Truncated pyramid structures for see-through solar cells

Abstract

The present disclosure presents a partially-transparent (see-through) three-dimensional thin film solar cell (3-D TFSC) substrate. The substrate includes a plurality of unit cells. Each unit cell structure has the shape of a truncated pyramid, and its parameters may be varied to allow a desired portion of sunlight to pass through.

What is claimed is: 
     
         1 . A method for making a see-through three-dimensional monocrystalline silicon thin film solar cell substrate, comprising the steps of:
 patterning a reusable monocrystalline silicon template;   forming a sacrificial porous silicon release layer on a surface of said reusable monocrystalline silicon template;   depositing a doped monocrystalline silicon film onto said sacrificial porous silicon release layer, said doped monocrystalline silicon film being substantially conformal to said sacrificial porous silicon release layer and having a thickness in the range of 2 to 50 microns for forming a three-dimensional monocrystalline silicon thin film solar cell substrate and having a three-dimensional topography corresponding to said patterned reusable monocrystalline silicon template and comprising:
 a plurality of discrete and isolated inverted pyramidal cavities at predetermined locations on said three-dimensional monocrystalline silicon thin-film solar cell substrate each comprising a pyramidal tip and tapered sidewalls, said plurality of inverted pyramidal cavities having a pyramidal cavity height in the range of approximately 100 to 400 microns on a front surface of said three-dimensional monocrystalline silicon thin-film solar cell substrate, said discrete and isolated pyramidal cavities having central axes substantially perpendicular to said front surface of said three-dimensional monocrystalline silicon thin-film solar cell substrate and having a ratio between height and side dimensions ranging from approximately 1.5 to 3; and 
 a plurality of interconnected continuous ridges interspersed among and bordering said plurality of discrete and isolated pyramidal cavities and associated to construct said monocrystalline silicon thin-film solar cell substrate as a free-standing, self-supporting substrate, and further having a ridge width ranging from approximately 0.5 to 5 microns on said front surface of said three-dimensional monocrystalline silicon thin-film solar cell substrate, wherein 
 said three-dimensional monocrystalline silicon thin-film solar cell substrate, said plurality of discrete and isolated inverted pyramidal cavities, and said plurality of interconnected continuous ridges cooperate to enable a free-standing, self-supporting three-dimensional monocrystalline silicon thin-film solar cell with sufficient mechanical rigidity and resilience for reduced cell breakage rate in a solar cell production factory; 
   detaching said three-dimensional monocrystalline silicon thin-film solar cell substrate from said reusable monocrystalline silicon template through separation at said sacrificial porous silicon release layer; and   selectively removing a predetermined portion of a plurality of said pyramidal tips from said pyramidal cavities to create a plurality of see-through holes of specified opening area.   
     
     
         2 . The method of  claim 1 , wherein:
 said pyramidal cavities comprise hexagonal pyramidal cavities.   
     
     
         3 . The method of  claim 1 , wherein:
 said pyramidal cavities comprise quadrilateral pyramidal cavities.   
     
     
         4 . The method of  claim 1 , wherein:
 said pyramidal cavities comprise triangular pyramidal cavities.   
     
     
         5 . The method of  claim 1 , wherein said patterning step comprises laser micromachining. 
     
     
         6 . The method of  claim 1 , wherein said patterning step comprises photolithography and reactive ion etching. 
     
     
         7 . The method of  claim 1 , wherein said sacrificial porous silicon release layer comprises a first layer having a first porosity and a second layer having a second porosity. 
     
     
         8 . The method of  claim 1 , wherein said step of detaching said three-dimensional monocrystalline silicon thin-film solar cell substrate from said reusable monocrystalline silicon template comprises:
 mechanically separating said silicon film from said sacrificial layer.   
     
     
         9 . The method of  claim 1 , wherein said step of detaching said three-dimensional monocrystalline silicon thin-film solar cell substrate from said reusable monocrystalline silicon template comprises:
 chemically etching said sacrificial layer.   
     
     
         10 . The method of  claim 1 , wherein said step of forming base and emitter metallization comprises fire-through metallization.