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Separation of boron from silicon by steam-added electron beam melting
摘要： Removal of boron from silicon is a tough task by traditional directional solidification and vacuum refining techniques, due to its large and inappropriate segregation coefficient and low saturated vapor pressure. At high temperature boron react with oxygen to form volatile boron oxides which can be evaporated. So, the removal procedure of boron from silicon melt is investigated by incorporating a small amount of water vapor above the melted surface. The results show that boron is oxidized to mainly form BO and evaporated with 28% removal efficiency by average. It is considered that oxygen atoms experience a series of physical and chemical processes, such as a chemical reaction in the bulk of the melt, evaporation from the melt surface, transportation across the gas phase and ionization due the electron beam, which is conducive to the continuous removal of boron.
关键词： Electron beam melting,Photovoltaic,Boron removal,Oxygen self-circulating path,Solar-grade silicon
更新于2025-09-23 15:23:52
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22.6% Efficient Solar Cells with Polysilicon Passivating Contacts on n‐type Solar‐Grade Wafers
摘要： Czochralski (Cz)-grown upgraded metallurgical-grade (UMG) silicon wafers degrade signi?cantly during high-temperature processes, eroding their appeal as a low-cost alternative to conventional electronic-grade silicon wafers. However, the thermal degradation in UMG wafers can be delayed by utilizing a prefabrication annealing step. Based on this, a high-ef?ciency solar-cell process is modi?ed by selecting a single-boron diffusion step and applying phosphorus-doped polycrystalline ?lms as electron-selective contacts with excellent impurity-gettering properties to minimize the thermal budget. The application of this modi?ed high-ef?ciency solar-cell process to n-type UMG-Cz wafers results in a solar cell with a conversion ef?ciency of 22.6% on a cell area of 2 (cid:1) 2 cm2.
关键词： solar-grade silicon,polycrystalline contacts,ring defects,tabula rasa
更新于2025-09-19 17:13:59
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Impact of pre-fabrication treatments on n-type UMG wafers for 21% efficient silicon heterojunction solar cells
摘要： Silicon heterojunction solar cells achieve high conversion efficiency due to the excellent surface passivation provided by the hydrogenated intrinsic amorphous silicon films. However, they require a high-quality wafer as a starting material because their low-temperature processing does not allow for gettering. Czochralski-grown upgraded metallurgical-grade (UMG-Cz) silicon is a low-cost alternative to electronic-grade silicon for silicon solar cells, but is often limited in lifetime by grown-in defects. We have previously shown that pre-fabrication treatments, namely tabula rasa, phosphorus diffusion gettering, and hydrogenation, can significantly improve the bulk quality of UMG-Cz wafers. These help to mitigate the impact of grown-in oxygen precipitate nuclei and metallic impurities. In this work, we fabricate rear-junction silicon heterojunction solar cells on both as-grown and pre-treated UMG-Cz and electronic-grade wafers. We show that pre-fabrication treatments have a marked impact on solar cell efficiencies. With pre-fabrication treatment, the efficiency improves from 18.0% to 21.2% for the UMG-Cz cells and 21.2%–22.7% for the electronic-grade cells. Comparison of the open-circuit voltages of the as-grown and pre-treated UMG-Cz and electronic-grade cells using Quokka simulations reveals that the bulk lifetime remains the primary limiting factor for the UMG-Cz wafers.
关键词： Hydrogenation,Phosphorus diffusion gettering,Czochralski silicon,Solar-grade silicon,Tabula rasa,Silicon heterojunction solar cells
更新于2025-09-16 10:30:52