Hou Yanbing

Effect of TiO2 Nanotubes on Polymer-Fullerene Bulk Heterojunction Solar Cells

We investigate the photovoltaic properties of hybrid organic solar cell based on the blend of poly[2-methoxy-5-(2_-ethylhexoxy-1,4-phenylenevinylene) (MEH-PPV), C60 and titanium dioxide (TiO2) nanotubes. In comparison of the composite devices with different TiO2:[MEH-PPV +C60] weight ratios of 1wt.% (D1?1), 2wt.% (D1?2), 3wt.% (D1?3), 5wt.% (D1?4), 10wt.% (D1?5) and 20wt.% (D1?6), it is found that the device D1?3 exhibits the best performance. The conversion efficiency is improved by a factor of 3 compared with the MEH-PPV:C60 device.

The studies on the upconversion mechanism of ZBLAN: Er3+, Yb3+

Abstract ZBLAN glass is an interesting host for rare earth doped up-conversion materials due to a lot of advantages. In this paper, we studied the up-conversion mechanism of ZBLAN co-doped with Er 3+ and Yb 3+ ions. The energy transfer between Yb 3+ and Er 3+ was described.

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.

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.

Blue polymer light emitting diode based on ladder poly(para-phenylene)

Abstract A blue polymer light emitting diode was prepared by inserting an electron transport layer between cathode and poly (N-vinylene carbazole) (PVK) doped by ladder poly (para-phenylene) (LPPP) layer. In comparison with the single layer LPPP device, the brightness of the device was improved by about one order of magnitude. An explanation based on energy diagram of the devices was presented.

EXCITON RECOMBINATION DYNAMICS IN CdTe/CdZnTe QUANTUM WELLS

Quantum wells of CdTe/CdZnTe were grown by molecular beam epitaxy. The highest order of satellite peak of the sample is 5 from XRD spectra and excition emission linewidth is about 4.8 nm at 77 K. It was shown that our samples are very good. The recombination dynamics of exciton in high-quality CdZnTe/CdTe multiquantum wells were investigated by means of time-resolved photoluminescence(PL) spectra with different excitation power at 77 K and photoluminescence spectra with different temperature. When weaker excitation was used, radiative recombination decay time of the exciton was reduced as the excitation intensity was decreased; the results indicate that the dominant mechanism may be the quenching of exciton emission by impurities and defects. The linewidth of the exciton emission becomes broader with increasing temperature, the linewidth at low temperature is only due to the well thickness, and the broadening linewidth at high temperature is contributed by the interactions among the exciton and LO and TO phonons and ionized donor impurities. The PL intensities are reduced with increasing temperature, which is mainly due to the thermal dissociation of excitons, i.e., the electrons or holes jump into the barriers from the wells by thermal excitations. The exciton emission from n=2 heavy hole exciton at 77 K has been observed, and the n=2 heavy hole exciton luminescence decay time is shorter than that from n=1. The investigation indicates that there is the exciton energy relaxation from the n=2 to n=1 heavy hole exciton state by phonons.

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.

Effect of TPD films as electron blocking layer on EL spectrum

In an organic thin film electroluminescence (OTFEL) device with an ITO/PPV/Alq:DCM1/A1 structure, a TPD layer was inserted between the PPV and Alq:DCM1 layers. A device without the TPD layer or with a 5-nm thick TPD layer operating at higher DC voltage (≥8 V) exhibited EL emission from both the PPV (513 nm) and Alq:DCM1 (591 nm) layers, however, a device with a 5-nm thick TPD layer operating at lower voltage (<7 V) or with a 10-nm thick TPD layer had an EL emission peak at 591 nm, implying that the TPD layer can effectively block electron transportation. Hence we can spatially control the carrier recombination zone and obtain different EL emissions by adjusting the thickness of the carrier blocking layer and the driven voltage.

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.

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.