JPS59125669A - Solar battery - Google Patents

Abstract

PURPOSE:To obtain the same effect as a reflection preventive film coated in double without increasing the number of manufacturing steps by satisfying a special inequality among the refractive index n1 of a transparent conductive film, the refractive index n2 of the first conductor layer and the refractive index n3 of the second semiconductor layer. CONSTITUTION:Inequalities of n1<n2<n3 and n3-n2>0.3 are satisfied among the refractive index n1 of a transparent conductive film of, the refractive index n2 of the first semiconductor layer of and the refractive index n3 of the second semiconductor layer of a junction type solar battery in which the first semiconductor layer is formed in contact with the transparent conductive film, the same or different conductive type semiconductor layer as or from the first conductor layer is formed in contact with the first semiconductor layer, and the second semiconductor layer becomes main photocurrent generating region by the junction produced between the first layer and the second layer. For example, an amorphous silicon is formed by a blow discharge decomposition method in the sequence of a P type layer 2, an I type layer 3 and an n type layer 14 on a stainless substrate 1, and an ITO layer 5 is further formed thereon so as to satisfy the above inequalities.

Description

[Detailed description of the invention] The present invention relates to improving the characteristics of solar cells.

Conventionally, various efforts have been made to improve the conversion efficiency of solar cells. In order to increase the amount of light incident on the photocurrent generation area, methods such as roughening the surface or double coating with an anti-reflection film that gradually increases the refractive index from the air to the semiconductor layer reduce manufacturing costs. It's expensive.

In the present invention, the layer on the light incident side is formed so that its refractive index becomes gradually smaller toward the light incident surface than the refractive index of the photocurrent generation region, and the layer is double coated without increasing the number of manufacturing steps. It aims to achieve the same effect as the anti-reflection coating.

The purpose of this is to provide a first semiconductor layer on a transparent four-electrode film, and a second semiconductor layer of the same or different conductivity type as the first semiconductor layer in contact with the first semiconductor layer. The refractive index n1 of the transparent conductive film and the refractive index n1 of the first semiconductor layer of a junction solar cell in which the second semiconductor layer becomes the main photocurrent generation region due to the junction formed between the first semiconductor layer and the second semiconductor layer. Between the refractive index n2 and the refractive index n of the second semiconductor layer, nl
t depends on the inequality of <r+2<n3 and n3-n2>0.3 being satisfied. Nine layers of amorphous silicon are deposited on a stainless steel substrate 1 using glow discharge decomposition method 1 2.1
Layer 3.1 layer 4 are formed in this order. Furthermore, an ITO (indium tin oxide) layer 5 is formed as a transparent conductive film thereon. As described later, the refractive index of amorphous silicon and ITO
Due to the large difference in refractive index between the two, when light 6 enters, there is a large reflection at the interface between the two, which reduces the amount of light reaching layer 1 3, which is the main photocurrent generation area, and deteriorates the characteristics of the solar cell. ing.

FIG. 2 shows a first embodiment of the present invention, and like the following figures, parts common to those in FIG. 1 are designated by the same reference numerals. Nine layers of amorphous silicon are formed on a stainless steel substrate 1 in the order of 2, 1, 3, and 14 by glow discharge decomposition. However, this one layer 14 is made of amorphous silicon containing microcrystalline grains with a size of about 60A. Further on top of that is an ITO layer 5.
Figure 3 shows a second embodiment of the present invention. An ITO layer 5 is formed on a transparent glass substrate 21, and nine layers 22 of amorphous silicon carbide are formed thereon by a glow discharge decomposition method.
, the refractive index of amorphous silicon containing microcrystalline grains formed in the order of 1 layer 3, 1 layer 4 of amorphous silicon, and the aluminum electrode 25 is usually 'the refractive index of amorphous silicon containing microcrystalline grains. 32 is approximately 2.8. At 0.5 μm or less, both increase, but in any case, the difference in refractive index is about 0.4.

On the other hand, the refractive index 33 of ITO is approximately constant, approximately 2.0.

Generally, the reflectance at the interface between two media with different refractive indexes increases as the difference in refractive index increases. The presence of the layer reduces the reflectance.

FIG. 5 compares the measured values of reflectance of solar cells. Curve 41 is the reflectance of a conventional type of solar cell using amorphous silicon as shown in FIG. One-way line 42
is the reflectance of the solar cell shown in FIG. 2, which was formed under exactly the same conditions except that the n-layer amorphous silicon was replaced with an n-layer containing microcrystalline grains. By using n-layers with different refractive indexes, the reflectance decreases and the amount of light reaching the current generation region increases accordingly. This increases the output current of the solar cell.

This situation is exactly the same in the second embodiment using amorphous silicon carbide. As shown in FIG. 4, the refractive index 34 of amorphous silicon-carbide is approximately 2.6 at wavelengths of 0.5 μm or more, which is between the refractive index 31 of ordinary amorphous silicon and the refractive index 33 of ITO. is the value of Therefore, the reflectance of the solar cell shown in FIG. 3 in which this amorphous silicon carbide p-layer is used on the incident side of the first layer 3, which is the main photocurrent generating region, decreases, and the output current increases.

In the above examples, solar cells using amorphous silicon containing microcrystalline grains or amorphous silicon carbide as an additive layer on the light incident side have a different refractive index from normal amorphous silicon. It has been shown that the conversion efficiency increases. Such improvement in characteristics can be obtained when the refractive index of the doped layer on the incident side is two or more smaller than the refractive index of the main photocurrent generating region.

Therefore, in the structure shown in FIG. 2, the content of microcrystalline grains is adjusted in accordance with the refractive index.

The present invention can be applied to a material base in which the refractive index of the doped layer on the light incident side of the photocurrent generation region is different from the refractive index of the photocurrent generation region, or a pn junction between different conductivity types, or between the same conductivity types with different resistivities. Needless to say, bonding may also be used.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of the structure of a conventional solar cell, FIGS. 2 and 3 are cross-sectional views showing two different embodiments of the solar cell according to the present invention, and FIG. 4 is a cross-sectional view showing an example of the structure of a conventional solar cell. FIG. 5 is a diagram showing changes in reflectance depending on wavelength in the solar cell shown in FIG. 1 and the solar cell shown in FIG. 2. 2...79 layers of amorphous silicon, 3...1 amorphous silicon
R15...ITO layer, 14...Amorphous silicon layer containing microcrystalline grains, 22...9 layers of amorphous silicon carbide. Patent applicant Makoto Ishizaka - Kei1'1 (2) 'A-2 Figure? 3 Figure θ3 θ4~ θSθj60'708 (da) nokuj
21 Jaw i (7) L If Bow '7 N O 4 (2) 4/ /-g0.3 0.40S O,60,70S Kump Length (to μ) 7.3 Figure">, q t,. ?0,'?t,0

Claims (1)

[Claims] 1) A gap occurs between a transparent conductive film, a first semiconductor layer that is in contact with the transparent conductive film, and a first semiconductor layer that is in contact with the first semiconductor layer and has the same or different conductivity type as the first semiconductor layer. In a junction type solar cell including a second semiconductor layer which becomes a main photocurrent generating region by junction, the refractive index n1 of the transparent conductive film, the refractive index n2 of the first semiconductor layer, and the refractive index of the second semiconductor layer A solar cell characterized in that the inequality nl < n2 (n3 and n, nl n 0.3) is satisfied between the ratio n3 and nl < n2.