阅读说明：本技术 倒装生长的双异质结四结柔性太阳能电池及其制备方法 (Inverted growth double-heterojunction four-junction flexible solar cell and preparation method thereof ) 是由 黄辉廉 黄珊珊 文宏 叶旺 刘建庆 于 2019-12-02 设计创作，主要内容包括：本发明公开了一种倒装生长的双异质结四结柔性太阳能电池及其制备方法,包括采用倒装方式在GaAs衬底上依次生长的AlGaInP双异质结子电池、GaAs子电池、Ga<Sub>m</Sub>In<Sub>1-m</Sub>P渐变层、第一Ga<Sub>x</Sub>In<Sub>1-x</Sub>As双异质结子电池、Ga<Sub>n</Sub>In<Sub>1-n</Sub>P渐变层和第二Ga<Sub>y</Sub>In<Sub>1-y</Sub>As双异质结子电池,各子电池之间通过隧道结连接,且生长完各子电池后剥离出GaAs衬底,所述AlGaInP双异质结子电池上设置有上电极,所述第二Ga<Sub>y</Sub>In<Sub>1-y</Sub>As双异质结子电池上设置有下电极,并粘结在一支撑衬底上。本发明实现四结太阳能电池合理的带隙组合,在提高太阳能电池的整体开路电压和填充因子的同时,保持电池的光电流匹配,以提供更多的应用场景。(The invention discloses a flip-chip grown double-heterojunction four-junction flexible solar cell and a preparation method thereof m In 1‑m P graded layer, first Ga x In 1‑x As double heterojunction subcell, Ga n In 1‑n P graded layer and second Ga y In 1‑y As double-heterojunction subcells, the subcells are connected through tunnel junctions, and the GaAs substrate is stripped after the subcells grow, the AlGaInP double-heterojunction subcells are provided with upper electrodes, and the second Ga is y In 1‑y As double heterojunction electronThe cell is provided with a lower electrode and is bonded to a support substrate. The invention realizes reasonable band gap combination of the four-junction solar cell, improves the integral open-circuit voltage and the fill factor of the solar cell, and simultaneously keeps the photocurrent matching of the cell so as to provide more application scenes.)

1. The flexible solar cell of two heterojunction four-junction of flip-chip growth, its characterized in that: comprises AlGaInP double-heterojunction sub-battery, GaAs sub-battery and Ga which are grown on a GaAs substrate in turn by adopting a flip-chip mode_mIn_1-mP graded layer, first Ga_xIn_1-xAs double heterojunction sub-battery,Ga_nIn_1-nP graded layer and second Ga_yIn_1-yAs double-heterojunction subcells, the subcells are connected through tunnel junctions, and the GaAs substrate is stripped after the subcells grow, the AlGaInP double-heterojunction subcells are provided with upper electrodes, and the second Ga is_yIn_1-yThe As double heterojunction sub-battery is provided with a lower electrode and is bonded on a supporting substrate; the Ga is_mIn_1-mThe m value of the P gradual change layer gradually changes from top to bottom in the range of 0.52-0, and the corresponding lattice constant gradually changes from being matched with the GaAs sub-battery to being matched with the first Ga_xIn_1-xAs double heterojunction subcell matching, 0.4<x<0.5; the Ga is_nIn_1-nThe n value of the P gradient layer is gradually changed from top to bottom in the range of 0.52-0, and the corresponding lattice constant is gradually changed from the first Ga_xIn_1-xAs double heterojunction subcell matching gradually to second Ga_yIn_1-yAs double heterojunction subcell matching, 0.4<y<0.5。

2. The flip-chip grown double heterojunction four-junction flexible solar cell of claim 1, wherein: the AlGaInP double-heterojunction sub-cell adopts GaInAsP capable of adjusting the lattice constant and the band gap as a base region of a double heterojunction, the band gap of the sub-cell is 2.06eV, and the AlGaInP double-heterojunction sub-cell sequentially comprises an n-type window layer, an n-type AlGaInP emitting region, a P-type AlGaInP and GaInAsP base region and a P-type back field layer from top to bottom; the n-type window layer and the p-type back field layer are made of III-V semiconductor materials with a band gap wider than that of the AlGaInP double-heterojunction sub-cell.

3. The flip-chip grown double heterojunction four-junction flexible solar cell of claim 1, wherein: the first Ga_xIn_1-xThe As double heterojunction sub-cell adopts GaInAsP capable of adjusting the lattice constant and the band gap As the base region of the double heterojunction, the band gap of the sub-cell is 1.04eV, and the sub-cell sequentially comprises an n-type window layer, an n-type GaInP emitter region, p-type GaInAsP and Ga from top to bottom_xIn_1-xAn As base region and a p-type back field layer; the n-type window layer and the p-type back field layer adopt lattice constants and first Ga_xIn_1-xAs double heterojunction subcells are consistent and have band gaps wider than 1.04 eV.

4. The flip-chip grown double heterojunction four-junction flexible solar cell of claim 1, wherein: the second Ga_yIn_1-yThe As double heterojunction sub-cell adopts GaInAsP capable of adjusting the lattice constant and the band gap As the base region of the double heterojunction, the band gap of the sub-cell is 0.70eV, and the sub-cell sequentially comprises an n-type window layer, an n-type GaInP emitter region, p-type GaInAsP and Ga from top to bottom_yIn_1-yAn As base region and a p-type back field layer; the n-type window layer and the p-type back field layer adopt lattice constants and second Ga_yIn_1-yAs double heterojunction subcells are consistent and have band gaps wider than 0.7 eV.

5. The flip-chip grown double heterojunction four-junction flexible solar cell of claim 1, wherein: the GaAs sub-cell band gap is 1.42 eV.

6. The flip-chip grown double heterojunction four-junction flexible solar cell of claim 1, wherein: the AlGaInP double-heterojunction sub-battery, the GaAs sub-battery and the Ga_mIn_1-mP graded layer, first Ga_xIn_1-xAs double heterojunction subcell, Ga_nIn_1-nP graded layer and second Ga_yIn_1-yThe As double heterojunction subcells are both lattice matched to the GaAs substrate.

7. The method for preparing a flip-chip grown double heterojunction four junction flexible solar cell as claimed in claim 1, comprising the steps of:

1) selecting a GaAs substrate, and sequentially growing a GaAs buffer layer, an AlAs sacrificial layer and a GaAs front ohmic contact layer on the GaAs substrate;

2) growing an AlGaInP double-heterojunction sub-battery, a first tunnel junction, a GaAs sub-battery, a second tunnel junction and Ga on the GaAs front ohmic contact layer in sequence_mIn_1-mP graded layerFirst Ga_xIn_1-xAs double heterojunction sub-battery, third tunnel junction and Ga_nIn_1-nP graded layer, second Ga_yIn_1-yAn As double heterojunction sub-battery and a GaInAs back ohmic contact layer;

3) preparing a lower electrode on the GaInAs back ohmic contact layer and bonding the lower electrode with a supporting substrate;

4) and stripping the GaAs substrate and the buffer layer to expose the light receiving surface, and preparing an upper electrode on the ohmic contact layer on the front surface of the GaAs to obtain the target solar cell.

8. The method for preparing a flip-chip grown double heterojunction four-junction flexible solar cell according to claim 7, wherein: in the step 3), the supporting substrate is bonded and treated at high temperature by adopting a Teflon film, or a copper-molybdenum-copper flexible substrate bonding method is adopted.

9. The method for preparing a flip-chip grown double heterojunction four-junction flexible solar cell according to claim 7, wherein: in the step 4), the GaAs substrate is stripped by a wet etching method.

10. The method for preparing a flip-chip grown double heterojunction four-junction flexible solar cell according to claim 7, wherein: in the steps 1) and 2), each structural layer is grown by adopting a metal organic chemical vapor deposition technology, a molecular beam epitaxy technology or a vapor phase epitaxy technology.

Technical Field

The invention relates to the technical field of solar photovoltaic power generation, in particular to a double-heterojunction four-junction flexible solar cell with inverted growth and a preparation method thereof.

Background

For the traditional gallium arsenide multi-junction solar cell, the main structure of the solar cell is a GaInP/GaInAs/Ge three-junction solar cell which integrally keeps lattice matching and has the band gap combination of 1.85/1.40/0.67 eV. However, the solar cell is limited by the current of the series structure due to the unreasonable distribution of the solar spectrum by the cell structure, and cannot fully convert and utilize the solar energy of the long-wave band, so that the improvement of the cell performance is limited. Therefore, in order to realize the lattice matching and the photocurrent matching between the sub-cells, a GaInNAs sub-cell with a band gap close to 1.0eV is inserted between the GaInAs and the Ge sub-cell in the triple-junction cell structure to form a GaInP/GaInAs/GaInN-As/Ge four-junction solar cell with a band gap combination of 1.9/1.42/1.02/0.75eV, so that the cell conversion efficiency can be greatly improved, theoretically, the efficiency of the solar cell with the structure under the AM0 spectrum can reach 33-34%, however, for the four-junction solar cell under the lattice matching condition, the GaInNAs epitaxial material grown by the existing technical means has poor crystal quality, not only many material defects and low carrier mobility, but also the cost of the N source is higher, and the growth difficulty is high.

The heat generated in the solar cell cannot be dissipated in time due to the small thermal conductivity coefficient of the substrate material Ge or GaAs, so that the cell efficiency is reduced; meanwhile, the Ge or GaAs substrate is large in thickness, poor in flexibility, extremely fragile and not easy to carry, so that the actual conversion efficiency and application of the solar cell are limited. If the rigid solar cell can be made into the flexible solar cell, the weight of the solar cell can be greatly reduced, and the flexible solar cell has the characteristics of thin thickness, good heat dissipation, flexibility, high efficiency, firmness, reliability, long service life and easiness in carrying, can provide electric power for people in various production scenes such as wearable equipment and even the aerospace field and the like, and has wide application prospect and potential.

How to realize reasonable band gap combination of a multi-junction solar cell, reduce current mismatch without increasing the manufacturing cost and difficulty of the cell, and provide more application scenes becomes a problem to be solved urgently in the current III-V group solar cell.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings of the prior art, and provides a double-heterojunction four-junction flexible solar cell with inverted growth and a preparation method thereof, so that reasonable band gap combination of the four-junction solar cell is realized, the whole open-circuit voltage and the filling factor of the solar cell are improved, and the photocurrent matching of the cell is kept, so that more application scenes are provided.

In order to achieve the purpose, the technical scheme provided by the invention is as follows: the flip-chip grown double-heterojunction four-junction flexible solar cell comprises an AlGaInP double-heterojunction sub-cell, a GaAs sub-cell and Ga which are grown on a GaAs substrate in turn in a flip-chip mode_mIn_1-mP graded layer, first Ga_xIn_1-xAs double heterojunction subcell, Ga_nIn_1-nP graded layer and second Ga_yIn_1-yAs double-heterojunction subcells, the subcells are connected through tunnel junctions, and the GaAs substrate is stripped after the subcells grow, the AlGaInP double-heterojunction subcells are provided with upper electrodes, and the second Ga is_yIn_1-yThe As double heterojunction sub-battery is provided with a lower electrode and is bonded on a supporting substrate; the Ga is_mIn_1-mThe m value of the P gradual change layer gradually changes from top to bottom in the range of 0.52-0, and the corresponding lattice constant gradually changes from being matched with the GaAs sub-battery to being matched with the first Ga_xIn_1-xAs double heterojunction subcell matching, 0.4<x<0.5; the Ga is_nIn_1-nThe n value of the P gradient layer is gradually changed from top to bottom in the range of 0.52-0, and the corresponding lattice constant is gradually changed from the first Ga_xIn_1-xAs double heterojunction subcell matching gradually to second Ga_yIn_1-yAs double heterojunction subcell matching, wherein0.4<y<0.5。

Furthermore, the AlGaInP double-heterojunction sub-cell adopts GaInAsP capable of adjusting the lattice constant and the band gap as a double-heterojunction base region, the band gap of the sub-cell is 2.06eV, and the sub-cell sequentially comprises an n-type window layer, an n-type AlGaInP emitting region, a P-type AlGaInP and GaInAsP base region and a P-type back field layer from top to bottom; the n-type window layer and the p-type back field layer are made of III-V semiconductor materials with a band gap wider than that of the AlGaInP double-heterojunction sub-cell.

Further, the first Ga_xIn_1-xThe As double heterojunction sub-cell adopts GaInAsP capable of adjusting the lattice constant and the band gap As the base region of the double heterojunction, the band gap of the sub-cell is 1.04eV, and the sub-cell sequentially comprises an n-type window layer, an n-type GaInP emitter region, p-type GaInAsP and Ga from top to bottom_xIn_1-xAn As base region and a p-type back field layer; the n-type window layer and the p-type back field layer adopt lattice constants and first Ga_xIn_1-xAs double heterojunction subcells are consistent and have band gaps wider than 1.04 eV.

Further, the second Ga_yIn_1-yThe As double heterojunction sub-cell adopts GaInAsP capable of adjusting the lattice constant and the band gap As the base region of the double heterojunction, the band gap of the sub-cell is 0.70eV, and the sub-cell sequentially comprises an n-type window layer, an n-type GaInP emitter region, p-type GaInAsP and Ga from top to bottom_yIn_1-yAn As base region and a p-type back field layer; the n-type window layer and the p-type back field layer adopt lattice constants and second Ga_yIn_1-yAs double heterojunction subcells are consistent and have band gaps wider than 0.7 eV.

Further, the GaAs sub-cell band gap is 1.42 eV.

Further, the AlGaInP double-heterojunction sub-battery, the GaAs sub-battery and the Ga_mIn_1-mP graded layer, first Ga_xIn_{1- x}As double heterojunction subcell, Ga_nIn_1-nP graded layer and second Ga_yIn_1-yThe As double heterojunction subcells are both lattice matched to the GaAs substrate.

The preparation method of the flip-chip grown double-heterojunction four-junction flexible solar cell provided by the invention comprises the following steps:

1) selecting a GaAs substrate, and sequentially growing a GaAs buffer layer, an AlAs sacrificial layer and a GaAs front ohmic contact layer on the GaAs substrate;

2) growing an AlGaInP double-heterojunction sub-battery, a first tunnel junction, a GaAs sub-battery, a second tunnel junction and Ga on the GaAs front ohmic contact layer in sequence_mIn_1-mP graded layer, first Ga_xIn_1-xAs double heterojunction sub-battery, third tunnel junction and Ga_nIn_1-nP graded layer, second Ga_yIn_1-yAn As double heterojunction sub-battery and a GaInAs back ohmic contact layer;

3) preparing a lower electrode on the GaInAs back ohmic contact layer and bonding the lower electrode with a supporting substrate;

4) and stripping the GaAs substrate and the buffer layer to expose the light receiving surface, and preparing an upper electrode on the ohmic contact layer on the front surface of the GaAs to obtain the target solar cell.

In the step 3), the supporting substrate is bonded and treated at high temperature by adopting a Teflon film, or a copper-molybdenum-copper flexible substrate bonding method is adopted.

In the step 4), the GaAs substrate is stripped by a wet etching method.

In the steps 1) and 2), each structural layer is grown by adopting a metal organic chemical vapor deposition technology, a molecular beam epitaxy technology or a vapor phase epitaxy technology.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the band gap combination of the double-heterojunction four-junction flexible solar cell is 2.06eV, 1.42eV, 1.04eV and 0.70eV, the open-circuit voltage is high, and the cell efficiency is improved.

2. The invention uses GaInAsP material to independently change the forbidden bandwidth and lattice constant to realize the self characteristics of GaAs lattice matching and InGaAs lattice matching, and introduces double heterojunction sub-batteries; the GaInAsP material is used as a base region of the double heterojunction, and in the AlGaInP double heterojunction sub-cell, the lattice matching with the GaAs substrate is kept, and the AlGaInP material with a high band gap of 2.06eV can be replaced to absorb light with a wave band of 0.66-0.78 um; in a similar way, the GaInAsP can also respectively keep lattice matching with InGaAs with band gaps of 1.04eV and 0.70eV, and supplement and absorb light with wave bands of 0.91-1.67 um.

3. And introducing a GaInP gradient layer, and adjusting the In component of GaInP to solve the problem of lattice mismatch between the GaAs material and the GaInAs material. Therefore, the double-heterojunction four-junction flexible solar cell can provide higher open-circuit voltage on one hand, and can effectively help the four-junction solar cell to match photocurrent on the other hand, thereby reducing heat energy loss in the photoelectric conversion process and effectively improving the efficiency of the cell.

4. The flexible solar cell manufactured by adopting the flip-chip growth mode has the characteristics of thin thickness, good heat dissipation, flexibility, high efficiency, firmness, reliability, long service life and easiness in carrying, and the stripped substrate can be recycled, so that the production cost is reduced; in a word, the invention can more fully utilize the solar energy, improve the photoelectric conversion efficiency of the GaAs multi-junction cell and is worthy of popularization.

Drawings

Fig. 1 is a schematic structural diagram of a flip-chip grown double-heterojunction four-junction flexible solar cell provided by an embodiment.

FIG. 2, FIG. 3, and FIG. 4 show an AlGaInP double heterojunction sub-cell and a first Ga, respectively_xIn_1-xAs double heterojunction subcell, second Ga_yIn_1-yAnd the structural schematic diagram of the As double heterojunction subcell.

Fig. 5 is a schematic structural diagram of a flip-chip grown double heterojunction four junction flexible solar cell product.

Fig. 6 is a flowchart of steps of a method for manufacturing a flip-chip grown double-heterojunction four-junction flexible solar cell according to an embodiment.

Detailed Description

The present invention will be further described with reference to the following specific examples.

As shown in fig. 1, in the flip-chip grown double-heterojunction four-junction flexible solar cell provided in this embodiment, a GaAs buffer layer 02, an AlAs sacrificial layer 03, and a GaAs front-side european junction are sequentially grown on a GaAs substrate 01 in a flip-chip mannerM contact layer 04, AlGaInP double heterojunction sub-cell 05, first tunnel junction 06, GaAs sub-cell 07, second tunnel junction 08, Ga_mIn_1-mP graded layer 09, first Ga_xIn_1-xAs double heterojunction sub-cell 10, third tunnel junction 11, Ga_nIn_1-nP graded layer 12, second Ga_yIn_1-yThe As double heterojunction sub-cell 13 and the GaInAs back ohmic contact layer 14, the band gap combination of the flip-chip grown double heterojunction four-junction flexible solar cell is 2.06eV, 1.42eV, 1.04eV and 0.70 eV.

As shown in fig. 5, the structure of the flip-chip grown double-heterojunction four-junction flexible solar cell product is schematically shown, wherein, according to fig. 6, after each junction cell is grown on a GaAs substrate 01, a lower electrode 15 is prepared on a GaInAs back ohmic contact layer 14, an epitaxial cell structure is bonded with a support substrate 16, the GaAs substrate is peeled off from the epitaxial cell structure, and an upper electrode 17 is prepared on a GaAs front ohmic contact layer 04, so as to obtain a target flexible solar cell chip.

The embodiment also provides a method for manufacturing the flip-chip grown double-heterojunction four-junction flexible solar cell, which includes, but is not limited to, a metal organic chemical vapor deposition technique, a molecular beam epitaxy technique, and a vapor phase epitaxy technique, and preferably adopts the metal organic chemical vapor deposition technique, and the method specifically includes the following steps:

a GaAs substrate 01 is selected, and a GaAs buffer layer 02, an AlAs sacrificial layer 03 and an n-type heavily doped GaAs front ohmic contact layer 04 are sequentially and respectively grown in the direction gradually away from the GaAs substrate 01.

The AlGaInP double heterojunction sub-cell 05 comprises an n-type AlGaInP window layer 051, an n-type AlGaInP emitter region 052, a p-type AlGaInP base region 053, a p-type GaInAsP base region 054 and a p-type AlGaAs back field layer 055 which are arranged in sequence in a direction gradually away from a GaAs substrate 01, and is shown in figure 2; the bandgap of the AlGaInP material is about 2.06eV, and the bandgap of the GaInAsP material is within the interval of 1.58-1.88 eV.

The first tunnel junction 06 includes a p-type AlGaAs heavily doped layer and an n-type GaInP heavily doped layer sequentially arranged in a direction gradually away from the GaAs substrate 01.

The GaAs sub-cell 07 comprises an n-type AlInP window layer, an n-type GaInP emitting region, a p-type GaAs base region and a p-type GaInP back field layer which are arranged in sequence in a direction gradually away from a GaAs substrate by 01; the GaAs subcell 07 bandgap is about 1.42 eV.

The second tunnel junction 08 includes a p-type AlGaAs heavily doped layer and an n-type GaInP heavily doped layer sequentially arranged in a direction gradually away from the GaAs substrate 01.

The Ga is_mIn_1-mA P graded layer 09 having an In composition graded such that a lattice constant is graded, and Ga_mIn_1-mThe lattice constant of the P graded layer 09 is shifted from the lattice constant of the GaAs material to the first Ga_xIn_1-xThe lattice constant of the As double heterojunction sub-battery 10 is gradually changed, wherein the value of m is in the range of 0.52-0, and Ga is added_mIn_1-mP graded layer 09 for overcoming the first Ga_xIn_1-xThe lattice mismatch between the As double heterojunction subcell 10 and the remaining epitaxial structure.

The first Ga_xIn_1-xThe As double heterojunction sub-cell 10 comprises an n-type AlInP window layer 101, an n-type GaInP emitter region 102, a p-type GaInAsP base region 103 and a p-type Ga arranged in sequence in a direction gradually away from a GaAs substrate 01_xIn_1-xAn As base region 104, a p-type GaInP back field layer 105, As shown in fig. 3; the band gap of the GaInAsP material is in the range of 1.24-1.36 eV; the Ga is_xIn_1-xThe band gap of the As material is in the range of 0.9-1.24 eV, wherein 0.4<x<0.5。

The third tunnel junction 11 includes a p-type GaAs heavily-doped layer and an n-type GaAs heavily-doped layer sequentially arranged in a direction gradually away from the GaAs substrate by 01.

The Ga is_nIn_1-nA P graded layer 12 In which an In composition is graded so that a lattice constant is graded, the Ga_nIn_1-nThe lattice constant of the P-graded layer 12 is defined by the first Ga_xIn_1-xLattice constant of As double heterojunction subcell 10 towards the second Ga_yIn_1-yThe lattice constant of the As double heterojunction subcell 13 is graded, and the Ga_nIn_1-nP graded layer 12 for overcoming the second Ga_yIn_1-yLattice mismatch between As double heterojunction subcells and the remaining epitaxial structure, where n has a value of 0Interval 52-0.

The second Ga_yIn_1-yThe As double heterojunction sub-cell 13 comprises an n-type AlInP window layer 131, an n-type GaInP emitter region 132, a p-type GaInAsP base region 133 and a p-type Ga arranged in sequence in a direction gradually away from a GaAs substrate 01_yIn_1-y As base region 134, p-type AlGaAs back field layer 135, As shown in fig. 4; the band gap of the GaInAsP material is in the range of 0.9-1.04 eV; the Ga is_yIn_1-yThe band gap of the As material is in the range of 0.7-0.9 eV, wherein 0.4<y<0.5。

In the second Ga_yIn_1-yAnd the p-type heavily-doped GaInAs back ohmic contact layer 14 grows on the As double heterojunction sub-cell 13 according to the direction gradually departing from the GaAs substrate 01.

And manufacturing a lower electrode on the GaInAs back ohmic contact layer 14, wherein the lower electrode is a p-electrode 15. Then, the second Ga_yIn_1-yThe As sub-battery 13 is bonded with a supporting substrate 16; after the GaAs substrate 01 is peeled off, an upper electrode 17 is formed on the GaAs front ohmic contact layer 04, thereby obtaining a desired solar cell. The supporting substrate 16 may be, but not limited to, a teflon film or a copper-molybdenum-copper flexible substrate.

Next, a specific implementation of the method for manufacturing the above-mentioned flip-chip grown double-heterojunction four-junction flexible solar cell of this embodiment is given, and further detailed description is made with reference to the steps shown in fig. 6.

Step S601, growing a GaAs buffer layer, an AlAs sacrificial layer and an n-type heavily doped GaAs front ohmic contact layer on a GaAs substrate in sequence.

And step S602, growing an AlGaInP double-heterojunction sub-cell on the GaAs front ohmic contact layer in sequence, wherein the AlGaInP double-heterojunction sub-cell comprises an n-type AlInP window layer, an n-type AlGaInP emitting region, a p-type AlGaInP base region, a p-type GaInAsP base region and a p-type AlGaAs back field layer which are arranged in sequence in a direction gradually away from the GaAs substrate.

Step S603, disposing a p-type AlGaAs heavily doped layer and an n-type GaInP heavily doped layer in the first tunnel junction in a direction gradually away from the GaAs substrate.

Step S604, the GaAs sub-battery comprises an n-type AlInP window layer, an n-type GaInP emitting region, a p-type GaAs base region and a p-type GaInP back field layer which are sequentially arranged in the direction gradually far away from the GaAs substrate.

Step S605, the second tunnel junction includes sequentially disposing a p-type AlGaAs heavily doped layer and an n-type GaInP heavily doped layer in a direction gradually away from the GaAs substrate.

Step S606, the Ga_mIn_1-mA P graded layer having a graded In composition such that a lattice constant is graded, the Ga_mIn_1-mThe lattice constant of the P-graded layer is changed from the lattice constant of the GaAs material to the first Ga_xIn_1-xThe lattice constant of the As double heterojunction sub-battery is gradually changed, wherein the value of m is in the range of 0.52-0, and the Ga_mIn_1-mP graded layer for overcoming the first Ga_xIn_1-xLattice mismatch between the As double heterojunction subcell and the remaining epitaxial structure.

Step S607, the first Ga_xIn_1-xThe As double heterojunction sub-battery comprises an n-type AlInP window layer, an n-type GaInP emitter region, a p-type GaInAsP base region and a p-type Ga arranged in sequence in the direction gradually away from a GaAs substrate_xIn_1-xAn As base region and a p-type GaInP back field layer; the band gap of the GaInAsP material is in the range of 1.24-1.36 eV; the Ga is_xIn_1-xThe band gap of the As material is in the range of 0.9-1.24 eV, wherein 0.4<x<0.5。。

And step S607, arranging a p-type GaAs heavily doped layer and an n-type GaAs heavily doped layer in sequence in the direction gradually far away from the GaAs substrate.

Step S608, the Ga_nIn_1-nA P graded layer having a graded In composition such that a lattice constant is graded, the Ga_nIn_1-nThe lattice constant of the P-graded buffer layer is formed by first Ga_xIn_1-xLattice constant of As double heterojunction subcell towards second Ga_yIn_1-yThe lattice constant of the As double heterojunction subcell is gradually changed, and the Ga is_nIn_1-nP graded layer for overcoming second Ga_yIn_1-yLattice mismatch between the As double heterojunction sub-cell and the rest epitaxial structure, wherein the value of n is in the range of 0.52-0.

Step S609, the second Ga_yIn_1-yThe As double heterojunction sub-battery comprises an n-type AlInP window layer, an n-type GaInP emitter region, a p-type GaInAsP base region and a p-type Ga arranged in sequence in the direction gradually away from a GaAs substrate_yIn_1-yAn As base region and a p-type GaInP back field layer; the Ga is_yIn_1-yThe band gap of the As material is between 0.7 and 0.9eV, the band gap of the GaInAsP material is between 0.74 and 1.36eV, wherein 0.4<x<0.5; the band gap of the GaInAsP material is in the range of 0.9-1.04 eV; the Ga is_yIn_1-yThe band gap of the As material is in the range of 0.7-0.9 eV, wherein 0.4<y<0.5。

Step S610, in the second Ga_yIn_1-yAnd growing the p-type heavily-doped GaInAs back ohmic contact layer on the As double-heterojunction sub-battery according to the direction gradually far away from the GaAs substrate.

Step S611, manufacturing a lower electrode on the GaInAs back ohmic contact layer and bonding the lower electrode with a supporting substrate; and after the GaAs substrate is stripped, manufacturing an upper electrode on the GaAs front ohmic contact layer, thereby obtaining the target solar cell. The supporting substrate can be made of but not limited to a teflon film or a copper-molybdenum-copper flexible substrate.

Next, a preferred embodiment of the present invention is given with reference to fig. 1, 2, 3, 4, and 5, and a technical solution provided by the present invention is further explained, where the preferred embodiment adopts a metal organic chemical vapor deposition technique to grow the flip-chip grown double-heterojunction four-junction flexible solar cell of the present invention.

1) Sequentially growing buffer layers 02 with the thickness of 0.5umGaAs on the n-type GaAs substrate 01 respectively; AlAs sacrificial layer 03 with thickness of 10 nm; about 5 x 10 n-type doping¹⁸cm^-3And a GaAs layer with the thickness of 0.3um is used as the front ohmic contact layer 04.

2) Sequentially growing n-type doping about 2X 10 with the thickness of about 30nm¹⁸cm^-3The AlInP window layer 051, and the n-type doping with the thickness of about 100nm is about 2 multiplied by 10¹⁸cm^-3 AlGaInP emitting region 052, p-type doping about 1X 10 with thickness about 600nm¹⁷cm^-3 AlGaInP base region 053, p-type doping about 1 x 10 with thickness of about 300nm¹⁷cm^-3GaInAsP base region of054 and about 600nm thick p-type doping about 2X 10¹⁸cm^-3To form the AlGaAs double heterojunction subcell 05.

3) Sequentially growing p-type doping with thickness of about 15nm larger than 1 × 10¹⁹cm^-3The above AlGaAs heavily doped layer has an n-type doping of more than 1 × 10 thickness of about 20nm¹⁹cm^-3The above GaInP heavily doped layer forms the first tunnel junction 06.

4) Sequentially growing n-type doping about 3X 10 with thickness of about 30nm¹⁸cm^-3Of an AlInP window layer, about 2X 10 n-type doping with a thickness of about 100nm¹⁸cm^-3GaInP emitting region, about 1 x 10 p-type doping thickness of about 3000nm¹⁷cm^-3GaAs base region, about 1.3X 10 p-type doping with a thickness of about 100nm¹⁸cm^-3The GaInP back field layer of (a) forming a GaAs sub-cell 07.

5) Sequentially growing p-type doping with thickness of about 15nm larger than 1 × 10¹⁹cm^-3The above AlGaAs heavily doped layer has an n-type doping of more than 1 × 10 thickness of about 20nm¹⁹cm^-3The second tunnel junction 08 is formed by the GaInP heavily doped layer described above.

6) Sequentially growing n-type doping with the thickness of 2000-3000 nm and the doping concentration of 3 multiplied by 10¹⁸cm^-3Growing Ga_mIn_1-mThe P gradual change layer 09, m is in the range of 0.52-0.

7) Sequentially growing n-type doping about 1 × 10 with thickness of about 50nm¹⁸cm^-3Of an AlInP window layer 101, about 1X 10 n-type doping with a thickness of about 200nm¹⁸cm^-3GaInP emitter region 102, p-type doping of about 1X 10 with a thickness of about 600nm¹⁷cm^-3With a GaInAsP base region 103, p-type doping of about 1X 10 with a thickness of about 1200nm¹⁷cm^-3Ga of (2)_xIn_1-xAs base region 104, about 3X 10 p-type doping with a thickness of about 100nm¹⁸cm^-3Forming the first Ga on the GaInP back field layer 105_xIn_1-xAn As double heterojunction subcell 10.

8) Sequentially growing p-type doping with thickness of about 15nm larger than 1 × 10¹⁹cm^-3The GaAs heavily doped layer has n-type doping greater than 1 × 10 with thickness of about 20nm¹⁹cm^-3Ga aboveAnd an As heavily doped layer, forming a second tunnel junction 11.

9) Sequentially growing n-type doping with the thickness of 2000-3000 nm and the doping concentration of 3 multiplied by 10¹⁸cm^-3Growing Ga_nIn_1-nThe value of n of the P gradient layer 12 is in the range of 0.52-0.

10) Sequentially growing n-type doping about 1 × 10 with thickness of about 50nm¹⁸cm^-3The AlInP window layer 131, about 200nm thick n-type doping of about 1 x 10¹⁸cm^-3GaInP emitter 132, p-type doping of about 1X 10 with a thickness of about 600nm¹⁷cm^-3With a GaInAsP base region 133, p-type doping of about 1X 10 with a thickness of about 1200nm¹⁷cm^-3Ga of (2)_xIn_1-xAs base region 134, about 3X 10 p-type doping with a thickness of about 100nm¹⁸cm^-3Forming a second Ga on the GaInP back field layer 135_yIn_1-yAn As double heterojunction subcell 13;

11) finally, p-type doping with the thickness of about 300nm is grown to be about 3 multiplied by 10¹⁸cm^-3A GaInAs back ohmic contact layer 14; a double heterojunction four-junction solar cell as shown in figure 1 is obtained.

The preparation process of the flexible solar cell comprises the following steps: manufacturing a lower electrode 15 on the GaInAs back ohmic contact layer 14 and bonding the lower electrode with a Teflon film supporting substrate 16; and stripping the GaAs substrate 01, the GaAs buffer layer 02 and the AlAs sacrificial layer 03 from the epitaxial structure of the cell by adopting a wet etching method to expose the light receiving surface, and preparing an upper electrode 17 on the GaAs front ohmic contact layer 04 to obtain the target solar cell, as shown in FIG. 2.

The above-mentioned embodiments are merely preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, so that variations based on the shape and principle of the present invention should be covered within the scope of the present invention.