JPH04130671A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To reduce interfacial level by providing an intrinsic non-single crystal semiconductor having a film thickness of 250Angstrom or less between both semiconductors in a photovoltaic device which is formed by sequentially stacking a single crystal semiconductor and non-single crystal semiconductor which have mutually opposed conductivity types. CONSTITUTION:It becomes possible that recoupling of light generating carrier is reduced and the number of light generating carriers which can be extracted to the outside of a photovoltaic device can be increased by providing an intrinsic non-single crystal semiconductor 2 having a film thickness of 250Angstrom or less between an N-type single crystal semiconductor 1 and a P-type non-single crystal semiconductor 3. Namely, many localized levels exist in a band gap of a conductive non-single crystal semiconductor and these localized levels promote generation of interfacial level in the case of forming semiconductor junction. Therefore, elimination of light generating carrier by recoupling can be suppressed by providing an intrinsic non-single crystal semiconductor 2 having good film quality between a single crystal semiconductor 1 and a non-single crystal semiconductor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to photovoltaic devices such as solar cells and optical sensors.

(b) Conventional technology In general, photovoltaic devices are classified into single crystal systems, non-single crystal systems, and polycrystal systems, depending on the type of semiconductor used as the power generation layer. Active research and development has been carried out on
This is a photovoltaic device made of a non-single crystal system. The reason for this is that compared to conventional single-crystal systems, non-single-crystal systems are easier to form over large areas, and the manufacturing process requires less energy, so lower costs can be expected. This is because of this.

However, despite the many research results obtained so far,
In terms of performance, it still cannot match single-crystal photovoltaic devices.

Therefore, in recent years, a new attempt in the development of photovoltaic devices has been made by appropriately combining non-single-crystalline semiconductors and polycrystalline semiconductors to form semiconductor junctions, making use of the advantages of the physical properties of each. Research is underway to obtain higher photoelectric conversion efficiency.

(c) Problems to be Solved by the Invention However, it is generally not possible to form a good semiconductor junction simply by bringing the semiconductors of each of the crystal systems into contact with each other. For example, even if a single crystal semiconductor and a non-single crystal semiconductor of opposite conductivity types are brought into direct contact with each other to form a pn junction,
It is not possible to obtain sufficient photoelectric conversion efficiency as a photovoltaic device.

This is because most of the photogenerated carriers in the semiconductor generated by light irradiation are lost due to recombination at the pn junction interface, and the photogenerated carriers cannot be extracted to the outside.

The cause of such recombination is thought to be due to localized levels of the non-single crystal semiconductor.

That is, in general, in a non-single crystal semiconductor, the film quality is significantly deteriorated by doping with a conductivity type determining impurity. This effect appears as an increase in localized levels within the bandgap. Then, the localized level acts to generate an interface level at the pn junction interface, and as a result, the photocarriers are recombined.

In view of the above circumstances, an object of the present invention is to provide a photovoltaic device that reduces recombination of photogenerated carriers at the junction interface.

(d) Means for Solving the Problems The photovoltaic device of the present invention is characterized by a photovoltaic device in which a single-crystal semiconductor and a non-single-crystal semiconductor having opposite conductivity types are laminated. In this case, an intrinsic non-single crystal semiconductor having a film thickness of 250 Å or less is interposed between the two semiconductors.

(e) By interposing an intrinsic non-single-crystal semiconductor having a film thickness of 250 Å or less between the single-crystal semiconductor and the non-single-crystal semiconductor that have a relationship of opposite conductivity types, recombination of photogenerated carriers is prevented. It becomes possible to increase the number of photogenerated carriers that can be taken out of the photovoltaic device.

That is, as mentioned above, a conductive non-single crystal semiconductor has many localized levels within its bandgap, and these localized levels generate interface levels when a semiconductor junction is formed. Encourage.

Therefore, by interposing an intrinsic non-single-crystal semiconductor having good film quality between the single-crystal semiconductor and the non-single-crystal semiconductor, it becomes possible to suppress the extinction of photogenerated carriers due to recombination.

Further, although the intrinsic non-single crystal semiconductor is superior in terms of film quality compared to the conductive non-single crystal semiconductor, it is still not sufficient when compared to the single crystal semiconductor.

Therefore, if the film thickness of the conductive non-single crystal semiconductor becomes too thick, the characteristics of the photovoltaic device will deteriorate.

Therefore, in the present invention, by setting the film thickness of the intrinsic non-single crystal semiconductor to 250 Å or less, the interface states can be reduced while suppressing the characteristic deterioration that occurs when the film thickness of the semiconductor is increased. We are making it happen.

(f) Example wi1 FIG. 1 is an element structure diagram showing an example of the photovoltaic device of the present invention.

(1) is a single crystal semiconductor made of an n-type single crystal silicon substrate, and (2) is an intrinsic non-single crystal semiconductor that is a feature of the present invention.
(3) is a non-single-crystal semiconductor having a conductivity type opposite to that of the n-type single-crystal silicon substrate, which is p-type amorphous silicon; (4) is an n-type single-crystal silicon substrate (1);
The electrode (5) made of aluminum or the like is in contact with the transparent conductive film.

As a method for forming the photovoltaic device of this embodiment, first, an n-type single crystal silicon substrate (1) is placed in a plasma CVD device, and after the inside of the device is evacuated, it is heated to about 120°C. Next, a glow discharge is generated in the plasma CVD apparatus, and silicon compound gas such as silane is decomposed by the energy of the plasma, and intrinsic amorphous silicon (2) with a thickness of 250 Å or less is converted into the n-type single crystal silicon substrate (1). ) of −
Formed on the main surface.

Subsequently, p-type amorphous silicon (3) having a conductivity type opposite to that of the single crystal silicon substrate (1) is formed on the intrinsic amorphous silicon (2). In the example, p-type amorphous silicon (3) was formed by the same plasma gas decomposition method as that used for intrinsic amorphous silicon (2).

As the reaction gas, the silicon compound gas to which diborane gas was added was used.

The method of forming the p-type amorphous silicon (3) and the intrinsic amorphous silicon (2) using a plasma CVD apparatus is a conventionally well-known technique.

Next, tin oxide, ITO was used as the window electrode of the photovoltaic device.
A transparent conductive film (5) such as a film (Indium Tin Oxide) is formed.

Finally, a metal electrode (4) is formed as a back electrode on the other main surface of the n-type single crystal silicon substrate (1), and the photovoltaic device is completed.

Note that the term "intrinsic amorphous silicon" here refers to amorphous silicon that is formed without adding any doping gas as a conductivity type determining impurity, for example, if it is formed by the plasma gas decomposition method as explained in the example. It goes without saying that it includes a crystalline silicon film, but it also includes an amorphous silicon film that is controlled to be substantially intrinsic by forming it by adding a small amount of doping gas.

This is because non-single-crystal semiconductors such as amorphous silicon generally exhibit a slight amount of conductivity even when formed without adding any impurities. Indicates n-type. In the present invention, such a substantially intrinsic semiconductor can also be used as the intrinsic non-single crystal semiconductor.

FIG. 2 shows the intrinsic amorphous silicon (
2) is a characteristic diagram showing the relationship between the film thickness and the power generation voltage and conversion efficiency of the photovoltaic device. FIG. The horizontal axis of the figure shows the film thickness of the intrinsic amorphous silicon (2), the vertical axis shows the conversion efficiency at the bottom, and the generated voltage at the top.

The state in which the film thickness is zero shown in the same figure means that, in the structure of the photovoltaic device of the example, an n-type single crystal silicon substrate (1) and a p-type single crystal silicon substrate (1) are formed without intervening intrinsic amorphous silicon (2). This means a case where the amorphous silicon (3) is brought into direct contact to form a so-called pn junction.

As shown in the figure, at any film thickness, the generated voltage is improved compared to the "zero state".

Further, by setting the film thickness of the intrinsic amorphous silicon (2) to 250 Å or less, in addition to improving the power generation voltage, photoelectric conversion efficiency is also improved. In particular, by setting the film thickness to a thin film of 100 Å or less, the maximum value of the photoelectric conversion efficiency can be obtained.

On the other hand, in the case of a film thickness of 250 Å or more, the value gradually decreases. This is because the intrinsic amorphous silicon (2) in the present invention has the main function of reducing the interface state, and the photocarriers generated in the layer of the amorphous silicon (2) itself hardly contribute to the conversion efficiency. Rather, this is because increasing the thickness of the amorphous silicon causes a decrease in the photoelectric conversion efficiency.

Note that the lower limit of the film thickness of the intrinsic amorphous silicon (2) employed in the present invention is as follows: Although it exhibits the effect of the invention,
From the viewpoint of ease of controlling the film thickness, a thickness of 20 Å or more is preferable.

The intrinsic amorphous silicon used in the present invention is a p-type semiconductor and an n-type semiconductor.
Interposed between the photovoltaic device and the type semiconductor is the p-layer of the photovoltaic device, which is made only of amorphous silicon.

It is thought that this structure is similar to a so-called pin junction structure in which an i-layer and an n-layer are sequentially laminated.

However, the photovoltaic device of the present invention has a structural feature of forming an intrinsic non-single-crystal semiconductor device between semiconductors in different crystal states such as single-crystalline and non-single-crystalline semiconductors. Photogenerated carriers in intrinsic non-single crystal semiconductors do not contribute to photoelectric conversion efficiency;
In terms of the film thickness, the major feature is that the intrinsic non-single crystal semiconductor is made thin to the extent that no photogenerated carriers are generated.

Therefore, the pin structure in the conventional photovoltaic device made only of amorphous silicon is completely different from its purpose, structure,
They have different effects.

In the embodiment, the case where an n-type semiconductor is used as the single-crystal semiconductor has been described, but the photovoltaic device of the present invention is not limited to this. Needless to say, it shows exactly the same effect.

(G) Effects of the Invention According to the photovoltaic device of the present invention, the interface level caused by the localized level of the conductive non-single crystal semiconductor can be reduced, and photocarriers can be efficiently collected and converted. Increased efficiency.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the device structure for explaining the device structure of the photovoltaic device of the present invention, and FIG. 2 shows the relationship between the film thickness of the intrinsic non-single crystal semiconductor, the generated voltage, and the conversion efficiency in the device structure. It is a characteristic diagram.

Claims (1)

[Claims] (1) In a photovoltaic device in which a single crystal semiconductor and a non-single crystal semiconductor having mutually opposite conductivity types are sequentially stacked, an intrinsic non-single crystal semiconductor having a film thickness of 250 Å or less is formed between the two semiconductors. A photovoltaic device characterized by interposing a crystalline semiconductor.