JPS60207319A - Amorphous semiconductor solar cell - Google Patents

Abstract

PURPOSE:To obtain a P-I-N type amorphous semiconductor solar cell having enhanced conversion efficiency by a method wherein the impurity layer on the window side of the solar cell is made to have a multilayer construction. CONSTITUTION:As the impurity layer on the window side of a solar cell, a transparent substrate 1, a transparent electrode 2, a hetero-p type layer 3, a microcrystalline p type layer 4, an i-type layer 5, an n type layer 6, and a metal electrode 7 on the back are provided, and the respective constituting elements thereof have the functions the same with the case of a P-I-N type element. According to this method, a semiconductor having a small light absorptivity coefficient, and having the most suitable index of refraction can be offered, and a semiconductor effective as a light incident side material for a P-I-N type amorphous solar cell can be supplied. At this solar cell, a short-circuit current and a curve factor are improved as compared with the usual P-I-N type element, and conversion efficiency is enhanced markedly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel solar cell using an amorphous semiconductor. More specifically, the present invention relates to a novel amorphous semiconductor solar cell with improved photoelectric conversion efficiency.

In recent years, solar cells using amorphous semiconductors have attracted attention because their manufacturing costs are extremely low compared to single-crystalline solar cells, and they are being actively developed as a promising solar cell. Various structures have already been proposed for this solar cell, but among these, the intrinsic layer (
A p-1-n type or n-1-p type (hereinafter abbreviated as a pin type in this specification) in which an i layer) is sandwiched between impurity layers (p or n layer) achieves high efficiency. known as a thing.

Conventionally, when these pin-type amorphous silicon semiconductors function as solar cells, pl! Alternatively, it is known that photogenerated carriers that serve as photocurrent are generated in the i-layer because the lifetime of carriers (hereinafter referred to as photogenerated carriers) that are generated when the amorphous silicon of the n-layer absorbs light is short. There is. However, in the case of a pin type solar cell, the i layer is sandwiched between the p layer and the n layer, so light enters the i layer through the p layer or the n layer. For this reason, it is preferable that the p-layer or n-layer be made of a material with a wide optical gap and low light absorption.However, the light absorption coefficient of conventional n-type and p-type amorphous silicon is Since the absorption coefficient was about the same as or larger than that, light absorption loss in the n-layer or p-layer was one of the causes of lowering the photoelectric conversion efficiency.

In addition, pin-type amorphous solar cells are made of glass/transparent electrode/(pin or n1p)/metal, transparent electrode/(pin
or n1p)/metal, and light is incident from the transparent electrode. Therefore, light loss due to light reflection from solar cells also prevents an increase in photoelectric conversion efficiency. In this case, although it is desirable to control the refractive index of the p-layer or n-layer in order to minimize light reflection at the interface between the transparent electrode and the p-layer or n-layer, conventional p-layer or n-layer of,
For example, the refractive index at 1500 nm is 3.4 to 3.6, which is the same as that of the amorphous silicon of the i-layer, and there is a large difference from the refractive index of 2.0 of the transparent electrode, so reflection loss is considered to be inevitable. It was getting worse.

Furthermore, conventional pin-type amorphous silicon semiconductor devices have the disadvantage that semiconductor devices cannot be manufactured efficiently because the adhesion between the pin or nip and the stainless steel substrate and transparent electrode is insufficient. Ta. These drawbacks are considerably improved when using amorphous hydrogenated silicon (a-31; H) as the amorphous semiconductor, which gives high efficiency, but conventional amorphous hydrogenated silicon detection The optical gap was narrower than that of the conventional method, and the matching with the electrode in terms of refractive index, adhesion, ohmic properties, etc. was insufficient.

Amorphous silica 1 containing carbon and hydrogen as impurities is used as a material to solve these conventional drawbacks.
(a-31+C:H) material (JP-A-57-12617
5 etc.) and amorphous silicon containing microcrystals (μc-3t;
H) has been proposed and put into practical use. However, a
Although -5i:C:H can suppress light absorption and improve photoelectric conversion efficiency from that aspect, it is still insufficient in terms of improving light reflection and adhesion to stainless steel and transparent electrodes. Above, there was a drawback that the conductivity was lower than that of the conventional a-3i;H, and in the case of μc-3l:H, the compatibility with the transparent electrode was not particularly good. .

On the other hand, as the window side semiconductor, the total amount of oxygen and nitrogen contained in the film or the total amount of carbon and oxygen contained in the film is 1 atomic % or more, respectively;
When 0.1 atomic % or more of semiconductor is used as the window side material, it has good adhesion to the electrode and can reduce reflection loss (Japanese Patent Application No. 111098/1982 and Japanese Patent Application No. 58/1989). 139073 specification).

As a result of intensive research based on such conventional knowledge, the present inventors have determined that the window-side impurity layer is divided into an amorphous silicon layer containing microcrystals (microcrystalline layer) and an amorphous silicon layer containing certain elements (heterolayer). ) It was discovered that the performance of an amorphous semiconductor solar cell could be improved by forming it into a multilayer structure, and the present invention was achieved based on this finding.

(Object of the Invention) Therefore, the first object of the present invention is to provide a pin-type amorphous semiconductor solar cell with significantly increased conversion efficiency.

A second object of the present invention is to provide an impurity layer with a wide optical gap and low optical loss, which is effective as a window-side impurity layer of a pin-type amorphous semiconductor solar cell.

A third object of the present invention is to provide an impurity layer with low electrical resistance that is effective as a window-side impurity layer of an amorphous semiconductor solar cell.

Furthermore, a fourth object of the present invention is to provide a window-side impurity layer of an amorphous semiconductor solar cell that has good compatibility with a transparent electrode.

(Structure of the Invention) Various aspects of the present invention include a semiconductor device having an amorphous semiconductor layer.
This was achieved using an amorphous semiconductor solar cell which is an n-type solar cell and is characterized in that the window-side impurity layer of the solar cell has a multilayer structure.

(Disclosure of the Invention) As the transparent substrate used in the present invention, it is usually preferable to use glass, but other transparent materials such as plastics can also be used.

In the present invention, the transparent electrode provided on the transparent tetracarbonate may be made of, for example, 5n02 or indium tin oxide (ITO).
A commonly used transparent electrode such as (abbreviated as ) can be used. These transparent electrodes can be formed on a transparent substrate using conventional methods such as chemical vapor deposition, sputtering, and spraying of metal salt solutions.

Especially when a combination of an amorphous silicon layer containing microcrystals and an amorphous silicon layer containing a certain element is selected as the multilayer window-side impurity layer according to the present invention, a good pin can be obtained.
type solar cell element can be obtained. In this case, the amorphous silicon containing microcrystals preferably contains hydrogen and/or halogen atoms. As the halogen atom, fluorine and chlorine are preferred, with fluorine atom being particularly preferred.

A method for manufacturing an amorphous silicon thin film containing such microcrystals is described, for example, in Japanese Patent Laid-Open No. 59-39713.

As mentioned above, the amorphous silicon layer containing microcrystals and the other amorphous silicon betaro layer forming a multilayer include one or two types selected from hydrogen, nitrogen, carbon, and oxygen. Contains the above elements.

As is well known, in order to produce a silicon thin film containing hydrogen as an impurity by plasma decomposition, a hydrogen-containing silicon compound such as silane or its derivatives is used as a raw material gas, or hydrogen (H2) is used as a carrier for discharge. , it is sufficient to realize a plasma atmosphere, and in addition, oxygen (02
) into the raw material gas, it is possible to produce a silicon thin film containing oxygen and hydrogen as impurities. Similarly, various dopants can be introduced into an amorphous silicon semiconductor.

The physical properties of amorphous silicon semiconductor thin films largely depend on the type and amount of impurities contained in the thin film.
In particular, among physical properties, improvements in absorption coefficient and adhesion to metal substrates and/or transparent electrodes largely depend on the amount of oxygen, nitrogen, and carbon contained as impurities. For example, the presence of carbon and oxygen contained in amorphous silicon semiconductors makes silicon carbide (~6
゜0eV), M monster IA (9, o e v) 17J
Since each time the structure is made to exist partially, a-3i
The bandgap of the semiconductor is widened, which allows the absorption coefficient to be reduced. Furthermore, regarding the refractive index, a-
The refractive index of the 3l semiconductor can be controlled.

Moreover, since C and O can enter into the 4-coordinated Sl network, the amorphous silicon semiconductor WI
IMIJ! As a result, the adhesion to the CC metal-based transparent electrode substrate can be improved.

Even when nitrogen is used as an impurity, the situation is almost the same as the above case, and the band gap of partially existing silicon nitride is about 5. Because of its large OeV, it not only contributes to reducing the absorption coefficient of amorphous silicon semiconductor, but also
Since the refractive index is also improved, reflection loss is reduced, and nitrogen can enter the St net kayanok, so that
Structural stress on the amorphous silicon semiconductor thin film can be alleviated, and as a result, adhesion to transparent electrodes can be improved.

In particular, the total amount of carbon and oxygen contained in the amorphous silicon thin film is 0.1 atomic % (in this case, atomic % is 100X(C+O)/(S i
+C+O) or more, or the total amount of nitrogen and oxygen is 1 atomic% (in this case, atomic% is 100x (N+O)/(S i +N
(meaning 10)), the effects of these impurities are clear.

or,! When using elements as impurities, there is a risk of explosion depending on the type of raw material gas, so special conditions must be selected for the production of semiconductor thin films. The raw material gas for these impurities and its introduction method are disclosed in, for example, the patent application filed in 1973.
No. 8-111098 and Japanese Patent Application No. 58-139073.

On the other hand, hydrogen contained as an inert substance in the amorphous silicon semiconductor thin film eliminates the dangling bonds of silicon atoms that occur when forming the amorphous silicon thin film, and reduces the density of localized ranks in the silicon thin film. This is significant for controlling the electrical resistance of the semiconductor device according to the present invention.

The total thickness of the multilayer window-side impurity layer in the present invention is 70 mm.
~120 people is preferable. On such a multilayer window side impurity layer, after forming one layer by a known method, a p layer or an n layer is further formed, and by bonding with an electrode, a pin type or nip type is formed. type of solar cell element can be obtained. In this case, as the impurity layer on the metal electrode side, an a-3tsH layer whose conduction of impurities is controlled, a hydrogenated silicon layer containing microcrystals (μc-3t:H), or the like can be used.

Methods for sequentially depositing each amorphous layer on the transparent electrode include plasma CVD, sputtering, and thermal CVD.

It can be appropriately selected from known amorphous film manufacturing methods such as photo-CVD. That is, for example, when using the plasma CVD method, a predetermined reaction gas is introduced into a vacuum reaction tank in which a transparent substrate on which a transparent electrode is deposited is installed, a predetermined internal pressure is achieved, and then high-frequency discharge and low-frequency discharge are applied. It can be manufactured by forming plasma using any method, such as various discharge methods such as direct current discharge. Apart from sputtering, when adopting the CVD method, as mentioned above (reactant gas is required.
Among the methods, plasma CV is particularly effective in terms of reaction efficiency, etc.
It is preferable to adopt method D.

Next, the raw material gas when carrying out the present invention by the CVD method will be described.

As a silicon source that can be used in the present invention, any silane represented by the general formula 5LnH2n+2 or a halogenated silane represented by the general formula SiH□~3X4~l (X represents a halogen atom) is selected. can be selected. These may be used alone or in combination of two or more.

The carbon source can be arbitrarily selected from hydrocarbons (eg, methane, ethane, etc.) that have a vapor pressure sufficient to carry out the CVD method at room temperature.

Of course, oxygen gas and ozone gas can be used as oxygen sources, but especially when carbon and oxygen are simultaneously contained as impurities, , carboxylic acids, ketonic acids, etc.) is preferably used.

Similarly, it is natural that nitrogen gas can be used as a nitrogen source, but if carbon is to be included as an impurity at the same time, one or more types of nitrogen-containing organic compounds should be selected as appropriate. is preferable, and when nitrogen and oxygen are simultaneously contained as impurities, No, NO
2. It is preferable to select one or more types from among N20.

The ratio of the silane-containing compound forming the reaction gas and the raw material gas for impurities can be changed as appropriate depending on the desired physical properties and reaction conditions.2 For example, if the input power for plasma generation is about 4 W, The reaction pressure was set to about 0. When ITorr, substrate temperature is set to about 300° C., and gas flow rate is set to about 1103 CC, good results can be obtained with a mixing ratio of impurity elements of about 1% by volume.

In the present invention, when imparting p-type or n-type properties to the silicon thin film, it is necessary to further add a dopant gas within the above film forming conditions. The p-type dopant gas is an element of Group 1 of the Periodic Table of Elements or a compound thereof, and is preferably a hydride, particularly boron hydride (B2H5). The n-type dopant gas is an element of group Ⅰ of the periodic table of elements or a compound thereof, preferably a hydride, particularly phosphine (PH3) or arsine (ASH3). Although the mixing ratio of these dopant gases is not constant depending on plasma conditions and the like, good results can be obtained if the mixing ratio is about 0.2% by volume based on the silicon-containing compound.

In the present invention, specific examples of the metal electrode used as the substrate include aluminum, antimony, stainless steel, and the like.

A typical configuration example of the solar cell of the present invention is shown in FIG. In the figure, reference numeral 1 indicates a transparent substrate such as glass;
2 is a transparent electrode, 3 is a hetero9 layer, 4 is a microcrystalline p layer, 5
6 is the n-layer, and 7 is the metal electrode on the back surface. Each of these components has a function similar to that of a so-called pin type element.

(Effects of the Invention) According to the present invention, it is possible to provide a semiconductor having a small light absorption coefficient and an optimum refractive index, which is an extremely effective semiconductor as a material on the light incident side of a pin-type amorphous solar cell. can be supplied.

The solar cell manufactured according to the present invention has improved short circuit current and fill factor, and has significantly improved conversion efficiency, compared to a conventional pin-type device, so the present invention has great significance.

The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto.

(Example) Using the CVD method, as shown in FIG. A solar cell with this structure was fabricated. .

First, silane gas (S
iH4), approximately 1. 0 volume% No.
A mixed gas of about 0.1% by volume of B2H5 with respect to silane gas was introduced so that the pressure inside the reaction chamber was about 0.1 Torr. Next, plasma discharge was started with an input power of 4 W, and the substrate temperature was 300°C and the gas flow rate was 103C and 103C.
Under C conditions, 9 hetero layers (3) of about 30 people were deposited on the transparent electrode.

Next, after evacuating the reaction chamber, silane gas and a mixed gas of 0.2% by volume of B2H to the silane gas were diluted 30 times with hydrogen gas and introduced, and the pressure inside the reaction chamber was reduced to 0.2% by volume. IT
It was set as orr. Input power 20W, gas flow rate 7.53CC
M. At a substrate temperature of 300°C, an amorphous silicon layer containing about 70 microcrystals (
4) to form a window-side impurity layer of about 100 people in total.

On the impurity layer thus formed, an i-layer and an n-layer were further formed by a conventional method, and metal electrodes were attached to obtain a sample (D) of the present invention.

This sample, the i-layer and the n-layer are all the same (A
), a comparative sample (B) with a single layer of μc-5i:H,
Table 1 shows the results of comparison with comparative sample (C), which was a single layer of a-31:N:O:H.

Table 1 Sample Window side Open Short circuit curve Conversion impurity layer Voltage Current Factor Efficiency A a-5i:11 1.0 1.0 1.0 1. O
B μc-3t: HO, 550, 290, 280, 04
Ca-3i:N:0:H1,111,130,871,
08D a-3i:N:O;H.

and +'c-3i: H1,101,280,901,2
76 However, the conversion efficiency in the table is a relative value with respect to Sample A.

From this result, it was demonstrated that the solar cell obtained by the present invention has extremely high photoelectric conversion efficiency.

[Brief explanation of the drawing]

FIG. 1 shows a typical configuration example of the solar cell of the present invention. In the figure, reference numeral 1 indicates a transparent substrate, 2 indicates a transparent electrode, 3 indicates nine hetero layers, 4 indicates a microcrystalline p layer, 5 indicates five layers, 6 indicates an n layer, and 7 indicates a metal electrode on the back surface. Patent applicant Toa Fuel Industries Co., Ltd.

Claims (1)

[Scope of Claims] 1) A pin-type solar cell having an amorphous semiconductor layer, characterized in that a window-side impurity layer of the solar cell has a multilayer structure. 2) The window side impurity layer is an amorphous silicon layer containing microcrystals (
A patent characterized by a multilayer structure of a microcrystalline layer) and an amorphous silicon layer (heterolayer) containing one or more elements selected from hydrogen, nitrogen, carbon, and oxygen. The amorphous semiconductor solar cell according to claim 1.