JPH02306670A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To extend light sensitivity to the side of a long wavelength and to improve characteristics by providing a first layer made of N-type or P-type polycrystalline semiconductor, and a second layer made of P-type or N-type amorphous semiconductor via hetero junction to the first layer. CONSTITUTION:A first layer 2 made of N-type or P-type polycrystalline semiconductor, and a second layer 3 made of a P-type or N-type amorphous semiconductor via hetero junction to the first layer are provided. That is, since the polycrystalline silicon has light sensitivity to longer wavelength side than that of the amorphous semiconductor, the light of the short wavelength side is mainly absorbed by the layer 3, and the light of the long wavelength side is mainly absorbed by the layer 2. Thus, the light sensitivity of a device can be extended to the long wavelength side, thereby increasing a photocurrent.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to photovoltaic devices such as solar cells.

[Conventional technology]

Conventionally, photovoltaic devices such as solar cells have mainly used amorphous silicon (hereinafter referred to as a-3i) as a base material, and the structure thereof is, for example, as described in Japanese Patent Publication No. 115854/1983 (101L 31104). To.

A transparent electrode is formed on a transparent substrate such as glass, p, i, and n layers made of a-3i, and a back surface made of a metal vapor-deposited film, etc.
The poles are stacked one after the other. At this time, light enters from the p layer, that is, the transparent substrate.

Another idea is to sequentially stack an i-layer made of a-3i:H and a p-layer made of amorphous silicon (nm) on an a-3i:H p-layer.

[Problem to be solved by the invention]

In the case of a conventional pin-structured photovoltaic device using an a-5ift base material, the sensitive wavelength is at most 800 nm, and there is almost no sensitivity to longer wavelengths, so the characteristics of the photovoltaic device There is a problem that it is not possible to improve the quality of the products.

Further, since the n-layer made of a-5i as a base material has a high resistance and cannot be used as an electrode as it is, it is necessary to form a back electrode on this n-layer.

The present invention has been made with the above points in mind, and aims to enhance photosensitivity toward longer wavelengths, improve characteristics, and eliminate the need for the conventional back electrode.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a first layer made of an n-type or p-type polycrystalline semiconductor, and a second layer made of a p-type or n-type amorphous semiconductor heterojunctioned to the l-th layer. It has a layer of

[For production]

In the above configuration, polycrystalline semiconductors have photosensitivity to longer wavelengths than amorphous semiconductors, so
Light on the short wavelength side is mainly absorbed in the second layer, and light on the long wavelength side is mainly absorbed in the first layer, so that the photosensitivity of the photovoltaic device is extended to the long wavelength side compared to the conventional one.

Furthermore, since the polycrystalline semiconductor has low resistance, the first layer can be used as an electrode for extracting photocurrent, and there is no need to provide a back electrode as in the conventional case.

〔Example〕

Examples will be described with reference to the drawings.

In Figure 1, (1) is a transparent substrate made of η such as glass, and (2) is polycrystalline silicon (hereinafter referred to as poly-8i), which is an n-type polycrystalline semiconductor formed on the substrate (1). ), (3) is a p-type amorphous semiconductor heterojunctioned to the first layer (2) a-5i:
The second layer (4) made of H is an electrode for Schottky junction, and is made of gold (Au) or ITO (Indium Tin).
In the case of Au, the substrate (1
) side, or in the case of ITO, from this electric IM (4) side.

Note that (5) is a lead connection portion provided on the first layer (2) and the electrode (4).

At this time, the first layer (2) is formed by solid phase growth from n-type a-8i formed on the substrate (1) by plasma CVD.

By the way, when we investigated the relationship between the solid phase growth temperature of the first N(2) of poly-8i, the sheet resistance, and the mobility, the results were shown in Figures 2 and 3, respectively, and from Figure 2, , the sheet resistance is approximately 40Ω/at a solid phase growth temperature of 800°C.
From FIG. 3, the mobility reaches a maximum of about 40 CI/I/v-s at an internal phase growth temperature of 700°C.

Therefore, the optimal range of solid phase growth temperature for the first layer (2) is 7
00 to 800°C, but in order to effectively utilize the light absorption of the first layer (2) and utilize it as a power generation layer, solid phase growth is preferably performed at 700°C, where the mobility is maximum.

To reduce the sheet resistance as a charge flow extraction electrode 8
It is preferable to perform solid phase growth at 00°C.

In addition, the formation of the first layer (2) is divided into two steps, and the first layer (2) is formed on the substrate (1).
The side closest to
By performing solid phase growth at 0° C., it becomes possible to effectively utilize the first layer (2) as a power generation layer and an electrode.

Next, the optical absorption coefficients of n-type poly-8i and a-5i:h were measured, and the results were as shown in FIG.

The solid line in the figure is n-type poly-3i, and the broken line is a-3i.
:H, and from the same figure, on the long wavelength side of 800 to IQQQ nm, n-type poly-5i (D light absorption coefficient is a-5
i: is more than one digit larger than H, and from this, 8
Light on the short wavelength side up to 00 nm is mainly p-type a-3i.
Absorbed by the second layer (3) consisting of :H, gQQ
Light with wavelengths longer than nm is mainly n-type poly-S
It can be seen that it is absorbed by the first layer (2) consisting of i.

Furthermore, we compared the collection efficiency of the photovoltaic device I with the configuration shown in Figure 1 and the conventional transparent electrode/pin layer/layer back electrode structure photovoltaic device ■, and the results were as shown in Figure 5. Ta.

Note that the solid phase growth conditions for the first layer (2) are 700'C,
100 hours, doping amount is PHa/SiH4~8X1
0-2, the film thickness at this time was 10 μm, and the sheet resistance was 20 Ω/hole.

The mobility is 100 cd/Vs.

The solid line in FIG. 5 indicates the photovoltaic device 1. The broken line indicates the photovoltaic device ■, and from the same figure, it can be seen that the photovoltaic device I has a high collection efficiency on the long wavelength side of 800 nm or more, and the photocurrent is larger than the conventional one. , it becomes possible to significantly improve the characteristics of the photovoltaic device.

In addition, in the above embodiment, n-type poly-3i and p-type a-3
The case of i:H heterojunction was explained, but p-type p
Of course, it may be a heterozygous combination of oly-3i and n-type a-3i:H.

In addition, the above-mentioned S as a polycrystalline and amorphous semiconductor
It is not limited to i.

〔Effect of the invention〕

Since the present invention is configured as described above, it achieves the effects described below.

Light at shorter wavelengths is mainly absorbed by the second layer made of an amorphous semiconductor, and light at longer wavelengths is mainly absorbed by the first layer made of polycrystalline semiconductors, so the light sensitivity of the device has been lowered than before. It can be extended to longer wavelengths, the photocurrent can be made dramatically larger and louder than before, and a photovoltaic device with extremely high efficiency can be obtained.

In addition, since polycrystalline semiconductors have low resistance, it is possible to use the first layer as an electrode for extracting light commercially.2 There is no need to provide a back electrode as in the conventional method, and costs can be reduced. Moreover, reliability can be improved.

[Brief explanation of drawings]

The drawings show one embodiment of the photovoltaic device of the present invention, and the first
The figure is a cross-sectional view, Figures 2 and 3 are relationship diagrams of the solid phase growth temperature, sheet resistance, and mobility of the first layer, respectively, Figure 4 is a diagram showing the optical absorption coefficient spectrum, and Figure 5 is a diagram showing the relationship between the solid phase growth temperature and sheet resistance and mobility of the first layer. It is a figure showing a collection efficiency spectrum. (2)...first layer, (3)...second layer.

Claims (1)

[Claims] (1) A first layer made of an n-type or p-type polycrystalline semiconductor, and a second layer made of a p-type or n-type amorphous semiconductor heterojunctioned to the first layer. Features of photovoltaic device.