WO2017100800A1

WO2017100800A1 - Rear contact and infrared mirror structures and manufacturing methods for back contact solar cells

Info

Publication number: WO2017100800A1
Application number: PCT/US2016/066243
Authority: WO
Inventors: Mehrdad M. Moslehi
Original assignee: Beamreach Solar, Inc.
Priority date: 2015-12-10
Filing date: 2016-12-12
Publication date: 2017-06-15

Abstract

A back contact solar cell comprises a backside passivation dielectric layer over the backside of a crystalline silicon absorber having backside base regions and backside emitter regions. A plurality of base contact openings through the backside passivation dielectric layer to the backside base regions and a plurality of emitter contact openings through the backside passivation dielectric layer to the backside emitter regions. A patterned metal stack over the backside passivation dielectric layer, the metal patterned stack having a contact metal layer with a thickness of less than I 0 nanometers and electrically contacting the plurality of doped base and emitter regions through the plurality of base and emitter contact openings, the metal patterned stack having a reflectance layer over the contact metal layer, the reflectance layer reflecting infrared light.

Description

REAR CONTACT AND INFRARED MIRROR STRUCTURES AND MANUFACTURING METHODS FOR BACK CONTACT SOLAR

CELLS

CROSS-REFERENCE TO RELATED APPLICATIONS

[001] This application claims the benefit of U.S. provisional patent application

62/265,953 filed on December 10, 2015, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

[002] The present disclosure relates in general to the fields of solar photovoltaics (PV), and more particularly to solar PV cells.

BACKGROUND

[003] As solar photovoltaic (PV) cell technology is increasingly adopted for power generation, pressure to increase solar PV cell power generation, improve conversion efficiency, and reduce solar cell and fabrication costs per watt and complexity become more widespread. Various material properties, structural features and fabrication processes contribute to the power generation capacity and efficiency of a solar PV cell (and the resulting solar PV module). Solar PV cell structure for power extraction and transfer, typically contacting base and emitter regions of a solar PV cell, often provides limited functionality specific to power extraction and transfer.

BRIEF SUMMARY OF THE INVENTION

[004] Therefore, a need has arisen for back contact solar cells with increased power generation, improved conversion efficiency, and reduced solar cell and fabrication costs and complexity. In accordance with the disclosed subject matter, a back contact solar cells are provided which may substantially eliminate or reduces disadvantage and deficiencies associated with previously developed back contact solar cells.

[005] According to one aspect of the disclosed subject matter, a back contact solar cell is provided. The back contact solar cell comprises a backside passivation dielectric layer over the backside of a crystalline silicon absorber having backside base regions and backside emitter regions, the backside base regions having a polarity opposite the backside emitter regions. A plurality of base contact openings through the backside passivation dielectric layer to the backside base regions and a plurality of emitter contact openings through the backside passivation dielectric layer to the backside emitter regions. A patterned metal stack over the backside passivation dielectric layer and contacting the plurality of doped base regions through the plurality of base contact openings and contacting the plurality of doped emitter regions through the plurality of emitter contact openings, the metal patterned stack having a contact metal layer with a thickness of less than 10 nanometers and electrically contacting the plurality of doped base and emitter regions through the plurality of base and emitter contact openings, the metal patterned stack having a reflectance layer over the contact metal layer, the reflectance layer reflecting infrared light.

[006] These and other aspects of the disclosed subject matter, as well as additional novel features, will be apparent from the description provided herein. The intent of this summary is not to be a comprehensive description of the claimed subject matter, but rather to provide a short overview of some of the subject matter's functionality. Other systems, methods, features and advantages here provided will become apparent to one with skill in the art upon examination of the following FIGURES and detailed description. It is intended that all such additional systems, methods, features and advantages that are included within this description, be within the scope of any claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[007] The features, natures, and advantages of the disclosed subject matter may become more apparent from the detailed description set forth below when taken in conjunction with the drawings (dimensions, relative or otherwise not drawn to scale) in which like reference numerals indicate like features and wherein:

[008] Fig. 1A is a drawing of an interdigitated back contact solar cell in accordance with the disclosed subject matter;

[009] Fig. IB is a drawing of an interdigitated back contact solar cell consistent with Fig. 1A and further showing barrier and seed metal 16 and plated metal 18; [010] Fig. 1C is a drawing of an interdigitated back contact solar cell consistent with Fig. IB and further showing a multi-stack backside dielectric passivation layer; and,

[011] Figs. 2 through 20 are graphs showing IR reflectance spectrums for detailed embodiments.

DETAILED DESCRIPTION

[012] The following description is not to be taken in a limiting sense, but is made for the purpose of describing the general principles of the present disclosure. The scope of the present disclosure should be determined with reference to the claims. Exemplary embodiments of the present disclosure are illustrated in the drawings (dimensions, relative or otherwise not drawn to scale), like aspects and identifiers being used to refer to like and corresponding parts of the various drawings.

[013] And although the present disclosure is described with reference to specific embodiments, fabrication processes, and materials, one skilled in the art could apply the principles discussed herein to other materials such as contact metals, reflectance metals and dielectric passivation materials, fabrication processes, as well as alternative technical areas and/or embodiments without undue experimentation.

[014] The comprehensive solar PV cell rear contact and infrared mirror solutions (dielectric-metal mirror) described provide improved infrared (IR) light reflectance from the rear or backside of the solar cell (opposite the sunlight-receiving frontside) for increased solar PV cell absorber photon absorption (including enhanced harvesting of the infrared photons in the wavelength range of approximately 800 nanometers to 1250 nanometers) in combination with reduced base and emitter contact resistance (for increased solar cell fill factor). Back contact solar cells typically have both base and emitter semiconductor regions positioned on the backside of the solar cell, for example an n-type (e.g., phosphorus doped) silicon solar cell absorber with both backside n+ base regions and a p+ emitter regions to separate and collect the photogenerated electrons and holes, respectively. Thus, backside base and emitter metallization contacts are required to the corresponding doped n+ and p+ semiconductor base and emitter regions. The metallization stacks described provide excellent ohmic contacts with low contact resistance to n+ and p+ semiconductor base and emitter regions and maximize infrared light reflectance to maximize solar cell semiconductor absorber absorption of photons (e.g., light reflectance in the range of approximately 800 nanometers and 1250 nanometers for a crystalline silicon absorber with a semiconductor energy bandgap of approximately 1150 nanometers).

[015] For fabrication simplicity it is highly preferred to use the same metallization material for both n+ and p+ polarity base and emitter contacts. For example, a single metallization layer may be deposited (for instance, using a method such as physical-vapor deposition) on the passivated backside of the back-contact solar cell semiconductor absorber (with contact openings through the backside dielectric passivation for both base and emitter contacts) contacting the backside base and emitter semiconductor regions and then the single metallization layer may then be patterned to divide and define base and emitter metallization (for instance, in an interdigitated pattern) - thus the same metal contacts both n+ and p+ regions and provides low-resistance ohmic contacts to both base and emitter regions. Physical-vapor deposition is a preferred method for deposition of the contact metallization layer. Alternatively, this metallization layer may be patterned printed, for example screen printed, as defined base and emitter metallization. A limited number of metallization materials provide sufficiently low ohmic resistance contacts for both n+ and p+ polarity contacts. Importantly, ohmic losses should be minimized during solar cell power extraction to maximize solar cell efficiency. And as solar cell fill factor (one of the underlying factors reflecting the potential obtainable generated power of a solar cell) is strongly and detrimentally affected by the parasitic resistance of the solar cell, and contact resistance is a component of undesirable parasitic resistance, contact resistance reduces solar cell fill factor. Additionally, avoiding high-temperature post- metal deposition annealing further reduces process complexity and cost and as-deposited metals (for instance, deposited by physical-vapor deposition methods such as plasma sputtering) not requiring subsequent thermal annealing may be advantageous. Thus, balancing tradeoffs for metal materials and systems that make superior low-resistance contacts to both p+ and n+ doped semiconductor regions may result in a limited selection of metals, such as refractory metals such as titanium and tantalum and titanium-tungsten alloy, and other metals such as nickel, nickel -vanadium alloy, and cobalt. However, many of these metals, such as titanium and nickel, have relatively poor (e.g., less than 90%) infrared (IR) reflectance in the wavelength range of interest (about 800 nanometers to 1250 nanometers) for crystalline silicon solar cells. As a solar cell contact metal, titanium (Ti) provides excellent ohmic contacts with low contact resistance (e.g., minimized ohmic losses) to both solar cell base and emitter regions, resulting in relatively high solar cell fill factor values. However, titanium has relatively poor IR light reflectance, a key component of solar cell power generation improvement. A poor IR rear reflectance will result in less-than-optimal short-circuit current for the solar cell since a larger portion of the IR photons may be lost because of absorption losses on the rear side contact metal of the solar cell.

[016] Fig. 1A is a drawing of an interdigitated back contact solar cell in accordance with the disclosed subject matter. Interdigitated doped base regions 6 and doped emitter regions 8 are formed in the backside of semiconductor absorber 2. The doping polarity of doped base regions 6 is the same as the background doping polarity of the semiconductor absorber 2 (e.g., n-type crystalline silicon absorber). The doping polarity of doped emitter regions 8 is opposite the doping polarity of the semiconductor absorber 2 (for instance, p- type doped emitter regions 8 formed in n-type semiconductor absorber 2). Frontside passivation dielectric layer 4 (e.g., a passivation material such as AI2O3, S1O2, H/SiN, or combination thereof, which may also provide an anti-reflective coating property besides excellent passivation property) and backside dielectric passivation layer 10 (e.g., a passivation material such as aluminum oxide: AI2O3 or silicon oxide: S1O2 or

combination thereof described in detail herein) are formed on the frontside (i.e., sunnyside) and backside of semiconductor absorber 2, respectively. Thus, frontside passivation dielectric layer 4 is on the frontside (i.e., sunnyside or sunlight-receiving side) of the back-contact solar cell and base regions 6 and emitter regions 8 are on the backside of the back contact solar cell (i.e., side opposite the sunlight-receiving frontside). Backside dielectric passivation layer 10 may be a single layer or a multilayer dielectric stack. The backside dielectric passivation layer (or stack of layers), which may comprise of AI2O3 and/or S1O2, can be deposited using techniques such as Atmospheric- Pressure Chemical-Vapor Deposition (APCVD) or Plasma-Enhanced Chemical-Vapor Deposition (PECVD) methods. The frontside dielectric passivation layer is preferably deposited using a PECVD method, or combination of PECVD with another method (such as atomic-layer deposition). Contact metal 12 contacts base regions 6 and emitter regions 8. Contact metal 12 provides electrical contact to base regions 6 and emitter regions 8. Reflectance metal 14 is formed on contact metal 12. Reflectance metal 14 provides light reflectance, particularly infrared light reflectance. Both contact metal 12 and reflectance metal 14 may be deposited during the same deposition process in a single manufacturing equipment (such as in a PVD tool/equipment performing plasma sputtering), and are patterned to form the patterned (e.g., interdigitated) solar cell metallization. Semiconductor absorber 2 is an n-type crystalline silicon substrate (for an n-type back-contact solar cell), base region 6 is an n+ doped region, and emitter region 8 is a p+ doped region. Both base regions 6 and emitter regions 8 are formed as a plurality of alternating doped regions on the backside of the semiconductor absorber 2. Contact metal 12 and reflectance metal 14 provide electrically conductive metallization for solar cell power extraction and transfer as well as improved light reflectance for additional photo capture and power generation by semiconductor absorber 2. The contact metal 12, reflectance metal 14, and backside dielectric passivation layer 10 materials and thicknesses are optimized to maximize solar power generation and power extraction and transfer (while reducing the manufacturing cost).

[017] Contact metal 12 makes contact to doped silicon regions (i.e., doped base regions 6 and doped emitter regions 8) and is sufficiently thin so that in the light range of interest (e.g., infrared photons in the wavelength range of about 800 nanometers to 1250 nanometers, for rear side reflectance back into semiconductor absorber 2) contact metal 12 is highly non-absorptive and relatively transparent. In other words, contact metal 12 is transparent and non-absorptive to allow IR light to pass through to reflectance metal 14 without appreciable absorption of IR photons. Superior contact metallization materials for both n+ and p+ polarities may be refractory metals that are more absorptive than reflective, such as titanium or tantalum or nickel or cobalt or titanium-tungsten alloy, or nickel -vanadium alloy. Any IR absorbed by contact metal 12 are lost and cannot contribute to solar power generation. Thus, the absorptive loss of contact metal 12 is minimized by forming it thin as to be highly non-absorptive and transparent, while also providing superior low-resistance electrical contacts to both base and emitter regions, such that the IR light goes through this thin contact metal layer (which is in contact with silicon through the contact openings, and with the backside passivation dielectric elsewhere) to a second more reflective (and highly reflective for IR photons) layer (e.g., reflectance metal 14). Practically this results in a contact metal having a thickness less than about ten nanometers and advantageously having a thickness in the range of about two to six nanometers. This thickness range is sufficient to make excellent ohmic contacts to the base and emitter regions while causing negligible absorption of IR photons. Material and thickness considerations for the contact metal include superior contact to both n+ and p+ polarities, relatively good IR transparency and negligible IR absorption.

[018] Reflectance metal 14 provides very high reflectance (e.g., silver or aluminum with greater than 90% IR reflectance), while also providing conductive power transfer, and is formed sufficiently thick such that infrared light does not pass through it. In the case of silver this metal layer thickness may be at least 40 nanometers.

[019] A backside dielectric such as backside dielectric passivation layer 10 (also serving as the rear or backside surface passivation dielectric), only a relatively small percentage of which is open (contact openings or contact holes through the backside passivation dielectric) for electrical contact to underlying base and emitter regions, provides select electrical insulation between semiconductor absorber and solar cell metallization. In combination with this backside dielectric layer, for example dielectric layer materials providing superior passivation such as silicon oxide (S1O2) and aluminum oxide (AI2O3), the backside metallization stack described provides a hybrid dielectric-metal mirror for enhanced solar cell backside IR light reflectance and thus improved semiconductor absorber photon capture for the IR photons in the range of about 800 nanometers and 1250 nanometers. The dielectrics described (such as silicon oxide S1O2 and aluminum oxide AI2O3, or a stacked combination thereof) are substantially electrically insulating and substantially optically non-absorptive of light (for the IR photons in the spectral range of interest of about 800 nanometers to 1250 nanometers wavelengths), thus providing in combination with optimal thicknesses of metals improved infrared reflectance in addition to solar cell absorber passivation functionality.

[020] Thus, the described solutions provide rear dielectric passivation and metallization structures which provide a combination of low-contact-resistance electrical contacts to the base and emitter regions and high-infrared-reflecting dielectric-metal rear mirror for back-contact solar cells.

[021] Fig. IB is a drawing of an interdigitated back contact solar cell consistent with Fig. 1A and further showing barrier and seed metal 16 and plated metal 18 (e.g., plated copper). Contact metal 12, reflectance metal 14, and barrier and seed metal 16 may be deposited as a metal stack. Fig. 1C is a drawing of an interdigitated back contact solar cell consistent with Fig. IB and further showing backside dielectric passivation layer 10 as a backside dielectric passivation layer stack of layers 10a, 10b, 10c, and lOd (e.g., 10a is AI2O3, 10b is S1O2, IOC is AI2O3, and lOd is S1O2).

[022] Back contact solar cell frontside structure may have a frontside passivation and anti -reflection coating layer (e.g., PECVD silicon nitride or a combination of PECVD aluminum oxide and silicon nitride serving as frontside passivation and anti -reflection coating) serving as the sunlight receiving side of the solar cell. The semiconductor absorber (e.g., crystalline silicon) is sandwiched between the frontside passivation and anti-reflection coating layer and backside of solar cell having base and emitter regions (and backside passivation dielectric made of AI2O3 or S1O2 or a combination thereof).

[023] Detailed solar cell embodiments relating to metallization stacks and backside passivation layers particularly applicable to silicon absorbers are provided below. An additional plated metallization (such as plated copper with a barrier/seed layer made of nickel or nickel -vanadium) on the reflectance layer may be used for reduced cost or improved conductivity for solar cell power transfer. For example, a plated metallization on physical vapor deposition (PVD) metal stack of titanium (Ti) then silver (Ag) then nickel vanadium (Ni V) or a stack of Ti then Ag then nickel (Ni). In this case, titanium acts as the contact metal for n+ and p+ polarities, silver as the reflectance metal for backside infrared reflectance, and nickel vanadium/nickel as a barrier and seed layer for a plated metal layer (such as plated copper formed over the barrier and seed layer) for improved conductivity and power transfer. For example, the backside of the solar cell having: 1) backside dielectric passivation having at least two different oxide layers (such as at least one layer of aluminum oxide and at least one layer of silicon oxide); 2) a metal stack comprising: titanium in contact with base and emitter silicon regions and the backside dielectric passivation, silver in contact with titanium; and, 3) a plating barrier / seed layer such a layer having nickel (e.g., Ni or nickel-vanadium NiV alloy) in contact with silver. The thicknesses of the three layers in the 3 -layer metal stack Ti / Ag / NiV may be: 1 to 10 nm of Ti (advantageously 3 to 6 nm of Ti), 30 to 200 nm of Ag

(advantageously 40 to 70 nm of Ag), and 100 to 1000 nm of NiV or Ni (advantageously 250 to 500 nm of NiV or Ni). The final backside metal structure may include a plated copper layer (e.g., having a thickness in the range of 10 to 80 microns and more particularly in the range of 20 to 50 microns) in contact with the plating barrier / seed layer (e.g., plated copper in contact with sputter deposited NiV or Ni). The Ti/Ag/NiV metal stack may be deposited on the backside dielectric passivation by a PVD technique such as plasma sputtering (after formation of contact holes through the passivation dielectric to allow for the metal structure to make patterned electrical contacts to the silicon base and emitter regions). The backside dielectric passivation advantageously may have at least two different oxides and in combination with Ti/Ag/Ni(V) metal stack provides high (greater than 90% spectral weighted in the wavelength range of about 800 nanometers to 1250 nanometers) reflectance in most of 800 nm to 1250 nm IR range. Plating may be performed after PVD of Ti/Ag/Ni or Ti/Ag/NiV metal stack as follows: (i) print a patterned resist on Ti/Ag/Ni (V) stack; (ii) plate metal (e.g., copper or copper with a capping layer such as tin); (iii) selectively strip the resist; and, (iv) selectively etch the exposed Ti/Ag/Ni (V) stack. The backside dielectric/metal stack of this embodiment provides an improved and superior combination of low-resistivity contacts to silicon, high IR reflectance, and plating barrier and seed.

[024] With reference to a three layer metal contact/reflector/barrier and seed structure in a solar cell having silicon as power generation medium, then AI2O3 as backside dielectric, and three layer metal structure of Ti + Ag + NiV as contact/mirror/seed structure. Ti serves as mostly-transparent / non-absorptive electrical contact for both doped n+ and p+ regions (preferable Ti thickness of approximately 3 to 10 nm, and advantageously approximately 3 to 6 nm thick, for contact and semi-transparency). Ag serves as the main high-reflectance IR reflector (preferable Ag thickness of

approximately 30 to 100 nm, and advantageously approximately 50 nm thick, for high IR transparency while managing the Ag material consumption cost). NiV or Ni serves as the diffusion barrier and plating seed layer (preferable NiV thickness of approximately 200 to 500 nm, and advantageously NiV thickness of approximately 300 nm). The materials and thicknesses of the backside dielectric (e.g., AI2O3, S1O2, or a multi -layer combination thereof) may be optimized for maximum dielectric/metal hybrid mirror IR reflectance (while reducing production cost).

[025] In another embodiment, tantalum is the contact metallization. For example, a plated metallization on physical vapor deposition (PVD) metal stack of tantalum (Ta) then silver (Ag) then nickel -vanadium (NiV) or a stack of Ta then Ag then nickel (Ni). In this case, tantalum acts as the contact metal for n+ and p+ polarities, silver as the high reflectance metal for backside infrared reflectance, and nickel vanadium/nickel as a barrier and seed layer for a plated metal layer (such as plated copper) for improved conductivity and power transfer. For example, the backside of the solar cell having: 1) backside dielectric passivation having at least two different oxide layers (such as at least one layer of aluminum oxide and at least one layer of silicon oxide); 2) a metal stack comprising: tantalum in contact with base and emitter silicon regions and the backside dielectric passivation, silver in contact with tantalum; and, 3) a plating barrier / seed layer such a layer having nickel (e.g., Ni or nickel -vanadium NiV alloy) in contact with silver. The thicknesses of the three layers in the 3-layer metal stack Ta / Ag / NiV may be: 1 to 10 nm of Ta (advantageously 3 to 6 nm of Ta), 30 to 200 nm of Ag (advantageously 40 to 70 nm of Ag), and 100 to 1000 nm of NiV or Ni (advantageously 250 to 500 nm of NiV or Ni). The final backside metal structure may include a plated copper layer in contact with the plating barrier / seed layer (e.g., plated copper in contact with sputter deposited NiV or Ni). The Ta/Ag/NiV metal stack may be deposited on the backside dielectric passivation by sputtering (after formation of contact holes in the passivation dielectric to allow for the metal structure to make electrical contacts to the silicon base and emitter regions). The backside dielectric passivation advantageously may have at least two different oxides and in combination with Ta/Ag/Ni(V) metal stack provides high (greater than 90% spectral weighted in the wavelength range of about 800 nanometers to 1250 nanometers) reflectance in most of 800 nm to 1250 nm IR range. Plating may be performed after PVD of Ta/Ag/Ni or Ta/Ag/NiV metal stack as follows: (i) print a patterned resist on Ta/Ag/Ni(V) stack; (ii) plate metal (e.g., copper or copper with a capping layer such as tin); (iii) selectively strip the resist; and, (iv) selectively etch the exposed Ta/Ag/Ni(V) stack. The backside dielectric/metal stack of this embodiment provides an improved and superior combination of low-resistivity contacts to silicon, high IR reflectance, and plating barrier and seed.

[026] With reference to a three layer metal contact/reflector/barrier and seed structure in a solar cell having silicon as power generation medium, then AI2O3 as backside dielectric, and three layer metal structure of Ta + Ag + NiV as contact/mirror/seed structure. Ta serves as mostly-transparent / non-absorptive electrical contact for both doped n+ and p+ regions (preferable Ta thickness of approximately 3 to 10 nm, and advantageously approximately 3 to 6 nm thick, for contact and semi-transparency). Ag serves as the main high-reflectance IR reflector (preferable Ag thickness of approximately 30 to 100 nm, and advantageously approximately 50 nm thick, for high IR transparency while managing the Ag material consumption cost). NiV or Ni serving as the diffusion barrier and plating seed layer (preferable NiV thickness of approximately 200 to 500 nm, and advantageously NiV thickness of approximately 300 nm). The materials and thicknesses of the backside dielectric (e.g., AI2O3, S1O2, or a multi-layer combination thereof) may be optimized for maximum dielectric/metal hybrid mirror IR reflectance.

[027] Advantageous notes for consideration based on multi-layer simulations are detailed following. The IR reflectance of the multi-layer oxide / metal stack mirror may be optimized using a relatively thick (400 - 450 nanometers or nm) backside oxide stack if required. Improved contact/mirror/barrier/seed metal structure for plated cells with Ta (3-5 nm) / Ag (50 nm) / NiV (250 - 500 nm) provides superior IR reflectance values compared to a Ti (3 - 5 nm) / Al (2000 nm) / NiV (250 - 5000 nm) structure (for all non- optimal and optimal dielectric stacks). For backside oxide dielectric stack multi-layers and thicknesses of 450 nm total AI2O3 and S1O2 thickness, the Ta (5 nm) / Ag (50 nm) / NiV on backside oxide mirror provides 88.8% - 96.4% IR reflectance in the 800 - 1250 nm range. For optimized backside oxide dielectric stack layers and thicknesses of 425 nm total AI2O3 and S1O2 thickness (with modified S1O2 thicknesses and AI2O3 layer thicknesses of 75 nm and 75 nm unchanged), the Ta (5 nm) / Ag (50 nm) / NiV on backside oxide mirror provides 93.7% - 97.5% IR reflectance (800 - 1250 nm range).

[028] Additional advantageous notes for consideration based on multi-layer simulations are detailed following, particularly applicable to copper plated solar cells with Ta/Ag/NiV. For the Si + Dielectric + 5 nm Ta / 50 nm Ag / NiV material solution: the use of a dielectric (e.g., a minimum thickness of approximately 50 nm of AI2O3) between the metal stack and silicon suppresses the parasitic losses and improves the overall IR reflectance; dielectric plus metal mirror is superior to a metal only mirror; in absence of silver (i.e., metal mirror being 5 nm Ta + thick NiV), any thickness of the dielectric layer (even a thick 1000 nm to 2000+ nm AI2O3 or S1O2) may result in relatively poor IR mirror (hence, cannot depend on dielectric mirror); for AI2O3 dielectric, an optimum thickness of AI2O3 for the best IR (800 - 1250 nm) reflectance is approximately 100 nm - 125 nm (for 5 nm Ta/50 nm Ag/NiV), for the optimum AI2O3 thickness (approximately 100 - 125 nm), the [AI2O3 + 5 nm Ta + 50 nm Ag + NiV] IR reflectance is -95% to 97% (in the 800 nm to 1250 nm IR wavelength range); for AI2O3 dielectric, the AI2O3 dielectric thickness may be as thick as about 150 nm for the IR reflectance values being above 90% in the 800 - 1250 nm range; for AI2O3 dielectric, the max AI2O3 thickness may be limited to approximately 200 nm to retain good IR reflectance (-80% to 97% with 200 nm AI2O3 for 800 -1250 nm spectral range); the optimum thickness range for S1O2 may on the order of 125 nm to 150 nm (for 5 nm Ta + 50 nm Ag + NiV), which is also near the optimum thickness range for AI2O3. Thus, a design rule may control the total dielectric (AI2O3) thickness to be in the range of about 100 nm up to 200 nm (with the optimum range being -100 - 125 nm) and make the metal stack as 5 nm Ta + 50 nm Ag + NiV (250 to 500 nm).

[029] Figs. 2 through 20 are graphs showing IR reflectance spectrums for detailed embodiments consistent with the disclosed subject matter. The calculations are based on a simulator using the complex-matrix form of the Fresnel equations. Particularly, the thickness of the contact metal (e.g., tantalum, titanium) may be adjusted to optimize their transparency for increased reflectance by the reflectance metal in consideration with other solar cell structural and fabrication factors. The backside oxide dielectric layer thickness may also be adjusted to optimize backside oxide dielectric and metal mirror reflectance in consideration with other solar cell structural and fabrication factors.

[030] Figs. 2 through 4 show the IR reflectance for a tantalum contact metal and a silver reflectance metal. Fig. 2 is a graph showing the IR reflectance spectrum of AI2O3 (100 nm) + Ta (5 nm) + Ag (50 nm) + NiV (approximately 250 - 500 nm) with a silicon solar cell substrate absorber medium. The mirror comprising approximately 100 nm AI2O3 + 5 nm Ta + 50 nm Ag + NiV has an IR reflectance of 95.1% to 96.9% (800 - 1250 nm IR band range). An optimum condition of 100 nm AI2O3 dielectric thickness may be observed.

[031] Fig. 3 is a graph showing the IR reflectance spectrum S1O2 (100 nm) + Ta (5 nm) + Ag (50 nm) + NiV (approximately 250 - 500 nm) with a silicon solar cell substrate absorber medium. The mirror comprising approximately 100 nm S1O2 + 5 nm Ta + 50 nm Ag + NiV has an IR reflectance of 96.5% to 97.4% (800 - 1250 nm IR band range). A near optimum condition of 100 nm S1O2 dielectric thickness may be observed.

[032] Fig. 4 is a graph showing the IR reflectance spectrum S1O2 (150 nm) + Ta (5 nm) + Ag (50 nm) + NiV (approximately 250 - 500 nm) with a silicon solar cell substrate absorber medium. The mirror comprising approximately 150 nm Si02 + 5 nm Ta + 50 nm Ag + NiV has an IR reflectance of 95.9% to 98.0% (800 - 1250 nm IR band range). A near optimum condition of 150 nm S1O2 dielectric thickness may be observed.

[033] Fig. 5 shows the IR reflectance for a titanium contact metal and an aluminum reflectance metal. Fig. 5 is a graph showing the IR reflectance spectrum AI2O3 (100 nm) + Ti (5 nm) + Al (2000 nm) + NiV (approximately 250 - 500 nm) with a silicon solar cell substrate absorber medium. The mirror comprising approximately 100 nm AI2O3 + 5 nm Ta + 2000 nm Al + NiV has an IR reflectance of 86.6% to 94.8% (800 - 1250 nm IR band range). A near optimum condition of 100 nm AI2O3 dielectric thickness and 2000 nm Al reflectance metal thickness may be observed.

[034] Multi-layer dielectric stacks of (listed starting with the layer in contact with silicon and ending with the layer in contact with rear metal) 75 nm AI2O3 (e.g., 10a in Fig. 1C) then 250 nm S1O2 (e.g., 10b in Fig. 1C) then 75 nm AI2O3 (e.g., 10c in Fig. 1C) then 50 nm S1O2 (e.g., lOd in Fig. 1C), resulting in a total backside oxide dielectric stack thickness of 450 nm, may be advantageous for both reflectance and passivation. The AI2O3 layer in contact with silicon (e.g., 10a in Fig. 1C) may be a doped AI2O3 layer, for example having a doping opposite the silicon absorber for forming emitter regions.

[035] Figs. 6 through 20 show the IR reflectance for a multi-layer dielectric stacks and metal mirror stacks in accordance with the disclosed subject matter. In consideration with other factors, it may be advantageous to maintain AI2O3 layers in the stack described above at a thickness of 75 nm while adjusting the thicknesses of the S1O2 layers. Fig. 6 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (250 nm) + AI2O3 (75 nm) + S1O2 (50 nm) + Ta (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (250 nm) + AI2O3 (75 nm) + S1O2 (50 nm) + Ta (3 nm)/Ag (50 nm)/NiV has an IR reflectance of 91.5% to 97.0% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 450 nm of AI2O3 and S1O2 may be observed. For example, with this embodiment tantalum thickness may adjusted, for example increased to 5 nm, which may result in IR impact.

[036] Fig. 7 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ta (5 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ta (5 nm)/Ag (50 nm)/NiV has an IR reflectance of 93.7% to 97.5% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 425 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 6, the S1O2 layer thicknesses are adjusted, the AI2O3 layer thicknesses remain unchanged, and the contact metallization tantalum thickness is adjusted.

[037] Fig. 8 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ta (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ta (3 nm)/Ag (50 nm)/NiV has an IR reflectance of 94.4% to 98.0% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 425 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 7 the contact metallization tantalum thickness is adjusted.

[038] Fig. 9 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ta (5 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ta (5 nm)/Ag (50 nm)/NiV has an IR reflectance of 94.2% to 97.5% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 435 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 8, the Si02 layer thicknesses are adjusted, the

AI2O3 layer thicknesses remain unchanged, and the contact metallization tantalum thickness is adjusted.

[039] Fig. 10 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ta (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ta (3 nm)/Ag (50 nm)/NiV has an IR

reflectance of 94.4% to 98.0% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 435 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 9 the contact metallization tantalum thickness is adjusted.

[040] Fig. 11 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (250 nm) + AI2O3 (75 nm) + S1O2 (50 nm) + Ti (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising A1203 (75 nm) + S1O2 (250 nm) + AI2O3 (75 nm) + S1O2 (50 nm) + Ti (3 nm)/Ag (50 nm)/NiV has an IR reflectance of 84.7% to 94.9% (800 - 1250 nm IR band range), and specifically greater than 90% in the 840 - 1250 nm IR band range. A near optimum condition of total dielectric stack thickness of 450 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 10 the contact metallization material is titanium as compared to tantalum. Additionally, as compared to Fig. 10, the S1O2 layer thicknesses are adjusted, and the AI2O3 layer thicknesses remain unchanged. For example, with this embodiment titanium thickness may adjusted, for example increased to 5 nm, which may result in IR impact.

[041] Fig. 12 is a graph showing the IR reflectance spectrum AI2O3 (50 nm) + S1O2 (50 nm) + AI2O3 (50 nm) + S1O2 (0 nm) + Ti (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (50 nm) + S1O2 (50 nm) + AI2O3 (50 nm) + S1O2 (0 nm) + Ti (3 nm)/Ag (50 nm)/NiV has an IR reflectance of 91.6% to 96.8% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 150 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 11, the multi -layer dielectric materials are adjusted (specifically the S1O2 layer contacting the contact metallization of titanium is removed resulting in a three layer dielectric stack), and the first S1O2 layer and both AI2O3 layers thicknesses are adjusted.

[042] Fig. 13 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (5 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (5 nm)/Ag (50 nm)/NiV has an IR reflectance of 88.3% to 94.8% (800 - 1250 nm IR band range), and specifically greater than 90% in the 800 - 1210 nm IR band range. A near optimum condition of total dielectric stack thickness of 425 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 11, the S1O2 layer thicknesses are adjusted, the AI2O3 layer thicknesses remain unchanged, and the contact metallization titanium thickness is adjusted.

[043] Fig. 14 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (3 nm)/Ag (50 nm)/NiV has an IR reflectance of 91.3% to 96.4% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 425 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 13, the contact metallization titanium thickness is adjusted.

[044] Fig. 15 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (5 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (5 nm)/Ag (50 nm)/NiV has an IR reflectance of 89.1% to 94.7% (800 - 1250 nm IR band range), and specifically greater than 90% in the 805 - 1227 nm IR band range. A near optimum condition of total dielectric stack thickness of 435 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 14, the S1O2 layer thicknesses are adjusted and the contact metallization titanium thickness is adjusted. [045] Fig. 16 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (3 nm)/Ag (50 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (3 nm)/Ag (50 nm)/NiV has an IR reflectance of 91.9% to 96.4% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 435 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 15, the contact metallization titanium thickness is adjusted.

[046] Fig. 17 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (5 nm)/Al (2000 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (5 nm)/Al (2000 nm)/NiV has an IR

reflectance of 89.3% to 94.3% (800 - 1250 nm IR band range), and specifically greater than 90% in the 820 - 1250 nm IR band range. A near optimum condition of total dielectric stack thickness of 425 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 16 the reflectance metallization material is aluminum as compared to silver. Additionally, as compared to Fig. 16, the S1O2 layer thicknesses are adjusted and the contact metallization titanium thickness is adjusted.

[047] Fig. 18 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (3 nm)/Al (2000 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (125 nm) + AI2O3 (75 nm) + S1O2 (150 nm) + Ti (3 nm)/Al (2000 nm)/NiV has an IR

reflectance of 90.3% to 95.2% (800 - 1250 nm IR band range). A near optimum condition of total dielectric stack thickness of 425 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 17, the contact metallization titanium thickness is adjusted.

[048] Fig. 19 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (5 nm)/Al (2000 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (5 nm)/Al (2000 nm)/NiV has an IR

reflectance of 87.7% to 94.5% (800 - 1250 nm IR band range), and specifically greater than 90% in the 855 - 1250 nm IR band range. A near optimum condition of total dielectric stack thickness of 435 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 18, the S1O2 layer thicknesses are adjusted and the contact metallization titanium thickness is adjusted.

[049] Fig. 20 is a graph showing the IR reflectance spectrum AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (3 nm)/Al (2000 nm)/NiV with a silicon solar cell substrate absorber medium. The mirror comprising AI2O3 (75 nm) + S1O2 (150 nm) + AI2O3 (75 nm) + S1O2 (135 nm) + Ti (3 nm)/Al (2000 nm)/NiV has an IR reflectance of 94.8% to 98.0% (800 - 1250 nm IR band range), and specifically greater than 90% in the 825 - 1250 nm IR band range. A near optimum condition of total dielectric stack thickness of 435 nm of AI2O3 and S1O2 may be observed. For example, in this embodiment as compared to Fig. 19, the contact metallization titanium thickness is adjusted.

[050] The backside structures shown in Figs. 1A, IB, and 1C may show metal- insulator-semiconductor structures in all the backside regions except for the base and emitter contact regions. In other words, referring to Fig. 1A, the metal-insulator- semiconductor structure comprises the following: metal portion of the metal-insulator- semiconductor structure made of the stack of metal formed by contact metal 12 and reflectance metal 14; insulator portion of the metal-insulator-semiconductor structure made of backside dielectric passivation layer 10; semiconductor portion of the metal- insulator-semiconductor structure made of semiconductor absorber 2. Similarly, referring to Fig. IB, the metal-insulator-semiconductor structure comprises the following: metal portion of the metal-insulator-semiconductor structure made of the stack of metal formed by contact metal 12, reflectance metal 14, barrier and seed metal 16, and plated metal 18; insulator portion of the metal-insulator-semiconductor structure made of backside dielectric passivation layer 10; and, semiconductor portion of the metal- insulator-semiconductor structure made of semiconductor absorber 2. Similarly, referring to Fig. 1C, the metal-insulator-semiconductor structure comprises the following: metal portion of the metal-insulator-semiconductor structure made of the stack of metal formed by contact metal 12, reflectance metal 14, barrier and seed metal 16, and plated metal 18; insulator portion of the metal-insulator-semiconductor structure made of backside multilayer dielectric passivation layer made of dielectric layers 10a, 10b, 10c, and lOd; and, semiconductor portion of the metal-insulator-semiconductor structure made of semiconductor absorber 2.

[051] The foregoing description of the exemplary embodiments is provided to enable any person skilled in the art to make or use the claimed subject matter. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the innovative faculty. Thus, the claimed subject matter is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

CLAIMS What is claimed is:

1. A back contact solar cell, comprising: a backside passivation dielectric layer over the backside of a crystalline silicon absorber having backside base regions and backside emitter regions, said backside base regions having a polarity opposite said backside emitter regions; a plurality of base contact openings through said backside passivation dielectric layer to said backside base regions; a plurality of emitter contact openings through said backside passivation dielectric layer to said backside emitter regions; and, a patterned metal stack over said backside passivation dielectric layer and contacting said plurality of doped base regions through said plurality of base contact openings and contacting said plurality of doped emitter regions through said plurality of emitter contact openings, said metal patterned stack having a contact metal layer with a thickness of less than 10 nanometers and electrically contacting said plurality of doped base and emitter regions through said plurality of base and emitter contact openings, said metal patterned stack having a reflectance layer over said contact metal layer, said reflectance layer reflecting infrared light.

2. The back contact solar cell of Claim 1, wherein said refractor metal layer has a thickness in the range of approximately 2 nanometers and 7 nanometers.

3. The back contact solar cell of Claim 2, wherein said refractor metal layer is substantially transparent to the infrared photons in the wavelength range of approximately 800 nanometers and 1250 nanometers.

4. The back contact solar cell of Claim 1, wherein said refractor metal layer is a titanium (Ti) layer.

5. The back contact solar cell of Claim 1, wherein said refractor metal layer is a nickel (Ni) layer.

6. The back contact solar cell of Claim 1, wherein said refractor metal layer is a titanium- tungsten (TiW) layer.

7. The back contact solar cell of Claim 1, wherein said refractor metal layer is a nickel- vanadium (NiV) layer.

8. The back contact solar cell of Claim 1, wherein said infrared-reflecting metal layer is a silver layer.

9. The back contact solar cell of Claim 8, wherein said silver layer has a thickness larger than approximately 30 nanometers.

10. The back contact solar cell of Claim 9, wherein said silver layer has a thickness in the range of approximately 30 nanometers and 70 nanometers.

11. The back contact solar cell of Claim 1, wherein said backside passivation dielectric layer comprises an electrically insulating oxide layer.

12. The back contact solar cell of Claim 1, wherein said backside passivation dielectric layer has an aluminum oxide layer in contact with said backside of said crystalline silicon layer.

13. The back contact solar cell of Claim 12, wherein said backside passivation dielectric layer further has a silicon oxide layer in contact with said aluminum oxide layer.

14. The back contact solar cell of Claim 12, wherein said aluminum oxide layer is doped with said second doping type.

15. The back contact solar cell of Claim 1, wherein said infrared-reflecting metal layer is an aluminum layer.

16. The back contact solar cell of Claim 1, wherein said infrared-reflecting metal layer is an aluminum-containing alloy layer.

17. The back contact solar cell of Claim 1, wherein said infrared-reflecting metal layer is a

silver-containing alloy layer.

18. The back contact solar cell of Claim 1, wherein said patterned metal stack further comprises a barrier and seed metal layer over and contacting said infrared-reflecting layer and a copper layer over and contacting said barrier and seed layer.

19. The back contact solar cell of Claim 18, wherein said barrier and seed layer is a nickel (Ni) layer.

20. The back contact solar cell of Claim 18, wherein said barrier and seed layer is a nickel- vanadium (NiV) layer.

21. The back contact solar cell of Claim 18, wherein said copper layer is a plated copper layer.

22. The back contact solar cell of Claim 2, wherein said refractor metal layer has a thickness in the range of approximately 3 nanometers and 7 nanometers.

23. The back contact solar cell of Claim 1, wherein said backside passivation layer and said patterned metal stack provide a hybrid dielectric-metal mirror with greater than 90% effective spectral-weighted reflectance into said crystalline silicon layer, for infrared portion of sunlight photons in the spectral range of approximately 800 nanometers and 1250 nanometers.

24. The back contact solar cell of Claim 1, wherein said refractory metal layer makes low- resistance ohmic contacts to said plurality of doped base and emitter regions through said plurality of base and emitter contact openings.

25. The back contact solar cell of Claim 24, wherein said refractor metal is titanium (Ti).

26. The back contact solar cell of Claim 25, wherein said infrared-reflecting metal layer is silver (Ag).

27. A semiconductor-insulator-metal stack structure, comprising: a backside dielectric passivation layer with a plurality of contact openings on the backside of a crystalline semiconductor layer; and, a patterned metal stack having at least two metal layers: i. a refractory metal layer with a thickness of less than 10 nanometers,

contacting said backside dielectric layer and portions of said crystalline semiconductor layer through said plurality of contact openings ii. an infrared-reflecting metal layer over and contacting said refractory metal layer

28. The semiconductor-insulator-metal stack structure of Claim 27, wherein said refractor metal layer is a metal chosen from the group of titanium (Ti), tantalum (Ta), nickel (Ni), nickel- vanadium (NiV), and titanium-tungsten (TiW).

29. The semiconductor-insulator-metal stack structure of Claim 28, wherein said infrared- reflecting metal layer is silver (Ag) or an alloy of silver.

30. The semiconductor-insulator-metal stack structure of Claim 28, wherein said infrared- reflecting metal layer is aluminum (Al) or an alloy of aluminum.

31. The semiconductor-insulator-metal stack structure of Claim 28, wherein said semiconductor- insulator-metal stack structure provides a hybrid dielectric-metal mirror with an effective spectral-weighted reflectance of greater than 90% in the infrared spectral range of approximately 800 nanometers and 1250 nanometers for sunlight photons.

32. The semiconductor-insulator-metal stack structure of Claim 27 wherein said semiconductor is crystalline silicon.

33. The semiconductor-insulator-metal stack structure of Claim 32 wherein said insulator

comprises aluminum oxide.

34. The semiconductor-insulator-metal stack structure of Claim 32 wherein said insulator

comprises a stack of aluminum oxide and silicon oxide.

35. The semiconductor-insulator-metal stack structure of Claim 32 wherein said patterned metal stack further comprises a barrier and seed layer over and contacting said infrared-reflecting metal layer and a copper layer over and contacting said barrier and seed layer.

36. The semiconductor-insulator-metal stack structure of Claim 32 wherein said barrier and seed layer is chosen from the group of nickel (Ni) and nickel -vanadium (NiV).

37. The semiconductor-insulator-metal stack structure of Claim 36 wherein said copper layer is a plated copper layer.