Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
  • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
  • H01L31/0687—Multiple junction or tandem solar cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/042—PV modules or arrays of single PV cells
  • H01L31/047—PV cell arrays including PV cells having multiple vertical junctions or multiple V-groove junctions formed in a semiconductor substrate
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/544—Solar cells from Group III-V materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• solar energy which employs photovoltaic (PV) technology for conversion of light into electricity.
• PV photovoltaic
• solar energy can be exploited for heat generation (e.g., in solar furnaces, steam generators, and the like).
• Solar technology is typically implemented in a series of PV cells, or solar cells, or panels thereof that receive sunlight and convert the sunlight into electricity, which can be subsequently delivered into a power grid.
• Significant progress has been achieved in design and production of solar panels, which has effectively increased efficiency while reducing manufacturing cost thereof.
• solar energy collection systems like solar concentrators can be deployed to convert solar energy into electricity which can be delivered to power grids, and to harvest heat as well.
• solar concentrators In addition to development of solar concentrator technology, development on solar cells directed to utilization is solar concentrators has been pursued.
• VMJ vertical multi- junction
• the unique VMJ cell design can inherently provides high-voltage low-series resistance output characteristics, making it ideally suited for efficient performance in high intensity photovoltaic concentrators.
• Another key feature of the VMJ Cell is its design simplicity that leads to low manufacturing cost.
• VMJ efficacy of VMJ can be evidenced on performance data taken on an experimental VMJ cell with 40 series-connected junctions over the range of 100 to 2500 suns intensities where the output power density exceeded 400,000 watts/m 2 at 25 volts with near 20% efficiency.
• the foregoing performance in VMJ solar cells is accomplished with low manufacturing cost(s) and low manufacturing complexity.
• Such aspects are believe to be the needed drivers for feasible technical performance and economic efficiencies needed to enable photovoltaic concentrator systems to be significantly more cost effective and viable in solving global energy problems.
• any increase in cell efficiency e.g., more watts in output
• concentrator system size e.g., less cost associated with bill of materials
• photovoltaic power is widely recognized as an ideal renewable energy technology, its associated cost(s) can be a major impediment to adoption and market penetration.
• photovoltaic -based power needs to become cost-competitive with traditional power sources, including coal-fired power which is well developed, adopted among consumers and substantially cost effective.
• access to low cost electrical power is considered essential in all global economies; so terawatts (e.g., thousands of Giga Watts) of photovoltaic power systems can be needed.
• Market studies show installed photovoltaic power systems must drop to a benchmark cost of $3/watt, or less, before being cost-competitive without subsidies in large utility scale applications. Since installed photovoltaic system costs currently exceed $6/watt, substantial cost improvements are still required.
• VMJ solar cell technology is substantially different from conventional concentrator solar cells.
• the VMJ solar cell technology provides at least two advantages with respect to other technologies: (1) it does not require photolithography, and (2) a single high-temperature diffusion step, at temperatures greater than 1000 0 C, can be employed to form both junctions. Consequently, lower manufacturing cost is a given.
• VMJ solar cells can be operated at high intensities; e.g., operation at 2500 suns. It is readily apparent from such operation that series-resistance is not a problem in VMJ cell design; even at intensities an order of magnitude higher conventional wisdom suggested it was not economically viable.
• the current density in VMJ unit cells at 2500 suns is typically near 70 A/cm 2 , a radiation level that can be substantially detrimental to most solar cells based on other technologies.
• Triple-junction Solar Cells made with III-V materials containing gallium (Ga), phosphorus (P), arsenide (As), indium (In) and germanium (Ge).
• Triple-junction cell may use 20 to 30 different semiconductors layered in series upon germanium wafers: doped layers Of GaInP 2 and GaAs grown in a metal-organic chemical vapor deposition (MOCVD) reactor where each type of semiconductor will have a characteristic band gap energy that causes it to absorb sunlight most efficiently at a certain color.
• MOCVD metal-organic chemical vapor deposition
• the semiconductors layers are carefully chosen to absorb nearly the entire solar spectrum, thus generating electricity from as much of the sunlight as possible.
• These multi-junction devices are the most efficient solar cells to date, reaching a record high of 40.7% efficiency under modest solar concentration and laboratory conditions. But since they are expensive to manufacture, they require application in photovoltaic concentrators.
• III- V solar cell materials are rapidly increasing.
• the cost of pure gallium increased from about $350 per Kg to $680 per kg and germanium prices increased substantially to $1000-$ 1200 per Kg.
• the price of indium which was $94 per Kg in 2002 increased to nearly $1000 per Kg in 2007.
• indium is a rare element that is widely used to form transparent electrical coatings in the form of indium-tin oxide for liquids crystal displays and large flat-panel monitors. Realistically, these materials appear not viable long term photovoltaic (PV) solutions needed to provide terawatts of low cost power in solving major global energy problems.
• PV photovoltaic
• III- V semiconductor solar cell of area 0.26685 cm 2 may generate a power of 2.6 watts, or about 10 W/cm 2 , and it has been estimated that such technology may eventually produce electricity at 8-10 cents/kWh, substantially similar to the price of electricity from conventional sources, further analysis may be needed to support such estimate.
• VMJ solar cells showed output power exceeding 40 W/cm 2 at 2500 suns intensity using the least costly semiconductor material with low cost manufacturing. (This output power is over 400,000 W/m 2 .)
• Si-based solar cell technology remains substantially dominant in photovoltaic elements and applications.
• silicon is the only semiconductor material with an existing industrial base that would be capable of supplying terawatts of photovoltaic power within the foreseeable future for widespread global application.
• the subject innovation provides semiconductor-based photovoltaic cells and processes that mitigate recombination losses of photogenerated carriers.
• diffuse doping layers in active photovoltaic elements are coated with patterns of dielectric material(s) that reduce contact between metal contacts and the active PV element.
• Various patterns can be utilized, and one or more surfaces of the PV element can be coated with one or more dielectrics.
• Vertical Multi- Junction (VMJ) solar cells can be produced with patterned PV elements, or unit cells.
• Patterned PV elements can increase series resistance of VMJ solar cells, and patterning one or more surfaces in the PV element can add complexity to a process utilized to produce VMJ solar cells; yet, reduction of carrier losses at diffuse doping layers can increase efficiency of solar cells and thus provide with PV operational advantages that outweigh increased manufacturing complexity.
• a system that enables fabrication of the semiconductor-based PV cells is also provided. [0018] Aspects or features described herein, and associated advantages, such as reduction of recombination losses of photogenerated carriers, can be exploited in any class of photovoltaic cells such as solar cells, thermophotovoltaic cells, or cells excited with laser sources of photons. Additionally, aspects of the subject innovation also can be implemented in other class(es) of energy-conversion cells such as betavoltaic cells.
• the subject innovation mitigates bulk recombination losses in a vertical multi junction (VMJ) cell via a texturing on its light receiving surface.
• the textures can be in form of cavity shaped grooves - as "V" shaped cross section configurations, "U” shaped cross configurations, and the like - wherein a plane that includes such cross section configuration is substantially perpendicular to the direction of stacking the unit cells that form the VMJ.
• a plane that includes substantially repetitive cross sections e.g. cross-sectioning a direction that grooves are extended thereon) is substantially perpendicular to the direction of stacking the unit cells.
• Such an arrangement facilitates directing the refracted light away from the p+ and n+ diffused doped regions of the VMJ- while at the same time creating desired carriers in a decreasing volume. Accordingly, incident light can be refracted in the plane that includes the cross section configuration, and which is substantially perpendicular to the direction of stacking the unit cells.
• conventional silicon photovoltaic cells are typically textured to incline the penetration of the light, so that more of the longer wavelengths are absorbed closer to PN junctions (positioned horizontally) for better current collection of carriers - and hence mitigate poor spectral response to longer wavelengths in the solar spectrum.
• PN junctions positioned horizontally
• such is not required in the VMJ of the subject innovation that includes vertical junctions, and hence already provides for an enhanced spectral response to the longer wavelengths in the solar spectrum.
• an outcome for implementing grooves of the subject innovation is to mitigate bulk recombination losses by reducing the bulk volume - (as opposed to conventional solar surfaces with texturing, which reduce reflection, or cause reflected or refracted light to become closer to the junctions).
• the VMJ cell has demonstrated better carrier current collection for both the short wavelengths and the long wavelengths, wherein the short wavelength response is due to eliminating a highly doped horizontal junction at the top surface, and the long wavelength respond is due to the enhanced collection efficiency of vertical junctions.
• the cavity shaped grooved texture of the subject innovation e.g., random, pyramids, domes, and similar raised configurations
• incident light becomes refracted in all directions, resulting in light absorption in the p+ and n+ diffused regions and hence reduced efficiency.
• a VMJ can be formed by stacking multiple cell units, wherein each cell itself can include a plurality of parallel semiconductor substrates or layers that are stacked together. Each layer can consist of impurity doped semiconductor material that form a PN junction, and further include a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction. Subsequently a plurality of such cell units are integrated to shape a VMJ. Next, on a surface of the VMJ cell that receives light, cavity shaped grooves can be formed (e.g., via a dicing saw) - wherein the plane that includes the cross section configuration is substantially perpendicular to the direction of stacking the unit cells, which form the VMJ.
• incident light can be refracted in the plane that includes the repetitive cross section configurations, and which is substantially perpendicular to the direction of stacking the unit cells (e.g., hence supply a higher absorption for a given depth.)
• various back surface(s) and side surface(s) with reflection coatings can be implemented in conjunction with various aspects of the subject innovation.
• a grooved surface of the subject innovation further improves carrier collection, while reducing bulk recombination losses.
• the V-grooves can be positioned perpendicular to the p+nn+ (or n+pp+) unit cells, to increase optical absorption paths of the longer wavelengths in the solar spectrum and enable light absorption being substantially confined within the n-type bulk region of p+nn+ unit cells.
• such V-grooves can have an anti-reflection coating applied to improved incident light absorption in the cell.
• the subject innovation mitigates bulk recombination losses in a vertical multi junction (VMJ) cell via a texturing on its light receiving surface.
• VMJ vertical multi junction
• the textures can be in form of cavity shaped grooves - as "V" shaped cross section configurations, "U” shaped cross configurations, and the like - wherein a plane that includes such cross section configuration is substantially perpendicular to the direction of stacking the unit cells that form the VMJ.
• a plane that includes substantially repetitive cross sections e.g. cross-sectioning a direction that grooves are extended thereon
• incident light can be refracted in the plane that includes the cross section configuration, and which is substantially perpendicular to the direction of stacking the unit cells.
• the texturing for the VMJ of the subject innovation is different from prior art for conventional silicon photovoltaic cell textures - both in terms of orientation of PN junctions; and/or interaction with incident light.
• conventional silicon photovoltaic cells are typically textured to incline the penetration of the light, so that more of the longer wavelengths are absorbed closer to PN junctions (positioned horizontally) for better current collection of carriers - and hence mitigate poor spectral response to longer wavelengths in the solar spectrum.
• an outcome for implementing grooves of the subject innovation is to mitigate bulk recombination losses by reducing the bulk volume - (as opposed to conventional solar surfaces with texturing, which reduce reflection, or cause reflected or refracted light to become closer to the junctions).
• the VMJ cell has demonstrated better carrier current collection for both the short wavelengths and the long wavelengths, wherein the short wavelength response is due to eliminating a highly doped horizontal junction at the top surface, and the long wavelength respond is due to the enhanced collection efficiency of vertical junctions.
• the cavity shaped grooved texture of the subject innovation e.g., random, pyramids, domes, and similar raised configurations
• incident light becomes refracted in all directions, resulting in light absorption in the p+ and n+ diffused regions and hence reduced efficiency.
• a VMJ can be formed by stacking multiple cell units, wherein each cell itself can include a plurality of parallel semiconductor substrates or layers that are stacked together. Each layer can consist of impurity doped semiconductor material that form a PN junction, and further include a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction. Subsequently a plurality of such cell units are integrated to shape a VMJ. Next, on a surface of the VMJ cell that receives light, cavity shaped grooves can be formed (e.g., via a dicing saw) - wherein the plane that includes the cross section configuration is substantially perpendicular to the direction of stacking the unit cells, which form the VMJ.
• incident light can be refracted in the plane that includes the repetitive cross section configurations, and which is substantially perpendicular to the direction of stacking the unit cells (e.g., hence supply a higher absorption for a given depth.)
• various back surface(s) and side surface(s) with reflection coatings can be implemented in conjunction with various aspects of the subject innovation.
• a grooved surface of the subject innovation further improves carrier collection, while reducing bulk recombination losses.
• the V-grooves can be positioned perpendicular to the p+nn+ (or n+pp+) unit cells, to increase optical absorption paths of the longer wavelengths in the solar spectrum and enable light absorption being substantially confined within the n-type bulk region of p+nn+ unit cells.
• V-grooves can have an anti-reflection coating applied to improved incident light absorption in the cell.
• the subject innovation supplies a buffer zone(s) at end layers of a high voltage silicon vertical multi junction (VMJ) photovoltaic cell, to provide a barrier that protects the active layers while providing an ohmic contact.
• VJ vertical multi junction
• Such buffer zone(s) can be in form of an inactive layer(s) arrangement that is additionally stacked upon and/or below end layers of the VMJ cell.
• the VMJ cell itself can include a plurality of cell units, wherein each cell unit employs several active layers (e.g., three) to form a PN junction and a "built -in" electrostatic drift field (which enhances minority carrier movement toward the PN junction.)
• various active layers such as nn+ and/or p+n junctions located at either ends of a VMJ cell (and as part of cell units thereof) can be safeguarded against adverse forms of stress and/or strain (e.g., thermal/mechanical compression, torsion, moment, shear and the like - which can be induced in the VMJ during fabrication and/or operation thereof.)
• the buffer zone can be formed via materials that have substantially low resistivity ohmic contact, either metals or semiconductors, such that it will not contribute any substantial series resistance loss in the photovoltaic cell at operating conditions
• the buffer zone can be formed by employing low resistivity silicon wafers that are p-type doped, so that when using other p-type dopants such as aluminum alloys in manufacturing the VMJ photovoltaic cell, it will mitigate a risk of auto-doping (in contrast to employing n- type wafers that can create unwanted pn junctions - when an object is to create a substantially low resistivity ohmic contact.
• the subject innovation can be implemented as part of any class of photovoltaic cells such as solar cells or thermophotovoltaic cells. Additionally, aspects of the subject innovation also can be implemented in other class(es) of energy-conversion cells such as betavoltaic cells.
• the buffer zone can be in form of a rim on a surface of an end layer of a cell unit, which acts as a protective boundary for such active layer and further frames the VMJ cell for ease of handling and transportation.
• a secure grip to the VMJ cell such rim formation also eases operation related to the anti reflective coating (e.g., coating can be applied uniformly when the cell is securely maintained during operation, such as by mechanically clamping thereon.)
• the buffer zones e.g., the inactive layers positioned at ends of the VMJ
• the buffer zones can be physically positioned adjacent to other buffer zones during the deposition - and hence any unwanted dielectric coating material that inadvertently penetrates down onto the contact surfaces can be readily removed without damaging active unit cells.
• the buffer zone can be formed from substantially low resistivity and highly doped silicon (e.g., a thickness of approximately 0.008") Such buffer zone can subsequently contact conductive leads that partition or separate a VMJ cell from another VMJ cell in a photovoltaic cell array.
• the buffer zone can be sandwiched between an electrical contact, and the active layers of the VMJ cells.
• such buffer zones can have thermal expansion characteristics that substantially match those of the active layers, hence mitigating performance degradation (e.g., mitigation of stress/strain caused when leads are welded or soldered in manufacturing.)
• highly doped low resistivity silicon layers can be employed, which match the thermal expansion coefficient (3 x 10 "6 /°C) of all active unit cells. Accordingly, substantially strong ohmic contacts can be provided to the active unit cells, which additionally mitigate stress problems caused by welding/ soldering and/or from mismatched thermal expansion coefficients in contact materials.
• Other examples include introducing metallic layers, such as tungsten (4.5 x 10 "6 /°C), or molybdenum (5.3 x 10 "6 /°C), which are chosen for thermal expansion coefficients substantially similar to the active silicon (3 x 10 "6 /°C) p+nn+ unit cells.
• the metallization applied to the outer layers of the low resistivity silicon layers of the buffer zone, or to the metallic layers of electrodes that are alloyed to the active unit cells, can be welded or soldered without introducing deleterious stress to the high intensity solar cell or photovoltaic cell- wherein such outer layers serve as ohmic contacts; rather than segments of unit cells in series with the other unit cells.
• Various aspect of the subject innovation can be implemented as part of wafers having miller indices (111) for orientation of associated crystal planes of the buffer zones, which are considered mechanically stronger and slower etching than (100) crystal orientation silicon typically used in making active VMJ unit cells.
• low resistivity silicon layers can have a different crystal orientation than that of the active unit cells, wherein by employing such alternative orientation, a device with improved mechanical strength/end contacts is provided.
• edges of (100) orientated unit cells typically etch faster and essentially round off corners of the active unit cells with such crystal orientation - as compared to the inactive (111) orientated end layers - hence resulting in a more stable device structure with higher mechanical strength for welding or otherwise connecting end contacts.
• the subject innovation employs a vertical multi junction (VMJ) photovoltaic cell, to provide electrolysis for compounds (e.g., water), via incident lights and current generation for an electrolysis thereof (e.g., generation of hydrogen and oxygen).
• VJ vertical multi junction
• Such VMJ includes a plurality of cell units in contact with the electrolyte, wherein each cell unit employs several active layers (e.g., three) to form a PN junction and a "built -in" electrostatic drift field (which enhances minority carrier movement toward the PN junction.)
• the VMJ can be partially or totally submerged within water/electrolytes, as part of a transparent housing such as glass or plastic, wherein as light encounters such VMJ a plurality of electrolysis electrodes (anodes/cathodes) can be formed through out the VMJ. Current flowing among such electrolysis electrodes flows through the water and decompose the water to hydrogen and oxygen, whenever threshold voltage of electrolysis is reached.
• such decomposition threshold voltage lies within a range of 1.18 volts to 1.6 volt to split the water and create hydrogen and oxygen. It is to be appreciated that higher voltages can be reached through the stacked plurality of cell units (e.g., a plurality of cells connected in series).
• catalyst additives can further be employed to increase hydrogen and oxygen evolution efficiency, and reduce semiconductor corrosion caused by high electrode potential and the electrolyte solutions.
• the electrolyte can be formed of any solution that does not adversely affect stacked layers that form the VMJ cell (e.g., iridium-based material made of iridium, a binary alloy thereof, or an oxide thereof.)
• the VMJ is partially or totally submerged in the water/electrolyte, and can include raised metal areas (e.g., VMJ electrodes) that protrude above the silicon of the VMJ cell to increase contact area with the water and electrolyte, and enhance hydrogen production.
• VMJ electrodes e.g., VMJ electrodes
• protrusions can be of several millimeters, for example.
• substantially thin layers of electro-catalyst materials such as platinum, RuC ⁇ , or titanium, can be incorporated in to the metallization during VMJ cell fabrication to enhance the formation of hydrogen.
• electro-catalyst material since the n+ negative (-) side of the metallization can be different from that for the p+ positive (+) side. It is to be appreciated that one skilled in the art can readily select catalyst materials that will enhance hydrogen production and are stable and compatible with VMJ cell fabrication. Moreover, ultrasonic units can be employed to free the generated oxygen or hydrogen bubbles that remain attached to electrolysis electrodes. It is to be appreciated the flow of the electrolyte can also remove such formed bubbles.
• the electrolyte solution is introduced into a container that contains the VMJ, wherein it is fully or substantially immersed. Such system is then subjected to incident light and a current flow generated from the VMJ.
• the incident light on the VMJ can generate electric current throughout the electrolyte solution, and any location wherein a threshold for decomposing water is reached or passes (e.g., around 1.6 volts) electrolysis of water occurs. For example, across each unit cell a voltage of 0.6 volts can be generated (e.g., for a 1000 suns) and between regions of a first unit cell and a third unit cell electrolysis can occur.
• various collection mechanisms e.g., membranes, sieved plates, and the like
• water electrolysis e.g., around 1.6 volts
• decomposition of water e.g., around 1.6 volts
• collection mechanisms can also be positioned in the downstream flow of the electrolyte to collect generated oxygen and hydrogen gases.
• Fig. 1 illustrates a schematic perspective of a textured or grooved surface as part of vertical multi junction (VMJ) cell in accordance with an aspect of the subject innovation.
• Fig. 2 illustrates exemplary cross sections for implementing grooves of the subject innovation.
• Fig. 3 illustrates an exemplary stacking of cell units to form a VMJ with a grooved surface according to an aspect of the subject innovation.
• Fig. 4 illustrates a particular unit cell that in part forms a VMJ according to an aspect of the subject innovation.
• Fig. 5 illustrates a related methodology of creating a VMJ with grooved surfaces to mitigate bulk recombination losses according to an aspect of the subject innovation.
• Fig. 6 illustrates a schematic block diagram of an arrangement for buffer zones as part of a vertical multi junction (VMJ) cell in accordance with an aspect of the subject innovation.
• Fig. 7 illustrates a particular aspect of a unit cell, an array of which can from a VMJ cell in accordance with a particular aspect of the subject innovation.
• Fig. 8 illustrates an exemplary cross section for a buffer zone in form of a rim formation on surfaces of unit cells located at either end of a VMJ.
• Fig. 9 illustrates a related methodology of employing buffer zones at end layers of a high voltage silicon vertical multi junction (VMJ) photovoltaic cell, to provide a barrier that protects the active layers thereof.
• VMJ vertical multi junction
• Fig. 10 illustrates a schematic cross sectional view for a solar assembly that includes a modular arrangement of photovoltaic (PV) cells, which can implement VMJs with buffer zones.
• PV photovoltaic
• Fig. 11 illustrates a schematic block diagram of an electrolysis system that employs a vertical multi junction (VMJ) cell for water electrolysis in accordance with an aspect of the subject innovation.
• VMJ vertical multi junction
• Fig. 12 illustrates protrusions of metal layers from a surface of the
• VMJ that can facilitate the electrolysis process.
• Fig. 13 illustrates a voltage gradient across the VMJ and throughout the stacked cells as part thereof.
• Fig. 14 illustrates a methodology of water electrolysis via a VMJ according to an aspect of the subject innovation.
• Fig. 15 illustrates a VMJ cell that can be employed for electrolysis of the subject innovation.
• Fig. 16 illustrates a single cell unit, a plurality of which form the VMJ for electrolysis of the subject innovation.
• Fig. 17 illustrates a VMJ cell with a grooved surface to improve efficiency of the electrolysis process.
• Fig. 18 illustrates exemplary grooving for a surface of a VMJ employed for electrolysis according to an aspect of the subject innovation.
• FIGs. 19A and 19B are diagrams of example configuration of patterned surfaces of PV elements in accordance with aspects disclosed in the subject application.
• FIG. 19C displays a diagram of example set of precursors and derived
• PV elements that can be produced through doping in accordance with aspects described herein.
• FIGs. 20A-20C illustrate diagrams of example configurations of patterned dielectric coating of PV elements and an illustrative VMJ stack in accordance with aspects described herein.
• FIG. 2OD illustrates a VMJ PV cell processed to expose a specific crystalline surface.
• FIGs. 21A-21C illustrate diagrams of example configurations of patterned dielectric coating of PV elements and an illustrative VMJ stack in accordance with aspects described herein.
• FIG. 22 illustrates a cross-section diagram of an example configuration of patterned dielectric coating of an active PV element with a reduced diffuse doping layer in accordance with aspects described herein.
• FIGs. 23A and 23B illustrate diagrams of example configurations of patterned dielectric coatings of a PV element in accordance with aspects described herein.
• FIG. 24 presents a perspective illustration of an embodiment of a photovoltaic cell with textured surface in accordance with aspects described herein.
• FIG. 25 is a flowchart of an example method for producing a photovoltaic cell with reduced carrier recombination losses according to aspects disclosed herein.
• FIG. 26 displays a flowchart of an example method for producing VMJ solar cells with reduced carrier recombination losses according to aspects described herein.
• FIG. 27 is a block diagram of an example system that enables fabrication of solar cells in accordance with aspects described herein.
• n-type and N-type are employed interchangeably, so are the terms “n+-type” and “N+-type.”
• p- type and P -type are also utilized interchangeably, and so are the terms “p+-type” and "P+-type.”
• doping type also appears abbreviated, e.g., n-type is labeled as N, p+-type is indicated as P+, etc.
• Multi-layer photovoltaic elements or unit cells are labeled as a set of letters, each of which indicates doping type of the layer; for instance, a p-type/n-type junction is labeled PN, whereas a p+-type/n-type/n+-type junctions is indicated with P+NN+; labeling of other junction combinations also adhere to this notation.
• Fig. 1 illustrates a schematic perspective of a grooved surface 100 as part of a vertical multi junction (VMJ) cell 120 in accordance with an aspect of the subject innovation.
• VMJ vertical multi junction
• Such an arrangement for texturing 100 enables the refracted light to be directed away from the p+ and n+ diffused doped regions - while at the same time creating desired carriers. Accordingly, incident light can be refracted in the plane 110 having a normal vector n.
• plane 110 is parallel to the PN junction planes of the VMJ 120, and can include the cross section configuration of the grooves 100.
• an anti-reflection coating can be applied to the textured 100 surface to increase incident light absorption in the cell.
• Fig. 2 illustrates exemplary textures for grooving a surface of the VMJ, which receives light thereon.
• Such grooving can be in form of cavity shaped grooves - for example, as "V" shaped cross section configurations having a variety of angles
• V grooves are to mitigate bulk recombination losses by reducing the bulk volume - (as opposed to conventional solar surfaces with texturing, which reduce reflection, or cause reflected or refracted light to become closer to the junctions).
• VMJ cell has demonstrated better carrier current collection for both the short wavelengths and the long wavelengths, wherein the short wavelength response is due to eliminating a highly doped horizontal junction at the top surface and the long wavelength respond is due to the enhanced collection efficiency of vertical junctions.
• other textures e.g., random, pyramids, domes, and similar raised configurations
• incident light becomes refracted in all directions, resulting in light absorption in the p+ and n+ diffused regions and hence reduced efficiency.
• U and "V" shaped grooves are exemplary in nature and other configurations are well within the realm of the subject innovation.
• Fig. 3 illustrates an arrangement of unit cells 311, 313, 317 that can implement grooved texture on a side 345 in accordance with an aspect of the subject innovation.
• the VMJ 315 itself is formed from a plurality integrally bonded cell units 311, 313, 317 (1 to k, k being an integer), wherein each cell unit itself is formed from stacked substrates or layers (not shown).
• each cell unit 311 can include a plurality of parallel semiconductor substrates stacked together, and consisting of impurity doped semiconductor material, which form a PN junction and a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction.
• the textures on a light receiving surface 345 facilitate refracted light to be directed away from the p+ and n+ diffused doped regions - while at the same time creating desired carriers are created.
• incident light can be refracted in the plane that includes the cross section configuration, and which is substantially perpendicular to the direction of stacking the unit cells (e.g., perpendicular to vector n.)
• Fig. 4 illustrates a particular aspect of a unit cell, an array of which can form a VMJ cell having a textured grooving of the subject innovation.
• the unit cell 400 includes layers 411, 413, 415 stacked together in a substantially parallel arrangement.
• Such layers 411, 413, 415 can further include impurity doped semiconductor material, wherein layer 413 is of one conductivity type and layer 411 is of an opposing conductivity type - to define a PN junction at intersection 412.
• layer 415 can be of the same conductivity type as layer 413-yet with substantially higher impurity concentration, hence generating a built-in electrostatic drift field that enhances minority carrier movements toward the PN junction 412.
• Such unit cells can be integrally bonded together to form a VMJ, and surface grooved according to various aspects of the subject innovation.
• PNN+ (or NPP+) junctions can be formed to a depth of approximately 3 to 10 ⁇ m into flat wafers of high resistivity (e.g., more than 100 ohm- cm) of N type (or P type) silicon -having a thickness of approximately 0.008 inch. Subsequently, such PNN+ wafers are stacked together with a thin layer of aluminum interposed therebetween, wherein each wafer's PNN+ junction and crystal orientation can be oriented in the same direction.
• aluminum-silicon eutectic alloys can be employed, or metals such as molybdenum, or tungsten, which have thermal coefficient(s) that substantially matches the thermal coefficient of silicon.
• metals such as molybdenum, or tungsten, which have thermal coefficient(s) that substantially matches the thermal coefficient of silicon.
• Buffer zones with substantially low resistivity can also be supplied in form of an inactive layer(s) arrangement that is additionally stacked upon and/or below end layers of the VMJ cell - hence implementing a barrier that protects the active layers against adverse forms of stress and/or strain (e.g., thermal/mechanical compression, torsion, moment, shear and the like - which can be induced in the VMJ during fabrication and/or operation thereof.)
• the surface of such cell can then be grooved to mitigate bulk recombination losses, as described in detail supra.
• other material such as germanium and titanium can also be employed.
• aluminum-silicon eutectic alloys can also be employed.
• Fig. 5 illustrates a related methodology 500 of grooving a surface of a
• VMJ that receives light. While the exemplary method is illustrated and described herein as a series of blocks representative of various events and/or acts, the subject innovation is not limited by the illustrated ordering of such blocks. For instance, some acts or events may occur in different orders and/or concurrently with other acts or events, apart from the ordering illustrated herein, in accordance with the innovation. In addition, not all illustrated blocks, events or acts, may be required to implement a methodology in accordance with the subject innovation. Moreover, it will be appreciated that the exemplary method and other methods according to the innovation may be implemented in association with the method illustrated and described herein, as well as in association with other systems and apparatus not illustrated or described.
• each cell unit itself can include a plurality of parallel semiconductor substrates that are stacked together.
• Each layer can consist of impurity doped semiconductor material that form a PN junction, and further include a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction.
• buffer zones can also be implemented as a protection for such cells (e.g., stress/strain induced thereon during fabrication.)
• a surface of the VMJ cell that receives light cavity shaped grooves can be formed (e.g., via a dicing saw) - wherein the plane that includes the cross section configuration is substantially perpendicular to the direction of stacking the unit cells that form the VMJ.
• incident light can be refracted in the plane that includes the cross section configuration (and/or parallel to the PN junctions), and which is substantially perpendicular to the direction of stacking the unit cells
• Fig. 6 illustrates a schematic block diagram of an arrangement for buffer zones as part of vertical multi junction (VMJ) cell in accordance with an aspect of the subject innovation.
• the VMJ 615 itself is formed from a plurality of integrally bonded cell units 611, 617 (1 to n, n being an integer), wherein each cell unit itself is formed from stacked substrates or layers (not shown).
• each cell unit 611, 617 can include a plurality of parallel semiconductor substrates stacked together, and consisting of impurity doped semiconductor material, which form a PN junction and a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction.
• each of the buffer zones 610 612 can be formed via material that have substantially low resistivity ohmic contact (e.g., any range with upper limit less than approximately 0.5 ohm-cm), while mitigating and/or eliminating unwanted auto doping.
• the buffer zones 610, 612 can be formed by employing low resistivity wafers that are p-type doped, with other p-type dopants such as aluminum alloys, to mitigate a risk of auto-doping (in contrast to employing n-type wafers that can create unwanted pn junctions - when it is desired to create a substantially low resistivity ohmic contact.)
• Fig. 7 illustrates a particular aspect of a unit cell, an array of which can form a VMJ cell.
• the unit cell 700 includes layers 711, 713, 715 stacked together in a substantially parallel arrangement.
• Such layers 711, 713, 715 can further include impurity doped semiconductor material, wherein layer 713 is of one conductivity type and layer 711 is of an opposing conductivity type - to define a PN junction at intersection 712.
• layer 715 can be of the same conductivity type as layer 713-yet with substantially higher impurity concentration, hence generating a built-in electrostatic drift field that enhances minority carrier movements toward the PN junction 712.
• Such unit cells can be integrally bonded together to form a VMJ, wherein a buffer zone of the subject innovation can be positioned to safe guard the VMJ and associated unit cells and/or layers that form them.
• PNN+ (or NPP+) junctions can be formed to a depth of approximately 3 to 10 ⁇ m into flat wafers of high resistivity (e.g., more than 100 ohm- cm) of N type (or P type) silicon - having a thickness of approximately 0.008 inch. Subsequently, such PNN+ wafers are stacked together with a thin layer of aluminum interposed between each wafer, wherein each wafer's PNN+ junction and crystal orientation can be oriented in the same direction.
• aluminum-silicon eutectic alloys can be employed, or metals such as molybdenum or tungsten with thermal coefficient(s) that substantially matches the thermal coefficient of silicon.
• the silicon wafers and aluminum interfaces can be alloyed together, such that the stacked assembly can be bonded together.
• aluminum-silicon eutectic alloys can also be employed. It is to be appreciated that various N+-type and P-type doping layers can be implemented as part of the cell units and such arrangements are well within the realm of the subject innovation.
• Buffer zones with substantially low resistivity can also be supplied in form of an inactive layer(s) arrangement that is additionally stacked upon and/or below end layers of the VMJ cell - hence implementing a barrier that protects the active layers against adverse forms of stress and/or strain (e.g., thermal/mechanical compression, torsion, moment, shear and the like - which can be induced in the VMJ during fabrication and/or operation thereof.)
• stress and/or strain e.g., thermal/mechanical compression, torsion, moment, shear and the like
• Fig. 8 illustrates an exemplary cross section for a buffer zone in form of a rim formation 810 (812) on surfaces of an end layer 831 (841) of unit cells 830 (840), which in part forms the VMJ cell 800.
• rim formations 810, 812 act as a protective boundary for active layers of the cell units, and further partially frame the VMJ cell 800 for ease of handling and transportation (e.g., a low resistivity buffer zone and edge or end contact of the VMJ cell.)
• the rim formation also eases operation related to the anti reflective coating (e.g., coating can be applied uniformly when the cell is securely maintained during operation, such as by mechanically clamping thereon.)
• such rim formations can physically be positioned adjacent to other rim formations during the deposition process, wherein any unwanted dielectric coating material that inadvertently penetrates down onto the contact surfaces can be readily removed without damaging the unit cells 830, 840.
• the rim formation 810 (812) representing the buffer zone can be formed from substantially low resistivity and highly doped silicon (e.g., a thickness of approximately 0.008"), wherein the rim formation can subsequently contact conductive leads that partition a VMJ cell from another VMJ cell in a photovoltaic cell array.
• the conductive leads are not required to have full electrical contact to the buffer zone. As such, they can be partial contacts, such as a point contact, or a series of point contacts, while nevertheless providing good electrical contact. It is to be appreciated that Fig.
• the buffer zone 810 formed in manufacturing reaching the surfaces of 800 with 810 bonding to active layers 841 - are well within the realm of the subject innovation.
• the shape of 810 can represent a partial lead contact to the metalized layer on the buffer zone as discussed earlier.
• the conductive leads can be in form of electrode layers, which are formed by depositing a first conductive material on a substrate - and can comprise; tungsten, silver, copper, titanium, chromium, cobalt, tantalum, germanium, gold, aluminum, magnesium, manganese, indium, iron, nickel, palladium, platinum, zinc, alloys thereof, indium-tin oxide, other conductive and semiconducting metal oxides, nitrides and suicides, polysilicon, doped amorphous silicon, and various metal composition alloys.
• Fig. 8 is exemplary in nature and other configurations for the buffer zone such as, rectangular, circular, cross sections having a range of surface contact with the active layers are well within the realm of the subject innovation.
• various aspect of the subject innovation can be implemented as part of wafers having miller indices (111) for orientation of associated crystal planes of the buffer zones, which are considered mechanically stronger and slower etching than (100) crystal orientation silicon typically used in fabricating active VMJ unit cells.
• low resistivity silicon layers can have a different crystal orientation than that of the active unit cells, wherein by employing such alternative orientation, a device with improved mechanical strength/end contacts is provided.
• edges of (100) orientated unit cells typically etch faster to essentially round off corners of the active unit cells with such crystal orientation - as compared to the inactive (111) orientated end layers, hence resulting in a more stable device structure with higher mechanical strength for welding or otherwise connecting end contacts.
• Fig. 9 illustrates a related methodology 900 of employing buffer zones at end layers of a high voltage silicon vertical multi junction (VMJ) photovoltaic cell, to provide a barrier that protects the active layers thereof.
• VJ vertical multi junction
• the exemplary method is illustrated and described herein as a series of blocks representative of various events and/or acts, the subject innovation is not limited by the illustrated ordering of such blocks. For instance, some acts or events may occur in different orders and/or concurrently with other acts or events, apart from the ordering illustrated herein, in accordance with the innovation. In addition, not all illustrated blocks, events or acts, may be required to implement a methodology in accordance with the subject innovation.
• each cell unit itself can include a plurality of parallel semiconductor substrates that are stacked together.
• Each layer can consist of impurity doped semiconductor material that form a PN junction, and further include a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction.
• a plurality of such cell units are integrated to shape a VMJ.
• a buffer zone can be implemented that contacts end layers of the VMJ, to provide a barrier that protects the active layers thereof.
• Such buffer zone(s) can be in form of an inactive layer(s) arrangement that is additionally stacked upon and/or below end layers of the VMJ cell.
• the VMJ can then be implemented as part of a photovoltaic cell at 940.
• Fig. 10 illustrates a schematic cross sectional view 1000 for a solar assembly that includes a modular arrangement 1020 of photovoltaic (PV) cells 1023, 1025, 1027 (1 through k, where k is an integer).
• PV photovoltaic
• Each PV cell can employ a plurality of VMJs with buffer zones according to an aspect of the subject innovation.
• each of the PV cells (also referred to as photovoltaic cells) 1023, 1025, 1027 can convert light (e.g., sunlight) into electrical energy.
• the modular arrangement 1020 of the PV cells can include standardized units or segment that facilitate construction and provide for a flexible arrangement.
• DSC dye-sensitized solar cell
• Such DSC can further include a semiconductor layer such as Ti ⁇ 2 particles, a sensitizing dye layer, an electrolyte and a catalyst layer such as Pt- (not shown)- which can be sandwiched between the glass substrates.
• a semiconductor layer can further be deposited on the coating of the glass substrate, and the dye layer can be sorbed on the semiconductor layer as a monolayer, for example.
• an electrode and a counter electrode can be formed with a redox mediator to control of electron flows therebetween.
• the cells 1023, 1025, 1027 experience cycles of excitation, oxidation, and reduction, which produce a flow of electrons, e.g., electrical energy.
• incident light 1005 excites dye molecules in the dye layer, wherein the photo excited dye molecules subsequently inject electrons into the conduction band of the semiconductor layer.
• Such can cause oxidation of the dye molecules, wherein the injected electrons can flow through the semiconductor layer to form an electrical current.
• the electrons reduce electrolyte at catalyst layer, and reverse the oxidized dye molecules to a neutral state.
• Such cycle of excitation, oxidation, and reduction can be continuously repeated to provide electrical energy.
• Fig. 11 illustrates a schematic block diagram of an electrolysis system that employs a vertical multi junction (VMJ) cell 1110 for electrolysis in accordance with an aspect of the subject innovation.
• the VMJ 1110 can be partially or totally submerged within water/electrolytes, as part of a transparent housing such as quartz, glass or plastic 1130.
• a plurality of electrolysis electrodes in form of anodes and/or cathodes can be formed throughout the VMJ, and/or on a surface 1137 thereon.
• Current flowing among such electrolysis electrodes that are formed on the surface 1137 then flows through the water and decompose the water to hydrogen and oxygen - whenever threshold voltage of electrolysis is reached.
• the VMJ 1110 includes a plurality of integrally bonded cell units 1111, 1117 (1 to n, where n is an integer), wherein each cell unit itself is formed from stacked substrates or layers (not shown).
• each cell unit 1111, 1117 can include a plurality of parallel semiconductor substrates stacked together, and consisting of impurity doped semiconductor material, which form a PN junction and a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction.
• incident light 1135 is directed to the surface 1137, in various regions of the VMJ 1110, then a plurality of cathodes and anodes can be formed that subsequently function as electrodes for the electrolysis operation.
• the electrolyte can be formed of any solution that does not adversely affect stacked layers that form the VMJ cell (e.g., iridium-based catalyst made of iridium, a binary alloy thereof, or an oxide thereof.)
• ultrasonic transducers can operatively interact with the electrolysis system to free oxygen or hydrogen bubbles, which remain attached to the electrolysis electrodes.
• the VMJ 1110 can further be positioned on a heat regulating assembly
• Such heat regulating assembly 1119 can be in form of a heat sink arrangement, which includes a plurality of heat sinks to be surface mounted to a back side of the VMJ, wherein each heat sink can further include a plurality of fins (not shown) extending substantially perpendicular the back side.
• the fins can expand a surface area of the heat sink to increase contact with cooling medium (e.g., electrolyte, cooling fluid such as water), which can be further employed to dissipate heat from the fins and/or photovoltaic cells.
• cooling medium e.g., electrolyte, cooling fluid such as water
• heat from the VMJ can be conducted through the heat sink and into surrounding electrolyte, and/or substance that does not affect electrolysis operation.
• heat from the VMJ cell can be conducted through thermal conducting paths (e.g., metal layers), to the heat sinks to mitigate direct physical or thermal conduct of the heat sinks to the VMJ cells, and provide a scalable solution for proper operation of the electrolysis.
• each heat sink can be positioned in a variety of planar or three dimensional arrangements as to monitor, regulate and over all manage heat flow away from the VMJ cell.
• each heat sink can further employ thermo/electrical structures (not shown) that can have a shape of a spiral, twister, corkscrew, maze, or other structural shapes with a denser pattern distribution of lines in one portion and a relatively less dense pattern distribution of lines in other portions.
• thermo/electrical structures (not shown) that can have a shape of a spiral, twister, corkscrew, maze, or other structural shapes with a denser pattern distribution of lines in one portion and a relatively less dense pattern distribution of lines in other portions.
• one portion of such structures can be formed of a material that provides relatively high isotropic conductivity and another portion can be formed of a material that provides high thermal conductivity in another direction.
• each thermo/electrical structure of the heat regulating assembly provides for a heat conducting path that can dissipate heat from the hot spots and into the various heat conducting layers, or associated heat sinks, of the heat regulating device, and hence facilitate the electrolysis operation.
• the heat sinks can be cooled via an independent cooling medium that is separate from the electrolyte medium.
• Fig. 12 illustrates a further aspect of the subject innovation that includes protrusions 1211, 1215 of metal layers that are associated with electrodes of a single unit cell 1201.
• protrusions 1211, 1215 protrude (e.g., several millimeters) from a surface 1241 of the VMJ 1200 to facilitate the electrolysis process, via increasing a contact surface area.
• substantially thin layers of electro-catalyst materials such as platinum, RuC ⁇ , or titanium, can be incorporated in to the metallization during VMJ cell fabrication to enhance hydrogen production.
• the electrolyte disassociates into captions and anions; wherein the anions rush towards the anode and neutralize the buildup of positively charged H + therein; similarly, the captions rush towards the cathode and neutralize the buildup of negatively charged OH therein.
• the choice of electrolyte should be considered in conjunction with the material employed for the VMJ cell, as not to adversely affect its material and operation. Additional factors in choosing an electrolyte pertain to the fact that an anion from the electrolyte is in competition with the hydroxide ions to give up an electron.
• Fig. 13 illustrates a voltage-distance graph for various points on the
• the VMJ 1310 includes a plurality of unit cells 1311, 1317 that are serially connected, wherein the voltage can increase as a linear function of number of cells that are stacked together (e.g., from left to right on the horizontal axis).
• voltage difference between both ends of celli is 0.6 volts, and by stacking cell 2 thereon, such voltage difference in the combined cells is increased to 1.2 volts.
• stacking cell 3 thereon the voltage difference can be increased to 1.8 volts.
• electrolysis can occur between any two points on a surface of the VMJ that exceeds the threshold value for decomposing the water.
• VMJ cell for an open circuit voltage of a 40 junction VMJ cell at 1000 suns 32 volts can be generated (e.g., 0.8 volts per unit cell.) Assuming electrolysis in initiated at 1.6 volts only two unit cells are sufficient to provide the voltage. In another aspect, as the current loading increases, the voltage determined by the VMJ cell IV characteristics at maximum power at 1000 suns drops to 24 volts, or 0.6 volts per unit cell. As such, three unit cells can be required, which contribute to 1.8 volts for powering the electrolysis reaction. (Typically an over voltage may also be required for electrolysis at higher current densities.)
• the electrolysis is described in context of a single VMJ, the subject innovation is not so limited and can be implemented as part of a plurality of VMJ cells (e.g., in parallel and/or series, or operatively separate from each other).
• VMJ cells e.g., in parallel and/or series, or operatively separate from each other.
• various forms of pressurization can be employed to improve electrolysis efficiency and/or collection (e.g., sieving mechanisms, filtering mechanisms, and the like) for products of decompositions (e.g., hydrogen, oxygen).
• products of decompositions e.g., hydrogen, oxygen.
• the subject innovation is not limited to electrolysis of water and electrolysis of other compounds that can suitably interact with the VMJ are well within the realm of the subject innovation.
• Fig. 14 illustrates a related methodology 1400 of water electrolysis via a VMJ according to an aspect of the subject innovation. While the exemplary method is illustrated and described herein as a series of blocks representative of various events and/or acts, the subject innovation is not limited by the illustrated ordering of such blocks. For instance, some acts or events may occur in different orders and/or concurrently with other acts or events, apart from the ordering illustrated herein, in accordance with the innovation. In addition, not all illustrated blocks, events or acts, may be required to implement a methodology in accordance with the subject innovation. Moreover, it will be appreciated that the exemplary method and other methods according to the innovation may be implemented in association with the method illustrated and described herein, as well as in association with other systems and apparatus not illustrated or described.
• the electrolyte solution is introduced into a container that contains the VMJ, wherein it is fully or substantially immersed. Such system is then subjected to incident light at 1420, and a current flow generated from the VMJ.
• the incident light can generate water electrolysis throughout the electrolyte solution at 1430, and any location wherein a threshold for decomposing water is reached or passes (e.g., around 1.2 volts) electrolysis occurs. For example, across each unit cell a voltage of 0.6 volts can be generated (e.g., for a 1000 suns) and between regions of a first unit cell and a third unit cell electrolysis can occur.
• Fig. 15 illustrates a VMJ cell that can be employed for electrolysis in accordance with an aspect of the subject innovation.
• the VMJ 1515 itself is formed from a plurality of integrally bonded cell units 1511, 1517 (1 to n, n being an integer), wherein each cell unit itself is formed from stacked substrates or layers (not shown).
• each cell unit 1511, 1517 can include a plurality of parallel semiconductor substrates stacked together, and consisting of impurity doped semiconductor material, which form a PN junction and a "built -in" electrostatic drift field that enhance minority carrier movement toward such PN junction.
• each of such buffer zones 1510 1512 can be formed via material that have substantially low resistivity ohmic contact (e.g., any range with upper limit less than approximately 0.5 ohm-cm), while mitigating and/or eliminating unwanted auto doping.
• the buffer zones 1510, 1512 can be formed by employing low resistivity wafers that are p-type doped, with other p-type dopants such as aluminum alloys, to mitigate a risk of auto- doping (in contrast to employing n-type wafers that can create unwanted pn junctions - when it is desired to create a substantially low resistivity ohmic contact.)
• Catalytic materials e.g., platinum, titanium, and the like
• Fig. 16 illustrates a particular aspect of a unit cell 1600, an array of which can form a VMJ cell for the electrolysis of the subject innovation.
• the unit cell 1600 includes layers 1611, 1613, 1615 stacked together in a substantially parallel arrangement. Such layers 1611, 1613, 1615 can further include impurity doped semiconductor material, wherein layer 1613 is of one conductivity type and layer 1611 is of an opposing conductivity type - to define a PN junction at intersection 1612. Likewise, layer 1615 can be of the same conductivity type as layer 1613-yet with substantially higher impurity concentration, hence generating a built-in electrostatic drift field that enhances minority carrier movements toward the PN junction 1612. Such unit cells can be integrally bonded together to form a VMJ (e.g., using catalytic material for such bondage to enhance electrolysis), which performs electrolysis as described in detail supra.
• VMJ e.g., using catalytic material for such bondage to enhance electrolysis
• PNN+ (or NPP+) junctions can be formed to a depth of approximately 3 tolO ⁇ m inch into flat wafers of high resistivity (e.g., more than 100 ohm-cm) of N type (or P type) silicon -having a thickness of approximately 0.008 inch. Subsequently, such PNN+ wafers are stacked together with a thin layer of aluminum interposed between each wafer, wherein each wafer's PNN+ junction and crystal orientation can be oriented in the same direction.
• aluminum-silicon eutectic alloys can be employed, or metals such as germanium and titanium, or metals such as molybdenum or tungsten that have thermal coefficient(s) that substantially matches the thermal coefficient of silicon can also be employed.
• the silicon wafers and aluminum alloy interfaces can be alloyed together, such that the stacked assembly can be bonded together (e.g., further including catalytic material.)
• other material such as germanium and titanium can also be employed.
• aluminum-silicon eutectic alloys can also be employed.
• the electrolyte should be chosen such that it does not adversely affect the operation of the VMJ, and/or result in chemical reactions harmful to the VMJ.
• various N+-type and P-type doping layer formation can be implemented as part of the cell units and such arrangements are well within the realm of the subject innovation.
• FIG. 17 illustrates a further aspect of the subject innovation that includes a VMJ employed for electrolysis with a textured surface.
• a schematic perspective of a grooved surface 1700 is depicted as part of a vertical multi junction (VMJ) cell 1720 in accordance with an aspect of the subject innovation.
• VMJ vertical multi junction
• Such an arrangement for texturing 1700 enables the refracted light to be directed away from the p+ and n+ diffused doped regions - while at the same time creating desired carriers. Accordingly, incident light can be refracted in the plane 1710 having a normal vector n.
• Such plane 1710 is parallel to the PN junction planes of the VMJ 1720, and can include the cross section configuration of the grooves 1700. Put differently, the orientation of the plane 1710 is substantially perpendicular to the direction of stacking the unit cells 1711, 1713, 1715.
• Such grooved surface can increase efficiency of the electrolysis process.
• Fig. 18 illustrates exemplary textures for grooving a surface of the
• VMJ which receives light thereon for electrolysis of an electrolyte.
• Such grooving can be in form of cavity shaped grooves - for example, as "V" shaped cross section configurations having a variety of angles ⁇ , (e.g., 0° ⁇ ⁇ ⁇ 180°)"U" shaped cross configurations, and the like - wherein the plane that includes the cross section configuration is substantially perpendicular to the direction of stacking the unit cells that form the VMJ, and/or substantially parallel to the PN junctions of the VMJ.
• the texturing 1810, 1820, 1830 for the VMJ of the subject innovation is different from prior art for conventional silicon photovoltaic cell textures, in orientation of PN junctions and/or interaction with incident light.
• conventional silicon photovoltaic cells are typically textured to incline the penetration of the light, so that more of the longer wavelengths are absorbed closer to PN junctions (positioned horizontally) for better current collection of carriers - and hence mitigate poor spectral response to longer wavelengths in the solar spectrum.
• such is not required in the VMJ of the subject innovation that includes vertical junctions, and which already provides an enhanced spectral response to the longer wavelengths in the solar spectrum.
• one aspect for implementing grooves of Fig. 7 is to mitigate bulk recombination losses by reducing the bulk volume - (as opposed to conventional solar surfaces with texturing, which reduce reflection, or cause reflected or refracted light to become closer to the junctions).
• VMJ cell has demonstrated better carrier current collection for both the short wavelengths and the long wavelengths, wherein the short wavelength response is due to eliminating a highly doped horizontal junction at the top surface and the long wavelength respond is due to the enhanced collection efficiency of vertical junctions.
• other textures e.g., random, pyramids, domes, and similar raised configurations
• incident light becomes refracted in all directions, resulting in light absorption in the p+ and n+ diffused regions and hence reduced efficiency.
• reflection coatings can be applied to the back side of the VMJ cell to further enhance light absorption.
• the subject innovation relates to improving performance of photovoltaic cells, e.g., solar cells, particularly high-intensity solar cells such as edge-illuminated or vertical junction structures that can produce a substantially high power output under high intensity radiation levels.
• photovoltaic cells e.g., solar cells, particularly high-intensity solar cells such as edge-illuminated or vertical junction structures that can produce a substantially high power output under high intensity radiation levels.
• PV elements that form unit cells employed to fabricate VMJ photovoltaic cells are set forth herein unit to reduce recombination losses of photogenerated carriers via patterned contacts.
• the VMJ cell has an inherent theoretical limit efficiency exceeding
• aspects or features of the subject innovation are illustrated with solar cells, such aspects or features and associated advantages, such as reduction of recombination losses of photogenerated carriers, can be exploited in other photovoltaic cells, e.g., thermophotovoltaic cells, or cells excited with laser source(s) of photons.
• aspects of the subject innovation also can be implemented in other classes of energy- conversion cells such as betavoltaic cells.
• VMJ unit cells that incorporate an array of semiconductor physics reveal specific regions in VMJ unit cells where recombination losses of photogenerated carriers occur at high intensities. At least some of such regions present complex loss mechanisms that are intensity dependent. Computer simulation(s) reveal regions in PV elements, or VMJ unit cells, that can be improved upon in order to reduce recombination losses and improve performance of VMJ cells. Aspects of the subject innovation provide such improvements.
• aspects or features of solar cells, and associated process(es) for production thereof, set forth in the subject innovation can increase efficiency performance of high- intensity VMJ cells operating in the range of 1000 suns or higher. Efficiency increase can make VMJ solar cells or other solar cells that exploit aspects of the subject innovation more cost effective and viable, even though it can involve additional manufacturing and a potential increase in series resistance for intensities greater than 1000 suns. Aspects or features described herein can provide adequate engineering tradeoffs to make photovoltaic concentrator systems using solar cells, VMJ cells or otherwise, that exploit aspects of the subject innovation more viable and cost effective in providing lower $/watt performance.
• the subject innovation is directed to reducing recombination losses in the foregoing diffusion regions in order to improve the performance of VMJ cells.
• V oc 0.8 volts per unit cell junction at high intensities.
• V oc is determined by sunlight-generated currents and diffused emitter reverse saturation currents (J 0 ), with both the P+N and NN+ junctions present in the unit cell(s) of a VMJ solar cell contributing to the open-circuit voltage.
• FIG. 19A illustrates a diagram 1900 of a photovoltaic element 1910 with a patterned dielectric coating 1920 between one of the surfaces of the PV element and a metal contact 1925.
• surfaces of PV element 1910, dielectric coating 1920, and metal contact 1925 are illustrated as not in contact for clarity. However, in solar cell(s) discussed herein, such surfaces are in contact.
• Pattern dielectric coating 1920 is illustrated as disconnected elliptical regions assembled in a periodic array or lattice.
• the PV element 1910 is typically a slab of N- type semiconductor material, wherein the semiconductor material is one of Si; Ge; GaAs, InAs, or other III-V semiconducting compounds; II- VI semiconducting compounds; CuGaSe; CuInSe; CuInGaSe.
• the slab can include a doped P+ diffuse region 1916 (labeled as P+) on a first surface of the slab and a doped N+ diffuse region 1914 (labeled as N+) on a second surface substantially parallel to the first surface. Thickness of the active PV element 1910 affords an N-type (N) layer 1912 among the diffused doped layers 1914 and 1916.
• Thickness of diffusion layers 1914 and 1916 can range from 3-10 ⁇ m, and are determined by doping process employed to introduce carriers into a slab of N-type material (e.g., slab 1912). Inclusion of diffuse doped layers can be accomplished with substantially any doping means, e.g., techniques and dopant materials, typically employed in semiconductor processing. Dopant materials can include phosphorous and boron, for N+ and P+ doping, respectively.
• dopant materials can include phosphorous and boron, for N+ and P+ doping, respectively.
• interfaces between diffuse layers N+ 1914 and P+ 1916 and N-type (N) layer 1912 are idealized as sharp abrupt boundaries; however, such interfaces can be irregular, with areas of intermixing between neutral and doped materials.
• PV element 1910 can be a slab of P-type doped semiconductor material that can include P+ diffuse layer 1916 on a first surface, and its vicinity, of the slab and N+-doping diffuse layer 1914 a second surface, and its vicinity, substantially parallel to the first surface, as described supra.
• patterned dielectric coating 1920 reduces formation of metal-diffuse doping layer interface (e.g., metal and N+ layer 1914 interface) upon metallization of active PV element 1910 — openings in a patterned dielectric coating are the regions where the metal and diffuse doping layer form an interface. Since such interfaces have high recombination losses, the reduction of the metal-diffuse doping layer contact thus mitigates nonradiative losses of photogenerated carriers (e.g., electrons and holes), with ensuing increase in photovoltaic efficiency of PV element 1910.
• coating a PV element, e.g., 1910, with dielectric material produces passivation of surface states and thus reduces surface recombination losses.
• Patterning of dielectric coating can be accomplished through photolithographic techniques, or substantially any other technique that allows controlled patterning of a dielectric surface; for instance, wet etching. Such photolithographic techniques generally afford pattern formation through multiple processing steps of masking and removal of the dielectric material in the dielectric coating. Alternatively or additionally, patterning of dielectric coating can be accomplished through deposition techniques, e.g., vapor coating like chemical vapor deposition (CVD) and its variations, plasma etched CVD (PECVD); molecular beam epitaxy (MBE), etc., in the presence of a mask that shadows deposited material in order to dictate a specific pattern.
• CVD chemical vapor deposition
• PECVD plasma etched CVD
• MBE molecular beam epitaxy
• dielectric coating layer 1920 can adopt various planar geometries and configurations that provide electrical contact among N+-doping diffuse layer 1914 and metal contact 1925. As indicated supra, in example diagram 1920, dielectric coating 1920 adopts a square-lattice arrangement of elliptical disconnected areas. Other lattices of dielectric regions also can be formed. Such lattices can include triangular lattice, monoclinic lattice, face-centered square lattice, or the like. Alternative or additional arrangements of portion(s) of dielectric material within a patterned dielectric coating can include disconnected or connected stripes of dielectric material.
• a patterned dielectric coating such as coating 1920, can be placed among metal contact 1935 and P+ diffuse doping layer 1916 (see, e.g., FIG. 19B). Location of patterned dielectric coating 1920 is dictated by the neutral-doped junction that has dominant losses at operating radiation intensity in a solar concentrator or other solar-electric energy conversion apparatus or device.
• N+ diffused region, or layer, and its contact to metal 1925 can have substantially larger losses at high electromagnetic radiation intensities, thus patterned dielectric coating 1920 in the configuration displayed in diagram 1900 can be the substantially least expensive configuration to reduce recombination (e.g., radiative and nonradiative) losses and improve performance of the PV element 1910, particularly at high intensities.
• substantially any pattern of dielectric material e.g., a disconnected array of openings, such as the space between dielectric elliptic areas in dielectric coating 1920
• a single diffuse layer e.g., N+ layer 1914
• metallization applied in a later step can assure all or substantially all open, contact areas are mutually connected when fully bonded to the next planar unit cell within the VMJ cell structure.
• Unit cell(s) employed to produce a VMJ photovoltaic cell as described herein consist of PV element 1910 coated with a dielectric pattern and metalized as described supra.
• unit cell(s) are different from conventional unit cell(s) employed for fabrication of conventional VMJ solar cells.
• Recombination losses can include radiative or nonradiative recombination of photogenerated carriers, wherein nonradiative recombination can comprise Auger scattering, carrier-phonon relaxation, or the like.
• Auger recombination rate increases as the cube of carrier density, e.g., density of photogenerated carriers; doubling the volume of a photovoltaic device can lead to a sixteen-fold increase in recombination losses when Auger bulk scattering in accounted for.
• thinner slabs 1910 or substantially any design modification that renders PV element 1910 thinner such as the use of light trapping with textured surfaces, such as V-grooved surfaces, U-grooved surfaces ..., or back side reflectors, can be utilized to mitigate bulk Auger recombination at high intensities through reduction of the thickness of unit cells that form a VMJ photovoltaic cell. Collection efficiency in PV cells can increase significantly when VMJ unit cells as designed in accordance with aspects described herein afford a 50% reduction in recombination losses.
• dielectric coating 1920 can be a thermal oxide layer, which has a low surface recombination velocity.
• making electrical contacts to end of unit cells, or PV elements, of semiconductor-based (e.g., Si-based) VMJ photovoltaic cells with patterned openings in the dielectric can require a full electrical contact that can be provided by low resistivity silicon that thermally matches or substantially matches the thermal expansion coefficient of the unit cells, or a metal such as molybdenum or tungsten which have thermal coefficient(s) that nearly matches the thermal coefficient(s) of silicon.
• metallization of patterned dielectric coating can be effected with conductive material(s), e.g., metals or low- resistivity doped semiconductors, that have thermal coefficient(s) that nearly matches thermal coefficient(s) of semiconductor material of the unit cells that form the VMJ solar cells.
• conductive material(s) e.g., metals or low- resistivity doped semiconductors
• metal contact layer 1925 and metal contact layer 1935 can be disparate.
• a first metal contact layer e.g., layer 1925
• a second contact layer e.g., layer 1935
• FIG. 19B is a diagram 1950 of a photovoltaic element 1910 with patterned dielectric coatings in both diffusion doping regions.
• a first patterned dielectric coating 1920 between a N+ diffuse doping layer 1914 and a first metal contact 1925 and a second patterned dielectric coating 1960 between a P+ diffuse doping layer 1916 and a second metal contact 1935.
• dielectric coating 1960 is substantially the same as those of dielectric coating 1920.
• metal contact layer 1925 and 1935 can be disparate.
• mitigation of recombination losses of photogenerated carriers and ensuing increased PV element performance provided by the introduction of the second patterned dielectric coating outweighs the added complexity and possible extra expense(s) of additional processing act(s) associated with preparation of a second patterned dielectric coating.
• the first pattern in dielectric coating 1920 is to be correlated with the second pattern in coating 1960 so as to have a set of one or more opening(s), and section(s) of metal layers 1925, in opposition.
• patterned dielectric coating 1920 is "out-of- phase" with respect to patterned dielectric coating 1960, and the dielectric coatings mutually occlude section(s) of respective metal layers 1925, resistance among unit cells in a stack of PV elements 1910 increases and efficiency of a VMJ solar cell decreases.
• openings formed through pattern dielectric coating 1920 can be different in size, e.g., different area, that openings generated via dielectric coating 1960. For instance, it can be more desirable to have the openings area for the N+ contacts wider than those for the P+ contacts in PV element 1910, or P+NN+ unit cells, to more effectively reduce overall losses, particularly if there are higher losses at the N+ diffused region and metal contacts. As described above, such disparate among opening sizes can be implemented or exploited irrespective of the particular pattern of the dielectric coating.
• FIG. 19C displays a diagram of example set of precursors and derived
• PV element(s) that can be produced through doping in accordance with aspects described herein.
• three precursor types can be employed to produce PV elements that are processed to introduce patterned dielectric coating(s) and metal contact(s) as described herein: (i) N-type doped precursor 1980, (ii) P-type doped precursor 1985, and (iii) intrinsic precursor 1990.
• Precursors are semiconducting materials such as Si; Ge; GaAs, InAs, or other III-V semiconducting compounds; II- VI semiconducting compounds; CuGaSe; CuInSe; CuInGaSe.
• N-type precursor 1980 can lead to PV element 1982, which includes an N+- type diffuse doping region and a P+-type doping region, such PV element is PV element 1910.
• doping of precursor 1980 can lead to PV element 1984, with layers, or regions, of N-type and P-type diffuse doping.
• Precursor 1985 enable formation of PV elements 1986 and 1988, with N+ and P+ diffuse doping layers in PV element 1986, and N+ diffuse doping and P-type doping in element 1988.
• Various doping of intrinsic precursor 1990 result in PV elements 1992-1998.
• PV element 1992 P-type and N-type regions of doping are included; PV element 1994 includes N+-type and P-type doping layers; PV element 1996 includes N-type and P+-type doping layers; and N+-type and P+-type layer are included in PV element 1998. While the different regions of doping introduced in the precursor materials 1980, 1985, and 1990 are illustrated as extended regions, such regions can be spatially confined or nearly-confined, as described herein.
• the various PV elements illustrated herein can be coated with a patterned dielectric material and metalized as described herein in order to form unit cell(s) that can stacked to produce a monolithic photovoltaic cells in accordance with aspects of the subject innovation.
• patterned contacts formed through coating with patterned dielectric material in P+NN+ PV elements, or unit cells can be employed for terrestrial PV concentrators, whereas P+PN+ PV elements, or unit cells, can be more radiation hardened and thus exploited for space applications.
• FIG. 2OA is a diagram 2000 of a cross section of a PV element with a single surface patterned with a dielectric coating. The pattern of dielectric material results in sections 2005 of dielectric deposited atop an N+ diffuse doping layer 2014. It is to be noted that an additional, or alternative, configuration of a PV element with a patterned dielectric coating on P+ diffuse doping layer 2016 is possible. In PV element illustrated in diagram 2000, an N-type region 2012 separates diffuse doping regions 2014 and 2016. As discussed above, such configuration can be effective at mitigation of recombination losses associated with operation of the PV element at high intensity. [00129] FIG. 2OB illustrates PV elements of diagram 2030 upon metallization with metal contacts 2025 and 2035.
• FIG. 2OC illustrates an example embodiment of a VMJ photovoltaic cell 2060 in which constituent unit cells 2070 I -2070 M (M is a positive integer) stacked along direction 2080 exploit a one-side, asymmetric patterned dielectric coating (e.g., coating with dielectric regions 2005) on N+ diffuse doping layer.
• two classes of VMJ photovoltaic cells can be formed: (a) homogeneouse and (b) heterogeneous.
• units cell(s) 2070 I -2070 M are based on the same or substantially the same precursor, whereas in (b) the unit cell(s) are based on disparate precursors.
• Disparate precursors can be based on the same semiconducting compounds, e.g., Si; Ge; GaAs, InAs, or other III- V semiconducting compounds; II- VI semiconducting compounds; CuGaSe; CuInSe; CuInGaSe, but differ in doping type or, for alloyed compounds, in alloying concentrations.
• VMJ photovoltaic cells can exploit various portions of the emission spectrum of a source of electromagnetic radiation, e.g., solar light spectrum.
• M ⁇ 40 is typically utilized to form a VMJ solar cell.
• a 1 cm 2 VMJ with M ⁇ 40 can output nearly 25 volts under typical operation conditions, such as incident photon flux, radiation wavelength, temperature, or the like.
• stacks of active PV elements, or unit cells, that form the VMJ photovoltaic cell can be current-matched or nearly current-matched based on a performance characterization conducted in a test- bed under conditions (e.g., radiation wavelength(s), concentration intensity) substantially similar to those expected under normal operating conditions of a solar collector system in the field.
• the current that is matched is current produced by a PV element, or unit cell, upon solar-electric energy conversion.
• the monolithic stack of PV elements 2070i-2070 M that produces the VMJ solar cell can be processed, e.g., sawn, cut, etched, peeled, or the like, in order to expose or nearly expose a specific crystalline plane (qrs), with q, r, s Miller indices, which are integer numbers, to sunlight when the VMJ solar cell is part of a PV module or device.
• specific crystalline plane(s) can (100) planes.
• FIG. 2OD illustrates a VMJ PV cell 2090 produced through a stack of PV elements, or unit cells, 2092 with patterned contacts in the fashion presented in FIG.
• FIG. 21A is a diagram that illustrates example dielectric coating pattern(s) to a PV element. Patterns 2130 and 2140 correspond to patterns for a first and second surface in a PV element.
• Openings in the dielectric coating are lines, or stripes, with a defined width w 2135 and pitch separation Wp 2145 from each other.
• the preferred pattern of lines, or stripes, for reducing the contacts area ratios are high density of closely spaced smaller lines, or stripes, openings. The density can be varied to optimize performance for a given radiation intensity at which the PV element is expected to operate as part of a solar cell, or PV cell, in a PV module.
• lines, or stripes, openings can be made on opposite sides of each PV element 1910, or a wafer, and misoriented 90 degrees from one side to the other; namely, stripes in patterned dielectric coating 2130 are oriented at an angle of 1935 degrees with respect to the (100) direction, whereas stripes in patterned dielectric coating 2140 are aligned at an angle of 45 degrees with respect to (100) . It is noted that other relative misorientations are also possible and advantageous.
• openings formed through patterned dielectric coating 2130 can be different in size, e.g., span a different area, that openings generated via dielectric coating 2140.
• N+ contacts can be generally more desirable to have openings area for the N+ contacts wider than those for the P+ contacts in a PV element with P+NN+ unit cell(s), to more effectively reduce overall losses, particularly when there are higher losses at the N+ diffused region and metal contacts.
• openings area for the P+ contacts wider than those for the N+ contacts can be desirable to implement openings area for the P+ contacts wider than those for the N+ contacts to mitigate recombination losses in N+PP+ unit cell(s) (e.g., PV element 1986).
• N+PP+ unit cell(s) e.g., PV element 1986.
• the contact points facilitated through the openings in dielectric coatings 2130 and 2140, are directly aligned and mutually adjacent in a controlled pattern, with P+ contacts of one wafer interfacing at points to N+ contacts of the next wafer in order to keep series resistance low in finished VMJ cells.
• fabricated VMJ cells can be sawn to have a preferred (100) crystal orientation at the illuminated surface in order to establish the lowest surface states for passivation.
• relative orientation of the lines, or stripes, on a first surface of a patterned PV element can be relatively misoriented at an angle ⁇ such as 90 degrees from the lines or stripes in a second surface, wherein the first and second surfaces include the (100) crystal direction, e.g., are normal to the (100) crystalline plane.
• angle ⁇ such as 90 degrees from the lines or stripes in a second surface
• the first and second surfaces include the (100) crystal direction, e.g., are normal to the (100) crystalline plane.
• Other orientations of lines or stripes are also possible and advantageous.
• relative misorientation ⁇ of lines or stripes at different surfaces can be implemented.
• misorientation ⁇ is a finite real number; e.g., dielectric coating patterns are not mutually aligned at disparate surfaces.
• stripes in a dielectric coating can be oriented at an angle a with respect to crystalline directions (qrs), with q, r, and s Miller indices.
• FIG. 21B illustrates a cross-section diagram of a PV element 2150 with dielectric coating patterns deposited on both a P+ diffuse doping layer 2176 and an N+ diffuse doping layer 2174.
• N-type region 2172 separates diffuse doping regions 2014 and 2016.
• the illustrated cross section is a cut that illustrates alignment of dielectric regions on a first surface, e.g., dielectric regions 2155, with those dielectric regions on a second surface, e.g., dielectric regions 2165. It should be appreciated that other cross-section cuts can display misaligned regions of dielectric material the first surface and second surface.
• FIG. 22 illustrates a cross-section diagram of an example PV element
• N+ diffusion region(s) 2214 is structured to reduce doping layer volume and thus mitigate recombination losses of photogenerated carriers. Regions of N+ doping can be determined by the openings structure in the patterned dielectric coating; e.g., N+ diffuse region(s) 2214 can be stripes oriented along pitch spacing(s) in a striped pattern of dielectric coating 2202. Such regions are formed through utilization of dielectric coating regions 2205 as a mask to control or manipulate N+ doping.
• N+ diffuse doping area(s) or volume(s) 2214 can be fully confined or quasi-confined, e.g., confined in two or less directions and extended in a third direction.
• regions of N-type material 2212 are interspersed with N+ diffuse doping regions 2214.
• P+ diffuse doping region 2216 is not coated with a patterned dielectric material.
• a set of metalized PV elements can be stacked, and processed, e.g., soldered or alloyed through a high temperature manufacture step, to form a VMJ photovoltaic cell with reduced recombination losses in accordance with aspects described herein.
• FIG. 23A illustrates a cross-section diagram of a PV element 2300 with dielectric coating patterns deposited on opposed diffuse doping regions.
• a first dielectric coating pattern e.g., a striped pattern 2330 oriented along a direction 135 degrees rotated with respect to the (100) crystalline direction
• a second dielectric coating pattern e.g., a striped pattern 2340 oriented 45 degrees with respect to the (100) crystalline direction.
• Both N+ and P+ diffuse doping regions can include, respectively, doping regions 2314 and 2316 confined in two or more directions.
• Openings in the dielectric coating patterns can serve as masks to generate reduced-volume doping diffuse layers; the openings formed between regions 2305 and 2325 of coated dielectric. Reduction of metal contact surface and volume of doping regions at both diffuse doping layers can provide enhanced mitigation of carrier recombination losses with respect to dielectric coating and doping volume reduction in a single doping region. As discussed above, benefit of improved PV performance of a VMJ produced with patterned PV elements, or unit cells, surpass additional processing complexity and costs associated with surface patterning. Moreover, openings formed through pattern dielectric coating 2330 can be different in size, e.g., span a different area, than openings generated via dielectric coating 2340, in order to further control recombination losses originated from diffuse doping areas. For instance, it can be more desirable to have openings that produce larger N+ doping regions than those that produce P+ doping regions, to more effectively reduce overall losses, particularly when there are higher losses at the N+ diffused region and metal contacts.
• FIG. 23B illustrates a cross-section of patterned PV element 2350 with metal contact layers 2365 and 2375, which can be mutually different as discussed above.
• the illustrated cross-section cut displays metal regions 2365 (e.g., among spaces of dielectric material) on the surface of N+ diffuse doping layer aligned with metal regions 2375 (e.g., region among spaces of dielectric material) on the surface of P+ diffuse doping layer.
• metal regions 2365 e.g., among spaces of dielectric material
• metal regions 2375 e.g., region among spaces of dielectric material
• VMJ vertical multi-junction
• Unit cell(s) in a texture VMJ photovoltaic cell can be embodied in unit cell(s) 2070 ⁇ , 2180 ⁇ , or 2350, or any other unit cell(s) produced as described herein.
• textured surface 2412 is a V- grooved surface; however, other grooves or cavities of various shapes can be formed, e.g., U groove.
• the textured surface is formed onto a plane (qrs) that is exposed or substantially exposed to electromagnetic radiation as a result of processing the monolithic stack of unit cell(s), or PV elements with patterned metal contacts described herein; see, e.g., FIG. 2OD.
• Incident light can be refracted in the plane 2430 having a normal vector n 2432.
• plane 2430 is parallel to the surface(s) of unit cell(s) 2410 K onto which the patterned dielectric material is coated, and can include the cross section configuration of the grooves 2415 — plane 2430 is substantially perpendicular to the direction of stacking unit cells 2410 K .
• Texturing of surface of the monolithic stack of unit cell(s) 2410 K which leads to textured surface 2412, enables the refracted light to be directed away from the P+ and N+ diffuse doping regions without hindering photogeneration of carriers, thus effectively making the unit cells that compose the textured photovoltaic cell 2405 thinner, and reducing recombination losses as indicated supra.
• an anti-reflection coating can be applied to the textured surface 2410 to increase incident light absorption in the cell.
• a method described herein can alternatively be represented as a series of interrelated states or events, such as in a state diagram, or interaction diagram. Moreover, not all illustrated acts may be required to implement example method in accordance with the subject specification. Additionally, the example methods described herein can be implemented conjunctly to realize one or more features or advantages.
• FIG. 25 is a flowchart of an example method 2500 for producing VMJ solar cells with reduced carrier recombination losses according to aspects disclosed herein.
• the subject example method is not limited to solar cells and it also can be effected to produce any or substantially any photovoltaic cell.
• One or more component(s) or module(s) described herein can effect the subject example method 2500.
• a set of surfaces of a photovoltaic element e.g., PV element 1910
• Patterning the PV element with the dielectric coating includes utilizing any suitable technique for produce one or more of the dielectric coatings discussed supra. As an example, patterning can proceed through deposition and photolithography techniques.
• etching techniques can also be employed to complement or supplement employed patterning protocols.
• Substantially any or any dielectric material can be employed to coat the set of surfaces.
• a metal contact is deposited onto one or more of the patterned surfaces of the PV element.
• Alternative or additional realization of act 2530 can include deposition of an ohmic contact or conductive contact onto the one or more of the patterned surfaces of the PV element.
• the material for the metal contact, or ohmic contact can be embodied in substantially any or any conductive material, e.g., a low-resistivity doped semiconductor or a metal.
• the conductive material preferably has thermal coefficient(s) that nearly matches thermal coefficient(s) of semiconductor material of the PV element.
• the conductive material has bonding characteristics that facilitate stacking of patterned and metalized PV elements.
• pattern(s) of dielectric material coating(s) ensures that metallization of opposing surfaces results in regions of low resistance by aligning metal regions on disparate surfaces (e.g., 90 degree-misoriented striped openings in patterns 2330 and 2340 result in metal contact regions aligned along a stacking direction (e.g., z direction 2080).
• a set of patterned, metalized photovoltaic elements is stacked to form a VMJ solar cell. It should be appreciated that such PV elements can include confined regions of diffuse doping as discussed above.
• the formed VMJ solar cell is processed to facilitate deployment in a PV device, optimize photovoltaic performance, or a combination thereof.
• processing can include various manufacturing steps or procedures such as cutting procedures, polishing procedures, cleaning procedures, integrating procedures, and the like. Such procedures can be directed, at least in part, to expose a specific crystalline plane to sunlight when the formed VMJ solar cell is deployed in a PV device.
• processing comprises cutting formed VMJ cell(s) so as to expose or substantially expose (100) crystal planes to sunlight in order to establish the lowest surface states for passivation.
• FIG. 26 is a flowchart of an example method 2600 for producing solar cells with reduced carrier recombination losses according to aspects described herein.
• the subject example method 2600 is not limited to manufacturing solar cells; example method 2600 also can be effected to produce any or substantially any photovoltaic cell.
• One or more component(s) or module(s) described herein can effect the subject example method 2600.
• a set of surfaces of a photovoltaic element e.g., PV element 1910
• Patterning the PV element with the dielectric coating includes utilizing any suitable technique for produce one or more of the dielectric coatings discussed supra. As an example, patterning can proceed through deposition and photolithography techniques.
• etching techniques can also be employed to complement or supplement employed patterning protocols.
• Substantially any or any dielectric material can be employed to coat the set of surfaces.
• a patterned dielectric coating can be utilized to generate confined regions of diffuse doping in the PV element.
• the patterned dielectric coating can be employed as a mask that dictates the degree of confinement of doping regions.
• confinement of the doping regions can be nearly two- dimensional, with the doping substantively extending along one dimension and confined along two disparate directions. Confinement of doping regions also can be nearly three-dimensional, wherein doping in the PV element is limited to a set of one or more localized areas substantially smaller than the size of the PV element (see, e.g., FIG.
• a striped pattern of dielectric material when utilized as a mask for doping, can lead to diffuse doping layers that are substantially confined in two directions, e.g., the diffusion direction towards a center of a slab of nominally non-doped semiconductor material and the direction normal to the pitch or stripe in the patterned coating. Confined regions of diffused doping region(s) reduce volume thereof and mitigate photogenerated carrier recombination losses.
• an ohmic contact is deposited onto one or more of the patterned surfaces of the PV element.
• the material for the ohmic contact can be embodied in substantially any or any conductive material, e.g., a low-resistivity doped semiconductor or a metal.
• the conductive material nearly matches the thermal coefficient(s) of the semiconductor material e.g., Si; Ge; GaAs, InAs, or other III- V semiconducting compounds; II- VI semiconducting compounds; CuGaSe; CuInSe; CuInGaSe ..., of the PV element and is suitable for alloying.
• pattern(s) of dielectric material coating(s) ensures that deposition of an ohmic contact onto opposing patterned surfaces results in regions of low electrical resistance by aligning metalized regions on disparate surfaces (e.g., 90 degree-misoriented striped openings in patterns 2330 and 2340 result in metal contact regions aligned along a stacking direction (e.g., z direction 2080).
• a set of patterned, metalized photovoltaic elements is stacked to form a solar cell.
• the set of photovoltaic elements that form the solar cell spans M elements, with M a natural number determined at least in part by a target operation voltage of the solar cell.
• the set of PV elements can be homogeneous or heterogeneous. In a homogeneous set each element, or unit cell, in the set is based on the same or substantially the same precursor, whereas in a heterogeneous set each element is based on disparate precursors.
• Disparate precursors can be based on the same semiconducting compounds, e.g., Si; Ge; GaAs, InAs, or other III-V semiconducting compounds; II- VI semiconducting compounds; CuGaSe; CuInSe; CuInGaSe, but differ in doping type or, for alloyed compounds, in alloying concentrations.
• patterned, metalized PV elements include confined regions of diffuse doping as discussed above.
• the solar cell is processed to facilitate deployment in a PV device, optimize photovoltaic performance, or a combination thereof. Processing can include various manufacturing steps or procedures such as cutting procedures, polishing procedures, cleaning procedures, integrating procedures, or the like.
• processing comprises cutting the formed solar cell(s) so as to expose or substantially expose (100) crystal planes to sunlight in order to establish the lowest surface states for passivation. It should be appreciated that the solar cell can be processed to expose or substantially expose other crystal planes, e.g., (qrs) planes such as (311)..
• FIG. 27 is a block diagram of an example system 2700 that enables fabrication of solar cells in accordance with aspects described herein.
• Deposition reactor(s) 2710 enable processing of semiconductor-base wafers to produce PV elements or unit cells that compose solar cells, e.g., VMJ solar cells, as described herein.
• Deposition reactor(s) 2710 and module(s) therein include various hardware components, software components, or combination(s) thereof, and related electric or electronic circuitry to accomplish the processing.
• coater module(s) 2712 allows patterning a surface of a semiconductor wafer or substrate with a dielectric coating.
• the wafer or substrate can be nominally-undoped or doped, and is the precursor of PV elements utilized for production of the solar cells.
• Deposition reactor(s) 2710 also include doping module(s) 2714 that allows inclusion of dopants within the semiconductor precursor of the PV elements. Dopants can form diffuse doping layers as described above (see, e.g., FIG. 19 or FIG. 23); however, doping module(s) 2714 also afford substantially any type of doping such as epitaxy-based doping, e.g., delta doping. In addition, doping module(s) 2714 allow formation of diffusion barriers that can prevent autodoping.
• coating a PV element with a dielectric material can occur prior or subsequent to doping. Doping subsequent to patterned dielectric coating exploits such coating as a mask for generation of confined or nearly-confined doping regions (see, e.g., FIG. 22).
• Metallization module(s) 2716 enables deposition of metallic layer(s) to a PV element that includes doping regions, extended or confined, and patterned dielectric coating(s). Metallization can be accomplished through deposition of semiconductor material with subsequent doping, or a metal material. In an aspect, such materials have thermal coeff ⁇ cient(s) that matches or nearly matches thermal coefficient(s) of PV element with doping regions.
• Deposition reactor(s) 2710 can include sputtering chamber(s), epitaxy chamber(s), vapor deposition chamber(s); electron beam gun(s); source material holder(s); wafer storage; sample substrate; oven(s), vacuum pump(s); e.g., turbomolecular pump, diffusion pump; or the like.
• deposition reactor(s) 2710 can include computer(s), including processor(s) and memories therein, with memories being volatile or non-volatile; programmable logic controller(s); dedicated processor(s) such as purpose-specific chipset(s); or the like.
• Deposition reactor(s) 2710 also can include software application(s) such as operating system(s), or code instructions to effect one or more processing acts, including at least those described supra. Described hardware, software, or combination thereof, facilitate or enable at least a portion of the functionality of deposition reactor(s) 2710 and module(s) therein.
• a bus 2718 allows communication of information, e.g., data or code instructions; transfer of materials; exchange of processed elements; and so forth, amongst the various hardware, software, or combination(s) thereof, in deposition reactor(s) 2710.
• Photovoltaic element(s) can be supplied to a package platform 2730 for further processing.
• An exchange link e.g., a conveyer link, or an exchange chamber and electromechanical components therein, can supply the PV element(s); at least one of the exchange link or exchange chamber illustrated with arrow 2720.
• Assembly module(s) 2732 can collect a set of PV element(s) and allow stacking of each of the PV elements through a high-temperature process or step in order to produce a solar cell, e.g., a VMJ solar cell.
• test module(s) 2760 can determine crystallographic orientation of the PV elements, or unit cells, in the solar cell; such determination can be established via X- ray spectroscopy, e.g., diffraction spectrum and rocking curve spectra.
• test module(s) 2760 can probe precursor materials or processed materials various stages of solar cell manufacturing.
• test module(s) 2760 can probe density of openings in a patterned dielectric coating of PV element(s) to determine whether such density is adequate for an expected sunlight intensity, or photon flux, in a solar concentrator.
• test module(s) can determine defect density that can arise from thermal cycling in a PV element with metallic layers, to establish if the material or process utilized for metallization is adequate.
• test module(s) 2760 can implement or enable minority-carrier lifetime measurements, X-ray spectroscopy, scanning electron microscopy, tunneling electron microscopy, scanning tunneling microscopy, electron energy loss spectroscopy, or the like.
• Probe(s) implemented by test module(s) 2760 can be in situ or ex situ. Samples of precursor of processed materials or devices, e.g., solar cells, can be supplied to test module(s) via exchange links 2740 and 2750.
• Processing unit(s) can effect logic to control at least part of the various processes described herein in connection with operation of system 2700.
• processing unit(s) can include processor(s) that execute code instructions that effect the control logic; the code instructions, e.g., program module(s) or software applications, can be retained in memory(ies) (not shown) functionally coupled to the processor(s).

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