TW201533921A - Silicon solar cells with epitaxial emitters - Google Patents

Abstract

Embodiments of the disclosure generally relate to forming solar cells having epitaxial emitters. The emitters of the solar cells, as well as the bases of the solar cells, are epitaxially grown in a process chamber using a template substrate to form an epitaxial substrate. During the formation process of the epitaxial substrate, dopants can be introduced into the process chamber to dope the emitters and the bases with desired dopant profiles and concentrations. In one example, the epitaxial material is silicon and the dopants are n-type and p-type dopants.

Description

Solar cell with epitaxial emitter

Embodiments of the invention are large systems relating to solar cells and methods of formation.

The use of solar cells to convert solar energy into a stream of electrons produces electricity. Photoelectric effect means that a photon of light excites electrons to a higher energy state, making it a charged carrier of current. Solar cells generate direct current from sunlight to provide power supply or to charge the battery. However, solar cell efficiency is currently insufficient, for example, solar cells convert insufficient solar energy into electrical energy.

Therefore, there is a need for a more efficient solar cell and method of formation.

Embodiments of the invention are directed to forming solar cells with epitaxial emitters. In the processing chamber, the emitter of the solar cell and the base of the solar cell are epitaxially grown using a template substrate to form an epitaxial substrate. During the epitaxial substrate formation process, dopants may be introduced into the processing chamber to dope the emitter and base with the desired dopant distribution and concentration. In one example, the epitaxial material is tantalum, and the dopant is n-type and p-type dopants.

In one embodiment, a method of forming a solar cell includes epitaxial formation The first emitter comprising a p-type or n-type dopant, the epitaxial growth base to the first emitter, and the epitaxial growth include a second emitter of a p-type or n-type dopant. The second emitter is textured, and the first passivation layer is applied to the first emitter. A second passivation layer is applied to the second emitter, the first metal contact being applied to the first emitter and the second metal contact being applied to the second emitter.

In another embodiment, the solar cell comprises a single crystal germanium base, a first single crystal germanium emitter disposed on a first side of the single crystal germanium base, and the first single crystal germanium emitter has a thickness of about 5 micrometers. A second single crystal germanium emitter of about 15 microns and placed on the second side of the single crystal germanium base. The second single crystal germanium emitter has a thickness of from about 5 microns to about 15 microns. The solar cell further includes a first passivation layer disposed over the first single crystal germanium emitter, a first metal layer disposed over the first passivation layer, and a second metal layer disposed over the second passivation layer.

100‧‧‧ chamber

102‧‧‧ cavity wall

104‧‧‧Cover

106‧‧‧ bottom

108‧‧‧Processing area

110‧‧‧匣 box

112‧‧‧Base

114‧‧‧Substrate

114a‧‧‧ epitaxial substrate

120‧‧‧Top cover

122‧‧‧Loading area

124‧‧‧ openings

125‧‧‧Lamps

127‧‧‧ reflector

128‧‧‧cooling channel

129‧‧‧ entrance

130‧‧‧Export

131‧‧‧Constant temperature zone

132‧‧‧ heating element

133‧‧‧Insulator

134‧‧‧ gas inlet

135‧‧‧ shaft

136‧‧‧Rotor

137‧‧‧ Stator

212‧‧‧ electrodes

214A‧‧‧ epitaxial layer

214‧‧‧Substrate

240‧‧‧Porous layer

241, 243‧‧ ‧ emitter

241a, 241b‧‧‧ doped area

242‧‧‧ base

244, 249‧‧‧ surface

245‧‧‧Contact area

246, 248‧‧‧ Passivation layer

247‧‧‧Contacts

256‧‧‧ operation

270‧‧‧ openings

271‧‧‧metal layer

272‧‧‧ solar cells

350‧‧‧ Flowchart

351-353, 355-364‧‧‧ operations

414a‧‧‧ epitaxial substrate

444, 449‧‧‧ surface

446, 448‧‧‧ Passivation layer

447‧‧‧Contacts

470‧‧‧through hole

471‧‧‧metal layer

472‧‧‧ solar cells

490‧‧ ‧ emitter surface

491‧‧‧ mask

581-589‧‧‧ operation

614A‧‧‧ epitaxial substrate

646‧‧‧passivation layer

649‧‧‧ Non-light receiving surface

691‧‧‧ mask

692‧‧‧ Polycrystalline layer

765‧‧‧flow chart

766-771‧‧‧ operation

814A, 914A‧‧‧ epitaxial substrate

949‧‧‧ Non-light receiving surface

975‧‧‧flow chart

976-979‧‧‧ operation

993‧‧‧ Essential amorphous layer

994‧‧‧Doped amorphous layer

995‧‧‧conductive oxide layer

1101‧‧‧Flowchart

1102-1108‧‧‧Operation

1214A‧‧‧ epitaxial substrate

1396‧‧‧Oxide layer

1420‧‧‧flow chart

1421-1427‧‧‧ operation

1449, 1549‧‧‧ Non-light receiving surface

1571‧‧‧metal layer

1572‧‧‧Solar battery

1590‧‧‧Back field

1671‧‧‧Interlaced back contact structure

1671a, 1671b‧‧ ‧ contacts

1672‧‧‧Solar battery

In order to make the above summary of the present invention more obvious and understood, the description may be made in conjunction with the reference embodiments. It is to be understood that the appended claims are not intended to

Figure 1 is a perspective view of a chamber according to an embodiment.

2A through 2L illustrate a solar cell forming process in accordance with an embodiment.

3A-3B illustrate a flow chart of a method of forming a solar cell, in accordance with an embodiment.

4A to 4G illustrate a solar cell forming process according to another embodiment.

Figure 5 illustrates a flow chart of a method of forming a solar cell, in accordance with another embodiment.

6A to 6F illustrate a solar cell forming process according to still another embodiment.

Figure 7 illustrates a flow chart of a method of forming a solar cell, in accordance with yet another embodiment.

8A to 8D illustrate a solar cell forming process according to still another embodiment.

Figure 9 illustrates a flow chart of a method of forming a solar cell, according to yet another embodiment.

10A through 10G illustrate solar cell formation processes in accordance with another embodiment.

Figure 11 illustrates a flow chart of a method of forming a solar cell, in accordance with another embodiment.

Figure 12 illustrates a partial solar cell in accordance with another embodiment of the present invention.

13A to 13G illustrate a solar cell forming process according to still another embodiment.

Figure 14 illustrates a flow chart of a method of forming a solar cell, according to yet another embodiment.

Fig. 15 illustrates a solar cell according to another embodiment.

Figure 16 illustrates a solar cell according to still another embodiment.

To facilitate understanding, the same component symbols are used to represent common similar components in the various figures. It should be understood that the elements and features of an embodiment may be Other embodiments are beneficially incorporated and are not described in detail herein.

Embodiments of the invention are directed to forming solar cells with epitaxial emitters. In the processing chamber, the emitter of the solar cell and the base of the solar cell are epitaxially grown using a template substrate to form an epitaxial substrate. During the epitaxial substrate formation process, dopants may be introduced into the processing chamber to dope the emitter and base with the desired dopant distribution and concentration. In one example, the epitaxial material is tantalum, and the dopant is n-type and p-type dopants. The solar cells formed according to the described embodiments have higher conversion efficiencies than solar cells with solid state diffused emitters, at least in part because of the formation of emitters during epitaxial growth. Since the emitter is formed during the epitaxial growth process, the emitter can have a greater thickness and a lower dopant concentration.

1 is a cross-sectional perspective view of a chamber 100 in accordance with an embodiment. The chamber 100 has a chamber wall 102, a cover 104 and a bottom 106. The cavity wall 102 can be cylindrical and can be formed from transparent quartz. The chamber wall 102, the lid 104, and the bottom 106 can define a treatment zone 108 within which the cassette 110 is placed. The cassette 110 can include a plurality of pedestals 112 in a stacked configuration, each pedestal 112 can support one or more substrates 114 on the upper surface of the pedestal. The pedestal 112 can be configured to support the substrate 114 for deposition on one side or on both sides. During the deposition process, the cassette 110 is continuously rotated to improve deposition uniformity.

Above the lid 104 is a top cover 120, which is defined by a top cover 120. Openings 124 may be formed in the top cover 120 to assist in the entry and exit of the substrate 114 into and out of the loading area 122. During loading/unloading of the substrate 114, the cassette 110 is vertically actuated into the loading area 122 and the substrate 114 is loaded/unloaded via the opening 124.

A heating element (eg, luminaire 125) is disposed adjacent to the cavity wall 102 to The processing zone 108 is thermally energized. The heating element can be any suitable heating element. In an embodiment, the heating element includes a plurality of infrared (IR) lamps surrounding the cassette 110. In an embodiment, the light fixture 125 surrounds the cavity wall 102. The arrangement of the walls 102 can be determined by the process. In one example, the luminaire 125 is circular. The luminaires 125 can be stacked to provide axial multi-zone heating. In another embodiment, each of the luminaires 125 is a linear luminaire, and the luminaire 125 is provided with a support surface for the vertical pedestal 112. In this embodiment, a plurality of linear luminaires 125 are arranged to surround the periphery of the cavity wall 102. Additionally or alternatively, the heating element can include one or more inductive heaters. The inductive heater can be a ferrite core that coils the cassette 110, such as around the chamber wall 102. One or more metal wires may be wound around the ferrite core, and each metal wire may be connected to a power source to form an electrical circuit.

A selective reflector 127 surrounds the luminaire 125 to more effectively control the heat treatment zone 108. The reflector 127 includes a plurality of curved rings, each of which circumscribes the periphery of each of the lamps 125. Thus, the heat generated by the luminaire 125 can be directed to the processing zone 108. The reflector 127 can have a cooling passage 128 disposed therein. Each cooling passage 128 has an inlet 129 and an outlet 130 (one shown), and the reflector 127 can be cooled with a coolant, such as water flowing out of the outlet 130 from the inlet 129 via the cooling passage 128. A chamber liner (not shown) is disposed between the cassette 110 and the chamber wall 102. The shape of the chamber liner can be similar to chamber wall 102, such as cylindrical, to provide thermal uniformity and to form a constant temperature zone 131 within processing zone 108. The chamber liner can be made of tantalum carbide coated graphite.

In addition to the luminaire 125, the heating element 132 can also be disposed above and/or below the cassette 110 to provide radial multi-zone heating. Heating element 132 can be any suitable heating element. In an embodiment, the heating element 132 is resistive The heating element, the resistive heating element is made of solid tantalum carbide or tantalum carbide coated graphite. A heat insulator 133 is disposed between the heating element 132 and the cover 104/bottom 106.

A plurality of gas inlets 134 are provided through the luminaires 125 on the chamber wall 102. In an embodiment, the gas inlet 134 is substantially perpendicular to the cavity wall 102. As shown in Figure 1, the gas inlet 134 and the luminaire 125 are in a staggered configuration. In other words, each gas inlet 134 is disposed between two adjacent lamps 125. A plurality of purge gas lines (not shown) may be provided between the chamber liner and the chamber wall 102. The purge gas line is substantially parallel to the chamber wall 102. During operation of chamber 100, one or more process gases may be introduced into chamber 100 to deposit material onto substrate 114, such as an epitaxial layer. During deposition, the substrate 114 can be heated to the desired temperature. One or more substrates 114 can be processed simultaneously.

The edge of the cassette 110 can be coupled to a plurality of shafts 135 that are coupled to the rotor 136. The rotor 136 can be coupled to the stator 137. In one embodiment, rotor 136 and stator 137 are both permanent magnets and rotor 136 is magnetically coupled to stator 137. The cassette 110 is continuously floated and rotated during operation. In another embodiment, the rotor 136 and the stator 137 are parts of a linear arc motor that is continuously rotated by the linear arc motor during operation.

2A through 2L illustrate a solar cell forming process in accordance with an embodiment. 3A through 3B illustrate a flow chart 350 of a method of forming a solar cell, in accordance with an embodiment. In order to facilitate the description of the embodiments of the present invention, FIGS. 2A to 2L and FIGS. 3A to 3B will be described.

Figure 2A illustrates a substrate 114 that is placed on a support, such as electrode 212 in an electrolytic cell (not shown). In an example, the substrate can be a single A germanium substrate composed of wafers, and the substrate is used as a template for epitaxial growth. Although only a single substrate 114 is shown placed on electrode 212 for clarity, it should be understood that multiple substrates 114 can be placed on electrode 212.

In operation 351, as shown in FIG. 2B, the substrate 114 is brought into contact with an etching solution including hydrogen fluoride, isopropyl alcohol, and deionized water to form a porous layer 240 on the substrate 114. Surface tension can be adjusted by replacing isopropyl alcohol or by using ethanol, acetic acid or other chemical agents. Current is passed through the electrolyte and the substrate to anodically etch the surface. The same electrolyte can be used for back contact instead of electrode 212. In one example, porous layer 240 is a "double porous" layer, such as a layer containing one or more porosity. For example, the porous layer 240 can have an upper portion having a low porosity and a thickness of from about 0.01 micrometers to about 2 micrometers and a lower portion having a relatively high porosity and a thickness of from about 0.1 micrometers to about 1 micrometer. In some processes, as shown in FIG. 2G, the lower layer can serve as a release layer to assist in the release of the epitaxial layer 214A that is epitaxially grown on the substrate 114.

In operation 352, as shown in FIG. 2C, the substrate 114 having the porous layer 240 is heat treated (eg, annealed or crystallized) to form a smooth tantalum surface on the porous layer 240. The heat treatment process can be carried out in a hydrogen environment and can be performed using a variety of heating methods, including laser or luminaire illumination. The smoothness of the porous layer 240 helps to form a high quality epitaxial material thereon.

In operation 353, for example, in the chamber 100, a first epitaxial emitter 241 is epitaxially formed (eg, grown) on the upper surface of the substrate 114. The first epitaxial emitter can be formed by a vapor phase epitaxy process by reacting a ruthenium-containing precursor with a reducing agent (for example, trichloromethane and hydrogen) in the presence of a dopant (for example, an n-type dopant or a p-type dopant). 241. Other ruthenium containing precursors such as dichloromethane, ruthenium tetrachloride, decane or dioxane may also be used. Suitable n-type dopant gases include phosphine (PH ₃ ), phosphorus oxychloride (POCl ₃ ) or other phosphorus, arsenic or antimony compounds. Suitable p-type dopants include borane or diborane, or other boron, aluminum or gallium containing compounds. The first epitaxial emitter 241 may have a dopant concentration of from about 1 x 10 ¹⁷ to about 1 x 10 ¹⁸ atoms per cubic centimeter (cm ³ ) and may have a thickness of from about 1 micron to about 15 microns, such as about 5 microns. About 10 microns. The epitaxial formation process can be carried out at a temperature of about 1200 ° C or less and a pressure of about 1 atm or less.

In operation 355, as shown in FIG. 2E, after the first epitaxial emitter 241 is formed, the base 242 is epitaxially formed on the first epitaxial emitter 241. Base 242 is typically formed using the same ruthenium containing precursor as the first epitaxial emitter 241 and a reducing agent, such as trichlorodecane and hydrogen. Base 242 may have a thickness of from about 1 micron to about 200 microns. In one example, the formation of the first epitaxial emitter 241 and the base 242 is a continuous process. In this process, after the first epitaxial emitter 241 is formed, different dopants that flow into the dopant gas, reduce the concentration, or change to a reduced concentration may be suspended while maintaining the inflow of the ruthenium-containing precursor and the reducing agent. The dopant concentration of the base can also be graded (eg, continuously varying with thickness) to provide an internal electric field to aid in collecting light to generate carriers. Although FIG. 2E depicts the first epitaxial emitter 241 and the base 242 as two different layers, the first epitaxial emitter 241 and the base 242 may be continuous epitaxial materials, and the first epitaxial layer The emitter 241 and the base 242 each have a different dopant concentration and/or distribution.

In operation 356, a second epitaxial emitter 243 is formed on the base 242 as shown in FIG. 2F. The second epitaxial emitter 243 is formed similar to the first epitaxial emitter 241; however, the second epitaxial emitter 243 comprises a dopant of the opposite conductivity type. For example, if the first epitaxial emitter 241 is doped with a p-type dopant, the second epitaxial emitter 243 can be doped with an n-type dopant, and vice versa. The second epitaxial emitter 243 can be formed from the base 242 in a continuous manner using the same hafnium-containing precursor and reducing agent as the base 242. The second epitaxial emitter 243 may have a dopant concentration of from about 5 x 10 ¹⁶ to about 1 x 10 ¹⁸ atoms/cm ³ and a thickness of from about 1 micron to about 15 microns. The dopant concentration of the emitter 241 or 243 can be varied in a continuous manner to form an internal electric field to assist in collecting light to generate a carrier.

In operation 357, as shown in FIG. 2G, the first epitaxial emitter 241, the base 242, and the second epitaxial emitter 243 are removed from the bottom template substrate 114, and the first epitaxial emitter 241 and the base 242 are removed. And the second epitaxial emitter 243 is collectively referred to as an epitaxial layer 214A. The epitaxial layer 214A can be cleaved mechanically, energetically or chemically from the substrate 214. If any of the porous layers 240 remain on the epitaxial layer 214A, the porous layer 240 deposited on the epitaxial layer 214A can be removed by etching, polishing, or the like.

In operation 358, the first surface 244 of the epitaxial substrate (the light receiving surface of the final device) is textured, for example by contact with an etchant (eg, potassium hydroxide) to reduce the light reflection quality of the final device. Although FIG. 2H illustrates the second epitaxial emitter 243 as a light receiving surface, the first epitaxial emitter 241 can be on the light receiving surface. In this embodiment, the texturing operation can also be used to remove any residual porous material attached to the epitaxial layer 214A. Therefore, there is no need to remove the operation individually.

In operation 359, a selective emitter process is performed on the first surface 244 of the epitaxial layer 214A as shown in FIG. A selective emitter process can be performed using a masked ion implant or dopant paste. In one example, the dopant paste can be printed on the surface and exposed to a laser or other heat source to drive the dopant into the second epitaxial emitter 243. The dopants referred to by ion implantation can be activated by high temperature annealing, which can be carried out in an oxygen atmosphere. Surface oxidation helps to passivate surface defects. The selective emitter process can form a region on the first surface 244 having a higher dopant concentration than the second epitaxial emitter 243, such as an n++ or p++ contact region 245, to facilitate ohmic contact and subsequent placement on the first surface 244. Metal contacts or electrodes. Contact region 245 can be formed in accordance with a pattern of corresponding metal contacts. In one example, the n++ or p++ concentration can be about 5 x 10 ¹⁹ atoms/cm ³ or more, such as about 1 x 10 ²⁰ atoms/cm ³ or more.

In operation 360, passivation layer 246 is deposited onto first surface 244, such as hafnium oxide, tantalum nitride or aluminum oxide, as shown in FIG. 2J. The passivation layer 246 can reduce recombination at the light receiving surface. The passivation layer can be deposited by chemical vapor deposition, atomic layer deposition, plasma enhanced chemical vapor deposition, and the like using appropriate precursor gases and reducing or oxidizing agents.

In operation 361, as shown in FIG. 2K, a passivation layer 248 is deposited onto the second surface (eg, the back or non-light receiving surface). Passivation layer 248 is similar to passivation layer 246 and can be formed in a similar manner. In an embodiment, the passivation layers 246, 248 may be formed simultaneously or within the same tool.

In operation 362, as shown in FIG. 2L, metal contacts 247 are formed on first surface 244 of epitaxial layer 214A. The metal contacts 247 can be applied by screen printing one or more conductive pastes to the first surface 244 followed by heat treatment to remove the solvent ("dry"). The conductive paste can include one or more metals, such as silver or aluminum within the polymer matrix. In operation 363, one or more openings 270 are formed in the second surface 249 of the epitaxial layer 214A through the passivation layer 248, such as by laser scribing. Opening 270 preferably only scribes passivation layer 248 and exposes the surface of epitaxial emitter 241. It is contemplated that the opening 270 can be formed prior to operation 362 but after operation 361.

In operation 364, a metal layer 271 is formed on the epitaxial layer 214A. The second surface 249 is above. Metal layer 271 is deposited over passivation layer 248 and within opening 270. The metal layer 271 may include one or more conductive materials such as silver or aluminum, and may be formed using screen printing, chemical vapor deposition, atomic layer deposition, physical vapor deposition, or the like. In one example, the metal layer 271 includes aluminum. After depositing the metal layer 271, the heat-treated or fired metal layer 271 and the metal contact 247 reach a temperature higher than the eutectic point of bismuth and aluminum, thereby producing a bismuth aluminum alloy. The bismuth aluminum alloy forms a heavily doped p++ region to promote ohmic contact between the aluminum and the crucible. The metal contact 247 is simultaneously sintered via the front passivation layer 246 to ohmically contact the second epitaxial emitter 243. The structure shown in Fig. 2L shows a solar cell 272 formed in accordance with the embodiment.

2A to 2L and 3A to 3B illustrate an embodiment in which the solar cell 272 is formed; however, additional embodiments may be considered. For example, operations 363, 364 can be performed prior to operation 362.

4A to 4G illustrate a solar cell forming process according to another embodiment. Figure 5 illustrates a flow chart of a method of forming a solar cell, in accordance with another embodiment. For convenience of explanation, the descriptions of Figs. 4A to 4G and Fig. 5 will be made. 4A through 4G and 5 illustrate alternative embodiments for forming a solar cell, and may replace FIGS. 2G through 2I and operations 357-364.

In operation 581, this may be performed after operation 356 of FIG. 3, as shown in FIG. 4A, epitaxially growing the highly doped emitter surface 490 on the second epitaxial emitter 243. The dopant type of the highly doped emitter surface 490 (e.g., p-type or n-type) is the same as the second epitaxial emitter 243, but with a higher dopant concentration. For example, the highly doped emitter surface 490 can be an n++ or p++ layer having a thickness of about 2 microns or less, such as from about 0.1 to about 1 micron. The highly doped emitter surface 490 facilitates ohmic contact with subsequent metal contacts or grids deposited thereon. Or, highly doped emitter The surface may be formed on the second epitaxial emitter 243 using a gaseous diffusion, ion implantation or dopant paste.

In operation 582, the epitaxial substrate 414a is removed from the template substrate 114, similar to the operation 357 described above. The epitaxial substrate 414a shown in FIG. 4B is similar to the epitaxial substrate 114a; and the epitaxial substrate 414a includes a highly doped emitter surface 490. In operation 583, as shown in FIG. 4C, a mask 491 is placed over the first surface 444 of the highly doped emitter surface 490. Mask 491 can be a wet or dry etch mask, can be applied using screen printing or inkjet printing, and can include a polymer.

In operation 584, as shown in FIG. 4D, the first surface 444 of the epitaxial substrate 414a is contacted with an etchant, such as a wet etchant or dry etchant, to texture the first surface 444. Contacting the etchant will remove the exposed portions of the highly doped emitter surface 490, thereby texturing the second epitaxial emitter 243. The remaining portion of the highly doped emitter surface 490 defines a contact area on which the metal contacts are subsequently deposited. In operation 585, as shown in FIG. 4E, the mask 491 is removed. Alternatively, the mask may be partially or completely removed during the etching process of operation 584.

In operation 586, passivation layers 446, 448 are deposited to first surface 444 and second surface 449 as shown in FIG. 4F. Passivation layers 446, 448 are similar to passivation layers 246, 248 and may be formed in a similar manner. In operation 587, metal contacts 447 are deposited on first surface 444 to contact the remainder of highly doped emitter surface 490. In operation 588, as shown in FIG. 4G, a via 470 is formed in the second surface 449 of the epitaxial substrate 414a, which is similar to operation 363 described above. In operation 589, as shown in FIG. 4G, a metal layer 471 is deposited over the second surface 449 of the epitaxial substrate 414a to contact the passivation layer 448 and deposited into the via 470. Depositing a metal layer 471 to deposit a metal layer 271 as described in operation 364 and A solar cell 472 is formed.

The solar cells formed using the described embodiments are more efficient than solar cells having a dopant paste forming, implanting, diffusing (e.g., solid state diffusing) emitter. As the emitter, the emitter formed during the epitaxial growth process can form a dopant material having a greater depth or thickness and a lower dopant concentration, which cannot be achieved by the large system dopant paste or gaseous diffusion emitter. For example, the solid diffusion forms an emitter having a thickness or depth of less than 1 micron, such as about 3,000 angstroms, and a surface dopant concentration, such as from 1 x 10 ²⁰ to about 3 x 10 ²⁰ atoms/cm ³ . On the contrary, according to the embodiment, the emitter formed during the epitaxial growth process has a lower dopant concentration, so that many undesirable qualities of the high dopant enthalpy, such as carrier recombination, energy gap narrowing, and crystal defects, can be avoided.

Table 1 lists a comparison of solar cells formed using epitaxial emitters and solid state diffused emitters. The epitaxial emitter solar cell comprises n+ and p+ emitters having a thickness of about 5 microns and a dopant concentration of about 1 x 10 ¹⁷ atoms/cm ³ . The solid state diffused emitter solar cell comprises n+ and p+ emitters having a thickness of about 3000 angstroms and a dopant concentration of about 3 x 10 ²⁰ atoms/cm ³ . As shown in Table 1, the solar cell formed according to the embodiment has better short circuit current density, open circuit voltage, and efficiency. Furthermore, the solar cell of embodiments of the present invention has a desirable lower saturation current density. Solid state diffusion emitter solar cell having about 100 femtoamp / cm ^ (fA / cm ²⁾ or greater saturation current density, having a saturation current density from about 1 to about 10fA / cm ² solar cell formed in accordance with the embodiment.

Example 1: Epitaxial n+ emitter was grown on a template substrate to form a solar cell. The epitaxial n+ emitter is formed by reacting trichloromethane with hydrogen in the presence of POCl ₃ and at a temperature of less than about 1200 ° C and a pressure of about 1 atm. The n+ emitter is formed to a thickness of about 5 μm and a dopant concentration of about 3 × 10 ¹⁷ atoms/cm ³ . The flow rate of trichlorodecane and hydrogen is maintained while the inflow of n+ dopant is suspended to form an epitaxial base by epitaxy. The base is formed to a thickness of about 100 microns. Next, the inflow of the p-type dopant and the inflow of the n-type dopant (for example, diborane) are suspended to form an epitaxial n-type emitter having a thickness of about 5 μm and a concentration of about 3 × 10 ¹⁷ atoms/cm ³ . The flow rate of the n-type dopant is then further increased to form a heavily doped (n++) surface on the n-type emitter, for example at a concentration of about 1 x 10 ²⁰ atoms/cm ³ or more. The epitaxial layer is then removed from the template substrate.

The n-type emitter is then patterned and etched, a passivation layer is applied, and a silver contact layer is placed over the n++ emitter surface. Similarly, a passivation layer is applied to the p+ emitter, the via is scribed, and an aluminum layer is applied over the p+ emitter and through the via of the back passivation layer. The solar cell is fired to form a yttrium aluminum eutectic layer. Note that other examples and embodiments may also be covered.

6A to 6F illustrate a solar cell forming process according to still another embodiment. Figure 7 illustrates a flow chart of a method of forming a solar cell, in accordance with yet another embodiment. For ease of explanation, the descriptions of Figs. 6A to 6D and Fig. 7 will be made. 6A to 6D and 7 illustrate an alternative embodiment of forming a solar cell, and may replace FIGS. 2H-2K and 358-362.

In operation 766 of flowchart 765, polysilicon layer 692 is deposited onto the upper or light receiving side of epitaxial layer 214A to form epitaxial substrate 614A. many The germanium layer 692 can be deposited in the same processing chamber as used to form the first epitaxial emitter 241, the base 242, and the second epitaxial emitter 243. The processing chamber is adapted to perform epitaxial and polycrystalline formations by adjusting one or more process parameters, such as deposition temperature, process gas flow rate, and process gas composition. In one example, decane can be used to form polysilicon layer 692. The polysilicon layer 692 can be deposited to a thickness of about 0.1 microns or greater, such as about 0.3 microns or greater.

The inclusion of polysilicon layer 692 helps to form passivated contacts, thereby reducing recombination losses at the metal contact interface, which is subsequently deposited to electrically contact epitaxial substrate 614A. The inclusion of polycrystalline germanium layer 692 can modify the energy gap and selectively pass only a single carrier type. In one example, the polysilicon layer 692 is a heavily doped polysilicon layer, such as an n++ or p++ polysilicon layer. In this embodiment, during the polysilicon formation process, a dopant gas (eg, a p-type or an n-type dopant gas) may be added to the source gas (eg, decane or trichloromethane) to help form the desired dopant distribution. Doped polysilicon layer with concentration.

The thin oxide between the polycrystalline germanium and the surface of the single crystal germanium contributes to improved electrical properties. The interfacial oxide layer can be formed in the same tool after epitaxial emitter deposition and before polycrystalline germanium deposition. Alternatively, interfacial oxide formation (chemical or thermal oxidation) and polycrystalline germanium deposition can be performed in different tools after epitaxial deposition.

In operation 767, as shown in FIG. 6B, an etch photoresist mask 691 is applied to the surface of the polysilicon layer 692 to facilitate selective removal of portions of the polysilicon layer 692. Etched photoresist mask 691 can be a wet or dry etch mask, can be applied using screen printing or inkjet printing, and can include a polymer. In operation 768, a texturing operation is performed. Texture operation 768 operates similarly to 358, but does not texture the masking portions of polysilicon layer 692 and second epitaxial emitter 243. In operation 768, as in the first As shown in Figure 6C, the texturing agent and degree of exposure are selected to remove the undesirable portions of the polysilicon layer 692 and properly texture the surface of the second epitaxial emitter 243. Optionally, the mask may be etched to remove the etched photoresist mask 691 during operation 358, or the process removal mask 691 may be removed separately.

In operation 769, as shown in FIG. 6D, the etched photoresist mask 691 is removed (if not previously removed). In operation 770, as shown in FIG. 6E, a passivation layer 646 is applied over the second epitaxial emitter 243 and the polysilicon layer 692. In operation 771, as shown in FIG. 6F, a metal contact 247 is deposited on the surface of the passivation layer 646 over the remaining portion of the polysilicon layer 692. Although only a single metal contact 247 is illustrated, a plurality of metal contacts 247 can be formed and include, for example, grid lines and/or fingers. After operation 771, the back or non-light receiving surface 649 is processed by operations 363, 364 shown in Figures 3A through 3B. Metal contact 247 is then cured and fired via passivation layer 646.

8A to 8D illustrate a solar cell forming process according to still another embodiment. Figure 9 illustrates a flow chart of a method of forming a solar cell, according to yet another embodiment. For ease of explanation, explanations 8A to 8D and 9 will be incorporated. 8A to 8D and 9 illustrate an alternative embodiment of forming a solar cell, and may replace FIGS. 2I-2K and 358-362.

In operation 976 of flowchart 975, as shown in FIG. 8A, an intrinsically amorphous germanium layer 993 is deposited onto the upper or light receiving surface of epitaxial layer 214A to form epitaxial substrate 914A. The intrinsically amorphous layer 993 can be formed using plasma enhanced chemical vapor deposition (PECVD) and can be performed in a chamber other than the first epitaxial emitter 241, the base 242, and the second epitaxial emitter 243. . In one example, a helium-containing gas (eg, decane) can contribute to the formation of an intrinsically amorphous layer 993. In operation 977, as shown in FIG. 8B, a doped amorphous germanium layer 994 is deposited on the intrinsically amorphous germanium layer 993. The doped amorphous germanium layer 994 can be obtained by using a germanium-containing gas (for example, germane) and a dopant-containing gas and depositing it by PECVD. The doped amorphous germanium layer 994 can be p-type or n-type doped, such as a p+ or n+ layer, the layer having a dopant concentration of from about 1 x 10 ¹⁸ to about 1 x 10 ²⁰ atoms/cm ³ , for example about 1 ×10 ¹⁹ atoms/cm ³ .

In operation 978, as shown in FIG. 8C, a conductive oxide layer 995 is deposited on the doped amorphous germanium layer 994. The conductive oxide layer 995 can be formed in the same PECVD chamber as the amorphous amorphous layer 993 and the doped amorphous layer 994. The conductive oxide layer 995 can be, for example, aluminum zinc oxide (AlZnO), indium tin oxide (ITO), fluorine-doped tin oxide (FTO), and doped zinc oxide. The intrinsically amorphous layer 993, the doped amorphous layer 994, and the conductive oxide layer 995 can each have a thickness of from about 3 to about 50 nanometers, such as from about 5 to 15 nanometers, such as about 10 nanometers.

In operation 979, as shown in FIG. 8D, metal contacts 247 are deposited on conductive oxide layer 995. The metal contacts 247 may optionally be cured in operation 979 or cured in later operation. As the case may be, prior to operation 979, the back or non-light receiving surface 949 may undergo an essential and doped amorphous layer, transparent conductive oxide deposition, and metal deposition. The doped amorphous layer can be of the same conductivity type as the epitaxial emitter on the back side. The front and back amorphous layers can be deposited in the same tool. Likewise, a transparent conductive oxide layer can be deposited in the same tool. The metal layer and contacts can be cured after deposition.

The inclusion of an intrinsically amorphous tantalum layer 993, a doped amorphous tantalum layer 994 and a conductive oxide layer 995 help form passivated contacts to reduce Recombination at the location between the epitaxial substrate 814A. Therefore, the intrinsically amorphous layer 993, the doped amorphous layer 994 and the conductive oxide layer 995 will function similarly to the polysilicon layer 692 of FIG. Furthermore, the lateral conductive strip carriers attributable to the second epitaxial emitter 243 allow for the formation of a thinner intrinsic amorphous germanium layer 993, a doped amorphous germanium layer 994 and a conductive oxide layer 995, for example less than 50 nanometers. Meters, for example about 10 nm. The amorphous amorphous layer 993, the doped amorphous germanium layer 994, and the conductive oxide layer 995 without epitaxially forming the emitter substrate require a thicker and/or doped intrinsic amorphous layer 993, doped amorphous layer 994 and conductive oxide layer 995, which will be responsible for most of the carrier mobility. However, reducing the thickness and/or reducing the doping of the amorphous amorphous layer 993, the doped amorphous layer 994 and the conductive oxide layer 995 allow more sunlight to penetrate the intrinsically amorphous layer 993, doped amorphous layer 994 And a conductive oxide layer 995 to increase the energy produced by the completed device. Furthermore, the presence of an intrinsically amorphous layer 993 in the final device helps to enhance the passivation light receiving surface.

10A through 10G illustrate solar cell formation processes in accordance with another embodiment. Figure 11 illustrates a flow chart of a method of forming a solar cell, in accordance with another embodiment. For ease of explanation, the 10A to 10G and 11th drawings will be explained. FIGS. 10A through 10G and 11 illustrate alternative embodiments of forming a solar cell, and may replace FIGS. 2H-2K and 358-362. The embodiment of Fig. 11 is similar to the embodiment of Fig. 9, but the amorphous amorphous layer 993, the doped amorphous layer 994 and the conductive oxide layer 995 are etched to remove portions between the metal contacts.

Flowchart 1101 begins at operation 1102, in which an amorphous amorphous layer 993 is deposited on the lei as shown in FIG. 10A and similar to operation 976 of FIG. On the layer 214A. In operation 1103, as described in FIG. 10B and similar to operation 977 of FIG. 9, a doped amorphous germanium layer 994 is deposited on the intrinsically amorphous germanium layer 993. In operation 1104, as shown in FIG. 10C and similar to operation 978 of FIG. 9, a conductive oxide layer 995 is deposited over the doped amorphous germanium layer 994.

In operation 1105, as shown in FIG. 10D, an intrinsic amorphous germanium layer 993, an doped amorphous germanium layer 994, and a conductive oxide layer 995 are patterned using a laser (not shown) to selectively remove portions of the amorphous The layers 993, 994 and the conductive oxide layer 995. The laser can be configured to remove selected portions of doped amorphous germanium layer 994 and conductive oxide layer 995 while not removing essential amorphous germanium layer 993. In another embodiment, the etchant and one or more masks may be used in place of the laser to remove selected portions of the doped amorphous germanium layer 994 and the conductive oxide layer 995.

In operation 1106, as shown in FIG. 10E, a texturing operation is performed to texture the epitaxial emitter layer 243. Texture operation 1106 is similar to texture operation 768. Although not shown, a mask can be placed over the remainder of the doped amorphous germanium layer 994 and conductive oxide layer 995 to prevent or reduce the texture doping of the amorphous germanium layer 994 and the conductive oxide layer 995. In operation 1107, as shown in FIG. 10F, metal contacts 247 are deposited on conductive oxide layer 995. The metal contacts 247 may optionally be cured in operation 1107 or subsequently cured. In operation 1107, as shown in FIG. 10G, passivation layer 246 is selectively deposited over the textured essentially amorphous layer 993.

After operation 1108, the back or non-light receiving surface 949 is processed by operations 363, 364 shown in Figures 3A through 3B. In addition, the epitaxial substrate 814A can include a passivation layer similar to the passivation layer 248 shown in FIG. 2K on the second surface or back side (as formed by operation 361), which can be performed prior to operation 363. Metal layer And the contacts can be cured after deposition.

Figure 12 illustrates an epitaxial substrate in accordance with another embodiment of the present invention. The epitaxial substrate 1214A of FIG. 12 is similar to the epitaxial substrate shown in FIG. 10G; however, the essentially amorphous germanium layer 993 of the epitaxial substrate 1214A is patterned simultaneously with the doped amorphous germanium layer 994 and the conductive oxide layer 995 in operation 1105. . Therefore, the passivation layer 246 is deposited on the second epitaxial emitter 243. The patterned intrinsic amorphous layer 993 allows more solar radiation to reach the first epitaxial emitter 241, the base 242, and/or the second epitaxial emitter 243, thereby increasing the amount of power produced by the device.

13A to 13G illustrate a solar cell forming process according to still another embodiment. Figure 14 illustrates a flow chart of a method of forming a solar cell, according to yet another embodiment. For ease of explanation, the descriptions of Figures 13A through 13G and Figure 14 will be used. FIGS. 13A-13G and 14 illustrate an alternate embodiment of forming a solar cell, and may replace FIGS. 2H-2K and 358-362.

Flowchart 1420 begins at operation 1421 where an oxide layer 1396 (eg, a hafnium oxide layer) is deposited on epitaxial layer 214A as shown in FIG. 13A. In one example, oxide layer 1396 can be a tunneling oxide layer having a thickness of less than about 10 nanometers, such as less than about 3 nanometers. The oxide layer 1396 can be deposited to the upper surface of the epitaxial emitter 243 by atomic layer deposition or other suitable formation methods, such as thermal oxidation at temperatures below about 500 °C. In operation 1422, as shown in FIG. 13B, a doped polysilicon layer 692 is deposited over oxide layer 1396. The doped polysilicon layer 692 is similar to the doped polysilicon layer 692 described in FIG. 6 and can be formed in a similar manner.

In operation 1423, an etched photoresist mask 691 is deposited over the doped polysilicon layer 692 as shown in FIG. 13C. Doped polysilicon layer 692 is helpful for selection The oxide layer 1396 and the doped polysilicon layer 692 are selectively patterned. In operation 1424, as shown in FIG. 13D, oxide layer 1396 and doped polysilicon layer 692 are patterned. Oxide layer 1396 and doped polysilicon layer 692 can be removed, for example, by contact etchant, dry etching, or using laser patterning to remove regions of oxide layer 1396 and doped polysilicon layer 692. In operation 1425, as shown in FIG. 13E, a texture etch is performed to texture the second epitaxial emitter 243 and optionally remove the mask 691. The mask 691 can be removed in different operations without being simultaneously textured with the second epitaxial emitter 243.

In operation 1426, a passivation layer 246 is deposited on the second epitaxial emitter 243 as shown in FIG. 13F. Subsequently, in operation 1427, a metal contact 247 is formed over the polysilicon layer 692 to facilitate electrical connection to complete the device. After operation 1427, the back or non-light receiving surface 1449 is processed by operations 363, 364 shown in Figures 3A through 3B. Moreover, prior to operation 363, a passivation layer (eg, passivation layer 248 shown in FIG. 2K) can be applied to the non-light receiving surface 1449. The metal layer and contacts can be cured after deposition.

In one example, replacing the amorphous germanium with a polysilicon to form a passivated contact helps reduce processing costs. In one example, during the metal contact curing process, the polysilicon can undergo temperatures of 800 ° C, 900 ° C or above, and the polysilicon is not converted to crystalline germanium. Therefore, inexpensive metal pastes can be used to form metal contacts without the use of expensive low temperature alternatives.

Figure 15 illustrates a solar cell 1572 in accordance with another embodiment. The solar cell 1572 is similar to the solar cell 272 shown in FIG. 2L; however, the solar cell is a passivated emitter back contact (perc) solar cell. In this embodiment, the epitaxial growth of solar cell 272 can begin at base 242 to exclude the first The epitaxial emitter 241 can reduce manufacturing costs. The formation of the solar cell 1572 can continue to grow the second epitaxial emitter 243.

Unlike the solar cell 272, the solar cell 1572 has no epitaxial emitter on the non-light receiving face of the solar cell 1572 and is therefore electrically connected to the back surface field 1590 to remove current through the doped metal layer 1571. In particular, after the passivation layer 248 is deposited and the through opening 270 is formed, the doped metal layer 1571 is deposited onto the passivation layer 248 and within the opening 270. Subsequently, the solar cell 1572 having the doped metal layer 1571 is subjected to an annealing operation to cause an alloy between the metal in the doped metal layer 1571 and the base 242 at the back surface field 1590, such as a doped metal layer 1571 and a base. Extremely 242 interface. In one example, the alloy is a yttrium aluminum eutectic alloy. The dopant of the doped metal layer 1571 may have a conductivity type opposite that of the dopant of the second epitaxial emitter 243. For example, if the second epitaxial emitter 243 includes an n-type dopant, the doped metal layer 1571 can include a p-type dopant. When the solar cell 1572 is formed, the annealing operation can be performed after the operation 364 shown in FIG. 3B.

Solar cell 1572 can be formed using a flow diagram 350 similar to that described above. When solar cell 1572 is formed using flow diagram 350, operation 353 can be eliminated. Additionally, as described above, an anneal or fire operation may be performed after operation 364 to help form a eutectic material at the interface between the doped metal layer 1571 and the base 242 within the opening 270.

While the embodiments generally describe the growth of epitaxial emitters and bases from a porous template substrate, it should also be understood that one or more epitaxial emitters can be grown directly from the epitaxial substrate, such as base 242, without the use of a template. Substrate 114. In this embodiment, the substrate 114 will be excluded. The epitaxial emitters 241 and/or 243 grow directly on the base 242. For example, the base 242 can be placed on the support to assist in the base The first side of the 242 grows the epitaxial emitter 241, and then the base 242 is flipped to grow the second epitaxial emitter 243 on the second side of the base 242. This embodiment allows the base 242 to be grown or prepared at other times or locations to provide process flexibility without the use of the substrate 114, thereby reducing material costs.

Figure 16 illustrates a solar cell 1672 in accordance with yet another embodiment. Solar cell 1672 is similar to solar cell 272, although solar cell 1672 includes a staggered back contact structure 1671. The staggered back contact structure 1671 includes a contact 1671a that electrically connects the doped region 241a of the first epitaxial emitter 241. The doped region 241a is doped with a first conductivity type dopant. The staggered back contact structure 1671 also includes a contact 1671b that is interleaved with the contact 1671a. The contact 1671b is electrically connected to the doped region 241b of the first epitaxial emitter 241. The doped region 241b is doped with a second conductivity type dopant opposite the first conductivity type to assist in removing current from the solar cell 1672. The contacts 1671a, 1671b are electrically isolated from each other. Since the contacts 1671a, 1671b abut the second surface 249 of the solar cell 1672, it is not necessary to form an emitter on the front side of the solar cell 1672 (e.g., the reverse side of the base 242). When a staggered back contact solar cell utilizing an emitter-winding-through or emitter-winding-surrounding technique is employed, the solar cell 1672 may include a second emitter, such as the second epitaxial emitter 243 shown in FIG. 2L. .

The solar cell 1672 can be formed using a flow chart similar to that shown in FIGS. 3A and 3B. When solar cell 1672 is formed, operation 256 can be eliminated. Additionally, during operation 359, the second surface 249 of the solar cell 1672 is selectively implanted. Selective emitter implantation can be used to implant dopants of opposite conductivity types into doped regions 241a, 241b, respectively. Although not shown, it should be understood that the doped regions 241a, 241b may be separated by undoped regions.

Further, when the solar cell 1672 is formed, the operation 362 may be omitted because the contacts 1671a and 1671b are both located on the non-light receiving surface of the solar cell 1672. In operation 364, the blanket metal layer is not deposited to the second surface 249 to cover the passivation layer, but one or more metal pastes are screen printed in accordance with the desired staggered contact pattern. A metal paste can be deposited over the passivation layer 248 and within the opening 270 to electrically contact the doped regions 241a, 241b.

The advantages of the solar cell generally include increased efficiency compared to previously known solar cells.

While the above is directed to the embodiments of the present invention, the scope of the present invention is defined by the scope of the appended claims.

241, 243‧‧ ‧ emitter

242‧‧‧ base

246, 248‧‧‧ Passivation layer

247‧‧‧Contacts

249‧‧‧ surface

270‧‧‧ openings

271‧‧‧metal layer

272‧‧‧ solar cells

Claims (33)

A method of forming a solar cell, comprising the steps of: epitaxial growth comprising a first emitter of a p-type or n-type dopant; epitaxial growth of a base to the first emitter; epitaxial growth comprising a p a second emitter of a type or n-type dopant; forming a heavily doped region of the same conductivity type as the second emitter to the second emitter, a surface concentration of the heavily doped region being higher than the second An emitter; a second emitter is applied; a first passivation layer is applied to the first emitter; a second passivation layer is applied to the second emitter; and a first metal contact is applied to the first emitter And applying a second metal contact to the second emitter, the second metal contact being aligned with the heavily doped region. The method of claim 1, wherein the heavily doped region has a dopant concentration of about 1 x 10 ²⁰ atoms/cm ³ or more on a surface. The method of claim 2, wherein the texturing step is a selective texturing step and is performed after forming the heavily doped region. The method of claim 3, wherein the selectively texturing step comprises applying a mask to a surface of the second emitter, followed by etching the surface of the second emitter. The method of claim 3, wherein the heavily doped region is epitaxially grown and spreads over a uniform concentration. The method of claim 3, further comprising forming the heavily doped emitter on the second emitter by vapor diffusion, ion implantation or deposition of a dopant source and diffusion prior to texture of the second emitter surface. The method of claim 2, further comprising etching the second emitter before forming the heavily doped region. The method of claim 7, wherein the heavily doped region is formed by applying a dopant paste to the second emitter or implanting the second emitter with a masking ion, wherein the solar cell comprises a beam Crystal. The method of claim 1, wherein the first emitter, the base, and the second emitter are grown on a template substrate, wherein the first emitter, the base, and the second emitter are The template substrate is removed. The method of claim 1, wherein the first emitter is n-doped or p-doped, and the second emitter is different from the first emitter of n-doped or p-doped The other. A solar cell produced according to the method of claim 1. A method of forming a solar cell, comprising the steps of: epitaxial growth comprising a p-type or n-type dopant on a first emitter to an n-type or p-type substrate; epitaxial growth comprising a p-type or n-type a second emitter of the dopant to an opposite surface of the substrate; forming a heavily doped region of the same conductivity type as the second emitter to the second emitter, a surface concentration of the heavily doped region is higher than The second emitter; the second emitter is patterned; a first passivation layer is applied to the first emitter; a second passivation layer is applied to the second emitter; and a first metal contact is applied to the first And an application of a second metal contact to the second emitter, the second metal contact being aligned with the heavily doped region. The method of claim 12, wherein the heavily doped region has a dopant concentration of about 5 x 10 ¹⁹ atoms/cm ³ or more on a surface. The method of claim 13, wherein the texturing step is a selective texturing step and is performed after forming the heavily doped region. The method of claim 14, wherein the selectively texturing step comprises applying a mask to a surface of the second emitter, followed by etching the surface of the second emitter. The method of claim 14, wherein the heavily doped region is epitaxially grown and spreads over a uniform concentration. The method of claim 14, wherein the heavily doped region is formed by applying a dopant paste to the second emitter or implanting the second emitter with a masking ion. The method of claim 13, wherein the second emitter is textured prior to forming the heavily doped region. The method of claim 18, wherein the heavily doped region is formed by printing a dopant paste or by implanting a masking ion. The method of claim 12, wherein the first emitter, the second emitter, and the substrate each comprise germanium. The method of claim 12, wherein the first emitter is n-doped or p-doped, the second emitter being different from the first emitter of n-doped or p-doped The other. The method of claim 12, wherein the heavily doped region is formed by applying a dopant paste to the second emitter. A solar cell comprising: a single crystal germanium base; a first single crystal germanium emitter, the first single crystal germanium emitter being disposed on a first side of the single crystal germanium base, a thickness of the first single crystal germanium emitter From about 5 micrometers to about 15 micrometers; a second single crystal germanium emitter, the second single crystal germanium emitter is disposed on a second side of the single crystal germanium base, the second single crystal germanium emitter a thickness of from about 5 microns to about 15 microns; a first passivation layer disposed on the first single crystal germanium emitter; a second passivation layer, the second passivation layer being disposed on the second a single crystal germanium emitter; a first metal layer disposed on the first passivation layer; and a second metal layer disposed on the second passivation layer. The solar cell of claim 23, wherein the first single crystal germanium emitter and the second single crystal germanium emitter comprise a dopant having a concentration of about 1×10 ¹⁷ to about 1×10. ¹⁹ atoms/cm ³ . The solar cell of claim 23, wherein the first single crystal germanium emitter comprises a heavily doped region having a dopant concentration of about 5 x 10 ¹⁹ atoms/cm ³ or more, wherein The first metal layer is aligned with the heavily doped region. The solar cell of claim 23, further comprising a doped polycrystal And a doped polysilicon layer disposed between the second single crystal germanium emitter and the second metal layer. The solar cell of claim 26, further comprising a tunneling oxide layer disposed between the doped polysilicon layer and the second metal layer. The solar cell of claim 23, further comprising: an intrinsically amorphous layer of germanium deposited on the first single crystal germanium emitter; a doped amorphous layer, the doped amorphous A germanium layer is deposited on the intrinsically amorphous germanium layer; and a conductive oxide layer is deposited on the doped amorphous germanium layer. The solar cell of claim 23, further comprising: an intrinsically amorphous germanium layer deposited on the second single crystal germanium emitter; a doped amorphous germanium layer, the doped amorphous A germanium layer is deposited on the intrinsically amorphous germanium layer; and a conductive oxide layer is deposited on the doped amorphous germanium layer. The solar cell of claim 23, further comprising: an intrinsically amorphous layer of germanium deposited on the first sheet a doped amorphous germanium layer, the doped amorphous germanium layer deposited on the intrinsically amorphous germanium layer; and a conductive oxide layer deposited on the doped amorphous germanium layer on. The solar cell of claim 23, further comprising: an intrinsically amorphous layer of germanium deposited on the second single crystal germanium emitter; a doped amorphous layer, the doping A shaped ruthenium layer is deposited on the essentially amorphous ruthenium layer; and a conductive oxide layer is deposited on the doped amorphous ruthenium layer. A method of forming a solar cell, comprising the steps of: epitaxial growth comprising a p-type or n-type dopant on a first emitter to an n-type or p-type substrate; forming a conductivity type and the first emitter a same heavily doped region to the first emitter, a surface concentration of the heavily doped region is higher than the first emitter; applying a first passivation layer to the first emitter; and applying a first metal touch Point to the top of the first emitter. The method of claim 32, further comprising fabricating the first emitter.