JPH0545072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a solar cell in which a single crystal film is formed on a substrate made of glass, metal, ceramics, plastics, or the like.

[Prior Art] It goes without saying that solar cells using single crystals generally have higher performance than those using polycrystals.

Conventionally, when manufacturing a solar cell using a single crystal film, a bulk single crystal wafer cut from an ingot was used as a substrate, and a single crystal film was grown on it.

However, in the above method, the single crystal wafer used as the substrate is expensive, and the substrate is only 1 mm thick.
Moreover, there were economic and resource disadvantages, such as the need for considerable thickness, and the waste of expensive materials as cutting allowances during crystal cutting.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to solve the problem without using an expensive single crystal substrate.
That is, a single crystal film of a desired compound is grown using a substrate other than a single crystal substrate, specifically, a substrate made of any material such as a glass substrate, a metal plate, a ceramic substrate, or a plastic substrate if temperature conditions permit. The object of the present invention is to provide a method for manufacturing a high-performance, low-cost, and resource-saving solar cell.

[Means for Solving the Problems] A method for manufacturing a solar cell according to the present invention includes a step of depositing a compound semiconductor layer for forming an active layer including a junction of a solar cell on a substrate that is not a single crystal substrate. , a step of depositing an elemental metal layer of a component constituting the compound semiconductor on the compound semiconductor layer, and heating the compound semiconductor layer covered with the elemental metal layer to a temperature in a range including its melting point, and then cooling it to room temperature. The method is characterized by comprising a step of forming a single crystal layer of a compound semiconductor between the single metal layer and the substrate.

That is, a desired compound semiconductor film for solar cells (usually a polycrystalline film) is deposited on a substrate made of any desired material other than a single-crystal substrate, and a compound semiconductor film with a low melting point and low vapor pressure among the deposited compound components is deposited on top of the substrate. The metal element is further deposited to cover the compound, and then the substrate temperature is raised to a temperature close to the melting point of the compound to cause recrystallization, and then the temperature is lowered to room temperature to perform recrystallization and liquid crystallization. A single crystal film is formed on the substrate by a method combining phase growth.

The single metal component layer covering the deposited layer of compound semiconductor can be configured as one side electrode of a solar cell, or by removing such a single metal component layer,
Furthermore, by epitaxially growing a compound semiconductor on the produced single crystal film, a high quality single crystal film is grown to construct various solar cells, that is, solar cells having heterojunctions, pn junctions, Schottky junctions, etc. You may.

[Function] According to the present invention, any desired substrate other than a single crystal substrate, that is, it has been considered extremely difficult to
By producing a single-crystalline semiconductor film on a substrate of any desired material such as glass, metal, ceramics, plastics, etc., and obtaining a relatively large-area single-crystalline film, the cost is much higher than that of polycrystalline film solar cells. This makes it possible to manufacture highly efficient solar cells at low cost and while contributing to resource conservation, greatly contributing to the development and spread of solar cells.

[Example] The present invention will be described in detail below with reference to the drawings.

1A and 1B show an example of a heterojunction solar cell manufactured according to the present invention, where 1 is a transparent glass substrate, 7 is an In ₂ O ₃ disposed on the substrate 1,
7 _' is an electrode attached to the NESA film 7, 3 is a compound semiconductor layer such as InP or GaAs deposited on the NESA film 7, and 5 is In, Ga, etc. that covers this compound semiconductor layer 3. A single metal coating layer is shown. 5' indicates an electrode taken out from above layer 5. The electromotive force is extracted from between electrodes 5' and 7'. The compound semiconductor layer 3
In the case of InP, the electrode 5 is made of In, and when the compound semiconductor layer 3 is made of GaAs, the electrode 5 is made of Ga. When InP is used as the compound semiconductor layer 3, the thickness of this layer 3 is about 1 to 5 μm, and the thickness of In as the electrode 5 is about 10 μm. In this case, for example, if the NESA film 7 is an n-type semiconductor, InP or
A p-type dopant (impurity) is mixed into the semiconductor layer 3 or the single metal coating layer 5 so that GaAs becomes a p-type semiconductor.

After laminating the layers as shown in FIG. The P contained in the In during heating was recrystallized together with the In.
It comes into contact with the InP single crystal plane, so-called
Liquid phase growth of InP occurs, and an InP single crystal film sandwiched between the Nesa film of the electrode 7 and the In of the electrode 5 is generated.

FIG. 3 shows an example of the relationship between the temperature change of the substrate 1 and the elapsed time in a series of steps of forming the compound semiconductor layer 3 and the single metal layer 5 by vapor deposition and single crystallization treatment described above. First, set the temperature of substrate 1 to 270℃.
All use 6nine purity indium while maintaining
Molecular beam deposition, that is, ultra-high vacuum deposition, is performed on the Nesa film 7 from separate deposition source crucibles containing In and red phosphorus P, respectively. The degree of vacuum before vapor deposition is 5.5×
10 ^-9 Torr, and the degree of vacuum during vapor deposition was approximately 1.5×10 ^-7 Torr due to the vapor pressure of phosphorus P. In addition, indium In was evaporated at 700 to 800°C, and phosphorus P was evaporated at about 300°C. After synthetically depositing the InP compound film 3 with a thickness of 3 μm in this manner, the temperature of the P crucible is lowered to stop the evaporation of phosphorus P, and only indium In is deposited from the In crucible. Continue to thickness approx.
An 18 μm In film 5 is laminated on the compound film 3. The formation of the laminated layers 3 and 5 is performed while the temperature of the substrate 1 is maintained at 270 DEG C. in the section b-c in the time chart shown in FIG. Subsequently, board 1
Once the temperature of the substrate 1 is lowered sequentially in sections c-f, the temperature of the substrate 1 is lowered to approximately
After rapidly raising the temperature to 1000℃, the temperature is lowered to room temperature through natural cooling. The melting point of the compound InP is 1060
℃, the compound InP recrystallizes in the process of rapid temperature rise to 1000℃, its crystal grains enlarge, and all crystal grains
The (111) plane parallel to the plane is the dominant orientation. During recrystallization, if the impurities in the pre-deposited InP compound are extremely low, the impurities that form grain boundaries will also be extremely low, and grain boundaries will either be almost absent or only slightly present.

However, the phosphorus P, which has a high vapor pressure and exists in the InP compound, tries to dissociate and escape, but the surface
Since it is covered by the film, it cannot escape, and some of the phosphorus P dissolves into the indium In. Then,
As mentioned above, if the substrate temperature reaches the recrystallization temperature of approximately 1000°C and is immediately lowered to room temperature by natural heat dissipation, the natural cooling process produces a single crystal or close to a single crystal (111 )
The melt of indium In in which phosphorus P is dissolved as described above comes into contact with the underlying InP compound film 3 which is in a plane-preferential orientation state, and liquid phase epitaxial growth or recrystallization is performed. It is thought that liquid phase growth occurs simultaneously. It should be noted here that if the recrystallization temperature is kept at 1000°C for a long time, the InP compound layer 3 and the In coating 5 will diffuse and fuse with each other, and there is a risk that the desired film formation will not be obtained. Therefore, keep the temperature near the melting point for as short a time as possible.
For example, keep it to about 1 to 3 minutes.

In short, in the process of single-crystal film growth in the present invention, an InP compound film that is in a single-crystal or near-single-crystal state by recrystallization and has a preferential orientation of the (111) plane parallel to the substrate surface is grown as a seed monolayer. It is thought that improvement of single crystallization is promoted by forming a crystalline film and performing liquid phase epitaxial growth of the InP compound thereon.

Further, by attaching power extraction electrodes 5' and 7' to layers 5 and 7, respectively, a heterojunction solar cell is constructed. Sunlight is irradiated from the glass substrate 1 side. Needless to say, if the Nesa film 7 has a wider forbidden band width than InP, even higher efficiency can be obtained due to its window effect.

An example of the pn junction solar cell of the present invention is shown in FIGS. 2A and 2B. Here, 1 is a transparent glass substrate, 2 is a comb-shaped or grid-shaped electrode made of an ohmic electrode arranged on the substrate 1 and in contact with the compound semiconductor layer 3;
3 is a compound semiconductor layer such as InP or GaAs, 5 is In,
Indicates a coating layer made of a simple metal such as Ga. The electromotive force is taken out between the electrode 2' attached to the electrode 2 and the electrode 5' attached to the layer 5. Compound semiconductor layer 3
When the layer 3 is InP, In is used as the layer 5, and when the layer 3 is GaAs, the layer 5 is Ga. A p- or n-type semiconductor single crystal film 4 is arranged between layers 3 and 5. Note that when the layer 3 is an n-type semiconductor layer, a p-type dopant such as Zn, Mg, Be or the like is mixed into the layer 5 on the side closer to the membrane 4. Now, when InP is used as the layer 3, for example, the thickness of the compound semiconductor layer 3 is about 1~
The thickness is about 5 μm, and on top of that, a layer mixed with the above-mentioned dopant for forming a pn junction is formed as an In layer or InP layer.
It is constructed by mixing a dopant into the layer. After that,
This stack is heated for a short time to around the melting point of InP, and then allowed to cool naturally to return to room temperature. In exactly the same way as the principle explained in FIG. It is formed. The above constitutes a pn junction solar cell.

Sunlight is irradiated from the glass substrate 1 side.

Furthermore, for example, after forming the InP or GaAs single crystal layer 3 using this method, an InP single crystal layer or
The In or Ga layer coated on the GaAs single crystal layer 3 is heated at a temperature higher than its melting point (for example, about 200
℃), or removed by rotational centrifugal force, or removed by etching, while epitaxially growing a desired single crystal on the surface of the resulting single crystal layer 3, forming a p-n junction, a heterojunction, etc. Alternatively, a single crystal film solar cell can be fabricated by forming a Schottky junction or the like.

The formation and configuration of the above-mentioned stacked layers is performed by a vapor deposition method, a sputtering method, a CVD method, etc., and the recrystallization and liquid phase growth are performed in a vacuum or using Ar, N ₂
It is carried out in an inert gas such as

Furthermore, it goes without saying that an antireflection film can be provided on the sunlight receiving side to improve solar cell efficiency.

[Effects of the Invention] As is clear from the above, according to the present invention, it is possible to produce a single crystal semiconductor film on a substrate made of any desired material such as glass, metal, ceramics, plastics, etc., which has been considered extremely difficult in the past. Moreover, by obtaining a single crystal film with a relatively large area, it becomes possible to manufacture solar cells with much higher efficiency than polycrystalline film solar cells at low cost and while contributing to resource conservation. It will greatly contribute to the development and popularization.

[Brief explanation of the drawing]

Figures 1A and B show an example of a heterojunction solar cell manufactured by the method of the present invention, respectively, a top view and a cross-sectional view, and Figures 2A and B show a pn junction solar cell manufactured by the method of the present invention. FIG. 3 is a top view and a cross-sectional view showing an example of the structure, respectively, and a time chart showing an example of substrate temperature change in an embodiment of the single crystal semiconductor film production process of the present invention. 1... Substrate, 2... Comb-shaped or grid-shaped electrode, 3
...Compound semiconductor layer and single crystal compound n(p) type semiconductor layer, 4...Compound semiconductor layer and single crystal compound n(n) type semiconductor layer, 5...Single metal coating layer, 7...
...Nesa membrane, 2', 5', 7'... electrode.

Claims (1)

[Claims] 1. A step of depositing a compound semiconductor layer for forming an active layer including a junction of a solar cell on a substrate that is not a single crystal substrate, and a step of depositing a compound semiconductor layer on the compound semiconductor layer, and a component constituting the compound semiconductor on the compound semiconductor layer. heating the compound semiconductor layer covered with the single metal layer to a temperature in a range including its melting point and then cooling it to room temperature to create a gap between the single metal layer and the substrate. A method for manufacturing a solar cell, comprising: forming a single crystal layer of the compound semiconductor. 2. A step of depositing a compound semiconductor layer for forming an active layer including a solar cell junction on a substrate that is not a single crystal substrate, and depositing an elemental metal layer of a component constituting the compound semiconductor on the compound semiconductor layer. a step of heating the compound semiconductor layer covered with the single metal layer to a temperature in a range including its melting point and then cooling it to room temperature to form a single layer of the compound semiconductor between the single metal layer and the substrate. A solar method comprising the steps of forming a crystal layer and forming a junction while epitaxially growing the single crystal on the exposed surface of the single crystal compound semiconductor layer from which the single metal layer has been removed. How to manufacture batteries.