Zhao Sl

High performance organic thin film transistor with phenyltrimethoxysilane-modified dielectrics

In this work, fabrication of organic thin film transistors (OTFTs) using a phenyltrimethoxysilane (PhTMS) modified SiO2 insulator greatly improves the device electrical properties over those with plain or octadecyltrichlorosilane (OTS) modified SiO2, particularly improves the carrier mobility, the subthreshold slope, and channel resistance resulted from reduced density of charge trapping states at the semiconductor/insulator interface. The pentacene OTFTs with modification from PhTMS (3.5‰ v/v) achieves carrier mobility of 1.03u2002cm2/Vu2009s, on/off current ratio of 1.98×105, and subthreshold slope of 0.20 V/decade. This work renders a new, simple approach to significantly improve the OTFT performance.

The effect of DCJTB doping concentration in PVK on the chromatic coordinate of electroluminescence

The dominant mechanism of electroluminescence (EL) from 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped in poly-(N-vinyl-carbazole) (PVK) system was demonstrated to be a charge carrier trapped by DCJTB molecular rather than Forster energy transfer from PVK to DCJTB. The chromatically coordinate EL emission of PVK:DCJTB changes from (0.41, 0.31) to (0.67, 0.31) with an increase in DCJTB doping concentration. The emission peak in DCJTB shows red-shift and the shoulder emission peak at 656u2009nm becomes stronger as the doping concentration increases. The effect of DCJTB doping concentration on EL spectra is attributed to strong dipole–dipole interaction between the DCJTB molecule with an increase in doping concentration.

The effect of multilayer quantum well structure on the characteristics of OLEDs

Abstract Organic light-emitting diodes (OLEDs) with multilayer quantum well (MQW) structure were fabricated, which consisted of alternate organic materials 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) and tris(8-hydroxyquinoline) aluminum (Alq 3 ). PBD is used as potential barrier layer, Alq 3 used as potential well layer and emitting layer. Compared with double-layer structure, the luminescent characteristics of the devices with MQW structure were investigated. MQW structures conduce to energy transfer between wells and barriers, which is attributed to good overlap and the decrease of the distance between layers. The MQW structures make electrons and holes distribute in different wells and then increase the number of the formation of excitons to further enhance their recombination efficiency. Hence, such device achieves the maximum brightness and efficiency of 3630xa0cd/m 2 and 3.28xa0cd/A, respectively.

Study on the influences of quantum well structure on the performance of organic light emitting devices

Abstract In this paper, six organic light emitting devices with different quantum well cycles and different position of well structures have been demonstrated. These well structures were composed by N,N′-diphenyl-N,N′-bis(1-napthyl)-1,1′-biphenyl-4,4′-diamine and tris-(8-hydroxyquinoline) aluminum, or tris-(8-hydroxyquinoline) aluminum and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. The device with one cycles well structure as electron transporting layer exhibits the highest brightness 3354xa0cd/m 2 and current efficiency of 3.46xa0cd/A. The current efficiency improved owing to carrier confinement and higher exciton formation probability in the well layer. Results illustrated that using proper period of well structure could improve the current efficiency of organic light emitting device and using well structure as electron transporting layer are better than as hole-transporting layer.

Use of multiple layers to adjust energy transfer for raising intensity of photoluminescence

Organic quantum well structure-like (OQWSL) samples and double-layer structure (DLS) samples were prepared, which consisted of alternate 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) and tris(8-hydroxyquinoline) aluminium (Alq3). In the case of OQWSL, the distance between the potential barrier material and the potential well material becomes shorter, so the energy transfer from PBD to Alq3 is increased. We investigate the energy transfer in OQWSL with different periods. This energy transfer goes to saturation when the period number is 4, which indicates that there is an optimal period number for the energy transfer efficiency. The effective distance of energy transfer from PBD to Alq3 could be estimated.

Comparison of photoexcited energy transfer in the organic double-layer and multilayer quantum well structures

Organic multiple quantum well structures (OMQWs) and double-layer structures (DLs) are prepared, which consist of alternate organic materials PBD (2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole) and Alq3 (tris (8-hydroxyquinoline) aluminum). From the energy diagram, it is similar to type-I quantum well structure of inorganic semiconductor, in which PBD and Alq3 are both electron-transporting materials, PBD is used as a barrier layer and Alq3 as a well layer and emitter. The photoluminescence characteristics of OMQWs and DLs are investigated. The photoexcited energy transfer from PBD to Alq3 in both structures is different with different periods and different layer thicknesses.

Blue solid state cathodoluminescence of ZnSe

Based on the layered optimization scheme, the inorganic/organic hetero-junction devices were prepared and solid state cathodoluminescence (SSCL) were found. According to this mind, blue SSCL of ZnSe film which is not appeared in the traditional sandwich structure was observed. The relationship between spectra characterization and applied conditions were studied in detail. The luminescence mechanism of the device was discussed. This phenomenon can provide a new way to realize blue inorganic electroluminescence.

Dissociation of excitons in organic light-emitting diodes

In this paper, the dissociation of excitons in both doped and undoped organic light-emitting diodes is investigated in detail by means of electric-field-induced photoluminescence quenching. The results show that the doped devices demonstrate lower quenching than that of undoped device. The reason is that the narrower energy band gap of guest molecules compared to that of the host molecules. In doped devices the increasing concentration of the guest molecules leads to a decrease in dissociation of excitons. The reason is that the increasing of the guest molecules concentration can result in an increase in the fraction of excitons residing on the guest molecules. Besides, the decreasing energy band gap of guest molecules can also make lower quenching in the doped devices.