JPH07321356A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To enhance photoelectric efficiency and reliability by changing an optical gap of an i-type layer. CONSTITUTION:A region 2c having the narrowest optical gap is provided near a boundary face to the p-type layer of light incident side in an i-type layer 2. A region 2e having a wide optical gap is provided on the n-type layer 3 side of the region 2c having the narrowest optical gap through a region 2d in which an optical gap makes gradually wider, and a region 2g having a narrow optical gap in the vicinity of a boundary face to the n-type layer 3 through a region 2f in which an optical gap makes gradually narrower. The optical gap of the region 2g is equal to the optical gap of the region 2c or wider than that and narrower than the optical gap of the region 2e.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pin type photovoltaic device.

[0002]

2. Description of the Related Art A pin-type photovoltaic device using an amorphous semiconductor is formed by laminating a p-type layer, an i-type layer and an n-type layer, and the i-type layer serves as a main power generation layer. Although such an amorphous photovoltaic device is recognized as a low-cost solar cell, it is still insufficient in terms of performance when it is used as a power solar cell. Therefore, in order to effectively use light of various wavelengths, a technique of adding carbon or germanium to amorphous silicon to change the optical gap has been studied, and the performance is being improved.

In particular, amorphous silicon germanium has attracted attention as a material for an i-type layer which is a photoactive layer of a stacked photovoltaic device, and a photovoltaic device using this has an amorphous performance. At present, the performance is significantly inferior to the performance of photovoltaic devices using silicon.

S. Guha et al., Proc. 20th IEEE PVSC,
In Las Vegas (1988) pp.79-84, as a method for improving the performance of a photovoltaic device using amorphous silicon germanium, the Ge composition amount in the i-type layer is changed to make the optical gap inclined. The method of making it is reported. That is, as shown in FIG. 13, the internal electric field of the i-type layer 2 sandwiched between the p-type layer 1 and the n-type layer 3 is strong in the portion near the interface with the p-type layer 1 on the light incident side. Has become. Therefore, when the region 20a having the narrowest optical gap in the i-type layer is provided in the portion near the interface with the p-type layer 1 where the internal electric field is strong, the generated charges can be efficiently extracted to the outside. Thereby, the fill factor, that is, the photoelectric conversion efficiency is improved.

Further, as shown in FIG. 14, by reducing the thickness of the i-type layer 2, only a portion having a strong internal electric field is utilized, and the region 20b having a relatively large thickness and a narrow optical gap.
There is also proposed a method of increasing the absorption of light and increasing the current by providing the above in the i-type layer 2.

13 and 14, the broken line shows the energy band when non-doped amorphous silicon is used for the i-type layer 2.

[0007]

However, as shown in FIG.
According to the above method, the electric field becomes weaker in a region farther from the light incident side than in the region 20a having a narrow optical gap, so that the transport characteristics of the electrons generated in the region 20a are deteriorated, and a sufficient current cannot be obtained. Further, according to the method of FIG. 14, although the current increases, the thickness of the i-type layer 2 is thin, so that the electric field does not spread and a sufficient voltage cannot be extracted.

Therefore, in the photovoltaic device using the method of FIGS. 13 and 14, high photoelectric conversion efficiency and high reliability sufficient for use as a power solar cell device cannot be obtained.

Therefore, it is an object of the present invention to provide a photovoltaic device having improved photoelectric conversion efficiency and reliability by changing the optical gap of the i-type layer.

[0010]

A photovoltaic device according to the present invention includes a first-conductivity-type layer, an i-type layer, and a second-conductivity-type layer, and is a photovoltaic device in which light is incident from the first-conductivity-type layer side. In the power device, a main light absorption region in the i-type layer is provided near an interface with the first conductivity type layer, and charge transport is performed between the main light absorption region in the i-type layer and the second conductivity type layer. An electric field forming region in which an electric field that promotes the electric field is formed is provided.

I near the interface with the first conductivity type layer in the i type layer
A main light absorption region having the narrowest first optical gap in the mold layer is provided, and a second optical gap wider than the first optical gap is provided between the main light absorption region and the second conductivity type layer. An optical gap tilt region having a gradually decreasing optical gap may be provided.

Preferably, a first region having the narrowest first optical gap in the i-type layer is provided near the interface with the first conductivity-type layer in the i-type layer, and the first region and the second conductivity type are provided. A second region having a second optical gap wider than the first optical gap is provided between the second conductive type layer and the second conductive type layer, and the second region is equal to or wider than the first optical gap near the interface with the second conductive type layer and has a first optical gap. A third region having a third optical gap narrower than the second optical gap is provided, the optical gap is inclined from the second region to the third region, and the impurities of the second conductivity type are gradually increased. And then add it.

[0013]

The electric charge generated by absorption of light in the i-type layer is transported to the first-conductivity-type layer and the second-conductivity-type layer by the electric field formed by the first-conductivity-type layer and the second-conductivity-type layer. In the region where the electric field is weak, the generated charges are recombined so much that the charges cannot be taken out and utilized.

In the photovoltaic device according to the present invention, since the main light absorption region is provided close to the interface on the light incident side where the electric field is strong, the recombination of charges generated in the main light absorption region is prevented. Less. As a result, the charge can be efficiently extracted.

Further, since an electric field forming region in which an electric field for promoting charge transport is formed is provided in a portion farther from the light incident side than the main light absorbing region, the electric field is far from the light incident side. The weakening is prevented, and the charges generated in the main light absorption region are easily transported to the second conductivity type layer. As a result, the charge extraction efficiency is enhanced and the stability is enhanced. By providing this electric field forming region, a sufficient film thickness of the i-type layer is secured, so that the electric field spreads over the entire i-type layer, the electric field in the main light absorption region is strengthened, and a sufficient voltage is obtained. Can be taken out.

The narrower the optical gap, the larger the refractive index, and the wider the optical gap, the smaller the refractive index.
When a structure that sandwiches a main light absorption region having a large refractive index with a region having a small refractive index is formed in the i-type layer, light is reflected between the regions having different refractive indices.
Light can be confined within the i-type layer. Thereby,
The output current increases and the photoelectric conversion efficiency also improves.

When impurities of the second conductivity type are added in a graded manner in the graded region of the optical gap, the photoelectric conversion efficiency is further improved.

[0018]

1 is a view showing the basic structure of a photovoltaic device according to an embodiment of the present invention.

In FIG. 1, a transparent electrode 5 made of a transparent conductive film such as tin oxide (SnO ₂ ) is formed on a transparent substrate 4 made of glass or the like. On the transparent electrode 5, p
P made of amorphous silicon carbide (a-SiC)
Type layer 1, i-type amorphous silicon germanium (a-SiG
e) i-type layer 2 and n-type amorphous silicon (a
An n-type layer 3 made of —Si) is sequentially stacked. Further, the back surface electrode 6 is formed on the n-type layer 3. Light enters from the transparent substrate 4 side.

FIG. 2 is a diagram showing a basic energy band structure of a pin junction of the photovoltaic device of this embodiment. In the figure, the broken line indicates the energy band when the i-type layer 2 does not contain germanium.

As shown in FIG. 2, an internal electric field is formed in i-type layer 2 by p-type layer 1 and n-type layer 3. The electric field in the portion of the i-type layer 2 near the interface with the p-type layer 1 on the light incident side is strong.

In this embodiment, in the i-type layer 2, a region 2c having the narrowest optical gap is provided in a portion near the interface with the p-type layer 1 on the light incident side. This region 2c becomes the main light absorption region. A region 2e is provided behind the region 2c (in a direction away from the light incident side) via a region 2d where the optical gap gradually widens. A region 2g is provided behind the region 2e via a region 2f where the optical gap is gradually narrowed. The optical gap of the region 2g is equal to or wider than the optical gap of the region 2c, and
It is narrower than the optical gap of e. Area 2c and area 2f
Is thick to some extent, for example, is formed to have a thickness of about 1000Å.

In the region 2c, electrons and holes are generated by absorption of light, the holes flow to the p-type layer 1 and the electrons flow to the n-type layer 3. Since the region 2c is provided in the portion where the electric field is strong, recombination of electrons and holes generated in the region 2c is reduced. As a result, the charge can be efficiently extracted.

Further, the region 2 is provided between the region 2c and the n-type layer 3.
Since e, 2f, and 2g are provided, a sufficient thickness of the i-type layer 2 is secured, and the electric field spreads over the entire i-type layer 2. Thereby, a sufficient voltage can be taken out.

Further, since the optical gap is gradually narrowed from the region 2e to the region 2g, it is possible to prevent the electric field from weakening in the portion far from the light incident side. This improves the transport characteristics of the electrons generated in the region 2c to the n-type layer 3 and increases the charge extraction efficiency.

Further, since the region 2c having a narrow optical gap and a high refractive index is sandwiched by the regions having a wide optical gap and a low refractive index, light is reflected between the regions having different refractive indexes, which causes , The light is confined in the region 2c.

As a result, the charge extraction efficiency is increased and a sufficient voltage can be extracted, and the output characteristics and stability of the photovoltaic device are improved.

Example 1, Example 2, and Example 3 shown below
In Example 4, the p-type layer 1, the i-type layer 2 and the n-type layer 3 were formed under the conditions shown in Table 1 by using the plasma CVD method, and then the back electrode 6 with high reflection was formed on the n-type layer 3. A metal was formed to a thickness of 1 μm by a known resistance heating vapor deposition method.

[0029]

[Table 1]

As shown in Table 1, the i-type layer 2 has a flow rate of germane (GeH ₄ ) in the source gas of 0 to 4 so that the optical gap changes in the range of 1.75 to 1.40 eV.
It was formed by appropriately changing it within a sccm range. On the other hand, the optical gap of the p-type layer 1 is 2.05 eV, and the optical gap of the n-type layer 3 is 1.70.

FIGS. 3, 4, 5 and 6 show i in Example 1, Example 2, Example 3 and Example 4, respectively.
The optical gap of the mold layer 2 is shown. 7 and 8 show the optical gaps of the i-type layers in Conventional Example 1 and Conventional Example 2, respectively.

In Example 1 of FIG. 3, when forming the region 2a of the i-type layer 2, the flow rate of GeH ₄ was set to 0 sccm,
It is set to 4 sccm when forming the region 2c, 0 sccm when forming the region 2e, and 1.5 s when forming the region 2g.
It was set to ccm. Table 2 shows the relationship among the GeH ₄ flow rate, the Ge composition amount, and the optical gap in the regions 2a, 2c, 2e, and 2g.

[0033]

[Table 2]

As shown in Table 2, area 2a and area 2
For Ge, the Ge composition was 0% and the optical gap was 1.
It is 75 eV. In the region 2c, the Ge composition amount is 4
0%, and the optical gap is 1.40 eV. In the region 2g, the Ge composition amount is 10% and the optical gap is 1.66 eV.

In the region 2b, the GeH ₄ flow rate was continuously changed so that the optical gap was inclined from 1.75 eV in the region 2a to 1.40 eV in the region 2c. Further, in the region 2d, Ge is so arranged that the optical gap is inclined from the optical gap 1.40 eV of the region 2c to the optical gap 1.75 eV of the region 2e.
The H ₄ flow rate is continuously changed, and in the region 2f, the optical gap changes from the optical gap 1.75eV of the region 2e to the region 2
so that the optical gap of g is 1.66 eV,
The GeH ₄ flow rate was continuously changed.

In the second embodiment of FIG. 4, the regions 2a and p are
A region 2h is provided between the mold layer 1 and the region 2i and a region 2i is provided between the region 2g and the n-type layer 3. The region 2h is p
The optical gap of the mold layer 1 is 2.05 eV and the optical gap of the region 2a is 1.75 eV. The region 2i has an optical gap of 1.66 eV from the region 2g to the optical gap of 1.70 eV of the n-type layer 3. Has an optical gap that is graded up to.

In particular, the region 2h includes a portion in which carbon is introduced into the film by mixing methane (CH ₄ ) when forming the vicinity of the interface with the p-type layer 1 to widen the optical gap. . Areas 2a, 2b, 2c, 2d, 2 of the second embodiment
The formation conditions of e, 2f, and 2g and the optical gap are the same as those of the corresponding regions of the first embodiment.

In the third embodiment of FIG. 5, the regions 2a and 2b of the first embodiment are not provided. The formation conditions and the optical gaps of the regions 2c, 2d, 2e, 2f, 2g are the same as the corresponding regions of the first embodiment.

In Example 4 of FIG. 6, the optical gap of the region 2b is graded from the optical gap of the p-type layer 1 of 2.05 eV to the optical gap of the interface of the region 2c of 1.40 eV. The optical gap of the region 2c is changed so as to be minimum in the central portion. The optical gap of the region 2d is from the optical gap 1.40 eV at the interface of the region 2c to the region 2
The optical gap of e is tilted to 1.75 eV,
The optical gaps of the regions 2e, 2f and 2g are inclined so as to continuously decrease from 1.75 eV to 1.66 eV.

In particular, the region 2b includes a portion in which carbon is introduced into the film by mixing methane (CH ₄ ) when the vicinity of the interface with the p-type layer 1 is formed to widen the optical gap. There is.

In the conventional example 1 of FIG. 7, the i-type layer 2 is composed of the regions 2b, 2c, 2d and 2e. The optical gap is graded from 1.75 eV to 1.40 eV from the interface of the region 2b on the p-type layer 1 side to the center of the region 2c,
The optical gap is graded from 1.40 eV to 1.66 eV from the center of the region 2c to the interface of the region 2e on the n-type layer 3 side.

In Conventional Example 2 of FIG. 8, i-type layer 2 is composed of regions 2a, 2b, 2c, 2d and 2e. Area 2a,
The formation conditions and optical gaps of 2b, 2c, 2d, and 2e are the same as the corresponding regions of the first embodiment.

Table 3 shows the film thickness of each region of the i-type layer in Examples 1 to 4 and Conventional Examples 1 and 2.

[0044]

[Table 3]

As shown in Table 3, in all of Examples 1 to 4 and Conventional Examples 1 and 2, the film thickness of the region 2c was 100.
It is 0Å, and the film thickness of the region 2e is 200Å. Also,
In Examples 1 to 4, the film thickness of the region 2f is 1000Å.

Table 4 shows the characteristics of the photovoltaic devices of Examples 1 to 4 in comparison with the characteristics of the photovoltaic devices of Conventional Examples 1 and 2.
The characteristics of Table 4 are as follows: the device area is 1 cm ² , and the irradiation light is AM 1.5 (sunlight spectrum) of 100 mW / cm ^2.
Was measured using.

[0047]

[Table 4]

As shown in Table 4, in all of the photovoltaic devices of Examples 1 to 4, higher fill factor and conversion efficiency were obtained than those of the photovoltaic devices of Conventional Examples 1 and 2.

Next, with respect to Example 2, which has the highest characteristics among the above Examples, a change in characteristics when the amount of germanium added to the i-type layer is changed will be described.

FIG. 9 shows the results obtained by changing the GeH ₄ flow rate during formation as shown in FIG.
2 shows a change in conversion efficiency when only the Ge composition amount (optical gap) in the region 2g is changed. The inclination of the optical gap of the region 2f was also changed according to the change of the optical gap of the region 2g. However, the thickness of each region is as shown in Table 3.

As is apparent from FIG. 9, Ge in the region 2g is
When the composition amount is less than 5%, the optical gap in the region 2g does not become narrow, and the electric field in the portion from the region 2f to the region 2g does not become strong, so that the fill factor is not improved and the conversion efficiency is improved. No improvement is seen. On the other hand, area 2
When the Ge composition amount of g is larger than 40% which is the Ge composition amount of the region 2c, the film quality in the region 2g portion deteriorates, the fill factor decreases, and the conversion efficiency also decreases.

Therefore, the Ge composition amount of the region 2g is 5%.
It is preferably within the range of from 40% to 40%.

Even if the Ge composition amount in the region 2c changes, the Ge composition amount in the region 2g changes to the Ge composition amount in the region 2c.
It has been confirmed that the output characteristic deteriorates when the optical gap becomes narrower as the amount becomes larger than the composition amount.

FIG. 10 shows a change in conversion efficiency when the GeH ₄ flow rate during formation is changed and only the Ge composition amount (optical gap) in the region 2c of FIG. 4 is changed. The vertical axis of FIG. 10 represents the ratio of the conversion efficiency of the second embodiment to the conversion efficiency of the second conventional example.

In this case, the Ge composition amount (optical gap) in the region 2e is constant. On the other hand, it is premised that the optical gap of the region 2g is wider than the optical gap of the region 2c. When the optical gap of the region 2c is widened, the optical gap of the region 2g is widened accordingly. The thickness of each region is as shown in Table 3.

As is apparent from FIG. 10, G in the region 2c
When the composition amount of e is less than 20%, the optical gap in the region 2c becomes wider, and the optical gap in the region 2g also widens accordingly. Therefore, the electric field in the region 2f cannot be increased, and the conventional example There is no improvement in conversion efficiency compared to 2. Further, when the Ge composition amount of the region 2c is more than 40%, the conversion efficiency is lower than that of the second embodiment when the Ge composition amount is 40%, but the region 2f is provided by providing the region 2f. The output characteristics are improved as compared with the conventional example 2 which does not have such a configuration. However, when the Ge composition amount is 60% or more, the conversion efficiency becomes low in both Example 2 and Conventional Example 2, and the error of the improvement rate becomes large, so it is not shown in the figure.

Therefore, the Ge composition amount of the region 2c is 20.
It is preferably in the range of -40%.

FIG. 11 shows a change in conversion efficiency when phosphine (PH ₃ ) is added while being graded during formation from the interface between the regions 2e and 2f to the region 2g. The P addition amount on the horizontal axis in FIG. 11 is the addition amount in the film in the region 2g.

When the interface between the regions 2e and 2f was formed, the addition amount of PH ₃ was set to 0, the addition amount when forming the region 2g was changed, and the addition amount when forming the region 2f was graded.

As is apparent from FIG. 11, P in the region 2g is
When the added amount is 0.1 ppm or less, the conversion efficiency is not improved. In addition, the amount of P added in the region 2g is 10 ppm
In the above case, the film quality of the region 2g is deteriorated, the fill factor is lowered, and the conversion efficiency is also lowered.

Thus, P is added as a graded impurity as an impurity that brings the i-type layer closer to n-type from the interface between the regions 2e and 2f to the region 2g, and the amount of P added in the region 2g is 0.1 ppm or more. Is preferably 10 ppm or less.

Next, the characteristics when the pin junctions of Examples 1 to 4 and Conventional Examples 1 and 2 are applied to a three-layer laminated photovoltaic device will be described.

FIG. 12 is a diagram showing the structure of a three-layer laminated photovoltaic device. In FIG. 12, the transparent electrode 5, the first power generation layer 10, the second power generation layer 20, the third power generation layer 30, and the back surface electrode 6 are sequentially stacked on the transparent substrate 4. The first power generation layer 10 includes a p-type layer 11, an i-type layer 12 and an n-type layer 13, the second power generation layer 20 includes a p-type layer 21, an i-type layer 22 and an n-type layer 23, and a third power generation layer. 30 is a p-type layer 31,
It is composed of an i-type layer 32 and an n-type layer 33. Light enters from the transparent substrate 4 side.

Here, in the third power generation layer 30 located farthest from the light incident side, the first to fourth examples and the conventional example 1,
Apply p-type layer, i-type layer and n-type layer in 2. The conditions for forming the third power generation layer 30 are as shown in Tables 1 to 3. On the other hand, the i-type layer 12 of the first power generation layer 10 and the i-type layer 22 of the second power generation layer 20 are formed of amorphous silicon (a-Si) having a film thickness of 1000Å and 4000Å, respectively. That is, under the conditions for forming the i-type layer in Table 1, GeH
₄ Set the flow rate to 0.

Table 5 shows the output characteristics of the three-layer laminated photovoltaic device manufactured under the above-mentioned forming conditions. The output characteristics in Table 5 are as follows: the device area is 1 cm ² and the irradiation light is 100 m.
It was measured using AM 1.5 (solar spectrum) of W / cm ² .

[0066]

[Table 5]

As is clear from Table 5, in all of the three-layer stacked photovoltaic devices to which Examples 1 to 4 are applied, it is higher than the three-layer stacked photovoltaic devices to which Conventional Examples 1 and 2 are applied. Conversion efficiency was obtained.

Table 6 shows the photodegradation characteristics of these three-layer laminated photovoltaic devices. The element area and 1 cm ^2, was irradiated with AM1.5 of 100 mW / cm ² to measure the conversion efficiency before degradation at a temperature 25 ° C. as the irradiation light, AM1.5 illumination 310 hours of 125 mW / cm ² as the irradiation light Then, the conversion efficiency after deterioration was measured at a temperature of 48 ° C.

[0069]

[Table 6]

As is clear from Table 6, in all of the three-layer stacked photovoltaic devices to which Examples 1 to 4 are applied, deterioration is caused as compared with the three-layer stacked photovoltaic devices to which Conventional Examples 1 and 2 are applied. The subsequent conversion efficiency was high and the deterioration rate was low.

As described above, by using the i-type layer in Examples 1 to 4, the output characteristics and stability are improved in both the single-junction photovoltaic device and the multi-junction laminated photovoltaic device. improves.

Further, these effects can be further enhanced by performing a slight amount of doping on the portion of the i-type layer where the electric field is likely to be weakened.

In the above embodiment, the optical gap of the i-type layer is changed by using germanium as the element for narrowing the optical gap, but instead of narrowing the optical gap, it is used as an element for widening the optical gap. By using carbon, the optical gap of the i-type layer may be changed as in the above embodiment. Also in this case, it has been confirmed that the output characteristics of the photovoltaic device are improved.

Although the optical gap of the i-type layer is continuously changed in the above embodiment, the same effect can be obtained even if the optical gap of the i-type layer is sequentially changed stepwise (stepwise). Is obtained.

[0075]

As described above, according to the present invention, the main light absorption region is provided in a portion of the i-type layer where the electric field on the light incident side is strong, and the electric field is weakened in a portion far from the light incident side where the electric field becomes weak. By providing an electric field forming region that promotes transport,
Since the charge extraction efficiency increases and the electric field spreads throughout the i-type layer, the current increases and a sufficient voltage can be extracted, and the stability also improves. Therefore, the output characteristics and reliability of the photovoltaic device are improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic structure of a photovoltaic device according to an embodiment of the present invention.

2 is a diagram showing a basic energy band structure of a pin junction of the photovoltaic device of FIG.

FIG. 3 is a diagram showing an optical gap of each region of an i-type layer in Example 1.

FIG. 4 is a diagram showing an optical gap of each region of an i-type layer in Example 2.

FIG. 5 is a diagram showing an optical gap of each region of an i-type layer in Example 3.

FIG. 6 is a diagram showing an optical gap of each region of an i-type layer in Example 4.

FIG. 7 is a diagram showing an optical gap in each region of an i-type layer in Conventional Example 1.

FIG. 8 is a diagram showing an optical gap in each region of an i-type layer in Conventional Example 2.

FIG. 9 is a diagram showing a change in conversion efficiency when the Ge composition amount in the region near the interface with the n-type layer is changed in Example 2.

FIG. 10 is a diagram showing a change in conversion efficiency when a Ge composition amount in a region near an interface with a p-type layer is changed in Example 2.

FIG. 11 is a diagram showing a change in conversion efficiency when changing the amount of P added in a region near the interface with the n-type layer in Example 2.

FIG. 12 is a diagram showing a structure of a three-layer stacked photovoltaic device to which Examples 1 to 4 are applied.

FIG. 13 is a diagram showing an energy band structure of a pin junction in a conventional photovoltaic device.

FIG. 14 is a diagram showing an energy band structure of a pin junction in another conventional photovoltaic device.

[Explanation of symbols]

1 p-type layer 2 i-type layer 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2
i region 3 n-type layer 30 third power generation layer 31 p-type layer 32 i-type layer 33 n-type layer In the drawings, the same reference numerals indicate the same or corresponding portions.

Claims (3)

[Claims] 1. A photovoltaic device comprising a first-conductivity-type layer, an i-type layer, and a second-conductivity-type layer, wherein light is incident from the side of the first-conductivity-type layer, wherein A main light absorption region is provided near the interface with the first conductivity type layer, and an electric field that promotes charge transport is formed between the main light absorption region in the i-type layer and the second conductivity type layer. A photovoltaic device comprising an electric field forming region. 2. A photovoltaic device comprising a first conductivity type layer, an i-type layer and a second conductivity type layer, wherein light is incident from the side of the first conductivity type layer, wherein A main light absorption region having the narrowest first optical gap in the i-type layer is provided near an interface with the first conductivity type layer, and the main light absorption region and the second conductivity type layer are provided between the main light absorption region and the second conductivity type layer. A photovoltaic device comprising: an optical gap tilt region having an optical gap that gradually decreases from a second optical gap wider than the first optical gap. 3. A photovoltaic device comprising a first conductivity type layer, an i-type layer and a second conductivity type layer, wherein light is incident from the side of the first conductivity type layer, wherein A first region having the narrowest first optical gap in the i-type layer is provided near the interface with the one-conductivity type layer, and the first region is provided between the first region and the second conductivity type layer. A second region having a second optical gap wider than the second optical gap, and near the interface with the second conductivity type layer equal to or wider than the first optical gap and larger than the second optical gap. A third region having a narrow third optical gap, the optical gap is inclined from the second region to the third region, and the second conductivity type impurities are gradually increased. A photovoltaic device characterized in that it is added in the form of a compound.