A solar cell

Abstract

The present application discloses a triple-junction gallium arsenide solar cell, comprising a thin film metal substrate, an InGaAs bottom cell, a GaAs middle cell and a GaInP top cell; wherein each sub-cell comprises a window layer, an emitter region, a base region and a back field layer, wherein the window layer, the emitter region, the base region and the back field layer are sequentially arranged along the light incident direction, wherein each sub-cell is connected by a tunnel junction, wherein the GaAs sub-cell sequentially comprises an N-type window layer, an N-type GaInP emitter region, an undoped stress-balanced multi-quantum well structure with Eg < 1.43 eV arranged in the i region, a P-type GaAs base region, a DBR structure composed of a cyclic stacking structure and a P-type doped back field layer. The present application solves the problem that the overall efficiency of the GaInP / GaAs / InGaAs triple-junction cell is limited due to the low current density of the GaAs middle cell under the AM0 spectrum, thereby improving the energy conversion efficiency of the GaInP / GaAs / InGaAs triple-junction gallium arsenide solar cell.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and in particular to gallium arsenide solar cells. Background Art

[0002] Multi-junction solar cells made of III-V materials have an absolute advantage in solar cells for current aerospace applications such as satellites due to their high efficiency and radiation resistance, which are highly compatible with the needs of space applications. Flexible triple-junction (GaInP / GaAs / InGaAs) solar cells based on GaAs substrate peeling technology have the advantages of lower cost, lighter weight, flexibility and high efficiency, and have very strong competitive advantages and application prospects in the current and future aerospace applications.

[0003] Energy conversion efficiency has always been one of the core technical indicators of solar cells. The energy conversion efficiency of solar cells is determined by three technical parameters: open circuit voltage, short circuit current, and fill factor. For GaInP / GaAs / InGaAs triple-junction solar cells, current density (Jsc) is currently the main obstacle to improving its energy conversion efficiency. The reason is that in a triple-junction cell, its current density is determined by the sub-cell with the smallest photocurrent density. Under the AM0 spectrum, when the GaInP top cell that matches the GaAs lattice reaches its maximum current density, due to the bandgap width limitation of the GaAs sub-cell, its current density will be significantly lower than that of the GaInP top cell, thereby limiting the improvement of the current density of the triple-junction cell. Summary of the invention

[0004] In view of this, the present invention provides a high-efficiency flip-chip GaInP / GaAs / InGaAs triple-junction gallium arsenide solar cell structure design, which improves the overall current by increasing the current density of the GaAs sub-cell or increasing the current density of the three sub-cells at the same time without reducing the open circuit voltage, thereby improving the energy conversion efficiency of the solar cell.

[0005] The first aspect of the present application provides a high-efficiency triple-junction gallium arsenide solar cell, comprising a metal substrate, an InGaAs bottom cell, a GaAs middle cell, and a GaInP top cell; each subcell comprises a window layer, an emitter region, a base region, and a back field layer, and the window layer, the emitter region, the base region, and the back field layer are sequentially arranged along the light incident direction; the subcells are connected by tunnel junctions,

[0006] It is characterized in that the GaAs sub-cell includes an N-type window layer, an N-type GaInP emitter region, an undoped stress-balanced multi-quantum well structure with Eg < 1.43 eV arranged in the PN junction i region (depletion region), a P-type thinned GaAs base region, and a DBR (distributed Bragg reflector) structure composed of a circular stacking structure behind the base region, and a P-type doped back field layer.

[0007] According to one embodiment, the stress-balanced multi-quantum well selection In x GaAs is used as the well layer, In x The In component of GaAs material is 0<x<0.15, the thickness is 5~15nm, GaAsP y As a barrier layer, GaAsP y The P component in the material is 0<y<0.45, the thickness is 2~30nm, and the number of multi-quantum well cycles is 20~200.

[0008] According to one embodiment, the GaAs base region is thinned to a thickness of 1000-2000 nm.

[0009] According to one embodiment, in the GaAs subcell, the window layer and the back field layer are made of AlInP, preferably Al 0.5 InP.

[0010] According to one embodiment, the DBR structure includes Al x1 Ga (1-x1) As、Al x2 Ga (1-x2) As cyclic stacking structure, cycle number 5<n<20, Al x1 Ga (1-x1) The thickness of As is 30 to 100 nm, the composition of Al is 0<x1<1, and Al x2 Ga (1-x2) The thickness of As is 30-100 nm, the composition of Al is 0<x2<1, and x1>x2, and the doping material of the DBR structure can be any one of Zn and Mg, with a doping concentration of 1-5×10 17 cm -3 .

[0011] According to one embodiment, the PN junction i region of the GaInP top cell is provided with an undoped Ga with Eg < 1.87 eV. x1 In (1-x1) P / Ga x2 In (1-x2) P stress-balanced multiple quantum well structure, in which Ga x1 In (1-x1) P is used as a well layer, x1<0.5, and the thickness is 2~20nm. Gax2In(1-x2)P is used as a barrier layer, x2>0.5 and x1<x2, and the thickness is 2~20nm.

[0012] According to one embodiment, the GaInP top cell adopts an NP+ heterojunction structure. According to the light incident direction, the GaInP emission region is located in front of the base region as a light absorption layer, the In component is 0.5, the thickness is 300-800nm, and the doping material is Si with a doping concentration of 2-8×1017 cm -3 The base region is made of AlGaInP material with a thickness of 30 to 100 nm; the In component of the base AlGaInP material is 0.51, the Al component is 0.15 to 0.25, and the doping material is Zn or Mg, with a doping concentration of 1 to 3×10 18 cm -3 .

[0013] According to one embodiment, a surface gridline electrode of the top cell is further included, and the surface gridline electrode occupies 2% to 4% of the surface area of ​​the top cell.

[0014] According to one embodiment, the bandgap of the InGaAs bottom cell is set to Eg<1.0 eV.

[0015] According to one embodiment, a metal mirror layer is provided between the thin film metal substrate and the InGaAs bottom cell.

[0016] The solar cell provided by the present invention can solve the problem that the overall efficiency improvement of the GaInP / GaAs / InGaAs triple junction cell is limited due to the low cell current density in GaAs under the AM0 spectrum.

[0017] On the one hand, by adding a low-bandgap InGaAs / GaAsP multi-quantum well structure with a bandgap Eg < 1.43 eV in the i region of the PN junction region of the GaAs sub-cell, the absorption wavelength of the GaAs sub-cell can break through the GaAs bandgap limitation, so as to improve the current density of the GaAs sub-cell; at the same time, by changing the GaAs junction from a GaAs / GaAs homogeneous structure to a GaInP / GaAs heterogeneous structure and reducing the thickness of the GaAs absorption layer, the problem of reduced open circuit voltage caused by the introduction of the multi-quantum well structure is compensated; in view of the insufficient light absorption ratio caused by the reduction of the thickness of the GaAs absorption layer, the present invention further introduces Al at the rear end of the GaAs base region x1 Ga (1-x1) As / Al x2 Ga (1-x2) As composed of DBR structure, the wavelength photons not absorbed by the GaAs junction are reflected into the GaAs junction base region for secondary absorption. Through the above design, the present invention improves the current density of the GaAs junction battery while keeping the open circuit voltage basically unchanged, and improves the current density matching degree of each junction battery of the three-junction battery, thereby effectively improving the photoelectric conversion efficiency of the GaAs battery.

[0018] On the other hand, the present invention increases the low bandgap width Ga with Eg < 1.87 eV in the GaInP subcell PN junction region. x1 In (1-x1) P / Ga x2 In (1-x2)P multi-quantum well layer and adjust the bandgap width of the GaInP junction to increase the battery current density. At the same time, the GaInP / AlGaInP NP+ heterojunction structure is used to reduce the dark current of the battery and increase the open circuit voltage of the battery. At the same time, compared with the traditional N + The P structure has higher lateral conductivity, so that fewer metal grid lines can be used (reducing the area percentage of the metal grid lines, that is, a larger light-receiving area), further improving the short-circuit current of the GaInP sub-cell and increasing the overall conversion efficiency of the cell.

[0019] On the other hand, the bandgap of the InGaAs bottom cell of the present invention is set to Eg<1.0eV.

[0020] The second aspect of the battery structure design of the present invention further improves the overall current based on the first aspect of the design. Although the total open circuit voltage is reduced, the product of the reduction in open circuit voltage and the increase in total current is greater than that of the first design, thereby increasing the overall conversion efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of a flip-chip high-efficiency triple-junction gallium arsenide solar cell device according to an embodiment of the present invention.

[0022] Figure 2 yes Figure 1 Schematic diagram of the epitaxial structure during the preparation of inverted high-efficiency triple-junction gallium arsenide solar cells.

[0023] Figure 3 yes Figure 1 Schematic diagram of the structure of the GaInP subcell of the flip-chip high-efficiency triple-junction GaAs solar cell.

[0024] Figure 4 yes Figure 1 Schematic diagram of the structure of the GaAs subcell of the inverted high-efficiency triple-junction GaAs solar cell.

[0025] Figure 5 yes Figure 1 Schematic diagram of the structure of the InGaAs subcell of the flip-chip high-efficiency triple-junction GaAs solar cell.

[0026] Figure 6 yes Figure 1 Schematic diagram of the structure of the InGaAs sub-cell lattice gradient layer of the inverted high-efficiency triple-junction gallium arsenide solar cell.

[0027] Figure 7 yes Figure 1 Diagram of the preparation process of flip-chip triple-junction high-efficiency gallium arsenide solar cells. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of the embodiment of the present invention. Unless otherwise defined, the same reference numerals in the embodiments of the present invention and the drawings represent the same meaning. It should be noted that for the sake of clarity, the drawings of the embodiments may not necessarily be drawn to scale; in addition, in the drawings of some embodiments of the present invention, only structures related to the concept of the present invention are shown, and some conventional structures and details that are not directly related to the concept of the present invention may be omitted. The embodiment of the present invention may include these undisplayed structures. In addition, it should be noted that the order of the method steps described in the embodiment of the present invention does not necessarily represent the actual execution order of the steps. Where feasible, the actual execution order may be different from the described order.

[0029] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words indicate an open meaning, and do not exclude other elements, components, parts or items except for the elements, parts, parts or items clearly listed. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. It is understood that when an element such as a layer, a film, a region or a substrate substrate is referred to as being "on" or "under" another element, the element may be "directly" located "on" or "under" another element, or there may be an intermediate element.

[0030] like Figure 1 As shown, a high-efficiency triple-junction gallium arsenide solar cell according to an embodiment of the present invention includes an active region 10 for absorbing sunlight, a thin film metal substrate 20, a surface anti-reflection film 40, and a surface grid line electrode 30. Figure 2 The active region 10 is an epitaxial structure, including a GaInP top cell 103, a GaAs middle cell 102 and an InGaAs bottom cell 101. Each sub-cell includes a window layer, an emitter region, a base region, and a back field layer. The window layer, the emitter region, the base region, and the back field layer are arranged in sequence in a direction away from the GaAs substrate. The sub-cells are connected by tunnel junctions 12 and 13.

[0031] See also Figure 4The cell 102 in the GaAs epitaxial structure sequentially includes an N-type window layer 1021, an N-type GaInP emitter region 1022, an undoped stress-balanced multi-quantum well structure 1023 with Eg < 1.43 eV set in the i region between the emitter region 1022 and the base region 1024, a P-type GaAs base region 1024, a distributed Bragg reflector (DBR) 1025 composed of multiple cyclic structures after the base region 1024, and a P-type doped back field layer 1026;

[0032] In the window layer of the GaAs junction cell 102, the material is preferably Al 0.5 InP, thickness is 15-50nm, the window layer is N-type doped, the doping material is any one of Si and Te, and the doping concentration is 1-5×10 18 cm -3 .

[0033] The GaAs subcell 102 emitter region material may be Ga 0.5 InP, thickness is 30-100nm, the emission region is N-type doped, the doping material is any one of Si and Te, and the doping concentration is 1-5×10 18 cm -3 .

[0034] The i region between the emitter region and the base region of the GaAs subcell 102 is provided with an undoped stress-balanced multi-quantum well structure with Eg < 1.43 eV, and the stress-balanced multi-quantum well is preferably In x GaAs is used as the well layer 10231, with a thickness of 5 to 15 nm, In x In composition of GaAs material 0<x<0.15, GaAsP y As the barrier layer 10232, the thickness is 2 to 30 nm, GaAsP y The P component in the material is 0<y<0.45, and the number of multiple quantum well cycles is 20-200.

[0035] The base material of the GaAs subcell 102 is GaAs, with a thickness of 1000-2000 nm. The base doping material can be any one of Zn and Mg, with a doping concentration of 1-5×10 17 cm -3 .

[0036] Preferably, the base region 102 is provided with a plurality of Al x1 Ga (1-x1) As / Al x2 Ga (1-x2) As cyclically stacked DBR structure 1025, the DBR structure reflects the wavelength photons not absorbed by the GaAs junction into the GaAs junction base region for secondary absorption, wherein the cycle number is 5<n<20, Alx1 Ga (1-x1) The thickness of As is 30 to 100 nm, the composition of Al is 0<x1<1, and Al x2 Ga (1-x2) The thickness of As is 30-100 nm, the composition of Al is 0<x2<1, the thickness is x1>x2, and the doping material of DBR structure can be any one of Zn and Mg, and the doping concentration is 1~5×10 17 cm -3 .

[0037] The back field layer 1026 of the GaAs junction cell 102 is preferably made of Al 0.5 InP, thickness is 15-50nm, the back field layer 1026 is P-type doped, the doping material is any one of Zn and Mg, and the doping concentration is 1-5×10 18 cm -3 .

[0038] Preferably, see Figure 3 , the GaInP top cell 101 sequentially stacks a window layer 1011, an emitter region 1012, a base region 1013 and a back field layer 1014 in a direction away from the GaAs substrate 1. The PN junction i region of the GaInP top cell 101 is provided with an undoped GaxlIn(1-x1)P / Gax2In(1-x2)P stress-balanced multi-quantum well structure with Eg<1.87eV, wherein GaxlIn(1-x1)P is used as a well layer, x1<0.5, and has a thickness of 2 to 20nm, and Gax2In(1-x2)P is used as a barrier layer, x2>0.5 and x1<x2, and has a thickness of 2 to 20nm;

[0039] Furthermore, the GaInP top cell 101 adopts an NP+ heterojunction structure. According to the light incident direction, the GaInP emission region is located in front of the base region as a light absorption layer, the In component is 0.5, the thickness is 300-800nm, and the doping material is Si with a doping concentration of 2-8×10 17 cm -3 The base region is made of AlGaInP material with a thickness of 30 to 100 nm; the In component of the base AlGaInP material is 0.51, the Al component is 0.15 to 0.25, and the doping material is Zn or Mg, with a doping concentration of 1 to 3×10 18 cm -3 .

[0040] Furthermore, the top cell surface gridline electrode 30 is also included, and the surface gridline electrode occupies 2%-4% of the surface area of ​​the top cell.

[0041] Furthermore, the bandgap of the InGaAs bottom cell 103 is set to Eg<1.0 eV.

[0042] The inverted high-efficiency triple-junction GaAs solar cell grows a P-type conductive layer 2 away from the outermost layer of the GaAs substrate, with a thickness between 100 and 400 nm, and the doping material is any one of Zn and Mg, with a doping concentration of 1 to 5×10 18 cm -3 ;

[0043] Further, see Figure 7 A metal reflector layer 22, a metal contact layer 21 and a thin film metal substrate 20 can be sequentially stacked on the P-type conductive layer 2. Specifically, the metal reflector layer, the metal contact layer and the metal triple junction substrate can be deposited by magnetron sputtering, thermal evaporation and the like.

[0044] The GaAs substrate 1 is removed by substrate stripping or substrate etching, and a thin film metal substrate 2 is used as a support. The N-type electrode, gate line, anti-reflection film, etc. are made by using mask technology to obtain an inverted high-efficiency triple-junction gallium arsenide solar cell with the thin film metal 2 as the substrate.

[0045] In order to solve the problem that the overall efficiency improvement of GaInP / GaAs / InGaAs triple junction cells is limited by the low cell current density in GaAs under the AM0 spectrum, the present application provides an epitaxial structure suitable for flip-chip high-efficiency triple junction gallium arsenide solar cells, and adopts a multi-junction cell epitaxial structure of three GaInP / GaAs / InGaAs sub-cells. On the one hand, by adding a low bandgap InGaAs / GaAsP multi-quantum well structure with a bandgap Eg < 1.43eV in the i region of the PN junction region of the GaAs sub-cell, the GaAs sub-cell can absorb wavelengths that break through the GaAs bandgap width limitation, thereby improving the maximum theoretical current density Jsc1 of the GaAs sub-cell. At the same time, the introduction of the InGaAs / GaAsP multi-quantum well structure will reduce the open circuit voltage Voc1 of the GaAs sub-cell, limiting the further improvement of the effective photoelectric conversion efficiency of the GaAs junction cell; to address this problem, the present invention reduces the thickness of the GaAs absorption layer to increase the Voc2 of the GaAs junction cell; to address the reduction in the thickness of the GaAs absorption layer to reduce the current density Jsc2 due to insufficient light absorption ratio, the present invention further introduces Al at the rear end of the GaAs base region. x1 Ga (1-x1) As / Al x2 Ga (1-x2)As composed of the DBR structure, the wavelength photons not absorbed by the GaAs junction are reflected into the GaAs junction base region for secondary absorption, thereby improving the GaAs junction current density Jsc3; in addition, the present invention changes the GaAs junction PN junction from an N-type GaAs / P-type GaAs homogeneous structure to an N-type GaInP / P-type GaAs heterogeneous structure, further improving the GaAs junction open circuit voltage Voc3, satisfying ΔJsc1+ΔJsc2+ΔJsc3>0, Voc>Voc1. Through the above design, the present invention improves the current density of the GaAs junction battery while keeping the open circuit voltage basically unchanged, improves the current density matching degree of each junction battery of the three-junction battery, thereby effectively improving the photoelectric conversion efficiency of the GaAs battery.

[0046] On the other hand, the present invention also increases the battery current density, extends the absorption wavelength of each sub-battery, and increases the short-circuit current of each sub-battery by adding a Gax1In(1-x1)P / Gax2In(1-x2)P multi-quantum well structure with a low bandgap width of Eg < 1.87eV in the PN junction region of the GaInP sub-battery and adjusting the bandgap width of the InGaAs junction to Eg < 1.0eV.

[0047] At the same time, the GaInP / AlGaInP NP+ heterojunction structure is adopted, compared with the traditional N + The P structure has higher lateral conductivity, so that fewer metal grid lines can be used (reducing the area percentage of the metal grid lines, that is, a larger light-receiving area), further improving the short-circuit current of the GaInP sub-cell and increasing the overall conversion efficiency of the cell; the above-mentioned heterojunction structure can effectively reduce the SNS non-radiative recombination current and improve the external quantum efficiency of the cell by moving the PN junction area to the wide bandgap region at the bottom of the cell, thereby reducing the dark current of the cell and increasing the open circuit voltage of the cell.

[0048] The second aspect of the epitaxial layer design of the present invention further improves the overall current based on the first design. Although the total open circuit voltage is reduced, the product of the reduction in open circuit voltage and the increase in total current is greater than that of the first design, thereby increasing the overall conversion efficiency of the battery.

[0049] Example 1

[0050] Reference Figure 1 As shown in FIG. 1 , the inverted high-efficiency triple-junction gallium arsenide solar cell prepared in the embodiment of the present invention comprises a thin film metal substrate 20, an active region 10 for absorbing sunlight, a surface anti-reflection film (ARC) 40 and a surface grid electrode 30. The active region for absorbing sunlight is the epitaxial layer of the solar cell, comprising Ga 0.5 InP subcell, GaAs subcell and InGaAs subcell.

[0051] Reference Figure 2As shown, the epitaxial structure of the flip-chip high-efficiency triple-junction gallium arsenide solar cell of this embodiment is as follows:

[0052] GaAs is selected as the substrate 1 for epitaxial growth, and the conductivity type of the GaAs substrate is not limited. The substrate sacrificial layer 11, GaAs substrate 2, and GaAs substrate 3 are epitaxially grown in sequence on the GaAs substrate 1 by using a vapor phase epitaxial growth technology (MOCVD) or a molecular beam epitaxy technology (MBE). 0.5 InP sub-cell 101 , tunnel junction 12 , GaAs sub-cell 102 , tunnel junction 13 , InGaAs sub-cell 103 , and P-type conductive layer 2 .

[0053] More specifically, in this embodiment, the substrate sacrificial layer 11 is stripped to select non-doped Al x GaAs material, AlxGaAs Al content 0.3<x≤1, thickness 15nm. x The GaAs method realizes the separation of the active region 10 absorbing sunlight from the GaAs substrate 1 .

[0054] For more specific information, see Figure 3 , Ga 0.5 The InP sub-cell 101 is stacked with a window layer 1011 , an emitter region 1012 , a base region 1013 and a back field layer 1014 in sequence in a direction away from the GaAs substrate 1 .

[0055] Furthermore, Ga 0.5 The material of the window layer 1011 of the InP sub-cell 101 is preferably Al 0.5 InP, thickness 30nm, window layer is N-type doped, doping material is Si, doping concentration is 2×10 18 cm -3 .

[0056] Furthermore, the Ga 0.5 The material of the emitter region 1012 of the InP subcell 101 is Ga 0.5 InP, thickness is 100nm. The emitter region is N-type doped, the doping material is Si, and the doping concentration is 1×10 18 cm -3 .

[0057] Furthermore, the Ga 0.5 The base region 1013 of the InP subcell 101 is made of Ga 0.5 InP, thickness 750nm, base doping material is Zn, doping concentration is 1×10 17 cm -3 .

[0058] Furthermore, Ga 0.5The material of the back field layer 1014 of the InP subcell 101 is preferably AlGaInP, with an Al component of 0.25 and a thickness of 50 nm. The back field layer is P-type doped, with Mg as the doping material and a doping concentration of 1×10 18 cm -3 .

[0059] Furthermore, the tunnel junction 12 material is Al 0.4 GaAs: C layer and Al 0.1 GaAs:Te layer, that is, the tunnel junction 12 includes sequentially stacked Al 0.4 GaAs: C layer and Al 0.1 GaAs: Te layer, Al 0.4 The GaAs:C material thickness is 20nm and the doping concentration is 1×10 20 cm -3 , Al 0.1 The GaAs:Te material thickness is also 20nm and the doping concentration is 5×10 19 cm -3 .

[0060] For further reference, Figure 4 The GaAs sub-cell 102 is stacked in sequence along a direction away from the GaAs substrate 1, including a window layer 1021, an emission region 1022, an i-region multi-quantum well structure 1023, a base region 1024, a DBR layer 1025, and a back field layer 1026.

[0061] Furthermore, the material of the window layer 1021 of the GaAs sub-cell 102 is preferably Al 0.5 InP, thickness 40nm, window layer is N-type doped, doping material is Si, doping concentration is 2×10 18 cm -3 .

[0062] Furthermore, the material of the emitter region 1022 of the GaAs subcell 102 is Ga 0.5 InP, thickness is 100nm. The window layer is N-type doped, the doping material is Si, and the doping concentration is 1×10 18 cm -3 .

[0063] Furthermore, the GaAs subcell 102 is provided with an undoped stress-balanced multi-quantum well structure 1023 with a bandgap width Eg < 1.43 eV in the PN junction, and the stress-balanced multi-quantum well structure 1023 is preferably In 0.1 GaAs is used as the well layer 10231, with a thickness of 10nm, GaAsP 0.1 As the barrier layer 10232, the thickness is 20 nm and the number of multi-quantum well cycles is 80.

[0064] Furthermore, the base region 1024 of the GaAs subcell 102 is made of GaAs, with a thickness of 1500 nm, and the base region doping material is Zn, with a doping concentration of 1×10 17 cm -3 .

[0065] Furthermore, a plurality of Al 0.7 GaAs / Al 0.1 The DBR structure 1025 composed of GaAs cyclic stacking reflects the wavelength photons not absorbed by the GaAs junction into the GaAs junction base region for secondary absorption. The cycle number is 15. Al 0.7 The thickness of GaAs material 10251 is 70nm, Al 0.1 The thickness of GaAs material 10252 is 60nm, and the doping material of DBR structure is Zn with a doping concentration of 3×10 17 cm -3 .

[0066] The back field layer 1026 of the GaAs junction cell 102 is preferably made of Al 0.7 GaAs, thickness is 50nm, the back field layer is P-type doped, the doping material is Mg, and the doping concentration is 1×1018cm-3.

[0067] Further, see Figure 5 The InGaAs subcell 103 is sequentially stacked with a lattice graded layer 1031, a window layer 1032, an emitter region 1033, a base region 1034 and a back field layer 1035 in a direction away from the GaAs substrate 1. The GaAs junction and the InGaAs junction are connected via a second tunnel junction 13.

[0068] Furthermore, the material of the second tunnel junction 13 is Al 0.4 GaAs: C layer and Al 0.1 GaAs:Te layer. That is, the tunnel junction 13 includes sequentially stacked Al 0.4 GaAs: C layer 131 and Al 0.1 GaAs: Te layer 132, Al 0.4 The GaAs:C material thickness is 30nm and the doping concentration is 1×10 20 cm -3 , Al 0.2 The GaAs:Te material thickness is also 30nm and the doping concentration is 5×10 19 cm -3 .

[0069] Further, see Figure 6As shown, in this embodiment, the lattice gradient layer 1031 of the InGaAs subcell 103 adopts a multi-layer design, with 7 layers, namely 10311, 10312, 10313, 10314, 10315, 10316 and 10317, with a total thickness of 2700nm, and the material is In x (Al y Ga (1-y) ) (1-x) As, by changing x and y layer by layer, the lattice constant gradually increases from matching GaAs to matching In 0.3 Ga 0.7 As subcell material matching. The thickness of 10311, 10312, 10313, 10315, and 10316 is 300nm, and the thickness of 10317 is 900nm. The lattice gradient layer adopts N-type doping, the doping material is Si, and the doping concentration is 2×10 17 cm -3 .

[0070] Furthermore, the window layer 1032 of the InGaAs subcell 103 is made of In 0.275 (Al 0.414 Ga 0.586 ) 0.725 As, thickness is 50nm. The window layer is N-type doped, doped with Si, and doping concentration is 2×10 18 cm -3 .

[0071] Furthermore, the material of the emission region 1033 of the InGaAs subcell 103 is In 0.3 Ga 0.7 As, thickness is 100nm, the emitter region is N-type doped, the doping material is Si, and the doping concentration is 2×10 18 cm -3 .

[0072] Furthermore, the base region 1034 of the InGaAs subcell 103 is made of In 0.3 Ga 0.7 As, thickness is 1800nm, base doping is Zn, doping concentration is 1×10 17 cm -3 .

[0073] Furthermore, the material of the back field layer 1035 of the InGaAs subcell 103 is Ga 0.38 In 0.62 P material, thickness 300nm, back field layer is P-type doped, doping material is Mg, doping concentration is 3×10 18 cm -3 .

[0074] Furthermore, the material of the P-type conductive layer 2 is In 0.3 (Al 0.41 Ga 0.59 ) 0.7 As, thickness is 300nm, doping is Zn, doping concentration is 2×10 18 cm -3 .

[0075] Further, see Figure 7 As shown, a metal reflector layer 22 and a metal contact layer 21 are sequentially stacked between the P-type conductive layer 2 and the metal substrate 20 .

[0076] Furthermore, the mask technology is used in Ga 0.5 An N-type electrode is fabricated on the surface of the InP window layer 1011 .

[0077] Furthermore, thermal evaporation is used to form metal gate lines 30 on the surface of the N-type electrode.

[0078] A ZnSe / MgF or Al2O3 / TiO2 anti-reflection film is evaporated on the surface of the GaInP window layer 1011 exposed except for the gate lines, and the thickness of each film layer is determined according to the reflection wavelength.

[0079] Furthermore, the inverted high-efficiency triple-junction gallium arsenide solar photovoltaic cell structure is obtained by cutting and separating.

[0080] Example 2

[0081] Example 2 also provides an inverted high-efficiency triple-junction gallium arsenide solar photovoltaic cell epitaxial structure and cell structure. In the description of Example 2, the same points as in Example 1 are not repeated, and only the differences from Example 1 are described. The gallium arsenide solar cell in Example 2 is different from the gallium arsenide solar cell in Example 1 in that:

[0082] like Figure 3 As shown, Ga 0.5 The InP top cell 101 sequentially stacks a window layer 1011 , an emitter region 1012 , a base region 1013 and a back field layer 1014 in a direction away from the GaAs substrate 1 .

[0083] Furthermore, Ga 0.5 The InP top cell window layer 1011 is Si-doped AlInP with a doping concentration of 2×10 18 cm -3 , thickness is 30nm:

[0084] Furthermore, Ga 0.5 The InP top cell emitter region 1012 is doped with Si-doped Ga 0.5 InP, doping concentration is 5×1017 cm -3 , thickness is 500nm;

[0085] Furthermore, Ga 0.5 The nip junction i region (between the emitter region 1012 and the base region 1013) of the InP top cell 101 introduces an undoped Ga with Eg < 1.87 eV. 0.45 In 0.55 P / Ga 0.55 In 0.45 P stress-balanced multiple quantum well structure, in which Ga 0.45 In 0.55 P is used as the well layer with a thickness of 6nm, Ga 0.55 In 0.45 P is used as a barrier layer with a thickness of 6nm;

[0086] Furthermore, Ga 0.5 The InP top cell base region 1013 is made of Zn-doped Al0.15Ga0.34In0.51P with a doping concentration of 2x10 18 cm -3 , thickness is 50nm;

[0087] Furthermore, Ga 0.5 The back field layer 1014 of the InP top cell is made of Zn-doped AlGaInP with a thickness of 50 nm. The Al component in the material increases linearly from 0.15 to 0.25 starting from the base interface, and the doping concentration increases from 1×10 18 cm -3 The index increases to 5×10 18 cm -3 .

[0088] The GaInP top cell adopts an NP+ heterojunction structure, and the surface grid lines of the top cell occupy 2%-4% of the surface area of ​​the top cell.

[0089] For further reference, Figure 4 The GaAs sub-cell 102 is stacked in sequence along a direction away from the GaAs substrate 1, including a window layer 1021, an emission region 1022, an i-region multi-quantum well structure 1023, a base region 1024, a DBR layer 1025, and a back field layer 1026.

[0090] Furthermore, an undoped stress-balanced multi-quantum well structure with a bandgap width Eg < 1.43 eV is added to the pn junction 1023 of the GaAs sub-cell 102, and the stress-balanced multi-quantum well structure is preferably In 0.15 GaAs is used as the well layer with a thickness of 10nm, GaAsP 0.3 As a barrier layer, the thickness is 10 nm and the number of multi-quantum well cycles is 120.

[0091] Further, the GaAs subcells 1021, 1022, 1024, 1025 and 1026 are consistent with those in Example 1;

[0092] Furthermore, the Ga 0.5 The InP sub-cell 101 and the GaAs sub-cell 102 are connected via a tunnel junction 12, and the tunnel junction growth conditions are consistent with those in Example 1;

[0093] Further, see Figure 5 The InGaAs subcell 103 is sequentially stacked with a lattice gradient layer 1031 , a window layer 1032 , an emission region 1033 , a base region 1034 and a back field layer 1035 in a direction away from the GaAs substrate 1 .

[0094] Further, see Figure 6 As shown, in this embodiment, the lattice gradient layer 1031 of the InGaAs subcell 103 adopts a multi-layer design, with 7 layers, namely 10311, 10312, 10313, 10314, 10315, 10316 and 10317, with a total thickness of 2700nm, and the material is In x (Al y Ga (1-y) ) (1-x) As, by changing x and y layer by layer, the lattice constant gradually increases from matching GaAs to matching In 0.35 Ga 0.65 As sub-battery materials match. The thickness of 10311, 10312, 10313, 10314, 10315, and 10316 is 300nm, and the thickness of 10317 is 900nm. The lattice gradient layer adopts N-type doping, the doping material is Si, and the doping concentration is 2×10 17 cm -3 .

[0095] Furthermore, the window layer 1032 of the InGaAs subcell 103 is made of In 0.35 (Al 0.6 Ga 0.4 ) 0.65 As, thickness is 50nm. The window layer is N-type doped, doped with Si, and doping concentration is 2×10 18 cm -3 .

[0096] Furthermore, the material of the emission region 1033 of the InGaAs subcell 103 is In 0.35 Ga 0.57 As, thickness is 100nm, the emitter region is N-type doped, the doping material is Si, and the doping concentration is 2×10 18 cm-3 .

[0097] Furthermore, the base region 1034 of the InGaAs subcell 103 is made of In 0.35 Ga 0.65 As, thickness is 1800nm, base doping is Zn, doping concentration is 1×10 17 cm -3 .

[0098] Furthermore, the material of the back field layer 1035 of the InGaAs subcell 103 is Ga 0.15 In 0.85 P material, thickness 300nm, back field layer is P-type doped, doping material is Mg, doping concentration is 3×10 18 cm -3 .

[0099] Furthermore, the material of the P-type conductive layer 2 is In 0.35 (Al 0.6 Ga 0.4 ) 0.65 As, thickness is 300nm, doping is Zn, doping concentration is 2×10 18 cm -3 .

[0100] Further, see Figure 7 As shown, a metal reflector layer 22 and a metal contact layer 21 are sequentially stacked between the P-type conductive layer 2 and the metal triple junction substrate 20 .

[0101] Furthermore, the GaAs sub-cell 102 and the InGaAs sub-cell 103 are connected via a tunnel junction 13, and the tunnel junction growth conditions are consistent with those in Example 1;

[0102] Furthermore, the mask technology is used in Ga 0.5 An N-type electrode is made on the surface of the InP window layer 1011;

[0103] Furthermore, thermal evaporation is used to form metal gate lines 30 on the surface of the N-type electrode.

[0104] A ZnSe / MgF or Al2O3 / TiO2 anti-reflection film is evaporated on the surface of the GaInP window layer exposed except for the gate lines, and the thickness of each film layer is determined according to the reflection wavelength.

[0105] Furthermore, the inverted high-efficiency triple-junction gallium arsenide solar photovoltaic cell structure is obtained by cutting and separating.

[0106] The disclosed embodiment provides a high-efficiency flip-chip GaInP / GaAs / InGaAs triple-junction gallium arsenide solar cell design, which can solve the problem that the overall efficiency improvement of the GaInP / GaAs / InGaAs triple-junction cell is limited by the low cell current density in GaAs under the AM0 spectrum. The disclosed embodiment adds a multi-quantum well structure with a low bandgap width to the PN junction region of the GaAs sub-cell to increase the cell current density in GaAs; at the same time, by changing the GaAs junction from a GaAs / GaAs homogeneous structure to a GaInP / GaAs heterogeneous structure and thinning the GaAs absorption layer thickness, the problem of reduced open circuit voltage caused by the introduction of the multi-quantum well structure is compensated; in order to solve the problem of reduced light absorption efficiency caused by thinning the GaAs absorption layer, the disclosed embodiment adds a DBR structure to the rear end of the GaAs sub-cell to reflect the photons that are not absorbed by the GaAs junction into the GaAs junction for secondary absorption. Through the above design, the problem of low GaAs junction current density in conventional designs can be solved while maintaining the open circuit voltage; on the other hand, the disclosed embodiment also introduces multiple quantum wells in the GaInP sub-cell and adopts NP + By using structural heterojunction and adjusting the bandgap width of the InGaAs junction, the current density of the two-junction sub-cells matches that of the GaAs sub-cell under AM0 spectral conditions, further increasing the overall current and thus achieving the purpose of improving the energy conversion efficiency of the inverted GaInP / GaAs / InGaAs triple-junction gallium arsenide solar cell.

[0107] The above embodiments are merely illustrative of the principles and structures of the present disclosure, and are not intended to limit the present disclosure. It should be understood by those skilled in the art that any changes and improvements made to the present disclosure are within the scope of the present disclosure without departing from the overall concept of the present disclosure. The scope of protection of the present disclosure shall be subject to the scope defined in the claims of this application. It should be noted that the wording "comprising" does not exclude other elements or steps, and the wording "one" or "an" does not exclude multiple elements. In addition, any element number in the claims should not be understood as limiting the scope of the present disclosure.

[0108] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A triple-junction gallium arsenide solar cell comprising a thin film metal substrate, an InGaAs bottom cell, a GaAs middle cell and a GaInP top cell; in, Each subcell includes a window layer, an emission region, a base region, and a back field layer, wherein the window layer, the emission region, the base region, and the back field layer are sequentially arranged along the light incident direction, and the subcells are connected by a tunnel junction. The GaAs cells sequentially include an N-type window layer, an N-type GaInP emission region, an undoped stress-balanced multi-quantum well structure with Eg<1.43eV arranged in the i region, a P-type GaAs base region, a DBR structure composed of a cyclic stacking structure, and a P-type doped back field layer; Among them, the stress-balanced multi-quantum well structure selects In x GaAs as the well layer, In x The In component in the GaAs material is 0 < x < 0.15, and the thickness is 5 - 15 nm; GaAsP y as the barrier layer, GaAsP y The P component in the material is 0 < y < 0.45, and the thickness is 2 - 30 nm; the number of cycles of the multi-quantum well structure is 20 - 200; The thickness of the GaAs base region is reduced to 1000-2000 nm; In the GaAs cell, the window layer and the back field layer are made of AlInP.

2. The solar cell according to claim 1, wherein: In the GaAs cell, the window layer and the back field layer are made of Al 0.5 InP.

3. The solar cell according to claim 1, wherein The DBR structure includes Al x1 Ga (1-x1) As、Al x2 Ga (1-x2) As cyclic stacking structure, cycle number 5 <n<20, Al x1 Ga (1-x1) The thickness of As is 30 - 100 nm, the component of Al is 0 < x1 < 1, Al x2 Ga (1-x2) The thickness of As is 30 - 100 nm, the component of Al is 0 < x2 < 1, and x1 > x2. The doping substance of the DBR structure is any one of Zn and Mg, and the doping concentration is 1 - 5×10 17 cm -3 。 4. The solar cell according to claim 1, wherein The i-region of the PN junction of the GaInP top cell is provided with undoped Ga x1 In (1-x1 )P / Ga x2 In (1-x2) P stress-balanced multiple quantum well structure, where Ga x1 In (1-x1) P serves as the well layer, x1 < 0.5, with a thickness of 2 - 20 nm, and Ga x2 In (1-x2) P serves as the barrier layer, x2 > 0.5 and x1 < x2, with a thickness of 2 - 20 nm.

5. The solar cell according to claim 1, wherein The GaInP top cell adopts an NP+ heterojunction structure. According to the light incident direction, the GaInP emission region is located in front of the base region as a light absorption layer. The In component is 0.5, the thickness is 300-800nm, and the doping material is Si with a doping concentration of 2-8×10 17 cm -3 The base region is made of AlGaInP material with a thickness of 30 to 100 nm. The In component of the base AlGaInP material is 0.51, the Al component is 0.15 to 0.25, and the doping material is Zn or Mg, with a doping concentration of 1 to 3×10 18 cm -3 .

6. The solar cell according to claim 1, wherein: It also includes a surface grid line electrode of the top battery, which occupies 2% to 4% of the surface area of ​​the top battery.

7. The solar cell according to claim 1, wherein: The bandgap of the InGaAs bottom cell is set to Eg<1.0 eV.

8. The solar cell according to claim 1, wherein A metal reflector layer is provided between the thin film metal substrate and the InGaAs bottom cell.

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