JP4691888B2 - Non-single crystal solar cell and method of manufacturing non-single crystal solar cell - Google Patents

Description

  The present invention relates to a p-type semiconductor layer of a thin film non-single crystal solar cell using a non-single crystal film such as a microcrystalline film, an amorphous film, or a polycrystalline film.

  In general, boron (B) has been used as a p-type doping material of a thin film silicon photoelectric conversion element mainly composed of silicon and germanium. The improvement in the characteristics of the p layer is the most important factor for increasing the open circuit voltage and the fill factor (FF) in the solar cell device.

  Boron conventionally used as a p-layer dopant has a big problem that it is easily passivated by hydrogen under a low temperature film formation condition of 150 ° C. or less and is not activated even if boron is introduced into the film. In a so-called super straight type solar cell (pin type solar cell), the i layer is produced after the p layer is formed. However, if the i layer is produced at a high temperature of 200 ° C. or higher, boron in the p layer is converted into the i layer. When boron diffuses to the pi interface, boron strips off hydrogen in the i layer (so-called auto-doping), induces a defect level at the pi interface, and significantly deteriorates the solar cell characteristics. It is known from Patent Documents 1 and 2.

  In order to solve the above-described problem, Patent Document 1 discloses that gallium is used as a p-type dopant of a thin film silicon photoelectric conversion element instead of boron having a small atomic radius. Since gallium has larger atoms than boron and therefore less diffusion, it has a characteristic that a defect level is hardly formed at the pi interface. However, since gallium is a metal element, it is difficult to segregate in the thin film, and there is a problem that it is difficult to form a gallium-doped p-type thin film having the same absorption coefficient and carrier concentration as the boron-doped p-type thin film. It was.

Patent documents etc. are as follows.
Japanese Patent Application No. 2003-090794 “Formation of interface defects by enhanced impurity diffusion in microcrystalline silicon silicon cells”. Nasuno et. al. Appl. Phys. Lett. 81, 3155 (2002) Perrin et. al. Surf. Sci. 210, 114 (1989)

  However, since gallium is a metal element, it is difficult to segregate in the thin film, and there is a problem that it is difficult to form a gallium-doped p-type thin film having the same absorption coefficient and carrier concentration as the boron-doped p-type thin film. It was.

  Therefore, in a solar cell having at least one pin junction in which a p-type semiconductor layer mainly composed of silicon or germanium, a substantially intrinsic i-type semiconductor layer, and an n-type semiconductor layer is stacked, at least one p-type semiconductor layer Has a structure in which a boron-doped p-type semiconductor layer and a gallium-doped p-type semiconductor layer are stacked, and the gallium-doped p-type semiconductor layer is stacked on the interface side with the i-type semiconductor layer. There has been a need to provide solar cells with efficiency.

The present invention according to claim 1 is a solar cell having at least one pin junction in which a p-type semiconductor layer mainly composed of silicon or germanium, a substantially intrinsic i-type semiconductor layer, and an n-type semiconductor layer are stacked. At least one p-type semiconductor layer is composed of a laminate of a boron-doped p-type semiconductor layer and a gallium-doped p-type semiconductor layer, and the gallium-doped p-type semiconductor layer is laminated on the interface side with the i-type semiconductor layer. The non-single crystal solar cell characterized by the above is provided.
Further, the present invention according to claim 2 includes a boron-doped p-type microcrystalline silicon layer, a gallium-doped p-type microcrystalline silicon layer, and an i-type microcrystalline silicon between the transparent conductive film and the back electrode from the transparent conductive film side. A non-single-crystal solar cell in which a layer and an n-type amorphous silicon layer are stacked in this order is provided.
According to a third aspect of the present invention, there is provided the non-single crystal according to the second aspect , wherein the back electrode has a laminated structure of a transparent electrode on the n-type amorphous silicon layer side and a metal layer. A solar cell is provided.

  When a gallium-doped p-type semiconductor layer is stacked at the interface with the i-type semiconductor layer, gallium has a larger atomic radius than boron and is difficult to diffuse into the i-layer, so that the pi interface characteristics are unlikely to deteriorate. Therefore, for example, in a pin type solar cell (super straight type), there is an advantage that cell characteristics are not deteriorated even if the i layer is produced at a higher temperature than the conventional one. In addition, by using a boron-doped p layer in combination, a p layer having a low absorption coefficient and high conductivity can be realized.

According to a fourth aspect of the present invention, there is provided a p-type semiconductor layer mainly composed of silicon or germanium composed of a laminate of a boron-doped p-type semiconductor layer and a gallium-doped p-type semiconductor layer, and the gallium-doped p-type semiconductor layer side. A method for manufacturing a non-single-crystal solar cell having at least one pin junction in which a substantially intrinsic i-type semiconductor layer and an n-type semiconductor layer are stacked at the interface of the p-type semiconductor layer. Non-single crystal characterized in that a p-type semiconductor layer and a gallium-doped p-type semiconductor layer are formed by introducing a gas containing a boron supply material and a gallium supply material into a manufacturing apparatus for forming the p-type semiconductor layer, respectively. A method for manufacturing a solar cell is provided.
According to a fifth aspect of the present invention, in the invention according to the fourth aspect, the p-type semiconductor layer is mainly composed of silicon, and the boron supply material is a gas of diborane, trimethylboron, or boron fluoride. The manufacturing method of the non-single-crystal solar cell characterized by these is provided.
The present invention according to claim 6 is the invention according to claim 4, wherein the boron-doped p-type semiconductor layer is formed by a plasma CVD method using a mixed gas of silane, hydrogen, and dibosilane. The manufacturing method of the non-single-crystal solar cell as described in 1 is provided.
The present invention according to claim 7 provides a method for producing a non-single-crystal solar cell according to claim 4, wherein the gallium feedstock is a gas of trimethylgallium or triethylgallium. It is.
The present invention according to claim 8 is characterized in that the p-type semiconductor layer is mainly composed of silicon, and the gallium-doped p-type semiconductor layer is formed by a plasma CVD method using a mixed gas of silane, hydrogen, and trimethylgallium. The manufacturing method of the non-single-crystal solar cell of Claim 4 is provided.

  This makes it possible to produce a p-type semiconductor material having a unique structure.

  According to the present invention, in a solar cell having at least one p-junction in which a p-type semiconductor layer containing silicon or germanium as a main component, a substantially intrinsic i-type semiconductor layer, and an n-type semiconductor layer is laminated, at least one p The p-type semiconductor layer is composed of a laminate of a boron-doped p-type semiconductor layer and a gallium-doped p-type semiconductor layer, and the gallium-doped p-type semiconductor layer is laminated on the interface side with the i-type semiconductor layer. A solar cell having excellent efficiency can be provided.

  The gallium-doped p-type semiconductor layer and the boron-doped p-type semiconductor layer according to the present invention are any combination of plasma CVD, photo-CVD, thermal CVD, and hot-wire CVD. Alternatively, it can be formed by a vapor deposition method, a sputtering method, or the like, but a plasma CVD method is preferable. In order to introduce gallium, trimethylgallium or triethylgallium cooled as disclosed in Patent Document 1 is used as a feedstock, and after these materials are cooled, hydrogen or the like is used as a carrier gas into a vacuum chamber. The method introduced is preferable, but not limited thereto. In order to introduce boron, a method of introducing a gas such as diborane, trimethylboron, boron fluoride, or the like into the vacuum tube can be mentioned, but the method is not limited thereto.

  FIG. 4 shows an example of a schematic cross-sectional view of a non-single crystal solar cell including the p-type semiconductor layer of the present invention. It is preferable to use triethyl gallium or trimethyl gallium as the gallium feedstock and further cool the source temperature to 0 ° C. or lower. In order to control the introduction amount of the gallium material, hydrogen, deuterium, rare gas (helium, neon, argon, krypton xenon, etc.) or the like can be used as a carrier gas, but is not limited thereto. In addition, diborane, trimethylboron, boron fluoride, etc. can be used as the boron, and these gases can be introduced into the vacuum chamber by separate systems as shown in FIG. It can be integrated into a single system and introduced into the vacuum chamber. It is also possible to open a large number of holes in the cathode-side electrode and introduce the raw material from there (so-called cathode shower). Note that a manufacturing apparatus capable of supplying both the gallium supply material and the boron supply material is not limited thereto.

  The film thickness of the entire p-type semiconductor layer needs to be 8 nm or more and 45 nm or less, and preferably 15 nm or more and 25 nm or less. The thickness of the p-type semiconductor layer doped with gallium is not particularly limited as long as it is 1 nm to 40 nm and the thickness of the p-type semiconductor layer doped with boron is 1 nm to 40 nm. Preferably, the thickness of the p-type semiconductor layer doped with gallium is 5% to 30% of the total thickness of the p-type semiconductor layer, and the thickness of the p-type semiconductor layer doped with boron is 70% of the total thickness of the p-type semiconductor layer. It is 95% or less.

  The p-type semiconductor layer doped with gallium and the p-type semiconductor layer doped with boron may take any form of amorphous, microcrystal, or a mixture of amorphous and microcrystal.

  It is also preferable that C or O is mixed into the p layer in order to increase the band gap of the p-type semiconductor layer and efficiently take light into the i layer. In this case, methane, ethylene, acetylene or the like is used to introduce C, and carbon dioxide gas or the like is used to introduce O, but is not limited thereto. In order to obtain a high open circuit voltage, it is also preferable to gradually decrease C and O toward the i layer at the pi interface.

  The non-single-crystal solar cell mainly composed of silicon and germanium may have either a pin type (super straight type) solar cell or a nip type (substrate type) solar cell, so-called tandem type or triple type. A plurality of elements may be stacked like a solar cell.

  Examples of the transparent electrode include oxides such as tin oxide, indium oxide, and zinc oxide having a thickness of 10 to 500 nm, or metal thin films such as gold, platinum, palladium, silver, and alloys thereof having a thickness of 5 to 15 nm. It is not limited to these. These light-transmitting conductive films are preferably layers that transmit incident sunlight well and have a low surface resistance, and are preferably 5 to 15 nm thick gold and platinum layers and 30 to 200 nm thick tin-doped indium oxide layers. The transparent electrode is deposited by sputtering, vacuum deposition, ion plating, plasma CVD, sol-gel, printing, or the like.

  A grid electrode made of metal or the like can be formed on the transparent electrode. In this case, the grid electrode can be produced by a screen printing method, a vacuum deposition method, a sputtering method, an ion plating method, a plasma CVD method, a sol-gel method, or the like.

  As the back electrode, a metal thin film made of a metal such as iron, chromium, titanium, tantalum, niobium, molybdenum, nickel, aluminum, cobalt, or an alloy such as nichrome, stainless steel is used, but is not limited thereto. These metal layers are provided by means of vacuum deposition, sputtering, ion plating, printing, or plating. It is also possible to provide a transparent electrode having a thickness of 2 nm to 500 nm between the metal layer and the photoelectric conversion layer. Also, a so-called “see-through type solar cell” can be used in which a transparent conductive oxide thin film is used as the back electrode to provide transparency to the entire surface of the solar cell.

  The substrate of the solar cell of the present invention may be either an insulating material or a conductive material, and may be either flexible or inflexible. Specifically, glass, quartz, polymethyl methacrylate, polycarbonate, polystyrene, polyethylene sulfide, polyethersulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, triacetyl cellulose, polyvinyl fluoride film, ethylene-tetrafluoroethylene copolymer resin, Use weather resistant polyethylene terephthalate, weather resistant polypropylene, glass fiber reinforced acrylic resin film, glass fiber reinforced polycarbonate, polyimide, transparent polyimide, fluororesin, cyclic polyolefin resin, polyacrylic resin, SUS thin plate, Al foil, etc. However, it is not limited to these. These may be used as a single substrate, but a composite substrate in which two or more kinds are laminated can also be used.

  In order to increase the weather resistance of the solar cell element, it is possible to provide a gas barrier layer on either the above layer or between the layers. Any one of silicon oxide (SiOx), silicon nitride (SiNx), aluminum oxide (AlxOy) alone, or a mixed deposition layer of two or more kinds, or an inorganic-organic hybrid coat layer Alternatively, a composite layer in which two or more kinds are combined can be suitably used.

  Evaporation layers such as silicon oxide (SiOx), silicon nitride (SiNx), and aluminum oxide (AlxOy) can be easily formed on a substrate film by vapor deposition, sputtering, CVD, dipping, sol-gel, etc. can do. The thickness of such a barrier layer is suitably in the range of 5 to 500 nm, particularly preferably in the range of 30 to 150 nm.

  FIG. 1 is a schematic cross-sectional view of a non-single-crystal solar cell including a p-type semiconductor layer of the present invention, and FIG. 4 is a schematic cross-sectional view of an apparatus used for manufacturing the non-single-crystal loan battery of this example.

[Example 1]
First, ZnO doped with aluminum by a sputtering method was provided on Corning 7059 glass (thickness 0.5 mm) to a thickness of 200 nm. Subsequently, the glass (11) having this ZnO thin film was put in a vacuum vessel 10 as shown in FIG. 4 and placed under the upper electrode 20, and then heated to 170 ° C. The hydrogen mass flow 16 and the diborane mass flow 17 were opened, a film forming gas was introduced into the vacuum chamber, and a boron-doped p-type microcrystalline silicon layer was formed to 15 nm by the plasma CVD method with the following parameters under the following conditions.

SiH ₄ flow rate: 0.5 sccm, _{H 2} diluted _B 2 _{H 6} gas _{(H 2: 99%, B} 2 H 6 gas: 1%) Flow rate: 1 SCCM, _{H 2} flow rate: 500 SCCM, operating pressure 100 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 170 ° C. After film formation, the residual gas was evacuated and after confirming that the pressure had dropped to 7 × 10 ⁻⁵ Pa, the valve 17 was opened and the carrier hydrogen mass flow 14 From the mass flow 15 for hydrogen, 10 SCCM, 0.5 SCCM of silane from the mass flow 15 for silane, and 500 SCCM of hydrogen from the mass flow 16 for hydrogen are flown and maintained at a pressure of 100 Pa. The dopant material container 12 contains triethylgallium and is kept at −20 ° C. by a constant temperature bath 13. Here, power is supplied from the power source 18 to the lower electrode 19 (input power 15 W, excitation frequency 54.24 MHz), and a p-type gallium-doped microcrystalline silicon thin film is formed to 5 nm by plasma CVD.

Further, a microcrystalline i layer and an amorphous n layer were produced under the following conditions.
Microcrystal i layer production conditions SiH ₄ flow rate: 7 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 150 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 250 ° C., film thickness 300 nm
n-type amorphous layer forming conditions SiH ₄ flow rate: 10 SCCM, PH ₃ gas diluted with _{H 2 (H 2: 99%} , PH 3 gas: 1%) flow rate: 20 SCCM, operating pressure 20 Pa, input power 10 W, the excitation frequency 13. 56 MHz, substrate temperature: 250 ° C., film thickness 25 nm
Thereafter, the ZnO film was formed by sputtering to a thickness of 30 nm, and Ag was further provided by 200 nm vacuum evaporation.

[Tests and results]
The microcrystalline silicon solar cell having the p-type semiconductor layer of the present invention thus prepared, the microcrystalline silicon solar cell using the microcrystalline p layer doped with boron, and the microcrystal using the microcrystalline p layer doped with gallium The characteristics of the silicon solar cell were compared with Comparative Examples 1 and 2 described later, respectively.

  As shown in the comparison results of Table 1, it can be seen that the use of the p-type semiconductor layer of the present invention has higher open circuit voltage and short circuit current, and exhibits excellent cell characteristics.

[Comparative Example 1]
FIG. 2 is a schematic cross-sectional view of a conventional non-single crystal solar cell including a p-type semiconductor layer, and FIG. 4 is a schematic cross-sectional view of an apparatus used for manufacturing the non-single crystal loan battery of this example.

  First, ZnO doped with aluminum by a sputtering method was provided on Corning 7059 glass (thickness 0.5 mm) to a thickness of 200 nm.

Subsequently, the glass (11) having this ZnO thin film is placed in a vacuum chamber 10 as shown in FIG. 4 and placed under the upper electrode 20, and then heated to 170 ° C., and then boron-doped by plasma CVD. A p-type microcrystalline silicon layer was provided at 20 nm under the following conditions.
SiH ₄ flow rate: 0.5 sccm, _{H 2} diluted _B 2 _{H 6} gas _{(H 2: 99%, B} 2 H 6 gas: 1%) Flow rate: 1 SCCM, _{H 2} flow rate: 500 SCCM, operating pressure 100 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 170 ° C.
Further, a microcrystalline i layer and an amorphous n layer were produced under the following conditions.

Microcrystal i layer production conditions SiH ₄ flow rate: 7 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 150 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 250 ° C., film thickness 300 nm
n-type amorphous layer preparation conditions SiH ₄ flow rate: 10 SCCM, PH 3 gas diluted with H ₂ (H 2: 99%, PH 3 gas: 1%) flow rate: 20 SCCM, operating pressure 20 Pa, input power 10 W, excitation frequency 13.56 MHz, substrate Temperature: 250 ° C., film thickness 25 nm
Thereafter, the ZnO film was formed by sputtering to a thickness of 30 nm, and Ag was further provided by 200 nm vacuum evaporation.

[Comparative Example 2]
FIG. 3 shows a schematic cross-sectional view of a conventional non-single crystal solar cell including a p-type semiconductor layer, and FIG. 4 shows a schematic cross-sectional view of an apparatus used for manufacturing the non-single crystal loan battery of this example.

  First, ZnO doped with aluminum by a sputtering method was provided on Corning 7059 glass (thickness 0.5 mm) to a thickness of 200 nm.

  Subsequently, the glass (11) having the ZnO thin film is placed in a vacuum chamber 10 as shown in FIG. Hydrogen is supplied at 500 SCCM from the hydrogen mass flow 16 at 0.5 SCCM, and the pressure is maintained at 100 Pa. The dopant material container 12 contains triethylgallium and is kept at −20 ° C. by a constant temperature bath 13. Here, power is supplied from the power source 18 to the lower electrode 19 (input power 15 W, excitation frequency 54.24 MHz), and a p-type gallium-doped microcrystalline silicon thin film is formed to 20 nm by plasma CVD.

Further, a microcrystalline i layer and an amorphous n layer were produced under the following conditions.
Microcrystal i layer production conditions SiH ₄ flow rate: 7 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 150 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 250 ° C., film thickness 300 nm
n-type amorphous layer forming conditions SiH ₄ flow rate: 10 SCCM, PH ₃ gas diluted with _{H 2 (H 2: 99%} , PH 3 gas: 1%) flow rate: 20 SCCM, operating pressure 20 Pa, input power 10 W, the excitation frequency 13. 56 MHz, substrate temperature: 250 ° C., film thickness 25 nm
Thereafter, the ZnO film was formed by sputtering to a thickness of 30 nm, and Ag was further provided by 200 nm vacuum evaporation.

  The present invention relates to a p-type semiconductor layer of a thin film non-single crystal solar cell using a non-single crystal film such as a microcrystalline film, an amorphous film, or a polycrystalline film.

The schematic sectional drawing of the non-single-crystal solar cell containing the p-type semiconductor layer of this invention is shown. The schematic sectional drawing of the non-single-crystal solar cell containing the p-type semiconductor layer only of boron dope of a prior art example is shown. The schematic sectional drawing of the non-single-crystal solar cell containing the p-type semiconductor layer only of a gallium dope of a prior art example is shown. The schematic sectional drawing of the apparatus used in order to produce the non-single-crystal loan battery of a present Example is shown.

1. Base material 2. 2. Transparent conductive film 3. Boron-doped p-type semiconductor layer 4. Gallium-doped p-type semiconductor layer 5. i-type microcrystalline thin film n-type thin film 7. Transparent conductive film 2
8). Metal electrode 10. Vacuum bowl 11. Sample 12. 14. Container for dopant raw material High temperature soot 14. 14. Mass flow for carrier hydrogen 16. Mass flow for silane 16. Mass flow for hydrogen Mass flow for diborane 18. Automatic pressure control device

Claims (8)

  In a solar cell having at least one pin junction in which a p-type semiconductor layer mainly composed of silicon or germanium, a substantially intrinsic i-type semiconductor layer, and an n-type semiconductor layer is laminated, at least one p-type semiconductor layer is boron-doped. A non-single crystal solar cell comprising a laminate of a p-type semiconductor layer and a gallium-doped p-type semiconductor layer, wherein the gallium-doped p-type semiconductor layer is laminated on the interface side with the i-type semiconductor layer . A boron-doped p-type microcrystalline silicon layer, a gallium-doped p-type microcrystalline silicon layer, an i-type microcrystalline silicon layer, and an n-type amorphous silicon layer between the transparent conductive film and the back electrode, Are non-single crystal solar cells stacked in this order. The non-single-crystal solar cell according to claim 2 , wherein the back electrode has a laminated structure of a transparent electrode on the n-type amorphous silicon layer side and a metal layer. A p-type semiconductor layer mainly composed of silicon or germanium composed of a laminate of a boron-doped p-type semiconductor layer and a gallium-doped p-type semiconductor layer, and a p-type semiconductor layer interface on the gallium-doped p-type semiconductor layer side. A method of manufacturing a non-single-crystal solar cell having at least one pin junction in which a substantially intrinsic i-type semiconductor layer and an n-type semiconductor layer are stacked,
  A boron-doped p-type semiconductor layer and a gallium-doped p-type semiconductor layer are formed by introducing a gas containing a boron supply material and a gallium supply material into a manufacturing apparatus for forming the p-type semiconductor layer, respectively. A method for producing a crystalline solar cell. The method for producing a non-single-crystal solar cell according to claim 4, wherein the boron feedstock is a gas of diborane, trimethylboron, or boron fluoride.   5. The non-single-crystal solar cell according to claim 4, wherein the p-type semiconductor layer is mainly composed of silicon, and the boron-doped p-type semiconductor layer is formed by a plasma CVD method using a mixed gas of silane, hydrogen, and dibosilane. Battery manufacturing method. The method for producing a non-single-crystal solar cell according to claim 4, wherein the gallium feedstock is a gas of trimethylgallium or triethylgallium.   5. The non-single-type semiconductor device according to claim 4, wherein the p-type semiconductor layer is mainly composed of silicon, and the gallium-doped p-type semiconductor layer is formed by a plasma CVD method using a mixed gas of silane, hydrogen, and trimethylgallium. A method for producing a crystalline solar cell.

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