JP2006216624A - Solar cell and its production process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance various characteristics of the solar cell in a thin film solar cell employing microscrystalline silicon germanium as an i-layer. <P>SOLUTION: The process for producing a solar cell comprises step (a) for forming a photoelectric conversion layer (8) on a transparent conductive film (2) formed on a transparent substrate (1), and step (b) for forming a back electrode layer (10) on the photoelectric conversion layer (8). The step (a) comprises step (a1) for forming a first microscrystalline silicon layer (3) as a p-layer on the transparent conductive film (2) side, and step (a2) for forming a first microscrystalline silicon germanium layer (4) as an i-layer above the first microscrystalline silicon layer (3) by plasma CVD at a film deposition rate of 0.2 nm/s or above using material gas for silicon and material gas for germanium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solar cell and a method for manufacturing a solar cell, and more particularly to a solar cell and a method for manufacturing a solar cell that can make a photoelectric conversion layer of high quality.

  Solar cells that convert sunlight energy into electrical energy are known. As one type of solar cell, a thin-film Si-based solar cell in which a photoelectric conversion layer is formed by plasma CVD is known. A microcrystalline silicon germanium film has been developed as one of photoelectric conversion layer films used for thin-film Si solar cells. Microcrystalline silicon germanium film has a narrow gap compared to microcrystalline silicon and has excellent absorption characteristics, so it absorbs long-wavelength sunlight by a laminated structure with other photoelectric conversion materials such as amorphous silicon and microcrystalline silicon. Therefore, it is expected as a photoelectric conversion material for improving efficiency.

  As a related technique, Japanese Patent Application Laid-Open No. 2001-284619 discloses a photovoltaic device. According to this publication, this photovoltaic device uses microcrystalline silicon germanium having a germanium composition ratio of 20% or more and 50% or less as a photoactive layer, and has a film thickness of 1 μm or less. . The microcrystalline silicon germanium may be formed by plasma CVD, and the substrate temperature at the time of film formation may be set to 200 ° C. or higher. In this specification, the target of the film forming speed is set to about 0.2 nm / s, and the improvement in quality in the higher speed film forming is not described. There is a need for a technology and structure for improving the quality of microcrystalline silicon germanium that can be applied even at higher film forming speeds.

JP 2001-284619 A

  Accordingly, an object of the present invention is to provide a solar cell manufacturing method and a solar cell capable of improving various characteristics of the solar cell in a thin film solar cell using microcrystalline silicon germanium as the i layer.

  Another object of the present invention is to provide a solar cell manufacturing method and a solar cell capable of improving the quality of a microcrystalline silicon germanium film in a thin film solar cell using microcrystalline silicon germanium as an i layer. is there.

  Still another object of the present invention is to provide a solar cell manufacturing method and a solar cell capable of improving the long wavelength sensitivity in a thin film solar cell using microcrystalline silicon germanium as the i layer.

  Hereinafter, means for solving the problem will be described using the numbers and symbols used in the best mode for carrying out the invention. These numbers and symbols are added in parentheses in order to clarify the correspondence between the description of the claims and the best mode for carrying out the invention. However, these numbers and symbols should not be used for interpreting the technical scope of the invention described in the claims.

  Therefore, in order to solve the above-mentioned problems, the method for manufacturing a solar cell of the present invention comprises (a) a transparent conductive film (2) on a transparent conductive film (2) on which a transparent conductive film (2) is formed. A step of forming a photoelectric conversion layer (8), and a step of (b) forming a back electrode layer (10) on the photoelectric conversion layer (8). The step (a) includes (a1) forming a first microcrystalline silicon layer (3) as a p layer on the transparent conductive film (2) side, and (a2) i on the first microcrystalline silicon (3). Forming a first microcrystalline silicon germanium layer (4) as a layer at a deposition rate of 0.2 nm / s or more by plasma CVD using a gas containing a silicon source gas and a germanium source gas; Is provided. In the step (a2), the distance between the discharge electrode (13) and the substrate (2) in the plasma CVD method is greater than 0 and 8 mm or less.

In the above solar cell manufacturing method, in the step (a2), the total flow rate of the silicon source gas and the germanium source gas in the plasma CVD method is 0 based on the unit area of the substrate (2). 0.05 SLM / m ² or more and ² SLM / m ² or less.

  In the above solar cell manufacturing method, in the step (a2), the temperature of the substrate (2) in the plasma CVD method is 170 ° C. or higher and 300 ° C. or lower.

In order to solve the above-described problems, a method for producing a solar cell of the present invention includes (a) a photoelectric conversion layer (2) on a transparent conductive film (2) in a transparent substrate (1) on which a transparent conductive film (2) is formed. 8) and (b) forming a back electrode layer (10) on the photoelectric conversion layer (8). The step (a) includes (a1) forming a first microcrystalline silicon layer (3) as a p-layer on the transparent conductive film (2) side, and (a2) above the first microcrystalline silicon (3). forming a first microcrystalline silicon germanium layer (4) as an i layer by a plasma CVD method using a gas containing a silicon source gas and a germanium source gas at a deposition rate of 0.2 nm / s or more. With. In the step (a2), the total flow rate of the silicon source gas and the germanium source gas in the plasma CVD method is 0.05 SLM / m ² or more and ² SLM / m based on the unit area of the substrate (1). ² or less.

  In the solar cell manufacturing method, in the step (a2), the temperature of the substrate (2) in the plasma CVD method is 170 ° C. or higher and 300 ° C. or lower.

  In order to solve the above-described problems, a method for producing a solar cell of the present invention includes (a) a photoelectric conversion layer (2) on a transparent conductive film (2) in a transparent substrate (1) on which a transparent conductive film (2) is formed. 8) and (b) forming a back electrode layer (10) on the photoelectric conversion layer (8). The step (a) includes (a1) forming a first microcrystalline silicon layer (3) as a p-layer on the transparent conductive film (2) side, and (a2) above the first microcrystalline silicon (3). forming a first microcrystalline silicon germanium layer (4) as an i layer by a plasma CVD method using a gas containing a silicon source gas and a germanium source gas at a deposition rate of 0.2 nm / s or more. With. In the step (a2), the temperature of the substrate (2) in the plasma CVD method is 170 ° C. or higher and 300 ° C. or lower.

  In the solar cell manufacturing method described above, the step (a) includes (a3) forming a buffer layer (9) above the first microcrystalline silicon (3) between the steps (a1) and (a2). The method further includes a step. The buffer layer (9) includes at least a second microcrystalline silicon layer different from the first microcrystalline silicon layer (3) and a second microcrystalline silicon germanium layer different from the first microcrystalline silicon germanium layer (4). Including one. In the step (a2), the first microcrystalline silicon germanium layer (4) is formed above the first microcrystalline silicon (3) and on the buffer layer (9).

  In the above solar cell manufacturing method, the buffer layer (9) includes the second microcrystalline silicon layer. The second microcrystalline silicon layer has a lower p-type impurity concentration than the first microcrystalline silicon layer (3). The thickness of the buffer layer is, for example, 2 nm to 50 nm.

  In the above solar cell manufacturing method, the buffer layer (9) includes the second microcrystalline silicon germanium layer. The second microcrystalline silicon germanium layer has a lower germanium concentration than the first microcrystalline silicon germanium layer (4).

  In the solar cell manufacturing method, the germanium concentration of the second microcrystalline silicon germanium layer decreases from the first microcrystalline silicon germanium layer (4) toward the first microcrystalline silicon layer (3). The film thickness of the buffer layer is, for example, not less than 2 nm and not more than 50 nm.

  In the solar cell manufacturing method, in the step (a2), the temperature of the substrate (1) in the plasma CVD method is 200 ° C. or higher and 240 ° C. or lower.

  In order to solve the above problems, a solar cell of the present invention includes a transparent conductive film (2) formed on a transparent substrate (1) and a photoelectric conversion layer (8) formed on the transparent conductive film (2). And a back electrode (10) formed on the photoelectric conversion layer (8). The photoelectric conversion layer (8) includes a first microcrystalline silicon layer (3) as a p layer formed on the transparent conductive film (2) side, and a buffer layer (on the first microcrystalline silicon (3)). 9) and a first microcrystalline silicon germanium layer (4) as an i layer formed on the buffer layer (9). The buffer layer (9) includes at least a second microcrystalline silicon layer different from the first microcrystalline silicon layer (3) and a second microcrystalline silicon germanium layer different from the first microcrystalline silicon germanium layer (4). Including one.

  In the above solar cell, the buffer layer (9) includes the second microcrystalline silicon layer. The second microcrystalline silicon layer has a lower p-type impurity concentration than the first microcrystalline silicon layer (3).

  In the above solar cell, the buffer layer (9) includes the second microcrystalline silicon germanium layer. The second microcrystalline silicon germanium layer has a lower germanium concentration than the first microcrystalline silicon germanium layer (4).

  In the above solar cell, the germanium concentration of the second microcrystalline silicon germanium layer decreases from the first microcrystalline silicon germanium layer (4) toward the first microcrystalline silicon layer (3).

  In the above solar cell, the second microcrystalline silicon germanium layer has a thickness of 2 nm to 50 nm.

  According to the present invention, the quality of microcrystalline silicon germanium used as an i layer which is a power generation layer of a thin film solar cell can be improved. Moreover, long wavelength sensitivity can be improved. And various characteristics of the solar cell which contains microcrystalline silicon germanium as a photoelectric converting layer can be improved.

  Hereinafter, embodiments of a solar cell and a method for manufacturing a solar cell of the present invention will be described with reference to the accompanying drawings. In this embodiment, a single microcrystalline silicon germanium thin film solar cell is described. However, it can also be used in combination with other solar cells such as a microcrystalline silicon thin film solar cell for a solar cell having a multilayer structure (example: tandem structure). Although the present invention describes a solar cell having a substrate surface incident type pin structure, the present technology can be expected to have the same effect for a nip structure and a film surface incident type solar cell.

(First to third embodiments)
FIG. 1 is a cross-sectional view showing the configuration of the first embodiment of the solar cell of the present invention. The solar cell includes a substrate 1, a surface electrode 2, a photoelectric conversion layer 8, and a back electrode 10.

The substrate 1 is a transparent substrate on which a solar cell is formed. The substrate 1 is exemplified by a thin plate-like white plate glass. The surface electrode 2 is an electrode on the incident side of sunlight in a solar cell, and is exemplified by a transparent conductive oxide such as tin oxide (SnO ₂ ) or zinc oxide (ZnO).

  The photoelectric conversion layer 8 is a layer that converts light into electricity. The photoelectric conversion layer 8 includes a p layer 3, an i layer 4, and an n layer 5. The p layer 3 is a semiconductor layer doped with p-type impurities. The p layer 3 is exemplified by p-type microcrystalline silicon. The i layer 4 is a semiconductor layer that is not actively doped with impurities. The i layer 4 contains microcrystalline silicon germanium. The n layer 5 is a semiconductor layer doped with n-type impurities. The n layer 5 is exemplified by n-type microcrystalline silicon. Other layers may be inserted between the p layer 3 and the i layer 4, between the i layer 4 and the n layer 5, and between the surface electrode 2 and the photoelectric conversion layer 8. Such a layer is exemplified by a layer that improves the crystallinity of the upper layer and a layer that prevents diffusion of impurities from other layers.

  The back electrode 10 is an electrode on the back side of the solar cell. The back electrode layer 10 includes a first back electrode layer 6 and a second back electrode layer 7. The first back electrode layer 6 is exemplified by a transparent conductive oxide such as ZnO or indium tin oxide (ITO). The second back electrode layer 7 is exemplified by a highly reflective metal such as silver (Ag) or aluminum (Al). Note that another layer (for example, a layer that improves the reflectance and light scattering property of the back electrode 10 may be inserted between the back electrode layer 10 and the photoelectric conversion layer 8.

  Next, a first embodiment of the solar cell manufacturing method of the present invention will be described. FIG. 2 is a schematic view showing an example of a plasma CVD apparatus for producing the solar cell of the present invention. The plasma CVD apparatus 20 includes a vacuum chamber 11, an ultra-high frequency power source 17, a gas supply unit 18 and a turbo molecular pump or rotary pump that evacuates a vacuum chamber (not shown), a dry pump (not shown) that exhausts a source gas. ). Although not shown in the drawings, the plasma CVD apparatus that forms a film on each of the p, i, and n layers is different, and each plasma CVD apparatus is configured so that the substrate can be transported in a vacuum via a transfer chamber. Yes.

  The ultrahigh frequency power supply 17 supplies ultrahigh frequency (plasma excitation frequency, for example, 60 to 120 MHz) power having desired characteristics to an electrode for discharge (described later) in the vacuum chamber 11. The gas supply unit 18 supplies the source gas 19 having a desired flow rate and flow rate ratio from the gas accumulation unit 16 to the vacuum chamber 11 via the gas flow rate control device 15. However, the gas accumulation unit 16 is exemplified by a gas cylinder of a plurality of types of gases. The gas flow rate control device 15 is exemplified by a mass flow meter provided corresponding to each of the plurality of gas cylinders. In the vacuum chamber 11, a film to be a layer of the thin film Si-based solar cell is formed on the substrate 2 by the supplied ultrahigh frequency power and the supplied one or more kinds of gases.

The vacuum chamber 11 includes a first electrode 12, a second electrode 13, and a source gas supply unit 14. The first electrode 12 includes a heater function for heating the substrate, holds the substrate 1 and is grounded. The second electrode 13 is supplied with desired power from the ultrahigh frequency power supply 17 and generates plasma of the source gas 19 supplied between the second electrode 13 and the first electrode 12. The second electrode 13, the distance between the substrate 2 is separated by the gap length d _G, and faces the first electrode 12. Here, a ladder electrode composed of a rectangular bar is used, but a parallel plate electrode may be used. The source gas supply unit 14 supplies the source gas 19 to the space where the plasma is formed (between the first electrode 12 and the second electrode 13) through the gap between the ladders of the second electrode 13. However, the second electrode 13 and the source gas supply unit 14 may be integrated, and one of them may include the other function.

A method for manufacturing a solar cell will be described.
(1) First, a base material in which SnO ₂ is formed as a surface electrode 2 on the surface of a white glass substrate as the substrate 1 by a thermal CVD method is washed using pure water or alcohol. A film necessary for growing SnO ₂ and a refractive index adjusting film for reducing the reflectance may be inserted between the white glass and SnO ₂ .
(2) Next, p as the p layer 3 of the photoelectric conversion layer 8 is placed on the surface electrode 2 in the substrate 1 where the substrate 1 is placed in the plasma CVD apparatus for forming the p layer and the surface electrode 2 is formed. A type microcrystalline silicon film is formed by plasma CVD. The film forming conditions were that the chamber 11 was evacuated to 10 ⁻⁴ Pa or less, and then the substrate 1 was heated to 150 ° C. Then, SiH ₄ and H ₂ as source gases and B ₂ H ₆ as a p-type impurity gas were introduced into the vacuum chamber 11 at ₃ , 300 and 0.02 sccm, respectively, and the pressure was controlled to 67 Pa. The gap length dg is 5 mm. Then, plasma is generated between the second electrode 13 and the substrate 1 by supplying ultrahigh frequency power 100 MHz-5 kW / m ² from the ultrahigh frequency power supply 17 to the second electrode 13, and the p layer 3 is formed on the surface electrode 2. A p-type microcrystalline silicon layer is formed to a thickness of 20 nm.
(3) Subsequently, a microcrystalline silicon germanium film as the i layer 4 is formed on the p layer 3 by a plasma CVD method to a thickness of 500 nm. At this time, the film forming conditions in the plasma CVD method will be described later.
(4) Next, an n-type microcrystalline silicon film as the n layer 5 is formed on the i layer 4 by the plasma CVD method. The film forming condition was that the chamber 11 was evacuated to 10 ⁻⁴ Pa or less, and then the substrate 1 was heated to 170 ° C. Then, SiH ₄ and H ₂ as source gases and PH ₃ as an n-type impurity gas were introduced into the vacuum chamber 11 at ₃ , 300 and 0.1 sccm, respectively, and the pressure was controlled to 93 Pa. The gap length dg is 5 mm. Then, by supplying ultrahigh frequency power 60 MHz-1.5 kW / m ² from the ultrahigh frequency power source 17 to the second electrode 13, plasma is generated between the second electrode 13 and the substrate 1, and n is formed on the i layer 4. As the layer 5, an n-type microcrystalline silicon layer is formed to a thickness of 30 nm.
(5) Thereafter, as the back electrode layer 10, the ZnO film as the first back electrode layer 6 is 80 nm on the n layer 5, and the Ag film as the second back electrode layer 7 is 300 nm on the first back electrode layer 6. Each is formed by sputtering. The film forming conditions are the same as those conventionally used.

  In this way, a microcrystalline silicon germanium thin film solar cell having a single photoelectric conversion layer structure is formed.

Next, conditions for forming a microcrystalline silicon germanium film as the i layer 4 will be described below.
According to the inventors' experiment, the solar cell of the present invention including the microcrystalline silicon germanium film in the i-layer 4 has excellent characteristics even when the film forming speed is 0.2 nm / s or higher than the conventional film forming speed. It became clear. In the plasma CVD method, the following film forming conditions are preferable as the film forming speed.
(A) A raw material gas for silicon and a raw material gas for germanium are used as the raw material gas. The silicon source gas contains at least one of SiH ₄ , Si ₂ H ₆ and SiF ₄ . The germanium source gas contains at least one of GeH ₄ and GeF ₄ . In the examples, SiH ₄ and GeH ₄ were used, respectively, and H ₂ was added thereto and used as the source gas. However, the same effect is obtained for the other source gases.
(B) The film forming pressure is set to 67 Pa to 1333 Pa.
(C) The excitation frequency of plasma CVD is set to 13.56 MHz to 120 MHz.
(D) The input power is set to 1 to 10 kW / m ² or more.

Under the above conditions (a) to (d), the gap flow rate d _G , the substrate temperature, the total flow rate of the gas serving as the raw material per unit area of the substrate (the silicon source gas supplied per unit area of the substrate, and The sum of the flow rates with the germanium source gas = the silicon source gas flow rate + the germanium source gas flow rate) and the H ₂ flow rate are as follows.

[First Embodiment]
(E) Gap length d _G
Figure 3 (a) ~ (d) is a graph showing the relationship between the gap length d _G and the solar cell characteristics. (A) shows the relationship between the short circuit current (vertical axis) and the gap length (horizontal axis). (B) shows the relationship between the open circuit voltage (vertical axis) and the gap length (horizontal axis). (C) shows the relationship between the shape factor (vertical axis) and the gap length (horizontal axis). (D) shows the relationship between conversion efficiency (vertical axis) and gap length (horizontal axis). The vertical axis of each graph indicates a value normalized by a value of gap length d _G = 10 mm. Film forming conditions are: film forming pressure: 267 Pa, excitation frequency: 100 MHz, input power: 2 kW / m ² , substrate temperature: 180 ° C., total flow rate: 0.4 SLM / m ² , H2 flow rate: 10 SLM / m ² , film formation The speed is about 0.5 nm / s and the germanium concentration in the film is about 19%.

As shown in FIG. 3 (a) ~ (d) , all cases it is understood that the more characteristics good short gap length d _G. That is, the gap length d _G (the distance between the first electrode 12 and the substrate 2) is preferably as small as possible. From the required characteristics, the upper limit is preferably 8 mm or less. It is more preferably 5 mm or less, which improves the characteristics more clearly. The lower limit is not limited as long as the plasma is stably formed as long as it is greater than zero. However, the design or manufacturing apparatus when manufacturing the actual production line, etc. manufacturing yield due to the uniformity of the gap length d _G, and more preferably 0.1mm or more. By forming the microcrystalline silicon germanium film within this range, the microcrystalline silicon germanium film can be improved in quality, and the solar cell characteristics can be improved.

[Second Embodiment]
(F) Substrate temperature FIGS. 4A to 4E are graphs showing the relationship between the substrate temperature and the characteristics of each solar cell. (A) shows the relationship between short circuit current (vertical axis) and substrate temperature (horizontal axis). (B) shows the relationship between the open circuit voltage (vertical axis) and the substrate temperature (horizontal axis). (C) shows the relationship between the shape factor (vertical axis) and the substrate temperature (horizontal axis). (D) shows the relationship between conversion efficiency (vertical axis) and substrate temperature (horizontal axis). (E) shows the relationship between the short circuit current (vertical axis) and the substrate temperature (horizontal axis) for wavelengths of 800 nm or more. The vertical axis of each graph indicates a value normalized by a value of substrate temperature = 160 ° C., respectively. Film forming conditions are film forming pressure: 267 Pa, excitation frequency: 100 MHz, input power: 2 kW / m ² , gap length d _G : 5 mm, 0.4 SLM / m ² , H2 flow rate: 10 SLM / m ² , film forming speed is About 0.5 nm / s, germanium concentration in the film: about 19%.

  As shown in FIGS. 4A to 4E, it can be seen that in any case, the characteristics have a peak in the range of the substrate temperature of 160 ° C. to 300 ° C. That is, from the required characteristics, the temperature range is preferably 170 ° C. or higher and 300 ° C. or lower. More preferably, it is 200 degreeC or more and 240 degrees C or less. By forming the microcrystalline silicon germanium film within this range, the microcrystalline silicon germanium film can be improved in quality, and the solar cell characteristics can be improved.

[Third Embodiment]
(G) Total flow rate of gas as raw material per unit area of substrate FIGS. 5A to 5D are graphs showing the relationship between the total flow rate per unit area of the substrate and the characteristics of each solar cell. (A) shows the relationship between the short circuit current (vertical axis) and the total flow rate per unit area (horizontal axis). (B) shows the relationship between the open circuit voltage (vertical axis) and the total flow rate per unit area (horizontal axis). (C) shows the relationship between the shape factor (vertical axis) and the total flow rate per unit area (horizontal axis). (D) shows the relationship between the conversion efficiency (vertical axis) and the total flow rate per unit area (horizontal axis). The vertical axis of each graph indicates a value normalized by the value of total flow rate per unit area = 1.5. The film forming conditions are: film forming pressure: 267 Pa, excitation frequency: 100 MHz, input power: 2 kW / m ² , gap length d _G : 5 mm, substrate temperature: 180 ° C., H ₂ flow rate: 25 of the total flow rate of the raw material gas. The film forming speed is about 0.5 nm / s, and the germanium concentration in the film is about 19%.

As shown in FIGS. 5A to 5D, it can be seen that in all cases, the smaller the total flow rate per unit area, the better the characteristics. That is, the smaller the total flow rate per unit area, the better. From the required characteristics, the upper limit is preferably 1 SLM / m ² or less. 0.5 SLM / m ² or less is more preferable because the characteristics are more clearly improved. The lower limit is preferably 0.05 SLM / m ² or more as a condition for stably forming plasma and maintaining a film forming rate of 0.2 nm / s or more. By forming the microcrystalline silicon germanium film within this range, the microcrystalline silicon germanium film can be improved in quality, and the solar cell characteristics can be improved. In this example, the film forming speed is about 0.5 nm / s, and it is effective for improving the film quality to form the film under conditions where the utilization efficiency of the source gas is high with respect to the film forming speed. I understand that there is. Considering SiH ₄ , microcrystalline Si has the same density as single crystal Si, and if the same amount of film is formed on both the substrate and the electrode per 1 m ² , the film forming speed of about 4.5 nm / s is the maximum at 1 SLM. Become. This more 0.5 nm / s with respect to a flow rate of 0.5 SLM / ^{m 2} per the gas utilization efficiency 22.2%, preferably not less than 22.2% gas utilization efficiency and the 0.5 SLM / ^{m 2} or less is desirable Means that.

However, when the experiment is performed at a film formation rate of about 1 nm / s, the characteristics corresponding to FIG. Accordingly, when the film forming speed is about 1 nm / s, 2SLM / m ² is the upper limit value in consideration of the required characteristics.

  By forming a microcrystalline silicon germanium film as the i layer 4 under the above conditions (a) to (g), the solar cell characteristics can be improved.

  In addition, in the preferable conditions shown by (e) (FIG. 3), FIGS. 4-5 is formed. Similarly, FIG. 3 and FIG. 5 hold under the preferable conditions shown in (f) (FIG. 4). (G) Under the preferable conditions shown in FIG. 5, FIGS. 3 to 4 are established.

[Fourth Embodiment]
FIG. 6 is a sectional view showing the configuration of the fourth embodiment of the solar cell of the present invention. The solar cell includes a substrate 1, a surface electrode 2, a photoelectric conversion layer 8, and a back electrode 10.

  The solar cell of the present embodiment is different from the first to third embodiments in that the photoelectric conversion layer 8 is provided with a buffer layer 9 between the p layer 3 and the i layer 4. The buffer layer 9 includes at least one of microcrystalline silicon different from the p-type microcrystalline silicon of the p layer 3 and microcrystalline silicon germanium different from the microcrystalline silicon germanium of the i layer 4.

Here, when the buffer layer 9 is microcrystalline silicon, the microcrystalline silicon has a lower p-type impurity concentration than the p-type microcrystalline silicon of the p layer 3. The microcrystalline silicon is more preferably i-type microcrystalline silicon.
On the other hand, when the buffer layer 9 is microcrystalline silicon germanium, the microcrystalline silicon germanium has a lower germanium concentration than the microcrystalline silicon germanium of the i layer 4. The germanium concentration may be substantially constant in the buffer layer 9 or may decrease from the i layer 4 toward the p layer 3.

  Since other configurations in the solar cell are the same as those in the first to third embodiments, the description thereof is omitted.

  Next, a fourth embodiment of the solar cell manufacturing method of the present invention will be described. FIG. 2 is a schematic view showing an example of a plasma CVD apparatus for producing the solar cell of the present invention. Since the plasma CVD apparatus 20 is the same as that of the first embodiment, the description thereof is omitted.

A method for manufacturing a solar cell will be described.
(1) First, a base material in which SnO ₂ is formed as a surface electrode 2 on the surface of a white glass substrate as the substrate 1 by a thermal CVD method is washed using pure water or alcohol. A film necessary for growing SnO ₂ and a refractive index adjusting film for reducing the reflectance may be inserted between the white glass and SnO ₂ .
(2) Next, p as the p layer 3 of the photoelectric conversion layer 8 is placed on the surface electrode 2 in the substrate 1 where the substrate 1 is placed in the plasma CVD apparatus for forming the p layer and the surface electrode 2 is formed. A type microcrystalline silicon film is formed by plasma CVD. The film forming conditions were that the chamber 11 was evacuated to 10 ⁻⁴ Pa or less, and then the substrate 1 was heated to 150 ° C. Then, SiH ₄ and H ₂ as source gases and B ₂ H ₆ as a p-type impurity gas were introduced into the vacuum chamber 11 at ₃ , 300 and 0.02 sccm, respectively, and the pressure was controlled to 67 Pa. The gap length dg is 25 mm. Then, plasma is generated between the second electrode 13 and the substrate 1 by supplying an ultrahigh frequency power of 100 MHz-5 kW / m ² from the ultrahigh frequency power source 17 to the second electrode 13, and on the first transparent conductive film 2. A p-type microcrystalline silicon layer is formed to a thickness of 20 nm as the p layer 3.
(3) Subsequently, an i-type microcrystalline silicon film as the buffer layer 9 is formed on the p layer 3 by the plasma CVD method. The buffer layer may be formed in either the p-layer film formation chamber or the i-layer film formation chamber, or of course, may be formed in a film formation chamber dedicated to the buffer layer. The film forming conditions were that the chamber 11 was evacuated to 10 ⁻⁴ Pa or less, and then the substrate 1 was heated to 180 ° C. Then, _SiH 4, _{H 2} as a source gas, respectively ^{0.4SLM / m 2, 11SLM / m} 2 was introduced into the vacuum chamber 11, and control the pressure in the 67 Pa. The gap length dg is 5 mm. Then, an ultrahigh frequency power 100 MHz-2 kW / m ² is supplied from the ultrahigh frequency power source 17 to the second electrode 13 to generate plasma between the second electrode 13 and the substrate 1, and a buffer is formed on the p-th layer 3. A microcrystalline silicon layer is formed as a layer. At this time, a buffer layer made of microcrystalline SiGe can be produced by adding GeH4 as a source gas. In addition, a buffer layer having a profile in which the Ge concentration increases from the p layer 3 to the i layer 4 can be manufactured by time-modulating the flow rates of SiH 4 and GeH 4.
(4) Subsequently, a microcrystalline silicon germanium film as the i layer 4 is formed on the buffer layer 9 by a plasma CVD method to a thickness of 500 nm. At this time, the film forming conditions in the plasma CVD method are the same as those in the first embodiment.
(5) Next, an n-type microcrystalline silicon film as the n layer 5 is formed on the i layer 4 by the plasma CVD method. The film forming condition was that the chamber 11 was evacuated to 10 ⁻⁴ Pa or less, and then the substrate 1 was heated to 170 ° C. Then, SiH ₄ and H ₂ as source gases and PH ₃ as an n-type impurity gas were introduced into the vacuum chamber 11 at ₃ , 300 and 0.1 sccm, respectively, and the pressure was controlled to 93 Pa. The gap length dg is 25 mm. Then, a plasma is generated between the second electrode 13 and the substrate 1 by supplying a super-high frequency power 60 MHz-1.5 kW / m ² from the super-high frequency power source 17 to the second electrode 13, and on the i layer 4. As the n layer 5, an n-type microcrystalline silicon layer is formed to a thickness of 30 nm.
(6) Thereafter, as the back electrode layer 10, the ZnO film as the first back electrode layer 6 is 80 nm on the n layer 5, and the Ag film as the second back electrode layer 7 is 300 nm on the first back electrode layer 6. Each is formed by sputtering. The film forming conditions are the same as those conventionally used.

  In this way, a microcrystalline silicon germanium thin film solar cell having a single photoelectric conversion layer structure is formed.

Next, the microcrystalline silicon film as the buffer layer 9 will be described below.
Although a method for forming a microcrystalline silicon film (or a microcrystalline silicon germanium film) and film forming conditions are shown as an example, they are the same as those conventionally used. In the present invention, the film thickness is more important. 7A to 7E are graphs showing the relationship between the thickness of the buffer layer and the characteristics of each solar cell. (A) shows the relationship between the short circuit current (vertical axis) and the thickness of the buffer layer (horizontal axis). (B) shows the relationship between the open circuit voltage (vertical axis) and the thickness of the buffer layer (horizontal axis). (C) shows the relationship between the shape factor (vertical axis) and the thickness of the buffer layer (horizontal axis). (D) shows the relationship between the conversion efficiency (vertical axis) and the thickness of the buffer layer (horizontal axis). (E) shows the relationship between the short circuit current (vertical axis) and the thickness of the buffer layer (horizontal axis) for wavelengths of 800 nm or more. The vertical axis of each graph indicates the value normalized by the value of the buffer layer thickness = 0.

  As shown in FIGS. 7A to 7D, it can be seen that the insertion of the buffer layer 9 improves each characteristic. On the other hand, referring to FIG. 7 (e), it can be seen that the characteristics of the short-circuit current for wavelengths of 800 nm or more are improved when the thickness of the buffer layer 9 is 50 nm or less. A microcrystalline silicon germanium solar cell can efficiently absorb a wavelength of 800 nm or more, which has a low absorption coefficient in the microcrystalline silicon solar cell, and thus a laminated structure with an amorphous silicon solar cell or a microcrystalline silicon solar cell is considered. Considering such a case, it is preferable that the upper limit of the thickness of the buffer layer 9 is 50 nm or less at which the short-circuit current with respect to a wavelength of 800 nm or more is improved. The lower limit is preferably 2 nm or more so that the buffer layer 9 can cover the p layer 3. Considering the production yield, 5 nm or more is more preferable. This tendency was the same when microcrystalline silicon germanium was used for the buffer layer. By forming the buffer layer 9 in this range, it is possible to improve the solar cell characteristics, particularly the short-circuit current characteristics for wavelengths of 800 nm or more.

FIG. 1 is a cross-sectional view showing the configuration of the first embodiment of the solar cell of the present invention. FIG. 2 is a schematic view showing an example of a plasma CVD apparatus for producing the solar cell of the present invention. Figure 3 (a) ~ (d) is a graph showing the relationship between the gap length d _G and the solar cell characteristics. 4A to 4E are graphs showing the relationship between the substrate temperature and each solar cell characteristic. 5A to 5D are graphs showing the relationship between the total flow rate per unit area of the substrate and the characteristics of each solar cell. FIG. 6 is a cross-sectional view showing the configuration of the second embodiment of the solar cell of the present invention. 7A to 7E are graphs showing the relationship between the thickness of the buffer layer and the characteristics of each solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Surface electrode 3 p layer 4 i layer 5 n layer 6 1st back electrode layer 7 2nd back electrode layer 8 Photoelectric conversion layer 9 Buffer layer 10 Back electrode layer 11 Vacuum chamber 12 1st electrode 13 2nd electrode 14 Raw material Gas supply unit 15 Gas flow control device 16 Gas storage unit 17 High frequency power supply 18 Gas supply unit 19 Source gas 20 Plasma CVD apparatus

Claims (16)

(A) forming a photoelectric conversion layer on the transparent conductive film in the transparent insulating substrate on which the transparent conductive film is formed;
(B) forming a back electrode on the photoelectric conversion layer, and
The step (a)
(A1) forming a first microcrystalline silicon layer as a p layer on the transparent conductive film side;
(A2) The first microcrystalline silicon germanium layer as the i layer on the first microcrystalline silicon is 0.2 nm / s or more by a plasma CVD method using a gas containing a silicon source gas and a germanium source gas. Forming at a film forming speed of
The step (a2)
The method for manufacturing a solar cell, wherein a distance between the discharge electrode and the substrate in the plasma CVD method is greater than 0 and equal to or less than 8 mm. In the manufacturing method of the solar cell of Claim 1,
The step (a2)
The total flow rate of the silicon source gas and the germanium source gas in the plasma CVD method is 0.05 SLM / m ² or more and ² SLM / m ² or less based on the unit area of the substrate. Production method. In the manufacturing method of the solar cell of Claim 1 or 2,
The step (a2)
The method for manufacturing a solar cell, wherein a temperature of the substrate in the plasma CVD method is 170 ° C. or higher and 300 ° C. or lower. (A) forming a photoelectric conversion layer on the transparent conductive film in the transparent substrate on which the transparent conductive film is formed;
(B) forming a back electrode on the photoelectric conversion layer, and
The step (a)
(A1) forming a first microcrystalline silicon layer as a p layer on the transparent conductive film side;
(A2) The first microcrystalline silicon germanium layer as the i layer on the first microcrystalline silicon is 0.2 nm / s or more by a plasma CVD method using a gas containing a silicon source gas and a germanium source gas. Forming at a film forming speed of
The step (a2)
The total flow rate of the silicon source gas and the germanium source gas in the plasma CVD method is 0.05 SLM / m ² or more and ² SLM / m ² or less based on the unit area of the substrate. Production method. In the manufacturing method of the solar cell of Claim 4,
The step (a2)
The method for manufacturing a solar cell, wherein a temperature of the substrate in the plasma CVD method is 170 ° C. or higher and 300 ° C. or lower. (A) forming a photoelectric conversion layer on the transparent conductive film in the transparent substrate on which the transparent conductive film is formed;
(B) forming a back electrode layer on the photoelectric conversion layer,
The step (a)
(A1) forming a first microcrystalline silicon layer as a p layer on the transparent conductive film side;
(A2) The first microcrystalline silicon germanium layer as the i layer on the first microcrystalline silicon is 0.2 nm / s or more by a plasma CVD method using a gas containing a silicon source gas and a germanium source gas. Forming at a film forming speed of
The step (a2)
The method for manufacturing a solar cell, wherein a temperature of the substrate in the plasma CVD method is 170 ° C. or higher and 300 ° C. or lower. In the manufacturing method of the solar cell as described in any one of Claims 1 thru | or 6,
In the step (a), between the steps (a1) and (a2),
(A3) further comprising a step of forming a buffer layer above the first microcrystalline silicon,
The buffer layer includes at least one of a second microcrystalline silicon layer different from the first microcrystalline silicon layer and a second microcrystalline silicon germanium layer different from the first microcrystalline silicon germanium layer,
The step (a2) includes forming the first microcrystalline silicon germanium layer above the first microcrystalline silicon and on the buffer layer. In the manufacturing method of the solar cell of Claim 7,
The buffer layer includes the second microcrystalline silicon layer,
The method for manufacturing a solar cell, wherein the second microcrystalline silicon layer has a lower concentration of p-type impurities than the first microcrystalline silicon layer. In the manufacturing method of the solar cell of Claim 7,
The buffer layer includes the second microcrystalline silicon germanium layer,
The method for producing a solar cell, wherein the second microcrystalline silicon germanium layer has a germanium concentration lower than that of the first microcrystalline silicon germanium layer. In the manufacturing method of the solar cell of Claim 9,
The method for manufacturing a solar cell, wherein the second microcrystalline silicon germanium layer has a germanium concentration decreasing from the first microcrystalline silicon germanium layer toward the first microcrystalline silicon layer. In the manufacturing method of the solar cell as described in any one of Claim 3, 5, and 6,
The step (a2)
The method for manufacturing a solar cell, wherein the temperature of the substrate in the plasma CVD method is 200 ° C. or higher and 240 ° C. or lower. A transparent conductive film formed on a transparent substrate;
A photoelectric conversion layer formed on the transparent conductive film;
Comprising a back electrode formed on the photoelectric conversion layer,
The photoelectric conversion layer is
A first microcrystalline silicon layer as a p-layer formed on the transparent conductive film side;
A buffer layer formed on the first microcrystalline silicon;
A first microcrystalline silicon germanium layer as an i layer formed on the buffer layer,
The buffer layer is
A solar cell comprising at least one of a second microcrystalline silicon layer different from the first microcrystalline silicon layer and a second microcrystalline silicon germanium layer different from the first microcrystalline silicon germanium layer. The solar cell according to claim 12,
The buffer layer includes the second microcrystalline silicon layer,
The second microcrystalline silicon layer has a lower concentration of p-type impurities than the first microcrystalline silicon layer. The solar cell according to claim 12,
The buffer layer includes the second microcrystalline silicon germanium layer,
The second microcrystalline silicon germanium layer has a lower germanium concentration than the first microcrystalline silicon germanium layer. The solar cell according to claim 14, wherein
The solar cell in which the second microcrystalline silicon germanium layer has a germanium concentration decreasing from the first microcrystalline silicon germanium layer toward the first microcrystalline silicon layer. The solar cell according to claim 14 or 15,
The second microcrystalline silicon germanium layer has a thickness of 2 nm to 50 nm.

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