Triple-junction quantum well solar cell epitaxial structure and manufacturing method thereof

Abstract

The invention provides a three-junction quantum well solar cell epitaxial structure and a manufacturing method thereof, the three-junction quantum well solar cell epitaxial structure comprises a substrate serving as a first sub-cell, a first tunnel junction, a second sub-cell, a second tunnel junction and a third sub-cell which are sequentially stacked from bottom to top, and the three sub-cells are connected through the tunnel junctions; wherein the first sub-cell is a Ge cell, the second sub-cell is an InGaAs cell, the third sub-cell is a GaInP / AlGaInP quantum well cell, the third sub-cell comprises a (Al < x > 1 < Ga < 1-x > 1 < y > 1 < In < 1-y > 1 < P) back field layer, a quantum well base region, a (Al < x > 4 < Ga < 1-x > 4 < y > 4 < In < 1-y > 4 < P) emitter region and an Al < x > 5 < In < 1-y > 5 window layer which are sequentially stacked from bottom to top, the quantum well base region is composed of a Ga < x > 2 < In < 1-x > 2 layer and a (Al < x > 3 < Ga < 1-x > 3 < y > 3 < In < 1 x is larger than or equal to 0.5 and smaller than or equal to 0.8, y is larger than or equal to 0.5 and smaller than or equal to 0.8, y is equal to 0.5, the GaInP / AlGaInP quantum well structure is used for replacing a traditional AlGaInP material to serve as a top cell material, the open-circuit voltage of the solar cell is increased, and meanwhile the defect that the short-circuit current of the AlGaInP / GaAs / Ge solar cell is insufficient is overcome.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor devices, and particularly relates to a three-junction quantum well solar cell epitaxial structure and a manufacturing method thereof. BACKGROUND

[0002] With the development of society, solar energy as a clean and sustainable energy is attracting more and more attention. The lattice-matched three-junction solar cell (GaInP / GaAs / Ge) is widely used in satellites and spacecrafts due to its high photoelectric conversion efficiency and low radiation damage. However, due to the bandgap limitation of the material and the current matching of the solar cell, the photoelectric conversion efficiency of the traditional GaInP / GaAs / Ge three-junction solar cell has reached the limit. In order to meet the market demand for higher photoelectric conversion efficiency, there are two existing methods: 1. Using GaInP / InGaAs / Ge large mismatch solar cell, using InGaAs material to expand the absorption spectrum of the middle cell (i.e. the second sub-cell), increasing the short-circuit current of the solar cell, and thus increasing the photoelectric conversion efficiency of the solar cell. However, the lattice of InGaAs material and Ge material is not matched, the material lattice mismatch is too large, which will reduce the material growth quality, and also will appear dislocation line, resulting in performance decline.

[0003] 2. Using AlGaInP / GaAs / Ge solar cell, using AlGaInP material to increase the bandgap of the top cell (i.e. the third sub-cell), to improve the open-circuit voltage of the solar cell, and to increase the absorption spectrum of the middle cell and the thickness of the top cell, to improve the overall short-circuit current, and thus to increase the photoelectric conversion efficiency of the solar cell. However, due to the high Al element in the AlGaInP material, the material will approach to the indirect bandgap, and the shorter the wavelength of the AlGaInP material, the closer to the indirect bandgap, the absorption efficiency will decrease sharply, which will result in that the short-circuit current of the solar cell cannot be compensated by increasing the thickness of the absorption region, and finally the designed current cannot be reached, resulting in low efficiency. SUMMARY

[0004] The present application aims to provide a three-junction quantum well solar cell epitaxial structure and a manufacturing method thereof, which uses GaInP / AlGaInP quantum well structure instead of traditional AlGaInP material as top cell material, to increase the open-circuit voltage of the solar cell, and to compensate for the shortcoming of insufficient short-circuit current of the AlGaInP / GaAs / Ge solar cell.

[0005] To achieve the above object, the solution of the present application is to provide a three-junction quantum well solar cell epitaxial structure, comprising a substrate as a first sub-cell, a first tunnel junction, a second sub-cell, a second tunnel junction and a third sub-cell which are sequentially stacked from bottom to top, and the three sub-cells are connected through the tunnel junctions; wherein the first sub-cell is a Ge cell, the second sub-cell is an InGaAs cell, and the third sub-cell is a GaInP / AlGaInP quantum well cell, the third sub-cell comprises a (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, quantum well base region, (Al x4 Ga 1-x4 ) y4 In 1- y4 P emitter region and Al x5 In 1-x5 P window layer, the quantum well base region is composed of alternately grown Ga x2 In 1-x2 P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer, wherein 0.5≤x2≤0.6, 0.5≤x3≤0.8, y3=0.5.

[0006] Optionally, the doping element of the quantum well base region is a P-type doping element Zn, and the doping amount is 1E 16 cm -3 -1E 17 cm -3 -1E x2 In 1-x2 P layer is 3nm-20nm, and the thickness of a single (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer is 10nm-20nm, and the alternately grown number is 80 pairs-150 pairs.

[0007] Optionally, in the alternately grown Ga x2 In 1-x2 P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer, x2=0.5, x3=0.8, y3=0.5, the thickness of a single Ga x2 In 1-x2 P layer is 8nm, and the thickness of a single (Al x3 Ga 1-x3 )y3 In 1-y3 The thickness of the P layer is 8nm, and the number of the alternating pairs is 110.

[0008] Optionally, the Ga x2 In 1-x2 The P layer and the (Al x3 Ga 1-x3 ) y3 In 1-y3 The number of the alternating pairs of the P layer is 100, and the Ga x2 In 1- x2 The total thickness of the P layer is 880nm.

[0009] Optionally, the (Al x1 Ga 1-x1 ) y1 In 1-y1 The P back field layer, the (Al x4 Ga 1-x4 ) y4 In 1-y4 The P emission area and the Al x5 In 1-x5 In the P window layer, 0.5≤x1≤0.8, y1=0.5, 0≤x4≤0.5, y4=0.5, and 0.5≤x5≤0.6.

[0010] Optionally, the second sub-cell comprises, from bottom to top, a DBR layer, an AlGaAs back field layer, an InGaAs base area, an InGaAs emission area, and an AlInP window layer.

[0011] Optionally, the substrate is a P-type Ge substrate, n-type phosphorus diffusion is performed on the P-type Ge substrate, the most surface layer of Ge is diffused into n-type to form a pn junction of the first sub-cell, and a GaInP nucleation layer and a GaAs buffer layer are grown on the P-type Ge substrate.

[0012] Optionally, the first tunnel junction is composed of n-type heavily doped GaAs and p-type heavily doped GaAs, and the total thickness is 10nm-30nm, wherein the n-type heavily doped GaAs is doped with Te, and the doping amount is 1E 19 cm -3 -2E 19 cm -3 ; the p-type heavily doped GaAs is doped with C, and the doping amount is 1E 20 cm -3 -2E 20 cm -3 .

[0013] Optionally, the second tunnel junction has a thickness of 10nm-30nm and is composed of n-type heavily doped Gax In 1-x P and p-type heavily doped Al x1 Ga 1-x1 As composition, wherein, 0.5≤x≤0.6, 0.4≤x1≤0.6, n-type heavily doped Ga x In 1-x P doped Si, and the doping amount is 1E 19 cm -3 -2E 19 cm -3 , p-type heavily doped Al x1 Ga 1-x1 As doped C, and the doping amount is 1E 20 cm -3 -2E 20 cm -3 .

[0014] The application also provides a manufacturing method of a three-junction quantum well solar cell epitaxial structure, which is used for preparing the epitaxial structure and comprises the following steps: providing a substrate, performing n-type phosphorus diffusion on the substrate to obtain a pn junction of a first sub-cell, i.e., the substrate is used as the first sub-cell, and the first sub-cell is a Ge cell; growing a first tunnel junction on the substrate; growing a second sub-cell on the first tunnel junction, and the second sub-cell is an InGaAs cell; growing a second tunnel junction on the second sub-cell; growing a third sub-cell on the second tunnel junction, and the third sub-cell is a GaInP / AlGaInP quantum well cell, and the third sub-cell comprises, from bottom to top, (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, quantum well base region, (Al x4 Ga 1-x4 ) y4 In 1-y4 P emission region and Al x5 In 1-x5 P window layer, and the quantum well base region is composed of alternately grown Ga x2 In 1-x2 P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer, wherein, 0.5≤x2≤0.6, 0.5≤x3≤0.8, and y3=0.5.

[0015] After the above scheme is adopted, the application has the following beneficial effects: 1、The third sub-cell of the application adopts GaInP / AlGaInP quantum well structure instead of traditional AlGaInP material as the base region of the third sub-cell, which is equivalent to using GaInP material with wider band gap as the well layer of quantum well and as the main absorption region, directly improving the band gap of the entire third cell, thereby reducing the light emitting wavelength of the quantum well, reducing the Al component of the absorption region, making up for the shortcomings of using pure AlGaInP material as the base region, and under the MQW structure, the Ga component x2 of the GaInP material is 0.5-0.6, which is a high Ga component, making the band gap wider, further reducing the light emitting wavelength and absorption spectrum of the quantum well, and the absorption spectrum of the GaInP material will be reduced to be consistent with the AlGaInP material, increasing the open circuit voltage of the solar cell.

[0016] 2、The third sub-cell uses GaInP material as the main component of the absorption region, increasing the absorption capacity of the material and making up for the shortcoming of insufficient short-circuit current of the AlGaInP / GaAs / Ge solar cell.

[0017] 3、The third sub-cell uses GaInP as the quantum well, which shortens the absorption wavelength of the top cell, allows a part of the absorption spectrum to be absorbed by the middle cell, thereby increasing the absorption spectrum of the middle cell, and can make the short-circuit current of the solar cell larger, thereby increasing the photoelectric conversion efficiency of the solar cell.

[0018] 4、GaInP and AlGaInP materials are lattice matched with Ge material, avoiding dislocations caused by lattice mismatch, improving the crystal quality of the grown material and ensuring the stability of the solar cell. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The figure is the epitaxial structure diagram of the solar cell of the application.

[0020] Figure 2 The figure is the structure diagram of the quantum well base region of the application.

[0021] Figure 3 The figure is the method flow chart of the application.

[0022] REFERENCE NUMERALS: 1、Substrate; 2、GaInP nucleation layer; 3、GaAs buffer layer; 4、First tunnel junction; 5、DBR layer; 6、AlGaAs back field layer; 7、InGaAs base region; 8、InGaAs emission region; 9、AlInP window layer; 10、Second tunnel junction; 11、AlGaInP back field layer; 12、Quantum well base region; 13、AlGaInP emission region; 14、AlInP window layer; 15、GaAs ohmic contact layer. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application, and the range of the present application includes two end values.

[0024] As Figures 1-2 indicated, the present application provides a three-junction quantum well solar cell epitaxial structure, which provides a three-junction quantum well solar cell epitaxial structure, including a first sub-cell, a first tunnel junction 4, a second sub-cell, a second tunnel junction 10 and a third sub-cell which are sequentially stacked from bottom to top, and the three sub-cells are connected through the corresponding tunnel junctions; wherein the first sub-cell is the bottom cell and also serves as the substrate 1, and is specifically a Ge cell; the second sub-cell is the middle cell, and is specifically an InGaAs cell; and the third sub-cell is the top cell, and is specifically a GaInP / AlGaInP quantum well cell.

[0025] Specifically, the third sub-cell includes an AlGaInP back field layer 11, a quantum well base region 12, an AlGaInP emission region 13 and an AlInP window layer 14 which are sequentially stacked from bottom to top.

[0026] As Figure 2 indicated, the quantum well base region 12 is composed of alternately grown GaInP / AlGaInP, and specifically composed of Ga x2 In 1-x2 P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer, wherein 0.5≤x2≤0.6, 0.5≤x3≤0.8, y3=0.5, the thickness of a single Ga x2 In 1-x2 P layer is 3nm-20nm, and the thickness of the Ga x2 In 1-x2 P layer can change the absorption spectrum of the quantum well base region, the thinner the thickness of the Ga x2 In 1-x2 P layer, the narrower the absorption spectrum, and the thickness of the Ga x2 In 1-x2The thickness of the P layer can be set according to requirements; the GaInP / AlGaInP quantum well structure is used instead of the traditional AlGaInP material as the base region of the third sub-cell, the GaInP / AlGaInP quantum well structure is used instead of the traditional AlGaInP material as the base region of the third sub-cell, which is equivalent to using the wider band gap material GaInP as the well layer of the quantum well, and using it as the main absorption region, directly increasing the band gap of the entire third cell, thereby reducing the light emission wavelength of the quantum well, reducing the Al component of the absorption region, making up for the shortcomings of using pure AlGaInP material as the base region, and under the MQW structure, the Ga component x2 of the GaInP material is 0.5-0.6, which is a high Ga component, so that the band gap is wider, further reducing the light emission wavelength and absorption spectrum of the quantum well, and the absorption spectrum of the GaInP material is reduced to be consistent with the AlGaInP material, increasing the open-circuit voltage of the solar cell, and at the same time, the third sub-cell uses GaInP material as the main component of the absorption region, increasing the absorption capacity of the material, making up for the shortcoming of insufficient short-circuit current of the AlGaInP / GaAs / Ge solar cell.

[0027] Optionally, the thickness of a single (Al x3 Ga 1-x3 ) y3 In 1-y3 The thickness of the P layer is 10nm-20nm, the Ga x2 In 1-x2 The thickness of the P layer and the (Al x3 Ga 1-x3 ) y3 In 1-y3 The alternating number of the P layer is 80 pairs-150 pairs, the doping element of the quantum well base region is a P-type doping element Zn, and the doping amount is 1E 16 cm -3 -1E 17 cm -3 .

[0028] Optionally, in an embodiment, in the alternatingly grown Ga x2 In 1-x2 P layer and the (Al x3 Ga 1-x3 ) y3 In 1-y3 In the P layer, x2=0.5, x3=0.8, y3=0.5, the thickness of a single Ga x2 In 1-x2 P layer is 8nm, the thickness of a single (Al x3 Ga 1-x3 ) y3 In 1-y3 The thickness of the P layer is 8nm, and the alternating number is 110 pairs, at this time the Ga x2 In1-x2 The PL wavelength of the P layer is 630 nm, and the band gap is 1.968 ev, which is higher than that of the GaInP sub-cell (PL wavelength 650 nm, band gap 1.907 ev) of a conventional GaInP / GaAs / Ge solar cell, thereby increasing the band gap and increasing the open circuit voltage of the solar cell.

[0029] Optionally, in another embodiment, the Ga x2 In 1-x2 The P layer and the (Al x3 Ga 1-x3 ) y3 In 1-y3 The number of pairs of the P layer is 100 pairs, and the thickness of the single Ga x2 In 1-x2 The thickness of the P layer is 8.8 nm, and the thickness of the single Ga x2 In 1-x2 The total thickness of the P layer is 880 nm, and the thickness of the single Ga x2 In 1- x2 The P layer can have a thickness and a band gap similar to those of the AlGaInP sub-cell of a conventional AlGaInP / GaAs / Ge solar cell. Since the absorption region mainly comprises GaInP material, the absorption capacity of the material is increased, thereby compensating for the shortcoming of insufficient short circuit current of the AlGaInP / GaAs / Ge solar cell.

[0030] In addition, the GaInP and AlGaInP materials in the third sub-cell are lattice matched with the Ge material, thereby avoiding dislocations caused by lattice mismatch, improving the crystal quality of the grown material, and ensuring the stability of the solar cell.

[0031] Optionally, the AlGaInP back field layer 11 specifically comprises (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, wherein 0.5≤x1≤0.8, and y1=0.5; the (Al x1 Ga 1-x1 ) y1 In 1-y1 The thickness of the P back field layer is 50 nm-100 nm, the doping element is a P-type doping element Zn, and the doping amount is 1E 18 cm -3 -4E 18 cm -3 .

[0032] Optionally, the AlGaInP emission region 13 specifically comprises (Al x4 Ga 1-x4 ) y4 In 1-y4P emission region, wherein 0≤x4≤0.5, y4=0.5, the (Al x4 Ga 1-x4 ) y4 In 1-y4 The energy band gap of the P emission region is adjusted to be consistent with the quantum well base region, and the (Al x4 Ga 1-x4 ) y4 In 1-y4 The thickness of the P emission region is 50nm-200nm, the doping element is N-type doping element Si, and the doping amount is 5E 17 cm -3 -5E 18 cm -3 .

[0033] Optionally, the AlInP window layer 14 is specifically Al x5 In 1-x5 P window layer, wherein 0.5≤x5≤0.6, the Al x5 In 1-x5 P window layer has a thickness of 20nm-50nm, the doping element is N-type doping element Si, and the doping amount is 1E 18 cm -3 -5E 18 cm -3 .

[0034] Optionally, the second sub-cell includes, from bottom to top, a DBR layer 5, an AlGaAs back field layer 6, an InGaAs base region 7, an InGaAs emission region 8, and an AlInP window layer 9.

[0035] The DBR layer 5 is a distributed Bragg reflector, which is a mirror structure and includes an adjustable multi-layer structure composed of two optical materials, and is grown by alternately growing In x1 Ga 1-x1 As / Al x2 Ga 1-x2 As two materials, wherein x1=0.01, 0.6≤x2≤1, the optical thickness of a single layer of In x1 Ga 1-x1 As material is one-fourth of the center wavelength of the reflection spectrum, the optical thickness of a single layer of Al x2 Ga 1-x2 As material is one-fourth of the center wavelength of the reflection spectrum, and the center wavelength of the reflection spectrum is between 850nm and 900nm; the alternating number of the DBR layer 5 is between 8 pairs and 25 pairs, the doping element is P-type doping element Zn, and the doping amount is 1E 18 cm -3 -4E 18 cm-3 .

[0036] Optionally, the thickness of the AlGaAs back field layer 6 is 80-100 nm, and the Al component is between 60-90%.

[0037] Optionally, the InGaAs base region 7 is specifically In x3 Ga 1-x3 As base region, with a thickness of 2000-3000 nm, wherein x3=0.01, the doping element is P-type doping element Zn, and the doping amount is 5E 17 cm -3 gradually changes to 1E 16 cm -3 .

[0038] Optionally, the InGaAs emitter region 8 is specifically In x4 Ga 1-x4 As emitter region, with a thickness of 50-200 nm, wherein x4=0.01, the doping element is N-type doping element Si, and the doping amount is 1E 18 cm -3 -3E 18 cm -3 .

[0039] Optionally, the AlInP window layer 9 is specifically Al x5 In 1-x5 P window layer, wherein 0.5≤x5≤0.6, the thickness is 50-200 nm, the doping element is N-type doping element Si, and the doping amount is 1E 18 cm -3 to 3E 18 cm -3 .

[0040] Optionally, the substrate 1 is a P-type Ge substrate, which can be specifically a 9-degree P-type Ge substrate, and n-type phosphorus diffusion is performed on the P-type Ge substrate to diffuse the Ge in the topmost layer into n-type to obtain the pn junction of the first sub-cell.

[0041] Optionally, a GaInP nucleation layer 2 matched with the Ge lattice is grown on the substrate 1, the thickness of the GaInP nucleation layer 2 is 20-50 nm, a GaAs buffer layer 3 is grown on the GaInP nucleation layer 2, the thickness of the GaAs buffer layer 3 is 200-300 nm, and the GaInP nucleation layer 2 and the GaAs buffer layer 3 serve as the window layer of the first sub-cell and also as the connecting layer between the Ge substrate and the subsequent epitaxial layer.

[0042] Optionally, the first tunnel junction 4 connects the first sub-cell and the second sub-cell by using the tunneling effect, the first tunnel junction 4 is composed of n-type heavily doped GaAs and p-type heavily doped GaAs, and the total thickness is 10nm-30nm, wherein the n-type heavily doped GaAs is doped with Te, and the doping amount is 1E 19 cm -3 -2E 19 cm -3 ; the p-type heavily doped GaAs is doped with C, and the doping amount is 1E 20 cm -3 -2E 20 cm -3 .

[0043] Optionally, the second tunnel junction 10 also connects the second sub-cell and the third sub-cell by using the tunneling effect, the thickness of the second tunnel junction 10 is 10nm-30nm, and the second tunnel junction 10 is composed of n-type heavily doped Ga x In 1-x P and p-type heavily doped Al x1 Ga 1- x1 As, wherein 0.5≤x≤0.6, 0.4≤x1≤0.6, the n-type heavily doped Ga x In 1-x P is doped with Si, and the doping amount is 1E 19 cm -3 -2E 19 cm -3 , the p-type heavily doped Al x1 Ga 1-x1 As is doped with C, and the doping amount is 1E 20 cm -3 -2E 20 cm -3 .

[0044] Optionally, a GaAs ohmic contact layer 15 is also grown on the third sub-cell, that is, the GaAs ohmic contact layer 15 is grown on the AlInP window layer 14, the thickness of the GaAs ohmic contact layer 15 is 500nm-800nm, and the doping element is N-type doping element Si, and the doping amount is 3E 18 cm -3 to 5E 18 cm -3 .

[0045] The application also provides a manufacturing method of a three-junction quantum well solar cell epitaxial structure, which specifically adopts an organic chemical vapor phase epitaxy deposition (MOCVD) method to grow, from bottom to top, a GaInP nucleation layer 2, a GaAs buffer layer 3, a first tunnel junction 4, a second sub-cell, a second tunnel junction 10, a third sub-cell, and a GaAs ohmic contact layer 15 on a substrate.

[0046] Referring to Figure 1 and Figure 3 , the manufacturing method specifically comprises the following steps: S1, providing a substrate 1, the substrate 1 is selected as a 9-degree P-type Ge substrate, n-type phosphorus diffusion is carried out on the 9-degree P-type Ge substrate, the Ge of the topmost layer is diffused into n-type, and the pn junction of the first sub-cell is obtained, that is, the substrate 1 is used as the first sub-cell, and the first sub-cell is a Ge cell; then a GaInP nucleation layer 2 matched with the Ge lattice is grown on the substrate 1, the growth thickness of the GaInP nucleation layer 2 is 20 nm-50 nm, then a GaAs buffer layer 3 is grown, the growth thickness of the GaAs buffer 3 is 200 nm-300 nm, and the GaInP nucleation layer 2 and the GaAs buffer layer 3 are used as the window layer of the first sub-cell and also as the connecting layer of the Ge substrate and the subsequent epitaxial layer.

[0047] S2, growing a first tunnel junction 4 on the substrate 1.

[0048] Specifically, the first tunnel junction 4 is composed of n-type heavily doped GaAs and p-type heavily doped GaAs, and the growth thickness is 10 nm-30 nm, wherein the n-type heavily doped GaAs is doped with Te, and the doping amount is 1E 19 cm -3 -2E 19 cm -3 ; the p-type heavily doped GaAs is doped with C, and the doping amount is 1E 20 cm -3 -2E 20 cm -3 . The first tunnel 4 junction utilizes the tunneling effect to connect the first sub-cell with the subsequently grown second sub-cell.

[0049] S3, growing a second sub-cell on the first tunnel junction 4, and the second sub-cell is an InGaAs cell.

[0050] Specifically, the second sub-cell comprises, from bottom to top, a DBR layer 5, an AlGaAs back field layer 6, an InGaAs base region 7, an InGaAs emission region 8, and an AlInP window layer 9, which are sequentially grown.

[0051] The DBR layer 5 is a distributed Bragg reflector, which is a mirror structure and comprises an adjustable multi-layer structure composed of two optical materials, which are alternately grown from In x1 Ga 1-x1 As / Al x2 Ga 1-x2 As two materials, wherein x1=0.01, 0.6≤x2≤1, and a single layer of In x1 Ga 1-x1The optical thickness of As material is one-quarter of the center wavelength of the reflection spectrum; a single layer of Al... x2 Ga 1-x2 The optical thickness of the As material is one-quarter of the center wavelength of the reflection spectrum, which is between 850 nm and 900 nm. The number of alternation pairs in the DBR layer 5 is between 8 and 25, and the doping element is the p-type dopant Zn with a doping amount of 1E. 18 cm -3 Up to 4E 18 cm -3 .

[0052] Optionally, the AlGaAs back field layer 6 has a growth thickness of 80nm-100nm and an Al content between 60% and 90%.

[0053] Optionally, the InGaAs base region 7 is specifically In x3 Ga 1-x3 The As-based region has a growth thickness of 2000nm-3000nm, where x3=0.01, and the doping element is p-type Zn, with a doping amount ranging from 5E. 17 cm -3 Gradient to 1E 16 cm -3 .

[0054] Optionally, the InGaAs emitter region 8 is specifically InGaAs... x4 Ga 1-x4 The As emitter region has a growth thickness of 50nm-200nm, where x4=0.01, and the doping element is N-type Si with a doping amount of 1E. 18 cm -3 -3E 18 cm -3 .

[0055] Optionally, the AlInP window layer 9 is specifically Al x5 In 1-x5 A P-window layer, wherein 0.5 ≤ x5 ≤ 0.6, with a growth thickness of 50 nm-200 nm, is doped with N-type Si at a doping level of 1E. 18 cm -3 Up to 3 E 18 cm -3 .

[0056] S4. Grow a second tunnel junction 10 on the second sub-cell.

[0057] Specifically, the second tunnel junction 10 has a growth thickness of 10nm-30nm and is composed of n-type heavily doped Ga. x In 1-x P- and p-type heavily doped Alx1 Ga 1-x1 As composition, wherein 0.5≤x≤0.6, 0.4≤x1≤0.6, n-type heavily doped Ga x In 1-x P-doped Si, doping amount 1E 19 cm -3 -2E 19 cm -3 , p-type heavily doped Al x1 Ga 1-x1 As-doped C, doping amount 1E 20 cm -3 -2E 20 cm -3 . The second tunnel junction 10 connects the second sub-cell and the third sub-cell by using the tunneling effect, S5, growing the third sub-cell on the second tunnel junction 10, the third sub-cell being a GaInP / AlGaInP quantum well cell, the third sub-cell comprising, from bottom to top, an AlGaInP back field layer 11, a quantum well base region 12, an AlGaInP emission region 13, and an AlInP window layer 14.

[0058] wherein the AlGaInP back field layer 11 is specifically (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, wherein 0.5≤x1≤0.8, y1=0.5; the (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer has a growth thickness of 50nm-100nm, and the doping element is a p-type doping element Z, and the doping amount is 1E 18 cm -3 -4E 18 cm -3 .

[0059] As Figure 2 shown, the quantum well base region 12 is composed of alternately grown Ga x2 In 1-x2 P layers and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layers, wherein 0.5≤x2≤0.6, 0.5≤x3≤0.8, y3=0.5, and a single Ga x2 In 1-x2 P layer has a growth thickness of 3nm-20nm, and the Ga x2 In 1-x2The thickness of the P layer can change the absorption spectrum of the quantum well base region, Ga x2 In 1-x2 The thinner the thickness of the P layer, the narrower the absorption spectrum, Ga x2 In 1-x2 The growth thickness of the P layer can be set according to requirements; the present application uses GaInP / AlGaInP quantum well structure instead of the traditional AlGaInP material as the base region of the solar cell, under the MQW structure, the absorption spectrum of the GaInP material is reduced to be consistent with the AlGaInP material, increasing the open circuit voltage of the solar cell, at the same time, the third sub-cell uses GaInP material as the main component of the absorption region, increasing the absorption capacity of the material, making up for the shortcoming of insufficient short circuit current of the AlGaInP / GaAs / Ge solar cell; the single (Al x3 Ga 1-x3 ) y3 In 1-y3 The growth thickness of the P layer is 10nm-20nm, Ga x2 In 1-x2 The P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 The alternating number of P layer growth is 80 pairs-150 pairs, the doping element of the quantum well base region is P-type doping element Zn, and the doping amount is 1E 16 cm -3 -1E 17 cm -3 .

[0060] Optionally, in an embodiment, the alternating growth of Ga x2 In 1-x2 P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 In the P layer, x2=0.5, x3=0.8, y3=0.5, the single Ga x2 In 1-x2 The growth thickness of the P layer is 8nm, the single (Al x3 Ga 1-x3 ) y3 In 1-y3 The growth thickness of the P layer is 8nm, and the alternating number is 110 pairs, at this time, the Ga x2 In 1-x2 The PL wavelength of the P layer is 630nm, and the band gap is 1.968ev, which is higher than that of the GaInP sub-cell (PL wavelength 650nm, band gap 1.907ev) of the conventional GaInP / GaAs / Ge solar cell, thereby increasing the band gap and the open circuit voltage of the solar cell.

[0061] Optionally, in another embodiment, the Ga x2 In 1-x2 P layer and the (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer is 100 pairs, the single Ga x2 In 1-x2 P layer is 8.8 nm, the Ga x2 In 1-x2 P layer is 880 nm, and the Ga x2 In 1-x2 P layer can have a thickness similar to that of the AlGaInP of a conventional AlGaInP / GaAs / Ge solar cell, and has a similar band gap. Since the absorption region is mainly composed of GaInP material, the absorption capacity of the material is increased, and the short-circuit current of the AlGaInP / GaAs / Ge solar cell is compensated.

[0062] In addition, the GaInP and AlGaInP materials in the third sub-cell are lattice matched with the Ge material, avoiding dislocations caused by lattice mismatch, improving the crystal quality of the grown material, and ensuring the stability of the solar cell.

[0063] Optionally, the AlGaInP emitter region 13 is specifically (Al x4 Ga 1-x4 ) y4 In 1-y4 P emitter region, wherein 0≤x4≤0.5 and y4=0.5. The energy band gap of the (Al x4 Ga 1-x4 ) y4 In 1-y4 P emitter region can be adjusted to be consistent with the quantum well base region by changing the Al component. x4 Ga 1-x4 ) y4 In 1-y4 P emitter region has a growth thickness of 50 nm-200 nm, and the doping element is an N-type doping element Si with a doping amount of 5E 17 cm -3 -5E 18 cm -3 .

[0064] Optionally, the AlInP window layer 14 is specifically an Al x5 In 1-x5 P window layer, wherein 0.5≤x5≤0.6. The Al x5 In 1-x5The growth thickness of the P-window layer is 20-50 nm, the doping element is N-type doping element Si, and the doping amount is 1E 18 cm -3 to 5E 18 cm -3 .

[0065] S6, growing a GaAs ohmic contact layer 15 on the third sub-cell.

[0066] Specifically, the GaAs ohmic contact layer 15 is grown on the AlInP window layer 14, the growth thickness of the GaAs ohmic contact layer 15 is 500-800 nm, the doping element is N-type doping element Si, and the doping amount is 3E 18 cm -3 to 5E 18 cm -3 .

[0067] It is worth noting that the thickness of the substrate 1, the GaInP nucleation layer 2, the GaAs buffer layer 3, the first tunnel junction 4, the DBR layer 5, the AlGaAs back field layer 6, the InGaAs base region 7, the InGaAs emitter region 8, the AlInP window layer 9, the second tunnel junction 10, the AlGaInP back field layer 11, the quantum well base region 12, the AlGaInP emitter region 13, the AlInP window layer 14, and the GaAs ohmic contact layer 15 shown in the drawings of the present application are only examples and do not represent their true thicknesses. Moreover, the true proportions between the substrate 1, the GaInP nucleation layer 2, the GaAs buffer layer 3, the first tunnel junction 4, the DBR layer 5, the AlGaAs back field layer 6, the InGaAs base region 7, the InGaAs emitter region 8, the AlInP window layer 9, the second tunnel junction 10, the AlGaInP back field layer 11, the quantum well base region 12, the AlGaInP emitter region 13, the AlInP window layer 14, and the GaAs ohmic contact layer 15 are not as shown in the drawings, but are only for reference.

[0068] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0069] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A triple-junction quantum well solar cell epitaxial structure, characterized by: The first sub-cell, the first tunnel junction, the second sub-cell, the second tunnel junction and the third sub-cell are sequentially stacked from bottom to top, and the three sub-cells are connected through the tunnel junctions; wherein the first sub-cell is a Ge cell, the second sub-cell is an InGaAs cell, and the third sub-cell is a GaInP / AlGaInP quantum well cell; the third sub-cell comprises, from bottom to top, a (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, a quantum well base region, a (Al x4 Ga 1-x4 ) y4 In 1-y4 P emission region and an Al x5 In 1-x5 P window layer; the quantum well base region is composed of alternately grown Ga x2 In 1-x2 P layers and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layers, wherein 0.5≤x2≤0.6, 0.5≤x3≤0.8, and y3=0.

5.

2. A triple junction quantum well solar cell epitaxial structure as set out in claim 1, characterised in that: The doping element of the quantum well base region is P-type doping element Zn, and the doping amount is 1E 16 cm -3 -1E 17 cm -3 , single Ga x2 In 1-x2 The thickness of the P layer is 3nm-20nm, and the single (Al x3 Ga 1-x3 ) y3 In 1-y3 The thickness of the P layer is 10nm-20nm, and the alternating logarithm is 80 pairs-150 pairs.

3. A triple junction quantum well solar cell epitaxial structure as set out in claim 2, characterised in that: Ga x2 In 1-x2 P layer and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer, x2=0.5, x3=0.8, y3=0.5, single Ga x2 In 1-x2 P layer is 8 nm, single (Al x3 Ga 1-x3 ) y3 In 1-y3 P layer is 8 nm, and the alternating pairs are 110 pairs.

4. A triple junction quantum well solar cell epitaxial structure as set out in claim 2, characterised in that: The Ga x2 In 1- x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3 The number of alternation pairs in the P layer is 100, Ga x2 In 1-x2 The total thickness of the P layer is 880 nm.

5. A triple junction quantum well solar cell epitaxial structure as set out in claim 1, wherein: 0.1 < x < 0.3, 0.1 < y < 0.3, and 0.1 < z < 0.

3. The (Al x1 Ga 1-x1 ) y1 In 1-y1 P backside layer, (Al x4 Ga 1-x4 ) y4 In 1-y4 P emitter region, and Al x5 In 1-x5 P window layer, 0.5≤x1≤0.8, y1=0.5, 0≤x4≤0.5, y4=0.5, 0.5≤x5≤0.

6. ​ 6. A triple junction quantum well solar cell epitaxial structure as set out in claim 1, characterised in that: The second sub-cell comprises, from bottom to top, a DBR layer, an AlGaAs back field layer, an InGaAs base region, an InGaAs emitting region and an AlInP window layer.

7. The epitaxial structure of a triple-junction quantum well solar cell as described in claim 1, characterized in that: The substrate is a P-type Ge substrate, n-type phosphorus diffusion is performed on the P-type Ge substrate, the most surface layer of Ge is diffused into n-type, a pn junction of the first sub-cell is formed, and a GaInP nucleation layer and a GaAs buffer layer are grown on the P-type Ge substrate.

8. A triple junction quantum well solar cell epitaxial structure as set out in claim 1, characterised in that: The first tunnel junction consists of n-type heavily doped GaAs and p-type heavily doped GaAs with a total thickness of 10 nm - 30 nm, wherein the n-type heavily doped GaAs is doped with Te at a doping of 1E 19 cm -3 -2E 19 cm -3 ; the p-type heavily doped GaAs is doped with C at a doping of 1E 20 cm -3 -2E 20 cm -3 .

9. A triple junction quantum well solar cell epitaxial structure as set out in claim 1, characterised in that: The second tunnel junction has a thickness of 10-30 nm and is composed of n-type heavily doped Ga x In 1-x P and p-type heavily doped Al x1 Ga 1-x1 As, where 0.5≤x≤0.6, 0.4≤x1≤0.6, n-type heavily doped Ga x In 1-x P doped Si with a doping of 1E 19 cm -3 -2E 19 cm -3 , p-type heavily doped Al x1 Ga 1-x1 As doped with C with a doping of 1E 20 cm -3 -2E 20 cm -3 .

10. A method for manufacturing a three-junction quantum well solar cell epitaxial structure for producing a three-junction quantum well solar cell epitaxial structure according to any one of claims 1 to 9, characterized by, Comprise: A substrate is provided, n-type phosphorus diffusion is performed on the substrate, a pn junction of the first sub-cell is obtained, that is, the substrate serves as the first sub-cell, and the first sub-cell is a Ge cell; A first tunnel junction is grown on the substrate; A second sub-cell is grown on the first tunnel junction, and the second sub-cell is an InGaAs cell; A second tunnel junction is grown on the second sub-cell; growing a third sub-cell on the second tunnel junction, the third sub-cell being a GaInP / AlGaInP quantum well cell, the third sub-cell comprising, from bottom to top, an (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, a quantum well base region, an (Al x4 Ga 1-x4 ) y4 In 1-y4 P emitter region and an Al x5 In 1-x5 P window layer, the quantum well base region being composed of alternately grown Ga x2 In 1-x2 P layers and (Al x3 Ga 1-x3 ) y3 In 1-y3 P layers, wherein 0.5≤x2≤0.6, 0.5≤x3≤0.8, y3=0.5.

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