JPS59123278A - Semiconductor solar battery - Google Patents

Abstract

PURPOSE:To contrive to reduce the deterioration of photoelectric conversion efficiency with time by interposing a metallic thin film layer of high purity between a metallic substrate electrode and a semiconductor photovoltaic element. CONSTITUTION:The metallic thin film layer 2 is interposed between the metallic substrate electrode 1 and the photovoltaic element 3 by vacuum deposition, etc. It is desired that the purity of the metal forming the thin film layer 2 is 99.99% or more, and metals such as nickel chromium, platinum, palladium, molybdenum, silver, aluminum are deposited and formed on the substrate 1 by vacuum deposition, sputtering, ion plating, etc. It is preferred that the thickness of the thin film layer 2 is approx. 500-3,000Angstrom . Thereby, the permeation of impurities from the substrate 1 to the photovoltaic element layer 3 is effectively inhibited, therefore the deterioration of characteristics on the physical property of the photovoltaic element 3 can be effectively prevented, and the decrease of photoelectric conversion efficiency after passing a long time becomes small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor solar cell in which deterioration of photoelectric conversion efficiency over time is reduced.

A semiconductor solar cell is a photoelectric conversion element that accelerates electrons and holes excited inside a semiconductor photovoltaic element by the energy of photons using the internal electric field of the semiconductor photovoltaic element and extracts them as a current flowing through an external circuit. It is. Semiconductor solar cells and recently amorphous silicon (a-3i)
Solar cells have attracted attention and are being extensively researched. This is a solar cell using a-3i as a photovoltaic element.

The reason why a-3i solar cells are attracting attention is because of their low cost.
, and that it is easy to increase the area, and a-3
i is due to the fact that the light absorption coefficient for light with a wavelength near 500 nm (-1), which is the peak of the energy distribution of sunlight, is about one order of magnitude larger than that of single crystal silicon.a-3
i solar cells consider dieminite recombination for photoexcited carriers. Therefore, in order to apply the electric field to most of the a −3i thin film, the 1)i
An n-junction or, schematically, a Schottky junction having a structure in which the p part of a pin junction is replaced with metal is used. In this specification, the explanation will be given below using an a-3i solar cell.

When a-3i solar cells are classified by the type of substrate, they are classified into those using metal as the substrate and those using a material with good light transmittance such as glass. The present invention relates to improvements in solar cells using metal substrates. In such a solar cell, the side on which the substrate is not located serves as the light-receiving surface. In addition,
In a solar cell using a substrate made of a material with good light transmittance, the substrate side is the light-receiving surface.

FIG. 1 schematically shows an example of the configuration of a conventional a-3i solar cell using a metal substrate.

As shown in Figure 1, the conventional A-8I using a metal substrate
The solar cell consists of a metal substrate 1, a photovoltaic cable 3 consisting of an a-3i thin film layer sequentially formed on the metal substrate 1, and a transparent electrode 4. That is, in the conventional a-3i solar cell,
The metal substrate 1 and the a-3i thin film layer are in direct contact. Here, as the material of the metal substrate 1, stainless steel is generally used in consideration of good resistance, but other materials such as iron and aluminum are also used.

Conventional solar cells with such a configuration have had a problem with a decrease in photoelectric conversion efficiency after long-term use. For example, the photoelectric conversion efficiency was 8.30% at the time of production, but it was 100%.
It decreased to 7.28% after hours and 6.47% after 300 hours.

The inventors have considered various reasons for this.

Figure 3 is a diagram showing the distribution state of sodium ions applied to a conventional solar cell in the thickness direction.
(b) shows the solar cell after use for 100 hours, and (C) shows the photo after 300 hours of use. From FIG. 3, the cause of the decrease in photoelectric conversion efficiency is the sodium ions (in Na) and potassium ions (in Na) contained in the metal substrate 1.
It is believed that this is because impurities such as K+), calcium ions, and Ca2+) penetrate into the photovoltaic element 3 over time, and these impurities form impurity units, which deteriorate the physical properties. I've come to a conclusion.

For this reason, the inventors of the present invention have conducted various trials to prevent impurities from penetrating. As a result, the inventors have found that: - high-purity nickel chromium was added between the metal substrate 1 and the photovoltaic cable 3 consisting of the a-3i thin film layer; It has been discovered that by interposing a thin film of metal such as (Ni-Cr'), the penetration of the impurities from the metal substrate 1 into the photovoltaic element 3 can be efficiently suppressed. Based on this knowledge, the present invention having the following configuration was devised.

FIG. 2 is a diagram schematically showing an example of the configuration of the semiconductor solar cell of the present invention. As shown in FIG. 2, the semiconductor solar cell of the present invention includes a metal substrate 1, a metal thin film layer 2 sequentially formed on the substrate 1, a semiconductor photovoltaic element 3,
A transparent electrode 4 (M) is formed.

Here, in J-3, the veneer 1 functions as one electrode and as a reinforcing material to ensure the strength of the solar cell.
It functions as a table on which the metal thin film layer 2 is deposited. In order to function as an electrode, higher conductivity is better. Increasing the thickness of the substrate 1 improves the strength of the solar cell. However, if it is desired to provide flexibility to the solar cell, the thinner the material, the better, and the thickness is preferably about 10 to 60 μII. As the substrate 1, stainless steel, aluminum, iron, copper, brass, or foils of these metals are suitable.

The metal thin film layer 2 is made of Na contained in the substrate 1.
It has a function of suppressing impurity forces (such as K+, Ca2+, etc.) from penetrating into the semiconductor photovoltaic element 3. The higher the purity of the metal forming the thin film layer 2, the better, and desirably 99.99% or more. If the purity is low, Na”, K+,
This is because if a large amount of impurities such as Ca2+ is contained, the impurities will penetrate into the semiconductor photovoltaic element 3. A thin film layer 2 is formed on the substrate 1 with nickel chromium<Ni-Cr
), platinum (Pt), palladium (Pd), molybdenum (MO), silver (AC+>, aluminum (A1), etc.) is deposited by vacuum evaporation, sputtering, ion plating, etc. According to experiments, the thickness of the thin film layer is about 500 to 3000 mm.

The photovoltaic element 3 must have an internal electric field that separates excited electrons and holes. This internal electric field is p
This occurs through an in junction, a pn junction, a Schottky junction, a heterojunction, etc., and in the a-3i solar cell, a p in junction or a Schottky junction is used as described above. a-3i The thin film layer 3 is formed by forming the metal '?' by plasma CVD using glow discharge. 7! j membrane layer 2
can be formed on top.

The transparent electrode 4 has a function as the other electrode with respect to the substrate 1, which is the one electrode. Therefore, the higher the conductivity, the better. Furthermore, since the transparent N-pole 4 serves as a light-receiving surface, the higher the light transmittance, the better. As the transparent electrode 4, an ITO film that is a mixture of indium oxide and tin dioxide, a tin dioxide film, or the like can be used. These can be formed by depositing on the a-3i thin film by electron beam or sputtering.

The transparent electrode 4 may have a two-layer structure consisting of a relatively thin tin dioxide film and a relatively thick ITO film in order from the a-3i thin film layer 3 side. This is because tin dioxide does not degrade the a-8i thin film relatively well, while ITO has a lower resistance than tin dioxide. Therefore, in order to make the transparent electrode 4 low in resistance and to make the a-8i thin film of high quality, it is preferable to use the above-mentioned two-layer structure. Note that the collecting electrode 5 may be formed on the transparent electrode 4 by depositing a low-resistance metal such as aluminum in a comb shape. This collector electrode 5 has the effect of reducing the series resistance of the solar cell.

In the amorphous semiconductor solar cell of the present invention having the above configuration, penetration of impurities from the substrate 1 into the photovoltaic element layer 3 is effectively suppressed, so that deterioration of the physical properties of the photovoltaic element 3 is prevented. is also effectively prevented. Therefore, the photoelectric conversion efficiency after a long period of time is also excellent.

It is extremely difficult to make the A3 metal substrate electrode 1 have a high purity of 99.99% or higher. Therefore, penetration of impurities can be efficiently suppressed only by interposing the metal thin film layer 2 between the metal substrate electrode 1 and the photovoltaic element 3 by vacuum deposition or the like as in the present invention.

The present invention will be explained in detail below.

First Embodiment FIG. 2 is a schematic cross-sectional view of an a-8i solar cell according to a first embodiment of the present invention.

The a-3i solar cell of the first embodiment uses stainless steel foil as the metal substrate 1 shown in FIG.
The J film layer 2 is made of nickel chromium (Ni-Cr), the photovoltaic element 3 is made of a-3i p10 heavy alloy, and the transparent electrode 4 is made of ITO and a 3N layer 2. Note that the thickness of the Ni-Cr layer was 1500.

The pin junction of a-3i is 0 layer 33 in order from the light receiving surface side.
．． It is a so-called similar type with 1 layer 32.0 layers 31,
The transparent electrode 4 made of ITO and 81102 is composed of ITO layers 42, 5, 02, 41, etc. in order from the light-receiving surface side.

In addition, an aluminum collection electrode 5 is placed on the transparent electrode 4.
is formed into a comb shape.

Figure 4 is a graph showing the distribution of Na + concentration in the thickness direction of the a-3i solar cell of the first example, with Figure 4 (a) at the time of production and Figure 4 (b) after 100 hours. After the elapse of time, <C> in the figure represents the time after 300 hours have elapsed. Here, the measurement of N a + 19 degrees is performed using SIMS (Second
ary ■on Mass 3pectrme
ter). In addition, the table shown at the end shows the effects of the conventional a-3i solar cell without a metal thin film layer, the a-3i solar cell of this first example, and the a-8i solar cell of the example described below under AM1 irradiation. It shows the transition of photoelectric conversion efficiency. Figure 5 shows the transition of charge conversion efficiency of the conventional A-8i solar cell and the A-3I solar cell of the first embodiment, and the transition of N a + I layer 1 degree at the boundary between the N layer and I layer on the horizontal axis. It is a diagram expressed in a semi-logarithmic graph using the inter-verse axis. Here a5 and Na"ilJ degree as nfJ and i
The reason why the Na+ concentration at the layer boundary was set to 1 to 1 is because a-3
In the i-solar cell, one layer mainly contributes to photoelectric conversion, so this layer was chosen as its representative point.

From FIG. 5, it seems that there is a correlation between the decrease in photoelectric conversion efficiency and the increase in Na+ concentration.

For example, in a conventional A-3I solar cell, the Na "1 degree" at the boundary between the n-layer and the i-layer is 7.4X1'0-12 (at the time of production), 1.3xlO-"<100 hours later), 2°4X
10-1'<300 hours), and correspondingly, the photoelectric conversion efficiency increased to 8.30% (manufactured as>,,7゜2).
It decreases to 8% (after 100 hours) and 6.47% (after 300 hours). On the other hand, in the a-3i solar cell of the first embodiment, Na
+ Density is 6.0X10-' (at the time of production), 6.2X1
0-12 (after 100 hours), 6.3X10-”
(after 300 hours), the photoelectric conversion efficiency hardly increased, and the photoelectric conversion efficiency was 8.25% (at the time of production), and 8.15% (after 100 hours).
, 8.10% (after 300 hours), which hardly decreases1. Using Figure 5, the charging conversion efficiency is 1/e (e
is the base of the natural logarithm).
The conventional a-3i solar cell has a battery life of about 1,200 hours, while the a-3: solar battery of the first embodiment has a battery life of 16,300 hours. That is, the life of the a-3i solar cell of the first embodiment is much longer than that of the conventional a-3i solar cell. This is 1
It is thought that this effect is due to the fact that the amount of Na+1lii1 degree that falls into the layer hardly increases.

Next, FIG. 4(a), (1)), and (C) are compared to the conventional a
Compare with Figure 3 (a), (1)), and (C) showing the distribution of I'Ja'' 1 degree for the -3i solar cell.At the time of production, 1
After 00 hours and after 300 hours, the Na+ concentration of the a-3i solar cell of the first example decreased rapidly in the Ni-Cr layer, and as a result, the N concentration in one layer, which contributes to photoelectric conversion, decreased rapidly.
It can be seen that the a10 concentration is lower. On the other hand, in the conventional a-3i solar cell, since Ni-Cr@ is not present, the curve of the graph is gentle and the concentration of Na0 in one layer is high.

From the above, the a-3i solar cell of the first embodiment is made of Ni-C
It can be seen that as a result of the r-layer suppressing the penetration of Na+ into the first layer, the photoelectric conversion efficiency hardly decreases even after long-term use.

The a-3i solar cell of this example was manufactured as follows.

(1) Prepare a stainless steel foil with a thickness of 50 to 80 μm and an area of 10 cm x 10 cm square as the metal substrate 1,
Ultrasonic cleaning, electric field to reduce surface roughness to 0.5 μm or less? t
After polishing and ultrasonic cleaning again, 80% Ni and Cr2O% were deposited on the stainless steel foil by electron beam evaporation.
, "to" 4-1 N1-Cp with a purity of 99.99% or more
A 1500 AJ tube was deposited under a vacuum of O-6 Torr.

2) 1) Type a S was formed on the NiCr film 2 by glow discharge decomposition using a 13.56 MHz high frequency power source.
! Thin film 31 was grown by 300 to 500 people. As the residue, silane (Stl-14): Bosph rn (1'H3)
): Argon (Ar) -10:0°01~0.3:90
Using a mixed gas, the conditions were a vacuum degree of 0°1 to 1 TOrr, a high frequency power density of 1 to 80 ITIW/Cm2, and a stainless steel foil temperature of 270 to 300°C.

(3) I-type a-3i thin film 32 is deposited on the n-type a-3i thin film 31 by a glow discharge decomposition method of 0.5 to 0.5%.
Growth of 8 μm was avoided. Silane (SiHa) for gas doji:
Using a mixed gas of argon (Ar) = 10:90,
The degree of vacuum, high frequency power density, and humidity of stainless steel foil are (2
).

(4) Using the glow discharge decomposition method, the p-type a-3i barrier film 33 is converted into the i-type aS! 100-3 on ell*32
00 people grew. Gases include silane (SiH4), nitrogen diphorane (B2H6): methane (CH4): argon (Ar) -10: 0.01~0°3=2~4:8
A mixed gas of 6 to 88 was used. The degree of vacuum, high frequency power density, and temperature of the stainless steel foil were the same as in (2).

5) Said P type a-3iml! On 33, ITt degree 99
99% tin dioxide was deposited by electron beam evaporation in a vacuum of 10"-4 to 1Q-6 Torr, and ITO42 (In 20") was deposited on the tin dioxide 41.
3.93~95%:5n025~7%) 500~30
Similarly to the thickness of 00, 1
Deposition was performed below 0''-4 to 10-'Torr.

(6) Apply 2 top coats on the 4 ITO films, 10-7～
A1 by electron beam evaporation method under 105 Torr.
The comb-shaped collecting electrode 5 was formed by depositing 2,000 to 5,000 people.

Second Example The a-3i solar cell of the second example is the a-3i solar cell of the first example.
It is almost the same as the i solar cell. The jaw pressure conditions are also similar.

The a-3i solar cell of the second embodiment is the a-3i solar cell of the first embodiment.
The difference from a solar cell is that serif'den (MO) is used as the +Δ layer of the metal thin film layer 2.

d′3 after long-time use of the a-3i solar cell of the second embodiment.
As shown in the table, the photoelectric conversion efficiency is also excellent as in the case of the first embodiment. Further, the characteristic curve representing the concentration of impurities was also similar to that shown in FIG. 4 of the first example.

Even when aluminum (A+>) was used in the metal thin film layer 2 instead of Mo, similar effects were obtained as shown in the table.

To summarize, the present invention provides a semiconductor solar cell using a metal as a substrate, in which a thin film layer of high purity metal is interposed between the substrate and a semiconductor photovoltaic element.

Table (Photoelectric conversion efficiency) <Durability test at 90°C and 95% humidity. The thickness of the Ni-Cr layer, MO layer, and A1 layer was 1,500 layers).As is clear from the detailed description in the examples, the semiconductor solar cell of the present invention is designed to prevent impurities from flowing from the substrate to the semiconductor photovoltaic element. Penetration is efficiently prevented.

Therefore, the impurity concentration of the photovoltaic element does not increase even after a long period of time has elapsed. As a result, it has excellent photoelectric conversion efficiency.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view of a conventional semiconductor solar cell, Fig. 2 is a schematic cross-sectional view of a semiconductor solar cell according to the first embodiment of the present invention, and Fig. 3 is a sodium ion concentration in a conventional a-3i solar cell. FIG. 3(a) shows the distribution at the time of production, FIG. 3(b) shows the distribution after 100 hours, and <C> shows the distribution after 300 hours. FIG. 4 is a diagram showing the distribution of sodium ion concentration in the A-8T solar cell of the first embodiment of the present invention, and FIG.
The figure (b) shows the distribution after 100 hours, and the figure (C) shows the distribution after 300 hours. Figure 5 shows the transition of the photoelectric conversion efficiency of the conventional a-3i solar cell and the a-3i solar cell of the first embodiment, and the transition of the Na'' concentration at the boundary between the 0 layer and 1@, with the horizontal axis It is a diagram expressed on a semi-logarithmic graph as a time axis. 1...Metallic substrate electrode 2...Metal thin Ilx layer 3...Semiconductor photovoltaic element 31...11 layer 32...
i layer 33...0 layer 4...transparent electrode'
11 =-S n O2 layer 42- I T 0 layer 5...
・Collecting electrode Figure 1 Aki・, 2 Figure 5-1 Figure 5 (Time)

Claims (1)

[Scope of Claims] <1> A semiconductor solar cell comprising a metal substrate electrode, a semiconductor photovoltaic element sequentially formed on the substrate electrode, and a transparent electrode, wherein the substrate electrode and the semiconductor photovoltaic element are formed in sequence on the substrate electrode. A semiconductor solar cell characterized by a highly pure metal thin film layer interposed between the power element and the power element. (2) The semiconductor solar cell according to claim 1, wherein the semiconductor photovoltaic device is an amorphous semiconductor photovoltaic device. (3) The high-purity metal thin film layer is composed of 99.99% or more of niracle chromium (Nl-Cr).
, platinum (Pt), palladium (Pd), molybdenum (M
O>, silver (A!II>), and aluminum (A1). (4) The semiconductor solar cell according to claim 1, wherein the metal thin film layer has a thickness of 500 to 300 O. The semiconductor solar cell according to item 1.