JPH08116080A - Thin film solar cell and its manufacture - Google Patents

Abstract

PURPOSE: To increase the open-circuit voltage of an element and improve the photoelectric conversion efficiency, by using a silicon thin film containing P-type microcrystalline phase wherein the amount of bonded hydrogen is larger than or equal to a specified value, and the volume ratio of microcrystalline phase in bulk structure is in a specified range. CONSTITUTION: On a rear electrode 2, an N-type amorphous silicon hydride film 3 is deposited, on which an I-type amorphous silicon hydride layer 4 is formed. On the I-type layer 4, a silicon thin film (P-type uc-SiH film) containing P-type microcrystalline phase wherein the volume ratio of microcrysLalline phase is changed is formed, as a P-layer 5 of an element. An ITO film as a transparent conducting film 6 is deposited on the P-type layer 5, and an aluminum film as a collector electrode 7 is formed. In particular, the P-type uc-Si:H film is used as the P-type layer which film is specified as follows; the amount of bonded hydrogen is 13at% or higher and the volume ratio of microcrystalline phase in bulk structure whose film thickness is 100nm or greater is in the range from 65% to 92%. Thereby the open-circuit voltage of an element can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film solar cell having a high photoelectric exchange efficiency, particularly to an amorphous solar cell.

[0002]

2. Description of the Related Art Thin film solar cells, especially amorphous solar cells, have already been put into practical use as solar cells for consumer use due to recent intensive research and development. However, as a solar cell for electric power, which is expected to be further expanded in applications, the photoelectric conversion efficiency of the element is about 10%, which is far inferior to the exchange efficiency of 15% to 20% of a crystalline solar cell. On the other hand, amorphous solar cells are characterized by the fact that the thickness required for photoelectric conversion is less than one-third of that of crystalline silicon solar cells, and that it is easy to increase the area due to the manufacturing process. Cost reduction can be expected compared to. From the viewpoint of today's so-called environmental problems, it is necessary to be able to compete with existing commercial power in order for solar power generation to be put into practical use, and for that purpose it is necessary to manufacture solar cells with high photoelectric exchange efficiency at low cost. is important.

Generally, an amorphous solar cell has an intrinsic layer (i
Type layer) is inserted between the p-type layer and the n-type layer to perform photoelectric exchange. At this time, the p-type layer and the n-type layer are
The i-junction and the in-junction play a role of generating a diffusion potential shown in FIG. 4 in the element. This diffusion potential is closely related to the open circuit voltage that represents the device performance, and a large diffusion potential gives a high open circuit voltage and is effective in improving the exchange efficiency of the device.

Conventionally, a p-type hydrogenated amorphous silicon carbon film (p-type a-SiC: H) found in JP-A-57-126175 has been used as a p-type layer on the light incident side of an amorphous solar cell. This is because the application of p-type a-SiC: H having a wide band gap improves the effective diffusion potential. Further, generally, the doped layer of an amorphous solar cell is a photoelectric exchange inactive layer, and the absorption of light therein causes a light absorption loss. In particular, this loss is large in the p-type layer on the light incident side, and for that reason, the above-mentioned p-type a-SiC: H having a wide band gap has advantageous physical properties. Such p-type a-Si currently used
As for the physical properties of C: H as a bulk, the optical band gap by Tauc plot is 1.9 eV to 2.0.
eV, the dark conductivity at room temperature is in the order of 1 × 10 ⁻⁶ S / cm, and the activation energy of this dark conductivity is about 0.4 to 0.5 eV.

In order to further improve the conversion efficiency of the amorphous solar cell, it is effective to increase the diffusion potential shown in FIG. Traditionally for this purpose,
As seen in JP-A-57-187971, p of fine crystals
It has been pointed out that the effectiveness of the n-type or n-type silicon film (μc-Si: H). For example, the p-type μc-Si: H that is usually obtained has a dark conductivity activation energy of about several tens of meV, which is smaller than that of the above-mentioned p-type a-SiC: H by one digit.
Therefore, as a result of the Fermi level being closer to the valence band, the diffusion potential of the device is increased.

[0006]

However, when p-type μc-Si: H having a good crystallinity in which the volume fraction of fine crystals is close to 100% is actually applied as a p-type layer of an amorphous solar cell. However, compared with the conventional p-type a-SiC: H, there is a problem in that the open circuit voltage of the device is not improved and therefore the device characteristics are not improved.

[0007]

In view of these problems, the present invention provides hydrogenated amorphous silicon (a-Si:
H) -based thin film (hydrogenated amorphous silicon carbon (a
-SiC: H), including hydrogenated amorphous silicon germanium (a-SiGe: H)), i layer
In a thin-film solar cell having at least one pair of a pin junction and an n-layer pin junction, the p-layer has a bound hydrogen content of 13 at% or more and a volume of a microcrystalline phase in a bulk structure (film structure with a film thickness of 100 nm or more). Of a silicon thin film (p-type μc-S) containing a p-type microcrystalline phase having a ratio of 65% to 92%.
i: H) is used. In addition, the p-type μ
The film thickness of the p layer using c-Si: H is 20 nm to 50 n
It is characterized in that it is in the range of m.

Further, in the thin-film solar cell, the p-type μc-Si: H manufacturing method uses a plasma chemical vapor deposition apparatus (p-CVD) to contain a gas containing silicon (Si) element, boron (B). ) When growing a silicon semiconductor thin film containing a p-type microcrystalline phase on a substrate with a mixed gas containing a gas containing an element and hydrogen, the substrate temperature is set to 60 °
It is characterized in that the temperature is controlled in the range of ℃ to 150 ℃.

[0009]

The film structure and film properties of the p-type μc-Si: H film for improving the open circuit voltage of the device as compared with the conventional a-SiC: H are shown in the drawings. FIG. 2 shows a band diagram of the device, and a solid line is an extreme example of a p-type μc-Si: H film having a volume ratio of 100%, and a film having physical properties of p-type crystalline silicon is assumed to be a virtually pin device structure. It is a band diagram when applied to. Table 1 shows the physical properties of each film. In this case, the diffusion potential of the element is 1.02e
It becomes V. FIG. 3 shows a conventional p-type a-SiC: H pin
3 is a band diagram when applied to the element of FIG. Table 2 shows these physical property values. Using this value, the diffusion potential of the device is 1.1 eV. From this, when the film having the physical properties of P-type crystalline silicon is used, the open circuit voltage of the device is rather lowered.

[0010]

[Table 1]

[0011]

[Table 2]

On the other hand, the structure of the silicon film containing the microcrystalline phase has a grain size (microcrystal) of crystalline silicon having a grain size of about 10 nm.
Are considered to exist in the hydrogenated amorphous silicon phase. Since this microcrystalline phase is crystalline silicon, it has a high doping efficiency, and if an appropriate amount of, for example, a boron atom is added, it exhibits high conductivity, and it is possible to bring the Fermi level sufficiently close to the valence band (see, for example, FIG. In 2,
The Fermi level was set to 50 meV from the valence band). However, if the volume ratio of this microcrystalline layer is 100%,
And the band gap 1.1 which is a physical property value of crystalline silicon.
Assuming 2 eV and electron affinity of 4.05 eV, the open circuit voltage may decrease as described above.
Therefore, the electrical and optical characteristics of the p-type μc-Si: H film are controlled by reducing the proportion of the microcrystalline phase and adding a large amount of bonded hydrogen to the amorphous silicon phase around or surrounding the microcrystalline phase. The conventional p-type a-
It was confirmed that an element having a larger diffusion potential than that of SiC: H can be obtained. The broken line in FIG. 2 indicates this p-type μc-Si: H.
The electrical characteristics of the film include a band gap of 1.40 eV,
3 is a band diagram of the device when the Fermi level is 50 meV from the valence band and the electron affinity is 3.90 eV. In this case, the diffusion potential of the element is 1.15 eV, which is higher than 1.1 eV when the conventional p-type a-SiC: H is applied to the pin element.

In general, it is not known what kind of band structure the p-type μc-Si: H film having a film structure in which a microcrystalline phase and an amorphous phase coexist, but here, the microcrystalline phase By reducing the proportion and adding a large amount of bonded hydrogen to the amorphous silicon phase around the microcrystal or surrounding it, it is possible to increase the average bandgap of the p-type μc-Si: H film. I was able to assume.

[0014]

【Example】

Example 1 In this example, a film in which the volume ratio of the microcrystalline phase according to claim 1 was changed was used as a p-layer of the device, and in particular, a was used as an i-layer.
This is an example of using -Si: H.

The cell structure of such a solar cell is shown in FIG. The substrate 1 on which the film has been deposited is a glass substrate on which a tin oxide film having a textured structure is formed by about 850 nm by a thermal CVD method. However, the glass substrate on which this tin oxide film was formed was used to increase the amount of light absorption due to the good texture structure of the tin oxide film, and the content of this embodiment is not limited to such a substrate. Not something. On this tin oxide film, a metal film was laminated with titanium / silver as a metal film by a sputtering method or vapor deposition to form a metal electrode 2 on the back surface.

Amorphous silicon-based thin films were sequentially formed on the above-mentioned back metal substrate using the usual capacitive coupling type plasma CVD apparatus under the following film forming conditions. The n-type hydrogenated amorphous silicon film 3 formed first is
SiH ₄ gas 10 sccm, H ₂ gas 10 sccm, PH
₃ gas 0.1sccm mixed gas reaction pressure 0.22T
A film having a thickness of 30 nm was deposited on the back electrode under the film forming conditions of orr, RF power of 20 W and substrate temperature of 200 ° C. Then, the i-type hydrogenated amorphous silicon layer 4 was mixed with SiH ₄ gas at 10 sccm and H ₂ gas at 10 sccm in a reaction gas pressure of 0.22 Torr, RF power of 20 W, and substrate temperature of 200 ° C. under a film forming condition of 450 nm in thickness. Formed on layer 3. On this i-layer 4, a p-type μc-Si: H film having a changed volume ratio of the microcrystalline phase was formed as a p-layer 5 of the device with a thickness of 20 nm
The thickness was formed.

On this p-layer 5, an indium tin oxide (ITO) film was deposited as a transparent conductive film 6 by a sputtering method to a thickness of about 60 nm, and an aluminum film was further formed as a collecting electrode 7 to a thickness of 600 nm by an electron beam evaporation method. . As described above, the substrate / back surface electrode / nip / collecting electrode type a-
A Si: H solar cell was produced.

Table 3 shows the device characteristics with respect to changes in the volume fraction of the microcrystalline phase and the amount of bound hydrogen in the film. Here, the volume ratio of the microcrystalline phase is defined by the volume ratio of the microcrystalline phase in the bulk structure of the film (film structure with a film thickness of 100 nm or more) obtained by the following procedure. The experimental procedure for obtaining this value was performed as follows. Using crystalline silicon as a substrate, a film having a film thickness of 100 nm or more is deposited on this substrate under the same conditions as the film forming conditions in which a p-type μc-Si: H film is applied to an element. Next, when the X-ray diffraction patterns of the films deposited on these substrates were measured by the X-ray diffraction method, the diffraction peak of (111) (around 28.3 °) and the diffraction peak of the (220) plane (47.2). (Around °), the diffraction peak of the (311) plane (56
Three peaks (around °) appear. The sum (S) of the respective peak areas is obtained. Next, this film is heated to 800 ° C.
After heat annealing at ˜1000 ° C. to crystallize all the amorphous phase contained in the film, the X-ray diffraction pattern is measured again, and the total area of the three diffraction peaks (S
Find c). Whether all the amorphous phases in the film have been crystallized is judged by the fact that the value of Sc is saturated even if thermal annealing is further performed. The ratio of the values thus obtained S /
Sc is a bulk structure of p-type μc-Si: H film (film thickness is 10
The volume ratio of fine crystals at 0 nm or more). Further, the amount of hydrogen bonded in the film is obtained from the infrared absorption spectrum.
Table 6 shows the electrical and optical characteristics of other p-type μc-Si: H.

[0019]

[Table 3]

From Table 3, it can be seen that the open circuit voltage of the device is 0.90 vo when the volume ratio of the fine crystals is smaller than 92%.
It can be seen that the photoelectric conversion efficiency of the device is improved as compared with the conventional p-type a-SiC: H film by exceeding lt. The fact that such an improvement in open circuit voltage is accompanied by an increase in the diffusion potential of the device is described in S. S. The method of Hegedus et al. (Jou
rnal of Applied Physics, 6
3, 1988, p5126).
For example, the diffusion potential of the element having a volume ratio of 87% in Table 1 is 1.
20 volt, conventional p-layer a-SiC: H in the table
The element had a diffusion potential of 1.12 volt.

On the other hand, in this embodiment, the amount of hydrogen in the film changes with the volume ratio as shown in Table 3. Generally, such bound hydrogen is incorporated around the microcrystals or in the amorphous phase, and the optical band gap of the film obtained by the Tauc plot increases monotonically with the amount of bound hydrogen as shown in Table 6. You can see that Therefore, as the structure of the film, the amount of hydrogen in the film is set to 13 at% and the volume ratio is made smaller than 92%, that is, the proportion of the microcrystalline phase is reduced to surround the microcrystal or the amorphous silicon phase surrounding the microcrystal. By using a p-type μc-Si: H film with many bonded hydrogen atoms,
It can be seen that the diffusion potential of the device is improved. On the contrary, the fact that the ratio of the microcrystalline phase is reduced, and the p-type μc-Si: H in which a large amount of bonded hydrogen is added to the amorphous silicon phase around or surrounding the microcrystalline is the average band gap Suggests that the band diagram as shown by the broken line in FIG. 2 can be assumed.

On the other hand, as shown in Table 3, the fill factor of the device starts to decrease from a volume ratio of about 65%, and when the volume ratio is 0%, the entire device characteristics deteriorate significantly. This is because a sufficient pi junction cannot be formed due to the decrease in the volume ratio of the microcrystalline phase.

In summary, in order to improve the open circuit voltage of the device, the volume ratio of the microcrystals in the bulk is controlled within the range of 92% to 65%, and the amorphous silicon phase around the microcrystals or surrounding the microcrystals is controlled. The amount of bound hydrogen of 13at%
From the above, it can be seen that mixing an amorphous phase with a wide band gap is effective in improving the device characteristics.

Example 2 In this example, a film in which the volume ratio of the microcrystalline phase according to claim 1 was changed was used as the p layer of the device, and in particular, a-SiC: H and a- were used as the i layer. The present invention relates to an amorphous solar cell using SiGe: H.

The substrate on which the film is deposited, and the n-type aS
The process up to the i: H layer is the same as in the first embodiment. This n layer is subsequently subjected to Si as a reference condition for the i-type a-SiC: H layer.
Reaction pressure of a mixed gas of H ₄ gas 10 sccm, CH ₄ gas 10 sccm, and H ₂ gas 300 sccm was 0.20 Torr.
A film having a thickness of 150 nm was formed on the n-layer under the conditions of r, RF power of 20 W, and substrate temperature of 200 ° C. However, in order to improve the collection efficiency of the device in the i layer, a so-called bandgap profile in which the amount of carbon in the film is changed by continuously changing the mixing ratio of CH ₄ gas and SiH ₄ gas is provided. There is. On this i layer, a p-type μc-Si: H film in which the volume ratio of the microcrystalline phase was changed was formed as the p layer of the device. On the p-layer, indium tin oxide (ITO) was used as a transparent conductive film by sputtering.
A film was deposited to a thickness of about 60 nm, and an aluminum film was further formed to a thickness of 600 nm as a collecting electrode by the electron beam evaporation method. As described above, the substrate / back surface electrode / nip / transparent electrode /
A collector electrode type a-SiC: H solar cell was produced.

Similarly, as a reference condition for the i-type a-SiGe: H layer, 5 sccm of SiH ₄ gas and 5 sc of GeH ₄ gas are used.
cm, mixed gas of H ₂ gas 200 sccm, reaction pressure 0.35 Torr, RF power 15 W, substrate temperature 200
It was formed on the n-layer with a thickness of 250 nm under the film forming condition of ° C.
However, in order to improve the collection efficiency of the element even in this i layer, G
A so-called band gap profile is provided in which the amount of germanium in the film is changed by continuously changing the mixing ratio of the eH ₄ gas and the SiH ₄ gas. On this i-layer, p-type μc-S with the deposition rate of the microcrystalline layer changed
An i: H film was formed as a p layer of the device with a thickness of 25 nm. On this p layer, an indium tin oxide (ITO) film having a thickness of about 60 nm was deposited as a transparent conductive film by a sputtering method, and an aluminum film having a thickness of 600 nm was formed as a collecting electrode by an electron beam evaporation method. As described above, substrate / back surface electrode / nip / transparent electrode / collecting electrode type a-Si
A Ge: H solar cell was produced.

The characteristics of the element manufactured as described above are shown in Tables 4 and 5. As is clear from the table, the open-circuit voltage of the i-layer is 13 at% or more and the volume ratio of the microcrystal is smaller than 92% in any of the devices, the open circuit voltage is lower than that of the conventional p-type μc-Si: H film. It can be seen that there is an improvement of 20 mV to 50 mV. Furthermore, it is noted that such an improvement in open circuit voltage is accompanied by an increase in the diffusion potential of the element.
Similarly, S. S. It was confirmed by the measurement by the method of Hedgedus et al. For example, the diffusion potential of the device having a volume ratio of 87% in Table 4 is 0.92 volt, and the conventional p layer a in the table
The diffusion potential of the -SiC: H device was 0.84 volt.

[0028]

[Table 4]

[0029]

[Table 5]

On the other hand, the fill factor of the device starts to decrease from a volume ratio of about 65%, and at a volume ratio of 0%, the overall device characteristics deteriorate significantly. This is because a sufficient pi junction cannot be formed due to the decrease in the volume ratio of the microcrystalline layer.

Summarizing the above, the i layer is a-SiC:
Even in the case of H and a-SiGe: H, it is effective that the volume ratio of microcrystals in the bulk range from 92% to 65% and the amount of bonded hydrogen is 13 at% or more in order to improve the open circuit voltage of the device. It became clear.

From the above Examples 1 and 2, the effectiveness of the present invention has been described especially for the substrate / back surface electrode / nip / transparent electrode / collector electrode type amorphous silicon solar cell. The p-type μc-Si: H film having the film structure of the present invention also works effectively for improving the open circuit voltage of a translucent substrate / transparent electrode / pin / back electrode type device in the reverse order. Is self-evident. This is because a p-type μc- having a similar film structure on the transparent electrode.
By forming the Si: H film, an element having the same band diagram as the solid line in FIG. 2 can be formed.

Example 3 In this example, the p-type μc-Si: H described in claim 1 was
The present invention relates to a film thickness when applied to a p-layer of an amorphous solar cell having a pin junction.

It is generally known that in a thin film semiconductor, the physical properties and film structure change depending on the film thickness. Also for the solar cell in which the volume ratio of the microcrystalline layer of the present invention is controlled, defining the film structure with a bulk structure of the film (film structure with a film thickness of 100 nm or more) is simple in terms of experimental procedure, and The method is highly accurate in terms of experimental accuracy. However, in practice, the film thickness of p-type μc-Si: H used in a solar cell is about 1/10 of the thickness of the bulk, and the film structure with such a thickness is essentially a problem. Come on.

Therefore, the film thickness is 5 nm to 2 on the glass substrate.
A-SiC: H, a- on a sample in which different p-type μc-Si: H is deposited in the range of 00 nm, or on stainless steel
After depositing several hundreds nm of Si: H and a-SiGe: H, respectively, a sample in which p-type μc-Si: H having different film thickness is deposited is prepared, and RHEED (reflection high-energy electron diffraction) is prepared.
The crystallinity of the thin film was investigated by the method. As a result, p-type μc
In any of the above cases, -Si: H is in an amorphous state without crystallinity when the film thickness is 5 nm, but the film thickness is 10 n.
At m, the Debye-Scherrer ring began to be seen, that is, microcrystallization started, and further, at 25 nm, the strength was equivalent to that of the Debye-Scherrer ring in the bulk, that is, it was close to the bulk structure. .

Therefore, when the p-type μc-Si: H is applied to the device, the film thickness of the conventional p-type μc-Si: H is 10
It has been found that there is a big problem in the range of about 20 nm to 20 nm, and it is necessary to design the film thickness in consideration of the above facts.

The manufacturing method and device structure used in the experiment are
Same as described in Example 1 and Example 2, except that a-SiC: H is used for the i layer, and p-type μc-Si: H is formed under the film forming conditions of a volume ratio of 87%. , P-type μc-Si:
H film thickness only 1 by changing its volume time
It was changed to 5 nm, 20 nm, 25 nm, 30 nm and 50 nm. The results of evaluation of device characteristics are shown in FIG. As is clear from the figure, the open-circuit voltage is set to a value of 20 nm or more for the p-type μc-Si: H film, so that the p-type a
It can be seen that it is higher than the element using -SiC: H. This result almost reflects the above-mentioned result that microcrystallization starts at 10 nm or more and has microcrystallinity close to bulk at 25 nm. From the result of device characteristics in FIG. 4, p-type μc-Si: H It can be seen that it is important to set the film thickness to 20 nm or more. However, the structure of the thin film may vary greatly depending on the manufacturing method and manufacturing conditions, and it is generally necessary to design the element according to the structure of the thin film.

On the other hand, the decrease in the short-circuit current is not observed even when the film thickness is 30 nm because the absorption coefficient for short-wavelength light is p-type μc-S which was used this time as compared with p-type a-SiC: H.
This is because i: H is smaller, but the absorption loss of light cannot be wiped off when the film thickness is 50 nm. Therefore, the short circuit current is reduced. From the above results, p-type μ
To improve the characteristics by applying c-Si: H, the film thickness should be 20
It can be seen that it is important to change from 50 nm to 50 nm.

In this embodiment, the description is made only when the i layer is a-SiC: H, but the i layer is a-Si: H or a-Si.
The same result was obtained with Ge: H.

Example 4 This example relates to a method for producing p-type μc-Si: H having different volume fractions of the microcrystalline phase described in claim 1.

In the p-type μc-Si: H according to the present invention in which the volume fraction of the microcrystalline phase is reduced, the amount of bound hydrogen is increased in the hydrogenated amorphous silicon phase around the microcrystal and surrounding the microcrystalline phase to increase the p-type. It is necessary that μc-Si: H has a wide band gap. The following studies have found an effective range of film forming conditions for simultaneously achieving such a decrease in the volume fraction of the microcrystalline phase and an increase in the amount of bound hydrogen in the film.

The film forming apparatus used in this example is a capacitively coupled RF plasma CVD apparatus. In a reaction chamber equipped with a high vacuum exhaust system, there is an anode electrode which is installed facing the RF electrode, and a substrate on which a film is deposited is attached to this anode electrode. A substrate heating heater is attached to this anode electrode, and the substrate temperature can be controlled by this heater. The flow rate of the reaction gas is controlled by the mass flow controller, and the reaction gas whose flow rate is controlled by the gas introduction piping system is guided to the reaction chamber. The reaction gas pressure in the reaction chamber is detected and controlled by a Baratron pressure gauge.

The substrate is heated to a preset substrate temperature to stabilize the temperature, and at the same time, the high vacuum exhaust system allows 2 ×.
In the reaction chamber evacuated to 10 ⁻⁶ Torr, SiH ₄ gas 1 sccm, H ₂ gas 160 sccm, B ₂ H ₆ gas 0.
A mixed gas of 01 sccm was introduced. The reaction pressure was 0.16 Torr with a Baratron pressure gauge. By inputting 200 W of RF power to this reaction gas system to the RF electrode, the reaction gas is plasma decomposed in the gas phase and p
The type μc-Si: H was deposited.

By changing the substrate temperature from room temperature to 200 ° C. under such film forming conditions, Table 6 is obtained as a change in the electrical and optical properties of the p-type μc-Si: H film structure. It was However, for the optical bandgap in the table, a value obtained from a (αhν) ^1/2 vs hν plot (Tauc plot) originally applied to an amorphous silicon-based thin film is conveniently used.

[0045]

[Table 6]

As can be seen from this table, by lowering the substrate temperature at the time of film formation to less than 150 ° C., the volume ratio of fine crystals can be made 92% or less, and at the same time, the amount of bound hydrogen in the film increases. This can increase the optical bandgap of the film. Also, according to this method, it was found that by setting the substrate temperature to 60 ° C. or higher, a film having a wide optical band gap by Tauc plot can be obtained while maintaining high conductivity.

In the film forming method described above, the control of the structure of the p-type μc-Si: H containing the microcrystalline phase is mainly determined by the substrate temperature, so it is presumed that it does not depend largely on the starting material gas. To be done. Therefore, higher order silanes such as disilane other than SiH ₄ can be used as the source gas, and BF ₃ or the like can be used as the p-type doping gas other than B ₂ H ₆ .

[0048]

INDUSTRIAL APPLICABILITY When applying a silicon film containing a microcrystalline phase to an amorphous solar cell, the volume ratio of the microcrystal in the bulk of the present invention is controlled to 92% to 65%, and around the microcrystal, Alternatively, the amount of bound hydrogen in the amorphous silicon phase surrounding the microcrystals is set to 13 at% or more, and the amorphous phase having a wide band gap is mixed with the p-type μc-Si:
By applying H to the p layer of the device, the diffusion potential of the device can be increased and the open circuit voltage of the device can be improved. Further, according to the present invention, it is possible to manufacture a p-type μc-Si: H having such a structure and characteristics by the same plasma chemical vapor deposition method as other amorphous silicon-based film manufacturing methods. It is possible to manufacture such a thin film solar cell without investing new equipment. Therefore, it becomes possible to manufacture a solar cell with high photoelectric conversion efficiency at low cost, and it becomes possible to provide a solar cell that can compete with existing commercial power.

[Brief description of drawings]

FIG. 1 is a schematic structural diagram of a solar cell that represents an embodiment of the present invention.

FIG. 2 is a band diagram of a solar cell device based on Table 1.

FIG. 3 is a band diagram of a solar cell device based on Table 2.

FIG. 4 is a diagram showing characteristics of an element when the p-type μc-Si: H film thickness is changed.

[Explanation of symbols]

 1 substrate 2 back surface electrode 3 n-type layer 4 i-type layer 5 p-type layer 6 transparent conductive film 7 collector electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Yamamoto 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (3)

[Claims] 1. Hydrogenated amorphous silicon (a-S)
i: H) -based thin film (including hydrogenated amorphous silicon carbon (a-SiC: H) and hydrogenated amorphous silicon germanium (a-SiGe: H)) p-layer,
In a thin-film solar cell having at least one pair of i-layer and n-layer pin junctions, the p-layer has a bonded hydrogen content of 13 at% or more and a microcrystalline phase of a bulk structure (film structure with a film thickness of 100 nm or more). Silicon thin film containing a p-type microcrystalline phase having a volume ratio of 65% to 92% (p-type μc-S
i: H) is used, The thin-film solar cell characterized by the above-mentioned. 2. The thin-film solar cell according to claim 1, wherein the p-type layer using p-type μc-Si: H has a thickness of 20 nm to 50 nm. 3. The thin film solar cell according to claim 1, wherein
The method for producing p-type μc-Si: H is a mixture of a gas containing a silicon (Si) element, a gas containing a boron (B) element, and hydrogen using a plasma enhanced chemical vapor deposition apparatus (p-CVD). A method for manufacturing a thin-film solar cell, wherein the temperature of the substrate is controlled in the range of 60 ° C. to 150 ° C. when a silicon semiconductor thin film containing a p-type microcrystalline phase is grown on the substrate by gas.