JP4529370B2 - Solar cell and method for manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar cell and a manufacturing method thereof, and more particularly to a silicon thin film solar cell having a high photoelectric conversion rate and a manufacturing method thereof.
[0002]
[Prior art]
Depending on the type of power generation layer, solar cells that are photoelectric conversion elements include solar cells using amorphous silicon (for example, hydrogenated amorphous silicon (a-Si: H)), non-single materials such as polycrystalline silicon. A solar cell using crystalline silicon (hereinafter referred to as a silicon thin film solar cell) is known.
[0003]
A silicon thin film solar cell generally has a pin structure, and photogenerated carriers are generated mainly in the i layer by irradiation of light incident from the p layer side, and the photogenerated carriers drift due to the built-in electric field of the solar cell. Move by.
Therefore, in order to effectively use light, it is desirable to increase the light transmittance in the p layer (hereinafter also simply referred to as transmittance). As a material for forming the p layer, for example, hydrogenated amorphous silicon carbide (a-SiC) A material having a wider band gap than a-Si: H such as: H) is used. It is known that the increase in the light transmittance in the p layer increases the intensity of the light transmitted through the i layer, so that the number of photogenerated carriers generated in the i layer can be increased.
[0004]
Further, it is generally known that B (boron) is added to the p layer as an impurity. For example, by adding boron to the p layer, a built-in electric field is generated in the solar cell, and the electric conductivity of the p layer is increased. It is described that becomes higher.
However, if the amount of boron added is large, boron diffuses in the direction of the i layer, and a carrier recombination center is formed at the interface between the p layer and the i layer, thereby reducing the open-circuit voltage or reducing the fill factor. There has been a problem of deteriorating the characteristics of solar cells. In addition, since the band gap of the p layer is narrowed by the addition of boron, it is also known that the light transmittance of the p layer is lowered and the number of photogenerated carriers generated in the i layer is reduced.
[0005]
In order to solve the above-described problems and to maximize the characteristics of the solar cell, the balance (balance) between the high transmittance of the p layer and the high electrical conductivity of the p layer, and the diffusion of boron into the i layer Various studies have been made for the purpose of prevention.
For example, Patent Document 1 discloses a non-single-crystal silicon semiconductor device having a pin-type structure as a semiconductor device that achieves high transmittance and high electrical conductivity. The layer and / or the n-type layer has a taper-shaped in-film hydrogen concentration profile and a taper-shaped band profile, and band coupling occurs at the interfaces of the p-type layer, i-type layer, and n-type layer. A semiconductor device characterized by being continuous is proposed,
Further, as a method for manufacturing the semiconductor device, a non-single crystal silicon layer is deposited on a substrate as the p-type layer and / or i-type layer and / or n-type layer, and then hydrogen plasma is applied to the non-single crystal silicon layer. The step of irradiating is performed as one step, and film formation is performed while repeating a plurality of the steps. In at least some of the steps, the deposition time and / or the hydrogen plasma irradiation time is changed for each step, and the film is formed. There has been proposed a method for manufacturing a semiconductor device, characterized in that a semiconductor layer having a tapered band profile is formed by controlling the intermediate hydrogen concentration in a tapered shape.
[0006]
However, in the method of manufacturing a semiconductor device described in Patent Document 1, since film formation and plasma processing are performed alternately, there is a problem that the film formation apparatus becomes complicated because two exhaust systems are required. Also, there are problems such as exhausting the raw material gas wastefully, a long film forming time, and poor productivity.
[0007]
[Patent Document 1]
JP-A-5-48130
[0008]
[Problems to be solved by the invention]
The present invention has been made to solve the various problems described above. That is, the present invention can be formed without complicating the conventional film-forming apparatus, and achieves a balance (balance) between the high transmittance of the p layer and the high electrical conductivity of the p layer, and boron in the i layer. An object of the present invention is to provide a solar cell excellent in diffusion prevention and a method for producing the solar cell.
[0009]
[Means for Solving the Problems]
  As a result of intensive studies, the present inventors have found that a solar cell in which the boron concentration in the p layer has a specific concentration distribution is a balance between increasing the transmittance of the p layer and increasing the electrical conductivity of the p layer, and i. The present invention has been completed by finding that it is excellent in preventing diffusion of boron into the layer. That is, the present invention shows the following (1) to (3) Solar cell and method for producing the same.
[0025]
  (1A solar cell having a back electrode layer through a photoelectric conversion layer in which a p layer, an i layer and an n layer are formed in this order on a substrate with a transparent conductive oxide film,
  Boron concentration in the p layer (¹¹B⁺/³⁰Si⁺) Has a concentration distribution that decreases toward the i layer in a part or all of the p layer, and is 0.05 or less at the interface between the p layer and the i layer,
  The transparent conductive oxide film is a continuous layer made of a discontinuous hill portion made of a first oxide and a second oxide formed thereon, and a microscopic layer is formed on the surface of the continuous layer. A transparent conductive oxide film consisting of a continuous layer having a large number of convex portions,
  A solar cell, wherein an oxide layer made of an oxide having a composition different from that of the first oxide and the second oxide is formed between the small mountain portion and the continuous layer.
[0026]
  (2) The first oxide is SnO₂The different oxide is SiO₂SnO in which the second oxide contains fluorine₂The above (characterized by1).
[0039]
  (3) On the substrate with a transparent conductive oxide film, a back electrode layer is provided via a photoelectric conversion layer in which a p layer, an i layer and an n layer are formed in this order,
  Boron concentration in the p layer (¹¹B⁺/³⁰Si⁺) Has a concentration distribution that decreases toward the i layer in a part or all of the p layer, and is 0.05 or less at the interface between the p layer and the i layer,
  The transparent conductive oxide film is a continuous layer made of a discontinuous hill portion made of a first oxide and a second oxide formed thereon, and a microscopic layer is formed on the surface of the continuous layer. A transparent conductive oxide film consisting of a continuous layer having a large number of convex portions,
  Manufacture of a solar cell for manufacturing a solar cell in which an oxide layer made of an oxide having a composition different from that of the first oxide and the second oxide is formed between the small mountain portion and the continuous layer. A method,
  A transparent conductive oxide film forming step of forming the transparent conductive oxide film on the substrate;
  After the transparent conductive oxide film forming step, a photoelectric conversion layer forming step of forming the p layer, i layer, and n layer in this order by the plasma CVD method,
  A back electrode layer forming step for forming the back electrode layer after the photoelectric conversion layer forming step;
  In the transparent conductive oxide film forming step, the discontinuous ridges made of the first oxide are formed on the substrate by atmospheric pressure CVD, and then the second oxide is formed on the ridges and the substrate. Forming the transparent conductive oxide film by forming a continuous layer comprising:
  A continuous layer made of the second oxide is formed on the mounds and the substrate by an atmospheric pressure CVD method,
  A method for producing a solar cell, comprising forming an oxide layer made of the different oxide between the small mountain portion and the continuous layer by an atmospheric pressure CVD method.
[0043]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The solar cell of the present invention is a solar cell having a back electrode layer through a photoelectric conversion layer in which a p layer, an i layer and an n layer are formed in this order on a substrate with a transparent conductive oxide film,
Boron concentration in the p layer (¹¹B⁺/³⁰Si⁺) Is a solar cell having a concentration distribution that decreases toward the i-layer in a part or all of the p-layer, and 0.05 or less at the interface between the p-layer and the i-layer.
Hereinafter, a suitable example showing the configuration of the solar cell of the present invention will be described with reference to FIG. 1, but the solar cell of the present invention and the manufacturing method thereof are not limited thereto.
[0044]
As shown in FIG. 1, the solar cell 1 of the present invention includes a transparent conductive oxide film 3, a photoelectric conversion layer 7 (p layer 4, i layer 5, n layer 6) on a glass substrate 2, And a back electrode layer 8. This configuration is one of photoelectric conversion devices that can be manufactured at a relatively low cost, and the solar cell 1 is configured such that light 9 is incident from the glass substrate 2 side and is mainly absorbed in the i layer 5. Designed, electricity is extracted from the solar cell through the conductor 10.
[0045]
Here, the boron concentration of the p-layer forming the photoelectric change layer of the solar cell of the present invention (¹¹B⁺/³⁰Si⁺) Has a concentration distribution that decreases in the direction of the i layer in a part or all of the p layer as described above, and 0.05 or less at the interface between the p layer and the i layer. And is preferably 0.
[0046]
Further, the boron concentration in the entire region of the p layer (¹¹B⁺/³⁰Si⁺) Is preferably 1.0 or less, more preferably 0.7 or less. If the boron concentration is within this range, the p-layer is sufficiently p-type doped to increase the open-circuit voltage of the solar cell, and the p-layer has high electrical conductivity to maintain a high fill factor. This is preferable.
Here, “¹¹B⁺/³⁰Si⁺"Is a secondary ion detected at the time of measuring the boron concentration using the SIMS (secondary ion mass spectrometry) method described later (¹¹B⁺and³⁰Si⁺) Ratio.
[0047]
Below, each structure of the solar cell of this invention is demonstrated.
<Substrate with transparent conductive oxide film>
The transparent conductive oxide film used in the solar cell of the present invention is not particularly limited as long as it is a known transparent conductive oxide film that can be used for semiconductor devices, photovoltaic devices, etc. And a plurality of flat portions, and a transparent conductive oxide film in which the surface of the peak portion and the flat portion has a large number of micro convex portions is preferably exemplified.
Here, the shape and configuration of the substrate with a transparent conductive oxide film having the above-described preferred transparent conductive oxide film will be described with reference to FIG. 2 and FIG. The battery and its manufacturing method are not limited to these. As shown in FIG. 2, the substrate with a transparent conductive oxide film has a macro unevenness (texture) due to a plurality of discontinuous peaks 22 on a glass substrate 21 and a plurality of gaps between the peaks. The ridges 22 and the outer surface of the flat part 23 have a structure having a large number of microscopic irregularities (textures). Hereinafter, a structure having two irregularities as described above is referred to as a double texture structure.
[0048]
Height of the peak (height from the top of the micro-projection on the flat part) H_aIs preferably 0.2 to 2.0 μm, more preferably 0.3 to 1.0 μm, and still more preferably 0.4 to 0.7 μm. Spacing between the above peaks (distance between flat portions between adjacent peaks) W_aIs preferably 0 to 2.0 μm in a straight line, more preferably 1.2 μm or less, and further preferably 0.4 μm or less, particularly 0.1 μm or more (all peaks are discontinuous). ) Is preferable. In the present invention, the plurality of peak portions may include a discontinuous portion and a continuous portion, and the interval W between the peak portions._a0 to 2.0 μm means that there may be a portion without a flat portion.
The bottom diameter D of the peak_aIs preferably 1.0 to 3.0 μm, more preferably 1.0 to 2.0 μm.
Furthermore, the pitch between the peaks (the distance between the peaks between adjacent peaks) P_aIs preferably from 0.1 to 2.0 μm, more preferably from 0.5 to 1.5 μm, and even more preferably from 0.7 to 1.2 μm.
[0049]
FIG. 3 shows an enlarged view of FIG. 2 showing a large number of micro irregularities. As shown in FIG. 3, the height H of the convex portion 30_bIs preferably 0.05 to 0.4 μm, more preferably 0.1 to 0.2 μm. Also, the pitch between the convex portions (the distance between the vertices between adjacent convex portions) P_bIs preferably from 0.1 to 0.8 μm, more preferably from 0.1 to 0.6 μm.
Furthermore, the bottom diameter D of the convex portion 30_bIs preferably 0.1 to 0.8 μm, more preferably 0.15 to 0.5 μm, and the height H of the protrusion 30 is_b/ Bottom diameter D_bThe ratio is preferably 0.06 to 4.
[0050]
By making the outer surfaces of the ridges 22 and the flat part 23 uneven (micro unevenness) smaller than the unevenness (macro unevenness) due to such ridges, light of short wavelengths can be strongly scattered. As a whole, it is possible to effectively scatter a wide area of light. That is, light having a long wavelength can be scattered by a peak portion having large unevenness, and light having a short wavelength can be scattered from a surface having small unevenness.
[0051]
Moreover, the base | substrate with a transparent conductive oxide film which has the said double texture structure has the relationship between the wavelength and haze ratio which are shown below in the whole base | substrate. That is, the haze ratio is 2 to 95% over the entire wavelength range of 400 to 800 nm. The haze ratio is preferably 10 to 90% (400 to 600 nm average) on average in the wavelength region of 400 to 600 nm, and particularly 2 to 40% (600 to 800 nm average) on average in the wavelength region of 600 to 800 nm. ) Is preferable. Moreover, it is preferable that the difference (maximum value-minimum value) between the maximum value and the minimum value of the haze ratio is 50% or less. When the haze ratio is within this range, the short-circuit current and the open-circuit voltage of the solar cell can be maintained high, and the photoelectric conversion efficiency is improved, which is preferable.
Here, the haze ratio indicates the ratio of the scattering component in the transmitted light. The haze rate depends on the wavelength, the haze rate is Hz (λ), and the total transmittance is T._total(Λ), T_direct(Λ), the scattered component of transmitted light is T_diffuseIf (λ), the relationship shown in the following formula is established.
T_total(Λ) = T_direct(Λ) + T_diffuse(Λ)
Hz (λ) = T_diffuse(Λ) / T_total(Λ) × 100 [%]
[0052]
The substrate used for the substrate with the transparent conductive oxide film is not necessarily flat and plate-like, and may be curved or atypical. Examples of the substrate include a glass substrate, a ceramic substrate, a plastic substrate, and a metal substrate. The substrate is preferably a transparent substrate having excellent translucency, and is preferably a glass substrate from the viewpoint of strength and heat resistance. Specific examples of the glass substrate include colorless and transparent soda lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, quartz glass, borosilicate glass substrate, non-alkali glass substrate, and other various glasses. A transparent glass plate can be used. The thickness of such a glass substrate is preferably 0.2 to 6.0 mm. It is preferable for the thickness of the glass substrate to be in this range because the glass substrate has high strength and high transmittance.
The substrate preferably has a high transmittance in the wavelength region of 350 to 800 nm, for example, a transmittance of 80% or more. Moreover, it is desirable that it is sufficiently insulating and has high chemical and physical durability.
In addition, in the case of a glass substrate made of glass containing sodium such as soda lime silicate glass or a glass substrate made of glass containing low alkali, diffusion of alkali components from the glass to the transparent conductive film formed on the upper surface thereof is performed. In order to minimize it, an alkali barrier layer such as a silicon oxide film, an aluminum oxide film, or a zirconium oxide film may be provided on the glass substrate surface.
Furthermore, you may have the layer for reducing the difference in the refractive index of the surface of a glass substrate, and the layer provided on it on the surface of a glass substrate.
[0053]
As an alkali barrier layer formed on a soda lime glass substrate, SiO₂And SiO₂And SnO₂These mixed oxides and multilayer films can be used, and the film thickness is preferably 20 to 100 nm. It is preferable for the thickness of the alkali barrier layer to be in this range since reflection and absorption of transmitted light from the glass substrate can be controlled. Further, as an example of the multilayer film, specifically, SnO on a soda lime glass substrate.₂Film or TiO₂Film and SiO₂The film | membrane which laminated | stacked the film | membrane sequentially is mentioned, It is preferable that a film thickness is 20-30 nm and 20-40 nm, respectively. In particular, the thickness of the alkali barrier layer is preferably 40 to 60 nm.
[0054]
As the measurement of the surface property, the shape of the micro unevenness formed on the outer surface can be measured by the following method.
(1) Surface shape analysis
The convex part on the film surface was observed with a scanning electron microscope (SEM), and the bottom diameter of the convex part was measured from the obtained micrograph. Moreover, the uneven | corrugated shape of the film | membrane surface was observed with SEM and atomic force microscope (AFM), and the uneven | corrugated shape of the film | membrane surface and the height of a convex part were analyzed from the obtained micrograph.
(2) Measurement of surface coverage
The coverage of the small hill portion made of the first oxide, which will be described later, on the substrate was measured from the SEM photograph. The surface coverage was evaluated by dividing the area occupied by the small ridges on the substrate by the area of the entire coated surface of the substrate.
[0055]
The solar cell of the present invention is preferably a solar cell having a photoelectric conversion layer and a back electrode layer, which will be described later, on the substrate with a transparent conductive oxide film having the double texture structure described above. The structure of such a transparent conductive oxide film may be composed of a single oxide, but is composed of the first and second oxides, specifically, the first oxidation A discontinuous hill portion made of a material, and a continuous layer made of a second oxide formed thereon, and a continuous layer having a large number of micro convex portions continuously on the surface of the continuous layer. It is preferable to be configured.
Further, as shown in FIG. 2, the shape of the substrate with the transparent conductive oxide film having such a configuration is composed of the peak portion 22 and the flat portion 23, and the configuration is preferably on the glass substrate 21. The ridges 22 and the flat portions 23 are formed by the discontinuous ridges 24 made of the first oxide formed on and the continuous layer 25 made of the second oxide formed thereon. Is preferred.
[0056]
The first oxide may be any oxide that is highly transparent in the visible light region. Specifically, for example, SnO₂, In₂O_Three, ZnO, CdO, CdIn₂O_Four, CdSnO_ThreeMgIn₂O_Four, CdGa₂O_Four, GaInO_ThreeInGaZnO_Four, Cd₂Sb₂O₇, Cd₂GeO_FourCuAlO₂, CuGaO₂, SrCu₂O₂TiO₂, Al₂O_ThreeEtc. Of these, SnO₂, ZnO, and In₂O_ThreeIt is preferable to use one or more oxides selected from the group consisting of:
A small ridge portion made of such a highly transparent oxide is formed on the substrate, and a desired concavo-convex structure can be formed on the substrate by changing the height.
The refractive index of the first oxide is preferably 1.7 to 2.2 and more preferably 1.8 to 2.1 at a wavelength of 400 to 800 nm.
[0057]
In addition, since the small hill portion made of the first oxide is a discontinuous protrusion and not a continuous film, the base portion not covered by the protrusion is naturally absorbed loss of incident light by the small ridge. Becomes zero, so that the amount of light incident on the photoelectric conversion layer can be increased.
These small ridges are portions that increase the haze ratio (to increase the degree of light scattering), which will be described later, and preferably have no electrical conductivity in order to suppress absorption by free electrons and to make them highly transparent. Therefore, SnO is used as the first oxide.₂When SnO is used, SnO₂Even in the case of containing fluorine, the fluorine content is SnO₂The amount is preferably 0.01 mol% or less, more preferably 0.005 mol% or less.
[0058]
Here, the height H of the hill portion made of the first oxide._cIs preferably 0.2 to 2.0 μm, more preferably 0.2 to 1.0 μm, and still more preferably 0.4 to 0.7 μm. Spacing W between the above hills_cIs preferably from 0.1 to 2.0 μm, more preferably from 0.1 to 1.5 μm.
Also, the bottom diameter D of the small mountain part_cIs preferably 0.2 to 2.0 μm, more preferably 0.2 to 1.0 μm, and the pitch between the ridges (the distance between the vertices between adjacent ridges) P_cIs P_aIt is preferably 0.1 to 2.0 μm, more preferably 0.5 to 1.5 μm, and still more preferably 0.7 to 1.2 μm.
[0059]
The method for forming the small ridges made of the first oxide on the substrate is not particularly limited. As will be described later, the substrate is heated using a metal chloride as a raw material, and the oxide is formed by atmospheric pressure CVD. The metal element concentration in the medium of the mixture of metal chloride, hydrogen halide and water is adjusted. Specifically, the amount of hydrogen halide and water relative to the metal chloride is adjusted.
[0060]
The second oxide is preferably a transparent conductive oxide that is transparent in the visible light region and further has conductivity. Specifically, for example, SnO₂, ZnO, TiO₂, In₂O_Three2 or more may be used in combination, and it is preferable that a dopant for developing conductivity is contained.
Of these, SnO₂Uses SnO as fluorine or antimony as dopant₂It is preferable to contain 0.01-4 mol% with respect to. ZnO preferably contains at least one selected from the group consisting of B, Al and Ga as a dopant in an amount of 0.05 to 5 mol% with respect to ZnO. In₂O_ThreeSn In₂O_ThreeIt is preferable to contain 0.02-4 mol% with respect to.
The refractive index of the second oxide is preferably 1.7 to 2.2, and more preferably 1.8 to 2.1, at a wavelength of 400 to 800 nm.
[0061]
In addition, SnO containing fluorine as the second oxide₂By using, the conductive electron density is improved. As a substrate used for a solar cell, the conductive electron density is 5 × 10.¹⁹~ 4x10²⁰cm^-3Is preferably within the range of 1 × 10.²⁰~ 2x10²⁰cm^-3If it is the range, it is more preferable. If the conductive electron density is within this range, the light absorption of the continuous layer made of the second oxide is small, highly transparent, and highly durable against active hydrogen species. The transparency is not impaired even by hydrogen plasma irradiation generally used in forming a battery, which is preferable.
[0062]
Further, as the second oxide, SnO₂Is used, a halogen element may be doped with hydrogen halide in order to improve the conductivity of the second oxide. Specific examples of the hydrogen halide include HF, HCl, HBr, and HI. SnO doped with hydrofluoric acid₂Is preferred. Specifically, for example, fluorine is SnO.₂On the other hand, it is preferable to contain 0.01-4 mol%, and it is more preferable to contain 0.1-1 mol%.
[0063]
Here, as shown in FIG. 2, the continuous layer 25 made of the second oxide is continuously formed on the glass substrate 21 in the portion where the small ridges 24 and the small ridges 24 are not formed. Yes.
Further, the surface of the continuous layer 25 has a large number of micro-convex portions 30 shown in FIG. 3, and the thickness H of the continuous layer 25 on the small ridge portion 24._dThe thickness (including micro protrusions) is preferably 0.4 to 1.0 μm, and more preferably 0.5 to 0.7 μm. Similarly, the thickness H of the continuous layer 25 on the glass substrate 21_eThe thickness (including micro protrusions) is preferably 0.4 to 1.0 μm, and more preferably 0.5 to 0.7 μm.
[0064]
The method for forming the continuous layer made of the second oxide is not particularly limited. For example, as described later, the discontinuous hill portion made of the first oxide is flat and is not covered with the hill portion. A continuous layer can be formed on a glass substrate by using a transparent conductive oxide, which is a second oxide, using an atmospheric pressure CVD method, an electron beam vapor deposition method, a vacuum deposition method, a sputtering method, a spray method, or the like. .
In order to obtain a low-resistance transparent conductive substrate, a continuous layer made of a transparent conductive oxide (hereinafter referred to as the second oxide) (hereinafter referred to as a second oxide) is also formed on a small glass portion and a flat glass substrate not covered with the small mountain portion. And also referred to as a second oxide layer). In addition, since a large number of microscopic irregularities formed on the outer surface can be formed without using an etching process when the atmospheric pressure CVD method is used, the transparent conductive oxide film as the second oxide layer is It is preferably formed by an atmospheric pressure CVD method.
[0065]
  Further, the first oxide and the second oxide described above may be the same oxide, and both are SnO.₂Is preferably used.
  Furthermore, the second oxide layer is formed as a continuous layer on the small ridges and the substrate made of the first oxide, and a transparent conductive oxide film that can be suitably used for the solar cell of the present invention is obtained. And forming an oxide layer made of an oxide having a composition different from that of the first and second oxides between the first and second oxides.The
  Therefore, an oxide layer (hereinafter referred to as a different oxide layer) made of an oxide having a composition different from that of the first and second oxides is formed on the surface of the flat glass substrate including the discontinuous ridges made of the first oxide. It is preferable to add a second oxide layer after forming the material layer. By forming such different oxide layers on the first oxide, a large number of micro projections are easily formed on the surface of the second oxide layer, and a structure having peaks and flats is easily formed. It is preferable because it can be formed.
  In such a multilayer structure, it is necessary to reduce reflection at the interface of each layer and maximize the amount of light incident on the photoelectric conversion layer described later. In other words, it is desirable to reduce light reflection at each interface of the glass substrate, the first oxide, the different oxide layer, and the second oxide layer as much as possible. For that purpose, the refractive index of the first oxide, the second oxide layer and the different oxide layer should be as close as possible, or if the refractive index is separated, the film made of different oxide layers should be as thin as possible. desirable.
  Specifically, examples of such different oxides include oxides of one or more atoms selected from the group consisting of Si, Sn, Al, Zr and Ti. It is preferable to have an article as a main component. In addition, since the different oxides need to have high translucency, they are non-crystalline SiO.₂It is more preferable that
  The film thickness of the different oxide layers is preferably 2 to 40 nm, and more preferably 10 to 30 nm.
[0066]
In the solar cell of the present invention, as described above, the first oxide is preferably formed in order to improve the haze ratio, and the second oxide has conductivity and high transparency. It is preferable that it is an oxide. Furthermore, the refractive indexes of the first oxide layer and the second oxide layer are preferably approximately the same, and specifically, it is preferably 1.7 to 2.2 at a wavelength of 400 to 800 nm. When the refractive indexes of the first oxide and the second oxide are both within this range, light reflection at the interface between the first oxide and the second oxide is controlled, and the transmittance does not decrease. To preferred.
In addition, as described above, the solar cell of the present invention preferably has a substrate with a transparent conductive oxide film having a double texture structure, and includes a peak from the top of the substrate (including micro protrusions). ) Is preferably 0.8 to 3.0 μm, more preferably 0.8 to 1.0 μm, and the conductivity is such that the sheet resistance of the entire film is 5 to 20 Ω / □. Preferably, it is 5 to 12Ω / □, and the transmittance (transparency) at 550 nm is preferably 70 to 95%, more preferably, when measured by the immersion method described in detail later in Examples. Is 85 to 90%. Further, as described above, the haze ratio is preferably 2 to 95% over the entire wavelength range of 400 to 800 nm.
If the substrate with a transparent conductive oxide film used for solar cells has such a configuration, the light incident through the substrate is refracted and scattered by the transparent electrode and is incident on the photoelectric conversion layer. Pass through the layer for a long distance. As a result, a lot of light is absorbed by the photoelectric conversion layer, which is useful because the photoelectric conversion efficiency is improved.
[0067]
<Photoelectric conversion layer>
The photoelectric conversion layer used in the solar cell of the present invention is a layer in which a p layer, an i layer, and an n layer are formed in this order, and the boron concentration in the p layer that forms the photoelectric change layer (¹¹B⁺/³⁰Si⁺) Is a photoelectric conversion layer having a concentration distribution that decreases in the i-layer direction in a part or all of the p-layer, and 0.05 or less at the interface between the p-layer and the i-layer. .
Specifically, as the structure of the photoelectric conversion layer, for example, as shown in the photoelectric conversion layer 7 of FIG. 1, a single structure composed of three layers in which a p layer 4, an i layer 5, and an n layer 6 are formed in this order. Further, a tandem structure in which a p layer, an i layer, and an n layer are further laminated in this order on the single structure can be given.
[0068]
The source gas for forming the p layer is not particularly limited as long as it contains Si, H, and B (boron) atoms, and preferably contains C atoms. As such a source gas, specifically, for example, SiH_Four, CH_Four, H₂, B₂H₆, SiCl_Four, SiHCl_Three, SiH₂Cl₂, SiH₂F₂, BF_Three1,3-disilabutane (H_ThreeSiCH₂SiH₂CH_Three) And the like include those containing Si, C, H and B atoms. Of these, SiH_Four, CH_Four, H₂And B₂H₆Is preferable because it is easily available and easy to handle.
By forming a p-layer using these source gases, hydrogenated amorphous silicon carbide (a-SiC: H), amorphous silicon (a-Si), microcrystalline silicon (μc-) doped with the contained boron Si), microcrystalline silicon carbide (μc-SiC), or the like is formed as a material for the p layer.
[0069]
Moreover, it is preferable that the film thickness of a p layer is 3-50 nm, and it is more preferable that it is 5-30 nm. If the thickness of the p layer is within this range, the open voltage and the fill factor of the solar cell can be maintained high, which is preferable because the photoelectric conversion efficiency is improved, and the short circuit current of the solar cell can also be maintained high. Since it can do, since photoelectric conversion efficiency improves, it is preferable.
[0070]
Boron concentration in the p layer (¹¹B⁺/³⁰Si⁺) Has a concentration distribution that decreases in the direction of the i layer in part or all of the p layer, as described above, and is 0.05 or less at the interface between the p layer and the i layer. ing.
Such a boron concentration distribution is determined by a gas containing boron (for example, B₂H₆) And a gas containing silicon (for example, SiH_FourIn the step of forming the p layer using a mixed gas (hereinafter also referred to as a raw material mixed gas), the mixing ratio (B₂H₆/ SiH_Four) To adjust. Specifically, such adjustment is performed by mixing the raw material mixed gas (B) shown in FIG.₂H₆/ SiH_Four) And the thickness of the p layer (11 nm), the region where the boron concentration is reduced may be a partial region of the p layer. The concentration distribution of boron to be reduced is not limited to the linear function-like straight line shown in FIG. 4A, and may be a quadratic function, an exponential function, or a stepped shape, or a combination of these. It may be.
In the initial stage of forming the p layer, the mixing ratio of the raw material mixed gas (for example, B₂H₆/ SiH_Four) Is preferably 0.001 to 0.1, and more preferably 0.005 to 0.05. If the mixing ratio of the raw material mixed gas is within this range, the p layer is sufficiently p-type doped, the electric conductivity is increased, the open circuit voltage and the fill factor of the solar cell can be maintained high, and the photoelectric conversion efficiency is improved. In addition, boron diffusion into the i layer and formation of a carrier recombination center at the interface between the p layer and the i layer are suppressed, so that the photoelectric conversion efficiency is improved, which is preferable. Here, the initial stage refers to a stage where the thickness of the p layer to be formed is 0 to 0.5 when the thickness of the p layer is 1.
Further, when reducing the boron concentration, the mixing ratio of source gases other than the source gas containing B atoms (for example, SiH_Four, CH_FourAnd H₂Is used as the source gas, CH_Four/ SiH_Four, H₂/ SiH_Four) May be changed in accordance with the reduction of the boron concentration. Specifically, B as a source gas containing B atoms₂H₆When using₂H₆Is generally diluted with hydrogen, so H₂/ SiH_FourH to be constant₂Is preferably introduced.
[0071]
Specifically, as the source gas for forming the i layer, for example, SiH_FourAnd SiCl_Four, SiHCl_Three, SiH₂Cl₂, SiH₂F₂Halogenated silane such as H₂May be used in combination.
By forming the i layer using these source gases, microcrystalline silicon (μc-Si), hydrogenated amorphous silicon (a-Si: H), hydrogenated amorphous silicon germanium (a-SiGe: H), micro Crystalline silicon germanium (μc-SiGe) or the like is formed as the material of the i layer.
The film thickness of the i layer is preferably 100 to 600 nm, more preferably 250 to 400 nm. If the film thickness of the i layer is within this range, the short-circuit current of the solar cell can be maintained high, and the open-circuit voltage and the fill factor can be maintained high, which is preferable because the photoelectric conversion efficiency is improved.
[0072]
Specifically, as the source gas for forming the n layer, for example, SiH_Four, H₂, PH_ThreeAnd SiCl_Four, SiHCl_Three, SiH₂Cl₂, SiH₂F₂You may use together halogenated silanes, such as.
By using these source gases to form an n layer, microcrystalline silicon (μc-Si), hydrogenated amorphous silicon (a-Si: H), hydrogenated amorphous silicon germanium (a-SiGe: H), Crystalline silicon germanium (μc-SiGe) or the like is formed as an n-layer material.
PH, which is the mixing ratio of the source gases forming the n layer_Three/ SiH_FourIs preferably 0.001 to 0.1, and more preferably 0.005 to 0.05. PH_Three/ SiH_FourIs within this range, the open circuit voltage of the solar cell can be maintained high, the diffusion of phosphorus (P) into the i layer is suppressed, and the short circuit current and the fill factor can be maintained high. It is preferable because photoelectric conversion efficiency is improved.
The film thickness of the n layer is preferably 5 to 100 nm, and more preferably 10 to 50 nm. If the film thickness of the n layer is within this range, the open circuit voltage of the solar cell can be maintained high, and the short circuit current and the fill factor can be maintained high, which is preferable because the photoelectric conversion efficiency is improved.
[0073]
The photoelectric conversion layer has three layers (hereinafter referred to as a-Si) in which an a-SiC: H layer is formed as a p layer, an a-Si: H layer is formed as an i layer, and an a-Si: H layer is formed as an n layer in this order. It is also preferable that the single structure be composed of a p-i-n layer.
Further, as another example of the photoelectric conversion layer, a tandem electromotive layer in which another pin layer is further formed on the pin layer of a-Si is preferably exemplified. Specifically, another pin layer formed on the pin layer of a-Si includes an a-Si: H layer as a p layer, a microcrystalline Si layer as an i layer, and n Three layers in which an a-Si: H layer is formed in this order, or an a-Si: H layer as a p layer, an a-SiGe: H layer as an i layer, and an a-Si: H layer as an n layer An electromotive layer having a tandem structure, which is a three-layer structure, is formed in this order. In the case of such a tandem structure, boron concentration (¹¹B⁺/³⁰Si⁺) May have a concentration distribution that decreases in the i-layer direction. Further, by using such a tandem electromotive layer for the photoelectric conversion layer, it becomes possible to perform photoelectric conversion of light not only at a short wavelength but also at a long wavelength side. Therefore, the solar cell of the present invention has the above tandem structure. Use of the electromotive layer is useful because the effect of improving the photoelectric conversion efficiency becomes clearer.
[0074]
Further, a buffer layer may be provided between each of the p layer, the i layer, and the n layer forming the photoelectric conversion layer.
If the buffer layer is provided between the p layer and the i layer, diffusion of boron contained in the p layer into the i layer is suppressed. Since the current can be maintained high, it is preferable for the reason that the photoelectric conversion efficiency is improved. If it is provided between the i layer and the n layer, the phosphorus (P) i layer contained in the n layer can be obtained. Since the diffusion voltage of the solar cell is suppressed, the open circuit voltage, the fill factor, and the short circuit current of the solar cell can be maintained high, which is preferable because the photoelectric conversion efficiency is improved.
As a material of the buffer layer (hereinafter also referred to as p / i buffer layer) when a buffer layer is provided between the p layer and the i layer, hydrogenated amorphous silicon carbide (a- SiC: H), hydrogenated amorphous silicon (a-Si: H), and the like. When the buffer layer is provided between the i layer and the n layer, the material of the buffer layer is doped with phosphorus. Non-hydrogenated amorphous silicon (a-Si: H) and the like.
Although the film thickness of the buffer layer varies depending on the place where it is formed, it is preferably 1 to 20 nm, and more preferably 5 to 10 nm.
[0075]
<Back electrode>
The electrode material for the back electrode layer used in the solar cell of the present invention is preferably exemplified by Ag or Ag alloy, Al or Al alloy, palladium, chromium, and the like. Specifically, the crystalline Ag is 95 atomic%. It is preferable to use the metal film contained above. By using crystalline Ag for the metal film of the back electrode, it is possible to reflect the light transmitted through the photoelectric conversion layer and return the reflected light to the photoelectric conversion layer again, thereby improving the photoelectric conversion efficiency. This is preferable because it leads to an effect.
The metal film may contain Pd and / or Au as components. The content of Pd and Au in the metal film is preferably 0.3 to 5 atom%, more preferably 0.3 to 3 atom%, respectively, with respect to the total with Ag.
Moreover, when the said back surface electrode layer is a layer which consists only of Ag, it is preferable that the sum total of impurity amount is 1 atomic% or less.
The film thickness of the back electrode layer is preferably 100 to 1000 nm. In particular, the film thickness when the back electrode layer is Ag is preferably 150 to 250 nm. If the film thickness of the back electrode layer is within this range, the sheet resistance of the back electrode layer is low, and the curve factor of the solar cell can be kept high, which is preferable because the photoelectric conversion rate is improved. Since the light which permeate | transmitted the conversion layer can be reflected in this back surface electrode layer and the short circuit current of a solar cell can be maintained high, it is preferable from a photoelectric conversion rate improving. In particular, if the thickness of the back electrode layer is 300 nm or less, it is preferable in the back electrode layer forming step by the CVD method to be described later because the formation time of the back electrode layer is short and productivity is improved.
[0076]
The solar cell of the present invention may have a contact improving layer between the photoelectric conversion layer and the back electrode layer.
Here, although an example of the solar cell of the present invention having the contact improvement layer will be described with reference to FIG. 5, the solar cell of the present invention and the manufacturing method thereof are not limited thereto.
As shown in FIG. 5, the solar cell 40 includes a glass substrate 44, a transparent conductive oxide film 45, a photoelectric conversion layer 42, a contact improvement layer 41, and a back electrode 43.
[0077]
As shown in FIG. 5, the contact improvement layer 41 is between the photoelectric conversion layer 42 and the back electrode 43 and is used to improve the contact between the photoelectric conversion layer 42 and the back electrode 43.
Moreover, it is preferable that the contact improvement layer 41 has a small specific resistance and absorption coefficient. Specifically, the specific resistance is 1 × 10.^-2Preferably it is Ω · cm or less, 5 × 10^-3More preferably, it is Ω · cm or less. When the specific resistance of the contact improvement layer 41 is within this range, it is possible to pass through the back electrode 43 without reducing the electromotive force photoelectrically converted by the photoelectric conversion layer 42.
The absorption coefficient is 5 × 10 5 in the wavelength region of 500 to 800 nm.^Threecm^-1Preferably, it is 2 × 10^Threecm^-1The following is more preferable. If the absorption coefficient of the contact improvement layer 41 is within this range, the light transmitted through the photoelectric conversion layer 42 is transmitted to the back electrode 43 without being absorbed, and the light reflected by the back electrode 43 is again transmitted to the photoelectric conversion layer 42. It can be transmitted.
[0078]
The material of the contact improvement layer 41 is mainly composed of zinc oxide (ZnO), and 90 atomic% or more of all metal components in the contact improvement layer is preferably Zn. More preferably, gallium (Ga) or aluminum (Al) is contained. By containing Ga or Al, the conductive electron density is increased, and by acting as a dopant for zinc oxide, there is an effect of improving the electrical conductivity of the entire contact improvement layer 41.
In addition, when Ga or Al is contained, the content is preferably 0.3 to 10 atomic%, more preferably 0.3 to 5 atomic% with respect to the total with Zn. Within this range, it is possible to prevent an increase in the absorption coefficient of the contact improvement layer 41 due to an excessive increase in electrical conductivity.
Furthermore, when the contact improvement layer is a zinc oxide layer containing Ga or Al, it may contain impurities, and the total amount of impurities is preferably 1 atomic% or less.
The film thickness of such a contact improving layer is preferably 5 to 200 nm, more preferably 10 to 150 nm. The film thickness when the contact improving layer is a GZO layer and has a double texture structure is preferably 50 to 150 nm. When the film thickness of the contact improvement layer is within this range, it is preferable because it has a sufficient contact improvement effect even on a substrate with a transparent conductive oxide film having a double texture structure.
[0079]
The method for producing a solar cell for producing the solar cell of the present invention includes a transparent conductive oxide film forming step of forming the transparent conductive oxide film on a substrate,
After the transparent conductive oxide film forming step, a photoelectric conversion layer forming step of forming the p layer, i layer, and n layer in this order by the plasma CVD method,
And a back electrode layer forming step of forming the back electrode layer after the photoelectric conversion layer forming step.
[0080]
In the transparent conductive oxide film forming step, after forming a discontinuous hill portion made of the first oxide on the substrate by an atmospheric pressure CVD method, the second oxide is formed on the hill portion and the substrate. It is preferable that the transparent conductive oxide film is formed by forming a continuous layer made of the above, and the small ridge is formed by atmospheric pressure CVD using tin tetrachloride, water and hydrogen chloride. More preferably.
[0081]
In the following, an example of using the atmospheric pressure CVD method is shown as a suitable example of the formation of the small mountain portion in the transparent conductive oxide film forming step, but the method for manufacturing the solar cell of the present invention is limited to this. Not.
A soda lime glass substrate is heated to 500 ° C. in a belt conveyor furnace, and a silica film is produced by simultaneously spraying 4 L / min of nitrogen gas containing 5 mol% of silane gas and 20 L / min of oxygen gas on the glass substrate. Next, the glass substrate with the silica film is heated to 540 ° C., and tin tetrachloride, methanol, water, and hydrogen chloride gas are simultaneously sprayed, whereby the discontinuous hills made of the first oxide described above are formed on the silica film. Forming part.
The surface coverage of the discontinuous hills made of the first oxide on the glass substrate is 10 to 70%, the transmittance at 550 nm is 80% or more, and after the second oxide is formed, haze The rate is 10 to 90% (400 to 600 nm average), 2 to 40% (600 to 800 nm average), and the difference between the maximum value and the minimum value of the haze rate (maximum value−minimum value) is 50%. The following is preferable.
The surface coverage can be adjusted by controlling the amount of the hydrogen chloride gas and the water. It is preferable to increase the rate of adding hydrogen chloride gas during the formation of the discontinuous ridges made of the first oxide by the atmospheric pressure CVD method. The proportion of hydrogen chloride added is the molar ratio of hydrogen chloride to tin tetrachloride (hereinafter referred to as HCl / SnCl_FourHCl / SnCl_FourIs preferably 1.0 to 4.0. HCl / SnCl_FourIs within this range, small ridges are easily formed, and the surface coverage can be controlled. In particular, HCl / SnCl_FourIs preferably 2.0 to 3.0.
[0082]
In the transparent conductive oxide film forming step, the continuous layer made of the second oxide formed on the small ridge and on the base on which the small ridge is not formed is formed by an atmospheric pressure CVD method. Preferably,
Furthermore, it is preferable that the different oxide layer is formed by an atmospheric pressure CVD method between the ridge portion and the base body on which the ridge portion is not formed and the continuous layer.
[0083]
Hereinafter, an example using the atmospheric pressure CVD method is shown as a preferable example of the formation of the different oxide layers and the continuous layer, but the method for manufacturing the solar cell of the present invention is not limited thereto.
As the different oxide layer, SiO₂A layer consisting of Using atmospheric pressure CVD, SiO₂Are formed on the discontinuous ridges made of the first oxide and on a flat glass substrate without the ridges.
Specifically, the glass substrate on which the small ridges are formed is heated to 520 ° C., and 4 L / min of nitrogen gas containing 5 mol% of silane gas and 3 L / min of oxygen gas are simultaneously sprayed on the glass substrate. By the atmospheric pressure CVD method, the different oxide layers are non-crystalline and SiO 2₂A layer consisting of is formed. Further, this glass substrate is heated to 540 ° C., tin tetrachloride, water, hydrogen fluoride, and methanol are simultaneously sprayed, and an atmospheric pressure CVD method is used to form fluorine (which is a continuous layer made of the second oxide) F) Doped SnO₂A transparent conductive oxide film is formed.
In addition, as the second oxide, specifically, for example, F-doped SnO₂Antimony doped SnO₂, Sn-doped In₂O_ThreeExamples thereof include transparent conductive oxides such as (ITO), aluminum-doped ZnO, and gallium-doped ZnO.
[0084]
In the photoelectric conversion layer forming step, the p layer is formed on the transparent conductive oxide film by a plasma CVD method using the raw material mixed gas, and the i layer and the n layer are formed on the p layer. Each of these steps is a formation process formed by a plasma CVD method,
Boron concentration (¹¹B⁺/³⁰Si⁺) Has a concentration distribution that decreases in the i-layer direction in a part or all of the p-layer, and is 0.05 or less at the interface between the p-layer and the i-layer. It is preferable to reduce the ratio of the gas containing boron to the gas.
Here, “reducing the ratio of the boron-containing gas” means a gas containing silicon (for example, SiH in the formation of the p layer by the plasma CVD method)._FourGas containing boron (e.g. B)₂H₆) Mixing ratio (e.g. B₂H₆/ SiH_Four) Is reduced to substantially zero at the end of the formation of the p layer. Specifically, the mixing ratio (B of the raw material mixed gas shown in FIG.₂H₆/ SiH_Four) And the thickness of the p layer (11 nm), when the thickness of the p layer reaches 11 nm, B₂H₆/ SiH_FourIs to be zero.
In addition, as described above, the formation of the p layer by the plasma CVD method is performed at the initial stage of forming the p layer, as described above.₂H₆/ SiH_Four) Is preferably 0.001 to 0.1, and more preferably 0.005 to 0.05.
[0085]
Formation of the i layer and the n layer by the plasma CVD method can be performed by a conventionally known method shown in Examples described later using the various source gases described above.
The p layer, i layer, and n layer may be formed by RF plasma CVD, VHF plasma CVD, microwave CVD, hot wire cell, catalytic vapor phase chemical deposition (Cat-CVD). Alternatively, a photo CVD method, an ECR plasma CVD method, or the like may be used.
[0086]
The back electrode layer forming step is a step of forming the back electrode layer on the photoelectric conversion layer, and is preferably formed using a sputtering method. Moreover, it is preferable to form the said contact improvement layer on the said photoelectric converting layer using a sputtering method before forming a back surface electrode layer.
Specifically, the formation of the contact improvement layer using the sputtering method is performed by sputtering in an inert gas atmosphere using, for example, zinc oxide doped with Ga (hereinafter, GZO) as a target. A GZO layer that is a contact improvement layer is formed on the photoelectric conversion layer.
Further, as the method for forming the contact improvement layer, a physical vapor deposition method or a chemical vapor deposition method other than the sputtering method may be used, but it is preferable to use a sputtering method which can obtain good conductive film characteristics at a lower substrate temperature. . In the embodiments described later, a direct current sputtering method is used, but this may be performed by a high frequency sputtering method.
[0087]
Similarly, the back electrode layer is formed by sputtering using a metal containing 95 atomic% or more of Ag (hereinafter referred to as an Ag-based material) on the contact improvement layer (a photoelectric conversion layer when there is no contact improvement layer). The back electrode layer is formed by sputtering in an inert gas atmosphere using a metal).
[0088]
The contact improvement layer can be formed, for example, as shown below.
First, a GZO target for forming a contact improvement layer is attached to the cathode of a DC magnetron sputtering apparatus. Further, the substrate with the transparent conductive oxide film on which the photoelectric conversion layer is formed is attached to the substrate holder. Next, after the film formation chamber is evacuated to vacuum, argon gas is introduced as a sputtering gas. As the sputtering gas, an inert gas such as He, Ne, or Kr can be used in addition to the argon gas, but an argon gas that is stable in discharge and inexpensive is preferable. Moreover, it is more preferable that it is an inert gas containing 0.3-20 vol% of carbon dioxide, More preferably, it is 0.3-10 vol%. By containing carbon dioxide, it is possible to prevent an increase in absorption coefficient due to excessive improvement in conductivity due to Ga doping.
The pressure during sputtering is suitably 0.1 to 1.5 Pa. The residual gas pressure is 1.0 × 10^-Five~ 2.5 × 10^-3Pa is preferred. The substrate temperature is suitably room temperature to 200 ° C., particularly 100 to 150 ° C. from the viewpoint of solar cell characteristics.
In addition, it is preferable that the formation by sputtering is performed while the GZO target is inclined by 30 to 90 ° with respect to the substrate because both low resistance and low absorption can be achieved.
[0089]
The back electrode layer is formed in the same manner as the contact improving layer, first, an Ag-based metal target for forming the back electrode layer is attached to the cathode of the DC magnetron sputtering apparatus. Further, the substrate on which the contact improving layer is formed as described above is attached to the substrate holder. Next, after the film formation chamber is evacuated to vacuum, argon gas is introduced as a sputtering gas. As the sputtering gas, an inert gas such as He, Ne, or Kr can be used in addition to the argon gas, but an argon gas that is stable in discharge and inexpensive is preferable.
The pressure during sputtering is the same as that of the contact improvement layer, and 0.1 to 1.5 Pa is appropriate. The residual gas pressure is 1.0 × 10^-Five~ 2.5 × 10^-3Pa is preferred. The temperature of the substrate during sputtering is suitably from room temperature to 200 ° C., particularly from 100 to 150 ° C., from the viewpoint of adhesion between the substrate and the film. Heating the substrate during sputtering is preferable because it improves the crystallinity of Ag as the back electrode, improves the reflectivity, and lowers the resistance of the entire substrate.
Further, when an Ag layer containing Pd and / or Au is formed as the back electrode layer, it may be formed using Pd and / or Au as separate targets, respectively, and Pd and Alternatively, an Ag alloy containing Au may be prepared and used as a target.
[0090]
The solar cell of the present invention having the back electrode layer through the photoelectric conversion layer in which the p layer, the i layer and the n layer are formed in this order on the substrate with the transparent conductive oxide film,
Boron concentration in the p layer (¹¹B⁺/³⁰Si⁺) Is reduced toward the i-layer in a part or all of the p-layer, so that the band gap of the p-layer can be prevented from becoming too narrow, and the transmittance of the p-layer can be improved. Have. Thereby, since the short circuit current of a solar cell can be maintained high, it is useful because it also has an effect of improving the photoelectric conversion rate.
Further, the boron concentration in the p layer (¹¹B⁺/³⁰Si⁺) Is 0.05 or less at the interface between the p layer and the i layer, so that diffusion of boron contained in the p layer to the i layer is suppressed, and the open-circuit voltage of the solar cell, the fill factor and This is useful because the short-circuit current can be kept high and the photoelectric conversion efficiency is improved.
Furthermore, the formation of the p layer is performed by using a gas containing boron in the raw material mixed gas (for example, B₂H₆Therefore, the solar cell manufacturing apparatus does not require modification, and there are no manufacturing problems (for example, extended formation time, waste of raw material gas, etc.). A battery can be manufactured.
[0091]
【Example】
Hereinafter, the solar cell of the present invention and the manufacturing method thereof will be described in detail using examples. However, the present invention is not limited to this.
Example 1
As Example 1, a solar cell using a substrate with a transparent conductive differential oxide film having a double texture structure shown below was manufactured.
<Formation of alkali barrier layer>
First, a 300 mm × 300 mm × 1.1 mm thick soda lime glass substrate is heated to 500 ° C. in a belt conveyor furnace (belt speed: 1 m / min), and nitrogen gas containing 5 mol% of silane gas is 4 L / min and oxygen gas is 20 L / min. The silica film was produced by spraying the minutes at the same time.
<Formation of first oxide>
Next, this glass substrate with an alkali barrier layer is heated to 540 ° C., and tin tetrachloride, methanol, water, and hydrogen chloride gas are simultaneously sprayed to form SnO as the first oxide.₂Formed. Tin tetrachloride and methanol were heated to 45 ° C. in advance, bubbled with nitrogen gas 2 L / min, and transferred onto the glass substrate. Further, water heated to 100 ° C. was sprayed onto the glass substrate at 15 g / min and hydrogen chloride gas at 0.5 L / min.
After the formation of the first oxide, when the uneven shape of the film surface was observed by SEM, SnO which is the first oxide was observed.₂Was found not to be a continuous film, but to form ridges of macro unevenness. When the SEM image obtained by observing the substrate from directly above was image-processed and calculated, SnO forming a small mountain portion₂The glass substrate surface coverage by 60% is SnO₂Height of a small mountain part consisting of_cIs 0.4 to 0.6 μm, SnO₂The bottom diameter D of the hill part by_c0.5 to 0.7 μm, spacing W between adjacent ridges_cIs 0.2 to 0.5 μm, and the pitch P between adjacent small peaks_cWas 0.7 to 1.2 μm. Further, according to the measurement method described later, the sheet resistance of the small hill portion made of the first oxide is 20 MΩ / □ or more, the haze ratio is 70% (400 to 600 nm average), 55% (600 to 800 nm average), The transmittance at 550 nm by the liquid method was determined to be 88%.
[0092]
<Formation of different oxide layers>
Next, amorphous SiO 2 is formed as a different oxide layer on the small hill portion made of the first oxide and on the soda lime glass substrate on which the small ridge portion is not formed using an atmospheric pressure CVD method.₂A film was formed. The temperature of the glass substrate was 520 ° C., the amount of nitrogen gas containing 5 mol% of silane gas was 0.6 L / min, and the amount of oxygen gas was 3 L / min.
<Formation of second oxide layer>
Further, the glass substrate on which the different oxide layers are formed is heated to 540 ° C., and tin tetrachloride, water, HF gas, and methanol are simultaneously sprayed to form F-doped SnO that is the second oxide layer.₂A film was formed. Tin tetrachloride and methanol were heated to 45 ° C. in advance, bubbled with nitrogen gas 12 L / min, and transferred onto the glass substrate. Further, water heated to 100 ° C. was sprayed on the glass substrate at 90 g / min and HF gas at 3 L / min. Furthermore, methanol was sprayed on the glass substrate by heating to 30 ° C. in advance and transferring it with nitrogen gas at 0.1 L / min.
[0093]
After the formation of the second oxide layer, the uneven shape of the film surface was observed by SEM and AFM. According to SEM observation, the F-doped SnO that is the second oxide layer₂The film is a continuous layer, F-doped SnO₂The coverage of the glass substrate surface by the film was 100%. According to SEM and AFM observations, the height H of the mountain_aIs 0.4 to 0.6 μm, and the interval W between adjacent peaks._aIs 0 to 0.4 μm, the bottom diameter D of the peak_aIs 1.0 to 1.5 μm, pitch P between adjacent peaks_aWas 0.3 to 1.2 μm, and the height from the top of the substrate to the peak of the peak (including the micro-projections) was 0.8 to 1.0 μm. Also, F-doped SnO₂The surface of the film has a large number of micro irregularities, and the height H of the convex parts._bIs 0.1 to 0.2 μm, and the pitch P between the convex portions_bIs 0.1 to 0.2 μm, and the bottom surface diameter D of the convex portion_bIs 0.2 to 0.3 μm, and the height H of the convex portion_b/ Bottom diameter D_bWas 0.73. Further, according to the measurement method described later, the sheet resistance is 10Ω / □, the haze ratio is 42% (400 to 600 nm average), 20% (600 to 800 nm average), and 12 to 61% over the entire wavelength range of 400 to 800 nm. The transmittance at 550 nm by the immersion method was 87%.
F-doped SnO as second oxide layer₂In order to quantify the fluorine content and the conductive electron density in the film, tin tetrachloride, water, HF gas, and methanol were sprayed onto a glass substrate previously coated with silica to obtain F-doped SnO.₂A film was formed. The substrate temperature and gas flow rate were the same as the conditions for forming the second oxide layer in this example. Obtained F-doped SnO₂When the membrane was dissolved in hydrochloric acid containing zinc and then quantitatively analyzed by gas chromatography, the fluorine content was SnO.₂The amount was 0.05 mol%. Further, when the conductive electron density was determined by measurement by the Hall effect (van der Pauw method), 1.5 × 10 5 was obtained.²⁰cm^-3Met. F-doped SnO₂The film thickness was 0.6 μm as measured with a stylus thickness meter.
[0094]
FIG. 6 shows an electron micrograph of the film surface after the second oxide layer is formed. (A) and (B) of FIG. 6 are electron micrographs showing the concavo-convex shape of the film surface represented at a magnification of 20000 times and a magnification of 3500 times, respectively. Thereby, it turned out that the base | substrate with a transparent conductive oxide film used in Example 1 has a double texture structure.
[0095]
A method for measuring the sheet resistance, haze ratio, and transmittance of the obtained substrate with a transparent conductive oxide film will be described below. Sheet resistance was measured by a four-terminal method. A substrate with a conductive oxide film is cut into a 3 cm square, and a pair of 3 cm long electrodes are attached in parallel on the conductive oxide film so that the distance between the electrodes is 3 cm on two opposite sides. It was. Next, the resistance between the electrodes was measured with a tester to obtain sheet resistance.
[0096]
The haze ratio was measured using a spectrophotometer (U3400 manufactured by Hitachi, Ltd.). The measurement wavelength range was 400 to 800 nm, and the measurement interval was 10 nm. First, the transmittance was measured by a regular transmission method using the light incident surface as a glass surface. The transmittance at each wavelength at this time is Td (λ). Next, an integrating sphere having an inner sphere diameter of 150 mmφ was attached, and the membrane surface of the sample was brought into close contact with the integrating sphere, and the integrating sphere transmittance was measured. The transmittance at each wavelength at this time is Tt (λ). From the above measurement results, the haze rate Hz (λ) was calculated by the following equation.
Hz (λ) = (Tt (λ) −Td (λ)) × 100 / Tt (λ) [%]
[0097]
The transmittance was measured using an immersion method in order to minimize a measurement error due to the difference in the size of the irregularities on the surface of the conductive oxide substrate. The immersion method is a method in which a few drops of diiodomethane are dropped on the surface of a substrate with a conductive oxide film, and the transmittance is measured by sandwiching the solution with transparent quartz glass. Since absorption by diiodomethane is mainly 400 nm or less, there is almost no absorption by diiodomethane and quartz glass in the range of 400 to 800 nm. The transmittance was measured by attaching a spectrophotometer (U3400, manufactured by Hitachi, Ltd.) with an integrating sphere (Hitachi, Ltd .: 150-0901) having an inner spherical diameter of 150 mmφ.
[0098]
<Formation of photoelectric conversion layer>
The obtained substrate with a transparent conductive oxide film was cut into a size of 40 mm × 40 mm, and a photoelectric conversion layer and a p / i buffer layer having a pin junction on the transparent conductive oxide film were plasma-treated. It formed on the conditions shown in following Table 1 using the CVD apparatus (SLCM-14, Shimadzu Corp. make). A p-i-n junction is a p-layer, i-layer, and n-layer formed (junction) in this order.
In particular, the formation of the p layer is performed during the formation of the p layer by mixing the raw material mixed gas (B) shown in FIG.₂H₆/ SiH_Four) And the thickness of the p layer (11 nm), the mixing ratio of the raw material mixed gas (from the center of the p layer thickness of 5.5 nm to the end of the formation of the p layer) ( B₂H₆/ SiH_Four) Is zero so that boron (B₂H₆) Was linearly decreased.
In Table 1 below, the buffer layer is a p / i buffer layer.
[0099]
[Table 1]
[0100]
Here, the boron concentration in the p layer of the substrate with the transparent conductive oxide film on which the photoelectric conversion layer is formed is measured by performing secondary ion mass spectrometry (SIMS) on the formed photoelectric conversion layer in the depth direction. Represents the boron concentration¹¹B⁺/³⁰Si⁺It was performed by measuring. As a result, in the p layer¹¹B⁺/³⁰Si⁺The ratio was 0.7 at the interface with the transparent conductive oxide film, 0 at the interface with the i layer, and a gradually decreasing concentration distribution in the p layer.
The boron concentration was determined by using a secondary ion mass spectrometer (Physical Electronics Inc.) as a SIMS measuring device and using a primary ion O₂It is a secondary ion detected under the measurement conditions of (ion energy 500 eV, ion current 50 nA), primary ion irradiation angle 45 deg, raster 300 × 300 μm □ (sputter region).¹¹B⁺and³⁰Si⁺Measure and¹¹B⁺When³⁰Si⁺It calculated | required by ratio with.
[0101]
<Formation of contact improvement layer and back electrode layer>
Next, a GZO layer as a contact improvement layer was formed to a thickness of about 100 nm on the photoelectric conversion layer by a direct current magnetron sputtering method. The sputtering was performed using a GZO target having a glass substrate surface temperature of 100 ° C. and containing 5 atomic% of Ga with respect to the sum of zinc.
In addition, the sputtering is performed in advance by using a vacuum apparatus 10.^-FourAfter depressurizing to Pa or less, Ar gas was 75 sccm, CO₂1 sccm of gas is introduced, and the pressure during sputtering is 4 × 10^-1Pa, sputtering power 2.4 W / cm²Went as. Moreover, Ga content in a GZO layer was 5 atomic% with respect to the sum total of Ga and zinc similarly to the said GZO target.
The performance of the GZO layer has a specific resistance of 5 × 10^-3The absorption coefficient is 1 × 10 at Ω · cm, 500 to 800 nm.^Threecm^-1Met.
Finally, an Ag film containing 100 atomic% of crystalline Ag as a back electrode layer is formed on the GZO layer by sputtering in an Ar gas atmosphere using an Ag target (pressure during sputtering: 4 × 10^-1Pa, sputtering power: 1.4 W / cm²) To form a solar cell having a thickness of about 200 nm and finally producing a solar cell having a size of 5 mm × 5 mm.
[0102]
(referenceExample 2)
  referenceAs Example 2, a solar cell using a substrate with a transparent conductive differential oxide film having no double texture structure shown below was manufactured.
  <Formation of alkali barrier layer and second oxide layer>
  Without forming the first oxide and the different oxide layer, the alkali barrier layer and the second oxide layer were made into a 300 mm × 300 mm × 1.1 mm thick soda lime glass substrate in the same manner as in Example 1. Formed on top.
[0103]
After the formation of the second oxide layer, the uneven shape of the film surface was observed by SEM and AFM. According to SEM observation, the F-doped SnO that is the second oxide layer₂The film is a continuous layer, F-doped SnO₂The coverage of the glass substrate surface by the film was 100%. According to SEM and AFM observations, the height from the top of the substrate to the peak of the peak (including the micro-projections) was 0.6 to 1.0 μm. Also, F-doped SnO₂The surface of the film has a large number of micro irregularities, and the height H of the convex parts._bIs 0.1 to 0.4 μm, and the pitch P between the protrusions_bIs 0.2 to 0.8 μm, and the bottom surface diameter D of the convex portion_bIs 0.2 to 0.8 μm, and the height H of the convex portion_b/ Bottom diameter D_bWas 0.3 to 0.5. Furthermore, the sheet resistance is 9Ω / □, the haze ratio is 42% (400 to 600 nm average), 20% (600 to 800 nm average), and is found to be 4 to 41% over the entire wavelength range of 400 to 800 nm. The transmittance was 88%.
In addition, the F-doped SnO that is the second oxide layer₂As a result of quantifying the fluorine content and the conductive electron density in the film, the fluorine content was SnO as in Example 1.₂The conductive electron density is 1.5 × 10 5.²⁰cm^-3Met. F-doped SnO₂The film thickness was 0.6 to 1.0 μm as measured with a stylus thickness meter.
[0104]
<Formation of photoelectric conversion layer>
Next, a photoelectric conversion layer was formed on the second oxide layer in the same manner as in Example 1.
The boron concentration in the p layer of the substrate with the transparent conductive oxide film on which the photoelectric conversion layer was formed was measured by the same method as in Example 1, and the p layer¹¹B⁺/³⁰Si⁺The ratio was 0.7 at the interface with the transparent conductive oxide film, 0 at the interface with the i layer, and a gradually decreasing concentration distribution in the p layer.
[0105]
  <Formation of contact improvement layer and back electrode layer>
  Next, a contact improvement layer and a back electrode layer are formed on the photoelectric conversion layer in the same manner as in Example 1,referenceThe solar cell of Example 2 was produced.
[0106]
(Example 3)
As Example 3, a solar cell using a substrate with a transparent conductive differential oxide film having a double texture structure shown below was manufactured.
<Formation of alkali barrier layer and first oxide>
An alkali barrier layer and a first oxide were formed in the same manner as in Example 1.
<Formation of different oxide layer and second oxide layer>
Different oxide layers and second oxide layers were formed in the same manner as in Example 1.
[0107]
<Formation of photoelectric conversion layer>
The photoelectric conversion layer was formed in the same manner as in Example 1 except that the thickness of the p / i buffer layer was changed to 6 nm.
The boron concentration in the p layer of the substrate with the transparent conductive oxide film on which the photoelectric conversion layer was formed was measured by the same method as in Example 1, and the p layer¹¹B⁺/³⁰Si⁺The ratio was 0.7 at the interface with the transparent conductive oxide film, 0 at the interface with the i layer, and a gradually decreasing concentration distribution in the p layer.
[0108]
<Formation of contact improvement layer and back electrode layer>
Next, a contact improvement layer and a back electrode layer were formed on the photoelectric conversion layer in the same manner as in Example 1 to produce a solar cell of Example 3.
[0109]
(Comparative Example 1)
As Comparative Example 1, a solar cell using a substrate with a transparent conductive differential oxide film having a double texture structure shown below was manufactured.
<Formation of alkali barrier layer and first oxide>
An alkali barrier layer and a first oxide were formed in the same manner as in Example 1.
<Formation of different oxide layer and second oxide layer>
Different oxide layers and second oxide layers were formed in the same manner as in Example 1.
[0110]
<Formation of photoelectric conversion layer>
In the formation of the photoelectric conversion layer, the p layer is formed by mixing the raw material mixed gas (B) shown in FIG.₂H₆/ SiH_Four) And the thickness of the p layer (11 nm), the mixing ratio (B₂H₆/ SiH_Four) Is constant at 0.01 so that boron (B₂H₆) Was carried out in the same manner as in Example 1 except that the addition was not reduced.
The boron concentration in the p layer of the substrate with the transparent conductive oxide film on which the photoelectric conversion layer was formed was measured by the same method as in Example 1, and the p layer¹¹B⁺/³⁰Si⁺The ratio was 0.7 at the interface with the transparent conductive oxide film, and 0.7 at the interface with the i layer.
[0111]
<Formation of contact improvement layer and back electrode layer>
Next, a contact improvement layer and a back electrode layer were formed on the photoelectric conversion layer in the same manner as in Example 1, and a solar cell of Comparative Example 1 was produced.
[0112]
  Example 1 produced in this way, Reference example 2, Example3 and the solar cell of Comparative Example 1, the haze ratio of the substrate with a transparent conductive oxide film (600 to 800 nm average), B when forming the i layer₂H₆/ SiH_FourTable 2 below shows the thickness of the buffer layer.
[0113]
[Table 2]
[0114]
  Example 1, Reference example 2, Example3 and the solar cell of Comparative Example 1 (electrode surface: 1 cm²) In the solar simulator, AM (air mass) 1.5, strength 100mA / cm²The short-circuit current, the open-circuit voltage, and the fill factor, which are the output characteristics of the solar cell, were measured using a CE-24 solar simulator manufactured by Ohto Research, and the photoelectric conversion efficiency was determined from the measurement results. . The results are shown in Table 3 below.
[0115]
[Table 3]
[0116]
  From the results shown in Table 3, Example 1, Reference example 2, ExampleEach of the solar cells of the present invention indicated by 3 showed higher photoelectric conversion efficiency than Comparative Example 1. In addition, Example 1Reference example2 was compared, it was revealed that it is preferable to use a substrate with a transparent conductive oxide film having a double texture structure because Example 1 has a greater improvement in photoelectric conversion efficiency.
  Example 1, Reference example 2, ExampleIt can be seen that the open-circuit voltage and the fill factor of the solar cell indicated by 3 are greatly improved. This is considered to be because the diffusion of boron contained in the p layer into the i layer was suppressed, and the suppression of this diffusion could be confirmed by SIMS (secondary ion mass spectrometry) described above.
  Further, Example 1, Reference example 2, ExampleIt can be seen that the short-circuit current of the solar cell indicated by 3 is greatly improved. This is because the boron concentration (¹¹B⁺/³⁰Si⁺) Is reduced, the band gap is widened, and the transmittance of the p layer is improved. This was confirmed from the fact that the photoelectric conversion efficiency at the short wavelength of the solar cell was improved. Further, since the fill factor does not decrease even when the boron concentration is reduced, it is considered that the electrical conductivity of the p layer is maintained high.
[0117]
【The invention's effect】
The solar cell of the present invention and the method for manufacturing the solar cell can be formed without complicating the conventional film forming apparatus for manufacturing the solar cell, and can achieve both high transmittance of the p layer and high electrical conductivity of the p layer ( It is possible to provide a solar cell that is excellent in balance) and prevention of diffusion of boron into the i layer, and further excellent in output characteristics.
[Brief description of the drawings]
FIG. 1 is a partially cutaway sectional view showing a configuration of a solar cell of the present invention.
FIG. 2 is a partially cutaway sectional view showing the shape and configuration of a substrate with a transparent conductive oxide film having a double texture structure.
FIG. 3 is an enlarged view of the mountain portion shown in FIG. 2;
4A and 4B are graphs showing the relationship between the mixing ratio of the raw material mixed gas and the film thickness of the p layer. FIG.
FIG. 5 is an enlarged view of a portion other than the conducting wire shown in FIG. 1;
6 (A) and 6 (B) are electron micrographs showing the concavo-convex shape on the surface of the transparent conductive oxide film obtained in Example 1. FIG.
[Explanation of symbols]
1 Solar cell
2 Glass substrate
3 Transparent conductive oxide film
4 p layer
5 i layer
6 n layers
7 Photoelectric conversion layer
8 Back electrode layer
9 Light
10 Lead wire
21 Glass substrate
22 Yamabe
23 Flat part
24 Oyamabe
25 continuous layers
30 Convex
W_a  Spacing between peaks
W_c  Spacing between hills
H_a  Mountain height
H_b  Convex height
H_c  Oyama Height
H_d, H_e  Continuous layer thickness
D_a  Bottom diameter of mountain
D_b  Bottom diameter of convex part
D_c  Bottom diameter of mountain
P_a  Pitch between mountains
P_b  Pitch between convex parts
P_c  Pitch between hills
40 Solar cell substrate
41 Contact improvement layer
42 Photoelectric conversion layer
43 Back electrode
44 glass substrate
45 Transparent conductive oxide film

Claims (3)

A solar cell having a back electrode layer through a photoelectric conversion layer in which a p layer, an i layer and an n layer are formed in this order on a substrate with a transparent conductive oxide film,
The boron concentration ( ¹¹ B ⁺ / ³⁰ Si ⁺ ) in the p layer has a concentration distribution that decreases toward the i layer in a part or all of the p layer, and the p layer and the i layer 0.05 or less at the interface with
The transparent conductive oxide film is a continuous layer made of a discontinuous hill portion made of a first oxide and a second oxide formed thereon, and a micro layer is formed on the surface of the continuous layer. A transparent conductive oxide film consisting of a continuous layer having a large number of convex portions,
A solar cell, wherein an oxide layer made of an oxide having a composition different from that of the first oxide and the second oxide is formed between the small mountain portion and the continuous layer. _2. The solar cell according to claim 1, wherein the first oxide is SnO ₂ , the different oxide is SiO ₂ , and the second oxide is SnO ₂ containing fluorine. On the substrate with a transparent conductive oxide film, a back electrode layer is provided via a photoelectric conversion layer in which a p layer, an i layer and an n layer are formed in this order,
The boron concentration ( ¹¹ B ⁺ / ³⁰ Si ⁺ ) in the p layer has a concentration distribution that decreases toward the i layer in a part or all of the p layer, and the p layer and the i layer 0.05 or less at the interface with
The transparent conductive oxide film is a continuous layer made of a discontinuous hill portion made of a first oxide and a second oxide formed thereon, and a micro layer is formed on the surface of the continuous layer. A transparent conductive oxide film consisting of a continuous layer having a large number of convex portions,
Manufacture of a solar cell in which an oxide layer made of an oxide having a composition different from that of the first oxide and the second oxide is formed between the small mountain portion and the continuous layer. A method,
A transparent conductive oxide film forming step of forming the transparent conductive oxide film on a substrate;
After the transparent conductive oxide film forming step, a photoelectric conversion layer forming step of forming the p layer, the i layer, and the n layer in this order by a plasma CVD method,
A back electrode layer forming step for forming the back electrode layer after the photoelectric conversion layer forming step;
In the transparent conductive oxide film forming step, after forming a discontinuous ridge portion made of the first oxide on the substrate by an atmospheric pressure CVD method, the second oxide is formed on the ridge portion and the substrate. Forming the transparent conductive oxide film by forming a continuous layer comprising:
A continuous layer made of the second oxide is formed on the mounds and the substrate by an atmospheric pressure CVD method,
A method for producing a solar cell, wherein an oxide layer made of the different oxide is formed between the small mountain portion and the continuous layer by an atmospheric pressure CVD method.