Do-Hoon Hwang

Observation of new wavelength electroluminescence from multilayer structure device using poly(p- phenylenevinylene) derivative

We observe a new electroluminescent (EL) peak from a two-layer polymer device, which does not appear in EL spectra of each layer. The polymers of both layers are poly(p- phenylenevinylene) derivative with monoalkoxy substituents, poly(2-methoxy-1,4-phenylene- vinylene, abbreviated as PMPV), but dialyzed for different periods respectively. A new peak is located at 590 nm and has comparable intensity. The origin of this peak is discussed. Absorption and photoluminescence spectra are also measured and device properties show typical diode characteristics.

Syntheses and electrical properties of halogen substituted PPV derivatives

Summary form only given. Halogen substituted PPV derivatives (PFPV, PClPV, FBrPV, PIPV) were prepared in film form from water soluble precursor route. The properties of these polymers were studied by UV-visible spectroscopy and electrical conductivity. According as phenylene ring was combined from fluorine to iodine, the position of maximum absorption shifts to the longer wavelength region. This indicates that the substituents halogen cause a bathochromic shift with changing from strong electron-withdrawing fluorine to weak electron-withdrawing iodine. The maximum absorptions and absorption edges due to /spl pi/-/spl pi/* transition of the polyconjugated systems show 400-430 nm and 510-530 nm, respectively. The electrical conductivity values of FeC1/sub 3/-doped polymer films are in the range of 10-sup -3/ S/cm and the drawn (L/L//sub /spl ring// = 5) ones are in the range of 10/sup -1/ S/cm. As the substituents are changed from fluorine to iodine, the conductivity values slightly increase because of their electronic and morphological effect.

The electroluminescent and photodiode device made of a polymer blend

Abstract Organic thin film diodes made by a polymer blend of poly[2-methoxy,5-(2-ethyl-hexoxy)-1.4-phenylenevinylene] (MEH-PPV) and poly[1.3-propanedioxy-1.4-phenylene-1,2-ethenylene-(2.5-bis(trimethylsilyl)-1,4-phenylene)-1,2-ethenylene-1,4-phenylene] (called the B-polymer) are investigated. The device of sandwich configuration indium-tin oxide (ITO)/polymer-blend/A1 emits orange light under forward bias at + 10 V and the same device acts as a photodiode under reverse bias. To investigate the photodiode characteristics, the 516 nm wavelength with 9.5 mW/cm2 intensity of light is illuminated through the A1 contact side of the device. The I-V characteristic measurement shows the short circuit current and the open circuit voltage of −1.22 × 10−9 A/cm2 and 0.8 V, respectively. The ratio of the photocurrent to the dark current is about 4 × 102 at − 2.5 V reverse bias. The maximum d.c. sensitivity is 1.35 × 10 −5 A/W at 4× 7 V reverse bias voltage with 16 mW/cm2 intensity of the incident light. The results indicate the possibility of making photosensors using this device.

Green electroluminescent diode from poly(2-trimethylsilyl-1,4-phenylene vinylene)

SummaryPoly(2-trimethylsilyl-1,4-phenylenevinylene) (TMS-PPV) was synthesized through a organic-soluble precursor polymer, and its properties were characterized by UV-visible, FT-IR spectroscopy and thermal anaylsis. The EL devices were fabricated with TMS-PPV as an emitting layer, and ITO and aluminum as positive and negative electrodes, respectively. Threshold voltage of the device was about 15 V and the emission maximum was at about 540 nm with quantum efficiency of 3.5x10-4% photons per electron in air and room temperature condition.

Electroluminescent Behaviour in Multilayer Structure Device Using Poly(P-Phenylenevinylene) Derivative

Abstract We observe a new electroluminescent(EL) peak from a two-layer polymer device, which does not appear in EL spectra of each layer. The polymers of both layers are poly(p-phenylenevinylene) derivative with monoalkoxy substituents, poly(2-methoxy-1,4-phepylene-vinylene, abbreviated as PMPV derivatives), but dialyzed for different periods respectively. A new peak is located at 590 nm and has comparable intensity. The origin of this peak is attributed to the emissive transition at the interface between two emitting layers, which is supported by the transient EL experiment. The multilayer device showed typical diode characteristics and large enhancement of quantum efficiency.

Electro-optic properties of (2-cyano-5-methoxy-1,4-phenylenevinylene) and paraphenylenevinylene copolymers

Abstract The electro-optic response of poly(CMPV-co-PV) is demonstrated to be stable up to 100°C when the polymers were poled during the elimination. The thermal stability and mechanical strength of PPV and its derivatives, and easy processibility from the precursor polymers suggest a new approach to the molecular design of the poled electro-optic polymers.

Synthesis, electrical and optical properties of asymmetrically monoalkoxy-substituted PPV derivatives

Abstract Poly(2-methoxy-1,4-phenylenevinylene), PMPV, and its copolymers containing both unsubstituted and 2-methoxy-1,4-phenylenevinylene (MPV) units were prepared in thin films from their water-soluble proecursor polymers, and monobutoxy- and monododecyloxy-substituted PPV derivatives were also prepared via the water-soluble precursor method. Drawn films (L/Lo = 6) of PMPV could be doped with I2 vapor and FeCl3 to give conductivities of 3.2 and 4.0 Scm−1, respectively. Conductivity values of long alkoxy-substituted PPVs were decreased by increasing the carbon number of mono substituted alkoxy side chain. Conductivity of FeCl3 doped copolymer films ranged from 1–100 Scm−1 depending on the composition of the copolymers. The third-order nonlinear optical susceptibility, χ(3)(3ω; ω,ω,ω) for PMPV thin film has been investigated by degenerate four-wave mixing technique using 400 femtosecond pulses at 602nm. A relatively large 3rd-order susceptibilty value (χ(3) = 7.9 × 10−10 esμ) with a subpicosecond response was observed.

Synthesis, electroconductivity and third-order nonlinear optical property of poly(2-isopropoxy-5-methoxy-1,4-phenylenevinylene)

SummaryAsymmetrically disubstituted poly(2-isopropoxy-5-methoxy-1,4-phenylene-vinylene), PIMPV, was prepared in thin films via organic-soluble precursor polymer method. These polymer films could be easily stretched up to 7 times, and the drawn films of the PIMPV could be doped with FeCl3 and I2 to give conductivities of 26.9 and 11.3 Scm-1, respectively. The third-order nonlinear optical susceptibility of the polymer was determined using third harmonic generation(THG) method at 1907 nm, fundamental wavelength. Measured χ(30) (-3α: α, α, α) value was 3.7x10-12 esu.

Optical third harmonic generation of poly(2-trimethylsilyl-1,4 phenylene vinylene) and poly(2,5-bis(trraethylsilyl)-1,4-phenylene vinylene)

Abstract Silicon atom substituted new PPV derivatives, poly(2-trimethylsilyl-1,4-phenylenevinylene) (TMS-PPV) and poly[2,5-bis(trimethylsilyl)-1,4-phenylenevinylene] (BTMS-PPV) were synthesized through water-soluble precursor route. The third-order nonlinear optical susceptibilities, χ (3) (−3ω;ω,ω,ω), were determined by third-harmonic generation measurement technique at 1907 nm, fundamental wavelength. The measured χ (3) values of PPV, TMS-PPV and BTMS-PPV were 3 × 10 −12 esu, 3 × 10 −12 esu and 4 × 10 −12 esu, respectively.

Steady State Photoconductivity of a Polymer Blend

Abstract The spectral responses of steady state photoconductivity of a polymer blend, poly[2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene](MEH-PPV) and poly[1,3-propanedioxy-1,4-phenylene-1,2-ethenyllene-(2,5-bis(trimethylsilyl)-1,4-phenylene)-1,2-etheny lene-I,4-phenylene](called B-polymer) are investigated. Two peaks of photocurrent(PC) at 2.16 eV and 3.01 eV are observed under continuous illumination. The peak at 3.01 eV is rather broad and has a strong polarity dependence on the applied voltage, which could be due to the rectified microjunction formation in the polymer blend. The incident beam intensity dependences of the two peaks in PC are I pc ∝ I α with α = 1.05. It indicates that the monomolecular recombination kinetics is important in this polymer blend. The observed spectral response of PC is discussed in comparison with the optical absorption as well as the photoluminescence spectra reported earlier in the same polymer blend.