Liquid Phase Crystallization Research Articles

The liquid–liquid phase separation and crystallization of vanillin in 1-propanol/water solution

In this study, the liquid–liquid phase separation and crystallization of vanillin from 1-propanol/water solution were investigated. It was found that water could contribute to the improvement of vanillin solubility in 1-propanol/water solution, but the solubility of vanillin decreased with the increasing water/1-propanol ratios, when the water content was over 30 wt.%. High water fraction in 1-propanol/water solvents will result in the liquid–liquid phase separation in the crystallization process, and the liquid–liquid phase separation dominated the process before the nucleation of crystals during the crystallization of vanillin. A ternary phase diagram (vanillin/1-propanol/water) including the solubility curves and the liquid–liquid phase separation curves was measured and could, in certain cases, clearly illustrate the liquid–liquid phase separation and crystallization process of vanillin in 1-propanol/water solutions. As shown in the ternary phase diagram, liquid–liquid phase separation under high initial vanillin concentration results in low purity of vanillin crystals due to the inhibited crystallization process by liquid–liquid phase separation. Partial phase immiscibility was a function of temperature and the range of immiscibility decreased with increasing temperature. Moreover, nucleation and crystal growth of vanillin in the presence of liquid–liquid phase separation were investigated; process parameters such as the composition of solvent, cooling profiles and seeding were optimized to avoid liquid–liquid phase separation and thus increase the purity of crystallization products.

Properties of Liquid Phase Crystallized Interdigitated Back-contact Solar Cells on Glass

We fabricated interdigitated back-contact silicon hetero-junction solar cells based on thin-film absorbers on glass. The Si absorbers were directly deposited on the glass and crystallized using liquid phase crystallization. To compare whether our contact system is applicable to a wide range of initial absorber conditions two different types of precursors were prepared with absorber thicknesses between 2.5-9μm. Furthermore, glass superstrates, doping densities and interlayer stacks were varied. With a KOH random pyramid light trapping texture at the back more than 30mA/cm2 were achieved on an electron beam evaporated precursor material and 655mV on a PECVD precursor material.

Effects of front and rear texturing on absorption enhancement in laser-crystallized silicon thin-films on glass

The paper reports effects of front and rear texturing and their combinations on absorption enhancement in liquid phase crystallized (LPC) silicon (Si) thin-films on glass. In order for Si films to remain continuous after LPC, the root-mean-square (RMS) roughness of the glass at the glass–Si interface has to be less than 600 nm. The LPC Si on textured glass produces elongated grains of several hundred microns in width and up to centimeters in length, comparable to the films crystallized on planar glass. Texturing of the glass–Si interface is found to give the highest potential Jsc; 25.3 mA/cm2, or 24% enhancement compared to a planar reference film, with air as back surface reflector. It confirms the largest light-trapping effect at this interface in superstrate-oriented LPC Si thin-film solar cells due to both lower reflection and enhanced light scattering over the whole solar spectrum.

Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

Liquid phase crystallized Si thin-film solar cells on nanoimprint textured glass substrates exhibiting two characteristic, but distinct different surface structures are presented. The impact of the substrate texture on light absorption, the structural Si material properties, and the resulting solar cell performance is analyzed. A pronounced periodic substrate texture with a vertical feature size of about 1 μm enables excellent light scattering and light trapping. However, it also gives rise to an enhanced Si crystal defect formation deteriorating the solar cell performance. In contrast, a random pattern with a low surface roughness of 45 nm allows for the growth of Si thin films being comparable to Si layers on planar reference substrates. Amorphous Si/crystalline Si heterojunction solar cells fabricated on the low-roughness texture exhibit a maximum open circuit voltage of 616 mV and internal quantum efficiency peak values exceeding 90%, resulting in an efficiency potential of 13.2%. This demonstrates that high quality crystalline Si thin films can be realized on nanoimprint patterned glass substrates by liquid phase crystallization inspiring the implementation of tailor-made nanophotonic light harvesting concepts into future liquid phase crystallized Si thin film solar cells on glass.

Towards monocrystalline silicon thin films grown on glass by liquid phase crystallization

Liquid phase crystallization of silicon is a promising technology to grow crystalline silicon thin films on glass. It has already been demonstrated that open circuit voltages of up to 656mV and efficiencies of up to 11.8% can be achieved by this technique. Nevertheless further improvements are required to become competitive with wafer based silicon solar cells. A possibility to improve the quality is to enlarge the grain size and to control the crystallographic orientation of the resulting layers. While a preferential {100} surface orientation can be triggered utilizing suitable crystallization parameters, the in-plane orientation still remains random. Also the grain size stays within the same range. By introducing a local monocrystalline seed at the beginning of the crystallization process, we are able to control both the surface and the in-plane orientation of the silicon films. In addition the grain size is significantly increased in scanning direction and only limited by the substrate size of 5cm. This high morphological quality is accompanied by an improved electrical quality confirmed by photoluminescence imaging and Hall measurements. This is a big step towards the final goal to directly grow monocrystalline silicon thin films on glass substrates.

Change of Structure and Properties of Sintered Alloys under the Influence Nanosized Carbon Additives

There was considered influence of nanosized carbon additives on structural phase state and properties of the sintered alloys on the copper, iron and tungsten-cobalt base. There was demonstrated that under liquid phase sintering and crystallization process of powder compositions that contain nanosized carbon particles. non-dissolved fraction of nanosized additive could be stands as additional nucleation centers, that promotes atomization of structure. There was established that for alloys that could be form solid solutions with carbon or hardening carbide phases. nanosized diamond- graphite additives increase of hardness of sintered composites and improve its tribotechnical characteristics

Preferential {100} grain orientation in 10 micrometer-thick laser crystallized multicrystalline silicon on glass

Liquid phase crystallization of 10μm thin silicon layers on glass substrates was performed with a line-shaped continuous wave laser beam. The process window was investigated in terms of the scanning velocity of the laser, the pre-heating of the specimens and the applied laser intensity. We have identified the entire process window, in which large-scale crystallization without deformation or destruction of the substrate and cracking of the silicon layer can be obtained. The grain orientations of the resulting Si layers were analyzed using both electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The influence of the critical crystallization parameters on the grain orientation of the silicon film was examined. EBSD and XRD measurements show that a preferential {100} surface texture and {100} and {101} orientations in scanning direction of the laser can be achieved if appropriate crystallization parameters are used. This texture formation is accompanied with a substantial decrease of high angle grain boundaries.

MoO3 incorporation in magnesium aluminosilicate glasses

Molybdate has a very low solubility in silicate and borosilicate glass systems and its excess presence in nuclear waste glass can cause the formation of a readily soluble “yellow phase”. In this study, the incorporation of molybdenum oxide (MoO3) in a magnesium aluminosilicate glass system has been investigated. The prepared glasses show a higher than 90% molybdenum retention rate and up to 5.34mol% (12.28wt%) MoO3 can be incorporated into these glasses without causing visible phase separation. The incorporation of MoO3 increases glass density, decreases glass transition and crystallisation temperatures and intensifies Raman bands assigned to vibrations of MoO42− units. When excess molybdate is added liquid–liquid phase separation and crystallisation occurs. The separated phase is spherical, 200–400nm in diameter and randomly dispersed. Based on powder X-ray diffraction, Raman spectroscopy and transmission electron microscopy, the separated phase is identified as MgMoO4.

Silicon Thin-Film Solar Cells on Glass With Open-Circuit Voltages Above 620 mV Formed by Liquid-Phase Crystallization

Liquid-phase crystallization (LPC) using line-shaped energy sources such as laser or electron beam has proven to be a suitable method to grow large grained high-quality silicon films onto commercially well-available glass substrates. In this study, we compare cw-diode laser-crystallized absorbers with electron beam-crystallized material using back contacted back junction solar cells. Furthermore, the influence of the absorber doping concentration thickness on the solar cell performance is studied. Using experimental data obtained on test structures, as well as solar cells and 1-D device simulations, an ideal dopant concentration is determinedtobe 2 - 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , in combination with an absorber thickness of 10-20 μm. Finally, we present a slightly modified cell process to reduce the optical losses, which resulted in conversion efficiencies of up to 11.8%.

Micro-structural defects in polycrystalline silicon thin-film solar cells on glass by solid-phase crystallisation and laser-induced liquid-phase crystallisation

The microstructural properties of polycrystalline silicon films obtained by either solid-phase crystallisation (SPC) or laser-induced liquid-phase crystallisation (LPC) were investigated by transmission electron microscopy (TEM). In SPC films, the most common intra-grain defects are dislocations with the density as high as 1E10cm−2 determined from cross-sectional weak-beam dark-field images. The highest dislocation density in LPC film is at least two orders of magnitude lower than the SPC film, 1E8cm−2 and typically it is below 1E6cm−2. The most common defect type in LPC films is twin boundaries and other junctions of different coincidence site lattice (CSL) boundaries. Such differences in the material structural properties result in far superior electrical performance of solar cells made of LPC films, such as mobility up to 400cm2V−1s−1, similar to c-Si wafers, and the higher open-circuit voltage up to 585mV.

Double-side textured liquid phase crystallized silicon thin-film solar cells on imprinted glass

Emerging liquid phase crystallization (LPC) techniques recently rendered a possible substantial progress in the fabrication of high quality crystalline silicon thin-film solar cells on glass. The implementation of an efficient light trapping texture into such LPC silicon devices is still challenging as an excellent bulk material quality and well-passivated interfaces have to be guaranteed. In this paper we present recent advances in light management for LPC silicon thin-film solar cells on imprinted glasses. A double-sided 2µm periodic texture is realized by sandwiching the silicon film during the electron-beam induced crystallization process between an imprinted glass substrate coated with silicon oxide and a silicon oxide capping layer. Amorphous-crystalline silicon (a-Si:H/c-Si) heterojunction solar cells with single sided contacting scheme are fabricated. Textured prototype devices and simultaneously processed planar solar cells exhibit a comparable electronic material quality featuring open circuit voltages above 550mV and efficiencies up to 8.1%. Optical absorption properties of 10µm thick double-side textured silicon films even predict maximum achievable short circuit current densities in solar cells up to 38mA/cm2 assuming zero parasitic absorption.

Thermal stresses and cracking behavior during laser crystallization of silicon on glass for thin film solar cells

, Phone: þ49 3641 206 459, Fax: þ49 3641 206 499During the preparation of silicon thin film solar cells on glasssubstrates by diode laser induced liquid phase crystallization(LPC), cracking is an issue. This is due to thermal stressescaused by high temperature gradients withinthe sample. In thispaper, the relation between thermal stress and the temperaturedistribution within the sample during LPC is discussed.Experiments for two sets of laser irradiation parameters weredoneleading to crack free or crackedcrystallization of the film.Additionally, the evolution of temperature during LPC wasmodeled numerically. Based on the simulation, the thermalstresses introduced were calculated. The complex viscoelasticproblem was simplified to an elastic multilayer model, whichcan be solved analytically. The theoretical results can explainthe experimental behavior.

Towards wafer quality crystalline silicon thin-film solar cells on glass

In this paper we present our latest progress in fabricating high quality crystalline silicon thin film solar cells on glass. Large silicon grains are directly formed via electron-beam induced liquid phase crystallization (LPC) from a nanocrystalline precursor film. The LPC process is carried out on an amorphous SiO2 layer, and both a high quality self-passivating interface and excellent electronic bulk properties are obtained. Solar cells with stable efficiencies of 11.5% and open-circuit voltages well above 600mV with a maximum value of 656mV are presented. So far, such high VOC values have only been achieved on wafer-based silicon solar cells.

Formation of chromium hydride in chromium being electrodeposited alloyed with hydrogen

The aim of the work was experimental verification of validity of the recently discovered phenomenon of phase formation through a stage of liquid state in metals being electrodeposited. The idea of the work was based on the known fact, that during crystallization of liquid phase of a transitional metal (e.g. chromium) alloyed in significant concentration with non-metal of minor atomic radius (e.g. hydrogen) intermediate phases with simple crystal lattices (e.g. hydrides) appear. Therefore, if in electrodeposited chromium alloyed with hydrogen the chromium hydride will be detected, this result will indicate validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited. To find the variants of chromium alloying with hydrogen during its electrodeposition the method for estimation of the degree of hydrogen saturation of metals being electrodeposited was developed. Electrodeposition of chromium was accomplished in such conditions where the volume of hydrogen being formed on the cathode was 62700 times higher than the volume of chromium being formed, which indicated alloying of chromium during its electrodeposition with hydrogen in significant concentration. On the basis of the accomplished experiments the formation of chromium hydride during electrodeposition of chromium alloyed with hydrogen was found. The conclusion, that existence of intermediate phases in electrodeposited metals is a result of crystallization of liquid metallic phase being formed during electrochemical deposition of metals, was made. The obtained result proves the validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited.

Reentrant condensation, liquid–liquid phase separation and crystallization in protein solutions induced by multivalent metal ions

Abstract We briefly summarize the recent progress in tuning protein interactions as well as phase behavior in protein solutions using multivalent metal ions. We focus on the influence of control parameters and the mechanism of reentrant condensation, the metastable liquid–liquid phase separation and classical vs. non-classical pathways of protein crystallization.

Conversion efficiency and process stability improvement of electron beam crystallized thin film silicon solar cells on glass

Liquid phase crystallization (LPC) using e-beam or CW-laser line sources of amorphous or nanocrystalline silicon films has emerged as new method to form high quality absorbers on cheap substrates. A disadvantage of electron beam crystallization was the necessity to use amorphous SiCx layers in contact with the silicon to maintain a stable crystallization process, resulting in high surface recombination. In this work we investigate capping layers to enable e-beam induced LPC on alternative interlayer materials especially SiO2 and characterize the morphological and electrical properties of these layer stacks. Photoluminescence measurements of LPC absorbers on SiO2 layers exhibit significantly increased radiative recombination compared to SiCx. Fabricated hetero-junction cells achieved a new emitter area efficiency record for electron beam induced LPC solar cells of 9% using the FrontERA contact system and H passivation.

SAPO-34分子筛晶化过程的研究

The structure and composition of SAPO-34 zeolite synthesized by conventional hydrothermal process and dry gel liquid phase crystallization process were investigated by XRD,SEM,ICP-AES and MAS NMR characterization methods.The results showed that SAPO-34 zeolite with impurity was obtained by conventional hydrothermal process.Impurity was appeared due to fewer active silicon species with high rate of silica source depolymerization and polycondensation.Pure SAPO-34 zeolite was synthesized by dry gel liquid-phase crystallization process.The rate of nucleation and growth was controlled by slower rate of silica source depolymerization.Samples of relative crystallinity increased gradually.

Liquid-phase separation and crystallization of high silicon canasite-based glass ceramic

The phase separation of high silicon composition 7.6Na2O·4K2O·8.4 CaO·70SiO2·8.9 CaF2·1.0 Al2O3 canasite-based glass ceramic during heat treatment was studied. The crystallization rate of calcium fluoride and canasite was estimated by using quantitative analysis of XRD. The non-isothermal DTA study shows that high silicon content increases the activation energy and restrains the crystallization of canasite appropriately. Through FE-SEM and SAXS, the early stage liquid–liquid phase separation was discovered in this kind of glass ceramic by long time heat treatment at 555°C. Interestingly, the SAXS result shows that the small scale liquid–liquid phase separation has existed in the glass matrix intrinsically even after quenching.

Interpreting the Activated Rate Theory for Solid-Phase Crystallization: Comparing Lactose and Sucrose

The activated rate theory (ART) for solid-phase crystallization has been interpreted to assess its key features with previous data for spray-dried lactose and new data for spray-dried sucrose. The theory implies that the kinetic parameters for the two sugars should be different due to the differences in their structural configurations. The activation enthalpy for solid-phase crystal growth has been found to be 39 ± 2 kJ/mol for lactose and 68 ± 4 kJ/mol for sucrose. These activation enthalpies are close to the values for liquid-phase crystallization (40 kJ mol−1 for lactose; 66–75 kJ mol−1 for sucrose) from previous literature, suggesting that the theory might apply to both liquid- and solid-phase crystallization. There are also physical arguments for suggesting that the activated state in the new theory has features of both solid- and liquid-phase crystallization. For lactose and sucrose, the crystal growth rate constants at 25°C have been found to be 1.4 × 10−4 s−1and 2.5 × 10−5 s−1, respectively, similar to the literature values of 1.3 × 10−4 s−1and 3 × 10−5 s−1, respectively. The difference in the thermodynamic parameters between the two sugars has been found to be significant, as expected from the differences in their structures. Interpreting the sucrose data in terms of the Williams-Landel-Ferry equation and the Avrami equation has shown their limitations and inconsistencies for the new sucrose data, as found previously for lactose. Key features of the ART are highlighted and discussed. These features include minimum activation enthalpies and maximum activation entropies at particular moisture contents for each sugar and minimum and maximum moisture contents below which crystallization is predicted to occur very slowly.

Polycrystalline silicon on glass thin-film solar cells: A transition from solid-phase to liquid-phase crystallised silicon

The paper presents a review of major features of the crystalline silicon on glass (CSG) technology, its achievements, limitations and challenges, and latest developments. CSG cells are fabricated by solid-state crystallisation (SPC) of 1.5–3.5 µm thick precursor diodes prepared by PECVD or ebeam evaporation followed by thermal annealing, hydrogen passivation and metallisation. The highest efficiency of 10.4% was demonstrated on a PECVD minimodule on textured borosilicate glass. The best performing ebeam-evaporated cells on planar glass reached 8.6% efficiency. CSG cells were also produced on low-cost soda-lime glass with 8.1% and 7.1% efficiencies on PECVD and ebeam material respectively. The performance of SPC CSG cells is limited to below 11% because high defect density in SPC material limits VOC and 1.5–3.5 µm cell thickness limits JSC. A breakthrough came about when thicker poly-Si films with low defect density on glass were prepared by liquid-phase crystallisation (Amkreutz, 2011) leading to development of the next generation, liquid-phase crystallised silicon on glass (LPCSG) solar cells. The best performing LPCSG cells are made by line-focus laser crystallisation of 10 µm thick ebeam silicon films on dielectric layer coated borosilicate glass. High material quality is confirmed by low defect density observed in TEM images, high carrier mobilities, and minority carrier lifetime longer than 260 ns. An intermediate dielectric layer can be SiCx, SiOx, SiNx or their combination and its properties are crucial for cell fabrication and performance. Dopants are introduced into the LPCSG cell absorber either during film deposition or diffused from doped intermediate layer during crystallisation. Light-trapping texture is formed on the exposed silicon surface by wet etching. A cell emitter is created by diffusion from spin-on-dopant source. Cell metallisation is based on point contacts between Al and cell emitter and absorber accessed through vias etched through cell layers to different depths. LPCSG cells outperformed CSG cells, with record VOC of 585 mV and efficiency of 11.7%. Efficiencies above 13% are achievable by improving light-coupling and contacting.