JPH01280367A - solar cells - Google Patents

Abstract

PURPOSE:To obtain a solar cell whose crystallinity in an active region is good, whose quality of a GaAs/AlxGa1-xAs interface is good, whose recombination rate of a carrier in an interface is small, whose BSF effect is high and whose photoelectric conversion efficiency is high by a method wherein an intermediate layer generating a BSF effect is constituted of a superlattice layer whose lattice constant is the same as that of a first semiconductor layer. CONSTITUTION:In a solar cell provided with an intermediate layer 2, generating a BSF effect, between a substrate 1, of a first conductivity type, and a second semiconductor layer 4, of a second conductivity type, formed on the substrate 1 and a first semiconductor layer 3, of the first conductivity type, forming a p-n junction, the semiconductor layer 2 is constituted of a superlattice layer whose lattice constant is the same as that of the first semiconductor layer 3. For example, an AlxGa1-xAs/GaAs superlattice layer 2 as an intermediate layer of a first conductivity type is formed on a GaAs substrate 1 of the first conductivity type; a GaAs layer 3 of the first conductivity type and a GaAs layer 4 of a second conductivity type are formed on it; a p-n junction is formed. In addition, an AlyGa1-yAs window layer 5 of the second conductivity type and an antireflection film 6 are formed on them; a contact hole is formed in one part of them; an upper-part electrode 7 and a lower-part electrode 8 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solar cell with improved conversion efficiency.

[Conventional technology]

Figure 2 shows the conventional BSF (Back 5urfac
FIG. 2 is a cross-sectional view showing the structure of an example of a field type GaAs solar cell.

In this figure, 1 is a GaAs substrate of the first conductivity type, 2a
is AflXGal-XAs as the first conductivity type intermediate layer.
Layer 3 is GaAs as the first semiconductor layer of the first conductivity type.
layer 4 is GaAs as a second semiconductor layer of the second conductivity type.
Layer 5 is AJ! , Ga, -.

An As window layer, 6 an antireflection film, 7 an upper electrode, and 8 a lower electrode.

This conventional solar cell has a first conductivity type AA, Ga, -xAs layer 2a provided on a first conductivity type GaAs substrate 1, and a first conductivity type GaAs layer 3. A second conductivity type GaAs layer 4 is provided to form a pn junction. Furthermore, on top of that are second conductivity type An, Ga, -,
Although an As window layer 5 and an antireflection film 6 are provided, some of them are etched away to form a contact hole. An upper electrode 7 is provided within this contact hole, and a lower electrode 8 is provided below the GaAs substrate 1.

In the solar cell with this structure, since the Afl, Ga, -xAs layer 2a is provided between the GaAs substrate 1 and the GaAs layer 3, the reverse saturation current (Io) of the pn junction is effectively reduced by the BSF effect. As a result, the open circuit voltage (VOC) of the thick ISM cell increases and the light decreases. Layers 3 and 4 have different lattice constants A, ex
Ga+-, must be grown on the cAs layer 2a, its crystallinity deteriorates, and GaAs/Any G
Since the quality of the a+-x As interface is also poor, there are problems in that the recombination rate of carriers is high, the BSF effect is not sufficiently obtained, and the photoelectric conversion efficiency is low.

This invention was made to solve these problems, and has good crystallinity in the active region and GaAs/AJ2
．． The quality of the Gap-xAs interface is also good, the recombination rate of carriers at the interface is low, the BSF effect is high, and the solar cell according to the present invention has a high photoelectric conversion rate.
The intermediate layer that produces the effect is composed of a superlattice layer whose lattice constant is the same as that of the first semiconductor layer.

(Function) In the present invention, the crystallinity of the first semiconductor layer grown on the intermediate layer is improved, and good interface characteristics are obtained.

〔Example〕

FIG. 1 is a sectional view showing the structure of an embodiment of the solar cell of the present invention.

In this figure, 2 is A℃8Gap-X as the intermediate layer.
It is an As/GaAs superlattice layer.

The basic structure and operation of the solar cell of this invention are similar to those shown in FIG. 2, but the intermediate layer is made of AuXGa,
-The difference is that an XAs/GaAs superlattice layer 2 is used.

That is, in this invention, the GaAs layer 3 which is the active region
．． 4 is AJ2.4 with uniform lattice constants. Ga+-XAs/G
Since it is grown on the aAs superlattice layer 2, the GaAs layer 3
．． The crystallinity of AnxGa, - of the uppermost layer of superlattice layer 2 is improved.

Very good GaAs substrate J:1XGa, -XAs interface characteristics can be obtained between As and the GaAs layer 3.

Therefore, in addition to increasing the recombination rate, AnxGa
, -, the BSF effect due to the As/GaAs superlattice layer 2 is A
This is higher than the BSF effect due to the flXGat-xAs/GaAs single layer, improving the open circuit voltage (VC) of the solar cell and improving the photoelectric conversion efficiency.

(Effects of the Invention) As explained above, in this invention, the intermediate layer that causes the BSF effect is composed of a superlattice layer that has the same lattice constant as the first semiconductor layer, so that in addition to reducing crystal defects, the BSF effect is This has the effect of increasing the developed end voltage and improving the photoelectric conversion efficiency.

[Brief explanation of the drawing]

FIG. 1 is a structural sectional view showing the structure of an embodiment of the solar cell of the present invention, and FIG. 2 is a sectional view showing the structure of an example of a conventional solar cell. In the figure, 1 is a GaAs substrate, 2 is an AJZXG a
1-, As/GaAs superlattice layer, 3 and 4 are GaAs layers, 5 is Aj2. Ga, -, As window layer 6 is an antireflection film. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Masuo Oiwa (2 others) Figure 1 Figure 2 Procedural amendment (voluntary) 1. Indication of case: Japanese Patent Application No. 111221/1988 2.
Title of the invention Solar cell 3, relationship to the amended case Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Moriya Shiki, representative of Mitsubishi Electric Corporation 4, agent residence Address: 2-2-3-5 Marunouchi, Chiyoda-ku, Tokyo
, 71n positive versus Shigeaki, column 6 for detailed description of the invention of ig5 and brief description of the drawings, ? In positive content (11 Specification, page 5, line 7, "In addition to the recombination Mi degree becoming thicker," is changed to "In addition to the recombination speed becoming smaller,"?I
! 1 Correct. (2) Similarly, r(Vc)J on page 5, line 11, r(Vo
c) Correct with J. (3) Similarly, on page 6, line 7, “It is a preventive film.”
In the prevention film, 7 is an upper electrode, and 8 is a lower electrode. and correct it. that's all

Claims (1)

[Claims] (1) BSF effect between a substrate of a first conductivity type and a first semiconductor layer of a first conductivity type that is provided on this substrate and forms a pn junction with a second semiconductor layer of a second conductivity type. What is claimed is: 1. A solar cell comprising an intermediate layer that generates a lattice constant, wherein the intermediate layer is a superlattice layer having a lattice constant that is the same as that of the first semiconductor layer.