A triple-junction solar cell and its preparation method

Abstract

The present invention relates to the technical field of solar cells, and in particular to a triple-junction solar cell and a preparation method thereof. The triple-junction solar cell comprises, from bottom to top, a Ge substrate, a bottom cell, a buffer layer, a middle-bottom tunnel junction, a DBR, a middle cell, a middle-top tunnel junction, a top cell, and an ohmic contact layer; the middle cell comprises a base region, an emitter region, and a window layer, and the materials of the base region and the emitter region are both In x1 GaAsP, where 0.03≤x1≤0.10. The present invention effectively improves the radiation resistance of the middle cell by introducing P into the InGaAs material of the base region and the emitter region of the middle cell, and at the same time compensates for the lattice mismatch caused by the introduction of P by increasing the In component, thereby further improving the radiation resistance of the triple-junction solar cell; by adjusting the ratio of In and P in the middle cell material to adjust the strain of the epitaxial material, optimize the warping of the germanium substrate during the growth process, improve the crystal quality of the epitaxial material, and enhance the photoelectric conversion efficiency of the cell chip.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a triple-junction solar cell and a preparation method thereof. Background Art

[0002] Gallium arsenide triple-junction solar cells, with their excellent photoelectric conversion efficiency, outstanding high temperature resistance and long service life, have shown irreplaceable importance in the field of space exploration, especially as the main power source for artificial satellites, spacecraft and space laboratories. However, with the deepening and expansion of space exploration, more stringent requirements are placed on the performance of solar cells. The new generation of solar cells for space use must not only have higher photoelectric conversion efficiency, but also have stronger resistance to radiation attenuation.

[0003] The InGaAs material of the middle cell of the triple-junction solar cell has poor radiation resistance, so a distributed Bragg reflector (DBR) is introduced to effectively increase the optical path and reduce the thickness of the middle cell, thereby reducing the damage to the middle cell by high-energy radiation particles in space and effectively improving the radiation resistance. However, this improvement in radiation resistance has its limits and is difficult to meet the more stringent needs of space exploration in the future. At the same time, since the germanium substrate material is relatively soft, it is easy to deform during the high-temperature growth of epitaxial materials, which affects the crystal quality and photoelectric conversion efficiency.

[0004] Therefore, it is of great significance to develop a triple-junction solar cell that can improve radiation resistance and photoelectric conversion efficiency without changing the cell structure. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a triple-junction solar cell and a method for preparing the same, aiming to improve the radiation resistance and photoelectric conversion efficiency of the entire triple-junction solar cell without changing the cell structure.

[0006] The purpose of the present invention is to provide a triple-junction solar cell, wherein the triple-junction solar cell comprises, from bottom to top, a Ge substrate, a bottom cell, a buffer layer, a middle bottom tunnel junction, a DBR, a middle cell, a middle top tunnel junction, a top cell, and an ohmic contact layer; the middle cell comprises a base region, an emitter region, and a window layer, and the materials of the base region and the emitter region are both In x1 GaAsP, where 0.03≤x1≤0.10.

[0007] In this technical solution, by introducing P into the InGaAs material of the base region and the emission region of the middle cell, the radiation resistance of the middle cell InGaAs can be effectively improved. At the same time, after the introduction of P, the lattice mismatch caused by the introduction of P can be compensated by increasing the In component, and the increase in the In component can narrow the band gap of the middle cell, so that the middle cell can absorb a wider spectrum, thereby increasing the current of the middle cell and further improving the radiation resistance of the triple-junction solar cell. The triple-junction solar cell does not need to change the cell structure while improving the radiation resistance, and has little impact on the epitaxy, chip and packaging processes.

[0008] Furthermore, the total thickness of the base region and the emitter region is 1.5 μm to 2.5 μm, and is InGaAsP material grown alternately under two different growth conditions; the material of the window layer is AlInP or GaInP, and the thickness is 0.05 μm to 0.2 μm.

[0009] Furthermore, the material of the buffer layer is In 0.01 GaAs; the bottom tunnel junction is N ++ GaAs / P ++ GaAs structure.

[0010] Furthermore, the DBR is a multi-period In 0.01 GaAs / In 0.01 AlGaAs material, period number > 5 pairs.

[0011] Furthermore, the middle top tunnel junction is N ++ GaInP / P ++ AlGaAs structure, thickness is 0.01μm~0.03μm.

[0012] Furthermore, the top battery is made of Al x2 The top cell is composed of a GaInP back electric field, a GaInP base region, a GaInP emission region and an AlInP window layer, wherein 0.15≤x2≤0.4, and the lattice constant of the top cell matches the lattice constant of the middle cell.

[0013] Furthermore, the material of the ohmic contact layer is In 0.01 GaAs, thickness is 0.4μm~0.6μm.

[0014] The present invention also provides a method for preparing a triple-junction solar cell, which specifically comprises the following steps:

[0015] S1. Growing a bottom cell on a Ge substrate;

[0016] S2. Growth buffer layer;

[0017] S3. Growth of bottom tunnel junction;

[0018] S4. Growth of DBR;

[0019] S5. Growing battery;

[0020] S6. Top tunneling junction during growth;

[0021] S7. Growth of top cell;

[0022] S8. Growing an ohmic contact layer.

[0023] Furthermore, when growing the bottom cell, an emission region is first formed by diffusion of PH3, and then a GaInP or AlGaInP nucleation layer is grown, and the nucleation layer also serves as a window layer of the bottom cell.

[0024] Furthermore, in the growing battery x1 In the process of growing GaAsP material, firstly, AsH3 is introduced at a flow rate of 400sccm, and PH3 is introduced at a flow rate of 200sccm to grow InGaAsP with a thickness of 150nm, then AsH3 is introduced at a flow rate of 300sccm, and PH3 is introduced at a flow rate of 500sccm to grow InGaAsP with a thickness of 100nm, and this method is repeated for 5 to 9 times. In this technical solution, the ratio of P doping can be adjusted by adjusting the thickness ratio of InGaAsP grown under the two conditions. Generally, the thickness grown by AsH3:400 / PH3:200 is thinner, and the thickness grown by AsH3:300 / PH3:500 is thicker, which can increase the doping ratio of P.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention makes improvements in terms of materials and component contents, introduces P into the InGaAs material of the base region and the emitter region of the middle cell, and adjusts the doping ratio of P by controlling the growth conditions, which can effectively improve the radiation resistance of the InGaAs of the middle cell. At the same time, by increasing the In component to compensate for the lattice mismatch caused by the introduction of P, the band gap of the middle cell can be narrowed, and a wider spectrum can be absorbed, thereby increasing the current of the middle cell, and further improving the radiation resistance of the triple-junction solar cell. There is no need to change the cell structure, and the impact on the epitaxy, chip and packaging processes is small, and the applicability is stronger.

[0027] 2. Since the germanium substrate used is relatively soft and easily deformed during the high-temperature growth of epitaxial materials, the present invention adjusts the ratio of In and P in the battery to adjust the strain of the epitaxial material and optimize the warping of the germanium substrate during the growth process, thereby improving the crystal quality of the epitaxial material, increasing the open circuit voltage, and improving the photoelectric conversion efficiency of the battery chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of the triple-junction solar cell of the present invention.

[0029] Explanation of the numbers in the schematic diagram:

[0030] 1. Ge substrate; 2. Bottom cell; 3. Buffer layer; 4. Middle-bottom tunnel junction; 5. DBR; 6. Middle cell; 7. Middle-top tunnel junction; 8. Top cell; 9. Ohmic contact layer. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] In the description of the present application, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present application.

[0033] In the description of the present application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0034] See also Figure 1 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the form, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0035] An embodiment of the present invention provides a triple-junction solar cell, the structural schematic diagram of which is shown in FIG. Figure 1As shown, the triple-junction solar cell comprises, from bottom to top, a Ge substrate 1, a bottom cell 2, a buffer layer 3, a middle bottom tunnel junction 4, a DBR 5, a middle cell 6, a middle top tunnel junction 7, a top cell 8, and an ohmic contact layer 9.

[0036] In some specific embodiments, the middle battery includes a base region, an emitter region and a window layer, and the materials of the base region and the emitter region are both In x1 GaAsP, where 0.03≤x1≤0.10. Specifically, the total thickness of the base region and the emitter region is 1.5μm to 2.5μm, and is an InGaAsP material grown alternately under two different growth conditions; the material of the window layer is AlInP or GaInP, and the thickness is 0.05μm to 0.2μm. By introducing P into the InGaAs material of the base region and the emitter region of the middle cell, and by controlling the ratio of the thickness of the InGaAsP grown under the two conditions, the doping ratio of P is controlled, and the radiation resistance of the middle cell InGaAs can be effectively improved; at the same time, by increasing the In component to compensate for the lattice mismatch caused by the introduction of P, the current of the middle cell is increased, and the radiation resistance of the triple-junction solar cell is further improved.

[0037] In some specific embodiments, the material of the buffer layer is In 0.01 GaAs; the bottom tunnel junction is N ++ GaAs / P ++ GaAs structure.

[0038] In some specific embodiments, the DBR is a multi-period In 0.01 GaAs / In 0.01 AlGaAs material, period number > 5 pairs.

[0039] In some specific embodiments, the top tunnel junction is N ++ GaInP / P ++ AlGaAs structure, thickness is 0.01μm~0.03μm.

[0040] In some specific embodiments, the top cell is made of Al x2 The top cell is composed of a GaInP back electric field, a GaInP base region, a GaInP emission region and an AlInP window layer, wherein 0.15≤x2≤0.4, and the lattice constant of the top cell matches the lattice constant of the middle cell.

[0041] In some specific embodiments, the material of the ohmic contact layer is In 0.01 GaAs, thickness is 0.4μm~0.6μm.

[0042] Some embodiments of the present invention provide a method for preparing a triple-junction solar cell, which specifically includes the following steps:

[0043] S1. Growing a bottom cell on a Ge substrate; specifically, forming a bottom cell emitter region by PH3 diffusion at a high temperature of 680°C to 730°C, and then growing a GaInP or AlGaInP nucleation layer, which also serves as a window layer of the bottom cell;

[0044] S2. growing a buffer layer; specifically, the material of the buffer layer is InGaAs, and the thickness is 0.1 μm to 0.8 μm;

[0045] S3. Growing a mid-bottom tunnel junction; specifically, the mid-bottom tunnel junction adopts N ++ GaAs / P ++ GaAs structure, thickness is 0.01μm~0.03μm;

[0046] S4. Growth of DBR; specifically, DBR is a multi-period In 0.01 GaAs / In 0.01 AlGaAs material, period number>5 pairs;

[0047] S5. Growing a middle battery; Specifically, the middle battery includes a base region, an emitter region and a window layer, and the materials of the base region and the emitter region are In x1 GaAsP, where 0.03≤x1≤0.10, the total thickness of the base region and the emitter region is 1.5μm to 2.5μm, and the In x2 In the process of growing GaAsP material, firstly, AsH3 is introduced at a flow rate of 400 sccm, and PH3 is introduced at a flow rate of 200 sccm to grow InGaAsP with a thickness of 150 nm, then AsH3 is introduced at a flow rate of 300 sccm, and PH3 is introduced at a flow rate of 500 sccm to grow InGaAsP with a thickness of 100 nm, and the above method is alternately cycled for 5 to 9 times, and the material of the window layer is AlInP or GaInP, and the thickness is 0.05 μm to 0.2 μm;

[0048] S6. Growing a middle top tunnel junction; specifically, the middle top tunnel junction adopts N ++ GaInP / P ++ AlGaAs structure, thickness is 0.01μm~0.03μm;

[0049] S7. Growth of the top cell; specifically, the top cell lattice constant matches the middle cell, consisting of Al x2 It is composed of GaInP back electric field, GaInP base region, GaInP emission region and AlInP window layer, wherein 0.15≤x2≤0.4;

[0050] S8. Growing an ohmic contact layer; specifically, the material of the ohmic contact layer is In 0.01 GaAs, thickness is 0.4μm~0.6μm.

[0051] In order to further illustrate the present invention, a method for preparing a triple-junction solar cell provided by the present invention is described in detail below in conjunction with specific embodiments.

[0052] Example 1

[0053] A method for preparing a triple-junction solar cell comprises the following steps:

[0054] S1. A bottom cell is grown on a Ge substrate, and a bottom cell emission region is formed by PH3 diffusion at 680°C, and then a GaInP or AlGaInP nucleation layer is grown, which also serves as a window layer of the bottom cell;

[0055] S2. growing an InGaAs buffer layer with a thickness of 0.1 μm;

[0056] S3. Growth structure is N ++ GaAs / P ++ GaAs, mid-bottom tunnel junction with a thickness of 0.01 μm;

[0057] S4. Growth of 10 cycles of In 0.01 GaAs / In 0.01 AlGaAs material as DBR;

[0058] S5. Growing battery; the battery includes a base region, an emitter region and a window layer, and the materials of the base region and the emitter region are In 0.03 GaAsP, the total thickness of the base and emitter regions is 2.5 μm. x2 In the process of growing GaAsP material, firstly, AsH3 is introduced at a flow rate of 400sccm, and PH3 is introduced at a flow rate of 200sccm to grow InGaAsP with a thickness of 150nm, then AsH3 is introduced at a flow rate of 300sccm, and PH3 is introduced at a flow rate of 500sccm to grow InGaAsP with a thickness of 100nm, and the above method is alternately cycled for 9 times, and the material of the window layer is AlInP or GaInP, and the thickness is 0.05μm;

[0059] S6. Growth structure is N ++ GaInP / P ++ AlGaAs, mid-top tunnel junction with a thickness of 0.01 μm;

[0060] S7. Growth of a top cell with a lattice constant matching that of the middle cell; the top cell is made of Al 0.15 It is composed of GaInP back electric field, GaInP base region, GaInP emission region and AlInP window layer;

[0061] S8. Growth material is In 0.01GaAs, ohmic contact layer with a thickness of 0.4μm.

[0062] Example 2

[0063] A method for preparing a triple-junction solar cell comprises the following steps:

[0064] S1. A bottom cell is grown on a Ge substrate, and a bottom cell emission region is formed by PH3 diffusion at 730°C, and then a GaInP or AlGaInP nucleation layer is grown, which also serves as a window layer of the bottom cell;

[0065] S2. growing an InGaAs buffer layer with a thickness of 0.8 μm;

[0066] S3. Growth structure is N ++ GaAs / P ++ GaAs, mid-bottom tunnel junction with a thickness of 0.03 μm;

[0067] S4. Growth of 8 cycles of In 0.01 GaAs / In 0.01 AlGaAs material as DBR;

[0068] S5. Growing battery; the battery includes a base region, an emitter region and a window layer, and the materials of the base region and the emitter region are In 0.1 GaAsP, the total thickness of the base and emitter regions is 1.5 μm. x2 In the process of growing GaAsP material, firstly, AsH3 is introduced at a flow rate of 400 sccm, and PH3 is introduced at a flow rate of 200 sccm to grow InGaAsP with a thickness of 150 nm, then AsH3 is introduced at a flow rate of 300 sccm, and PH3 is introduced at a flow rate of 500 sccm to grow InGaAsP with a thickness of 100 nm, and the above method is alternately cycled for 5 times, and the material of the window layer is AlInP or GaInP, and the thickness is 0.2 μm;

[0069] S6. Growth structure is N ++ GaInP / P ++ AlGaAs, mid-top tunnel junction with a thickness of 0.03 μm;

[0070] S7. Growth of a top cell with a lattice constant matching that of the middle cell; the top cell is made of Al 0.4 It is composed of GaInP back electric field, GaInP base region, GaInP emission region and AlInP window layer;

[0071] S8. Growth material is In 0.01 GaAs, ohmic contact layer with a thickness of 0.6μm.

[0072] In summary, the present invention makes improvements in terms of materials and component contents. By introducing P into the InGaAs material of the base region and the emitter region of the middle cell, and by controlling the ratio of the thickness of InGaAsP grown under two conditions, the doping ratio of P is controlled, thereby effectively improving the radiation resistance of the InGaAs of the middle cell; at the same time, by increasing the In component to compensate for the lattice mismatch caused by the introduction of P, the current of the middle cell can be increased, and the radiation resistance of the triple-junction solar cell can be further improved; by adjusting the ratio of In and P in the middle cell material, the strain of the epitaxial material is adjusted, and the warping of the germanium substrate during the growth process is optimized, thereby improving the crystal quality of the epitaxial material, increasing the open circuit voltage, and improving the photoelectric conversion efficiency of the battery chip.

[0073] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A triple-junction solar cell, characterized in that: The triple-junction solar cell comprises, from bottom to top, a Ge substrate, a bottom cell, a buffer layer, a middle bottom tunnel junction, a DBR, a middle cell, a middle top tunnel junction, a top cell, and an ohmic contact layer; the middle cell comprises a base region, an emitter region, and a window layer, and the materials of the base region and the emitter region are both In x1 GaAsP, where 0.03≤x1≤0.10; The total thickness of the base region and the emitter region is 1.5μm to 2.5μm, and is an InGaAsP material grown alternately under two different growth conditions; the two different growth methods are: first, AsH3 is introduced at a flow rate of 400sccm, and PH3 is introduced at a flow rate of 200sccm to grow InGaAsP with a thickness of 150nm, and then AsH3 is introduced at a flow rate of 300sccm, and PH3 is introduced at a flow rate of 500sccm to grow InGaAsP with a thickness of 100nm.

2. A triple-junction solar cell according to claim 1, characterized in that: The material of the window layer is AlInP or GaInP, and the thickness is 0.05 μm to 0.2 μm.

3. A triple-junction solar cell according to claim 1, characterized in that: The material of the buffer layer is In 0.01 GaAs; the bottom tunnel junction is N ++ GaAs / P ++ GaAs structure.

4. A triple-junction solar cell according to claim 1, characterized in that: The DBR is a multi-period In 0.01 GaAs / In 0.01 AlGaAs material, period number > 5 pairs.

5. A triple-junction solar cell according to claim 1, characterized in that: The top tunnel junction is N ++ GaInP / P ++ AlGaAs structure, thickness is 0.01μm~0.03μm.

6. A triple-junction solar cell according to claim 1, characterized in that: The top cell is made of Al x2 The top cell is composed of a GaInP back electric field, a GaInP base region, a GaInP emission region and an AlInP window layer, wherein 0.15≤x2≤0.4, and the lattice constant of the top cell matches the lattice constant of the middle cell.

7. A triple-junction solar cell according to claim 1, characterized in that: The material of the ohmic contact layer is In 0.01 GaAs, thickness is 0.4μm~0.6μm.

8. A method for preparing a triple-junction solar cell according to any one of claims 1 to 7, characterized in that: The specific steps include: S1. Growing a bottom cell on a Ge substrate; S2. Growth buffer layer; S3. Growth of bottom tunnel junction; S4. Growth of DBR; S5. Growing battery; S6. Top tunneling junction during growth; S7. Growth of top cell; S8. Growing an ohmic contact layer.

9. The method for preparing a triple-junction solar cell according to claim 8, characterized in that: When growing the bottom cell, an emission region is first formed by diffusion of PH3, and then a GaInP or AlGaInP nucleation layer is grown, and the nucleation layer also serves as a window layer of the bottom cell.

10. The method for preparing a triple-junction solar cell according to claim 8, characterized in that: In the growth battery x1 In the process of GaAsP material, AsH3 is first introduced at a flow rate of 400sccm and PH3 is introduced at a flow rate of 200sccm to grow InGaAsP with a thickness of 150nm, and then AsH3 is introduced at a flow rate of 300sccm and PH3 is introduced at a flow rate of 500sccm to grow InGaAsP with a thickness of 100nm. This method is then repeated for 5 to 9 times.

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