Ling Shen

Fabrication of Highly Oriented TiO2 Nanotube Arrays and their Application in DSSC

A two-electrode technique has been employed to anodize Ti foils for obtaining highly oriented TiO2 nanotube (NT) arrays. The morphology of the NT arrays was characterized by scanning electron microscope. With increasing anodization time, the lengths and diameters of TiO2 NT arrays was added from 6.7 to 19.5 μm, and 90 to 110 nm, respectively. As confirmed by X-ray diffraction and Raman spectra, the as-anodized TiO2 NTs were amorphous but transformed into anatase phase after thermal annealing at 450°C for 3 hours. Reflectance spectrum of TiO2 NT arrays showed that the layer with longer NTs can lower the reflectance in the visible spectrum because of the stronger light scattering effects of NTs, thus enhancing light harvesting from NTs. Dye-sensitized solar cells were fabricated using TiO2 NT arrays (tube-lengths: 6.7, 12.8, 16.3 and 19.5 μm). The characteristic of photocurrent density-voltage (J-V) showed that higher conversion efficiencies can be achieved with the longer NTs.

Mechanism of Blue Shift of Optical Band Gap in Aluminum-Doped ZnO Thin Films with Blend Bond

In this paper, aluminum–doped nano-crystalline zinc oxide (ZnO:Al or AZO) thin films were deposited on fused quartz substrate by pulsed laser ablation at various temperatures. The physical phase and surface morphology were characterized by using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. The variation of the optical band gap (Egopt) of the films with the temperature was measured through transmittance in UV-VIS wavelength. The results showed that there was a blue shift of Egopt from 3.44 eV to 3.62 eV as the growing temperature decreased from 500°C to 200°C. The value of Egopt immediately recurred from 3.30 to 3.35 eV after a thermal annealing of the samples at 700 °C, inclining to a normal value of bulk zinc oxide. The analyses of XRD and AFM testified that the presence of amorphous phase in the AZO films was the main reason for the blue shift of the optical band gap Egopt.

Light Trapping in Dye Sensitized Solar Cells with Length-Modulated TiO2 Nanotubes

Highly Oriented TiO2 Nanotube (NT) Arrays Were Fabricated by Anodizing Ti Foils. the Morphology of the NT Arrays Was Characterized by Scanning Electron Microscope. by Adjusting the Anodization Time, the Lengths and Diameters of TiO2 NT Arrays Changed from 6.7 to 19.5 μm, and 90 to 110 Nm, Respectively. as Confirmed by X-Ray Diffraction and Raman Spectra, the as-Anodized TiO2 NTs Were Amorphous but Transformed into Anatase Phase after Annealing at 450°C for 3 H. Reflectance Spectrum of TiO2 NT Arrays Showed that NT Layer of Longer Length Lowered the Reflectance in the Visible Spectrum because of Light Trapping Effects of NTs, Thus Enhancing Light Harvesting of NTs. Dye-Sensitized Solar Cells Were Fabricated Using TiO2 NT Arrays with Different Tube-Lengths. Analysis of Photocurrent Density-Voltage (J-V) Characteristics Showed that Higher Photoconversion Efficiencies Were Achieved with Longer NT Lengths.

Comparative Study on the Optical Band Edge of ZnO Films with Different Measurement Techniques

ZnO films were prepared by radio frequency (rf) magnetron sputtering. The absorption coefficients as a function of incident photon energy were obtained by means of spectroscopic ellipsometer (SE), as well as by using transmission and reflection measurement (T&R). The optical absorption band gap decided by SE is 3.32 eV, while that decided by T&R is 3.26 eV. The difference is ascribed to the fact that SE probes only the surface of films whereas the T&R measurement probes the bulk of the films. The same fact can also be used to explain that, at optical band edge region, the absorption coefficient decided by SE is lower than that decided by T&R. When the incident photon energy is larger than the optical band gap, exitonic transitions in the bulk of the films are used to discuss the change of the absorption coefficient vs. incident photon energy.

Fabrication and opto-electric properties of silicon based heterojunction SIS cells

ITO/AZO double films were deposited by RF sputtering on p-Si texturized substrate to fabricate ITO/AZO/SiO2/p-Si SIS heterojunction. The structural, optics and electrical properties of the ITO/AZO films were characterized by UV-VIS spectrophotometer, four point probe, respectively. The results show that ITO/AZO films have good quality. The electrical junction properties were investigated by I–V measurement, which reveals that the heterojunction shows typical good rectifying behavior and great photoelectric effect.

Fabrication and photoelectrical properties of AZO/SiO2/p-Si heterojunction

ZnO thin films doped with aluminum (AZO) were deposited on silicon dioxide covered p-Si (100) substrates by radio frequency magnetron sputtering, to fabricate AZO/SiO2/p-Si heterojunction, as an absorber for ultraviolet cell. The optical and electrical properties of the Al doped - ZnO films were characterized by UV-VIS spectrophotometer, current-voltage measurement, and four point probe technique, respectively. The results show that AZO films have good quality. The electrical junction properties were investigated by I-V measurement, which reveals that the heterojunction shows typical rectifying behavior.