JP2005311292A - Substrate for thin film solar cell, manufacturing method therefor, and thin film solar cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive thin film solar cell that can improve the performance of a thin film solar cell by effectively increasing the uneveness of the substrate suface of the thin film solar cell to augment an optical confinement effect, and a manufacturing method therefor, and further, a thin film solar cell using the substrate, whose performance is improved. <P>SOLUTION: A substrate for the thin film solar cell has a translucent insulating substrate and a transparent electrode layer that includes at least zinc oxide (ZnO) deposited on it. The translucent insulating substrate has minute surface irregularity on the transparent electrode layer-side interface, the surface irregularity whose (RMS) roughness is 5 to 50nm, and the convex part of the irregularity is of a curved surface. Further, since a haze ratio, which is an index of a substrate's irregularity, i.e., a ratio of the diffuse transmittance vs total transmittance measured by a C light source, can be 20% or more, optical confinement can be effectively caused, thus improving the performance of the thin film solar cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a substrate for a thin film solar cell, a method for producing the same, and a thin film solar cell using the same.

  In recent years, thin-film solar cells that require less raw materials in order to achieve both low cost and high efficiency of solar cells have attracted attention and have been vigorously developed. In particular, a method of forming a high-quality semiconductor layer on an inexpensive translucent substrate such as glass using a low-temperature process is expected as a method capable of realizing low cost.

  When manufacturing such a thin film solar cell as a large area thin film solar cell capable of producing high output at high voltage for power, a plurality of thin film solar cells formed on a large substrate are used in series connection. In general, in order to improve the yield, a thin film solar cell formed on a large substrate is divided into a plurality of cells, and these cells are connected in series and integrated. In particular, in a thin film solar cell of a type in which light is incident from the glass substrate side using a glass plate as a substrate, after forming a semiconductor layer sequentially on the glass substrate, the loss due to the resistance of the transparent electrode layer on the glass substrate is reduced. In order to reduce this, it is common to provide a separation groove for processing the transparent electrode into a strip with a predetermined width by a laser scribing method, and integrate each cell in series in a direction perpendicular to the longitudinal direction of the strip Is.

  FIG. 2 is a conceptual plan view of such an integrated thin film solar cell. FIG. 3 is a structural cross-sectional view of a region surrounded by an ellipse 2A in FIG. FIG. 4 is a more detailed cross-sectional view of the laminated structure in the region surrounded by the ellipse 3A in FIG.

In the manufacture of the integrated thin film solar cell 6 as shown in FIGS. 2 to 4, a glass substrate 11 is generally used as the translucent insulating substrate 11. On the glass substrate 11, as the transparent electrode layer 12, for example, a SnO ₂ film having a thickness of 700 nm is formed by a thermal CVD method. The transparent electrode layer 12 is separated into strip-shaped transparent electrodes having a width W of about 10 mm by forming transparent electrode layer separation grooves 62 having a width of about 100 μm by laser scribing. The residue after scribing is removed by ultrasonic cleaning using water or an organic solvent. In addition, as a cleaning method, a method of removing residues using an adhesive or a jet gas is also possible.

  Further, after one or more amorphous units 2 or crystalline photoelectric conversion units 3 are formed, these units are divided into a plurality of strip-like regions within the plane by the connection grooves 63. Since the connection groove 63 is used to electrically connect the transparent electrode layer 12 and the back electrode layer 4 between adjacent cells, there is a problem even if a scribe residue remains partially. Instead, ultrasonic cleaning may be omitted. Subsequently, when the back electrode layer 4 is formed, the back electrode layer 4 is electrically connected to the transparent electrode layer 12 formed in a strip shape as described above via the connection groove 63.

  The back electrode layer 4 is patterned by laser scribing similar to that of one or more amorphous units 2 or crystalline photoelectric conversion units 3, and the back electrode layer together with one or more amorphous units 2 or crystalline photoelectric conversion units 3. After the plurality of back surface electrode separation grooves 64 are formed by blowing off 4 locally, ultrasonic cleaning is performed. As a result, a plurality of strip-shaped solar battery cells 61 are formed, and these cells are electrically connected in series with each other through the connection groove 63. Finally, the back side of the thin film solar cell is protected by attaching a sealing resin (not shown).

  By the way, a thin film solar cell can make a photoelectric conversion layer thinner than a solar cell using conventional bulk single crystal or polycrystalline silicon. However, the light absorption of the entire thin film is limited by the film thickness. There is a problem of being done. Therefore, in order to use light incident on the photoelectric conversion unit including the photoelectric conversion layer more effectively, the surface of the transparent conductive film or metal layer in contact with the photoelectric conversion unit is made uneven (textured), and light is transmitted at the interface. After scattering, the optical path length is extended by making it enter into a photoelectric conversion unit, and the device which makes the light absorption amount in a photoelectric converting layer increase is made | formed. This technology is called “optical confinement” and is an important elemental technology for practical use of a thin film solar cell having high photoelectric conversion efficiency.

An amorphous silicon solar cell which is an example of a thin film solar cell often uses a tin oxide (SnO ₂ ) film formed on a transparent substrate such as glass and having a surface asperity as a transparent electrode layer. The surface unevenness of the transparent electrode layer effectively contributes to light confinement in the photoelectric conversion layer. However, a glass substrate on which an SnO ₂ film is formed by a thermal chemical vapor deposition method (thermal CVD method) as a transparent electrode layer having surface irregularities effective for light confinement is about 550 to 650 in order to form the transparent electrode layer. Since a high temperature process at ℃ is required, there is a problem that the manufacturing cost is high. In addition, since the film forming temperature is high, there is a problem that an inexpensive substrate such as glass or plastic film after solidification cannot be used. When tempered glass is exposed to a high-temperature process, it can be tempered, so it is not possible to use tempered glass as a substrate, and when applying to large area solar cells, it is necessary to thicken the glass to ensure the strength of the glass substrate. As a result, there is a problem of becoming heavy.

In addition, the SnO ₂ film has low plasma resistance, and the SnO ₂ film is reduced in the deposition environment of the photoelectric conversion layer at a high plasma density using hydrogen. When the SnO ₂ film is reduced, it is blackened, and incident light is absorbed by the blackened transparent electrode layer portion, and the amount of light transmitted to the photoelectric conversion layer is reduced, which causes a decrease in conversion efficiency.

Furthermore, the amorphous silicon solar cell has a problem that the initial photoelectric conversion efficiency is lower than that of a single crystal or polycrystalline solar cell, and further, the conversion efficiency is lowered due to a light deterioration 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 is expected and studied as being capable of achieving 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 of about 800 nm on the long wavelength side, while the crystalline silicon photoelectric conversion layer photoelectrically converts light having a longer wavelength of about 1200 nm. can do. However, a plasma density larger than the deposition conditions used at the time of forming amorphous silicon is necessary, and when the SnO ₂ film is used as a transparent electrode, it is difficult to greatly improve the conversion efficiency.

  In the specification of the present application, the terms “crystalline” and “microcrystal” include those partially including amorphous.

On the other hand, zinc oxide (ZnO) has advantages that it is cheaper than SnO ₂ or indium tin oxide (ITO) widely used as a material for the transparent electrode layer and has high plasma resistance, and is a thin film It is suitable as a transparent electrode layer material for solar cells.

(Prior Example 1)
For example, the method for forming a ZnO film disclosed in Patent Document 1 discloses that a thin film having unevenness can be formed at a low temperature by a low-pressure thermal CVD method (also called MOCVD method) of 200 ° C. or lower. Compared with high-pressure thermal CVD, a low-temperature process at 200 ° C. or lower can reduce the cost. In addition, an inexpensive base such as glass or plastic film after solidification can be used. Further, since tempered glass can be used, the glass substrate of the large area solar cell can be made thin by about 2/3 and light. In addition, the low-pressure thermal CVD method is preferable for a thin film solar cell in terms of manufacturing cost because it can be formed at a film forming speed one digit or more faster than the sputtering method and the utilization efficiency of raw materials is high.

(Prior Example 2)
On the other hand, in order to make the substrate for thin film solar cells uneven, instead of forming unevenness on the transparent electrode layer itself, an underlying layer with unevenness is provided on the surface of the glass substrate, and a transparent electrode layer is formed thereon This technique is disclosed in Patent Document 2. On the glass substrate, an underlying layer having irregularities composed of insulating fine particles having an average particle size of 0.1 to 1.0 μm and a binder is formed, and a transparent electrode layer is deposited thereon, whereby fine particles are formed. Since unevenness is formed on the glass substrate, it is not necessary to form unevenness in the transparent electrode layer itself.
JP 2000-252501 A JP 2003-243676 A

  An object of the present invention is to provide an inexpensive thin film solar cell substrate capable of improving the performance of the thin film solar cell by effectively increasing the unevenness of the thin film solar cell substrate to increase the light confinement effect, and its An object of the present invention is to provide a thin film solar cell provided by a manufacturing method and further improved in performance using the substrate.

  First, as shown in FIG. 1, when ZnO is formed on a substrate without an underlayer as in the first example, it is difficult to increase the haze ratio to be high, for example, 20% or more. Could not be activated. In particular, when there is no underlayer, the haze ratio decreases when the transparent electrode layer is formed at a substrate temperature of 150 ° C. or higher. Therefore, in the conventional method of the first example, when the substrate temperature is increased to 150 ° C. or higher, the short-circuit current of the thin-film solar cell There is a problem that the density decreases. In silicon-based thin-film solar cells, a thin-film silicon-based semiconductor layer of amorphous silicon or crystalline silicon is generally produced at a substrate temperature of 180 to 300 ° C. by plasma CVD. In this case, the production temperature of the silicon-based semiconductor layer is higher than the production temperature of the transparent electrode layer. Generally, as the temperature difference between the production temperature of the transparent electrode layer and the silicon-based semiconductor layer increases, thermal damage to the transparent electrode layer tends to increase. The problem of reduced reliability occurs.

  Further, in the integrated thin film solar cell including the crystalline photoelectric conversion layer as in the preceding example 1, when the transparent electrode 102 formed at a low temperature is used, ultrasonic cleaning after the back electrode separation groove 105 is formed by laser scribing. The present inventor has found that peeling of the film is likely to occur in many areas near the separation groove. In such film peeling, the peeled area tends to increase as the area of the thin-film solar cell increases. Moreover, film peeling may already occur after scribing. And when such film peeling occurs, it naturally becomes the cause of the performance fall of a thin film solar cell.

  Furthermore, when the haze ratio is increased by the method of the preceding example 2, for example, 20% or more, it is necessary to increase the unevenness in the underlayer, and as a result, it is necessary to increase the particle size of the insulating fine particles. When large insulating fine particles are used, the dispersion of the insulating fine particles on the substrate becomes non-uniform, for example, a region without fine particles is generated, and the average thin film photoelectric conversion efficiency of the entire substrate is lowered. Or color unevenness occurs due to the in-plane haze ratio distribution. Furthermore, it has been found that if large irregularities are formed using large insulating fine particles, the adhesion of the fine particles to the substrate is insufficient and the reliability of the thin film solar cell itself may be lowered. .

  This invention is made | formed in view of such a subject, and it aims at providing the board | substrate for thin film solar cells with high electric power generation efficiency, its manufacturing method, and a thin film solar cell using the same. Yes. In addition, in increasing the area of an integrated thin film solar cell, to provide a substrate for a thin film solar cell capable of facilitating the integration and improving the production yield while maintaining the high power generation efficiency of the integrated thin film solar cell. Is also aimed at.

  In view of the above problems, as a result of intensive studies on a method for forming sufficient irregularities with the transparent electrode layer itself, surprisingly, although the irregularity of the underlayer itself is small by forming an underlayer with a small particle diameter, The present inventors have found that the unevenness of the transparent electrode layer deposited on the substrate can be greatly formed, and have devised the present invention.

  In order to solve the above problems, a thin film solar cell substrate of the present invention has a transparent insulating substrate and a transparent electrode layer containing at least zinc oxide (ZnO) deposited thereon, and the transparent insulating layer. The substrate is characterized by having fine surface irregularities having a root mean square roughness (RMS) of 5 to 50 nm at the interface on the transparent electrode layer side, and the convex portions are curved surfaces.

  In particular, when the transparent electrode layer has a thickness of 1 μm or more, the use of the translucent insulating substrate has the effect of suppressing film peeling from the translucent insulating substrate caused by internal stress in the thick transparent electrode layer. It is clear.

  The thin film solar cell substrate of the present invention was measured using a C light source, which is an index of substrate unevenness, by forming a transparent electrode layer on a transparent insulating substrate having fine surface unevenness as described above. The haze ratio, which is the ratio between the diffuse transmittance and the total transmittance, is 20% or more, and light confinement can be effectively caused. Therefore, the performance of the thin film solar cell can be improved.

  Further, when the translucent insulating substrate is mainly composed of a translucent substrate having a smooth surface such as glass, the fine irregularities on the transparent electrode layer side are composed of at least silicon oxide having a particle size of 10 or more and less than 100 nm. It is preferably formed of a light-transmitting underlayer containing fine particles. In addition, the transparent base layer is preferably a film in which fine particles are covered with a metal oxide from the viewpoint of adhesive strength with the transparent insulating substrate.

  Further, the integrated thin film solar cell according to the present invention is separated by a plurality of separation grooves so as to form a plurality of photoelectric conversion cells having at least one crystalline photoelectric conversion unit layer on the substrate for the thin film solar cell. The plurality of cells are electrically connected in series with each other through the connection groove, and the crystalline photoelectric conversion layer included in the crystalline photoelectric conversion unit layer is deposited to a thickness of 1 μm or more. It is characterized by being.

  Such a substrate for a thin-film solar cell of the present invention has a light-transmitting underlayer having surface irregularities and a transparent electrode layer containing at least zinc oxide in order on a light-transmitting substrate using a low-pressure thermal CVD method. It can be manufactured by depositing the conductive insulating substrate at a temperature of 150 ° C. or higher.

  ADVANTAGE OF THE INVENTION According to this invention, the unevenness | corrugation of a board | substrate with a transparent electrode layer can be increased effectively with an inexpensive manufacturing method, and the board | substrate for thin film solar cells with a big light confinement effect can be provided. Moreover, by applying this thin film solar cell substrate to a thin film solar cell, the power generation current can be increased by the optical confinement effect, and the performance of the thin film solar cell can be improved. Furthermore, it becomes possible to produce a substrate for a thin film solar cell with a transparent electrode layer having large irregularities at a substrate temperature of 150 ° C. or more, and it is possible to suppress thermal damage to the transparent electrode layer during the production of the semiconductor layer, and to provide a light confinement effect And low resistance are effective in improving the performance and reliability of the thin-film solar cell.

  Furthermore, according to the present invention, it is possible to provide an inexpensive thin film solar cell substrate that can exhibit the effect of suppressing film peeling of an integrated thin film solar cell and that has high photoelectric conversion efficiency.

  The inventors diligently studied the production of a thin-film solar cell substrate centering on a transparent electrode layer formed by a low-pressure thermal CVD method. As a result, in the transparent electrode layer using the low pressure thermal CVD method, the unevenness of the thin film solar cell substrate varies depending on the presence or absence of the underlayer, and the substrate temperature dependency of the unevenness of the thin film solar cell substrate varies greatly depending on the presence or absence of the underlayer. I discovered that.

  In the present invention, the haze ratio is mainly used as an evaluation index of the unevenness of the thin film solar cell substrate. The haze ratio is expressed by (diffuse transmittance / total light transmittance) × 100 [%] (JIS K7136).

FIG. 1 is a first embodiment of the present invention, and the haze ratio of the substrate 1 for thin film solar cells shown in FIG. 5 with respect to the substrate temperature when zinc oxide (ZnO) is formed as the transparent electrode layer 12 by low pressure thermal CVD. Indicates. This thin-film solar cell substrate 1 has a light-transmitting insulating substrate 11 on a glass plate 111 that is a light-transmitting substrate 111, and silica fine particles 1121 that are light-transmitting fine particles 1121 as a light-transmitting underlayer 112 having irregularities. The silicon oxide containing is formed. The transparent electrode layer 12 can be formed by a low pressure thermal CVD method using a mixed gas of diethyl zinc (DEZ), water, diborane (B ₂ H ₆ ), hydrogen, and argon as a source gas. The film thickness of the transparent electrode layer 12 formed in FIG. 1 is constant at about 1.5 μm. Moreover, the haze rate of the translucent insulating substrate 11 in which only the translucent underlayer 112 was formed on the glass plate 111 was 0.7% or less, and there was almost no optical scattering effect.

  As can be seen from FIG. 1, in the absence of the translucent underlayer 112, the haze ratio increases rapidly when the temperature of the translucent insulating substrate 11 during deposition of the zinc oxide layer 12 is 140 ° C. or higher, and the haze ratio increases at 150 ° C. However, at higher temperatures, the haze rate decreases. On the other hand, when the transparent base layer 112 is present, the haze ratio increases rapidly when the temperature of the transparent insulating substrate 11 when the zinc oxide layer 12 is deposited is 140 ° C. or higher. Similar to the case without 112, the haze rate continues to increase even at 150 ° C. or higher. When the temperature of the translucent insulating substrate 11 at the time of depositing the zinc oxide layer 12 is low, the difference in haze ratio depending on the presence or absence of the translucent underlayer 112 is substantially constant at 4 to 6%. However, at 150 ° C. or higher, the difference in haze rate due to the presence or absence of the light-transmitting underlayer 112 becomes significantly larger as the temperature increases. Therefore, in the deposition of zinc oxide (ZnO) 12 by the low-pressure thermal CVD method, when the temperature of the light-transmitting insulating substrate 11 is 150 ° C. or higher, the film growth pattern is determined depending on the presence or absence of the light-transmitting underlayer 112 having unevenness. Is different. It is estimated that when the temperature of the translucent insulating substrate 11 during deposition of the zinc oxide layer 12 is 150 ° C. or higher, the growth of ZnO is further promoted at the convex portions of the translucent underlayer 112 and the haze ratio is increased. The

  As a result, it was found that the haze ratio can be greatly increased even when the film thickness of the transparent electrode layer 12 is constant. Further, at a relatively thin ZnO film thickness of 1.5 μm, a high haze ratio of 20% or more that could not be obtained without the light-transmitting underlayer 112 can be obtained.

  When there is a translucent underlayer 112, there is no problem of a decrease in haze rate even at the temperature of the translucent insulating substrate 11 when the zinc oxide layer 12 is deposited at 150 ° C. or higher. In comparison, the temperature at the time of forming the transparent electrode layer 12 can be further increased. Therefore, it is possible to reduce the influence of thermal damage during the formation of one or more amorphous units 2 or crystalline photoelectric conversion units 3 deposited on the transparent electrode layer 12 by plasma CVD or the like. 5 and the long-term reliability can be improved.

  FIG. 5 is a schematic cross-sectional view of the thin film solar cell substrate 1 of the present invention. The thin film solar cell substrate 1 of the present invention is formed by depositing a transparent electrode layer 12 on a translucent insulating substrate 11 formed by forming a translucent base layer 112 on a translucent substrate 111.

  The translucent insulating substrate 11 is formed by forming a translucent base layer 112 on a translucent substrate 111.

  In addition, since the translucent insulating substrate 11 is located on the light incident side when the thin film solar cell 5 is configured, it transmits more sunlight and absorbs it in the amorphous or crystalline photoelectric conversion unit. In addition, it is preferable to be as transparent as possible, and as the material, a glass plate, a translucent plastic film or the like is used. For the same purpose, it is desirable to apply a non-reflective coating to the light incident surface of the translucent substrate 111 so as to reduce the light reflection loss on the light incident surface of sunlight.

  The light-transmitting underlayer 112 is preferably provided with fine surface irregularities in order to promote the growth of the ZnO layer 12 irregularities. In the case where ZnO grows, it is considered that the growth of ZnO is further promoted in the convex portions of the underlayer 2 and the unevenness of the ZnO becomes larger and the haze ratio is improved. The root mean square roughness (RMS) of the fine surface irregularities formed by the translucent underlayer 112 is preferably 5 nm or more. This is because if the RMS is too small, the shape is close to a smooth surface, and it is difficult to obtain a difference in ZnO growth due to fine irregularities on the surface.

  In addition, it is preferable that the fine uneven protrusions formed on the light-transmitting underlayer 112 have a curved surface. Since the convex portion is a curved surface, it is possible to prevent an increase in crystal grain boundary starting from the shape of the light-transmitting underlayer 112 during the crystal growth of the thin film sequentially deposited thereon, and the electric power of the thin film solar cell 5 This is because deterioration of characteristics can be suppressed.

  In FIG. 6, the thin film solar cell 5 by embodiment of this invention is shown with typical sectional drawing. The thin-film solar cell 5 includes a translucent underlayer 112, a transparent electrode layer 12, a crystalline photoelectric conversion unit layer 3, and a back electrode layer 4 that are sequentially deposited on a translucent substrate 111. The crystalline photoelectric conversion unit layer 3 includes one conductivity type layer 31, a substantially intrinsic semiconductor crystalline photoelectric conversion layer 32, and a reverse conductivity type layer 33, which are sequentially deposited. Sunlight (hν) to be subjected to photoelectric conversion is incident on the thin film solar cell 5 from the translucent insulating base 111 side.

  In the thin-film solar cell 5 of FIG. 6, the translucent insulating substrate 11 is constituted by the translucent base 111 and the translucent underlayer 112. However, the translucent insulating substrate 11 may be constituted alone. It is only necessary that the convex portions of the eleventh transparent electrode layer 12 side have fine irregularities with curved surfaces. Further, the thin film solar cell substrate 1 is obtained by forming the transparent electrode layer 12 on the translucent insulating substrate 11. However, since a general-purpose glass plate or film generally used as the translucent insulating substrate 11 has a smooth surface, it is difficult to obtain a surface having uniform fine irregularities by the polishing method, and the area is increased. Is more difficult. Therefore, as the translucent insulating substrate 11 having fine surface irregularities having the peeling prevention effect of the present invention, the translucent base layer 112 is formed on the translucent substrate 111 having a smooth surface. It is preferable to provide fine surface irregularities by the translucent underlayer 112. The RMS of the fine surface irregularities formed by the translucent underlayer 112 is preferably 5 to 50 nm, and more preferably 10 to 40 nm. This is because if the RMS is too small, the shape is close to a smooth surface, so that a sufficient improvement effect of the adhesion due to the fine irregularities on the surface cannot be obtained, and if it is too large, the thin film solar cell 5 formed thereon This is because electrical and mechanical defects are caused, and the photoelectric conversion efficiency of the solar cell is lowered.

  Moreover, it is preferable that the convex part of the fine unevenness | corrugation formed in the translucent insulating substrate 11 consists of a curved surface. Since the convex portion is a curved surface, an increase in crystal grain boundary starting from the shape of the light-transmitting underlayer 112 can be prevented during crystal growth of the thin film sequentially deposited thereon, and the electrical characteristics of the thin film are deteriorated. This is because it can be suppressed.

  The translucent underlayer 112 formed in the present invention preferably includes translucent fine particles 1121. Irregularities are formed in the light-transmitting underlayer 112 by the light-transmitting fine particles 1121, and the film growth of the transparent electrode layer 12 deposited thereon can be changed as compared with the case where the light-transmitting underlayer 112 is not provided.

As an example of the light-transmitting underlayer 112 formed in the present invention, one containing at least fine particles made of silicon oxide (SiO ₂ ) as the light-transmitting fine particles 1121 can be given. This is because SiO ₂ has a refractive index lower than that of the transparent conductive layer 12 and has a value close to that of the translucent substrate 111 such as a glass plate. Further, since SiO ₂ has high transparency, it is suitable as a material used on the light incident side. Further, for the purpose of adjusting the refractive index of the light-transmitting underlayer 112, in addition to SiO ₂ , the material of the light-transmitting fine particles 1121 is a material having a refractive index close to that of glass, for example, silica (SiO ₂ ), Titanium oxide (TiO ₂ ), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), indium tin oxide (ITO), magnesium fluoride (MgF ₂ ), or the like can be used. The refractive index is preferably 1.4 to 2.5. Silica fine particles are particularly preferable in terms of transparency of the material and compatibility with the glass plate. In order to set the root mean square roughness of the surface irregularities in the light-transmitting underlayer 112 to 5 to 50 nm, the particle size of the fine particles used is preferably 10 or more and less than 100 nm. Further, in order to uniformly form as fine as possible unevenness, the shape of the fine particles is preferably spherical.

A method for forming the light-transmitting base layer 112 including the light-transmitting fine particles 1121 on the surface of the light-transmitting substrate 111 is not particularly limited, but the light-transmitting binder 1122 is made transparent by applying it together with a binder-forming material including a solvent. A method of forming between the light-sensitive fine particles 1121 is desirable. The translucent binder 1122 that plays a role of improving the adhesion strength between the translucent fine particles 1121 and between the translucent fine particles 1121 and the translucent substrate 111 functions as an adhesive layer. In view of durability against the layer formation conditions (particularly temperature), inorganic materials are preferred. Specific examples include metal oxides such as silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and tantalum oxide. In particular, when the SiO ₂ fine particles 1121 are attached to the glass plate 111, if silicon oxide having the same silicon as a main component is used as the translucent binder 1122 as an adhesive layer, the adhesion is strong due to the formation of silicide bonds. It is preferable because it has good transparency and a refractive index close to that of the substrate or fine particles.

As mentioned above, the transparent base layer 112 does not need to be the same material as the transparent electrode layer 12 described later. Further, the light-transmitting underlayer 112 does not need to be in a crystalline phase, and can be similarly applied even if a part or all of it is in an amorphous phase. For example, when the light-transmitting underlayer 112 is formed using SiO ₂ fine particles as the light-transmitting fine particles 1121 and silicon oxide as the light-transmitting binder binder 1122, the light-transmitting underlayer 112 is usually amorphous. is there.

  Examples of the method for applying the coating solution on the surface of the translucent substrate 111 include a dipping method, a spin coat method, a bar coat method, a spray method, a die coat method, a roll coat method, and a flow coat method. In order to form the fine particles 1121 densely and uniformly, a roll coat method is preferably used. When the coating operation is completed, the coated thin film is immediately dried by heating. Since the translucent underlayer 112 film thus formed contains fine particles, the shape of the convex portion is a curved surface, and the height of the concave and convex portions is relatively uniform. Therefore, the transparent electrode layer 12 to be formed later and the thin film photoelectric conversion unit are less likely to cause defects.

  When a soda lime glass plate is used as the translucent substrate 111, the translucent underlayer 112 is used as an alkali barrier film in order to prevent alkali components from the glass from entering the transparent electrode layer 12 and the photoelectric conversion unit. Can be used.

  In addition, since the thin film solar cell substrate 1 on which the transparent electrode layer 12 is formed is a laminate of transparent thin films, uneven color due to light interference is likely to occur. In order to prevent the color unevenness, a combination of a plurality of thin films having different refractive indexes may be interposed between the transparent base layer 2 and the transparent electrode layer 102.

As a material of the transparent electrode layer 12, it is preferable to use a transparent conductive oxide film containing at least ZnO formed by a low pressure thermal CVD method. This is because ZnO is suitable for the thin film solar cell 5 having the crystalline photoelectric conversion unit 3 because ZnO can form a texture having a light confinement effect even at a low temperature of 200 ° C. or less and has a high plasma resistance. For example, the ZnO transparent electrode layer 12 of the substrate for a thin film solar cell of the present invention has a substrate temperature which is the temperature of the transparent insulating substrate 11 as a base, 150 ° C. or higher, a pressure of 5 to 1000 Pa, and diethyl zinc (DEZ) as a source gas. ), Water, doping gas, and dilution gas. In addition to this, dimethylzinc can also be used as the zinc source gas. Examples of oxygen source gases include oxygen, carbon dioxide, carbon monoxide, dinitrogen oxide, nitrogen dioxide, sulfur dioxide, dinitrogen pentoxide, alcohols (R (OH)), and ketones (R (CO) R ′). , Ethers (ROR ′), aldehydes (R (COH)), amides ((RCO) _x (NH _3−x ), x = 1,2,3), sulfoxides (R (SO) R ′) (However, R and R ′ are alkyl groups). As the dilution gas, a rare gas (He, Ar, Xe, Kr, Rn), nitrogen, hydrogen, or the like can be used. As the doping gas, diborane (B ₂ H ₆ ), alkylaluminum, alkylgallium, or the like can be used. The ratio of DEZ to water is preferably 1: 1 to 1: 5, and the ratio of B ₂ H _{6 to} DEZ is preferably 0.05% or more. Since DEZ and water are liquids at normal temperature and normal pressure, they are vaporized by methods such as heat evaporation, bubbling, and spraying before being supplied. When the film thickness of ZnO is 0.5 to 3 μm, a thin film having surface irregularities with a particle size of approximately 50 to 500 nm and an irregularity height of approximately 20 to 200 nm is obtained, and the light confinement effect of the thin film solar cell is obtained. It is preferable in terms of obtaining. Here, the substrate temperature refers to the temperature of the surface where the translucent insulating substrate 11 is in contact with the heating part of the film forming apparatus.

  When the transparent electrode layer 12 is composed of a thin film mainly composed of ZnO, the average thickness of the ZnO film is preferably 0.5 to 3 μm. This is because if the ZnO film is too thin, it is difficult to sufficiently provide unevenness that effectively contributes to the light confinement effect, and it is difficult to obtain the necessary conductivity as a transparent electrode, and if it is too thick, the light absorption by the ZnO film itself is difficult. This is because the amount of light that passes through ZnO and reaches the photoelectric conversion unit is reduced, so that the efficiency is lowered. Furthermore, when it is too thick, the film forming cost increases due to an increase in the film forming time.

  In the integrated thin film solar cell, the transparent electrode layer 12 is formed with a transparent electrode layer separation groove 62 by laser scribing so as to be separated into a plurality of regions corresponding to a plurality of solar cells 16 to be integrated. . These transparent electrode layer separation grooves 62 extend linearly in a direction perpendicular to the paper surface of FIG.

  The crystalline photoelectric conversion unit 3 is formed on the transparent electrode layer 12 in which the transparent electrode layer separation groove 62 is formed.

  FIG. 7 is a schematic cross-sectional view of a thin-film solar cell 5 according to one embodiment of the present invention. A crystalline photoelectric conversion unit 3 and a back electrode layer 4 are sequentially formed on the thin film solar cell substrate 1 shown in FIG.

  The crystalline photoelectric conversion unit 3 includes a one conductivity type layer 31, a crystalline intrinsic photoelectric conversion layer 32, and a reverse conductivity type layer 33. Although FIG. 7 shows the thin film solar cell 5 in which only one unit of the crystalline photoelectric conversion unit 3 is present, a plurality of photoelectric conversion units having different properties may be stacked. As the crystalline photoelectric conversion unit 3, one having absorption in the main wavelength range (400 to 1200 nm) of sunlight is preferable. For example, a crystalline silicon photoelectric conversion using a crystalline silicon thin film as a crystalline intrinsic photoelectric conversion layer 32 is preferable. Unit 3 may be used. In addition to silicon, “silicon-based” materials include silicon alloy semiconductor materials containing silicon such as silicon carbide and silicon germanium.

  The crystalline silicon-based photoelectric conversion unit 3 is 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 microcrystalline silicon-based 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 31, and an intrinsic crystalline silicon layer 32 serving as a photoelectric conversion layer. And an n-type microcrystalline silicon-based layer doped with 0.01 atom% or more of phosphorus, which is a conductivity type determining impurity atom, may be deposited as the reverse conductivity type layer 33 in this order. However, these layers are not limited to the above. For example, an amorphous silicon film may be used as the p-type layer. Further, an alloy material such as amorphous or microcrystalline silicon carbide or silicon germanium may be used for the p-type layer. Note that the film thickness of the conductive (p-type, n-type) microcrystalline silicon-based layer is preferably 3 nm to 100 nm, and more preferably 5 nm to 50 nm.

The intrinsic crystalline silicon layer 42 which is the crystalline intrinsic photoelectric conversion layer 32 is preferably formed at a substrate temperature of 300 ° C. or less by a plasma CVD method. By forming at a low temperature, it is preferable to include many hydrogen atoms that terminate and inactivate defects in the grain boundaries and grains. Specifically, the hydrogen content of this layer is preferably in the range of 1-30 atomic%. This layer is preferably formed as a thin film that is substantially an intrinsic semiconductor having a conductivity type determining impurity atom density of 1 × 10 ¹⁸ cm ⁻³ or less. Further, most of the crystal grains contained in the intrinsic crystalline silicon layer grow in a columnar shape from the transparent electrode layer 12 side, and preferably have a (110) preferential orientation plane with respect to the film surface. The thickness of the intrinsic crystalline silicon layer is preferably 1 μm or more from the viewpoint of light absorption, and preferably 10 μm or less from the viewpoint of suppressing peeling due to internal stress of the crystalline thin film. However, since the crystalline photoelectric conversion unit 3 preferably has absorption in the main wavelength region (400 to 1200 nm) of sunlight, instead of the intrinsic crystalline silicon layer, a crystalline silicon carbide layer (alloy material) ( For example, a crystalline silicon carbide layer made of crystalline silicon containing 10 atomic% or less of carbon or a crystalline silicon germanium layer (for example, a crystalline silicon germanium layer made of crystalline silicon containing 30 atomic% or less of germanium) It may be formed.

  The crystalline photoelectric conversion unit layer 3 laminated in this way is divided into a plurality of strip-shaped semiconductor regions by connection grooves 63 which are semiconductor layer dividing grooves formed by laser scribing as in the case of the transparent electrode layer 12. These connection grooves 63 also extend linearly in a direction perpendicular to the paper surface of FIG.

  A back electrode layer 4 is formed on the one or more photoelectric conversion units subjected to laser patterning.

As the back electrode layer 4, it is preferable to form at least one material selected from Al, Ag, Au, Cu, Pt and Cr as at least one metal thin film by sputtering or vapor deposition. Further, it is preferable to form a conductive oxide layer such as ITO, SnO ₂ , or ZnO as a part of the back electrode layer 4 between one or more photoelectric conversion units. This conductive oxide layer enhances the adhesion between one or more photoelectric conversion units and the back electrode layer 4, increases the light reflectivity of the back electrode layer 4, and further prevents chemical changes of the photoelectric conversion unit. It has the function to do.

  The back electrode layer 4 is patterned by laser scribing similar to that of one or more photoelectric conversion units, and a plurality of back electrode layer separation grooves 64 are formed by locally blowing the back electrode layer 4 together with the one or more photoelectric conversion units. . As a result, a plurality of strip-shaped solar cells 61 are formed, and these cells 61 are electrically connected in series with each other through the connection groove 63.

  FIG. 8 is a schematic cross-sectional view of a thin-film solar cell 5 according to one embodiment of the present invention. This is a tandem-type thin film solar cell in which an amorphous photoelectric conversion unit 2 and a crystalline photoelectric conversion unit 3 are sequentially laminated on a thin film solar cell substrate 1. The amorphous photoelectric conversion unit 2 includes a front one conductivity type layer, an intrinsic amorphous photoelectric conversion layer, and a front reverse conductivity type layer. If an amorphous silicon-based material is selected as the amorphous photoelectric conversion unit 2, it has sensitivity to light of about 360 to 800 nm, and if a crystalline silicon-based material is selected for the crystalline photoelectric conversion unit 3, it is longer than that. Sensitive to light up to about 1200 nm. Therefore, the thin film solar cell 5 arranged in the order of the amorphous silicon photoelectric conversion unit 2 and the crystalline silicon photoelectric conversion unit 3 from the light incident side is a thin film solar cell that can effectively use incident light in a wider range. 5 The crystalline photoelectric conversion unit 3 is formed in the same manner as in the above-described embodiment. In this case, since the entire film thickness of one or more photoelectric conversion unit portions formed on the transparent electrode layer 12 is increased, internal stress increases. Therefore, the thin film solar cell substrate 1 of the present invention is also preferable for a tandem thin film solar cell including such a crystalline photoelectric conversion unit 3.

  The amorphous photoelectric conversion unit 2 is 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-based layer doped with 0.01 atomic% or more of boron, which is a conductivity-determining impurity atom, an intrinsic amorphous silicon-based layer that becomes a photoelectric conversion layer, and a conductivity-type determination An n-type amorphous silicon-based layer doped with 0.01 atomic% or more of phosphorus, which is an impurity atom, may be deposited in this order. However, these layers are not limited to the above. For example, a microcrystalline silicon film may be used as the p-type layer. Further, an alloy material such as amorphous or microcrystalline silicon carbide, silicon nitride, silicon oxide, silicon germanium, or the like may be used for the p-type layer. As the intrinsic amorphous photoelectric conversion layer, an alloy material such as silicon carbide or silicon germanium may be used. The intrinsic amorphous silicon-based layer preferably contains 2 to 15% of hydrogen in the film in order to reduce the defect density in the film and reduce the recombination current loss of the thin film solar cell. In addition, the intrinsic amorphous silicon-based layer desirably has a thickness of 50 nm to 500 nm in order to reduce deterioration due to light irradiation. A microcrystalline silicon film may be used as the n-type layer. Note that the film thickness of the conductive type (p-type, n-type) microcrystalline silicon-based layer or amorphous silicon-based layer is preferably 3 nm to 100 nm, and more preferably 5 nm to 50 nm.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to the following description examples, unless the meaning is exceeded.

(Example 1)
As Example 1, a thin film solar cell 5 as shown in FIG.

A glass substrate having a thickness of 0.7 mm and a 125 mm square was used as the light-transmitting substrate 111, and a light-transmitting underlayer 112 including SiO ₂ fine particles 1121 was formed thereon. The coating liquid used for forming the light-transmitting underlayer 112 is tetraethoxysilane added to a mixture of a spherical silica dispersion having a particle size of 50 nm, water, and ethyl cellosolve, and then hydrochloric acid is added. The hydrolyzed product was used. The coating liquid is applied on the glass substrate 111 with a printing machine, dried at 90 ° C. for 30 minutes, and then heated at 350 ° C. for 5 minutes, whereby the light-transmitting insulating substrate 11 having fine irregularities formed on the surface. Got. When the surface of the translucent insulating substrate 11 was observed with an atomic force microscope (AFM), irregularities in which the convex portions were curved reflecting the shape of the fine particles were confirmed.

  The RMS of the light-transmitting underlayer 112 formed under these conditions was 7.2 nm. In addition, RMS in this invention 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). The non-contact mode of Nano-R system (manufactured by Pacific Nanotechnology) was used for this AFM measurement.

  A transparent electrode layer 12 made of ZnO was formed on the obtained light-transmitting base layer 112. The transparent electrode layer 12 is formed by a CVD method with a base temperature of the translucent insulating substrate 11 set to 180 ° C., diethyl zinc (DEZ) and water as source gases, and diborane gas as a dopant gas. doing. The thickness of the transparent electrode layer 12 made of the obtained ZnO film was 1.6 μm, the sheet resistance was about 8Ω / □, and the haze ratio was 20%. The haze ratio is expressed by (diffuse transmittance / total light transmittance) × 100 (JIS K7136). Further, the total light transmittance of the thin film solar cell substrate 1 thus obtained was measured with a spectrophotometer by entering light from the glass side. A transmittance of 80% or more was exhibited in the wavelength range of 400 nm to 1200 nm.

  The obtained transparent electrode layer 12 is separated into strip-shaped transparent electrodes having a width W of about 10 mm and a length L of 10 cm by forming a transparent electrode layer separation groove 62 having a width of about 100 μm by laser scribing. Residues after scribing were removed by ultrasonic cleaning using water.

  On the transparent electrode layer 12, a p-type microcrystalline silicon layer 31 having a thickness of 15 nm, an intrinsic crystalline silicon photoelectric conversion layer 32 having a thickness of 1.5 μm, and an n-type microcrystalline silicon layer 33 having a thickness of 15 nm are formed. Crystalline silicon photoelectric conversion layer units 3 were sequentially formed by a plasma CVD method.

  After the connection groove 63 was formed by laser scribing, 90 nm thick Al-doped ZnO 121 and 200 nm thick Ag 122 were sequentially formed as the back electrode layer 4 by sputtering. When the back electrode layer separation groove 64 was subjected to ultrasonic cleaning after laser scribing, no film peeling region on the substrate was confirmed. The number of cells connected in series after integration was ten.

When the integrated silicon thin film solar cell 6 obtained as described above was irradiated with AM 1.5 light at a light amount of 100 mW / cm ² and the output characteristics were measured, the open circuit voltage (Voc) per stage was 0. .547V, short circuit current density (Jsc) of 23.1 mA / cm ² , fill factor (FF) of 72.8%, and conversion efficiency of 9.2%.

(Example 2)
Also in Example 2, an integrated crystalline silicon thin film solar cell 6 was produced in the same manner as in Example 1. However, the difference from Example 1 is that a glass substrate 111 having an area of 910 mm × 455 mm and a thickness of 4 mm was used. The RMS of the light-transmitting underlayer 112 formed under these conditions was 9.8 nm.

  When the back electrode layer separation groove 64 was subjected to ultrasonic cleaning after laser scribing, no film peeling region on the substrate was confirmed. The number of cells connected in series after integration was 48.

When the integrated silicon thin film solar cell 6 of Example 2 manufactured in this way was irradiated with AM 1.5 light at a light quantity of 100 mW / cm ² and the output characteristics were measured, Voc per stage was 0.541 V, Jsc Of 23.6 mA / cm ² , F.I. F. Was 71.7%, and the conversion efficiency was 9.2%.

  The integrated thin-film solar cell 6 produced in Example 2 was able to maintain the conversion efficiency despite the larger area than Example 1.

(Example 3)
In Example 3, an integrated silicon thin film solar cell 6 was fabricated in substantially the same manner as in Example 2. However, the difference is that when forming the light-transmitting underlayer 112, the SiO ₂ fine particles 1121 used have a particle diameter of 80 nm and the RMS is intentionally increased. The RMS of the light-transmitting underlayer 112 formed under these conditions was 19.3 nm. Further, when the back electrode layer separation groove 64 was subjected to ultrasonic cleaning after laser scribing, no film peeling region on the substrate was confirmed.

When the output characteristics were measured by irradiating the obtained integrated silicon thin film solar cell 6 with AM1.5 light at a light quantity of 100 mW / cm ² , Voc per stage was 0.532 V, and Jsc was 24.3 mA / cm ² , F.M. F. Was 70.5%, and the conversion efficiency was 9.1%.

Example 4
In Example 4, an integrated silicon thin film solar cell 6 was produced in substantially the same manner as in Example 2. However, the difference is that when forming the light-transmitting underlayer 112, the particle diameter of the SiO ₂ fine particles 1121 used is 90 nm and the RMS is intentionally increased. In addition, the thickness of the crystalline intrinsic silicon photoelectric conversion layer 32 was set to 3.0 μm. The RMS of the light-transmitting underlayer 112 formed under these conditions was 23.0 nm. Further, when the back electrode layer separation groove 64 was subjected to ultrasonic cleaning after laser scribing, the film peeling region on the substrate was not confirmed even though the crystalline intrinsic silicon photoelectric conversion layer 32 was thickened.

When the output characteristics were measured by irradiating the obtained integrated silicon thin film solar cell 6 with AM1.5 light at a light quantity of 100 mW / cm ² , Voc per stage was 0.529 V, and Jsc was 27.6 mA / cm ² , F.M. F. Was 70.0%, and the conversion efficiency was 10.2%.

(Example 5)
In Example 5, an integrated tandem thin film solar cell 6 was produced using the same thin film solar cell substrate 1 as in Example 3. A 15 nm thick p-type amorphous silicon layer, a 350 nm thick intrinsic amorphous silicon photoelectric conversion layer, and a thickness are formed on the transparent electrode layer 12 of the laser-scribing thin film solar cell substrate 1 by plasma CVD. An amorphous silicon photoelectric conversion unit 2 made of an n-type microcrystalline silicon layer having a thickness of 15 nm was formed, and then a crystalline silicon photoelectric conversion unit 3 was formed in the same manner as in Example 1. At this time, the intrinsic crystalline silicon photoelectric conversion layer 32 has a thickness of 2.0 μm. Thereafter, a connection groove 63 is formed by laser scribing, and a 90 nm thick Al-doped ZnO 121 and a 200 nm thick Ag 122 are sequentially formed as the back electrode layer 4 by sputtering to form a back electrode layer separation groove 64. Thus, an integrated tandem silicon thin film solar cell 6 was obtained.

When the output characteristics were measured by irradiating the obtained integrated silicon thin film solar cell 6 with AM1.5 light at a light quantity of 100 mW / cm ² , Voc per stage was 1.38 V, Jsc was 13.1 mA / cm ² , F.M. F. Was 71.2%, and the conversion efficiency was 12.9%.

(Comparative Example 1)
In Comparative Example 1, the transparent electrode layer 12 made of ZnO was directly formed on a glass substrate 111 having a thickness of 0.7 mm and a 125 mm square in substantially the same manner as in Example 1. Compared to Example 1, the difference is that the translucent underlayer 112 does not exist. The RMS of the surface of the glass substrate 111 was 0.5 nm or less.

  Similar to Example 1, a 15-nm-thick p-type microcrystalline silicon layer 31 having a thickness of 1.5 μm is formed on the transparent electrode layer 12 on which the transparent electrode layer separation groove 62 is formed by laser scribing. A crystalline silicon photoelectric conversion layer unit 3 including an intrinsic crystalline silicon photoelectric conversion layer 32 and an n-type microcrystalline silicon layer 33 having a thickness of 15 nm was sequentially formed by a plasma CVD method. After that, a connection groove 63 was formed, and 90 nm thick Al-doped ZnO 121 and 200 nm thick Ag 122 were sequentially formed as the back electrode layer 4 by sputtering. After the back electrode layer 4 was formed, the back electrode layer separation groove 64 was formed by laser scribing and ultrasonic cleaning was performed. As a result, peeling of the film occurred in the vicinity of the transparent electrode layer separation groove 62. The total peeled area corresponded to about 6% of the total area of the integrated thin film solar cell 6. Moreover, since the conductivity was not confirmed in the portion where the film was peeled off, it was found that the film peeling occurred at the interface between the glass substrate 111 and the transparent electrode layer 12.

  Generally, when a silicon thin film is deposited on a substrate by plasma CVD, internal stress due to residual strain exists in the thin film. In particular, since the atoms are regularly arranged in the crystalline silicon layer, residual strain tends to be difficult to relax. Therefore, when an external mechanical force is applied, such as vibration during ultrasonic cleaning, the external force and the internal stress are superimposed so that the crystalline photoelectric conversion unit 3 and the transparent electrode layer 12 It is considered that a force for peeling near the interface acts. However, since the surface of the transparent electrode layer 12 has a relatively large texture, the adhesion due to the anchor effect is relatively strong. Therefore, it is considered that peeling is likely to occur between the transparent electrode layer 12 having weak adhesion to the glass substrate 111 having a smooth surface for low temperature formation.

When the output characteristics were measured by irradiating the obtained integrated silicon thin film solar cell 6 with AM 1.5 light at a light quantity of 100 mW / cm ² , Voc per stage was 0.499 V, and Jsc was 22.7 mA / cm ² , F.M. F. Was 67.1%, and the conversion efficiency was 7.6%.

(Comparative Example 2)
In Comparative Example 2, an integrated crystalline silicon thin film solar cell 6 was fabricated in substantially the same manner as in Example 2. However, the difference is that the transparent electrode layer 12 is directly formed on the glass substrate 111 as in Comparative Example 1. Therefore, the RMS of the surface as the translucent insulating substrate 11 is 0.5 nm or less.

  In Comparative Example 2, film peeling occurred at several places from the time when the connection groove 63 was formed. After the separation groove 64 was formed in the back electrode layer 4, the total area of the integrated thin film solar cell 6 was reduced. The area corresponding to about 15% was peeled off.

When the output characteristics were measured by irradiating the obtained integrated silicon thin film solar cell 6 with AM1.5 light at a light quantity of 100 mW / cm ² , Voc per stage was 0.473 V, and Jsc was 20.9 mA / cm ² , F.M. F. Of 65.7% and a conversion efficiency of 6.5%.

  In Comparative Example 2, in addition to the increase in the size of the glass substrate 111 as compared with Comparative Example 1, the thickness of the glass substrate 111 is increased, so that the flexibility of the glass substrate 111 is reduced. It is considered that the result of an increase in strain generated between the electrode layer 12 and the electrode layer 12 is reflected. All the parameters of the solar cell characteristics were reduced by numerous film peeling.

(Comparative Example 3)
In Comparative Example 3, an integrated crystalline silicon thin film solar cell 6 was produced in substantially the same manner as in Example 2. However, a difference is that when the light-transmitting underlayer 112 is formed, a layer made of only a metal oxide that is a material of the light-transmitting binder 1122 is formed without adding a fine particle component. The RMS of the surface of the translucent substrate 111 formed under these conditions was 2.8 nm. Further, the rate of film peeling after the formation of the integrated thin film solar cell 6 was about 10%.

The obtained integrated silicon-based thin film solar cell 6 was irradiated with AM 1.5 light at a light quantity of 100 mW / cm ² to measure the output characteristics. As a result, Voc per stage was 0.491 V, and Jsc was 21.8 mA / cm ² , F.M. F. Of 68.6% and a conversion efficiency of 7.3%.

(Comparative Example 4)
In Comparative Example 4, an integrated crystalline silicon-based thin film solar cell 6 was fabricated in substantially the same manner as in Example 2. However, the difference is that, when forming the light-transmitting underlayer 112, the SiO ₂ fine particles 1121 used have a particle diameter of 200 nm and the RMS is intentionally increased. The RMS of the substrate surface formed under these conditions was 66.9 nm. Further, no film peeling was confirmed after the integrated thin film solar cell 6 was formed.

When the output characteristics were measured by irradiating the obtained integrated silicon thin film solar cell 6 with AM1.5 light at a light quantity of 100 mW / cm ² , Voc per stage was 0.452 V, and Jsc was 22.0 mA / cm ² , fill factor F. F. Was 60.1%, and the conversion efficiency was 6.0%.

In Comparative Example 4, although the film peeling was not confirmed, Eff. Had fallen. This is because the grain size of the SiO ₂ fine particles 1121 used is too large, the unevenness of the light-transmitting underlayer 112 becomes large, and the crystal grain boundaries that are defective in the ZnO transparent electrode layer 12 formed thereon are formed. This is probably because a large number of the defects were caused to cause mechanical and electrical defects in the crystalline silicon photoelectric conversion unit 3. Therefore, when the thin film solar cell substrate 1 having a peeling prevention function is prepared using fine particles having a large particle size, the uneven particle size and height difference of the transparent electrode layer 12 formed thereon tend to increase. It has been found that this makes it easier to cause mechanical and electrical defects in crystalline solar cells.

  Table 1 shows the main characteristics of the thin film solar cell substrate 1 according to Examples 1 to 5 and Comparative Examples 1 to 4 described above, and the measurement results of the output characteristics of the integrated thin film solar cell 6 using them. Moreover, the main characteristic of the board | substrate 1 for thin film solar cells by Examples 6-10 and Comparative Examples 5-8 mentioned later, and the output characteristic in the thin film solar cell 5 of a small area using them are shown collectively.

  As can be seen from the results in Table 1, film peeling was not confirmed in any of Examples 1 to 5. In Comparative Examples 1-3, since the unevenness | corrugation of the interface between the translucent insulated substrate 11 and the transparent electrode layer 12 formed at low temperature was small, adhesive force was insufficient and film peeling was confirmed. It can be seen that when the film peeling occurs between the translucent insulating substrate 11 and the transparent electrode layer 12, all the characteristic parameters are lowered. In particular, Voc and F. F. Therefore, the film peeling between the translucent insulating substrate 11 and the transparent electrode layer 12 may increase the series resistance in the integrated solar cell structure 5 in which a plurality of cells 61 are connected in series. It is shown. Further, when film peeling occurs, the light receiving area of the power generation layer decreases, which causes a decrease in the value of Jsc.

  As described in detail above, according to the present invention, it is possible to provide an integrated thin film solar cell 6 with improved performance using the thin film solar cell substrate 1 that can be manufactured at low cost.

(Example 6)
As Example 6, the thin-film solar cell substrate 1 of FIG. A light-transmitting underlayer 112 having unevenness including SiO ₂ fine particles 1121 was formed on a glass substrate 111. The coating liquid used for forming the light-transmitting underlayer 112 was tetraethoxysilane added to a mixture of a spherical silica dispersion having an average particle size of 70 nm, water, and ethyl cellosolve, and hydrochloric acid was added to add tetraethoxysilane. A product obtained by hydrolyzing silane was used. The coating liquid is applied on the glass substrate 111 with a printing machine, dried at 90 ° C. for 30 minutes, and then heated at 350 ° C. for 5 minutes, whereby the light-transmitting underlayer 112 having fine irregularities formed on the surface. Got. When the surface of the light-transmitting underlayer 112 was observed with an atomic force microscope (AFM), irregularities in which the convex portions were curved surfaces were confirmed reflecting the shape of the fine particles.

  The root mean square roughness (RMS) of the light-transmitting underlayer 112 formed under these conditions was 17.2 nm. In addition, RMS in this invention 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). The non-contact mode of Nano-R system (manufactured by Pacific Nanotechnology) was used for this AFM measurement.

  About the translucent insulated substrate 11 which formed only the translucent base layer 112 on the glass substrate 111, the haze rate measured using C light source was 0.31%.

A transparent electrode layer 12 made of ZnO was formed on the obtained transparent base layer 112 by a low pressure thermal CVD method. The transparent electrode layer 12 has a substrate temperature set at 160 ° C., a pressure of 100 Pa, a flow rate of diethyl zinc (DEZ) of 500 sccm, a flow rate of water of 1000 sccm, a diborane (B ₂ H ₆ ) flow rate of 5 sccm, an argon flow rate of 1000 sccm, and a hydrogen flow rate of 1000 sccm. Formed with. The thickness of the transparent electrode layer 12 made of the obtained ZnO film was 1.5 μm, and the sheet resistance was 8.7Ω / □. The haze ratio measured using the C light source of the thin film solar cell substrate 1 constituted of the glass substrate 111, the light-transmitting underlayer 112, and the transparent electrode layer 123 was 27.2%. That is, a haze ratio that greatly exceeds the haze ratio of the translucent underlayer 112 is obtained by producing the transparent electrode layer 12 by a low-pressure thermal CVD method. Moreover, since the thin film solar cell substrate 1 having a haze ratio of 20% or more at a substrate temperature of 150 ° C. or higher is obtained, thermal damage to the transparent electrode layer 12 during the formation of the semiconductor layer should be reduced as compared with the conventional method. Can do. In addition, when the total light transmittance of this board | substrate 1 entered light from the glass side and measured with the spectrophotometer, the transmittance | permeability of 80% or more was shown in the wavelength range of 400 nm-1200 nm.

(Example 7)
As Example 7, the thin film solar cell substrate 1 of FIG. A transparent base layer 112 was formed in the same manner as in Example 6 except that a spherical silica dispersion having an average particle size of 95 nm was used. The RMS of this translucent underlayer 112 was 32.5 nm. Moreover, about the translucent insulated substrate 11 which formed only the translucent base layer 112 on the glass substrate 111, the haze rate measured using C light source was 0.72%.

  A transparent electrode layer 12 made of ZnO was formed on the obtained transparent base layer 112 under the same conditions as in Example 6 by low pressure thermal CVD. The thickness of the transparent electrode layer 12 made of the obtained ZnO film was 1.5 μm, and the sheet resistance was 9.3Ω / □. The RMS measured by AFM was 67.8 nm. The haze ratio measured using a C light source of the thin film solar cell substrate 1 constituted of the glass substrate 111, the light-transmitting underlayer 112, and the transparent electrode layer 123 was 35.7%. Further, the total light transmittance of the substrate 1 was measured with a spectrophotometer by entering light from the glass side. A transmittance of 80% or more was exhibited in the wavelength range of 400 nm to 1200 nm. In Example 7, the unevenness of the underlayer 2 was larger than that in Example 6, and the haze ratio increased.

(Comparative Example 5)
As the thin film solar cell substrate 1 of Comparative Example 5, the ZnO layer 12 was directly formed on the glass substrate 111 without using the light-transmitting underlayer 112 by a low pressure thermal CVD method. The conditions for forming the ZnO layer are the same as in Example 6. The RMS of the glass substrate 111 was 0.5 nm or less, and was flat below the AFM measurement limit. Moreover, about the glass substrate 111, the haze rate measured using C light source was 0.01% or less and below the measurement limit. The thickness of the transparent electrode layer 12 made of the obtained ZnO film was 1.5 μm, and the sheet resistance was 8.3Ω / □. The haze ratio measured using the C light source of the thin film solar cell substrate 1 of Comparative Example 5 was 15.1%. Further, the total light transmittance of the substrate 1 was measured with a spectrophotometer by entering light from the glass side. A transmittance of 80% or more was exhibited in the wavelength range of 400 nm to 1200 nm. Compared to Example 6, the haze ratio is small and about half with the same film thickness of the ZnO layer 12.

(Comparative Example 6)
As Comparative Example 6, a thin film solar cell substrate 1 was produced. A transparent base layer 112 was formed in the same manner as in Example 6 except that a spherical silica dispersion having an average particle diameter of 8 nm was used. The under layer 112 had an RMS of 3.1 nm. Moreover, about the glass substrate 111 which formed only the base layer 112, the haze rate measured using C light source was 0.01% or less and below the measurement limit. A transparent electrode layer 12 made of ZnO was formed on the obtained underlayer 2 by the low pressure thermal CVD method under the same conditions as in Example 6. The thickness of the transparent electrode layer 12 made of the obtained ZnO film was 1.5 μm, and the sheet resistance was 8.5Ω / □. The haze ratio measured using the C light source of the thin film solar cell substrate 1 composed of the glass substrate 111, the base layer 112, and the transparent electrode layer 12 was 15.5%. Further, the total light transmittance of the substrate 1 was measured with a spectrophotometer by entering light from the glass side. A transmittance of 80% or more was exhibited in the wavelength range of 400 nm to 1200 nm. The haze ratio of Comparative Example 6 is almost the same as that of Comparative Example 5, and it can be said that there is almost no effect of improving the haze ratio by the underlayer 2 when the unevenness of the underlayer 112 is small and the RMS is small.

(Example 8)
Using the thin film solar cell substrate 1 of Example 6, a 10 mm square thin film solar cell 5 having the structure shown in FIG. On the transparent electrode layer 12 of the thin-film solar cell substrate 1, a one-conductive layer 31 of p-type microcrystalline silicon having a thickness of 15 nm, an intrinsic crystalline photoelectric conversion layer 32 of intrinsic crystalline silicon having a thickness of 1.5 μm, The crystalline photoelectric conversion layer unit 3 composed of the n-type microcrystalline silicon reverse conductivity type layer 33 having a thickness of 15 nm was sequentially formed by the plasma CVD method. Thereafter, an Al-doped ZnO conductive oxide layer having a thickness of 90 nm and an Ag metal layer having a thickness of 300 nm were sequentially formed as the back electrode layer 4 by sputtering.

When the output characteristics were measured by irradiating the silicon-based thin film solar cell 5 obtained as described above with AM 1.5 light at a light quantity of 100 mW / cm ² , the open circuit voltage (Voc) was 0.515 V, and the short-circuit current was measured. The density (Jsc) was 27.8 mA / cm ² , the fill factor (FF) was 0.711, and the conversion efficiency was 10.2%.

(Comparative Example 7)
As Comparative Example 7, a thin film solar cell 5 was produced using the thin film solar cell substrate 1 of Comparative Example 5. The structure and manufacturing method of the thin-film solar cell are the same as in Example 8 except that the base layer 112 is not provided. When the output characteristics were measured by irradiating the obtained silicon-based thin film solar cell 5 with AM 1.5 light at a light quantity of 100 mW / cm ² , Voc was 0.517 V, Jsc was 26.5 mA / cm ² , F.R. F. Was 0.702, and the conversion efficiency was 9.6%. Since the haze ratio of the substrate 1 is lower than that of the thin film solar cell of Example 8, the light confinement effect is not sufficient, the short-circuit current density is lowered, and the conversion efficiency is lowered.

(Comparative Example 8)
As the comparative example 8, the thin film solar cell 5 was produced using the thin film solar cell substrate 1 of the comparative example 6. In addition to using a spherical silica dispersion having an average particle size of 8 nm when forming the underlayer 112, the structure and manufacturing method of the thin-film solar cell are the same as in Example 8. When the output characteristics were measured by irradiating the obtained silicon-based thin film solar cell 5 with AM 1.5 light at a light quantity of 100 mW / cm ² , Voc was 0.515 V, Jsc was 26.5 mA / cm ² , F.R. F. Was 0.705, and the conversion efficiency was 9.6%. Since the haze ratio of the substrate was almost the same as that of Comparative Example 7, the conversion efficiency was the same as that of Comparative Example 7 regardless of Jsc.

Example 9
As Example 9, the thin film solar cell 5 of FIG. 7 was produced using the thin film solar cell substrate 1 of Example 7. In addition to using a spherical silica dispersion having an average particle size of 100 nm when forming the underlayer 112, the structure and manufacturing method of the thin-film solar cell are the same as in Example 8. When the output characteristics were measured by irradiating the obtained silicon-based thin film solar cell 5 with AM 1.5 light at a light quantity of 100 mW / cm ² , Voc was 0.522 V, Jsc was 28.4 mA / cm ² , F.R. F. Was 0.705, and the conversion efficiency was 10.5%. Since the haze ratio of the substrate is increased as compared with the thin film solar cell of Example 8, Jsc is increased and the conversion efficiency is improved.

(Example 10)
In Example 10, the thin film solar cell substrate 1 of Example 7 was used to produce the tandem thin film solar cell 5 of FIG. On the transparent electrode layer 12 of the thin film solar cell substrate 1, a front one conductivity type layer of p-type amorphous silicon carbide having a thickness of 15 nm and an amorphous amorphous silicon having a thickness of 350 nm are formed by plasma CVD. An amorphous photoelectric conversion unit 2 composed of a photoelectric conversion layer and a forward reverse conductivity type layer of n-type microcrystalline silicon having a thickness of 15 nm is formed, and then the crystalline photoelectric conversion unit 3 is formed in the same manner as in Examples 8 and 9. Formed. However, the intrinsic crystalline photoelectric conversion layer 32 of the crystalline photoelectric conversion unit 3 has a thickness of 2.0 μm. Thereafter, an Al-doped ZnO conductive oxide layer having a thickness of 90 nm and an Ag metal layer having a thickness of 300 nm were sequentially formed as the back electrode layer 4 by a sputtering method, whereby a tandem-type thin film solar cell 5 was obtained. .

When the output characteristics were measured by irradiating the obtained tandem-type thin film solar cell 5 with AM1.5 light at a light quantity of 100 mW / cm ² , Voc was 1.35 V, Jsc was 13.7 mA / cm ² , F.D. F. Was 0.733, and the conversion efficiency was 13.6%.

  Table 1 shows the main characteristics of the thin film solar cell substrates according to Examples 6 to 10 and Comparative Examples 5 to 8 and the output characteristics of the small area thin film solar cells using them. Compared with the solar cell characteristics of Comparative Examples 7 and 8, the solar cells of Examples 8 and 9 have particularly improved characteristics due to an increase in Jsc. In the small-area cell, neither the comparative example nor the example had an appearance defect or film peeling.

  As described above in detail, according to the present invention, the transparent electrode layer 12 is formed on the uneven base layer 112 at a substrate temperature of 150 ° C. or higher by using low-pressure thermal CVD, so that a thin film solar cell is formed. The unevenness of the substrate 1 can be increased effectively, and the thin film solar cell substrate 1 having a large light confinement effect can be provided. Further, by applying this thin film solar cell substrate 1 to the thin film solar cell 5, the power generation current can be increased by the optical confinement effect, and the performance of the thin film solar cell 5 can be improved. Furthermore, since the haze ratio does not decrease at a substrate temperature of 150 ° C. or higher, the transparent electrode layer 12 can be formed at a substrate temperature higher than that of the conventional method. Thermal damage can be suppressed, which is effective in improving the performance and reliability of the thin-film solar cell 5.

The haze ratio of ZnO with respect to the substrate temperature of the film formed by low pressure thermal CVD. The typical top view which shows the element surface of a typical example of an integrated thin film solar cell. FIG. 3 is a schematic cross-sectional view showing, in an enlarged manner, a laminated structure in a region surrounded by an ellipse 2A in FIG. FIG. 4 is a schematic cross-sectional view further enlarging a more detailed laminated structure in a region surrounded by an ellipse 3A in FIG. 3. Sectional drawing of the board | substrate for thin film solar cells which is 2nd embodiment of this invention. Typical sectional drawing which expands and shows an example of the thin film solar cell which is 3rd embodiment which concerns on this invention in the area | region enclosed by the ellipse 3A in FIG. Sectional drawing of the thin film solar cell which is 4th embodiment of this invention. Sectional drawing of the tandem-type thin film solar cell which is the fifth embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate for thin film solar cells 11 Translucent insulating substrate 111 Translucent substrate 112 Translucent base layer 1121 Translucent fine particles 1122 Translucent binder 12 Transparent electrode layer 2 Amorphous photoelectric conversion unit 22 Amorphous intrinsic semiconductor Layer 3 Crystalline photoelectric conversion unit 31 One conductivity type layer 32 Crystalline intrinsic semiconductor layer 33 Reverse conductivity type layer 4 Back electrode layer 5 Thin film solar cell 6 Integrated thin film solar cell 61 Solar cell cell 62 Transparent electrode layer separation groove 63 Connection groove 64 Back electrode layer separation groove

Claims (7)

  A thin film solar cell substrate comprising a translucent insulating substrate and a transparent electrode layer containing at least zinc oxide deposited on the translucent insulating substrate, the translucent insulating substrate on the transparent electrode layer side A thin film solar cell substrate having fine surface irregularities having a root mean square roughness of 5 to 50 nm at the interface, and the convex portions are curved surfaces.   It is a board | substrate for thin film solar cells of Claim 1, Comprising: The said transparent electrode layer has a film thickness of 1 micrometer or more, The board | substrate for thin film solar cells characterized by the above-mentioned.   It is a board | substrate for thin film solar cells in any one of Claim 1 or 2, Comprising: The haze rate which is ratio of the diffuse transmittance measured using C light source and total transmittance is 20% or more, It is characterized by the above-mentioned. Thin film solar cell substrate.   It is a board | substrate for thin film solar cells in any one of Claims 1-3, Comprising: The said translucent insulated substrate consists of a laminated body of the translucent base | substrate and translucent base layer which have a smooth surface, The light-transmitting underlayer includes a light-transmitting fine particle having an average particle size of 10 nm or more and less than 100 nm, and a light-transmitting binder.   The thin film solar cell provided with the board | substrate for thin film solar cells in any one of Claims 1-4.   A thin film solar cell substrate according to any one of claims 1 to 4, further comprising at least one crystalline photoelectric conversion unit layer deposited on the transparent electrode layer, and a back electrode layer, These layers are separated by a plurality of separation grooves so as to form a plurality of photoelectric conversion cells, and the plurality of photoelectric conversion cells are electrically connected in series to each other through the plurality of connection grooves. An integrated thin film solar cell.   It is a manufacturing method of the board | substrate for thin film solar cells in any one of Claims 1-4, Comprising: The temperature of the said translucent insulated substrate is 150 degreeC or more, and deposits the transparent electrode layer containing the said at least zinc oxide. The manufacturing method of the board | substrate for thin film solar cells characterized by these.

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