Multicrystalline Silicon Ingots Research Articles

Preparation of High-performance Multicrystalline Silicon Ingot Based on Innovative Seeding Strategy for Recycled Seeds

Preparation of High-performance Multicrystalline Silicon Ingot Based on Innovative Seeding Strategy for Recycled Seeds

Crystallization processes for photovoltaic silicon ingots: Status and perspectives

The choice of the crystallization process plays a crucial role in determining the quality and performance of the photovoltaic (PV) silicon ingots, which are subsequently used to manufacture solar cells. Silicon ingots are typically grown using either the Czochralski (Cz) process or the direction solidification (DS) method, with each technique influencing the microstructure and defects density as well as the final solar cells’ performance. In this work, we describe these two processes with a brief overview of the main challenges. For monocrystalline silicon ingots, we discuss the role of crucible and bubble development as well as structure loss. For multicrystalline silicon ingots, we briefly review some of the methods that have been developed in the past years and present results of high-performance multicrystalline (HPMC) ingots.

Effect of Silicon Nitride Coated Carbon Crucible on Multi-Crystalline Silicon Ingot during Directional Solidification Process: Numerical Simulation

Effect of Silicon Nitride Coated Carbon Crucible on Multi-Crystalline Silicon Ingot during Directional Solidification Process: Numerical Simulation

Simulation analysis on furnace pressure for reducing the impurities concentrations distribution during the growth of mc-Si ingot by DS process: Solar cell applications

A numerical investigation is carried out for the directional solidification (DS) process with various furnace pressures such as 300 mbar, 400 mbar, 500 mbar, and 600 mbar. During the multi-crystalline silicon (mc-Si) ingot growth process, the pressure inside the furnace affects the species' transport. The oxygen and carbon concentrations for various furnace pressures have been analyzed, and the results were compared. In the gas phase, a furnace pressure of less than 500 mbar enhances the strong back diffusion of the species into the silicon melt. The furnace pressure is higher than 500 mbar, which enhances the convection transport of the species in the lab-scale furnace. The optimized furnace pressure (500 mbar) enhances the quality of multi-crystalline silicon ingot. The oxygen concentration and carbon concentration values are reduced when the furnace pressure is around 500 mbar, which reduces the light-induced degradation (LID) effects and SiC precipitation.

Relationship between interstitial oxygen,substitutional carbon, resistivity and minority carrier lifetime in metallurgical multicrystalline silicon

. In this study we try to indentify relation between carrier lifetime, resistivity and two mains impurities concentration in a p-type upgrade metallurgical multicrystalline (UMG) silicon ingot. Thanks to this relation, we could prevent the Light Induced Degradation (LID) phenomenon and the SiC particles formation which are, respectively, at the origin of Voc losses and shunts in solar cells. So these 2 parameters are important for photovoltaic panels’ efficiency. Lifetime measurements are achieved by means of the Microwave Photoconductivity Decay “μw-PCD” technique, and concentration measurements are determined by FTIR. We demonstrate that resistivity variations depend on oxygen’s concentration but carbon analyses must be continued.

Numerical Investigation on Effect of Side Heater Modification on the Stress Distribution and Dislocation Density of Multi-Crystalline Silicon Ingot Grown by DS Process

Numerical Investigation on Effect of Side Heater Modification on the Stress Distribution and Dislocation Density of Multi-Crystalline Silicon Ingot Grown by DS Process

Effect of Coating Properties on the Crystal Quality Near the Sidewalls of Multicrystalline Silicon Ingot

Effect of Coating Properties on the Crystal Quality Near the Sidewalls of Multicrystalline Silicon Ingot

The impact on mc-Si ingot grown in a directional solidification furnace by partially replacing the susceptor bottom with an insulation material: A numerical investigation

Directional solidification (DS) is the major process for growing the multi-crystalline silicon (mc-Si) ingots with low cost and low power consumption. Here, the investigation of mc-Si growth has been carried out by two-dimensional numerical simulations on the simplified axisymmetric DS furnace. The mc-Si ingots were grown in the DS furnace with conventional susceptor and a furnace with partially replaced susceptor bottom. The susceptor bottom of size 278 mm × 42 mm × 20 mm is partially replaced with an insulation material. The temperature distribution and melt-crystal interface shape of the grown ingots were analysed at 25%, 50% and 75% of the solidification fraction. The von Mises stress and max shear stress were investigated on both the ingots at the end of the DS-Si process. The better quality mc-Si ingot with low power consumption has been attained by the partial replacement of susceptor bottom with insulation block.

Numerical and experimental investigation of the removal of Fe impurity during different DS process under axial magnetic field

The effects of axial magnetic field on the different directional solidification (DS) process were studied by using a transient numerical model of heat and mass transfer and corresponding experiments. The shape of melt-crystal (m-c) interface, melt flow morphology, thermal stress and Fe impurity concentration in the crystal for different DS process have been studied. The simulation results indicate that axial magnetic field provided a slight convex m-c interface shape, better flow pattern, lower thermal stress as well as lower Fe impurity concentration throughout the entire DS process. To further verify the simulation results, multi-crystalline silicon (mc-Si) ingots were prepared and testing were carried out. The experimental results are in good agreement with the simulation results. The experimental results show that a slight convex m-c interface shape was obtained, and the Fe impurity concentration in the middle area of the ingot was lower and higher minority carrier lifetime could be achieved by using the axial magnetic field.

Numerical simulation approach to investigate the effect of gas tube design on the impurities distribution and thermal properties of multi-crystalline silicon ingot grown by directional solidification process

Multi-crystalline Silicon (mc-Si) grown by directional solidification (DS) system is considered as a crucial photovoltaic material due to its relatively low cost and high yield. The numerical modelling is very useful for understanding the impurities segregation during mc-Si growth process. In the present paper, numerical simulation is carried out to investigate the impact of Argon gas tube design as shower head. In this Argon gas tube modification act on the non-metallic impurities, melt-crystal interface, temperature distribution and stress levels in the silicon ingot during the different stages of solidification process. The proposed design resulted in remarkable reduction in the back transfer of CO from heater component of the DS furnace. The generated von misses stress is also discussed as the function of different stage of solidification. The results concluded that the stress level at the initial stage of solidification is lower but it is large at above 75 % solidification rate. Also, we found that the modified gas tube design gives better temperature distribution with melt-crystal interface (m-c) shape. The modified argon tube design will be helpful for enhancing the quality of silicon ingot by controlling the chemical reaction between silicon melt and impurity transport.

Quality improvement of multi-crystalline silicon ingot by the Hot-Zone modification

Directional solidification process is the dominant method for the multi-crystalline silicon wafer production due to the lower production cost, simple operating process and mass production. Numerical simulation is the best tool to understand and enhance the multi-crystalline silicon ingot quality by using the directional solidification process for photovoltaic application. We improved the multi-crystalline silicon ingot quality by adding an additional graphite layer on the hot-zone of directional solidification furnace. We have simulated both modified and conventional directional solidification process and compared the temperature distribution, growth rate and stress distribution of both systems. The modified directional solidification system significantly increases the multi-crystalline silicon ingot quality compared to the conventional directional solidification process grown multi-crystalline silicon ingot. With the modified directional solidification system we have prevented the wall growth during the casting process.

Effects of Heat Extraction Methods on the Quality of High Performance Multi-Crystalline Silicon Ingot

Effects of Heat Extraction Methods on the Quality of High Performance Multi-Crystalline Silicon Ingot

Impurity-impurity interaction during the growth of UMG-Si-based mc-Si

This article investigates the relationship between the chemical composition and electrophysical properties of p- and n-type multicrystalline silicon ingots based on metallurgical silicon with a purity of 99.99 at.%. In particular, the role of impurity-impurity interactions in the production of multisilicon by the Bridgman vertical method is evaluated in order to identify approaches to controlling this process effectively. The phase equilibrium calculations in the “silicon–all impurities” and “silicon-impurity-oxygen” systems were carried out based on the Gibbs energy minimization in the Selector software package. The study investigates the rank correlations of the concentrations of various impurities with each other, as well as with the specified electrical resistivity (SER) and the lifetime of nonequilibrium charge carriers (NCC) in the direction of crystal growth. Pair correlations of the element distribution profiles were considered based on the role of the main factor represented by the ratio of individual impurity solubilities in solid or liquid silicon (k0), as well as from the standpoint of direct interaction between two elements. It was found that the k0 value for two individual impurities in silicon does not automatically lead to the pair correlation of their distribution profiles in the ingot. A significant effect on the distribution profiles of impurities in multisilicon with k0→0 has the factor of binding some part of the impurity into such a form that this impurity can be incorporated easily into a growing crystal. Binding may be induced by the interaction of the impurity in the melt with the oxygen background, its segregation at the grain boundaries, and its capture by the crystallization front in the composition of the liquid inclusion. Significant correlations of impurity distribution profiles in the ingot were demonstrated by the pairs whose elements interact without the formation of chemical compounds in the 25–1413 °C temperature range. The conducted phase equilibrium calculations for the “silicon–all impurities” system revealed the possibility of forming the VB2, TiB2, ZrB2, and MgTiO4 solid phases in the melt.

Numerical and experimental investigation on mc-Silicon growth process by varying the Si3N4 coating thickness of crucible

In the present work, the bottom-opening directional solidification technique was adopted to grow multi-crystalline silicon ingot. By varying the thickness of Si3N4 coating on the quartz crucible, the variation in carbon and oxygen concentration in the ingot has been analyzed. The axis-symmetric time-dependent 2D modeling has been done to analyze heat and mass transfer within the directional solidification furnace. We have analyzed the concentration of carbon monoxide, silicon oxide, silicon carbide, carbon and oxygen in the grown mc-Si ingots by varying the Si3N4 thickness. The oxygen and carbon impurities concentration are higher for the Si3N4 coating thickness of 50 μm to 150 μm and lower for 200 μm. The minority carrier lifetimes of the top, middle and bottom wafers have been analysied. The results show that the middle wafer has higher minority carrier lifetime compared to top and bottom wafers.

Investigation of orientation, surface morphology, impurity concentration and reflectivity of the multi-crystalline silicon wafers

Multi-crystalline silicon (mc-silicon) ingot was grown using the directional solidification (DS) method. The grown ingot was sliced, and the grain orientations, grain size, surface morphology, and impurities concentration in the wafers were studied. The XRD pattern of as-cut wafers exhibited the formation of a more number of (111) oriented plane in the grown ingot. The scanning electron microscopy images showed the formation of worm-like trenches after the chemical etching of the sliced wafers. FTIR spectra showed the higher carbon concentration on the top wafers and higher oxygen concentration at the bottom wafers. At the central wafer of the middle brick, the calculated carbon and interstitial oxygen concentration result exhibited 4.740 × 1016 and 1.369 × 1017 atoms/cm3, respectively. The impurity concentration of carbon and oxygen is validated with simulation results. The reflectivity spectra revealed low reflectivity for the wafers sliced from the central brick compared to the peripheral brick. The presence of very less impurity concentration and low reflectivity of the middle wafer in the central portion of the ingot enhances the light absorption, which is beneficial for photovoltaic energy generation.

Improve solar cell performance of high-performance multicrystalline silicon seeded with low-cost compact nucleation layer

In order to further improve the quality of high efficiency multicrystalline silicon and the performance of multicrystalline silicon solar cells, we designed a compact nucleation layer on the crucible bottom for casting high performance multicrystalline silicon ingots. The morphology of nucleation grains, the minority carrier lifetime mappings and the defects were analyzed and compared with that of the conventional nucleation layer. The results show that the initial nucleation grains of the compact nucleation layer were finer and more uniform, and there are fewer grains with high defect density at the ingot bottom，which is beneficial to reduce the defect ratio of the whole ingot. Moreover, the solar cell efficiency and electrical performance parameters, such as Rsh was also discussed. It was found that the Rsh has a great impact on the efficiency of multi-busbars solar cells, and the average solar cell conversion efficiency of the wafers grown with the compact nucleation layer is 0.11% higher than that of the wafers grown with the conventional nucleation layer.

Migration behavior and aggregation mechanism of SiC particles in silicon melt during directional solidification process

SiC inclusions in a multicrystalline silicon ingot have a negative effect on the performance of solar cells. The migration behavior and aggregation mechanism of SiC particles in the silicon melt during the directional solidification process was studied. Results show that SiC particles collide and aggregate in the melt due to the effect of melt flow. Larger aggregation of SiC particles is easily deposited at the bottom of the melt, whereas smaller SiC particles are pushed to the top of melt. Meanwhile, the particles migrate to the edge of melt under the effect of electromagnetic force. Furthermore, the enrichment region of SiC particles can be controlled by adjusting the temperature field distribution of the melt. With an increase of the melt temperature, the SiC particles are enriched at the top of the silicon ingot, indicating that SiC particles can be effectively separated from silicon.

Effect of power ratio of side/top heaters on the performance and growth of multi-crystalline silicon ingots

A transient global model for the growth process of multi-crystalline silicon ingots was constructed and validated, and the effect of different power ratios of side/top heaters on the liquid–solid interfacial shape and the crystallization rate was simulated using CGSIM software. The results show that the flat liquid–solid interface can be obtained by increasing the power ratio of the side/top heaters to more than 1.8, and the crystallization rate increases with the decrease of power ratio, and the crystal growth period is shortened by the decrease of power ratio.

Numerical Investigation of Cone Shape Grooved DS Block to Improve the mc–Si Ingot Quality

AbstractMulticrystalline silicon solar cells occupy 62% in crystalline silicon solar cell production. It is grown by the directional solidification process. Solidification control has a vital role in directional solidification process. Cone shape groove is made in the directional solidification block to enhance the outgoing heat flux in the center region than the peripheral region. Five directional solidification furnaces are simulated for making a multicrystalline silicon ingot. First furnace is the conventional furnace, the second furnace has 30 mm × 85 mm groove block, the third furnace has 40 mm × 85 mm groove block, the fourth furnace has 50 mm × 85 mm groove block and the fifth furnace has 60 mm × 85 mm groove block. The von Mises stress in the maximum volume of the conventional and modified grown ingots are below the range of critical value. In conventional case 7% of the ingot volume is above critical stress value and in the modified cases 2.5% of the ingot volume is above critical stress value. If axial and radial temperature gradient is combined in the 50 mm × 85 mm groove block leads to better results.

Influence of crucible properties and Si3N4-coating composition on the oxygen concentration in multi-crystalline silicon ingots

In this work, the influence of the silica ceramic crucible type and the properties of the Si3N4-coating on the oxygen contamination of directionally solidified silicon ingots was investigated by G0 and G1 crystallization experiments.It was found that crucibles with rough inner surfaces with values of Rq > 18 µm lead to higher oxygen contamination levels in the silicon melt of more than one order of magnitude in contrast to the ones with smooth inner surfaces. The use of colloidal SiO2 particles in the nm-scale within the Si3N4-coating, which generate the required non-wetting behavior towards the silicon melt, will also result in higher oxygen concentrations, while its degree is proportional to the used SiO2/Si3N4 ratio. Thick Si3N4-coatings in the range of 150–350 µm reduce or even suppress the influence of the crucible type on the oxygen contamination and the coating itself becomes the new main oxygen source.Higher argon flow velocities throughout the crystallization can be used as one effective influencing parameter to reduce the oxygen contamination of the melt. However, the effect might be compensated by certain crucible types.From these results conclusions will be drawn, how to achieve the lowest possible oxygen contamination during direction solidification of silicon ingots in the industrial scale.