Papers by Author: Teen Hang Meen

Abstract: In this study, the flexible dye-sensitized solar cell is fabricated by pressurization-transfer technique, which involves assembling TiO₂ films on ITO/PEN flexible substrates via high temperature sintering. During the experiment, we change not only the film thickness and structure of TiO₂ but also the dye of working electrodes. The surface morphology of TiO₂ films are examined by field emission scanning electron microscopy (FE-SEM). The analyses of UV-Vis show that N3 dye could be adsorbed on the TiO₂ thin films, and the TiO₂ thin film with scattering layer has better absorption than that of without scattering layer. The current-voltage of the DSSC is illuminated by the solar simulator whose incident light intensity was 1000 W/m². These results indicate that the best efficiency of flexible dye-sensitized solar cell with high-temperature sintering TiO₂ film and scattering layer is 6.13%.

Abstract: In this study, nano-crystallized TiO₂ photoelectrodes prepared by doctor-blade method on ITO-PEN substrate applied on flexible tandem dye sensitized solar cells (DSSCs) have been investigated by field emission scanning electron microscopy (FE-SEM), UV-Vis spectrophotometer (UV-Vis), and I-V characteristics analyses. In the analysis of FE-SEM, TiO₂ thin films prepared by doctor-blade method have the porous structure. The analyses of UV-Vis show that N3 and black dye could be adsorbed on the TiO₂ thin films, and the absorption wavelength of TiO₂ photoelectrodes could be obviously promoted from the ultraviolet ray to the visible light scope with N3 and Black dye adsorbed. It is great help for conversion efficiency of DSSCs. Under the irradiation of the sunlight simulator (AM 1.5,100 mW/cm²), the flexible dye-sensitized solar cell with double sensitized layers has the best conversion efficiency η =5.59 %.

Abstract: A blue organic light-emitting diode (OLED) with a double hole-transporting (DHT) structure has been developed. The blue color purity was improved by modulation the thickness of CBP layer. When the thicknesses of left CBP and right CBP are respectively 8 nm and 2 nm, the more pure blue coordinates are (0.155, 0.079), which are very close to the blue coordinates of the national television system committee (NTSC) standard (0.14, 0.08). Furthermore the current density, brightness and the luminous efficiency of device with the left CBP of 8 nm and the right CBP of 2 nm are respectively 144.7 mA/cm2, 1065 cd/m2 and 0.93 cd/A.

Abstract: Small molecule organic solar cell with an optimized structure of indium tin oxide (ITO)/copper phthalocyanine (CuPc) (10nm)/CuPc: C₆₀ mixed (20nm)/fullerene (C₆₀) (20nm)/bathocuproine (BCP) (10nm)/Al) was fabricated. With optimizing the hybrid planar-mixed molecular heterojunction (PM-HJ) from the double layer heterojunction (HJ) and the bulk heterojunction (BHJ), the short-circuit current density (J_sc) increased from 3.09 to 5.11mA/cm2, the open-circuit voltage (Voc) increased from 0.40 to 0.47V, and the power conversion efficiency (η_p) increased from 0.66 to 1.28% under 100mW/cm2 AM1.5G illumination. These improvements were attributed to reach the optimal balance among the light absorption efficiency, the exciton dissociation efficiency and the carrier collection efficiency of the device, resulting in enhancement of J_sc without affecting the value of fill factor (FF) and the reduction of the dark current. Furthermore a decrease of dark current is caused to the higher V_oc.

Abstract: Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with gold, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties. However, it is difficult to prepare Fe-core/Au-shell (Fe@Au) nanoparticles under ambient pressure because iron nanoparticles are very easily to be oxidized in the air. In this study, we synthesized Fe@Au nanoparticles by modified reverse micelle method under ambient pressure and investigated them by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet-visible absorption spectra, and magnetic susceptibility measurements. X-ray diffraction analysis shows that the pattern of iron is hidden under the pattern of gold. TEM image reveals that the core-shell structure is obviously observed and the average size of Fe@Au nanoparticles is about 12 nm, with about 8 nm diameter core and 2 nm shell. The absorption band of the Fe@Au nanoparticles shifts to a longer wavelength and broadens relative to that of the pure gold. The magnetic susceptibility of Fe@Au nanoparticles is measured with a SQUID magnetometer and found to be superparamagnetic with a blocking temperature Tb ~25 K.

Abstract: In this study, well-aligned single-crystalline zinc oxide (ZnO) nanorods arrays were synthesized on Si substrate by simple hydrothermal process in dilute aqueous solution which consisting of zinc nitrate tetrahydrate (Zn(NO3)2•4H2O) and hexamethyltetramine (C6H12N4, HMT) at 90 °C, in the autoclave. ZnO thin film was pre-deposited on Si substrate by the sputter deposition to serve as the seed layer. Aluminum nitrite (Al(NO3)3) also has been mixed into reaction solution. Al doped ZnO nanorod arrays were fabricated successfully. ZnO nanorods were characterized by high resolution X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, and photoluminescence measurement.

Abstract: In this research, vertically oriented TiO2 nanotube was fabricated on ITO glass by electrochemistry method, and investigated by the measurements of X-ray diffractometer (XRD), scanning electron microscopy (SEM), and ultraviolet-visible (UV/VIS) spectrometer. X-ray diffraction patterns show that the best sintering temperature of TiO2 nanotube is 500°C, at which TiO2 anatase phase forms best. SEM images reveal that the diameter and height of TiO2 nanotube are 70 nm and 230 nm, respectively. Transmittance curves reveal that the transmittance of annealed TiO2 nanotube is about 80%~90%, and is obviously higher than non-annealed TiO2 nanotube. The absorption band of annealed TiO2 nanotube is at 330~370 nm. The results of current-voltage (I-V) characteristics analysis reveal that dye-sensitized solar cell with TiO2 nanotube electrode has better I-V characteristics and efficiency than TiO2 film electrode. This result may be due to the annealed TiO2 nanotube applied on the electrode of dye-sensitized solar cell can increase the contact area between TiO2 and dye, resulting in the enhancement of I-V characteristics and efficiency for dye-sensitized solar cell.

Abstract: In this investigation, the effect of the thickness in the flexible organic light-emitting diode (FOLED) is studied. The larger luminance and luminance efficiency, 1160 cd/m2 and 2.71 lm/W, can be obtained at NPB thickness of 45 nm with the Alq3 thickness of 35 nm. The luminance dramatically rises when the Alq3 thickness is 45 nm at bias voltage of 19 V. The highest luminance is up to 2190 cd/m2. The extreme characteristic of FOLED may be useful to an organic electrically pumped laser.

Abstract: In this paper, the improvements in luminance and efficiency have been demonstrated in a white polymer light-emitting device (PLED) with the structure of ITO/ poly (N-vinylcarbazole) (PVK): 1,1,4,4- tetraphenyl-1,3-butadiene (TPB):5,6,11,12-tetrapheny lanpthacene (rubrene) /LiF(1 nm)/Ca(10 nm)/Al(100 nm). The luminance of the white PLED is up to 4940 cd/m2 at 17 V. The current efficiency and Commission Internationale d’Eclairage (CIE) coordinates is 1.66 cd/A and (0.325, 0.326), respectively. The enhancement of the luminance and efficiency can be attributed to an improved hole-injection ability and balance carrier recombination through two ways: (1) enhancing the hole-injection from ITO by using O2 plasma treatment, and (2) balance the recombination of hole and electron by produce a buffer layer with σ-bonded segments of polymer between the ITO and the polymer layer. Besides, orange-emitting rubrene provides that direct recombination of holes and electrons occurred on the dopant molecules and trapping significantly enhanced the luminance and efficiency.

Abstract: In this research, applications of different TiO2 electrode structures on Dye-Sensitized Solar Cell were investigated. The different TiO2 electrode structures include: (1) synthesis of TiO2 nano-particles and TiO2 film electrode by sol-gel and spin-coating method; (2) fabrication of the TiO2 film electrode by RF Sputtering; (3) fabrication of the rod TiO2 electrode by photo lithography. X-ray diffraction patterns show that the best sintering temperature of nano-TiO2 thin film is 500oC, at which TiO2 anatase phase forms best and the smallest particle-size (8-10 nm) can be obtained. Ultraviolet-visible absorption spectra reveal that the rod TiO2 electrode with TCPP sensitizer adsorbed on has the best optical absorption from 400 nm to 700 nm. The results of current-voltage analyses reveal that the solar cell with rod TiO2 electrode has higher conversion efficiency than the others. This result also provides clear evidence for the contact area between TiO2 electrode and TCPP sensitizer plays an important role on the efficiency of dye-sensitized solar cell.