Teng Feng

Characteristics of Solid State Cathodoluminescence of PPV

Based on our previous discovery [Chem. Phys. Lett. 325 (2000) 420] of the solid-state cathodoluminescence from organic luminescent materials in inorganic/organic heterojunction, we study characteristics of this new kind of electric-field-induced luminescence by means of examining its oscillogram. We prepared three devices with different structures in which PPV was used as luminescent layer, and SiO2 was used as accelerating layer. The experimental results might be understood only by means of the existence of solid-state cathodoluminescence. This new kind of luminescence makes it possible to produce new type of flat panel display.

Electric Field-Induced Quenching of Photoluminescence from Ir(PPY)3-Doped PVK

We study the photoluminescence (PL) and the PL dynamics of Ir(PPY)3-doped poly(N-vinylcarbazol) (PVK) under the modulation of an electric field. The results show that the electric-field-induced quenching of PL from Ir(PPY)3-doped PVK mainly comes from the dissociation of excitons in the chains of PVK. There is no significant difference in the excited state lifetime of Ir(PPY)3 to be observed under the different applied negative biases. Our experiments demonstrate that the excitons attached to the molecules of Ir(PPY)3 are very stable.

Enhanced organic electroluminescence (OEL) by integration with cathodoluminescence-like (cl-like) emission ☆

Using the secondary properties of inorganic material such as electron multiplication and acceleration, we discovered the cathodoluminescence-like (CL-like) emission. Now, using heterojunction and brightness waveform we investigated the temporary properties of the two peaks in CL-like emission. Further we found the identity of phase relation of luminescence relative to sinusoidal voltage for two different unsymmetrical devices and revealed the existence of CL-like excitation and the mutual enhancement of CL-like emission and organic electroluminescence. These processes are mutually compensatory additive and one strengthening the others. Choosing appropriate material and structural parameters might control the luminescence properties.

Synthesis and Optical Properties of Water-Soluble CdTe Nanocrystals

CdTe nanocrystals were synthesized in aqueous solution with different stabilizers (L-cysteine hydrochloride (L-Cys), 3-mercaptopropionic acid (MPA), 1-thioglycerol (TG), and thioglycolic acid (TGA)) by a simple route, and were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and X-ray diffraction pattern (XRD). The effect of aqueous synthesis conditions on the optical properties of CdTe nanocrystals was investigated and it was found that the molar ratio of Cd/Te, pH value, refluxing time, and different stabilizers significantly affected the optical properties of CdTe nanocrystals. The obtained CdTe nanocrystals exhibited a favorable narrow emission band under different conditions. The photoluminescence (PL) peaks and absorption peaks could be tuned by changing the synthesis conditions of CdTe nanocrystals. Different PL quantum yields (QY) were obtained using different stabilizers. The PL peak position of CdTe nanocrystals did not show significant shift under different excitation wavelengths.

Electrical bistable devices using composites of zinc sulfide nanoparticles and poly-(N-vinylcarbazole)*

N-dodecanethiol capped zinc sulfide (ZnS) nanocrystals were synthesized by the one-pot approach and blended with poly (N-vinylcarbazole) (PVK) to fabricate electrical bistable devices. The corresponding devices did exhibit electrical bistability and negative differential resistance (NDR) effects. A large ON/OFF current ratio of 104 at negative voltages was obtained by applying different amplitudes of sweeping voltage. The observed conductance switching and the negative differential resistance are attributed to the electric-field-induced charge transfer between the nanocrystals and the polymer, and the charge trapping/detrapping in the nanocrystals.

Organic Light Emitting Diode Using Inorganic Material as Electron Transport Layer

In this letter we report a new kind of organic light emitting diode in which an inorganic material was used as electron transport layer. The incorporation of this inorganic material layer increased the brightness in one order.

Improvements of the Analytical Model of Monte Carlo

By extending the conduction band structure, we set up a new analytical model in ZnS. Compared the results with both the old analytical model and the full band model, it is found that they are possibly in reasonable agreement with the full band method and we can improve the calculation precision. Another important work is to reduce the programme computation time using the method of data fitting scattering rate curves.

Carrier transport behaviour of molecular doped poly (N-vinylcarbozole) in polymer light-emitting diodes

Single-layer polymer light-emitting diodes are prepared from blends of poly(N-vinylcarbozole) (PVK) doped with tris(8-hydroxy-quinoline) aluminium (Alq3) of 2 wt% (sample a) and 0.2 wt% (sample b). The onset of PVK transient electroluminescence (EL) is delayed with respect to that of Alq3 in sample a under pulsed excitation, while the EL onsets of Alq3 and PVK in sample b are simultaneous. The total carrier mobility of the Alq3-rich regions in sample a is larger than that of the PVK-rich regions. However, the total carrier mobility is homogeneous in sample b. The phase image of atomic force microscopy and photoluminescence spectra of samples a and b indicate that the separated phase of samples a and b exists in the PVK-rich and Alq3-rich regions. The variance of the doping concentration and separated phase in blends results in the different carrier transport mobility of Alq3-rich and PVK-rich regions.

Effect of slow-solvent-vapour treatment on performance of polymer photovoltaic devices

In this work, enhanced poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulkheterojunction photovoltaic devices are achieved via slow-solvent-vapour treatment. The correlations between the morphology of the active layer and the photovoltaic performance of polymer-based solar cell are investigated. The active layers are characterized by atomic force microscopy and optical absorption. The results show that slow-solvent-vapour treatment can induce P3HT self-organization into an ordered structure, leading to the enhanced absorption and efficient charge transport.