-hexylthiophene) as the collector, common-emitter current gain of 25 is obtained with operation voltage as low as 5 V.
Polymer space-charge-limited transistor
(2006-05-29)
Chao, YC
;
Meng, HF
;
Horng, SF
;
物理研究所
;
電子工程學系及電子研究所
A metal grid is sandwiched between poly(3-hexylthiophene) to form a solid-state version of vacuum tube triode, where the vertical space-charge-limited current is modulated by the grid potential. The Al grid contains random submicron openings formed by a nonlithographic method. The multilayer polymer structure is made by spin coating. The operating voltage of the polymer space-charge-limited transistor is 3 V, and the current gain of 506 is obtained. The characteristics of the transistor can be tuned by the diameters and the density of the openings on the grid. Similar to the vacuum tube triode, the current follows a power law voltage dependence.
Strong red emission in heterojunctions of conjugated polymer blends
(2004-06-14)
Li, ZL
;
Meng, HF
;
Horng, SF
;
Hsu, CS
;
Chen, LC
We demonstrate strong red electroluminescence in bilayer polymer light-emitting diodes with poly(3-hexylthiophene) and polyfluorene copolymers. The emission spectrum of the diode, peaked at 612 nm, is different from either of the two polymer layers, and is attributed to the exciplex state existing only at the heterojunction. The efficiency of this junction emission is very high for red polymer light-emitting diodes. Peak luminance of 3500 cd/m(2) with yield 1.3 cd/A is achieved. The emission color can be made more saturated by blending red-emitting polymers into the polyfluorene to eliminate the small residual green emission. (C) 2004 American Institute of Physics.
Triplet exciton formation and decay in polyfluorene light-emitting diodes
(2005-09-01)
Liao, HH
;
Meng, HF
;
Horng, SF
;
Shy, JT
;
Chen, K
We study the triplet excitons in poly (9,9-dioctylfluorene-2,7-diyl) light-emitting diode using infrared induced absorption. The infrared absorption is exclusively due to the triplet excitons and there is no spectral overlap with any other species. A strong suppression of the triplet exciton density relative to the singlet by voltage is observed. Through an unique independent measurement on the triplet exciton lifetime it is shown that the suppression solely comes from triplet exciton quenching by current injection. The triplet-to-singlet exciton formation ratio is independent of voltage as well as temperature, implying a spin-independent exciton formation.
Triplet exciton formation ratio in poly(p-phenylene-vinylene) light-emitting diode
(2003-04-04)
Lin, LC
;
Meng, HF
;
Shy, JT
;
Horng, SF
;
Yu, LS
The triplet to singlet exciton formation ratio in a poly(2-methoxy-5(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) light-emitting-diode is measured by comparing the triplet induced-absorptions with optical and electric excitations at same singlet exciton density. The ratio is a strong universal decreasing function of the averaged electric field. Using 4 ns for singlet to triplet intersystem crossing time, the ratio is significantly larger than the spin-statistics value 3 at intermediate field but is reduced to about 1 for higher field.
Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes
(2003-01-24)
Lin, LC
;
Meng, HF
;
Shy, JT
;
Horng, SF
;
Yu, LS
The triplet to singlet exciton formation ratio in a MEH-PPV light-emitting diode is measured by comparing the triplet-induced absorptions with optical and electric excitations at the same singlet exciton density. The ratio is a strong universal decreasing function of the averaged electric field. Using 4 ns for singlet to triplet intersystem crossing time, the ratio is significantly larger than the spin-independent value 3 at intermediate field but is reduced to about 2 for higher field.