Solid State Phenomena Vols. 181-182

Abstract: Corona aging of 100CR polyimide (PI) film under bipolar pulse voltage was studied by using atomic force microscopy (AFM) and Confocal Raman microspectroscopy. AFM results show that the 100CR film near the breakdown hole is much rougher than the outside region. In the region away from the breakdown hole, no Raman shift is detected, but the intensity of all Raman peaks shows clearly decrease with the measuring region approaching more closely to the aging center. It is suggested that the damage of the PI film initiates from the surface in the presence of voids due to the partial discharge, and then gradually extends to interior, and these partial discharge cause progressive deterioration, and ultimately lead to the electrical breakdown of PI film with continuous aging.

Abstract: In order to understand the influence of morphology of vacuum-evaporated conjugated organic thin film on organic photovoltaic performance, oligothiophene derivatives, 2,3,4,5-tetrathienylthiophene (X-5T) and 2,5-dithienyl-3,4-di ((2,2') bithiophene-5yl) thiophene (X-7T), were prepared. The thermal behaviour and morphologies of vacuum-deposited X-5T and X-7T films were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The influence of morphologies of vacuum-evaporated X-5T and X-7T films on organic photovoltaic performance was hen investigated. It was found that vacuum-evaporated oligothiophene derivative films possessing crystalline morphology could be beneficial to improve organic photovoltaic performance of device by promoting forward interfacial electron transfer and transport.

Abstract: The effects of B₂O₃ on the sinter ability and microwave dielectric properties of Ca [(Li_1/3Nb_2/3)_0.92Zr_0.08]O_3−δ−0.05TiO₂ (CLNZ−0.05TiO₂) ceramics were investigated. B₂O₃ doping can effectively reduce sintering temperature by 150~200 °C. The temperature coefficient of resonator frequency τ_f increased with an increase of B₂O₃ content and sintering temperature. When B₂O₃ of 2.5 wt % were added, the optimum microwave dielectric properties: ε_r =34.2, Qf =15680GHz and τ_f = − 4.7×10⁻⁶/°C were obtained at the sintering temperature of 950 °C.

Abstract: It is necessary to improve the open circuit voltage of amorphous silicon solar cells for its applications. In this paper, we discuss the effects of hydrogen plasma treatment on the P layer and the performance of the amorphous silicon solar cells. The result shows that the open circuit voltage increased by 0.0257V, the fill factor increased by 0.039 and the energy conversion efficiency increased by 9%. The highest V_OC we got was 0.99V. Treating P layer with hydrogen plasma has been demonstrated to result in materials with improved crystalline volume fraction which was very effective to increase the light absorption of the intrinsic layer. What is more, it could be easily integrated into the amorphous silicon solar cell mass production process.

Abstract: Pure α-Bi₂O₃ with nanoneedle array structure was synthesized directly by hydrothermal method. The optic absorption of the α-Bi₂O₃ paricles was cut off at ~483 nm and the band gap of the α-Bi₂O₃ was estimated to be 2.57 eV. The photocatalytic activity of the α-Bi₂O₃ samples was higher than TiO₂ under a visible light irradiation. As a conclusion, relative narrow band gap of α-Bi₂O₃ nanoneedle array compared to anatase and the special morphology of nanoneedle array structures may improve the photocatalytic activity in visible light irradiation.

Abstract: A new tunnel-recombination junction model was proposed to increase the recombination of n/p junctions in tandem solar cells. According to the model, we fabricated a new tunnel junction with a nanostructured amorphous silicon p⁺ (na-Si p⁺) layer inserted between the n layer and the p layer. To compare with the conventional method, we fabricated another tunnel junction with an amorphous p⁺ (a-Si p⁺) insertion layer. Both devices were characterized by their dark current-voltage behavior (I-V), activation energy (E_a) and quantum efficiency (QE). The result shows that the tunnel junction with a na-Si p⁺ insertion layer has higher recombination rates with higher density of defect states of about 2.7×10¹⁹cm^-3 , lower resistance with activation energy of 22meV. The tunnel junction with a na-Si p⁺ insertion layer could be easily integrated into the tandem solar cell deposition process.

Abstract: ZrO₂ –PVP thin films were prepared with sol-gel and spin coating method. The films were characterized or examined by many kinds of instruments. With different heating treatment temperature, the surface toughness Ra of ZrO₂-PVP thin films are different from 0.421nm to 0.738. And 1-on-1 laser-induced damage threshold tests on ZrO₂ films were carried out with a Q–switched Nd-YAG high power laser at 1064 nm with a pulse width of 1ns. The experimental results showed that ZrO₂ thin films could achieve good surface micro morphology and high laser induced damage threshold.

Abstract: The electronic transport of the single molecule via different anchoring groups is studied using density functional theory in conjunction with the nonequilibrium Green’s function. The results show that the electronic transport properties are strongly dependent on the anchoring groups. Asymmetric electrical response for opposite biases is observed resulting in significant rectification in current. The transmission coefficients and spatial distributions of molecular orbitals under various external biases voltage are analyzed, and it suggests that the asymmetry of the coupling between the molecule and the electrodes with external bias leads to rectifying performance.

Abstract: TiO₂ nanoparticles doped with different cobalt concentrations were fabricated by using so-gel method. The crystal structures and the morphology of the samples were characterized by using x-ray diffractmetry (XRD) and transmission electron microscopy (TEM), respectively. It was found that all the samples are anatase phase and the nanoparticles are of the size around 10 nm. Investigations of the binding energies of different element with X-ray photoelectron spectrometry (XPS) revealed that Co ions are in Co²⁺ state and take the substitutional sites. No Co clusters were detected in the samples. The optical absorption properties of the samples were studied by using UV-vis absorption spectroscopy. It was noticed that cobalt doped TiO₂ has a significant visible light absorption in contrast to pure TiO₂: besides a noticeable red shift in absorption edge, an extra visible light absorption peak appears at a wavelength around 600 nm. The visible absorption in cobalt doped TiO₂ may attribute to the electron transition from impurity levels induced by the substitutional Co ions and the oxygen vacancies to the conduct band.

Abstract: Co_2.73Fe_0.27O₄ nanoparticles were synthesized using the heat-decomposition method followed by annealing treatment. X-ray diffraction (XRD) analysis shows that most of the peaks are close to the data for antiferromagnetic Co₃O₄, while weak peaks of CoFe₂O₄ are also detected. It indicates that the prepared particles can be reckoned as a composite with a small size of the FM particles embed in a large thickness of the AFM matrix. The magnetic hysteresis loops of Co_2.73Fe_0.27O₄ powders were measured at 10 K by using the zero-field cooling (ZFC) and field cooling (FC) procedures and show negative and downward shifts, and the shifts finally disappear when temperature increases to 200 K. We suggest that exchange bias effect in Co_2.73Fe_0.27O₄ is mainly related with the exchange interactions at the interfaces between the FM CoFe₂O₄ nanoparticles and the frozen spins around them.