Yun Lei

Removal of B from Si by Hf addition during Al–Si solvent refining process

Abstract A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al–Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al–Si melt was estimated to range from 4.9 × 10−6 to 8.8 × 10−7 for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (<1025 parts per million atoms, ppma) significantly improved the B removal. It was confirmed that the use of an increased Hf addition, slower cooling rate, and Al-rich Al–Si melt as the refining solvent removed B more efficiently. B in Si could be removed as much as 98.2% with 410 ppma Hf addition when the liquidus temperature of the Al–Si melt was 1173 K and the cooling rate was 4.5–7.6 K min–1. The B content in Si could be controlled from 153 ppma to 2.7 ppma, which meets the acceptable level for solar-grade Si.

B Removal by Zr Addition in Electromagnetic Solidification Refinement of Si with Si-Al Melt

This study investigated a new process of enhancing B removal by adding small amounts of Zr in the electromagnetic solidification refinement of Si with Si-Al melt. B in Si was removed by as much as 97.2 pct by adding less than 1057 ppma Zr, and the added Zr was removed by as much as 99.7 pct. In addition, Zr is more effective in enhancing B removal than Ti in the same electromagnetic solidification refining process.

Research on surface nano-texturation and wet-chemical passivation of multi-crystalline silicon wafer

Surfaces nano-texturing has triggered off much attention for trapping sunlight to improve the efficiency of solar cells. Silicon nanowire (SiNWs) arrays, with excellent antireflection performance, will hopefully improve photoelectric conversion of solar cells, however, the deteriorated effective carrier lifetime seriously limits efficiency enhancement of solar devices. Until now, the effect of SiNWs structure on effective carrier lifetime remains unexplored. Herein, the effects of fabrication parameters on the morphology structure and effective carrier lifetime of textured mc-Si were studied in detail. We also firstly discover that the relationship of SiNWs arrays length and effective carrier lifetime shows the negative exponential relation. Moreover, the effects of ethanolic iodine (I–E) concentration, immersion time, and surface pre-conditioning (with and without native oxide) on surface passivation of SiNWs arrays were investigated. It is found that more effective surface passivation could be achieved for the SiNWs arrays with shorter length. Meanwhile, the HF dipping pretreatment is conducive for SiNWs passivation, and which is attributed to Si–Hx termination with lower dissociation energy.

A Study of the Performance of Submerged Arc Furnace Smelting of Industrial Silicon

The consumption of energy and carbonaceous reductants is one of the more important factors that significantly influence the cost of industrial silicon production. The effect of raw materials on the silicon yield and the energy consumption in the process of producing silicon was investigated in this study using data collected from various submerged arc furnaces. Following analysis of a large quantity of industrial data, the results showed that a 12.5 MVA submerged arc furnace was the most efficient in utilizing the consumption of coal. In addition, the 8 MVA furnaces consumed the petroleum coke (petcoke) more efficiently in a silicon production process. To decrease the raw materials consumption and the energy loss in an industrial silicon production process, the petcoke/coal ratios for the 8 MVA and 12.5 MVA furnaces should be 1.25∼1.4 and 0.4∼0.6, respectively, for the production of one ton of silicon.

Boron Removal from Silicon Using Secondary Refining Techniques by Metallurgical Method

Impurity removal, the purification process from metallurgical grade silicon (MG-Si) required to obtain solar grade silicon (SoG-Si), is crucial to the preparation of silicon-based solar cells. Some processes for boron removal by metallurgical method were reviewed. Secondary refining techniques, including gas blowing, slag treatment, plasma refining, solvent refining and other refining silicon techniques were summarized. The effects of gas species and slag systems on boron removal efficiency were emphatically discussed. Experimental and theoretical investigations show that a united technique of combining water vapor and oxygen gases blowing with slag treatment containing chloride or fluoride has achieved an amazing improvement for boron removal from molten silicon. Plasma refining and solvent refining also display high efficiency but acid leaching treatments, vacuum volatilization, electron beam and directional solidifications are hardly effective to boron removal. As for the potential industrial application of this united technique, the authors propose that some experimental and theoretical studies in dynamics should be further explored.

Effect of acetic acid on the leaching behavior of impurities in metallurgical grade silicon

ABSTRACT To explore the potential of acid leaching in purification metallurgical grade silicon (MG-Si) for solar cells, the effect of acetic acid on the leaching behavior was investigated in the present work by focusing on the behavior of impurities affected by the addition of acetic acid to a conventional acid mixture composed of hydrochloric acid and hydrofluoric acid. The etching results reveal that the HCl–HF–CH3COOH mixture is a better lixiviant for dissolving impurity inclusions in MG-Si. The extraction yield of impurities in HCl–HF–CH3COOH leaching was found to increase by 7% compared to conventional HCl–HF leaching.

Effect of Zirconium on Boron Removal in Electromagnetic Solidification Refinement of Silicon from Si-Al Melt

This work investigates the removal of B in Si by the addition of Zr in the electromagnetic solidification refinement of silicon-aluminum melts. As Zr has a strong affinity for B and can form the thermodynamically stable compound of ZrB2, the B content of lower-grade Si is expected to be effectively removed by adding a small amount of Zr to the Si-55 at% Al melt. The results show that Zr is strongly responsible for the decrease in B content of refined Si. The removal fraction of B significantly increased from 60.2% to 97.3% by adding a small amount of Zr (0 to 3500 ppmw). In addition, the removal fraction of Zr from Si was found to be as high as 98.6%; however, its residual content in the refined Si was significantly larger than its solid solubility in Si, possibly due to the non-equilibrium solidification occurring during the refining process.