JP2004087933A - Plasma enhanced cvd system, method of manufacturing photovoltaic element, and photovoltaic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma enhanced CVD system with which a photovoltaic element having an excellent photoelectric conversion characteristic can be manufactured without giving damages to a transparent electrode which is the base layer of a p-type microcrystalline layer or an n-type amorphous layer, and to provide a method of manufacturing photovoltaic element and a photovoltaic element. <P>SOLUTION: The plasma enhanced CVD system 30 is provided with a substrate heater 7 which heats a substrate 22 by holding the rear surface of the substrate 22 and an electrode 2 provided to face the heater 7. The system 30 forms a semiconductor layer on the surface side of the substrate 22 by generating a plasma gas between the heater 7 and electrode 2 by supplying a gaseous starting material between the heater 7 and electrode 2. This system 30 is also provided with a heater 12 which heats the surface side of the substrate 22 between the substrate heater 7 and electrode 2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a photovoltaic element manufactured by a plasma CVD method, a photovoltaic element, and an apparatus for manufacturing the same.
[0002]
[Prior art]
A typical example of a photovoltaic element using a silicon-based thin film is an amorphous silicon-based solar cell. Amorphous silicon is usually manufactured by a plasma CVD method using a silicon hydride gas such as silane or disilane as a source gas. In general, a high frequency power supply having a frequency of 13.56 MHz is most commonly used for generating plasma. Amorphous silicon is characterized in that it can be formed on an inexpensive substrate such as glass, metal, or plastic at a low temperature of 200 ° C. or lower, and that a large-area film can be formed. Amorphous silicon-based solar cells are expected to be superior to bulk silicon solar cells made of single-crystal silicon or polycrystalline silicon. Is being promoted.
[0003]
However, when the amorphous silicon solar cell is irradiated with light, defects occur in the i-layer, which is a photoelectric conversion layer, and photocarriers are trapped. Therefore, the photoelectric conversion efficiency is reduced by 10% compared to the initial state. The photodegradation phenomenon (the so-called Stepler-Lonski effect), which is reduced by about 30%, is a major obstacle to practical use. Although various studies have been conducted energetically on the mechanism of the photodegradation phenomenon, it has not been completely elucidated, and at present, no drastic solution has been established.
[0004]
In contrast, in recent years, attempts have been reported to use microcrystalline silicon instead of amorphous silicon as the i-type photoelectric conversion layer (J. Meier et al., Mat. Res. Soc. Symp. Proc. Vo.420.P3 (1996)). According to this, a pin-type photovoltaic element is formed by a high-frequency plasma CVD method using a power supply in a VHF band at a frequency of 110 MHz, and it is reported that the pin-type photovoltaic element does not involve a photodegradation phenomenon such as amorphous silicon. . In addition, a photovoltaic element using microcrystalline silicon as a photoelectric conversion layer has a peak in a spectral sensitivity spectrum on a longer wavelength side as compared with a photovoltaic element using amorphous silicon, It is also possible to increase the efficiency of photoelectric conversion by a so-called tandem type of stacked photovoltaic element in which porous silicon is used as a top cell and microcrystalline silicon is used as a photoelectric conversion layer in a bottom cell.
[0005]
As described above, the photovoltaic element using microcrystalline silicon has an advantage that a film can be formed by a plasma CVD method having a configuration basically similar to that of the related art, and there is no light deterioration phenomenon. Here, the microcrystalline silicon film means a film other than amorphous silicon, and includes a polycrystalline silicon film and a crystalline silicon film containing amorphous in the film. In a photovoltaic element using a layer, a so-called pin type is usually adopted, and in this case, microcrystalline silicon is used for the p layer and the n layer similarly to the i layer. Photovoltaic elements using this microcrystalline silicon can be roughly classified into a substrate type and a superstrate type from the structural difference.
[0006]
The substrate type element is provided with a substrate that does not transmit light, for example, a substrate made of stainless steel or the like, and has a configuration in which light is incident from the side opposite to the substrate. On the other hand, the superstrate type element includes a substrate such as glass that transmits light, and has a configuration in which light is incident from the substrate side. This superstrate element has a feature that an integrated module similar to that of amorphous silicon can be formed.
[0007]
Here, the crystalline silicon p-type semiconductor layer (hereinafter, referred to as a microcrystalline p-layer) usually contains boron as a doping element in order to control its electric characteristics. It is empirically known that the boron element hinders the crystal growth of silicon. Therefore, in order to grow a microcrystalline p-layer containing boron, the film is formed under a film-forming condition set at a higher substrate temperature or a higher VHF power than other layers in order to promote crystal growth. .
[0008]
[Problems to be solved by the invention]
However, under such a film formation condition set at a high substrate temperature or a high VHF power, severe conditions are applied to the underlayer, such as deterioration of the film quality of the underlayer. For example, when a transparent electrode of a metal oxide is an underlayer, when a microcrystalline p-layer is formed at a high substrate temperature or under a high VHF power, the transparent electrode is reduced, and the light transmittance and electrical conductivity of the transparent electrode are reduced. However, there is a problem that the metal element deposited by this reduction is diffused into the microcrystalline p-layer and the electrical characteristics thereof are significantly reduced.
In the case of a tandem element, when a microcrystalline p-layer is formed on an amorphous n-layer as a base layer under the same film-forming conditions as described above, the amorphous n-layer is etched, and the thickness of the amorphous n-layer is reduced. There is a problem of becoming thin. Further, there is a problem that phosphorus which is a doping element of the amorphous silicon n-layer is precipitated and diffuses into the microcrystalline p-layer, thereby significantly deteriorating its electrical characteristics.
[0009]
The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a transparent electrode or an amorphous n-layer which is a base layer of a microcrystalline p-layer, and have good photoelectric conversion characteristics. It is an object of the present invention to provide a plasma CVD apparatus for manufacturing a photovoltaic element having a photovoltaic element, a method for manufacturing a photovoltaic element, and a photovoltaic element.
[0010]
[Means for Solving the Problems]
In order to solve the above problems and achieve such an object, the present invention proposes the following means.
The plasma CVD apparatus of the present invention includes a substrate heater for holding the back surface of a substrate and heating the substrate, and an electrode provided opposite to the substrate heater, and a source gas is provided between the substrate heater and the electrode. A plasma CVD apparatus that generates a plasma gas between the substrate heater and the electrode to form a semiconductor layer on the substrate surface side, wherein the substrate heater and the electrode A heater for heating the front surface side of the substrate is provided.
[0011]
Further, in the plasma CVD apparatus according to the present invention, the heater is provided with a wire mesh heater body or a flat heater body having a plurality of holes penetrating the front and back surfaces.
[0012]
Further, in the plasma CVD apparatus according to the present invention, the source gas is a gas containing silicon, and a microcrystalline silicon layer is formed as the semiconductor layer.
[0013]
In these plasma CVD apparatuses, since a heater for heating the front surface of the substrate is provided between the substrate heater and the electrode, when a semiconductor layer is formed on the front surface of the substrate, the semiconductor layer is heated from the front side and the back side of the substrate. The substrate can be heated. Accordingly, the semiconductor layer can be favorably formed even when film forming conditions for forming the semiconductor layer, for example, high-frequency power, substrate temperature, and the like are conditions under which the load on the underlying layer is low. Furthermore, since the heater includes a wire mesh heater body or a plate-like heater body having a plurality of holes penetrating through the front and back surfaces, a plasma gas can be favorably generated between the substrate and the electrode. In addition, it is possible to form a semiconductor layer exhibiting the above-mentioned effects without causing a manufacturing defect.
[0014]
The method of manufacturing this photovoltaic element comprises simultaneously supplying a source gas containing silicon and a hydrogen gas between a substrate and an electrode, applying a high frequency to generate a plasma gas, and forming microcrystalline silicon on the substrate surface side. A microcrystalline p-layer, a microcrystalline i-layer, and a microcrystalline n-layer in which a microcrystalline n-layer is sequentially stacked, the method comprising the steps of: Before forming the silicon bulk layer, an initial layer of microcrystalline silicon is previously formed on the substrate front side while heating the substrate from the substrate front side and the back side using the plasma CVD apparatus according to claim 3. It is characterized by forming.
[0015]
Further, in the method of manufacturing a photovoltaic device of the present invention, before forming the bulk layer, the initial layer is heated at a lower heating temperature than the heating temperature of the substrate rear surface when the bulk layer is formed. It is characterized by forming.
[0016]
In these photovoltaic device manufacturing methods, before forming a microcrystalline silicon bulk layer, the substrate is heated in advance from the substrate front side and the back side, and an initial layer of microcrystalline silicon is formed on the substrate front side. Since the back surface of the substrate is heated to form the bulk layer on the initial layer, the temperature of the back surface of the substrate can be set to a low temperature among the film forming conditions for forming the initial layer. That is, since the initial layer is formed by heating not only the front surface but also the back surface of the substrate, the surface diffusion of hydrogen radicals and silicon-based radicals involved in the formation of the initial layer is promoted even under the above-mentioned film forming conditions. State. This makes it possible to form a favorable photovoltaic element without hindering the crystallization of the microcrystalline p-layer initial layer even under film-forming conditions that can minimize the load applied to the underlayer. it can. As described above, a photovoltaic element having high photoelectric conversion efficiency can be favorably formed. In the above-described manufacturing method, the same effect as described above can be obtained even when the VHF power is set to a low power among the film forming conditions.
[0017]
In the method for manufacturing a photovoltaic element according to the present invention, the thickness of the initial layer is set to 5 nm or more and 100 nm or less. The thickness is particularly preferably from 10 nm to 50 nm.
[0018]
In this method for manufacturing a photovoltaic element, the thickness of the initial layer is set to 5 nm or more and 100 nm or less, so that diffusion of elements and the like deposited from the underlayer into the microcrystalline p layer is suppressed, and the semiconductor of the microcrystalline p layer is formed. The occurrence of characteristic deterioration can be suppressed. Further, the amount of light absorption in the initial layer can be optimized, and a decrease in short-circuit current as a photovoltaic element can be suppressed. As described above, a photovoltaic element having high photoelectric conversion efficiency can be formed.
[0019]
Further, in the method of manufacturing a photovoltaic device according to the present invention, before forming the cell, an amorphous p layer, an amorphous i layer, and an amorphous silicon It is characterized in that an amorphous n-layer is sequentially formed.
[0020]
In this method of manufacturing a photovoltaic element, before forming the cell, an amorphous p layer, an amorphous i layer, and an amorphous n Since the layers are sequentially stacked, a tandem photovoltaic element having high photoelectric conversion efficiency can be formed.
[0021]
A photovoltaic device according to the present invention is manufactured by the method for manufacturing a photovoltaic device according to any one of claims 4 to 7.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of a photovoltaic element and a method for manufacturing the same according to the present invention will be described with reference to FIGS.
The photovoltaic element 23 shown in FIG. 1 includes a substrate 22, a cell 21 made of a microcrystalline silicon element, and a back electrode 17, which are sequentially stacked. The substrate 22 is made of a glass substrate 9 that transmits light, ITO, tin oxide SnO ₂ Alternatively, a transparent electrode 13 made of a metal oxide such as zinc oxide ZnO is provided, and these are sequentially laminated. The cell 21 includes a microcrystalline p-layer 14 made of p-type microcrystalline silicon, a microcrystalline i-layer 15 made of i-type microcrystalline silicon, and a microcrystalline n-layer 16 made of n-type microcrystalline silicon. , Are sequentially laminated.
[0023]
The microcrystalline p-layer 14 is composed of an initial layer 14a laminated on the surface of the transparent electrode 13 in an initial stage of film formation described later, and a bulk layer 14b laminated on the surface of the initial layer 14a. The temperatures of the substrate 9 and the transparent electrode 13 when forming the initial layer 14a are set to be lower than the temperatures when forming the bulk layer 14b, as described later.
[0024]
A method of manufacturing the microcrystalline p-layer 14, the microcrystalline i-layer 15, and the microcrystalline n-layer 16, that is, the microcrystalline silicon layer in the photovoltaic element 23 configured as described above will be described. First, the plasma CVD apparatus 30 used for manufacturing the initial layer 14a constituting the microcrystalline p layer 14 of the microcrystalline silicon layer will be described with reference to FIG.
[0025]
The plasma CVD apparatus 30 shown in FIG. 2 is provided so as to oppose the substrate heater 7, the stainless steel vacuum vessel 1, the gas mixing box 11, the substrate heater 7 for holding the back surface of the substrate 22 and heating the substrate 22. The electrode 2 for discharging, the vacuum pump 8 for reducing the pressure in the vacuum vessel 1, and the substrate 2 are provided between the substrate heater 7 and the electrode 2 and connected to the power supply 12b to heat the front side of the substrate 22. A heater 12 is provided. The substrate heater 7 includes a mechanism (not shown) for closely holding the surface of the substrate 22 on which the glass substrate 9 is formed, and a temperature sensor (not shown) provided so that the temperature of the substrate 22 can be detected indirectly or directly. . The temperature sensor is connected to an input section of a controller (not shown). When a temperature detection signal is input to the controller, the controller controls the amount of power supplied to the substrate heater 7 based on the signal.
[0026]
The electrode 2 is disposed so as to face the substrate heater 7, and is connected to the impedance matching device 5 and the high frequency power supply 4 via the coaxial cable 10. Further, the power supply line from the high-frequency power supply 4 to the electrode 2 is branched, and a multipoint power is supplied to a plurality of points of the electrode 2 via each branch line. Can be alleviated.
[0027]
As shown in FIG. 3, the heater 12 that heats the front side of the substrate 22 abuts the heater main body 31 in a rectangular shape formed in a wire mesh, and two opposing sides of the heater main body 31 to contact the heater main body 31. Fixing jigs 32 to be held, tension adjusting mechanisms 33 provided at both ends of each fixing jig 32 so as to protrude in a direction away from the heater main body 31, and having a spring member 33 a at a distal end thereof; And an insulator member 34 provided on the fixing jig 32 so as to cover 33, and these components are covered with an outer frame 35 except for the tension adjusting mechanism 33 and the distal end portion of the insulator member 34. I have. That is, the distal ends of the tension adjusting mechanism 33 and the insulator member 34 are configured to protrude from the outer frame 35. A power supply terminal 32a is provided on one end side of one fixing jig 32 provided on one side of the heater main body 31, so that the heater main body 31 can be heated and adjusted in temperature. I have. Here, the heater main body 31 is formed in a wire mesh shape as described above, and has a configuration in which a plasma gas can be favorably generated between the electrode 2 and the substrate heater 7.
[0028]
In the plasma CVD apparatus 30 configured as described above, first, the substrate 22 that has been degreased, washed and dried is held in close contact with the surface of the substrate heater 7, and then the inside of the vacuum vessel 1 is exhausted by the vacuum pump 8 through the exhaust pipe 3. 1.33 × 10 ^-4 Exhaust to below Pa. Next, the raw material gas is supplied to the gas mixing box 11 at a predetermined flow rate via the raw material gas introduction pipe 6. The flow rate of the source gas is controlled by a mass flow controller (not shown).
[0029]
As a source gas, a gas containing at least silicon, specifically, a silicon hydride gas such as silane or disilane, a silicon fluoride gas, a halosilane gas such as dichlorosilane or trichlorosilane, and hydrogen are used. Further, a gas containing a group III element such as B ₂ H ₆ , BF ₃ A gas containing boron is added. Here, the flow rate ratio of hydrogen to the flow rate of the gas containing silicon is set to 5 times or more and 100 times or less. This is because, when the flow rate ratio of hydrogen is less than 5, the amount of hydrogen radicals generated is small, so that the termination of dangling bonds on the surface of the growing film becomes insufficient. Is insufficient, and microcrystalline silicon having good crystallinity is not sufficiently grown. On the other hand, when the flow rate ratio of hydrogen exceeds 100 times, although microcrystalline silicon grows, since the silicon-based radicals involved in film formation are small, the film formation speed becomes extremely low and is thicker than amorphous silicon. This is because, in the case of a microcrystalline silicon-based photovoltaic element requiring a photoelectric conversion layer, productivity is significantly reduced.
[0030]
Next, the pressure inside the vacuum vessel 1 is set to 13.3 Pa or more and 665 Pa or less by a pressure adjusting valve (not shown). If the pressure is less than 13.3 Pa, since the amount of silicon-based radicals involved in film formation is small, the film formation speed is extremely low, and the productivity is significantly reduced. On the other hand, if the pressure exceeds 665 Pa, powder is likely to be generated in the gas phase during film formation. The powder generated during the film formation is taken into the film and extremely deteriorates the film quality of the microcrystalline silicon, and also has an adverse effect such as increasing the frequency of the open maintenance of the vacuum vessel 1.
[0031]
Concurrently with the pressure adjustment in the vacuum vessel 1, the substrate heater 7 and the heater 12 are energized and heated so that the substrate 22 is heated to 100 ° C. or more and 500 ° C. or less even when the substrate 22 is provided with an inexpensive material such as glass. . If the substrate temperature is lower than 100 ° C., the surface diffusion of silicon-based radicals involved in film formation adsorbed on the surface of the substrate 22 becomes insufficient, so that microcrystalline silicon having good crystallinity does not grow sufficiently.
[0032]
After the substrate temperature and pressure are stabilized, high-frequency power having a frequency of 10 MHz or more and 300 MHz or less is supplied from the high-frequency power supply 4 to the electrode 2 to generate plasma gas, and the initial layer 14 a of the microcrystalline p-layer 14 is formed on the surface of the substrate 22. Form. At this time, the impedance matching device 5 is adjusted so that the reflected power is minimized. Here, when the frequency is less than 10 MHz, the plasma density is low and the number of hydrogen radicals excited in the plasma is small, so that the termination of dangling bonds on the surface of the growing film becomes insufficient. This is because there is a problem that the surface diffusion of the silicon-based radicals becomes insufficient and the crystallization of microcrystalline silicon is not promoted. On the other hand, when the frequency exceeds 300 MHz, the voltage distribution in the electrode 2 becomes large, and uniform discharge becomes difficult.
Then, after forming the film for a predetermined time, the raw material gas is exhausted, the substrate 22 is cooled, and then the substrate 22 on which the initial layer 14 a is formed is taken out from the vacuum vessel 1.
[0033]
After that, in the plasma CVD apparatus 30, the substrate 22 on which the initial layer 14a is formed is installed in another plasma CVD apparatus not having the heater 12 and the power supply 12b. That is, after the glass substrate 9 forming surface of the substrate 22 is held in close contact with the substrate heater 7, a gas containing a group III element as the source gas is supplied to the gas mixing box 11, and the substrate temperature when the initial layer 14 a is formed is determined. The bulk layer 14b of the microcrystalline p-layer 14 is formed on the initial layer 14a at a high temperature or at a power higher than the high-frequency power.
[0034]
Thereafter, the source gas is supplied to the gas mixing box 11 to form the microcrystalline i-layer 15 in the same manner as described above, and thereafter, a gas containing a group V element, for example, PH ₃ A gas containing phosphorus or the like is supplied to the gas mixing box 11 to form the microcrystalline n-layer 16 in the same manner as described above. Thus, a microcrystalline silicon layer is formed.
[0035]
Next, a method for manufacturing the photovoltaic element 23 shown in FIG. 1 will be described.
First, the degreased and washed glass substrate 9 is subjected to a PVD method such as a CVD method or a sputtering method to form ITO or fluorine oxide-doped tin oxide SnO. ₂ In the present embodiment, among the metal oxides such as zinc oxide ZnO doped with aluminum Al or gallium Ga, in the present embodiment, a 700 nm-thick transparent electrode 13 made of zinc oxide ZnO doped with aluminum Al is formed by lamination. 22 is formed. Next, the initial layer 14a of the microcrystalline p-layer 14, the bulk layer 14b of the microcrystalline p-layer 14, the microcrystalline i-layer 15, and the microcrystalline n-layer 16 are sequentially formed on the substrate 22 by the above-described method. A cell 21 is formed. At this time, the initial layer 14a was formed by applying a power of 150 W to the heater 12 and setting the substrate heater 7 to 150 ° C.
[0036]
Here, the initial layer 14a is formed to have a thickness of 5 nm to 100 nm. If the thickness of the initial layer 14a is less than 5 nm, the transparent electrode 13 is partially exposed, that is, so-called island growth. In this case, since a normal semiconductor pn junction cannot be realized in a portion where the initial layer 14a is not formed, the photoelectric conversion characteristics as a photovoltaic element are significantly reduced. On the other hand, if the thickness of the initial layer 14a exceeds 100 nm, the amount of light absorbed by the initial layer 14a, which is the light incident side layer, becomes excessive, and the amount of light reaching the microcrystalline i-layer 15, which is the photoelectric conversion layer, decreases. This is because the short-circuit current as a photovoltaic element decreases.
[0037]
The thickness of the bulk layer 14b is 5 nm or more and 100 nm or less. When the thickness of the bulk layer 14b is less than 5 nm, the transparent electrode 13 is partially exposed, that is, so-called island growth. In this case, since a normal semiconductor pn junction cannot be realized in a portion where the bulk layer 14b is not formed, characteristics as a photovoltaic element are significantly reduced. On the other hand, when the thickness of the bulk layer 14b exceeds 100 nm, the amount of light absorbed by the bulk layer 14b on the light incident side becomes excessive, and the amount of light reaching the microcrystalline i-layer 15 as the photoelectric conversion layer decreases. This is because the short-circuit current as a photovoltaic element decreases.
[0038]
The thickness of the microcrystalline i-layer 15 depends on the light trapping state depending on the surface shape of the transparent electrode 13, the bulk layer 14b of the microcrystalline p-layer 14, and the microcrystalline i-layer 15, but is not less than 1000 nm and not more than 10,000 nm. Form. This is because if the thickness of the microcrystalline i-layer 15 is less than 1000 nm, the incident light cannot be sufficiently absorbed, and a short-circuit current as a photovoltaic element is reduced. On the other hand, when the thickness of the microcrystalline i-layer 15 exceeds 10000 nm, the internal electric field generated in the microcrystalline i-layer 15 is weakened, the open-circuit voltage as a photovoltaic element is reduced, and the film forming time is prolonged. This is because the productivity is lowered.
[0039]
The microcrystalline n-layer 16 is formed to have a thickness of 5 nm or more and 100 nm or less. This is because when the film thickness of the microcrystalline n-layer 16 is less than 5 nm, the microcrystalline i-layer 15 is partially exposed, so-called island-like growth. In this case, since a normal semiconductor pn junction cannot be realized in a portion where the microcrystalline n-layer 16 is not formed, the photoelectric conversion characteristics as a photovoltaic element are significantly reduced. On the other hand, when the thickness of the microcrystalline n-layer 16 exceeds 100 nm, the amount of light absorbed by the microcrystalline n-layer 16 becomes excessive, and the light reflected by the back electrode 17 cannot be used effectively, and as a photovoltaic element This is because the short-circuit current of the semiconductor device decreases.
[0040]
Thereafter, a back electrode 17 made of aluminum Al, silver Ag, titanium Ti, nickel Ni, chromium Cr, copper Cu or an alloy thereof is formed on the cell 21 thus formed by physical vapor deposition or sputtering. It is formed using an evaporation method. In this embodiment, it is formed of aluminum Al having a thickness of 500 nm by a vacuum evaporation method. The back electrode 17 is preferably formed with a thickness of 200 nm or more so that the light transmitted through the microcrystalline i-layer 15 can be sufficiently reflected. Thus, the photovoltaic element 23 shown in FIG. 1 is completed.
[0041]
The effect of the photovoltaic element 23 formed as described above will be described below.
First, as a comparison object of the photovoltaic element 23, a photovoltaic element having the same configuration as the photovoltaic element 23 was formed. In this configuration, when the initial layer 14a is formed on the substrate 22, only the substrate heater 7 is used without using the heater 12 for heating the surface side of the substrate 22, and the temperature is set to 200 ° C., and all other conditions are as described above. A photovoltaic element was formed under the same film forming conditions as in the first embodiment (hereinafter, this photovoltaic element is referred to as Comparative Example 1). Then, simulated sunlight (AM (passing air amount) 1.5, 100 mW / cm) was applied to the photovoltaic element 23 of Comparative Example 1 and the first embodiment from the glass substrate 9 side. ² ) And the respective photoelectric conversion efficiencies were measured. As a result, when the photoelectric conversion efficiency of Comparative Example 1 was 1.00, the photoelectric conversion efficiency of the photovoltaic element 23 was 1.12, and it was confirmed that the photoelectric conversion efficiency was improved by 12%.
[0042]
This is because, in the first embodiment, the temperature of the substrate heater 7 when forming the initial layer 14a is set to be lower than the temperature of the substrate heater 7 when forming the initial layer 14a in Comparative Example 1. The reduction of the transparent electrode 13 serving as the underlying layer was suppressed, and the reduction in the light transmittance and the electrical conductivity of the transparent electrode 13 could be suppressed. This is because the diffusion of the metal element precipitated from 13 into microcrystalline p-layer 14 could be suppressed.
[0043]
Next, a plurality of photovoltaic elements 23 are formed by making only the film thickness of the initial layer 14a of the microcrystalline p-layer 14 different from each other, and setting all the film forming conditions except for the other time to be the same as those of the first embodiment. In the same manner as described above, the photoelectric conversion efficiency of each photovoltaic element 23 was measured. Here, as a comparative object, a photovoltaic element in which the microcrystalline p-layer 14 is composed only of the microcrystalline silicon bulk layer 14b is also formed (hereinafter, this photovoltaic element is referred to as Comparative Example 2), and the same as described above. And the photoelectric conversion efficiency was measured. These results are shown in FIG. FIG. 4 shows the relative values when the photoelectric conversion efficiency of Comparative Example 2 is 1.00.
[0044]
In FIG. 4, it can be confirmed that the photoelectric conversion efficiency was improved when the thickness of the initial layer 14a was in the range of 5 nm to 100 nm. This is because the above-described effect of suppressing the occurrence of damage to the transparent electrode 13 and the optimization of the amount of light absorbed in the initial layer 14a, that is, the suppression of the occurrence of a decrease in the short-circuit current as a photovoltaic element, have been achieved. Is improved. It can be confirmed that the improvement of the photoelectric conversion efficiency is remarkable particularly when the thickness of the initial layer 14a is in the range of 10 nm to 50 nm.
[0045]
Next, a second embodiment according to the present invention will be described. Parts similar to those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
As shown in FIG. 5, the photovoltaic element 25 according to the second embodiment includes a substrate 22, a top cell 26 made of an amorphous silicon element, a bottom cell 27 made of a microcrystalline silicon element, and a back electrode 17. , And these are sequentially laminated.
[0046]
The top cell 26 includes an amorphous p-layer 18 of p-type amorphous silicon, an amorphous i-layer 19 of i-type amorphous silicon, and an amorphous And an n-type layer 20, which is sequentially laminated. The bottom cell 27 includes a microcrystalline p-layer 14, a microcrystalline i-layer 15, and a microcrystalline n-layer 16, which are sequentially stacked. , And a back electrode 17 is provided on the microcrystalline n-layer 16. Here, the microcrystalline p-layer 14 is composed of an initial layer 14a formed on the surface of the transparent electrode 13 in the initial stage of film formation, and a bulk layer 14b formed on the surface of the initial layer 14a.
[0047]
Here, the film thickness of the amorphous p layer 18 is 5 nm or more and 50 nm or less. This is because when the film thickness is less than 5 nm, the transparent electrode 13 is partially exposed, that is, so-called island-shaped growth. In this case, the portion where the amorphous p-layer 18 is not formed is a normal semiconductor. This is because the pn junction is not formed, so that the characteristics as a photovoltaic element are significantly reduced. On the other hand, when the thickness of the amorphous p-layer 18 exceeds 50 nm, the amount of light absorbed by the amorphous p-layer 18 which is a light incident layer becomes excessive, and the amorphous i-layer 19 and the photoelectric conversion layer This is because the amount of light incident on the microcrystalline i-layer 15 decreases, and the short-circuit current as a photovoltaic element decreases.
[0048]
Further, the film thickness of the amorphous i-layer 19 is 100 nm or more and 500 nm or less. This is because if the film thickness is less than 100 nm, the incident light cannot be sufficiently absorbed, and the short-circuit current as a photovoltaic element decreases. On the other hand, when the film thickness of the amorphous i-layer 19 exceeds 500 nm, the light degradation becomes large due to the so-called Stebralonski effect, in which the absorbed light increases defects in the amorphous i-layer 19.
[0049]
The thickness of the amorphous n-layer 20 is 5 nm or more and 50 nm or less. This is because, when the film thickness is less than 5 nm, the amorphous i-layer 19 is partially exposed, that is, a so-called island-like growth. In this case, the portion where the amorphous n-layer 20 is not formed is This is because a normal semiconductor pn junction is not formed, so that characteristics as a photovoltaic element are significantly reduced. On the other hand, when the film thickness of the amorphous n-layer 20 exceeds 50 nm, the amount of light absorbed by the amorphous n-layer 20 becomes excessive, the amount of light incident on the bottom cell 27 decreases, and a short circuit as a photovoltaic element occurs. This is because the current decreases.
[0050]
Next, a method for manufacturing the photovoltaic element 25 shown in FIG. 5 will be described.
First, the substrate 22 including the glass substrate 9 and the transparent electrode 13 is formed as in the first embodiment. Next, a top cell 26 is formed on the surface of the substrate 22 on which the transparent electrode 13 is formed. That is, a plasma CVD method is performed on the transparent electrode 13, and an amorphous p layer 18, an amorphous i layer 19, and an amorphous n layer 20 are sequentially stacked.
[0051]
Here, the source gas used for the plasma CVD method is silane SiH ₄ Or disilane Si ₂ H ₆ Or a halosilane-based gas such as dichlorosilane or trichlorosilane, and the power supply frequency at this time is set to 13.56 MHz. When the amorphous p-layer 18 is formed, B containing a group III element as a doping gas is used. ₂ H ₆ , BF ₃ And so on. When the amorphous n-layer 20 is formed, PH containing a group V element is used as a doping gas. ₃ And so on.
[0052]
Next, the microcrystalline p-layer 14 and the microcrystalline p-layer 14 are formed on the top cell 26 using the same apparatus and the same film forming conditions as those used when forming the cell 21 and the back electrode 17 in the first embodiment. The i-layer 15 and the microcrystalline n-layer 16 are sequentially laminated to form a bottom cell 27, and a back electrode 17 made of aluminum Al is laminated on the bottom cell 27 to form a photovoltaic element 25.
[0053]
The effect of the photovoltaic element 25 formed as described above will be described below.
First, as a comparison object of the photovoltaic element 25, a photovoltaic element having the same configuration as the photovoltaic element 25 was formed. In this configuration, when the initial layer 14a is formed on the substrate 22, only the substrate heater 7 is used without using the heater 12 for heating the surface side of the substrate 22, and the temperature is set to 200 ° C., and all other conditions are as described above. A photovoltaic element was formed under the same film forming conditions as in the second embodiment (hereinafter, this photovoltaic element is referred to as Comparative Example 2). Then, simulated sunlight (AM (passing air amount) 1.5, 100 mW / cm) was applied to the photovoltaic element 25 of Comparative Example 2 and the second embodiment from the glass substrate 9 side. ² ) And the respective photoelectric conversion efficiencies were measured. As a result, when the photoelectric conversion efficiency of Comparative Example 2 was set to 1.00, the photoelectric conversion efficiency of the photovoltaic element 25 was 1.10, and it was confirmed that the photoelectric conversion efficiency was improved by 10%.
[0054]
This is because, in the second embodiment, the temperature of the substrate heater 7 when forming the initial layer 14a is lower than the temperature of the substrate heater 7 when forming the initial layer 14a in Comparative Example 2. The reduction of the transparent electrode 13 serving as the underlying layer was suppressed, and the reduction in the light transmittance and the electrical conductivity of the transparent electrode 13 could be suppressed. This is because the diffusion of the metal element precipitated from 13 into microcrystalline p-layer 14 could be suppressed.
[0055]
Next, a third embodiment according to the present invention will be described. Parts similar to those in the above-described second embodiment are denoted by the same reference numerals, and description thereof will be omitted.
As shown in FIG. 6, a photovoltaic device 28 according to the third embodiment includes a substrate 22, a top cell 26 made of an amorphous silicon device, zinc oxide ZnO doped with aluminum Al or gallium Ga, or fluorine. F-doped tin oxide SnO ₂ And a bottom cell 27 made of a microcrystalline silicon element, and a back electrode 17, which are sequentially laminated.
[0056]
Here, the thickness of the intermediate layer 21 is formed to be 10 nm or more and 100 nm or less. This is because if the film thickness is less than 10 nm, the light transmitted through the amorphous i-layer 19 cannot be effectively reflected. On the other hand, if the thickness of the intermediate layer 21 exceeds 100 nm, the amount of light absorbed in the intermediate layer 21 becomes excessive, and the amount of light reaching the microcrystalline i-layer 15 decreases.
[0057]
Next, a method for manufacturing the photovoltaic element 28 shown in FIG. 6 will be described.
First, in the same manner as in the second embodiment, after forming a substrate 22 including the glass substrate 9 and the transparent electrode 13, an amorphous p layer 18 and an amorphous i layer 19 and the amorphous n-layer 20 are sequentially laminated to form a top cell 26. Next, the intermediate layer 21 made of a metal oxide of zinc oxide ZnO doped with aluminum Al is formed on the top cell 26 by a sputtering method. Then, similarly to the second embodiment, the microcrystalline p-layer 14, the microcrystalline i-layer 15, and the microcrystalline n-layer 16 are sequentially formed on the intermediate layer 21 to form a bottom cell 27. A back electrode 17 made of aluminum Al is formed by lamination to form a photovoltaic element 28.
[0058]
The effect of the photovoltaic element 28 formed as described above will be described below.
First, as a comparison object of the photovoltaic element 28, a photovoltaic element having the same configuration as the photovoltaic element 28 was formed. In this configuration, when the initial layer 14a is formed on the substrate 22, only the substrate heater 7 is used without using the heater 12 for heating the surface side of the substrate 22, and the temperature is set to 200 ° C., and all other conditions are as described above. A photovoltaic element was formed under the same film forming conditions as in the second embodiment (hereinafter, this photovoltaic element is referred to as Comparative Example 3). Then, simulated sunlight (AM (passing air amount) 1.5, 100 mW / cm) was applied to the photovoltaic element 28 of Comparative Example 3 and the third embodiment from the glass substrate 9 side. ² ) And the respective photoelectric conversion efficiencies were measured. As a result, when the photoelectric conversion efficiency of Comparative Example 3 was 1.00, the photoelectric conversion efficiency of the photovoltaic element 28 was 1.10, and it was confirmed that the photoelectric conversion efficiency was improved by 10%.
[0059]
This is because, in the third embodiment, the temperature of the substrate heater 7 when forming the initial layer 14a is lower than the temperature of the substrate heater 7 when forming the initial layer 14a in Comparative Example 3. The reduction of the transparent electrode 13 serving as the underlying layer was suppressed, and the reduction in the light transmittance and the electrical conductivity of the transparent electrode 13 could be suppressed. This is because the diffusion of the metal element precipitated from 13 into microcrystalline p-layer 14 could be suppressed.
[0060]
Note that the technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in the first to third embodiments, as a means for reducing the load applied to the underlying layer, the temperature of the substrate 22 when the initial layer 14a of the microcrystalline p-layer 14 is formed is reduced by changing the temperature of the substrate when the bulk layer 14b is formed. Although the temperature is set lower than the temperature of 22, the VHF power when forming the initial layer 14a of the microcrystalline p-layer 14 may be set lower than the VHF power when forming the bulk layer 14b.
[0061]
Although the heater main body 31 is formed in a wire mesh shape, the present invention is not limited to this shape. A plurality of rods are provided in a rectangular frame at substantially the same pitch in parallel with one set of sides of the frame. It may be formed in an arrangement or a flat plate having a plurality of holes penetrating the front and back surfaces. Further, although the plasma CVD apparatus 30 is used only when forming the initial layer 14a of the microcrystalline p-layer 14, it is not limited to this, and may be used for forming other semiconductor layers.
[0062]
【The invention's effect】
As is clear from the above description, according to the plasma CVD apparatus, the method for manufacturing a photovoltaic element, and the photovoltaic element according to the present invention, the film forming conditions capable of minimizing the load applied to the underlayer. Even below, a photovoltaic element can be favorably formed without inhibiting the crystallization of the initial layer of the microcrystalline p-layer. Thereby, a photovoltaic element having high photoelectric conversion efficiency can be favorably formed.
[0063]
In addition, the amount of light absorption in the initial layer can be optimized, and a decrease in short-circuit current as a photovoltaic element can be suppressed. Thereby, a photovoltaic element having high photoelectric conversion efficiency can be reliably formed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a photovoltaic element in a first embodiment according to the present invention.
FIG. 2 is a schematic view showing an apparatus for manufacturing a photovoltaic element according to an embodiment of the present invention.
FIG. 3 is a plan view of the heater shown in FIG. 2;
FIG. 4 is a diagram showing the relationship between the thickness of an initial layer of a microcrystalline p-layer and the photoelectric conversion efficiency of a photovoltaic element.
FIG. 5 is a cross-sectional view showing a photovoltaic element according to a second embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a photovoltaic element in a third embodiment according to the present invention.
[Explanation of symbols]
2 ... electrode
7 ... substrate heater
12 ... heater
14 ... microcrystalline p-layer
14a: Initial layer
14b ... bulk layer
15 ... Microcrystalline i-layer
16 ... Microcrystalline n-layer
21 ... cell
22 ... Substrate
23, 25, 28 ... photovoltaic elements
27 ... Bottom cell (cell)
30 ... plasma CVD equipment
31 ... heater body

Claims (8)

A substrate heater that holds the back surface of the substrate and heats the substrate, comprising an electrode provided to face the substrate heater, supplying a source gas between the substrate heater and the electrode, A plasma CVD apparatus that generates a plasma gas between the electrodes and forms a semiconductor layer on the substrate surface side,
A plasma CVD apparatus, wherein a heater for heating a front surface side of the substrate is provided between the substrate heater and the electrode. The plasma CVD apparatus according to claim 1,
The plasma CVD apparatus according to claim 1, wherein the heater includes a wire mesh heater body or a flat heater body having a plurality of holes penetrating the front and back surfaces. The plasma CVD apparatus according to claim 1,
The plasma CVD apparatus, wherein the source gas is a gas containing silicon, and forms a microcrystalline silicon layer as the semiconductor layer. A source gas containing silicon and a hydrogen gas are simultaneously supplied between the substrate and the electrode; a high frequency is applied to generate a plasma gas; and a microcrystalline p-layer made of microcrystalline silicon is formed on the substrate surface side; A method for manufacturing a photovoltaic device having a cell in which a crystalline i layer and a microcrystalline n layer are sequentially stacked,
In forming the microcrystalline p-layer, before forming the microcrystalline silicon bulk layer, the substrate is heated from the front surface side and the rear surface side by using the plasma CVD apparatus according to claim 3 in advance. A method for manufacturing a photovoltaic device, comprising forming an initial layer of microcrystalline silicon on the substrate surface side. The method for manufacturing a photovoltaic device according to claim 4,
A method for manufacturing a photovoltaic device, comprising: before forming the bulk layer, forming the initial layer at a heating temperature lower than a heating temperature on the back side of the substrate when the bulk layer is formed. . The method for manufacturing a photovoltaic device according to claim 4 or 5,
A method for manufacturing a photovoltaic device, wherein the thickness of the initial layer is 5 nm or more and 100 nm or less. The method for manufacturing a photovoltaic device according to any one of claims 4 to 6,
Before forming the cell, an amorphous p-layer, an amorphous i-layer, and an amorphous n-layer made of amorphous silicon are sequentially formed on the substrate surface side in advance. A method for manufacturing a photovoltaic element. A photovoltaic device manufactured by the method for manufacturing a photovoltaic device according to claim 4.

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