JP5243697B2 - Transparent conductive film for photoelectric conversion device and manufacturing method thereof - Google Patents

Description

  The present invention relates to improvement of a transparent conductive film for a photoelectric conversion device and a method for producing the same.

  Photoelectric conversion devices are used in various fields such as light receiving sensors and solar cells. In particular, solar cells are in the limelight as one of the energy sources that are friendly to the earth, and their spread is rapidly progressing due to the recent growing interest in environmental issues and the introduction acceleration policies of each country. In order to achieve both cost reduction and high efficiency of a photoelectric conversion device including such a solar cell, a thin film photoelectric conversion device that requires less raw materials has attracted attention and its development has been energetically performed. In particular, a method of forming a high-quality semiconductor layer on an inexpensive substrate such as glass using a low-temperature process is expected as a method capable of realizing low cost.

  In general, in order to manufacture a photoelectric conversion device, it is indispensable to use a transparent conductive film for a part thereof. This is because the photoelectric conversion device includes one or more photoelectric conversion units between the transparent conductive film and the back electrode layer, and light is incident on the photoelectric conversion units through the transparent conductive film. The photoelectric conversion unit includes a plurality of semiconductor layers that form a pn junction or a pin junction. When the photoelectric conversion unit includes a pin junction, the p-type layer, the i-type layer, and the n-type layer are stacked in this order or in the reverse order, and the i-type photoelectric conversion layer that occupies the main part is amorphous. Are called amorphous photoelectric conversion units, and those having an i-type layer crystalline are called crystalline photoelectric conversion units.

The transparent conductive film is formed using a conductive metal oxide such as ITO (indium tin oxide), tin oxide (SnO ₂ ), or zinc oxide (ZnO), for example, CVD (chemical vapor deposition), sputtering, Or it can form by methods, such as vapor deposition. The transparent conductive film desirably has an effect of increasing the scattering of incident light by having fine irregularities on its surface. This is because the optical path length in the photoelectric conversion unit can be extended by scattering the incident light, thereby increasing the short-circuit current density of the photoelectric conversion device and improving the photoelectric conversion efficiency. It is. The effect of light scattering due to the surface unevenness of the transparent conductive film is not only effective in a so-called bulk photoelectric conversion device including a photoelectric conversion unit composed of a single crystal silicon layer or a polycrystalline silicon layer having a thickness of 100 to 500 μm. It is particularly effective in a so-called thin film photoelectric conversion device including a thin film photoelectric conversion unit having a thickness of 0.1 to 10 μm.

Thin film photoelectric conversion devices are classified according to semiconductor materials used in the photoelectric conversion units included in them, and silicon-based thin film photoelectric conversion devices, CdTe thin film photoelectric conversion devices, and CIS (abbreviation of CuInSe ₂ ) thin film photoelectric conversion devices are typical. . In a silicon-based thin film photoelectric conversion device, the photoelectric conversion unit includes a pin junction composed of a thin film such as amorphous silicon, microcrystalline silicon, and / or polycrystalline silicon, and light is emitted from the substrate side or the opposite side. The transparent conductive film and the p-type layer are disposed on the light incident side. In the CdTe thin film photoelectric conversion device, the photoelectric conversion unit includes a pn junction composed of an n-type CdS layer and a p-type CdTe layer, and light is incident from the opposite side of the substrate, and a transparent conductive film is formed on the light incident side. And an n-type layer are disposed. In the CIS thin film photoelectric conversion device, the photoelectric conversion unit includes a pn junction composed of an n-type CdS layer and a p-type CuInSe ₂ layer, and light is incident from the opposite side of the substrate, and the light incident side is transparent. A conductive film and an n-type layer are disposed.

  The photoelectric conversion unit in the silicon-based thin film photoelectric conversion device includes a pin junction including a p-type layer, an i-type layer that is a substantially intrinsic photoelectric conversion layer, and an n-type layer. A unit including an i-type layer of amorphous silicon is referred to as an amorphous silicon photoelectric conversion unit, and a unit including an i-type layer of crystalline silicon is referred to as a crystalline silicon photoelectric conversion unit. Note that as the amorphous or crystalline silicon-based material, not only a case where silicon is included as a main element but also an alloy material including an element such as carbon, oxygen, nitrogen, or germanium can be used. The main constituent material of the conductive layer is not necessarily the same as that of the i-type layer. For example, amorphous silicon carbide can be used as the p-type layer of the amorphous silicon photoelectric conversion unit. A microcrystalline silicon (also expressed as μc-Si) layer can also be used as the mold layer.

  By the way, a plate-like member such as glass or transparent resin or a sheet-like member can be used for a transparent insulating substrate used in a photoelectric conversion device of a type in which light enters from the substrate side. On the transparent insulating substrate, the transparent conductive film is formed using a conductive metal oxide such as tin oxide or zinc oxide as described above, and can be formed by a method such as CVD, sputtering, or vapor deposition. The transparent conductive film desirably has an effect of increasing the scattering of incident light by having fine irregularities on the surface. As the back electrode layer formed on the photoelectric conversion unit, for example, a metal layer such as Al or Ag can be formed by sputtering or vapor deposition. It is also preferable to form a conductive oxide layer made of ITO, tin oxide, zinc oxide or the like between the photoelectric conversion unit and the metal layer.

  In the amorphous silicon thin film photoelectric conversion device, the initial photoelectric conversion efficiency is lower than that of bulk single crystal and polycrystal photoelectric conversion devices, and conversion is caused by the photodegradation phenomenon (Staebler-Wronsky effect) due to long-term light irradiation. There is a problem that efficiency decreases. Therefore, a crystalline silicon thin film photoelectric conversion device using crystalline silicon such as thin film polycrystalline silicon or microcrystalline silicon as a photoelectric conversion layer is expected to be compatible with both low cost and high efficiency. Has been. This is because the crystalline silicon thin film photoelectric conversion device can be formed at a low temperature by the plasma CVD method similarly to the formation of the amorphous silicon layer, and further, the light deterioration phenomenon hardly occurs. The amorphous silicon photoelectric conversion layer can photoelectrically convert light having a wavelength up to about 800 nm on the long wavelength side, whereas the crystalline silicon photoelectric conversion layer photoelectrically converts light having a wavelength up to about 1200 nm. Can be converted.

  Furthermore, as a method for improving the conversion efficiency of the photoelectric conversion device, a stacked photoelectric conversion device obtained by stacking two or more photoelectric conversion units is known. In this method, a front unit including a photoelectric conversion layer having a large optical forbidden bandwidth (energy band gap) is disposed on the light incident side of the photoelectric conversion device, and a photoelectric conversion layer having a small band gap is sequentially disposed behind the front unit. The conversion efficiency of the entire device is improved by disposing the rear unit including the photoelectric conversion and enabling photoelectric conversion over a wide wavelength range of incident light.

  By the way, in the thin film photoelectric conversion device, it is possible to make the photoelectric conversion layer thinner than the photoelectric conversion device using conventional bulk single crystal or polycrystalline silicon, but on the other hand, the light absorption of the entire thin film Is limited by the film thickness. Therefore, in order to use light incident on the photoelectric conversion unit more effectively, the surface of the transparent conductive film or metal layer in contact with the photoelectric conversion unit is roughened (textured), and light is scattered at the interface to perform photoelectric conversion. A device has been devised to extend the optical path length by entering the unit and to increase the amount of light absorption in the photoelectric conversion layer. This technique is called “optical confinement”, and is an important technique for putting a thin film photoelectric conversion device having high photoelectric conversion efficiency into practical use.

  Here, in order to obtain the surface uneven shape of the transparent conductive film optimal for the photoelectric conversion device, an index that quantitatively represents the surface uneven shape is desired. Haze rate and surface area ratio (Sdr) are used as an index representing such a surface irregularity shape.

  The haze ratio is an index for optically evaluating the surface unevenness of a transparent substrate, and is represented by (diffuse transmittance / total light transmittance) × 100 [%] (JIS K7136). Regarding the measurement of the haze ratio, a haze meter capable of automatic measurement is commercially available and can be easily measured. In general, a C light source is used as the light source for the measurement.

  The surface area ratio is an index that represents not only the height difference of the surface unevenness but also the shape of the unevenness. If the surface unevenness of the transparent conductive film is sharpened, the open circuit voltage and the fill factor of the photoelectric conversion device may decrease. Therefore, the surface area ratio is effective as an index representing the surface unevenness state of the transparent conductive film for the photoelectric conversion device. is there. The surface area ratio is also called a developed surface area ratio, and Sdr is used as an abbreviation thereof. Sdr is defined by the following equations 1 and 2 (KJ Stout, PJ Sullivan, WP Dong, E. Manisah, N. Luo, T. Mathia: "The development of methods for characterization of roughness on three dimensions", Publication no. EUR 15178 EN of the Commission of the European Communities, Lucembourg, 1994).

Here, M and N respectively represent numbers obtained by dividing the entire measurement region into a minute length ΔX in the x direction and a minute length ΔY in the y direction. Z (x, y) represents the height at a predetermined position (x, y) in the minute measurement region ΔXΔY. Sdr represents the rate at which the actual surface area increases with respect to the flat area of the entire measurement region. That is, Sdr increases as the unevenness becomes larger and sharper. Sdr can be measured by a scanning microscope such as AFM (Atomic Force Microscope) or STM (Scanning Transmission Microscope).

  Amorphous silicon thin film photoelectric conversion devices are often formed on a transparent substrate such as glass, and a tin oxide film having surface irregularities is often used as a transparent conductive film thereon. As described above, the surface unevenness of the tin oxide film can effectively contribute to light confinement in the photoelectric conversion layer. However, when a tin oxide film having surface irregularities effective for light confinement is formed on a glass substrate by an atmospheric pressure thermal CVD method, a high temperature process of about 550 to 650 ° C. is required, and there is a problem that the manufacturing cost is high. . In addition, there is a problem that an inexpensive substrate such as glass or plastic film cannot be used because the film forming temperature is high. Furthermore, if the tempered glass is subjected to a high temperature process, the tempering effect disappears, so that it cannot be used for the substrate. Therefore, in the case of a large area solar cell, the glass substrate must be thick in order to ensure its strength, resulting in a problem that the weight of the solar cell increases.

  Further, the tin oxide film has low plasma resistance, and the tin oxide film is reduced in the deposition environment of the photoelectric conversion layer at a high plasma density containing hydrogen. Since the tin oxide film is blackened when reduced, incident light is absorbed by the blackened tin oxide film and the amount of light transmitted to the photoelectric conversion layer is reduced, which causes a reduction in conversion efficiency.

  Furthermore, as described above, the amorphous silicon thin film solar cell has a problem that the initial photoelectric conversion efficiency is lower than that of a bulk single crystal or polycrystalline solar cell, and further, the conversion efficiency is lowered due to a photodegradation phenomenon. Therefore, a crystalline silicon thin film solar cell using crystalline silicon such as thin film polycrystalline silicon or microcrystalline silicon as a photoelectric conversion layer has been studied with the expectation that it can achieve both low cost and high efficiency. ing. This is because the crystalline silicon thin film solar cell can be formed at a low temperature by the plasma CVD method similarly to the formation of amorphous silicon, and further, the light deterioration phenomenon hardly occurs. The amorphous silicon photoelectric conversion layer can photoelectrically convert light having a wavelength up to about 800 nm on the long wavelength side, whereas the crystalline silicon photoelectric conversion layer photoelectrically converts light having a wavelength up to about 1200 nm. Can be converted. However, the crystalline silicon layer requires a higher plasma density than the deposition condition of the amorphous silicon layer, and it has been difficult to significantly improve the photoelectric conversion rate when a tin oxide film is used for the transparent conductive film. .

  On the other hand, zinc oxide has the advantage that it is cheaper than tin oxide or ITO, which is widely used as a material for transparent conductive films, and has high plasma resistance, and is used as a transparent conductive film material for thin film solar cells. Is preferred. In particular, a crystalline silicon layer such as a thin-film polycrystalline silicon layer or a microcrystalline silicon layer that uses a large amount of hydrogen and requires a high plasma density compared to the deposition condition of an amorphous silicon layer is used as a photoelectric conversion unit. In the crystalline silicon thin film photoelectric conversion device included as a part, the conductive film of zinc oxide is effective.

  Note that the terms “crystalline” and “microcrystal” in the present specification also mean those partially containing amorphous.

  In Japanese Patent Application Laid-Open No. 2002-25350 of Patent Document 1, two Ga-doped zinc oxide layers that are laminated under different DC (direct current) sputtering conditions are formed as a transparent conductive film on a glass substrate. The first layer is deposited to a thickness of 500 nm at a deposition temperature of 250 ° C., the second layer is deposited to a thickness of 400 nm at a deposition temperature of 100 ° C., and then wet etched with hydrochloric acid to form a surface irregularity on the transparent conductive film. Is formed. In this case, the adhesion between the transparent conductive film and the substrate is increased by forming the first zinc oxide layer at a high temperature, and the etching rate during wet etching is increased by forming the second zinc oxide layer at a low temperature. It is said that surface irregularities are easily formed.

As a method for forming surface irregularities on a transparent conductive film of zinc oxide without performing wet etching, for example, in Japanese Patent Application Laid-Open No. 2000-252501, Patent Document 2 discloses a low pressure thermal CVD method (MOCVD (organometallic CVD) at a low temperature of 200 ° C. or less. It is also disclosed that a zinc oxide thin film having surface irregularities can be formed. Since this low-pressure thermal CVD method is a process at a temperature of 200 ° C. or lower, which is lower than that of atmospheric pressure CVD, the cost can be reduced. In the low pressure thermal CVD method, an inexpensive substrate such as glass or plastic film can be used. Further, in the low pressure thermal CVD method, tempered glass can be used, and the glass substrate of the large area solar cell can be thinned to about 2/3, and the weight can be reduced. Further, the low-pressure thermal CVD method is preferable for manufacturing a thin-film solar cell from the viewpoint of manufacturing cost because it can form a film at a speed one digit or more faster than the sputtering method and has high utilization efficiency of raw materials.
JP 2002-25350 A JP 2000-252501 A

  In order to enhance the light confinement effect, the present inventors have examined a method for increasing the surface irregularities of a transparent conductive film including a zinc oxide layer produced by sputtering. In the method for producing a transparent conductive film according to Patent Document 1, Since wet etching is performed with hydrochloric acid to form surface irregularities in the transparent conductive film, the following various problems have been found. That is, the etching ability decreases with the number of times the etchant is used and the reproducibility of the surface unevenness becomes poor, the problem that uniform surface unevenness cannot be obtained due to etching unevenness in a large-area transparent conductive film, and the glass substrate When an antireflective coating (AR coat) is applied, a problem has been found that the AR coat is melted by hydrochloric acid or damaged. In addition, the sputtering method has a problem that the deposition rate of the transparent conductive film is slow, which increases the manufacturing cost.

  When a method for increasing the surface irregularities of the zinc oxide film using the low-pressure thermal CVD method was examined, the zinc oxide film manufacturing method disclosed in Patent Document 2 requires a thick zinc oxide film. Therefore, in the transparent conductive film of the thick zinc oxide film, the light absorption loss is increased, the light scattering effect due to the surface unevenness is offset, and the short circuit current density becomes insufficient.

  In view of the problems in the prior art as described above, an object of the present invention is to provide a transparent for a photoelectric conversion device in which the surface unevenness is effectively increased without performing wet etching of the transparent conductive film and without increasing the film thickness. It is to provide a conductive film.

In the transparent conductive film for photoelectric conversion devices of the present invention, the transparent conductive film has an atomic concentration of 2 × 10 ¹⁹ atoms / cm ³ or more and 2 × 10 ²⁰ atoms as measured by secondary ion mass spectrometry (SIMS). It is made of zinc oxide containing H atoms of / cm ³ or more, and the value of the ratio of B atom concentration / H atom concentration is varied so as to have a minimum value at a predetermined position in the thickness direction of the transparent conductive film. It is characterized by. Thereby, the surface unevenness | corrugation of the transparent conductive film for photoelectric conversion apparatuses can be enlarged effectively.

The transparent conductive film is formed on a transparent insulating substrate, and the position of the minimum value of the B atom concentration / H atom concentration ratio is at a distance of 0.1 μm to 0.3 μm from the substrate surface. It is preferable that it exists in the range by the side of a board | substrate from half of the total thickness of this. The minimum value of the ratio of B atom concentration / H atom concentration is preferably 0.01 or more and 0.1 or less. Furthermore, the transparent conductive film also has a maximum value of the ratio of B atom concentration / H atom concentration at a predetermined position in the thickness direction, and the maximum value is preferably 0.05 or more. The transparent conductive film also includes C atoms, and the value of the ratio of B atom concentration / C atom concentration is varied so as to have a maximum value at a predetermined position in the thickness direction of the transparent conductive film. .5 or more is preferable.

  The transparent insulating substrate provided with the above-described transparent conductive film for photoelectric conversion device can be preferably used as a substrate for photoelectric conversion device. Moreover, the thin film photoelectric conversion apparatus which has the improved photoelectric conversion characteristic can be obtained by pinching | interposing one or more photoelectric conversion units with the above transparent conductive films for photoelectric conversion apparatuses, and a back surface electrode layer.

The transparent conductive film for a photoelectric conversion device as described above was formed in a low-pressure CVD method with a thickness of 0.1 μm to 0.3 μm from the substrate surface at the initial deposition of the transparent conductive film at the first substrate temperature. After that, at least a part of the remaining thickness of the transparent conductive film is formed at the second substrate temperature, and the first substrate temperature can be preferably set higher than the second substrate temperature. . Moreover, the transparent conductive film for photoelectric conversion devices as described above has a thickness of 0.1 μm to 0.3 μm from the substrate surface at the initial stage of deposition of the transparent conductive film at the first B ₂ H ₆ gas flow rate in the low pressure CVD method. after forming the portion is, performs deposition of the remaining at least a portion of the thickness of the portion of the transparent conductive film in the second B ₂ H ₆ gas flow rate, the first B ₂ H ₆ gas flow rate is the second It can also be preferably formed by setting it relatively larger than the B ₂ H ₆ gas flow rate.

  In the present invention, the term “low-pressure thermal CVD method” means a thermochemical vapor deposition method using a gas having a pressure lower than atmospheric pressure. That is, the low pressure thermal CVD method is also called a low pressure CVD method or a low pressure CVD method (low pressure CVD: abbreviated as LP-CVD), and is a thermochemical vapor deposition method using a gas having a pressure lower than atmospheric pressure. Defined. Normally, the term “CVD” means “thermal CVD” except when the energy source is clearly indicated, such as “plasma CVD”, “photo CVD”, etc. It is synonymous with “thermal CVD method”. The low-pressure thermal CVD method also includes an organic metal CVD method under reduced pressure (abbreviation, MO-CVD method).

According to the present invention, the transparent conductive film is composed of zinc oxide containing 2 × 10 ¹⁹ atoms / cm ³ or more of B atoms and 2 × 10 ²⁰ atoms / cm ³ or more of H atoms, and B atom concentration / H atom concentration. The value of the ratio has a minimum value at a predetermined position in the thickness direction of the transparent conductive film, so that even if the total thickness of the zinc oxide film is thin, the surface unevenness becomes large and the light confinement effect is improved, and low A resistive transparent conductive film can be obtained. Moreover, since wet etching is not used for forming the surface irregularities of the transparent conductive film, the surface irregularities can be formed with good reproducibility. In addition, when this transparent conductive film is applied to a thin film photoelectric conversion device, a short circuit current density (Jsc) and a fill factor (FF) of the thin film photoelectric conversion device are improved, and a thin film photoelectric conversion device with improved photoelectric conversion characteristics is provided. can do.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings of the present application, dimensional relationships such as thickness and length are appropriately changed for the sake of clarity and simplification, and do not represent actual dimensional relationships.

  In the photoelectric conversion device, it is important to increase the surface concavity and convexity of the transparent conductive film to increase the light confinement effect and maintain a low electrical resistance. However, as described in the problem to be solved by the invention, it is not preferable to use wet etching or increase the film thickness of the transparent conductive film in order to form surface irregularities in the transparent conductive film. In order to solve the problem, the present inventors examined a zinc oxide film as a transparent conductive film for a thin film photoelectric conversion device by paying attention to its composition. As a result, the surface roughness was increased without increasing the total film thickness. And it discovered that the transparent conductive film by which resistance was suppressed low was obtained.

That is, according to the present invention, a transparent conductive film made of zinc oxide containing 2 × 10 ¹⁹ atoms / cm ³ or more B atoms and 2 × 10 ²⁰ atoms / cm ³ or more H atoms as atom concentration measured by SIMS The B atom concentration / H atom concentration ratio has a minimum value at a predetermined position in the thickness direction of the transparent conductive film.

  If a minimum value of B atom concentration / H atom concentration is provided at a predetermined position in the thickness direction of the zinc oxide film, surface irregularities can be increased without increasing the thickness of the zinc oxide film. As an index of the increase in surface irregularities, the haze rate increases. Further, the conventional wet etching for forming the surface irregularities becomes unnecessary.

The B atom concentration / H atom concentration ratio (B concentration / H concentration) and the B atom concentration / C atom concentration ratio (B concentration / C concentration) in the zinc oxide film were measured by SIMS using a Cs ⁺ ion source. can do. The zinc oxide film, which is the transparent conductive film of the present invention, has a minimum value of B concentration / H concentration at a predetermined thickness from the substrate side to the surface side. It is preferable that the position of the minimum value of B concentration / H concentration is closer to the substrate than half the total thickness of the zinc oxide film. Further, a maximum value of B concentration / H concentration may exist on the substrate side from the position of the minimum value of B concentration / H concentration.

  When the zinc oxide film contains C, it is preferable that the B concentration / C concentration also has a minimum value. Further, a maximum value of B concentration / C concentration may exist on the substrate side from a minimum value of B concentration / C concentration. When a maximum value exists in the B concentration / C concentration, it is preferable that the position substantially coincides with the position of the maximum value of the B concentration / H concentration.

  In the deposition of a zinc oxide film containing H and B, B tends to be concentrated on the growth surface of the film, and if B is concentrated on the growth surface, the surface unevenness tends to be reduced. On the other hand, B acts as a dopant, and the higher the concentration of B, the lower the resistance of the zinc oxide film. Therefore, normally, the low resistance of the zinc oxide film and the increase in surface irregularities are not compatible. In addition to the dopant, those that contribute to the reduction in resistance of the zinc oxide film include interstitial Zn and oxygen vacancies, which are considered to be affected by the H concentration.

  In the present invention, since the B concentration / H concentration has a minimum value, a seed layer having a low B concentration on the surface is once provided during the growth of the zinc oxide film. On the surface of this seed layer, the surface unevenness becomes larger compared to the case where the zinc oxide film having the same thickness does not have the minimum value of B concentration / H concentration, and the zinc oxide layer formed subsequently on this seed layer The growth of the surface irregularities of the film is promoted even when the B concentration increases. Therefore, even when the total thickness of the zinc oxide film is thin, the surface unevenness increases, and the low resistance due to the high B concentration can be realized, and the short-circuit current density (Jsc) and the fill factor ( FF) can be improved.

  The absolute value of the concentration measured by SIMS may have an error of about 1/2 to 2 times depending on the state of the measuring device and the sample. Therefore, since the reproducibility of the measured value is higher in the element concentration ratio under the same measurement conditions than in the absolute value of the concentration, it is possible to evaluate the B concentration / H concentration or B concentration / C concentration of the zinc oxide film. is important. Further, as described above, interstitial Zn and oxygen vacancies can be cited as factors contributing to lowering the resistance of the zinc oxide film in addition to the dopant, and if these exist, carrier electrons increase and the resistance decreases. The bond energy of O—H is 428 kJ / mol, and the bond energy of O═C is also 444 kJ / mol, which is large. Therefore, if H and C are contained in the zinc oxide film, interstitial Zn and oxygen deficiency It is thought to be involved in generation. Therefore, the B concentration / H concentration and the B concentration / C concentration can be important parameters regarding the surface roughness and resistance of the zinc oxide film.

  In the present invention, the minimum value of B concentration / H concentration is preferably 0.01 or more from the viewpoint of reducing the resistance of the transparent conductive film, and the minimum value is set to 0.1 or less from the viewpoint of promoting the growth of surface irregularities. It is preferable to do. From the viewpoint of reducing the resistance of the zinc oxide film, the maximum value of B concentration / H concentration is preferably 0.05 or more. In the case of a zinc oxide film containing C, it is preferable that the B concentration / C concentration has a maximum value of 1.5 or more at the position of the maximum value of B concentration / H concentration from the viewpoint of reducing the resistance.

  The position of the minimum value of B concentration / H concentration is preferably in a range closer to the substrate than half the total thickness of the zinc oxide film. This is because a seed layer of a zinc oxide film having a low surface B concentration can be formed at the initial stage of the growth of the zinc oxide film, so that an increase in surface irregularities and a reduction in resistance of the zinc oxide film can be realized effectively.

  In FIG. 1, the board | substrate for thin film photoelectric conversion apparatuses and thin film photoelectric conversion apparatuses by an example of embodiment of this invention are shown with typical sectional drawing. A thin film photoelectric conversion device substrate 1 in FIG. 1 includes a transparent insulating substrate 11 and a transparent conductive film 12 formed thereon. On the transparent conductive film 12, the front photoelectric conversion unit 2, the rear photoelectric conversion unit 3, and the back electrode layer 4 are laminated in this order, and the thin film photoelectric conversion device 5 is configured by these layers.

  As the transparent insulating substrate 11, a plate-like member or a sheet-like member made of glass, transparent resin or the like is mainly used. In particular, since the glass substrate has high light transmittance and is inexpensive, it can be preferably used as the transparent insulating substrate 11.

  That is, since the transparent insulating substrate 11 is located on the light incident side of the thin film photoelectric conversion device 5, it is preferably as transparent as possible so that more sunlight can be transmitted and absorbed by the photoelectric conversion units 2 and 3. A glass plate is suitable as the material. From the same viewpoint, it is preferable that a non-reflective coating (not shown) is applied to the light incident surface of the transparent insulating substrate 11 so as to reduce the light reflection loss on the light incident surface of sunlight.

Although the transparency insulating substrate 11 as described above it is possible to use a glass substrate alone, further, transparency insulating substrate 11 is light-transmitting substrate 111 and the transparent under such glass having a smooth surface More preferably, it consists of a laminate with the formation 112. At this time, the translucent underlayer 112 preferably has fine surface irregularities having a root mean square roughness of 5 to 50 nm at the interface on the transparent conductive film 12 side, and the convex portions are preferably curved surfaces. Also by providing such a light-transmitting underlayer 112, it is possible to control the surface area ratio of the thin film photoelectric conversion device substrate 1 to a preferable value.

The translucent underlayer 112 can be formed by applying translucent fine particles 1121 together with a binder 1122 containing a solvent, for example. More specifically, a metal oxide such as silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and tantalum oxide can be used as the light-transmitting binder 1122. The light-transmitting fine particles 1121 include silica (SiO ₂ ), titanium oxide (TiO ₂ ), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), indium tin oxide (ITO), or magnesium fluoride. (MgF ₂ ) or the like can be used. Examples of the method for applying the binder 1122 and the light-transmitting fine particles 1121 to the surface of the light-transmitting substrate 111 include a dipping method, a spin coating method, a bar coating method, a spray method, a die coating method, a roll coating method, and a flow coating method. However, a roll coat method is more preferable for applying the translucent fine particles 1121 densely and uniformly. When the coating operation is completed, the coated thin film 112 is immediately heated and dried.

Zinc oxide is used as a material for the transparent conductive film 12 disposed on the transparent insulating substrate 11. The zinc oxide film contains 2 × 10 ¹⁹ atoms / cm ³ or more of B atoms and 2 × 10 ²⁰ atoms / cm ³ or more of H atoms as impurities. A zinc oxide film is preferable for manufacturing a thin film photoelectric conversion device including a crystalline photoelectric conversion unit because a texture having a light confinement effect can be formed even at a low temperature of 200 ° C. or less and has high plasma resistance. That is, the zinc oxide transparent conductive film of the substrate for a thin film photoelectric conversion device of the present invention can be formed at a substrate temperature of 200 ° C. or less by a low pressure thermal CVD method. Note that the substrate temperature here means the temperature of the surface where the substrate is in contact with the heating unit of the film forming apparatus.

In forming the zinc oxide film, diethyl zinc (DEZ) or dimethyl zinc (DMZ) as an organic metal vapor, water as an oxidant vapor, and B as a doping gas into a vacuum chamber maintained at a pressure of 5 to 200 Pa. _In addition to ₂ H ₆ , it is preferable to introduce a mixed gas containing at least one of H ₂ , N ₂ , and a rare gas (He, Ar, Ne, Kr, Rn) as a carrier gas. More specifically, for example, the flow rate of DEZ is preferably 10 to 1000 sccm, the flow rate of water is 10 to 1000 sccm, the flow rate of H ₂ is 100 to 10,000 sccm, and the flow rate of Ar is preferably 100 to 10,000 sccm. B ₂ H ₆ is preferably contained at a ratio of 0.1% to 10% with respect to DEZ.

  As a method of providing the minimum value of B concentration / H concentration in the thickness direction of the zinc oxide film, there is a method of increasing the substrate temperature at the initial stage of film formation by using a low pressure thermal CVD method and then lowering the substrate temperature. It is done. If the substrate temperature is increased, a large amount of B is incorporated in the zinc oxide film, and the B atom concentration increases. Thereafter, if the substrate temperature is lowered, the B concentration in the film is lowered. However, even if film formation is continued while maintaining a low substrate temperature thereafter, B tends to be concentrated on the growth surface, so the B concentration in the zinc oxide film gradually increases in the thickness direction. This is presumably because the temperature of the growth surface becomes higher than the substrate temperature due to the heat of formation of zinc oxide. As a result, a minimum value is obtained for the B concentration / H concentration in the thickness direction of the zinc oxide film. After the minimum value is obtained, the substrate temperature may be constant or the substrate temperature may be increased. On the other hand, the maximum value is obtained on the substrate side from the position of the minimum value of B concentration / H concentration. Further, when C is contained in the zinc oxide film, a minimum value and a maximum value are obtained for the B concentration / C concentration. Typically, the substrate temperature is preferably relatively higher by 10 ° C. or more in the initial stage of film formation than in the latter stage of film formation.

As another method of providing a minimum value for the B concentration / H concentration in the thickness direction of the zinc oxide film, a method of increasing the flow rate of B ₂ H _{6 at} the initial stage of film formation and then lowering it by using a low pressure thermal CVD method. Is mentioned. After the minimum value is obtained, the B ₂ H ₆ flow rate may be increased again. Since the B atom concentration in the zinc oxide film can be controlled by the flow rate of B ₂ H ₆ , the minimum value of B concentration / H concentration can also be obtained in this method. Typically, it is preferable that the ratio of the B ₂ H ₆ flow rate to the DEZ flow rate is relatively larger by 0.1% or more in the initial stage of film formation than in the latter stage of film formation.

  In the zinc oxide film, it is preferable from the viewpoint of obtaining the light confinement effect of the thin film photoelectric conversion device that the crystal grain size is approximately 50 to 500 nm and surface irregularities having a height difference of 20 to 200 nm are formed. Further, the haze ratio of the zinc oxide film is preferably 15% or more, more preferably 20% or more from the viewpoint of the light confinement effect. The sheet resistance of the zinc oxide film is preferably 15Ω / □ or less, more preferably 10Ω / □ or less, in order to suppress resistance loss.

  The average thickness of the zinc oxide film is preferably 0.7 to 5 μm, and more preferably 1 to 3 μm. This is because if the zinc oxide film is too thin, it becomes difficult to provide surface irregularities that effectively contribute to the light confinement effect, and it becomes difficult to obtain the conductivity necessary for the transparent conductive film. On the other hand, if it is too thick, the amount of light that passes through the zinc oxide film itself and reaches the photoelectric conversion unit is reduced and the photoelectric conversion efficiency is lowered. Further, when the zinc oxide film is too thick, the film formation cost increases due to the increase of the film formation time.

  The surface area ratio (Sdr) of the zinc oxide film is preferably 55% or more and 95% or less. When Sdr is too large, the open circuit voltage (Voc) and the fill factor (FF) are lowered, and the conversion efficiency (Eff) is lowered. In some cases, the short circuit current density (Jsc) decreases and the conversion efficiency (Eff) decreases. The reason why Voc and FF decrease when Sdr is large is that the surface unevenness of the substrate 1 for a thin film photoelectric conversion device is acute, the coverage of the silicon semiconductor layer on the transparent conductive film 12 deteriorates, and the contact resistance This is thought to be due to an increase in the leakage current or an increase in leakage current. The reason why Jsc decreases when Sdr is large is thought to be that the growth of the semiconductor layer on the transparent conductive film is inhibited, the film quality of the semiconductor layer is decreased, and loss due to carrier recombination increases. On the contrary, when Sdr is too small, the surface unevenness of the thin film photoelectric conversion device substrate 1 becomes small, so that the effect of light confinement is weakened, and Jsc is lowered and Eff is lowered. The surface area ratio can be set to an optimum value by controlling the deposition conditions of the zinc oxide film. For example, in the low-pressure thermal CVD method, the surface area ratio of the zinc oxide film varies greatly depending on the film forming conditions such as the substrate temperature, the raw material gas flow rate, and the pressure, so that the surface area ratio is set to a desired value by controlling them. It is possible.

  If an amorphous silicon-based material is selected as the front photoelectric conversion unit 2, it has sensitivity to light with a wavelength of about 360 to 800 nm, and if a crystalline silicon-based material is selected for the rear photoelectric conversion unit 3, it is more Sensitive to long light up to about 1200 nm wavelength. Therefore, the thin film photoelectric conversion device 5 stacked in this order from the light incident side to the front photoelectric conversion unit 2 of the amorphous silicon-based material and the rear photoelectric conversion unit 3 of the crystalline silicon-based material has the incident light in a wider wavelength range. It becomes possible to use it effectively. However, “silicon-based” materials include silicon alloy semiconductor materials containing silicon such as silicon carbide and silicon germanium in addition to silicon.

  The front photoelectric conversion unit 2 can be formed by stacking each semiconductor layer by a plasma CVD method in the order of, for example, a pin type. Specifically, for example, a p-type amorphous silicon carbide layer doped with 0.01 atomic% or more of boron, which is a conductivity type determining impurity atom, is used as one conductivity type layer 21, and an intrinsic amorphous silicon layer is a photoelectric conversion layer. 22 and an n-type microcrystalline silicon layer doped with 0.01 atomic% or more of phosphorus, which is a conductivity type determining impurity atom, may be deposited in this order as a reverse conductivity type layer 23.

  The rear photoelectric conversion unit 3 can also be formed by laminating each semiconductor layer by a plasma CVD method in the order of, for example, a pin type. Specifically, for example, a p-type microcrystalline silicon layer doped with 0.01 atomic% or more of boron is used as one conductivity type layer 31, an intrinsic crystalline silicon layer is used as a photoelectric conversion layer 32, and phosphorus is 0.01 atom. % Or more doped n-type microcrystalline silicon layer may be deposited as the reverse conductivity type layer 33 in this order.

  As the back electrode layer 4, at least one selected from Al, Ag, Au, Cu, Pt, and Cr can be preferably deposited as the at least one metal layer 42 by a sputtering method or an evaporation method. In addition, a conductive oxide layer 41 such as ITO, tin oxide, or zinc oxide is preferably formed as a part of the back electrode layer 4 between the photoelectric conversion unit 3. The conductive oxide layer 41 enhances the adhesion between the photoelectric conversion unit 3 and the back surface metal layer 42, increases the light reflectance of the back electrode layer 4, and further prevents chemical changes of the photoelectric conversion unit 3. It can also function as a protective layer.

It will be apparent that the transparent conductive film for a photoelectric conversion device of the present invention is not limited to a silicon-based thin film photoelectric conversion device, and is equally effective in other thin film photoelectric conversion devices. For example, in a CdTe thin film photoelectric conversion device, a structure in which a substrate, p-type CdTe, n-type CdS, and the transparent conductive film of the present invention are sequentially laminated is also effective. Further, in the CIS thin film photoelectric conversion device, a structure in which a substrate, a Mo back electrode, p-type CuInSe ₂ , n-type CdS, and the transparent conductive film of the present invention are sequentially laminated is also effective. The transparent conductive film of the present invention is also effective in an abbreviation CIGS thin film photoelectric conversion device using CuInSe ₂ to which Ga is added.

  Moreover, although the light confinement effect is limited, the transparent conductive film of the present invention is also effective in a bulk photoelectric conversion device having a single crystal or polycrystalline layer thickness of 50 μm or more.

  In the following, various embodiments of the present invention will be described in more detail in comparison with comparative examples according to the prior art.

Example 1
As Example 1 of the present invention, a transparent conductive film for a photoelectric conversion device corresponding to FIG. 1 was produced. Specifically, the transparent insulating substrate 11 was produced by forming the transparent base layer 112 containing the SiO ₂ fine particles 1121 on the glass substrate 111 having a thickness of 910 mm × 455 mm and a thickness of 4 mm. As a coating solution for forming the light-transmitting underlayer 112, tetraethoxysilane is added to a mixture of a spherical silica dispersion having an average particle diameter of 100 nm, water, and ethyl cellosolve, and hydrochloric acid is added to add tetraethoxysilane. A hydrolyzed silane was used. After applying this coating liquid on the glass substrate 111 with a printing machine, it is dried at 90 ° C. for 30 minutes, and then heated at 450 ° C. for 5 minutes, thereby forming a transparent insulation with fine irregularities formed on the surface. A substrate 11 was obtained. When the surface of the transparent insulating substrate 11 was observed with an atomic force microscope (AFM), the surface irregularities with convex portions reflecting the shape of the fine particles 1121 were confirmed, and their root mean square roughness (RMS) Was 5-50 nm. In addition, RMS in this application is calculated | required from the atomic force microscope (AFM) image which observed the square area | region whose one side is 5 micrometers (ISO 4287/1). For this AFM measurement, a non-contact mode of a Nano-R system (manufactured by Pacific Nanotechnology) was used.

A transparent conductive film 12 made of zinc oxide was formed on the obtained transparent insulating substrate 11 by a low pressure thermal CVD method. In order to obtain the minimum value of B concentration / H concentration in the thickness direction of the zinc oxide film 12 which is a feature of the present invention, the film is formed at a substrate temperature of 170 ° C. until the initial thickness of about 0.2 μm, and the rest The film was formed at 160 ° C. with the substrate temperature lowered by 10 ° C. This zinc oxide film 12 was deposited under the deposition conditions of a pressure of 20 Pa, a flow rate of diethyl zinc (DEZ) of 400 sccm, a flow rate of water of 1000 sccm, a diborane (B ₂ H ₆ ) flow rate of ₂ sccm, an argon flow rate of 500 sccm, and a hydrogen flow rate of 500 sccm. . The B ₂ H ₆ flow rate was 0.5% with respect to the DEZ flow rate.

In the graph of FIG. 2, the distribution in the depth direction of the B concentration / H concentration and the B concentration / C concentration measured by SIMS for the zinc oxide film 12 of Example 1 is shown. That is, in this graph, the horizontal axis represents the depth (μm) from the surface of the zinc oxide film, and the vertical axis represents the concentration ratio of B concentration / H concentration and the concentration ratio of B concentration / C concentration. Further, the bold curve in the graph represents the B concentration / H concentration, and the thin curve represents the B concentration / C concentration. Note that a Cs ⁺ ion source was used for SIMS.

  As can be seen from the graph of FIG. 2, from the transparent insulating substrate 11 side toward the surface side of the zinc oxide film 12, the B concentration / H concentration once increases and passes through the maximum value, then decreases and then decreases. Gradually increases toward the surface. The absolute value of the B concentration / C concentration is different from that of the B concentration / H concentration, but is almost the same as the B concentration / H concentration, from the transparent insulating substrate 11 side toward the surface side of the zinc oxide film 12. It has a local minimum value that has increased once and then passed through a local maximum value, and then gradually increases toward the surface side.

In FIG. 2, the minimum value of B concentration / H concentration was 4.9 × 10 ⁻² . The total thickness of the zinc oxide film obtained from the SIMS sputtering rate was 1.65 μm, and the position of the minimum value of B concentration / H concentration was at a position of about 0.2 μm from the substrate. Further, the maximum value of B concentration / H concentration was 6.1 × 10 ⁻² , and the position thereof was a position about 0.1 μm thick from the substrate. On the other hand, the minimum value of B concentration / C concentration was 1.1. The B concentration / C concentration also had a local maximum value at a thickness of about 0.1 μm from the substrate, and the local maximum value was 1.8. The reason why the B concentration / H concentration and the B concentration / C concentration are low on the outermost surface of the zinc oxide film is that the SIMS measurement sensitivity becomes unstable on the outermost surface, and the substantial concentration ratio is It is not represented.

The B concentration in the zinc oxide film measured by SIMS has a distribution in the depth direction, but was in the range of 1.1 × 10 ^{20 to} 3.6 × 10 ²⁰ pieces / cm ³ . The H concentration in the zinc oxide film was in the range of 8.7 × 10 ^{20 to} 2.9 × 10 ²¹ pieces / cm ³ . Furthermore, the C concentration in the zinc oxide film was in the range of 5.0 × 10 ^{19 to} 1.0 × 10 ²⁰ pieces / cm ³ .

  The thickness obtained from the interference of the reflection spectrum with respect to the obtained zinc oxide film 12 was 1.65 μm, which substantially coincided with the film thickness obtained from the sputtering rate of SIMS. Further, in the obtained zinc oxide film 12, the sheet resistance was 12.3Ω / □, the surface area ratio (Sdr) was 75.5%, and the haze ratio measured using a C light source was 32.2. %Met. In addition, Sdr in this application is also calculated | required from the atomic force microscope (AFM) image which observed the square area | region whose one side is 5 micrometers. The non-contact mode of Nano-R system (manufactured by Pacific Nanotechnology) was also used for this AFM measurement.

(Comparative Example 1)
Also in Comparative Example 1 according to the conventional method, similar to Example 1, the zinc oxide film 1 2 as shown in FIG. 1 is formed. That is, Comparative Example 1 was different from Example 1 only in that the substrate temperature during deposition of the zinc oxide film was maintained at a constant 160 ° C.

  In the graph of FIG. 3 similar to FIG. 2, B direction / H concentration and B concentration / C concentration depth direction distributions of the zinc oxide film of Comparative Example 1 measured by SIMS are shown. In this graph, the B concentration / H concentration monotonously increases from the transparent insulating substrate 11 side toward the surface side of the zinc oxide film 12, and the minimum value does not exist. The absolute value of the B concentration / C concentration is also different from that of the B concentration / H concentration, but is monotonous from the transparent insulating substrate 11 side to the surface side of the zinc oxide film 12 in the same manner as the B concentration / H concentration. The minimum value does not exist. As described above, even in the case of FIG. 3, the B concentration / H concentration and the B concentration / C concentration are low on the outermost surface because the SIMS measurement sensitivity becomes unstable on the outermost surface. It does not represent the concentration ratio. In FIG. 3, since the B concentration / H concentration monotonously increases from the substrate side to the surface side, it can be seen that B tends to be concentrated on the growth surface side when the substrate temperature is constant.

  The thickness obtained from the interference of the reflection spectrum with respect to the zinc oxide film obtained in this Comparative Example 1 was 1.65 μm, which substantially coincided with the film thickness of 1.65 μm obtained from the sputtering rate of SIMS. In the zinc oxide film obtained in Comparative Example 1, the sheet resistance is 12.4 Ω / □, the surface area ratio (Sdr) is 85.3%, and the haze ratio is 23.0%. there were.

(Comparison between Example 1 and Comparative Example 1)
In Example 1 and Comparative Example 1, although the zinc oxide film has the same film thickness, in Example 1, the haze ratio is increased by about 10% (surface irregularities are increased). It can be seen that the confinement effect can be increased. The sheet resistance of the zinc oxide film of Example 1 is not substantially changed as compared with the case of Comparative Example 1. Further, in Example 1, although the haze rate is increased as compared with Comparative Example 1, Sdr is decreased. Therefore, in Example 1, the level difference of the surface unevenness of the zinc oxide film is large, but it can be said that the shape of the surface unevenness is gentle, which is to suppress the decrease in FF in the photoelectric conversion device. It can be said that it is effective.

  In the graph of FIG. 4, immersion liquid transmission spectra of the zinc oxide film of Example 1 and the zinc oxide film of Comparative Example 1 are shown. That is, in this graph, the horizontal axis represents the wavelength (nm) of light, and the vertical axis represents the transmittance (%). If light is directly incident on the zinc oxide film on the substrate and measured, the amount of light incident on the detector of the spectroscope decreases due to light scattering due to the surface irregularities of the zinc oxide film, and as a result, the transmittance is lower than actual. Will be displayed. Therefore, after the iodomesylene solution was dropped on the surface of the zinc oxide film and the cover glass was placed, the transmission spectrum was measured. The transmittance measured by this method is called immersion liquid transmittance. Since the refractive index of the iodomesylene liquid is 1.74, which is close to the refractive index of zinc oxide 2, the dripped iodomesylene liquid fills the surface irregularities of the zinc oxide film and flattens it, thereby suppressing the influence of light scattering. The transmission spectrum of the zinc oxide film can be measured more accurately.

  In the graph of FIG. 4, the thick curve represents the transmittance of the zinc oxide film of Example 1, and the thin curve represents the transmittance of the zinc oxide film of Comparative Example 1. As can be seen from this graph, in Example 1 and Comparative Example 1, the immersion liquid permeation spectra of the zinc oxide films are almost the same. In other words, in the zinc oxide film of Example 1, it can be said that the surface unevenness is increased while keeping the transmittance high.

(Example 2 and Comparative Example 2)
The graph of FIG. 5 shows the haze ratio with respect to the film thickness of the zinc oxide film in Example 2 of the present invention and Comparative Example 2 by the conventional method. That is, the horizontal axis of this graph represents the total thickness (nm) of the zinc oxide film, and the vertical axis represents the haze ratio (%).

  In Example 2, an initial thickness of about 0.2 μm was deposited at a substrate temperature of 170 ° C., and then deposited at various temperatures while changing the remaining thickness at a substrate temperature of 160 ° C. The thickness was varied. Comparative Example 2 was different from Example 2 only in that the zinc oxide film was deposited at a constant substrate temperature of 160 ° C.

  In the graph of FIG. 5, black square marks represent the zinc oxide film of Example 2, and white square marks represent the zinc oxide film of Comparative Example 2. As is clear from this graph, it can be seen that the haze ratio in Example 2 is increased by about 10% in comparison with Comparative Example 2 when compared with the same total film thickness of the zinc oxide films. On the other hand, the sheet resistance value is shown at each measurement point of the haze ratio in FIG. 5, but when compared with the same total film thickness, the sheet resistance of the zinc oxide film of Example 2 is the zinc oxide film of Comparative Example 2 It can be seen that the sheet resistance is maintained almost the same value.

(Example 3)
As Example 3 of the present invention, a zinc oxide film was produced in which the position from the substrate having the minimum value of B concentration / H concentration was changed. That is, Example 3 is different from Example 1 only in that the deposition thickness was variously changed at the substrate temperature of 170 ° C. at the initial stage of film formation, and the remaining film thickness was deposited at about 1.45 μm at the substrate temperature of 160 ° C. It was different.

  The graph of FIG. 6 shows the relationship between the position of the minimum value of B concentration / H concentration in the zinc oxide film of Example 3 and the haze ratio. That is, in this graph, the horizontal axis represents the distance (μm) from the substrate surface to the position of the minimum value of B concentration / H concentration, and the vertical axis represents the haze ratio (%). From this graph, it can be seen that the haze rate increases as the distance from the substrate surface to the position of the B concentration / H concentration minimum value increases.

  On the other hand, the graph of FIG. 7 shows the relationship between the position of the minimum value of B concentration / H concentration in the zinc oxide film of Example 3 and the sheet resistance. That is, in this graph, the horizontal axis represents the distance (μm) from the substrate surface to the position of the minimum value of B concentration / H concentration, and the vertical axis represents the sheet resistance (Ω / □). From this graph, it can be seen that the sheet resistance decreases as the distance from the substrate surface to the position of the minimum value of B concentration / H concentration increases.

  That is, from FIG. 6 and FIG. 7, as the distance from the substrate surface to the position of the minimum value of B concentration / H concentration in the zinc oxide film increases, the surface unevenness of the zinc oxide film increases and the haze rate increases. It can be seen that the sheet resistance can be reduced.

Example 4
As Example 4 of this invention, the thin film photoelectric conversion apparatus corresponding to FIG. 1 was produced. That is, in the fourth embodiment, the amorphous silicon photoelectric conversion unit 2, the crystalline silicon photoelectric conversion unit 3, and the back electrode layer 4 are formed on the zinc oxide film 12 of the first embodiment, so that the laminated thin film A photoelectric conversion device was produced.

More specifically, on the zinc oxide film 12 of Example 1, a p-type layer 21 composed of a stack of a p-type microcrystalline silicon layer having a thickness of 10 nm and a p-type amorphous silicon carbide layer having a thickness of 15 nm, An amorphous photoelectric conversion unit 2 including an intrinsic amorphous silicon photoelectric conversion layer 22 having a thickness of 350 nm and an n-type microcrystalline silicon layer 23 having a thickness of 15 nm is formed, and a p-type microcrystalline silicon layer having a thickness of 15 nm is further formed. 31, the crystalline silicon photoelectric varying 換Yu knit 3 including an intrinsic crystalline silicon photoelectric conversion layer 32 and having a thickness of 15 nm n-type microcrystalline silicon layer 33, a thickness of 1.5μm was formed by sequentially plasma CVD method. Further, an Al-doped zinc oxide layer 41 having a thickness of 90 nm and an Ag layer 42 having a thickness of 200 nm are sequentially formed as the back electrode layer 4 by sputtering, and thus a stacked thin film photoelectric conversion device corresponding to FIG. 1 is manufactured. It was done.

When the output characteristics were measured by irradiating the thin film photoelectric conversion device 5 of Example 4 thus obtained with AM 1.5 light at a light quantity of 100 mW / cm ² , the open circuit voltage (Voc) was 1.323 V, and the short circuit current was measured. The density (Jsc) was 12.63 mA / cm ² , the fill factor (FF) was 0.713, and the conversion efficiency (Eff) was 11.92%.

(Comparative Example 3)
Also in Comparative Example 3, a thin film photoelectric conversion device corresponding to FIG. That is, the stacked thin film photoelectric conversion device manufactured in Comparative Example 3 was different from Example 4 only in that it was manufactured using the zinc oxide film of Comparative Example 1 instead of the zinc oxide film of Example 1. . When the output characteristics of the thin-film photoelectric conversion device of Comparative Example 3 was measured, Voc is 1.266V, Jsc is 12.39mA / cm ^2, FF is 0.662, and Eff was 10.39%.

From a comparison between Example 4 and Comparative Example 3, it can be seen that the EFF of the stacked thin film photoelectric conversion device of Example 4 is about 1.5% higher than that of Comparative Example 3. Further, the Jsc was improved in Example 4 as compared with Comparative Example 3 because the haze ratio of the zinc oxide film 12 increased (surface irregularities increased) and the light confinement effect increased. I can say that. Furthermore, it is considered that the reason why Voc and FF improved in Example 4 as compared with Comparative Example 3 was that the Sdr of the zinc oxide film was reduced (the sharpening of the surface irregularities).

(Example 5)
In the stacked thin film photoelectric conversion device manufactured as Example 5 of the present invention, the position of the minimum value of B concentration / H concentration in the zinc oxide film was set at a distance of 0.1 μm in the thickness direction from the substrate surface. This was different from Example 4 only. In the zinc oxide film included in the multilayer thin film photoelectric conversion device of Example 5, the haze ratio was 25.8%, the sheet resistance was 16.6 Ω / □, and Sdr was 58.1%. The output characteristics of the obtained thin film photoelectric conversion device of Example 5 were measured. As a result, Voc was 1.318 V, Jsc was 12.60 mA / cm ² , FF was 0.694, and Eff was 11.53%.

  That is, in Example 5, even if the position of the minimum value of B concentration / H concentration in the zinc oxide film is as small as 0.1 μm from the substrate surface, compared with the photoelectric conversion device of Comparative Example 3. Eff about 1% higher is obtained. However, compared with Example 4, in Example 5, since the haze ratio of the zinc oxide film is low, Jsc is slightly low, and since sheet resistance is high, FF and Voc are low, and as a result, Eff is slightly low. It has become.

(Example 6)
In the stacked thin film photoelectric conversion device manufactured as Example 6 of the present invention, the position of the B concentration / H concentration minimum value in the zinc oxide film was set at a distance of 0.3 μm in the thickness direction from the substrate surface. Only in the difference from Example 4. In the zinc oxide film included in the multilayer thin film photoelectric conversion device of Example 6, the haze ratio was 36.7%, the sheet resistance was 9.9Ω / □, and Sdr was 80.0%. When the output characteristics of the obtained thin film photoelectric conversion device of Example 6 were measured, Voc was 1.280 V, Jsc was 12.62 mA / cm ² , FF was 0.686, and Eff was 11.09%.

  That is, in Example 6, even when the position of the minimum value of B concentration / H concentration of the zinc oxide film is 0.3 μm from the substrate surface, Eff about 0.5% higher than that of Comparative Example 3 is obtained. I understand that. However, compared with Example 4, in Example 6, since Sdr is increased (surface irregularities are sharpened), Voc and FF are decreased and Eff is decreased.

( Reference example )
Reference examples and to work made by the multilayer thin-film photoelectric conversion device of the present invention, carried out in only the position of the B concentration / H density minima in the zinc oxide film is set to a distance 0.5μm from the substrate surface It was different from Example 4. In the zinc oxide film included in the laminated thin film photoelectric conversion device of this reference example , the haze ratio was 40.1%, the sheet resistance was 6.9 Ω / □, and Sdr was 154.0%. When obtained was measured output characteristics of the thin-film photoelectric conversion device of Reference Example, Voc is 0.474V, Jsc is 12.35mA / cm ^2, FF is 0.616, and Eff was 3.60%.

In the reference example , Sdr is 154.0%, which is twice or more that in the case of Example 4. Therefore, the silicon oxide thin film has poor coverage on the surface due to sharpening of the surface irregularities of the zinc oxide film. As a result, it can be said that Voc is significantly reduced. Therefore, in order to improve the Eff of the thin film photoelectric conversion device, the position of the minimum value of B concentration / H concentration in the zinc oxide film is preferably located on the substrate side with respect to half of the total film thickness. More preferably, the distance is less than 5 μm.

(Example 8)
In Example 8 of the present invention, the position of the minimum value of B concentration / H concentration in the thickness direction in the zinc oxide film is set at a distance of 0.2 μm from the substrate surface by controlling the flow rate of B ₂ H _6. This was different from Example 4 only. Specifically, when the zinc oxide film is formed by low-pressure thermal CVD, the substrate temperature is maintained at a constant 160 ° C., and the B ₂ H ₆ flow rate is set to 2. at a deposition thickness of about 0.2 μm at the initial stage of film formation. The flow rate was 5 sccm, and the B ₂ H ₆ flow rate was 1.5 sccm for the remaining thickness of deposition. The ratio of the B ₂ H ₆ flow rate to the DEZ flow rate was 0.625% at the initial thickness of the film formation, and 0.375% at the remaining thickness portion.

In the zinc oxide film included in the multilayer thin film photoelectric conversion device of Example 8, the haze ratio was 26.5%, the sheet resistance was 10.9Ω / □, and Sdr was 63.4%. When the output characteristics of the obtained thin film photoelectric conversion device of Example 8 were measured, Voc was 1.332 V, Jsc was 12.48 mA / cm ² , FF was 0.675, and Eff was 11.22%.

From Example 8, it can be seen that Eff is improved as compared with Comparative Example 3 even when the B ₂ H ₆ flow rate is controlled and the minimum value of B concentration / H concentration is set during deposition of the zinc oxide film.

  In Table 1, the output characteristics of the thin film photoelectric conversion devices according to Examples 4 to 8 and Comparative Example 3 of the present invention and the deposition conditions and characteristics of the zinc oxide film are collectively shown.

  It will be readily understood by those skilled in the art that the effects of the present invention can be obtained in the same manner even if the conductive layers of the p-type layer and the n-type layer are inverted from each other in the various embodiments described above.

1 is a schematic cross-sectional view illustrating a substrate for a photoelectric conversion device and a stacked thin film photoelectric conversion device according to an embodiment of the present invention. It is a graph showing the depth direction distribution of B density | concentration / H density | concentration and B density | concentration / C density | concentration in the zinc oxide film | membrane by Example 1 of this invention. It is a graph showing the depth direction distribution of B concentration / H concentration and B concentration / C concentration in the zinc oxide film by the comparative example 1 of the conventional method. It is a graph showing the immersion liquid transmission spectrum in the zinc oxide film by Example 1 of this invention, and the zinc oxide film by the comparative example 1 of the conventional method. It is a graph which shows the relationship between the film thickness and haze rate in the zinc oxide film by Example 2 of this invention, and the zinc oxide film by the comparative example 2 of the conventional method. It is a graph which shows the relationship between the position of the minimum value of B density | concentration / H density | concentration in the zinc oxide film | membrane by Example 3 of this invention, and a haze rate. It is a graph which shows the relationship between the position of the minimum value of B density | concentration / H density | concentration in the zinc oxide film | membrane by Example 3 of this invention, and sheet resistance .

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Substrate for thin film photoelectric conversion devices, 11 Transparent insulating substrate, 111 Translucent base, 112 Translucent underlayer, 1121 Translucent fine particles, 1122 Translucent binder, 12 Zinc oxide film, 2 Front photoelectric conversion unit, 21 p-type layer, 22 photoelectric conversion layer, 23 n-type layer, 3 backward photoelectric conversion unit, 31 p-type layer, 32 photoelectric conversion layer, 33 n-type layer, 4 back electrode layer, 41 conductive oxide layer, 42 metal layer 5 Thin film photoelectric conversion device.

Claims (9)

A transparent conductive film for a photoelectric conversion device formed on a substrate, having an atomic concentration measured by secondary ion mass spectrometry of 2 × 10 ¹⁹ atoms / cm ³ or more and 2 × 10 ²⁰ atoms / cm ³ or more. Consisting of zinc oxide containing H atoms of
And the value of the ratio of B atom concentration / H atom concentration is varied so as to have a minimum value at a predetermined position in the thickness direction of the transparent conductive film,
The transparent conductive film for a photoelectric conversion device, wherein the position of the minimum value of the B atom concentration / H atom concentration ratio is at a distance of 0.1 μm to 0.3 μm from the substrate surface.
The transparent conductive film is formed on the transparency on an insulating substrate, said position of minimum value of the B atom concentration / H atomic concentration ratio is in the range of the substrate side than half of the total thickness of the transparent conductive film The transparent conductive film for photoelectric conversion devices according to claim 1.
  3. The transparent conductive film for a photoelectric conversion device according to claim 1, wherein a minimum value of the ratio of B atom concentration / H atom concentration is 0.01 or more and 0.1 or less.   4. The transparent conductive film according to claim 1, wherein the transparent conductive film has a maximum value of a ratio of B atom concentration / H atom concentration at a predetermined position in the thickness direction, and the maximum value is 0.05 or more. The transparent conductive film for photoelectric conversion apparatuses in any one.   The transparent conductive film also includes C atoms, and the value of the ratio of B atom concentration / C atom concentration is varied so as to have a maximum value at a predetermined position in the thickness direction of the transparent conductive film. It is 1.5 or more, The transparent conductive film for photoelectric conversion apparatuses in any one of Claim 1 to 4 characterized by the above-mentioned.   A photoelectric conversion device substrate comprising the transparent conductive film for a photoelectric conversion device according to claim 1, comprising a transparent insulating substrate and the transparent conductive film formed thereon. A substrate for a photoelectric conversion device.   It is a photoelectric conversion apparatus containing the transparent conductive film for photoelectric conversion apparatuses in any one of Claim 1-5, Comprising: The said transparent conductive film, 1 or more photoelectric conversion units, and a back surface electrode layer, Said 1 or more The thin film photoelectric conversion device is characterized in that the photoelectric conversion unit is sandwiched between the transparent conductive film and the back electrode layer. A method for producing a transparent conductive film for a photoelectric conversion device on a substrate using a low-pressure CVD method,
The transparent conductive film made of zinc oxide containing 2 × 10 ¹⁹ atoms / cm ³ or more B atoms and 2 × 10 ²⁰ atoms / cm ³ or more H atoms as atom concentration measured by secondary ion mass spectrometry,
After forming the thickness portion of 0.1 μm to 0.3 μm from the substrate surface at the initial deposition of the transparent conductive film at the first substrate temperature, at least one remaining of the transparent conductive film at the second substrate temperature. A method for producing a transparent conductive film for a photoelectric conversion device, wherein the first substrate temperature is relatively higher than the second substrate temperature by depositing a thickness portion of the portion.
A method for producing a transparent conductive film for a photoelectric conversion device on a substrate using a low-pressure CVD method,
The transparent conductive film made of zinc oxide containing 2 × 10 ¹⁹ atoms / cm ³ or more B atoms and 2 × 10 ²⁰ atoms / cm ³ or more H atoms as atom concentration measured by secondary ion mass spectrometry,
After forming a thickness portion of 0.1 μm to 0.3 μm from the substrate surface in the initial stage of deposition of the transparent conductive film at the first B ₂ H ₆ gas flow rate, the second B ₂ H ₆ gas flow rate A thickness of at least a part of the remaining transparent conductive film is formed, and the first B ₂ H ₆ gas flow rate is relatively larger than the second B ₂ H ₆ gas flow rate. The manufacturing method of the transparent conductive film for photoelectric conversion apparatuses.

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