JPS59138386A - Solar battery - Google Patents

Abstract

PURPOSE:To obtain a multi-layer cell structural solar battery of a high efficiency by facilitating the electric connection of a discrete cell by a method wherein a plurality of cells having P-N junctions of semiconductor layers of different forbidden band widths are laminated in planar form to a multi-layer, and the electric connection part of each of the cells is arranged on the surface or the back surface of the main body of the solar battery. CONSTITUTION:The solar battery of a multi-layer is composed of the upper cell semiconductor material 11 and the lower one 12 whose forbidden band widths are different respectively. Here, a P type layer 16 and an N type layer 17 of the upper cell are formed of the material 11, thus generating a P-N junction 13 therebetween. A P type layer 18 and an N type layer 19 of the lower cell are formed of the material 12, thus generating a P-N junction 14 therebetween. In this constitution, the relation of the forbidden band widths Eg1 and Eg2 of the materials 11 and 12 is decided as Eg2<Eg1, and carrier density, thickness, etc. are selected according to desired characteristics. Thereafter, electrodes 21, 22 and 23 are installed on the surface exposed planes of the layers 17, 18, and 19, and a lattice form electrode 20 is formed on the layer 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar cell in which conversion efficiency is increased by stacking pn junctions of semiconductors having different bandgap widths in a planar manner.

Many of the conventional solar cells are
and ``x,'' a homo pn junction structure made of the same materials, GaAs.As long as these single semiconductors are used, solar energy cannot be used effectively, and especially due to the forbidden band width of the semiconductor. Low-energy light can contribute to photovoltaic power generation in solar cells, and the photoelectric conversion efficiency is A
MO (on satellite orbit) maximum approximately 22%, hM/, s
The maximum value is approximately J.

Therefore, in order to achieve even higher efficiency, it is necessary to utilize a wide range of sunlight spectra by using many types of semiconductors with different band gaps. Such a solar cell is shown in FIG. 1 [F]).

There is a so-called monolithic cascade type solar cell in which pn junctions of semiconductors with different forbidden band widths are stacked in multiple layers on the same substrate as individual cells. Here, ko is GaAl
As layer, 3 is p formed in GaAjtAs l@2
In the n junction, Il is a GaAs layer, S is a pn junction formed in GaAs layer G, and 6 is a tunnel junction arranged between layers C and G.

However, the conversion efficiency of the monolithic cascade solar cells produced so far has been significantly lower than what would be theoretically expected.

For example, the pn of the GaAJAs layer shown in FIG.
Although a monolithic cascade solar cell consisting of a junction 3 and a pn junction 5 of a GaAs layer q is theoretically expected to have a conversion efficiency of 25 to 30, the actual efficiency is about 73 to 15. This was much lower than the efficiency of 20 cm in the case of a solar cell made of GaA,s alone. The cause is inside the Ga and AlAs layers and inside the CaA and s layers.
The problem lies in the electrical connection mechanism between these two layers, usually the tunnel junction, in order to effectively take out the optical carriers generated at each pn junction 3 and S within the layer.

In this way, conventional monolithic cascade solar cells have a structure that uses high impurity concentration junctions (tunnel junctions) for electrical connection between each semiconductor layer as an individual cell, so the resistance of the electrical connection increases. However, the conversion efficiency could not be improved because light absorption at the junction with high impurity concentration could not be ignored.

An object of the present invention is to solve these drawbacks and facilitate the electrical connection of individual cells, thereby providing a highly efficient solar cell with a multilayer cell structure.

In order to achieve such an object, the present invention improves conversion efficiency by stacking a plurality of cells having p-n junctions made of semiconductors with different bandgap widths in a multi-layered planar configuration, thereby increasing the conversion efficiency and connecting electrical connections to the surface of the solar cell or the like. Placing it on the back surface facilitates electrode wiring and electrical connection of each cell.

The present invention will be described in detail below using examples with reference to the drawings, but these examples are merely illustrative of the present invention, and it is understood that various improvements and modifications may be made within the scope of the present invention. Of course.

FIG. 2 (■) shows the basic configuration of the solar cell according to the present invention.

First, nine layers 16 and n layers/7. and bottom cell semiconductor material
The pn junctions /3 and /2 respectively formed by λ (p , and Eg2 (<Eg, ), the conduction type of each semiconductor layer (the above-mentioned p-type and n-type can be reversed), the carrier concentration, thickness, etc. shall be determined according to the desired characteristics. The first layer from the light-receiving surface side of the solar panel is a window layer 1 that prevents loss of carriers due to surface recombination.
5. ＠, 2nd and 3rd layers are p (straddle n) layer/B and n (or p) layer/7 consisting of upper cell semiconductor material l/.
The 5th and 5th layers consist of lower cell semiconductor material 7.2.
(yet n) layer/g and n(t or p) layer 19.

Next, electrical connections for each cell are placed on the solar cell surface. As shown in FIG. 2(A), the upper cell p i) Required electrode - is placed on the window layer/upper left. Upper cell n battle) slide'
7g The second group placed on each exposed surface of the window layer/S
It is an anti-reflection coating coated on the surface.

As described above, according to the solar cell of the present invention, since semiconductor layers with different band gaps can be laminated in multiple layers, the sunlight spectrum can be widely used, and the electrical connections of a large number of individual cells can be connected to the surface of the solar cell. Since the solar cells can be arranged, electrical connection of each cell can be easily made in any desired form on the surface of the solar cell. Furthermore, the conventional problem of light absorption at high impurity concentration junctions can be solved.

In order to clarify the effects of the present invention, an upper cell and a lower cell were formed using a combination of MBE (molecular beam epitaxial growth) method and etching method, as shown in Figure a, CB).
Solar cells were fabricated with GaAlAs and GaAs, respectively, where the first layer was GaAlAs and GaAs, where the first layer was GaAlAs and GaAs.
l c , a A S window layer 3S, U and 3 layers are 9 layers 36 and n layer 3 made of Gao, 6AJ, and 4As.
7. The G and 5 layers were a p layer 3g and an n layer 39 made of GaAs, and an antireflection film +p was placed on the window layer 3S to fabricate a multilayer solar cell.

When such solar cells are connected in series, AM/!
When operated under conditions of r, the conversion efficiency was 2g! i%
was gotten. This efficiency is higher than that of conventional GaAjlAs-Ga
AS's monolithic cascade solar cell/tachi,
It is clear that the present invention is extremely superior to the 22 ratio of GaAJAs/GaAs heteroface solar cells.

In the above examples, GaA71As and Ga, A
Although the invention has been described in terms of examples using
X2A71x1Gax2AS+Ga1-y engineering nyAS,
Constituent materials such as -zPz can also be used. Also,
Although the present invention has been explained by taking as an example a multilayer solar cell consisting of one individual cell, it is clear that a multilayer solar cell consisting of three or more individual cells can also be constructed.

Furthermore, as shown in FIG. 3, the main electrical connections 2/, n and N of each cell /A, /7 and 1g, /q of the solar cell according to the present invention are arranged on the back side of the solar cell. You can also. In this case, Figure 2 (G) and [
F]) has the advantage that the loss of light incident on the solar cell due to the surface electrode portion can be reduced.

Figure 2 shows still another example of the structure of the solar cell of the present invention. In the embodiment shown in FIG. 2 (to) or (B) or FIG. 3 of the present invention, the main electrical connections are arranged on the surface, so the series resistance of each semiconductor layer cannot be ignored. Cases also occur. In such cases.

As shown in FIG. 9, for the upper cells /A, /7 and the lower cells /g, /q, for example, the middle of each cell,
That is, a highly electrically conductive semiconductor layer between layer /7 and 1g.

For example, n”(p+) layer S/and p+(n”) layer S
2 is provided in a planar shape, and electrodes 2/ and 2- are provided on the portions of these layers S/ and 3.2 exposed on the surface side of the solar cell main body.
By arranging , series resistance loss can be reduced. Even in this case, the light absorption loss in the highly conductive layer can be ignored since a highly doped layer as in the tunnel junction of a monolithic cascade solar cell is not required.

Furthermore, in the solar cell according to the present invention, it is expected that electrical isolation may be required between each cell, for example, between the upper cell /A, /2 and the lower cell G, /9.

In such a case, as shown in FIG.
, /7 and 1g, /9, that is, between the left and right layers, electrical isolation of each cell is achieved by providing a semi-insulating semiconductor layer 33 in a planar manner.

Note that in this example, the highly electrically conductive semiconductor layer 5 for layer /q
For example, an n+(1)+) layer S is also provided, and the electrode unit 3 is placed on the exposed surface side of this layer/9. Such a semi-insulating semiconductor layer can be easily fabricated by adding impurities such as Fe, Or, or 0 during epitaxial growth using the MBE method, and since a small amount of impurity addition is sufficient, light absorption loss in this layer can be reduced. It is still negligible, and high conversion efficiency can be achieved.

As explained above, in the solar cell of the present invention, the spectral sensitivity band for sunlight is expanded by stacking a plurality of cells having p-n junctions of semiconductors with different bandgap widths in a planar shape. , it has higher efficiency than conventional solar cells, and in addition, in the present invention, part of the electrical connection of each cell is placed on the front or back side of the solar cell body, making electrode wiring and electrical connection of each cell easy. ,
Thus, a multilayer solar cell with high conversion efficiency can be realized.

[Brief explanation of the drawing]

Figures 7 (2) and 2) are cross-sectional views showing two examples of the configuration of a conventional solar cell; Figure 2 (2) is a cross-sectional view showing an example of the basic configuration of a solar cell according to the present invention; Figure 2 (J3) is a sectional view showing one embodiment of the solar cell of the present invention;
FIG. S is a sectional view showing another embodiment of the solar cell of the present invention. /-homo pn junction, 2-=Ga, AlAs layer 1, ? -= pn junction of GaAjlAs layer. G... pn junction between CaAs layer and 5-GaAs layer. 6.Tunnel junction //... Upper cell semiconductor material. /3...lower cell semiconductor material, /3...pn junction for upper cell. /Da... pn junction for lower cell. lS...window layer, /A...upper cell p(n) layer. /7... Upper cell n(p) layer, 1g... Lower cell p(n) layer. /q...lower cell n (p) layer. 〃... Upper cell p(c) required electrode, 2/... Upper cell n(p) required electrode 5... Lower cell p(n) required electrode. Sword... lower cell n) required electrode, 21/,... anti-reflection film. J...Sunlight. 3k −= p −Gao, 2Aj! , 8As layer, 3
6-p-Ga, 6AJ. , 4As layer. , 77-n -Ga, , 6AJ, 4As layer, 3g...
p-GaAs layer 1. 79 ・n-GaAs layer, qθ・=p-Ga, 6A1°, 4As layer electrode. y/-n -Ga, 6A, 4As layer electrode, q2-
Electrode for p-GaAs layer. '43-N-GaAS layer electrode, t...Antireflection film Sl High electrical conductivity n+ (p+) layer. View: Highly conductive p+ (n+) layer, left J...
Semi-insulating layer, 5g... Highly electrically conductive n+ (p+) layer. Patent applicant Nippon Telegraph and Telephone Public Corporation (A) (B) JJLJ+ JNN (B)

Claims (1)

[Claims] 1) A plurality of cells having p-n junctions made of semiconductors with different forbidden band widths are laminated in a multilayer planar shape, and the electrical connection portions of each of the cells are arranged on the front or back surface of the solar cell main body. A solar cell characterized by: 2. The solar cell according to claim 1, further comprising a highly electrically conductive semiconductor layer electrically connected to the cell. 3) The solar cell according to claim 1 or 1, characterized in that a semi-insulating semiconductor layer is provided between each of the cells to electrically isolate the cells. solar cells.