WO2013123818A1 - 高效三结太阳能电池及其制作方法 - Google Patents

高效三结太阳能电池及其制作方法 Download PDF

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WO2013123818A1
WO2013123818A1 PCT/CN2012/087916 CN2012087916W WO2013123818A1 WO 2013123818 A1 WO2013123818 A1 WO 2013123818A1 CN 2012087916 W CN2012087916 W CN 2012087916W WO 2013123818 A1 WO2013123818 A1 WO 2013123818A1
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cell
band gap
growth substrate
lattice constant
solar cell
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French (fr)
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毕京锋
林桂江
刘建庆
王良均
熊伟平
宋明辉
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厦门市三安光电科技有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H01L31/0687—Multiple junction or tandem solar cells
    • H01L31/06875—Multiple junction or tandem solar cells inverted grown metamorphic [IMM] multiple junction solar cells, e.g. III-V compounds inverted metamorphic multi-junction cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1892—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof methods involving the use of temporary, removable substrates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/544—Solar cells from Group III-V materials

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  • the invention relates to a high-efficiency strain-compensating three-junction solar cell and a manufacturing method thereof, and belongs to the technical field of semiconductor materials.
  • epitaxial growth of lattice-matched GaInP/GaAs/Ge triple junction solar cells on a Ge substrate is a relatively mature technology, and its photoelectric conversion efficiency is maximum without condensing conditions. Up to 41%.
  • the Ge bottom cell has a band gap of 0.66 eV and the photocurrent density Jph ⁇ 27.0 mA/cm2 under AM1.5D is a GaInP/GaAs/Ge triple junction.
  • the photocurrent of the laminated solar cell is twice, and the operating current of the multi-junction cell is determined by the battery with the shortest short-circuit current in each sub-battery, so the current mismatch makes the efficiency of the Ge-bottom cell lower.
  • the solution to this problem is to find a sub-cell with a band gap of 1 eV instead of the Ge sub-cell to achieve three-junction battery current matching.
  • the commonly used candidate material is In 0.3 Ga 0.7 As ( 1eV ), but its lattice constant does not match the GaAs substrate or the Ge substrate.
  • a gradient buffer layer is introduced, but the gradient buffer layer is Crystal quality greatly affects battery efficiency.
  • the Chinese patent application publication 'a high-efficiency three-junction solar cell with current matching and lattice matching' proposes the use of strain-compensated superlattice as a sub-cell to achieve current matching and lattice matching, but
  • the energy band gap distribution of each sub-pool is 1.65 ⁇ 1.75eV/1.0eV/0.67eV, which is only the second best choice for capturing solar spectrum.
  • the conversion rate of solar cells is limited, and the expensive Ge substrate is used, which is costly.
  • Emcore Solar Power, Inc. proposed InGP/GaAs/InGaAs, a flip-chip deformed multi-junction solar cell that satisfies the above-mentioned band gap distribution, but the flip-chip growth process is complicated, and the subsequent process is more complicated and greatly limited. The application of this technology in industry.
  • the present invention proposes an efficient triple junction solar cell and a method of fabricating the same.
  • the band gap distribution of the three-junction solar cell satisfies the best choice for capturing the solar spectrum, and the current matching and lattice matching effectively improve the photoelectric conversion efficiency of the three-junction solar cell;
  • a high efficiency three-junction solar cell comprising: a growth substrate having two polishing surfaces; a bottom cell composed of a strain-compensated superlattice structure, flip-chip grown on a growth substrate a back surface having a first band gap whose equivalent lattice constant matches the lattice constant of the growth substrate; a middle cell formed on the front surface of the growth substrate having a second band gap greater than the first band gap, The lattice constant is matched to the green substrate; the top cell is formed over the middle cell having a third band gap greater than the second band gap and the lattice constant is matched to the medium cell lattice constant.
  • the growth substrate is an ultra-thin substrate which is double-sided polished, and a p-type GaAs having a thickness of 200 to 250 ⁇ m may be selected.
  • the middle battery has a growth substrate as a base region and a band gap of 1.4 to 1.5 eV.
  • the top cell material is InGaP with a band gap of 1.8 ⁇ 1.9eV.
  • the bottom battery has a band gap of 0.9eV ⁇ 1.1 eV, the equivalent lattice constant is 5.65 ⁇ ⁇ 5.66 ⁇ ; the material of the emitter is GaAs, and the base is compensated by GaAsP/GaAs/GaInAs Superlattice composition, equivalent lattice constant matched to GaAs.
  • the thickness of the barrier layer GaAsP is 5-10 nm;
  • the GaAs isolation layer is very thin, and its thickness is less than 5 nm, which acts as a buffer stress and adjusts the lattice constant.
  • the In component of the GaInAs battery is 0.3 to 0.4, preferably 0.3. .
  • a distributed Bragg reflection layer may be disposed under the bottom cell.
  • the underside of the high-efficiency triple junction solar cell ie, under the bottom cell) can be bonded to a supporting substrate for increasing the mechanical strength of the battery.
  • a method for fabricating a highly efficient three-junction solar cell the specific steps of: providing a growth substrate having two sides thereof for polishing; forming a battery in a front surface of the growth substrate, A first band gap is formed thereon; a top cell is formed over the middle cell having a second band gap greater than the first band gap, and a lattice constant is matched with a medium cell lattice constant; The back side forms a bottom cell which is composed of a stress compensated superlattice structure and whose equivalent lattice constant matches the lattice constant of the middle and top cells.
  • the growth substrate is an ultra-thin substrate which is double-sided polished, and a p-type GaAs having a thickness of 200 to 250 ⁇ m may be selected.
  • the middle battery is formed by using a growth substrate as a base region, and an emitter region is formed on the upper surface thereof, and the band gap is 1.4 to 1.5 eV.
  • the top cell is epitaxially deposited on the surface of the middle cell, and the material thereof is InGaP Bandgap is 1.8 ⁇ 1.9eV .
  • the back surface of the growth substrate is annealed prior to forming the bottom cell.
  • a material of a predetermined thickness homogenous to the growth substrate is epitaxially grown on the back surface of the growth substrate to obtain a smooth surface, and the material layer of the bottom cell is epitaxially grown to form a bottom cell.
  • the growth substrate is subjected to double-sided growth of the sub-battery material layer, and the thickness of the substrate is required to be not too thick and double-side polishing treatment is required.
  • the method of double-sided growth is based on the principle of minimizing the contamination of the grown structure by external factors, and inverting the substrate containing the completed growth structure in situ, and then starting the growth of the other surface structure. In situ annealing under anion source protection is performed before the other side begins to grow. Annealing temperature is controlled at 600 ⁇ 700 °C, its function is to drive off the oxide layer and impurity adsorption layer of the growth surface (the back side of the original substrate) after the flipping. Thereafter, the growth of the homogenous material with the substrate is performed after growing a certain thickness (about 200 to 500 nm). A smooth surface can be obtained, which is a guarantee for the high crystal quality extension of the reverse structure.
  • the invention has the beneficial effects that on the special ultra-thin double-sided polished substrate, the sub-cells with different band gaps are deposited on the two sides of the substrate in a high-to-low order, the middle and the top batteries and the double-sided growth substrate.
  • Substrate lattice matching; the bottom cell is grown by strain compensation structure, and its effective band gap is about 1.0 eV, the effective lattice constant is lattice matched to the substrate and the middle and bottom cells.
  • DBR under the bottom battery The layer can effectively reflect the transmitted photons to reabsorb, reduce dark current and improve conversion efficiency. Supporting the substrate can increase the mechanical strength of the battery and reduce the fragmentation rate.
  • the invention can effectively configure the band gap of each sub-battery, and the spectral absorption is sufficient and reasonable, and a high-efficiency strain-compensating triple junction solar cell with lattice matching, current matching and high lattice quality of each sub-cell is formed.
  • the special double-sided growth process effectively overcomes the cumbersome process brought by the existing flip-chip manufacturing method, improves the product yield, reduces the production cost, and vigorously promotes the practical application of the high-efficiency solar battery.
  • FIG. 1 is a schematic view showing the structure of an efficient triple junction solar cell according to an embodiment of the present invention.
  • 010 growth substrate; 020: support substrate; 100: bottom battery; 110: bottom battery back field layer; : bottom battery base; 130: bottom battery emitter; 140: bottom battery window; 200: medium battery; 210: medium battery back field; 220: medium battery base; : medium battery emission area; 240: medium battery window layer; 310: top battery back field layer; 320: top battery base area; 330: top battery emission area; 340: top battery window layer; : bottom, neutron cell tunneling junction; 410: medium and top cell tunneling junction; 500: highly doped cap layer; 600: DBR reflective layer.
  • the embodiments of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, in which the present invention can be applied to the technical problems, and the implementation of the technical effects can be fully understood and implemented. It should be noted that the various embodiments of the present invention and the various features of the various embodiments may be combined with each other, and the technical solutions formed are all within the scope of the present invention. It should be particularly noted here that the 'ultra-thin substrate' is repeatedly mentioned in the present invention, which is generally thicker than the conventional substrate in the prior art. Above 450 microns, the growth substrate used in the present invention has a thickness of 200 to 250 microns.
  • FIG. 1 is a schematic view showing the structure of an efficient triple junction solar cell according to an embodiment of the present invention.
  • an efficient triple junction solar cell includes a support substrate 020 and a DBR reflective layer 600.
  • the bottom battery 100, the middle battery 200, the top battery 300, the highly doped cap layer 500, and the junction batteries are connected by tunneling junctions 410, 420.
  • the bottom battery 100 The pour is grown on the back side of the growth substrate 010, and the middle cell has the growth substrate 010 itself as the base region 220, and the emission region 230
  • the epitaxial growth is on the front side of the growth substrate, and the top cell is formed on the middle cell. The specific structure will be described in detail below.
  • the growth substrate 010 is an ultra-thin substrate which is subjected to double-side polishing.
  • a p-type GaAs substrate having a thickness of about 200 ⁇ m is selected, and its doping concentration is 2 ⁇ 10 17 cm -3 to 5 ⁇ 10 17 cm -3 .
  • the middle battery 200 is formed on the growth substrate, and includes a back field layer 210, a base region 220, and an emission region 230.
  • the window layer 240 has a band gap of 1.4 to 1.5 eV.
  • the junction cell 200 has a growth substrate 010 as a base region 220 and a back field layer 210 formed in a base region 010.
  • the lower side i.e., the back side of the growth substrate
  • the emitter region 230 is formed on the front surface of the growth substrate 010 with a thickness of preferably 100 nm; the window layer 240 is formed in the emitter region 230.
  • the material is n-type InAlP with a thickness of 25 nm and a doping concentration of about 1 ⁇ 1018 cm-3.
  • the top cell 300 is formed above the middle cell 200, and includes a back field layer 310, a base region 320, an emitter region 330, and a window layer 340, with a band gap of 1.4 to 1.5 eV.
  • the material of the back field layer 310 is p-AlGaInP
  • the thickness is 50 nm
  • the doping concentration is 1 ⁇ 2 ⁇ 10 18 cm -3
  • the material of the base region 320 is p-In 0.485 Ga 0.515 P
  • the strip The gap is 1.89 eV
  • the thickness is 2 microns
  • the gradient doping method is used
  • the concentration is 1 ⁇ 5 ⁇ 10 17 cm -3
  • the material of the emitter region 330 is n+- In 0.485 Ga 0.515 P
  • the thickness is 100nm
  • the doping concentration is about 2 ⁇ 10 18 cm -3
  • the material of the window layer 340 is n-type InAlP, the thickness of which is 25 nm, and the do
  • the middle and top batteries are connected by the middle and top sub-cell tunneling junctions 420.
  • the material of the tunneling junction 420 is heavily doped p++/n++-InGaP with a total thickness of about 50 nm and a doping concentration of 2 ⁇ 10 19 cm -3 .
  • the bottom cell 100 is epitaxially grown under the middle cell 200 (ie, the back side of the growth substrate), and includes a back field layer 110, a base region 120, an emitter region 130, and a window layer 140 with a band gap of 0.9 eV. ⁇ 1.0eV.
  • the base region 120 is composed of a p-type GaAsP/GaAs/GaInAs superlattice, and a desired lattice constant and a forbidden band width can be obtained by changing the composition and the thickness of the quantum well GaInAs, thereby obtaining a 1 eV subcell.
  • the effective bandgap of the strain-compensated GaAsP/GaAs/GaInAs superlattice is adjusted to be around 1.01eV according to the composition of In in GaInAs.
  • the composition and thickness of the GaAsP barrier can be selected to make the whole
  • the superlattice equivalent lattice constant ⁇ a> matches GaAs.
  • the relationship between the band gap of GaInAs and the composition of In at room temperature, and the above equivalent lattice constant are calculated as follows:
  • E GaInAs is the GaInAs band gap
  • x In is the composition of In
  • t w and a GaInAs are the thickness and lattice constant of the GaInAs quantum well, respectively
  • t b and a GaAsP are the GaAsP barrier thickness and the lattice constant, respectively.
  • the lattice constant a GaInAs of GaInAs varies with the composition of In
  • the lattice constant of GaAsP a GaAsP as a function of As composition is calculated as follows (unit ⁇ ):
  • the window layer 140 is composed of n-type InP having a thickness of 40 nm and a doping concentration of about 1 ⁇ 10 18 cm -3 .
  • the emitter region 130 is composed of n-type GaAs having a thickness of 100 nm and a doping concentration of 2 ⁇ 10 18 cm -3 .
  • the base region 120 has a total thickness of 3.2 microns and a doping concentration of 1 ⁇ 10 16 cm -3 to 1 ⁇ 10 17 cm -3 , which is compensated by 200 cycles of superlattice GaAs 1-y P y / GaAs /Ga 1-x In x As constitutes.
  • the thickness of the isolation layer GaAs is very high. Thin (less than 5nm), which acts as a buffer stress and adjusts the lattice constant; the In composition of the quantum well Ga 1-x In x As is 0.3 to 0.4, preferably 0.3, and its lattice constant is 5.9368 ⁇ , quantum The well width is 8 nm.
  • the strained superlattice has an effective lattice constant of 5.666 ⁇ and an effective band gap of 1.01 eV.
  • the back field layer 110 is composed of p-type GaAs having a thickness of 50 nm and a doping concentration of 1 to 2 ⁇ 10 18 cm -3 .
  • the middle and bottom batteries are connected by a middle and top cell tunneling junction 410.
  • the material of the tunnel junction 410 is P++/n++-InP, which has a thickness of 50 nm and a doping concentration of up to 2 ⁇ 10 19 cm -3 .
  • a Distributed Bragg Reflector (DBR) 600 is located below the bottom cell 100 and is composed of a variable composition Al x Ga 1-x As superlattice whose lattice constant matches the growth substrate 010.
  • DBR Distributed Bragg Reflector
  • a 20-cycle AlAs/Al Z Ga 1-Z As superlattice is selected as the DBR layer, and the Al composition in AlGaAs is selected to be 0.15.
  • the DBR layer can effectively reflect the transmitted photons to reabsorb, reduce dark current and improve conversion efficiency.
  • Support substrate 020 Located below the distributed Bragg reflector layer, it is the bottom end of the solar cell, which is used to support the structure of the solar cell, improve the mechanical strength of the battery, and reduce the fragmentation rate.
  • silicon is selected as the supporting substrate 020 s material.
  • a GaAs sub-battery (medium cell) is formed by growing a substrate with GaAs, and the band gap is 1.4 ⁇ 1.5eV; forming an InGaP subcell (top cell) lattice-matched to the growth substrate on the GaAs subcell, the band gap of which is on the back side of the GaAs grown substrate 1.8 ⁇ 1.9eV; epitaxial inverted growth strain compensation on the back side of GaAs growth substrate GaAsP/GaAs/GaInAs superlattice as the base of the bottom cell. Strain compensation The GaAsP/GaAs/GaInAs superlattice can obtain the required lattice constant and band gap by changing the composition and changing the thickness of the quantum well GaInAs to obtain a 1eV subcell.
  • This embodiment is a preparation process of an efficient three-junction solar cell described in Example 1, which includes sub-batteries 100, 200, and 300. And the formation process of each layer between each sub-battery.
  • the specific preparation process includes the following steps:
  • a growth substrate 010 is provided.
  • the growth substrate 010 is an ultra-thin substrate which is subjected to double-side polishing.
  • a p-type GaAs substrate having a thickness of about 200 ⁇ m is selected, and its doping concentration is 2 ⁇ 10 17 cm -3 to 5 ⁇ 10 17 cm -3 .
  • a neutron cell 020 is formed on the front surface of the growth substrate 010 with a band gap of 1.4 to 1.5 eV.
  • the specific process is as follows: in the MOCVD system, the double-sided polished GaAs substrate 010 is used as the middle battery base region 220, and the n-type emitter region 230 is epitaxially grown on the surface of the substrate, and the band gap is 1.42 eV, and the thickness is preferably 100 nm; an n-type InAlP material layer is grown on the emitter region 230 as a window layer 240 having a thickness of 25 nm and a doping concentration of about 1 ⁇ 10 18 cm -3 .
  • heavily doped p++-InGaP/n++-InGaP is epitaxially grown over the middle cell 200 as a tunnel junction 420 having a total thickness of 50 nm and a doping concentration of up to 2 ⁇ 10 19 cm -3 .
  • a top cell 300 is formed over the tunnel junction 420, which includes a back field layer 310, a base region 320, an emitter region 330, and a window layer 340, with a band gap of 1.4 to 1.5 eV.
  • the specific process is as follows: a p-type AlGaInP material layer is grown as a back field layer 310 above the tunneling junction 420, having a thickness of 50 nm, a doping concentration of 1 to 2 ⁇ 10 18 cm -3 , and growth over the back field layer 310.
  • the p-type In 0.485 Ga 0.515 P material layer has a band gap of 1.89 eV and a thickness of 2 ⁇ m, a graded doping method with a concentration of 1 to 5 ⁇ 10 17 cm -3 , and an n - type In 0.485 Ga grown above the base region 320 .
  • the 0.515 P material layer serves as an emitter region 330 having a thickness of 100 nm and a doping concentration of about 2 ⁇ 10 18 cm -3 ; an n-type InAlP material layer is grown on the emitter region 330 as a window layer 340 having a thickness of 25 nm.
  • the impurity concentration is around 1 ⁇ 10 18 cm -3 .
  • a heavily doped n++-InAlAsP material layer is grown over the top cell 300 as a capping layer 500 having a thickness of 1000 nm and a doping concentration of 1 ⁇ 10 19 cm -3 .
  • the back side is annealed.
  • the substrate is first inverted in situ, and an in situ annealing is performed under the protection of an anion source.
  • the annealing temperature is controlled at 600 ⁇ 700. °C, its function is to drive off the oxide layer and the impurity adsorption layer of the growth surface (the back surface of the original substrate) after the inversion.
  • the growth of the homogenous material with the substrate is performed on the back surface of the growth substrate, after a certain thickness is grown (generally 200 to 500 nm) A smooth surface is obtained, which is a guarantee for the high crystal quality extension of the reverse structure.
  • the back field layer 210 has a thickness of 100 nm and a doping concentration of 1 ⁇ 2 ⁇ 10 18 Cm -3 .
  • the heavily doped P++/n++-InP is epitaxially grown under the back surface layer 210 of the middle cell.
  • the material layer acts as a tunneling junction 410 with a thickness of 50 nm and a doping concentration of up to 2 ⁇ 10 19 Cm -3 .
  • the bottom cell 100 is poured under the tunneling junction 410, and the bottom-up includes: the back-field layer 110, the base region 120, the emission area 130, the window layer 140, the band gap is 0.9eV ⁇ 1.0eV.
  • the specific process is as follows: epitaxial growth of n-type InP under tunneling junction 500
  • the material layer serves as a window layer 140 having a thickness of 40 nm and a doping concentration of approximately 1 ⁇ 10 18 Cm -3 ; at the window level 140
  • An n-type GaAs material layer is epitaxially grown as an emitter region 130 having a thickness of 100 nm and a doping concentration of 2 ⁇ 10 18 Cm -3 ; strain compensation for epitaxial growth under the emitter 130 GaAs 1-y P y /Ga 1-x In x
  • the As superlattice structure serves as the base region 120.
  • doping concentration is 1 ⁇ 2 ⁇ 10 18 Cm -3 .
  • base 120 is compensated by a 200-cycle strained superlattice GaAs 1-y P y /Ga 1-x In x
  • the strained superlattice has an effective lattice constant of 5.666 ⁇ and an effective band gap of 1.01 eV.
  • the total thickness of the strained superlattice base is 3.2 Micron
  • doping concentration is 1 ⁇ 10 16 Cm -3 ⁇ 1 ⁇ 10 17 Cm -3 .
  • AlAs/AlGaAs superlattice are epitaxially grown under the bottom cell back field layer 110 as DBR.
  • the Al composition in AlGaAs was chosen to be 0.15.
  • the support substrate is bonded by metal bonding to increase the mechanical strength of the overall sample.
  • Support substrate can be used Si.
  • the surface of the sample is subjected to anti-reflection film evaporation, metal electrode preparation and other post-processes to complete the required solar cells.
  • the invention effectively selects materials and adopts double-sided growth technology, so that the solar cell solves the problem of lattice matching and current matching between the sub-cells while obtaining the best energy band gap.
  • the special double-sided growth process effectively overcomes the cumbersome process brought about by the late flip-chip growth, improves the product yield, reduces the production cost, and vigorously promotes the practical application of the high-efficiency solar battery.

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Abstract

一种高效三结太阳能电池及其制作方法。高效三结太阳能电池包括：生长衬底（010），其具有两个抛光表面；底电池（100），由应变补偿超晶格结构构成，倒装生长于生长衬底（010）的背面，具有第一带隙，等效晶格常数与生长衬底（010）的晶格常数匹配；中电池（200），形成于生长衬底（010）正面上，具有大于第一带隙的第二带隙，晶格常数与生长衬底（010）匹配；顶电池（300），形成于中电池（200）上，具有大于第二带隙的第三带隙，晶格常数与中电池（200）晶格常数匹配。如此三结太阳能电池的能带隙分布满足了捕获太阳能光谱的最佳选择，且电流匹配和晶格匹配，有效提高了三结太阳能电池的光电转换效率。其制作方法采用生长衬底双面生长的方式，克服倒装生长后期带来的繁琐工艺，提高了产品良率。

Description

高效三结太阳能电池及其制作方法
本申请要求于 2012 年2月21日 提交中国专利局、申请号为201210038878.5、发明名称为“高效三结太阳能电池及其制作方法 ”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及一种高效应变补偿三结太阳能电池及其制作方法，属半导体材料技术领域。
背景技术
近年来，太阳能电池作为实用的新能源，吸引了越来越多的关注。它是一种利用光生伏打效应将太阳能转化成电能的半导体器件，这在很大程度上减少了人们生产生活对煤炭、石油及天然气的依赖，成为利用绿色能源的最有效方式之一。随着聚光光伏技术的发展，Ⅲ - Ⅴ族化合物半导体太阳能电池因其高光电转换效率而越来越受到关注。
目前，制约Ⅲ - Ⅴ族化合物半导体太阳能电池产业发展的主要障碍之一是其组件成本高，最终导致太阳能发电的成本较高。降低太阳能电池发光成本的最关键在于进一步提高太阳电池的光电转换效率。影响多三结 III-V 族太阳能电池的光电转换效率的主要因素包括：晶格匹配、电流匹配和能带隙分布。多结Ⅲ - Ⅴ族太阳能电池各子电池短路电流越接近（匹配程度越高），对光谱的利用程度也就越高，对于三结或三结以上的太阳能电池，最高效率材料组合均需要带隙在 1.0eV 附近的材料来满足电流匹配条件。
对于Ⅲ - Ⅴ族化合物半导体领域来言，在 Ge 衬底上外延生长晶格匹配的 GaInP/GaAs/Ge 三结太阳能电池是一项比较成熟的技术，其在无聚光条件下光电转换效率最大达 41% 。在晶格匹配的 GaInP/GaAs/Ge 三结太阳电池中， Ge 底电池带隙为 0.66eV ， AM1.5D 条件下，其光电流密度 Jph ≈ 27.0mA/cm2 ，为 GaInP/GaAs/Ge 三结叠层太阳电池光电流的两倍，而多结电池的工作电流由各子电池中短路电流最小的电池决定，因此电流不匹配使得 Ge 底电池效率降低。解决这一问题的方法就是寻找带隙为 1 eV 的子电池来取代 Ge 子电池，实现三结电池电流匹配。普遍采用的候选材料是 In0.3Ga0.7As （ 1eV ），但其晶格常数与 GaAs 衬底或者 Ge 衬底不匹配，为了克服这一晶格失配要引入渐变缓冲层，但是渐变缓冲层的晶体质量极大地影响着电池效率。中国专利申请公开案'一种电流匹配和晶格匹配的高效率三结太阳电池'（申请号 CN200910019869.X ）提出了应用应变补偿超晶格作为子电池实现了电流匹配和晶格匹配，但其各子池的能带隙分布为 1.65~1.75eV/1.0eV/0.67eV ，仅为捕获太阳光谱的次佳选择，太阳能电池转换率有限，且用昂贵的 Ge 衬底，成本较高。
理论上，三结太阳能电池的能带隙分布为 1.8~1.9eV/1.2~1.5eV/0.9~1.0eV 为捕获太阳能光谱的最佳选择，其转化效率会更高。安科太阳能公司（ Emcore Solar Power, Inc ）提出了倒装变形多结太阳能电池 InGaP/GaAs/InGaAs ，其满足了上述能带隙分布，但倒装生长过程复杂，后续的工艺更加复杂，大大限制了这项技术在工业上的应用。
发明内容
针对现在技术中的上述问题，本发明提出了一种高效三结太阳能电池及其制作方法。该三结太阳能电池的能带隙分布满足了捕获太阳能光谱的最佳选择，且电流匹配和晶格匹配，有效提高了三结太阳能电池的光电转换效率；其制作方法采用生长衬底双面生长的方式，克服倒装生长后期带来的繁琐工艺，提高了产品良率。
根据本发明的一方面，提供了一种高效三结太阳能电池，其包括：生长衬底，其具有两个抛光表面；底电池，由应变补偿超晶格结构构成，倒装生长于生长衬底的背面，具有一第一带隙，其等效晶格常数与生长衬底的晶格常数匹配；中电池，形成于生长衬底正面上，其具有大于第一带隙的第二带隙，其晶格常数与生底衬底匹配；顶电池，形成于中电池之上，其具有一大于第二带隙的第三带隙，且晶格常数与中电池晶格常数匹配。
在本发明中，生长衬底为经双面抛光处理的超薄衬底，可选用 p 型厚度为 200~250 微米的 GaAs 衬底。所述中电池以生长衬底为基区，其带隙为 1.4~1.5eV 。顶电池的材料为 InGaP ，其带隙为 1.8~1.9eV 。底电池的带隙为 0.9eV ～ 1.1 eV, 等效晶格常数为 5.65 Å ～ 5.66 Å ；发射区的材料为 GaAs ，基区由应变补偿 GaAsP/GaAs/GaInAs 超晶格构成，等效晶格常数与 GaAs 匹配。应变补偿 GaAsP/GaAs/GaInAs 超晶格中，势垒层 GaAsP 的厚度为 5 ～ 10nm ；中间的 GaAs 隔离层很薄，其厚度小于 5nm ，起到缓冲应力，调整晶格常数的作用； GaInAs 电池的 In 组份为 0.3 ～ 0.4 ，优选值为 0.3 。进一步地，可在底电池的下方设置分布式布拉格反射层。前述高效三结太阳能电池的下方（即底电池的下方）可键合一支撑衬底，用以增加电池的机械强度。
根据本发明的另一方面，提供了一种高效三结太阳能电池制备方法，其具体步骤包括：提供生长衬底，其两个面作抛光处理；在所述生长衬底正表面形成中电池，其具有第一带隙；在所述中电池之上形成顶电池，其具有一大于第一带隙的第二带隙，且晶格常数与中电池晶格常数匹配；在所述生衬底的背面形成底电池，其由应力补偿超晶格结构构成，且其等效晶格常数与中、顶电池的晶格常数匹配。
在本发明中，生长衬底为经双面抛光处理的超薄衬底，可选用 p 型厚度为 200~250 微米的 GaAs 衬底。所述中电池以生长衬底为基区，在其上表面形成发射区构成，其带隙为 1.4~1.5eV 。所述顶电池通过外延沉积在中电池的表面上，其材料为 InGaP ，带隙为 1.8~1.9eV 。在形成底电池前，对所述生长衬底背面进行退火处理。完成退火后，在所述生长衬底背面上外延生长预定厚度的与生长衬底同质的材料，获得平滑表面，继续外延生长底电池的材料层，形成底电池。
在本制作方法中，在生长衬底进行双面生长子电池材料层，要求衬底的厚度不能太厚且需进行双面抛光处理。双面生长的方法以最大限度的降低外界因素对已生长结构污染为原则，将包含已完成生长结构的衬底进行原位翻转，然后开始另一面结构的生长。在另一面生长开始前要进行阴离子源保护下的原位退火。退火温度控制在 600~700 ℃，其作用是驱除翻转后生长面（原衬底背面）的氧化层和杂质吸附层。此后进行与衬底同质材料的生长，在生长一定厚度后（约 200~500 nm ）可以获得平滑的表面，这是反面结构高晶体质量外延的保障。
本发明的有益效果为：在特制超薄双面抛光衬底上，采用双面生长的方法，将带隙不同的子电池按照由高到低的顺序沉积于衬底两面，中、顶电池与衬底晶格匹配；底电池采用应变补偿结构生长，其有效带隙约为 1.0eV ，有效晶格常数与衬底和中、底电池晶格匹配。底电池下方的 DBR 层能够有效地反射透过的光子产生重新吸收，降低暗电流，提高转化效率。支撑衬底能够提高电池的机械强度，降低破片率。通过本发明能够有效配置各子电池的带隙，光谱吸收充分且合理，形成了各子电池晶格匹配、电流匹配、高晶格质量的高效应变补偿三结太阳能电池。本发明的制作方法中，特殊的双面生长工艺，有效地克服现有倒装制作方法后期带来的繁琐工艺，提高了产品良率，降低生产成本，大力推进高效太阳能电池的实际应用。
本发明的其它特征和优点将在随后的说明书中阐述，并且，部分地从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他优点可通过在说明书、权利要求书以及附图中所特别指出的结构来实现和获得。
虽然在下文中将结合一些示例性实施及使用方法来描述本发明，但本领 域技术人员应当理解，并不旨在将本发明限制于这些实施例。反之，旨在覆盖包含在所附的权利要求书所定义的本发明的精神与范围内的所有替代品、修正及等效物。
附图说明
附图用来提供对本发明的进一步理解，并且构成说明书的一部分，与本发明的实施例一起用于解释本发明，并不构成对本发明的限制。此外，附图数据是描述概要，不是按比例绘制。
图 1 是根据本发明实施的一种高效三结太阳能电池的结构示意图。
图中各标号表示：
010 ：生长衬底； 020 ：支撑衬底； 100 ：底电池； 110 ：底电池背场层； 120 ：底电池基区； 130 ：底电池发射区； 140 ：底电池窗口层； 200 ：中电池； 210 ：中电池背场层； 220 ：中电池基区； 230 ：中电池发射区； 240 ：中电池窗口层； 310 ：顶电池背场层； 320 ：顶电池基区； 330 ：顶电池发射区； 340 ：顶电池窗口层； 400 ：底、中子电池隧穿结； 410 ：中、顶子电池隧穿结； 500 ：高掺杂盖帽层； 600 ： DBR 反射层。
具体实施方式
以下将结合附图及实施例来详细说明本发明的实施方式，借此对本发明如何应用技术手段来解决技术问题，并达成技术效果的实现过程能充分理解并据以实施。需要说明的是，只要不构成冲突，本发明中的各个实施例以及各实施例中的各个特征可以相互结合，所形成的技术方案均在本发明的保护范围之内。在此应特别注意地是，在本发明中多次提及'超薄衬底'，其是相对现有技术中的普通衬底而言，普通生长衬底的厚度一般为 450 微米以上，而本发明涉用到的生长衬底的厚度为 200~250 微米。
实施例一
图 1 为根据本发明实施的一种高效三结太阳能电池的结构示意图。
如图 1 所示，一种高效三结太阳能电池，包括支撑衬底 020 ， DBR 反射层 600 ，底电池 100 ，中电池 200 ，顶电池 300 ，高掺杂盖帽层 500 ，各结子电池之间通过隧穿结 410 、 420 连接。其中，底电池 100 倒生长在生长衬底 010 的背面上，中电池以生长衬底 010 本身作为基区 220 ，发射区 230 外延生长于生长衬底的正面上，顶电池形成于中电池之上。以下对其具体结构进行详细描述。
生长衬底 010 为经双面抛光处理的超薄衬底。在本发明中，在本实施中，选用 p 型厚度约为 200 微米的 GaAs 衬底，其掺杂浓度为在 2 × 1017cm-3 ~5 × 1017cm-3 。
中电池 200 形成于生长衬底上，其到下而上包括：背场层 210 、基区 220 、发射区 230 、窗口层 240 ，带隙为 1.4~1.5eV 。本结子电池 200 以生长衬底 010 作为基区 220 ，背场层 210 形成于基区 010 的下方（即生长衬底的背面）；发射区 230 形成于生长衬底 010 的正面上，其厚度为优选值为 100 nm ；窗口层 240 形成于发射区 230 上，其材料为 n 型 InAlP ，厚度为 25 nm ，掺杂浓度在 1 × 1018cm-3 左右。
顶电池 300 形成于中电池 200 的上方，其至下而上包括：背场层 310 、基区 320 、发射区 330 、窗口层 340 ，带隙为 1.4~1.5eV 。在本实施例中，背场层 310 的材料为 p-AlGaInP ，厚度为 50nm ，掺杂浓度为 1~2 × 1018cm-3 ；基区 320 的材料 p-In0.485Ga0.515P ，其带隙为 1.89 eV ，厚度为 2 微米，采用渐变掺杂方式，浓度 1~5 × 1017cm-3 ；发射区 330 的材料为 n+- In0.485Ga0.515P ，其厚度为 100nm ，掺杂浓度大约 2 × 1018cm-3 ；窗口层 340 的材料为 n 型 InAlP ，其厚度为 25 nm ，掺杂浓度在 1 × 1018cm-3 左右。
中、顶电池通过中、顶子电池隧穿结 420 连结。在本实施例中，隧穿结 420 的材料为重掺杂的 p++/n++-InGaP ，总厚度约 50 nm ，掺杂浓度为 2 × 1019cm-3 。
底电池 100 通过外延生长于中电池 200 的下方（即生长衬底的背面），其到下而上包括：背场层 110 、基区 120 、发射区 130 、窗口层 140 ，带隙为 0.9eV ～ 1.0eV 。基区 120 由 p 型 GaAsP/GaAs/GaInAs 超晶格组成，可以通过组分和量子阱 GaInAs 厚度的改变来获得需要的晶格常数和禁带宽度，从而获得 1eV 子电池。应变补偿 GaAsP/GaAs/GaInAs 超晶格的有效带隙根据 GaInAs 中 In 的组分调整在 1.01eV 附近，确定了 GaInAs 的组分和厚度之后，通过选择 GaAsP 势垒的组分和厚度可以使得整个超晶格等效晶格常数 <a> 与 GaAs 匹配。室温下 GaInAs 的带隙与 In 的组分的关系、以及上述等效晶格常数的计算公式如下：
E GaInAs = 1.42-1.49x In + 0.43x In 2 (eV) 　　（ 1 ）
Figure PCTCN2012087916-appb-I000001
其中， E GaInAs 为 GaInAs 带隙， x In 为 In 的组分， t w 和 a GaInAs 分别为 GaInAs 量子阱的厚度和晶格常数， t b 和 a GaAsP 分别为 GaAsP 势垒厚度和晶格常数。 GaInAs 的晶格常数 a GaInAs 随 In 组分的变化关系，以及 GaAsP 的晶格常数 a GaAsP 随 As 组分的变化关系计算公式如下（单位 Å ）：
a GaInAs =5.6533+0.405x In （ 3 ）
a GaAsP =5.4505+0.20275x As （ 4 ）
在本实施例中，窗口层 140 由 n 型 InP 构成，其厚度为 40 nm ，掺杂浓度大约 1 × 1018cm-3 。发射区 130 由 n 型 GaAs 组成，厚度为 100 nm ，掺杂浓度为 2 × 1018cm-3 。基区 120 基区总厚度为 3.2 微米，掺杂浓度为 1 × 1016cm-3 ～ 1 × 1017cm-3 ，其由 200 个周期的应变补偿超晶格 GaAs 1-y P y / GaAs/Ga 1-x In x As 构成。势垒层 GaAs 1-y P y 中 P 组分为 y= 0.3 ，其晶格常数可为 5.65 Å ～ 5.66 Å ，优选值为 5.5113Å ，势垒层厚度为 8 nm ；隔离层 GaAs 的厚度很薄（小于 5nm ），起到缓冲应力、调整晶格常数的作用；量子阱 Ga 1-x In x As 中 In 组份为 0.3 ～ 0.4 ，优选值为 0.3 ，其晶格常数是 5.9368 Å ，量子阱宽度为 8 nm 。应变超晶格的有效晶格常数为 5.666 Å ，有效带隙为 1.01eV 。背场层 110 由 p 型 GaAs 构成，其厚度为 50 nm ，掺杂浓度为 1~2 × 1018cm-3 。
中、底电池通过中、顶子电池隧穿结 410 连结。在本实施例中，隧穿结 410 的材料为 P++/n++-InP 构成，其厚度为 50 nm ，掺杂浓度高达 2 × 1019cm-3 。
分布式布拉格反射层（ Distributed Bragg Reflector ， DBR ） 600 位于底电池 100 的下方，由变组分 Al x Ga 1-x As 超晶格构成，其晶格常数与生长衬底 010 匹配。在本实施例中，选用 20 个周期的 AlAs/Al Z Ga 1-Z As 超晶格作为 DBR 层， AlGaAs 中 Al 组分选择为 0.15 。 DBR 层能够有效地反射透过的光子产生重新吸收，降低暗电流，提高转化效率。
支撑衬底 020 位于分布式布拉格反射层的下方，为太阳能电池的最底端，用于支撑太阳能电池的结构，提高电池的机械强度，降低破片率。在本实施例中，选用硅作为支撑衬底 020 的材料。
在本实施中的高效三结太阳能电池，以 GaAs 生长衬底以基区，形成 GaAs 子电池（中电池），其带隙为 1.4~1.5eV ；在 GaAs 子电池上形成与生长衬底晶格匹配的 InGaP 子电池（顶电池），其生 GaAs 生长衬底背面上，其带隙为 1.8~1.9eV ；在 GaAs 生长衬底的背面外延倒生长应变补偿 GaAsP/GaAs/GaInAs 超晶格作为底电池的基区。应变补偿 GaAsP/GaAs/GaInAs 超晶格，可以通过组分改变和量子阱 GaInAs 厚度的改变来获得需要的晶格常数和禁带宽度，从而获得 1eV 子电池。
实施例二
本实施例为实例一中所述的一种高效三结太阳能电池的制备工艺，其包括子电池 100 、 200 、 300 、及各子电池之间各层的形成工艺。
具体制备工艺包括如下步骤：
第一步，提供一生长衬底 010 。生长衬底 010 为经双面抛光处理的超薄衬底。在本实施中，选用 p 型厚度约为 200 微米的 GaAs 衬底，其掺杂浓度为在 2 × 1017cm-3 ~5 × 1017cm-3 。
下一步，在生长衬底 010 的正表面形成中子池 020 ，带隙为 1.4~1.5eV 。其具体工艺如下：在 MOCVD 系统中，以上述双面抛光的 GaAs 衬底 010 作为中电池基区 220 ，在衬底表面外延生长 n 型发射区 230 ，其带隙为 1.42 eV ，厚度优选值为 100 nm ；在发射区 230 上面生长 n 型 InAlP 材料层作为窗口层 240 ，其厚度为 25 nm ，掺杂浓度在 1 × 1018cm-3 左右。
下一步，在中电池 200 的上方外延生长重掺杂的 p++-InGaP /n++-InGaP 作为隧穿结 420 ，其总厚度是 50 nm ，掺杂浓度高达 2 × 1019cm-3 。
下一步，在隧穿结 420 上方形成顶电池 300 ，其至下而上包括：背场层 310 、基区 320 、发射区 330 、窗口层 340 ，带隙为 1.4~1.5eV 。其具体工艺如下：在隧穿结 420 上方生长 p 型 AlGaInP 材料层作为背场层 310 ，其厚度为 50 nm ，掺杂浓度为 1~2 × 1018cm-3 ；在背场层 310 上方生长 p 型 In0.485Ga0.515P 材料层作为其带隙为 1.89 eV ，厚度为 2 微米，采用渐变掺杂方式，浓度 1~5 × 1017cm-3 ；在基区 320 上方生长 n 型 In0.485Ga0.515P 材料层作为发射区 330 ，其厚度为 100 nm ，掺杂浓度大约 2 × 1018cm-3 ；在发射区 330 上面生长 n 型 InAlP 材料层作为窗口层 340 ，其厚度为 25 nm ，掺杂浓度在 1 × 1018cm-3 左右。
下一步，在顶电池 300 的上方生长重掺杂 n++-InAlAsP 材料层作为盖帽层 500 ，厚度为 1000 nm ，掺杂浓度为 1 × 1019cm-3 。
下一步，对生长衬底 010 背面进行退火处理。先将衬底进行原位翻转，进行阴离子源保护下的原位退火，退火温度控制在 600~700 ℃，其作用是驱除翻转后生长面（原衬底背面）的氧化层和杂质吸附层。
下一步，在所述生长衬底背面上进行与衬底同质材料的生长，在生长一定厚度后（一般是 200~500 nm ）获得平滑的表面，这是反面结构高晶体质量外延的保障。
下一步，在平滑的生长衬底 010 背面外延生长 p 型 InAlP 材料层作为中电池 200 的背场层 210 ，其厚度为 100 nm ，掺杂浓度为 1~2 × 1018cm-3 。
下一步，在中电池背场层 210 的下方外延生长重掺杂的 P++/n++-InP 材料层作为隧穿结 410 ，其厚度为 50 nm ，掺杂浓度高达 2 × 1019cm-3 。
下一步，在隧穿结 410 下方倒生长底电池 100 ，其到下而上包括：背场层 110 、基区 120 、发射区 130 、窗口层 140 ，带隙为 0.9eV ～ 1.0eV 。其具体工艺如下：在隧穿结 500 下方外延生长 n 型 InP 材料层作为窗口层 140 ，其厚度为 40 nm ，掺杂浓度大约 1 × 1018cm-3 ；在窗口层 140 下方外延生长 n 型 GaAs 材料层作为发射区 130 ，其厚度为 100nm ，掺杂浓度为 2 × 1018cm-3 ；在发射区 130 下方外延生长应变补偿 GaAs 1-y P y /Ga 1-x In x As 超晶格结构作为基区 120 。在基区的下方外延生长 p 型 GaAs 材料层作为背场层，其厚度为 50nm ，掺杂浓度为 1~2 × 1018cm-3 。在本实例中，基区 120 由 200 个周期的应变补偿超晶格 GaAs 1-y P y /Ga 1-x In x As 构成，应变超晶格的有效晶格常数为 5.666 Å ，有效带隙为 1.01eV 。应变超晶格基区总厚度为 3.2 微米，掺杂浓度为 1 × 1016cm-3 ～ 1 × 1017cm-3 。其中，势垒层 GaAs 1-y P y 中 P 组分为 y= 0.3 ，其晶格常数为 5.5113Å ，势垒层厚度为 8 nm ，量子阱 Ga 1-x In x As 中 In 组分为 x=0.3 ，其晶格常数是 5.9368 Å ，量子阱宽度为 8 nm 。
下一步，在底电池背场层 110 的下方外延生长 20 个周期的 AlAs/AlGaAs 超晶格作为 DBR 反射层， AlGaAs 中 Al 组分选择为 0.15 。
下一步，在 DBR 反射层背面，采用金属键合的方法粘接支撑衬底，用以增加整体样品的机械强度。支撑衬底可选用 Si 。在样品表面进行减反膜蒸镀，金属电极的制备等后期工艺，完成所需要的太阳能电池。
本发明通过材料地有效选取，采用双面生长技术，使得该太阳能电池在获得最佳能带隙的同时，解决了其各子电池间的晶格匹配和电流匹配的问题。本发明的制作方法中，特殊的双面生长工艺，有效地克服倒装生长后期带来的繁琐工艺，提高了产品良率，降低生产成本，大力推进高效太阳能电池的实际应用。

Claims (13)

  1. 高效三结太阳能电池的制作方法，其具体步骤包括：
    提供生长衬底，其两个表面进行抛光处理；
    在所述生长衬底正表面形成中电池，其具有第一带隙，晶格常数与生长衬底匹配；
    在所述中电池之上形成顶电池，其具有一大于第一带隙的第二带隙，且晶格常数与中电池晶格常数匹配；
    在所述生衬底的背面形成底电池，其由应力补偿超晶格结构构成，且其等效晶格常数与中、顶电池的晶格常数匹配。
  2. 根据权利要求 1 所述的高效三结太阳能电池的制作方法，其特征在于：所述生长衬底的材料为 GaAs 。
  3. 根据权利要求 1 所述的高效三结太阳能电池的制作方法，其特征在于：所述中电池的制备工艺为：以生长衬底本身作为基区，在其上表面形成发射区。
  4. 根据权利要求 1 所述的高效三结太阳能电池的制作方法，其特征在于：所述顶电池材料为 InGaP 。
  5. 根据权利要求 1 或所述的高效三结太阳能电池的制作方法，其特征在于：在形成底电池前，对所述生长衬底背面进行退火处理。
  6. 根据权利要求 5 所述的高效三结太阳能电池的制作方法，其特征在于：完成退火后，在所述生长衬底背面上外延生长预定厚度的与生长衬底同质的材料，获得平滑表面，继续外延生长底电池的材料层，形成底电池。
  7. 高效三结太阳能电池，其包括：
    生长衬底，其具有两个抛光的表面；
    底电池，由应变补偿超晶格结构构成，倒装生长于生长衬底的背面，具有一第一带隙，其等效晶格常数与生长衬底的晶格常数匹配；
    中电池，形成于生长衬底正面上，其具有大于第一带隙的第二带隙，其晶格常数与生底衬底匹配；
    顶电池，形成于中电池之上，其具有一大于第二带隙的第三带隙，且晶格常数与中电池晶格常数匹配。
  8. 根据权利要求 7 所述的高效三结太阳能电池，其特征在于：所述底电池的带隙为 0.9eV ～ 1.1 eV ，中电池的带隙为 1.4~1.5eV ，顶电池的带隙为 1.8~1.9eV 。
  9. 根据权利要求 7 所述的高效三结太阳能电池，其特征在于：还包括一分布式布拉格发射层，形成于底电池的下方。
  10. 根据权利要求 7 所述的高效三结太阳能电池，其特征在于：所述生长衬底的材料为 GaAs 。
  11. 根据权利要求 7 所述的高效三结太阳能电池，其特征在于：所述第所述顶电池材料为 InGaP ；底电池的基区由应变补偿 GaAsP/GaAs/GaInAs 超晶格构成，其等效晶格常数与所述生长衬底匹配，发射区的材料为 GaAs 。
  12. 根据权利要求 11 所述的高效三结太阳能电池，其特征在于：所述底电池的等效晶格常数为 5.65 Å ～ 5.66 Å 。
  13. 根据权利要求 11 所述的高效三结太阳能电池，其特征在于：所述应变补偿 GaAsP/GaAs/GaInAs 超晶格结构中， GaAsP 层的厚度为 5 ～ 10 nm ， GaAs 层的厚度小于 5nm ， GaInAs 层的 In 组份为 0.3 ～ 0.4 。
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