Zhongquan Ma

Enhanced broadband emission from Er-Tm codoped ZnO film due to energy transfer processes involving Si nanocrystals

Er-Tm-Si codoped ZnO film was synthesized by co-sputtering, in which Si nanocrystals (Si-NCs) were observed to form by annealing at 1173 K for 30 min. A fairly flat emission with ∼375 nm bandwidth is achieved, and its intensity is enhanced by nearly an order of magnitude by the Si-NCs, which acted as broadband sensitizers, compared with that without Si-NCs. The film also exhibits broadband emission with relatively stable spectral shape under different excitation lines. The 1.80 μm emission intensity increases by a factor of 3 while the 1.53 μm emission is almost constant with decreasing the operating temperature from 300 to 20 K, attributed to competition between three energy transfer processes from Si-NCs to Er3+/Tm3+ and from Er3+ to Tm3+, and their back transfer processes.

Raman spectral analysis of TiO2 thin films doped with rare-earth samarium.

TiO(2) thin films doped with rare-earth samarium were prepared on a quartz plate by the sol-gel/spin-coating technique. The samples were annealed at 700 °C to 1100 °C, and the Raman spectra of the samples were obtained. Analyses of Raman spectra show that samarium doping can inhibit the anatase-rutile phase transition. Samarium doping can refine grains of TiO(2) thin films and increase the internal stress, thereby preventing lattice vibration. Nanocrystalline TiO(2) thin films obviously show the phonon confinement effect, i.e., the blueshift of characteristic Raman peak and full width at half-height increase, and the peak shapes asymmetrically broaden with a decrease in the grain sizes of the samples.

Temperature-dependent photoluminescence spectra of Er-Tm codoped calcium boroaluminate glasses

The temperature dependence of photoluminescence (PL) spectra of Er-Tm codoped calcium boroaluminate (CABAL) glasses with different dopant concentrations was investigated under 15-298 K, by pumping at 795 nm. The intensities of three band emissions located at 1.46, 1.53, and 1.80 μm decreased monotonically when increasing the temperature from at lower concentrations. However, the emissions peaked at 1.80 μm increase with the increasing temperature at higher concentrations. This was attributed to the increasing of cross relaxation (CR) resulting from the high doping concentration of Tm ions. This was evidenced by the much shorter fluorescence lifetime of 56 μs for the 3F4 emission due to 3F4→3H6 transition for the CABAL glass codoped with 2.00 mol.% Tm2O3, in comparison with 185 μs for that of 0.2 mol.% Tm2O3. The energy transfer (ET) and CR processes between Er3+ and Tm3+ ions have been discussed at different doping concentrations and operating temperatures. The nonexponential character of the decays of 4I(13/2) and 3H4 with the increasing concentration indicated the occurring of a dipole-dipole quenching processes in the framework of a diffusion-limited regime. The average critical distances of CR between Tm3+ ions and ET between Er3+ and Tm3+ ions were approximately 1 nm.

Multi-layer antireflection coatings for silicon solar cells using a sol-gel technique

In order to improve the opto-electronic conversion efficiency of solar cells, antireflection coatings (ARCs) have been drew a great attention for the application in the terrene. Generally, the coating is obtained by vacuum processing such as thermal evaporation, reactive sputtering and plasma-enhanced chemical vapor deposition (PECVD). In this work, multi-layer antireflection coatings have been performed by a modified sol-gel technique, which is low-cost and simple. The multi-layer films consisted of SiO2 and TiO2. The physical phase and morphology of each layer were characterized by atomic force microscopy (AFM). The TiO2 single-layer and SiO2/TiO2 double-layer antireflection coatings were respectively annealed at 150°C, 350°C and 550°C. The sols of TiO2 and SiO2 were aged for 24 hours and then were spin coated on the Si substrate. It was found that the reflectance of double-layer ARCs was generally lower than that of single-layer ones. The reflectance of films without being aged was lower than that of sols were aged for 24 hours. In all samples, the SiO2/TiO2 double-layer film which was annealed at 150°C and which sols were not aged for 24 hours had the lowest reflectance.

Synthesis of ordered ZnO nanorod film on ITO substrate using hydrothermal method

By using low cost, low-temperature hydrothermal approach and spin-coating technique, well-aligned ZnO nanorods have been successfully prepared on ITO substrates. The ITO substrate was pre-patterned with ZnO particles as a seed layer for the subsequent nucleic hybridization. The intuitionistic crystallinity of oriented ZnO nanorod array was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. It is shown that the preferred orientation growth of the wurtzite structure along (002) plane is easily obtained with the approach. The size of the ZnO nanorods has been found to be dramatically dependent on the concentration of zinc content in the solution.

Global structure search and physical properties of Os2C.

The crystal structures of Os2C were extensively investigated using the structure search method from the first-principles calculations. In contrast to the P6 3 /mmc phase previously proposed as the ground state at ambient pressure, an energetically favorable structure with space group P-6m2 was found more stable at ambient condition. The structural stabilities of the new phase are confirmed by the phonon dispersion and elastic constants. Further calculations indicate that the newly predicted P-6m2 phase is ultra-incompressible with a high bulk modulus of 387 GPa and has a larger ideal shear strength than the P6 3 /mmc phase.

Bifunctional Hybrid a-SiOx(Mo) Layer for Hole-Selective and Interface Passivation of Highly Efficient MoOx/a-SiOx(Mo)/n-Si Heterojunction Photovoltaic Device

The promising n-Si-based solar cell is constructed for the purpose of realizing hole- and electron-selective passivating contact, using a textured front indium tin oxide/MoO x structure and a planar rear a-SiO x/poly(Si(n+)) structure severally. The simple MoO x/n-Si heterojunction device obtains an efficiency of 16.7%. It is found that the accompanying ternary hybrid SiO x(Mo) interlayer (3.5-4.0 nm) is formed at the MoO x/n-Si boundary zone without preoxidation and is of amorphous structure, which is determined by a high-resolution transmission electron microscope with energy-dispersive X-ray spectroscopy mapping. The creation of lower-oxidation states in MoO x film indicates that the gradient distribution of SiO x with Mo element occurs within the interlayer, acting as a passivation of silicon substrate, which is revealed by X-ray photoelectron spectroscopy with depth etching. Specifically, calculations by density functional theory manifest that there are two half-filled levels (localized states) and three unoccupied levels (extended states) relating to Mo component in the ternary hybrid a-SiO x(Mo) interlayer, which play the roles of defect-assisted tunneling and direct tunneling for photogenerated holes, respectively. The transport process of photogenerated holes in the MoO x/n-Si heterojunction device is well-described by the tunnel-recombination model. Meanwhile, the a-SiO x/poly(Si(n+)) has been assembled on the rear of the device for direct tunneling of photoinduced electrons and blocking photoinduced holes.

J sc improvement of CdS/Cu(In,Ga)Se 2 solar cells after rapid thermal annealing

The thermal dynamic influence of microstructure and physical phase leading to the variation on the short-circuit density (Jsc) for the large size of CIGS solar cell has been investigated by the subsequent rapid thermal annealing (RTA) and optical and electrical analyses, respectively. The annealing temperature of 300°C is an optimized point for a high efficiency of 11.75% to a 125 × 125 mm2 cell. The photoluminescence (PL) and Raman spectra are used to electrical analysis on the improvement of Jsc. After RTA at 300°C treatment, the PL intensity increase about 15 times accompany with the vanish of deep level centers or traps such as vacancies and interstitials. The feature of the intensity and FWHM of Raman peak A1 is related to the grain sizes. The results indicate that subsequent thermal treatment of CIGS device directly leads to the reduction of deep levels and an increase of the concentration of minor carriers. The observation from the front reflection spectrum (FRS) and atomic force microscope (AFM) indicates that the increase of surface roughness causes the decrease of front reflection. It is obvious that the enhancement of Jsc can be ascribed to the less optical losses on the surface reflection and the increase of the diffusion current in the bulk.

THE SURFACE AND INTERFACE BEHAVIOR OF EMITTER REGION OF SOLAR CELLS IN PRODUCT LINE

Based on the Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), the specific surface and interface characteristics of emitter region of commercial mono-crystal Si solar cells were examined. Four chemical compositions C, O, Si, and P were detected, and the atomic concentrations (%) of C and O at the surface were much higher than their solid solubility in mono-crystal Si. The high concentration of C and O at the surface was attributed to adhered remains. The single element Si, stable oxide SiO2, as well as intermediate oxidation states such as Si1+ and Si3+ corresponding to Si2O and Si2O3, respectively, have been analyzed. The atomic concentrations (%) of these compositions and their respective chemical states at the surface and interface are likely correlative to the various defects such as electronic-like ramification of hanging bonds, vacancy cluster, or dislocations. Furthermore, the normalized quantum efficiency (QE) of the solar cells made from the wafers was measured to be lower than 74% at short wavelength (

The role of ion-assisted deposition in PVD

An optimal energy interval in ion-assisted deposition of high crystalline films is predicted in the modeling of ion impacting on surface. The result is in good agreement with the presented experiments. The possible application of the evaluation of ion role for the fabrication of potential thin film materials is expected.