JPH03235376A - Manufacture of tandem-type solar battery - Google Patents

Abstract

PURPOSE:To manufacture the title solar batteries of high efficiency by a method wherein the silicon solar batteries are heteroepitaxially deposited on III-V group compound semiconductor solar batteries. CONSTITUTION:An Al As layer 11, an n<+>GaAs layer 10, an n<+>A GaAs layer 9, an n-AlGaAs layer 8, p-A GaAs layer 7, an n<+>AlGaAs layer 6, an n-AlGaAs layer 5, an n-GaAs layer 4, a p<+>-GaAs layer 3 are deposited on a semiinsulating GaAs substrate 12 and after forming polysilicon to form a reticulated electrode on the formed epitaxial substrate 12, an n-silicon layer 2 and a p-silicon layer 1 are formed. Next, the Al As layer 11 is selectively etched away releasing the epitaxial layers from the substrate 12 to form electrodes 14-16 and a rear surface electrode 13. Through these procedures, silicon is deposited on the III-V group compound semiconductor substrate 12 so that the crystalline defects in crystals of compound semiconductor solar batteries may be diminished thereby enabling the solar batteries of high efficiency to be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a tandem solar cell that is a composite of a silicon solar cell and a compound semiconductor solar cell.

[Conventional technology] Solar cells rely on sunlight as their energy source, so they were developed as a clean energy source that does not cause the global warming problems caused by carbon dioxide caused by conventional thermal power generation or the safety problems associated with nuclear power generation. is in progress. Depending on the material, solar cells can be made of compound semiconductors, single crystal or polycrystalline silicon, or amorphous silicon. Compound semiconductors exhibit superior properties in terms of photoelectric conversion efficiency, but amorphous silicon systems are superior in terms of cost, and each material has its advantages and disadvantages. In addition, a conventional set of p
Solar cells with an n-junction can convert only a portion of the solar energy into electrical energy, so attempts have been made to improve conversion efficiency using tandem solar cells, which are stacked with multiple solar cells made of materials with different energy gaps. There is.

[Problems to be Solved by the Invention] Furthermore, since compound semiconductor solar cells are expensive and can only be manufactured with a small area, the use of silicon substrates that are inexpensive, lightweight, and have a large area have been considered. There is. However, because there are differences in lattice constant and crystal polarity between silicon and compound semiconductors, "many crystal defects occur in compound semiconductor crystals and Currently, highly efficient batteries have not been realized.For example, m-v group compound semiconductors grown heteroepitaxially on silicon substrates, such as GaAs, have different lattice constants and silicon is nonpolar. Since GaAs is polar, it contains many crystal defects (dislocations).For this reason, the conversion efficiency of GaAs solar cells is significantly inferior to those grown homoepitaxially on a GaAs substrate.

In order to reduce dislocations in such heteroepitaxial growth, grating buffer layers, superlattice buffer layers,
Although methods such as a temperature growth method and a thermal cycle annealing method have been used, so far no material with a dislocation density of 1×10 6 cm −2 or less has been obtained.

An object of the present invention is to provide a method for manufacturing a highly efficient solar cell by reducing crystal defects in the crystal of a compound semiconductor solar cell.

[Means for Solving the Problems] A method for manufacturing a tandem solar cell of the present invention includes forming at least one m-v group compound semiconductor solar cell above an m-v group compound semiconductor substrate, The method includes steps of forming a silicon solar cell on a compound semiconductor solar cell, and removing the ①-V group compound semiconductor substrate after forming the silicon solar cell.

According to a preferred embodiment of the invention, an etch removal layer is formed on the m-v compound semiconductor substrate, and at least one m-v compound semiconductor solar cell is formed on the etch removal layer; The method includes steps of forming a silicon solar cell on an m-v group compound semiconductor solar cell, and peeling off the m-v group compound semiconductor substrate by etching and removing an etching removal layer after forming the silicon solar cell. .

In this preferred embodiment, the etching removal layer is, for example, an aluminum arsenic layer, which can be etched and removed by immersing it in hydrofluoric acid.

In this invention, materials that can be used as the m-v group compound semiconductor solar cell include, for example, GaAs,
Binary compound semiconductors such as GaP and InP, and A
lGaAs, InGaP.

AII nAs, AII nP, AlGaP and Ga
Examples include ternary compound semiconductors such as AsP.

Further, in the present invention, the m-v group compound semiconductor solar cell formed above the m-v group compound semiconductor substrate may be one in which two or more sets of solar cells are stacked in a tandem structure.

In the present invention, the method for removing the ■-V group compound semiconductor substrate after forming the silicon solar cell includes, for example, removing the entire substrate mechanically or by etching, or selectively etching the entrance window portion. You can remove it with

Further, as in the preferred embodiment described above, an etching removal layer may be formed between the substrate and the solar cell, and the substrate may be peeled off by etching and removing the etching removal layer. According to such a preferred embodiment, the peeled substrate can be recovered and re-polished for use, which is economical.

[Operations and Effects of the Invention] As mentioned above, when stacking ■-V group compound semiconductor solar cells on a silicon substrate, the lattice constants are different and silicon is nonpolar while compound semiconductors are polar. Many crystal defects and dislocations occur due to antiphase domains.

According to the present invention, since silicon is grown on the m-v group compound semiconductor substrate, problems such as the above-mentioned antiphase domain do not occur. Furthermore, even if dislocations exist in silicon, it is thought that they do not have a significant effect on the conversion efficiency. This is clear from the fact that highly efficient solar cells are made of polycrystalline silicon or amorphous silicon. Therefore, by heteroepitaxially growing a silicon solar cell on a ■-■ group compound semiconductor solar cell as in the present invention, it is possible to obtain a solar cell with higher efficiency than before.

[Example 1] FIG. 1 is a sectional view for explaining an example of the present invention. Figure 1 shows the state after the substrate has been removed and electrodes have been formed after solar cells have been grown in accordance with the present invention, and shows the state when used upside down after fabrication. . Referring to FIG. 1, semi-insulating GaAs
On the substrate 12, a non-doped AlAs layer 11 with a thickness of 100 OA
SSi-doped n''-GaAs layer 10, Si
Doped n” A109Gao, 1000 As layer 9
A, Si-doped n-Alo,s Gao2As layer 8 4
μm, Zn-doped pAl! o, s Gao2As layer 7 of 5 μm, Si-doped n”-AI!., Ga.

As layer 6 is doped with 1000 ASSi n-A I 0.3
5G ao6. The As layer 5 is 1 μm thick and Si-doped n-
The GaAs layer 4 was grown to a thickness of 1 μm, and the Zn-doped p''-GaAs layer 3 was grown to a thickness of 3 μm.
1), arsine (AsH3: diluted with 10% hydrogen), silane (S I H4), and dimedylzinc (TMZn). The growth temperature was 730°C, and the AsH3/TMGa ratio was 75.

On the epitaxial substrate obtained in this way, C
Polycrystalline silicon was formed by the VD method to form mesh electrodes at intervals of 2 mm, and then a pn junction of Si was formed by the CVD method to form an n-silicon layer 2 and a p-silicon layer 1. Next, the surface of the silicon epitaxial layer was coated with wax, and then immersed in hydrofluoric acid to form AA'AsAl.
The epitaxially grown layer was stripped from the GaAs substrate 12 by selectively etching the As layer.

Next, selective etching was performed using the RIE method, and an AuGe electrode was deposited. As shown in FIG. 1, an electrode 14, n"-A I 0.35Ga 0.6
．． A 8 Electrode 15 on layer 5, n''-GaAs layer 10
An electrode 16 is placed on top of the p-silicon layer 1, and a back electrode 1 is placed on the back side of the p-silicon layer 1.
3 was formed.

AM
When irradiated with standard sunlight of 1.5 V, an open voltage of 1.5, 1.1, and 0.7 V was generated between the three pn junctions, respectively.

In addition, when the photoelectric conversion efficiency was measured, it was 33%,
The photoelectric conversion efficiency was significantly higher than that of conventional tandem solar cells, which is approximately 20%.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention. In the figure, 1 is a p-silicon layer, 2 is an n-silicon layer, 3 is a p''-GaAs layer, 4 is an n-GaAs layer, 5 is n AI 0.35G ao, 6.A
S layer, 6 is n” A1.), g Gao, As layer, 7
is pAA'. BGao, 2As layer, 8 is n A109Gao2AS
layer, 9 is n" AIo9Gao, IAs layer, 10 is n"-GaAs layer, 11 is AlAs layer, 12 is GaAs layer.
On the substrate, 13, 14, 15, and 16 indicate electrodes.

Claims (5)

[Claims] (1) forming at least one III-V compound semiconductor solar cell above the III-V compound semiconductor substrate; forming a silicon solar cell on the III-V compound semiconductor solar cell; A method for manufacturing a tandem solar cell, comprising the steps of removing the III-V group compound semiconductor substrate after forming the cell. (2) forming an etching removal layer on the III-V group compound semiconductor substrate, and forming at least one III-V etching removal layer on the etching removal layer;
forming a group compound semiconductor solar cell; forming a silicon solar cell on the III-V compound semiconductor solar cell; and etching and removing the etching removal layer after forming the silicon solar cell; A method for manufacturing a tandem solar cell, comprising steps of peeling off a group compound semiconductor substrate. (3) The III-V compound semiconductor solar cell is made of GaAs.
The method for manufacturing a tandem solar cell according to claim 1 or 2, wherein P. (4) The III-V compound semiconductor solar cell is made of GaA
The method for manufacturing a tandem solar cell according to claim 1 or 2, wherein the tandem solar cell is s. (5) The III-V compound semiconductor solar cell comprises GaA
3. The method for manufacturing a tandem solar cell according to claim 1, wherein the solar cell is a solar cell in which S and AlGaAs are stacked in a tandem structure.