Truncated pyramid structures for see-through solar cells
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.
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 discrete and isolated 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 plurality of discrete and isolated inverted 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 inverted 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 plurality of discrete and isolated inverted pyramidal cavities to create a plurality of see-through holes of specified opening area.
2. The method of claim 1 , wherein:
said plurality of discrete and isolated inverted pyramidal cavities comprise hexagonal pyramidal cavities.
3. The method of claim 1 , wherein:
said pyramidal cavities comprise quadrilateral plurality of discrete and isolated inverted pyramidal cavities.
4. The method of claim 1 , wherein:
said pyramidal cavities comprise triangular plurality of discrete and isolated inverted 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 three-dimensional monocrystalline silicon thin 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 porous silicon release layer.
10. The method of claim 1 , further comprising a step of forming base and emitter metallization by fire-through metallization.