JP5109230B2 - Non-single crystal solar cell manufacturing method - Google Patents

Description

  The present invention relates to 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, and a method for manufacturing the same.

  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. It is known that boron diffuses into the pi interface and boron in the i layer is stripped of hydrogen in the i layer (so-called auto-doping), induces defect levels at the pi interface, and greatly deteriorates the solar cell characteristics. It has been.

Known documents are shown below.
“Formation of interface defects by enhanced impurity diffusion in microcrystalline silicon solar cells” Y. Nasuno et.al. Appl.Phys.Lett. 81, 3155 (2002). "Perrin et.al. Surf. Sci. 210, 114 (1989)".

  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. For this reason, it was a non-single crystal solar cell with inferior fill factor and conversion efficiency.

The known patent documents are shown below.
Japanese Patent Application No. 2003-090794

  The present invention has been made in view of such problems. A non-single-crystal solar cell having excellent cell characteristics, a good fill factor and conversion efficiency, and a method for manufacturing the non-single crystal solar cell, as compared with a boron-doped p-type thin film. The issue is to provide.

  Therefore, in order to achieve the above-mentioned problems, the present invention takes the following measures.

The invention of claim 1 of the present invention, p-type semiconductor layer composed mainly of silicon down, the production of substantially intrinsic i-type semiconductor layer, a solar cell having at least one pin junction formed by laminating an n-type semiconductor layer In the method, at least one p-type semiconductor layer is formed by alternately laminating a gallium-doped p-type semiconductor layer and a boron-doped p-type semiconductor layer to form a delta-doped layer, and the gallium-doped p-type semiconductor layer comprises: , Silane and hydrogen are introduced into a vacuum chamber, trimethylgallium or triethylgallium is further cooled, hydrogen is introduced into the vacuum chamber as a carrier gas, and formed by a plasma CVD method. The boron-doped p-type semiconductor layer is formed by: Silane and hydrogen are introduced into the vacuum chamber, and then diborane, trimethylboron, or boron fluoride is introduced into the vacuum chamber and plasma is introduced. It is obtained by a method for producing a non-single-crystal solar cells, and forming the VD method.

The invention of claim 2 of the present invention, the delta doped p-type semiconductor layer, and a method for producing a non-single-crystal solar cell according to claim 1, wherein the pi interface side and forming gallium-doped p-type semiconductor layer Is.

  A gallium / boron-doped p layer without segregation can be produced by using a p-layer having a structure in which gallium-doped p-layer / boron-doped p-layer are stacked in a superlattice form (delta-doped). 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 in the past. In addition, gallium and boron are easily activated by this technique, and the doping efficiency is increased, so that a solar cell device with high conversion efficiency can be provided.

  In addition, gallium has a characteristic that it is difficult to diffuse into the i layer as compared with boron. Therefore, if the p-type semiconductor layer is formed of a gallium-doped p-type semiconductor layer at the interface between the p-type semiconductor layer and the i-type semiconductor layer, i Since the diffusion of the dopant into the mold layer can be prevented, higher conversion efficiency can be realized.

  In addition, the p-type semiconductor material according to claim 1 can be produced by using an apparatus capable of supplying both a gallium feedstock and a boron feedstock.

  As described above, according to the present invention, 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. In the above, at least one p-type semiconductor layer is a delta doped layer including a gallium doped p layer and a boron doped p layer, so that a solar cell having excellent efficiency can be provided.

  Specific embodiments of the invention will be described in detail below.

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 of introduction is preferable, but is 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. 2 is an explanatory view showing an example of an apparatus for manufacturing a non-single crystal solar cell including a p-type semiconductor layer according to the present invention. It is preferable to use triethyl gallium or trimethyl gallium as the gallium feedstock (stored in the dopant material container 12), and further cool the source temperature to 0 ° C. or lower (using the thermostatic chamber 13). 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. As the boron, diborane, trimethylboron, boron fluoride, etc. can be used, and these gases can be introduced into the vacuum chamber 10 by separate systems as shown in FIG. Among them, they can be integrated into one system and introduced into a vacuum chamber (using carrier hydrogen mass flow 14, silane mass flow 15, hydrogen mass flow 16, diborane mass flow 17, etc.). It is also possible to open a large number of holes in the electrode on the cathode side and introduce the source 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 unit layer constituting the delta dope is preferably 1 A or more and 5 nm or less, but is not limited thereto. In order to increase the band gap of the gallium-doped and boron-doped p-type semiconductor layers constituting the delta dope, it is also preferable to incorporate carbon or oxygen into the film. In this case, methane, ethylene, acetylene, or the like is used to introduce carbon, and carbon dioxide gas or the like is used to introduce oxygen, but is not limited thereto. In order to obtain a high open circuit voltage, it is also preferable to gradually reduce carbon and oxygen toward the i layer direction 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 CV D, 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.

A method for manufacturing a solar cell having a p-type semiconductor layer of the present invention will be specifically described below. However, the present invention is not limited to these.
[Example 1]
FIG. 1A is a schematic cross-sectional view of an embodiment of a non-single crystal solar cell including a p-type semiconductor layer, and FIG. 1B is a schematic cross-section of a p-type semiconductor layer according to the non-single crystal solar cell of the present invention. FIG. FIG. 2 is an explanatory view showing an example of an apparatus for manufacturing a non-single crystal solar cell including a p-type semiconductor layer according to the present invention.

  First, on the Corning 1737 glass (thickness 0.5 mm) of the substrate 1, ZnO of the transparent electrode 2 doped with aluminum by a sputtering method was provided with a film thickness of 200 nm. Subsequently, the glass having this ZnO thin film was used as a sample 11 in a vacuum chamber 10 as shown in FIG. 2 and placed under the upper electrode 21. Then, the temperature was raised to 170 ° C., the valve 20 was opened, and silane was used. A film forming gas was introduced into the vacuum chamber through the mass flow 15, the hydrogen mass flow 16, and the diborane mass flow 17, and a boron-doped p-type microcrystalline silicon layer 32 was provided by 5A by the plasma CVD method with the following parameters (FIG. 1B). )).

SiH ₄ flow rate: 2.5 sccm, H ₂ flow rate: 500SCCM, B ₂ H ₆ gas diluted with _{H 2 (H 2: 99%} , B 2 H 6 gas: 1%) Flow rate: 1 SCCM, operating pressure 200 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 170 ° C.
After film formation, the introduced gas is stopped and the inside of the vacuum chamber is evacuated to 7 × 10 ⁻⁵ Pa. Then, the valves 19 and 20 are opened, the silane mass flow 15, the hydrogen mass flow 16, the carrier hydrogen mass flow 14, automatic pressure control. A film forming gas was introduced into the vacuum chamber 10 through the apparatus 18, and a 5A gallium-doped p-type microcrystalline silicon layer 31 was provided by plasma CVD with the following parameters (
FIG. 1 (b)). The dopant material container 12 contains triethylgallium and is kept at −20 ° C. by a constant temperature bath 13.

SiH ₄ flow rate: 2.5 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 200 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 170 ° C.
This operation was repeated 20 times, and a delta-doped p-type semiconductor layer 3 composed of [gallium-doped p-type microcrystalline layer (5A) / boron-doped p-type microcrystalline layer (5A)] was laminated to a thickness of 20 nm (FIG. 1B). ).

Further, a microcrystalline i layer 5 and an amorphous n layer 6 were produced under the following conditions.
Microcrystal i layer 5 preparation conditions SiH ₄ flow rate: 15 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 266 Pa, input power 5 W, excitation frequency 54.24 MHz, substrate temperature: 250 ° C., film thickness 2 μm
n-type amorphous layer 6 creates 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 as a transparent conductive film (2) 7 with a thickness of 30 nm by sputtering, and Ag as a metal electrode 8 was provided with a thickness of 500 nm by vacuum deposition.

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

  First, on the Corning 1737 glass (thickness 0.5 mm) of the base material 1, ZnO of the transparent electrode film 2 doped with aluminum by a sputtering method was provided with a film thickness of 200 nm. Subsequently, the glass having this ZnO thin film was used as a sample 11 in a vacuum trough 10 as shown in FIG. 2 and placed under the upper electrode 21, and then heated to 170 ° C., and the valves 19 and 20 were opened. , Silane mass flow 15, hydrogen mass flow 16, carrier hydrogen mass flow 14, and automatic pressure controller 18 are used to introduce a deposition gas into the vacuum chamber and gallium-doped p-type microcrystalline silicon by plasma CVD with the following parameters: A layer of 20 nm was provided. The dopant material container 12 contains triethylgallium and is kept at −20 ° C. by a constant temperature bath 13.

SiH ₄ flow rate: 2.5 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 200 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 170 ° C.
Further, a microcrystalline i layer 5 and an amorphous n layer 6 were produced under the following conditions.

Microcrystal i layer 5 preparation conditions SiH ₄ flow rate: 15 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 266 Pa, input power 5 W, excitation frequency 54.24 MHz, substrate temperature: 250 ° C., film thickness 2 μm
n-type amorphous layer 6 creates 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 as a transparent electrode film (2) 7 with a thickness of 30 nm as a transparent electrode film (2) 7 by a sputtering method, and Ag was further provided by a 500 nm vacuum evaporation method.

[Comparative Example 2]
FIG. 1A is a schematic cross-sectional view of a non-single-crystal solar cell including a p-type semiconductor layer of another comparative example, and FIG. 2 is a schematic cross-sectional view of an apparatus used for producing the non-single-crystal solar cell of this example. The figure is shown.

  First, on the Corning 1737 glass (thickness 0.5 mm) of the base material 1, ZnO of the transparent electrode film 2 doped with aluminum by a sputtering method was provided with a film thickness of 200 nm. Subsequently, the glass having this ZnO thin film was used as a sample 11 in a vacuum chamber 10 as shown in FIG. 4 and placed under the upper electrode 21, then heated to 170 ° C., the valve 20 was opened, A film forming gas was introduced into the vacuum chamber 10 through the mass flow 15 for hydrogen, the mass flow 16 for hydrogen, and the mass flow 17 for diborane, and a boron-doped p-type microcrystalline silicon layer having a thickness of 20 nm was formed by plasma CVD using the following parameters.

SiH ₄ flow rate: 2.5 sccm, H ₂ flow rate: 500SCCM, B ₂ H ₆ gas diluted with _{H 2 (H 2: 99%} , B 2 H 6 gas: 1%) Flow rate: 1 SCCM, operating pressure 200 Pa, input power 15 W, excitation frequency 54.24 MHz, substrate temperature: 170 ° C.
Further, a microcrystalline i layer 5 and an amorphous n layer 6 were produced under the following conditions.
Microcrystal i layer 5 preparation conditions SiH ₄ flow rate: 15 SCCM, H ₂ flow rate: 500 SCCM, operating pressure 266 Pa, input power 5 W, excitation frequency 54.24 MHz, substrate temperature: 250 ° C., film thickness 2 μm
n-type amorphous layer 6 creates 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 as a transparent electrode film (2) 7 with a thickness of 30 nm as a transparent electrode film (2) 7 by sputtering, and Ag was provided as a metal electrode 8 with a vacuum evaporation method at 500 nm.

[Tests and results]
The characteristics of the microcrystalline silicon solar cell having the p-type semiconductor layer of the present invention thus fabricated, the microcrystalline p layer doped with gallium, and the microcrystalline silicon solar cell using the microcrystalline p layer doped with boron are compared. did. A comparative example is shown in Table 1.

  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.

It is a schematic sectional drawing of the Example of the non-single-crystal solar cell containing a p-type semiconductor layer. It is explanatory drawing which showed an example of the manufacturing apparatus of the non-single-crystal solar cell containing the p-type semiconductor layer of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Transparent conductive film 3 ... p-type semiconductor layer 31 ... Gallium doped p-type microcrystalline silicon layer 32 ... Boron doped p-type microcrystalline silicon layer 5 .... Microcrystalline i layer 6 ... Amorphous n layer 7 ... Transparent conductive film (2)
8 .... Metal electrode 10 ... Vacuum bowl 11 ... Sample 12 ... Dopant material container 13 ... Constant temperature bowl 14 ... Carrier hydrogen mass flow 15 ... Silane mass flow 16 ...・ Hydrogen mass flow 17 ・ ・ ・ Diborane mass flow 18 ・ ・ ・ Automatic pressure controller 19 ・ ・ ・ Valve 20 ・ ・ ・ Valve 21 ・ ・ ・ Upper electrode 22 ・ ・ ・ Lower electrode 23 ・ ・ ・ Power supply

Claims (2)

P-type semiconductor layer to the silicon down mainly in a substantially intrinsic i-type semiconductor layer, the manufacturing method of the solar cell having at least one pin junction formed by laminating an n-type semiconductor layer,
Forming at least one p-type semiconductor layer by alternately laminating gallium-doped p-type semiconductor layers and boron-doped p-type semiconductor layers, and forming a delta-doped layer; and
The gallium-doped p-type semiconductor layer is formed by plasma CVD by introducing silane and hydrogen into a vacuum chamber, further cooling trimethylgallium or triethylgallium and introducing hydrogen into the vacuum chamber as a carrier gas,
The boron-doped p-type semiconductor layer is formed by a plasma CVD method by introducing silane and hydrogen into a vacuum chamber and further introducing any one of diborane, trimethylboron, and boron fluoride into the vacuum chamber. A method for producing a non-single crystal solar cell. 2. The method for producing a non-single-crystal solar cell according to claim 1, wherein a pi-doped p-type semiconductor layer is formed on a pi interface side of the delta-doped p-type semiconductor layer.

Images