JP2908616B2 - Solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell, and more particularly to a solar cell having a stable output characteristic.

[0002]

2. Description of the Related Art In recent years, the demand for electric power has rapidly increased worldwide, and the problem of environmental pollution has become more serious as electric power production has been activated to meet such demand.

[0003] Under such circumstances, a power generation system using solar cells utilizing sunlight does not cause problems such as radioactive contamination and global warming due to emission of greenhouse gases. Is falling all over the earth, so energy sources are less unevenly distributed, and relatively high power generation efficiency can be obtained without the need for complicated large-scale facilities. Attention has been paid to a clean power generation system that can respond without causing environmental destruction, and various R & Ds have been made for practical use.

[0004] In order to establish a power generation system using a solar cell so as to satisfy the power demand, the solar cell used has a sufficiently high photoelectric conversion efficiency and excellent characteristics stability. It is basically required to be mass-produced.

[0005] For this reason, a gaseous raw material gas such as silane, which is easily available, is used and decomposed by glow discharge to form a non-single crystalline silicon or the like on a relatively inexpensive substrate such as glass or a metal sheet. A solar cell that can be manufactured by depositing a thin semiconductor layer of this type has the potential to be mass-produced and to be manufactured at lower cost and with less energy consumption than a solar cell manufactured using single-crystal silicon or the like. Attention has been paid to it.

Research on applying this non-single-crystalline silicon to photovoltaic devices such as solar cells has been reported by W. Wagner. E. FIG. Spear and P.M. G. FIG. Successful doping by LeComber (S
olid State Communication,
Vol. 17, pp 1193-1196, 197
Based on 5), D.I. E. FIG. Invention of a solar cell by Carlson (US Pat. No. 4,064,521)
, And many fruitful studies have been made in spite of its short history.

A semiconductor layer, which is an important component of a solar cell, has a semiconductor junction such as a so-called pn junction or pin junction. These semiconductor junctions are formed by sequentially laminating semiconductor layers of different conductivity types, implanting dopants of different conductivity types into a semiconductor layer of one conductivity type by ion implantation, or diffusing them by thermal diffusion. Achieved. In view of this point, in the case of a solar cell using a thin film semiconductor such as amorphous silicon, which has attracted attention, the phosphine (PH ₃ , n
A semiconductor material) and a source gas containing an element serving as a dopant, such as diborane (B ₂ H ₆ , p-type semiconductor), with silane or the like as a main source gas, and decompose using glow discharge or the like to obtain desired conductivity. It is known that a semiconductor film having a mold can be obtained, and a semiconductor junction can be easily achieved by sequentially forming these semiconductor films on a desired substrate in the order of pin or nip.

As a result of such research, solar cells using non-monocrystalline silicon have already been used in watches, small computers,
Although it has begun to be used in small-scale power generation applications such as street lamps, when generating electricity on a large scale, for example, for power use, conversion is lower than that of single crystal solar cells or compound solar cells. There are still barriers that must be overcome, such as efficiency and degradation problems, which are cited as disadvantages of non-monocrystalline silicon solar cells. Many attempts have been made to overcome this.

For example, a p-type non-single-crystal silicon carbide having a wide band gap is used as a window layer on the light incident side (YU).
chida, US-Japan Joint Semi
nar, Technical Applica
Tions of Tetrahedral Amorp
house Solids, Palato Alto, Cal
ifornia (1982)), or using p-type microcrystalline silicon carbide for the window layer (Y. Uchida)
et. al, TechnicalDigest®f
the International PVSEC-
3, Tokyoо, Japan 9887 A-IIa
-3).

When non-single-crystal silicon carbide having a wide band gap is used for the window layer, a step in an energy band occurring at a pi interface is eliminated, and photoelectric conversion efficiency in a short wavelength region due to carrier back diffusion and recombination. A method of providing a so-called graded buffer layer in which the forbidden band width changes continuously at the interface for the purpose of preventing a decrease in the density (RR Arya
et. al, Technical Digest®
f theInternational PVSEC-
3, Tokyo, Japan 9887 A-IIIa
-4) has been attempted.

Further, in order to increase the moving distance of carriers in the i-layer, a very small amount of 10 ppm or less of phosphorus (P) or boron (B) is added to the i-layer (W. Ku).
wano et. al, The Technology
record of the teneneenth
IEEE photovoltaic special
ists conference-1987, p59
9, M.P. Kondo et. al, the confes
rence record of the ninet
eenth IEEE photovoltaics
peacelists conference-198
7, p604) has also been attempted.

Further, the diffusion of the p-type and n-type dopants into the semiconductor layer having another conductivity type causes the pn interface, p
Attempts have also been made to prevent the semiconductor junction at the i-interface and the ni-interface from weakening and consequently lowering the photoelectric conversion efficiency of the optical memory device. An example of this is disclosed in
JP-A-5-125681 (Applicant Sanyo Electric) discloses a method of forming a solar cell by providing a partition door between plasma reaction chambers through which a glass substrate placed on a belt conveyor passes. U.S. Pat. No. 4,226,897 (Plasma Physics Co., Ltd.) discloses that a space for forming each semiconductor layer in a device for continuously forming a solar cell on a long strip-shaped substrate is formed by a gas gate. Disclosed is a method in which a gas that does not contribute to film formation is strongly flowed to separate the film formation gas using a mechanism that functions as a substantial partition wall, thereby preventing dopant from being mixed into another film formation space. Have been.

JP-A-56-69875 (Fuji Electric Co., Ltd.) discloses a solar cell having a semiconductor layer formed on a conductive substrate, in which a transparent conductive layer is provided between the conductive substrate and the semiconductor layer. There is disclosed a method of improving the adhesion between the semiconductor layer and the substrate by interposing the substrate, or improving the characteristics of the solar cell by reducing unevenness on the surface of the substrate. In addition, the metal element forming the back electrode located on the side opposite to the light receiving surface of the semiconductor layer diffuses into the semiconductor layer, and the decrease in light reflectance at the interface due to the formation of an alloy with semiconductor atoms is reduced by the back electrode. Japanese Patent Application Laid-Open No. 55-108780 (Applicant Sharp) discloses a method for preventing such a problem by interposing a transparent conductive layer such as zinc oxide between the semiconductor layer and the semiconductor layer.

Attempts to lower the electrical resistivity of the zinc oxide layer by doping the zinc oxide layer with tin or indium (CX Qiu, I. Shin, Solar)
Energy Materials, Vol. 13,
No. 2, 1986). In addition, examples of doping aluminum in a zinc oxide layer (Igasaki, Shimaoka, Shizuoka University Research Institute of Electronics, Vol. 21,
No. 1, 1986) and examples of doping with fluorine (Koinuma et al., Journal of the Ceramic Society of Japan, Vol. 9).
7, No. 10, 1989).

As a result of the efforts of many researchers including these attempts, disadvantages of the non-single-crystal silicon solar cell, such as photoelectric conversion efficiency and deterioration, are gradually improving. The problem remained.

That is, when a solar cell is constructed by providing a semiconductor layer on a conductive substrate with a zinc oxide layer interposed therebetween, if the adhesion between the zinc oxide layer and the conductive substrate or the semiconductor layer is sufficient. However, there is a case where minute peeling occurs due to a temperature shock, vibration, or the like given in the formation of the semiconductor layer and a subsequent step, which causes a decrease in photoelectric conversion efficiency of the solar cell due to an initial characteristic. The problem was left.

Furthermore, since the electrical resistivity of the zinc oxide layer cannot be made so small as to be negligible, the series resistance of the solar cell is increased, and as a result, the photoelectric conversion efficiency of the solar cell is reduced. However, there still remains a problem in the initial characteristics of causing such a phenomenon.

This is not limited to the case where a semiconductor layer is provided on a conductive substrate, and the same applies to a solar cell in which a transparent conductive layer is provided on a light-transmitting insulating substrate and a semiconductor layer is provided thereon. Met. That is, due to insufficient adhesion between the transparent conductive layer and the semiconductor layer, small peeling occurs between the transparent conductive layer and the semiconductor layer during the manufacturing process, resulting in low solar cell photoelectric conversion efficiency. However, there still remains a problem in the initial characteristics that the above-mentioned phenomenon occurs.

Further, even if the above-mentioned minute peeling does not occur during the solar cell manufacturing process and the photoelectric conversion efficiency in the initial stage of the manufacturing is high to some extent, the actual performance under various weather conditions and installation conditions is high. In a use state, there has been a reliability problem that the photoelectric conversion efficiency of the solar cell gradually decreases due to minute peeling between the conductive layer or the transparent conductive layer and the semiconductor layer.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a solar cell having a structure in which a semiconductor layer for performing photoelectric conversion is sandwiched between a first electrode and a second electrode. In a battery, an object of the present invention is to provide a solar cell with improved initial characteristics by improving adhesion between the respective layers and effectively preventing a decrease in characteristics due to minute film peeling occurring during a manufacturing process. And

Further, the present invention provides a solar cell having improved reliability by improving the adhesion between the respective layers and effectively preventing the deterioration of characteristics caused by minute peeling occurring under actual use conditions. It is intended to provide a battery.

Further, the present invention reduces the series resistance of the solar cell by reducing the resistance value of the zinc oxide layer,
As a result, an object is to provide a solar cell with improved initial efficiency.

[0023]

SUMMARY OF THE INVENTION The present invention has been made as a result of intensive studies by the present inventors to achieve the above-mentioned object, and the photoelectric conversion is performed by a first electrode and a second electrode.
In the solar cell having a structure for holding the semiconductor layer for performing conversion, the one of the first and second electrodes, carbon <br/> element in contact with them during the at least one electrode said semiconductor layer wherein the zinc oxide layer containing the atoms are arranged.

The concentration of the carbon atoms in the zinc oxide layer is constant within a range of 5 atomic% or less, or
It is characterized by being continuously changed within the range of at most atomic%.

[0025]

According to the present invention, a zinc oxide layer containing carbon atoms is used as compared with a solar cell manufactured by a conventional technique in which a zinc oxide layer to which carbon atoms are not added is provided at an interface between an electrode and a semiconductor layer. The solar cell manufactured by the method has excellent adhesion between the layers, and as a result, the initial characteristics and the reliability are excellent.

The reason why the adhesion is improved by including carbon atoms in the zinc oxide layer is not yet known in detail, but the carbon atoms in the zinc oxide layer cause a change in the bonding state and crystallinity, and It is thought that this is to effectively alleviate various mechanical and thermal stresses that cause minute film peeling during the battery manufacturing process or in actual use.

In the present invention, the carbon concentration in the zinc oxide layer is desirably set to a constant value within a range of 5 atomic% or less. In this range, the adhesion of the film is further improved, and the photoelectric conversion efficiency and the like are improved. The initial characteristics are further improved. In addition, the term “constant density” in the present invention means that the variation is within 10% with respect to the average density.

Further, by continuously changing the carbon concentration in the zinc oxide layer within the range of 5 atomic% or less, the adhesion is further improved, and the initial characteristics and reliability of the solar cell are further improved. . The reason for this is that the distribution of the concentration of carbon atoms in the zinc oxide layer changes the structure in the zinc oxide layer, which leads to the formation of different types of deposited films on both sides of the zinc oxide layer. This is thought to be effective in effectively relaxing stress generated by the above and various stresses applied from the outside, and effectively preventing minute peeling of the film which occurred during manufacturing or during actual use.

Further, the solar cell manufactured by the technique of the present invention has a greatly improved series resistance as compared with the solar cell manufactured by the conventional technique, and as a result, the fill factor and, consequently, the photoelectric conversion efficiency are increased. ing.
This is considered to be because the electrical resistivity of the zinc oxide layer is effectively reduced by the carbon atoms entering the zinc oxide layer effectively functioning as a doping material.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A configuration for realizing the present invention will be described below with reference to the drawings.

FIG. 1 is a conceptual schematic diagram showing the configuration of a typical example of a solar cell according to the present invention. The solar cell 100 of this typical example shown in FIG. 1 has a conductive substrate 101 as a first electrode.
A zinc oxide layer 102 containing carbon atoms is formed thereon, and a pin-type solar cell element 106 including an n-type semiconductor layer 103, an i-type semiconductor layer 104, and a p-type semiconductor layer 105, and a second electrode are formed thereon. The transparent electrode 107 and the current collecting electrode 108 are sequentially formed, and it is assumed that light enters through the transparent electrode 107.

The solar cell of the present invention is significantly different from the conventional solar cell in that it has the above-described zinc oxide layer 102 containing carbon atoms.

FIG. 2 is a conceptual schematic diagram showing the configuration of another typical example of the solar cell according to the present invention. The solar cell 200 of this typical example shown in FIG. 2 has a conductive substrate 20 as a first electrode.
1, a zinc oxide layer 202 containing carbon atoms is formed thereon, and a pin type solar cell element 206 including an n-type semiconductor layer 203, an i-type semiconductor layer 204, and a p-type semiconductor layer 205 is formed thereon.
A zinc oxide layer 207 containing carbon atoms, a transparent electrode 208 as a second electrode, and a current collecting electrode 209 are sequentially formed.
It is assumed that light enters through the transparent electrode 208.

FIG. 3 is a conceptual schematic diagram showing the configuration of another typical example of the solar cell according to the present invention. The solar cell 300 of this typical example shown in FIG. 3 has a transparent electrode 302 as a first electrode and a zinc oxide layer 3 containing carbon atoms on a transparent substrate 301.
03 are sequentially formed, on which a pin-type solar cell element 307 including a p-type semiconductor layer 304, an i-type semiconductor layer 305, and an n-type semiconductor layer 306, and a zinc oxide layer 30 containing carbon atoms.
8, a back electrode 309 as a second electrode is sequentially formed, and it is assumed that light enters through the transparent substrate 301.

FIG. 4 is a conceptual schematic diagram showing the configuration of another typical example of the solar cell according to the present invention. The solar cell 400 of the present typical example includes a pin-type solar cell element using two types of semiconductor layers having different band gaps or layer thicknesses as i-layers.
This is a tandem solar cell formed by stacking elements. The solar cell 400 shown in FIG. 4 has a zinc oxide layer 4 containing a carbon atom on a conductive substrate 401 which is a first electrode.
02, a first pin-type solar cell element 406 composed of a first n-type semiconductor layer 403, a first i-type semiconductor layer 404, and a first p-type semiconductor layer 405, and a second n-type Semiconductor layer 407, second i-type semiconductor layer 408, second p-type
A second pin type solar cell element 410 composed of a type semiconductor layer 409, a zinc oxide layer 411 containing carbon atoms, a transparent electrode 412 as a second electrode, and a current collecting electrode 413 are sequentially formed, and light is transmitted through the transparent electrode. 412 is assumed.

In each of the examples of solar cells, n
The p-type semiconductor layer and the p-type semiconductor layer can be used by changing the lamination order according to the purpose. However, providing the p-type semiconductor layer closer to the light incident surface more effectively generates generated carriers. It is desirable to use it.

Next, the components of these solar cells will be described.

(Substrate) Conductive substrate 1 applicable to the present invention
Examples of the material No. 01 include a plate and a film of molybdenum, tungsten, titanium, cobalt, chromium, iron, copper, tantalum, niobium, zirconium, aluminum metal, or an alloy thereof. Among them, stainless steel, nickel chromium alloy and nickel, tantalum, niobium, zirconium, titanium metal and / or alloy are particularly preferable from the viewpoint of corrosion resistance. In addition, these metals and / or
Alternatively, it is also possible to use an alloy formed on a film or sheet of a synthetic resin such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyamide, glass, ceramic, and the like. .

Although the substrate 101 can be used alone, providing a layer having substantially reflectivity and conductivity for visible light (hereinafter referred to as a reflective conductive layer) on the substrate 101 is absorbed by the semiconductor layer. It is desirable to further utilize the light transmitted without being broken or to reduce the series resistance of the solar cell. Materials for the reflective conductive layer applicable to the present invention include silver, silicon, aluminum, iron, copper, nickel,
Chromium, molybdenum or their alloys are applicable. Among them, silver, copper, aluminum, and aluminum silicon alloy are preferable. By setting the thickness of the reflective conductive layer sufficiently large, the reflective conductive layer itself can be used as the base.

As a method preferably used for forming the reflective conductive layer on the surface of the substrate 101, there are a resistance heating evaporation method, an electron beam evaporation method, a sputtering method and the like.

Examples of the material of the transparent substrate 301 applicable to the present invention include films or sheets of synthetic resin such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide, glass, etc. Is mentioned.

(Electrode) In the solar cell of the present invention, an appropriate electrode is selected and used depending on the configuration of the element.
Examples of these electrodes include a lower electrode, an upper electrode (transparent electrode), and a collecting electrode. (However, the upper electrode referred to here refers to the electrode provided on the light incident side, and the lower electrode refers to the electrode provided opposite to the upper electrode with the semiconductor layer interposed therebetween.) As the lower electrode used in the above solar cell, the surface on which light is incident is different depending on whether or not the above-described base material is translucent, and therefore, the place where the lower electrode is installed is different.

More specifically, in the case of a layer configuration as shown in FIGS. 1, 2, and 4, the conductive bases 101, 201, and 401 can also serve as lower electrodes.

In the case of the layer structure as shown in FIG. 3, a light-transmitting substrate 301 is used, and light is incident from the side of the substrate 301. In order to effectively reflect light that has reached the electrode without lowering, a lower electrode 309 is provided opposite to the base 301 with a semiconductor layer and a zinc oxide layer containing carbon atoms interposed therebetween.
Materials of the lower electrode suitably used in the solar cell of the present invention include silver, gold, platinum, nickel, chromium, copper, aluminum, titanium, zinc, molybdenum, tungsten and other metals or alloys thereof. Is formed by using a method such as vacuum evaporation, electron beam evaporation, or sputtering. Further, care must be taken that the formed metal thin film does not become a resistance component with respect to the output of the solar cell, and the sheet resistance value is preferably 50Ω or less, more preferably 10Ω or less.

The transparent electrode 10 used in the present invention
7, 208, 302, and 412 desirably have a light transmittance of 70% or more and 80% or more in order to efficiently absorb light from the sun, a white fluorescent lamp, or the like into the semiconductor layer.
More preferably, the above is satisfied. Further, it is desirable that the sheet resistance is not more than 300Ω so as not to become a resistance component electrically with respect to the output of the solar cell. Materials having such characteristics include SnO ₂ , In ₂ O ₃ , ZnO,
CdO, Cd ₂ SnO ₄ , ITO (In ₂ O ₃ + SnO ₂ )
And a metal thin film formed of a metal such as Au, Al, or Cu in a very thin and translucent state. As a method for manufacturing the transparent electrode, a resistance heating evaporation method, an electron beam heating evaporation method, an ion plating method, a sputtering method, a spray method, or the like can be used, and is appropriately selected according to desired characteristics of the solar cell.

Current collecting electrode 10 used in the present invention
8, 209, 413 are transparent electrodes 107, 208, 41
2 is provided on the transparent electrode for the purpose of reducing the sheet resistance value. In the solar cell having the structure as shown in FIGS. 1, 2 and 4, since the formation of the transparent electrode is performed after the formation of the semiconductor layer, the temperature of the base during the formation of the transparent electrode cannot be too high. For this reason, the sheet resistance value of the transparent electrode must be relatively high, so that the current collecting electrodes 108, 20
It is particularly preferred to form 9,413. On the other hand, FIG.
In the solar cell having the configuration shown in FIG.
Since the substrate 2 is formed directly on the substrate, the substrate temperature at the time of formation can be increased, and the sheet resistance of the transparent electrode 302 can be relatively reduced, so that the current collecting electrode is unnecessary or small.

The material of the current collecting electrode suitably used for the solar cell of the present invention is silver, gold, platinum, nickel, chromium,
Metals such as copper, aluminum, titanium, zinc, molybdenum, tungsten, or alloys or carbons thereof, and the like. Vapor deposition, electron beam deposition, sputtering, printing, and the like of a layer made of these metals, alloys, or carbon. It is formed by using. Advantages of each metal, alloy or carbon by stacking and using these metals, alloys or carbon (low resistance, low diffusion into semiconductor layer, robust, easy electrode formation by printing, etc.) Can be used in combination.

The shape and area of the current collecting electrode are appropriately designed so that the amount of light incident on the semiconductor layer is sufficiently ensured. The shape uniformly spreads over the light receiving surface of the solar cell. And the area is preferably 15% with respect to the light receiving area.
Or less, more preferably 10% or less.

It is desirable that the sheet resistance be 50 Ω or less, more preferably 10 Ω or less.

(Zinc Oxide Layer) The zinc oxide layer suitably used in the solar cell of the present invention is characterized by containing carbon atoms, preferably at a certain concentration of 5 atomic% or less.

The zinc oxide layer suitably used for the solar cell of the present invention contains carbon atoms, and preferably contains such that its concentration continuously changes within a range of 5 atomic% or less. It is characterized by:

Examples of the method for forming a zinc oxide layer suitably used for the solar cell of the present invention include a vacuum deposition method, a sputtering method, an ion cluster beam method, a chemical vapor deposition method, and a method such as heating after spraying a metal salt solution. Can be

As a method of including carbon atoms in the zinc oxide layer, for example, there is a method in which carbon atoms are previously mixed in a predetermined ratio in the zinc raw material when the zinc raw material is heated and vapor-deposited in an oxygen atmosphere. In the case where the zinc oxide layer is formed by a sputtering method, sputtering may be performed using a sintered zinc oxide powder containing carbon atoms as a sputtering target, or a metal to which carbon atoms are added. The zinc oxide layer may be formed while reacting with oxygen of the sputtering gas using zinc as a target. Further, nitrogen may be taken into the zinc oxide layer by mixing and flowing a carbon dioxide gas or the like in the sputtering gas.

When carbon atoms are contained in the zinc oxide layer at a constant concentration, in a general deposition film forming method typified by the above method, as long as the film forming parameters are kept constant, the zinc oxide layer contains Variations in carbon concentration can be made within 10%.

On the other hand, as a method for including carbon atoms in the zinc oxide layer with a desired concentration distribution, the following method can be mentioned. For example, when heating and depositing a zinc raw material in an oxygen atmosphere, the zinc raw material placed in a crucible or boat is heated, and zinc oxide is formed by appropriately charging a carbon atom material into the crucible or boat while performing the deposition. It is possible to include carbon atoms having a desired concentration distribution. Further, a method of previously mixing carbon atoms in a zinc raw material at a predetermined ratio may be used. In this case, it is possible to give a distribution to the concentration of carbon atoms in the zinc oxide layer by utilizing the fact that the composition of the evaporation source changes as the evaporation proceeds because the melting points of zinc and carbon atoms are different. It is possible to realize a desired concentration distribution by adjusting the amount and the temperature.

When the zinc oxide layer is formed by the sputtering method, the discharge power and pressure are appropriately changed while performing sputtering by using a sintered zinc oxide powder containing carbon atoms as a sputtering target. By doing so, it is possible to realize a desired concentration distribution. This method can also be used when forming a zinc oxide layer while reacting with oxygen of a sputtering gas using metal zinc to which carbon atoms are added as a target.

Furthermore, a method of placing a strip or a thin wire of carbon atoms appropriately sized so as to obtain a desired concentration distribution on a target not containing carbon atoms, or by welding. Can be used. In this case, it is possible to give a distribution to the concentration of carbon atoms in the zinc oxide layer depending on the manner in which strips or wires made of carbon atoms are consumed.

The method of forming a zinc oxide layer containing a carbon atom suitably used for the solar cell of the present invention may be other methods, and the present invention is not limited by these methods.

A method of forming a zinc oxide layer containing carbon atoms will be described in detail by using a planar DC magnetron sputtering method as an example, but the present invention is not limited thereto.

FIG. 5 is a conceptual diagram showing the structure of a planar DC magnetron sputtering apparatus. The advantage of using the planar type DC magnetron sputtering is that high-speed sputtering can be realized with a small-sized apparatus.
And RF magnetron types.

In FIG. 5, reference numeral 501 denotes a vacuum vessel, and a heating plate 503 is supported by a supporting portion 502 having an insulating property. A heater 506 and a thermocouple 504 are embedded in the heating plate 503, and are controlled to a predetermined temperature by a temperature controller 505. The temperature of the substrate 508 during sputtering is determined by the properties of the desired zinc oxide layer,
At that time, the setting can be changed depending on whether the semiconductor layer has already been formed on the base 508 or, if the semiconductor layer has already been formed, on the conditions such as the formation temperature of the semiconductor layer. In general, when a substrate on which a semiconductor layer is already formed is heated to the substrate temperature at the time of formation of the semiconductor layer, hydrogen is released from the semiconductor material constituting the semiconductor layer or impurity atoms move and diffuse, so that the characteristics of the semiconductor material are reduced. It is known that the characteristics of semiconductor junctions are easily deteriorated. Further, depending on the type of the metal constituting the base or the reflective conductive layer, the crystal grain boundaries may be emphasized by heating, so that care must be taken in setting the temperature of the base. On the assumption that these conditions are taken into consideration, the temperature of the substrate is set at room temperature to 500 ° C. The base 508 is supported by a base holder 509.

A target 510 is disposed to face the base 508. The target 510 is set on a target table 512, has a magnet 513 on the back surface, and has a plasma space 5.
A magnetic field can be formed in the reference numeral 25. In order to cool the target heated during sputtering, cooling water from a cooling water introduction pipe 514 is introduced to the back surface of the target.
After the introduced water cools the target, it is discharged from a cooling water discharge pipe. As described above, the target 510 may be obtained by sintering a powder of zinc oxide containing carbon atoms, or may be made of metallic zinc to which carbon atoms are added.

The target 510 has a target table 512.
A DC voltage is applied from a sputter power supply via. The DC current supplied from the sputtering power source is preferably 0.0
It is set to 1A or more, more preferably 0.1A or more.
According to the experiments performed by the present inventors, the larger the current supplied to the sputter, the smaller the absorption of light by the produced zinc oxide layer, and the higher the photoelectric conversion efficiency of the solar cell, especially, the larger the generated current. This is the same even when the zinc oxide layer is formed using the RF sputtering method.
The solar cell manufactured by increasing the F power was more advantageous in terms of generated current than the solar cell when the RF power was smaller.

As a sputtering gas, an argon gas and an oxygen gas are supplied via a mass flow controller 520 or 521, respectively. Of course, it is also possible to perform fluorine doping on a zinc oxide layer formed by mixing another gas such as a SiF ₄ gas with a sputtering gas. The flow rate of the argon gas is preferably 1
The flow rate of oxygen gas is preferably set to 100 sccm or less.

The internal pressure can be monitored by a vacuum gauge 523 attached to the vacuum vessel 501. Vacuum container 5
01 is a main valve 5 connected to an exhaust system (not shown).
A vacuum state is established via 24. The background internal pressure before starting the sputtering is preferably 10 ^-4 To
rr or less, more preferably 10 ^-5 Torr or less,
Internal pressure during sputtering is 1 mTorr or more and 1 Torr
It is as follows.

The formation of the zinc oxide layer is started while maintaining the above conditions, and after the thickness of the zinc oxide layer reaches a desired value,
After the supply of power from the sputtering power supply and the supply of the sputtering gas are appropriately stopped, and the substrate is appropriately cooled, the inside of the vacuum vessel is leaked to the atmosphere and the substrate on which the zinc oxide layer is formed is taken out. If possible, it is preferable to perform annealing in a vacuum after the formation of the zinc oxide layer because the light transmittance and conductivity of the zinc oxide layer can be improved.

(Semiconductor Layer) As the semiconductor material constituting the i-type semiconductor layer suitably used in the solar cell of the present invention, amorphous (hereinafter abbreviated as “a−”) Si: H,
a-Si: F, a-Si: H: F, a-SiC: H, a
-SiC: F, a-SiC: H: F, a-SiGe:
H, a-SiGe: F, a-SiGe: H: F, polycrystalline Si: H, polycrystalline Si: F, polycrystalline Si: H: F
And so-called group IV and group IV alloy-based semiconductor materials.

The amount of hydrogen atoms contained in the i-type semiconductor layer is preferably 20 atomic% or less, more preferably 10 atomic% or less.
Atomic% or less.

The semiconductor material constituting the p-type or n-type semiconductor layer suitably used in the solar cell of the present invention is as follows.
It is obtained by doping the semiconductor material constituting the i-type semiconductor layer described above with a valence electron controlling agent. However, it is more preferable that the semiconductor material constituting the p-type or n-type semiconductor layer contains a crystal phase, It is preferable because the utilization factor and the carrier density can be increased. In this case, the crystal size is 3
It is preferably 0 ° or more.

The concentration of hydrogen contained in the p-type or n-type semiconductor layer is preferably 5 atomic% or less,
More preferably, it is 1 atomic% or less.

As the source gas for forming a semiconductor layer used for forming these semiconductor layers, simple substances, hydrides, halides, organometallic compounds, etc. of the above-mentioned constituent elements of the various semiconductor layers may be used. Those which can be introduced in a gaseous state are preferably used.

Of course, these source gases can be used alone or in combination of two or more. These source gases may be introduced as a mixture with a rare gas such as He, Ne, Ar, Kr, Xe, or Rn and a diluent gas such as H ₂ , HF, or HCl.

As means for forming each semiconductor layer used in the solar cell of the present invention, microwave plasma CVD,
RF plasma CVD, sputtering and reactive sputtering, ion plating, optical CVD
Method, thermal CVD method, MOCVD method, MBE method and HR-
Means for realizing a method used for forming a so-called semiconductor deposited film, such as a CVD method, can be given, and a means is appropriately selected and used for forming a desired semiconductor layer.

A method for forming a semiconductor layer suitably used for the solar cell of the present invention will be described in detail with reference to the drawings.
Here, a microwave (2.45 GHz, hereinafter abbreviated as “μW”) plasma CVD method and an RF plasma CVD method will be described as examples, but the present invention is not limited thereto. (ΜW Plasma CVD Method) FIG. 6 is a conceptual schematic diagram showing a configuration of a μW plasma CVD apparatus.

In FIG. 6, a substrate 602 contained in a vacuum vessel 601 is attached to a substrate heater 603.
150 ° C. or higher, more preferably 2 ° C. or more during the formation of the semiconductor layer.
Heated and maintained at 00 ° C or higher. A vacuum pump (not shown) is connected to the vacuum vessel 601 via a conductance valve 604, and the opening of the conductance valve 604 is adjusted while watching the vacuum gauge 605 in a state in which the source gas for forming a semiconductor layer is introduced. By doing so, it is possible to set the pressure in the vacuum vessel 601 to a desired pressure of preferably 50 mTorr or less, more preferably 20 mTorr or less. Further, the vacuum vessel 601 is provided with a leak valve 606 for air leak. As a source gas for forming a semiconductor layer, SiH ₄ gas is preferably 5 sccm to 500 sccm, and H ₂ gas is preferably 0 sccm to 1 slm, and is introduced into the vacuum vessel 601 from a gas supply device (not shown) via a gas introduction pipe 607. . In forming the p-layer and the n-layer, a B ₂ H ₆ gas diluted with hydrogen (“B ₂ H ₆ / H”) is used as a doping gas.
₂ gas) and PH ₃ gas diluted with hydrogen (abbreviated as “PH ₃ / H ₂ gas”).
Through a gas supply device (not shown) into the vacuum vessel 601. SiH _{4 of} B ₂ H ₆ gas and PH ₃ gas
The flow rate ratio to the gas is appropriately determined depending on desired solar cell characteristics and semiconductor layer formation parameters, but is preferably set to 0.5% to 50%.

The μW power supplied from a μW power supply (not shown) is introduced into the vacuum vessel 601 through the μW waveguide 608 and the dielectric window 609, and is introduced into the vacuum vessel 601 by generating plasma. The source gas for forming the semiconductor layer is decomposed and excited to form a semiconductor layer on the base 602. μW power is preferably 100W
The above can be set to more preferably 150 W or more.
Also, a DC bias of 0 V to 120 V by the DC power supply 610 and a DC bias of 0 W
It is also possible to apply the sum of W high-frequency power (frequency 13.56 MHz) to the bias application electrode 612. Further, a mesh 613 made of a conductive metal that can be removed by rotation is provided between the base 602 and the bias application electrode 612. Further, it is also possible to control the formation of the semiconductor layer by providing a shutter (not shown) which can be arbitrarily moved immediately before the base.

(RF Plasma CVD Method) FIG. 7 is a conceptual diagram showing the configuration of an RF plasma CVD apparatus.

In FIG. 7, a substrate 702 contained in a vacuum vessel 701 is attached to a substrate heater 703.
100 ° C. or higher, more preferably 1 ° C. or more during the formation of the semiconductor layer.
Heated and maintained at 50 ° C. or higher. A vacuum pump (not shown) is connected to the vacuum vessel 701 through a conductance valve 704, and the opening of the conductance valve 704 is adjusted while watching the vacuum gauge 705 in a state where the source gas for forming the semiconductor layer is introduced. By doing so, it is possible to set the pressure in the vacuum vessel 701 to a desired pressure of preferably 5 Torr or less, more preferably 2 Torr or less. Further, the vacuum vessel 701 is provided with a leak valve 706 for atmospheric leak. As a source gas for forming a semiconductor layer, SiH ₄ gas is preferably 0.5 sccm to 50 sccm, and H ₂ gas is preferably 5 sccm to 100 sccm. The gas is supplied from a gas supply device (not shown) into the vacuum vessel 701 through a gas introduction pipe 707. be introduced. When forming the p-layer and the n-layer, B ₂ H ₆ / H ₂ gas and PH ₃ / H ₂ gas as doping gases are appropriately introduced into a vacuum vessel 701 from a gas supply device (not shown) via a gas introduction pipe 707. be introduced. B ₂ H ₆ gas and PH
_The flow ratio of the _three gases to the SiH ₄ gas is appropriately determined according to desired solar cell characteristics and semiconductor formation parameters, but is preferably set to 0.5% to 50%.

The RF power supplied from the RF power source 708 is introduced into the vacuum chamber 701, and RF plasma is generated between the grounded substrate heater 703 and the substrate 702 and the plate electrode 709 provided in parallel to the grounded heaters 703 and 702. The generated source gas for forming a semiconductor layer introduced into the vacuum vessel 701 is decomposed and excited, and
A semiconductor layer is formed thereon. RF power is preferably 1
mW / cm ³ or more, more preferably set to 3 mW / cm ³ or more.

[0080]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

(Embodiment 1) a- having the configuration shown in FIG.
An Si: H solar cell was fabricated as described below.

In this embodiment, as a substrate 101, a 0.3-μm-thick silver was formed as a reflective conductive layer on a 10 cm square, 0.1 mm thick stainless steel (SUS304) plate having a mirror-polished surface by a known vacuum deposition method. Formed to a thickness of.

On this, a zinc oxide layer 10 containing carbon atoms is formed.
2 was formed as follows using a planar DC magnetron sputtering apparatus shown in FIG.

The substrate 50 on which silver was previously deposited on the heating plate 503
After attaching 8, the inside of the vacuum vessel 501 was evacuated by a pump (not shown). The degree of vacuum in the vacuum vessel 501 is 1
After confirming with a vacuum gauge 523 that the pressure has become 0 ^-5 Torr or less, the heater 506 is energized and the temperature controller 50 is turned on.
5, the heating plate 503 was heated and held at 400 ° C.

In the present embodiment, the target 510 was obtained by sintering a powder of zinc oxide containing 3 atomic% of carbon atoms. Argon gas for 24 seconds as sputtering gas
Mass flow controller 5 so that the flow rate becomes ccm
After adjusting the flow rate at 20 and the flow rate was stabilized, a DC voltage was set and applied to the target 510 from the sputtering power source via the target base 512 so that the sputtering current became 0.3 A. The internal pressure during sputtering is 7 mT
orr.

The formation of the zinc oxide layer is started as described above. After the thickness of the zinc oxide layer reaches 1.0 μm, supply of power from a sputtering power source, supply of a sputtering gas, and After stopping the energization and cooling the substrate, the vacuum vessel 5
The substrate on which the zinc oxide layer was formed was taken out by leaking air from the inside of No. 01.

Subsequently, an n-layer made of a-Si: H
The type semiconductor layer 103, the i-type semiconductor layer 104, and the p-type semiconductor layer 105 were formed using a μW plasma CVD apparatus shown in FIG.

After attaching the substrate 602 on which the zinc oxide layer containing carbon atoms is formed as described above to the substrate heater 603, the inside of the vacuum vessel 601 is evacuated by a vacuum pump (not shown). About 1 × 10 ^-4 Torr
At time r, the substrate heater 603 was energized to heat and maintain the substrate heater 603 at 380 ° C.

Next, the material gas introducing valve (not shown) for forming the semiconductor layer is gradually opened to open the SiH ₄ gas, H ₂ gas and H ₂ gas.
PH ₃ gas diluted to 10% with ₂ gases (hereinafter “PH ₃ /
H ₂ gas ”) was introduced into the vacuum vessel 601 through the gas introduction pipe 607. At this time, the mass flow controller (not shown) adjusted the flow rate of the SiH ₄ gas to 10 sccm, the flow rate of the H ₂ gas to 100 sccm, and the flow rate of the PH ₃ / H ₂ gas to 1.0 sccm.

When the gas flow rate becomes stable, the vacuum vessel 6
01 vacuum gauge 605 so that the pressure in 01 becomes 5 mTorr.
, The opening of the conductance valve 604 was adjusted. Next, a DC bias of +100 V from the DC power supply 610 was applied to the bias application electrode 612. Thereafter, the power of a μW power supply (not shown) is set to 400 W, and μW power is introduced into the vacuum vessel 601 through a waveguide (not shown), a waveguide 608, and a dielectric window 609 to generate μW glow discharge. The formation of an n-type semiconductor layer on 602 was started.

When the thickness of the n-type semiconductor layer 103 becomes about 20 nm, the introduction of the μW power is stopped, and the DC power
Was cut off, and the introduction of gas into the vacuum vessel 601 was stopped, and the formation of the n-type semiconductor layer 103 was completed.

Next, the formation of the i-type semiconductor layer 104 was performed as follows. First, the substrate 602 is heated and held at 250 ° C. by the substrate heater 603, and the SiH ₄ gas 1
50 sccm is supplied through the gas introduction pipe 607 to the vacuum vessel 60.
1 was introduced. The pressure in the vacuum vessel 601 is 5 mTorr
The opening of the conductance valve 604 was adjusted while watching the vacuum gauge 605 so as to obtain r. Next, at that time, the rotatable mesh grid 603 was rotated and removed from the vicinity of the substrate 602. Next, +60 by DC power supply 610
V DC bias and 10
The sum of 0 W high-frequency power (frequency 13.56 MHz) was applied to the bias application electrode 612. Then, μ (not shown)
The power of the W power supply is set to 300 W, and the vacuum vessel 60 is set through a waveguide, a waveguide 608 and a dielectric window 609 (not shown).
1 to introduce μW electric power to generate μW glow discharge,
The formation of the i-type semiconductor layer on the n-type semiconductor layer was started.

The thickness of the i-type semiconductor layer 104 is about 400 nm.
At the point where the introduction of μW power was stopped and the DC power supply 61
0 and the output of the high frequency power supply 611 are turned off.
The introduction of the gas into the inside of the semiconductor device 01 was stopped, and the formation of the i-type semiconductor layer 104 was completed.

Next, formation of the p-type semiconductor layer 105 was performed as follows. First, the substrate 602 is heated and maintained at 200 ° C. by the substrate heater 603, and the SiH ₄ gas,
H ₂ gas, BF ₃ gas diluted to 10% with H ₂ gas (hereinafter abbreviated as “BF ₃ / H ₂ gas”) is introduced into a gas introduction pipe 607.
And introduced into the vacuum vessel 601. At this time, SiH
₄ Gas flow rate is 10 sccm, H ₂ gas flow rate is 100 sccc
m and BF ₃ / H ₂ gas flow rate were adjusted by each mass flow controller so as to be 1 sccm. Vacuum container 60
The opening of the conductance valve 604 was adjusted while watching the vacuum gauge 605 so that the pressure inside 1 became 5 mTorr. Next, a DC bias of +100 V from the DC power supply 610 was applied to the bias application electrode 612. Thereafter, the power of a μW power supply (not shown) is set to 400 W, and μW power is introduced into the vacuum vessel 601 through a waveguide (not shown), a waveguide 608 and a dielectric window 609 to generate a μW glow discharge, The formation of the p-type semiconductor layer on the i-type semiconductor layer was started.

When the thickness of the p-type semiconductor layer 105 becomes about 10 nm, the introduction of μW power is stopped, and the DC power
Was turned off, and the introduction of gas into the vacuum vessel 601 was stopped to complete the formation of the p-type semiconductor layer 105.

Next, the inside of the vacuum vessel 601 and the gas introduction pipe 607 are repeatedly purged with argon three times, and then the gas introduction valve is closed, the leak valve 606 is opened, and the inside of the vacuum vessel 601 is leaked to the atmosphere. The substrate 602 on which the n-type semiconductor layer, the i-type semiconductor layer, and the p-type semiconductor layer were formed was taken out of the vacuum vessel 601.

Next, as a transparent electrode 107, a 75 nm thick ITO (In ₂ O ₃ ) was formed on the p-type semiconductor layer 105 of the a-Si: H solar cell formed as described above.
+ SnO ₂ ) is vacuum-deposited by a well-known resistance heating vacuum deposition method, and a 2 μm thick Al
Is deposited by a known resistance heating vacuum deposition method, and a-Si:
An H solar cell was produced.

Further, except that the zinc oxide layer 102 was formed by variously changing the concentration of carbon atoms in the zinc oxide serving as the target in the planar DC magnetron sputtering method, the other conditions were not changed at all. By manufacturing a Si: H solar cell, the dependency of the solar cell characteristics on the carbon atom concentration in the zinc oxide layer 102 formed on the substrate 101 was measured as follows.

The current-voltage characteristics of these solar cells were measured under simulated sunlight (AM-1.5, 100 mW / cm ² ) using a solar simulator (Yamashita Denso, YSS-150), and photoelectric conversion was performed. SIMS was used to determine the efficiency and to determine the carbon atom concentration in the zinc oxide layer of each solar cell.
And their relationships were investigated. FIG. 8 shows the result. Each data in FIG. 8 is a value normalized by setting the maximum value to 1.

In each of the solar cells, the concentration of carbon atoms in the zinc oxide layer was constant within a variation range of 10%.

As a comparative example, a solar cell having the same other conditions, configurations, and the like except that no carbon atom was added to the zinc oxide layer was prepared. The conversion efficiency of the solar cell of the comparative example was significantly lower than 0.87 when the highest value among the solar cells of Example 1 was 1. It is clear from this that the conversion efficiency of the solar cell of this example is improved. In addition, it was found that the photoelectric conversion efficiency of the solar cell containing carbon atoms in the zinc oxide layer at a certain concentration of 5 atomic% or less was dramatically improved. Also, when examining which point is the most improved in the solar cell with improved photoelectric conversion efficiency, especially the series resistance in the solar cell element has been greatly improved, and as a result, the fill factor and, consequently, the photoelectric conversion efficiency have been improved. Was found to be elevated. This is considered to be because the electrical resistivity of the zinc oxide layer was effectively reduced by doping carbon atoms into the zinc oxide layer.

Further, in order to examine the reliability of these solar cells under actual use conditions, the following durability test was performed.

Each of the solar cells manufactured in Example 1 was vacuum-sealed with a protective film made of polyvinylidene fluoride (VDF), and used under actual use conditions (installed outdoors, a fixed resistance of 50 ohms was connected to both electrodes). After one year, the photoelectric conversion efficiency is evaluated again, and the deterioration rate caused by light irradiation, temperature difference, wind and rain (the value of the photoelectric conversion efficiency impaired by the deterioration is divided by the initial photoelectric conversion efficiency value). ). FIG. 9 shows the result of normalizing the obtained data. The deterioration rate of the solar cell of the comparative example was 1.22 times the minimum value of the data in FIG. From these results, it can be seen that the reliability has been dramatically improved particularly in a solar cell in which the zinc oxide layer contains carbon atoms at a constant concentration of 5 atomic% or less.

Example 2 As shown in FIG. 2, zinc oxide layers 202 and 207 containing carbon atoms were formed between a substrate 201 and an n-type semiconductor layer 203 and between a p-type semiconductor layer and a transparent conductive layer 2.
A-Si having a configuration formed on both sides during the period 08:
H solar cells were fabricated as described below.

In this embodiment, a 10 cm square, 1 mm thick aluminum plate having a mirror-polished surface is used as the substrate 101. On this, a zinc oxide layer 20 containing carbon atoms is formed.
2 was formed in the same manner as in Example 1, and an n-type semiconductor layer 203, an i-type semiconductor layer 204, and a p-type semiconductor layer 2 were formed thereon.
05 using the RF plasma CVD apparatus shown in FIG.
It was formed by the method described below.

After the substrate 702 on which the zinc oxide layer containing carbon atoms is formed is attached to the substrate heater 703, the inside of the vacuum vessel 701 is evacuated by a vacuum pump (not shown), and the vacuum gauge 705 reads about 1 × 10 ^{−. At 4} Torr, the substrate heater 703 is energized by turning on the substrate heater 703.
Heated and maintained at 00 ° C.

Next, the semiconductor layer forming raw material gas introduction valve (not shown) is gradually opened, and the SiH ₄ gas, the H ₂ gas and the P
H ₃ / H ₂ gas is introduced into the vacuum vessel 70 through the gas introduction pipe 707.
1 was introduced. At this time, the flow rate of the SiH ₄ gas is 2 sc
cm, H ₂ gas flow rate was adjusted to 50 sccm, and PH ₃ / H ₂ gas flow rate was adjusted to 1 sccm by a mass flow controller (not shown). The pressure inside the vacuum vessel 701 is 1T
The opening of the conductance valve 704 was adjusted while looking at the vacuum gauge 705 so that the pressure became orr.

When the pressure in the vacuum chamber 701 is stabilized, the power of an RF power source (not shown) is set to 200 mW / cm ³ , and RF power is introduced to the cathode 709 through the RF matching box 708 to generate RF glow discharge. Then, the formation of the n-type semiconductor layer 203 on the zinc oxide layer 202 was started.

When the thickness of the n-type semiconductor layer reached 5 nm, the RF glow discharge was stopped, the gas flow into the vacuum vessel 701 was stopped, and the fabrication of the n-type layer was completed.

Next, an i-type semiconductor layer 204 was formed on the n-type semiconductor layer 203 as follows. Substrate 702
Is heated and held at 280 ° C. by the substrate heater 703,
SiH ₄ gas and H ₂ gas were introduced into the vacuum vessel 701 through the gas introduction pipe 707. At this time, the SiH ₄ gas flow rate was adjusted to ₂ sccm and the H ₂ gas flow rate was adjusted to 20 sccm. The opening of the conductance valve 704 was adjusted while watching the vacuum gauge 705 so that the pressure in the vacuum vessel 701 became 1 Torr. Thereafter, the power of an RF power supply (not shown) is set to 5 mW / cm ³ , and RF power is introduced to the cathode 709 through the RF matching box 708,
An RF glow discharge was caused to start forming an i-type semiconductor layer 204 on the n-type semiconductor layer 203.

When the thickness of the i-type semiconductor layer 204 becomes 400 nm, the RF glow discharge and the introduction of gas are stopped.
The formation of the i-type semiconductor layer 204 has been completed.

Next, a p-type semiconductor layer 207 was formed on the i-type semiconductor layer 204 as follows. Substrate 7
02 was heated and maintained at 250 ° C. by the substrate heater 703, and SiH ₄ gas, H ₂ gas, and B ₂ H ₆ / H ₂ gas were introduced into the vacuum vessel 701 through the gas introduction pipe 707. At this time, the flow rate of the SiH ₄ gas was ₂ sccm, and the flow rate of the H ₂ gas was 2 sccm.
It was adjusted with a mass flow controller so that the flow rate of the B ₂ H ₆ / H ₂ gas was 1 sccm at 0 sccm. Vacuum gauge 705 so that the pressure in vacuum vessel 701 becomes 1 Torr.
, The opening of the conductance valve 704 was adjusted. Thereafter, the power of an RF power source (not shown) was increased to 10 mW / cm.
^The RF power is introduced to the cathode 709 through the RF matching box 709 to generate RF glow discharge, and the p-type semiconductor layer 205 is set on the i-type semiconductor layer 204.
Began to form.

When the thickness of the p-type semiconductor layer 205 becomes 10 nm, the RF glow discharge and the introduction of gas are stopped,
The formation of the mold semiconductor layer 205 has been completed.

After the formation of the p-type semiconductor layer 205 is completed, argon purging inside the vacuum vessel 701 and the gas introduction pipe 707 is repeated three times, then the gas introduction valve is closed, the leak valve 706 is opened, and the vacuum vessel is opened. The substrate 702 having an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer formed on its surface is leaked to the atmosphere
Removed from inside 1.

Next, a zinc oxide layer 208 containing carbon atoms is formed on the p-type semiconductor layer 205 by setting the temperature of the heating plate 503 to 2.
Except that the temperature was set at 30 ° C., it was formed in the same manner as when the zinc oxide layer 202 was formed.

Subsequently, a transparent electrode 208 and a current collecting electrode 209 were formed on the zinc oxide layer 207 in the same manner as in Example 1, and an a-Si: H solar cell was manufactured.

The same measurement as in Example 1 was performed on the solar cell manufactured as described above.

The concentration of carbon atoms contained in the zinc oxide layer of the solar cell fabricated in Example 2 was 3 atomic%, and the variation was 1
It was constant at 0%.

A comparison was made between the solar cells fabricated in Example 1 and those having the same concentration of carbon atoms in the zinc oxide layer. As a result, the photoelectric conversion efficiency and the deterioration rate of the solar cell manufactured in Example 2, that is, the solar cell having the zinc oxide layer on both sides of the semiconductor layer, are lower than those of the solar cell manufactured in Example 1, that is, the substrate side. When the value of the photoelectric conversion efficiency and the deterioration rate of a solar cell having only a zinc oxide layer is set to 1,
They were 0.98 and 0.95, respectively.

From these results, it can be seen that the solar cell having the zinc oxide layer containing carbon atoms on both sides of the semiconductor layer as manufactured in this example is slightly inferior in initial efficiency to the solar cell having only one side on one side. It turns out that it is excellent in reliability.

Example 3 In this example, an ion plating method was used to form a zinc oxide layer. In the formation of the zinc oxide layer by the ion plating method, the raw material uses metallic zinc (purity 99.9%), and since the zinc is a sublimable metal, a molybdenum sublimable metal boat is used. 13.56 MHz for couple electrodes
Of high frequency power was applied. The gas used was a mixed gas of oxygen gas and carbon dioxide gas (mixing ratio of 5% to oxygen gas).

An a-Si: H solar cell was manufactured in the same manner as in Example 1 except for the above-mentioned points, and the same measurement as in Example 1 was performed on the manufactured solar cell. Was.

The concentration of carbon atoms contained in the zinc oxide layer of the solar cell manufactured in Example 3 was constant at 2 atomic%.

A comparison was made between the solar cells fabricated in Example 1 and those having substantially the same carbon atom concentration in the zinc oxide layer. As a result, the photoelectric conversion efficiency and the deterioration rate of the solar cell manufactured in Example 3 were 1.06 and 1.06, respectively, when the value of the photoelectric conversion efficiency and the deterioration rate of the solar cell manufactured in Example 1 was 1. 0.99.

Example 4 As shown in FIG. 3, a transparent electrode 302, a zinc oxide layer 303 containing carbon atoms, a p-type semiconductor layer 304, an i-type semiconductor layer 305, and n
Semiconductor layer 306, a zinc oxide layer 308 containing carbon atoms,
An a-Si: H solar cell in which the back electrode 309 was sequentially formed was manufactured. As the glass substrate 301, a Corning # 7059 glass substrate having both surfaces polished was used, and tin oxide (S
nO ₂ ) film transparent electrode 302 and back electrode 309
Is formed using a normal vacuum heating deposition method, the zinc oxide layers 303 and 308 containing carbon atoms are formed using a normal RF sputtering method, and each semiconductor layer is formed using an RF plasma CV.
Method D was used. The concentration of carbon atoms contained in the zinc oxide layers 303 and 308 was measured by SIMS.
It was constant at atomic%. A produced in this way
As a comparative example for the -Si: H solar cell, an a-Si: H solar cell was produced in the same manner as in Example 4 except that the zinc oxide layers 303 and 308 containing carbon atoms were not provided.

The characteristics of these solar cells were measured in the same manner as in Example 1. As a result, the solar cell of Example 4 was extremely superior to the solar cell of the comparative example, with a photoelectric conversion efficiency value of 1.10 times and a deterioration rate value of 0.85 times.

(Embodiment 5) In this embodiment, the zinc oxide layer 1
A solar cell having the configuration shown in FIG. 1 was manufactured in the same manner as in Example 1 except for the method of forming No. 02.

In this embodiment, a zinc oxide layer 102 containing a carbon atom whose concentration changes continuously is formed on a substrate 101 on which a reflective conductive layer is formed by using a planar DC magnetron sputtering apparatus shown in FIG. It was formed as follows.

The substrate 50 on which silver is deposited in advance on the heating plate 503
After attaching 8, the inside of the vacuum vessel 501 was evacuated by a pump (not shown). The degree of vacuum in the vacuum vessel 501 is 1
After confirming with a vacuum gauge 523 that the pressure has become 0 ^-5 Torr or less, the heater 506 is energized and the temperature controller 50 is turned on.
5, the heating plate 503 was heated and held at 400 ° C.

In the present embodiment, the target 510 was obtained by sintering a powder of zinc oxide containing 3 atomic% of carbon atoms. Argon gas for 24 seconds as sputtering gas
Mass flow controller 5 so that the flow rate becomes ccm
After adjusting the flow rate at 20 and the flow rate was stabilized, a DC voltage was set and applied to the target 510 from the sputtering power source via the target base 512 so that the sputtering current became 0.3 A. The internal pressure during sputtering is 7 mT
orr.

After the formation of the zinc oxide layer was started as described above, the sputter current was gradually increased by adjusting the sputtering power source and continuously increasing DC. When the thickness of the zinc oxide layer reached 1.0 μm, the sputter current was 0.5 A. The thickness of the zinc oxide layer is 1.0μ
m, the supply of power from the sputtering power supply, the supply of sputtering gas, and the supply of power to the heater 506 are stopped, and after cooling the substrate, the substrate on which the zinc oxide layer is formed is leaked from the vacuum vessel 501 to the atmosphere. Was.

Further, except that the zinc oxide layer 102 was formed by changing the concentration of carbon atoms in the zinc oxide serving as the target in the planar DC magnetron sputtering method in various ways, the other conditions were not changed at all and a- By manufacturing a Si: H solar cell, the dependency of the solar cell characteristics on the concentration of carbon atoms in the zinc oxide layer 102 formed on the substrate 101 was examined as follows.

The current-voltage characteristics of these solar cells were measured under simulated sunlight (AM-1.5, 100 mW / cm ² ) using a solar simulator (Yamashita Denso, YSS-150), and photoelectric conversion was performed. The efficiency was determined, and the carbon atom concentration in the zinc oxide layer of each solar cell was measured by SIMS, and their relationship was examined. The result is shown in FIG. In the figure, the length of the bar represents the width of the density distribution.

In each of the solar cells, the concentration ratio of carbon atoms in the initial stage of the zinc oxide layer formation and immediately before the end of the film formation was about 30.

In addition, the conversion efficiency of the solar cell of this embodiment is set to 1
Then, in the formation of the zinc oxide layer by the DC magnetron sputtering method, the conversion efficiency of the solar cell of Example 1 which was formed without changing the DC voltage and, consequently, the sputtering current was 0.3.
94.

From these results, it is found that the photoelectric conversion efficiency of the solar cell containing carbon atoms in the zinc oxide layer and continuously changing its concentration within the range of 5 atomic% or less is further enhanced. I knew it was there.

Each of the solar cells manufactured in this example was vacuum-sealed with a protective film made of polyvinylidene fluoride (VDF), placed under actual use conditions for one year, and the conversion efficiency deterioration rate was measured. . The result is shown in FIG. In the figure, the length of the bar represents the width of the density distribution.

As shown in FIG. 11, the reliability of a solar cell containing carbon atoms in the zinc oxide layer and continuously changing its concentration within the range of 5 atomic% or less is dramatically improved. It can be seen that it has been raised. Although the reason for this has not yet been clarified, the distribution of the concentration of carbon atoms in the zinc oxide layer changes the structure in the zinc oxide layer, which results in different types of deposition on both sides of the zinc oxide layer. It is because the stress generated by forming the film and various external stresses are effectively relieved, and the minute film peeling that occurred during manufacturing and under actual use conditions is effectively prevented. Guessed.

Example 6 As shown in FIG. 2, zinc oxide layers 202 and 207 containing carbon atoms were formed between a substrate 201 and an n-type semiconductor layer 203, a p-type semiconductor layer and a transparent conductive layer 208.
An a-Si: H solar cell having a configuration formed on both sides was manufactured as described below. In this example, a solar cell was manufactured in the same manner as in Example 2, except for the method of forming the zinc oxide layers 202 and 208. The zinc oxide layer 202 is formed in the same manner as in Example 5. On the other hand, in forming the zinc oxide layer 208, the temperature of the heating plate 503 is set to 230 ° C. The opposite was the case with the zinc layer 202, that is, from 0.5A to 0.3A.

With respect to the solar cell thus manufactured,
The same measurement as in Example 5 was performed.

The solar cell 2 prepared in Example 6
In the zinc oxide layer, the concentration of carbon atoms contained in each layer continuously changes from 100 atomic ppm to 0.3 atomic%, and is almost equal except that the directions of change are opposite. there were.

The solar cell of this example was compared with the solar cell manufactured in Example 5 in which the concentration of carbon atoms in the zinc oxide layer was almost equal. As a result, the photovoltaic conversion efficiency and the deterioration rate of the solar cell manufactured in Example 6, that is, the solar cell having the zinc oxide layer on both sides of the semiconductor layer, were measured in Example 5.
Assuming that the values of the photoelectric conversion efficiency and the deterioration rate of the solar cell manufactured by the method described above, that is, the solar cell having the zinc oxide layer only on the substrate side of the semiconductor layer, are respectively 0.97 and 0.9.
92.

From these results, it can be seen that the solar cell having the zinc oxide layer containing carbon atoms on both sides of the semiconductor layer as manufactured in this example has a slightly lower initial efficiency than the solar cell having only one side. It turns out that it is excellent in reliability.

Example 7 In this example, an ion plating method was used for forming a zinc oxide layer. To give the desired distribution of the concentration of carbon atoms in the zinc oxide layer,
The ratio of carbon dioxide gas in the gas used for forming the zinc oxide layer was 0.5% from the start to the end of the formation of the zinc oxide layer.
To 10%.

An a-Si: H solar cell shown in FIG. 1 was prepared in the same manner as in Example 3 except for the above points and the method was the same as in Example 3, and the same measurement as in Example 1 was performed.

The concentration of carbon atoms contained in the zinc oxide layer of the solar cell manufactured in Example 7 was continuously changed from 800 atomic ppm to 0.3 atomic%.

The solar cell of this example was compared with the solar cell manufactured in Example 5 in which the concentration of carbon atoms in the zinc oxide layer was almost equal. As a result, the photoelectric conversion efficiency and the deterioration rate of the solar cell manufactured in Example 7 were 1.06 and 1.06, respectively, when the value of the photoelectric conversion efficiency and the deterioration rate of the solar cell manufactured in Example 5 was 1. 0.91.

Example 8 A solar cell having the structure shown in FIG. 3 was produced in the same manner as in Example 4 except for the method of forming the zinc oxide layer. The zinc oxide layers 303 and 308 were formed according to the method of the sixth embodiment.

When the concentration of carbon atoms in the two zinc oxide layers of the a-Si: H solar cell manufactured as described above was examined, both changed continuously from 0.1 at% to 3 at%. I was As a comparative example with respect to the solar cell of this embodiment, zinc oxide layers 303 and 308 containing carbon atoms are provided.
A- in the same manner as in Example 8 except that
A Si: H solar cell was produced.

The characteristics of these solar cells were measured in the same manner as in Example 1. As a result, the solar cell manufactured in Example 8 had a photoelectric conversion efficiency of 1.10 compared to the solar cell of Comparative Example.
The value was 15 times, and the deterioration rate was 0.83 times, which was excellent.

[0151]

As described above, the first electrode and the second electrode
In the solar cell having a structure for holding the semiconductor layer for performing photoelectric conversion by the electrodes, the one of the first and second electrodes, carbon atoms adjacent to them between the at least one electrode said semiconductor layer zinc oxide layer containing a is arranged
By using the present invention, characterized by that, the following effects can be obtained.

That is, when a solar cell is formed by providing a semiconductor layer on a conductive substrate via a zinc oxide layer, the adhesion between the zinc oxide layer and the conductive substrate or the semiconductor layer is improved, and It is possible to prevent minute peeling due to temperature shock, vibration, and the like given in the formation of the layer and subsequent steps, and as a result, it is possible to provide a solar cell with significantly improved photoelectric conversion efficiency.

Furthermore, since the electrical resistivity of the zinc oxide layer can be reduced, it is possible to provide a solar cell having a greatly improved photoelectric conversion efficiency without increasing the series resistance.

In a solar cell in which a semiconductor layer is provided on a transparent conductive layer provided on a light-transmitting insulating substrate, the adhesion between the transparent conductive layer and the semiconductor layer is improved. In this case, minute peeling between the transparent conductive layer and the semiconductor layer can be effectively prevented, and a solar cell with significantly improved photoelectric conversion efficiency can be provided.

In addition, the reliability has been greatly improved by effectively preventing minute peeling occurring between the conductive substrate and the transparent conductive layer and the semiconductor layer in actual use conditions under various weather conditions and installation conditions. A solar cell can be provided.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining a configuration of an embodiment of the present invention.

FIG. 2 is a conceptual diagram for explaining a configuration of another embodiment of the present invention.

FIG. 3 is a conceptual diagram for explaining a configuration of another embodiment of the present invention.

FIG. 4 is a conceptual diagram for explaining a configuration of another embodiment of the present invention.

FIG. 5 is a conceptual diagram showing a configuration of a planar type DC magnetron sputtering apparatus as one means for realizing the present invention.

FIG. 6 is a conceptual diagram showing a configuration of a μW plasma CVD apparatus as one means for realizing the present invention.

FIG. 7 is a conceptual diagram showing a configuration of an RF plasma CVD apparatus as one means for realizing the present invention.

FIG. 8 is a graph showing the relationship between the concentration of carbon atoms in a zinc oxide layer and the photoelectric conversion efficiency of the solar cell manufactured in Example 1.

FIG. 9 is a graph showing the relationship between the concentration of carbon atoms in the zinc oxide layer of the solar cell manufactured in Example 1 and the deterioration rate.

FIG. 10 is a graph showing the relationship between the concentration of carbon atoms in a zinc oxide layer of a solar cell manufactured in Example 5 and photoelectric conversion efficiency.

FIG. 11 is a graph showing the relationship between the concentration of carbon atoms in a zinc oxide layer of a solar cell manufactured in Example 5 and a deterioration rate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 solar cell, 101 substrate, 102 zinc oxide layer, 103 n-type (p-type) semiconductor layer, 104 i-type semiconductor layer, 105 p-type (n-type) semiconductor layer, 106 pin-type solar cell element, 107 transparent electrode, 108 Current collecting electrode, 200 solar cell, 201 substrate, 202 zinc oxide layer, 203 n-type (p-type) semiconductor layer, 204 i-type semiconductor layer, 205 p-type (n-type) semiconductor layer, 206 pin-type solar cell element, 207 Zinc oxide layer, 208 transparent electrode, 209 collector electrode, 300 solar cell, 301 substrate, 302 transparent electrode, 303 zinc oxide layer, 304 p-type (n-type) semiconductor layer, 305 i-type semiconductor layer, 306 n-type (p Type) semiconductor layer, 307 pin type solar cell element, 308 zinc oxide layer, 309 back electrode, 400 solar cell, 401 substrate, 402 zinc oxide 403 a first n-type (p-type) semiconductor layer, 404 a first i-type semiconductor layer, 405 a first p-type (n-type) semiconductor layer, 406 a first pin-type solar cell element, 407 a second n-type (p-type) semiconductor layer, 408 second i-type semiconductor layer, 409 second p-type (n-type) semiconductor layer, 410 second pin-type solar cell element, 411 zinc oxide layer, 412 transparent electrode, 413 collecting electrode, 501 vacuum vessel, 502 support, 503 heating plate, 504 thermocouple, 505 temperature controller, 506 heater, 507 heat uniform body, 508 base, 509 base holder, 510 target, 512 target base, 513 magnet, 514 cooling water introduction pipe, 516 sputter power supply, 520, 521 mass flow controller, 523 vacuum gauge, 524 main valve, 01 vacuum vessel, 602 substrate, 603 substrate heater, 604 conductance valve, 605 vacuum gauge, 606 leak valve, 607 gas inlet tube, 608 μW waveguide, 609 dielectric window, 610 DC power supply, 611 high frequency power supply, 612 bias application Electrodes, 613 mesh, 701 vacuum vessel, 702 substrate, 703 substrate heater, 704 conductance valve, 705 vacuum gauge, 706 leak valve, 707 gas inlet tube, 708 RF power supply, 709 plate electrode.

Claims (12)

(57) [Claims] 1. A photoelectric conversion device comprising : a first electrode and a second electrode;
In the solar cell having a structure for holding the semiconductor layer for performing conversion, the one of the first and second electrodes, carbon <br/> element in contact with them during the at least one electrode said semiconductor layer solar cell, wherein a zinc oxide layer containing the atoms are arranged. 2. The solar cell according to claim 1 , wherein the concentration of the carbon atoms in the zinc oxide layer is constant within a range of 5 atomic% or less. 3. The solar cell according to claim 1 , wherein the concentration of the carbon atoms in the zinc oxide layer continuously changes within a range of 5 atomic% or less. 4. The semiconductor layer according to claim 1, wherein said semiconductor layer is a P-type, N-type or I-type semiconductor layer.
2. The method according to claim 1, wherein the conductive film includes at least one set.
The solar cell according to 1. 5. The substrate according to claim 1, wherein the first electrode has a conductive surface.
Wherein the second electrode is a transparent electrode.
The solar cell according to claim 1. 6. Between the first electrode and the semiconductor layer
Only the zinc oxide layer is provided.
A solar cell according to claim 5. 7. A gap between the first electrode and the semiconductor layer
And between the second electrode and the semiconductor layer, respectively.
The zinc oxide layer is provided.
The solar cell according to 1. 8. The method according to claim 1, wherein the first electrode is a reflective conductive layer,
The second electrode is a transparent electrode, and the zinc oxide layer is
Being disposed between the first electrode and the semiconductor layer.
The solar cell according to claim 1, wherein: 9. The transparent electrode is made of SnO. _Two , In _Two O _Three Or
The solar cell according to claim 8, wherein the solar cell is ITO.
pond. 10. The first electrode is a reflective conductive layer.
The second electrode is a transparent electrode, and the zinc oxide layer
Is disposed only between the first electrode and the semiconductor layer.
The solar cell according to claim 1, wherein: 11. The transparent electrode is made of SnO. _Two , In _Two O _Three or
Is ITO. 12. The method according to claim 10, wherein
Positive battery. 12. The zinc oxide layer further contains nitrogen.
Claims characterized by the following: 2. The solar cell according to 1.