Shougen Yin

Heterocycle-substituted poly (p-phenylene vinylene) for light-emitting devices

Abstract Results are presented which explore the synthesis, characterization and electroluminescence performance of a new type of conjugated polymer, poly(2,5-diphenyl-1,3,4-oxadiazolyl)-4,4′-vinylene (O-PPV). A light-emitting diode consisting of ITO/O-PPV/Al is driven at about 6 V and has a peak emission wavelength of 483 nm, and this is in agreement with the result determined by the X-ray photoelectron spectroscopy (XPS) technique.

Blue electroluminescence from tris- 8-hydroxyquinoline aluminum thin film

We report the fabrication of symmetrically configured alternating-current (ac) light-emitting devices based on tris-(8-hydroxyquinoline) aluminum (Alq3). The devices consist of an emissive layer of Alq3 sandwiched between two layers of silicon dioxide. A blue emission at 457 nm could be obtained from the devices under the ac driving. The blue emission corresponds to the direct recombination from the lowest unoccupied molecular orbital (LUMO) to the highest occupied molecular orbital (HOMO) of Alq3. According to the dependence of luminescent intensity on the voltage and frequency, we ascribed this direct recombination to the dissociation of Frenkel excitons and the charge accumulation at the interface of SiO2 and Alq3.

Improved efficiency of molecular organic EL devices based on super molecular structure

Abstract A novel aluminum chelate, tris(5-hydroxymethyl-8-quinolinolato)aluminum (AlOq) as the emitter has been developed. The device (ITO/PVK/AlOq/Al) emitting green light has a luminance of more than 1000 cd/m2. The highest quantum efficiency of light-emitting devices is about 1.44 lm/W, better by three times than that of similar structure device made with Alq as the emitter duo to the formation of super molecular structure in AlOq thin films.

Electroluminescent properties of naphthalimide derivative thin film devices

Abstract N -alkyl or arenyl-4-acetylamide-1,8-naphthalimides (NA) were synthesized by reaction of 4-acetylamide-1,8-naphthalic acid with organic amines. Optical properties were studied in the UV-visible region. By using Joule evaporation thin films of the NA, the double layer of EL devices (ITO/PVK/NA/Al) were fabricated. Yellow and green EL emission at around 569.0–504.2 nm was observed. It was found that the emission wavelength of the devices using naphthalimides with bulkier N -alkyl groups shifted to red while the emission wavelength of those devices using naphthalimides with N -arenyl substituted groups shifted to blue. This is identified with the results calculated by the MINDO/3 model. Moreover, experimental results revealed that the Joule heat by non-radiative decay has a significant affect on the device life, and the life of the device using naphthalimide compounds with high melting points is longer than that of the device fabricated using those with low melting points.

Organic negative-resistance devices using PPV containing electron-transporting groups on the main chain

A kind of novel structure polymer, a poly(phenylenevinylene) (PPV) derivative containing electron-transporting groups on the main chain (OPPV), was developed according to the polycondensation mechanism. The I–V characteristics at the low-voltage region with negative differential resistance were observed in the same model of organic light-emitting diodes with the OPPV polymer. The different external parameters, including the device structure, layer thickness, morphology, and homogeneity of indium tin oxide and the polymer, were also investigated. The performance improvement in the organic negative differential resistance and a possible mechanism are discussed.

Interchain charge-transfer states in poly[(2,5-diphenylene-1,3,4-oxadiazole)-4,4′-vinylene] (O-PPV) oligomer

Abstract We synthesized the soluble poly[(2,5-diphenylene-1,3,4-oxadiazole)-4,4′-vinylene] (O-PPV) oligomer. The photoluminescence (PL) properties are investigated using absorption and selective excitation measurements for different O-PPV concentrations in solid-state O-PPV/PEO blends, as well as comparing PL spectra in dilute solution and solid state pristine O-PPV. The results show that solid-state O-PPV emission arises from interchain charge-transfer states due to interchain effects. In the O-PPV/PEO blends PL spectra, we find that the PL spectra excited at 300 nm are different from those at 350 nm. We think that this is directly associated with the properties of intrachain excited states in conjugated polymers.

Blue photo- and electroluminescence from a novel poly (phenelene vinylene) derivative containing oxadiazole segment in main and side chains

Abstract Optical and electroluminescent properties of a novel PPV derivative (OPPV) which contains oxadiazole segments in main and side chains were studied. Both the single-layer EL device and the triple-layer EL devices fabricated with OPPV as the active layer emitted blue light from OPPV with a peak of spectrum at around 460 nm. The device structure: ITO/PVK+OPPV(2:1 weight ratio)/OXD(40 nm)/Alq(20 nm)/Al, was fabricated, which showed much better performance than the single-layer EL device and the triple-layer EL device without PVK in the emitter material.

A novel oligomer poly (phenylene vinylene) derivative containing oxadiazole segment

A novel oligomer PPV derivative (OPPV) is reported, which is designed to contain the oxadiazole function segment in the main chain. Photoluminescence of the OPPV thin film originates from aggregated states. In a double layer device consisting of poly phenylene vinylene (PPV) and OPPV, emission only from PPV layer was observed and the efficiency of the device was improved by about one order of magnitude compared with the single layer PPV device, this indicates the electron transport characteristic of OPPV. In the OPPV/Tb complex device, OPPV functions as the hole transport layer. A possible explanation is proposed.