JP2012114296A - Thin-film solar cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin-film solar cell having a tandem structure where two layers or more of photoelectric conversion unit are laminated and exhibiting excellent photoelectric conversion efficiency.SOLUTION: The thin-film solar cell comprises: a prestage photoelectric conversion unit 3 including a first p-conductivity type layer 31, a first photoelectric conversion layer 32 and a first n-conductivity type layer 33 from the light incident side; and a post-prestage photoelectric conversion unit including a second p-conductivity type layer 41, a second photoelectric conversion layer 42 and a second n-conductivity type layer 43 from the light incident side in contact with the first n-conductivity type layer 33. The first n-conductivity type layer 33 has a high refractive index layer 332 having a refractive index higher than those of the first photoelectric conversion layer 32 and the second p-conductivity type layer 41, and antireflection layers 331 and 333 provided either on the light incident side and/or the light emission side of the high refractive index layer 332 in contact therewith.

Description

  The present invention relates to a thin film solar cell and a manufacturing method thereof, and more particularly to a thin film solar cell having an antireflection structure for improving photoelectric conversion efficiency and a manufacturing method thereof.

  In the thin film solar cell, by adopting a tandem structure in which two or more photoelectric conversion units are stacked, sunlight in a wide wavelength region is absorbed by the photoelectric conversion layer, and the photoelectric conversion efficiency is improved. In order to improve the photoelectric conversion efficiency of a tandem thin film solar cell, it is necessary to improve the light utilization efficiency and the output current.

  Moreover, in the solar cell, in order to absorb sunlight more efficiently in the photoelectric conversion layer, loss due to reflection is reduced. In order to reduce the loss due to reflection, for example, a structure has been proposed in which at least two non-single-crystal semiconductors having different energy bandwidths have continuous energy bandwidths and continuous refractive indexes at or near the boundaries. In such a structure, since the boundary between both non-single-crystal semiconductors does not substantially exist, both non-single-crystal semiconductors are made non-reflective films (see, for example, Patent Document 1).

JP 58-40871 (Claims, page 6, lines 10 to 20)

  However, when the above conventional technology is applied to a tandem thin film solar cell, the refractive index of the semiconductor layer is continuously formed in all of the plurality of photoelectric conversion units. Realization is difficult from the viewpoint.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the thin film solar cell excellent in the photoelectric conversion efficiency in the thin film solar cell of the tandem structure which laminated | stacked two or more photoelectric conversion units.

  In order to solve the above-described problems and achieve the object, a thin film solar cell according to the present invention includes a translucent insulating substrate, a transparent conductive film, and a semiconductor film from the light incident side, and the first p-type from the light incident side. A photoelectric conversion unit including a conductive layer, a first photoelectric conversion layer, and a first n-type conductivity type layer in this order to perform photoelectric conversion, and a semiconductor film in contact with the first n-type conductivity type layer. Comprising a second p-type conductivity type layer, a second photoelectric conversion layer, and a second n-type conductivity type layer in this order from the side, and a subsequent photoelectric conversion unit for performing photoelectric conversion, wherein the first n-type conductivity type layer comprises: A high refractive index layer having a higher refractive index than the first photoelectric conversion layer adjacent to the light incident side of the first n-type conductivity type layer and the second p-type conductivity type layer adjacent to the light emission side; The high refractive index on at least one of the light incident side and the light emitting side of the high refractive index layer And the antireflection layer provided on the light incident side of the high refractive index layer, the antireflection layer adjacent to the first n-type conductivity type layer. The antireflective layer having a refractive index between the refractive index of the layer and the refractive index of the high refractive index layer and provided on the light exit side of the high refractive index layer is the first n-type conductivity type layer. It has a refractive index between the refractive index of the adjacent second p-type conductivity type layer and the refractive index of the high refractive index layer.

  According to the present invention, in a tandem-structure thin film solar cell in which a plurality of photoelectric conversion units are stacked, an n-type conductivity type layer having high conductivity can be realized and light reflection loss can be reduced. It is possible to obtain an excellent thin film solar cell.

FIG. 1 is a cross-sectional view showing a configuration of a thin-film solar cell according to Embodiment 1 of the present invention. FIG. 2 is a diagram for explaining a refractive index profile in the film thickness direction of each layer from the first photoelectric conversion layer to the second p-type conductivity type layer of the thin-film solar cell according to the first embodiment of the present invention. FIG. 3 is a diagram for explaining a conductivity profile in the film thickness direction of each layer from the first photoelectric conversion layer to the second p-type conductivity type layer of the thin-film solar cell according to the first embodiment of the present invention. FIG. 4 is a diagram for explaining a profile of carbon concentration in each layer from the first n-type conductivity type layer to the third n-type conductivity type layer of the thin-film solar cell according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining a profile of oxygen concentration in the film in each layer from the first n-type conductivity type layer to the third n-type conductivity type layer of the thin-film solar cell according to the first embodiment of the present invention. FIGS. 6-1 is sectional drawing for demonstrating an example of the manufacturing process of the thin film solar cell concerning Embodiment 1 of this invention. FIGS. 6-2 is sectional drawing for demonstrating an example of the manufacturing process of the thin film solar cell concerning Embodiment 1 of this invention. 6-3 is sectional drawing for demonstrating an example of the manufacturing process of the thin film solar cell concerning Embodiment 1 of this invention. 6-4 is sectional drawing for demonstrating an example of the manufacturing process of the thin film solar cell concerning Embodiment 1 of this invention. 6-5 is sectional drawing for demonstrating an example of the manufacturing process of the thin film solar cell concerning Embodiment 1 of this invention. FIG. 7: is sectional drawing which shows the structure of the thin film solar cell concerning Embodiment 2 of this invention. FIG. 8: is sectional drawing which shows the structure of the thin film solar cell concerning Embodiment 3 of this invention.

  Embodiments of a thin film solar cell and a method for manufacturing the same according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing a configuration of a thin-film solar cell 10 according to an embodiment of the present invention. The thin-film solar cell 10 according to the first embodiment includes a transparent conductive film 2, a first photoelectric conversion unit 3, a second photoelectric conversion unit 4, which are sequentially stacked on a translucent insulating substrate 1 and serve as a first electrode layer. A third photoelectric conversion unit 5 and a back electrode layer 6 to be a second electrode layer are included. In the thin film solar cell 10, the light L incident from the translucent insulating substrate 1 side is photoelectrically converted in the thin film solar cell 10.

  The first photoelectric conversion unit 3 includes a first p-type conductivity layer 31, a first photoelectric conversion layer 32, and a first n-type conductivity type layer 33 that are stacked in order from the transparent conductive film 2 side. Similarly, the second photoelectric conversion unit 4 includes a second p-type conductivity type layer 41, a second photoelectric conversion layer 42, and a second n-type conductivity type layer 43, which are sequentially stacked from the transparent conductive film 2 side. Similarly, the third photoelectric conversion unit 5 includes a third p-type conductivity type layer 51, a third photoelectric conversion layer 52, and a third n-type conductivity type layer 53, which are sequentially stacked from the transparent conductive film 2 side. The first n-type conductivity type layer 33 includes, in order from the transparent conductive film 2 side, a first first n-type conductivity type layer 331, a second first n-type conductivity type layer 332, and a third first n-type conductivity type layer. 333 is provided.

  As the translucent insulating substrate 1, for example, a translucent glass substrate or film is used. As the glass substrate, an alkali-free glass substrate may be used, or an inexpensive blue plate glass substrate may be used. In order to transmit more sunlight and make the first photoelectric conversion layer 32, the second photoelectric conversion layer 42, and the third photoelectric conversion layer 52 absorb the sunlight, the translucent insulating substrate 1 is as transparent as possible and has high light transmittance. It is preferable. For the same purpose, even if the surface of the translucent insulating substrate 1 on the side on which sunlight is incident is coated with anti-reflection coating so as to reduce the light reflection loss, the photoelectric conversion efficiency can be increased. Good.

As the transparent conductive film 2, a transparent conductive oxide is used. Examples of the material constituting the transparent conductive oxide include SnO ₂ , In ₂ O ₃ , ZnO, CdO, CdIn ₂ O ₄ , CdSnO ₃ , MgIn ₂ O ₄ , CdGa ₂ O ₄ , GaInO ₃ , InGaZnO ₄ , and Cd. ₂ Sb ₂ O ₇ , Cd ₂ GeO ₄ , CuAlO ₂ , CuGaO ₂ , SrCu ₂ O ₂ , TiO ₂ , Al ₂ O ₃ can be used, and a transparent conductive film formed by stacking these can be used. You can also. Since the transparent conductive film 2 is also located on the light incident side, it is preferable that the transparent conductive film 2 has as high a light transmittance as possible as the transparent insulating substrate 1. As a dopant in the transparent conductive film 2, at least one element selected from Al, Ga, In, B, Y, Si, Zr, Ti, and F is used. Moreover, it is preferable that the surface of the transparent conductive film 2 has unevenness as a texture structure. The shape and size of the surface irregularities can be controlled by the film forming conditions and chemical treatment of the material. An antireflection layer may be included at the interface between the translucent insulating substrate 1 and the transparent conductive film 2.

  In addition, although the thin film solar cell 10 concerning this Embodiment shown in FIG. 1 contains the three photoelectric conversion units, the number of photoelectric conversion units is not limited to three. That is, the thin film solar cell 10 may be configured by stacking a plurality of photoelectric conversion units, and may be configured by stacking two photoelectric conversion units, or by stacking four or more photoelectric conversion units. It may be configured.

  Moreover, except between the 1st photoelectric conversion unit 3 and the 2nd photoelectric conversion unit 4, the layer inserted in order to reflect and scatter a part of light, ie, an intermediate | middle layer, is between the photoelectric conversion units laminated | stacked. It may be selected and inserted at all or any position of the boundary.

As described above, the first photoelectric conversion unit 3 includes the first p-type conductivity layer 31, the first photoelectric conversion layer 32, and the first n-type conductivity type layer 33, which are sequentially stacked from the transparent conductive film 2 side. The material of the first p-type conductivity layer 31 contains a Group III element such as boron (B) as an impurity. For example, amorphous or microcrystalline Si _(1-X) C _X (X is greater than 0 and less than or equal to 0.5 ), Amorphous or microcrystalline Si _(1-X) O _X (where X is greater than 0 and 0.66 or less). Si _(1-X) C _X is a film in which carbon atoms are present in a silicon film and a state in which the carbon atoms and silicon atoms are bonded to each other exists. Si _(1-X) O _X is a film in which oxygen atoms are present in the silicon film and a state in which the oxygen atoms and silicon atoms are bonded to each other. The thickness of the first p-type conductivity layer 31 constituting the first photoelectric conversion unit 3 is preferably in the range of 1 nm to 50 nm.

A buffer layer may be inserted between the first p-type conductivity type layer 31 and the first photoelectric conversion layer 32. Examples of the material of the buffer layer include i-type amorphous or i-type microcrystalline Si _(1-X) C _X (X is greater than 0 and 0.5 or less), and amorphous or microcrystalline Si _{(1- X)} O _X (X is larger than 0 and 0.66 or less).

Examples of the material of the first photoelectric conversion layer 32 include i-type amorphous Si _(1-X) C _X (X is greater than 0 and 0.5 or less) and i-type amorphous Si _(1-X) O _X ( X is larger than 0 and 0.66 or less). The first photoelectric conversion layer 32 preferably has a refractive index in the range of 2.0 to 3.5 at a wavelength of 600 nm. Moreover, it is preferable that the film thickness of the 1st photoelectric converting layer 32 exists in the range of 100 nm-1 micrometer.

  The first n-type conductivity type layer 33 includes, in order from the transparent conductive film 2 side, a first first n-type conductivity type layer 331 that is a high refractive index layer and a second first n-type conductivity type layer 332 that is an antireflection layer. And a third first n-type conductivity type layer 333. The film thickness of the first first n-type conductivity type layer 331 is in the range of 1 nm to 30 nm. The film thickness of the second first n-type conductivity type layer 332 is in the range of 10 nm to 50 nm. The film thickness of the third first n-type conductivity type layer 333 is in the range of 1 nm to 30 nm. Each of these layers contains a V group element such as phosphorus as an impurity.

  As shown in FIG. 2, the second first n-type conductivity type layer 332 has a higher refractive index than the first photoelectric conversion layer 32 adjacent to the light incident side of the first n-type conductivity type layer 33. The second first n-type conductivity type layer 332 has a higher refractive index than the second p-type conductivity type layer 41 of the second photoelectric conversion unit 4 adjacent to the light emission side. Moreover, it has a higher refractive index than the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333. FIG. 2 is a diagram for explaining a refractive index profile in the film thickness direction of each layer from the first photoelectric conversion layer 32 to the second p-type conductivity type layer 41. For example, the second first n-type conductivity type layer 332 has a refractive index in the range of 3.0 to 5.0 at a wavelength of 600 nm.

  As shown in FIG. 3, the second first n-type conductivity type layer 332 has higher conductivity than the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333. FIG. 3 is a diagram for explaining the conductivity profile in the film thickness direction of each layer from the first photoelectric conversion layer 32 to the second p-type conductivity type layer 41. By increasing the conductivity of the second first n-type conductivity type layer 332, even if the conductivity of the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333 is low, the first n The conductivity of the entire type conductivity type layer 33 can be maintained. Thereby, the fall of the fill factor of a solar cell characteristic can be suppressed. The second first n-type conductivity type layer 332 preferably contains microcrystalline silicon. When the second first n-type conductivity type layer 332 contains microcrystalline silicon, high conductivity can be easily obtained, and the conductivity of the entire first n-type conductivity type layer 33 can be secured at a good level.

The second first n-type conductivity type layer 332 preferably has a conductivity of 1 × 10 ⁻¹ S / cm or more. If the resistance of the entire first n-type conductivity layer 33 becomes so high that it cannot be ignored as compared with the entire solar cell, the fill factor is lowered. In order to prevent this, it is preferable that the second first n-type conductivity type layer 332 has the above conductivity. Since the second first n-type conductivity type layer 332 has a high conductivity, the conductivity of the entire first n-type conductivity type layer 33 can be ensured at a good level, an increase in resistance is suppressed, and a photoelectric conversion efficiency is achieved. Can be improved.

The second first n-type conductivity type layer 332 preferably has a conductivity of 2 × 10 ¹ S / cm or less. As the conductivity increases, the band gap generally becomes narrower and the amount of light absorbed increases. Thereby, the utilization efficiency of light falls and the output current of a solar cell falls. In order to prevent this, it is preferable that the second first n-type conductivity type layer 332 has the above conductivity.

Further, the second first n-type conductivity type layer 332 is formed of carbon (C) as compared with the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333 as shown in FIGS. ) And oxygen (O) concentrations are low. The second first n-type conductivity type layer 332 preferably does not contain carbon (C) and oxygen (O). For example, the concentration of carbon (C) and oxygen (O) detected by SIMS (secondary ion mass spectrometry) may be 5 × 10 ¹⁸ / cm ³ or less, and more preferably 1 × 10 ¹⁸ / cm ³ or less. desirable. FIG. 4 is a diagram for explaining the profile of carbon (C) concentration in each layer from the first first n-type conductivity type layer 331 to the third first n-type conductivity type layer 333. FIG. FIG. 5 is a diagram for explaining the profile of oxygen (O) concentration in the film in each layer from the first first n-type conductivity type layer 331 to the third first n-type conductivity type layer 333. FIG.

  The refractive index can be controlled by reducing at least one of the carbon (C) and oxygen (O) concentrations. By reducing at least one of the carbon (C) and oxygen (O) concentrations in the second first n-type conductivity type layer 332, the second first n-type conductivity type layer 332 having high conductivity can be obtained. In addition, the conductivity of the entire first n-type conductivity type layer 33 can be ensured at a good level. Further, the concentration of carbon (C) and oxygen (O) in each of the first first n-type conductivity type layer 331, the second first n-type conductivity type layer 332, and the third first n-type conductivity type layer 333 is set as follows. By controlling each refractive index, an intermediate refractive index layer can be formed at the interface of the second first n-type conductivity type layer 332, so that an increase in resistance can be suppressed and reflection loss can be suppressed, and photoelectric conversion can be achieved. Efficiency can be improved.

  As shown in FIG. 2, the first first n-type conductivity type layer 331 has a refractive index between the refractive index of the first photoelectric conversion layer 32 and the refractive index of the second first n-type conductivity type layer 332. In the light incident side region of the second first n-type conductivity type layer 332, the refractive index of the first photoelectric conversion layer 32 adjacent to the first n-type conductivity type layer 33 and the refraction of the second first n-type conductivity type layer 332. By providing the first first n-type conductivity type layer 331 having a refractive index between the first and second refractive indexes, reflection at the interface between the first photoelectric conversion layer 32 and the second first n-type conductivity type layer 332 is achieved. The light reflection loss can be reduced and the photoelectric conversion efficiency can be improved. That is, the light reflection loss caused by the difference in refractive index between the first photoelectric conversion layer 32 and the second first n-type conductivity type layer 332 can be reduced, and the photoelectric conversion efficiency can be improved.

  The first first n-type conductivity type layer 331 preferably has a refractive index in the range of 2.5 to 4.0 at a wavelength of 600 nm, for example. By controlling the refractive index of the first first n-type conductivity type layer 331 in the range of 2.5 to 4.0, the second first n-type conductivity type layer 332 (refractive index: 3.0-5. 0) and a refractive index between the refractive index of the first photoelectric conversion layer 32 (refractive index: 2.0 to 3.5) can be obtained.

Further, the first n-type conductivity type layer 331 includes Si _(1-X) O _X (X is greater than 0 and not more than 0.66 ₎ containing oxygen in the film, or Si _(1-X) containing carbon. It is preferable to consist of C _X (X is greater than 0 and 0.5 or less). When the first first n-type conductivity type layer 331 is composed of these materials, the refractive index of the first first n-type conductivity type layer 331 can be controlled to a desired value by adjusting the amount of impurities. In addition, the first first n-type conductivity type layer 331 may include a microcrystalline phase. Although the conductivity of the first first n-type conductivity type layer 331 may decrease as the refractive index decreases, the first first n-type conductivity type layer 331 includes the microcrystalline phase, so that the first This is effective for maintaining the conductivity of the first n-type conductivity type layer 331 as high as possible.

  As shown in FIG. 2, the third first n-type conductivity type layer 333 includes the refractive index of the second p-type conductivity type layer 41 of the second photoelectric conversion unit 4 and the refractive index of the second first n-type conductivity type layer 332. With a refractive index between. The second p-type conductivity type of the second photoelectric conversion unit 4 adjacent to the first n-type conductivity type layer 33 in the region opposite to the light incident side (light emission side region) of the second first n-type conductivity type layer 332. By providing a third first n-type conductivity type layer 333 having a refractive index between the refractive index of the layer 41 and the refractive index of the second first n-type conductivity type layer 332, the second p-type conductivity type layer 41 and Reflection at the interface with the second first n-type conductivity type layer 332 can be suppressed to reduce light reflection loss, and photoelectric conversion efficiency can be improved. That is, the light reflection loss caused by the difference in refractive index between the second p-type conductivity type layer 41 and the second first n-type conductivity type layer 332 can be reduced, and the photoelectric conversion efficiency can be improved.

  The third first n-type conductivity type layer 333 preferably has a refractive index in the range of 2.5 to 4.0 at a wavelength of 600 nm, for example. By controlling the refractive index of the third first n-type conductivity type layer 333 in the range of 2.5 to 4.0, the second first n-type conductivity type layer 332 (refractive index: 3.0-5. 0) and the refractive index of the second p-type conductivity type layer 41 (refractive index: 2.0 to 3.5) of the second photoelectric conversion unit 4 can be obtained.

In addition, the third first n-type conductivity type layer 333 includes Si _(1-X) O _X containing oxygen in the film (X is larger than 0 and 0.66 or less), or Si _(1-X) containing carbon. It is preferable to consist of C _X (X is greater than 0 and 0.5 or less). When the third first n-type conductivity type layer 333 is composed of these materials, the refractive index of the third first n-type conductivity type layer 333 can be controlled to a desired value by adjusting the amount of impurities. Further, the third first n-type conductivity type layer 333 may include a microcrystalline phase. Although the conductivity of the third first n-type conductivity type layer 333 may decrease as the refractive index decreases, the conductivity of the third first n-type conductivity type layer 333 is reduced by including a microcrystalline phase. It is effective to keep it as high as possible.

As described above, the second photoelectric conversion unit 4 includes the second p-type conductivity type layer 41, the second photoelectric conversion layer 42, and the second n-type conductivity type layer 43 that are sequentially stacked from the transparent conductive film 2 side. The material of the second p-type conductivity type layer 41 includes a group III element such as boron (B) as an impurity. For example, amorphous or microcrystalline Si _(1-X) C _X (where X is greater than 0 and 0.5 And the like, and amorphous or microcrystalline Si _(1-X) O _X (where X is greater than 0 and 0.66 or less). The second p-type conductivity type layer 41 has a lower refractive index than the first n-type conductivity type layer 33.

  The second photoelectric conversion unit 4 has a refractive index in the range of 2.0 to 3.5 at a wavelength of 600 nm, for example. The film thickness of the second p-type conductivity layer 41 constituting the second photoelectric conversion unit 4 is preferably in the range of 5 nm to 50 nm.

  Examples of the material of the second photoelectric conversion layer 42 include i-type amorphous silicon germanium, i-type amorphous or microcrystalline silicon, and the like. Examples of the material of the second n-type conductivity type layer 43 include amorphous or microcrystalline silicon containing a V group element such as phosphorus as an impurity.

The 3rd photoelectric conversion unit 5 is comprised by the 3rd p type conductivity type layer 51, the 3rd photoelectric conversion layer 52, and the 3rd n type conductivity type layer 53 which were laminated | stacked in order from the transparent conductive film 2 side as mentioned above. The material of the third p-type conductivity type layer 51 contains a group III element such as boron (B) as an impurity, and is, for example, amorphous or microcrystalline Si _(1-X) C _X (where X is greater than 0 and 0.5 And the like), amorphous or microcrystalline Si _(1-X) O _X (X is greater than 0 and 0.66 or less), amorphous or microcrystalline silicon, and the like.

  Examples of the material of the third photoelectric conversion layer 52 include i-type microcrystalline silicon and i-type microcrystalline silicon germanium. Examples of the material of the third n-type conductivity type layer 53 include amorphous or microcrystalline silicon containing a group V element such as phosphorus as an impurity.

  The first photoelectric conversion layer 32, the second photoelectric conversion layer 42, and the third photoelectric conversion layer 52 have a role of absorbing light and performing photoelectric conversion, and therefore have different band gaps, that is, different absorption wavelength regions. Is preferred. Moreover, although the film-forming method of the thin film which comprises each layer of the 1st photoelectric conversion unit 3, the 2nd photoelectric conversion unit 4, and the 3rd photoelectric conversion unit 5 is not specifically limited, For example, plasma CVD method, CVD using a heating job medium Any one of a method, a thermal CVD method and a reactive sputtering method is preferable.

The back electrode layer 6 is made of a conductive film that reflects light. The back electrode layer 6 has a high reflectance with respect to light from visible light to infrared light, and preferably has high conductivity. Examples of such a material include at least one metal selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), copper (Cu), and platinum (Pt), or an alloy containing these metals. Can be mentioned. In order to prevent metal diffusion of the third photoelectric conversion unit 5 into the silicon, zinc oxide (ZnO) and indium tin oxide (ITO) are interposed between the third photoelectric conversion unit 5 and the back electrode layer 6. ) Or a transparent conductive film such as tin oxide (SnO ₂ ) may be inserted. The back electrode layer 6 is formed by a known means such as a sputtering method, a CVD method, or a spray method.

  The thin-film solar cell 10 according to the first embodiment configured as described above has the refractive index of the first photoelectric conversion layer 32 and the second refractive index in the light incident side region of the second first n-type conductivity type layer 332. A first n-type conductivity type layer 331 having a refractive index between that of the first n-type conductivity type layer 332 is provided. That is, an intermediate refractive index n-type conductivity type layer is provided outside the second first n-type conductivity type layer 332 so as to reduce the difference in refractive index between the second first n-type conductivity type layer 332 and the outer layer. . Thereby, reflection at the interface between the first photoelectric conversion layer 32 and the second first n-type conductivity type layer 332 can be suppressed to reduce light reflection loss and improve photoelectric conversion efficiency. Can do.

  In addition, the thin-film solar cell 10 according to the first embodiment includes the second p-type conductivity type layer 41 in the region opposite to the light incident side of the second first n-type conductivity type layer 332 and the second second n-type conductivity type layer 332. A third first n-type conductivity layer 333 having a refractive index between that of the 1n-type conductivity type layer 332 is provided. That is, an intermediate refractive index n-type conductivity type layer is provided outside the second first n-type conductivity type layer 332 so as to reduce the difference in refractive index between the second first n-type conductivity type layer 332 and the outer layer. . Thereby, reflection at the interface between the second p-type conductivity type layer 41 and the second first n-type conductivity type layer 332 can be suppressed to reduce the light reflection loss, and the photoelectric conversion efficiency is improved. be able to.

  As described above, in the thin film solar cell 10 according to the first embodiment, in the tandem thin film solar cell in which a plurality of photoelectric conversion units are stacked, at the interface of the preceding photoelectric conversion unit arranged on the light incident side. Since reflection can be suppressed and reflection loss of light can be reduced, and incident light to the subsequent photoelectric conversion unit can be increased, photoelectric conversion efficiency can be improved.

  The second first n-type conductivity type layer 332 has higher conductivity than the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333. Formation of an intermediate refractive index n-type conductive layer having a relatively low refractive index tends to increase the resistance of the n-type conductive layer and lower the fill factor among the characteristics of the thin-film solar cell. However, in the thin film solar cell 10 according to the first embodiment, the first n-type conductive layer 332 having the high conductivity in the central region of the first n-type conductive layer 33 has the first n-type conductive layer. A decrease in the conductivity of the entire mold layer 33 can be suppressed. As a result, even if the conductivity of the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333 is lowered, the overall conductivity of the first n-type conductivity type layer 33 can be maintained. And the decrease in fill factor can be suppressed.

  Therefore, according to the thin film solar cell 10 according to the first embodiment, in the tandem thin film solar cell in which a plurality of photoelectric conversion units are stacked, the highly conductive first n-type conductivity type layer 33 is realized and the light is reflected. Since loss can be reduced, a thin film solar cell with excellent photoelectric conversion efficiency can be obtained.

  It is also possible to apply the configuration of the first n-type conductivity type layer 33 to the second n-type conductivity type layer 43.

  Next, a method for manufacturing the thin-film solar cell 10 according to the present embodiment configured as described above will be described with reference to FIGS. 6A to 6E are cross-sectional views for explaining an example of the manufacturing process of the thin-film solar cell 10 according to the first embodiment.

First, the translucent insulating substrate 1 is prepared. Here, a non-alkali glass substrate is used as the translucent insulating substrate 1 and will be described below. In addition, an inexpensive soda lime glass substrate may be used as the light-transmitting insulating substrate 1, but in this case, in order to prevent the diffusion of alkali components from the light-transmitting insulating substrate 1, an SiO ₂ film is formed by PCVD or the like. It is preferable to form about 50 nm.

Next, a tin oxide (SnO ₂ ) film is formed on the translucent insulating substrate 1 by a thermal CVD method to form a transparent conductive film 2 having macro unevenness on the surface (FIG. 6-1). As a method for forming the transparent conductive film 2, a physical method such as a vacuum deposition method or an ion plating method, or a chemical method such as a spray method, a dip method, or a CVD method may be used. In addition, heat treatment may be performed to control the size of crystal grains and improve the mobility of the film.

Next, the 1st photoelectric conversion unit 3, the 2nd photoelectric conversion unit 4, and the 3rd photoelectric conversion unit 5 are formed in order by plasma CVD method on the transparent conductive film 2. FIG. First, a 15-nm-thick p-type amorphous Si _(1-X) C _X (X is greater than 0 and 0.5 or less) film as the first p-type conductivity type layer 31 on the transparent conductive film 2, the first An i-type amorphous Si _(1-X) C _X (X is greater than 0 and less than or equal to 0.5) film (refractive index at a wavelength of 600 nm: about 2.9) as the photoelectric conversion layer 32, 30 nm thick n-type conductivity type layers are sequentially formed as the 1n-type conductivity type layer 33 (FIG. 6-2).

  Here, the first n-type conductivity type layer 33 includes a first first n-type conductivity type layer 331, a second first n-type conductivity type layer 332, and a third first n-type conductivity type on the first photoelectric conversion layer 32 film. A mold layer 333 is sequentially deposited. The thickness of the first first n-type conductivity type layer 331 is 5 nm to 10 nm, the thickness of the second first n-type conductivity type layer 332 is 15 nm to 25 nm, and the thickness of the third first n-type conductivity type layer 333 is 5 nm to 10 nm, both of which contain a V group element such as phosphorus as an impurity.

The film formation conditions of the first first n-type conductivity layer 331 are, for example, substrate temperature: 200 ° C., pressure: 2.5 Torr, power: 50 W, reaction gas flow rate: SiH ₄ / CH ₄ / H ₂ / PH ₃ = 10 / 10/500/100 sccm. By depositing under such deposition conditions, the first first n-type conductivity type having a refractive index in the range of 3 to 3.5 at a wavelength of 600 nm and a conductivity of 1 × 10 ⁻⁵ S / cm. Layer 331 is obtained.

The film formation conditions of the second first n-type conductivity type layer 332 are, for example, substrate temperature: 200 ° C., pressure: 2.5 Torr, power: 50 W, reaction gas flow rate: SiH ₄ / H ₂ / PH ₃ = 10/2000 / 100 sccm. By depositing under such deposition conditions, the second first n-type conductivity having a refractive index in the range of 3.6 to 5.0 at a wavelength of 600 nm and a conductivity of 1 × 10 ⁰ S / cm. A mold layer 332 is obtained.

The deposition conditions of the third first n-type conductivity type layer 333 are as follows: substrate temperature: 200 ° C., pressure: 2.5 Torr, power: 50 W, reaction gas flow rate: SiH ₄ / CH ₄ / H ₂ / PH ₃ = 10 / 10/500/100 sccm. By forming the film under such film forming conditions, the third first n-type conductivity type having a refractive index in the range of 3 to 3.5 at a wavelength of 600 nm and a conductivity of 1 × 10 ⁻⁵ S / cm. Layer 333 is obtained.

Next, the second photoelectric conversion unit 4 is formed on the first photoelectric conversion unit 3 (FIG. 6-3). The second photoelectric conversion unit 4 is formed by forming a 20 nm thick p-type amorphous Si _(1-X) C _X (X is greater than 0 and less than or equal to 0.5) film as the second p-type conductivity type layer 41 (wavelength). Refractive index at 600 nm: about 2.7), 150 nm thick i-type amorphous silicon germanium film as the second photoelectric conversion layer 42, 30 nm thick n-type microcrystal as the second n-type conductivity type layer 43 Silicon films are sequentially stacked on the first photoelectric conversion unit 3.

  Next, the third photoelectric conversion unit 5 is formed on the second photoelectric conversion unit 4 (FIG. 6-4). The formation of the third photoelectric conversion unit 5 includes a p-type microcrystalline silicon film having a thickness of 20 nm as the third p-type conductivity type layer 51, an i-type microcrystalline silicon film having a thickness of 2 μm as the third photoelectric conversion layer 52, An n-type microcrystalline silicon film having a thickness of 20 nm as the 3n-type conductivity type layer 53 is sequentially stacked on the second photoelectric conversion unit 4.

Next, the back electrode layer 6 is formed on the third photoelectric conversion unit 5 by sputtering (FIGS. 6-5). In this embodiment, an aluminum (Al) film having a film thickness of 300 nm is formed as the back electrode layer 6, but a silver (Ag) film having a high light reflectance may be used to prevent metal diffusion into silicon. In addition, a transparent conductive film such as zinc oxide (ZnO), indium tin oxide (ITO), tin oxide (SnO ₂ ) or the like may be formed between the third photoelectric conversion unit 5 and the back electrode layer 6. Thus, the thin film solar cell 10 as shown in FIG. 1 is completed.

  Next, characteristics evaluation of thin film solar cells (Examples) produced by the method for manufacturing a thin film solar cell according to the present embodiment and comparative examples will be described.

(Example)
The first first n-type conductivity type layer 331, the second first n-type conductivity type layer 332, and the third first n-type according to the method for manufacturing the thin-film solar cell according to the first embodiment and the conditions exemplified above. A thin film solar cell including the first n-type conductivity type layer 33 composed of the conductivity type layer 333 was formed, and the thin film solar cell of the example was obtained.

The refractive index at a wavelength of 600 nm is 3.0 to 3.5 for the first first n-type conductivity type layer 331, 3.6 to 4.5 for the second first n-type conductivity type layer 332, and the third third conductivity type. The 1n-type conductivity type layer 333 is 3.0 to 3.5. The film thickness is 5 nm to 10 nm for the first first n-type conductivity type layer 331, 15 nm to 25 nm for the second first n-type conductivity type layer 332, and 5 nm to 10 nm for the third first n-type conductivity type layer 333. . The conductivity is 1 × 10 ⁻⁵ S / cm for the first first n-type conductivity layer 331, 1 × 10 ⁰ S / cm for the second first n-type conductivity layer 332, and the third first n-type conductivity. The mold layer 333 is 1 × 10 ⁻⁵ S / cm.

(Comparative Example 1)
A thin-film solar cell was fabricated in the same manner as in the example except that the first n-type conductivity type layer was constituted only by the second first n-type conductivity type layer 332 (film thickness: 25 nm to 35 nm). A thin film solar cell was obtained. The second first n-type conductivity type layer 332 of Comparative Example 1 has a refractive index of 3.5 to 4.5 at a wavelength of 600 nm, a film thickness of 25 nm to 35 nm, and a conductivity of 1 × 10 ⁰ S / cm. .

(Comparative Example 2)
A thin-film solar cell was produced in the same manner as in the example except that the first n-type conductivity type layer was constituted only by the first first n-type conductivity type layer 331 (film thickness: 25 nm to 35 nm). A thin film solar cell was obtained. The first first n-type conductivity type layer 331 of Comparative Example 2 has a refractive index of 3.0 to 3.5 at a wavelength of 600 nm, a film thickness of 25 to 35 nm, and a conductivity of 1 × 10 ⁻⁵ S / cm. is there.

These thin-film solar cells were irradiated with pseudo-sunlight having a spectral distribution of AM1.5 and an energy density of 100 mW / cm ^{2 from} the translucent insulating substrate 1 side at a sample temperature of 25 ° C. ± 1 ° C. And the output characteristic of the thin film solar cell was measured by measuring the voltage and electric current between the positive electrode probe which contacted the transparent conductive film 2 through the contact region, and the negative electrode probe which contacted the back surface electrode layer 6. Table 1 shows the measurement results of the short-circuit current density (mA / cm ² ), open-circuit voltage (V), fill factor, and photoelectric conversion efficiency (%) for the thin film solar cells of Examples and Comparative Examples.

In the thin film solar cell of an Example, the short circuit current density was 10.0 mA / cm < ² >, the open circuit voltage was 2.1V, the fill factor was 0.70, and the photoelectric conversion efficiency was 14.7%. In the thin film solar cell of Comparative Example 1, the short circuit current density was 9.8 mA / cm ² , the open circuit voltage was 2.1 V, the fill factor was 0.71, and the photoelectric conversion efficiency was 14.4%. In the thin film solar cell of Comparative Example 2, the short-circuit current density was 10.1 mA / cm ² , the open-circuit voltage was 2.1 V, the fill factor was 0.65, and the photoelectric conversion efficiency was 13.8%.

  By comparing Example 1 and Comparative Example 1, it can be seen that the short-circuit current density and the photoelectric conversion efficiency of Example 1 are higher than those of Comparative Example 1. This is because the use efficiency of light is improved due to the antireflection effect of incident light due to the formation of the first first n-type conductivity layer 331 and the third third n-type conductivity type layer 333, and the output current is improved. It is thought that efficiency could be improved.

  Moreover, by comparing Example 1 with Comparative Example 2, it can be seen that Example 1 has a higher fill factor and photoelectric conversion efficiency than Comparative Example 2. This is because the conductivity of the first n-type conductivity type layer 33 is increased by forming the second first n-type conductivity type layer 332 having a high conductivity on the side opposite to the light incident side in the first first n-type conductivity type layer 331. It can be maintained high, and as a result, the file factor can be maintained, and the photoelectric conversion efficiency can be improved.

  Accordingly, by providing the first first n-type conductivity type layer 331, the second first n-type conductivity type layer 332, and the third first n-type conductivity type layer 333 as the first n-type conductivity type layer 33, a thin film solar cell is provided. It can be said that the photoelectric conversion efficiency can be improved.

  In the method for manufacturing the thin-film solar cell 10 according to the first embodiment described above, the refractive index of the first photoelectric conversion layer 32 and the second second n-type conductivity type layer 332 are incident on the light incident side region of the second first n-type conductivity type layer 332. A first first n-type conductive layer 331 having a refractive index between that of the 1n-type conductive layer 332 is provided. That is, the intermediate refractive index n-type conductivity type layer is provided outside the second first n-type conductivity type layer 332 so as to reduce the difference in refractive index between the second first n-type conductivity type layer 332 and the outer layer. . Thereby, reflection at the interface between the first photoelectric conversion layer 32 and the second first n-type conductivity type layer 332 can be suppressed to reduce light reflection loss and improve photoelectric conversion efficiency. Can do.

  In the method for manufacturing the thin-film solar cell 10 according to the first embodiment, the refractive index of the second p-type conductivity type layer 41 in the region opposite to the light incident side of the second first n-type conductivity type layer 332 A third first n-type conductivity type layer 333 having a refractive index between that of the second first n-type conductivity type layer 332 is provided. That is, an n-type conductivity type layer having an intermediate refractive index is arranged outside the second first n-type conductivity type layer 332 so as to reduce a difference in refractive index between the second first n-type conductivity type layer 332 and an outer layer thereof. Prepare for. Thereby, reflection at the interface between the second p-type conductivity type layer 41 and the second first n-type conductivity type layer 332 can be suppressed to reduce the light reflection loss, and the photoelectric conversion efficiency is improved. be able to.

  As described above, in the method for manufacturing the thin-film solar cell 10 according to the first embodiment, in the tandem-structured thin-film solar cell in which a plurality of photoelectric conversion units are stacked, the photoelectric conversion unit of the previous stage disposed on the light incident side. Since reflection at the interface can be suppressed and reflection loss of light can be reduced and incident light to the subsequent photoelectric conversion unit can be increased, photoelectric conversion efficiency can be improved.

  The second first n-type conductivity type layer 332 has higher conductivity than the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333. Formation of an intermediate refractive index n-type conductive layer having a relatively low refractive index tends to increase the resistance of the n-type conductive layer and lower the fill factor among the characteristics of the thin-film solar cell. However, in the method of manufacturing the thin-film solar cell 10 according to the first embodiment, the second first n-type conductivity type layer 332 having high conductivity is provided in the central region of the first n-type conductivity type layer 33, so that the first A decrease in the conductivity of the entire 1n-type conductivity type layer 33 can be suppressed. As a result, even if the conductivity of the first first n-type conductivity type layer 331 and the third first n-type conductivity type layer 333 is lowered, the overall conductivity of the first n-type conductivity type layer 33 can be maintained. And the decrease in fill factor can be suppressed.

  Therefore, according to the manufacturing method of the thin film solar cell 10 according to the first embodiment, in the tandem thin film solar cell in which a plurality of photoelectric conversion units are stacked, the highly conductive first n-type conductivity type layer 33 is realized. Since the reflection loss of light can be reduced, a thin film solar cell excellent in photoelectric conversion efficiency can be obtained.

Embodiment 2. FIG.
FIG. 7: is sectional drawing which shows the structure of thin film solar cell 10 'concerning Embodiment 2 of this invention. In the thin film solar cell 10 ′ according to the second embodiment, the same members as those in the thin film solar cell 10 according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The thin-film solar cell 10 ′ according to the second embodiment is different from the thin-film solar cell 10 according to the first embodiment in that the first first n-type is not formed without forming the third first n-type conductivity type layer 333. The conductive type layer 331 and the second first n type conductive type layer 332 constitute a first n type conductive type layer 33 ′.

  As described above, even when the first n-type conductivity type layer 33 ′ is composed of the first first n-type conductivity type layer 331 and the second first n-type conductivity type layer 332, the second first n with high conductivity is provided. The conductivity of the entire first n-type conductivity type layer 33 ′ can be kept high by the type conductivity type layer 332, and is generated due to a difference in refractive index between the first photoelectric conversion layer 32 and the second first n-type conductivity type layer 332. The reflection loss can be reduced and the photoelectric conversion efficiency can be improved.

  Therefore, according to the thin film solar cell 10 ′ according to the second embodiment, in the tandem thin film solar cell in which a plurality of photoelectric conversion units are stacked, the first n-type conductivity type layer 33 ′ having high conductivity is realized and light Therefore, a thin film solar cell excellent in photoelectric conversion efficiency can be obtained.

Embodiment 3 FIG.
FIG. 8: is sectional drawing which shows the structure of the thin film solar cell 10 "concerning Embodiment 3 of this invention. In the thin film solar cell 10" concerning Embodiment 3, the thin film solar cell 10 concerning Embodiment 1 and About the same member, detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol. The thin-film solar cell 10 ″ according to the third embodiment is different from the thin-film solar cell 10 according to the first embodiment in that the second first n-type is not formed without forming the first first n-type conductivity type layer 331. The conductive type layer 332 and the third first n type conductive type layer 333 constitute a first n type conductive type layer 33 ″.

  Thus, even when the first n-type conductivity type layer 33 ″ is constituted by the second first n-type conductivity type layer 332 and the third first n-type conductivity type layer 333, the second first n n having high conductivity is obtained. The conductivity of the entire first n-type conductivity type layer 33 ″ can be kept high by the type conductivity type layer 332, and is caused by the difference in refractive index between the second first n-type conductivity type layer 332 and the second p-type conductivity type layer 41. The reflection loss can be reduced, and the photoelectric conversion efficiency can be improved.

  Therefore, according to the thin film solar cell 10 ″ according to the third embodiment, in the tandem thin film solar cell in which a plurality of photoelectric conversion units are stacked, the first n-type conductivity type layer 33 ″ having high conductivity is realized and the light Therefore, a thin film solar cell excellent in photoelectric conversion efficiency can be obtained.

  As described above, the thin film solar cell according to the present invention is useful for realizing high photoelectric conversion efficiency in a tandem thin film solar cell in which a plurality of photoelectric conversion units are stacked.

DESCRIPTION OF SYMBOLS 1 Translucent insulated substrate 2 Transparent electrically conductive film 3 1st photoelectric conversion unit 4 2nd photoelectric conversion unit 5 3rd photoelectric conversion unit 6 Back surface electrode layer 10 Thin film solar cell 10 'Thin film solar cell 10 "Thin film solar cell 31 1st p type Conductive layer 32 First photoelectric conversion layer 33 First n-type conductivity layer 41 Second p-type conductivity type layer 42 Second photoelectric conversion layer 43 Second n-type conductivity type layer 51 Third p-type conductivity type layer 52 Third photoelectric conversion layer 53 Third n-type conductivity type layer 331 First first n-type conductivity type layer 332 Second first n-type conductivity type layer 333 Third first n-type conductivity type layer L Light

Claims (14)

A light-transmitting insulating substrate, a transparent conductive film, a semiconductor film, and a first p-type conductive layer, a first photoelectric conversion layer, and a first n-type conductive layer from the light incident side are included in this order. A preceding photoelectric conversion unit for performing photoelectric conversion, a second p-type conductivity type layer, a second photoelectric conversion layer, and a second n-type conductivity type layer made of a semiconductor film in contact with the first n-type conductivity type layer from the light incident side. A subsequent photoelectric conversion unit that performs photoelectric conversion in this order, and
The first n-type conductivity type layer is
A high refractive index layer having a higher refractive index than the first photoelectric conversion layer adjacent to the light incident side of the first n-type conductivity type layer and the second p-type conductivity type layer adjacent to the light emission side;
An antireflection layer provided in contact with the high refractive index layer on at least one of the light incident side or the light emitting side of the high refractive index layer;
Have
The antireflection layer provided on the light incident side of the high refractive index layer is between the refractive index of the first photoelectric conversion layer adjacent to the first n-type conductivity type layer and the refractive index of the high refractive index layer. Having a refractive index of
The antireflective layer provided on the light exit side of the high refractive index layer includes a refractive index of the second p-type conductivity type layer adjacent to the first n-type conductivity type layer and a refractive index of the high refractive index layer. Having a refractive index between,
A thin film solar cell characterized by The high refractive index layer has a higher conductivity than the antireflection layer;
The thin film solar cell according to claim 1. The high refractive index layer has a conductivity of 1 × 10 ⁻¹ S / cm or more and 2 × 10 ¹ S / cm or less,
The thin film solar cell according to claim 2. The high refractive index layer includes microcrystalline silicon;
The thin film solar cell according to claim 3. The high refractive index layer has a content of at least one of carbon and oxygen less than that of the antireflection layer;
The thin film solar cell according to claim 1, wherein: The antireflection layer has a refractive index between the refractive index of the first photoelectric conversion layer and the refractive index of the high refractive index layer, and is provided on the light incident side of the high refractive index layer;
The thin film solar cell according to any one of claims 1 to 5, wherein: The antireflection layer has a refractive index between the refractive index of the second p-type conductivity type layer and the refractive index of the high refractive index layer, and is provided on the light exit side of the high refractive index layer;
The thin film solar cell according to any one of claims 1 to 5, wherein: A transparent conductive film, a semiconductor film, and a first p-type conductivity type layer, a first photoelectric conversion layer, and a first n-type conductivity type layer in this order from the light incident side on the translucent insulating substrate are subjected to photoelectric conversion. The preceding photoelectric conversion unit to be performed, and the second p-type conductivity type layer, the second photoelectric conversion layer, and the second n-type conductivity type layer in this order from the light incident side made of a semiconductor film in contact with the first n-type conductivity type layer. In the method of manufacturing a thin-film solar cell including a step of sequentially forming a subsequent photoelectric conversion unit that performs photoelectric conversion,
The step of forming the first n-type conductivity type layer includes:
The first photoelectric conversion layer adjacent to the light incident side of the first n-type conductivity type layer and the high refractive index layer having a higher refractive index than the second p-type conductivity type layer adjacent to the light emission side are formed. Process,
Forming an antireflection layer in contact with the high refractive index layer on at least one of the light incident side or the light emitting side of the high refractive index layer;
Have
In the step of forming the antireflection layer,
The antireflective layer having a refractive index between the refractive index of the first photoelectric conversion layer adjacent to the first n-type conductivity type layer and the refractive index of the high refractive index layer is incident on the light of the high refractive index layer. Forming the antireflection layer having a refractive index between the refractive index of the second p-type conductivity type layer adjacent to the first n-type conductivity type layer and the refractive index of the high refractive index layer. Forming on the light exit side of the refractive index layer,
A method for producing a thin film solar cell. The high refractive index layer has a higher conductivity than the antireflection layer;
The method for producing a thin-film solar cell according to claim 8. The high refractive index layer has a conductivity of 1 × 10 ⁻¹ S / cm or more and 2 × 10 ¹ S / cm or less,
The method for producing a thin-film solar cell according to claim 9. The high refractive index layer includes microcrystalline silicon;
The method for producing a thin-film solar cell according to claim 10. The high refractive index layer has a content of at least one of carbon and oxygen less than that of the antireflection layer;
The method for producing a thin-film solar cell according to any one of claims 8 to 11. In the step of forming the antireflection layer, the antireflection layer having a refractive index between the refractive index of the first photoelectric conversion layer and the refractive index of the high refractive index layer is incident on the light of the high refractive index layer. Forming on the side,
The method for producing a thin-film solar cell according to any one of claims 8 to 12. In the step of forming the antireflective layer, the antireflective layer having a refractive index between the refractive index of the second p-type conductivity type layer and the refractive index of the high refractive index layer is changed to the light of the high refractive index layer. Forming on the exit side,
The method for producing a thin-film solar cell according to any one of claims 8 to 12.

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