JPH01194370A - Optical power generation device - Google Patents

Abstract

PURPOSE:To reduce a loss and to improve characteristics of a cell by disposing a P-type fine crystal Si layer of a dope factor 0.3-1.0% and of a thickness of 2-6nm on the surface of an N/P boundary between neighboring PIN junction elements. CONSTITUTION:A transparent conductive film 5 is formed on a glass substrate 4, and thereon are formed a P-type amorphous SiC layer 1-a, an I-type amorphous Si layer 1-b and an N-type amorphous Si layer 1-c to constitute a first power generation area. A P-type fine crystal Si layer 6 to which boron is doped at a dope ratio of 0.3-1.0% to a thickness of 2-6nm is formed thereon. Furthermore, a P-type amorphous SiC layer 2-a, an I-type amorphous layer 2-b and an N-type amorphous Si layer 2-c constituting a second power generation area are formed thereon. Lastly, an Al rear-side electrode 3 is formed. A novel improved constitution of such an N/P interface between power generation areas makes it possible to reduce a loss, and to improve cell characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photovoltaic device including an amorphous or microcrystalline semiconductor layer, and particularly to a stacked semiconductor solar cell.

[Conventional technology]

In a conventional photovoltaic device, for example, an amorphous silicon solar cell having a two-layer stacked structure, a first power generation region and a 52nd power generation region are electrically connected in series.

Therefore, in order to obtain high conversion efficiency, it is necessary to make ohmic contact between the n-type doped layer of the first power generation region and the n-type doped layer of the second power generation region.

However, in recent years, the quality of p-type amorphous SiC layers in particular has progressed, and it has become difficult to obtain ohmic contact.

Therefore, in boat fishing, n-type microcrystalline Si and heavily doped p-type amorphous SiC are used as the n-type doped layer and the n-type doped layer that define the n/p interface.

By increasing the doping rate of the n-type doped layer, n/
Although the p-interface becomes an ohmic contact, a narrow band gap of the n-type doped layer and auto-doping of impurities into the i-layer of the second power generation region occur, so that the cell characteristics are not improved.

Furthermore, in Japanese Patent Application Laid-Open No. 60-9178, by using a microcrystalline semiconductor layer as at least one of the n-type doped layer and the n-type doped layer, the recombination current at the n/p interface is increased and the loss is reduced. A method to reduce this has been proposed. However, according to survey tests conducted by the present inventors, this method is extremely ineffective. In other words, (1) Even if the n-type doped layer is made microcrystalline, photovoltaic force and photocurrent are generated at the n/p interface, and loss can hardly be reduced; It was the same.

(2) Although there is some improvement if the p-type doped layer is microcrystallized, the photovoltaic force still remains at the n/p interface.
A photocurrent is generated, and sufficient loss reduction is not achieved.

(3) As the doping rate of the p-type doped layer increases, n
/p junction characteristics are improved, but in this case, autodoping of impurities into one layer of the second power generation region occurs, deteriorating cell characteristics.

In this way, in conventional photovoltaic devices, a p-type amorphous SiC layer with a high doping rate of 0.5% or more is used as a second layer.
When used as a p-layer in a power generation region, characteristic deterioration occurs due to a decrease in the amount of incident light due to a decrease in the optical gap of this layer, or due to autodoping of boron from the p-layer to the first layer. Highly doped p-type microcrystal S
A similar result occurs when using i.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to provide a photovoltaic device with reduced loss and improved cell characteristics by providing a new and improved structure for the n/p interface between power generation regions.

[Failure to solve the problem]

According to the present invention, in a photovoltaic device including a structure in which a plurality of pin junction elements each made of an amorphous or microcrystalline semiconductor layer are sequentially laminated on a transparent conductive layer, adjacent pin junctions Doping rate 0.3 at n/p interface between elements
This is achieved by a photovoltaic device characterized in that a p-type microcrystalline Si layer of ~1.0% and a thickness of 2 to 5% m is interposed.

[For production]

The present invention makes ohmic contact at the n/p interface by interposing a highly doped, extremely thin microcrystalline Si layer at the n/p interface between two adjacent power generation regions, and reduces the amount of light incident on the subsequent power generation region. In addition, the p-type layer in contact with the i-type layer in the subsequent power generation region can be a p-type layer (for example, an amorphous SiC layer) with a normal doping rate, and the dopant content in the p-type layer can be reduced. By preventing autodoping into the type 1 layer, it is possible to improve the characteristics of the power generation region to which this type layer belongs.

In the present invention, p-type microcrystal S1 interposed at the n/p interface
The layer has a doping rate of 0.3-1.0%. This is 0.
If it is less than 3%, rectification occurs at the n/p interface and ohmic contact is lost, and if it exceeds 1.0%, the subsequent p-type layer (for example, p-type amorphous SiC layer) or l-type layer(
For example, autodoping into the type 1 amorphous S1 layer) occurs, resulting in a decrease in photovoltaic properties. Further, the thickness of the p-type microcrystalline S1 layer is 2 to 5n+++. If it is less than 20 m, rectification occurs at the n/p interface and ohmic contact is lost, and if it exceeds 6% m, light absorption loss increases, resulting in deterioration of the photovoltaic characteristics.

[Example 1] As a photovoltaic device according to the present invention, the pin shown in FIG.
A semiconductor solar cell having a structure in which two layers of bonding elements are stacked was manufactured.

A transparent conductive film 5 is formed on a glass substrate 4, and a p-type crystalline 5iC (silicon carbide) layer 1-a and an i-type amorphous Si (silicon) layer 1 are formed on the transparent conductive film 5 by plasma CVD.
-b1 and n-type amorphous Si layer lc were formed in this order to have thicknesses of 15% m, 80% m, and 2 Q nm, respectively, to constitute a first power generation region. Thereon, a p-type microcrystalline S1 layer 6 doped with boron at a doping rate of 0.5% (B2L/5IH4 gas flow rate ratio) was formed to a thickness of 5% m. Furthermore, on top of that, p-type amorphous S constituting the second power generation region
The iC layer 2-a, the l-type amorphous S1 layer 2-bl, and the n-type amorphous S1 layer 2-C were formed to have a thickness of 10% m, 500% m, and 3 Q nm, respectively. Finally, an Aβ back electrode 3 was formed to a thickness of 300% m by electron beam evaporation.

For both the first and second power generation regions, the composition of the mixed gas used to form the p-type amorphous SiC layers (1-a and 2-a) is CH4/5I84 = 7 in terms of volume ratio.
/3 and B2H6/C1l, +SiH4=0.15
%Met. l-type amorphous Si layer (1-b and 2-b)
For 5I84/H2=1/10 (volume ratio), for n-type amorphous Si layer (1-C and 2-C), P)+3/Sl)+4=1/100,
Sl)+4/H2=1/20, (volume ratio of each)
Met. Other plasma CVD conditions include a substrate temperature of 200 m
°C, internal pressure 1.0 to 1.5 Torr, 7 f power 20
W (however, 20 to 100 W for the n-type amorphous Si layer). When an n-type amorphous Si layer was formed with an RF power of 100 W, the layer changed from amorphous to microcrystalline, but the effect of the present invention did not change as will be explained later. The p-type microcrystalline Si layer 5 has a mixed gas composition (volume ratio) of 821 (6
/5I84=0.5%, SiH4/H2=1/
100, and the γf power was 100W.

[Example 2] The semiconductor solar cell shown in FIG. 1 was manufactured in the same manner as in Example 1.

However, the n-type layer (1-c) in the first power generation region was an n-type microcrystalline Si layer.

In FIG. 1, n/p of the p-type doped layer in the second power generation region
By forming an extremely thin highly doped layer 6 only near the interface and forming a normal lightly doped layer 2-a on the first layer side of the second power generation region, an ohmic junction at the n/p interface is obtained, and the It was possible to simultaneously suppress autodoping of dopant into one layer of two power generation regions.

According to the present invention, since the heavily doped layer 6 is formed extremely thin, the absorption of light by the layer is negligibly small, and the amount of light incident on the second power generation region is not reduced. . Furthermore, when forming the first layer 2-b of the second power generation region,
Since it is the low concentration beef 0 layer 2-a that is exposed on the surface, autodoping of impurities into the 1 layer 2-b is suppressed, and the photoelectric characteristics of the second power generation region are not deteriorated.

The method of forming each layer is not only the plasma CVD method but also the photo-C
A VD method, a microwave CVD method, or the like may be used.

Note that the present invention uses a stainless steel substrate instead of a glass substrate.
A ceramic substrate, a polymer film substrate, etc. may be used as the substrate.

As the photovoltaic characteristics of the example, open circuit voltage, short circuit current, fill factor, and conversion efficiency were each measured using conventional measurement methods. The results are shown in Table 1 along with comparative examples. The semiconductor solar cell used in the measurement has an element area of 1.0 Crl.

In Table 1, n, p, a, and μC mean n-type, p-type, amorphous, and microcrystalline, respectively.

Comparative Example 1 is an n-type amorphous Si layer (n-a-
3i) on which a p-type crystalline SiC layer (p
-a-3iC) is directly formed to a thickness of 15%m, and Comparative Example 2 is an n-type microcrystalline Si layer (n-a-3iC) in the first power generation region.
p-type microcrystalline S1 layer (p-AIC-3
i) was directly formed to a thickness of 15% m. In Comparative Example 2, the open circuit voltage is improved compared to Comparative Example 1 due to high concentration doping, but other characteristic values are rather decreased, and in particular, the fill factor is significantly deteriorated, resulting in an imbalance.
In the end, the overall cell characteristics are actually getting worse.

In the photovoltaic device of the present invention, all characteristic values are significantly improved compared to the case without high concentration doping (Comparative Example 1), and there is no imbalance as in the case of high concentration doping (Comparative Example 2). However, the overall cell characteristics are significantly improved.

〔Effect of the invention〕

From the above, by adopting the present invention, the open circuit voltage,
A photovoltaic device with significantly improved cell characteristics such as short circuit current, fill factor, and conversion efficiency can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing an example of a photovoltaic device according to the present invention. 1-a, 'l-a... p-type layer (p-type doped layer), 1-
b, 2-b...l type layer (i type doped layer), 1-c, 2
-c/n-type layer (n-type doped layer), 3... AI back electrode, 4... glass substrate, 5... transparent conductive film,
6...p-type microcrystalline Si layer.

Claims (1)

[Claims] In a photovoltaic device including a structure in which a plurality of pin junction elements made of amorphous or microcrystalline semiconductor layers are sequentially stacked on a transparent conductive layer, the n/
A photovoltaic device characterized in that a p-type microcrystalline Si layer with a doping rate of 0.3 to 1.0% and a thickness of 2 to 6 nm is interposed at the p-interface.