Xiaojiang Zhao

Charge transport in a blue-emitting alternating block copolymer with a small spacer to conjugated segment length ratio

We analyze current versus voltage data obtained using single carrier injection in several metal/polymer/metal sandwich structures. The polymer used in each case is a soluble blue-emitting alternating block copolymer. Our experimental results demonstrate that the electron transport is space-charge limited by the high density of traps having an exponential energy distribution (temperature dependent characteristic energy) in the copolymer. The electron mobility of 8×10−10 cm2/V s is directly determined using space-charge-limited current analytical expressions. Hole transport is also space-charge limited, with a mobility of 2×10−6 cm2/V s. A hole trap with energy 0.17 eV is observed. We compare these results with those obtained for related block copolymers with different spacer and conjugated segment lengths and discuss the influence of spacer length and conjugated segment length on the charge transport properties.

Bright green organic electroluminescent devices based on a novel thermally stable terbium complex

Abstract A novel thermally stable terbium carboxylate complex, Tb(MTP),(phen) (MTP=monotetradecyl phthalate, phen=1,10-phehanthroline). was synthesized and characterized. The device structure of glass substrate/indium-tin-oxide/poly(p-phenylenevinylene) (PPV)/poly (N-vinycarbazole) (PVK):Tb(MTP),(phen): 1,3,4-oxadizole derivative (PBD)/tris(8-hydroxyquinoline) (AIq 3 )/aluminum (Al) was employed to study the electroluminescent properties of Tb(MTP),(phen). A green emission with extremely sharp spectral band of less than 10 nm at 544 nm peak wavelength was observed. A maximum luminance of 152 cd/m 2 and an external quantum efficiency of 0.017% were achieved at a drive voltage of 24 V. A possible mechanism of energy transfer based on the polymer doped with lanthanide organic complex was also proposed.

Bright blue electroluminescent devices utilizing poly(N-vinylcarbazole) doped with fluorescent dye

Abstract Bright blue electroluminescent devices have been fabricated using poly( N -vinylcarbazole) (PVK) doped with perylene as the emissive layer, poly( p -phenylenevinylene) (PPV) as the hole-transporting layer, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), tris(8-hydroxyquinoline) aluminum (Alq 3 ) as the electron-transporting layer, and Al as the cathode. A luminance of 700 cd/m 2 and a luminescent efficiency of 0.8% are achieved at a drive voltage of 36 V. In the experiment, it is found that the introduction of electron-transporting layer PBD has a great effect on the emissive color of the electroluminescent devices prepared by PVK doped with perylene. Yellow-green emission is observed from the device structure of glass substrate/indium-tin-oxide/PVK:perylene/Al. The possible emissive mechanisms are given. The effect of the transporting layer on the electroluminescence is also discussed.

Charge carrier mobility and electroluminescence in a green-emitting alternating block copolymer with a methoxy bi-substituted chromophore

We determine the mobility of positive and negative charge carriers in a soluble green-emitting alternating block copolymer with a methoxy bi-substituted conjugated segment. The negative charge carrier mobility of 6 × 10-11 cm /V.s is directly determined using space-charge-limited current analytical expressions. Positive charge carrier transport is also space-charge-limited, with a mobility of 1 × 10-8 eV. The electron trap distribution is exponential, with a characteristic energy of ~ 0.12 eV. A hole trap with energy ~ 0.4 eV was observed. This copolymer is used as emissive material in organic light-emitting diodes that present brightness of ~ 900 dc/m2 at 12.5 V.

Luminescence enhancement by blending PVK with blue PPV copolymer

The PL and EL properties of the polymer blends of PVK and blue PPV copolymer were studied. Considerable enhancement of both the photoluminescent and the electroluminescent intensity were observed by using the polymer blends as emission layer in the LED devices. The energy transfer process and the formation of exciplex in the polymer blends were also discussed.

Nonisothermal crystallization of poly(3-dodecylthiophene) and poly(3-octadecylthiophene)

Abstract Poly(3-dodecylthiophene) (P3DDT) and poly(3-octadecylthiophene) (P3ODT) are chosen to investigate the nonisothermal crystallization behavior by using differential scanning calorimetry (DSC). When Jeziorny method is applied, the deviation from the line appears at the later stage of crystallization for both P3DDT and P3ODT. The Ozawa equation fails to describe the nonisothermal crystallization of P3DDT, but succeeds for P3ODT. However, a new method proposed by our laboratory has been proven to be convenient and applicable for both of the two polymers. The values of the crystallization activation energy of P3DDT and P3ODT are estimated as 184.79 and 246.93 kJ/mol, respectively, in light of the Kissinger method.

Synthesis and high efficiency green light-emitting diode of a soluble polymer

A soluble polymer emitting green color with high efficiency was synthesized. Bright green electroluminescence devices, both single layer and multilayer, were fabricated. The luminous efficiency was improved dramatically. Carrier injection from the electrodes to the emissive layer and concomitant green electroluminescence from the emissive layer were observed. A luminance of 920 cd/m(2) and luminous efficiency of 5.35 1m/W were achieved at a drive voltage of 15 V for the multilayer device

Poly(3-dodecylthiophenes) polymerized with different amounts of catalyst

The effect of the amount of the catalyst FeCl3, used during the direct oxidation polymerization, on the structure and properties of the obtained poly(3-dodecylthiophene) (P3DDT) was investigated in this paper. Such measurements as gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, X-ray diffraction, infrared spectroscopy (FTIR) and ultraviolet-visible (W-vis) spectroscopy were applied. It is found that a suitable addition of FeCl3 can contribute to generate a P3DDT with greater percentage of head-to-tail head-to-tail (HT-HT) linkages, which are generally favored. The reduction of the other linkage defects helps to lengthen conjugation length, thus leading to more orderly chain packing

Synthesis and enhancement of quantum efficiency of a series of novel PPV derivative copolymers

A series of novel PPV derivative copolymers with good solubility in common organic solvents were synthesized. The emitting color of these copolymers could range from red to blue by adjusting the structures and the compositions of monomers. Investigation on their optical properties showed that the PL quantum efficiency could be increased by energy transfer and conjugation reduction. The PL quantum efficiency of most green/blue copolymer films on slide glass was higher than 80%.