JP2004128110A - Manufacturing method of thin film solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin film solar cell capable of suppressing degradation in characteristics of it even if a high speed film forming is performed using a compact film forming device, in which (minimum proximity distance A between the reactive chamber wall and high frequency electrode)/(inter-electrode distance D between ground electrode and high frequency electrode) is 1 or below. <P>SOLUTION: A first electrode layer, a non-crystal photoelectric conversion layer, and a transparent electrode layer (second electrode layer) are laminated on the surface of a substrate having electrically insulating property. The photoelectric conversion layer is formed by a plasma CVD method in which a material gas is decomposed by glow discharge with a high frequency voltage applied in a vacuum reactive chamber. The reactive chamber comprises a ground electrode, a high frequency electrode, and a reactive chamber wall. Film-forming is performed with A/D being 1 or below, the film-forming pressure in the reactive chamber being 130-400 Pa, and the frequency of high frequency voltage being 13-60 MHz. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a thin-film solar cell in which a photoelectric conversion layer is formed by a plasma CVD method.
[0002]
[Prior art]
Thin-film solar cells are considered to be the mainstream of solar cells in the future because they are thin, lightweight, inexpensive in manufacturing cost, and easy to increase in area, so they are used not only for power supply but also for building roofs and windows. Demand is expanding for business use and general residential use.
[0003]
Conventional thin-film solar cells generally use a glass substrate. In recent years, research and development of a flexible type solar cell using a plastic film has been promoted in terms of weight reduction, workability, and mass productivity, and the solar cell has been put into practical use. Further, a device using a film substrate insulated from a flexible metal material has been developed. Taking advantage of this flexibility, mass production has become possible by roll-to-roll or stepping roll manufacturing methods.
[0004]
In the above-described thin-film solar cell, for example, a first electrode (hereinafter, also referred to as a lower electrode), a photoelectric conversion layer including a thin-film semiconductor layer, and a second electrode (hereinafter, also referred to as a transparent electrode) are formed on an electrically insulating film substrate. A plurality of stacked photoelectric conversion elements (or cells) are formed. By repeatedly electrically connecting the first electrode of a certain photoelectric conversion element and the second electrode of an adjacent photoelectric conversion element, the first electrode of the first photoelectric conversion element and the second electrode of the last photoelectric conversion element Required voltage can be output. For example, in order to obtain an AC of 100 V as a commercial power source by converting into an AC by an inverter, the output voltage of the thin-film solar cell is desirably 100 V or more, and actually several tens or more elements are connected in series.
[0005]
Such a photoelectric conversion element and its serial connection are formed by forming an electrode layer and a photoelectric conversion layer, patterning each layer, and combining them. An example of the configuration and manufacturing method of the solar cell is described in, for example, Patent Document 1 described below.
[0006]
FIGS. 10A and 10B show an example of the thin-film solar cell described in Patent Document 1, in which FIG. 10A is a plan view, FIG. 10B is a sectional view taken along lines ABCD and BQC in FIG. () Shows an EE sectional view in (a).
[0007]
A first electrode layer, a photoelectric conversion layer, and a second electrode layer are sequentially laminated on a long film substrate made of an electrically insulating and flexible resin, and a third electrode layer is provided on the opposite side (back surface) of the film substrate. , A fourth electrode layer, and a back surface electrode is formed. The photoelectric conversion layer is, for example, a pin junction of amorphous silicon. As the material for the film substrate, a polyimide film, for example, a film having a thickness of 50 μm is used.
[0008]
As a material of the film, polyethylene naphthalate (PEN), polyether sulfone (PES), polyethylene terephthalate (PET), an aramid-based film, or the like can be used.
[0009]
Next, an outline of the manufacturing process will be described below.
[0010]
First, a connection hole h1 having a diameter of, for example, 1 mm is formed using a punch on a film substrate, and silver is formed as a first electrode layer on one side (referred to as a front side) of the substrate by sputtering to a thickness of, for example, 100 nm. A silver electrode is similarly formed as a third electrode layer on the surface opposite to this (the back side). The first electrode layer and the third electrode layer overlap with each other on the inner wall of the connection hole h1 and conduct.
[0011]
As the electrode layer, in addition to silver (Ag), a metal such as Al, Cu, or Ti may be formed by sputtering or electron beam evaporation, or a multilayer film of a metal oxide film and a metal may be used as the electrode layer. After the film formation, on the front side, the first electrode layer is laser-processed into a predetermined shape, and the lower electrodes 11 to 16 are patterned. An adjacent portion of the lower electrodes 11 to 16 forms one separation line g2, and two separation lines g2 for separation between two rows of photoelectric conversion elements connected in series and the periphery conductive portion f. The electrodes 11 to 16 are surrounded by a separation line. After the collector hole h2 is opened again by using the punch, an a-Si layer is formed as a photoelectric conversion layer p on the front side by plasma CVD. A film having a width of W2 is formed using a mask, and the same separation line as that of the first electrode layer is formed only between the two-row elements by laser processing. The width W2 may extend over the connection hole h1.
[0012]
Further, a transparent electrode layer (ITO layer) is formed on the front side as a second electrode layer. However, a mask is applied between the two element rows and on both side edges of the substrate parallel to the two element rows so that the film is not formed in the connection hole h1, but is formed only in the element section. As the transparent electrode layer, in addition to ITO (indium oxide), SnO 2 ₂ And an oxide conductive layer such as ZnO.
[0013]
Next, a layer made of a low-resistance conductive film such as a metal film is formed as a fourth electrode layer on the entire back surface. Due to the formation of the fourth electrode, the second electrode and the fourth electrode are overlapped on the inner wall of the current collecting hole h2, and conduction is achieved. On the front side, a separation line having the same pattern as that of the lower electrode is formed by laser processing to form individual second electrodes u1 to u6. On the rear side, the third and fourth electrodes are simultaneously laser-processed, and connection electrodes e12 to e56 are formed. , And the power extraction electrodes o1 and o2 are separated from each other, a separation line g2 is formed at the periphery of the substrate so as to overlap the separation line g3 on the front side, and one separation line is formed between the adjacent electrodes.
[0014]
There is a separation line g3 on the periphery surrounding all the thin-film solar cells collectively and on the adjacent boundary between the two rows of series-connected solar cells (inside the peripheral conductive portion f). There are no layers in the separation line g3. On the back side, there is a separation line g2 (inside the peripheral conductive portion f) at the periphery surrounding all the electrodes collectively and at the adjacent boundary between the two rows of serially connected electrodes. There are no layers in the separation line g2.
[0015]
Thus, the power extraction electrode o1-current collection hole h2-upper electrode u1, photoelectric conversion layer, lower electrode 111-connection hole h1-connection electrode e12-upper electrode u2, photoelectric conversion layer, lower electrode 12-connection electrode e23 -... The series connection of the photoelectric conversion elements in the order of the upper electrode u6, the photoelectric conversion layer, the lower electrode 16-the connection hole h1-the power extraction electrode o2 is completed.
[0016]
Since the third electrode layer and the fourth electrode layer have the same electrical potential, they may be treated as a single connection electrode layer in the following description for convenience of description.
[0017]
FIG. 11 is a simplified perspective view of the configuration of a thin-film solar cell for easy understanding of the structure. In FIG. 11, the unit photoelectric conversion element 62 formed on the front surface of the substrate 61 and the connection electrode layer 63 formed on the back surface of the substrate 61 are each completely separated into a plurality of unit units, and are formed with their respective separation positions shifted. ing. Therefore, the current generated in the photoelectric conversion layer 65, which is the amorphous semiconductor portion of the element 62, is first collected in the transparent electrode layer 66, and then flows through the current collecting holes 67 (h2) formed in the transparent electrode layer region. Through the connection electrode layer 63 on the back side, and further through the connection hole 68 (h1) for series connection formed outside the transparent electrode layer region of the device in the connection electrode layer region, to allow the transparent connection of the device adjacent to the device. It reaches the lower electrode layer 64 extending outside the electrode layer region, and the two devices are connected in series.
[0018]
FIGS. 12A to 12G show a simplified manufacturing process of the thin film solar cell. Using the plastic film 71 as a substrate (step (a)), a connection hole 78 is formed in this (step (b)), and a first electrode layer (lower electrode) 74 and a third electrode layer (a lower electrode) on both surfaces of the substrate. After forming the (part) 73 (step (c)), a current collecting hole 77 is formed at a position separated from the connection hole 78 by a predetermined distance (step (d)). Between the step (c) and the step (d), there is a step of patterning the lower electrode by laser processing the first electrode layer (lower electrode) 74 into a predetermined shape. Omitted.
[0019]
Next, a semiconductor layer 75 serving as a photoelectric conversion layer and a transparent electrode layer 76 serving as a second electrode layer are sequentially formed on the first electrode layer 74 (step (e) and step (f)). A fourth electrode layer (connection electrode layer) 79 is formed on the electrode layer 73 (step (g)). Thereafter, the thin films on both sides of the substrate 71 are separated and processed using a laser beam to form a series connection structure as shown in FIG.
[0020]
In FIG. 12, the connection between the transparent electrode layer 76 and the fourth electrode layer 79 in the current collecting hole h2 is illustrated as two layers with the respective layers overlapped. However, in FIG. Are treated as a single layer and are shown in one layer.
[0021]
Incidentally, the configuration of the thin film solar cell shown in FIGS. 10 to 12 is a so-called SCAF (Series Connection Through Properties on Film) type, but in addition to the above configuration, for example, only on one side of a glass substrate, There is also known a single-sided thin-film solar cell in which a first electrode layer, a non-single-crystal photoelectric conversion layer, and a transparent electrode layer (second electrode layer) are laminated. Also, in the case of the single-sided formation type, the case where the transparent electrode layer is directly formed on the surface of the glass substrate, the case where the first electrode layer and the photoelectric conversion layer are formed, and then the transparent electrode layer is formed on the surface, etc. Various thin-film solar cell configurations are known.
[0022]
Next, a plasma CVD apparatus for forming the non-single-crystal photoelectric conversion layer will be described. The thin film formed by the plasma CVD is formed by, for example, the following apparatus. FIG. 13 shows an example of a schematic structure of a film forming chamber when an a-Si thin film solar cell is formed by plasma discharge, and shows an example of a structure described in Patent Document 2 described later. FIGS. 13A and 13B are schematic cross-sectional views when the film forming chamber is opened and when it is sealed, respectively.
[0023]
As shown in FIG. 13A, a box-shaped lower film-forming section chamber wall 21 and an upper film-forming section chamber wall 22 are arranged oppositely above and below a flexible substrate 10 conveyed intermittently. When the film chamber is sealed, an independent processing space composed of a lower film forming section chamber and an upper film forming section chamber is formed. In this example, the lower film forming unit chamber includes a high-frequency electrode 31 connected to a power supply 40, and the upper film forming unit room includes a ground electrode 32 having a built-in heater 33.
[0024]
At the time of film formation, as shown in FIG. 13B, the upper film-forming section chamber wall 22 is lowered, and the ground electrode 32 holds down the substrate 10 and is attached to the opening-side end face of the lower film-forming section chamber wall 21. The member 50 is brought into contact. As a result, an airtightly sealed film-forming space 60 communicating with the exhaust pipe 61 is formed from the lower film-forming section chamber wall 21 and the substrate 10. In the film forming chamber as described above, a high-frequency voltage is applied to the high-frequency electrode 31 to generate plasma in the film forming space 60 and to decompose the raw material gas introduced from an introduction pipe (not shown) to form a film on the substrate 10. Can be formed.
[0025]
[Patent Document 1]
JP-A-10-233517 (page 4, FIG. 1)
[Patent Document 2]
JP-A-8-250431 (page 2-3, FIG. 2)
[0026]
[Problems to be solved by the invention]
By the way, when a thin film typified by a-Si is formed on a substrate using the above-described plasma CVD apparatus, the distance between the ground electrode and the high-frequency electrode is generally D, and the reaction chamber wall is generally used. When the closest distance between the body and the high-frequency electrode is A, a configuration of A / D> 1 is used.
[0027]
FIG. 14 is a schematic view of a plasma CVD apparatus obtained by simplifying the apparatus shown in FIG. 13 for convenience of explanation, and shows a distance D between the high-frequency electrode d1 and the ground electrode d2 and a ground other than the ground electrode d2. The minimum distance A between the conductive portion d3 having a potential and the high-frequency electrode d1 is shown. That is, in the conventional apparatus, the closest distance A between the reaction chamber wall and the high-frequency electrode is set to be larger than the distance D between the electrodes, thereby preventing discharge in a region other than between the electrodes. , A / D are designed to be about 1.5 to 3.
[0028]
In the case of the above-described device configuration, there are the following problems. That is, the volume of the reaction chamber is 10 to 20 times as large as the discharge space, the installation space is large, the apparatus cost is high, the pressure control and evacuation take time, and the gas yield is difficult to improve. Problems.
[0029]
As a method for solving the above problem, the A / D is set to 1 or less, the apparatus is made compact by reducing the closest distance between the reaction chamber wall and the high-frequency electrode, and the discharge in a region other than between the electrodes is performed as follows. A method of suppressing the noise with an earth shield has been considered.
[0030]
However, it has been found that the use of a compact device having the A / D of 1 or less has the following new problems. That is, when the compact type device is used, there is a problem inherent in the compact type device that the characteristics of the solar cell are greatly reduced as the film forming speed of the i-layer in the photoelectric conversion layer increases.
[0031]
As an example, a pin-type a-Si single-cell solar cell having an i-layer of 300 nm is formed using a large-sized device (example of A / D = 2) and a compact device (example of A / D = 0.17). The result of comparing the characteristics will be described. FIG. 15 shows the relationship between the i-layer film formation speed and the conversion efficiency after light degradation (stable conversion efficiency after 300 hours of light irradiation). The film forming conditions were relatively general conditions, and the power supply frequency was 13 MHz and the film forming pressure was 65 Pa.
[0032]
As is clear from the results of FIG. 15, in the case of a large-sized apparatus (A / D> 1), the conversion efficiency after light degradation is 1 even if the i-layer deposition rate is increased from about 3 nm / min to about 30 nm / min. In contrast, in the case of the compact device (A / D ≦ 1), the conversion efficiency after light degradation is significantly reduced by 2 points or more in the case of the compact device (A / D ≦ 1).
[0033]
As for the compact device, the results were confirmed with two types of devices having different electrode sizes, but the results were similar, and it was found that this problem was unique to the compact device.
[0034]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a high-speed film forming apparatus using a compact film forming apparatus having an A / D of 1 or less. It is another object of the present invention to provide a method of manufacturing a thin-film solar cell capable of suppressing deterioration in characteristics of the thin-film solar cell.
[0035]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors conducted intensive studies on the film forming conditions of a compact type film forming apparatus by changing the film forming conditions. As a result, under the general film forming conditions, the plasma potential (the bulk of the plasma Potential), and the ions generated in the plasma are accelerated at a high potential to damage the thin film (defect generation, distortion of the bond angle, etc.), that is, the ion damage during film formation increases and the film quality deteriorates It turned out to be.
[0036]
The present invention has been made in view of the above. In the present invention, a first electrode layer, a non-single-crystal photoelectric conversion layer, and a transparent electrode layer (second electrode layer) are provided on the surface of an electrically insulating substrate. The method for manufacturing a thin-film solar cell, wherein the photoelectric conversion layer is formed by laminating the layers by a plasma CVD method in which a source gas is subjected to glow discharge decomposition under application of a high frequency voltage in a vacuum reaction chamber,
The reaction chamber is composed of a ground electrode, a high-frequency electrode, and a reaction chamber wall, and the distance between the ground electrode and the high-frequency electrode is D, and the closest distance between the reaction chamber wall and the high-frequency electrode is A. In this case, A / D is set to 1 or less, the film forming pressure in the reaction chamber is set to 130 to 400 Pa, and the frequency of the high frequency voltage is set to 13 to 60 MHz (the invention of claim 1).
[0037]
If the film forming conditions are controlled as described above, it is possible to suppress the plasma potential during high-speed film forming and suppress deterioration in film quality, as described in detail later. In addition, the film forming pressure is more preferably 130 to 340 Pa, and the frequency of the high frequency voltage is more preferably 13 to 50 MHz. According to the Radio Law, the frequency is an integral multiple of RF = 13.56 MHz, that is, 13.56 MHz, 27.12 MHz, 40.68 MHz... Therefore, in the following description, it may be a rough value (for example, an integer such as 13, 41) or a frequency other than the integer multiple.
[0038]
As an embodiment of the first aspect of the present invention, the following second to fourth aspects of the present invention are preferable. That is, in the manufacturing method according to claim 1, the thin-film solar cell comprises a first electrode layer, a photoelectric conversion layer, and a transparent electrode layer (second electrode layer) as lower electrode layers on a surface of an electrically insulating substrate. And a third electrode layer and a fourth electrode layer as connection electrode layers formed on the back surface of the substrate, wherein the photoelectric conversion unit and the connection electrode layer are displaced from each other. The adjacent unit photoelectric conversion portions (unit cells) patterned on each other on the surface are electrically connected to each other through a connection hole for electrical series connection formed in the transparent electrode layer formation region. (The invention of claim 2).
[0039]
Further, in the manufacturing method according to claim 1 or 2, the non-single-crystal photoelectric conversion layer is formed of non-single-crystal silicon, non-single-crystal silicon germanium, non-single-crystal silicon carbide, non-single-crystal silicon oxide, At least one of crystalline silicon nitride (the invention of claim 3).
[0040]
Furthermore, from the viewpoint of improving productivity, in the manufacturing method according to claim 1 or 2, the non-single-crystal photoelectric conversion layer is made of non-single-crystal silicon, and the source gas is SiH. ₄ To H ₂ Hydrogen dilution rate H ₂ / SiH ₄ Is set to 2 to 20 (the invention of claim 4). Although the details will be described later, the range of the hydrogen dilution rate is more preferably 5 to 15.
[0041]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0042]
FIG. 1 to FIG. 9 show examples of the results of experiments related to the present invention with variously changed film forming conditions. 1 to 5, FIGS. 1 to 5 show examples of the results of experiments performed with an apparatus with A / D = 0.17, and FIGS. 6 to 9 show apparatuses with A / D = 0.5. An example of the result of an experiment in which a thin-film solar cell was manufactured using the method shown in FIG.
[0043]
The A / D is based on the schematic diagram of the apparatus shown in FIG. 14, but the conductive portion d3 having the ground potential in FIG. 14 is not limited to the outer wall of the reaction chamber. The distance between d1 and d1 may be A. Further, the potential need not be the ground potential but may be any potential that is sufficiently smaller than the maximum potential applied to the high-frequency electrode.
[0044]
Here, the distance D between the electrodes at A / D = 0.17 was 3 cm, and A was 0.5 cm. The value of the distance D between the electrodes may be variable in the range of 2 cm ≦ D ≦ 5 cm in consideration of the correlation with the film forming speed of film formation, uniformity, etc., but may be variable in the range of 2 cm ≦ D ≦ 4 cm. Is preferred.
[0045]
Using the above compact apparatus, plasma measurement was performed to derive high-speed film formation conditions with low ion damage. For comparison, the same measurement was performed for a large-sized device (A / D = 2). FIG. 1 shows the experimental results of the plasma potential dependence of the plasma potential of both devices at a power supply frequency of 13 MHz. FIG. 1A shows the case of a conventional large-sized device (A / D = 2). Shows the case of A / D = 0.17 of the present invention. As a new finding, the results in FIG. 1 show that the pressure dependency of the plasma potential is significantly different between the two devices. That is, in the large-sized apparatus shown in FIG. 1A, the plasma potential (V) monotonically increases with an increase in the pressure (Pa). Actually, when an a-Si single cell was trial-produced using a large-sized apparatus with the i-layer deposition pressure as a parameter, it was found that the conversion efficiency after the photo-deterioration decreased as the pressure increased.
[0046]
On the other hand, in the compact device shown in FIG. 1B, there is a pressure at which the plasma potential becomes the lowest, and this lowest pressure may shift to the higher pressure side as the power density applied to the high frequency power supply increases. Do you get it. In addition, according to the results of an experiment conducted on a device other than A / D = 0.17, it was confirmed that if A / D was 1 or less, the same tendency as in FIG. 1B was exhibited. The preferred range of the film forming pressure will be described later with reference to FIG.
[0047]
Further, in the compact device, the power supply power density is 32 mW / cm ² FIG. 2 shows the result of examining the power supply frequency dependence of the plasma potential at a pressure of 130 Pa. According to the results of FIG. 2, it was found that the plasma potential (V) was reduced by increasing the power supply frequency (MHz).
[0048]
Based on the above experimental results, it is considered that high pressure and high frequency are effective in reducing ion damage.Furthermore, the film thickness distribution is confirmed and the cell is prototyped, and data for judging good or bad under various conditions is obtained. Was measured. The results are described below.
[0049]
3 and 4 show the relationship between the film forming pressure and the film thickness distribution R (%) of the photoelectric conversion layer, and the relationship between the power supply frequency and the same film thickness distribution R (%), respectively. Here, as an index of the film thickness distribution of the photoelectric conversion layer, R (%) is as follows:
R (%) = 100 (maximum thickness in plane−minimum thickness in plane) / (average thickness in plane)
And the cell of R ≧ 20% is determined to be a cell having an uneven film thickness, and is determined to be defective. Regarding the R value, it is desirable to obtain a uniformity of R ≦ 15% in consideration of the relationship between the appearance and the characteristics of the solar cell.
[0050]
According to the results shown in FIG. 3, the relationship between the film forming pressure (Pa) and the film thickness distribution R (%) shows a monotonous increase curve, and R exceeds 15% at 340 Pa or more, and R = 400% or more. More than 20%. Therefore, from the viewpoint of film thickness distribution, the film forming pressure is preferably 400 Pa or less, more preferably 340 Pa or less. The lower limit is preferably 130 Pa from the results in FIG. 1B, and the preferable range of the film forming pressure is 130 to 400 Pa, more preferably 130 to 340 Pa.
[0051]
Next, FIG. 4 will be described. It can be seen that the power supply frequency shown in FIG. 4 exceeds R = 15% at a power supply frequency of 50 MHz or more, and exceeds R = 20% as a failure determination line at a power supply frequency of 60 MHz or more. Therefore, a preferable range of the power supply frequency is 13 to 60 MHz, more preferably, 13 to 50 MHz.
[0052]
Next, FIG. 5 will be described. FIG. 5 shows the hydrogen dilution rate (H ₂ / SiH ₄ ) And the film formation rate (nm / min). When the hydrogen dilution rate is increased, the film quality is improved, and the characteristics as a solar cell are improved. However, as shown in FIG. 5, the film formation speed is reduced, and the productivity is reduced. Conventionally, a value of about 2 to 10 has been used for the hydrogen dilution rate. ₂ / SiH ₄ = About half of 10 ₂ / SiH ₄ = 20 is an acceptable limit. Therefore, the range of the hydrogen dilution rate is preferably 2 to 20, and more preferably 5 to 15 in view of the balance between productivity and cell characteristics.
[0053]
Next, experimental results such as fabrication and characteristics of the thin film solar cell will be described. The thin film solar cell is a SCAF type thin film solar cell shown in FIGS. ² Was manufactured. When the i-layer of the photoelectric conversion layer was formed, the A / D of the plasma CVD apparatus was set to 0.5. The film was formed using a stepping roll type film forming apparatus in the order of nip.
[0054]
The conditions for producing the single cell i-layer are as follows: the frequency of the high-frequency power supply is 13 to 41 MHz, the hydrogen dilution rate is 10, and the high-frequency power supply power density is 10 to 80 mW / cm. ² The film forming pressure was set to 65 to 400 Pa, and the film forming conditions were changed within this range, thereby producing an a-Si single cell. The film forming speed was calculated using the optically calculated film thickness and the film forming time in the a-Si thin film using the respective i-layer film forming conditions prepared in advance. At the time of manufacturing a single cell, the film forming time was adjusted using this film forming speed so that the designed film thickness became 300 nm. The i-layer thickness of the single cell was measured optically again after the cell was formed, and was confirmed to be around 300 nm.
[0055]
As described with reference to FIGS. 10 to 12, after forming the multistage serially connected solar cells, the sample fabrication was completed through the reverse bias applying process and the module forming process. After the sample was prepared, the sample was measured at 100 mW / cm to measure the cell characteristics after light degradation. ² And then exposed to light for about 300 hours. Thereafter, the sample was taken out and placed under white light (100 mW / cm) for each unit cell. ² ) Was measured. At the time of measurement, in order to make the area accurate, the measurement was performed with a mask having a known area covered on the solar cell. The measured data was corrected to a value equivalent to 25 ° C. by temperature correction.
[0056]
The results of plotting the relationship between the film formation speed and the conversion efficiency after 300 hours of light irradiation after performing the above-described measurement and correction are shown in FIGS. 6 to 8 show the results corresponding to the cells manufactured at the power supply frequencies of 13 MHz, 27 MHz and 41 MHz, respectively.
[0057]
Although the results of FIGS. 6 to 8 all show the same tendency, representatively, when comparing the cell characteristics by focusing on the example of the power supply frequency of 27 MHz shown in FIG. A comparison of the conversion efficiencies after 300 hours of light irradiation of a cell manufactured at a pressure of 65 Pa and a cell manufactured at a film formation speed of 4.8 nm / min and a cell manufactured at a film formation speed of 16.8 nm / min shows that the former is the former. Is 7.4% and the latter is 4.8%, which indicates that the conversion efficiency is significantly reduced by increasing the film forming speed.
[0058]
On the other hand, when the cell manufactured at a film forming speed of 130 nm and the cell manufactured at a film forming speed of 8.2 nm / min are compared with the cell manufactured at a film forming speed of 27.2 nm / min, the conversion efficiency after 300 hours of light irradiation is compared. The former is 7.5% and the latter is 6.1%, indicating that the effect of suppressing a decrease in conversion efficiency when the film forming speed is increased is large. In addition, it is clear that in the case of 200 Pa and 250 Pa, the effect of suppressing the decrease in the conversion efficiency when the film forming speed is increased is larger than that in the case of 130 Pa. When the film forming pressure is 400 Pa, the effect of suppressing the decrease in the conversion efficiency when the film forming speed is increased is smaller than when the film forming speed is 200 Pa and 250 Pa. Then, it can be said that there is an effect of suppressing a decrease in conversion efficiency.
[0059]
In the case of 400 Pa, the reason why the effect of suppressing the decrease in the conversion efficiency becomes small is considered to be that the in-plane film thickness distribution becomes large and the cell characteristics are deteriorated. Taking into account the results of the film thickness distribution described above, the range of the film forming pressure is preferably from 130 to 400 Pa, and more preferably from 130 to 340 Pa.
[0060]
Increasing the power supply frequency also has the effect of suppressing a decrease in conversion efficiency when the film forming speed increases. As an example, comparing the conversion efficiencies after 300 hours of light irradiation of cells manufactured at a film forming pressure of 200 Pa at a film forming speed of 30 nm / min in FIGS. It is 6.6% (FIG. 6), and it can be seen that the cell manufactured at 27 MHz is 7.2% (FIG. 7) and the cell manufactured at 41 MHz is 6.9% (FIG. 8).
[0061]
From these results, for example, when manufacturing a cell having a conversion efficiency of 7% or more after 300 hours of light irradiation, a cell manufactured under conventional conditions (13 MHz, 65 Pa) has a conversion efficiency of 7. nm / min at a film formation rate of 3.2 nm / min. The conversion efficiency was 7.3% at a deposition rate of 33.2 nm / min by applying an appropriate combination of power supply frequency and deposition pressure, for example, (27 MHz, 200 Pa). It becomes possible. From the above results, the power supply frequency is preferably 13 to 60 MHz, and more preferably 13 to 50 MHz, as described above.
[0062]
As described above, the effect of the present invention for improving the characteristics of the cell while suppressing the influence of the ion damage has been described. However, according to the present invention, there is the following effect different from the above-described effect. FIG. 9 shows the relationship between the film forming pressure and the radius of curvature of the plastic substrate after film formation. According to this figure, it can be seen that the radius of curvature increases as the film forming pressure increases. It is considered that the ion damage was reduced as described above by increasing the film forming pressure, and as a result, the internal stress of the film was reduced and the radius of curvature of the plastic substrate was increased. An increase in the radius of curvature of the substrate is preferable from the viewpoint of (1) an increase in the a-Si peeling limit film thickness of the electrode plate of the CVD apparatus, and (2) an improvement in film handling.
[0063]
By the way, the numerical value of the radius of curvature of the substrate shown in FIG. 9 is about 20 mm, and when the film substrate after the a-Si film formation is made free, the substrate is wound up like a bandage. However, during the process, the film substrate is stretched with tension, and if the film substrate is finally laminated with a resin or the like, curling is eliminated. However, since the internal stress remains, this causes the following problems.
[0064]
(1) Problem of a-Si film peeling from electrode of CVD device
This is a phenomenon in which the a-Si film adhered to the electrode peels off when the thickness exceeds the limit thickness due to stress. When this occurs, a large amount of pinholes are generated in the film. Will decide. Under the conventional high-speed conditions, the peeling limit film thickness (integrated value during mass production of cells) was 20 to 30 μm, but according to the application of the present invention, the limit film thickness could be increased to 70 μm or more. This is because the internal stress becomes small and the peeling is suppressed.
[0065]
(2) Handling problems during modularization work
When a film is cut into a module to be curled, workability becomes extremely poor. As a countermeasure, a method in which an adhesive resin (EVA) sheet is temporarily laminated is also employed. However, according to the application of the present invention, the curling is reduced, so that the module work can be performed without performing the temporary lamination. It becomes possible.
[0066]
(3) Reliability issues
When a high-temperature and high-humidity test of 2000 hours or more is performed as a weathering test, peeling occurs between the lower electrode and the film or between the electrode and a-Si due to internal stress of the a-Si film. According to the application of the present invention, this phenomenon is also mitigated.
[0067]
By the way, in the above description of the embodiment of the present invention, the case where the present invention is applied to an a-Si single cell has been described. It is also effective for a solar cell using an alloy film such as a-SiO or microcrystalline silicon. Further, the configuration of the thin-film solar cell is not limited to the SCAF type.
[0068]
【The invention's effect】
According to the present invention, as described above, the first electrode layer, the non-single-crystal photoelectric conversion layer, and the transparent electrode layer (second electrode layer) are laminated on the surface of the electrically insulating substrate. The layer is a thin-film solar cell manufacturing method in which a film is formed by a plasma CVD method in which glow discharge decomposition of a source gas is performed under application of a high-frequency voltage in a vacuum reaction chamber.
The reaction chamber is composed of a ground electrode, a high-frequency electrode, and a reaction chamber wall, and the distance between the ground electrode and the high-frequency electrode is D, and the closest distance between the reaction chamber wall and the high-frequency electrode is A. In this case, the A / D is set to 1 or less, the film forming pressure in the reaction chamber is set to 130 to 400 Pa, and the frequency of the high frequency voltage is set to 13 to 60 MHz to form a film.
The plasma potential at the time of high-speed film formation can be suppressed low, and the film quality can be prevented from deteriorating. Further, the internal stress of the formed thin film is also weakened, and effects such as an improvement in the productivity of the solar cell, an increase in the a-Si peeling limit film thickness, and an improvement in the handling of the film can be obtained. As described above, mass production of thin-film solar cells using a low-cost compact film-forming apparatus becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a film forming pressure and a plasma potential according to an embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between a power supply frequency and a plasma potential according to an embodiment of the present invention.
FIG. 3 is a diagram showing a relationship between a film forming pressure and a film thickness distribution R according to an embodiment of the present invention.
FIG. 4 is a diagram showing a relationship between a power supply frequency and a film thickness distribution R according to an embodiment of the present invention.
FIG. 5 is a diagram showing a relationship between a hydrogen dilution rate and a film formation rate according to an embodiment of the present invention.
FIG. 6 is a diagram showing a relationship between a film forming speed and a conversion efficiency after 300 hours of light irradiation according to an example of the present invention.
FIG. 7 is a relationship diagram similar to FIG. 6 when the power supply frequency is different from FIG. 6;
FIG. 8 is a relationship diagram similar to FIG. 6 when the power supply frequency is further different from FIG. 6;
FIG. 9 is a diagram showing a relationship between a film forming pressure and a radius of curvature of a substrate according to an embodiment of the present invention.
FIG. 10 is a configuration diagram of a conventional SCAF thin-film solar cell.
FIG. 11 is a perspective view showing a schematic configuration of a conventional SCAF thin-film solar cell.
FIG. 12 is a view schematically showing a manufacturing process of a conventional SCAF thin-film solar cell.
FIG. 13 is a diagram showing an example of a schematic structure of a film forming chamber of a conventional plasma CVD apparatus.
FIG. 14 is a schematic diagram obtained by simplifying FIG. 13;
FIG. 15 is a diagram showing the relationship between the i-layer film forming speed and the conversion efficiency after photodegradation during the formation of a-Si in each reaction chamber structure.
[Explanation of symbols]
61: substrate, 64: lower electrode layer, 65: photoelectric conversion layer, 66: transparent electrode layer, 67: collector hole, 68: connection hole, d1: high-frequency electrode, d2: ground electrode, d3: reaction chamber wall A: a conductive portion having a ground potential, A: the closest distance between the reaction chamber wall and the high-frequency electrode, D: the inter-electrode distance between the high-frequency electrode and the ground electrode.

Claims (4)

A first electrode layer, a non-single-crystal photoelectric conversion layer, and a transparent electrode layer (second electrode layer) are laminated on a surface of an electrically insulating substrate, and the photoelectric conversion layer is provided with a high-frequency voltage in a vacuum reaction chamber. In a method of manufacturing a thin film solar cell formed by a plasma CVD method of performing glow discharge decomposition of a source gas under application of
The reaction chamber is composed of a ground electrode, a high-frequency electrode, and a reaction chamber wall, and the distance between the ground electrode and the high-frequency electrode is D, and the closest distance between the reaction chamber wall and the high-frequency electrode is A. In this case, A / D is set to 1 or less, the film forming pressure in the reaction chamber is set to 130 to 400 Pa, and the frequency of the high frequency voltage is set to 13 to 60 MHz. Production method. 2. The manufacturing method according to claim 1, wherein the thin-film solar cell includes a first electrode layer, a photoelectric conversion layer, and a transparent electrode layer (second electrode layer) as a lower electrode layer sequentially on a surface of an electrically insulating substrate. A photoelectric conversion unit having a stacked structure, and a third electrode layer and a fourth electrode layer as connection electrode layers formed on the back surface of the substrate, wherein the photoelectric conversion unit and the connection electrode layer are displaced from each other to form a unit portion The adjacent unit photoelectric conversion portions (unit cells) that are patterned and adjacent to each other on the surface are electrically connected to each other through connection holes for electrical series connection formed in the transparent electrode layer formation region. A method for manufacturing a thin-film solar cell, comprising connecting in series. 3. The method according to claim 1, wherein the non-single-crystal photoelectric conversion layer is made of non-single-crystal silicon, non-single-crystal silicon germanium, non-single-crystal silicon carbide, non-single-crystal silicon oxide, non-single-crystal silicon nitride. A method for producing a thin-film solar cell, wherein the method is at least one of rides. 3. The method according to claim 1, wherein the non-single-crystal photoelectric conversion layer is made of non-single-crystal silicon, and a gas obtained by diluting SiH ₄ with H ₂ is used as the source gas, and a hydrogen dilution rate H ₂ is used. / SiH ₄ is 2 to 20. A method for producing a thin-film solar cell.

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