Three-dimensional semiconductor template for making high efficiency thin-film solar cells

1. A method for fabrication of a structure for use in a photovoltaic solar cell, the method comprising:

selectively removing material from a monocrystalline silicon wafer to form a reusable monocrystalline silicon template having a top surface aligned along a (100) crystallographic plane of said template and a plurality of walls each aligned along a (111) crystallographic plane of said template, said walls defining a plurality of inverted pyramidal cavities comprising a set of larger inverted pyramidal cavities with an opening size in the range of approximately 10 μm up to 1 mm and a set of smaller inverted pyramidal cavities with an opening size a fraction of said opening size of said larger inverted pyramidal cavities, said set of larger pyramidal cavities and said set of smaller inverted pyramidal cavities arranged in a staggered pattern on said template which limits the length of ridges of said pyramidal cavity openings to less than twice the width of the openings of said larger pyramidal cavities;

forming a substantially conformal sacrificial porous silicon layer comprising at least two different porosities coupled to said template; and

epitaxially depositing a monocrystalline silicon layer to form a thin-film solar cell substrate on said sacrificial porous silicon layer, said solar cell substrate having a surface topography defined by said inverted pyramidal cavities on said reusable template;

said inverted pyramidal cavities on said reusable template ensuring that said solar cell substrate is capable of being detached from said template as a free-standing, self-supporting substrate with sufficient mechanical rigidity for use in a manufacturing environment.

2. The method of claim 1 , wherein said step of selectively removing silicon material further comprises anisotropically etching the silicon template to form a plurality of walls each aligned along a (111) crystallographic plane of the silicon template wherein said walls form an inverted pyramidal cavity.

3. The method of claim 2 , wherein said step of anisotropically etching the silicon template utilizes KOH or NaOH as an etchant.

4. The method of claim 2 , wherein said step of anisotropically etching the silicon template utilizes TetraMethyl-Ammonium-Hydroxide (TMAH) as an etchant.

5. The method of claim 1 , wherein said step of selectively removing silicon material further comprises:

forming a hard masking layer on the surface of the silicon template;

depositing a patterned soft masking layer on said hard masking layer on selected surface areas of the silicon substrate to be preserved as top surfaces;

etching said exposed hard masking layer;

removing said patterned soft masking layer exposing said hard masking layer underneath;

anisotropically etching exposed surfaces of the silicon template to form a plurality of walls each aligned along a (111) crystallographic plane of the silicon template wherein said walls form an inverted pyramidal cavity; and

selectively removing the remaining patterned hard masking layer.