Pham Duy Long

Study on Electrical and Optical Properties of the Hybrid Nanocrystalline TiO 2 and Conjugated Polymer Thin Films

Recently, the conjugated polymer – inorganic nanocomposites have been increasingly studied due to the potential applications of these advanced materials in developing optoelectronic devices. In this work nanocomposite materials thin films based on poly [2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and nanocrystalline TiO2 (nc-TiO2) have been fabricated. The photoluminescence (PL) spectra of pure MEH-PPV and nanohybrid films have shown that the excitation at a 470 nm wavelength leads to the strong quenching in photoluminescent intensity due to the compositions of TiO2 component. Current-voltage (I-V) characteristics of multi-layer device with structure of Al//MEH-PPV:nc-TiO2//PEDOT:PSS//ITO//glass were investigated. The obtained results suggest the application of the hybrid MEH-PPV:nc-TiO2 materials in polymeric solar cells.

Dye laser picosecond convertor

The operation characteristics of a dye laser device designed for converting a fixed wavelength pump pulse emitted from a nanosecond non-mode lockable laser such as nitrogen, excimer laser into high-power picosecond laser pulses spectrally adjustable between 386 to 700 nm are presented. This device is made very compact, simple to operate, it produces a pulse-shortening factor greater than 100 (from 6 ns down to 50 - 80 ps) with a single stage. The spectral and time processes involved in this pulse shortening method are exposed with 2D-streak camera analysis and are discussed with a rate equation model.

Graphene Effect on Efficiency of TiO2-based Dye Sensitized Solar Cells (DSSC)

Colloidal paste of TiO2 embedded with graphene (GS) was fabricated and used to spread TiO\(_2\) film photo-electrode of DSSC solar cells. The dye N179 and Iodine-based electrolyte were used in the DSSC solar cells. Raman scattering, SEM images were used to identify the material phases and microstructure of the film photo-electrode. I/V characteristics of the DSSC cells were recorded at room temperature. Open-circuit voltage Voc, short-current \(J_{sc}\) and efficiency η of the DSSC cells were estimated. It shows that graphene addition has affected on \(V_{oc}\),\(J_{sc}\) and \(\eta\). The \(V_{oc}\),\(J_{sc}\) and \(\eta\) abnormally depend on graphene content. The efficiency reached a maximal value with graphen concentration of 0.005 wt %, after that decreased. It is supposed to be related with an improving the charge transfer in the working photo-electrode of DSSC.

Galvanic-Cell-Based Synthesis and Photovoltaic Performance of ZnO-CdS Core-Shell Nanorod Arrays for Quantum Dots Sensitized Solar Cells

Zinc oxide (ZnO) is recognized as one of the most attractive metal oxides because of its direct wide band gap (3.37 eV) and large exciton binding energy (60 meV), which make it promising for various applications in solar cells, gas sensors, photocatalysis and so on. Here, we report a facile synthesis to grow well-aligned ZnO nanorod arrays on SnO2: F (FTO) glass substrates without the ZnO seed layer using a Galvanic-cell-based method at low temperature (<100°C). CdS quantum dot thin films were then deposited on the nanorod arrays in turn by an effective successive ionic layer adsorption and reaction (SILAR) process to form a ZnO/CdS core-shell structure electrode. Structural, morphological and optical properties of the ZnO/CdS nanorod heterojunctions were investigated. The results indicate that CdS quantum dot thin films were uniformly deposited on the ZnO nanorods and the thickness of the CdS shell can be controlled by varying the number of the adsorption and reaction cycles. The number of quantum dots layers affects on photovoltaic performance of the ZnO/CdS core-shell nanorod arrays has been investigated as photoanodes in quantum dots sensitized solar cells.

Hydrothermal Synthesis and Enhanced Photocatalytic Activity of TiO\(_{2}\)-Fe@CNTs Nanocomposite for Methylene Blue Degradation under Visible Light Irradiation

TiO2 is one of the most attractive metal oxides because of the excellent chemical and photocatalytic properties. However, a problem in the application of TiO2 is the large band gap energy of 3.2 eV, corresponding to its photocatalytic activity under UV-light irradiation of wavelengths < 387 nm. In this work, TiO2 nanoparticles doped with iron were grown on the surface of functionalized carbon nanotubes (TiO2-Fe@CNTs) to expand the photoabsorbance of the nanocomposite materials in the visible light region and improve their photocatalytic activity. TiO2-Fe@CNTs nanocomposite materials were synthesized by hydrothermal route in Teflon-sealed autoclave at 180 ̊C for 10h. The FESEM and X-Ray diffraction measurements were taken for morphology and structural analysis of TiO2 nanoparticles doped with Fe coating on CNTs. The effects of the iron and CNTs on the enhanced photocatalytic activity for methylene blue degradation under AM 1.5 illumination of 100 mW.cm−2were investigated.

Investigation of Sodium Manganese Oxide Nanowires Synthesized by Hydrothermal Method for Alkaline Ion Battery

Sodium manganese oxide (NaxMnO2) has attracted much attention as cathode materials for alkaline ion battery due to the ability of the fast charge and discharge of Na+, in particular in nanoscale. We report on the synthesis of NaxMnO2 nanowires via hydrothermal synthesis route from Mn2O3 and NaOH solution. The morphological observation indicates that the obtained Na0.44MnO2nanowires with diameters of about 20 nm -30 nm, length up to several micrometers were formed by this process. The electrochemical properties of fabricated materials were investigated by means of cyclic voltammetry technique and show that sodium manganese oxide (NaxMnO2) is a promising material used for the alkaline ion battery.

Effect of Annealing Temperature on the Structure, optical and Electronic Properties of \(\text{TiO}_{2}\) Made by Thermal Treatment of \(\text{Ti}\)

In this work, TiO\(_{2}\) nanocrystalline thin films were obtained through evaporating Ti films by Electron Beam Deposition (EBD) followed by thermal treatment. The deposition speed of Ti thin fims was carried out at 0.15 nm/s and 1 nm/s. The results show that after annealing at 450\(^\circ\)C for 8 h, the obtained TiO\(_{2}\) thin films have nanoparticle structure with grain size of 20 nm for the Ti thin film deposited at the rate of 1nm/s, whereas at the a deposition rate of 0.15 nm/s, the TiO\(_{2}\) has a nanorod structure with the rod length of 300 -- 400 nm. At 700\(^\circ\)C for 8 h, the rutile phase was formed. At annealing temperature of 450\(^\circ\)C, all the samples are close to the stress free TiO\(_{2}\). The band gap of TiO\(_{2}\) thin films decreased with annealing temperature in both doposition rate of Ti thin films. The response of the films annealed at 450\(^\circ\)C presented a faster rise and fall in photocurrent under UV illumination on and off interval. Nanoporous structure TiO\(_{2}\) shows photoelectronic property better than that of nanorod structure. The obtained TiO\(_{2}\) films were characterized by X-ray diffraction (XRD) and a field emission scanning electron microscope (FE-SEM). The TiO\(_{2}\) films were used in a photo-electrochemical (PEC) cell as a working electrode and a platinum electrode as a counter electrode. The electrolyte solution contains 1 M KCl and 0.1 M Na\(_{2}\)S.

ZnO/CdS Bilayer used for Electrode in Photovoltaic Device

In this article we present the fabrication and characterization of the nanoporous ZnO and/or ZnO/CdS thin films onto indium doped-tin oxide (ITO) substrates, based on the thermal evaporation technique followed by thermal treatment. The preparation method was relatively simple and low-cost for large scale uniform coating to produce clean, dense and strong adhesion to substrate thin films. The nanostructured ZnO and ZnO/CdS thin films were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The nanostructured ZnO/CdS bilayer film was used in a photo-electrochemical (PEC) cell as a working electrode and a Pt net as a counter electrode. The results show that the photovoltaic cell with nanostructured ZnO/CdS bilayer film electrode has significantly improved photoelectric capability in comparison with that of ZnO electrode.

Nanocomposite Thin Film TiO 2 /CdS Electrodes Prepared by Thermal Evaporation Process for Photovoltaic Applications

The incorporation of cadmium sulfide (CdS) into TiO2 nanoparticle thin films was investigated. The nanoparticle TiO2 thin film onto an indium dopedtin oxide (ITO) substrate was deposited by Electron Beam Deposition (EBD) combined with thermal process. Then a CdS thin film was vacuum-deposited onto the pre-deposited TiO2 film by a thermal evaporation technique. The obtained TiO2/CdS was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM). The TiO2/CdS nanocomposite film was used in a photoelectrochemical (PEC) cell as a working electrode and a platinum electrode as a counter electrode. The electrolyte solution contains 1 M KCl and 0.1M Na2S. The results show that the cell with TiO2/CdS composite film electrode has significantly improved photoelectric capability in comparison with that of the pure TiO2 thin films.

Effect of Annealing Temperature on the Li\(^{ + }\) Ionic Conductivity of La\(_{0.67 - x}\)Li\(_{3x}\)TiO\(_{3 }\)

Perovskite La 0.67-x Li 3x TiO 3 with x = 0.10, 0.11, 0.12 and 0.13 were firstly annealed at 800 o C then treated by reactive milling, followed by post-annealing at temperatures from 1100 to 1200 o C. The crystalline structure of grain and grain-boundary were characterized by XRD and SEM. The impedance measurements showed that nanocrystalline La 0.67-x Li 3x TiO 3 after being annealed at 1150 o C possessed a grain conductivity as high as 1.3×10 -3 S.cm -1 . The grain-boundary conductivity was enhanced one order in magnitude after annealing at temperature higher 1100 o C and consists of 5.8×10 -5 S.cm -1 . The results have also showed the limitation of the adiabatic thermal treatment for the improvement of the grain-boundary conductivity and suggested the way to overcome the limitation by rapidly cooling the samples from the high temperature to room temperature.