CN104091849B - Multi-junction solar cell and manufacturing method thereof - Google Patents

Abstract

The present invention provides a multi-junction solar cell, comprising at least a bottom cell and a top sub-cell located on the bottom cell, the top sub-cell is only formed on a part of the surface of the bottom cell to reduce the number of top sub-cells When the light is incident on the multi-junction solar cell, part of the light is directly absorbed by the remaining sub-cells under the top sub-cell, reducing the current of the top sub-cell.

Description

Multi-junction solar cells and methods of making the same

technical field

The invention belongs to the field of compound semiconductor solar cells, and in particular relates to a multi-junction solar cell structure and a preparation method thereof.

Background technique

A solar cell is a semiconductor device that uses the photovoltaic effect to convert solar energy into electrical energy. It is composed of a p-type and n-type semiconductor. When sunlight irradiates the device, the sunlight with energy greater than the energy gap of the semiconductor will be absorbed, causing the semiconductor device to generate electron-hole pairs, which will form a current when it is turned on.

Figure 1 is a spectrum diagram of solar radiation. The main wavelength distribution ranges from ultraviolet light of 0.3 microns to infrared light of several microns. Converted into photon energy, it is approximately from 0.4 eV to 4 eV. In order to be able to absorb more sunlight energy, multi-junction solar cells have been proposed, which stack semiconductor elements with different energy gaps together, so that a variety of semiconductor material layers with different energy gaps can be used to absorb sunlight with different energies to Improve photoelectric conversion efficiency. Although the bandwidth of energy absorption can be increased in this way, due to the stacking of semiconductor material layers with different energy gaps, the current density difference between the top solar cell and the bottom solar cell is too large, and this current mismatch will cause the entire The photoelectric conversion efficiency of the device is reduced, so how to reduce the current mismatch is an important issue.

Contents of the invention

The purpose of the present invention is to provide a multi-junction solar cell structure and its preparation method which can reduce the current mismatch and improve the photoelectric conversion efficiency. The light is left for the lower sub-cells to absorb, increasing the current of the lower sub-cells, and finally achieving the current matching of the multi-junction sub-cells, thereby realizing the optimization of the efficiency of the multi-junction cells.

According to a first aspect of the present invention, a multi-junction solar cell includes at least a bottom cell and a top sub-cell located on the bottom cell, the top sub-cell is only formed on a part of the surface of the bottom sub-cell In order to reduce the light-receiving area of the top sub-cell, when light is incident on the multi-junction solar cell, part of the light is directly absorbed by the remaining sub-cells below the top sub-cell, reducing the current of the top sub-cell.

In some embodiments, the surface area of the top sub-cell accounts for 70%-99% of that of the bottom sub-cell.

In some embodiments, the top sub-cell has a groove pattern exposing the surface of the sub-cell below it, and when the light is incident on the groove pattern, it is directly absorbed by the sub-cell below the groove. Preferably, the area of the groove pattern accounts for 1%-30% of the total area. Preferably, the depth of the groove pattern is not greater than the thickness of the top sub-cell.

In some embodiments, the multi-junction solar cell includes three junction sub-cells, which are Ge first sub-cell, GaAs second sub-cell and GaInP third sub-cell respectively from bottom to top, wherein the third sub-cell It is only formed on a part of the surface of the second sub-battery, the part of the surface of the second sub-battery is exposed, and when the light is incident on the exposed part of the surface, it is directly absorbed by the second sub-battery. Preferably, the area of the top sub-cell accounts for 95%-99% of that of the neutron cell.

In some embodiments, the multi-junction solar cell includes four-junction sub-cells, which are respectively Ge first sub-cell, InGaAs second sub-cell, InGaAsP or AlInGaAs third sub-cell, AlInGaP fourth sub-cell from bottom to top , wherein the fourth sub-cell is only formed on a part of the surface of the third sub-cell, and the exposed part of the surface of the third sub-cell is directly absorbed by the third sub-cell when light is incident on the exposed part of the surface.

According to a second aspect of the present invention, a method for preparing a multi-junction solar cell comprises sequentially depositing an epitaxial stack comprising a bottom subcell and a top subcell on top of the bottom cell, characterized in that only A top sub-cell is formed on part of the surface of the bottom sub-cell to reduce the light-receiving area of the top sub-cell. When light is incident on the multi-junction solar cell, part of the light is directly absorbed by the remaining sub-cells below the top sub-cell, reducing the light-receiving area of the top sub-cell. The current of the top sub-battery.

In some embodiments, the method for preparing a multi-junction solar cell includes the step of: providing a substrate on which each junction cell is sequentially formed, which at least includes a bottom cell and a top cell located on the bottom cell ; A groove pattern is formed on the top sub-cell, exposing the surface of the sub-cell below it, and when light is incident on the groove pattern, it is directly absorbed by the sub-cell below the groove. Preferably, the area of the formed groove pattern accounts for 1%-30% of the total area.

Description of drawings

Figure 1 is a solar radiation spectrum diagram.

FIG. 2 is a side cross-sectional view of a triple-junction solar cell according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram of light absorption of the triple-junction solar cell shown in FIG. 2 .

FIG. 4 is a groove pattern of the triple-junction solar cell shown in FIG. 2 .

Fig. 5 is a graph of the spectral response of the GaInP sub-cell.

Fig. 6 is a graph of the spectral response of the GaAs sub-cell.

7 is a side cross-sectional view of a four-junction solar cell according to a second embodiment of the present invention.

8 to 11 show cross-sectional views of the structure of the four-junction solar cell in the second embodiment of the present invention during the manufacturing process.

detailed description

The multi-junction solar cell of the present invention reduces the light-receiving area of the top sub-cell, reduces the current of the top sub-cell, and leaves the remaining light for the sub-cell below to absorb, increases the current of the bottom sub-cell, and finally reaches the multi-junction cell. Current matching, which is applicable to any multi-junction cells, such as GaInP / GaAs double-junction cells, GaInP / GaAs / Ge lattice-matched triple-junction cells, GaInP/ InGaAs / InGaAs triple-junction cells, AlGaInP / InGaAsP / InGaAs /Ge quadruple-junction cells Battery, GaInP / InGaAs / InGaAs / InGaAs four-junction battery, GaInP / InGaAs /InGaNAsSb / Ge four-junction battery, AlGaInP / AlGaAs / GaAs / InGaNAs / Ge five-junction battery, etc. In general, the current limiting value of the sub-cell under the multi-junction solar cell is 5%~20%, so the light-receiving area of the top cell can be limited to 70%~97% of the total area. The implementation of the present invention will be described in detail below in conjunction with specific examples.

FIG. 2 shows a side cross-sectional view of a GaInP/GaAs/Ge triple-junction solar cell 100 according to the first embodiment of the present invention.

Referring to FIG. 2 , the triple-junction solar cell 100 includes a p-type Ge substrate 110 , a first Ge sub-cell 120 , a second GaAs sub-cell 130 , and a third GaInP sub-cell 140 . Generally, the first and second sub-cells, and the second and third sub-cells are respectively connected through tunnel junctions (not shown in the figure). Wherein the third GaInP sub-cell 140 has a groove pattern 150, which exposes part of the surface 130a of the second GaAs sub-cell 130 below it. Please refer to accompanying drawing 3, when the solar cell is placed in the sunlight environment, the light L _A is incident on the surface of the third sub-cell 140, absorbed by the third sub-cell, and when the light L _B is incident on the groove pattern, it is directly absorbed by the groove pattern. The GaAs second subcell 130 below the trench absorbs.

Please refer to FIG. 4 , the groove pattern 150 may consist of a series of parallel grooves, or a series of intersecting grooves, or a series of regularly arranged circular or square grooves. Preferably, the trench pattern 150 can also be filled with a light-transmitting dielectric material, such as silicon nitride, silicon oxide, etc., to protect the second sub-cell while ensuring the integrity of the physical structure of the third sub-cell.

Please refer to accompanying drawings 5 and 6, wherein Fig. 5 shows the spectral response curve of the GaInP sub-cell, and Fig. 6 shows the spectral response curve of the GaAs sub-cell. The spectral response is higher than that of the GaAs second sub-cell, and the current limit of the second sub-cell in a general GaInP/GaAs/Ge triple-junction solar cell is 5%, so the area of the groove pattern is less than 5% of the total area of the cell, generally the area The proportion is 95%~99%, preferably 97%.

FIG. 7 shows a side cross-sectional view of an AlGaInP/InGaAsP/InGaAs/Ge four-junction solar cell 200 according to the second embodiment of the present invention.

Please refer to accompanying drawing 7, four-junction solar cell 200, comprises p-type Ge substrate 210, Ge first sub-cell 220, p-type InGaAs stress gradient layer 230, InGaAs second sub-cell 240, InGaAsP third sub-cell 250 and AlInGaP The fourth sub-cell 260, wherein each junction sub-cell is connected through an n++-GaAs/p++-GaAs tunnel junction (not shown in the figure). Wherein the AlGaInP fourth sub-cell 260 has a groove pattern 270, which exposes part of the surface 250a of the InGaAsP third sub-cell 250 below it. The present embodiment will be described in detail below in conjunction with the preparation method.

First, epitaxial stacks of each junction cell are deposited in the MOCVD chamber, which includes growing the first sub-cell 220 , the second sub-cell 240 , the third sub-cell 250 and the fourth sub-cell 260 . details as follows:

1) An n-type Ga _0.5 In _0.5 P window layer is epitaxially grown on the p-type Ge substrate 210 with a doping concentration of 5E18/cm ³ to form the first Ge sub-cell 220 ;

2) Epitaxially grow the p-type InGaAs stress gradient layer 230 on the Ge first sub-cell 220, keep the flow rate of TMGa constant, and make the In composition gradually change from 0 to 0.17, the change method is a stepwise gradient, and the In composition is about 0.02. One step, 9 layers in total, each step grows 250nm;

3) On the p-type InGaAs stress gradient layer 230, epitaxially grow the second InGaAs sub-cell 240 with a bandgap of 1.2eV, first grow a 20nm p-type AlInGaAs back field layer, and then grow a 3µm thick layer with a doping concentration of 1×10 ¹⁷ cm ^-3 p-type In _0.17 Ga _0.83 As base region, then grow 200nm thick n-type In _0.17 Ga _0.83 As emission layer with a doping concentration of 2×10 ¹⁸ cm ^-3 , and finally grow 50nm thick 1×10 ¹⁸ cm ^-3 n-type InGaP window layer;

4) Epitaxially grow the third InGaAsP sub-cell 250 with a band gap of 1.55eV on the second InGaAs sub-cell 240, first grow a 20nm p-type AlInGaAs back field layer, and then grow a 3µm thick doping concentration of 1×10 ¹⁷ cm ^-3 p-type In _0.27 Ga _0.73 As _0.49 P _0.51 base region, and then grow 300nm thick, doping concentration of 2×10 ¹⁸ cm ^-3 n-type In _0.27 Ga _0.73 As _0.49 P _0.51 emitter layer, finally grow 50nm thick 1×10 ¹⁸ cm ^-3 n-type AlInP window layer;

5) Epitaxially grow the fourth AlInGaP sub-cell 260 with a bandgap of 1.85eV on the third InGaAsP sub-cell 250, first grow a 100nm p-type InAlGaAs back field layer, and then grow a 600nm thick layer with a doping concentration of 6×10 ¹⁶ cm ^-3 p-type AlInGaP base region, then grow an n-type AlInGaP emission layer with a thickness of 150nm and a doping concentration of 5×10 ¹⁸ cm ^-3 , and finally grow an n-type AlInP window layer with a thickness of 50nm and a thickness of 5×10 ¹⁸ cm ^-3 , Thus, an AlGaInP/InGaAsP/InGaAs/Ge lattice-mismatched four-junction solar cell is completed on a Ge substrate, and its side cross-sectional view is shown in FIG. 8 .

Next, a groove pattern 270 is formed on the AlInGaP fourth sub-cell 260, exposing part of the surface 250a of the InGaAsP third sub-cell 250 below it. The details are as follows: please refer to accompanying drawing 9, use photolithography process, make photolithography pattern 280 on the surface of AlInGaP fourth sub-cell 260; then use chemical etching to remove AlGaInP fourth sub-cell 260 without photoresist protection, and form groove 270 , as shown in FIG. 10 ; remove the photoresist 280 on the four-junction cell, and finally obtain a trench AlGaInP/InGaAsP/InGaAs/Ge lattice-mismatched four-junction cell, as shown in FIG. 11 .

In this embodiment, two samples were produced respectively, and the external quantum efficiencies of the two samples were tested. Both samples were AlGaInP/InGaAsP/InGaAs/Ge four-junction solar cells, and the fourth sub-cell 260 of sample 1 completely covered The third sub-cell 250 has no groove pattern, and the fourth sub-cell 260 of sample 2 only covers part of the surface of the third sub-cell 250, that is, it has a groove pattern (about 20% of the area), exposing part of the third sub-cell 250 part surface. The test results are as follows:

It can be seen from the above table that the current limitation of the InGaAsP third-junction sub-cell of sample 1 is serious, which is mainly caused by the lower band gap of the AlGaInP fourth sub-cell, while sample 2 (that is, the four-junction solar cell of this embodiment) is in The current matching between the sub-cells was realized while keeping other performance parameters of the battery unchanged, and the conversion efficiency reached 44.1% under the test conditions of 1000 times concentrated light.

But the above-mentioned ones are only preferred embodiments of the present invention, and should not limit the scope of implementation of the present invention with this, that is, all simple equivalent changes and modifications made according to the patent scope of the present invention and the content of the patent specification, All still belong to the scope covered by the patent of the present invention.

Claims (10)

1. multijunction solar cell, at least includes holder battery on described bottom battery for the bottom battery and, institute State holder battery and there is groove figure, be only formed on the part surface of described bottom battery to reduce the sensitive surface of holder battery Long-pending, expose the surface of sub- battery below, filling light transmission dielectric material in described groove figure, when light is incident to this many knot During solaode, some light is directly absorbed by its minor battery below holder battery, reduces the electricity of described holder battery Stream.

2. multijunction solar cell according to claim 1 it is characterised in that: the surface area of described holder battery accounts for bottom The 70% ~ 99% of battery.

3. multijunction solar cell according to claim 1 it is characterised in that: the area of described groove figure accounts for the gross area 1% ~ 30%.

4. multijunction solar cell according to claim 1 it is characterised in that: the depth of described groove figure is not more than institute State the thickness of holder battery.

5. multijunction solar cell according to claim 1 it is characterised in that: include three knot batteries, it is from top to bottom It is respectively the sub- battery of ge first, the sub- battery of gaas second, the sub- battery of gainp the 3rd, wherein said 3rd sub- battery is only formed at On the part surface of the second sub- battery, described second sub- battery exposed portion surface, when light is incident to this exposed portion surface When directly absorbed by the second sub- battery.

6. multijunction solar cell according to claim 5 it is characterised in that: the area of described 3rd sub- battery accounts for second The 95% ~ 99% of sub- battery.

7. multijunction solar cell according to claim 1 it is characterised in that: include four knot batteries, it is from top to bottom It is respectively the sub- battery of ge first, the sub- battery of ingaas second, the sub- battery of ingaasp or alingaas the 3rd, alingap the 4th Battery, wherein said 4th sub- battery is only formed on the part surface of the 3rd sub- battery, described 3rd sub- battery exposed portion Surface, is directly absorbed by the 3rd sub- battery when light is incident to this exposed portion surface.

8. the preparation method of multijunction solar cell, including being sequentially depositing extension lamination, it includes a bottom battery and and is located at Holder battery on described bottom battery it is characterised in that: form holder electricity only on the part surface of described bottom battery Pond, to reduce the light-receiving area of holder battery, the described holder battery of formation has groove figure, exposes sub- battery below Surface, and fill light transmission dielectric material, when light is incident to this multijunction solar cell, part in described groove figure Light is directly absorbed by its minor battery below holder battery, reduces the electric current of described holder battery.

9. the preparation method of multijunction solar cell according to claim 8, including step:

One substrate is provided, sequentially forms each knot battery thereon, it at least includes bottom battery and is located at described bottom battery On holder battery；

Form groove figure in described holder battery, expose the surface of sub- battery below, when light is incident to this groove figure When, directly absorbed by the sub- battery of beneath trenches.

10. according to claim 9 multijunction solar cell preparation method it is characterised in that: the face of described groove figure Amass and account for the 1% ~ 30% of the gross area.