JPH02168507A - Fluorine doped tin oxide film and method of reducing resistance thereof - Google Patents

Abstract

PURPOSE:To obtain a transparent conductive film having a high degree of transparency, high resistance against active hydrogen type and coudnctivity improved with the active hydrogen type by controlling the amount of fluorine added to a conductor and conductive electron density within a specified range. CONSTITUTION:A transparent electrode 3 comprising a alkali barrier coat 2 and a fluorine doped tin oxide, a photoelectric conversion layer 4 comprising amorphous silicon hydroxide and a conductive film 5 are respectively formed in sequence on a transparent substrate 1, thereby forming a solar battery. An electrode a has a transparent conductive film of tin oxide composed of 0.01 to 4mol% of fluorine added to tin oxide and the conductive electron density thereof is controlled within 5X10<19> to 4X10<20>cm<-2>. According to the aforesaid construction, a highly transparent film of a small absorption amount is obtained. Also, when the film is exposed to a hydrogen plasma in the formation of alpha-Si and the like, the resistance value of the film is reduced to about 1/5 maximum. As a result, high transparency and resistance quality is obtained and the conduc tivity of the film is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a tin oxide film having high performance, particularly a tin oxide film useful as a substrate for solar cells.

[Prior art] In general, oxide transparent conductive films are required to have low resistance and high transparency, but it is said that as the conduction electron density, which affects conductivity, increases, light absorption gradually increases in the visible light range. Generally, it is extremely difficult to achieve both low resistance and high transparency because they have contradictory aspects. However, in transparent conductive substrates for power solar cells, it is important to achieve transparency while maintaining conductivity as high as possible, and there is a need to develop substrates with good characteristics.

As a transparent conductive film, tin oxide, indium oxide, etc. deposited on a glass substrate are known, and are widely used for solar cell substrates, liquid crystals, electrodes for display elements such as electroluminescent elements, and the like. In particular, tin oxide film is a chemically stable material and is inexpensive, so it is useful as a large-area conductive substrate, and active research is being carried out mainly as a substrate for amorphous solar cells. Currently, the common methods for forming a tin oxide film on a glass substrate are a spray method using tin tetrachloride or a CVD method (chemical vapor deposition method). In this case, use the CVD method,
A common method is to introduce fluorine (F) as an activator.

However, when doping with fluorine (F) in this way,
The specific resistance of the tin oxide conductive film reaches the level of 1O-4Ω・cm, and while it has the advantage that a film with high conductivity can be obtained relatively easily, on the other hand, it tends to be difficult to obtain a film with high transmittance. Ta. This is because when using fluorine, it is possible to lower the resistance by increasing the conduction electron density relatively easily, but an increase in the conduction electrons causes optical absorption (conversely, the transmittance decreases). On the other hand, a film with a low conductive electron density improves transmittance, but the resistance increases significantly, making it difficult to obtain a practical low-resistance film that can be used in solar cells, etc. In order to reduce the resistance of a film with a low conduction electron density, it is necessary to increase the film thickness, but this leads to increased absorption.As a result, it has been difficult to achieve both high transparency and low resistance.

On the other hand, the above-mentioned general conductive films are, for example, J, H.

Thomasm (Appl, Phys, Lett,,
42 (1983) 794), Y.

Tawada AND Y, Hamakawa (Pro
c, Int'l PVSEC-1゜Kobe, Ja
(1984) 179), it is vulnerable to active reducing species, and when this conductive film is exposed to hydrogen plasma, it becomes black (discolored), loses transparency, and in extreme cases becomes powdery. Amorphous silicon (a-SL) is deposited on the conductor on which the tin oxide film is formed.
) The most common method of forming solar cells is plasma CVD using a glow discharge method. When this method is used, the conductive film is always exposed to hydrogen plasma in the early stages of forming amorphous silicon (a-Si), so deterioration of the conductive film due to the hydrogen plasma poses a problem. Therefore, even if it has a high transmittance before being exposed to plasma, if even a small amount of deterioration occurs due to plasma, if this substrate is used in a solar cell, the conductive film will be on the light incident side, so the conductor will become black. This causes a decrease in conversion efficiency. That is, it is extremely important for a transparent conductor to be used as a substrate for a solar cell to be highly transparent and at the same time to have characteristics that the transparency of the conductive film is not impaired by hydrogen plasma. However, to date no effective solution has been found that meets these requirements.

[Problems to be solved by the invention] The present invention solves the above-mentioned drawbacks of the prior art, and
A high-grade fluorine-doped transparent conductive film that has low resistance, high transmittance, and high durability against hydrogen active species such as hydrogen plasma and hydrogen ions, and is particularly useful as a substrate for a-Si solar cells. The purpose is to provide a transparent conductive film.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned problems,
By controlling the amount of fluorine added in the conductor and the conductive electron density within a specific range, the film has extremely low absorption, is highly transparent, has high durability against active hydrogen species, and is highly conductive due to active hydrogen species. The present invention provides a transparent conductive film that has improved performance in contrast to the conventional technology. That is, 0.0% fluorine to tin oxide.
Contains 01~4m01%, conductive electron density is 101g~
A fluorine-doped tin oxide film having a size of 4 x 10"cm-" is provided.

The present invention will be explained in detail below.

In order to improve the transmittance of the tin oxide transparent conductive film, the present inventors added fluorine in the tin oxide transparent conductive film in an amount of 0.00% relative to tin oxide. O1-4 mo1%, and conductive electron density is 5
A highly transparent film with extremely low film absorption can be obtained only when controlled within the range of X 10"cm-" or more and 4x 10"cm-" or less, and can be resistant to hydrogen plasma during the formation of a-Si, etc. When exposed, the resistance value of the conductive film increases to approximately 11
We have discovered a phenomenon in which the resistance decreases up to 5. The conductivity of these films is greatly improved in less than 10 seconds after exposure to a non-oxidizing atmosphere, the transmittance does not change at all, and the film has excellent plasma resistance.

The fluorine-doped tin oxide film of the present invention can be formed by a spray method, a CVD method, or a PVD method such as vacuum evaporation or sputtering, but the CVD method is particularly preferable because it is highly mass-producible and can easily produce a high-quality film. .

Further, when used as a transparent electrode of a solar cell, the thickness of the fluorine-doped tin oxide film of the present invention is preferably about 500 to 2 μm in consideration of both transmittance and resistance value.

By exposing the fluorine-doped tin oxide film of the present invention to a non-oxidizing atmosphere, the transmittance resistance value can be lowered to a maximum of about 115.

The non-oxidizing atmosphere preferably has an oxygen partial pressure of 100 Torr or less (see FIG. 8).

In such a non-oxidizing atmosphere, components other than oxygen may include nitrogen, H, 0, Ar, etc., and are not particularly limited.

In addition, the substrate temperature when exposed to a non-oxidizing atmosphere is as follows:
The temperature is preferably 150° C. or higher, particularly 200° C. or higher, since the resistance can be significantly lowered (see FIG. 9).

When using hydrogen plasma as a non-oxidizing atmosphere,
Hydrogen partial pressure is 0.3 to 1.5 Torr, discharge power is 1O
It is preferable to expose the substrate to a hydrogen plasma of about 50 mW/cm" at a temperature of 100 to 300 DEG C. for 10 to 120 seconds, since the most significant reduction in resistance can be achieved.

FIG. 3 shows a partial vertical cross-sectional view of an example of a solar cell using the fluorine-doped tin oxide film of the present invention as a transparent electrode. In FIG. 3, 1 is a transparent substrate, 2 is an alkali barrier coat, 3 is a first transparent electrode made of a fluorine-doped tin oxide film of the present invention, and 4 is made of hydrogenated amorphous silicon (a-3t:H). The photoelectric conversion layer 5 is a second conductive film, and the electromotive force obtained in the photoelectric conversion layer 4 is taken out through a conductive wire 6. ~ As the light-transmitting substrate 1 on which the fluorine-doped tin oxide film 3 of the present invention is formed, soda lime silicate glass plates, aluminosilicate glass plates, Alkali-containing glass plates such as borosilicate glass plates and lithium aluminosilicate glass plates,
A low alkali-containing glass plate, a non-alkali glass plate, a quartz glass plate, or the like is preferable, but a transparent plastic plate or a transparent plastic film may also be used depending on the case. In addition, in the case of an alkali-containing glass plate such as a soda lime silicate glass plate, or a low-alkali content glass plate, the alkaline component on the surface of the glass plate dissolves, causing haze (jelsu) on the transparent conductive film formed thereon. In order to prevent this, a sinusoid is placed on the side of the glass plate on which the transparent conductive film is formed.
It is preferable to form an alkali barrier coat 2 mainly composed of oxides such as □, Al2O3, and ZrC1a.

As mentioned above, the fluorine-doped tin oxide film of the present invention can be used in a non-oxidizing atmosphere with an oxygen partial pressure of 100 Torr or less, for example, with a hydrogen partial pressure of 0.3 to 1.5 Torr and a discharge power of 10 to 10 Torr.
When the substrate temperature is 1 in hydrogen plasma of about 50 mW/cm"
When exposed for 10 to 120 seconds at a temperature of 00 to 300°C, the resistance can be most significantly lowered while maintaining high transmittance.

On the other hand, when forming an a-Si:H film on a transparent conductive film by glow discharge, if at least 20 a-Si:H films are formed, the hydrogen plasma caused by the glow discharge will affect the transparent conductive film. That will almost never happen. Therefore, a-Si is deposited on the fluorine-doped tin oxide film of the present invention by glow discharge.
When forming the :H film, it is very preferable to perform glow discharge under the above-mentioned conditions for lowering the resistance, and to avoid being affected by hydrogen plasma any further when the lowest resistance is obtained. That is, the first 20 or so members of the a-3t:H film were
If the film is formed for ~120 seconds, an a-Si:H film can be formed on the doped tin oxide film with the lowest resistance, and it is expected to greatly contribute to improving the conversion efficiency of solar cells.

[Function] In the present invention, fluorine is added in an amount of 0.01 to 4 mo relative to tin oxide.
Contains 1%, conductive electron density is 5 x 10" to 4 x 10"
cm''''' fluorine-doped tin oxide film is heated to Nz, HzO
By exposing the tin oxide film to a non-oxidizing atmosphere such as an inert gas such as or Ar, some of the oxygen atoms are removed from the tin oxide film, resulting in an oxygen-deficient state, which increases the carrier concentration near the grain boundaries and decreases the hole mobility. It is thought that this increases the resistance, thereby promoting a reduction in resistance.

Furthermore, by exposure to hydrogen plasma, hydrogen neutralizes the charge at the grain boundaries of tin oxide, lowers the height of the potential barrier at the grain boundaries, and increases hole mobility, promoting lower resistance. It is considered that

The above effects are due to the fact that fluorine is 4 mo1 relative to tin oxide.
% or less, and is considered to be most noticeable in a fluorine-doped tin oxide film with a carrier concentration of 4 x 10"cl" or less.

In the present invention, the fluorine content in the tin oxide film is 4 mo
The reason why a remarkable reduction in resistance is observed in a film with a concentration of 1% or less is that when 4 mo1% or more of fluorine is contained in the film, Sn
This is thought to be because -F bonds are formed or F is segregated at grain boundaries, which removes oxygen atoms and prevents hole mobility from moving.

In addition, a remarkable reduction in resistance is observed in a film with a conductive electron density of 4 x 10"cl" or less at 4 x 102°c.
It is thought that this is because when the conduction electron density exceeds 4X, segregation of F to the grain boundaries occurs, which similarly removes oxygen atoms and prevents the ball mobility from increasing. When it exceeds 10"cm-", absorption by free electrons increases, which also has the disadvantage of lowering the transmittance.

In addition, the fluorine content is 0. If O1mo is less than 1%,
The crystallinity of the tin oxide film deteriorates, resulting in a film with a high resistance value, and the resistance value is inversely proportional to the product of the conduction electron density and mobility, so if the conduction electron density is less than 5 x 10"cm-' This is not preferable because the absolute value of the resistance becomes high and a film that is practical as a low-resistance transparent conductive film cannot be obtained.

[Example] Examples and comparative examples of the present invention will be described below.

Example and Comparative Example 1 Low resistance by E-hydrogen plasma] A glass substrate (locmxlocmX
1 mm), and after thorough washing, various tin oxide transparent conductive films as shown in Table 2 are formed on the silica film using the atmospheric pressure CVD method using tin tetrachloride as the main raw material and hydrolysis reaction with water. did. The amount of fluorine added to the film and the electrical properties were controlled by changing the amount of hydrofluoric acid, which is a dopant, supplied. Furthermore, methanol was added to promote fluorine doping. The substrate temperature is from 500℃ to 6
The film was formed in a temperature range of 00°C. As samples, membranes having various resistances and transmittances as shown in Table 2 were prepared. The fluorine content in the film was quantitatively analyzed by gas chromatography after dissolving the tin oxide film in hydrochloric acid containing zinc. The fluorine content was expressed in mol% relative to tin oxide.

Also, the electron density is determined by the Hall effect (van der Pauw method)
It was determined by the measurement of A hydrogen plasma exposure test was conducted on these under the conditions shown in Table 1. The results are shown in Table 2.

Table 1 Table 2 As is clear from Table 2, the fluorine concentration is 0. O
A film having a content of 1mol% or more and 4mol% or less shows a high transmittance during film formation, and the transmittance does not change even after plasma treatment. Furthermore, although the electrical properties (surface resistance) show a relatively high value after film formation, the resistance value decreases to a maximum of 115 after plasma exposure, resulting in low resistance. Especially for a film with low electron density as shown in sample 1, the transmittance is 86%.
It can be seen that although the resistance is extremely high, the resistance is sufficiently reduced after plasma exposure, achieving high transparency and low resistance.

On the other hand, as shown in sample 6, the fluorine content is 0.
．． Although a decrease in resistance can be seen in films with less than 0.01 mol %, since the absolute value is originally high, a practical low resistance value (10-odd Ω/mouth or less) cannot be obtained even after plasma treatment. In addition, as seen in sample 7, a film with a particularly high fluorine concentration relative to the electron concentration has low transmittance (compared to sample 3), and the reduction in resistance is also small, so the overall characteristics do not improve. The electrically conductive substrate of the invention exhibits improved electrical properties after hydrogen plasma treatment, and has high transparency and low resistance, making it ideal as a substrate for solar cells.

FIG. 1 shows the results of investigating the dependence of surface resistance change upon plasma exposure on hydrogen plasma exposure time for Samples 1 and 5 under the conditions shown in Table 3.

Table 3 For sample 1 (curve A), the resistance value is 11 after 10 seconds.
5 and maintains a constant resistance value until 120 seconds. On the other hand, in the case of sample 5 (curve B), the resistance value hardly changes. Treatment for 300 seconds or more causes reduction in the films, so the resistance of all films increases rapidly.

FIG. 2 shows the results of examining the substrate temperature dependence of surface resistance change upon exposure to hydrogen plasma for Samples 1 and 5 under the conditions shown in Table 4.

Table 4 In the case of sample 1 (curve C), the resistance value decreases from 1/2 to 115 at temperatures above about 100°C, and the resistance decreases in the temperature range up to 300°C. Although the resistance is low even at 350°C, there is a slight deterioration in transmittance, so the practical temperature range is limited to 100°C or higher and 300°C or lower. On the other hand, in the case of sample 5 (curve D), the resistance value hardly changes up to 300°C, and tends to increase above 350°C. As described above, it can be seen that in the case of the example, an improvement in electrical characteristics is observed due to the plasma treatment, but in the case of the comparative example, no improvement is observed at all.

Figure 4 shows the relationship between the fluorine content in the tin oxide film and the surface resistivity before and after the hydrogen plasma exposure test under the conditions shown in Table 1, and Figure 5 shows the conductive electron density in the tin oxide film. The relationship between surface resistivity before and after the hydrogen plasma exposure test under the conditions shown in Table 1 is shown.

Fluorine concentration is 4 mo1% or less, and conduction electron density is 4
It can be seen that the effect of lowering resistance due to hydrogen plasma exposure is obtained when X 10"cm-" or less.

As shown above, by controlling the fluorine concentration and conduction electron density within a certain range, a transparent conductive film with high transmittance can be realized.In addition, when exposed to a hydrogen plasma atmosphere that forms an a-Si shadow, , substrate temperature 100℃ or higher 3
It is possible to greatly improve electrical properties by exposure for 120 seconds or less in a wide temperature range of 00° C. or less.

There is no change in the optical properties due to the improvement in the electrical properties.

Therefore, when these substrates are used as solar cell substrates, the conversion efficiency can be greatly improved due to the synergistic effect of the three elements of high transparency, low resistance, and plasma resistance.

Examples and Comparative Example 2 [Reducing resistance by nitrogen annealing] Films having various resistances and transmittances as shown in Table 5 were prepared in the same manner as in Example 1 above. A membrane with fluorine content and transmittance was created. Fluorine content and electron density were also measured in the same manner as in Example 1.

Table 5 Table 6 Figure 6 shows the fluorine content in the tin oxide film and the approximately 100% N2 content.
Figure 7 shows the conduction electron density in the tin oxide film and the relationship between the change in surface resistance before and after nitrogen annealing at normal pressure, 500°C for 10 minutes, and after nitrogen annealing at about 100% N2, normal pressure, 500°C for 10 minutes. The relationship between surface resistance change before and after nitrogen annealing treatment is shown.

The fluorine concentration is 4 mol% or less, and the conductive electron density is 4
It can be seen that when X10"cm-" or less, the effect of lowering the resistance by nitrogen annealing treatment is obtained.

As is clear from Table 5, the fluorine concentration is 0.01 in molar ratio.
% or more and 4% or less exhibits high transmittance during film formation, and the transmittance does not change even after annealing in a nitrogen atmosphere. Further, even if the electrical property (surface resistance) shows a relatively high value after film formation, the resistance value decreases to a maximum of 175 after annealing, resulting in low resistance.

In particular, as shown in sample 1, it can be seen that a film with a low electron density has an extremely high transmittance of 85%, but a film with a high resistance becomes sufficiently low in resistance after annealing, achieving high transparency and low resistance. On the other hand, as shown in sample 5, a decrease in resistance can be seen in a film with a fluorine content of 0.01 mol% or less, but its absolute value is originally high, so even after annealing, it has a practical low resistance value (10s). Ω/mouth) cannot be obtained.

Further, in a film where the fluorine concentration is particularly high relative to the electron concentration, as seen in Sample 5, the transmittance is low (compared to Sample 3) and no change in resistance is observed, so the overall characteristics are not improved.

As described above, the conductive substrate of the present invention exhibits improved electrical properties after nitrogen annealing, and has high transparency and low resistance, making it ideal as a substrate for solar cells.

As shown above, by controlling the fluorine concentration and the conductive electron density within a certain range, a transparent conductive film with high transmittance can be realized.

FIG. 8 shows the dependence of surface resistance change on oxygen partial pressure in a nitrogen atmosphere due to nitrogen annealing treatment (normal pressure, 500° C., 10 minutes). It can be seen that the annealing effect is obtained at an oxygen partial pressure of 100 Torr or less.

Figure 9 shows nitrogen annealing treatment (normal pressure, approximately 100% N2, 1
3 shows the dependence of surface resistance change on substrate temperature during annealing treatment (0 minutes). Substrate temperature 150℃ or higher, especially 200℃
It can be seen from the above that a remarkable annealing treatment effect was obtained.

Note that the annealing treatment time is almost the same as that for hydrogen plasma exposure, and the effect of lowering the resistance can be achieved in about 10 seconds.

These characteristics can be improved even in an inert gas atmosphere other than nitrogen as long as the oxygen partial pressure is 100 Torr or less. Gases used include rare gases such as argon, neon, helium, etc.
Alternatively, hydrogen, which is a reducing atmosphere gas, is suitable. Furthermore, the same annealing effect can be obtained even under vacuum.

The ranges of fluorine concentration and conductivity density are 0 and O2N, respectively.
2 mo1%, 5 X 10”~4 X 10”cm-
', especially 0.1-4 mo1%, I x 10"-4
A range of X 10"cm-" is desirable, and in this case, an excellent transparent conductive film with particularly high transparency and low resistance can be obtained.

After annealing, the film shows no change in optical properties due to improvement in electrical properties. Therefore, when these substrates are used in solar cells, due to the synergistic effect of high transparency and low resistance,
It becomes possible to increase (improve) the conversion efficiency.

[Effects of the Invention] According to the present invention, it is possible to greatly reduce the resistance value by exposing the transparent conductive film to a hydrogen plasma atmosphere for only about 10 seconds while maintaining the transmittance of the transparent conductive film high. Therefore, when used in a solar cell substrate that requires high transparency, low resistance, and hydrogen plasma resistance, it is necessary to thicken (improve) the conversion efficiency after forming the amorphous layer in order to satisfy all these requirements. becomes possible.

Further, the fluorine-doped tin oxide film of the present invention can be left in a non-oxidizing atmosphere such as a nitrogen atmosphere, an H20 atmosphere, or an inert gas such as argon to obtain low resistance while maintaining high transmittance. Therefore, it can be applied to the other side.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the dependence of the surface resistance change of a fluorine-doped tin oxide film upon exposure to hydrogen plasma on the hydrogen plasma exposure time and on the substrate temperature, respectively. FIG. 3 is a partial longitudinal sectional view of an example of a solar cell using the fluorine-doped tin oxide film of the present invention as a transparent electrode. FIGS. 4 and 5 are graphs respectively showing the relationship between the fluorine content and conduction electron density in a fluorine-doped tin oxide film and the change in surface resistance due to a hydrogen plasma exposure test. FIGS. 6 and 7 are graphs respectively showing the relationship between the fluorine content and conduction electron density in a fluorine-doped tin oxide film and the change in surface resistance due to nitrogen annealing treatment. FIGS. 8 and 9 are graphs showing the dependence of the surface resistance change during nitrogen annealing on a fluorine-doped tin oxide film on the oxygen partial pressure in the annealing atmosphere and on the substrate temperature, respectively. 1: Transparent substrate 2: Alkali barrier coat 3: First transparent electrode made of the fluorine-doped tin oxide film of the present invention 4: Photoelectric conversion layer 5 made of hydrogenated amorphous silicon (a-Si:H): Second conductive layer Membrane 6: Conductor Ro: Surface resistance before exposure to non-oxidizing atmosphere R9: Surface resistance after exposure to non-oxidizing atmosphere S, '6 獍t (-), -/') 4th figure ka I kama 斥 (month Q "csr") 4th figure 7 zomei t (vehicle I/2 1st figure 4t) e & ( ylo'6cmJ Figure 7 Figure 1001 group 200 300 400 5
00h Rescue Sim Yasuji C) Figure 9

Claims (8)

[Claims] (1) Contains 0.01 to 4 mol% of fluorine based on tin oxide, and has a conductive electron density of 5 x 10^1^8 to 4 x 10^2^0
Fluorine-doped tin oxide film with cm^-^3. (2) A method for lowering the resistance of a fluorine-doped tin oxide film, which comprises exposing the fluorine-doped tin oxide film according to claim 1 formed on a substrate to a non-oxidizing atmosphere. (3) The method for reducing the resistance of a fluorine-doped tin oxide film according to claim 2, which comprises exposing the fluorine-doped tin oxide film according to claim 1 to a non-oxidizing atmosphere having an oxygen partial pressure of 100 Torr or less. (4) The method for lowering the resistance of a fluorine-doped tin oxide film according to claim 2 or 3, characterized in that the substrate is exposed to a non-oxidizing atmosphere at a temperature of 150° C. or higher. (5) A claim characterized in that the substrate is exposed for 10 to 120 seconds at a substrate temperature of 100 to 300°C in hydrogen plasma with a hydrogen partial pressure of 0.3 to 1.5 Torr and a discharge voltage of 10 to 50 mW/cm^2. Item 2. A method for reducing the resistance of a fluorine-doped tin oxide film. (6) Fluorine on a transparent substrate with a ratio of 0.01 to tin oxide
Contains 4 mol%, conductive electron density is 5 x 10^1^9~4
A first transparent electrode made of a fluorine-doped tin oxide film of x10^2^0cm^-^3 is formed, then an a-Si photoelectric conversion layer is formed by glow discharge using hydrogen plasma, and then a second conductive A method for manufacturing a solar cell, comprising forming a film. (7) The first 20 Å of the a-Si photoelectric conversion layer has a hydrogen partial pressure of 0.3 to 1.5 Torr and a discharge voltage of 10 to 50 mW/c.
7. The method for manufacturing a solar cell according to claim 6, wherein the film is formed within 120 seconds using glow discharge of m^2. (8) On a transparent substrate, fluorine is added at a ratio of 0.01 to tin oxide.
~ Contains 4 mol%, conductive electron density is 5 x 10^1^9 ~
A first transparent electrode made of a fluorine-doped tin oxide film with a size of 4×10^2^0 cm^-^3, an a-Si photoelectric conversion layer, and a second
A solar cell made by sequentially stacking conductive films.