AU2015264935B2 - Method and substrates for making photovoltaic cells - Google Patents

Abstract

H:\kxg\Interwoven\NRPortbl\DCC\KXG\9020604_I.docx-7/12/2015 Methods of and apparatuses for making a photovoltaic cell are provided. The photovoltaic cell is able to have a substrate made of a composite material. The composite material is able to be formed by mixing a binder and a physical property enhancing material to form a mixer. The binder is able to be pitch, such as mesophase pitch. The physical property enhancing material is able to be fiber glass. The substrate of the photovoltaic cell is able to be flexible, such that the photovoltaic cell is able to be applied on various surfaces. WO 2012/051603 PCT/U S2011/056481 Sat 402 r'404 Coat an adhesive layer Coat a Mo layer Deposit absorber 408 precursors Perform selenization _[;-410 process Perform CdS -- '412 deposition Coat a TCO layer Fabricate wiring 416 elements Stop 418 Fig. 4

Description

C AUsers \kll\AppData\Local\Temp\l 3086721 _l_75D3AF3.DOCX-7/02/2017 2015264935 07 Feb 2017

METHOD AND SUBSTRATES FOR MAKING PHOTOVOLTAIC CELLS

This is a divisional of Australian Patent Application No. 2011315847, the entire contents of which are incorporated herein by reference. 5

Field of the Invention:

The present invention relates to the field of green technology. More specifically, the present invention relates to the field of photovoltaic (PV) cells. 10 Background of the Invention:

Traditionally, sodalime glass is used for the fabrication of thin film solar cells. Problems are associated with the photovoltaic cells that use sodalime glass or stainless steel sheets as substrates. The sodalime glass substrates are brittle. Furthermore, the sodalime glass substrate is rigid and not flexible, which limits its applications to only flat surfaces. Moreover, 15 the sodalime glass substrate is an electrical insulator and is expensive, which is about 40% of PV fabrication cost. The high cost of the substrate material results in a high price of the finished devices. Additionally, the Tg (glass transition temperature) of sodalime glass substrate limits the selenization temperature. Comparing the more recent PV cell with a stainless steel sheet or a metallic sheet as a substrate with the traditional PV cell with sodalime 20 glass as a substrate, the stainless steel/metallic sheet substrate has a more flexible and conductive structure than the sodalime glass substrate. The flexibility increases the uses of the PV cell. Nonetheless, the rolled stainless steel sheet substrate is inferior than the sodalime glass substrate in a way that the stainless steel substrate has a rougher surface. Moreover, the metal contained in the typical stainless steel substrate is able to be a source of metallic 25 contamination (such as Fe, Ni, and other impurities) to CIGS semiconductors, because the metals contained (such as Fe and Ni) is able to diffuse through Mo grain boundaries to short the cell. Especially, the typical selenization temperature under inert atmosphere is between 500°C and 750°C. At such temperature, the diffusion rate of Fe and Ni becomes very fast and the kinetics favors Fe diffusion through the open grain boundary between Mo grains. Also, at 30 this high temperature, molten Se in the CIS (copper indium selenide) or CIGS (Copper indium gallium (di)selenide: a tetrahedrally bonded semiconductor) layer above the Mo diffuses through the Mo grain boundaries to attack the stainless substrate beneath the Mo, shorting out the solar cells. These defects typically result in cells with greatly reduced efficiencies and the substrates are often scrapped. High scrap losses and accompanying low efficiency cells -1- C:\Users\kll\AppData\Local\Temp\ 13086721 _l_75D3AF3.DOCX-7/02/2017 2015264935 07 Feb 2017 35 produces expensive solar cells, which are not commercially viable.

Summary of the Invention:

The present invention seeks to provide a method of and a novel substrate for making a photovoltaic cell. The photovoltaic cell is able to have a substrate made of a composite material. The composite is able to be formed by mixing a binder and a physical property 40 enhancing material to form a mixer. The binder is able to be pitch, such as mesophase pitch or neomesophase pitch. The physical property enhancing material is able to be a conducting material, a nonconducting is material, or fiber glass. The substrate of the photovoltaic cell is able to be flexible or rigid, such that the photovoltaic cell is able to be applied on various surfaces, 45 In the first aspect, the present invention provides a photovoltaic cell comprising a) an absorber capable of absorbing light; and b) a substrate, wherein the substrate comprises a laminate structure having a pitch layer sandwiched by a first fiber glass layer on a top side and a second fiber glass layer on a bottom side, wherein the pitch layer comprises glassy carbon formed during a high temperature 50 carbonization by adding an amount less than 5% of sulfur or organo-sulfur compounds to a mesophase pitch binder.

Also described is a photovoltaic cell comprising an absorber capable of absorbing light and a substrate, wherein the substrate comprises a carbon based material, a silicon based material, or a combination thereof, wherein the carbon based material, the silicon based 55 material, or the combination thereof is substantially free of metal. The carbon based material, the silicon based material, or the combination thereof may comprise a pitch. In some embodiments, the pitch comprises neomesophase pitch, oriented carbon structures or a combination thereof. In some other embodiments, the absorber comprises CIGS, CIG, or CIS. In some embodiments, the photovoltaic cell further comprises CdS, Mo, Cr, or a combination 60 thereof. In other embodiments, the substrate comprises fiber glass. In some other embodiments, the substrate comprises a conductive material. In some embodiments, the substrate comprises an insulator. In other embodiments, the substrate is flexible. In other embodiments, the substrate is rigid.

In the second aspect, the present invention provides a method of manufacturing a 65 photovoltaic cell comprising a) preparing a substrate containing a laminate structure having a pitch layer sandwiched by a first fiber glass layer on a top side and a second fiber glass layer on a bottom side, wherein the pitch layer comprises glassy carbon formed -2- C:\Users\kll\AppData\Loca l\Temp\13086721_l_75D3AF3.DOCX-7/02/20l7 2015264935 07 Feb 2017 70 75 85 90 100 during a high temperature carbonization by adding an amount less than 5% of sulfur or organo-sulfur compounds to a mesophase pitch binder; and b) coupling a light absorber with the substrate. Also described is a method of manufacturing a photovoltaic cell that comprises preparing a substrate containing a carbon based material, a silicon based material, an orientated carbon structure or a combination thereof, wherein the carbon based material, the silicon based material, or the combination thereof is substantially free of metal and coupling a light absorber with the substrate. The carbon based material, the silicon based material, or the combination thereof may comprise pitch. In other embodiments, the method further comprises coating an adhesive layer between the light absorber and the substrate. In some other embodiments, the adhesive layer comprises Cr. In some embodiments, the method further comprises forming a reflective layer between the adhesive layer and the light absorber. In other embodiments, the reflective layer comprises Mo. In some embodiments, the light absorber comprises CIGS, CIS, or CIG. In other embodiments, the method further comprises performing selenization. In some other embodiments, the pitch comprises mesophase pitch. In some embodiments, the substrate comprises a silicon/silicone based material or a carbon based material, such as fiber glass and ceramic compounds. In the third aspect, the present invention provides a method of manufacturing a photovoltaic cell comprising a) forming a mesophase pitch by performing a solvent extraction, a heat treatment, or a combination thereof; b) drying the mesophase pitch; c) adding a filler material; and d) stabilizing or cross-linking the pitch at a temperature above 200°C, such that a substrate of the photovoltaic cell is formed, wherein the substrate comprises a laminate structure having a pitch layer sandwiched by a first fiber glass layer on a top side and a second fiber glass layer on a bottom side, wherein the pitch layer comprises glassy carbon formed during a high temperature carbonization by adding an amount less than 5% of sulfur or organo-sulfur compounds to a mesophase pitch binder. Also described is a method of manufacturing a photovoltaic cell comprising forming a mesophase or neomesophase pitch by performing a solvent extraction, a heat treatment, or a combination thereof, drying the mesophase or neomesophase pitch, adding a filler material, extruding sheet of composite material, and stabilizing or cross-linking the pitch at a temperature above 200°C, such that a substrate of the photovoltaic cell is formed. In some -3- C:\Users\kll\AppData\Local\Temp\l 3086721 _l_75D3AF3.DOCX-7/02/2017 2015264935 07 Feb 2017 embodiments, the method further comprises performing extrusion of the mesophase or neomesophase pitch in sheet form above m 200°C. In some embodiments, the sheet structure 105 is similar to a plywood structure. In other embodiments, the method further comprises performing a high temperature treatment at a temperature between 600°C and 3000°C. In some other embodiments, the filler material comprises fiber glass. In some embodiments, the filler material comprises a conductor. In other embodiments, the filler material comprises an insulator. In some other embodiments, the method further comprises coupling a light absorber 110 with the substrate. In some embodiments, the light absorber comprises, CIGS, CIS, or CIG.

There is also described a method of forming an insulating apparatus comprising preparing a composite material containing pitch with fiber glass and coupling the composite material with a building structure, wherein the substrate is able to reflect heat, lights, or a combination thereof. In some embodiments, the composite material is able to reflect more 115 than 90% of incoming light, such as IR (infrared radiation) and UV (ultraviolet) light. In some embodiments, the composite material is able to reduce heat from entering into the building structure. In some embodiments, the composite material is able to conduct electricity.

Brief Description of the Drawings: 120 Figure 1 illustrates a method of making a material in accordance with some embodiments.

Figures 2A and 2B illustrate apparatuses for making a substrate material in accordance with some embodiments.

Figures 3 illustrates a photovoltaic cell in accordance with some embodiments. 125 Figure 4 illustrates a photovoltaic cell manufacturing method in accordance with some embodiments.

Figure 5 illustrates a mesophase pitch sheet fabrication method in accordance with some embodiments.

Figure 6 illustrates a mesophase pitch sheet fabrication method in accordance with 130 some embodiments.

Detailed Description:

In some aspects of the present invention, inexpensive and/or recycled industrial waste are used to make various materials. The materials have wide applications in industries. For 135 example the material is able to be used as part of the substrate of a photovoltaic cell. The industrial wastes that are used herein include pitch from the petrochemical industry and coal -4- C:\Users\kll\AppData\Local\Temp\l 3086721 _l_75D3AF3.DOCX-7/02/2017 2015264935 07 Feb 2017 ash from the coal industry and coal fired electric generating plants. The above-mentioned waste products (such as pitch and coal ash) are able to be used as a substrate material for flexible and non-flexible thin film photovoltaic cells. Above listed industrial wastes are examples that are used for illustration purposes. Other industrial waste products are 5 applicable.

In some other aspects of the present invention, materials and composite structures are formed using isotropic, anisotropic mesophase pitch, graphitizing pitch or liquid crystalline obtained from pitch (including commercially available pitch) as a binder or matrix material with other carbonaceous and/or non-carbonaceous materials. In the following, methods of and 10 apparatuses for making materials are disclosed in accordance with some embodiments. Figure 1 illustrates a method 100 of making the materials in accordance with some embodiments. The method 100 is able to include adding desired/pre-selected materials, creating a laminate with the added materials, stabilizing and/or cross-linking a binder material, and carbonizing. The steps of method 100 are optional. Additional steps are able to be added to the method 100. 15 The sequences of performing the steps of method 100 are able to be in any order. More details of performing method 100 are illustrated below. The method 100 is able to begin from Step 102.

At Step 104, selected materials/components are added based on a selected material property of the material. In some embodiments, woven fiberglass material (silica-based and/or 20 carbon-based material) is impregnated with a binder material by spraying, roll-coating, dipping, brushing, or a combination thereof. The fiberglass material combined with the binder material forms a binder material coated fiberglass material. A person of ordinary skill in the -4A- PCT/US2011/056481 WO 2012/051603 2015264935 07 Dec 2015 ait appreciates that other methods are able to be used to combine the binder material and the added material to gain predetermined physical interactions and properties, such as mixing, blending, and pressing. In other embodiments, non-woven fiberglass material is used to be combined with the binder material. The binder material described herein is able to be pitches, 5 coal ash, or any other materials that are able to be used as a binder material. A person of ordinary skill in the art appreciates that the binder material is able to be any materials that have property of adhesion, such as adhesives, glues, cement, and paints. The property of adhesion includes materials that show such property under pre-defined conditions, such as temperature, pressure, solvent, co-reactants, or a combination thereof. For example, a binder 10 material is within the scope of the present invention when the binder material demonstrates the property of adhesion under a pressure, such as 10 psi, and not adhesive under normal atmospheric pressure (e.g.. 1 atm). Various other components are able to be added at Step 104 based on the pre-selected property of the products. Some of the embodiments are discussed in the following paragraphs. 15 At Step 106, a laminate including the added materia! is created. In some embodiments, the above formed binder material coated fiberglass material is rolled or extruded to form a laminate, in some embodiments, the thickness of the laminate is thinner than 20 microns. In some other embodiments, the thickness of Lite laminate is thicker than 2000 microns. In some other embodiments, the thickness of the laminate is between 20 20 microns and 2000 microns. In some embodiments, the width of the laminate is in the range between 10cm and I m, such that a sheet of a laminate material is able to be made for further cutting. In some other embodiments, the width of the laminate is in the range between 0.5 cm and 3 cm. such that a cell/rectangular form of a substrate is formed for rcady-to-use. A person of ordinary skill in the art would appreciate that any width of the laminate is applicable 25 depending on a selected use of the substrate.

In some embodiments, the laminate includes a structure having a mesophase pitch layer sandwiched by layers of fiber glass on the top side and on the bottom side of the mesophase pitch layer. For example, a sandwich structure/laminate is formed by preparing a first layer of fiber glass sheet having a size of 1 nrf and a thickness of 3mm, adding a second 30 layer of a binder material (such as a mesophase pitch) having a size of Inf and a thickness of 5mm on top of the first layer, adding a third layer of fiber glass sheet having a size of Inf and a thickness of 2 mm. and extruding with a pressure press extruder to form a sandwiched laminate having a thickness of 7mm. In other embodiments, the laminate includes a layer of -5- PCT/US2011/056481 WO 2((12/051603 2015264935 07 Dec 2015 fiber glass sandwiched by two layers of pitch, hi some embodiments, the pitch is a low molecular weight neomesopliase pitch or is any other binder.

At Step 108, the binder material is stabilized or cross-linked below the softening temperature in an oxygen ambient to form a treated material. In some embodiments, the 5 temperature is in the range of 200°C to 450°C. A person of ordinary skill in the art appreciates that other temperature ranges are applicable. In some embodiments, the temperature is near the softening temperature. In some other embodiments, the temperature is higher than the softening temperature.

At Step 110, the treated material is heat treated to carbonize the mixture. In some 10 embodiments, the temperature of Step 110 is in the range of S00°C to 1700°C. In some other embodiments, the temperature is in the range of 700°C to 300QnC. In some embodiments, the Step 110 is performed under inert ambient, such as nitrogen, with a pressure between 2psi and 40psi. In some embodiments, the pressure applied is maintained during the cooling down step, such that shrinkage and warpage of the sheet structure is able to be minimized. The 15 method 100 is able to stop at Step 112.

Different material properties are selected for different applications, such as thermal, sound, electrical, vibrational, signal, and light conductivity/insulation, material strength, and material durability. Various materials are able to be added in the composite material to enhance the pre determined property, hi some embodiments, chopped or particulate 20 conducting materials are used as the reinforcing agent or material, such that the conductivity of the material produced is able to be enhanced. In some other embodiments, chopped or particulate non-conducting materials are used as the reinforcing agent or material, such that the property of insulation of the material produced is enhanced. In some embodiments, the materials that are incoiporated include coal ash, milled glass, milled quartz, glass beads, 25 chopped glass fiber, chopped quartz fiber mica flakes, ceramic powder/bcads/flakes. and non-carbonacequs material. In some other embodiments, the materials that are incorporated include conducting metallic or metal alloy powders, flakes or fibers. In some embodiments, the materials that are incorporated include nanoparticles, such as metal nanoparticles and metal oxide nanoparticles (e.g,, 0,0, nanoparticles are incoiporated as a catalyst for 3D neucleation.) A person of ordinary skill in the art appreciates that any conducting materials are able to be added including copper, chromium, carbon powder or carbon flakes, graphite flakes, or combinations thereof. -6- C:\Users\kll\AppData\Local\Temp\ 13086721 _l_75D3AF3.DOCX-7/02/20l 7 2015264935 07 Feb 2017

In some embodiments, the electrical resistivity of the substrate material (the materiel produced from the method 100) is selected. An amount of less than 5% of sulfur or organo-sulfur compounds with or without metallic oxides or metallic compounds is admixed into the mesophase pitch binder before the cross-linking step such that glassy carbon is formed during 5 the high temperature carbonization step. Any other materials that are able to be added to, for example, control the texture or strength and increase or decrease the resistivity of the substrate materials are within the scope of the present invention.

In the following, the apparatuses for making the substrate material are disclosed. Figures 2A and 2B illustrate apparatuses 200 and 211 for making the substrate material in 10 accordance with some embodiments. The reactants, such as the fiber glass 216 and binder materials 218, are able to be added in the mixing device 202 through the hopper 210 and 212, respectively. The reactants are able to be in solid and/or liquid form of solvent and/or compositions. In some embodiments, the mixing device 202 is able to be an extruder. The mixing device 202 is able to mix the materials added by the mixer 217, such as a screw mixer. 15 A person of ordinary skill in the art appreciates that any number of hoppers are able to be included in the mixing device 202. The mixing device 202 and/or the apparatus 200 are able to be performed under air atmosphere, inter atmosphere (such as N2 and Ar), or pressurized atmosphere (such as 2-10 psi and 1-3 atm). The hoppers 210 and 212 are able to be hermetically sealed chambers, top open chambers, hinged top opening chambers for solid and 20 fluids, such as gas, liquid, and supercritical fluids. The mixing device 202 is able to include a die 214 allowing the output material 201 to be shaped in a desired form and thickness, such as 1mm - 10mm. In some embodiments, the apparatus 200 is able to include a roller 204, such as a pull roller. The roller 204 is able to use its rolling wheels and belts compressing the output material 201 to a desired thickness, such as 20 to 500 microns. The laminate described in 25 Figure 1 is able to be fabricated in a batch mode or roll-to-roll depending on the thickness of the laminate using the mixing device 202 and/or the roller 204 described herein. The output material 201 is able to be heated in the oven 206 in a pre-determined temperature, such as 200°C - 450°C for stabilizing or cross-linking the binder material and 600°C - 1700°C for carbonizing the materials. In some embodiments, during the stabilization and carbonization 30 steps, a controlled fluid ambient is used to exact the pressure on both major sides of the substrate. For example, the oven/furnace 206 is able to be lined with tiny orifices 205 (with multiple heating zones), where the gap between the upper and the lower inner furnace walls is negligible compared to the width or length of the furnace. In some embodiments, inert gas is introduced into the oven/furnace 206 in the carbonizing -7- PCT/US2011/056481 WO 2012/051603 2015264935 07 Dec 2015 process through the tiny orifices 205 on both side of the laminate in the oven/fumace 206 and the pressure of the fluid is controlled to emanate on both sides of the laminate (output material 201), such that the fluid, such as inert gas. prevents the sheet laminate from touching the major sides of the oven/fumace 206. In some embodiments, the gap of the fluid exit 203 5 of the oven 206 is reduced, such that the applied fluid is able to be used to exact the pressure on the substrate during the cross-linking, carbonization, or a combination thereof. In some embodiments, the apparatus 200 is able to include one or more cooling device 207. The output material 201 is able to be cut and stored by a cutter 208 to a pre-determined dimension, such as 1 nr. The cutter 208 is able to be a pressure press-cut machine. 10 Similar to the protrusion setup device 202, Figure 2B shows a pultrusion device 220

The pultrusion device 220 is able to continuously manufacture composite materials. A fiber sheet 226 is able to be pulled through the pitch hath 224, which is supplied by a pitch source 222. The output material 201 in Figure 2B is able to be further compressed by the roller 204. heated by the over 206. cooling down by the cooler 207. and sized by the cutter 208 similar to 15 the processes described in Figure 2A and its associated texts.

Applications

The materials that are made by using the methods and apparatuses disclosed herein in accordance with some embodiments are able to be applied in various applications and used in 20 various ways. For example, in some embodiments, more than one laminate is able to be stacked and bonded by a thin layer of mesophase pitch binder. The orientation of the sheets is able to be parallel to each another, cross-ply, or in any selected orientations with respect to each other prior to the cross-linking step. The single sheet or stacked sheets arc able to be cut and formed in a suitable mold by known methods for fabricating a pre-selected structure or 25 shape, such as a substrate of a solar cell.

In some embodiments, an alternatively conductive layer structure is selected, which is able to be made by bonding the highly conductive laminates to each other by using the more insulative glassy carbon binder. The formed material having alternative layers of different conductivity is able to be used as a capacitor for low or high temperature applications. For 30 example, the capacitor is able to have a structure including a first layer of highly insulating layer, a second layer of conducting layer, a third layer of highly insulating layer, a fourth layer of conducting layer, and a fifth layer of highly insulating layer. The substrate made through -8- PCT/US2011/056481 WO 2(112/051603 2015264935 07 Dec 2015 the methods and apparatuses disclosed herein is able lo be used as flexible substrate for photovoltaic cells, electromagnetic shielding, casing for electronic appliances and architectural applications. 5 Photo Voltaic Cells

In the following, methods of making photovoltaic cells (PV) using the material/substrate made above are provided in accordance with embodiments.

Methods of and substances for making photovoltaic cells in accordance with some embodiments are disclosed. In some embodiments, the photovoltaic cells include a composite 10 or a non-composite carbonaceous substrate, in which isotopic or anisotropic mesophase pitch, neomesophase pitch, or a combination thereof is used as a binder, matrix material, or the neat material for the fabrication of planar and non planar sheets for the fabrication of thin film solar cells. In the following, a photovoltaic cell having a substrate using the material disclosed herein is provided in accordance with some embodiments. 15 Figure 3 illustrates a photovoltaic cell 300 in accordance with some embodiments. In some embodiments, the photovoltaic cell 300 includes a substrate 302. an adhesive layer 304. a Mo layer 306, an absorber layer 308. a buffer layer 310 (such as a CdS layer), and TCO (transparent conduction oxide) layer 312. The substrate 302 of the photovoltaic cell 300 is able to include a mesophase/neomesophase pitch backbone substrate. In some embodiments, 20 the thickness of the substrate 302 is able to be 20 microns to 1mm or more. In some other embodiments, the thickness of the substrate 302 is able to be thicker than 5mm. A person of ordinary skill in the ait appreciates that any thickness of the substrate 302 is applicable. The physical and material properties of the substrate 302 is adjustable by adding pre-selected fillers based on the applications. The rigidity/flexibility, conductivity, the degree of thermal 25 expansion, and surface roughness for the substrate 302 are all adjustable and controllable. For example, a conductive substrate 302 is able to be made by adding conductive materials, catalysts, nanoparticles, and metallic oxides (e.g., a filler) to the binder material during the manufacturing process. When an insulating substrate 302 is desired, the insulating substrate is able to be made by adding insulating materials to the binder material during the 30 manufacturing process. Similarly, a flexible substrate 302 is able to be made by adjusting the hardness or stiffness of the binder materials or the types of materials to be added. The -9- PCT/US2011/056481 WO 2((12/051603 2015264935 07 Dec 2015 substrate 302 made using the methods and materials disclosed herein is able 10 withstand a higher selenization temperature range than the substrate made by typical methods. Since the substrate 302 made using the methods and materials disclosed herein has minimal to no undesirable metallic impurities, short of the cell is able to be avoided when heating the 5 photovoltaic cell under a high temperature.

In some embodiments, the photovoltaic cell 300 includes an adhesive layer 304. The adhesive layer 304 is able to be a Cr layer and applied on top of the substrate 302 by sputtering and other known methods. The thickness of the adhesive layer 304 is able be between 20nm to lOOOnm. A person of ordinary skill in the ait appreciates that any thickness 10 of the adhesive layer 304 is applicable, such as 2mm or thicker. in some embodiments, the photovoltaic cell 300 includes a Mo layer 306. The Mo layer 306 is able to be on top of the adhesive layer 304. The Mo layer 306 is able to serve as the back contact and to reflect most unabsorbed light back into the absorber layer 308 (such as aCIGS layer). The Mo layer 306 is able to be a thin film deposited by PVD (physical 15 vapor deposition) such as sputtering and evaporation and other known methods, such as CVD (chemical vapor deposition). The thickness of the Mo layer 306 is able to be between lOOnm to 2000nm. A person of ordinary skill in the art appreciates that any thickness of the .Vlo layer 306 is applicable, such as 2 microns or thicker. In some embodiments, multiple Mo layers 306 are able to be included to attain a pre-defined Mo film thickness. In some embodiments, a 20 thin layer Mo alloy (such as a 2nm to lOnm MoSi layer) is inserted within the Mo laminate to modify the grain structure of the Mo film coated over the alloy layer.

In some embodiments, the photovoltaic cell 300 includes an absorber layer 308, such as CIGS layer or a CIG/CIS layer. The absorber layer 308 is able to be formed by depositing/sputtering/evaporating precursor materials/layers, such as Cu, In, Ga. or a 25 combination thereof on the Mo layer 306 followed by selenization. The absorber is able to be formed using typical methods of forming CIGS layers. In some embodiments, the precursor materials/layers are able to be coated with a thin layer of sodium fluoride prior to the selenization step in inert ambient between the temperature of 500°C and 800°C for 5 minutes to 120 minutes in excess selenium ambient, such as I l2Se or Se(gV 30 In some embodiments, the photovoltaic cell 300 includes a buffer layer 310. The buffer layer 310 is able to be n-type CdS. The buffer layer is able to be coated on the absorber layer 308 by typical methods. In some embodiments, the photovoltaic cell 300 includes a transparent conducting oxide layer (TCO) 312. The I CO layer 312 is able to be doped with Al. The TCO layer is able to collect and move electrons out of the cell while absorbing as -10- PCT/US2011/056481 WO 2012/051603 2015264935 07 Dec 2015 little light as possible. In some embodiments, the photovoltaic cell 300 includes electrical wiring elements 314 on the TCO layer 312 for conducting electronic signals and electricity.

In some embodiments, the photovoltaic cell 300 is able to be laminated with polymer films to form flexible solar cells. 5 Figure 4 illustrates a photovoltaic cell manufacturing method 400 in accordance with some embodiments. The method 400 is able to begin from Step 402. At Step 404. an adhesive layer is coated on a substrate. The substrate is able to be manufactured using the method described above. In some embodiments, the adhesive layer contains Cr or a Cr sheet/layer. In some embodiments, the substrate is a mesophase matrix substrate. The mesophase matrix 10 substrate is able to be a bottom electrode of the photovoltaic cell. In some other embodiments, the substrate is a composite carbonaceous substrate. In other embodiments, the substrate is a non-composite carbonaceous substrate. The substrate is able to be isotropic or anisotropic mesophase pitch, neomesopha.se pitch, or a combination thereof. A person of ordinary skill in die art appreciates that other materials that are adhesive or adhesive under 15 predetermined conditions are applicable. At Step 406, a Mo layer is coated on the adhesive layer, which is able to couple the substrate with an absorber layer. At Step 408, precursor materials, such as Cu, In, Ga, and Se (Copper indium gallium selenide), are coated on the Vlo layer. At Step 410, selenizaiion is performed. In the process of selenizalion, Se is able to be supplied in the gas phase (for example as H2Se or elemental Se) at high temperatures, and the 20 Se becomes incorporated into the Film by absorption and subsequent diffusion. By performing the selenization, an absorber of the photovoltaic cell is able to be formed At Step 412, CdS layer formation on the absorber (CIGS) layer is performed. At Step 414, a layer of TCO is coated on the CdS layer. At Step 416. wiring elements are fabricated on the TCO. The method 400 is able to stop at Step 4 IS, In the following, a method of forming the mesophase 25 pilch sheet that is able to be used as the Substrate in the method 400 described above is provided.

Figure 5 illustrates a mesophase pitch sheet fabrication method 500 in accordance with some embodiments. The method 500 begins from Step 502. At Step 504, a pitch is added. The pitch is able to be graphitizable isotropic carbonaceous pitch from Ashland 240 or 30 260 (petroleum pitch) from coal. A person of ordinary skill in the art appreciates that the pitch is able to be from various sources, such as directly from industrial waste. At Step 506, solvent extraction and heat treatment is performed with the pitch. At Step 508, mesophase or neomesophase materials are formed. In some embodiments, the mesophase or neomesophase materials contain liquid crystals more than 50% of the composition. At Step 510, the -11- PCT/US2011/056481 WO 20 ί 2/051603 2015264935 07 Dec 2015 mesophase or neomesophase materials are dried and comtnunition is performed. At Step 512, sheet extrusion is performed under inter ambient atmosphere at 250°C to 300CC. At Step 514, sheet stabilization is perform by heating the sheet at 250°C to 300°C. At Step 516, high temperature treatment is performed at inert ambient at 600°C to 3000°C. The method 500 is 5 able to slop at Step 518. In the following, a method of incorporating filler materials into the substrate material/mesophase sheet material is provided.

Figure 6 illustrates a mesophase pilch sheet fabrication method 600 in accordance with some embodiments. The method 600 begins from Step 602. At Step 604, a pitch is added. The pitch is able to be graphitizable isotropic carbonaceous pitch from Ashland 240 or 10 260 (petroleum pitch) from coal. A person of ordinary skill in the art appreciates that the pitch is able to be from various sources, such as directly from industrial waste. At Step 606. solvent extraction and heat treatment is performed. At Step 608. mesophase or neomesophase materials are formed. In some embodiments, the mesophase or neomesophase materials contain liquid crystals more than 50% of the composition. At Step 610. the mesophase or 15 neomesophase materials are dried and communition is performed. At Step 611, filler material is added. The filler to be added is able to be chosen based on the pre-selected physica'Vchemical property of the substrate (product). At Step 612, sheet extrusion is performed under inter ambient atmosphere at 250°C to 300°C. At Step 614, sheet stabilization is performed by heating the sheet at 250°C to 300°C. At Step 616. low melting 20 point and/or low molecular weight mesophase pitch is formed, which is able to be used to laminate multiple sheet material. The method 600 is able to stop at Step 618.

All steps described above are optional. The sequence of performing the steps that are included in the methods above is able to be in any order. Additional steps are able to be added. 25 The present application is able to be utilized in making various materials for industrial applications, such as the substrate of a solar cell. In operation, a photovoltaic solar cell writh a flexible substrate made with the methods provided herein is able to be bent to a desired shape and applies on a non-flat surface.

The term pitch used herein is able to include tar. asphaltene, viscoelastic polymers, 30 asphalt, bitumen, carbon disulfide, and resin. In some embodiments, the high viscosity of the chosen binder (such as pitch) or the added material provides a function to retain the metallic panicles in the substrate and prevent them from shorting the PV cell. In some embodiments, the materials/substrates made using the methods and compositions disclosed herein is able to be used as a heat insulation device, like thermal paint, which is able to be installed on/applv -12- 2015264935 07 Dec 2015 H:Ui*^fltoh*vm'A^PonbWX:nKXC\«02| 375_ I .ttocv7>12/2015 on or as a pari of the roof or wall of a building structure, such as a house or a barn. In some embodiments, the materials/substrales comprise conductive material having high electrical conductivity, so the materials/substrates are able to be used to conduct electricity. In some other embodiments, the materials/substrates have high reflectivity of heat and/or lights, and the substrates and the materials arc able to be used as mirrors on building structures. The mirrors described herein arc able to reflcct/insulale/isolalc heat. lights, or a combination thereof. In some embodiments, the subslratcs/materials are able to reflect more than 90% of the incoming lights or selected wavelengths of lights, such as IR and UV.

The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be readily apparent to one skilled in the art that other various modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention as defined by the claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not. and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of (he common general knowledge in the field of endeavour to which this specification relates. - 13-

Claims (23)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   1. A photovoltaic cell comprising a) an absorber capable of absorbing light; and b) a substrate, wherein the substrate comprises a laminate structure having a pitch layer sandwiched by a first fiber glass layer on a top side and a second fiber glass layer on a bottom side, wherein the pitch layer comprises glassy carbon formed during a high temperature carbonization by adding an amount less than 5% of sulfur or organo-sulfur compounds to a mesophase pitch binder.
2. 2. The photovoltaic cell of Claim 1, wherein the pitch comprises neomesophase pitch.
3. 3. The photovoltaic cell of Claim 1, wherein the absorber comprises CIGS or CIS.
4. 4. The photovoltaic cell of Claim 1, further comprising CdS, Mo, Cr, or a combination thereof.
5. 5. The photovoltaic cell of Claim 1, wherein the substrate comprises a conductive material.
6. 6. The photovoltaic cell of Claim 1, wherein the substrate comprises an insulator.
7. 7. The photovoltaic cell of Claim 1, wherein the substrate is flexible.
8. 8. The photovoltaic cell of Claim 1, wherein the substrate is rigid.
9. 9. A method of manufacturing a photovoltaic cell comprising a) preparing a substrate containing a laminate structure having a pitch layer sandwiched by a first fiber glass layer on a top side and a second fiber glass layer on a bottom side, wherein the pitch layer comprises glassy carbon formed during a high temperature carbonization by adding an amount less than 5% of sulfur or organo-sulfur compounds to a mesophase pitch binder; and b) coupling a light absorber with the substrate.
10. 10. The method of Claim 9, further comprising coating an adhesive layer between the light absorber and the substrate.
11. 11. The method of Claim 10, wherein the adhesive layer comprises Cr.
12. 12. The method of Claim 10, further comprising forming a reflective layer between the adhesive layer and the light absorber.
13. 13. The method of Claim 12, wherein the reflective layer comprises Mo.
14. 14. The method of Claim 9, wherein the light absorber comprises CIGS or CIS.
15. 15. The method of Claim 9, further comprising performing selenization.
16. 16. A method of manufacturing a photovoltaic cell comprising a) forming a mesophase pitch by performing a solvent extraction, a heat treatment, or a combination thereof; b) drying the mesophase pitch; c) adding a filler material; and d) stabilizing or cross-linking the pitch at a temperature above 200°C, such that a substrate of the photovoltaic cell is formed, wherein the substrate comprises a laminate structure having a pitch layer sandwiched by a first fiber glass layer on a top side and a second fiber glass layer on a bottom side, wherein the pitch layer comprises glassy carbon formed during a high temperature carbonization by adding an amount less than 5% of sulfur or organo-sulfur compounds to a mesophase pitch binder.
17. 17. The method of Claim 16, further comprising performing extrusion of the mesophase pitch above 200°C.
18. 18. The method of Claim 16, further comprising performing a high temperature treatment at a temperature between 600°C and 3000°C.
19. 19. The method of Claim 16, wherein the filler material comprises fiber glass.
20. 20. The method of Claim 16, wherein the filler material comprises a conductor.
21. 21. The method of Claim 16, wherein the filler material comprises an insulator.
22. 22. The method of Claim 16, further comprising coupling a light absorber with the substrate.
23. 23. The method of Claim 22, wherein the light absorber comprises CIGS or CIS.