Ebara Solar, Inc.

Balakrishnan R Bathey

A dendritic web formation process and apparatus for diffusing dopant impurities into a growing dendritic crystal web to produce photovoltaic cells. A solid dopant diffusion source is arranged in a holder mounted in a vertical thermal element either within the melt furnace or outside the furnace adjacent the furnace exit port. The solid diffusion source is heated by thermal conduction from the vertical thermal element and source holder using the furnace heat as a source. Auxiliary heater coils are optionally provided around the vertical thermal element to control the temperature of the solid diffusion source. The source and holder can also be mounted outside the furnace adjacent the exit port and heated using a secondary rapid temperature external heater. The growing dendritic crystal web is exposed to the dopant impurities as part of the web growing process, eliminating the need for a separate diffusion gaseous station and processing.

In-situ diffusion of dopant impurities during dendritic web growth of

A method for treating thin silicon web crystals used to produce solar cells in order to remove complex SiOx contaminants from the web after growth. A dendritic silicon web with {111} surface orientation is immersed in a caustic solution of KOH or NaOH at a temperature at a range from about 80 to about 85.degree. C. for a period of about five to about ten minutes. The caustic solution quickly removes the SiOx contaminants, while leaving relatively unaffected the silicon crystal in the surface. After the caustic solution treatment, the web is rinsed in deionized water and optionally subjected to an acid cleaning with HCL or HF in order to remove any residual contaminants on the web surface.

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Upper St. Clair, PA, United States of America

Balakrishnan R Bathey