JPH07321350A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To obtain any stable electric field distribution within an i-type layer by forming one or more Fermi level adjusting layers in the i-type layer to adjust the position of Fermi levels. CONSTITUTION:A translucent electrode 2, a p-type layer 3 composed of p-type amorphous semiconductor, an i-type layer 4 composed of i-type amorphous semiconductor, a n-type layer 5 composed of n-type amorphous semiconductor and a back electrode 6, are formed on a translucent substrate 1 in this order. Fermi level adjusting layers 4a, 4b containing p-type impurities and those 4c, 4d containing n-type impurities, are formed in the i-type layer 4. Separated from each other, the Fermi level adjusting layers 4a, 4b are placed in the region extending from the center of the i-type layer 4 to the boundary between it and the p-type layer 3. Separated from each other, the Fermi level adjusting layers 4c, 4d are placed in the region extending from the center of the i-type layer 4 to the boundary between it and the n-type layer 5. This unifies and stabilizes the electric field distribution in the i-type layer.

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 In a pin type photovoltaic device, a pi
An electric field is formed in the i-type layer by the n-junction. Electrons and holes generated in the i-type layer due to the absorption of light are separated into an n-type layer and a p-type layer by the electric field, and an electromotive force is generated. Therefore, if the electric field distribution of the i-type layer becomes nonuniform, the photoelectric conversion characteristics deteriorate. Therefore, it is desired that the electric field distribution of the i-type layer is uniform.

[0003]

However, in the conventional pin type photovoltaic device, when a defect occurs in the i type layer, the electric field distribution becomes non-uniform and the photoelectric conversion characteristic is deteriorated. In particular, after light irradiation, photo-induced defects occur, resulting in significant deterioration of characteristics.

FIG. 6 shows an energy band diagram of a conventional pin type amorphous photovoltaic device after light irradiation. The pin junction, the energy band is formed such that the Fermi level E _F of the p-type layer 3 of the Fermi level E _F and n-type layer 5 are matched, the energy band of the i-type layer 4 is inclined, An electric field is generated. However, after light irradiation, the electric field distribution of the i-type layer 4 becomes non-uniform due to the occurrence of photo-induced defects, and the electric field in the central portion of the i-type layer 4 becomes weak as shown in FIG. As a result, the photoelectric conversion characteristics deteriorate.

When an i-type layer is formed of an amorphous semiconductor containing no impurities, the energy band of the i-type layer may be biased toward the n-type. In such a case, conventionally, it has been attempted to correct the energy band to the i-type by uniformly mixing a trace amount of impurities throughout the i-type layer. However, even in this case, the i
In many cases, defects were generated in the mold layer and the photoelectric conversion characteristics were rather deteriorated.

Therefore, it is an object of the present invention to provide a photovoltaic device in which the i-type layer is stable and has the desired electric field distribution.

[0007]

In the photovoltaic device according to the present invention, at least one Fermi level adjusting layer for adjusting the position of the Fermi level is provided in the i-type layer.

The Fermi level adjusting layer is an impurity layer containing impurities, and the amount of impurities in the impurity layer is determined according to the position in the i-type layer.

In the region from the center of the i-type layer to the interface with the p-type layer, one or more impurity layers having a thickness of 10 to 500Å containing 10 ¹⁷ to 10 ²⁰ cm ^-3 of p-type impurities are present. It is preferable. When there are two or more impurity layers in this region, the impurity amount closer to the p-type layer has a larger amount of impurities.
Alternatively, it is preferable that the impurity level in the forbidden band is closer to the valence band as the impurity layer is closer to the p-type layer.

In the region from the center of the i-type layer to the interface with the n-type layer, one or more impurity layers having a thickness of 10 to 500Å containing 10 ¹⁷ to 10 ²⁰ cm ^-3 of n-type impurities are present. It is preferable. When there are two or more impurity layers in this region, the impurity amount closer to the n-type layer has a larger amount of impurities.
Alternatively, it is preferable that the impurity level closer to the n-type layer is closer to the conduction band in the forbidden band.

The p-type layer, the i-type layer and the n-type layer may be made of amorphous hydrogenated silicon containing hydrogen or an alloy semiconductor mainly composed of amorphous silicon. Further, the p-type impurities may be boron or aluminum, and the n-type impurities may be phosphorus, nitrogen or oxygen.

[0012]

In the photovoltaic device according to the present invention, the Fermi level adjusting layer provided in the i-type layer fixes the position of the Fermi level in the i-type layer. In particular, when the Fermi level adjusting layer is made of an impurity layer, the Fermi level of the impurity layer is determined by the position of each impurity layer and the amount of impurities.

When a plurality of impurity layers are provided in the i-type layer, the impurity level is closer to the valence band as it is closer to the p-type layer, and the impurity level is closer to the conduction band as it is closer to the n-type layer. If the position of each impurity layer and the amount of impurities are determined as
The electric field distribution of the mold layer can be made uniform. in this case,
Since the Fermi level of the i-type layer is fixed by the impurity layer, the electric field distribution does not change due to the defect caused by the light irradiation.

Further, the electric field distribution of the i-type layer can be set to an arbitrary shape by adjusting the position of each impurity layer and the amount of impurities.

[0015]

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

In FIG. 1, on a transparent substrate 1, a transparent electrode 2, a p-type layer 3 made of a p-type amorphous semiconductor, an i-type layer 4 made of an i-type amorphous semiconductor, and an n-type non-conductive layer. An n-type layer 5 made of a crystalline semiconductor and a back surface electrode 6 are laminated.

In the i-type layer 4, Fermi level adjusting layers 4a and 4b containing p-type impurities and Fermi level adjusting layers 4c and 4d containing n-type impurities are formed. The Fermi level adjusting layers 4a and 4b are formed from the central portion of the i-type layer 4 to the p-type layer 3
Are separated from each other in a region spanning the side interface, p
The closer to the mold layer 3, the larger the amount of impurities, and the Fermi level thereof is closer to the valence band. Fermi level adjustment layer 4c,
4d are arranged separately from each other in a region extending from the central portion of the i-type layer 4 to the interface on the n-type layer 5 side. The closer the n-type layer 5 is, the larger the amount of impurities, and the Fermi level thereof is closer to the conduction band. Has become.

Fermi level adjusting layers 4a, 4b, 4c, 4
Since the position of the Fermi level of each Fermi level adjusting layer 4a, 4b, 4c, 4d is determined by the amount of impurities mixed in d, the Fermi level adjusting layers 4a, 4b, 4c, 4d.
By adjusting the position of d and the amount of impurities, the i-type layer 4
The energy band shape, that is, the electric field distribution can be controlled. Examples 1 and 2 will be described below. (1) Example 1 The photovoltaic device of Example 1 has the structure shown in FIG.
The electric field in the mold layer 4 is made uniform.

On a transparent substrate 1 made of glass, a thermal CV is applied.
Light-transmissive electrode 2 made of tin oxide (SnO ₂ ) by method D
To form. On the transparent electrode 2, a p-type layer 3 made of amorphous silicon carbide (a-SiC) doped with boron (B) by a plasma CVD method, and made of undoped amorphous silicon (a-Si). An i-type layer 4 and an n-type layer 5 made of amorphous silicon (a-Si) doped with phosphorus (P) are formed. When forming the i-type layer 4, a small amount of boron is doped at a predetermined position in the i-type layer 4 to form the Fermi level adjustment layers 4a and 4b, and a small amount of phosphorus is doped to adjust the Fermi level. The layers 4c and 4d are formed. The boron doping amount of the Fermi level adjusting layer 4a close to the p-type layer 3 is set to i
The Fermi level adjusting layer 4b near the center of the i-type layer 4 is made larger than the boron doping amount of the Fermi level adjusting layer 4b. The amount is larger than the phosphorus doping amount of the adjustment layer 4c. Finally, the back surface electrode 6 made of metal is formed on the n-type layer 5 by vapor deposition or sputtering.

Table 1 shows the film thickness and the amount of impurities of each layer of the photovoltaic device of Example 1.

[0021]

[Table 1]

As shown in Table 1, the film thickness of the p-type layer 3 is 15
The thickness of the i-type layer 4 is 5000 Å, and the thickness of the n-type layer is 200 Å. The p-type layer 3 was doped with 10 ²⁰ cm ⁻³ of boron and 10 ²¹ cm ⁻³ of carbon, and the n-type layer 5 was formed.
Is doped with 10 ²¹ cm ^-3 of phosphorus. Further, a position 700 Å away from the p-type layer 3, a position 1500 Å away, 350
The Fermi level adjusting layers 4a, 4b, 4c having a film thickness of 100 Å are arranged at positions 0 Å and 4200 Å, respectively.
4d is formed. The Fermi level adjusting layer 4a has 10 ¹⁹ c
The m ⁻³ boron is doped, and the Fermi level adjusting layer 4 b is doped with 10 ¹⁸ cm ⁻³ boron. The Fermi level adjusting layer 4c is doped with 10 ¹⁷ cm ^-3 of phosphorus, and the Fermi level adjusting layer 4d is doped with 10 ¹⁸ cm ^-3 of phosphorus.

FIG. 2 is an energy band diagram of the photovoltaic device of the first embodiment. As shown in FIG. 2, the Fermi level adjusting layer 4 having the position and the amount of impurities shown in Table 1 in the i-type layer 4 was formed.
By forming a, 4b, 4c and 4d, the i-type layer 4
The Fermi level E _F inside is fixed by each Fermi level adjusting layer 4a, 4b, 4c, 4d, and the electric field of the i-type layer 4 is uniform.

FIG. 3 is an energy band diagram of the photovoltaic device of Example 1 after light irradiation. As shown in FIG. 3, in the photovoltaic device of Example 1, the Fermi level E _F is fixed by the Fermi level adjusting layers 4a, 4b, 4c, 4d in the i-type layer 4, so that the light irradiation is performed. Even if the number of defects increases due to
The electric field of the mold layer 4 hardly changes. The amount of defects due to light irradiation is usually about 10 ¹⁶ cm ^−3, which is one digit or more smaller than the amount of impurities in the Fermi level adjusting layers 4a, 4b, 4c, and 4d. It is considered that the defects do not affect the electric field formed by the Fermi level adjusting layers 4a, 4b, 4c and 4d.

The characteristics of the photovoltaic device of Example 1 after light irradiation are shown in Table 2 together with Comparative Examples. In the photovoltaic device of the comparative example, the Fermi level adjusting layers 4a, 4b, 4 are provided in the i-type layer 4.
It was produced under the same conditions as the photovoltaic device of Example 1, except that c and 4d were not formed.

[0026]

[Table 2]

As shown in Table 2, in the comparative example, the fill factor is 0.48 and the conversion efficiency is 6.9%, whereas in Example 1, the fill factor is 0.65 and the conversion efficiency is It keeps 10.0%. It is considered that this is because the electric field of the i-type layer 4 is made uniform by the Fermi level adjusting layers 4a, 4b, 4c, 4d.

The number, position, and amount of impurities of the Fermi level adjusting layers are not limited to those in the first embodiment, and the number of Fermi level adjusting layers is set so that the entire electric field of the i-type layer 4 becomes uniform. , And the amount of impurities (position of Fermi level) may be determined.

The amount of p-type impurities and the amount of n-type impurities are
Usually, it is desirable to select within the range of 10 ¹⁷ to 10 ²⁰ cm ^-3 . When the amount of impurities is less than 10 ¹⁷ cm ^-3, it becomes difficult to fix the Fermi level, and the amount of impurities is 1
Almost perfect p-type layer or n above 0 ²⁰ cm ^-3
This is because it becomes a mold layer.

Further, the film thickness of each Fermi level adjusting layer is preferably as thin as possible within a range in which the position of the Fermi level can be fixed sufficiently in order to reduce generation of defects due to impurities. It is desirable to select within the range. This is because it is difficult to form the Fermi level adjusting layer having a film thickness smaller than 10Å, and when the film thickness is larger than 500Å, the number of defects is increased. (2) Example 2 The photovoltaic device of Example 2 has the structure shown in FIG. 1 similarly to the photovoltaic device of Example 1, and has increased sensitivity to incident light of a relatively short wavelength. Is.

Table 3 shows the film thickness and the amount of impurities of each layer of the photovoltaic device of Example 2. Other conditions are the same as those of the photovoltaic device of the first embodiment.

[0032]

[Table 3]

As shown in Table 3, the film thickness and the amount of impurities of the p-type layer 3, the i-type layer 4 and the n-type layer 5 are the same as those in the first embodiment. Further, the Fermi level adjusting layers 4a, 4b, 4c, 4
The film thickness of d and the distance from the p-type layer 3 are the same as in the first embodiment. In the photovoltaic device of Example 2, the Fermi level adjusting layer 4a was doped with 10 ¹⁸ cm ⁻³ of boron, and the Fermi level adjusting layers 4b, 4c and 4d were each 10 ¹⁷ cm ⁻³ ,
It is doped with 10 ¹⁸ cm ^-3 and 10 ¹⁹ cm ^-3 phosphorus.

FIG. 4 is an energy band diagram of the photovoltaic device of the second embodiment. As shown in FIG. 4, the electric field of the i-type layer 4 is strong near the p-type layer 3 on the light incident side.
Since short-wavelength light is mostly absorbed near the interface with the p-type layer 3 on the incident side, electrons and holes generated by the short-wavelength light are preferentially separated by a strong electric field near the p-type layer 3. It Therefore, a photovoltaic device that can be used as an optical sensor having high sensitivity to short-wavelength light can be obtained.

FIG. 5 shows the spectral sensitivity characteristics of the photovoltaic device of Example 2 together with a comparative example. The photovoltaic device of the comparative example is
Fermi level adjusting layers 4a, 4b, 4c, 4 in the i-type layer 4
It was produced under the same conditions as the photovoltaic device of Example 2 except that d was not formed.

As is apparent from FIG. 5, in the photovoltaic device of Example 2, the sensitivity at a short wavelength is greatly improved as compared with the photovoltaic device of Comparative Example. It is considered that this is because the Fermi level adjusting layers 4a, 4b, 4c, and 4d strengthened the electric field near the p-type layer 3.

Also in the photovoltaic device of Example 2, the electric field distribution of the i-type layer 4 has the Fermi level adjusting layers 4a, 4b, 4.
Since it is stabilized by c and 4d, the characteristics do not change due to light irradiation or the like.

As described above, by adjusting the impurity amount or position of the Fermi level adjusting layers 4a, 4b, 4c, 4d formed in the i-type layer 4, an arbitrary electric field distribution can be obtained.
It can be stably formed.

[0039]

As described above, according to the present invention, by forming one or more Fermi level adjusting layers in the i-type layer,
It is possible to stably form an arbitrary electric field distribution in the i-type layer. When the Fermi level adjusting layer is formed of an impurity layer, a photovoltaic device having desired characteristics can be obtained by adjusting the position of the impurity layer and the amount of impurities.

[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.

FIG. 2 is an energy band diagram of the photovoltaic device of Example 1.

FIG. 3 is an energy band diagram of the photovoltaic device of Example 1 after light irradiation.

FIG. 4 is an energy band diagram of the photovoltaic device of Example 2.

FIG. 5 is a diagram showing the spectral sensitivity characteristics of the photovoltaic devices of Example 2 and Comparative Example.

FIG. 6 is an energy band diagram after light irradiation of a conventional photovoltaic device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 transparent substrate 2 translucent electrode 3 p-type layer 4 i-type layer 4a, 4b, 4c, 4d Fermi level adjusting layer 5 n-type layer 6 back electrode In addition, the same code | symbol shows the same or corresponding part in each figure. .

Claims (2)

[Claims] 1. The pin type photovoltaic device, wherein the i-type layer is provided with at least one Fermi level adjusting layer for adjusting the position of the Fermi level. 2. The Fermi level adjusting layer is made of an impurity layer containing impurities, and the amount of impurities in the impurity layer is determined according to the position in the i-type layer. Photovoltaic device.