CN103165720B - Formal dress triple-junction monolithic solar cell and preparation method thereof - Google Patents

Abstract

The invention provides a front-mounted three-junction cascaded solar cell and a preparation method thereof, which can realize a reasonable bandgap combination of multi-junction solar cells, reduce current mismatch without increasing the cost and difficulty of cell production. The cell comprises a GaAs substrate, a GaInP transition layer sequentially arranged on the GaAs substrate, an InGaAs bottom cell, a first tunnel junction, an InGaAsP middle cell, a second tunnel junction, an InAlAs top cell and an ohmic contact layer. The preparation method of the battery comprises the steps of: 1) providing a GaAs substrate; 2) sequentially growing a GaInP transition layer with stepped In composition, an InGaAs bottom cell, a first tunnel junction, an InGaAsP intermediate cell, and A second tunnel junction, an InAlAs top cell, and an ohmic contact layer; 3) preparing upper and lower electrodes on the ohmic contact layer and the GaAs substrate, respectively, to obtain a target solar cell.

Description

Front-mounted three-junction cascaded solar cell and preparation method thereof

technical field

The present invention relates to the field of solar cells, in particular to a GaAs substrate-based InAlAs/InGaAsP/InGaAs positive triple-junction cascaded solar cell and a preparation method thereof. It has a theoretical conversion efficiency higher than 51%.

Background technique

In the field of III-V solar cells, multi-junction systems are usually used to achieve segmental absorption and utilization of the solar spectrum in order to obtain higher conversion efficiency. GaInP/GaAs/Ge and GaInP/GaAs/InGaAs (~1.0eV) triple-junction cells are the most researched and technically mature systems. The former currently achieves a maximum conversion efficiency of 32-33% under one sun. However, there is still a major problem in this system that the Ge battery covers a wider spectrum, and its short-circuit current can reach twice that of the other two-junction batteries. Due to the constraints of the three-junction batteries connected in series, the energy of the solar spectrum corresponding to the Ge battery is not captured. Full conversion utilization. However, GaInP/GaAs/InGaAs (~1.0eV) triple-junction cells often use an inverted growth method due to a 2.1% lattice mismatch between GaAs and InGaAs cells, and then use techniques such as substrate lift-off to increase the growth rate. and the difficulty and cost of the process.

How to achieve a reasonable bandgap combination of multi-junction solar cells and reduce the current mismatch without increasing the cost and difficulty of cell manufacturing has become an urgent problem to be solved for current III-V solar cells.

Contents of the invention

The object of the present invention is to provide a front-mounted three-junction cascaded solar cell and a preparation method thereof, realize a reasonable bandgap combination of multi-junction solar cells, reduce current mismatch without increasing the cost and difficulty of cell manufacturing.

In order to achieve the above object, the present invention provides a positive three-junction cascaded solar cell, comprising a GaAs substrate, a GaInP transition layer sequentially arranged on the GaAs substrate, an InGaAs bottom cell, a first tunnel junction, an InGaAsP intermediate cell, a second Two tunnel junctions, InAlAs top cell and ohmic contact layer.

Further, the lattice constants of the InAlAs top cell, the InGaAsP middle cell, and the InGaAs bottom cell are matched, and the bandgap combinations of the positive triple-junction cascaded solar cell are 1.93eV, 1.39eV, and 0.94eV.

Further, there is a lattice mismatch between the positive triple-junction cascaded solar cell and the GaAs substrate, and the two are connected by growing the GaInP transition layer through lattice anomaly.

Further, the GaInP transition layer selects the Ga _1-x In _x P material with stepped In composition as the graded transition layer to realize the transition from the GaAs substrate to the InGaAs bottom cell, and the value of x changes from 0.49 to 0.85.

Further, the GaInP transition layer selects the Ga _1-x In _x P material with stepped In composition as the graded transition layer, and the graded transition layer suppresses threading dislocations from penetrating upwards to the InGaAs bottom cell through multiple interfaces, x The value of changed from 0.49 to 0.85.

Further, the GaAs substrate adopts a P-type GaAs substrate, or adopts an N-type GaAs substrate and realizes conversion from N-type to P-type through a tunnel junction.

In order to achieve the above object, the present invention also provides a method for preparing the front-mounted triple-junction cascaded solar cell described in the present invention, comprising the steps of: 1) providing a GaAs substrate; 2) sequentially growing In components on the GaAs substrate Stepped GaInP transition layer, InGaAs bottom cell, first tunnel junction, InGaAsP middle cell, second tunnel junction, InAlAs top cell, and ohmic contact layer; 3) Prepare top, The lower electrode is used to obtain the target solar cell.

Further, each structural layer in the positive three-junction cascaded solar cell is grown and formed by MOCVD, wherein the N-type dopant atoms are Si, Se, S or Te, and the P-type dopant atoms are Zn, Mg or C .

Further, each structural layer in the positive three-junction cascaded solar cell is grown by the MBE method, wherein the N-type dopant atoms are Si, Se, S, Sn or Te, and the P-type dopant atoms are Be, Mg or C.

The advantages of the front-mounted triple-junction cascaded solar cell and its preparation method provided by the present invention are:

1. The bandgap combination of the solar cell is 1.93eV, 1.39eV, 0.94eV, which effectively realizes the segmental absorption of the solar spectrum, and the current mismatch of each sub-cell is small, which reduces the heat loss during the photoelectric conversion process. Under 100 times concentrated light, its efficiency can reach more than 51%;

2. The lattice of each sub-cell of the solar cell is matched, and it is grown by the traditional formal method, and the growth process is simple;

3. The manufacturing process of the solar cell is simple.

Description of drawings

Figure 1 shows a schematic structural view of a front-mounted three-junction cascaded solar cell provided by a specific embodiment of the present invention;

Fig. 2 is a schematic structural view of the finished product of the front-mounted three-junction cascaded solar cell shown in Fig. 1;

FIG. 3 is a flow chart showing the steps of a method for preparing a front-mounted triple-junction cascaded solar cell provided by a specific embodiment of the present invention.

detailed description

The front-mounted triple-junction cascaded solar cell provided by the present invention and its preparation method will be described in detail below in conjunction with the accompanying drawings.

Firstly, the specific implementation manner of the front-mounted triple-junction cascaded solar cell of the present invention is given with reference to the accompanying drawings.

Referring to the accompanying drawings 1 and 2, wherein, Fig. 1 is a schematic structural view of a front-mounted three-junction cascaded solar cell provided in this specific embodiment, and Fig. 2 is a finished product of the front-mounted three-junction cascaded solar cell shown in Fig. 1 Schematic diagram of the structure, the structure shown in Figures 1 and 2 will be described in detail next.

This specific embodiment provides a positive three-junction cascaded solar cell, including: a GaAs substrate 31, an InGaAs bottom cell 24, a first tunnel junction 25, an InGaAsP middle cell 26, a second tunnel junction 27, an InAlAs top cell 28, and an ohmic contact layer 23 . Electrodes (electrodes 29 and 30 shown in FIG. 2 ) are respectively provided on the InAlAs top cell 28 and the GaAs substrate 31 .

The bandgap combinations of the three-junction sub-cells InAlAs top cell 28 , InGaAsP middle cell 26 and InGaAs bottom cell 24 are 1.93eV, 1.39eV, 0.94eV, and the lattice constants of each sub-cell are matched, all of which are 0.5807nm. The current matching of each sub-battery reduces the heat energy loss in the photoelectric conversion process and improves the battery efficiency.

As a preferred implementation manner, the positive-mounted triple-junction cascaded solar cell uses a P-type GaAs substrate 31 . Specifically: first grow a P-type GaAs buffer layer 01 on a P-type GaAs substrate 31, then grow a GaInP transition layer 02, and then grow an InGaAs bottom cell 24, an InGaAsP middle cell 26, and an InAlAs top cell 28 in sequence. The cells are connected in series through a tunnel junction, and finally a layer of N-type InGaAs ohmic contact layer 23 is grown.

As another preferred implementation manner, the positive-mounted triple-junction cascaded solar cell uses an N-type GaAs substrate 31 . Specifically: on the N-type GaAs substrate 31, first grow the N-type GaAs buffer layer 01, then grow a tunnel junction to realize the conversion from N-type to P-type, then grow the GaInP transition layer 02, and then grow the InGaAs bottom cell 24, The InGaAsP middle cell 26 and the InAlAs top cell 28 are three-junction sub-cells, and the sub-cells are connected in series through a tunnel junction, and finally a layer of N-type InGaAs ohmic contact layer 23 is grown.

There is a lattice mismatch between each sub-cell of the above-mentioned positive three-junction cascaded solar cell and the GaAs substrate 31 , and there is a lattice mismatch of 2.72% in this embodiment. The connection between the positive triple-junction cascaded solar cell and the GaAs substrate 31 can be achieved by growing the GaInP transition layer 02 through lattice anomaly growth. For example, the lattice constant can be achieved by growing a Ga _1-x In _x P (x=0.49~0.85) transition layer with stepped In composition between the GaAs substrate 31 and the InGaAs bottom cell 24 by lattice anomaly growth. Transition. The Ga _1-x In _x P composition gradient transition layer can fully release the lattice mismatch stress. The Ga _1-x In _x P graded transition layer with stepped In composition can suppress threading dislocations from penetrating upwards to reach the InGaAs bottom cell 24 through multiple interfaces.

The InGaAs bottom cell 24 includes a P-type GaInP back field layer 03 , a P-type InGaAs base region 04 , an N-type InGaAs emitter region 05 and an N-type GaInP window layer 06 arranged in sequence in a direction gradually away from the GaAs substrate 31 . Preferably, the composition of In in the InGaAs bottom cell 24 is about 38%, and its forbidden band width is about 0.94eV.

The first tunnel junction 25 includes an N-type Al(Ga)InP or InAlAs barrier layer 07, an N-type GaInP redoped layer 08, a P-type InGaAs redoped layer 09, and a P Type Al(Ga)InP or InAlAs barrier layer 10. Here, Al(Ga)InP represents AlInP or AlGaInP.

The InGaAsP intermediate cell 26 includes a P-type Al( _Ga )InP or InAlAs back field layer 11, a P-type InGaAsP base region 12, an N-type InGaAsP emitter region 13, and an N-type InGaAsP emitter region 13, which are arranged gradually away from the GaAs substrate 31. Al _0.63 As window layer 14 . Preferably, the composition of In and As in the InGaAsP intermediate cell 26 is about 38% and 57% respectively, and its forbidden band width is about 1.39eV.

The second tunnel junction 27 includes an N-type In _0.37 Al _0.63 As barrier layer 15, an N-type GaInP re-doped layer 16, a P-type InGaAs re-doped layer 17, a P-type In _0.37 Al _0.63 As barrier layer 18.

The InAlAs top cell 28 includes a P-type In _0.30 Al _0.70 As back field layer 19, a P-type In _0.37 Al _0.63 As base region 20, and an N-type In _0.37 Al _0.63 As emitter region arranged in sequence in a direction gradually away from the GaAs substrate 31 21. N-type In _0.3 Al _0.7 As window layer 22. Preferably, the In composition in the InAlAs top cell 28 is 37%, and its forbidden band width is about 1.93eV.

In this specific embodiment, an InGaAs layer is further provided on the InAlAs top cell 28 as the ohmic contact layer 23 , and its doping type is N type.

The positive three-junction cascaded solar cell is provided with electrodes on the ohmic contact layer 23 and the GaAs substrate 31 respectively. In this specific embodiment, the electrode 30 is provided on the ohmic contact layer 23, and the electrode 30 is located on the upper surface of the ohmic contact layer 23; the electrode 29 is provided on the GaAs substrate 31, so as to obtain the desired solar cell.

The grid of each sub-cell of the front-mounted three-junction cascaded solar cell provided by the present invention is matched, and the traditional front-mounting method is used for growth, and the growth process and manufacturing process are simple. Moreover, the bandgap combinations of the positive three-junction cascaded solar cells are ~1.93eV, ~1.39eV, and ~0.94eV, which effectively realizes segmental absorption of the solar spectrum, and the current mismatch of each sub-cell is small, reducing the The heat energy loss in the photoelectric conversion process can reach more than 51% under 100 times concentrated light.

Next, a specific implementation of the method for preparing a front-mounted triple-junction cascaded solar cell according to the present invention will be given in conjunction with the accompanying drawings.

Referring to FIG. 3 , the flow chart of the method for preparing a front-mounted triple-junction cascaded solar cell provided in this specific embodiment, the steps shown in FIG. 3 will be described in detail next.

Step S301, providing a GaAs substrate.

The positive-mounted triple-junction cascaded solar cell uses a P-type GaAs substrate 31, on which a P-type GaAs buffer layer 01 is grown first, and a GaInP transition layer 02 is grown next. As another preferred embodiment, the positive three-junction cascaded solar cell can also use an N-type GaAs substrate 31. On the N-type GaAs substrate 31, an N-type GaAs buffer layer 01 is first grown, and then a tunnel junction is grown. Realize the conversion from N-type to P-type, and then grow the GaInP transition layer 02.

Step S302 , sequentially growing a GaInP transition layer with stepped In composition, an InGaAs bottom cell, a first tunnel junction, an InGaAsP middle cell, a second tunnel junction, an InAlAs top cell, and an ohmic contact layer on the GaAs substrate.

A GaInP transition layer is grown on the GaAs substrate, and the GaInP transition layer selects the Ga _1-x In _x P material with stepped In composition as the gradient transition layer to realize the transition from the GaAs substrate to the InGaAs bottom cell, and the selection of x Values vary from 0.49 to 0.85. The Ga _1-x In _x P composition gradient transition layer can fully release the lattice mismatch stress. The Ga _1-x In _x P graded transition layer with stepped In composition can suppress threading dislocations from penetrating upwards to reach the InGaAs bottom cell through multiple interfaces.

An InGaAs bottom cell is grown on the GaInP transition layer, and the InGaAs bottom cell includes a P-type GaInP back field layer, a P-type InGaAs base region, an N-type InGaAs emitter region, and an N-type GaInP window layer arranged in a direction gradually away from the GaAs substrate. . Preferably, the composition of In in the InGaAs bottom cell is about 38%, and its forbidden band width is about 0.94eV.

A first tunnel junction is grown on the InGaAs bottom cell, and the first tunnel junction includes an N-type Al(Ga)InP or InAlAs barrier layer, an N-type GaInP re-doped layer, and a P-type InGaAs heavily doped layer, P-type Al(Ga)InP or InAlAs barrier layer.

An InGaAsP intermediate cell is grown on the first tunnel junction, and the InGaAsP intermediate cell includes a P-type Al(Ga)InP or InAlAs back field layer arranged in a direction gradually away from the GaAs substrate, a P-type InGaAsP base region, and an N-type InGaAsP emitter. area, N-type In _0.37 Al _0.63 As window layer. Preferably, the composition of In and As in the InGaAsP intermediate battery is about 38% and 57% respectively, and its forbidden band width is about 1.39eV.

A second tunnel junction is grown on the InGaAsP intermediate cell, and the second tunnel junction includes an N-type In _0.37 Al _0.63 As barrier layer, an N-type GaInP heavily doped layer, and a P-type InGaAs heavy Doped layer, P-type In _0.37 Al _0.63 As barrier layer.

An InAlAs top cell is grown on the second tunnel junction, and the InAlAs top cell includes a P-type In _0.30 Al _0.70 As back field layer, a P-type In _0.37 Al _0.63 As base region, and an N-type In _0.37 Al _0.63 As emission region, N-type In _0.3 Al _0.7 As window layer. Preferably, the In composition in the InAlAs top cell is 37%, and its forbidden band width is about 1.93eV.

A GaAs layer is grown on the InAlAs top cell as an ohmic contact layer, and its doping type is N type.

Step S303, preparing upper and lower electrodes on the ohmic contact layer and the GaAs substrate respectively to obtain a target solar cell.

Prepare the upper electrode (such as N electrode) on the surface of the ohmic contact layer of the grown InAlAs/InGaAsP/InGaAs positive mounted triple-junction cascaded solar cell on the InAlAs top cell, and prepare the lower electrode (such as P electrode) on the GaAs substrate, so that Get the solar cells you need.

The above growth process can be grown by MOCVD (MetalOrganic Chemical Vapor Deposition, metal organic compound chemical vapor deposition) or MBE (Molecular Beam Epitaxy, molecular beam epitaxy).

If grown by MOCVD, the N-type dopant atoms in the positive triple-junction cascaded solar cell are Si, Se, S or Te, and the P-type dopant atoms are Zn, Mg or C.

If it is grown by MBE method, the N-type dopant atoms in the positive triple-junction cascaded solar cell are Si, Se, S, Sn or Te, and the P-type dopant atoms are Be, Mg or C.

The preparation method of the front-mounted three-junction cascaded solar cell provided by the present invention adopts the front-mounted growth, which avoids the complicated process of first bonding with other supporting substrate materials and then removing the GaAs substrate for the inverted growth cell structure, and reduces the difficulty of manufacturing the cell. The composition-stepped Ga _1-x In _x P composition graded transition layer can suppress threading dislocations from penetrating upwards to the InGaAs bottom cell through multiple interfaces, and can fully release the lattice mismatch stress.

Next, a preferred embodiment of the present invention is given in conjunction with accompanying drawings 1 and 2, and the technical solution provided by the present invention is further described. This preferred embodiment adopts the MOCVD method to grow the front-mounted triple-junction cascaded solar cell of the present invention.

(1) On the P-type GaAs substrate 31 grow a P-type GaAs buffer layer 01 with a thickness of 0.1 μm, and then grow a P-type GaInP transition layer 02 with a thickness of 2.5 μm.

(2) Sequentially grow Ga _0.15 In _0.85 P with a P-type doping concentration of about 1×10 ¹⁸ cm ^-3 and a thickness of 0.02 microns as the back field layer 03, with a P-type doping of about 3×10 ¹⁷ cm ^-3 and a thickness of 2.0 microns The In _0.38 Ga _0.62 As of In 0.38 Ga 0.62 As is used as the base region 04, the N-type doping concentration is about 2×10 ¹⁸ cm ^-3 , and the In _0.38 Ga _0.62 As with a thickness of 0.2 microns is used as the emitter region 05, and the N-type is highly doped and the thickness is about 0.02 microns Ga _0.15 In _0.85 P is used as the window layer 06 to form the InGaAs bottom cell 24 .

(3) Sequentially grow In _0.37 Al _0.63 As or In _0.85 Al _0.15 P with an N-type doping concentration of 1×10 ¹⁸ cm ^-3 and a thickness of 0.03 microns as the barrier layer 07 with an N-type doping concentration of 1×10 ¹⁹ cm ^-3 Above, the Ga _0.15 In _0.85 P re-doped layer 08 with a thickness of 0.015 microns, the In _0.38 Ga _0.62 As re-doped layer 09 with a P-type doping concentration greater than 1×10 ¹⁹ cm ^-3 and a thickness of 0.015 microns, and the P-type doping concentration 1×10 ¹⁸ cm ⁻³ , In _0.37 (Ga)Al _0.63 As or In _0.85 (Ga)Al _0.15 P with a thickness of 0.03 μm is used as the barrier layer 10 to form the first tunnel junction 25 .

(4) Sequentially grow In _0.37 Al _0.63 As or In _0.85 Al _0.15 P with a P-type doping of 1×10 ¹⁸ cm ^-3 and a thickness of 0.02 microns as the back field layer 11 , with a P-type doping of about 3×10 ¹⁷ cm ^-3 InGaAsP with a thickness of 2.0 microns is used as the base region 12, and InGaAsP with an N-type doping of about 2×10 ¹⁸ cm ^-3 and a thickness of 0.2 microns is used as the emitter region 13, and an N-type highly doped, In _0.37 Al _0.63 As with a thickness of about 0.02 microns As the window layer 14, an InGaAsP bottom cell 26 is formed.

(5) Sequentially grow In _0.37 Al _0.63 As with an N-type doping concentration of 1×10 ¹⁸ cm ^-3 and a thickness of 0.03 microns as the barrier layer 15 , with an N-type doping concentration of 1×10 ¹⁹ cm ^-3 or more and a thickness of 0.015 microns Ga _0.15 In _0.85 P re-doped layer 16, In _0.38 Ga _0.62 As re-doped layer 17 with a P-type doping concentration greater than 1×10 ¹⁹ cm ^-3 and a thickness of 0.015 microns, and a P-type doping of 1×10 ¹⁸ cm ^-3 , In _0.37 Al _0.63 As with a thickness of 0.03 μm is used as the barrier layer 18 to form the second tunnel junction 27 .

(6) Sequentially grow In _0.30 Al _0.70 As with a P-type doping of 1×10 ¹⁸ cm ^-3 and a thickness of 0.02 microns as the back field layer 19 , with a P-type doping of about 3×10 ¹⁷ cm ^-3 and a thickness of 2.0 microns In _0.37 Al _0.63 As is used as the base region 20, the N-type doping concentration is about 2×10 ¹⁸ cm ^-3 , and the In _0.37 Al _0.63 As with a thickness of 0.2 microns is used as the emitter region 21, the N-type is highly doped, and the thickness is about 0.02 microns In _0.30 Al _0.70 As is used as the window layer 22 to form an InGaAs bottom cell 28 .

(7) Then grow In _0.38 Ga _0.62 As with an N-type doping concentration of about 6×10 ¹⁸ cm ⁻³ and a thickness of 0.5 μm as the ohmic contact layer 23 of the solar cell.

The structure of the InAlAs/InGaAsP/InGaAs positive triple-junction cascaded solar cell grown by MOCVD method is shown in Figure 1.

Solar cell electrode preparation process: prepare P electrode 29 on P-type GaAs substrate 31, and prepare N electrode 30 on the surface of N-type ohmic contact layer 11 to obtain the required solar cell. Its structure is shown in Figure 2.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered Be the protection scope of the present invention.

Claims (8)

1. a formal dress triple-junction monolithic solar cell, comprise GaAs substrate, it is characterized in that, comprise the GaInP transition zone, battery, the first tunnel junction, InGaAsP intermediate cell, the second tunnel junction, the InAlAs at the bottom of InGaAs that set gradually on gaas substrates and push up battery and ohmic contact layer, described GaInP transition zone selects the Ga1-xInxP material of In component stepping as gradual transition layer, realize by the transition of battery at the bottom of GaAs substrate to InGaAs, the value of x is changed to 0.85 by 0.49.

2. formal dress triple-junction monolithic solar cell according to claim 1, it is characterized in that, described InAlAs to push up at the bottom of battery, InGaAsP intermediate cell and InGaAs lattice constant match between battery, the band gap that described InAlAs pushes up battery at the bottom of battery, InGaAsP intermediate cell and InGaAs is combined as 1.93eV, 1.39eV, 0.94eV.

3. formal dress triple-junction monolithic solar cell according to claim 1, it is characterized in that, there is lattice mismatch between each sub-battery of described formal dress triple-junction monolithic solar cell and described GaAs substrate, the two realizes connecting by lattice mutation growth GaInP transition zone.

4. the formal dress triple-junction monolithic solar cell according to claim 1 or 3, it is characterized in that, described GaInP transition zone selects the Ga1-xInxP material of In component stepping as gradual transition layer, described gradual transition layer suppresses threading dislocation upwards to penetrate battery at the bottom of arrival InGaAs by multiple interface, and the value of x is changed to 0.85 by 0.49.

5. formal dress triple-junction monolithic solar cell according to claim 1, is characterized in that, described GaAs substrate adopts P type GaAs substrate, or adopts N-type GaAs substrate and realized by the conversion of N-type to P type by a tunnel junction.

6. a preparation method for formal dress triple-junction monolithic solar cell according to claim 1, is characterized in that, comprise step:

1) a GaAs substrate is provided;

2) grow battery, the first tunnel junction, InGaAsP intermediate cell, the second tunnel junction, InAlAs at the bottom of the GaInP transition zone of In component stepping, InGaAs on gaas substrates successively and push up battery and ohmic contact layer, described GaInP transition zone selects the Ga1-xInxP material of In component stepping as gradual transition layer, realize by the transition of battery at the bottom of GaAs substrate to InGaAs, the value of x is changed to 0.85 by 0.49;

3) on described ohmic contact layer and GaAs substrate, prepare upper and lower electrode respectively, obtain target solar cell, described bottom electrode is positioned at the lower surface of GaAs substrate.

7. formal dress triple-junction monolithic solar cell preparation method according to claim 6, it is characterized in that, each structure sheaf in described formal dress triple-junction monolithic solar cell all adopts mocvd method to grow and is formed, and N-type foreign atom is wherein Si, Se, S or Te, and P type foreign atom is Zn, Mg or C.

8. formal dress triple-junction monolithic solar cell preparation method according to claim 6, it is characterized in that, each structure sheaf in described formal dress triple-junction monolithic solar cell all adopts MBE method to grow and is formed, N-type foreign atom is wherein Si, Se, S, Sn or Te, and P type foreign atom is Be, Mg or C.