JP2011181852A - Thin film photoelectric conversion device and method of manufacturing thin film photoelectric conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film photoelectric conversion device that has high quantum efficiency for a wavelength longer than 1,000 nm of a photoelectric conversion unit of a thin film photoelectric conversion device including a crystalline germanium photoelectric conversion layer. <P>SOLUTION: A method of manufacturing the thin film photoelectric conversion device which has a first electrode 2, one or more photoelectric conversion units 3 each having a photoelectric conversion layer between a p-type semiconductor layer and an n-type semiconductor layer, and a second electrode layer 4 arranged in order on a substrate 1 includes a step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma during a step of laminating the crystalline germanium photoelectric conversion layer, at least one photoelectric conversion unit including, as its photoelectric conversion layer, a crystalline germanium photoelectric conversion layer composed of a substantially intrinsic or weak n-type crystalline germanium semiconductor including no silicon atom. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thin film photoelectric conversion device and a method for manufacturing the thin film photoelectric conversion device.

  In the future, energy and global environmental issues are becoming serious, and alternative energy alternatives to fossil fuels are being developed vigorously. Among alternative energy source candidates, photoelectric conversion devices that convert light into electricity using the photoelectric effect inside the semiconductor are attracting attention, and thin film photoelectric conversion devices that use silicon-based thin films as photoelectric conversion layers have been widely researched and developed. ing.

  The photoelectric conversion layer is a layer that absorbs light and generates electron-hole pairs, and the absorption characteristics are closely related to the power generation characteristics of the thin film photoelectric conversion device. For example, when a silicon-based thin film is used for the photoelectric conversion layer, light absorption in the photoelectric conversion layer is not sufficient at wavelengths longer than 1000 nm, and the power generation efficiency of the thin film photoelectric conversion device is significantly reduced. On the other hand, since sunlight falling on the ground includes a wavelength longer than 1000 nm, a thin film photoelectric conversion device capable of efficiently photoelectrically converting light having a wavelength longer than 1000 nm when the efficiency of the thin film photoelectric conversion device is increased. Development is desired.

As an attempt to improve the photoelectric conversion efficiency of long wavelength light in such a thin film photoelectric conversion device, Non-Patent Document 1 discloses a single junction thin film photoelectric conversion device using weak n-type microcrystalline germanium for the photoelectric conversion layer. Yes. The structure of the thin film photoelectric conversion device is stainless steel substrate / n-type amorphous silicon / i-type amorphous silicon / microcrystalline silicon germanium composition gradient layer / weak n-type microcrystalline germanium photoelectric conversion layer / microcrystalline silicon germanium composition. It is a structure in which an inclined layer / p-type microcrystalline silicon layer / indium tin oxide (ITO) are sequentially laminated. The characteristics of the thin film photoelectric conversion device are open circuit voltage Voc = 0.22V, short circuit current density Jsc = 25 mA / cm ² , fill factor FF = 0.36, conversion efficiency Eff = 2.0%, and quantum efficiency 10 on the long wavelength side. %, The wavelength at which the quantum efficiency is 5% is 1130 nm. The microcrystalline germanium photoelectric conversion layer is formed by an ECR remote plasma CVD method using microwave discharge.

  In Patent Document 1, in a film forming method for depositing and bonding a microcrystalline silicon thin film on an amorphous silicon thin film, a process of depositing a microcrystalline silicon thin film and a process of irradiating hydrogen plasma are alternately performed a plurality of times. A method for forming a microcrystalline silicon thin film is disclosed. By repeating the process of depositing the microcrystalline silicon thin film and the process of irradiating with hydrogen plasma a plurality of times, the junction characteristics of the laminated film are improved, and a device having high photoconductivity and carrier transportability is manufactured.

Xuejun Niu, Jeremy Booher and Vikran L. Dalal, "Nanocrystalline Germanium and Germanium Carbide Films and Devices", Materials Research Society Symposium Proceedings, Vol.862, A10.2 (2005).

JP-A-4-266019

  This invention makes it a subject to improve the photoelectric conversion efficiency with respect to the long wavelength light of the photoelectric conversion unit of the thin film photoelectric conversion apparatus containing a crystalline germanium photoelectric conversion layer.

  In the case of a thin film photoelectric conversion device using an amorphous silicon germanium (a-SiGe) photoelectric conversion unit or a crystalline silicon photoelectric conversion unit for the bottom cell of a two-junction or three-junction stacked thin film photoelectric conversion device, The upper limit of the wavelength that can be used is 900 to 1100 nm, and there is a problem that the use of long wavelength light is insufficient and the conversion efficiency is insufficiently improved.

  Further, as shown in Non-Patent Document 1, a thin film photoelectric conversion device using a weak n-type microcrystalline germanium photoelectric conversion layer in a microcrystalline germanium photoelectric conversion unit has a low open-circuit voltage and a low fill factor (FF), and conversion efficiency is low. There are low issues. In addition, there is a problem that sufficient improvement cannot be obtained when the upper limit of the wavelength of long-wavelength light having a quantum efficiency of 10% or more is about 1080 nm.

In addition, as a result of the study by the present inventors, in the thin film photoelectric conversion device including the crystalline germanium photoelectric conversion unit, one of the factors that the quantum efficiency at a wavelength longer than 1000 nm is low is the defect of the crystalline germanium photoelectric conversion layer and the crystal It has been found that the crystalline germanium photoelectric conversion layer has crystallinity.
In view of the above, an object is to provide a thin film photoelectric conversion device having high quantum efficiency for wavelengths longer than 1000 nm.

  According to the first aspect of the present invention, “a first electrode layer, one or more photoelectric conversion units each including a photoelectric conversion layer between a p-type semiconductor layer and an n-type semiconductor layer, and a second electrode layer are sequentially disposed on the substrate. The at least one photoelectric conversion unit is a crystalline germanium photoelectric conversion layer made of a substantially intrinsic or weak n-type crystalline germanium semiconductor in which the photoelectric conversion layer does not contain silicon atoms. A thin film photoelectric conversion unit comprising a step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma in the step of laminating the crystalline germanium photoelectric conversion unit. "Manufacturing method of apparatus".

  In the method for manufacturing the thin film photoelectric conversion device, a part of the crystalline germanium photoelectric conversion unit is exposed to hydrogen gas plasma. The step of exposing to hydrogen gas plasma refers to a step of generating a discharge in a state where hydrogen gas is introduced into the plasma CVD apparatus and exposing a part of the thin film photoelectric conversion device to the generated plasma. By exposing the crystalline germanium photoelectric conversion unit to hydrogen gas plasma, defects derived from dangling bonds in the crystalline germanium photoelectric conversion unit are reduced, and electrons generated by the crystalline germanium photoelectric conversion layer absorb light. And holes can move to lubrication, and as a result, the short-circuit current of the thin film photoelectric conversion device and the quantum efficiency in the long wavelength light region are improved.

  The second aspect of the present invention is “a method for producing a thin film photoelectric conversion device as described above, wherein the crystalline germanium photoelectric conversion layer is formed during the crystalline germanium photoelectric conversion layer lamination step or immediately after the crystalline germanium photoelectric conversion layer lamination step. “A method for producing a thin film photoelectric conversion device,” comprising performing a step of exposing a part of the photoelectric conversion unit to hydrogen gas plasma.

  In the method for manufacturing the thin film photoelectric conversion device, the step of exposing to a hydrogen gas plasma is performed during the step of laminating the crystalline germanium photoelectric conversion layer or immediately after the step of laminating the crystalline germanium photoelectric conversion layer. The conversion layer is exposed to hydrogen plasma. The crystalline germanium photoelectric conversion layer is a layer that absorbs light and generates electron / hole pairs, and occupies a major film thickness in the germanium photoelectric conversion unit. Therefore, whether or not the movement of electron-hole pairs in the crystalline germanium photoelectric conversion layer occurs by lubrication is a main factor that affects the performance of the thin film photoelectric conversion device. Therefore, by exposing the crystalline germanium photoelectric conversion layer to hydrogen gas plasma, dangling bonds in the crystalline germanium photoelectric conversion layer are terminated with hydrogen, and defects derived from the dangling bonds are reduced. It is preferable for improving the short circuit current.

  Further, by exposing the crystalline germanium photoelectric conversion layer to hydrogen plasma, the crystallinity of the crystalline germanium photoelectric conversion layer is improved, and the light absorption efficiency in the long wavelength light region is increased. It is preferable because the quantum efficiency in the long wavelength light region of the thin film photoelectric conversion device is improved by the effect of increasing the light absorption rate in the long wavelength light region and the effect of reducing the defects.

  A third aspect of the present invention is “a method for producing a thin film photoelectric conversion device as described above, wherein the step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma is a step of laminating a crystalline germanium photoelectric conversion layer”. The method for producing a thin film photoelectric conversion device, wherein the crystalline germanium photoelectric conversion layer is introduced in the period between and is exposed to hydrogen gas plasma and has a thickness of 1 nm to 50 nm.

  In the method for manufacturing the thin film photoelectric conversion device, the film thickness of the crystalline germanium photoelectric conversion layer when performing the step of exposing to the hydrogen gas plasma is 1 nm to 50 nm. Adjacent to the crystalline germanium photoelectric conversion layer by performing a step of exposing to a hydrogen plasma when the film thickness of the crystalline germanium photoelectric conversion layer is in the range of 1 nm to 50 nm in the lamination process of the crystalline germanium photoelectric conversion layer It is possible to reduce dangling bond-derived defects that exist in the vicinity of the bonding interface of the layer to be processed. It is preferable because the short-circuit current of the thin film photoelectric conversion device is improved by reducing defects near the bonding interface.

  In addition, the crystalline germanium photoelectric conversion layer exposed to hydrogen gas plasma has improved crystallinity, which not only increases the light absorption rate in the long wavelength light region, but also improves the crystallinity of the germanium photoelectric conversion layer laminated thereafter. It is preferable because it has the effect of improving, and the long wavelength light absorption efficiency in the germanium photoelectric conversion layer and the quantum efficiency in the long wavelength light region of 1000 nm or more of the thin film photoelectric conversion device are improved.

  When the film thickness of the crystalline germanium photoelectric conversion layer is in the range of 1 nm or more and 50 nm or less compared to the case where the step of exposing to hydrogen gas plasma is performed when the film thickness of the crystalline germanium photoelectric conversion layer is 50 nm or more. It was found that the short-circuit current of the thin film photoelectric conversion device was high when the step of exposure to hydrogen plasma was performed. This is because the crystallinity of the surface layer portion exposed to hydrogen plasma is improved and the effect of reducing defects derived from dangling bonds existing in the vicinity of the junction interface between the crystalline germanium photoelectric conversion layer and the adjacent layer appears. It is thought that this is because.

  Furthermore, as a result of the examination by the present inventors, it is surprising that the crystalline germanium photoelectric conversion layer is laminated more than the step of exposing the crystalline germanium photoelectric conversion layer and the step of exposing to hydrogen gas plasma multiple times. When the film thickness of the crystalline germanium photoelectric conversion layer is in the range of 1 nm to 50 nm, it has been found that the performance of the thin film photoelectric conversion device is higher when the step of exposing to hydrogen plasma is performed once. In the thin film photoelectric conversion device in which the step of laminating the crystalline germanium photoelectric conversion layer and the step of exposing to the hydrogen gas plasma are repeated a plurality of times, the leakage current in the germanium photoelectric conversion unit increased. This is presumably because the film density of the crystalline germanium photoelectric conversion layer was reduced by exposure to hydrogen gas plasma multiple times.

  A fourth aspect of the present invention is “a method for producing a thin film photoelectric conversion device as described above, wherein the step of exposing part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma is a step of laminating a crystalline germanium photoelectric conversion layer” Is performed immediately before the manufacturing method of the thin film photoelectric conversion device ”.

  In the method of manufacturing the thin film photoelectric conversion device, the step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma is performed immediately before the step of laminating the crystalline germanium photoelectric conversion layer. By exposing the surface layer that forms the bonding interface with the crystalline germanium photoelectric conversion layer to hydrogen gas plasma, defects in the surface portion that forms the bonding interface with the crystalline germanium photoelectric conversion layer are reduced, and the adjacent layer itself The crystallinity and the crystallinity of the crystalline germanium photoelectric conversion layer grown using the layer as a base are improved. Thereby, the short circuit current of the thin film photoelectric conversion device and the quantum efficiency in a long wavelength region of 1000 nm or more are preferable.

  The fifth aspect of the present invention is also “a method for producing the thin film photoelectric conversion device, wherein the crystalline germanium photoelectric conversion layer is formed by a plasma CVD method within a substrate temperature range of 120 ° C. to 250 ° C. A method for manufacturing a thin film photoelectric conversion device ”.

  When the substrate temperature when forming the crystalline germanium photoelectric conversion layer is 250 ° C. or less, diffusion of conductivity-determining impurities in the P-type semiconductor layer and structural change of the first interface layer can be reduced. It leads to improvement of voltage, short circuit current, and fill factor. In addition, when the substrate temperature when forming the crystalline germanium photoelectric conversion layer is 250 ° C. or lower, in the case of having a structure in which a plurality of photoelectric conversion units are stacked, the layer is formed before the crystalline germanium photoelectric conversion layer is formed. This is preferable because deterioration of the photoelectric conversion unit by heating can be prevented.

  If the substrate temperature when forming the crystalline germanium photoelectric conversion layer is 120 ° C. or more, a film having a high film density with few defects in the crystalline germanium photoelectric conversion layer can be formed, leakage current is reduced, and short circuit current is improved. Leads to. When the substrate temperature when forming the crystalline germanium photoelectric conversion layer is less than 120 ° C., not only the defect density in the crystalline germanium photoelectric conversion layer is high and the film density is low, but also the crystalline germanium photoelectric conversion layer is formed. This is not preferable because the crystallinity of the conversion layer is lowered and light absorption in a long wavelength region of 1000 nm or more is not sufficient and the short-circuit current is reduced.

  According to a sixth aspect of the present invention, “a first electrode layer, one or more photoelectric conversion units each including a photoelectric conversion layer between a p-type semiconductor layer and an n-type semiconductor layer, and a second electrode layer are sequentially disposed on the substrate. A thin film photoelectric conversion device, wherein at least one photoelectric conversion unit is a crystalline germanium photoelectric conversion layer in which the photoelectric conversion layer is substantially made of an intrinsic or weak n-type crystalline germanium semiconductor containing no silicon atom. A thin-film photoelectric conversion device, which is a germanium photoelectric conversion unit and has a crystal volume fraction of 2% to 50% at a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer ”.

  The crystal volume fraction having a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer is the film density, crystal volume fraction, crystal orientation, defect density, etc. of the crystalline germanium photoelectric conversion layer to be laminated thereafter. It is considered that the film quality is affected, and is considered to be important in evaluating the crystalline germanium photoelectric conversion layer.

  The crystal volume fraction having a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer is preferably 2% or more, so that light having a wavelength longer than 1000 nm can be photoelectrically converted. Further, when the crystal volume fraction is 50% or less compared to the case where the crystal volume fraction of the thickness of 50 nm near the substrate of the crystalline germanium photoelectric conversion layer is larger than 50%, the leakage in the germanium photoelectric conversion unit It has been found that the current is small and the performance of the thin film photoelectric conversion device is high. Therefore, it is preferable that the crystal volume fraction having a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer is 2% or more and 50% or less.

  In the present invention, a portion of the crystalline germanium photoelectric conversion unit is exposed to hydrogen gas plasma, thereby reducing defects in the crystalline germanium photoelectric conversion unit and improving the crystallinity of the crystalline germanium photoelectric conversion layer. Thus, the short-circuit current of the thin film photoelectric conversion device and the quantum efficiency in long wavelength light of 1000 nm or more can be improved.

1 is a schematic cross-sectional view of a single junction thin film photoelectric conversion device according to one embodiment of the present invention. It is typical sectional drawing of the 3 junction thin film photoelectric conversion apparatus which concerns on another embodiment of this invention. 1 is a schematic cross-sectional view of a single-junction thin-film photoelectric conversion device according to Examples 1 to 7 and Comparative Example 1 of the present invention. It is typical sectional drawing of the 3 junction thin film photoelectric conversion apparatus which concerns on Example 8 and Comparative Example 2 of this invention. It is typical sectional drawing of the 2 junction thin film photoelectric conversion apparatus which concerns on the comparative example 3 of this invention. It is typical sectional drawing of the semiconductor laminated film which concerns on Example 9 and Comparative Example 4 of this invention. It is a Raman spectrum of the semiconductor laminated film which concerns on Example 9 and Comparative Example 4 of this invention.

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

  Such a silicon-based thin film photoelectric conversion device generally includes a transparent electrode layer, one or more photoelectric conversion units, and a back electrode layer, which are sequentially stacked on a transparent insulating substrate. Here, the photoelectric conversion unit is generally formed by stacking a p-type semiconductor layer, an i-type layer, and an n-type semiconductor layer in this order or vice versa, and the i-type photoelectric conversion layer occupying the main part is amorphous. Are called amorphous photoelectric conversion units, and those having a crystalline i-type layer are called crystalline photoelectric conversion units.

  The photoelectric conversion layer is a layer that absorbs light and generates electron-hole pairs. In general, in a silicon-based thin film photoelectric conversion device, an i-type layer of a pin junction is a photoelectric conversion layer, and an i-type layer that is a photoelectric conversion layer occupies the main film thickness of the photoelectric conversion unit.

  The i-type layer is an intrinsic semiconductor layer that does not ideally contain a conductivity determining impurity. However, even if a small amount of impurities is included, if the Fermi level is in the middle of the forbidden band, it functions as a pin junction i-type layer, so this is called a “substantially i-type layer”. Generally, a substantially i-type layer is produced without adding a conductivity determining impurity to a source gas. In this case, a conductivity determining impurity may be included in an allowable range that functions as an i-type layer. Further, the substantially i-type layer may be formed by intentionally adding a small amount of conductivity-type determining impurities in order to remove the influence of impurities caused by the atmosphere or the underlayer on the Fermi level. Here, when an impurity that makes an i-type layer n-type is referred to as an n-type impurity, an i-type layer containing an n-type impurity within an allowable range that functions as an i-type layer is referred to as a weak n-type layer.

  As a method for improving the conversion efficiency of a photoelectric conversion device, a photoelectric conversion device employing a structure called a stacked 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 band width is disposed on the light incident side of the photoelectric conversion device, and a small optical forbidden band width is sequentially provided behind the photoelectric conversion unit (for example, silicon- By arranging a rear photoelectric conversion unit including a photoelectric conversion layer (such as a germanium alloy), it is possible to perform photoelectric conversion over a wide wavelength range of incident light, and improve the conversion efficiency of the entire device by effectively using incident light Is planned.

  For example, in the case of a two-junction thin film photoelectric conversion device in which an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are stacked, the wavelength of light that can be photoelectrically converted by i-type amorphous silicon is 700 nm on the long wavelength side. However, i-type crystalline silicon can photoelectrically convert light having a longer wavelength of about 1100 nm. Here, in the amorphous silicon photoelectric conversion layer made of amorphous silicon having a large light absorption coefficient, a thickness of about 0.3 μm is sufficient for light absorption sufficient for photoelectric conversion. The crystalline silicon photoelectric conversion layer made of crystalline silicon having a small light absorption coefficient preferably has a thickness of about 2 to 3 μm or more in order to sufficiently absorb long-wavelength light. That is, the crystalline silicon photoelectric conversion layer usually requires a film thickness about 10 times larger than that of the amorphous silicon photoelectric conversion layer. In the case of this two-junction thin film photoelectric conversion device, the photoelectric conversion unit on the light incident side is referred to as a top cell, and the photoelectric conversion unit on the rear side is referred to as a bottom cell.

  Further, a three-junction thin film photoelectric conversion device including three photoelectric conversion units is also used. In this specification, the photoelectric conversion units of the three-junction thin film photoelectric conversion device are referred to as a top cell, a middle cell, and a bottom cell in order from the light incident side. By using a three-junction stacked thin film photoelectric conversion device, the open-circuit voltage (Voc) is high, the short-circuit current density (Jsc) is low, and the amorphous silicon photoelectric conversion layer of the top cell is lower than in the case of two junctions. The film thickness can be reduced. For this reason, the optical deterioration of the top cell can be suppressed. Further, by making the optical forbidden band width of the photoelectric conversion layer of the middle cell narrower than that of the top cell and wider than that of the bottom cell, incident light can be used more effectively.

  As an example of a three-junction stacked thin film photoelectric conversion device, an amorphous silicon photoelectric conversion unit / amorphous silicon germanium photoelectric conversion unit / amorphous silicon germanium using amorphous silicon germanium for a photoelectric conversion layer of a middle cell Thin film photoelectric conversion devices stacked in the order of photoelectric conversion units, or thin film photoelectric conversion devices stacked in the order of amorphous silicon photoelectric conversion units / amorphous silicon germanium photoelectric conversion units / crystalline silicon photoelectric conversion units can be given. By appropriately adjusting the germanium concentration in the amorphous silicon germanium film, the optical band gap of amorphous silicon germanium in the photoelectric conversion layer of the middle cell can be controlled to a value between the top cell and the bottom cell. . Further, when an amorphous silicon germanium photoelectric conversion layer is used for both the middle cell and the bottom cell, the germanium concentration in the bottom cell is made higher than that in the middle cell.

  However, it is known that amorphous silicon germanium, which is an alloy layer, has a high defect density and inferior semiconductor characteristics as compared with amorphous silicon, and a large increase in defect density due to light irradiation. For this reason, a three-junction stacked thin film photoelectric conversion device using amorphous silicon germanium for the photoelectric conversion layer of the middle cell or the bottom cell is not sufficiently improved in efficiency as compared with the two-junction thin film photoelectric conversion device. Moreover, since amorphous silicon germanium has a large photodegradation, there is a problem that the photodegradation is not sufficiently suppressed even though a three-junction stacked thin film photoelectric conversion device is used.

  When the amorphous silicon germanium photoelectric conversion unit is used for the bottom cell, the wavelength of light that can be photoelectrically converted is about 900 nm on the long wavelength side, and the light that can be photoelectrically converted when the crystalline silicon photoelectric conversion unit is used for the bottom cell. The wavelength is up to about 1100 nm on the long wavelength side, and the limit of the usable wavelength on the long wavelength side is not improved at the same wavelength as the two-junction thin film photoelectric conversion device, and the conversion efficiency of the three-junction thin film photoelectric conversion device is improved. There are issues that are not enough.

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.
The terms “crystalline” and “microcrystalline” in the present invention also include a case where a partly amorphous material is used as used in the art.

  In order to improve the conversion efficiency of the thin film photoelectric conversion device, the present inventor has added a short-circuit current of a crystalline germanium photoelectric conversion unit, and in addition, the conventional silicon-based thin film photoelectric conversion device has a length exceeding 1000 nm. In order to efficiently photoelectrically convert light having a wavelength, a method for manufacturing a crystalline germanium photoelectric conversion device was studied. As a result, it was found that by exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma, long wavelength light exceeding 1000 nm can be efficiently photoelectrically converted in addition to the improvement of the short circuit current of the thin film photoelectric conversion device. .

  FIG. 1 is a schematic cross-sectional view of a single junction thin film photoelectric conversion device according to an example of an embodiment of the present invention. On the transparent substrate 1, the transparent electrode layer 2, the crystalline germanium photoelectric conversion unit 3, and the back electrode layer 4 are arranged in this order. In the present invention, the crystalline germanium photoelectric conversion unit 3 refers to a photoelectric conversion unit using a crystalline germanium photoelectric conversion layer 33 containing a substantially intrinsic or weak n-type crystalline germanium semiconductor in the photoelectric conversion layer.

  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. In particular, it is preferable to use a glass plate as the transparent substrate 1 because it has a high transmittance and is inexpensive.

  That is, since the transparent substrate 1 is located on the light incident side of the thin film photoelectric conversion device, it is preferable that the transparent substrate 1 be as transparent as possible so that more sunlight is transmitted and absorbed by the photoelectric conversion unit. From the same intention, it is preferable to provide a non-reflective coating on the light incident surface of the transparent substrate 1 in order to reduce the light reflection loss on the sunlight incident surface.

  The transparent electrode layer 2 is mentioned as a 1st electrode layer used with the photoelectric conversion apparatus of the type which injects light from a board | substrate side. In particular, the transparent electrode layer 2 is desirably transparent as much as possible in order to allow sunlight to pass through and be absorbed by the photoelectric conversion unit, and in order to transport holes generated in the photoelectric conversion unit without loss, it is conductive. It is desirable to have

Therefore, the transparent electrode layer 2 is preferably made of a conductive metal oxide such as tin oxide (SnO ₂ ) or zinc oxide (ZnO). For example, a method such as chemical vapor deposition (CVD), sputtering, or vapor deposition is used. Preferably it is formed. The transparent electrode layer 2 desirably has an effect of increasing the scattering of incident light by having a fine uneven shape on the surface thereof.

  The crystalline germanium photoelectric conversion unit 3 is formed by laminating a p-type semiconductor layer 31, a first interface layer 32, a crystalline germanium photoelectric conversion layer 33, a second interface layer 35, and an n-type semiconductor layer 34 in this order, for example, by plasma CVD. Formed. Here, the first interface layer 32 and the second interface layer 35 are preferably arranged because of the effect of reducing the leakage current in the crystalline germanium photoelectric conversion layer. It may be a crystalline germanium photoelectric conversion unit that does not contain any.

  The step of being exposed to the hydrogen gas plasma is included in the step of forming the crystalline germanium photoelectric conversion unit 3. For example, when the first interface layer 32 is exposed to hydrogen gas plasma after being stacked, the crystalline germanium photoelectric conversion layer 33 is stacked after the surface portion of the first interface layer 32 is exposed to hydrogen plasma. The step of exposing to hydrogen gas plasma includes any of the P-type semiconductor layer 31, the first interface layer 32, the crystalline germanium photoelectric conversion layer 33, the second interface layer 35, and the n-type semiconductor layer 34 in the crystalline germanium photoelectric conversion unit. It may be introduced after the laminating step, or may be introduced during the laminating step in each layer.

  The hydrogen gas plasma is preferably generated by high frequency plasma CVD using hydrogen gas. The hydrogen gas to be used preferably has a hydrogen gas purity of 99.99% or higher, and oxygen or dioxide dioxide is used in order not to dope elements other than hydrogen into a part of the thin film photoelectric conversion unit exposed to the hydrogen gas plasma. Preferably it does not contain carbon.

In order to generate hydrogen gas plasma uniformly over a large area by plasma CVD, it is preferable to use a capacitively coupled parallel plate electrode and a frequency of 10 to 100 MHz rather than using a microwave frequency such as 2.45 GHz. desirable. In particular, it is preferable to use 13.56 MHz, 27.12 Mz, and 40 MHz that are approved for industrial use. The high frequency power density is preferably 50 mW / cm ² or more, and more preferably 150 mW / cm ² or more in order to promote crystallization. The substrate temperature when a part of the photoelectric conversion unit is exposed to hydrogen gas plasma is preferably 120 ° C. or higher, more preferably 150 ° C. or higher in order to promote crystallization by hydrogen gas plasma. In order to suppress the diffusion of impurities from the conductive layer to the photoelectric conversion layer, the substrate temperature is preferably 250 ° C. or lower, and more preferably 230 ° C. or lower.

  Moreover, the pressure at the time of exposing a photoelectric conversion unit to hydrogen gas plasma has the preferable range of 40 Pa or more and 2000 Pa or less from a viewpoint of promoting crystallization of the photoelectric conversion unit to expose. Moreover, 200 Pa or more and 1500 Pa or less are more preferable from a viewpoint of improving the uniformity of discharge in a large area.

  The p-type semiconductor layer 31 is formed of at least one of crystalline silicon doped with p-type impurities, amorphous silicon, crystalline silicon germanium, amorphous silicon germanium, crystalline germanium, and amorphous germanium. Can be done. Moreover, the same film forming apparatus as the crystalline germanium photoelectric conversion layer 33 can be used. In particular, as the p-type semiconductor layer 31, it is preferable to use microcrystalline silicon doped with 0.01 atomic% or more of boron. It is more preferable that the p-type semiconductor layer 31 is made of microcrystalline silicon because the movement of holes from the crystalline germanium photoelectric conversion layer 33 to the p-type semiconductor layer 31 is lubricated.

  Crystalline germanium has an optical forbidden band width of 0.65 eV, which is narrower than 1.8 eV of amorphous silicon and 1.1 eV of crystalline silicon. Therefore, when crystalline germanium is used for the photoelectric conversion layer, Leakage current is likely to occur through defect levels and impurity levels in the optical forbidden band, which is considered to be a factor that significantly lowers the fill factor and open circuit voltage of the solar cell performance.

  This is a substantially genuine non-single-crystal silicon semiconductor layer disposed at the interface between the p-type semiconductor layer 31 and the crystalline germanium photoelectric conversion layer 33 in order to reduce the leakage current generated in the photoelectric conversion layer 33 by crystalline germanium. It is preferable to arrange the first interface layer 32. The first interface layer 32 preferably covers the entire surface of the P-type semiconductor layer 31.

The crystalline germanium photoelectric conversion layer 33 is desirably formed by a high frequency plasma CVD method using, for example, GeH ₄ or H ₂ as a reactive gas. At this time, the H ₂ / GeH ₄ ratio is desirably in the range of 200 to 5000. If the H ₂ / GeH ₄ ratio is smaller than 200, the crystallization rate tends to be reduced and the film tends to be amorphous. On the contrary, if the H ₂ / GeH ₄ ratio is larger than 5000, the film forming speed decreases. Productivity tends to decrease. In order to obtain good crystallinity and an industrially acceptable film forming speed, it is more desirable to set the H ₂ / GeH ₄ ratio in the range of 500 to 2000.

  The flow rate of the film-forming gas when passing through the shower plate when forming the crystalline germanium photoelectric conversion layer 33 is preferably 0.1 or more and 10 m / s or less. When the flow rate of the film-forming gas is 0.1 m / s or less, the reactive gas is decomposed to active species having high reactivity in the plasma, and the film density on the substrate becomes sparse. When the flow rate of the film-forming gas is 10 m / s or more, the rate at which the reaction gas is decomposed in the plasma is reduced, and unevenness occurs in the film formation on the substrate. Here, the flow rate indicates a flow rate at a pressure during film formation. The flow rate can be obtained by dividing the volume flow rate of the pressure in the film forming chamber by the total area of the holes in the shower plate.

In order to uniformly form the crystalline germanium photoelectric conversion layer 33 in a large area by the plasma CVD method, a capacitively coupled parallel plate electrode is used rather than a microwave frequency such as 2.45 GHz, and a frequency of 10 to 100 MHz is used. It is desirable to use frequency. In particular, it is preferable to use 13.56 MHz, 27.12 Mz, and 40 MHz that are approved for industrial use. RF power density, 200 mW / cm ² or more is desirable Shi properly in order to promote crystallization, it is more desirable to 550 mW / cm ² or more.

  The substrate temperature when the crystalline germanium photoelectric conversion layer 33 is formed is preferably 120 ° C. or higher and more preferably 150 ° C. or higher in order to suppress the generation of powder during film formation. In order to suppress the diffusion of impurities from the conductive layer to the photoelectric conversion layer, the substrate temperature is preferably 250 ° C. or lower, and more preferably 230 ° C. or lower.

  Moreover, the pressure at the time of forming the crystalline germanium photoelectric conversion layer 33 is preferably in the range of 40 Pa to 2000 Pa from the viewpoint of having good crystallinity. Moreover, 200 Pa or more and 1500 Pa or less are more preferable from a viewpoint of improving the uniformity of a large area. Furthermore, 500 Pa or more and 1330 Pa or less is more preferable in achieving both crystallinity and a high film forming speed.

  The crystalline germanium photoelectric conversion layer 33 preferably does not contain silicon atoms. Here, “does not contain silicon atoms” means that the measurement limit is approximately when measurement is performed using any of X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and Auger electron spectroscopy. It means that it is 1% or less. Since the crystalline germanium photoelectric conversion layer 33 does not contain silicon atoms, surprisingly, the crystallinity is improved as compared with silicon germanium, and the absorption coefficient of a long wavelength can be improved.

In addition, as a method for obtaining a crystal volume fraction having a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer, the crystalline germanium photoelectric conversion layer is stacked by 50 nm when the crystalline germanium photoelectric conversion unit is stacked on the substrate. At that time, the substrate can be taken out from the CVD apparatus, and can be calculated from the Raman spectrum measured by light incidence from the surface of the crystalline germanium photoelectric conversion layer. In the obtained Raman spectrum, a peak derived from crystalline germanium is observed near 300 cm ⁻¹ and a broad peak derived from amorphous germanium is observed near 280 cm ⁻¹ . These two peaks are divided into peaks, and the ratio of the peak area intensity derived from crystalline germanium to the area intensity of the entire peak (peak area intensity derived from crystalline germanium / (peak area intensity derived from crystalline germanium + amorphous germanium The crystal volume fraction is calculated from the derived peak area intensity)).

  In addition, as a method for obtaining a crystal volume fraction having a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer, there is a method of observing a transmission electron microscope image of a cross section of the thin film photoelectric conversion device. About 200 nm to 500,000 times are taken in a transmission electron microscope (TEM) cross-sectional image about 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer, and the ratio of the crystalline germanium phase to the amorphous germanium phase is determined. It can be confirmed. In particular, when a dark field image is taken, the portion that appears bright is a crystalline phase, so that a crystalline germanium phase can be easily confirmed.

Crystalline germanium photoelectric conversion layer 33 is preferably an absorption coefficient of infrared absorption peak at a wavenumber of 935 ± 5 cm ^-1 is less than 0 cm ^-1 or more 6000 cm ^-1, preferably less than 0 cm ^-1 or more 5000 cm ^-1, more preferably less than 10 cm ^-1 or more 2500 cm ^-1. Although the origin of the infrared absorption peak with a wave number of 935 ± 5 cm ⁻¹ has not been identified, it is thought to be derived from polymer or cluster-like germanium hydride or germanium oxide. It is estimated that crystalline germanium is formed and the characteristics of the thin film photoelectric conversion device are improved.
It is preferable that the absorption coefficient of the infrared absorption peak at a wavenumber of 960 ± 5 cm ^-1 is less than 0 cm ^-1 or more 3500 cm ^-1, more preferably less than 0 cm ^-1 or more 3000 cm ^-1, 10 cm ^-1 or more More preferably, it is less than 1300 cm ⁻¹ . The origin of the infrared absorption peak at 960 ± 5 cm ^-1 has not been identified, but it is thought to be derived from polymer or clustered germanium hydride or germanium oxide as described above, and this infrared absorption peak should be kept small. Thus, it can be said that dense crystalline germanium is formed, and the characteristics of the thin film photoelectric conversion device are improved.

  The infrared absorption spectrum can be measured by FTIR (Fourier Transform Infrared Spectroscopy). For example, an infrared absorption spectrum can be obtained by the following procedure. (1) A film is formed on a crystalline silicon substrate having a high resistance of 1 Ω · cm or more under the same film forming conditions as the photoelectric conversion layer, and an infrared transmission spectrum is measured. (2) Divide the transmittance of the sample by the transmittance of the crystalline silicon substrate without the film to obtain the transmission spectrum of only the crystalline germanium film. (3) Since the transmission spectrum obtained in (2) includes the influence of interference and offset, the base line is drawn by connecting non-absorption areas, and divided by the base line transmittance. (4) Finally, the absorption coefficient α is obtained by the following equation.

  The crystalline germanium photoelectric conversion layer 33 preferably has an intensity ratio of (220) peak and (111) peak measured by X-ray diffraction of 2 or more. (220) The crystalline germanium forms columnar crystals in the direction perpendicular to the substrate due to the strengthening of the (220) orientation, the crystal size in the film thickness direction increases, and the photoelectric conversion current easily flows, so that the thin film photoelectric conversion device Improved characteristics.

  The crystalline germanium photoelectric conversion layer 33 preferably has a refractive index of 4.0 or more with respect to light having a wavelength of 600 nm. More preferably, the refractive index for light with a wavelength of 600 nm is 4.7 or more. This is because when the refractive index with respect to light having a wavelength of 600 nm is 4.0 or more, dense crystalline germanium is formed, and it becomes possible to use long wavelength light having a wavelength of 1000 nm or more.

  The film thickness of the crystalline germanium photoelectric conversion layer 33 is preferably 50 nm or more and 1000 nm or less. The film thickness of the crystalline germanium photoelectric conversion layer 33 can be confirmed from an image observed with a transmission electron microscope. Since the crystalline germanium photoelectric conversion layer 33 has a high absorption coefficient, the film thickness of the crystalline germanium photoelectric conversion layer 33 is the same regardless of whether the crystalline germanium photoelectric conversion layer 33 is used for a single junction thin film photoelectric conversion device or a multijunction thin film photoelectric conversion device. The short-circuit current and the long wavelength light of 900 nm or more can be efficiently photoelectrically converted at 50 nm or more and 1000 nm or less. Moreover, when the film thickness is 1000 nm or less, there is an advantage that not only the film forming time is shortened but also the cost is lowered.

  Moreover, it is preferable to arrange | position the 2nd interface layer 35 which consists of a substantially intrinsic non-single-crystal silicon semiconductor layer in the interface of the n-type semiconductor layer 34 and the crystalline germanium photoelectric converting layer 33. FIG. Specifically, crystalline silicon or amorphous silicon can be used for the second interface layer 35. Furthermore, as shown in FIG. 3, the second interface layer 35 preferably has a structure in which a substantially intrinsic crystalline silicon layer and a substantially intrinsic amorphous silicon layer are laminated. In particular, a layer in which a substantially intrinsic amorphous silicon layer 352 and a substantially intrinsic crystalline silicon layer 351 are arranged in this order from the side closer to the n-type semiconductor layer 34 is preferable. This is considered to be due to the function of reducing the defect density at the bonding interface and suppressing current loss due to recombination of electrons and holes. The film thickness of the substantially intrinsic crystalline silicon layer 351 in the second interface layer 35 is preferably in the range of 0.5 nm to 500 nm. In particular, the film thickness is more preferably in the range of 1 nm to 100 nm. The film thickness of the substantially intrinsic amorphous silicon layer 352 in the second interface layer 35 is preferably in the range of 0.1 nm to 100 nm. In particular, a film thickness in the range of 0.5 nm to 50 nm is more preferable.

  Next, the n-type semiconductor layer 34 includes at least one of crystalline silicon, amorphous silicon, crystalline silicon germanium, amorphous silicon germanium, crystalline germanium, and amorphous germanium doped with an n-type impurity. It is preferable to form from two or more. By using any one of these layers, the crystalline germanium photoelectric conversion layer 33 and the junction can be suitably formed. Moreover, the same film forming apparatus as the crystalline germanium photoelectric conversion layer 33 can be used. For example, doped microcrystalline silicon doped with 0.01 atomic% or more of phosphorus can be used. As the n-type semiconductor layer, an amorphous silicon layer 341 is preferable to a crystalline silicon layer. This is because the optical forbidden band width of the amorphous silicon layer is wider than that of the crystalline silicon layer, so that the diffusion of holes from the crystalline germanium photoelectric conversion layer 33 to the n-type semiconductor layer is suppressed, This is considered to be due to the function of preventing recombination in the n-type semiconductor layer.

  The back electrode layer 4 is mentioned as a 2nd electrode layer used for the photoelectric conversion apparatus of the type which injects light from a board | substrate side. The back electrode layer 4 has a function of increasing the absorption efficiency of sunlight in the photoelectric conversion layer by reflecting sunlight transmitted through the photoelectric conversion unit to the photoelectric conversion unit side. Therefore, it is desirable that the back electrode layer 4 has a high reflectance with respect to sunlight. Moreover, in order to transport the electron which generate | occur | produced in the photoelectric conversion unit without loss, it is desirable to have electroconductivity.

Therefore, as the back electrode layer 4, at least one layer made of at least one material selected from aluminum (Al), silver (Ag), gold (Au), copper (Cu), platinum (Pt) and chromium (Cr). The metal layer is preferably formed by sputtering or vapor deposition. Between the photoelectric conversion unit and the metal layer, ITO, may be formed a layer made of SnO _2, conductive oxides such as ZnO (not shown).

  FIG. 2 is a cross-sectional view schematically illustrating a three-junction thin film photoelectric conversion device according to another embodiment of the present invention. This thin film photoelectric conversion device includes an amorphous silicon photoelectric conversion unit 5 and a crystalline silicon photoelectric conversion unit 6 between the transparent electrode layer 2 and the crystalline germanium photoelectric conversion unit 3 of the single junction thin film photoelectric conversion device of FIG. The structure is arranged sequentially. That is, in order from the light incident side, the amorphous silicon photoelectric conversion unit corresponds to the top cell, the crystalline silicon photoelectric conversion unit corresponds to the middle cell, and the crystalline germanium photoelectric conversion unit corresponds to the bottom cell. In this configuration, when the crystalline germanium photoelectric conversion unit has a bottom cell deposition temperature lower than 250 ° C, the amorphous silicon photoelectric conversion unit is the top cell and the crystalline silicon photoelectric conversion unit is heated to the middle cell. As a result, the performance of the three-junction thin film photoelectric conversion device can be improved.

  The substrate 1, the transparent electrode layer 2, the crystalline germanium photoelectric conversion unit 3 as the bottom cell, and the back electrode layer can be formed by the same configuration and manufacturing method as in FIG. However, the film thickness of the crystalline germanium photoelectric conversion layer 33 is appropriately adjusted so as to substantially match the spectral sensitivity currents of the top cell 5 and the middle cell 6.

  The amorphous silicon photoelectric conversion unit 5 that is a top cell is formed by stacking, for example, a p-type semiconductor layer, an i-type layer, and an n-type semiconductor layer in this order. Specifically, p-type amorphous silicon carbide layer 51 doped with 0.01 atomic% or more of boron, photoelectric conversion layer 52 of substantially i-type amorphous silicon, and 0.01 atomic% of phosphorus. The n-type amorphous silicon layer 53 thus doped is deposited in this order.

  The crystalline silicon photoelectric conversion unit 6 that is a middle cell is formed by stacking, for example, a p-type semiconductor layer, an i-type layer, and an n-type semiconductor layer in this order. Specifically, p-type microcrystalline silicon layer 61 doped with boron at 0.01 atomic% or more, substantially i-type crystalline silicon photoelectric conversion layer 62, and phosphorus doped at 0.01 atomic% or more. An n-type microcrystalline silicon layer 63 is deposited in this order.

  In FIG. 2, a three-junction thin film photoelectric conversion device is shown. However, if a crystalline germanium photoelectric conversion unit is arranged in the photoelectric conversion unit farthest from the light incident side, two or more junction photoelectric conversion units are stacked. Needless to say, the thin film photoelectric conversion device may be used.

  Although FIG. 1 shows a thin film photoelectric conversion device in which light is incident from the substrate side, it goes without saying that the present invention is also effective in a thin film photoelectric conversion device in which light is incident from the opposite side of the substrate. When light is incident from the side opposite to the substrate, for example, the substrate, the back electrode layer, the crystalline germanium photoelectric conversion unit, and the transparent electrode layer may be stacked in this order. In this case, the crystalline germanium photoelectric conversion unit is preferably stacked in the order of the n-type semiconductor layer, the crystalline germanium photoelectric conversion layer, and the p-type semiconductor layer. In the thin film photoelectric conversion device in which light is incident from the side opposite to the substrate, the first electrode layer is a back electrode layer, and the second electrode layer is a transparent electrode layer.

  Needless to say, the present invention is also effective in an integrated thin film photoelectric conversion device in which a series connection structure is formed on the same substrate using laser patterning. In the case of an integrated thin film photoelectric conversion device, laser patterning can be easily performed. Therefore, a structure in which light is incident from the substrate side as shown in FIG. 1 is desirable.

  Further, in the case of integration, it is preferable to arrange the p-type layer, the photoelectric conversion layer, and the n-type layer in order in accordance with the structure in which light is incident from the substrate side. This is because in a thin film photoelectric conversion device, since the mobility of holes is shorter than that of electrons, the conversion efficiency is higher when the p-type layer is arranged on the light incident side.

  Hereinafter, examples according to the present invention and comparative examples according to the prior art will be described in detail. 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
As Example 1, a single-junction thin-film photoelectric conversion device 7 having the structure shown in FIG. In Example 1, the step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced immediately before the step of laminating the crystalline germanium photoelectric conversion layer. As the transparent substrate 1, a glass substrate having a thickness of 1.8 mm was used. On the transparent substrate 1, the transparent electrode layer 2 as the first electrode layer was formed. The transparent electrode layer 2 was formed on the transparent substrate 1 by a thermal CVD method with a SnO ₂ film having minute pyramidal surface irregularities and an average thickness of 700 nm. Further, an Al-doped ZnO film having a thickness of 20 nm was formed by sputtering to produce a transparent electrode layer 2 in which SnO ₂ and ZnO were laminated. The sheet resistance of the obtained transparent electrode layer 2 was about 9Ω / □. The haze ratio measured with a C light source was 14%, and the average height difference d of the surface irregularities was about 100 nm. The haze ratio was measured based on JISK7136.

A crystalline germanium photoelectric conversion unit 3 was produced on the transparent electrode layer 2 using a capacitively coupled high-frequency plasma CVD apparatus provided with parallel plate electrodes having a frequency of 13.56 MHz. A step of exposing part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced immediately before the step of laminating the crystalline germanium photoelectric conversion layer. First, SiH ₄ , H ₂ and B ₂ H ₆ were introduced as reaction gases to form a p-type microcrystalline silicon layer 311 with a thickness of 10 nm. Thereafter, SiH ₄ and H ₂ were introduced as reaction gases, and a substantially intrinsic crystalline silicon layer 321 was laminated to 20 nm as the first interface layer 32, and further a substantially intrinsic amorphous silicon layer 322 was formed to 10 nm. . Subsequently, the first interface layer 32 was exposed to hydrogen gas plasma. At this time, hydrogen gas was introduced into the CVD apparatus, and hydrogen plasma was generated for 10 minutes at a substrate temperature of 230 ° C., a pressure of 1330 Pa, and a high frequency power density of 280 mW / cm ² . Thereafter, GeH ₄ and H ₂ were introduced to form a crystalline germanium photoelectric conversion layer 33 having a thickness of 500 nm. At this time, the flow rate ratio of H ₂ / GeH ₄ was 2700 times, the substrate temperature was 230 ° C., the pressure was 930 Pa, and the high frequency power density was 850 mW / cm ² . SiH ₄ and H ₂ were introduced as reaction gases, and as the second interface layer 35, a crystalline silicon layer 351 was laminated to 20 nm, and an amorphous silicon layer 352 was further formed to 10 nm. Subsequently, SiH ₄ , H ₂ and PH ₃ were introduced as reaction gases to form an n-type amorphous silicon layer 341 with a thickness of 10 nm, thereby forming a crystalline germanium photoelectric conversion unit 3.

  Thereafter, the back electrode layer 4 was formed as the second electrode layer. The back electrode layer 4 was formed by sputtering a 30 nm thick Al-doped ZnO film and a 300 nm thick Ag film by sputtering.

After the back electrode layer 4 is formed, the film formed on the transparent electrode layer 1 is partially removed by laser scribing and separated into a size of 1 cm ² , and a single junction thin film photoelectric conversion device 7 (light receiving area) 1 cm ² ) was produced.

When the output characteristics were measured by irradiating the single-junction thin-film photoelectric conversion device 7 (light-receiving area 1 cm ² ) obtained as described above with light of AM 1.5 at a light amount of 100 mW / cm ² , the implementation shown in Table 1 was performed. As shown in Example 1, the open circuit voltage (Voc) is 0.28 V, the short circuit current density (Jsc) is 23.0 mA / cm ² , the fill factor (FF) is 0.59, and the conversion efficiency (Eff) is 3.73. %Met. The quantum efficiency at a wavelength of 1000 nm was 26%.

(Example 2)
As Example 2, a single-junction thin film photoelectric conversion device 8 similar to Example 1 shown in FIG. In Example 2, a step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced during the stacking step of the crystalline germanium photoelectric conversion layer. Example 1 except that the crystalline germanium photoelectric conversion layer was deposited to a thickness of 5 nm and then subjected to the same step of exposure to hydrogen gas plasma as in Example 1, and then the crystalline germanium photoelectric conversion layer was deposited to a thickness of 490 nm. It produced similarly. The step of exposing to hydrogen gas plasma was not performed immediately before the laminating step of the crystalline germanium photoelectric conversion layer performed in Example 1.

When the single junction thin film photoelectric conversion device 8 (light receiving area 1 cm ² ) obtained as described above was irradiated with AM1.5 light at a light amount of 100 mW / cm ² , the output characteristics were measured. As shown in Example 2, the open circuit voltage (Voc) is 0.31 V, the short circuit current density (Jsc) is 29.4 mA / cm ² , the fill factor (FF) is 0.60, and the conversion efficiency (Eff) is 5. It was 47%. The quantum efficiency at a wavelength of 1000 nm was 32%.

(Example 3)
As Example 3, a single-junction thin film photoelectric conversion device 9 similar to Example 1 shown in FIG. In Example 3, a step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced during the stacking step of the crystalline germanium photoelectric conversion layer. Example 1 Except that the crystalline germanium photoelectric conversion layer was laminated to a thickness of 40 nm and then subjected to the same step of exposure to hydrogen gas plasma as in Example 1, and then the crystalline germanium photoelectric conversion layer was laminated to a thickness of 460 nm. It produced similarly. The step of exposing to hydrogen gas plasma was not performed immediately before the laminating step of the crystalline germanium photoelectric conversion layer performed in Example 1.

When the output characteristics were measured by irradiating the single junction thin film photoelectric conversion device 9 (light-receiving area 1 cm ² ) obtained as described above with AM 1.5 light at a light quantity of 100 mW / cm ² , the implementation shown in Table 1 was performed. As shown in Example 3, the open circuit voltage (Voc) is 0.32 V, the short circuit current density (Jsc) is 33.8 mA / cm ² , the fill factor (FF) is 0.61, and the conversion efficiency (Eff) is 6. 66%. The quantum efficiency at a wavelength of 1000 nm was 37%.

Example 4
As Example 4, a single-junction thin film photoelectric conversion device 10 similar to Example 1 shown in FIG. In Example 4, a step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced during the stacking step of the crystalline germanium photoelectric conversion layer. Example 1 except that the crystalline germanium photoelectric conversion layer was deposited to a thickness of 100 nm and then subjected to the same step of exposure to hydrogen gas plasma as in Example 1, and then the crystalline germanium photoelectric conversion layer was laminated to a thickness of 400 nm. It produced similarly. The step of exposing to hydrogen gas plasma was not performed immediately before the laminating step of the crystalline germanium photoelectric conversion layer performed in Example 1.

When the output characteristics were measured by irradiating the single-junction thin-film photoelectric conversion device 10 (light-receiving area 1 cm ² ) obtained as described above with AM 1.5 light at a light amount of 100 mW / cm ² , the implementation shown in Table 1 was performed. As shown in Example 4, the open circuit voltage (Voc) is 0.30 V, the short circuit current density (Jsc) is 27.1 mA / cm ² , the fill factor (FF) is 0.59, and the conversion efficiency (Eff) is 4. 80%. The quantum efficiency at a wavelength of 1000 nm was 26%.

(Example 5)
As Example 5, a single-junction thin film photoelectric conversion device 11 similar to Example 1 shown in FIG. In Example 5, a step of exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced immediately after the laminating step of the crystalline germanium photoelectric conversion layer. A crystalline germanium photoelectric conversion layer was produced in the same manner as in Example 1 except that a step of exposing to a hydrogen gas plasma similar to that in Example 1 was performed after laminating 500 nm. The step of exposing to hydrogen gas plasma was not performed immediately before the laminating step of the crystalline germanium photoelectric conversion layer performed in Example 1.

When the output characteristics were measured by irradiating the single junction thin film photoelectric conversion device 11 (light receiving area 1 cm ² ) obtained as described above with AM 1.5 light at a light quantity of 100 mW / cm ² , the implementation shown in Table 1 was performed. As shown in Example 5, the open circuit voltage (Voc) is 0.34 V, the short circuit current density (Jsc) is 26.6 mA / cm ² , the fill factor (FF) is 0.64, and the conversion efficiency (Eff) is 5. It was 84%. The quantum efficiency at a wavelength of 1000 nm was 27%.

(Example 6)
As Example 6, a single-junction thin-film photoelectric conversion device 12 similar to Example 1 shown in FIG. In Example 6, the step of exposing part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced four times during the step of laminating the crystalline germanium photoelectric conversion layer. A crystalline germanium photoelectric conversion layer was produced in the same manner as in Example 1 except that the step of exposing to hydrogen gas plasma was performed in the same manner as in Example 1 when the film thickness was 40 nm, 100 nm, 200 nm, and 400 nm. The step of exposing to hydrogen gas plasma was not performed immediately before the laminating step of the crystalline germanium photoelectric conversion layer performed in Example 1.

When the output characteristics were measured by irradiating AM1.5 light with a light amount of 100 mW / cm ² to the single-junction thin-film photoelectric conversion device 12 (light-receiving area 1 cm ² ) obtained as described above, the results shown in Table 1 were obtained. As shown in Example 6, the open circuit voltage (Voc) is 0.26 V, the short circuit current density (Jsc) is 24.9 mA / cm ² , the fill factor (FF) is 0.55, and the conversion efficiency (Eff) is 3. 55%. The quantum efficiency at a wavelength of 1000 nm was 28%.

(Comparative Example 1)
As Comparative Example 1, a single-junction thin-film photoelectric conversion device 13 similar to Example 1 shown in FIG. Comparative Example 1 was produced in the same manner as in Example 1 except that the step of exposing part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was not performed.

When a single junction thin film photoelectric conversion device 13 (light-receiving area 1 cm ² ) obtained as described above was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² , the output characteristics were measured. As shown in Example 1, the open circuit voltage (Voc) is 0.30 V, the short circuit current density (Jsc) is 19.6 mA / cm ² , the fill factor (FF) is 0.60, and the conversion efficiency (Eff) is 3. 53%. The quantum efficiency at a wavelength of 1000 nm was 15%.

(Example 7)
As Example 7, a single-junction thin-film photoelectric conversion device 14 similar to Example 1 shown in FIG. Example 7 was produced in the same manner as Example 1 except that a step of exposing part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma was introduced immediately after the step of laminating the second interface layer. The step of exposing to hydrogen gas plasma was not performed immediately before the laminating step of the crystalline germanium photoelectric conversion layer performed in Example 1.

The single junction thin film photoelectric conversion device 14 (light-receiving area 1 cm ² ) obtained as described above was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² , and the output characteristics were measured. As shown in Example 7, the open circuit voltage (Voc) is 0.30 V, the short circuit current density (Jsc) is 25.8 mA / cm ² , the fill factor (FF) is 0.66, and the conversion efficiency (Eff) is 5. 19%. The quantum efficiency at a wavelength of 1000 nm was 25%.

(Example 8)
As Example 8, a three-junction thin film photoelectric conversion device 15 shown in FIG. In Example 8, (1) an amorphous silicon photoelectric conversion unit 5 and a crystalline silicon photoelectric conversion unit 6 were sequentially disposed between the transparent electrode layer 2 and the crystalline germanium photoelectric conversion unit 3 of Example 3, ( 2) The film thickness of the crystalline germanium photoelectric conversion layer 33 is 1 μm, (3) the transparent electrode layer 2 is made of only SnO ₂ , and (4) the step of exposing to hydrogen gas plasma is performed by crystalline germanium photoelectric After the conversion layer is deposited to a thickness of 40 nm, the same step as that of Example 1 is performed to expose to hydrogen gas plasma, and then the crystalline germanium photoelectric conversion layer is deposited to a thickness of 960 nm, except for the four points. It produced similarly.

Only SnO ₂ was formed as the transparent electrode layer 2 on the transparent substrate 1.

An amorphous silicon photoelectric conversion unit 5 was produced on the transparent electrode layer 2 using a plasma CVD apparatus. SiH ₄ , H ₂ , CH ₄ and B ₂ H ₆ are introduced as a reaction gas to form a p-type amorphous silicon carbide layer 51 having a thickness of 15 nm, and SiH ₄ is introduced as a reaction gas to form substantially intrinsic amorphous silicon. The amorphous silicon photoelectric conversion unit 5 was formed by forming the photoelectric conversion layer 52 with a thickness of 80 nm, and then introducing SiH ₄ , H _2, and PH ₃ as reaction gases to form the n-type amorphous silicon layer 53 with a thickness of 10 nm.

After the amorphous silicon photoelectric conversion unit 5 is formed, SiH ₄ , H ₂ and B ₂ H ₆ are introduced as reaction gases to form a p-type microcrystalline silicon layer 61 having a thickness of 10 nm, and then SiH ₄ and H ₂ are introduced as reaction gases. A substantially intrinsic crystalline silicon photoelectric conversion layer 62 is formed to a thickness of 1.5 μm, and then SiH ₄ , H ₂ and PH ₃ are introduced as reaction gases to form an n-type microcrystalline silicon layer 63 having a thickness of 15 nm. A photoelectric conversion unit 6 was formed.

  After the crystalline silicon photoelectric conversion unit 6 was formed, the crystalline germanium photoelectric conversion unit 3 and the back electrode layer 4 were sequentially formed.

When the output characteristics were measured by irradiating the 3-junction thin-film photoelectric conversion device 15 (light-receiving area 1 cm ² ) obtained as described above with AM1.5 light at a light quantity of 100 mW / cm ² , the open circuit voltage (Voc) was measured. ) Was 1.68 V, the short circuit current density (Jsc) was 11.2 mA / cm ² , the fill factor (FF) was 0.75, and the conversion efficiency (Eff) was 14.1%.

(Comparative Example 2)
As Comparative Example 2, a three-junction thin film photoelectric conversion device 16 shown in FIG. Comparative Example 2 was produced in the same manner as Example 8 except that crystalline germanium photoelectric conversion unit 3 was produced in the same manner as Comparative Example 1.

When the output characteristics were measured by irradiating the three-junction thin-film photoelectric conversion device 16 (light-receiving area 1 cm ² ) obtained as described above with AM 1.5 light at a light amount of 100 mW / cm ² , the open circuit voltage (Voc) was measured. ) Was 1.65 V, the short circuit current density (Jsc) was 7.2 mA / cm ² , the fill factor (FF) was 0.73, and the conversion efficiency (Eff) was 8.67%.

(Comparative Example 3)
As Comparative Example 3, a two-junction thin film photoelectric conversion device 17 shown in FIG. Comparative Example 3 was produced in the same manner as Example 4 except that the crystalline germanium photoelectric conversion unit 3 was removed.

When the output characteristics were measured by irradiating AM1.5 light with a light amount of 100 mW / cm ² to the two-junction thin film photoelectric conversion device 17 (light receiving area 1 cm ² ) obtained as described above, the open circuit voltage (Voc) was measured. ) Was 1.38 V, the short circuit current density (Jsc) was 11.5 mA / cm ² , the fill factor (FF) was 0.72, and the conversion efficiency (Eff) was 11.4%.

Example 9
As Example 9, the semiconductor laminated film 18 shown in FIG. In Example 9, the crystalline germanium photoelectric conversion layer was stacked up to 50 nm in the stacking step shown in Example 3, and then taken out from the CVD apparatus and subjected to Raman spectroscopic measurement. A Raman spectrometer (manufactured by JASCO Corporation) equipped with a He—Ne laser having a wavelength of 633 nm was used to measure the Raman light by making light incident from the film surface. In the obtained Raman spectrum (FIG. 7), a peak derived from crystalline germanium near 300 cm ⁻¹ and a peak derived from amorphous germanium near 280 cm ⁻¹ were observed. The crystal volume fraction was determined from the peak area. As a result, the crystal volume fraction was estimated to be 5.4%.

(Comparative Example 4)
As Comparative Example 4, a semiconductor laminated film 19 shown in FIG. Comparative Example 4 is performed up to the point where the crystalline germanium photoelectric conversion layer is laminated to 50 nm among the lamination steps shown in Comparative Example 1, and is taken out of the CVD apparatus without performing the step of exposing to hydrogen gas plasma, and the Raman spectroscopic measurement is performed. It was. A Raman spectrometer (manufactured by JASCO Corporation) equipped with a He—Ne laser having a wavelength of 633 nm was used to measure the Raman light by making light incident from the film surface. In the obtained Raman spectrum (FIG. 7), a peak derived from crystalline germanium near 300 cm ⁻¹ and a peak derived from amorphous germanium near 280 cm ⁻¹ were observed. The crystal volume fraction was determined from the peak area. As a result, the crystal volume fraction was estimated to be 1.8%.

  FIG. 7 shows the Raman spectrum of the sample subjected to the exposure to hydrogen gas plasma (Example 9) and the sample not subjected to the exposure to hydrogen gas plasma (Comparative Example 4). As is clear from FIG. 7, when the crystalline germanium photoelectric conversion layer is exposed to hydrogen gas, the peak near 300 cm −1 derived from crystalline germanium is increased. This indicates that the step of exposing to hydrogen gas plasma is effective in improving the crystallinity of the crystalline germanium photoelectric conversion layer.

1. Transparent substrate 2. Transparent electrode layer Crystalline germanium photoelectric conversion unit 31. P-type semiconductor layer 311. P-type microcrystalline silicon layer 32. First interface layer 321. A substantially authentic crystalline silicon layer 322. Substantially intrinsic amorphous silicon layer 33. Crystalline germanium photoelectric conversion layer 34. n-type semiconductor layer 341. n-type amorphous silicon layer 35. Second interface layer 351. A substantially intrinsic crystalline silicon layer 352. 3. A substantially intrinsic amorphous silicon layer 4. Back electrode layer Amorphous silicon photoelectric conversion unit 51. p-type amorphous silicon carbide layer 52. Substantially i-type amorphous silicon photoelectric conversion layer 53. n-type amorphous silicon layer 6. Crystalline silicon photoelectric conversion unit 61. p-type microcrystalline silicon layer 62. Substantially i-type crystalline silicon photoelectric conversion layer 63. 6. n-type microcrystalline silicon layer 7. Single-junction thin-film photoelectric conversion device described in Example 1. 8. Single-junction thin film photoelectric conversion device described in Example 2 9. Single-junction thin-film photoelectric conversion device described in Example 3 10. Single-junction thin film photoelectric conversion device described in Example 4 11. Single-junction thin-film photoelectric conversion device described in Example 5 12. Single-junction thin-film photoelectric conversion device described in Example 6. 15. Single-junction thin film photoelectric conversion device described in Comparative Example 1. 15. Single-junction thin-film photoelectric conversion device described in Example 7. 15. Three-junction thin film photoelectric conversion device described in Example 8 16. Three-junction thin film photoelectric conversion device described in Comparative Example 2 18. Two-junction thin film photoelectric conversion device described in Comparative Example 3. 18. Semiconductor laminated film described in Example 9. Semiconductor laminated film according to Comparative Example 4

Claims (6)

  A method of manufacturing a thin film photoelectric conversion device in which a first electrode layer, one or more photoelectric conversion units each including a photoelectric conversion layer between a p-type semiconductor layer and an n-type semiconductor layer, and a second electrode layer are sequentially disposed on a substrate. The at least one photoelectric conversion unit is a crystalline germanium photoelectric conversion unit in which the photoelectric conversion layer is a crystalline germanium photoelectric conversion layer made of a substantially intrinsic or weak n-type crystalline germanium semiconductor that does not contain silicon atoms. A method for producing a thin film photoelectric conversion device, comprising: exposing a part of the crystalline germanium photoelectric conversion unit to hydrogen gas plasma in the step of laminating the crystalline germanium photoelectric conversion unit.   2. The method of manufacturing a thin film photoelectric conversion device according to claim 1, wherein the crystalline germanium photoelectric conversion unit is formed during the crystalline germanium photoelectric conversion layer stacking step or immediately after the crystalline germanium photoelectric conversion layer stacking step. A method of manufacturing a thin film photoelectric conversion device, comprising exposing a part to hydrogen gas plasma.   It is a manufacturing method of the thin film photoelectric conversion device of Claim 1 thru | or 2, Comprising: The process of exposing a part of said crystalline germanium photoelectric conversion unit to hydrogen gas plasma is between the lamination processes of a crystalline germanium photoelectric conversion layer. A method for producing a thin film photoelectric conversion device, wherein the film thickness of the crystalline germanium photoelectric conversion layer when introduced and exposed to hydrogen gas plasma is 1 nm or more and 50 nm or less.   It is a manufacturing method of the thin film photoelectric conversion device of Claim 1 thru | or 3, Comprising: The process of exposing a part of said crystalline germanium photoelectric conversion unit to hydrogen gas plasma immediately before the lamination | stacking process of a crystalline germanium photoelectric conversion layer A method for producing a thin film photoelectric conversion device, which is performed. 5. The method for manufacturing a thin film photoelectric conversion device according to claim 1, comprising a step of forming the crystalline germanium photoelectric conversion layer by a plasma CVD method within a range of a substrate temperature of 120 ° C. or more and 250 ° C. or less. A method of manufacturing a thin film photoelectric conversion device characterized by the above.   A thin film photoelectric conversion device in which a first electrode layer, one or more photoelectric conversion units including a photoelectric conversion layer between a p-type semiconductor layer and an n-type semiconductor layer, and a second electrode layer are sequentially disposed on a substrate. The at least one photoelectric conversion unit is a crystalline germanium photoelectric conversion unit, wherein the photoelectric conversion layer is a crystalline germanium photoelectric conversion layer made of a substantially intrinsic or weak n-type crystalline germanium semiconductor containing no silicon atom, and A thin film photoelectric conversion device characterized in that a crystal volume fraction having a thickness of 50 nm on the side close to the substrate of the crystalline germanium photoelectric conversion layer is 2% or more and 50% or less.