Patent Publication Number: US-2011048518-A1

Title: Nanostructured thin film inorganic solar cells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The application claims the benefit under 35 U.S.C. §119(e)(1) of U.S. Provisional Application No. 61/236,960 filed on Aug. 26, 2009, and No. 61/246,432 filed on Sep. 28, 2009, which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND INFORMATION 
     Photovoltaic cells generally provide electrical energy in exchange for light energy. This energy conversion results from absorption of photons providing electron-hole pairs. Providing p-type silicon material in contact with n-type silicon (e.g., p-n junction) provides diffusion of electrons from a region of high electron concentration (n-type silicon) to the region of low electron concentration (p-type silicon). As electrons diffuse across the p-n junction, they combine with holes in the p-type silicon creating an electric field. Photogenerated electron-hole pairs are separated by this electric field. Specifically, minority carrier-electrons in the p-type region diffuse to the n-type region, and vice versa resulting in an external circuit, i.e. the illuminated solar cell acts like a battery or an energy source. 
     Described herein are methods of forming photovoltaic cells using nano-fabrication methods. Nano-fabrication includes the fabrication of very small structures that have features on the order of 1000 nanometers or smaller. One application in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. The semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate; therefore, nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing continued reduction of the minimum feature dimensions of the structures formed. Other areas of development in which nano-fabrication has been employed include solar cell technology, biotechnology, optical technology, mechanical systems, and the like. For example, nano-fabrication has been employed in organic solar cells in U.S. Ser. No. 12/324,120, which is hereby incorporated by reference in its entirety. 
     An exemplary nano-fabrication technique in use today is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as U.S. Patent Publication No. 2004/0065976, U.S. Patent Publication No. 2004/0065252, and U.S. Pat. No. 6,936,194, all of which are hereby incorporated by reference. 
     An imprint lithography technique disclosed in each of the aforementioned U.S. patent publications and patent includes formation of a relief pattern in a formable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be coupled to a motion stage to obtain a desired positioning to facilitate the patterning process. The patterning process uses a template spaced apart from the substrate and a formable liquid applied between the template and the substrate. The formable liquid is solidified to form a rigid layer that has a pattern conforming to a shape of the surface of the template that contacts the formable liquid. After solidification, the template is separated from the rigid layer such that the template and the substrate are spaced apart. The substrate and the solidified layer are then subjected to additional processes to transfer a relief image into the substrate that corresponds to the pattern in the solidified layer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       So that the present invention may be understood in more detail, a description of embodiments of the invention is provided with reference to the embodiments illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the invention, and are therefore not to be considered limiting of the scope. 
         FIG. 1  illustrates a simplified side view of an exemplary prior art thin-film solar cell. 
         FIG. 2  illustrates a simplified side view of an exemplary solar cell design in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a simplified side view of another exemplary solar cell design. 
         FIGS. 4-6  illustrate top-down views of the solar cells illustrated in  FIGS. 2-3  along line X and Y. 
         FIG. 7  illustrates another exemplary solar cell design. 
         FIG. 8  illustrates another exemplary solar cell design. 
         FIG. 9  illustrates another exemplary solar cell design. 
         FIGS. 10-17  illustrate an exemplary method of forming the solar cell illustrated in  FIG. 2 . 
         FIG. 18  illustrates a simplified side view of a lithographic system in accordance with an embodiment of the present invention. 
         FIGS. 19-29  illustrate an exemplary method of forming the solar cell design in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Thin-film silicon solar cells  60 , as illustrated in  FIG. 1 , generally require far lower amounts of silicon material than “wafer based” crystalline solar cells known within the art. Currently, thin-film silicon solar cells  60  are formed using plasma-enhanced chemical vapor deposition (PECVD) and based on a p-i-n structure  62 . The p-i-n structure  62  includes a p-type material layer  64  and an n-type material layer  66  having an intrinsic silicon film  68  positioned therebetween. P-type material layer  64  may have a thickness t 1 , n-type material layer  66  may have a thickness t 2 , and intrinsic silicon film  68  may have a thickness t 3 . The excitons (electron/hole pairs) created in the intrinsic layer by incident photons may possess a drift length and a diffusion length L (i.e., the average length an electron or hole travels before recombining (e.g. approximately 100-300 nm)). 
     The p-i-n structure  62  may be positioned between electrodes  70   a  and  70   b.  Electrodes  70   a  and  70   b,  for example, may be transparent (e.g., ZnO). Additionally, a substrate layer  72  (e.g., glass) and a back reflector  74  may be positioned adjacent to electrodes  70   a  and  70   b  respectively. 
     Within the p-i-n structure  62 , a built-in-field  75  may be created in the intrinsic silicon film  68 . Field  75  may aid in guiding charges to the appropriate electrode  70  depending on design considerations. 
     Depending on deposition conditions, intrinsic film  68  may be amorphous (a-Si:H) or microcrystalline (μc-Si:H). See A. V. Shah et al., “Thin-film Silicon Solar Cell Technology,” Prog. Photovolt: Res. Appl. 2004; 12:113-142, which is hereby incorporated by reference in its entirety. While thin-film silicon solar cells, such as the one depicted in  FIG. 1 , may be cost effective, have relatively low efficiency, and/or low deposition rates. As such, formation may include long lag times in order to deposit even 1 μm films. 
     Further, thin-film silicon solar cells, similar to solar cell  60 , may only achieve efficiency values of approximately 10%. For production modules, this efficiency may be even further reduced based on numerous practical reduction factors. Therefore, the current practical efficiency values may be only approximately 6-8%. 
       FIGS. 2-9  provide multiple embodiments of solar cells  60   a - 60   e  in accordance with the present invention. Solar cells  60   a - 60   e  may include a nano-patterned p-n or p-i-n junction. The purpose of the patterning is to reduce electron and hole (created by incident photos) maximum travel distance d 1  that is less than the magnitude of the diffusion length L and/or drift length, and meanwhile to maintain adequate active material to absorb photos. Generally, solar cells  60   a - 60   e  include one or more protrusions  76 . Protrusions  76  may be formed using one or more nano-imprint lithography steps. By incorporating nano-imprint lithography steps in formation of solar cells  60   a - 60   e,  efficiency may be significantly increased as compared to the prior art without a major negative impact on cost. 
     Solar cells  60   a - 60   e  may include materials known in the art capable of forming thin-film silicon solar cells. Alternatively, one or more of solar cells  60   a - 60   e  designs may be formed of other solar thin-film materials. For example, design of solar cells  60   c - 60   d  may be used to provide CdTe solar cells and/or design of solar cells  60   a - 60   e  may be used to provide CuInGaSe solar cells. Design of solar cells  60   a - 60   e  may also increase efficiency of solar cells formed of other materials, such as Cu 2 O, CuInS, FeS 2 , and the like, generally known to posses relatively low efficiency. 
       FIG. 2  illustrates one embodiment of thin-film solar cell  60   a  having p-type material layer  64   a  with protrusions  76   a  and recessions  78   a.  P-type material layer  64   a  may include a base layer  80  with a thickness t 4  (e.g., approximately 100 nm or larger). Protrusions  76   a  may be adjacent to base layer  80   a  and have a height h (e.g., greater than approximately 100 nm). N-type material layer  66   a  may fill recessions  78   a  of p-type material layer  64   a  and include base layer  82   a  with a thickness t 3  (e.g., approximately 100 nm or larger). In one embodiment, protrusions  76   a  may be formed by etching. For example, protrusions  76   a  may be formed by etching Silicon using common Silicon etchants including, but not limited to, CF 4 , CHF 3 , SF 6 , Cl 2 , HBr, other Fluorine, Chlorine and Bromine based etchants, and/or the like. Additionally, protrusions  76   a  may be etched using an imprint resist as a mask, a hardmask for pattern transfer, or the like. For example, protrusions  76   a  may be etched using a hardmask formed of materials including, but not limited to, Cr, Silicon Oxide, Silicon Nitride, and/or the like. Note that this structure may be inverted, i.e. layer  64   a  is n-type and layer  66   a  is p-type. The working principle is similar. 
       FIG. 3  illustrates another embodiment of solar cell  60   b  similar to solar cell  60   a  with protrusions  76   b  of p-type material layer  64   b  including a variable width w 2 . For example, width w 2  of protrusion  76   b  may have a magnitude that varies to provide a non-vertical wall angle Θ. Non-vertical wall angle Θ may assist in deposition of n-type material  66   b  and/or intrinsic material (not shown) by providing a sloped edge as compared to a vertical edge. 
     Shape of protrusions  76   a  and/or  76   b  in solar cells  60   a  and  60   b  respectively may include different shapes and/or different spacing between protrusions  76   a  and/or  76   b.    FIGS. 4-6  illustrate top-down views of solar cells  60   a  and  60   b  having exemplary shapes and sizes for protrusions  76   a  and/or  76   b  along lines X and Y respectively. Protrusions  76   a  and/or  76   b  may be circle, square, rectangular, triangular, polygonal, or any other fanciful shape. Additionally, spacing between protrusions  76   a  and/or  76   b  may be increased or decreased, uniform or sporadic, based on design considerations. Exemplary formation of nanoshapes is further described in U.S. Ser. No. 12/616,896, which is hereby incorporated by reference in its entirety. 
       FIG. 7  illustrates another exemplary solar cell  60   c.  Solar cell  60   c  includes a p-i-n structure  62   c.  Intrinsic layer  68   c  may be formed between p-type material layer  64   c  and n-type material layer  66   c.  Intrinsic layer  68   c  may form a conformal or directional layer over protrusions  76   c  and/or recessions  78   c  of p-type material layer  64   c.  As such, intrinsic layer  68   c  may conform and thus include one or more protrusions  90   c  and recessions  92   c.    
     Formation of solar cell  60   c  may include multiple nanopatterning step to form protrusions  76   c  and recessions  78   c  of p-type material layer  64   c  and/or protrusions  90   c  and  92   c  of intrinsic layer  68   c.  For example, formation of p-type material layer  64   c  may be through the use of a first nanopatterning step to form protrusions  76   c  and  78   c.  Material of intrinsic layer  68   c  may be deposited (e.g., directional deposition, conformal deposition or partial conformal deposition) on p-type material layer  64   c  to form protrusions  90   c  and recessions  92   c.  N-type layer  66   c  may be deposited on top of  68   c.  Note layer  66   c  may not fill all the recessions completely (some voids left due to deposition techniques). 
     It should be noted that protrusions  76   c  of p-type material layer  64   c  and protrusions  90   c  of intrinsic layer  68   c  may include a variable width w to provide a non-vertical wall angle Θ as described herein and illustrated in  FIG. 3 . 
       FIG. 8  illustrates another exemplary solar cell  60   d.  Solar cell  60   d  includes a p-i-n structure  62   d.  Additionally, solar cell  60   d  includes an electrode layer  70   c  having one or more protrusions  94   a  and recessions  96   a.  In one embodiment, protrusions  94   a  and recessions  96   a  may be formed by etching. For example, protrusions  94   a  may be formed by metal etchants including, but not limited to, Cl 2 , BCl 3 , other Chlorine based etchants, and/or the like. It should be noted that the metal etchants are not limited to chlorine-based etchants. For example, some metals, such as Tungsten, may be etched using Fluorine based etchants. Protrusions  94   a  may be formed by etching using an imprinting resist as a mask or by using a hardmask for pattern transfer. For example, protrusions  95   a  may be formed by using a hardmask formed of materials including, but not limited to, Cr, Silicon Oxide, Silicon Nitride, and/or the like. 
     P-type material layer  64   d  may be deposited on protrusions  94   a  and recessions  96   a  or electrode layer  70   c  form protrusions  76   d  and recessions  78   d.  Intrinsic layer  68   d  may be deposited on p-type material layer  64   d  form protrusions  90   d  and  92   d.  N-type material layer  66   d  may then be deposited on intrinsic layer  68   d  forming p-i-n structure  62   d.  Note layer  66   d  may not fill all the recessions completely (some voids left due to deposition techniques). 
       FIG. 9  illustrates another exemplary solar cell  60   e.  Solar cell  60   e  includes electrode layer  70   d  having one or more protrusions  94   b  and recessions  96   b.  Similar to electrode layer  70   c  of  FIG. 8 , electrode layer  70   d  may include protrusions  94   b.  In one embodiment, protrusions may be formed by etching. For example, protrusions  94   b  may be formed by metal etchants including, but not limited to, Cl 2 , BCl 3 , other Chlorine based etchants, and/or the like. It should be noted that the metal etchants are not limited to chlorine-based etchants. For example, some metals, such as Tungsten, may be etched using Fluorine based etchants. Protrusions  94   b  may be formed by etching using an imprinting resist as a mask or by using a hardmask for pattern transfer. For example, protrusions  94   b  may be formed by using a hardmask formed of materials including, but not limited to, Cr, Silicon Oxide, Silicon Nitride, and/or the like. 
     P-type material layer  64   e  may be deposited (e.g., directional deposition or conformal deposition or partical conformal deposition) on electrode layer  70   d  and/or formed by using a nano-lithography step to form protrusions  76   e  and recession  78   e.  N-type material layer  66   e  may be deposited (e.g., directional deposition or conformal deposition or partical conformal deposition) on p-type material layer  64   e.  Note that this structure may be inverted, i.e. layer  64   e  is n-type and layer  66   e  is p-type. The working principle is similar. 
       FIGS. 10-17  illustrate an exemplary method for forming solar cells (similar to  60   a  illustrated in  FIG. 2 , but with an inverted structure) using a lithography system  10  illustrated in  FIG. 18 . It should be noted that steps described herein may be modified to provide solar cells  60   b - 60   e  as described above (e.g., incorporating one or more nanolithography steps of one or more layers). For example, in one embodiment, steps described herein may be modified to provide p-i-n structure  62   c  of  FIG. 7  that includes intrinsic layer  68   c.  In another embodiment, steps described herein may be modified to provide protrusions  94   b  of electrode layer  70   d.    
     Referring to  FIGS. 10 and 11 , a metal contact/reflector layer  98  may optionally be deposited on substrate layer  72 . Metal contact layer/reflector layer  98  may be formed of materials including, but not limited to, aluminum, tungsten, zinc, and/or the like. Electrode layer  70   a  (e.g., ZnO, Al, and the like) may be deposited (e.g., sputter) on reflector layer  98  as illustrated in  FIG. 12 . It should be noted that electrode layer  70   a  may be patterned to provide one or more features (e.g., protrusions). For example, electrode layer  70   a  may be patterned to provide protrusions as illustrated in  FIGS. 8 and 9 . 
     P-type material layer  64   a  may be deposited on electrode layer  70   a.  P-type material layer  64   a  may be formed to provide protrusions  76   a  and recessions  78   a.  It should be noted that either p-type material layer  64   a  or n-type material layer  66   a  may be formed to provide protrusions and recessions; however, for simplicity of description only the p-type material layer  64   a  is described herein. P-type material may include, but is not limited to, amorphous silicon, copper indium gallium selenide, microcrystalline silicone, nanocrystalline silicon, and the like. 
     Formation of protrusions  76   a  and recessions  78   a  in p-type material layer  64   a  may be through imprint lithography, optical lithography, x-ray lithography, extreme ultraviolet lithography, scanning probe lithography, atomic force microscopic nanolithography, magnetolithography, and/or the like. For example, protrusions  76   a  and recessions  78   a  of p-type material layer  64   a  may be formed using a lithographic system  10  illustrated in  FIG. 18 . 
     Referring to  FIG. 18 , substrate layer  72  may be coupled to substrate chuck  14 . As illustrated, substrate chuck  14  is a vacuum chuck. Substrate chuck  14 , however, may be any chuck including, but not limited to, vacuum, pin-type, groove-type, electrostatic, electromagnetic, and/or the like. Exemplary chucks are described in U.S. Pat. No. 6,873,087, which is hereby incorporated by reference. 
     Substrate layer  72  and substrate chuck  14  may be further supported by stage  16 . Stage  16  may provide motion along the x-, y-, and z-axes. Stage  16 , substrate layer  72 , and substrate chuck  14  may also be positioned on a base (not shown). 
     Spaced-apart from substrate layer  72  is a template  18 . Template  18  may include a mesa  20  extending therefrom towards substrate layer  72 , mesa  20  having a patterning surface  22  thereon. Further, mesa  20  may be referred to as mold  20 . Alternatively, template  18  may be formed without mesa  20 . 
     Template  18  and/or mold  20  may be formed from such materials including, but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, hardened sapphire, and/or the like. As illustrated, patterning surface  22  comprises features defined by a plurality of spaced-apart recesses  24  and/or protrusions  26 , though embodiments of the present invention are not limited to such configurations. Patterning surface  22  may define any original pattern that forms the basis of a pattern to be formed in p-type material layer  64   a.    
     Template  18  may be coupled to chuck  28 . Chuck  28  may be configured as, but not limited to, vacuum, pin-type, groove-type, electrostatic, electromagnetic, and/or other similar chuck types. Exemplary chucks are further described in U.S. Pat. No. 6,873,087, which is hereby incorporated by reference. Further, chuck  28  may be coupled to imprint head  30  such that chuck  28  and/or imprint head  30  may be configured to facilitate movement of template  18 . 
     System  10  may further comprise a fluid dispense system  32 . Fluid dispense system  32  may be used to deposit p-type material on electrode layer  70   a.  P-type material may be in fluid form. For example, p-type material may be a liquid positioned upon electrode layer  70   a  using techniques such as drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and/or the like. P-type material may be disposed upon electrode layer  70   a  before and/or after a desired volume is defined between mold  20  and electrode layer  70   a  depending on design considerations. Alternatively, p-type material may be a solid positioned adjacent to electrode layer  70   a  and etched. 
     System  10  may further comprise an energy source  38  coupled to direct energy  40  along path  42 . Imprint head  30  and stage  16  may be configured to position template  18  and substrate layer  72  in superimposition with path  42 . System  10  may be regulated by a processor  54  in communication with stage  16 , imprint head  30 , fluid dispense system  32 , and/or source  38 , and may operate on a computer readable program stored in memory  56 . 
     Referring to  FIGS. 14 and 18 , either imprint head  30 , stage  16 , or both may vary a distance between mold  20  and electrode layer  70   a  to define a desired volume therebetween that is filled by p-type material. For example, imprint head  30  may apply a force to template  18  such that mold  20  contacts p-type material. After the desired volume is filled with p-type material, source  38  produces energy  40 , e.g., ultraviolet radiation, causing p-type material to solidify and/or cross-link conforming to shape of a surface  44  of electrode layer  70   a  and patterning surface  22 , defining a patterned layer  100  on electrode layer  70   a.  Patterned layer  100  may comprise base layer  80   a  and a plurality protrusions  76   a  and recessions  78   a,  with protrusions  76   a  having height h and base layer  80   a  having a thickness t 4 . It should be noted that solidification and/or cross-linking of p-type material may be through other methods including, but not limited, exposure to charged particles, temperature changes, evaporation, and/or other similar methods. 
     The above-mentioned system and process may be further employed using imprint lithography processes and systems referred to in U.S. Pat. No. 6,932,934, U.S. Patent Publication No. 2004/0124566, U.S. Patent Publication No. 2004/0188381, and U.S. Patent Publication No. 2004/0211754, each of which is hereby incorporated by reference in their entirety. 
     Referring to  FIG. 15 , n-type material layer  66   a  may be deposited on p-type material layer  64   a  filling recessions  78   a  of p-type material layer  64   a.  Electrode layer  70   b  (e.g., transparent conductor (ZnO, ITO, SnO2, etc.) may then be deposited on n-type material layer  66   a  as illustrated in  FIG. 16 . It should be noted that a conductive grid  99  may be deposited on electrode layer  70   b  as illustrated in  FIG. 17 . Conductive grid  99  may provide additional conductivity in addition to electrode layer  70   b.  For example, materiality of electrode layer  70   b  may be selected such that electrode layer  70   b  is substantially translucent; however, conductivity of electrode layer  70   b  may be compromised. Conductive grid  99  may provide the additional conductivity needed for solar cell  60   a.    
       FIGS. 19-29  illustrate another exemplary method for forming solar cells  60   f  using a lithography system  10  illustrated in  FIG. 18 . It should be noted that steps described herein may be modified to provide solar cells  60   b - 60   e  as described above (e.g., incorporating one or more nanolithography steps of one or more layers). 
     Referring to  FIGS. 19 and 20 , a metal contact/reflector layer  98  may optionally be deposited on substrate layer  72 . Metal contact layer/reflector layer  98  may be formed of materials including, but not limited to, aluminum, silver, tungsten, zinc, and/or the like. 
     Referring to  FIGS. 21-24 , an electrode layer  70   f  deposited on reflector layer  98  may be patterned to provide one or more features such as protrusions  112  and recessions  114 . 
     Electrode layer  70   f  (e.g., ZnO, Al, and the like) may be deposited using techniques including, but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), sputter deposition, spin-coating, dispensing of liquid, and the like. To form features  112  and  114  in electrode layer  70   f,  a material layer  110  may be deposited and/or patterned on electrode layer  70   f  such that gaps  116  expose portions of electrode layer  70   f  to etching chemistry. 
     Material layer  110  may be an organic monomer. For example, material layer  110  may include a monomer mixture as described in U.S. Pat. No. 7,157,036 and U.S. Patent Publication No. 2005/0187339, both of which are herein incorporated by reference. 
     In one example, material layer  110  may be formed having gaps  116  using imprint lithography processes and systems referred to in U.S. Pat. No. 6,932,934, U.S. Patent Publication No. 2004/0124566, U.S. Patent Publication No. 2004/0188381, and U.S. Patent Publication No. 2004/0211754, each of which is hereby incorporated by reference in their entirety. In another example, material layer  110  may be formed having gaps  116  using optical lithography, x-ray lithography, electron-beam lithography, and the like. Alternatively, polymerized material layer  110  may be deposited on electrode layer  70   f  such that gaps  116  are formed using techniques including, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), sputter deposition, spin-coating, dispensing of liquid, and the like. 
     In one embodiment, gaps  116  in material layer  110  may be formed by a break through etch. For example, gaps  116  in material layer  110  may be formed using an oxygen-based reactive ion etching (RIE) process. Alternatively, gaps  116  in material layer  110  may be formed using VUV etching and/or UV ozone etching as described in U.S. Ser. No. 12/563,356 and U.S. Provisional No. 61/299,097, which are hereby incorporated by reference in their entirety. 
     Gaps  116  of material layer  110  may be sized and configured to provide expose portions of electrode layer  70   f  to etching chemistry to form protrusions  112  and recessions  114  as described herein. For example, gaps  116  of material layer  110  may be approximately 10-100 nm to expose electrode layer  70   f  to etching chemistry forming recessions  114  having a length L 1  of approximately 500 nm and protrusions  112  having a length L 2  of approximately 20 nm. 
     It should be noted that an adhesion layer (e.g., BT20) may be provided on material layer  110  and/or between material layer  110  and electrode layer  70   f.    
     In one embodiment, electrode layer  70   f  may be formed of Al. To form protrusions  112  and recessions  114 , etching chemistry may use a phosphoric acid, acetic acid, and/or other weak acids. Generally, weak acid may be used as strong oxidation acids (e.g., nitric acid) may oxidize material layer  110  causing delamination. Weak acids may be used alone or in combination with additives. For example, additives that etch electrode layer  70   f  (e.g., Al) without attacking organics. Alternatively, hydrogen fluoride (HF) containing a buffer oxide etch (BOE) solution may be used to etch electrode layer  70   f  forming protrusions  112  and recessions  114 . This may minimally affect material layer  110  and/or adhesion layer. 
     Referring to  FIG. 25 , P-type material layer  64   f  may be deposited on electrode layer  70   f  filling a portion of recessions  114  of electrode layer  70   f.  P-type material may be provided in fluid form for the formation of p-type material layer  64   f.  For example, p-type material layer  64   f  may be provided on electrode layer  70   f  using techniques such as drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and/or the like. Alternatively, P-type material layer  64   f  may be provided in solidified form and adhered to electrode layer  70   f.    
     Referring to  FIG. 26 , intrinsic film  68   f  may be deposited on P-type material layer  64   f.  Intrinsic film  68   f  may be amorphous (a-Si:H) or microcrystalline (μc-Si:H). See A. V. Shah et al., “Thin-film Silicon Solar Cell Technology,” Prog. Photovolt: Res. Appl. 2004; 12:113-142, which is hereby incorporated by reference in its entirety. Deposition of intrinsic film  68   f  on P-type material layer  64   f  may depend on materiality of intrinsic film  68   f.  Intrinsic film  68   f  may be deposited on P-type material layer  64   f  using techniques such as drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and/or the like. 
     N-type material layer  66   f  may be deposited on intrinsic film  68   f  as illustrated in  FIG. 27 . Deposition of N-type material layer  66   f  on intrinsic film  68   f  may depend on materiality of N-type material layer  66   f.  For example, N-type material layer  66   f  may be deposited using techniques such as drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and/or the like. Electrode layer  70   g  (e.g., substantially translucent layer) may then be deposited on N-type material layer  66   f  as illustrated in  FIG. 28 . 
     Referring to  FIG. 29 , it should be noted that a conductive grid  99  may be deposited on electrode layer  70   g.  Conductive grid  99  may provide additional conductivity in addition to electrode layer  70   g.  For example, materiality of electrode layer  70   g  may be selected such that electrode layer  70   g  is substantially translucent; however, conductivity of electrode layer  70   g  may be compromised. Conductive grid  99  may provide the additional conductivity needed for solar cell  60   f.  Note that this structure may be inverted, i.e. layer  64   f  is n-type and layer  66   f  is p-type. The working principle is similar.