Substrates for High-Efficiency Thin-Film Solar Cells Based on Crystalline Templates

Abstract

A three-dimensional thin-film semiconductor substrate having a plurality of ridges on the surface of the semiconductor substrate which define a base opening of an inverted pyramidal cavity and walls defining the inverted pyramidal cavity is provided. And a fabrication method for a 3-D TFSS by forming a porous silicon layer on a silicon template having a top surface aligned along a (100) crystallographic orientation plane of the silicon template and a plurality of walls each aligned along a (111) crystallographic orientation plane of the silicon template and forming an inverted pyramidal cavity. The porous silicon layer forms substantially conformal on the silicon template. Then forming a substantially conformal epitaxial silicon layer on the porous silicon layer and releasing the epitaxial silicon layer from the silicon template.

Description

[0001]This application claims the benefit of provisional patent application 61 / 114,378 filed on Nov. 13, 2008, which is hereby incorporated by reference.FIELD[0002]This disclosure relates in general to the field of photovoltaics and solar cells, and more particularly to semiconductor substrates and methods for making semiconductor substrates for use in manufacturing three-dimensional thin-film solar cells.DESCRIPTION OF THE RELATED ART[0003]Current methods for manufacturing a three-dimensional thin-film solar cell (3-D TFSC) include forming a 3-Dimensional thin-film silicon substrate (3-D TFSS) using a silicon template. The template may comprise a plurality of posts and a plurality of trenches between said a plurality of posts. The 3-D TFSS may then be formed by forming a sacrificial layer on the template, subsequently depositing a semiconductor layer, selective etching the sacrificial layer and releasing the semiconductor layer from the template. More specifically, the said semicon...

AI Technical Summary

Benefits of technology

[0007]Therefore a need has arisen for a three-dimensional thin-film substrate which provides fabrication process improvements and manufacturing costs reductions for forming a three-dimensional thin-film solar cell (3-D TFSC). In accordance with the disclosed subject matter, a three-dimensional thin-film semiconductor substrate (3-D TFSS) is provided which substantially eliminates or reduces disadvantages and problems associated with previously developed 3-D TFSS.

[0012]Technical advantages of the disclosed subject matter include fabrication process improvements and manufacturing cost reductions by utilizing the (111) crystallographic orientation plane to make inverted pyramid cavities on the substrate. Further, the inverted pyramidal cavities provide increased mechanical rigidity to the 3-D TFSS that is made from the template.

[0013]A technical advantage of the simplified fabrication processes and higher gas-to-silicon conversion ratio of epitaxial growth provided when using a template having inverted pyramidal cavities is an inverted pyramidal cavity based 3-D TFSS provides improved mechanical rigidity and strength. The strength of the template may be adjusted according to the arrays and staggered patterns of inverted pyramidal cavities provided.

[0017](3) Three-dimensional thin-film solar cells disclosed are mechanically robust because of their unique 3D structure, providing enhanced mechanical strength and handle-ability.

[0018]Further technical advantages of the disclosed subject matter include: 1) utilizing semiconductor templates consisting of known crystallographic silicon planes, i.e., the (111) and (100) planes and the epitaxial silicon layer grown from these two silicon planes yields better quality than from DRIE etched silicon 3-D surfaces, and 2) the large cavity opening angle) (70.6°) of the disclosed silicon template formed by the cavity sidewall (111) planes is much wider than that may be etched from using deep reactive ion etch (DRIE) silicon etch. Therefore, the porous silicon formation, epitaxial silicon growth, and releasing of 3-D TFSS are more practical and cost efficient than a DRIE etched template.

Problems solved by technology

These processes are often costly and difficult.

Also, flat thin-film silicon substrates may have reduced mean optical path length which reduces IR absorption and results in reduced cell quantum efficiency.

And flat thin-film crystalline silicon substrates may have poor mechanical strength for cell and module processing needs.

Micro cracking defects at substrate edges and pinholes defects within the substrate could cause cracking initiations and these cracks propagate easily along the crystallographic directions.

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