Case 6:20-cv-00139-ADA Document 1-6 Filed 02/21/20 Page 1 of 21
`111111
`1111111111111111111111111111111111111111111111111111111111111
`USO 1 0269999B2
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`c12) United States Patent
`Vasylyev
`
`(10) Patent No.: US 10,269,999 B2
`(45) Date of Patent:
`Apr. 23, 2019
`
`(54) LIGHT TRAPPING OPTICAL STRUCTURES
`EMPLOYING LIGHT CONVERTING AND
`LIGHT GUIDING LAYERS
`
`(71) Applicant: Sergiy Vasylyev, Elk Grove, CA (US)
`
`(72)
`
`Inventor: Sergiy Vasylyev, Elk Grove, CA (US)
`
`(73) Assignee: SVV TECHNOLOGY
`INNOVATIONS, INC., Sacramento,
`CA (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 263 days.
`
`(52) U.S. Cl.
`CPC ........ HOJL 3110547 (2014.12); G01J 110407
`(2013.01); G01J 510853 (2013.01); G02B
`510231 (2013.01); G02B 510294 (2013.01);
`G02B 1910028 (2013.01); HOJL 31102327
`(2013.01); HOJL 3110525 (2013.01); HOJL
`3110543 (2014.12); Y02E 10/52 (2013.01)
`(58) Field of Classification Search
`CPC ........... HOlL 31/02327; HOlL 31/0525; H01L
`31/0543; HOlL 31/0547
`USPC ........ 250/203.1, 203.3, 203.4, 216; 136/246,
`136/256, 259; 385/33, 36
`See application file for complete search history.
`
`(21) Appl. No.: 15/442,645
`
`(22)
`
`Filed:
`
`Feb. 25, 2017
`
`(65)
`
`Prior Publication Data
`
`US 2017/0170352 Al
`
`Jun. 15, 2017
`
`(63)
`
`(60)
`
`(51)
`
`Related U.S. Application Data
`
`Continuation of application No. 14/222,588, filed on
`Mar. 22, 2014, now abandoned, which
`is a
`continuation of application No. 13/181,482, filed on
`Jul. 12, 2011, now Pat. No. 8,735,791.
`
`Provisional application No. 61/399,552, filed on Jul.
`13, 2010, provisional application No. 61/402,061,
`filed on Aug. 21, 2010.
`
`Int. Cl.
`HOJL 27100
`HOJL 311054
`G01J 1104
`G01J 5108
`G02B 5102
`HOJL 3110232
`HOJL 3110525
`G02B 19100
`
`(2006.01)
`(2014.01)
`(2006.01)
`(2006.01)
`(2006.01)
`(2014.01)
`(2014.01)
`(2006.01)
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6,274,860 B1
`6,333,458 B1
`6,440,769 B2
`7,672,549 B2
`7,817,885 B1
`
`8/2001 Rosenberg
`12/2001 Forrest eta!.
`8/2002 Peumans et a!.
`3/2010 Ghosh et a!.
`10/2010 Moore eta!.
`(Continued)
`
`Primary Examiner- Kevin K Pyo
`
`(57)
`
`ABSTRACT
`
`A light converting optical system employing a planar light
`trapping optical structure. The light trapping optical struc(cid:173)
`ture includes a monochromatic light source, a light guiding
`layer, a lenticular lens array incorporating a plurality of
`linear cylindrical microlenses, a broad-area reflective sur(cid:173)
`face, and a generally planar photoresponsive layer located
`between the lens array and the reflective surface. The
`photoresponsive layer is configured at a sufficiently low
`thickness to transmit at least a portion of incident light
`without absorption in a single pass. A portion of the unab(cid:173)
`sorbed light is trapped within the light trapping optical
`structure and redirected back to the photoresponsive layer.
`
`13 Claims, 7 Drawing Sheets
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`Case 6:20-cv-00139-ADA Document 1-6 Filed 02/21/20 Page 2 of 21
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`US 10,269,999 B2
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`GOlJ 1/0407
`250/203.4
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`(56)
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`References Cited
`
`U.S. PATENT DOCUMENTS
`
`8,735,791 B2 * 5/2014 Vasylyev
`
`2004/0103938 A1
`2008/0264483 A1
`2008/0295882 A1
`2009/0067784 A1
`2009/0126792 A1
`2010/0186798 A1
`2010/0278480 A1
`201110226332 A1
`2012/0012741 A1
`* cited by examiner
`
`6/2004 Rider
`10/2008 Keshner et a!.
`12/2008 Stephens et a!.
`3/2009 Ghosh eta!.
`5/2009 Gruhlke et a!.
`7/2010 Tourmen et a!.
`1112010 Vasylyev
`9/2011 Ford eta!.
`112012 Vasylyev
`
`

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`Case 6:20-cv-00139-ADA Document 1-6 Filed 02/21/20 Page 3 of 21
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`U.S. Patent
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`Apr. 23,2019
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`Sheet 1 of 7
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`FIG. 1
`(PRI RART)
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`FIG. 2
`(PRIOR ART)
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`FIG. 3
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`14
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`U.S. Patent
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`V .s . P a t e n t
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`U.S. Patent
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`Sheet 3 of 7
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`FIG. 11
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`Sheet 4 of 7
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`FIG. 12
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`16~--~~------------------------
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`FIG. 13
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`U.S. Patent
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`Apr. 23, 2019
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`Sheet 5 of 7
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`34
`16~--~------~--------------~-
`FIG. 14
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`12--;;;..................,.......---~
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`34
`16~-~---~~------------~
`FIG. 15
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`U.S. Patent
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`Apr. 23, 2019
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`FIG. 16
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`FIG. 18
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`Case 6:20-cv-00139-ADA Document 1-6 Filed 02/21/20 Page 10 of 21
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`US 10,269,999 B2
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`1
`LIGHT TRAPPING OPTICAL STRUCTURES
`EMPLOYING LIGHT CONVERTING AND
`LIGHT GUIDING LAYERS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of application Ser. No.
`14/222,588, filed Mar. 22, 2014, which is a continuation of
`application Ser. No. 13/181,482, filed Jul. 12, 2011, now
`U.S. Pat. No. 8,735,791, which claims priority from U.S.
`provisional application Ser. No. 61/399,552 filed on Jul. 13,
`2010 and from U.S. provisional application Ser. No. 61/402,
`061 filed on Aug. 21, 2010.
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`Not Applicable
`
`INCORPORATION-BY-REFERENCE OF
`MATERIAL SUBMITTED ON A COMPACT
`DISC
`
`Not Applicable
`
`NOTICE OF MATERIAL SUBJECT TO
`COPYRIGHT PROTECTION
`
`A portion of the material in this patent document is subject 30
`to copyright protection under the copyright laws of the
`United States and of other countries. The owner of the
`copyright rights has no objection to the facsimile reproduc(cid:173)
`tion by anyone of the patent document or the patent disclo(cid:173)
`sure, as it appears in the United States Patent and Trademark
`Office publicly available file or records, but otherwise
`reserves all copyright rights whatsoever. The copyright
`owner does not hereby waive any of its rights to have this
`patent document maintained in secrecy, including without
`limitation its rights pursuant to 37 C.P.R. § 1.14.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to a device and method for
`harvesting radiant energy emanated by a distant radiant
`energy source, particularly, to collecting the sunlight and
`absorbing it by a light sensitive material, medium or device.
`More particularly, the present invention relates to photovol(cid:173)
`taic devices, solar cells and light detectors having light
`trapping microstructures or layers to improve absorption of
`light within the light sensitive layer, and to a method for
`generating electricity from sunlight thereof.
`2. Description of Background Art
`Conventionally, photovoltaic solar cells or light detectors
`employ an active photoresponsive layer that absorbs at least
`a portion of the electromagnetic spectrum of the light and
`generates charge carriers due to the photovoltaic effect.
`Since most photovoltaic materials absorb much more
`weakly in certain wavelengths than in the others, the active
`layer has to have at least a minimum thickness to be able to
`absorb most of the light to which the photovoltaic material
`is responsive.
`One exemplary material suitable for converting light into
`electricity is silicon (Si). However, Si is an indirect bandgap
`semiconductor and is poorly absorbing the long wavelength
`light. For the active layer made with crystalline silicon the
`
`5
`
`25
`
`2
`minimum thickness is typically between 200 and 400 f.tm
`(micro-meters). While Si is very abundant, stable and well(cid:173)
`suited for solar cell and light detector manufacturing, the
`cost of this thick layer of silicon is quite high which results
`in the high cost of the devices.
`Some other than crystalline silicon types of photovoltaic
`devices, such as amorphous silicon thin-film cells, for
`example, allow for a much smaller thickness of the active
`layer. However, with certain wavelengths being still
`10 absorbed very weakly, they usually require some form of
`light trapping that would cause the incident light to pass
`through the active layer multiple times thus improving the
`absorption. The light trapping is usually implemented in the
`prior art by texturing one or more surfaces comprising the
`15 solar cell in order to scatter the incident light at different
`angles thus resulting in a longer average light path through
`the active layer. In case of a monocrystalline silicon cell,
`light scattering and trapping is conventionally provided by
`microstructures such as periodic or random pyramids on the
`20 front surface and a reflective or light scattering surface at the
`rear of the cell. In case of an amorphous thin-film Si cell
`consisting of several layers, a transparent top conductor
`layer is often textured to scatter light and hence increase the
`light path through the active layer.
`During light trapping, some scattered light can be trapped
`in the active layer of the solar photovoltaic device by means
`of TIR which can even allow for the multiple passage of a
`portion of solar rays through the active layer thus resulting
`in a better absorption and sunlight conversion. However, the
`existing approaches for light trapping in the photovoltaic
`devices cannot prevent for a substantial portion of incident
`light to escape from the device without being absorbed. For
`example, in case of the front surface employing random
`pyramidal microstructures, a large portion of the escaping
`35 light is usually lost through this front surface due to the
`random nature of the secondary interactions of the light rays
`with the pyramids. Furthermore, up to 10 percent or more
`light can be lost in conventional photovoltaic systems due to
`the reflection from front contacts or absorption by layers or
`40 surfaces which produce no photovoltaic effect.
`An additional problem encountered in photovoltaic
`devices is that most photovoltaic materials have a relatively
`large refractive index which results in poor light coupling
`efficiency due to the high reflection losses from the light
`45 receiving surface. The bulk crystalline Si, for example, has
`the refractive index of 3.57 at 1,000 nm (nanometers) and
`5.59 at 400 nm which results in the Fresnel reflection of32%
`to 49% of the incident light at 1,000 nm and 400 nm,
`respectively. Typically, these problems can be addressed by
`50 adding an antireflective layer to the light receiving surface
`and/or surface micro structuring. However, the antireflective
`coating works efficiently only in a limited bandwidth and
`adds system cost and processing time, while the microstruc(cid:173)
`tures are still somewhat inefficient for light coupling or
`55 otherwise are quite expensive to be used for mass produc(cid:173)
`tion, considering that the entire area of the photovoltaic
`device must be processed to cover it with these microstruc(cid:173)
`tures.
`These drawbacks of the prior art approaches and the loss
`60 of useful light are hampering the utility of the photovoltaic
`devices. None of the previous efforts provides an efficient
`solution for coupling and trapping essentially all of the
`incident light and allowing it to pass through the sufficient
`effective depth of photosensitive material or allow the light
`65 to interact with the active layer as many times as necessary
`to cause the efficient light absorption in a controlled manner.
`It is therefore an object of this invention to provide an
`
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`US 10,269,999 B2
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`3
`improved light harvesting system employing a novel pho(cid:173)
`tovoltaic structure with efficient light coupling and trapping
`thus minimizing energy loss.
`The present invention solves the above problems by
`providing a layered structure having correlated surface relief
`features or microstructures that allow for enhancing the light
`coupling efficiency, increasing the light path through the
`photosensitive material and for trapping the incident light
`within the device by means of at least TIR. The light
`trapping causes multiple passage of the trapped light through
`the photoresponsive (active) layer thus improving the light
`absorption and energy conversion efficiency. Other objects
`and advantages of this invention will be apparent to those
`skilled in the art from the following disclosure.
`
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention solves a number of light harvesting
`problems within a compact system utilizing efficient light
`coupling and trapping mechanisms. Light is injected into a
`photoresponsive layer through light input ports using a
`focusing array and trapped within the layer so that the useful
`light absorption is substantially enhanced.
`A light harvesting system employing microstructures for
`efficient light trapping and comprising a focusing array and
`a photoresponsive layer is described. The focusing array
`comprises a plurality oflight collecting elements distributed
`over a planar surface of the array. Each light collecting
`element is configured to collect light from a larger area and
`focus the incident light onto a substantially smaller focal
`area. The photoresponsive layer comprises light input ports
`formed in its light receiving surface. Each light input port is
`disposed in energy receiving relationship with respect to at
`least one light collecting element of the focusing array. More
`particularly, each light input port is disposed in a vicinity of
`the respective light collecting element and aligned (cen(cid:173)
`tered) with respect to its optical axis. Each light input port
`is configured to receive a focused light beam and commu(cid:173)
`nicate it into the photoresponsive layer a sufficiently oblique
`angle so as to result in an improved light coupling and
`generally increased light path and absorption in said layer
`compared to the case when light enters the photoresponsive
`layer elsewhere through its light receiving surface.
`The invention is amenable to being embodied in a number
`of ways, including but not limited to the following descrip(cid:173)
`tions.
`At least one embodiment of the invention is configured as
`a light harvesting system comprising: (a) a photoresponsive
`layer configured to internally absorb at least a portion of the
`light propagating through its body; (b) a plurality of light
`input ports associated with a light receiving surface of said
`photoresponsive layer; and (c) a plurality of light collecting
`elements within a planar focusing array configured for
`focusing received light onto said light input ports. Each of
`the plurality of light input ports is configured to communi- 55
`cate the incident light into the photoresponsive layer at a
`sufficiently oblique angle so as to increase the optical path
`of the light rays through the designated layer. The device
`operates in response to the light received on the aperture of
`the focusing array being injected into the photoresponsive
`layer and angularly redirected at generally oblique angles
`with respect to the prevailing plane of the light harvesting
`system.
`In at least one implementation, the light harvesting system
`further comprises at least one electrical contact associated
`with the photoresponsive layer. In at least one further
`implementation, the electrical contact associated with the
`
`4
`photoresponsive layer is made from an optically transparent
`material. In at least one implementation, the electrical con(cid:173)
`tact associated with the photoresponsive layer comprises a
`reflective metallic material and is made in the form of a grid.
`In at least one implementation, the electrical contact com(cid:173)
`prises a reflective metallic material and is made in the form
`of a thin sheet or a film. In at least one implementation, the
`electrical contact comprises a plurality of electrical contact
`fingers disposed in spaces between adjacent pairs of light
`10 input ports and away from the light paths of the focused
`beams formed by the light collecting elements. In at least
`one implementation, the photoresponsive layer comprises at
`least one photovoltaic cell.
`In alternative implementations, the planar focusing array
`15 and its light collecting elements can be configured in dif(cid:173)
`ferent ways. In at least one implementation, the focusing
`array comprises a lenticular lens array. In at least one
`implementation, the focusing array comprises a point-focus
`lens array. In at least one implementation, the focusing array
`20 comprises point focus lenses which have a shape selected
`from the group consisting of round, rectangular, square, and
`hexagonal. In at least one implementation, each of the light
`collecting elements is selected from the group of optical
`elements consisting of imaging lenses, non-imaging lenses,
`25 spherical lenses, aspherical lenses, lens arrays, Fresnel
`lenses, TIR lenses, gradient index lenses, diffraction lenses,
`mirrors, Fresnel mirrors, spherical mirrors, parabolic mir(cid:173)
`rors, mirror arrays, and trough mirrors.
`In different implementations, the plurality of light input
`30 ports can be differently configured. In at least one imple(cid:173)
`mentation, each of the plurality of light input ports is
`disposed in a predetermined aligument with the plurality of
`light collecting elements. In at least one implementation, the
`oblique propagation angle within the photoresponsive layer
`35 is so selected as to result in the propagation of at least a
`substantial portion of light rays at sufficiently high angles,
`above the predetermined critical angle for total internal
`reflection (TIR), with respect to a surface normal to at least
`one surface of said photoresponsive layer. In at least one
`40 implementation, each of the plurality of light input ports
`comprises a refractive or reflective face inclined at an angle
`with respect to the prevailing plane of the photoresponsive
`layer. In at least one implementation, the plurality of light
`input ports comprises a parallel array of elongated grooves.
`45 In at least one implementation, each of the plurality of light
`input ports comprises at least one cavity. In at least one
`implementation, the cavity has a sufficiently high aspect
`ratio. In at least one implementation, each of the light input
`ports comprises at least one surface relief feature selected
`50 from the group of elements consisting of cavities, holes,
`extensions, bulges, prisms, prismatic grooves, cones, conical
`cavities, furmel-shaped cavities, surface texture, reflective
`surfaces, refractive surfaces, diffraction gratings, holograms,
`light scattering elements, and so forth.
`In further implementations, the light harvesting system is
`can be configured in various ways to enhance the light
`trapping in the photoresponsive layer. In at least one imple(cid:173)
`mentation, the light harvesting system further comprises an
`optical interface disposed between the photoresponsive
`60 layer and the focusing array and characterized by a drop in
`refractive index in the direction of light propagation from
`the photoresponsive layer toward the focusing array. In at
`least one implementation, the light harvesting system further
`comprises means for promoting a total internal reflection in
`65 the photoresponsive layer.
`In at least one implementation, the focusing array and the
`photoresponsive layer are adapted for being retained in a
`
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`6
`pairs of adjacent light input ports and away from the light
`paths of the focused beams formed by the light collecting
`elements.
`Another element of the invention is the use of linear
`arrays of light collecting elements and/or light input ports
`which span the surface of the device, or a portion thereof.
`Alternatively, another element of the invention is the use of
`point-focus arrays of light collecting elements and/or light
`input ports as well as portions and combinations of linear
`10 and point-focus arrays thereof.
`Another element of the invention is the use of a prede(cid:173)
`termined alignment for disposing the light collecting ele(cid:173)
`ments with respect to the light input ports and/or the
`15 electrical contacts.
`Another element of the invention is the use of light input
`ports in the form of cavities, holes or other microstructures
`having a sufficiently high aspect ratio.
`Another element of the invention is the use of light input
`20 ports each comprising a refractive or reflective face inclined
`at an angle to the light receiving surface of the photorespon(cid:173)
`sive layer for injecting at least a substantial part of the
`incident light into the layer at an oblique angle.
`Another element of the invention is the use of tracking
`25 means for tracking a light source.
`A still further element of the invention is a light harvesting
`system which can be utilized in a wide range of light
`collecting or light sensing applications.
`Further elements of the invention will be brought out in
`30 the following portions of the specification, wherein the
`detailed description is for the purpose of fully disclosing
`preferred embodiments of the invention without placing
`limitations thereon.
`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING(S)
`
`5
`translated, a reversed and/or a rotated orientation relative to
`each other toward adjusting the acceptance angle or for
`tracking the source of light. In at least one further imple(cid:173)
`mentation, the light harvesting system can comprise at least
`one tracking means for tracking a light source.
`At least one embodiment of the invention is configured as
`a light harvesting system having a layered structure and
`comprising: (a) a photovoltaic layer disposed between a first
`and a second reflective surfaces; and (b) a light focusing
`layer having surface relief features each configured to focus
`the incident light. At least one of the first and second
`reflective surfaces comprises light input ports disposed in
`energy receiving relationship to the surface relief features
`and configured to inject incident light into the space between
`the first and second reflective surfaces so as to cause
`multiple passage of light through the photovoltaic layer.
`In at least one implementation, at least one of the first and
`second reflective surfaces is configured for reflecting light
`by means of at least TIR. In at least one implementation, the
`light harvesting system is further comprising at least one
`cladding layer associated with at least one of the first and
`second reflective surfaces. In at least one implementation, at
`least one of the first and second reflective surfaces is
`associated with a mirror layer comprising a metallic mate(cid:173)
`rial. In at least one implementation, at least one of the first
`and second reflective surfaces is associated with a mirror
`layer comprising a Bragg reflector. In at least one imple(cid:173)
`mentation, the light focusing layer comprises a lens array. In
`at least one implementation, the photovoltaic layer com(cid:173)
`prises at least one photovoltaic cell. In at least one imple(cid:173)
`mentation, the photovoltaic layer is associated with at least
`one light detector. In at least one implementation, each of the
`light input ports is formed by a microstructured area in at 35
`least one of the first and second reflective surfaces.
`The present invention provides a number of beneficial
`elements which can be implemented either separately or in
`any desired combination without departing from the present
`teachings.
`An element of the invention is a light harvesting system
`collecting light over a given area and communicating the
`incident light into a photoresponsive layer, such as a pho(cid:173)
`tovoltaic layer, with an enhanced light coupling efficiency
`and with increasing the light path through the photorespon- 45
`sive layer.
`Another element of the invention is a plurality of light
`collecting elements within a focusing array which collec(cid:173)
`tively collect the incident light over a broad area and focus
`it into a plurality of small-aperture focal areas.
`Another element of the invention is the inclusion of
`distributed light input ports, such as areas having surface
`relief features, microstructures or texture, associated with a
`light receiving surface or the interior of photoresponsive
`layer and disposing them in a light receiving relationship to
`the light collecting elements of the focusing array.
`Another element of the invention is the inclusion of one
`or more cladding layers or mirrored surfaces to enhance
`respectively the total internal reflection or the specular
`reflection of light within the photoresponsive layer.
`Another element of the invention is the use of electrical
`contacts which can additionally be provided with enhanced
`reflective properties to promote retaining the light within the
`photoresponsive layer.
`Another element of the invention is the use of contact 65
`fingers associated with the light receiving surface of the
`photovoltaic layer and disposed in the spaces between the
`
`50
`
`The invention will be more fully understood by reference
`40 to the following drawings which are for illustrative purposes
`only:
`FIG. 1 and FIG. 2 are schematic diagrams and ray tracing
`for conventional photovoltaic systems.
`FIG. 3 is a schematic view and ray tracing of a light
`harvesting system in accordance with at least one embodi(cid:173)
`ment of the present invention.
`FIG. 4 is a perspective view of a focusing array according
`to at least one embodiment of the present invention, showing
`the use of a planar lenticular lens array.
`FIG. 5 is a perspective top view a focusing array accord(cid:173)
`ing to at least one embodiment of the present invention,
`showing the use of a planar lens array employing point focus
`lenses.
`FIG. 6 is a perspective top view of a focusing array
`55 according to at least one embodiment of the present inven(cid:173)
`tion, showing a different arrangement and shapes of point
`focus lenses than were shown in FIG. 5.
`FIG. 7 is a schematic view of a photovoltaic layer portion
`comprising an elongated V-shape groove, according to at
`60 least one embodiment of the present invention.
`FIG. 8 is a schematic view of a photovoltaic layer portion
`comprising a V-shape groove which has a shorter length than
`the elongated grove shown in FIG. 7, according to at least
`one embodiment of the present invention.
`FIG. 9 is a schematic view of a photovoltaic layer portion
`comprising a cavity having a pyramidal shape, according to
`at least one embodiment of the present invention.
`
`

`

`Case 6:20-cv-00139-ADA Document 1-6 Filed 02/21/20 Page 13 of 21
`
`US 10,269,999 B2
`
`7
`FIG. 10 is a schematic view of a photovoltaic layer
`portion comprising a cavity having a conical shape, accord(cid:173)
`ing to at least one embodiment of the present invention.
`FIG. 11 is a schematic view of a portion of light harvest(cid:173)
`ing system according to at least one embodiment of the
`present invention.
`FIG. 12 is a ray tracing of an incident ray being injected
`into a photovoltaic layer at oblique angles by a V-shaped
`cavity formed in a photovoltaic layer surface, according to
`at least one embodiment of the present invention.
`FIG. 13 is a ray tracing of an incident ray being injected
`into a photovoltaic layer by a funnel-shaped cavity or groove
`having curvilinear walls, according to at least one embodi(cid:173)
`ment of the present invention.
`FIG. 14 is a ray tracing of an incident ray being injected
`into a photovoltaic layer through a blind hole formed in a
`photovoltaic layer surface, according to at least one embodi(cid:173)
`ment of the present invention.
`FIG. 15 is a ray tracing of an incident ray being injected
`into a photovoltaic layer via a through hole, according to at
`least one embodiment of the present invention.
`FIG. 16 is a schematic ray tracing diagram of light
`trapping in a photovoltaic layer, according to at least one
`embodiment of the present invention.
`FIG. 17 is a schematic view and ray tracing of a light
`harvesting system portion further incorporating a layer of
`transparent material between a focusing array and a photo(cid:173)
`voltaic layer, according to at least one embodiment of the
`present invention.
`FIG. 18 is a schematic perspective view and raytracing of
`a light harvesting system portion in which light input ports
`are formed by textures areas in a photovoltaic layer, accord(cid:173)
`ing to at least one embodiment of the present invention.
`FIG. 19 is a schematic perspective view of a photovoltaic
`layer portion incorporating a plurality of prismatic surface
`relief features, according to at least one embodiment of the
`present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Referring more specifically to the drawings, for illustra(cid:173)
`tive purposes the present invention is embodied in the
`apparatus generally shown in the preceding figures. It will be
`appreciated that the apparatus may vary as to configuration
`and as to details of the parts without departing from the basic
`concepts as disclosed herein. Furthermore, elements repre(cid:173)
`sented in one embodiment as taught herein are applicable
`without limitation to other embodiments taught herein, and
`in combination with those embodiments and what is known
`in the art.
`A wide range of applications exist for the present inven(cid:173)
`tion in relation to the collection of electromagnetic radiant
`energy, such as light, in a broad spectrum or any suitable
`spectral bands or domains. Therefore, for the sake of sim(cid:173)
`plicity of expression, without limiting generality of this
`invention, the term "light" will be used herein although the
`general terms "electromagnetic energy", "electromagnetic
`radiation", "radiant energy" or exemplary terms like "visible
`light", "infrared light", or "ultraviolet light" would also be 60
`appropriate.
`In order to be able to compare and contrast the present
`invention with typical photovoltaic structures, FIG. 1 and
`FIG. 2 are shown to illustrate the operation of a common
`crystalline silicon (Si) solar cell typically employing a 65
`photovoltaic layer 4 of mono- or polycrystalline silicon with
`a p-n junction formed by joining n-type and p-type Si.
`
`8
`Individual rays interacting with the photovoltaic structure
`are illustrated by line segments that, by way of example and
`not limitation, can represent the paths of individual photons
`of the incident light beam or otherwise represent possible
`light paths. In FIG. 1, a front contact is formed by contact
`fingers 24 attached to a front surface 32 of photovoltaic layer
`4 and a back contact 16 is formed by a metallic layer
`attached to a back surface 34 of photovoltaic layer 4.
`Referring further to FIG. 1, an incident light ray 100
`10 emanated by a distant source and entering photovoltaic layer
`4 is absorbed within this layer with the generation of an
`electron-hole pair 50 due to the photo effect. The front and
`back contacts of the cell collect the charge carriers thus
`15 generating useful photocurrent in an external circuit (not
`shown). A ray 102 strikes a contact finger 24 and is absorbed
`or scattered without photocurrent generation. A ray 104
`entering photovoltaic layer 4 is reflected from back contact
`16 and exits back into the environment without being
`20 absorbed and thus without producing the photocurrent.
`Finally, a ray 106 striking front surface 32 of photovoltaic
`layer 4 is reflected from the surface without penetration into
`the photoactive layer and without useful absorption. Thus,
`ray 100 represents a useful, absorbed photon or photons
`25 while rays 102, 104 and 106 represent photons that are lost
`due to various optical loss mechanisms. It should be noted
`that the light rays shown in FIG. 1 do not necessarily
`represent all possible light paths or absorption and loss
`scenarios and are merely provided for the purpose of illus-
`30 trating some of the most common loss mechanisms.
`In FIG. 2, a conventio