Heat treatment of amorphous silicon p-i-n solar cells with high-pressure H2O vapor

We report improvement in characteristics of hydrogenated amorphous silicon (a-Si:H ) p-i-n structured solar cells by high-pressure H₂O vapor heat treatment. a-Si:H p-i-n solar cells were formed on glass substrates coated with textured SnO₂ layer. P-, i-, and n-type a-Si:H layers were subsequently formed by plasma enhanced chemical vapor deposition. Finally an indium-tin-oxide layer was coated on the n-type a-Si:H surface. Heat treatment at 210 °C with 2 × 10⁵ Pa H₂O vapor for 1 h was applied to the a-Si:H p-i-n solar cells. Electrical characteristics were measured when samples were kept in dark and illuminated with light of AM 1.5 at 100 mW/cm². The heat treatment with H₂O vapor increased fill factor (FF) and the conversion efficiency from 0.54 and 7.7% (initial) to 0.57 and 8.4%, respectively. Marked improvement in solar cell characteristics was also observed in the case of a poor a-Si:H p-i-n solar cell. FF and the conversion efficiency were increased from 0.29 and 3.2% (initial) to 0.56 and 7.7%, respectively.     

Structures of grain boundaries in sintered silicon

The investigation of near coincidence boundaries in sintered silicon by transmission electron microscopy revealed a fine structure (steps, dislocations). For a Σ = 9 coincidence orientation it will be demonstrated that faceting of an inclined grain boundary reduces the total energy.     

Enhanced diffusion of phosphorus at grain boundaries in multicrystalline silicon

Two different methods were applied to examine the diffusion of phosphorus at grain boundaries in silicon. Five solar-cells processed on multicrystalline silicon were investigated. These cells are distinguished by different materials, diffusion-temperature, and further preparation. Enhanced diffusion at grain boundaries was observed in two of these cells with both methods. One solar cell also showed enhanced diffusion at dislocations. A correlation of the phosphorus diffusion and an enhanced recombination activity of the grain boundaries of these cells is found.     

Effect of growth conditions on formation of grain boundaries in epitaxial silicon layers

The formation of grain boundaries of the general type, along with small-and large-angle symmetric grain boundaries with the 〈 〉 axis in the epitaxial layers grown onto bicrystal substrates by the method of thermal migration has been studied. The solvent was aluminum. It is shown that if the grain boundaries in the epitaxial layer are tilted to the crystallization front or if there is a temperature gradient tangential to this front, their orientation differs from their orientation in the substrate. The large-angle symmetric boundaries are more stable than the boundaries of the general type. The grain-boundary energy and rotation moment of large-angle symmetric boundaries are evaluated.     

Microscopic properties of silicon dihydride bonding in a-Si:H

We use proton nuclear magnetic resonance to probe stable silicon dihydride existing in high defect density hydrogenated amorphous silicon. The silicon dihydride line shape exhibits the well-known ‘Pake’ doublet form resulting from a dipole interaction between two protons. We simulate the line shape using the relevant Hamiltonian and broadening effects known to occur in this amorphous system and discuss the sets of simulation parameters that reproduce the experimental data. The sets share a common feature – they require the proton–proton separation to be approximately 1.8 Å, not the 2.4 Å determined by recent theoretical calculations.     

Configuration of grain boundaries

In the present paper a model of the configuration of grain boundaries from a general point of view in the framework of the CSL concept has been developed. Rotations and rotations with translations were taken under consideration. The main result is the determination of the coincidence conditions for symmetrical and asymmetrical grain boundary facets between two and three grains. The facet angles of grain boundaries in any crystal surface are determined.     

Controlling the quality of nanocrystalline silicon made by hot-wire chemical vapor deposition by using a reverse H2 profiling technique

Hydrogen profiling, i.e., decreasing the H₂ dilution during deposition, is a well-known technique to maintain a proper crystalline ratio of the nanocrystalline (nc-Si:H) absorber layers of plasma-enhanced chemical vapor-deposited (PECVD) thin film solar cells. With this technique a large increase in the energy conversion efficiency is obtained. Compared to PECVD, the unique characteristics of hot-wire CVD (HWCVD), such as the catalytic reactions, the absence of ion bombardment, the substrate heating by the filaments and filament aging effects, necessitate a different strategy for material and device optimization. We report in this paper the results of using a reverse H₂ profiling technique, i.e., increasing the H₂ dilution of silane instead of decreasing it, to improve the quality of HWCVD intrinsic nc-Si:H and the performance of this material in single junction n-i-p cells. Thus far, the efficiency of nc-Si:H n-i-p cells made on a stainless steel substrate with an Ag/ZnO textured back reflector has been improved to 8.5%, and the efficiency of triple junction solar cells with a structure of proto-Si:H(HWCVD) top cell/proto-SiGe:H (PECVD) middle cell/nc-Si:H (HWCVD, with reverse H₂ profiling) bottom cell has reached 10.9%. These efficiency values show the viability of n-i-p cells comprising HWCVD nanocrystalline i-layers.     

Relation of defects and grain boundaries to transport and photo-transport: Solved and unsolved problems in microcrystalline silicon

Defects and grain boundaries play a crucial role in the dark and photo-transport of charge carriers. Surprisingly, the transport (trapping and recombination) in microcrystalline silicon is better understood at low temperatures, while room-temperature operation is of interest for real-life devices. In the first part of this review, the advantages of photo-transport techniques, used for the defect density evaluation, will be recapitulated and commented on. The second part is devoted to the present understanding of the specific features of transport in microcrystalline silicon like anisotropy, dominant transport path and the role of H and O in the grain boundary formation. The results of macroscopic measurements on series of samples will be confronted with the results of local conductivity studies on a nanometer scale and finally, the influence of oxygen and the ability to explain it by our model of transport will be illustrated.     

BaBPO5和(H3O)Zn(H2O)2BP2O8·H2O的低温溶剂热合成及表征

以乙醇为溶剂,在低温条件下合成出了两种手性硼磷酸盐化合物BaBPO5(1)(T=120℃,t=5d)和(H3O)Zn(H2O)2BP2O8·H2O (2)(T=80℃,t=5d).XRD单晶衍射仪测定了化合物的结构,结果表明:(1)属三方晶系,P3221空间群,a=b=7.1162(3)(A),c=6.9979(6),(A)=3,该晶体含有一维线性链状阴离子结构;(2)属六方晶系,P6122空间群,a=b =9.513(2)(A),c=15.906(8),(A)=6.该晶体具有三维骨架结构.实验结果表明使用乙醇作溶剂可以极大降低硼磷酸盐的合成温度,进而有助于获得手性硼磷酸盐化合物,这为手性硼磷酸盐的合成提供了一种新思路.     

Elastic properties of the dithionates Na2S2O6 · 2 H2O,K2S2O6, Rb2S2O6, CaS2O6 · 4H2O and SrS2O6 · 4 H2O

Single crystals of the title compounds having optical quality and dimensions of several cm were grown from aqueous solutions. The elastic and thermoelastic constants were determined from ultrasonic resonance frequencies of thick plates. The true point symmetry of K₂S₂O₆ and Rb₂S₂O₆, which is screened by a hexagonal hypermorphy, could be clearly revealed to be trigonal (32) by the existence of the elastic constant c₁₄. In the case of CaS₂O₆ · 4H₂O and SrS₂O₆ · 4H₂O the constant c₁₄ of the specimens appeared too small to confirm the trigonal symmetry group required from electrooptic and non-linear optic effects unambiguously. The isotypy of K₂S₂O₂ and Rb₂S₂O₆ as well as that of CaS₂O₆ · 4H₂O and SrS₂O₆ · 4H₂O is confirmed by their elastic behaviour. The mean elastic stiffness of dithionates is closely related to that of the corresponding sulphates. In the vicinity of the second-order phase transition of K₂S₂O₆ near 235 K weak anomalies of the temperature derivatives of the longitudinal elastic stiffnesses are observed.     

Mechanisms of chemical vapor deposition of silicon

The distribution in the silicon epitaxial growth from SiCl₄ and hydrogen are observed in situ by IR absorption spectroscopy. Two methods are used complementarily, one is IR spectroscopy of reactants extracted from the reactor by a fine quartz tube which is not disturbing the reactions, and gives knowledge about the local distribution, the other is direct IR spectroscopy of hot reactants in the reactor which is useful to ascertain the results at the real high temperature situation. The intermediate species are SiHCl₃, SiH₂Cl₂ which is estimated from the induced emission bands at 500 and 570 cm^-1. HCl is a dominant waste product and contributes to reverse reactions. To investigate the reaction, HCl is intentionally injected into the reacting gas. This kind of injection method may also be very effective to analyze the reactions using other reactants such as SiCl₄, SiHCl₃ and SiH₂Cl₂.     

Morphology of cells at the grain boundaries of an anisotropic material

We have studied the formation of ridges on the grain boundaries of an anisotropic crystal known as pivalic acid. These results are compared with very well studied another isotropic material succinonitrile to understand the formation of defects in anisotropic crystals. Preliminary results show that along with anisotropy, orientation has a large influence on the morphology of solid-liquid interface formed after planar interface becomes unstable. The formation of ridges and hence the defects at the interfaces are more favoured in highly anisotropic materials.     

Growth of amorphous SiO2 nano-wires on pre-oxidized silicon substrate via chemical vapor deposition

Without an additional silicon source, amorphous SiO₂ nano-wires were grown on the pre-oxidized silicon substrate with the assistance of Ni-based catalyst under ambient pressure. The as-grown amorphous SiO₂ nano-wires were characterized by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and selected area diffraction. The micro-region chemical composition investigation on the as-grown amorphous SiO₂ nano-wires was carried out using X-ray energy dispersion spectroscopy (EDS) on the HRTEM. The present work focuses on the formation of atomic H on the surface of pure zinc powder by introducing moisture (N₂ + H₂O) into the furnace at high temperature. The growth mechanism has been discussed and attributed to the vapor–liquid–solid (VLS) mechanism instead of the adopted solid–liquid–solid (SLS) mechanism owing to the observed evidence of an etching reaction of atomic H at the SiO₂ buffer layer and/or that of H at the Si substrate to form a gaseous hydro-silicon radical (SiH_x) that is then transported to the growth sites. The intrinsic luminescent behavior of the amorphous SiO₂ nano-wires in the range of 350–430 nm was also reported and discussed. These results provide an alternative and simple procedure for nanostructures growth, which will be helpful to understand the growth mechanism of one dimensional SiO₂ nanostructures.     

Linear Optical Properties of the Nonlinear Optical Calcium and Strontium Tartrato-Antimonates (III), Ca[Sb2 {(+) - C4H2O6}2] x2H2O and Sr[Sb2{(+) - C4H2O6}2 ] x2H2O

The study of nonlinear optical properties of crystals requires a thorough knowledge of the linear optical properties: knowledge of the transparency range is necessary, some information about the optical activity is useful. Above all, high quality refractive indices (with errors less than 10^-4) and their dispersion are the most important basic data, as they enable a detailed analysis of phase-matching conditions of nonlinear optical processes and an estimation of the nonlinear optical potential of a new non-centrosymmetric crystal. Such high quality refractive indices are also necessary in other areas of nonlinear optics, for example for the evaluation of nonlinear optical measurements like measurements of Maker fringes. In this short communication we present the linear optical basis for nonlinear optical investigations of the title compounds. The Sr compound has been known for a long time; its morphological crystallography is already presented in the famous Chemische Krystallographie by Paul Groth (1910). The Ca salt was first synthesized 1983 by one of us (L.B.).     

Various Growth Shapes of Na2S2O3 5H2O Crystals

The relation between the growth shapes and supersaturations and/or supercoolings was investigated in the Na₂S₂O₃ 5H₂O crystals: (i) The growth shapes changed from a hexagonal prismatic crystal, aggregate of platy crystals and to a spherulite with an increase of supersaturations and/or supercooloings. (ii) The deposition rate suddenly increased at a certain supersaturation and/or supercooling, where the growth shape changed from the hexagonal prism to the aggregate of platy crystals. (iii) The deposition rates of spherulites become higher with increasing the solute concentrations. (iv) The formation process of the spherulites were in situ observed by the Schlieren and/or Mach‐zehnder interferometer methods.     

Vacuum-ultraviolet absorption of interstitial O2 and H2O molecules in SiO2 glass

Vacuum-ultraviolet (VUV) absorption of O₂ and H₂O molecules incorporated in interstitial voids in SiO₂ glass by thermal annealings was examined. Interactions of the interstitial molecules with the surrounding SiO₂ glass network lead to a redshift of the VUV absorption band of interstitial O₂, while a blueshift of that of interstitial H₂O, both accompanied by an increase in the intensity of the absorption bands. The Coulomb repulsion, London dispersion, and hydrogen bonding are the main interactions responsible for the modification of the VUV absorption bands.     

Characterisation of the Six-coordinated Octahedral Site in Cd(C4H2O4) · 2H2O Crystals

Optical absorption spectra of Co(II) and Ni(II) doped cadmium maleate dihydrate (CMDH) are recorded at room temperature and liquid nitrogen temperature. The UV–VIS–NIR spectra are characteristic of the transition metal ions in solids. The results and analyses of the spectra indicate near octahedral site symmetry for cobalt ion and trigonally distorted octahedral site symmetry for nickel ion. The following crystal field parameters are derived. The IR spectra are characteristic of the host lattice CMDH.     

Cracking assisted nucleation in chemical vapor deposition of silicon nanoparticles on silicon dioxide

Deposition of sub-monolayer silicon on SiO₂/Si(1 0 0) greatly facilitates nucleation in subsequent thermal chemical vapor deposition (CVD) of silicon nanoparticles. Sub-monolayer seeding is accomplished using silicon atoms generated via disilane decomposition over a hot tungsten filament. The hot-wire process is nonselective towards deposition on silicon and SiO₂, is insensitive to surface temperature below 825 K, and gives controlled coverages well below 1 ML. Thermal CVD of nanoparticles at 1×10⁻⁴ Torr disilane and temperatures ranging from 825 to 925 K was studied over SiO₂/Si(1 0 0) surfaces that had been subjected to predeposition of Si or were bare. Seeding of the SiO₂ surface with as little as 0.01 ML is shown to double the nanoparticle density at 825 K, and densities are increased twenty fold at 875 K after seeding the surface with 30% of a monolayer.