ChemInform Abstract: IMPROVED HIGH‐PURITY ARC‐FURNACE SILICON FOR SOLAR CELLS

Abstract

Durch Reduktion von SiO2 mit Kohle im 100 kW Lichtbogenofen dargestelltes Si besitzt eine B‐Verunreinigung von 1.8 ppma.

Development of Solar Grade (SoG) Silicon

“…It has been recognized that, other than B, P and Al, most impurities can be reduced sufficiently using directional solidification. Upgrading MG silicon in the past has included using high-purity starting materials during MG silicon production, hydro-, pyro-metallurgical refining, high-vacuum refining and plasma-arc reduction of impurities prior to directional solidification of molten charge [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] . None of these processes has reached commercialization because B and P could only be removed using special processes that were not cost Final Report for DOE SBIR Phase II, Contract Number DE-FG02-04ER83928 Crystal Systems, Inc., 27 Congress Street, Salem, MA 01970 effective.…”

Thin film solar cells using impure polycrystalline silicon

“…It may be possible, in future, to use directly UMG-Si to produce conventional solar cells. However this goal may imply a combined use of severe selection of quartz and carbon sources and/or prepurification of these raw materials [3] and/or sophisticated steps in UMG-Si processing [4] and/or double ingot crystallisation steps [5]. These production steps may well be too expensive when extrapolated to the high throughputs necessary for megawatt/year size solar cell factories.…”

“…reduce absorption losses by light trapping, using a back reflective surface, but this seems difficult in our case where the back surface is a Si/Si interface, -improve the cell processing technique, which seems to be feasible since the industrial process in use to-day for polycrystalline cells gives higher efficiencies than the integral screen printing technique and may even be further-refined [23]. 5. Economical analysis and comparison with other technologies presently being developed.…”

“…Today industrial cells are made from offgrade EG-Si, which is much cheaper (12 to 24 $/kg) than the material currently used in 1983. For the UMG-Si to be used in epitaxial cells, at least one commercial product has appeared on the market, as a result of the Elchem group work [5], and its cost seems to be lower than expected in 1983 (3 to 6 $/kg). Consequently it is realistic to admit an initial cost advantage of 15 $/kg for the raw material, in favour of epitaxial cells.…”

Control of metal impurities in “dirty” multicrystalline silicon for solar cells

“…process is 98-99% and even 95% because the raw materials used in this process contain high impurity levels. It is possible to obtain much higher degree of purity of silicon at a reasonable cost by using either naturally clean, or purified by leaching silica or quartz and carbon black or pelletized activated carbon with higher than average purity in specially designed arc furnaces with purified electrodes [2,[7][8][9][10][11][12][13][14]. (b) Acid leaching: This approach calls for pulverizing MG-Si in powder with 70 m or less particle size, and then treating this powder with various acids (e.g., aqua regia, hydrochloric acid, hydrofluoric acid) to dissolve metal clusters, which are frequently found in MG-Si at grain boundaries and are exposed during powdering [1].…”