WO2014101631A1 - Multi-junction solar cell and preparation method thereof - Google Patents

Abstract

A reverse multi-junction solar cell and a preparation method thereof comprise: a substrate (100), a first sub-cell (300) reversely growing on the substrate and comprising a first band gap; a second sub-cell (500) reversely formed on the first sub-cell and comprising a second band gap smaller than the first band gap; a third sub-cell (600) reversely formed on the second sub-cell and comprising a third band gap smaller than the second band gap; a fourth sub-cell (700) reversely formed on the third sub-cell and comprising a fourth band gap smaller than the third band gap, the first sub-cell, the second sub-cell, the third sub-cell and the fourth sub-cell being lattice matching with the substrate; a graded buffering layer (800) formed on the fourth sub-cell, used for overcoming the lattice mismatching between the fourth sub-cell and a fifth sub-cell, and comprising a fifth band gap smaller than the fourth band gap; the fifth sub-cell (900) reversely formed on the homogeneous graded buffering layer and comprising a sixth band gap smaller than the fifth band gap. The high-efficiency multi-junction solar cell with current matching and wider spectral-absorbing range can be prepared.

Description

Multi-junction solar cell and preparation method thereof

This application claims the following priority: Chinese Invention Patent Application No. 201210582092.X, entitled ' Multi-junction solar cells and their preparation methods' were submitted on December 28, 2012. The entire contents of the above application are incorporated herein by reference.

Technical field

The invention relates to a multi-junction solar cell and a preparation method thereof, and belongs to the technical field of semiconductor materials.

Background technique

In recent years, solar cells have attracted more and more attention as a practical new energy source. It is a semiconductor device that uses photovoltaic effect to convert solar energy into electrical energy, which greatly reduces the dependence of people's production and life on coal, oil and natural gas, and becomes one of the most effective ways to use green energy. Among all new energy sources, solar energy is one of the most ideal renewable energy sources, and fully exploiting solar energy has become a sustainable energy strategy decision for governments around the world. In recent years, concentrating multi-junction compound solar cells, which are the third generation photovoltaic power generation technology, have attracted much attention due to their high photoelectric conversion efficiency.

The current highly efficient GaInP/GaAs/Ge triple junction solar cells have achieved over 41.8% photoelectric conversion efficiency under concentrating conditions. However, due to the excessive absorption of low-energy photons by the Ge bottom cell, the short-circuit currents of the top cells of InGaP and GaAs do not match, so the conventional GaInP/GaAs/Ge triple junction solar cell structure is not an optimal combination of efficiency. Ideally, a three-junction cell current match can be achieved if a material with a band gap of 1 eV can be found instead of Ge. In _0.3 Ga _0.7 As has a forbidden band width of 1 eV and is one of the best choices, but it has a 2.14% lattice mismatch with GaAs. Flip-chip growth: In _0.5 Ga _0.5 P and GaAs top cells that are lattice-matched to the substrate GaAs; then transition to the InGaAs bottom cell through a graded buffer layer (InGaP, InAlP, or InGaAs); subsequent substrate Peeling, new substrate bonding and other processes are gradually implemented to achieve full structure preparation of the entire battery. The main technical difficulty in the whole preparation process is to overcome the 2.15% lattice mismatch generated from the transition of GaAs lattice constant 0.5653 nm to In _0.3 Ga _0.7 As lattice constant 0.5775 nm, which is the heterojunction gradient buffer layer. Growing.

Summary of the invention

The invention provides a method for obtaining 1eV The sub-battery idea, which introduces a homogenous graded buffer layer, can obtain a sub-cell with a lower dislocation density and better crystal quality.

According to an aspect of the invention, a multi-junction solar cell includes at least a bottom cell, a sub-bottom cell, and a top cell, wherein the bottom cell and the sub-bottom cell have a lattice mismatch, and the bottom cell and the bottom cell further comprise A graded buffer layer that is homogenous to the material of the bottom cell.

Preferably, the graded buffer layer is homogenous to the bottom cell, and the material is GaAs _1-x N _x , and the value of x is 0 to 0.0376. In GaAs _1-x N _x , x materials, when the composition of N is gradually increased to 3.76%, the band gap of the material is reduced from 1.42 eV of GaAs to 1 eV (as shown in Figure 1). Using GaAsN as the gradation buffer layer and the homogenous buffer layer technology of the subcell, a 1eV subcell with lower dislocation density and better crystal quality can be obtained. Applying this technology to the entire structure of a flip-chip multi-junction cell, a highly efficient solar cell with current matching and low dislocation density was prepared.

In some embodiments, the multi-junction solar cell is a triple junction solar cell, wherein the bottom cell has a band gap of 1.15 to 0.95 eV. The band gap of the secondary battery is 1.45~1.36eV, and the band gap of the top battery is 1.95~1.85eV.

In some embodiments, the multi-junction solar cell is a four-junction solar cell, wherein the bottom cell has a band gap of 1.15 to 0.95 eV. The band gap of the secondary battery is 1.45~1.36eV, the band gap of the middle battery is 1.65~1.55eV, and the band gap of the top battery is 1.95~1.85eV.

 In some embodiments, the multi-junction solar cell is a four-junction solar cell, wherein the band gap of the bottom cell is 1.15~0.95eV, the band gap of the bottom battery is 1.45~1.36eV, the band gap of the middle battery is 1.95~1.85eV, and the band gap of the top battery is 2.24~2.05eV. .

 In some embodiments, the multi-junction solar cell is a five-junction solar cell, wherein the bottom cell has a band gap of 1.15 to 0.95 eV. The band gap of the secondary battery is 1.45~1.36eV, the band gap of the middle battery is 1.65~1.55eV, the band gap of the secondary battery is 1.95~1.85eV, and the band gap of the top battery is 2.24~2.05eV.

According to a second aspect of the present invention, a method of fabricating a multi-junction solar cell, comprising the steps of: 1 Flip-grown the semiconductor material layer of each of the junction cells, which includes a top cell, a sub-bottom, a graded buffer layer, and a bottom cell to the bottom, wherein the bottom cell and the bottom cell have a lattice mismatch, and the gradient buffer layer The material is the same as the material of the bottom battery; 2) providing a support substrate on which the semiconductor material layer is reversely disposed.

In the present invention, the band gap of the GaAs _1-x N _x material is rapidly decreased as the N component is gradually increased, and the band gap of the GaAs is reduced from 1.42 eV to 1 eV by adding a small amount of N element. At the same time, the GaAs _1-x N _x material is used as the homogenous graded buffer layer, and the small component is gradually graded to gradually release the stress, thereby effectively reducing the dislocation density. Through the battery structure, the band gap of each sub-battery is reasonably configured, the spectral absorption range of the solar cell is broadened, and a current-matched high-efficiency multi-junction solar cell is formed.

DRAWINGS

 Figure 1 shows GaAs _1-x N _x  Material N component and band gap diagram.

2 to 3 are views showing the structure of a flip-chip multi-junction solar cell according to a preferred embodiment of the present invention.

In the picture:

 100 growth substrate

 101 support substrate

 200 etch stop layer

 300 first sub-battery

 301 first sub-cell window layer

 302 first sub-cell emission area

 303 first sub-battery base

 304 first sub-battery back field

 400 tunnel junction between the first and second sub-cells

 500 second sub-battery

 501 second sub-cell window layer

 502 second sub-cell emission area

 503 second sub-battery base

 504 second sub-battery back field layer

 410 second and third sub-cell tunneling junction

 600 third sub battery

 601 third sub-cell window layer

 602 third sub-cell emission area

 603 third sub-battery base

 604 third sub-battery back field layer

 420 third and fourth sub-cell tunneling junction

 700 fourth sub battery

 701 fourth sub-cell window layer

 702 fourth sub-cell emission area

 703 fourth sub-battery base

 704 fourth sub-battery back field layer

 430 tunnel junction between the fourth and fifth sub-batteries

 800 homogeneous gradient buffer layer

 900 fifth sub battery

 901 fifth sub-battery window layer

 902 fifth sub-cell emission area

 903 fifth sub-battery base

 904 fifth sub-battery back field layer

 102 heavily doped cap layer.

detailed description

The details of the invention will now be described, including exemplary embodiments and embodiments of the invention. See the illustration and the following description. The invention is further described below in conjunction with the examples, but should not be construed as limiting the scope of the invention.

The following embodiments disclose a flip-chip solar cell and a method of fabricating the same, which introduce a homogenous graded buffer layer between a bottom cell and a sub-bottom cell, and a sub-cell having a lower dislocation density and better crystal quality can be obtained. This structure can be applied to three-junction, four-junction, and five-junction solar cells, and the band gap is allocated according to actual needs. table 1 The band gap distribution of the three to five junction cells is exemplified.

Table 1, flip-chip multi-junction solar cell structure and its band gap distribution.

Subcell	Eg1	Eg2	Eg3	Eg4	Eg5
Three knot	1.95~1.85eV	1.45~1.36eV	1.15~0.95eV
Four knot	1.95~1.85eV	1.65~1.55eV	1.45~1.36eV	1.15~0.95eV
Four knot	2.24~2.05eV	1.95~1.85eV	1.45~1.36eV	1.15~0.95eV
Five knots	2.24~2.05eV	1.95~1.85eV	1.65~1.55eV	1.45~1.36eV	1.15~0.95eV

Embodiment 1

 This embodiment discloses a flip-chip five-junction solar cell, and the structure thereof will be specifically described below in conjunction with the growth method.

First, in the MOCVD system, a p-type GaAs substrate 100 is selected, which has a doping concentration of 2 × 10 ¹⁷ cm ^-3 - 5 × 10 ¹⁷ cm ^-3 ; and a GaInP etch-off layer 200 is epitaxially grown on the surface of the substrate. It has a thickness of 150 nm and a doping of about 1 × 10 ¹⁸ cm ^-3 .

Next, the AlGaInP first sub-battery 300 is flip-chip grown over the etch-off layer 200 with a band gap of 2.2 eV, specifically including: an n-type AlGaInP window layer 301 having a thickness of 25 nm and a doping concentration of 1 × 10 about ¹⁸ cm ^-3; 302 emitter thickness of 150 nm, in a doping concentration of 2 × 10 ¹⁸ cm ^-3; base region 303 is preferably a thickness of 900 nm, in cm ^-3 doping concentration 5 × 10 ^17; The p-type AlGaInP back field layer 304 has a thickness of 50 nm and a doping concentration of about 1 × 10 ¹⁸ cm ^-3 .

Next, a heavily doped p++/n++-AlGaAs tunneling junction 400 is grown over the first subcell with a thickness of 50 nm and a doping concentration of up to 2 × 10 ¹⁹ cm ^-3 .

Next, a GaInP second sub-cell 500 is flip-chip grown over the tunnel junction 400 with a band gap of 1.89 eV, specifically including: an n-type AlGaInP window layer 501 having a thickness of 25 nm and a doping concentration of 1 × 10 ¹⁸ about cm ^-3; emitter region 502 thickness of 150 nm, in a doping concentration of 2 × 10 ¹⁸ cm ^-3; base region 503 is preferably a thickness of 900 nm, in cm ^-3 doping concentration 5 × 10 ^17; p The AlGaInP back field layer 504 has a thickness of 50 nm and a doping concentration of about 1 × 10 ¹⁸ cm ^-3 .

Next, a heavily doped p++/n++-AlGaAs tunneling junction 410 is grown over the second subcell with a thickness of 50 nm and a doping concentration of up to 2 × 10 ¹⁹ cm ^-3 .

Next, an AlGaAs third sub-cell 600 is flip-chip grown over the tunneling junction 410 with a band gap of 1.6 eV, specifically including: an n-type GaInP window layer 601 having a thickness of 25 nm and a doping concentration of 1 × 10 ¹⁸ about cm ^-3; emitter region 602 thickness of 200 nm, in a doping concentration of 2 × 10 ¹⁸ cm ^-3; base region 603 is preferably a thickness of 1200 nm, in cm ^-3 doping concentration 5 × 10 ^17; p The GaInP back field layer 604 has a thickness of 50 nm and a doping concentration of about 1 × 10 ¹⁸ cm ^-3 .

 Next, a heavily doped p++/n++-AlGaAs tunneling junction 420 is grown over the third subcell. , its thickness is 50 nm, and the doping concentration is up to 2 × 10¹⁹Cm^-3 .

Next, a GaAs fourth sub-battery 700 is flip-chip grown over the tunnel junction 420 with a band gap of 1.42 eV, specifically including: an n-type GaInP window layer 701 having a thickness of 25 nm and a doping concentration of 1 × 1018 cm- 3 or so; the emitter region 702 has a thickness of 250 nm and a doping concentration of 2 × 10 ¹⁸ cm ^-3 ; the base region 703 has a thickness of preferably 1500 nm and a doping concentration of 5 × 10 ¹⁷ cm ^-3 ; p-type GaInP The back field layer 704 has a thickness of 50 nm and a doping concentration of about 1 × 10 ¹⁸ cm ^-3 .

Next, a heavily doped p++/n++-GaAs tunneling junction 430 is grown over the fourth subcell 700 with a thickness of 50 nm and a doping concentration of up to 2 x 10 ¹⁹ cm ^-3 .

Next, a GaAs _1-x N _x graded buffer layer 800 is grown over the tunnel junction 430, and a total of 8 layers are grown, each layer having a thickness of 250 nm, and the N component x varies from 0 to 0.0376, and the doping concentration of each layer is Both are controlled at 1 × 10 ¹⁸ cm ^-3 , and the band gap of GaAs is reduced from 1.42 eV to about 1.0 eV.

Next, a GaAs _1-x N _x fifth sub-battery 900 is flip-chip grown over the GaAs _1-x N _x graded buffer layer 800 with a band gap of 1 eV, specifically including: an n-type GaInP window layer 901 having a thickness of 25 nm with a doping concentration of about 1 × 10 ¹⁸ cm ^-3 ; GaAs _1-x N _x emitter region 902 with a thickness of 250 nm and a doping concentration of 2 × 10 ¹⁸ cm ^-3 ; GaAs _1-x N _x The base region 903 has a thickness of preferably 2000 nm, an N composition of 0.0375, a doping concentration of 5 × 10 ¹⁷ cm ^-3 , and a p-type GaInP back field layer 904 having a thickness of 50 nm and a doping concentration of 1 × 10 ¹⁸ cm ^-3 or so.

Next, a heavily doped n++-GaAs _1-x N _x capping layer 102 is covered over the fifth subcell 900 with a thickness of 500 nm and a doping concentration of 1 × 10 ¹⁹ cm ^-3 to complete epitaxial growth of the semiconductor material layer. The structure profile is shown in Figure 2.

Finally, the substrate material layer is reversely disposed on a support substrate by using a substrate bonding technique, and the GaAs substrate is removed. The surface of the sample is subjected to anti-reflection vapor deposition, metal electrode preparation and other post-processes to complete the required solar cells.

Fig. 3 is a view showing a simple structure of a solar cell of a finally formed flip-chip structure. The fifth sub-battery 900 is a bottom battery, and the 700 is a sub-bottom battery. The content of GaAs _1-x N _x , N in the GaAs _1-x N _x graded buffer layer 800 is increased by a small amount of zero, and the band gap of the GaAs _1-x N _x material band gap decreases rapidly as the N component is gradually increased. The characteristic is to reduce its band gap from 1.42 eV to 1.0 eV. On the one hand, the gradient buffer layer 800 is a small-layer multi-layer gradation, which gradually releases the stress and effectively reduces the dislocation density. On the other hand, due to the homogeneity with the material of the bottom battery, the dislocation density can be obtained lower and the crystal quality is better. Sub-battery.

Embodiment 2

 The embodiment discloses a flip-chip four-junction solar cell, and the AlGaInP first sub-battery 300 can be removed on the basis of the implementation, The GaInP second sub-battery 500 is the first sub-cell of the present embodiment, forming a 1.89 eV/1.65 eV/1.4 eV/1 eV flip-chip four-junction solar cell.

Embodiment 3

 This embodiment discloses a flip-chip four-junction solar cell, and the GaInP second sub-cell 500 can be removed on the basis of the implementation. 2.2 eV /1.65 eV/1.4 eV/ 1 eV flip-chip four-junction solar cell.

Embodiment 4

 The embodiment discloses a flip-chip three-junction solar cell, and the AlGaInP first sub-battery 300 can be removed on the basis of the implementation. The AlGaAs third subcell 600 forms a 1.89 eV/1.4 eV/1 eV flip-chip triple junction solar cell.

Claims (10)

1. The multi-junction solar cell comprises at least a bottom cell, a sub-bottom cell and a top cell, and a lattice mismatch between the bottom cell and the sub-bottom cell, characterized in that a gradient buffer layer is further included between the bottom cell and the sub-bottom cell, It is the same material as the bottom battery.
2. The multi-junction solar cell according to claim 1, wherein the graded buffer layer is homogenous to the bottom cell, and the material is GaAs _1-x N _x , and the value of x is 0 to 0.0376.
3. The multi-junction solar cell according to claim 2, wherein the multi-junction solar cell is a three-junction solar cell, wherein a band gap of the bottom cell is 1.15~0.95eV, the band gap of the bottom battery is 1.45~1.36eV, and the band gap of the top battery is 1.95~1.85eV.
4. The multi-junction solar cell according to claim 2, wherein the multi-junction solar cell is a four-junction solar cell, wherein a band gap of the bottom cell is 1.15~0.95eV, the band gap of the bottom battery is 1.45~1.36eV, the band gap of the middle battery is 1.65~1.55eV, and the band gap of the top battery is 1.95~1.85eV. .
5. The multi-junction solar cell according to claim 2, wherein the multi-junction solar cell is a four-junction solar cell, wherein a band gap of the bottom cell is 1.15~0.95eV, the band gap of the bottom battery is 1.45~1.36eV, the band gap of the middle battery is 1.95~1.85eV, and the band gap of the top battery is 2.24~2.05eV. .
6. The multi-junction solar cell according to claim 2, wherein the multi-junction solar cell is a five-junction solar cell, wherein a band gap of the bottom cell is 1.15~0.95eV, the band gap of the secondary battery is 1.45~1.36eV, the band gap of the middle battery is 1.65~1.55eV, and the band gap of the secondary battery is 1.95~1.85eV. The top cell has a band gap of 2.24~2.05eV.
7. The multi-junction solar cell according to claim 2, wherein the graded buffer layer is changed by the N component to have a band gap of 1.42 eV. Gradient to the bandgap of the battery.
8. According to claim 2 The multi-junction solar cell is characterized in that the gradation buffer layer is a multi-layer gradation, and the stress is gradually released, thereby effectively reducing the dislocation density.
9.  A method of manufacturing a multi-junction solar cell, comprising the steps of:

   1 Flip-grown the semiconductor material layer of each of the junction cells, which includes a top cell, a sub-bottom, a graded buffer layer, and a bottom cell to the bottom, wherein the bottom cell and the bottom cell have a lattice mismatch, and the gradient buffer layer The material is the same as the material of the bottom battery;

   2) providing a support substrate on which the semiconductor material layer is reversely disposed.
10. The method of fabricating a multi-junction solar energy according to claim 9, wherein the graded buffer layer is homogenous to the bottom cell, and the material is GaAs _1-x N _x , and the value of x is 0 to 0.0376.

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