A triple-junction quantum well solar cell epitaxial structure and a manufacturing method thereof

Abstract

The application provides a three-junction quantum well solar cell epitaxial structure and a manufacturing method thereof, which comprises, from bottom to top, 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, 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 emitter 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; the application uses a GaInP / AlGaInP quantum well structure to replace a conventional AlGaInP material as a top cell material, increases the open circuit voltage of the solar cell, and makes up for the shortcoming of insufficient short circuit current of an AlGaInP / GaAs / Ge solar cell.

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:

[0003] 1. Using GaInP / InGaAs / Ge large mismatch solar cell, using InGaAs material to expand the middle cell (i.e. the second subcell) absorption spectrum, increasing the short-circuit current of the solar cell, thereby 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.

[0004] 2. Using AlGaInP / GaAs / Ge solar cell, using AlGaInP material to increase the bandgap of the top cell (i.e. the third subcell), to improve the open-circuit voltage of the solar cell, and to increase the thickness of the middle cell and the top cell, to improve the overall short-circuit current, thereby increasing 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

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] Optionally, the substrate is a P-type Ge substrate, the P-type Ge substrate is subjected to n-type phosphorus diffusion, the most surface layer of Ge is diffused into n-type to form a pn junction of the first sub-cell, and the P-type Ge substrate has a GaInP nucleation layer and a GaAs buffer layer grown thereon.

[0013] Optionally, the first tunnel junction is composed of n-type heavily doped GaAs and p-type heavily doped GaAs, and has a total thickness of 10nm-30nm, wherein the n-type heavily doped GaAs is doped with Te at a doping amount of 1E 19 cm -3 -2E 19 cm -3 ; and the p-type heavily doped GaAs is doped with C at a doping amount of 1E 20 cm -3 -2E 20 cm -3 .

[0014] 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, doping amount is 1E 19 cm -3 -2E 19 cm -3 , p-type heavily doped Al x1 Ga 1-x1 As doped C, doping amount is 1E 20 cm -3 -2E 20 cm -3 .

[0015] The application also provides a manufacturing method of a three-junction quantum well solar cell epitaxial structure, for preparing the epitaxial structure, comprising:

[0016] 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 as the first sub-cell, and the first sub-cell is a Ge cell;

[0017] growing a first tunnel junction on the substrate;

[0018] growing a second sub-cell on the first tunnel junction, and the second sub-cell is an InGaAs cell;

[0019] growing a second tunnel junction on the second sub-cell;

[0020] 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.

[0021] After the above scheme, the beneficial effects of the present application are:

[0022] 1、The third sub-cell of the present application adopts GaInP / AlGaInP quantum well structure 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 emitting wavelength of the quantum well, reducing the Al component of the absorption region, making up for the shortcomings of 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 emitting wavelength and the 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.

[0023] 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.

[0024] 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.

[0025] 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

[0026] Figure 1 is the epitaxial structure diagram of the solar cell of the present application.

[0027] Figure 2 is the structure diagram of the quantum well base region of the present application.

[0028] Figure 3 is the method flowchart of the present application.

[0029] REFERENCE NUMERALS:

[0030] 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 emitter region; 9, AlInP window layer; 10, second tunnel junction; 11, AlGaInP back field layer; 12, quantum well base region; 13, AlGaInP emitter region; 14, AlInP window layer; 15, GaAs ohmic contact layer. DETAILED DESCRIPTION

[0031] 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. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application, and the range of the present application includes two end values.

[0032] As shown in the drawings, Figures 1-2 The present application provides a three-junction quantum well solar cell epitaxial structure, which comprises, from bottom to top, 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, and the three sub-cells are connected by corresponding tunnel junctions; wherein the first sub-cell is also the bottom cell and serves as the substrate 1, and is specifically a Ge cell; the second sub-cell is a middle cell and is specifically an InGaAs cell; and the third sub-cell is a top cell and is specifically a GaInP / AlGaInP quantum well cell.

[0033] Specifically, the third sub-cell comprises, from bottom to top, an AlGaInP back field layer 11, a quantum well base region 12, an AlGaInP emitter region 13 and an AlInP window layer 14, which are sequentially stacked.

[0034] As shown in the drawings, Figure 2 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 adjusting the thickness of the Ga x2 In 1-x2 P layer can change the absorption spectrum of the quantum well base region.x2 In 1-x2 The thinner the P-layer, the narrower the absorption spectrum of Ga. x2 In 1-x2 The thickness of the P layer can be set according to requirements. This application uses a GaInP / AlGaInP quantum well structure to replace the traditional AlGaInP material as the base region of the third sub-cell. The third sub-cell of this application uses a GaInP / AlGaInP quantum well structure to replace the traditional AlGaInP material as the base region of the third sub-cell. This is equivalent to using GaInP, a material with a wider band gap, as the well layer of the quantum well and as the main absorption region, which directly improves the band gap of the entire third cell, thereby reducing the emission wavelength of the quantum well and reducing the Al composition of the absorption region. This makes up for the shortcomings of using only AlGaInP material as the base region. In the MQW structure, the Ga composition x2 in the GaInP material is 0.5-0.6, which is a high Ga composition, making its band gap wider. This further reduces the emission wavelength and absorption spectrum of the quantum well. The absorption spectrum of the GaInP material will be reduced to be consistent with that of 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, which increases the absorption capacity of the material and makes up for the shortcomings of insufficient short-circuit current in AlGaInP / GaAs / Ge solar cells.

[0035] Optional, single (Al) x3 Ga 1-x3 ) y3 In 1-y3 The thickness of the P layer is 10nm-20nm, 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 80-150, and the dopant element in the quantum well base region is the p-type dopant Zn, with a doping amount of 1E. 16 cm -3 -1E 17 cm -3 .

[0036] Optionally, in one embodiment, alternating 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, a single Ga x2 In 1-x2 The thickness of the P layer is 8 nm, and a single (Al) layer... x3 Ga 1-x3 )y3 In 1-y3 The P-layer has a thickness of 8 nm and an alternation logarithm of 110 pairs. At this point, the Ga... x2 In 1-x2 The P-layer has a PL wavelength of 630 nm and a band gap of 1.968 eV. Compared with the GaInP sub-cell of conventional GaInP / GaAs / Ge solar cells (PL wavelength 650 nm, band gap 1.907 eV), the band gap is increased, thus increasing the open-circuit voltage of the solar cell.

[0037] Optionally, in another embodiment, 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, and a single Ga... x2 In 1-x2 The thickness of the P layer is 8.8 nm, and the Ga layer... x2 In 1-x2 The total thickness of the P layer is 880 nm. At this point, Ga x2 In 1- x2 The P-layer can achieve a similar thickness and band gap to the AlGaInP sub-cells of conventional AlGaInP / GaAs / Ge solar cells. Since the absorption region is mainly composed of GaInP material, the absorption capacity of the material is increased, which makes up for the short-circuit current deficiency of AlGaInP / GaAs / Ge solar cells.

[0038] Furthermore, 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 materials, and ensuring the stability of the solar cell.

[0039] Optionally, the AlGaInP back field layer 11 is specifically (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, where 0.5≤x1≤0.8, y1=0.5; the (Al) x1 Ga 1-x1 ) y1 In 1-y1 The thickness of the P-type backfield layer is 50nm-100nm, and the doping element is the p-type dopant Zn, with a doping concentration of 1E. 18 cm -3 -4E 18 cm -3 .

[0040] Optionally, the AlGaInP emitter region 13 is specifically (Al x4 Ga 1-x4 ) y4 In 1-y4 The P-emission region, where 0 ≤ x⁴ ≤ 0.5 and y⁴ = 0.5, can utilize the change in Al composition to (Al x4 Ga 1-x4 ) y4 In 1-y4 The energy bandgap adjustment of the P-emitting region is consistent with that of the quantum well base region, as stated in (Al). x4 Ga 1-x4 ) y4 In 1-y4 The thickness of the p-emitter region is 50nm-200nm, and the doping element is N-type Si with a doping concentration of 5E. 17 cm -3 -5E 18 cm -3 .

[0041] Optionally, the AlInP window layer 14 is specifically Al x5 In 1-x5 P-window layer, where 0.5 ≤ x5 ≤ 0.6, the Al x5 In 1-x5 The thickness of the P-window layer is 20nm-50nm, and the doping element is N-type Si with a doping amount of 1E. 18 cm -3 Up to 5E 18 cm -3 .

[0042] Optionally, the second sub-cell includes a DBR layer 5, an AlGaAs back field layer 6, an InGaAs base region 7, an InGaAs emitter region 8, and an AlInP window layer 9, which are stacked sequentially from bottom to top.

[0043] The DBR layer 5 is a distributed Bragg reflector layer, a mirror structure containing an adjustable multilayer structure composed of two optical materials, and is made of In... x1 Ga 1-x1 As / Al x2 Ga 1-x2 As is formed by alternating growth of two materials, where x1 = 0.01, 0.6 ≤ x2 ≤ 1, and a single layer of In... x1 Ga 1-x1 The optical thickness of As material is one-quarter of the center wavelength of the reflection spectrum; a single layer of Al... x2 Ga 1-x2The 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 .

[0044] Optionally, the thickness of the AlGaAs back field layer 6 is 80nm-100nm, and the Al content is between 60% and 90%.

[0045] Optionally, the InGaAs base region 7 is specifically In x3 Ga 1-x3 The As base region has a thickness of 2000nm-3000nm, where x3=0.01, and the doping element is the p-type dopant Zn, with a doping amount ranging from 5E. 17 cm -3 Gradient to 1E 16 cm -3 .

[0046] Optionally, the InGaAs emitter region 8 is specifically InGaAs... x4 Ga 1-x4 The As emitter region has a 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 .

[0047] 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 thickness of 50 nm-200 nm, is doped with N-type Si with a doping amount of 1E. 18 cm -3 Up to 3 E 18 cm -3 .

[0048] Optionally, the substrate 1 is a P-type Ge substrate, specifically a 9-degree P-type Ge substrate. N-type phosphorus diffusion is performed on the P-type Ge substrate to diffuse the outermost Ge into the n-type, thereby obtaining the pn junction of the first sub-cell.

[0049] Optionally, a GaInP nucleation layer 2 matching the Ge lattice is grown on the substrate 1. The thickness of the GaInP nucleation layer 2 is 20nm-50nm. A GaAs buffer layer 3 is grown on the GaInP nucleation layer 2. The thickness of the GaAs buffer layer 3 is 200nm-300nm. The GaInP nucleation layer 2 and the GaAs buffer layer 3 serve as window layers for the first sub-cell and also as bonding layers between the Ge substrate and subsequent epitaxial layers.

[0050] Optionally, the first tunnel junction 4 utilizes the tunneling effect to connect the first sub-cell and the second sub-cell. The first tunnel junction 4 is composed of heavily n-type doped GaAs and heavily p-type doped GaAs, with a total thickness of 10nm-30nm. The heavily n-type doped GaAs is doped with Te with a doping amount of 1E. 19 cm -3 -2E 19 cm -3 p-type heavily doped GaAs with C doping at a doping level of 1E 20 cm -3 -2E 20 cm -3 .

[0051] Optionally, the second tunnel junction 10 also utilizes the tunneling effect to connect the second sub-cell and the third sub-cell. The thickness of the second tunnel junction 10 is 10nm-30nm, and it is composed of n-type heavily doped Ga. x In 1-x P- and p-type heavily doped Al x1 Ga 1- x1 The composition is As, where 0.5≤x≤0.6, 0.4≤x1≤0.6, and n-type heavily doped Ga. x In 1-x P-doped Si, with a doping level of 1E 19 cm -3 -2E 19 cm -3 p-type heavily doped Al x1 Ga 1-x1 As doped with C, the doping amount is 1E. 20 cm -3 -2E 20 cm -3 .

[0052] Optionally, a GaAs ohmic contact layer 15 is also grown on the third sub-cell, that is, a 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 the N-type dopant Si with a doping amount of 3E. 18 cm -3 Up to 5E18 cm -3 .

[0053] This application also provides a method for manufacturing a triple-junction quantum well solar cell epitaxial structure, specifically using organic chemical vapor deposition (MOCVD) to grow a GaInP nucleation layer 2, a GaAs buffer layer 3, a first tunnel junction 4, a second subcell, a second tunnel junction 10, a third subcell, and a GaAs ohmic contact layer 15 sequentially from bottom to top on a substrate.

[0054] Please refer to Figure 1 and Figure 3 The manufacturing method specifically includes the following steps:

[0055] S1. A substrate 1 is provided, wherein the substrate 1 is a 9-degree p-type Ge substrate. n-type phosphorus diffusion is performed on the 9-degree p-type Ge substrate to diffuse the outermost Ge into the n-type, thereby obtaining the pn junction of the first sub-cell. That is, the substrate 1 serves as the first sub-cell, and the first sub-cell is a Ge cell. Then, a GaInP nucleation layer 2 matching the Ge lattice is grown on the substrate 1. The growth thickness of the GaInP nucleation layer 2 is 20nm-50nm. Next, a GaAs buffer layer 3 is grown. The growth thickness of the GaAs buffer layer 3 is 200nm-300nm. 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 connection layer between the Ge substrate and the subsequent epitaxial layer.

[0056] S2. Grow the first tunnel junction 4 on substrate 1.

[0057] Specifically, the first tunnel junction 4 is composed of heavily n-type doped GaAs and heavily p-type doped GaAs, with a growth thickness of 10 nm-30 nm. The heavily n-type doped GaAs is doped with Te with a doping amount of 1E. 19 cm -3 -2E 19 cm -3 p-type heavily doped GaAs with C doping at a doping level of 1E 20 cm -3 -2E 20 cm -3 The first tunnel junction utilizes the tunneling effect to connect the first sub-cell to the subsequently grown second sub-cell.

[0058] S3. A second sub-cell is grown on the first tunnel junction 4. The second sub-cell is an InGaAs cell.

[0059] Specifically, 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 emitter region 8, and an AlInP window layer 9.

[0060] The DBR layer 5 is a distributed Bragg reflector layer, a mirror structure containing an adjustable multilayer structure composed of two optical materials, and is made of In... x1 Ga 1-x1 As / Al x2 Ga 1-x2 As is formed by alternating growth of two materials, where x1 = 0.01, 0.6 ≤ x2 ≤ 1, and a single layer of In... x1 Ga 1-x1 The 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 .

[0061] Optionally, the AlGaAs back field layer 6 has a growth thickness of 80nm-100nm and an Al content between 60% and 90%.

[0062] 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 .

[0063] 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 .

[0064] 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 .

[0065] S4. Grow a second tunnel junction 10 on the second sub-cell.

[0066] 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 Al x1 Ga 1-x1 The composition is As, where 0.5≤x≤0.6, 0.4≤x1≤0.6, and n-type heavily doped Ga. x In 1-x P-doped Si, with a doping level of 1E 19 cm -3 -2E 19 cm -3 p-type heavily doped Al x1 Ga 1-x1 As doped with C, the doping amount is 1E. 20 cm -3 -2E 20 cm -3 The second tunnel junction 10 utilizes the tunneling effect to connect the second sub-cell to the third sub-cell.

[0067] S5. A third sub-cell is grown on the second tunnel junction 10. The third sub-cell is a GaInP / AlGaInP quantum well cell. The third sub-cell includes an AlGaInP back field layer 11, a quantum well base region 12, an AlGaInP emitter region 13, and an AlInP window layer 14 grown sequentially from bottom to top.

[0068] Specifically, the AlGaInP back field layer 11 is (Al x1 Ga 1-x1 ) y1 In 1-y1 P back field layer, where 0.5≤x1≤0.8, y1=0.5; the (Al) x1 Ga 1-x1 ) y1 In 1-y1 The thickness of the P-type backfield layer is 50nm-100nm, and the doping element is the p-type dopant Z, with a doping amount of 1E. 18 cm -3 -4E 18 cm -3 .

[0069] like Figure 2 As shown, the quantum well base region 12 is composed of alternating Ga... x2 In1-x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3 Composed of P layers, where 0.5≤x2≤0.6, 0.5≤x3≤0.8, y3=0.5, and a single Ga x2 In 1-x2 The growth thickness of the P layer is 3nm-20nm, adjusting the Ga... x2 In 1-x2 The thickness of the P-layer can alter the absorption spectrum of the quantum well base region, Ga x2 In 1-x2 The thinner the P-layer, the narrower the absorption spectrum of Ga. x2 In 1-x2 The growth thickness of the P-layer can be set according to requirements; this application utilizes a GaInP / AlGaInP quantum well structure to replace the traditional AlGaInP material as the base region of the solar cell. Under the MQW structure, the absorption spectrum of GaInP material is reduced to be consistent with that of 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 and compensating for the short-circuit current deficiency of AlGaInP / GaAs / Ge solar cells; a single (Al x3 Ga 1-x3 ) y3 In 1-y3 The P-layer is grown to a thickness of 10nm-20nm, 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 growth is 80-150 pairs, and the dopant element in the quantum well base region is the p-type dopant Zn with a doping amount of 1E. 16 cm -3 -1E 17 cm -3 .

[0070] Optionally, in one embodiment, alternating 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, a single Ga x2 In 1-x2 The P-layer is 8 nm thick, and each (Al) layer is grown to a single thickness. x3 Ga 1-x3 ) y3 In1-y3 The P-layer is 8 nm thick with 110 alternation pairs. At this point, the Ga... x2 In 1-x2 The P-layer has a PL wavelength of 630 nm and a band gap of 1.968 eV. Compared with the GaInP sub-cell of conventional GaInP / GaAs / Ge solar cells (PL wavelength 650 nm, band gap 1.907 eV), the band gap is increased, thus increasing the open-circuit voltage of the solar cell.

[0071] Optionally, in another embodiment, 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, and a single Ga... x2 In 1-x2 The P-layer was grown to a thickness of 8.8 nm, and the Ga... x2 In 1-x2 The total thickness of the P-layer is 880 nm. At this point, Ga x2 In 1-x2 The P-layer can achieve a similar thickness and band gap to the AlGaInP layer in conventional AlGaInP / GaAs / Ge solar cells. Since the absorption region is mainly composed of GaInP material, the absorption capacity of the material is increased, which makes up for the short-circuit current deficiency of AlGaInP / GaAs / Ge solar cells.

[0072] Furthermore, 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 materials, and ensuring the stability of the solar cell.

[0073] Optionally, the AlGaInP emitter region 13 is specifically (Al x4 Ga 1-x4 ) y4 In 1-y4 The P-emission region, where 0 ≤ x⁴ ≤ 0.5 and y⁴ = 0.5, can utilize the change in Al composition to (Al x4 Ga 1-x4 ) y4 In 1-y4 The energy bandgap adjustment of the P-emitting region is consistent with that of the quantum well base region, as stated in (Al). x4 Ga 1-x4 ) y4 In 1-y4 The growth thickness of the P-emitter region is 50nm-200nm, and the doping element is N-type Si with a doping concentration of 5E. 17 cm -3-5E 18 cm -3 .

[0074] Optionally, the AlInP window layer 14 is specifically Al x5 In 1-x5 P-window layer, where 0.5 ≤ x5 ≤ 0.6, the Al x5 In 1-x5 The P-window layer is grown to a thickness of 20nm-50nm, and the doping element is N-type Si with a doping concentration of 1E. 18 cm -3 Up to 5E 18 cm -3 .

[0075] S6. Grow a GaAs ohmic contact layer 15 on the third sub-cell.

[0076] Specifically, a 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 Si with a doping amount of 3E. 18 cm -3 Up to 5E 18 cm -3 .

[0077] It is worth noting that the thicknesses of the substrate 1, GaInP nucleation layer 2, GaAs buffer layer 3, first tunnel junction 4, DBR layer 5, AlGaAs back field layer 6, InGaAs base region 7, InGaAs emitter region 8, AlInP window layer 9, second tunnel junction 10, AlGaInP back field layer 11, quantum well base region 12, AlGaInP emitter region 13, AlInP window layer 14, and GaAs ohmic contact layer 15 shown in the accompanying drawings are merely examples and do not represent their actual thicknesses. Furthermore, the actual proportions of the substrate 1, GaInP nucleation layer 2, GaAs buffer layer 3, first tunnel junction 4, DBR layer 5, AlGaAs back field layer 6, InGaAs base region 7, InGaAs emitter region 8, AlInP window layer 9, second tunnel junction 10, AlGaInP back field layer 11, quantum well base region 12, AlGaInP emitter region 13, AlInP window layer 14, and GaAs ohmic contact layer 15 are not as shown in the accompanying drawings and are for reference only.

[0078] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0079] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded 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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