JPS61222278A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To suppress the deteriorating phenomenon or photoelectric conversion efficiency due to long time projection of intense light, by providing a structure for a generating layer so that a low doped layer, in which conducting-type determining impurities are included by a slight amount less than a doped layer, is laminated on a non-doped layer, in which the conducting-type determining impurities are not included. CONSTITUTION:A semiconductor light active layer 3 comprises a generating layer 3g and different-conducting-type first and second doped layers 3d1 and 3d2. The generating layer 3g generates optical carriers of electrons and holes, which contribute to electric generation when light is imputted. The doped layers 3d1 and 3d2 hold the generating layer 3g in order to generate a junction electric field, which accelerates the movement of the optical carriers of the electrons and holes generated in the generating layer 3g to a back surface electrode 4 or a light receiving surface electrode 2. The layer 3g has a laminated structure, wherein a low doped layer 3gd, which includes slight conducting-type determining impurities less than the doped layers 3d1 and 3d2, is overlapped on a non-doped layer 3gn, which does not include the conducting-type determining impurities. Thus, the decrease in field intensity of the junction electric field can be corrected at the intermediate part of the thickness, and the deterioration in photoelectric conversion efficiency due to intense light projection can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Pin Industrial Application Field The present invention relates to a photovoltaic device that generates photovoltaic force by irradiation with light, and is used, for example, in solar power generation.

First Prior Art As a typical example of this type of photovoltaic device, a 181 electrode on the light receiving surface side, a pin junction type amorphous semiconductor film, and a 181 electrode on the back side are sequentially formed on one main surface of a glass substrate forming the light incident surface. There is one in which two electrodes are laminated; for example, Japanese Patent Application Laid-Open No. 57-95677
In the publication, it is described that amorphous silicon (a-81) obtained by plasma decomposition of silicon compound gas is used as the p, in junction type amorphous semiconductor film, and that p It is proposed to use amorphous silicon carbide (a-BixOl-1) as the mold layer.

That is, by using amorphous silicon carbide in place of the p-type layer of amorphous silicon that forms the conventional pin homojunction, a pin heterojunction is constructed, and the light absorption loss in the p-type layer is reduced. The aim is to increase the photoelectric conversion efficiency by increasing the amount of light irradiated onto the power generation layer consisting of a type 1 (intrinsic) layer or a substantially intrinsic (non-doped) layer that contributes to power generation by obtaining a so-called window effect that reduces the power generation.

However, it is known that when the power generation layer that contributes to the power generation described above is exposed to strong light for a long time, it causes a deterioration phenomenon in which the photoelectric conversion efficiency decreases. (For example, regarding such deterioration phenomena, please refer to the First International Photovoltaic Science and
photo, ovaxtaic 3cienee
ana Iiingineering Qonfere
no@Kot+e) November 13th to 16th 1984
p.213-@216, Nis-Rada et al.

I “Dera Tsuji, Indeuest Degradation Op.”
Nisilicon Films and Solar Cells J
(E3- Tauda et al. he Light.

Degradation Of &-
81FLIms and 5olar 0ell
s”). ) (C) Problems to be Solved by the Invention The photovoltaic device of the present invention attempts to solve the phenomenon of deterioration of photoelectric conversion efficiency due to long-term irradiation with strong light.

(2) Means for Solving the Problems In order to solve the above-mentioned photovoltaic conversion efficiency deterioration phenomenon, the photovoltaic device of the present invention has a conductive layer between the doped layer of one conductivity type and the doped layer of the opposite conductivity type. The structure includes a low doped layer containing less type determining impurities than the doped layer, a non-doped layer containing no conductivity type determining impurities, and a power generation layer having an fJ layer structure overlapping at least one layer.

(E) Function As mentioned above, by making the power generation layer have at least a two-layer structure, the Fermi levels of the two layers are made different.

This prevents the junction electric field strength from loosening in the middle of the thickness direction of the power generation layer.

(f) Example FIG. 1 shows an embodiment of the photovoltaic device of the present invention.

(1) is a transparent and insulating substrate such as glass; (2) is indium (In) for the t-light receiving side of the substrate (1);
I which is a transparent conductive oxide (TOO) such as tin (8n)
A light-receiving surface electrode made of n20iS, ITO, Bn02, etc., and (3) a semiconductor photoactive layer formed on the light-receiving surface electrode (2) and having a pin junction parallel to the film surface.

(4) is a back electrode provided on the back side of the photoactive layer (3).

The semiconductor photoactive layer (3) includes a power generation layer (3g) that generates photocarriers of electrons and holes that contribute to power generation (photoelectric conversion) when light is incident, and a power generation till (3g) that generates photocarriers of electrons and holes that contribute to power generation (photoelectric conversion). The photocarriers of electrons and holes are each connected to the back electrode (4).
Alternatively, the light-receiving surface electrode (2) (doped #1.J2 (3a1) (312) of different conductivity types that sandwich the power generation layer (3g) to generate a junction electric field that promotes movement; Further, the power generation layer (5g) is the dope II (3a1).
It has a laminated structure in which a lightly doped layer (3811) slightly containing less conductivity type determining impurities than (3az) and a non-doped layer (3gn) containing no conductivity type determining impurities are superimposed.

Low dope II containing a small amount of the conductivity type determining impurity (
3al) is the first or second doped l1l (3al) or (!1
(12) and the non-doped layer (3gn). In this example, the above-mentioned lightly doped t11ga
) is provided in contact with 1J117)l'-pull1 (3a1), and this IJ! It slightly contains a determining impurity of the same conductivity type as the dope 11 (3dl) of No. 1.

Figure 2 shows the change over time of the deterioration phenomenon of nine photoelectric conversion efficiency normalized by the initial value using a solar simulator that radiates the sunlight spectrum (AM-1) just below the equator.
This shows the situation when intense light of mW/- is directly irradiated. The solid line shows the deterioration characteristics of the photovoltaic device of the present invention in which the power generation layer (3g) has a two-layer structure of lightly doped s (3al) and non-doped a (to 3g), and the broken line shows the deterioration characteristics of the photovoltaic device in which the power generation layer is a non-doped layer. This is the deterioration characteristic of a conventional photovoltaic device consisting of The semiconductor photoactive layer (3) in the photovoltaic device of the present invention is formed by a 15.56 MHz radio frequency (RF) plasma OVD method under the following conditions.

0 Substrate temperature 150°C to 250°C 0 Gas pressure CL3 Torr The conventional photovoltaic device used for comparison has an RF power of 20 W as a power generation layer, and a non-doped layer formed to a thickness of 5000λ using 81EI4 gas as a raw material. Nasi,
It was formed under the same conditions as above except that the lightly doped layer was not present.

Results of comparison of such deterioration characteristics 1. What is the photoelectric conversion efficiency of the photovoltaic device of the present invention under strong light of AM-1,100 mW/-? Even after 10 hours of irradiation, it was confirmed that the deterioration rate was only reduced by about 5% from the initial value, and compared to the 15% decrease in the conventional example, the deterioration rate was significantly reduced.Using this, the following discussion was made. ing. In other words, if the power generation layer has a single layer structure like prisoner 39,
In the initial state without strong light irradiation, the potential of the power generation layer gradually decreases from the p-type layer to the n-type layer, but after irradiation with strong light, the potential of the power generation layer decreases. As a result, the potential in the middle of one power generation layer decreases, resulting in a decrease in electric field strength (relaxation) in the range indicated by W in FIG. Therefore, in this conventional photovoltaic device, the photocarriers generated by light irradiation are recombined in the range (region) where the electric field strength decreases, and the first and second doped resins are recombined. (3a1) (3a2) The amount of photocarriers reaching the light-receiving surface electrode (2) and the back electrode (4) via t- was reduced, causing deterioration of photoelectric conversion efficiency.

I infer that. On the other hand, in the photovoltaic device of the present invention, the power generation 711 (Ag) is 2 as shown in Figure 39).
Because it is divided into layered structures, the lightly doped layer (3g+1
) and the non-doped layer (!ign) even if the potential in each film drops as shown by the broken line due to light irradiation.

Since the Fermi level is different at the interface in the middle of this power generation layer (3g), it does not move. As a result, the junction electric field that promotes the movement of photocarriers does not decrease significantly due to light irradiation, but is corrected at the interface, and the photocarriers reach the light-receiving surface electrode (2) and the back electrode (4). It will become.

Figure 1%4 shows the lightly doped layer (3gd) of the photovoltaic device of the present invention.
It shows the relationship between the doping amount of conductivity type determining impurities and the deterioration rate of photoelectric conversion efficiency in the photoelectric conversion efficiency. It shows. From the same figure, it is clear that the bottle is low-doped.
When diborane (B2Ir6) containing boron @, which is a p-type determining impurity, is used as ie (3ga), -f-/
T? Gas composition ratio B 2 H6/ 8 with y (81H4)
i H4 is about 10-5 to 10-5. That is, 110p
It has been found that the rate of deterioration is lower than that of the conventional example, which is 15% lower than the initial value at pm to 11,000 ppm, and is particularly effective near iooppm.

On the other hand, when using phosphine (pus) containing phosphorus, which is an n-type determining impurity, the gas composition ratio P with 81H4 is
II S/8L H4 approximately 10~10”-
', that is, in tppm to ioooppm, the deterioration rate is lower than in the conventional example, and is particularly effective near 1 oppm.

Figure 5 shows the deterioration rate of photoelectric conversion efficiency and B2Ha/8ii
This is to explain the relationship with the film thickness of the low doped layer (3gd) created with the gas composition ratio of i4-1 (1m)H, and it is more effective than the conventional example in the film thickness range up to 3000A. It shows that there is.

In the above embodiment, one power generation It (3 g) is obtained by converting either P plastic or n-type conductivity type determining impurity into the first one of the same conductivity type. It had a two-layer structure consisting of a lightly doped layer (3 ga) doped with a lower content of R2 (3(11)(342)) and an undoped non-doped layer (sgn), but the non-doped layer A three-layer structure in which different types of lt-type low dope layers are placed on both sides of (3gn), and a non-doped I!t (3gn) structure formed without doping with conductivity type determining impurities
In order for gn) to exhibit slightly n-type properties as in Japanese Patent Publication No. 59-29157, its n-type properties were brought close to the true intrinsic type (type 1) by doping a small amount of type-determining impurities. Low doped layer (la) and non-doped jll (3gn
) and the first lightly doped layer slightly doped with a p-type determining impurity to compensate for type 1. @1(
3a1) or (112) or a three-layer structure in which a low doped layer of $2 doped with less than (112) is laminated.

(G) Effects of the Invention As is clear from the above description, the photovoltaic device of the present invention uses a power generation layer that generates photocarriers that contribute to power generation upon irradiation with light as a lightly doped layer containing a small amount of conductivity type-determining impurities. ,
Since it has a laminated structure of at least a non-doped layer that does not contain impurities that determine the conductivity type, an interface with a different Fermi level is formed in the middle of the thickness of one power generation layer, and the decrease in the electric field strength of the junction electric field is corrected in the middle of the thickness. 1. Deterioration of photoelectric conversion efficiency due to strong light irradiation can be suppressed.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing a typical example of the photovoltaic device of the present invention, Fig. 2 is a deterioration characteristic diagram showing an example of the present invention, a conventional example, and a change in photoelectric conversion efficiency over time, and Fig. 39 is a conventional example. Fig. 39 is a schematic band structure diagram for explaining the deterioration phenomenon of the present invention, and Fig. 4 is a schematic band structure diagram for explaining the suppression of the deterioration phenomenon in the embodiment of the present invention. Deterioration characteristic diagram showing the relationship with the doping amount of conductivity type determining impurity, No. 5
The figures each show a deterioration characteristic diagram showing the relationship between the deterioration rate of photoelectric conversion efficiency and the film thickness of the lightly doped layer. (1)...Substrate, (3)...Semiconductor photoactive layer, (5
a'1) (3a2)...first iJ2 doped layer, (
3g)...Power generation layer, (3ga)...Low doped layer, (
3gn)...Non-doped layer.・Figure 2Figure 3 (A)

Claims (3)

[Claims] (1) An amorphous silicon-based power generation layer that generates photocarriers that contribute to power generation is arranged between a doped layer of one conductivity type and a doped layer of the opposite conductivity type, and the power generation layer is free of impurities that determine the conductivity type. A photovoltaic device characterized in that it has a laminated structure in which a lightly doped layer containing a slightly smaller amount than the doped layer and a non-doped layer containing no conductivity type determining impurity are overlapped at least. (2) The photovoltaic device according to claim 1, wherein the conductivity type determining impurity slightly contained in the lightly doped layer is about 10 ppm to 1000 ppm of the p type determining impurity. (3) The photovoltaic device according to claim 1, wherein the conductivity type determining impurity slightly contained in the lightly doped layer is about 1 ppm to 1000 ppm of an n type determining impurity.