Loading patent…
AssigneeAstroPower, Inc.
InventorsRobert B. Hall, Allen M. Barnett, Sandra R. Collins, Joseph C. Checchi, David H. Ford, Christopher L. Kendall, Steven M. Lampo, James A. Rand
Estimating the term…
The invention relates to techniques for manufacturing columnar-grained polycrystalline sheets which have particular utility as substrates or wafers for solar cells. The sheet is made by applying granular silicon to a setter material which supports the granular material. The setter material and granular silicon are subjected to a thermal profile all of which promote columnar growth by melting the silicon from the top downwardly. The thermal profile sequentially creates a melt region at the top of the granular silicon and then a growth region where both liquid and a growing polycrystalline sheet layer coexist. An annealing region is created where the temperature of the grown polycrystalline silicon sheet layer is controllably reduced to effect stress relief.
A process of making an improved columnar-grained polycrystalline sheet for functioning as a substrate for a solar cell, comprising (a) applying granular silicon to a setter material having a release coating at its upper surface and which supports the granular silicon, (b) preheating the setter material and granular silicon in a preheat zone, (c) subjecting the setter material and granular silicon to a thermal profile which causes melting of the granular silicon from the top downwardly, wherein 25 to 90% of the granular silicon depth is melted and the partially melted silicon below the melted material functions as a net to stabilize the melt and to minimize molten silicon contact with the underlying setter material and release coating and to nucleate subsequent crystal growth, (d) transporting the melt pool on the silicon net into a growth zone wherein a thermal profile is created to promote columnar growth of a columnar grain size greater than 20 microns in a direction approximately perpendicular to the plane of the setter material and where both liquid and a growing polycrystalline layer coexist and where the entire layer experiences a liquid state prior to solidification, (e) transporting the grown sheet into an anneal zone wherein a linear temperature gradient along the direction of setter material motion is provided to promote low stress cooling of the sheet, (f) removing the polycrystalline sheet from the setter material, facilitated by a release agent, and (g) reusing the setter material for the making of further columnar-grained polycrystalline sheets.
A process of making an improved columnar-grained polycrystalline sheet for functioning as a substrate for a solar cell, comprising (a) applying a net to a setter material, (b) applying granular silicon to the setter material and the net whereby to support the granular silicon, (c) preheating the setter material and the net and the granular silicon in a preheat zone, (d) subjecting the setter material and the net and the granular silicon to a thermal profile which causes melting of the granular silicon from the top downwardly, wherein 25 to 90% of the granular silicon depth is melted and the partially melted silicon below the melted material functions as a nucleation site to nucleate subsequent crystal growth and the net functions to stabilize the melt and to minimize molten silicon contact with underlying setter and the net functions as a release coating, (e) transporting the melt pool on the net into a growth zone wherein a thermal profile is created to promote columnar growth of a columnar grain size greater than 20 microns in a direction approximately perpendicular to the plane of the setter material and where both liquid and a growing polycrystalline layer coexist and where the entire layer experiences a liquid state prior to solidification, (f) transporting the grown sheet into an anneal zone wherein a linear temperature gradient along the direction of setter material motion is provided to promote low stress cooling of the sheet, (g) removing the polycrystalline sheet from the setter material, facilitated by a release agent, and (h) reusing the setter material for the making of further columnar-grained polycrystalline sheets.
The process of claim 22 wherein the net is made from a graphite material.
A process of making an improved columnar-grained polycrystalline sheet for functioning as a substrate for a solar cell, comprising (a) providing a layer of graphite material, (b) applying granular silicon to the graphite material whereby to support the granular silicon, (c) preheating the graphite material and the granular silicon in a preheat zone, (d) subjecting the graphite material and the granular silicon to a thermal profile which causes melting of the granular silicon from the top downwardly, wherein 25 to 90% of the granular silicon depth is melted and the partially melted silicon below the melted material functions as a nucleation site to nucleate subsequent crystal growth and the graphite material functions as a release coating, (e) transporting the melt pool on the graphite material into a growth zone wherein a thermal profile is created to promote columnar growth of a columnar grain size greater than 20 microns in a direction approximately perpendicular to the plane of the graphite material and where both liquid and a growing polycrystalline layer coexist and where the entire layer of experiences a liquid state prior to solidification, (f) transporting the grown sheet into an anneal zone wherein a linear temperature gradient along the direction of graphite material motion is provided to promote low stress cooling of the sheet, (g) removing of the polycrystalline sheet from the graphite material, and (h) reusing the graphite material for the making of further columnar-grained polycrystalline sheets.
Dependencies are inferred from the claim text.