Peng Gu

Investigations on Structural, Optical and X-Radiation Responsive Properties of a-Se Thin Films Fabricated by Thermal Evaporation Method at Low Vacuum Degree

Amorphous selenium (a-Se) thin films with a thickness of 1200 nm were successfully fabricated by thermal evaporation at a low vacuum degree of 10−2 Pa. The structural properties involving phase and morphology showed that a-Se thin films could be resistant to 60 °C in air. Also, a transformation to polycrystalline Selenium (p-Se) was shown as the annealing temperature rose to 62 °C and 65 °C, with obvious changes in color and surface morphology. Moreover, as the a-Se transformed to p-Se, the samples’ transmittance decreased significantly, and the band gap declined dramatically from 2.15 eV to 1.92 eV. Finally, the X-radiation response of a-Se was investigated as an important property, revealing there is a remarkable response speed of photogeneration current both X-ray on and X-ray off, with a requirement of only a very small electrical field.

Influence of substrate on structural, morphological and optical properties of TiO2 thin films deposited by reaction magnetron sputtering

Titanium dioxide (TiO2) films have been prepared by DC reaction magnetron sputtering technique on different substrates (glass, SiO2, platinum electrode-Pt, Silicon-Si). X-ray diffraction (XRD) patterns showed that all TiO2 films were grown along the preferred orientation of (110) plane. Samples on Si and Pt substrates are almost monophasic rutile, however, samples on glass and SiO2 substrates accompanied by a weak anatase structure. Atomic force microscopy (AFM) images revealed uniform grain distribution except for films on Pt substrates. Photoluminescence (PL) spectra showed obvious intrinsic emission band, but films on glass was accompanied by a distinct defect luminescence region. Raman spectroscopy suggested that all samples moved to high wavenumbers and films on glass moved obviously.

Influence of substrate and Ar/N 2 gas flow ratio on structural, optical and electrical properties of TiN thin films synthetized by DC magnetron sputtering

Titanium nitride (TiN) thin films have been prepared by direct-current reaction magnetron sputtering technique on different substrates (glass and Si) and the influence of substrate and Ar/N2 gas flow ratio on structural, optical and electrical properties of TiN thin films were discussed. X-ray diffraction suggested that with the ratio of Ar/N2 decreasing, the diffraction intensity of (111) plane gradually diminished while (200) plane increased and films on Si substrate exhibited better crystalline quality than glass substrate. Improvement of Ar/N2 ratio is contribute to enhance the deposition rate and the obvious surface roughness were observed when the ratio up to 49. Photoluminescence spectra showed that TiN films on Si substrate showed higher intrinsic emission and lower defect emission. Moreover, the resistivity of TiN films showed obviously decreasing as the flow rate ratio of Ar/N2 increased, especially films on Si substrate.

Influence of sputtering power on structural, optical and electrical properties of CdTe thin films prepared by DC magnetron sputtering

The cadmium telluride (CdTe) thin films have been successfully deposited on glass substrates by direct-current (DC) magnetron sputtering method, and the structural, optical and electrical properties of samples were investigated in this paper. X-ray diffraction patterns revealed that all samples exhibited a preferred orientation along (111) plane with cubic phase, and the crystallite size was first increased from 13.6 to 42xa0nm and then decreased to 31xa0nm as the sputtering power increased from 10 to 80xa0W. AFM images showed that surface morphology of CdTe films was affected by the sputtering power and the particles in the films exhibited uniform distribution with obvious RMS roughness (25.9xa0nm) as the sputtering power was 40xa0W. Meanwhile, CdTe films appeared a higher transmission properties in the range of 850–1000xa0nm, and the band gap of films gradually decreased from 1.96 to 1.51xa0eV and then increased to 1.67xa0eV as the sputtering power constantly increased. Raman spectrum revealed that the peak at 140xa0cm−1 exhibited dominant among other peaks, associated to the E mode of Te. The current–voltage (I–V) curves indicated that the conductivity of CdTe films was strongly dependent on the sputtering power and the optimal electrical properties could be achieved at the sputtering power of 40xa0W.

Effect of the nitrogen–oxygen ratio on the position of N atoms in the TiO2 lattice of N-doped TiO2 thin films prepared by DC magnetron sputtering

The nitrogen-doped TiO2 thin films are deposited on the glass substrate by using a direct-current (DC) magnetron sputtering technique. The film properties are analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements. The results show that, under the same working pressure and other conditions, nitrogen doping promotes the phase transition from anatase to rutile. Also, on changing the nitrogen–oxygen ratio, nitrogen atoms enter the TiO2 lattice in different positions. When oxygen is abundant, nitrogen atoms will be presented in the interstitial positions; when oxygen is insufficient, nitrogen atoms enter the oxygen vacancies first, forming a substituted position. Finally, we find that, with the increase in nitrogen–oxygen ratio, the sample has a better response to visible light, attributed to the change in the energy band-gap.

Influence of electrolyte proportion on the performance of dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSSC) depends strongly on the electrolyte. In this paper, the electrolytes with various solvents and different potassium iodide (KI) & iodine (I2) concentration were prepared and their influence on the DSSC performance were investigated. The results revealed DSSC with electrolyte prepared by organic solvent show better performance than that of inorganic solvent. Meanwhile, the increasing of KI concentration from 0.1 to 0.6 mol/L can effectively improve the short-circuit current density (Jsc) from 0 2, correspondingly, the DSSC conversion efficiency (η) increased from 0.04% to 0.11%. On the other hand, the Jsc and η of DSSC increased firstly then decreased with the I2 concentration raised from 0.025 mol/L to 0.125 mol/L. It is worth to notice that the open-circuit voltage (Voc) of DSSC is almost unchanged with the concentration of KI and I2. In this paper, the best performance DSSC (Jsc=0.87 mA/cm2, Voc=0.57 mV, η=0.23%) can be obtained with electrolyte at a K...