A method for manufacturing a three-junction quantum well solar cell epitaxial structure

Abstract

The application discloses a manufacturing method of a three-junction quantum well solar cell epitaxial structure, which is manufactured by adopting an MOCVD process. Firstly, n-type phosphorus diffusion is performed on a P-type Ge substrate to form a pn junction of a first sub-cell; then a first tunnel junction is grown on the substrate; then a second sub-cell is grown on the first tunnel junction; then a second tunnel junction is grown on the second sub-cell; finally, a third sub-cell is grown on the second tunnel junction, wherein the third sub-cell comprises, from bottom to top, an AlGaInP back field layer, a quantum well base region, an AlGaInP emitting region and an AlInP 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, and y3=0.5. The application uses a GaInP / AlGaInP quantum well structure as top cell material, increases the open circuit voltage of the solar cell, and solves the shortcoming of insufficient short circuit current of an AlGaInP / GaAs / Ge solar cell.

Description

[0001] This case is a divisional application of a Chinese patent, with the parent application number being 202511449759.2 and the application date being 2025-10-11. Technical Field

[0002] This invention belongs to the field of semiconductor device technology, and specifically relates to a method for manufacturing an epitaxial structure of a triple-junction quantum well solar cell. Background Technology

[0003] With societal development, solar energy, as a clean and sustainable energy source, is receiving increasing attention. Lattice-matched triple-junction solar cells (such as GaInP / GaAs / Ge) are widely used in satellites and spacecraft due to their high photoelectric conversion efficiency and low radiation damage. However, due to material bandgap limitations and current matching considerations, the photoelectric conversion efficiency of traditional GaInP / GaAs / Ge triple-junction solar cells is nearing its limit. To meet market demands for higher photoelectric conversion efficiency, current technologies generally fabricate GaInP / InGaAs / Ge or AlGaInP / GaAs / Ge solar cells to improve photoelectric conversion efficiency. In GaInP / InGaAs / Ge solar cells, InGaAs materials broaden the absorption spectrum of the middle cell (i.e., the second sub-cell), increasing the short-circuit current and thus the photoelectric conversion efficiency. In AlGaInP / GaAs / Ge solar cells, AlGaInP materials increase the band gap of the top cell (i.e., the third sub-cell), improving the open-circuit voltage. Simultaneously, they increase the absorption spectrum of the middle cell and the thickness of the top cell, improving the overall short-circuit current and thus increasing the photoelectric conversion efficiency.

[0004] However, in the fabrication of GaInP / InGaAs / Ge solar cells, the InGaAs material exhibits a lattice mismatch with the Ge material. Excessive lattice mismatch reduces the material growth quality and introduces dislocation lines, leading to performance degradation. In the fabrication of AlGaInP / GaAs / Ge solar cells, the high Al content in AlGaInP material causes it to approach the indirect bandgap. The shorter the wavelength of AlGaInP material, the closer it is to the indirect bandgap, resulting in a sharp decrease in absorption efficiency. Consequently, the short-circuit current of the solar cell cannot be compensated for by increasing the thickness of the absorption region, ultimately failing to reach the designed current and resulting in low efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a method for manufacturing a triple-junction quantum well solar cell epitaxial structure, using GaInP / AlGaInP quantum well structure as the top cell material to increase the open-circuit voltage of the solar cell and solve the short-circuit current deficiency of AlGaInP / GaAs / Ge solar cells.

[0006] To achieve the above objectives, this invention provides a method for manufacturing a triple-junction quantum well solar cell epitaxial structure, which employs MOCVD technology and includes the following steps: S1. Provide a P-type Ge substrate, and perform n-type phosphorus diffusion on the P-type Ge substrate to form a pn junction of the first sub-cell; S2. Grow the first tunnel junction on the substrate; S3. Grow the second sub-cell on the first tunnel junction; S4. Grow a second tunnel junction on the second sub-cell; S5. A third sub-cell is grown on the second tunnel junction. The third sub-cell comprises, from bottom to top, an AlGaInP back field layer, a quantum well base region, an AlGaInP emitter region, and an AlInP window layer. The quantum well base region is composed of alternating layers of Ga... x2 In 1-x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3 The system consists of layer P, where 0.5≤x2≤0.6, 0.5≤x3≤0.8, and y3=0.5.

[0007] Furthermore, in step S5, a single Ga x2 In 1-x2 The growth thickness of the P layer is 3nm-20nm, and a single (Al) layer... x3 Ga 1-x3 ) y3 In 1-y3 The growth thickness of the P layer is 10nm-20nm, and the alternation log number is 80-150 pairs.

[0008] Furthermore, in step S5, Ga is grown alternately. 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 In 1-y3 The P-layer has a growth thickness of 8 nm and an alternation pair number of 110.

[0009] Furthermore, in step S5, 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.

[0010] Furthermore, in step S5, the doping element of the quantum well base region is the p-type dopant Zn, with a doping amount of 1E16cm. -3 -1E17cm -3 .

[0011] Furthermore, in step S5, the AlGaInP back field layer is (Al x1 Ga 1-x1 ) y1 In 1-y1 The P-back field layer, wherein the AlGaInP emitter region is (Al x4 Ga 1-x4 ) y4 In 1-y4 P emission region, the AlInP window layer is Al x5 In 1-x5 P-window layer, where 0.5≤x1≤0.8, y1=0.5, 0≤x4≤0.5, y4=0.5, 0.5≤x5≤0.6.

[0012] Further, in step S3, the second sub-cell includes, from bottom to top, a DBR layer, an AlGaAs back surface layer, an InGaAs base region, an InGaAs emitter region, and an AlInP window layer, wherein the InGaAs base region is In... x3 Ga 1-x3 The InGaAs base region is InGaAs emitter region. x4 Ga 1-x4 As is the emission region, where x3 = 0.01 and x4 = 0.01.

[0013] Furthermore, in step S1, after n-type phosphorus diffusion, a GaInP nucleation layer and a GaAs buffer layer are sequentially grown on a p-type Ge substrate. The GaInP nucleation layer and the GaAs buffer layer serve as window layers for the first sub-cell and also as bonding layers between the Ge substrate and subsequent epitaxial layers.

[0014] Furthermore, in step S2, the first tunnel junction is composed of heavily n-type doped GaAs and heavily p-type doped GaAs, with a growth thickness of 10 nm-30 nm, wherein the heavily n-type doped GaAs is doped with Te with a doping amount of 1E19 cm⁻¹. -3 -2E19cm -3 p-type heavily doped GaAs with C doping at a doping level of 1E20cm⁻¹-3 -2E20cm -3 Furthermore, in step S4, the growth thickness of the second tunnel junction 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 concentration of 1E19cm⁻¹ -3 -2E19cm -3 p-type heavily doped Al x1 Ga 1-x1 As doped with C, with a doping concentration of 1E20cm⁻¹ -3 -2E20cm -3 .

[0015] Furthermore, after step S5, the following is also included: Step S6: Grow a GaAs ohmic contact layer on the third sub-cell. The GaAs ohmic contact layer has a thickness of 500 nm-800 nm and is doped with N-type Si at a doping concentration of 3E18 cm⁻¹. -3 -5E18cm -3 .

[0016] After adopting the above solution, the beneficial effects of the present invention are as follows: 1. In the preparation of the third sub-cell, this application uses alternating growth of Ga... x2 In 1-x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3 The P-layer is used to form the quantum well base region. That is, the GaInP / AlGaInP quantum well structure is used instead of 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 using it as the main absorption region. This directly improves the band gap of the entire third cell, thereby reducing the emission wavelength of the quantum well and reducing the Al content in the absorption region. This makes up for the shortcomings of using AlGaInP material as the base region alone. In the MQW structure, the Ga content x2 in the GaInP material is 0.5-0.6, which is a high Ga content, 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.

[0017] 2. The third sub-cell uses GaInP material as the main component of the absorption region, which increases the absorption capacity of the material and shortens the absorption wavelength of the top cell. This allows some of the absorption spectrum to be given to the middle cell, thereby increasing the absorption spectrum of the middle cell (second sub-cell). This allows the short-circuit current of the solar cell to be made larger, making up for the short-circuit current deficiency of AlGaInP / GaAs / Ge solar cells and increasing the photoelectric conversion efficiency of the solar cell.

[0018] 3. 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.

[0019] Furthermore, in the fabrication of the second sub-cell, its base region and emitter region are respectively In x3 Ga 1-x3 As base region and In x4 Ga 1- x4 As the emitter region, and x3=0.01, x4=0.01, thus the In composition of the InGaAs material in the second sub-cell is set to be very low, its lattice constant is very close to that of GaAs, and is consistent with the lattice constant of the P-type Ge substrate. This low-In composition InGaAs can be directly grown on the P-type Ge substrate with high quality, with almost no introduction of lattice mismatch and dislocation, keeping the lattice distortion to a minimum, and can also broaden the absorption spectrum of the second cell to a longer wavelength range to increase the current.

[0020] 4. This invention provides a complete, ordered, and parameter-defined MOCVD growth process that optimizes and combines modules such as substrate processing, tunneling junctions, InGaAs cells, and quantum well cells into a coherent process sequence. This systematic solution ensures the perfect integration of complex multilayer structures within a single growth cycle, greatly improving process repeatability, intra-wafer uniformity, and batch-to-batch stability.

[0021] 5. The third sub-cell prepared in this application can be widely used in various multi-junction cells that require a high bandgap top cell. It is not limited to the Ge / InGaAs system in which the first sub-cell and the second sub-cell of Ge are combined. It can also be combined with sub-cells such as GaAs and InP, for example, with the Ge / GaAs system. That is, the quantum well base structure of this application is itself a substantial improvement on the existing AlGaInP top cell. Its technical effect does not depend on specific middle and bottom cells and has universality. Attached Figure Description

[0022] Figure 1 This is an epitaxial structure diagram of the solar cell of the present invention.

[0023] Figure 2 This is a structural diagram of the quantum well base region of the present invention.

[0024] Figure 3 This is a flowchart of the method of the present invention.

[0025] Label Explanation: 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 Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application, and the range values ​​mentioned in this application all include endpoint values.

[0027] like Figures 1-2 As shown, this application provides a triple-junction quantum well solar cell epitaxial structure, including a first sub-cell, a first tunneling junction 4, a second sub-cell, a second tunneling junction 10, and a third sub-cell stacked sequentially from bottom to top. The three sub-cells are connected by corresponding tunneling junctions. The first sub-cell is the bottom cell, which also serves as the substrate 1, and is specifically a Ge cell. The second sub-cell is the middle cell, specifically an InGaAs cell. The third sub-cell is the top cell, specifically a GaInP / AlGaInP quantum well cell.

[0028] Specifically, 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, which are stacked sequentially from bottom to top.

[0029] Among them, such as Figure 2 As shown, the quantum well base region 12 is composed of alternating GaInP / AlGaInP layers, specifically Ga... x2 In 1-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 Gax2 In 1-x2 The 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 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.

[0030] 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 concentration of 1E16cm. -3 -1E17cm -3 .

[0031] Optionally, in one embodiment, alternating Ga... x2 In 1-x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3In 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.

[0032] 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.

[0033] 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.

[0034] 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-y1The 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 1E18cm. -3 -4E18cm -3 .

[0035] 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 5E17cm. -3 -5E18cm -3 .

[0036] 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 concentration of 1E18cm⁻¹. -3 Up to 5E18cm -3 .

[0037] 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.

[0038] 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 Ga1-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 1E18cm⁻¹. -3 Up to 4E18cm -3 .

[0039] Optionally, the thickness of the AlGaAs back field layer 6 is 80nm-100nm, and the Al content is between 60% and 90%.

[0040] 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 p-type Zn, with a doping amount of 5E17cm. -3 Gradient to 1E16cm -3 .

[0041] 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 concentration of 1E18cm. -3 -3E18cm -3 .

[0042] 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 at a doping concentration of 1E18 cm⁻¹. -3 Up to 3 E18cm -3 .

[0043] 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.

[0044] 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.

[0045] 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 1E19cm. -3 -2E19cm -3 p-type heavily doped GaAs with C doping at a doping level of 1E20cm⁻¹ -3 -2E20cm -3 .

[0046] 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 concentration of 1E19cm⁻¹ -3 -2E19cm -3 p-type heavily doped Al x1 Ga 1-x1 As doped with C, with a doping concentration of 1E20cm⁻¹ -3 -2E20cm -3 .

[0047] 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 3E18cm. -3 Up to 5E18cm -3 .

[0048] 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.

[0049] Please refer to Figure 1 and Figure 3 The manufacturing method specifically includes the following steps: 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.

[0050] S2. Grow the first tunnel junction 4 on substrate 1.

[0051] 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. Among them, the heavily n-type doped GaAs is doped with Te, and the doping amount is 1E19 cm⁻¹. -3 -2E19cm -3 p-type heavily doped GaAs with C doping at a doping level of 1E20cm⁻¹ -3 -2E20cm -3 The first tunnel junction utilizes the tunneling effect to connect the first sub-cell to the subsequently grown second sub-cell.

[0052] S3. A second sub-cell is grown on the first tunnel junction 4. The second sub-cell is an InGaAs cell.

[0053] 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.

[0054] 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 1E18cm⁻¹. -3 Up to 4E18cm -3 .

[0055] Optionally, the AlGaAs back field layer 6 has a growth thickness of 80nm-100nm and an Al content between 60% and 90%.

[0056] 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 5E17cm. -3 Gradient to 1E16cm -3 .

[0057] 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 1E18cm. -3 -3E18cm -3 .

[0058] 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 concentration of 1E18 cm⁻¹. -3 Up to 3 E18cm -3 .

[0059] S4. Grow a second tunnel junction 10 on the second sub-cell.

[0060] 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 concentration of 1E19cm⁻¹ -3 -2E19cm -3 p-type heavily doped Alx1 Ga 1-x1 As doped with C, with a doping concentration of 1E20cm⁻¹ -3 -2E20cm -3 The second tunnel junction 10 utilizes the tunneling effect to connect the second sub-cell to the third sub-cell. 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.

[0061] 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 concentration of 1E18cm. -3 -4E18cm -3 .

[0062] like Figure 2 As shown, the quantum well base region 12 is composed of alternating Ga... x2 In 1-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-x2The 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 concentration of 1E16cm. -3 -1E17cm -3 .

[0063] 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 In 1-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.

[0064] Optionally, in another embodiment, the Ga x2 In 1-x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3The 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.

[0065] 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.

[0066] 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 5E17cm. -3 -5E18cm -3 .

[0067] 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 1E18cm⁻¹. -3 Up to 5E18cm -3 .

[0068] S6. Grow a GaAs ohmic contact layer 15 on the third sub-cell.

[0069] 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 3E18cm. -3 Up to 5E18cm -3 .

[0070] 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.

[0071] 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.

[0072] 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 method for manufacturing an epitaxial structure of a triple-junction quantum well solar cell, characterized in that: The manufacturing process using MOCVD includes the following steps: S1. Provide a P-type Ge substrate, and perform n-type phosphorus diffusion on the P-type Ge substrate to form a pn junction of the first sub-cell; S2. Grow the first tunnel junction on the substrate; S3. Grow the second sub-cell on the first tunnel junction; S4. Grow a second tunnel junction on the second sub-cell; S5. A third sub-cell is grown on the second tunnel junction. The third sub-cell comprises, from bottom to top, an AlGaInP back field layer, a quantum well base region, an AlGaInP emitter region, and an AlInP window layer. The quantum well base region is composed of alternating layers of Ga... x2 In 1-x2 P layer and (Al) x3 Ga 1-x3 ) y3 In 1-y3 The system consists of layer P, where 0.5≤x2≤0.6, 0.5≤x3≤0.8, and y3=0.

5.

2. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: In step S5, a single Ga x2 In 1-x2 The growth thickness of the P layer is 3nm-20nm, and a single (Al) layer... x3 Ga 1-x3 ) y3 In 1-y3 The growth thickness of the P layer is 10nm-20nm, and the number of alternation pairs is 80-150.

3. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 2, characterized in that: In step S5, Ga grows alternately 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 In 1-y3 The P-layer has a growth thickness of 8 nm and an alternation pair number of 110.

4. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 2, characterized in that: In step S5, 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. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: In step S5, the doping element of the quantum well base region is p-type dopant Zn, and the doping amount is 1E16cm. -3 -1E17cm -3 .

6. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: In step S5, the AlGaInP back field layer is (Al x1 Ga 1-x1 ) y1 In 1-y1 The P-back field layer, wherein the AlGaInP emitter region is (Al x4 Ga 1-x4 ) y4 In 1-y4 P emission region, the AlInP window layer is Al x5 In 1-x5 P-window layer, where 0.5≤x1≤0.8, y1=0.5, 0≤x4≤0.5, y4=0.5, 0.5≤x5≤0.

6.

7. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: In step S3, the second sub-cell includes, from bottom to top, a DBR layer, an AlGaAs back surface layer, an InGaAs base region, an InGaAs emitter region, and an AlInP window layer, wherein the InGaAs base region is In x3 Ga 1-x3 The InGaAs base region is InGaAs emitter region. x4 Ga 1-x4 As is the emission region, where x3 = 0.01 and x4 = 0.

01.

8. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: In step S1, after n-type phosphorus diffusion, a GaInP nucleation layer and a GaAs buffer layer are sequentially grown on a p-type Ge substrate. The GaInP nucleation layer and the GaAs buffer layer serve as window layers for the first sub-cell and also as bonding layers between the Ge substrate and subsequent epitaxial layers.

9. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: In step S2, the first tunnel junction 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 at a doping level of 1E19 cm⁻¹. -3 -2E19cm -3 p-type heavily doped GaAs with C doping at a doping level of 1E20cm⁻¹ -3 -2E20cm -3 Furthermore, in step S4, the growth thickness of the second tunnel junction 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 concentration of 1E19cm⁻¹ -3 -2E19cm -3 p-type heavily doped Al x1 Ga 1-x1 As doped with C, with a doping concentration of 1E20cm⁻¹ -3 -2E20cm -3 .

10. The method for manufacturing a triple-junction quantum well solar cell epitaxial structure as described in claim 1, characterized in that: The process after step S5 also includes: Step S6: Grow a GaAs ohmic contact layer on the third sub-cell. The GaAs ohmic contact layer has a thickness of 500 nm-800 nm and is doped with N-type Si at a doping concentration of 3E18 cm⁻¹. -3 -5E18cm -3 .

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