JP2004095881A - Thin film solar cell - Google Patents

Abstract

A thin-film solar cell capable of improving photoelectric conversion efficiency by increasing the amount of sunlight that can be used in a short wavelength region of light is provided.
A thin-film solar cell according to the present invention includes a transparent conductive layer formed of indium oxide containing zinc, formed on a surface of a substrate, and a p-layer, an i-layer, and an optical layer that convert light energy into electric energy. It has a unit cell 106 composed of an n-layer 105 and a collecting electrode layer 107 for extracting converted electric energy.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solar cell having a structure for improving power generation efficiency.
[0002]
[Prior art]
With the deterioration of the global environment in recent years, there is a pressing need to review the current energy production system relying on biofuels such as coal and oil or nuclear power.
Here, the former emits carbon dioxide, which causes global warming, when burning fuel, and the latter has difficulty in handling the radioactivity of uranium fuel.
For this reason, photovoltaic power generation is being promoted and promoted as an earth-friendly clean power source among new energies expected to be put to practical use.
[0003]
At present, a power generation system using sunlight has attracted attention as a clean and easily usable energy source.
Moreover, sunlight can be regarded as an inexhaustible energy source that does not need to be depleted for the time being, and therefore has an advantage over other resources in terms of continuity of energy use.
The earth is not a perfect sphere, but a spheroid extending in the direction of the rotation axis. When the short radius of the ellipsoid is used, the solar radiation energy falling on the surface of the earth is about 1.3 × 10 3 per unit time. ¹⁴ kW / year.
[0004]
This amount of energy is, for example, approximately 90 times the global energy consumption per unit time in 1995.
However, the solar radiation energy per unit time received on the ground is 1 kW / m ² Therefore, a large area is required to obtain sufficient generated power.
In order to reduce the installation area of the solar cell panel and effectively use land, it is desired to improve the conversion efficiency of the solar cell.
As solar cells become more widespread, even a slight increase in efficiency will make a significant difference in overall power generation costs. Therefore, improving the conversion efficiency of solar cells is an important issue.
[0005]
The solar radiation energy spectrum distribution obtained on the earth's surface rises from an ultraviolet region around a wavelength of 300 nm and has a maximum radiation energy around 500 nm in a visible region.
The intensity of the radiant energy monotonically decreases from 500 nm onward to an infrared light region of about 2.7 μm.
For this reason, in order to perform efficient solar power generation, a solar cell that can effectively utilize solar radiation energy over a wide region of the solar radiation energy spectrum distribution is required.
In particular, since the radiation energy intensity in the short wavelength region is high, it is important to increase the photoelectric conversion efficiency of the solar cell in the short wavelength region.
[0006]
[Problems to be solved by the invention]
However, in a unit cell of a solar cell composed of p-type, i-type, and n-type semiconductors, the i-layer can use only solar radiation energy in a specific wavelength region defined by the band gap width.
For this reason, Japanese Patent Publication No. 63-48197 proposes a solar cell having a structure in which a plurality of semiconductors having different band gap widths, that is, a plurality of semiconductors having high sensitivity in a specific wavelength region are stacked.
[0007]
This has a structure in which i-layers of a plurality of stacked unit cells are arranged in ascending order of the energy gap from the side closer to the light incident side.
Here, from the viewpoint of photoelectric conversion efficiency, it is efficient to use a microcrystalline silicon semiconductor for the i-layer in the long wavelength region, while an amorphous silicon semiconductor or amorphous silicon carbide semiconductor is used in the short wavelength region. It is used.
In a conventional solar cell, indium oxide containing tin has been widely used as a material used for a conductive layer.
[0008]
The conductive layer made of indium oxide containing tin has a property that light transmission in a short wavelength region is not sufficient, that is, a ratio of light absorbed in a short wavelength region is high.
For this reason, in the conventional solar cell, when indium oxide containing tin is used for the conductive layer, light absorption is large in the short wavelength region of the solar radiation energy spectrum distribution, and reaches the semiconductor layer that performs photoelectric conversion. There is a problem that the amount of light is reduced and the photoelectric conversion efficiency in the short wavelength region is reduced.
[0009]
The present invention has been made under such a background. In consideration of the fact that the solar radiation energy spectrum has the maximum value in the short wavelength region, the amount of sunlight available in the short wavelength region is increased, An object of the present invention is to provide a solar cell capable of improving conversion efficiency.
That is, by combining a semiconductor having a high photoelectric conversion efficiency in the short wavelength region of the solar radiation energy spectrum distribution and a conductive layer material having low light absorption in the short wavelength region of the solar radiation energy spectrum distribution according to the present invention. In addition, it is possible to provide a solar cell having high photoelectric conversion efficiency in a short wavelength region of the solar radiation energy spectrum distribution.
[0010]
[Means for Solving the Problems]
The thin-film solar cell of the present invention has at least one photoelectric conversion unit that converts light energy into electric energy, and a conductive layer formed on both sides of the photoelectric conversion unit, one of which is made of indium oxide containing zinc. It is characterized by the following.
In the thin-film solar cell of the present invention, the conductive layer includes a transparent conductive layer made of indium oxide containing zinc, and a collection electrode layer for extracting electric energy generated by the photoelectric conversion unit together with the transparent conductive layer. It is characterized by the following.
[0011]
In the thin-film solar cell of the present invention, the photoelectric conversion unit is a p-layer made of p-type semiconductor silicon and intrinsic semiconductor silicon, and the amorphous silicon matrix has a microcrystal having a particle size of 1 nm to 15 nm. It is a unit cell comprising an i-layer containing silicon and an n-layer which is n-type semiconductor silicon.
In the thin-film solar cell of the present invention, the photoelectric conversion unit is a p-layer made of p-type semiconductor silicon and intrinsic semiconductor silicon, and the amorphous silicon has a volume fraction of this amorphous silicon. It is a unit cell including an i-layer containing 5% or less of microcrystalline silicon and an n-layer which is n-type semiconductor silicon.
[0012]
In the thin-film solar cell of the present invention, the photoelectric conversion unit is a p-layer made of p-type semiconductor silicon and intrinsic semiconductor silicon, and the amorphous silicon matrix has a microcrystal having a particle size of 1 nm to 15 nm. It is characterized in that a plurality of unit cells each composed of an i-layer containing silicon and an n-layer made of n-type semiconductor silicon are stacked.
In the thin-film solar cell of the present invention, the photoelectric conversion unit is a p-layer made of p-type semiconductor silicon and intrinsic semiconductor silicon, and the amorphous silicon has a volume fraction of this amorphous silicon. A plurality of unit cells each including an i-layer containing 5% or less of microcrystalline silicon and an n-layer of n-type semiconductor silicon are stacked.
[0013]
The thin-film solar cell according to the present invention is characterized in that in the plurality of stacked unit cells, the film thickness is sequentially increased from the unit cell closer to the light incident side to the farther unit cell.
The thin-film solar cell according to the present invention is characterized in that in the plurality of stacked unit cells, at least one unit cell i layer is a thin film formed of microcrystalline silicon.
The thin-film solar cell of the present invention is characterized in that in the plurality of stacked unit cells, the i-layer of at least one unit cell is a thin film of silicon containing germanium or tin.
[0014]
The thin-film solar cell according to the present invention is characterized in that, in the semiconductor unit cell, a p-layer, an i-layer, and an n-layer are sequentially stacked from the light incident side.
The thin-film solar cell of the present invention is characterized in that, in the unit cell of the semiconductor, an n-layer, an i-layer, and a p-layer are sequentially stacked from the light incident side.
[0015]
The thin-film solar cell of the present invention is characterized in that the light transmittance of the conductive layer of indium oxide containing zinc is 75% or more at a wavelength of 380 nm.
The thin-film solar cell of the present invention is characterized in that the conductive layer and the photoelectric conversion unit are formed on a plastic film substrate surface.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a laminated structure of each thin film of a solar cell according to one embodiment of the present invention.
In FIG. 1, a solar cell 100 is formed by sequentially stacking a unit cell 106 including a substrate 101, a transparent conductive layer 102, a p-layer 103, an i-layer 104, and an n-layer 105, and a collecting electrode layer 107.
That is, the transparent electrode layer 102 and the collecting electrode layer 107 are formed on both sides of the unit cell 106.
[0017]
When sunlight enters from the back side of the substrate 101, a transparent conductive layer 102 is formed on the surface of the substrate 101 as shown in FIG.
On the surface of the transparent conductive layer 102, a unit cell 106 is formed in the order of the p layer 103, the i layer 104, and the n layer 105.
The unit cell 106 converts light energy of incident sunlight into electric energy.
[0018]
In the unit cell 106, electrons and holes are mostly generated in the i-layer 104, and electrons and holes are efficiently distributed to the p-layer 103 and the n-layer 105 by the internal electric field effect of the i-layer 104. (The same applies to unit cells 206 and 210 in solar cell 200 having a multi-layer structure shown in FIG. 2 described later).
Finally, a collecting electrode layer 107 for extracting electric power (electric energy) generated by photoelectric conversion is formed on the surface of the n-layer 105.
[0019]
That is, the unit cell 106 for converting the light energy of incident sunlight into electric energy is sandwiched between the transparent conductive layer 102 and the collecting electrode layer 107 for extracting electric energy.
Here, in the transparent conductive layer 102, a transparent transparent conductive layer is used in order to supply sunlight to the unit cell.
When efficiently using light in a wide wavelength range of sunlight, a solar cell 200 having a structure in which a plurality of unit cells (unit cells 206 and 210) are stacked as shown in FIG. 2 is manufactured.
The transparent conductive layer 102 and the collecting electrode layer 107 are formed on both sides of the unit cells 206 and 210.
[0020]
In the case where a plurality of unit cells are formed, the i-layers are arranged in ascending order of the energy gap from the side closer to the light incident surface.
Assuming that light is incident on the solar cell 200 in the unit cells 206 and 210 from the top in the figure, the i-layer 204 of the unit cell 206 near the light incident side is the i layer 204 of the unit cell 210 far from the incident surface. The thickness is smaller than that of the layer 208.
That is, the thickness of the i-layer of each stacked unit cell is increased in order from the unit cell closer to the sunlight incident side to the farther unit cell so that the amount of incident light is equal. Is done.
For example, in solar cell 200, i-layer 208 is thicker than i-layer 204.
[0021]
2, the configuration of each unit cell 206 and 210 is the same as that of the unit cell 106 of FIG. 1. The unit cell 206 includes a p-layer 203, an i-layer 204, and an n-layer 205. 207, an i-layer 208, and an n-layer 209 (the thickness of each layer is different as described above).
In the solar cell 100 of FIG. 1 and the solar cell 200 of FIG. 2, when sunlight enters from the opposite direction (the lower direction in each figure), the positional relationship between the transparent electrode layer 102 and the collecting electrode layer 107 is reversed. Become.
[0022]
Further, in solar cell 200, the positions of unit cells 206 and unit cells 210 are exchanged in accordance with the incident direction of sunlight.
In the solar cells 100 and 200, the positions of the p layer and the n layer of each unit cell may be reversed with respect to the incident direction of sunlight. That is, the order of stacking the p-layer and the n-layer can be exchanged, but it is known that the carrier can be effectively used in the photoelectric conversion when the unit cell is configured so that light enters from the p-layer. Have been.
[0023]
For example, when sunlight enters the solar cell 100 from above in FIG. 1, the p layer 103 is formed on the surface of the transparent electrode layer 102 so that sunlight enters from the p layer 103, and the i layer 104 and the n layer Alternatively, the n-layer 105 may be formed on the surface of the transparent electrode layer 102 so that sunlight enters from the n-layer 105, and the i-layer 104 and the p-layer 103 may be formed in this order. .
In addition, the collecting electrode layer 107 is formed on the surface of the substrate 101 so that the solar light is efficiently supplied to each unit cell, and the transparent electrode layer 102 is formed on the lower part of the solar cell (100, 200) (the solar light from the upper part). As in the case of incidence, the solar cell 200 is formed on the surface of the p-layer 203, and the solar cell 100 is formed on the surface of the p-layer 103).
[0024]
In the solar cell 100 (or the solar cell 200), a transparent material is used for the substrate 101 because it is necessary to transmit light in each wavelength region of sunlight.
Considering the development of a flexible solar cell that can be bent and wound, the substrate 100 is made of plastic such as polyethylene terephthalate, polyethylene naphthalate, polyethylene sulfone, polycarbonate, polyester, polyethylene, polypropylene, vinyl chloride, fluororesin, and epoxy resin. Materials are preferred.
Furthermore, unless considering development of a flexible solar cell, glass, quartz, sapphire, and inorganic materials such as MgO, SiC, ZnO, TiO2, LiF, and CaF2 are used for the substrate 100.
[0025]
As the transparent conductive layer 102, indium oxide containing zinc is used instead of indium oxide containing tin, which has been widely used as a transparent conductive layer.
Conventional indium oxide containing tin absorbs light in a short wavelength region, and thus has insufficient light transmittance.
In addition, there is a problem that the internal stress of the formed thin film is large and it is easy to peel off from the substrate.
The properties of indium oxide containing zinc used in the present invention are such that when the temperature is 350 ° C. and the film thickness is 140 nm, the specific resistance is 300 μΩ · cm to 400 μΩ · cm, the light transmittance at a wavelength of 550 nm is 81%, The refractive index is 2.0 to 2.1.
[0026]
That is, a thin film of indium oxide containing zinc has a higher light transmittance in a short wavelength region than a conventional thin film of indium oxide containing tin.
FIG. 3 shows the wavelength of light on the horizontal axis and the transmittance (%) on the vertical axis, and compares indium oxide containing zinc and indium oxide containing tin.
Here, both film thicknesses are 160 nm.
From the graph of FIG. 3, for example, at a wavelength of 380 nm, it can be seen that the transmittance of indium oxide containing zinc is around 75%, and the transmittance of indium oxide containing tin is around 70%.
[0027]
Indium oxide containing zinc has a higher light transmittance in a short wavelength region than indium oxide containing tin.
Further, since a thin film of indium oxide containing zinc is amorphous, the stress of the film is small and the film has a characteristic that it is difficult to peel off from the substrate 100.
In addition, the sheet resistance of the thin film of indium oxide containing zinc is less dependent on the film formation temperature than the sheet resistance of indium oxide containing tin, and a low resistance can be obtained even at a low temperature. It is.
The properties of a thin film of indium oxide containing zinc are suitable as a development material for a flexible solar cell using a plastic material for the substrate 100.
[0028]
On the other hand, indium oxide containing tin cannot be sufficiently crystallized in a film formed at room temperature, and a low sheet resistance cannot be obtained. In order to obtain a sufficient sheet resistance, it is necessary to increase the temperature of the substrate 100 to 200 ° C. or higher for crystallization.
In the transparent conductive layer 102 of the present invention, in addition to indium oxide containing zinc, indium oxide containing a transition metal such as tin, gallium, antimony, arsenic, titanium, chromium, iron, silver, gold, tungsten, or titanium is used. good.
The transparent conductive layer 102 in the present invention is formed by using the above-described materials by a resistance heating evaporation method, an electron impact evaporation method, a sputtering method, an ion plating method, a thermal CVD method, an atmospheric pressure plasma CVD method, a glow discharge method, or the like. , With a thickness of 5 nm to 200 nm on the surface of the substrate 100.
[0029]
Each semiconductor layer in the unit cell 106 is formed by a thermal CVD method, an optical CVD method, an atmospheric pressure plasma CVD method, a sputtering method, an ion plating method, a glow discharge method, a helicon wave plasma method, an inductively coupled plasma method, or the like. .
For example, in the method using glow discharge, the substrate 100 (on which the transparent electrode layer 102 is already formed) heated to 50 ° C. to 400 ° C. is tightly fixed to a substrate holder, and the substrate holder is pressed to a pressure of 10 Pa to 100 Pa. It is set in the vacuum vessel of the maintained glow discharge device.
A substrate holder is used as one electrode, and high-frequency power having an excitation frequency of 13.56 MHz or a frequency that is a multiple of the excitation frequency is supplied between the substrate holder and the other electrode to generate and maintain glow discharge.
[0030]
A predetermined flow rate of hydrogen is introduced into the vacuum vessel together with monosilane, tetrafluorosilane or dichlorosilane, and a glow discharge is caused to deposit gas decomposition products on the surface of the transparent electrode layer 102 on the substrate 100.
The i-layer is made of silicon containing microcrystalline silicon having a particle diameter of 1 nm to 15 nm in a matrix of amorphous silicon, or microcrystal having a volume fraction of 5% or less of amorphous silicon in amorphous silicon. The amount of monosilane, tetrafluorosilane, or dichlorosilane introduced, the amount of hydrogen introduced, the temperature of the substrate 100, and the power supplied to glow discharge are adjusted so that silicon-containing silicon or microcrystalline silicon is generated.
In the unit cell 106, the p-layer 103 is formed of a p-type silicon layer containing boron, and the n-layer 105 is formed of a semiconductor layer of an n-type silicon layer containing phosphorus or arsenic.
[0031]
For the collection electrode layer 107, a metal electrode is used, and silver, gold, platinum, nickel, chromium, copper, aluminum, titanium, zinc, molybdenum, tungsten, or the like is used as this material.
In the collecting electrode layer 107, the above-described metal material is formed on the back surface of the n-layer 105 by using a resistance heating evaporation method, an electron impact evaporation method, a sputtering method, or the like.
[0032]
<First Embodiment>"
Next, a method for manufacturing a solar cell according to one embodiment will be described with reference to FIG.
Here, a plastic substrate of polyethylene terephthalate is used as the substrate 101.
A transparent conductive layer 102 of indium oxide containing zinc was formed with a thickness of 160 nm on a substrate 101 by a DC magnetron sputtering method.
The ratio of the number of atoms of indium to zinc in the transparent conductive layer 102 was 1: 2. The graph of FIG. 3 shows the case where the thickness of the transparent conductive layer 102 is 160 nm, and shows the wavelength dependence of the light transmittance of indium oxide containing zinc.
[0033]
The solar cell 200 has a tandem structure in which two unit cells 206 and unit cells 210 are vertically stacked as a photoelectric conversion unit.
The substrate 101 having the transparent electrode layer 102 formed on the surface thereof is taken out of the sputtering apparatus, closely adhered to a substrate holder in a vacuum vessel in a glow discharge device (not shown), and the substrate holder is heated by a heater or the like to reduce the temperature of the substrate 101. Adjust the temperature so that it is stable at 70 ° C.
After the temperature of the substrate 101 is stabilized at 70 ° C., a mixed gas of monosilane, phosphine, ammonia and hydrogen is introduced into the vacuum vessel, and a high frequency power of 10 W is applied at an excitation frequency of 13.56 MHz to generate glow discharge.
Thus, a p-layer 203 in the unit cell 206 having a thickness of 50 nm was formed on the surface of the transparent conductive layer 102.
[0034]
Next, monosilane and hydrogen were introduced into the vacuum chamber, high frequency power of 20 W was applied at an excitation frequency of 54.24 MHz, and the i-layer 204 was formed by glow discharge.
The i-layer 204 includes microcrystalline silicon having a grain size of 1 nm to 15 nm in an amorphous silicon matrix, or microcrystalline silicon having a volume fraction of 5% or less of the amorphous silicon in the amorphous silicon. The hydrogen dilution was adjusted to 72 to make it silicon. The hydrogen dilution amount is a numerical value obtained by dividing the volume of a mixture of a reaction gas (for example, a monosilane gas in this case) and hydrogen gas by the volume of the reaction gas.
During the formation of the i-layer 204, the operating pressure in the vacuum vessel was set to 20 Pa.
Measurement by CPM (constant photocurrent method) spectrum confirmed that 3.8% of microcrystalline silicon of 1 nm to 15 nm was present in the volume of amorphous silicon.
[0035]
Subsequently, a mixed gas of monosilane, phosphine, and hydrogen was introduced into the vacuum vessel, an RF power of 10 W was applied at an excitation frequency of 13.56 MHz, and an n-layer 205 was formed to a thickness of 50 nm by glow discharge.
The p-layer 203, the i-layer 204, and the n-layer 205 constitute a set of unit cells 206.
[0036]
Further, a unit cell 210 farther from the light incident side was manufactured as follows.
The p layer 207 and the n layer 209 were manufactured in the same manner as the p layer 203 and the n layer 205 of the unit cell 206 closer to the light incident side.
With respect to the i-layer 208, the substrate holder holding the solar cell 200 is heated by a heater or the like, and the temperature of the substrate 101 is adjusted to a stable state at 70 ° C.
[0037]
After the temperature of the substrate 101 is stabilized at 70 ° C., a mixed gas of monosilane and hydrogen is introduced into the vacuum vessel, and a high frequency power of 20 W is applied at an excitation frequency of 54.24 MHz to generate glow discharge and deposit microcrystalline silicon. I let it.
At this time, the hydrogen dilution amount was set to 101, and the operating pressure in the vacuum vessel was set to 20 Pa. In addition, the thickness of the i-layer 209 of the unit cell 210 farther from the light incident side is formed larger than the thickness of the i-layer 204 of the unit cell 206 closer to the light incident side.
[0038]
That is, in order to efficiently perform photoelectric conversion using light in the short wavelength region of sunlight, the light absorption coefficient of the i-layer 204 of the unit cell 206 is increased, while the light absorption coefficient of the i-layer 209 of the unit cell 210 is reduced. ing.
The p layer 207, the i layer 208, and the n layer 209 were used as another set of unit cells 210. That is, in a unit cell in which a plurality of unit cells are stacked, the i-layer of at least one unit cell (unit cell 208) is formed of microcrystalline silicon.
[0039]
In each of the two unit cells 206 and 210 of the solar cell 200, the side closer to the light incident side is defined as a p-layer (p-layers 203 and 207), followed by an i-layer (i-layers 204 and 208) and an n-layer (n (Layers 205 and 209) in this order.
Using a 3 cm × 3 cm square mask, a silver collecting electrode layer 107 was formed on the surface of the n-layer 209 by an electron impact vapor deposition method, and finally each layer of the solar cell 200 was completed.
[0040]
<Second embodiment>
As a second embodiment, the i-layer 208 in the unit cell 210 described above may be changed from microcrystalline silicon to an i-layer 208B that is silicon containing germanium.
Here, the configuration and manufacturing method of the other layers in the second embodiment are the same as those in the first embodiment.
At this time, in the fabrication of the i-layer 208B, the substrate holder holding the solar cell 200 is heated by a heater or the like in a vacuum vessel, and the temperature of the substrate 101 is adjusted to a stable state at 70 ° C. I do.
[0041]
After the temperature of the substrate 101 is stabilized at 70 ° C., a mixed gas of monosilane, monogermane and hydrogen is introduced into the vacuum vessel, and a high frequency power of 20 W is applied at an excitation frequency of 54.24 MHz to generate a glow discharge. The decomposition product of the above mixed gas was deposited on the surface of 207 as an i-layer 208B.
The thickness of the i-layer 208B may be the same as that of the i-layer 208.
Here, the flow rate, operating pressure, and supply power of the mixed gas are adjusted so that the i-layer 208B is generated as amorphous silicon.
[0042]
Next, a comparison result between the embodiment and the conventional configuration example will be described.
The solar cell of the conventional configuration example is manufactured using a thin film of indium oxide containing tin having a thickness of 160 nm instead of the transparent conductive layer 102 of the solar cell 200.
There is no difference between the conventional configuration example and the solar cell 200 of the first embodiment except for the material of the transparent conductive layer.
The table of FIG. 4 shows the characteristics of the solar cell of the conventional configuration example, the first embodiment, and the second embodiment.
The measurement conditions were as follows: air mass passing air volume Air Mass = 1.5 and 100 mW / cm ² Is used.
[0043]
The photoelectric conversion efficiency of each solar cell was measured by obtaining the ratio of the generated electric energy to the supplied light energy from a solar simulator.
As a result, the photoelectric conversion efficiencies of the solar cells of the first embodiment, the second embodiment, and the conventional configuration are 7.7%, 7.2%, and 5.9%, respectively, from the table of FIG. there were.
[0044]
Further, in the solar cells of the first embodiment, the second embodiment, and the conventional configuration, the short-circuit photocurrent and the open-circuit voltage are not significantly different, but the fill factor indicating the characteristics of the diode is greatly improved. I have.
Thus, as compared with the solar cell of the conventional configuration using the indium oxide containing tin for the transparent conductive layer, the solar cells according to the first and second embodiments using the indium oxide containing zinc for the transparent conductive layer are compared with the solar cell of the conventional configuration example. It can be seen that the photoelectric conversion efficiency of the battery is high and the performance as a solar cell is excellent.
[0045]
That is, in the i-layer 204 of the unit cell 206, the amorphous silicon matrix contains microcrystalline silicon having a particle diameter of 1 nm to 15 nm or amorphous silicon having a volume fraction of 5% or less. By using silicon containing microcrystalline silicon and using indium oxide containing zinc for the transparent conductive layer 102, photoelectric conversion efficiency was improved.
[0046]
That is, as the i-layer 204 of the unit cell 206 close to the light incident side, a semiconductor layer having a large light absorption coefficient in a short wavelength region (microcrystalline silicon having a grain size of 1 to 15 nm in an amorphous silicon matrix, or amorphous Of silicon containing microcrystalline silicon having a volume fraction of 5% or less of amorphous silicon in porous silicon, and combining this with a conductive layer material having high light transmittance in a short wavelength region. This is because a solar cell having high photoelectric conversion efficiency in a short wavelength region has been realized.
By using a semiconductor layer having a large light absorption coefficient in a short wavelength region as in the i layer 204 of the solar cell 200 as the i layer 104 of the unit cell 106 of the solar cell 100, the photoelectric conversion efficiency in the short wavelength region is improved. It became possible.
[0047]
As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like within a range not departing from the gist of the present invention. Are also included in the present invention.
In the above-described embodiment, a configuration in which the present invention is applied to an amorphous or microcrystalline silicon solar cell has been described. However, a single crystal silicon solar cell, a polycrystalline silicon solar cell, a dye-sensitized solar cell (wet solar cell or It can also be used as a transparent conductive layer of a (Gretzel solar cell).
[0048]
【The invention's effect】
According to the solar cell of the present invention, a unit cell composed of p-type, i-type and n-type semiconductors is formed on at least a conductive layer on a substrate, and the i-layer of the unit cell is made of amorphous silicon. The matrix contains microcrystalline silicon having a particle diameter of 1 nm to 15 nm, or amorphous silicon contains silicon containing microcrystalline silicon having a volume fraction of 5% or less of amorphous silicon, and in addition, sunlight By using a material (indium oxide containing zinc) that has high transmittance of light in the short wavelength region for the transparent conductive layer on the incident side, it exceeds the photoelectric conversion efficiency of conventional solar cells in the short wavelength region, and as a result is wider It is possible to improve the efficiency over the wavelength range.
As a result, in the present invention, it has become possible to provide a thin-film solar cell having a photoelectric conversion characteristic with high photoelectric conversion efficiency that effectively utilizes the short wavelength region of the solar radiation energy spectrum.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a stacked structure of a solar cell having a single unit cell according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a stacked structure of a solar cell having a plurality of unit cells according to an embodiment of the present invention.
FIG. 3 is a graph showing a comparison of transmittance between indium oxide containing zinc and indium oxide containing tin.
FIG. 4 is a table showing characteristics of solar cells of indium oxide containing zinc and indium oxide containing tin.
[Explanation of symbols]
100,200 solar cells
101 substrate
102 Transparent conductive layer
103, 203, 207 p-layer
104, 204, 208 i-layer
105, 205, 209 n-layer
106, 206, 210 unit cell
107 Collection (back) electrode layer

Claims (13)

At least one photoelectric conversion unit that converts light energy into electric energy;
A thin-film solar cell, comprising: a conductive layer formed on both sides of the photoelectric conversion unit, one of which is made of indium oxide containing zinc. The conductive layer,
A transparent conductive layer made of indium oxide containing zinc,
The thin-film solar cell according to claim 1, comprising a collection electrode layer for extracting electric energy generated by the photoelectric conversion unit together with the transparent conductive layer. The photoelectric conversion unit,
a p-layer, which is a p-type semiconductor silicon;
An i-layer, which is intrinsic semiconductor silicon and includes microcrystalline silicon having a particle size of 1 nm to 15 nm in an amorphous silicon matrix;
3. The thin-film solar cell according to claim 2, wherein the unit cell comprises an n-layer made of n-type semiconductor silicon. The photoelectric conversion unit,
a p-layer, which is a p-type semiconductor silicon;
An i-layer which is intrinsic semiconductor silicon, and in which the amorphous silicon contains microcrystalline silicon having a volume fraction of 5% or less of the amorphous silicon;
3. The thin-film solar cell according to claim 2, wherein the unit cell comprises an n-layer made of n-type semiconductor silicon. The photoelectric conversion unit,
a p-layer, which is a p-type semiconductor silicon;
An i-layer, which is intrinsic semiconductor silicon and includes microcrystalline silicon having a particle size of 1 nm to 15 nm in an amorphous silicon matrix;
3. The thin-film solar cell according to claim 2, wherein a plurality of unit cells each including an n-layer made of n-type semiconductor silicon are stacked. The photoelectric conversion unit,
a p-layer, which is a p-type semiconductor silicon;
An i-layer which is intrinsic semiconductor silicon, and in which the amorphous silicon contains microcrystalline silicon having a volume fraction of 5% or less of the amorphous silicon;
3. The thin-film solar cell according to claim 2, wherein a plurality of unit cells each including an n-layer made of n-type semiconductor silicon are stacked. 7. The thin film solar cell according to claim 5, wherein, in the unit cells stacked in a plurality, the film thickness is sequentially increased from a unit cell closer to a light incident side to a unit cell farther from the unit cell. 8. battery. 8. The thin-film solar cell according to claim 5, wherein in the plurality of stacked unit cells, the i-layer of at least one unit cell is a thin film formed of microcrystalline silicon. 9. The thin-film solar cell according to any one of claims 5 to 8, wherein in the plurality of stacked unit cells, the i-layer of at least one unit cell is a thin film of silicon containing germanium or tin. The thin-film solar cell according to any one of claims 2 to 9, wherein, in the semiconductor unit cell, a p-layer, an i-layer, and an n-layer are stacked in this order from the light incident side. The thin-film solar cell according to any one of claims 2 to 9, wherein in the semiconductor unit cell, an n-layer, an i-layer, and a p-layer are stacked in this order from the light incident side. The thin-film solar cell according to any one of claims 1 to 11, wherein the light transmittance of the conductive layer of indium oxide containing zinc is 75% or more at a wavelength of 380 nm. The thin-film solar cell according to any one of claims 1 to 12, wherein the conductive layer and the photoelectric conversion unit are formed on a substrate surface of a plastic film.

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