TWI559563B - Hybrid polycrystalline germanium heterojunction back contact battery - Google Patents

Description

Hybrid polycrystalline germanium heterojunction back contact battery

The embodiments of the subject matter described in this specification relate generally to the manufacture of solar cells. In particular, the embodiments of the application are directed to thin tan solar cells and manufacturing techniques.

A well-known solar cell is a device that converts solar radiation into electrical energy. It can be fabricated on semiconductor wafers using semiconductor process technology. Solar cells include P-type and N-type diffusion regions. The solar radiation that is incident on the solar cell generates electrons and holes that migrate to the diffusion region, thus creating a pressure difference between the diffusion regions. In the backside contact solar cell, the diffusion region and the metal contact fingers coupled to the diffusion region are both located on the back side of the solar cell. The contact fingers enable an external circuit to be coupled to and powered by the solar cell.

Efficiency is an important feature of solar cells because it is directly related to the ability of solar cells to generate electricity. Therefore, it is generally desired to have a technology for improving the production process, reducing the manufacturing cost, and increasing the efficiency of the solar cell. Such techniques include the formation of polycrystalline germanium and heterojunction layers on a germanium substrate by a thermal process wherein the present invention increases solar cell efficiency. These and other similar embodiments form the background of the invention.

The disclosed method is a method of manufacturing a solar cell. The method includes providing a germanium substrate having a thin dielectric layer on the back side and a deposited germanium layer over the thin dielectric layer; forming a dopant material layer over the deposited germanium layer; forming over the dopant material layer An oxide layer; partially removing the oxide layer, the dopant material layer, and the deposited germanium layer in an interdigitated pattern; growing the oxide layer while increasing temperature to drive the dopant from the dopant material layer into the deposited germanium layer Layer; doping the deposited tantalum layer with a dopant from the doped material layer to form a crystallized doped polysilicon layer; depositing a wide band gap doped semiconductor and anti-reflection on the back side of the solar cell a coating; and depositing a broad band gap doped semiconductor and an anti-reflective coating on the front side of the solar cell.

The disclosed method is another method of manufacturing a solar cell. The method includes providing a germanium substrate having a thin dielectric layer on the back side and a deposited germanium layer over the thin dielectric layer; forming a dopant material layer over the deposited germanium layer; forming an oxide over the dopant material layer a layer of the oxide layer, a layer of doped material, and a layer of deposited germanium; the exposed germanium substrate is etched to form a roughened germanium region; the oxide layer is grown while the temperature is raised to drive the dopant From the doped material layer into the deposited germanium layer; doping the deposited germanium layer with a dopant from the doped material layer to form a doped polysilicon layer; covering the wide band gap on the back side of the solar cell a first thick layer of an amorphous germanium and an anti-reflective coating; a second thin layer of the doped amorphous germanium with a wide band gap and an anti-reflective coating on the front side of the solar cell, wherein the thin layer is smaller than 10% to 30% of the thickness of the thick layer.

The disclosed method is another method of manufacturing a solar cell. The method includes providing a germanium substrate having a thin dielectric layer on the back side and a doped germanium layer over the thin dielectric layer; forming an oxide layer over the doped germanium layer; partially removing the interdigitated pattern An oxide layer and a doped germanium layer; by heating the germanium substrate in an oxygen-containing environment to grow a germanium oxide layer over the back side of the solar cell, wherein the germanium oxide layer is doped The doped layer is crystallized to form a doped polysilicon layer; a broad band gap-doped semiconductor is deposited on the back side of the solar cell; and a broad band gap is doped semiconductor on the front side of the solar cell Reflective coating.

The disclosed method is another method of manufacturing a solar cell. The method includes providing a germanium substrate having a thin dielectric layer on the back side and a doped germanium layer over the thin dielectric layer; forming an oxide layer over the doped germanium layer; partially removing the interdigitated pattern An oxide layer and a doped germanium layer; etching the exposed germanium substrate to form a roughened germanium region; by heating the germanium substrate in an oxygen-containing environment to grow a germanium oxide layer over the back side of the solar cell, wherein the germanium oxide layer is grown The hybrid layer is crystallized to form a doped polysilicon layer; a broad band gap-doped amorphous germanium and anti-reflective coating is deposited on the back side of the solar cell; and a broad band is deposited on the front side of the solar cell The gap is doped with an amorphous germanium and an anti-reflective coating.

The disclosed is another embodiment of a method of making a solar cell. The method includes providing a germanium substrate having a thin dielectric layer on the back side and a doped germanium layer over the thin dielectric layer; forming an oxide layer over the doped germanium layer; partially removing the interdigitated pattern An oxide layer and a doped germanium layer; etching the exposed germanium substrate to form a roughened germanium region; by heating the germanium substrate in an oxygen-containing environment to grow a germanium oxide layer over the back side of the solar cell, wherein The doped lanthanum layer is crystallized to form a doped polysilicon layer; a broad band gap is doped with an amorphous yttrium and an anti-reflective coating simultaneously on the front side and the back side of the solar cell; partially removing the wide band gap The semiconductor and oxide layers are doped to form a series of contact openings; and the first metal gate and the second metal gate are simultaneously formed, the first metal gate is electrically coupled to the doped polysilicon layer, and the second The metal gate is electrically coupled to the emitter region on the back side of the solar cell.

An improved technique for fabricating solar cells is to provide a thin dielectric layer and a deposited germanium layer on the back side of the germanium substrate. The dopant can be driven into the deposited germanium layer to form a doped The polysilicon region is formed, or the doped polysilicon region is formed in situ. An oxide layer and a wide band gap doped semiconductor layer can then be formed on the front side and the back side of the solar cell. Another approach is to roughen the front and back surfaces before the oxide and wide band gaps are formed by the doped semiconductor. A contact hole through the upper layer may then be formed to expose the doped polysilicon region. A metallization process can then be performed to form the contacts onto the doped polysilicon layer. A second set of contacts may also be formed by directly connecting the metal to the emitter region on the germanium substrate, wherein the emitter region is a wide band gap semiconductor layer between the doped polysilicon regions on the back side of the solar cell. Formed.

100‧‧‧ solar cells

102‧‧‧矽 substrate

104‧‧‧Sedimentary layer

106‧‧‧thin dielectric layer

108‧‧‧Doped material layer

109‧‧‧Dopants

110‧‧‧First oxide layer

112‧‧‧Second oxide layer

114‧‧‧ third oxide layer

124‧‧‧ exposed polysilicon area

130‧‧‧First roughening area

132‧‧‧Second roughening area

140‧‧‧heating

150‧‧‧Doped polysilicon layer

160‧‧‧First wide band gap doped semiconductor layer

162‧‧‧Second wide band gap doped semiconductor layer

170‧‧‧Anti-reflective coating

180‧‧‧Contact opening

190‧‧‧First metal gate line

192‧‧‧Second metal gate line

200‧‧‧ solar cells

202‧‧‧矽 substrate

206‧‧‧thin dielectric layer

209‧‧‧Doped materials

210‧‧‧First oxide layer

212‧‧‧Second oxide layer

214‧‧‧ third oxide layer

220‧‧‧矽 exposed areas of the substrate

230‧‧‧First roughening area

232‧‧‧Second roughening area

240‧‧‧heating

250‧‧‧Doped polysilicon layer

260‧‧‧The first wide band gap doped semiconductor layer

262‧‧‧Second wide band gap doped semiconductor layer

270‧‧‧Anti-reflective coating

290‧‧‧First metal gate line

292‧‧‧Second metal gate line

A more complete understanding of the subject matter of the present application can be made by referring to the detailed description and claims.

1 to 12 are schematic cross-sectional views of a solar cell fabricated in accordance with an embodiment of the present invention.

13 to 18 are schematic cross-sectional views showing a solar cell manufactured according to another embodiment of the present invention.

The following detailed description is merely for the purpose of illustration, and is not intended to limit the embodiments of the application or the application or use of the embodiments. In the present specification, the term "exemplary" means "as an example, an example or a description." Any one of the specification described as an exemplary embodiment is not necessarily to be construed as preferred or advantageous over other embodiments. In addition, the present invention is not intended to be limited by the scope of the present invention, the prior art, the invention, or the following detailed description.

Various embodiments relating to the manufacturing method are shown in Figs. 1 to 18. In addition, some of the various embodiments are not necessarily in the order shown, and may be incorporated in a more complete procedure, process or method of manufacture having other functions not described herein.

FIGS. 1 through 3 illustrate an embodiment for fabricating a solar cell 100 that includes a germanium substrate 102, a thin dielectric layer 106, and a deposited germanium layer 104. In some embodiments, the germanium substrate 102 can be cleaned, ground, planarized, and/or thinned or otherwise processed prior to forming the thin dielectric layer 106. The thin dielectric layer 106 and the deposited germanium layer 104 can be grown using a thermal process. The doped material layer 108 and the first oxide layer 110 may be sequentially deposited over the deposited germanium layer 104 using an existing deposition process. The doped material layer 108 may include a dopant material or dopant 109, but is not limited to a layer of positive dopant material, such as boron, or a layer of negative dopant material, such as phosphorus. Although the thin dielectric layer 106 and the deposited germanium layer 104 are grown by a thermal process, respectively, or by an existing deposition process, as in any other forming, deposition, or growth process steps described or referenced herein. Each layer or substance may also be formed using any suitable process. For example, when referring to the formation method, a chemical vapor deposition (CVD) process, a low-pressure chemical vapor deposition (LPCVD), an atmospheric pressure chemical vapor deposition (atmospheric pressure) may be used. Chemical vapor deposition (APCVD), plasma-enhanced chemical vapor deposition (PECVD), thermal growth, sputtering, and any other desirable technique. Thus, as previously described, the doping material 108 can be formed on the substrate using deposition techniques, sputtering or printing processes such as inkjet printing or screen printing.

4 depicts the same solar cell 100 as in FIGS. 1 through 3, and has completed a material removal process to form exposed polysilicon regions 124. Some examples of material removal processes include masking and etching processes, laser ablation processes, and the like. The exposed polysilicon region 124 and dopant material layer 108 can be formed into any desired shape, including an interdigitated pattern. If a mask process is used, the mask ink can be applied in a predetermined interdigitated pattern using a screen printer or ink jet printer. Therefore, existing chemical wet etching techniques can be used to remove the masking ink to form an exposed polysilicon region. The intersection of the domain 124 and the layer of dopant material 108. In at least one embodiment, some or all of the first oxide layer 110 can be removed. This can be accomplished in the same etching or ablation process where the regions of the deposited germanium layer 104 and the thin dielectric layer 106 are removed, as shown in Figures 4 and 5.

Referring to FIG. 5, the solar cell 100 may undergo a second etching process to etch the exposed polysilicon region 124, while forming a first roughened germanium region 130 on the back side of the solar cell and a second thick on the front side of the solar cell. The pupation area 132 is used to promote the collection of solar radiation. The roughened surface can be a surface having a regular or irregular shape to scatter incident light, thereby reducing the amount of light reflected back from the surface of the solar cell.

Referring to FIG. 6, solar cell 100 can be heated 140 to drive dopant material 109 from dopant material layer 108 into deposited germanium layer 104. The same heating 140 may also form a tantalum oxide or second oxide layer 112 over the doped material layer 108 and the first roughened germanium region 130. During this process, a third oxide layer 114 can be grown over the second roughened germanium region 132. Both oxide layers 112, 114 can comprise high quality oxides. High quality oxides are oxides of low interfacial density which are typically grown by thermal oxidation at temperatures above 900 degrees Celsius to provide improved passivation.

Referring to FIG. 7, the deposited germanium layer 104 may thus be doped with dopant material 109 from the dopant material layer 108 to form a doped polysilicon layer 150. In one embodiment, the oxide layer can be grown while simultaneously increasing the temperature to drive dopants 109 from the dopant material layer 108 into the deposited germanium layer 104 to form a doped polysilicon layer, wherein the dopant layer 108 is utilized. The dopant 109 is doped to the deposited germanium layer 104 to form a crystallized doped polysilicon layer or doped polysilicon layer 150. In one of several embodiments, if a positive dopant material is used, the doped polysilicon layer 150 can comprise a layer of positively doped polysilicon. In the illustrated embodiment, the germanium substrate 102 comprises a body N-type germanium substrate. In some embodiments, if a negative type is used For the doped material, the doped polysilicon layer 150 comprises a layer of negatively doped polysilicon. In an embodiment, the germanium substrate 102 should comprise a body P-type germanium substrate.

Referring to FIG. 8, a first wide band gap doped semiconductor layer 160 may be deposited on the back side of the solar cell 100. In one embodiment, the first wide band gap is partially electrically conductive through the doped semiconductor layer 160 and has a resistivity of at least 10 ohm-cm. In the same embodiment, the band gap may be greater than 1.05 electron volts (eV) as a heterojunction in the backside region of the solar cell that has been covered by the first roughened germanium region 130 and the second oxide layer 112 ( Heterojunction). Examples of wide band gap doped semiconductors include tantalum carbide and aluminum gallium nitride. Any other wide band gap doped semiconductor material having the above properties and characteristics can also be used. The first wide band gap doped semiconductor layer 160 may be composed of a first thick wide band gap and a doped amorphous layer.

Referring to FIG. 9, a second wide band gap doped semiconductor layer 162 may be deposited over the second roughened germanium region 132 on the front side of the solar cell 100. In one embodiment, the two wide band gap-doped semiconductor layers 160, 162 on the back side and the front side of the solar cell 100 may each comprise a wide band gap via a negatively doped semiconductor. In another embodiment, the second wide band gap via doped semiconductor layer 162 can be relatively thin compared to the first thick wide band gap via the doped semiconductor layer. Thus, in some embodiments, the second thin wide band gap doped semiconductor layer can comprise a thickness of 10 to 30% of the first thick wide band gap doped semiconductor layer. In yet another embodiment, the two wide band gap doped semiconductor layers 160, 162 respectively located on the back side and the front side of the solar cell may comprise a wide band gap via a negative doped semiconductor or a wide band gap Positive doped semiconductor. Thereafter, an anti-reflective coating (ARC) 170 may be deposited over the second wide band gap doped semiconductor layer 162 in the same process. In another embodiment, the anti-reflective coating 170 can be deposited over the first wide band gap over the doped semiconductor layer 160 in the same process. In some embodiments, the anti-reflective coating 170 can be comprised of tantalum nitride.

FIG. 10 illustrates that the first wide band gap on the back side of the solar cell 100 is partially removed by the doped semiconductor layer 160, the doped material layer 108, and the second oxide layer 112 to form a series of contact openings 180. In an embodiment, the removal technique can be accomplished using an ablation process. One such ablation process is a laser ablation process. In another embodiment, the removal technique can be any existing etching process, such as inkjet printing or screen printing of a mask, followed by an etching process.

Referring to FIG. 11, a first metal gate or gate line 190 can be formed on the back side of the solar cell 100. The first metal gate line 190 can be electrically coupled to the doped polysilicon layer 150 within the contact opening 180. In an embodiment, the first metal gate line 190 may be formed through the contact opening 180 to the first wide band gap-doped semiconductor layer 160, the second oxide layer 112, and the doped material layer 108 to A positive terminal that connects an external circuit powered by a solar cell.

Referring to FIG. 12, a second metal gate or gate line 192 may be formed on the back side of the solar cell 100. The second metal gate line 192 is electrically coupled to the second roughened germanium region 132. In an embodiment, the second metal gate line 192 can be coupled to the first wide band gap doped semiconductor layer 160, the second oxide layer 112, and the first roughened germanium region 130 as a solar cell back. A heterojunction in the side region to connect the negative terminal of the external circuit powered by the solar cell. In some embodiments, the metal gate line forming method shown in FIGS. 11 and 12 may be performed by an electroplating process, a screen printing process, an inkjet process, plating on a metal formed of aluminum metal nanoparticles or by Any other metallization or metal forming process step is achieved.

13 to 18 illustrate another embodiment of manufacturing the solar cell 200. Unless otherwise indicated below, the component numbers used to indicate the elements in FIGS. 13 to 18 are similar to those in the foregoing FIGS. 1 to 12 for indicating the elements or technical features, the difference being that the labels are Plus 100.

Referring to FIGS. 13-14, another embodiment for fabricating solar cell 200 can include forming a first oxide layer 210, a thin dielectric layer 206, and a doped polysilicon layer 250 over the germanium substrate 202. As previously described, the tantalum substrate 202 can be cleaned, ground, planarized, and/or thinned or otherwise processed prior to forming the thin dielectric layer 206. The first oxide layer 210, the dielectric layer 206, and the doped polysilicon layer 250 may be grown using a thermal process. In one embodiment, by heating the germanium substrate 202 in an oxygen-containing environment, a germanium oxide layer or oxide layer 210 is grown over the back side of the solar cell, wherein the doped germanium layer is crystallized to form an admixed layer. A heteropolycrystalline layer 250. In another embodiment, the step of growing the doped polysilicon layer 250 over the dielectric layer 206 comprises growing a positively doped polysilicon, wherein the positively doped polysilicon can be composed of a dopant material 209, such as boron doping. Agent. In another embodiment, a negatively doped polysilicon can be used. Although the thin dielectric layer 206 and the doped polysilicon layer 250 are grown by a thermal process, respectively, or by an existing deposition process, as in any other formation, deposition, or growth process steps described or referenced herein. In general, the layers or materials may be formed using any of the suitable processes described above.

The first oxide layer 210, the doped polysilicon layer 250, and the dielectric layer 206 may be partially removed to further process the solar cell 200, thereby exposing the exposed regions 220 of the germanium substrate in an interdigitated pattern using existing masking and etching processes. . In the case of using existing masking and etching processes, an ablation process can be used. If an ablation process is used, the first oxide layer 210 may remain partially intact over the doped polysilicon layer 250, as shown in FIG. In another embodiment, screen printing or ink jet printing techniques can be used in conjunction with an etching process. In such an embodiment, the first oxide layer 210 can be etched away from the doped polysilicon layer 250.

Referring to FIG. 15, the exposed germanium substrate 220 and the exposed regions on the front side of the solar cell 200 can be simultaneously etched to form a first roughened germanium region 230 and a second roughened germanium region 232 for promoting solar radiation. collect.

Referring to FIG. 16, the solar cell 200 can be heated 240 to a temperature higher than 900 degrees Celsius, while the second oxide layer 212 is formed on the back side of the solar cell 200 and the third oxide layer 214 is formed on the front side. In another embodiment, both oxide layers 212, 214 may comprise the aforementioned high quality oxide.

Referring to FIG. 17, a first wide band gap doped semiconductor layer 260 may be simultaneously deposited on the back side and the front side of the solar cell. The first wide band gap may be partially conductive through the doped semiconductor layer 260 and may have a resistivity greater than 10 ohm-cm. The band gap of the first wide band gap via the doped semiconductor layer 260 may also be greater than 1.05 eV. In addition, the first wide band gap semiconductor layer can serve as a heterojunction in the back side region of the solar cell covered by the first roughened germanium region 230 and the second oxide layer 212.

The first wide band gap doped semiconductor layer 260 may be 10% to 30% thicker than the second wide band gap via the doped semiconductor layer 262. In other embodiments, the thickness can be varied to less than 10% or greater than 30% without departing from the techniques described herein. The two wide band gap doped semiconductor layers 260, 262 can be positively doped semiconductors, although in other embodiments using different substrates and polysilicon doping polarity, a negatively doped broad energy can also be used. A semiconductor layer with a gap. An anti-reflective coating (ARC) 270 can then be deposited over the doped semiconductor layer 262 over the second wide band gap. In an embodiment, the anti-reflective coating 270 can be composed of tantalum nitride. In some embodiments, an anti-reflective coating can also be deposited over the doped semiconductor layer 260 at a first wide band gap.

Referring to FIG. 18, a first wide band gap doped semiconductor layer 260 and a second oxide layer 212 may be partially removed over the doped polysilicon layer 250 to form a series of contact openings similar to the foregoing. Figures 10 through 12 are achieved with similar techniques. A first metal gate line 290 can then be formed on the back side of the solar cell 200, wherein the first metal gate line 290 can be electrically coupled to the doped polysilicon layer 250 within the contact opening. A second metal gate can be formed on the back side of the solar cell 200 The second metal gate line 292 is electrically coupled to the first roughened germanium region or the N-type emitter region 230. In an embodiment, the first and second metal gate lines can be formed simultaneously. Additional contact to the first and second metal gate lines 290, 292 can then be accomplished by other components of the energy system of the solar cell 200.

While at least one exemplary embodiment has been presented in the foregoing embodiments, it will be appreciated that a number of variations can be present. It should be understood that the illustrative embodiments or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed application. Rather, the foregoing embodiments are provided to provide a simple description of one or more embodiments. It will be appreciated that various changes can be made in the function and arrangement of the elements without departing from the scope of the invention, and the scope of the application includes the known equivalents and the foreseeable in the application of this patent application. Equal.

100‧‧‧ solar cells

102‧‧‧矽 substrate

104‧‧‧Secondary layer

106‧‧‧thin dielectric layer

Claims (40)

A method for fabricating a solar cell, the solar cell comprising a substrate having a front side and a back side opposite the front side, the front side being configured to face the sun during normal operation, and the method comprising: providing The germanium substrate has a thin dielectric layer on the back side, and a deposited germanium layer over the thin dielectric layer; a doped material layer is formed over the deposited germanium layer; Forming an oxide layer thereon; partially removing the oxide layer, the doping material layer and the deposited germanium layer in an interdigitated pattern; growing an oxide layer while increasing temperature to drive a dopant from the doping a layer of impurity material enters the deposited germanium layer; the deposited germanium layer is doped with the dopant from the dopant material layer to form a crystallized doped polysilicon layer; the back of the solar cell A wide band gap is doped on the side of the doped semiconductor and an anti-reflective coating; and a wide band gap doped semiconductor and the anti-reflective coating are deposited on the front side of the solar cell. The method of claim 1, wherein the step of providing the germanium substrate comprises providing a germanium substrate having an N-type body. The method of claim 1, wherein the sulfhydryl group is provided The step of the board includes providing a germanium substrate having a P-type body. The method of claim 1, wherein the step of forming the doped material layer over the deposited germanium layer comprises forming a positive doped material layer over the deposited germanium layer. The method of claim 1, wherein the step of forming the doped material layer over the deposited germanium layer comprises forming a negative doped material layer over the deposited germanium layer. The method of claim 1, wherein the step of depositing the wide band gap through the doped semiconductor comprises depositing a broad band gap doped amorphous germanium. The method of claim 1, wherein the step of depositing the broad band gap through the doped semiconductor comprises depositing a semiconductor having a band gap greater than 1.05 electron volts. The method of claim 1, wherein the step of partially removing the oxide layer, the doped material layer, and the deposited germanium layer in the interdigitated pattern comprises using an etching process to remove the oxide a layer, the doped material layer, and the deposited tantalum layer. The method of claim 1, wherein the step of partially removing the oxide layer, the dopant material layer and the deposited germanium layer in the interdigitated pattern comprises using an ablation process to remove the oxide a layer, the doped material layer, and the deposited tantalum layer. The method of claim 1, wherein the step of depositing the anti-reflective coating on the front side of the solar cell comprises depositing Tantalum nitride. The method of claim 1, wherein the step of depositing the wide band gap on the back side of the solar cell by doping a semiconductor comprises depositing a portion of a conductive wide band gap doped semiconductor having Typical resistivity greater than 10 ohm-cm. The method of claim 1, wherein the step of depositing the wide band gap on the back side and the front side of the solar cell by doping a semiconductor comprises depositing a wide band gap via a negative doped semiconductor . The method of claim 1, wherein the step of depositing the wide band gap on the back side and the front side of the solar cell by doping a semiconductor comprises depositing a broad band gap via a positive doped semiconductor . The method of claim 1, wherein the step of partially removing the oxide layer, the doped material layer and the deposited germanium layer in the interdigitated pattern further comprises subsequently etching the exposed germanium substrate to form a The roughened area is roughened. The method of claim 1, further comprising partially removing the wide band gap-doped semiconductor, the oxide layer and the doped material layer on the back side of the solar cell to form A series of contact openings. The method of claim 15, further comprising forming a first metal gate on the back side of the solar cell, the first metal gate being doped through the wide band gap semiconductor, The oxide layer and the series of contact openings of the dopant material layer are electrically coupled to the crystallized doped polysilicon layer. The method of claim 16, wherein the step of forming the first metal gate on the back side of the solar cell comprises forming a first metal gate comprising aluminum. The method of claim 17, further comprising forming a second metal gate on the back side of the solar cell, the second metal gate being electrically coupled to a portion of the interdigitated pattern. A method for fabricating a solar cell, the solar cell comprising a substrate having a front side and a back side opposite the front side, the front side being configured to face the sun during normal operation, and the method comprising: providing The germanium substrate has a thin dielectric layer on the back side and a deposited germanium layer over the thin dielectric layer; a doped material layer is formed over the deposited germanium layer; Forming an oxide layer thereon; partially removing the oxide layer, the doping material layer and the deposited germanium layer in an interdigitated pattern; etching the exposed germanium substrate to form a roughened germanium region; growing an oxide And simultaneously increasing the temperature to drive the dopant from the dopant material layer into the deposited germanium layer; doping the deposited germanium layer with a dopant from the dopant material layer to form a crystallized Doped polysilicon layer; And covering the back side of the solar cell with a first thick layer of a wide band gap doped amorphous germanium and an anti-reflective coating; and covering the front side of the solar cell with a wide band gap a second thin layer of doped amorphous germanium and the anti-reflective coating; wherein the thin layer is less than 30% of the thickness of the thick layer. The method of claim 19, wherein the thin layer is 10% of the thickness of the thick layer. A method for fabricating a solar cell, the solar cell comprising a substrate having a front side and a back side opposite the front side, the front side being configured to face the sun during normal operation, and the method comprising: providing The germanium substrate has a thin dielectric layer on the back side and a doped germanium layer over the thin dielectric layer; an oxide layer is formed over the doped germanium layer; Partially removing the oxide layer and the doped germanium layer; etching the exposed germanium substrate to form a roughened germanium region; by heating the germanium substrate in an oxygen-containing environment to be above the back side of the solar cell Growing a layer of oxide, wherein the doped layer is crystallized to form a doped polysilicon layer; and a broad band gap is doped amorphous on the front side and the back side of the solar cell矽 and an anti-reflective coating; Partially removing the anti-reflective coating, the wide band gap-doped amorphous germanium and the oxide layer to form a series of contact openings; and simultaneously forming a first metal gate on the back side of the solar cell And a second metal gate electrically coupled to the doped polysilicon, the second metal gate being electrically coupled to a portion of the interdigitated pattern. The method of claim 21, wherein the doped polysilicon layer comprises a negatively doped polysilicon layer. The method of claim 21, wherein the doped polysilicon layer comprises a positively doped polysilicon layer. The method of claim 21, wherein the step of depositing the anti-reflective coating on the front side and the back side of the solar cell comprises depositing tantalum nitride on the back side and the front side of the solar cell. . A method for fabricating a solar cell, the solar cell comprising a substrate having a front side and a back side opposite the front side, the front side being configured to face the sun during normal operation, and the method comprising: providing The germanium substrate has a thin dielectric layer on the back side and a doped germanium layer over the thin dielectric layer; an oxide layer is formed over the doped germanium layer; Partially removing the oxide layer and the doped germanium layer; etching the exposed germanium substrate to form a roughened germanium region; Heating the germanium substrate in an oxygen-containing environment to grow an oxide layer over the back side of the solar cell, wherein the doped germanium layer is crystallized to form a doped polysilicon layer; Depositing a broad band gap-doped amorphous germanium and an anti-reflective coating on the back side of the solar cell; and depositing a broad band gap doped amorphous germanium on the front side of the solar cell and the anti-reflection Reflective coating. The method of claim 25, wherein the doped polysilicon layer comprises phosphorus. The method of claim 25, wherein the doped polysilicon layer comprises boron. A method for fabricating a solar cell, the solar cell comprising a substrate having a front side and a back side opposite the front side, the front side being configured to face the sun during normal operation, and the method comprising: providing The germanium substrate has a thin dielectric layer on the back side and a doped germanium layer over the thin dielectric layer; an oxide layer is formed over the doped germanium layer; Partially removing the oxide layer and the doped germanium layer; by heating the germanium substrate in an oxygen-containing environment to grow an oxide layer over the back side of the solar cell, wherein the germanium oxide layer is doped The layer is crystallized to form a doped polysilicon layer; Depositing a broad band gap-doped semiconductor on the back side of the solar cell; and depositing a broad band gap doped semiconductor and an anti-reflective coating on the front side of the solar cell. The method of claim 28, wherein the step of providing the germanium substrate comprises providing a germanium substrate having an N-type body. The method of claim 28, wherein the step of providing the germanium substrate comprises providing a germanium substrate having a P-type body. The method of claim 28, wherein the step of removing the oxide layer and the doped germanium layer by the interdigitated pattern to expose an exposed region of the germanium substrate comprises using an etching process to shift The oxide layer and the doped germanium layer are removed. The method of claim 28, wherein the step of removing the oxide layer and the doped germanium layer by the interdigitated pattern to expose an exposed region of the germanium substrate comprises using an ablation process to remove The oxide layer and the doped germanium layer are removed. The method of claim 28, wherein the step of depositing the broad band gap through the doped semiconductor comprises depositing a broad band gap doped amorphous germanium. The method of claim 28, wherein the step of depositing the broad band gap through the doped semiconductor comprises depositing a semiconductor having a band gap greater than 1.05 electron volts. The method of claim 28, wherein the method is The step of depositing the anti-reflective coating on the front side of the solar cell includes depositing tantalum nitride on the front side of the solar cell. The method of claim 28, wherein the step of partially removing the oxide layer and the doped germanium layer in the interdigitated pattern further comprises subsequently etching the exposed germanium substrate to form a roughened germanium region. The method of claim 28, further comprising partially removing the wide bandgap-doped semiconductor, the oxide layer, and the doped polysilicon layer on the back side of the solar cell to A series of contact openings are formed. The method of claim 37, further comprising forming a first metal gate on the back side of the solar cell, the first metal gate being doped through the wide band gap The semiconductor and the series of contact openings of the oxide layer are electrically coupled to the doped polysilicon layer. The method of claim 38, further comprising forming a second metal gate on the back side of the solar cell, the second metal gate being electrically coupled to a portion of the interdigitated pattern. The method of claim 39, wherein the step of forming the first metal gate and the second metal gate on the back side of the solar cell comprises simultaneously forming the first metal gate and the first Two metal gates.