JP2006319068A - Multi-junction silicone thin film photoelectric converter and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-junction silicon thin film photoelectric converter with high conversion efficiency, where short-circuit current density which occurs in respective thin film photoelectric conversion units is balanced with a high value, and to provide a manufacturing method of the converter. <P>SOLUTION: The multi-junction silicon thin film photoelectric converter is provided with the silicon thin film photoelectric conversion units which are connected in series through an intermediate layer. In the multi-junction silicon thin film photoelectric converter having multiple layers, the intermediate layer is formed of one or above n-type μc-Si layers and two or above conductive SiO<SB>X</SB>layers, which are formed by a plasma CVD method. Both faces of the n-type μc-Si layer are arranged so that they are brought into contact with the conductive SiO<SB>X</SB>layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multi-junction silicon-based thin film photoelectric conversion device having an intermediate layer and a method for manufacturing the same.

  In recent years, photoelectric conversion devices that convert light into electricity using the photoelectric effect inside semiconductors have attracted attention and development has been vigorously conducted. Among these photoelectric conversion devices, silicon-based thin film photoelectric conversion devices are large at low temperatures. Since it can be formed on a glass substrate or a stainless steel substrate having an area, cost reduction can be expected.

  A thin film photoelectric conversion device generally includes a first electrode, a surface of which is sequentially laminated on an insulating substrate, one or more semiconductor thin film photoelectric conversion units, and a second electrode. Here, the photoelectric conversion unit is generally laminated in the order of a p-type layer, an i-type layer, and an n-type layer, and the i-type photoelectric conversion layer that occupies the main part is amorphous when it is amorphous. It is called a photoelectric conversion unit, and a crystal whose i-type layer is crystalline is called a crystalline photoelectric conversion unit.

As a method for improving the conversion efficiency of a photoelectric conversion device, a photoelectric conversion device employing a structure called a multi-junction type in which two or more photoelectric conversion units are stacked is known. In this method, a front photoelectric conversion unit including a photoelectric conversion layer having a large optical forbidden bandwidth is arranged on the light incident side of the photoelectric conversion device, and a rear photoelectric conversion including a photoelectric conversion layer having a small band gap in order behind the photoelectric conversion layer. By arranging the conversion unit, photoelectric conversion over a wide wavelength range of incident light is possible, and the conversion efficiency of the entire apparatus is improved by effectively using incident light. (In the present application, a photoelectric conversion unit disposed relatively on the light incident side is referred to as a front photoelectric conversion unit, and a photoelectric conversion unit disposed adjacent to a side farther from the light incident side than this is referred to as a rear photoelectric conversion unit. Called a conversion unit.)
In addition, a plurality of photoelectric conversion units including a photoelectric conversion layer having a smaller band gap at the rear of the rear photoelectric conversion unit are arranged to enable photoelectric conversion over a wider wavelength range of incident light. A technique for improving the conversion efficiency of the entire apparatus by adopting a so-called structure has been developed.

  However, the characteristics of the entire multi-junction photoelectric conversion device, particularly the short-circuit current density, is limited to the smaller short-circuit current density of the short-circuit current densities of the front photoelectric conversion unit and the rear photoelectric conversion unit. Therefore, in order to improve the characteristics of the entire multi-junction photoelectric conversion device, it is necessary to balance the short-circuit current density generated in each photoelectric conversion unit.

  Therefore, in recent years, there has been proposed a stacked photoelectric conversion device having a structure in which both a light transmitting property and a light reflecting property are interposed between a plurality of stacked photoelectric conversion units and a conductive intermediate layer is interposed. In this case, a part of the light reaching the intermediate layer is reflected, the amount of light absorption in the front photoelectric conversion unit located on the light incident side of the intermediate layer is increased, and the current value generated in the front photoelectric conversion unit Can be increased. For example, when an intermediate reflective layer is inserted into a hybrid photoelectric conversion device composed of an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit, the amorphous silicon photoelectric conversion is performed without increasing the film thickness of the amorphous silicon layer. The current generated by the unit can be increased. Alternatively, the amorphous silicon photoelectric conversion unit due to photodegradation that becomes conspicuous as the thickness of the amorphous silicon layer increases because the thickness of the amorphous silicon layer necessary to obtain the same current value can be reduced. It is possible to suppress the deterioration of characteristics. In such an intermediate layer, it is preferable that the wavelength region of light absorbed by the front photoelectric conversion unit is selectively reflected and the wavelength region of light absorbed by the rear photoelectric conversion unit is selectively transmitted.

For example, Patent Document 1 discloses that the reflection characteristics of the intermediate layer are improved so that the reflectance is high for light in the short wavelength region and low for light in the long wavelength region. In order to provide a stacked solar cell having a high photoelectric conversion efficiency in which the photoelectric current densities of the conversion layer and the lower photoelectric conversion layer are balanced at a high value, the photoelectric conversion layers are electrically connected in series with each other interposed between the photoelectric conversion layers. An intermediate layer to be connected is provided, and the intermediate layer is a multilayer film formed by alternately laminating two or more materials, and has a characteristic of selectively reflecting light in a specific wavelength region. A layer is disclosed.
JP 2001-308354 A

  If the intermediate layer is formed by using a multilayer film formed by alternately laminating two or more materials as described above, it is more suitable for light in a shorter wavelength region than using an intermediate layer formed by a single layer. It can be improved so that the reflectivity is high and the reflectivity is low for light in the long wavelength region, but an intermediate layer having the characteristic of selectively reflecting light in such a specific wavelength region is formed. For this purpose, a chamber for forming an intermediate layer is required separately from the conventional CVD chamber, and the cost burden is large.

  The present invention has been made in consideration of the above-described circumstances, and has a short-circuit current generated in each silicon-based thin film photoelectric conversion unit by having an intermediate layer exhibiting a reflection characteristic excellent in wavelength selection according to the present invention. Provided a multi-junction silicon photoelectric conversion device with high photoelectric conversion efficiency that balances the density at a high value, and a manufacturing method capable of uniformly forming the multi-junction silicon photoelectric conversion device over a large area at a low cost. To do.

The multi-junction silicon-based thin film photoelectric conversion device of the present invention is a multi-junction silicon-based thin film photoelectric conversion device including silicon-based thin film photoelectric conversion units connected in series via an intermediate layer, the intermediate layer being It is composed of one or more n-type μc-Si layers and two or more conductive SiO _x layers formed by plasma CVD, and both surfaces of the n-type μc-Si layer are in contact with the conductive SiO _x layers. Since the multilayer film is arranged in such a manner, it is possible to form an intermediate layer having a uniform and excellent reflection characteristic over a large area without forming a resistance layer at each layer interface. A high value of the short-circuit current density generated in each silicon-based thin film photoelectric conversion unit by selectively reflecting light in a specific wavelength region as a multilayer film composed of repeated type μc-Si layers and conductive SiO _x layers Light balanced by It is possible to obtain a high conversion efficiency multijunction silicon-based thin-film photoelectric conversion device.

  Further, in the multi-junction silicon thin film photoelectric conversion device of the present invention, the silicon thin film photoelectric conversion unit is laminated in the order of a p-type layer, an i-type layer, and an n-type layer, and the intermediate layer continues to n. A multi-junction silicon-based thin film photoelectric conversion device formed by laminating a type μc-Si layer is preferable. As a result, the intermediate layer can be formed while minimizing the electrical resistance with the n-type layer of the silicon-based thin film photoelectric conversion unit.

Further, the conductive SiO _x layer in the intermediate layer preferably contains Si having a crystal structure. As a result, the semiconductor layer constituting the intermediate layer becomes a highly conductive film, and the intermediate layer of the multi-junction silicon-based thin film photoelectric conversion device can be easily achieved in series connection of the photoelectric conversion units formed before and after the intermediate layer. It is possible to reduce the electrical loss caused by.

  In the present invention, when forming a multi-junction silicon-based thin film photoelectric conversion device, it is desirable that the intermediate layer be continuously formed in the same chamber. The intermediate layer can be formed smoothly and easily at low cost without producing a resistance layer.

Further, the formation of the conductive SiO _x layer in the intermediate layer is formed by introducing CO ₂ gas into a reaction gas such as silane, and by continuously changing the amount of CO ₂ gas introduced into the chamber. It is desirable to form the intermediate layer, and by using this manufacturing method, it is possible to form an intermediate layer having excellent reflection characteristics with smooth, easy and low-cost selection at each layer interface without causing a resistance layer. Therefore, a multi-junction silicon-based photoelectric conversion device with higher characteristics can be provided.

According to the present invention, the following specific effects can be obtained. That is, by using, as an intermediate layer, a multilayer film composed of an n-type μc-Si layer formed by a plasma CVD method and a conductive SiO _x layer as an intermediate layer, the wavelength selectivity can be achieved without causing a resistance layer at each layer interface. Since the multi-junction silicon photoelectric conversion device having the intermediate layer exhibiting excellent reflection characteristics can be formed, the characteristics of the multi-junction silicon photoelectric conversion device can be improved.

  In addition, since the intermediate layer can be formed uniformly in a large area at a low cost by continuously forming the intermediate layer in the same chamber of plasma CVD, the flexibility of the manufacturing process can be improved and the production efficiency can be improved. A manufacturing method can be provided.

  Due to the above effects, the present invention can provide a high-performance and low-cost multi-junction silicon-based photoelectric conversion device.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each drawing of the present application, dimensional relationships such as thickness and length are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Moreover, in each figure, the same referential mark represents the same part or an equivalent part.

  FIG. 1 shows a cross-sectional view of a multi-junction silicon-based photoelectric conversion device according to an example of an embodiment of the present invention. On the transparent substrate 1, it arrange | positions in order of the transparent electrode layer 2, the front photoelectric conversion unit 3, the intermediate | middle layer 4, the back photoelectric conversion unit 5, and the back surface electrode layer 6. FIG. In FIG. 1, the photoelectric conversion unit is a two-junction photoelectric conversion device including a front photoelectric conversion unit and a rear photoelectric conversion unit. In the present invention, three or more photoelectric conversion units are stacked. It can also be applied to a multi-junction silicon-based photoelectric conversion device. For example, in the three-junction silicon-based photoelectric conversion device arranged in the order of the first photoelectric conversion unit, the second photoelectric conversion unit, and the third photoelectric conversion unit from the light incident side, the first photoelectric conversion unit and the second photoelectric conversion unit are Each may be regarded as a front photoelectric conversion unit and a rear photoelectric conversion unit, and an intermediate layer may be provided in the vicinity of the boundary between them. Alternatively, the second photoelectric conversion unit and the third photoelectric conversion unit may be regarded as a front photoelectric conversion unit and a rear photoelectric conversion unit, respectively, and an intermediate layer may be provided in the vicinity of the boundary between them. Of course, a structure in which a silicon composite layer is provided both near the boundary between the first photoelectric conversion unit and the second photoelectric conversion unit and near the boundary between the second photoelectric conversion unit and the third photoelectric conversion unit may be used. Examples of the 3-junction silicon photoelectric conversion device include an amorphous silicon photoelectric conversion unit as the first photoelectric conversion unit, an amorphous silicon germanium or crystalline silicon photoelectric conversion unit as the second photoelectric conversion unit, and a third photoelectric conversion unit. Examples include the case where an amorphous silicon germanium or crystalline silicon photoelectric conversion unit is applied to the unit, but the combination is not limited thereto.

A plate-like member or a sheet-like member made of glass, transparent resin or the like is used for the transparent substrate 1 used in a photoelectric conversion device of a type in which light enters from the substrate side. The transparent electrode layer 2 is preferably made of a conductive metal oxide such as SnO ₂ or ZnO, and is preferably formed using a method such as CVD, sputtering, or vapor deposition. The transparent electrode layer 2 desirably has the effect of increasing the scattering of incident light by having fine irregularities on its surface.

As the back electrode layer 6, it is preferable to form at least one metal layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr by sputtering or vapor deposition. Between the photoelectric conversion unit and the metal electrode, ITO, may be formed a layer made of SnO _2, conductive oxides such as ZnO (not shown).

  A plurality of photoelectric conversion units are arranged behind the transparent electrode 2 when viewed from the light incident side. In the case of a structure in which two photoelectric conversion units are stacked as shown in FIG. 1, the front photoelectric conversion unit 3 disposed on the light incident side has a relatively wide bandgap material, for example, an amorphous silicon-based material. A conversion unit or the like is used. The rear photoelectric conversion unit 5 arranged on the rear side includes a material having a relatively narrow band gap, for example, a photoelectric conversion unit made of a silicon-based material containing crystalline material, an amorphous silicon germanium photoelectric conversion unit, or the like. Used.

  Each photoelectric conversion unit is preferably configured by a pin junction including a p-type layer, an i-type layer that is a substantially intrinsic photoelectric conversion layer, and an n-type layer. Among these, those using amorphous silicon for the i-type layer are called amorphous silicon photoelectric conversion units, and those using crystalline silicon are called crystalline silicon photoelectric conversion units. Note that the amorphous or crystalline silicon-based material is not only a case where only silicon is used as a main element constituting a semiconductor, but also an alloy material including elements such as carbon, oxygen, nitrogen, and germanium. Good. The main constituent material of the conductive layer is not necessarily the same as that of the i-type layer. For example, amorphous silicon carbide can be used for the p-type layer of the amorphous silicon photoelectric conversion unit, and n A silicon layer (also referred to as μc-Si) containing crystal in the mold layer can also be used.

In the present invention, between the front photoelectric conversion unit and the rear photoelectric conversion unit, the reflectance for light in the wavelength region that can be absorbed by the front photoelectric conversion unit is high, and the reflectance for light in the wavelength region that cannot be absorbed by the front photoelectric conversion unit is low. An intermediate layer 4 having such reflection characteristics is used. The intermediate layer 4 is characterized by using a multilayer film formed by repeating an n-type μc-Si layer and a conductive SiO _x layer. In order to function as an intermediate reflection layer, the photoelectric layer in the front photoelectric conversion unit 3 is used. It is necessary to arrange at any position between the conversion layer and the photoelectric conversion layer in the rear photoelectric conversion unit 5. Moreover, this intermediate | middle layer 4 can serve as a part of conductive type layer in a photoelectric conversion unit.

In the intermediate layer 4 of the present invention, in order to realize the selective reflection characteristics as described above, the intermediate layer is formed by laminating a multilayer film composed of repeated n-type μc-Si layers and conductive SiO _x layers. A multilayer intermediate layer is used. By adopting such a structure, the reflection characteristics of the intermediate layer can be freely set, and the optimum reflection characteristics can be obtained according to the configuration of the photoelectric conversion units arranged before and after the intermediate layer. The short-circuit photocurrent density of the photoelectric conversion unit can be improved, and the decrease of the short-circuit photocurrent density of the rear photoelectric conversion unit can be minimized, and the short-circuit photocurrent density of the upper photoelectric conversion layer and the lower photoelectric conversion layer is increased. Can be balanced by value.

In this intermediate layer 4, a conductive SiO _x layer is used, and this conductive SiO _x layer is additionally supplied with a CO ₂ gas in a chamber under the same conditions as those for producing the n-type μc-Si layer by the plasma CVD method. The refractive index of the conductive SiO _x layer to be manufactured can be controlled over a wide range by controlling the flow rate of the CO ₂ gas at the time of manufacturing. For this reason, a laminated structure of the conductive SiO _x layer and the n-type μc-Si layer can be easily produced by continuously changing the flow rate of the CO ₂ gas introduced in the same plasma CVD chamber. The conductive SiO _x layer desirably contains Si having a crystal structure. As a result, the semiconductor layer constituting the intermediate layer becomes a highly conductive film, and the intermediate layer of the multi-junction silicon-based thin film photoelectric conversion device is prepared while achieving serial connection of the photoelectric conversion units formed before and after the intermediate layer. It is possible to reduce the electrical loss caused by.

A specific example of forming the intermediate layer 4 in the present invention is as follows. The conductive SiO _x layer is produced by using SiH ₄ , CO ₂ , H ₂ , and PH ₃ as reaction gases under so-called microcrystal production conditions with a large H ₂ / SiH ₄ ratio and a CO ₂ / SiH ₄ ratio of 2. The plasma CVD method is used for the above range. The conditions of plasma CVD at this time are, for example, a power coupled frequency of 10 to 100 MHz, a power density of 50 to 500 mW / cm ² , a pressure of 50 to 1500 Pa, and a substrate temperature of 150 to 250 ° C. using capacitively coupled parallel plate electrodes. When the CO ₂ / SiH ₄ ratio is increased, the oxygen concentration in the film increases monotonously. Also may be using B ₂ H ₆ in place of PH ₃ as a doping gas, it may be mixed both gas PH ₃ and B ₂ H _6. Furthermore, at the time of producing the n-type μc-Si layer, SiH ₄ , CO ₂ , H ₂ , and PH ₃ are used as the reaction gas, and it is produced by the plasma CVD method under a condition where the H ₂ / SiH ₄ ratio is large. The conditions are, for example, a power coupling frequency of 10 to 100 MHz, a power density of 50 to 500 mW / cm ² , a pressure of 50 to 1500 Pa, and a substrate temperature of 150 to 250 ° C. using capacitively coupled parallel plate electrodes.

Furthermore, in the present invention, the front photoelectric conversion unit 3 is formed using the plasma CVD method, the substrate is once taken out into the atmosphere, and then the intermediate layer 4 and the rear photoelectric conversion unit 5 are continuously formed again by the plasma CVD method. Although there is a manufacturing method, even in such a manufacturing method, when the intermediate layer 4 is formed, it is desirable to first form an n-type μc-Si layer and then a conductive SiO _x layer. In this way, the electrical loss of the multi-junction silicon solar cell can be reduced while easily achieving series connection at the interface between the n-type conductivity type layer and the intermediate layer of the front photoelectric conversion unit 3. Therefore, photoelectric conversion characteristics can be improved.

The conductive SiO _x layer in the intermediate layer 4 of the present invention preferably has a refractive index of 2.5 or less for light having a wavelength of 600 nm, or an oxygen concentration in the film of 25 atomic% or more. The relationship between the refractive index and the oxygen concentration in the film has a relatively high correlation. The lower the refractive index, the thinner the film thickness for obtaining reflective properties with excellent selectivity as the intermediate reflective layer. The intermediate layer 4 is an inactive layer that does not contribute to photoelectric conversion, and light absorbed here hardly contributes to power generation. Therefore, the intermediate layer 4 needs to be as thin as possible, and the conductive layer is conductive here. The reason why the value of light having a wavelength of 600 nm is used as the index of refraction of the SiO _x layer is as follows. Spectral sensitivity of the amorphous silicon photoelectric conversion unit is one of the stacked photoelectric conversion devices in a hybrid photoelectric conversion device in which an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are stacked in two stages. The fall of the current and the rise of the spectral sensitivity current of the crystalline silicon photoelectric conversion unit intersect at a wavelength near 600 nm. Therefore, a film that reflects light in the vicinity of 600 nm, that is, a film having a small refractive index with respect to 600 nm light, can easily obtain a reflection characteristic that is excellent in selection, and increases the generated current of the front photoelectric conversion unit. It becomes suitable for. The refractive index can be evaluated using, for example, a spectroscopic ellipsometry method.

  In the following, an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are stacked as an example of a method for manufacturing a multi-junction silicon-based photoelectric conversion device including a stacked structure corresponding to the above-described embodiment. Further, a multi-junction silicon photoelectric conversion device having a two-stack superstrate structure will be given and will be described in detail while comparing with a comparative example. In the drawings, the same members are denoted by the same reference numerals, and redundant description is omitted. Moreover, this invention is not limited to a following example, unless the meaning is exceeded.

(Example 1 and Comparative Example 1)
Corresponding to the first embodiment described with reference to FIG. 1, a multi-junction silicon solar cell as Example 1 was fabricated. Glass was used for the transparent substrate 1 and SnO 2 was used for the transparent electrode layer 2. The film thickness of the transparent electrode layer 2 at this time was 800 nm, the sheet resistance was 10 ohm / □, and the haze ratio was 15 to 20%. On top of this, a boron-doped p-type silicon carbide (SiC) layer has a thickness of 10 nm, a non-doped amorphous silicon photoelectric conversion layer has a thickness of 300 nm, and a phosphorus-doped n-type μc-Si layer has a thickness of 20 nm. Filmed. Thereby, the amorphous silicon photoelectric conversion unit 3 of the pin junction which is a front photoelectric conversion unit was formed.

Further, on the amorphous silicon photoelectric conversion unit 3, a conductive SiO _x layer 41 is formed as an intermediate layer with a thickness of 70 nm, an n-type μc-Si layer 42 is formed with a thickness of 30 nm, and a conductive SiO _x layer 43 is formed thereon with a thickness of 70 nm. The intermediate layer 4 was formed by continuously depositing each of the n-type μc-Si layers constituting the front photoelectric conversion unit in the same chamber as that formed by the plasma CVD method.

Conductive SiO _X layer 41 and 43, were deposited in a parallel plate type RF plasma CVD method. Regarding the film forming conditions at that time, the plasma excitation frequency was 13.56 MHz, the substrate temperature was 160 ° C., and the pressure in the reaction chamber was 6 Torr. SiH ₄ , PH ₃ , B ₂ H ₆ , CO ₂ , and H ₂ were used as source gases introduced into the plasma CVD reaction chamber. After forming a 70 nm conductive SiO _x layer 41 under the above conditions, the CO ₂ gas supply was stopped in the same chamber as it was, and an n-type μc-Si layer 42 was formed to a thickness of 30 nm. Furthermore the gas supply of CO ₂ to resume in the same chamber as that film formation of n-type [mu] c-Si layer 42, the conductive SiO _X layer 43 under the same conditions as film formation conditions of the conductive SiO _X layer A 70 nm film was formed.

Further, when the conductive SiO _x layer is measured by Raman scattering spectroscopy, a peak at a wave number of 520 cm ⁻¹ peculiar to crystalline silicon is observed, and it is known that it has a microcrystalline structure. Moreover, the ratio of the peak resulting from crystalline silicon and amorphous silicon by this Raman scattering spectroscopy was about 2-6.

  Further, on the intermediate layer 4, a boron-doped p-type microcrystalline silicon layer having a thickness of 15 nm, a non-doped crystalline silicon photoelectric conversion layer having a thickness of 1.7 μm, and a phosphorus-doped n-type microcrystalline silicon layer having a thickness of 20 nm are formed by plasma CVD. The film was formed by the method. Thereby, the crystalline silicon photoelectric conversion unit 5 of the pin junction which is a back photoelectric conversion unit was formed. Further, a ZnO film having a thickness of 80 nm and an Ag film having a thickness of 300 nm were formed as the back electrode layer 6 on the rear photoelectric conversion unit 5 by sputtering.

In this embodiment, by using an intermediate layer having a structure in which the n-type μc-Si layer and the conductive SiO _x layer are repeated in two layers, the wavelength range of light that is absorbed by the front photoelectric conversion unit is wide. On the other hand, the reflectance with respect to light in the long wavelength region of 700 to 800 nm or more is low, and thus the reflectance in the wavelength region of light absorbed by the rear photoelectric conversion unit is 90 in a wide range. % Light transmittance can be effectively utilized by selectively reflecting incident light. With these effects, the short circuit current density of the front photoelectric conversion unit 3 can be improved, the short circuit current density of the rear photoelectric conversion unit 5 can be prevented from being lowered, and the short circuit current density generated by each photoelectric conversion unit can be balanced. done.

Similarly, a multi-junction thin film silicon solar cell having the configuration shown in FIG. Intermediate layer 4 in Comparative Example 1 is constituted only by n-type SiO _X layer, as 70nm thickness of the n-type SiO _X layer, other film forming conditions were the same as in Example 1. In this comparative example, since the intermediate layer composed of one n-type SiO _x layer is used, the reflectance is limited to about 70% at the maximum with respect to the wavelength region of light absorbed by the front photoelectric conversion unit. The light transmittance is low even in the wavelength region of light absorbed by the conversion unit, and the selective reflection of incident light cannot be performed sufficiently. While in Comparative Example 1 the film thickness of the n-type SiO _X layer to increase the light reflectance in a short wavelength region by thinning, and it is possible to higher light transmittance in a long wavelength region, n-type SiO _X When the reflectance is adjusted by thinning the layer, a phenomenon occurs in which light in the wavelength region of about 500 nm to 700 nm is not sufficiently reflected to the front photoelectric conversion unit side, which is sufficient for the wavelength region of light absorbed by the front photoelectric conversion unit. It cannot be an intermediate layer with selectivity.

  The short-circuit current density when the light of AM1.5 is irradiated to the multi-junction thin-film silicon solar cell of Example 1 as incident light at a light illuminance of 100 mW / cm 2 is about 12 to 13 mA / cm 2 in Comparative Example 1. In contrast, in Example 1, the short-circuit current density was improved by about 13 to 14 mA / cm 2 and about 10%, and it was confirmed that the conversion efficiency was improved by about 10% as well as the improvement of the short-circuit current density. .

In this example, the thickness of the conductive SiO _x layer and the n-type μc-Si layer was set to 70 nm and 30 nm, respectively, and the structure was repeated twice. However, even if the number of repetitions is increased to 3 times and 4 times, A structure satisfying the light reflection selectivity according to the present invention has the same effect. In addition, the film thickness ratio of the conductive SiO _x layer and the n-type μc-Si layer according to the present invention is an example, and the film thickness ratio is set in accordance with the change of the constituent material of the front photoelectric conversion unit and the change of the reflectance due to the surface shape. By appropriately adjusting, the intermediate layer 4 having the same effect can be formed.

(Example 2 and Comparative Example 2)
Corresponding to the second embodiment described with reference to FIG. 2, a multi-junction silicon solar cell as Example 2 was fabricated. Glass was used for the transparent substrate 1 and SnO 2 was used for the transparent electrode layer 2. The film thickness of the transparent electrode layer 2 at this time was 800 nm, the sheet resistance was 10 ohm / □, and the haze ratio was 15 to 20%. On top of this, a boron-doped p-type silicon carbide (SiC) layer has a thickness of 10 nm, a non-doped amorphous silicon photoelectric conversion layer has a thickness of 80 nm, and a phosphorus-doped n-type μc-Si layer has a thickness of 20 nm. Filmed. Thereby, the amorphous silicon photoelectric conversion unit 3 of the pin junction which is a front photoelectric conversion unit was formed.

  Further, a boron-doped p-type silicon carbide layer having a thickness of 20 nm, a non-doped amorphous silicon photoelectric conversion layer having a thickness of 300 nm, and a phosphorus-doped n-type microcrystalline silicon layer having a thickness of 20 nm are formed on the front photoelectric conversion unit 3. A film was formed by a CVD method. As a result, a pin junction amorphous silicon photoelectric conversion unit 7 as an intermediate photoelectric conversion unit was formed.

Further, a conductive SiO _x layer 41 is formed as an intermediate layer on the amorphous silicon photoelectric conversion unit 7 with a thickness of 80 nm, an n-type μc-Si layer 42 is formed with a thickness of 35 nm, and a conductive SiO _x layer 43 is formed thereon with a thickness of 80 nm. The intermediate layer 4 was formed by continuously depositing each of the n-type μc-Si layers constituting the front photoelectric conversion unit in the same chamber as that formed by the plasma CVD method.

Conductive SiO _X layer 41 and 43, were deposited in a parallel plate type RF plasma CVD method. Regarding the film forming conditions at that time, the plasma excitation frequency was 13.56 MHz, the substrate temperature was 160 ° C., and the pressure in the reaction chamber was 6 Torr. SiH ₄ , PH ₃ , B ₂ H ₆ , CO ₂ , and H ₂ were used as source gases introduced into the plasma CVD reaction chamber.

  Further, on the intermediate layer 4, a boron-doped p-type microcrystalline silicon layer is formed with a thickness of 15 nm, a non-doped crystalline silicon photoelectric conversion layer is formed with a thickness of 1.4 μm, and a phosphorus-doped n-type microcrystalline silicon layer is formed with a thickness of 20 nm. A film was formed by a CVD method. Thereby, the crystalline silicon photoelectric conversion unit 5 of the pin junction which is a back photoelectric conversion unit was formed. Finally, a ZnO film having a thickness of 80 nm and an Ag film having a thickness of 300 nm were formed as the back electrode layer 6 on the rear photoelectric conversion unit 5 by sputtering, thereby forming a three-junction silicon solar cell.

  In this embodiment, since it has a three-junction structure, not only the wavelength range of light absorbed by the front photoelectric conversion unit but also light in the wavelength range of light absorbed by the intermediate photoelectric conversion unit is efficiently reflected by the intermediate layer. Therefore, it is necessary to efficiently reflect light up to a long wavelength region near 800 nm as the reflection characteristic of the intermediate layer. In the reflection characteristics of the intermediate layer in this embodiment, the reflection peak is designed to reflect light having a wavelength of 600 nm and light having a relatively long wavelength. For this reason, the intermediate layer in the example has a light reflection characteristic of 50% or more even with light having a wavelength of 700 nm, and the light reflection region extends to the 800 nm region. On the other hand, the reflectance for light in the long wavelength region of 800 nm or more is designed to be low, and high light transmittance of 90% or more is shown for light in the long wavelength region of 900 nm or more. Also in the multi-junction solar cell, incident light can be selectively reflected to effectively use the light, and the short-circuit current density generated by each photoelectric conversion unit can be balanced.

Similarly, an amorphous silicon solar cell having the configuration shown in FIG. Intermediate layer 4 in Comparative Example 2 is configured with only n-type SiO _X layer, as 150nm and the thickness of the n-type SiO _X layer, other film forming conditions were the same as in Example 1. In this comparative example, an intermediate layer composed of one n-type SiO _x layer is used, and the thickness of the n-type SiO _x layer is thick. Is 50% or less at the maximum, and shows a low light transmittance with respect to the wavelength region of light absorbed by the rear photoelectric conversion unit, so that the selective reflection of incident light is not sufficiently performed.

  The short-circuit current density when the AM 1.5 light as the incident light is irradiated with the light illuminance of 100 mW / cm 2 to the three-junction silicon solar cell of Example 2 is about 6.5 mA / cm 2 in Comparative Example 1. On the other hand, in Example 1, the short circuit current density was improved by about 7.1 mA / cm 2 and about 10%, and the conversion efficiency was improved by about 10% as well as the short circuit current density. It was confirmed that the conversion efficiency of about 9.5% was greatly improved to about 10.8% in Example 2.

1 is a structural cross-sectional view of a multi-junction silicon-based photoelectric conversion device according to one embodiment of the present invention. The structure sectional view of the 3 junction type silicon system photoelectric conversion device concerning another embodiment of the present invention.

Explanation of symbols

Front photoelectric conversion unit 1 transparent substrate 2 transparent electrode layer 3 4 intermediate layer 41 conductive SiO _X layer 42 n-type [mu] c-Si layer 43 conductive SiO _X layer 5 back photoelectric conversion unit 6 back electrode layer 7 intermediate photovoltaic unit

Claims (5)

A multi-junction silicon-based thin film photoelectric conversion device including silicon-based thin film photoelectric conversion units connected in series via an intermediate layer, wherein the intermediate layer is formed of one or more n-type μc− films formed by a plasma CVD method. A multi-layer film comprising a Si layer and two or more conductive SiO _x layers, wherein both surfaces of the n-type μc-Si layer are disposed in contact with the conductive SiO _x layer. Junction silicon thin film photoelectric conversion device.   The silicon-based thin film photoelectric conversion unit is laminated in the order of a p-type layer, an i-type layer, and an n-type layer, and the intermediate layer is successively laminated from an n-type μc-Si layer. The multi-junction silicon-based thin film photoelectric conversion device according to claim 1. The multi-junction silicon-based thin film photoelectric conversion device according to claim 1, wherein the conductive SiO _x layer in the intermediate layer contains Si having a crystal structure.   4. The method of manufacturing a multi-junction silicon-based thin film photoelectric conversion device according to claim 1, wherein the intermediate layer is continuously formed in the same chamber. The formation of the conductive SiO _x layer in the intermediate layer is a method for manufacturing a multi-junction silicon-based thin film photoelectric conversion device formed by introducing CO ₂ gas into a reaction gas such as silane, and a CO ₂ gas chamber The method for producing a multi-junction silicon-based thin film photoelectric conversion device according to claim 1, wherein the intermediate layer is formed by continuously changing the amount introduced into the inside.

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