WO2013140549A1

WO2013140549A1 - Solar cell and method for manufacturing same

Info

Publication number: WO2013140549A1
Application number: PCT/JP2012/057190
Authority: WO
Inventors: 平　茂治; 志敦寺中
Original assignee: 三洋電機株式会社
Priority date: 2012-03-21
Filing date: 2012-03-21
Publication date: 2013-09-26

Abstract

A solar cell (10) is provided with: a photoelectric conversion unit (11); and a first electrode (20) and a second electrode (30), which contain a binder and a filler, and are provided on the main surfaces of the photoelectric conversion unit (11), respectively. At least a part of the first electrode (20) and at least a part of the second electrode (30) have an electrode height variation coefficient of 15 % or less for a length of 1 mm or more. The first electrode (20) and the second electrode (30) are manufactured by printing paste portions (50a, 50b) on respective main surfaces, said paste portions forming respective electrodes, flattening the upper surfaces (53a, 53b) of the paste portions (50a, 50b) by pressing, in the height direction, at least a part of each of the printed paste portions (50a, 50b), then, hardening the paste portions (50a, 50b).

Description

Solar cell and manufacturing method thereof

The present invention relates to a solar cell and a manufacturing method thereof.

The solar cell includes an electrode on the main surface of the photoelectric conversion unit in order to collect carriers generated by light reception. Such an electrode is required to suppress the resistance of the electrode itself, the contact resistance between the electrode and the photoelectric conversion unit, the contact resistance between the electrode and the wiring material, and the like. For example, Patent Documents 1 and 2 disclose a method for manufacturing a solar cell in which electrodes are formed by repeating screen printing of a conductive paste a plurality of times.

JP-A-11-103084 JP 2011-61109 A

According to the above prior art, the unevenness of the electrode surface can be reduced, for example, the contact resistance between the electrode and the wiring material can be lowered. However, in the current situation where the spread of solar cells is rapidly progressing, further improvement in photoelectric conversion efficiency is required.

A solar cell according to one embodiment of the present invention includes a photoelectric conversion unit, a binder, and an electrode provided on a main surface of the photoelectric conversion unit, and at least a part of the electrode has a length of 1 mm or more. The variation coefficient of the electrode height over the entire length is 15% or less.

A method for manufacturing a solar cell according to one embodiment of the present invention is a method for manufacturing a solar cell including an electrode on a main surface of a photoelectric conversion unit, and is printed by printing a paste for forming an electrode on the main surface. And pressing the at least part of the paste in the height direction to flatten the upper surface of the paste, and then curing the paste.

According to the present invention, a solar cell having good photoelectric conversion characteristics can be provided.

It is the top view which looked at the solar cell which is an example of embodiment which concerns on this invention from the light-receiving surface side. It is the sectional view on the AA line of FIG. It is sectional drawing which shows the modification of the solar cell which is an example of embodiment which concerns on this invention. It is a figure which shows the principle of the screen printing method in an example of embodiment which concerns on this invention. It is a figure which shows a part of manufacturing process of the solar cell which is an example of embodiment which concerns on this invention. It is a figure which shows a part of manufacturing process of the solar cell which is an example of embodiment which concerns on this invention. It is a figure which shows a part of manufacturing process of the solar cell which is another example of embodiment which concerns on this invention. It is a figure which shows a part of manufacturing process of the solar cell which is another example of embodiment which concerns on this invention. In the solar cell which is an example of embodiment which concerns on this invention, and the conventional solar cell, it is a figure which shows the measured value of the electrode height along the longitudinal direction of an electrode. It is sectional drawing which shows the conventional solar cell. In the solar cell which is an example of embodiment which concerns on this invention, it is sectional drawing which shows the modification of a photoelectric conversion part. In the solar cell which is an example of embodiment which concerns on this invention, it is sectional drawing which shows the other modification of a photoelectric conversion part.

Embodiments of the present invention will be described in detail with reference to the drawings.
The present invention is not limited to the following embodiments. The drawings referred to in the embodiments are schematically described, and the dimensional ratios of the components drawn in the drawings may be different from the actual products. Specific dimensional ratios and the like should be determined in consideration of the following description. Unless otherwise specified, the description of “numerical value X to numerical value Y” means “numerical value X or more and numerical value Y or less”.

In the present specification, the description “a second object (for example, a transparent conductive layer) is formed on a first object (for example, a main surface of a photoelectric conversion unit)” is not particularly limited. As long as the first and second objects are formed in direct contact, it is not intended. That is, this description includes a case where another object exists between the first and second objects.

FIG. 1 is a plan view of a solar cell 10 as an example of an embodiment of the present invention as viewed from the light receiving surface side. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1 and shows a cross section of the solar cell 10 cut in the thickness direction along the direction in which the

finger electrodes

21 and 31 extend.

The solar cell 10 includes a photoelectric conversion unit 11 that generates carriers by receiving light such as sunlight, a first electrode 20 that is a light-receiving surface electrode provided on the light-receiving surface of the photoelectric conversion unit 11, and photoelectric conversion. And a second electrode 30 that is a back surface electrode provided on the back surface of the portion 11. On the back surface of the solar cell 10, the second electrode 30 can be formed in a larger area than the first electrode 20 because the influence of the light blocking loss on the photoelectric conversion characteristics is less than that of the light receiving surface.

Here, the “light-receiving surface” means a main surface on which sunlight mainly enters from the outside of the solar cell 10. For example, more than 50% to 100% of the sunlight incident on the solar cell 10 enters from the light receiving surface side. Further, the “back surface” means a main surface opposite to the light receiving surface. In other words, the surface having the large electrode area among the main surfaces is the back surface.

The photoelectric conversion unit 11 includes a substrate made of a semiconductor material such as crystalline silicon (c-Si), gallium arsenide (GaAs), or indium phosphorus (InP). The photoelectric conversion unit 11 is, for example, a translucent conductive material mainly composed of an i-type amorphous silicon layer, a p-type amorphous silicon layer, indium oxide, and the like on a light-receiving surface of an n-type single crystal silicon substrate. And a transparent conductive layer made of an oxide (TCO). In addition, an i-type amorphous silicon layer, an n-type amorphous silicon layer, and a transparent conductive layer are sequentially provided on the back surface of the n-type single crystal silicon substrate. The photoelectric conversion unit 11 is not limited to this configuration, and various configurations can be adopted as will be described later.

It is preferable that the light receiving surface and the back surface of the photoelectric conversion unit 11 have a texture structure (not shown). The texture structure is a surface uneven structure having a height of about 1 μm to 15 μm that suppresses surface reflection and increases the light absorption amount of the photoelectric conversion unit 11. As a specific example of the texture structure, there is a pyramidal (quadrangular pyramid or quadrangular pyramid-shaped) uneven structure obtained by performing anisotropic etching on the light receiving surface of a substrate made of single crystal silicon having a (100) plane. It can be illustrated.

The first electrode 20 includes, for example, a plurality (for example, 50) of finger electrodes 21 and a plurality (for example, two) of bus bar electrodes 22. The finger electrode 21 is a thin line-shaped electrode formed over a wide range on the light receiving surface in order to collect carriers generated by the photoelectric conversion unit 11. The bus bar electrode 22 is an electrode that collects carriers from the finger electrodes 21, and is electrically connected to all the finger electrodes 21.

In the first electrode 20, two bus bar electrodes 22 are arranged in parallel with each other at a predetermined interval, and a plurality of finger electrodes 21 are arranged so as to intersect with each other. The plurality of finger electrodes 21 are arranged so that a part thereof extends from each of the bus bar electrodes 22 to the edge side of the light receiving surface and the remaining part connects the two bus bar electrodes 22. The second electrode 30 has the same electrode arrangement as that of the first electrode 20 and includes a plurality (for example, 250) of finger electrodes 31 and a plurality (for example, two) of bus bar electrodes 32.

The first electrode 20 and the second electrode 30 are both preferably formed using a conductive paste described later, and include an insulating binder and a conductive filler as electrode materials. The electrode material may contain a small amount of an additive such as a filler dispersant. The electrode material and composition may be changed between the finger electrode and the bus bar electrode, and between the first electrode 20 and the second electrode 30, but in this embodiment, the

finger electrodes

21 and 31 and the

bus bar electrodes

22 and 32 are It shall be comprised with the same material and the same composition.

The width (average value) of the finger electrode 21 is not particularly limited, but is preferably 30 μm to 150 μm from the viewpoint of reducing light shielding loss. The width may be narrowed as the distance from the bus bar electrode 22 increases. In this case, the width of the finest details is preferably 30 μm to 80 μm. The width (average value) of the bus bar electrode 22 is preferably 0.5 mm to 1.5 mm, for example. In the second electrode 30, the width of the finger electrode 31 is preferably larger than that of the finger electrode 21, and is set to 60 μm to 250 μm, for example.

The height (average value) of the first electrode 20 is not particularly limited, but is preferably 20 μm to 140 μm, more preferably 30 μm to 110 μm, and particularly preferably 40 μm to 90 μm from the viewpoint of reducing resistance loss. The height of the bus bar electrode 22 may be higher than that of the finger electrode 21, but in this embodiment, the average height of the finger electrode 21 and the bus bar electrode 22 is substantially equal. The “substantially equivalent” includes a state that can be regarded as substantially equivalent, for example, a case where the difference in average values is ± 5% or less (the same applies hereinafter). Hereinafter, the height of the first electrode 20 is “height h ₂₀ ”, the height of the finger electrode 21 is “height h ₂₁ ”, and the height of the bus bar electrode 22 is “height h ₂₂ ” as necessary. (Unless otherwise specified, description will be made assuming that height h ₂₀ = height h ₂₁ = height h ₂₂ ).

The height (average value) of the second electrode 30 is also not particularly limited. However, since the electrode area can be made larger than that of the first electrode 20, it can be made lower than that of the first electrode 20 from the viewpoint of reducing the electrode material. Is preferred. Specifically, it is preferably 5 μm to 70 μm, more preferably 10 μm to 60 μm, and particularly preferably 15 μm to 50 μm. The height of the bus bar electrode 32 may be higher than that of the finger electrode 31 as in the case of the first electrode 20, but in this embodiment, the average height of the finger electrode 31 and the bus bar electrode 32 is substantially equal. It is. Hereinafter, the height of the second electrode 30 is “height h ₃₀ ”, the height of the finger electrode 31 is “height h ₃₁ ”, and the height of the bus bar electrode 32 is “height h ₃₂ ” as necessary. (Unless otherwise specified, description will be made assuming that height h ₃₀ = height h ₃₁ = height h ₃₂ ).

The height h ₂₀ (the same applies to the height h ₃₀ ) is measured by cross-sectional observation using a scanning electron microscope (SEM), and is measured from the uppermost surface of the photoelectric conversion unit 11 (for example, the convex portion of the texture structure). This is the length to the top surface of one electrode 20. For example, the height h ₂₀ is measured for a cross section obtained by cutting the finger electrode 21 along its longitudinal direction.

In the solar cell 10, the coefficient of variation (referred to as “CV ₂₀ ”) of the height h ₂₀ of the first electrode 20 over a length of 1 mm or more and the height h ₃₀ of the second electrode 30 over a length of 1 mm or more. The coefficient of variation (referred to as “CV ₃₀ ”) is 15% or less. That is, in the solar cell 10, the upper surfaces 23 and 33 of the first electrode 20 and the second electrode 30 are flat and have less unevenness.

CV ₂₀ (same for CV ₃₀ ) is a value obtained by dividing the standard deviation of the height h ₂₀ measured over a length of 1 mm or more of the first electrode 20 by the average value of the height h _20. . As CV ₂₀ is smaller, the variation in height h ₂₀ is smaller and the flatness of the upper surface 23 of the first electrode 20 is higher. The standard deviation can be obtained using Microsoft's Excel STDEV function in the above-mentioned range.

The coefficient of variation (referred to as “CV ₂₁ ”) of the height h ₂₁ of the finger electrode 21 is such that CV ₂₁ is 15% or less over a length of 1 mm or more along the longitudinal direction. CV ₂₁ is preferably 12% or less, particularly preferably 8% or less. Further, the coefficient of variation (referred to as “CV ₂₂ ”) of the height h ₂₂ of the bus bar electrode 22 is substantially equal to, for example, CV ₂₁ . That is, in the first electrode 20, the

upper surfaces

24 and 25 of the finger electrode 21 and the bus bar electrode 22 are both flat and uneven.

The finger electrode 21 and the bus bar electrode 22 preferably have CV ₂₁ and CV ₂₂ within the above-mentioned range over their entire length. Furthermore, it is preferable that CV ₂₁ and CV ₂₂ are within the above range in more than half of the plurality of finger electrodes 21 and the plurality of bus bar electrodes 22. In particular, it is preferable CV ₂₂ CV ₂₁ and all of the bus bar electrodes 22 of all the finger electrodes 21 is within the above range. That is, CV ₂₀ is preferably 15% or less over the entire first electrode 20, more preferably 12% or less, and particularly preferably 8% or less.

Similarly to the first electrode 20, the CV ₃₀ of the second electrode 30 is preferably 15% or less, more preferably 12% or less, and particularly preferably 8% or less over the entire second electrode 30. . The coefficient of variation (referred to as “CV ₃₁ ”) of the height h ₃₁ of the finger electrode 31 and the coefficient of variation (referred to as “CV ₃₂ ”) of the height h ₃₂ of the bus bar electrode 32 are CV ₃₁ , CV over the entire length. ₃₂ is 15% or less, preferably 12% or less, particularly preferably 8% or less.

CV ₂₁ and CV ₂₂ (the same applies to CV ₃₁ and CV ₃₂ ) may be different from each other. For example, when the height h ₂₂ is set higher than the height h ₂₁ , the CV ₂₂ may be smaller than the CV ₂₁ . That is, the upper surface 25 of the bus bar electrode 22 may be flatter than the upper surface 24 of the finger electrode 21. By flattening the upper surface 25 to reduce the unevenness, for example, connectivity with a wiring material attached in the modularization is improved.

In FIG. 3, sectional drawing of the solar cell 10x which is a modification of the solar cell 10 is shown.
Similar to the solar cell 10, the solar cell 10 x includes a first electrode 20 x and a second electrode 30 x. On the other hand, in the solar cell 10x, a metal film 31x such as silver (Ag) is provided instead of the finger electrode 31. The metal film 31x is formed in substantially the entire region on the back surface of the photoelectric conversion unit 11 (for example, 95% or more on the transparent conductive layer). The bus bar electrode 32x is formed on the metal film 31x. As with the bus bar electrode 32, the bus bar electrode 32x has a height variation coefficient of 15% or less over a length of 1 mm or more along the longitudinal direction thereof.

In the solar cell 10x, the height of the finger electrode 21x and the bus bar electrode 22x varies greatly, the upper surface has large irregularities, and the coefficient of variation in height exceeds 15%. That is, in the solar cell 10x, the variation coefficient of the height of the bus bar electrode 32x (second electrode 30x) is smaller than the variation coefficient of the height of the finger electrode 21x and the bus bar electrode 22x (first electrode 20x). The flatness of the electrodes is different between 20x and the second electrode 30x.

It is good also as a structure provided with the 1st electrode 20 planarized instead of the 1st electrode 20x. In the configuration illustrated in FIG. 2, the second electrode 30 x including the metal film 31 x may be provided instead of the second electrode 30.

Hereinafter, the manufacturing method of the solar cell 10 provided with the said structure is explained in full detail.
FIG. 4 is a diagram for explaining the principle of the screen printing method. 5 and 6 are diagrams showing an electrode forming process of the solar cell 10. 7 and 8 are diagrams showing another example of the electrode forming process of the solar cell 10. 5 to 8 are schematic views of FIG. 5 to 8, the paste 50 printed on the light receiving surface of the photoelectric conversion unit 11 to form the first electrode 20 is “paste 50a”, and the paste 50 printed on the back surface to form the second electrode 30 is “ This is referred to as “paste 50b”. In addition, if necessary, a description will be given by attaching a and b to the related elements of the

pastes

50a and 50b.

In the manufacturing process of the solar cell 10, the photoelectric conversion unit 11 is manufactured by a known method. When the photoelectric conversion unit 11 is prepared, the paste 50a to be the first electrode 20 and the paste 50b to be the second electrode 30 are printed on the main surface. The electrode printing method is not particularly limited as long as the paste 50 containing the electrode material (the binder and the filler) can be printed on the main surface. For example, a stencil printing method (offset printing method, screen printing method) and a paste jet method can be used. In addition, although the printing order of the

pastes

50a and 50b is not limited, the following description will be made assuming that the paste 50b is printed first.

The paste 50b is preferably printed by a screen printing method from the viewpoint of productivity and accuracy. In the screen printing method, plate making and squeegee 44 are used. As the plate making, a screen plate 40 illustrated in FIG. 4 or a metal mask plate (not shown) can be used. Below, the screen printing method using the screen plate 40 is illustrated.

As shown in FIGS. 4 and 5, in the screen printing process of the paste 50 b, the screen plate 40 b having the opening 43 b corresponding to the shape of the second electrode 30 and the squeegee 44 are used on the back surface of the photoelectric conversion unit 11. The paste 50b is transferred to the substrate. The paste 50b is preferably printed at substantially the same height according to the shape of the finger electrode 31 and the bus bar electrode 32. That is, it is preferable that the paste 50b transferred onto the back surface has substantially the same height over the entire length of each electrode.

The screen printing process of the paste 50b is performed, for example, by placing the photoelectric conversion unit 11 on the flat table 51 with the back surface facing the screen plate 40b. More specifically, the paste 50 is placed on the screen plate 40b in which the opening 43b is formed only on the portion to which the paste 50b is to be transferred, and the squeegee 44 is slid to fill the opening 50 with the paste 50. Subsequently, when the portion of the screen plate 40b through which the squeegee 44 passes is separated from the back surface, the paste 50 is discharged from the opening 43b and transferred onto the back surface. In this embodiment, off-contact printing is described, but on-contact printing may be applied.

The screen plate 40 has a mesh 41 stretched on a frame (not shown). The mesh 41 is a woven fabric or the like that transmits the paste 50, and the mesh 41 is provided with a mask material 42 corresponding to a region on the main surface where the paste 50 is not desired to be applied. That is, the screen plate 40 allows the paste 50 to pass through only the opening 43 which is a portion of the mesh 41 that is not masked by the mask material 42.

The material, wire diameter, number of meshes, opening, opening rate, etc. of the mesh 41 are selected according to the width, height, etc. of the second electrode 30 to be formed. The mesh 41 is made of, for example, a resin fiber such as polyester or a metal wire such as stainless steel. The wire diameter of the mesh 41 is selected according to the height of the second electrode 30 and the like. The number of meshes is selected according to the strength of the mesh 41 and the definition of the second electrode 30. The opening is selected according to the particle size of the filler contained in the paste 50, and is generally preferably at least twice the particle size. The opening rate is selected according to the height and the width of the second electrode 30.

For the mask material 42, a photosensitive emulsion is usually used. The emulsion is selected according to the resolution, exposure sensitivity, and the like. For example, a diazo or stilbazolium material is used. In addition to the emulsion, a metal foil can be used. For example, the emulsion is coated on the mesh 41 and becomes a mask material 42 through an ultraviolet exposure process and an unexposed part removal process. Note that the thickness (plate thickness) of the screen plate 40 can be easily adjusted by increasing or decreasing the thickness (emulsion thickness) of the mask material 42. Usually, the electrode height can be increased as the plate thickness increases.

The squeegee 44 is made of a material suitable for spreading the paste 50 on the screen plate 40. The squeegee 44 is preferably composed of an elastic body having solvent resistance. For example, urethane rubber or the like is suitable. The shape of the squeegee 44 is not particularly limited, but a flat squeegee is suitable.

The paste 50 is a fluid fluid paste. As the paste 50, a heat-curing type conductive paste in which a binder and a filler, which are electrode materials, and a solvent are mixed is suitable. For the binder, for example, an epoxy resin, a urethane resin, a urea resin, an acrylic resin, an imide resin, a thermosetting resin such as a phenol resin, or a modified or mixture thereof can be used. Of these, epoxy resins are preferred. Moreover, you may mix a silicone type resin etc. with the said thermosetting resin. As the filler, for example, metal particles such as silver (Ag), copper (Cu), nickel (Ni), aluminum (Al), silver-coated copper, silver-coated aluminum, carbon, or a mixture thereof can be used. . Of these, silver particles are preferred. As the solvent, for example, alcohol-based, glycol ether-based, hydrocarbon-based organic solvents, or mixed solvents thereof can be used.

In the screen printing process, as main parameters for determining printing conditions, a squeegee angle, a squeegee speed, a squeegee printing pressure (also simply referred to as a printing pressure), a clearance that is a distance between the screen plate 40 and the photoelectric conversion unit 11, and the like. Can be mentioned. For example, the squeegee angle is preferably about 50 ° to 80 °, and the printing pressure is preferably about 2 to 6 kgf / cm ² .

6A, subsequently, the paste 50b printed on the back surface is pressed in the height direction, and the upper surface 53b of the paste 50b is flattened. In the flattening step, for example, a pressing device is placed on the paste 50b printed on the back surface and the upper surface 53b is pressed. As the pressing device, a flattening screen plate 45 that is a plate making without an opening and a squeegee 44 used in the screen printing step can be used. The flattening screen plate 45 is composed of the same mesh 41 and mask material 42 as the screen plate 40. However, the flattening screen plate 45 does not have an opening corresponding to the electrode shape. For example, the entire mesh 41 is masked by the mask material 42. In addition, the surface of the mask material 42 that contacts the paste 50b is a flat surface without unevenness, and preferably has no unevenness of 5 μm or more.

In the flattening step, the squeegee 44 is slid on the surface opposite to the surface that contacts the paste 50b of the screen plate 45 for flattening. As a result, as shown in FIG. 6B, the paste 50b is compressed and the upper surface 53b is flattened. The angle and speed of the squeegee 44, the pressing force by the squeegee 44 (the force by which the squeegee 44 pushes the flattening screen plate 45), etc. are not particularly limited, and can be set similarly to the screen printing step. Normally, the higher the pressing force by the squeegee 44, the stronger the paste 50b is compressed, the lower the height of the paste 50b, and the higher the flatness of the upper surface 53b.

Before proceeding to the flattening step, it is preferable to remove the solvent contained in the paste 50b as long as the upper surface 53b can be flattened. The solvent can be removed by heat treatment or the like. For example, the heat treatment (hereinafter referred to as “temporary drying process”) is performed at 150 ° C. for 5 minutes to eliminate the tack (adhesiveness) of the paste 50b and the paste with the printing pressure in the printing process of the paste 50a. 50b is crushed and adjusted to an amount of solvent that can be plastically deformed. At this time, the curing reaction of the binder resin may proceed as long as the upper surface 53b can be flattened.

Subsequently, the paste 50b whose upper surface 53b is flattened is subjected to a heat treatment (hereinafter referred to as “main drying treatment”) at a temperature higher than the temporary drying treatment for a long time (for example, 200 ° C. × 60 minutes). The paste 50b can be cured by removing the solvent and heat-curing the binder. The main drying process of the paste 50b is preferably performed together with the main drying process of the paste 50a from the viewpoint of reducing process costs. That is, it is preferable that the paste 50a is printed on the light receiving surface, and the upper surface 53a of the paste 50a is flattened using the flattening screen plate 45 similarly to the paste 50b, and then the

pastes

50a and 50b are simultaneously subjected to the main drying process. It is. In this case, if the paste 50a is printed on the table 51 as described later, the paste 50b may be further flattened. Thus, the first electrode ₂₀ having a CV ₂₀ of 15% or less and the second electrode 30 having a CV ₃₀ of 15% or less can be produced.

The screen printing of the paste 50a can be performed in the same manner as the screen printing of the paste 50b. However, since height h ₂₀ > height h ₃₀ , printing is performed using the screen plate 40a having a plate thickness larger than that of the screen plate 40b used for printing the paste 50a. In the screen plate 40a, it is possible to print a paste 50a in which the mask material 42a is thicker than the mask material 42b and higher than the paste 50b. Further, since the width of the finger electrode 21 <the width of the finger electrode 31, the opening width of the opening 43a is narrower than the opening width of the opening 43b, and a paste 50a having a smaller width than the paste 50b can be printed.

As shown in FIG. 7A, the paste 50b can be flattened by a method different from the above method. In the planarization step illustrated in FIG. 7, after printing the paste 50b on the back surface, the photoelectric conversion unit 11 is inverted, and the photoelectric conversion unit 11 is arranged on the table 51 with the light receiving surface facing the screen plate 40a side. To do. The paste 50a is printed on the light receiving surface while pressing the paste 50b printed on the back surface onto the table 51 to flatten the upper surface 53b. As shown in FIG. 7B, the paste 50b is strongly pressed in the height direction by the printing pressure of the paste 50a in the screen printing process, and the upper surface 53b is flattened. Also in this case, before proceeding to the printing process of the paste 50a, that is, before pressing the paste 50b printed on the back surface, it is preferable to remove the solvent contained in the paste 50b within a range in which the upper surface 53b can be flattened. It is.

The table 51 is, for example, a table having a flat surface without unevenness (preferably having no unevenness of 5 μm or more). Such a flat surface is larger than the main surface of the photoelectric conversion unit 11, and it is preferable that the entire main surface can be uniformly supported and pressed.

The printing pressure in the screen printing of the paste 50a affects not only the printing characteristics of the paste 50a but also the flattening of the paste 50b. Normally, as the printing pressure increases, the pressing force against the paste 50b increases and the paste 50b is strongly compressed, the height of the paste 50b decreases, and the flatness of the upper surface 53b improves.

Through the process illustrated in FIG. 7, the intermediate body 12 in which the paste 50 b having the flat upper surface 53 b is formed on the back surface of the photoelectric conversion unit 11 and the paste 50 a is printed on the light receiving surface can be obtained. Since the intermediate body 12 has not undergone the flattening process of the paste 50a, large irregularities exist on the upper surface 53a. By subjecting the intermediate body 12 to the main drying process, the solvent in the

pastes

50a and 50b can be removed, and the binder can be subjected to a thermosetting reaction to cure the

pastes

50a and 50b. In this case, for example, only the CV _{30 of} the second electrode 30 is 15% or less, and the CV ₂₀ of the first electrode 20 exceeds 15%. That is, the second electrode 30 is flatter than the first electrode 20.

As shown in FIG. 8A, a flattening step of the paste 50a can be further provided. For example, it is possible to flatten the upper surface 53a of the paste 50a by pressing the paste 50a of the intermediate body 12 using a flat press plate 52 without unevenness. Alternatively, instead of using the press plate 52, a flattening screen plate 45 may be used, or the photoelectric conversion unit 11 may be reversed and the paste 50 a may be pressed against the table 51. In addition, before pressing the paste 50a, it is preferable to perform the said temporary drying process in the range which can planarize the upper surface 53a.

The main drying process is performed after the flattening step of the paste 50a or in a state where pressing by the press plate 52 is continued. By this treatment, the solvents in the

pastes

50a and 50b can be removed, and the

pastes

50a and 50b can be cured by thermosetting the binder. Thus, as shown in FIG. 8B, the first electrode 20 having a flat upper surface 25 and CV ₂₀ of 15% or less and the second electrode 30 having a flat upper surface 35 and CV ₃₀ of 15% or less are manufactured. be able to.

In the manufacturing process of the solar cell 10x, it is preferable to first print the paste for forming the second electrode 30x by limiting the printing order of each paste for forming the first electrode 20x and the second electrode 30x. is there. Specifically, after the paste for forming the bus bar electrode 32x is printed on the metal film 31x and planarized, the paste for forming the first electrode 20x is printed on the light receiving surface. Thereby, the sulfidation and oxidation of the metal film 31x in the heat treatment step of the first electrode 20x can be prevented, and the contact resistance between the metal film 31x and the bus bar electrode 32x can be kept low.

The characteristics of the solar battery 10 will be described in comparison with a conventional solar battery 60 (hereinafter referred to as “conventional battery 60”).
FIG. 9A shows measured values of the height along the longitudinal direction of the finger electrode 81 of the conventional battery 60, and FIGS. 9B and 9C show the measured value along the longitudinal direction of the finger electrode 31 of the solar cell 10. The measured value of the height h ₃₁ is shown. In the figure, the horizontal axis represents the electrode length, and the vertical axis represents the electrode height. FIG. 10 shows a cross-sectional view of the conventional battery 60.

The solar cell 10 and the conventional battery 60 are provided with the same photoelectric conversion unit 11 and differ only in electrode form. Similar to the solar battery 10, the conventional battery 60 includes the finger electrode 71, the first electrode 70 including the bus bar electrode 72, and the second electrode 80 including the finger electrode 81 and the bus bar electrode 82. , 50b is different from the solar cell 10 in that it has not undergone the flattening process.

Figure 9 (b) to the finger electrode 31 measurements is shown a height h ₃₁ (hereinafter referred to as "finger electrodes 31A"), and the finger electrode measured value of the height h ₃₁ in FIG. 9 (c) are shown 31 (hereinafter referred to as “finger electrode 31B”) is obtained by flattening the upper surface 34 by pressing paste 50b printed at substantially the same height with different pressures. The finger electrode 31A was formed through a low-pressure (0.5 MPa) flattening step, and the finger electrode 31B was formed through a high-pressure (1.0 MPa) flattening step.

As shown in FIGS. 9B and 9C, the finger electrodes 31A and 31B both have a small variation in the height h _{31 and} the CV ₃₁ over a length of 1 mm or more is 15% or less. Specifically, in the finger electrode 31A, the average value of the height h ₃₁ was 33.1 μm, and the CV ₃₁ was 11.5%. In the finger electrode 31B, the average value of the height h ₃₁ was 30.3 μm, and the CV ₃₁ was 7.2%. That found the pressing force is higher in the flattening process, CV ₃₁ becomes paste 50b is compressed strongly height h ₃₁ low is reduced.

On the other hand, as shown in FIG. 9A, the finger electrode 81 had an average height value of 26.0 μm and a height variation coefficient of 17.9%. That is, the finger electrode 81 has a height variation coefficient of more than 15%, and the top surface has large irregularities compared to the finger electrodes 31A and 31B, and the height varies.

In the solar cell 10A including the finger electrode 31A, the solar cell 10B including the finger electrode 31B, and the conventional battery 60, the finger electrode on the light-receiving surface side having substantially the same dimensions as the finger electrodes 31A, 31B, and 81, and the light reception, respectively. Bus bar electrodes on the surface side and the back surface side were provided. And the wiring material was attached to the bus-bar electrode of each solar cell, and the output characteristic was evaluated. The evaluation results are shown as a ratio to the conventional battery 60 (curve factor of solar cells 10A and 10B / curve factor of conventional battery 60).
Solar cell 10A; 1.005 (the coefficient of variation is 11.5%)
Solar cell 10B; 1.010 (coefficient of variation of 7.2%)
Thus, the solar cells 10A and 10B having a high flatness on the electrode upper surface have lower output resistance than the conventional battery 60 having a lower flatness on the electrode upper surface and have good output characteristics. The output characteristics improve as the flatness increases.
In addition, as the flatness of the upper surface of the electrode increases, the photoelectric conversion unit 11 is less likely to be damaged when the wiring member is thermocompression bonded to the bus bar electrode. This tendency becomes remarkable when the coefficient of variation is about 15%.

As described above, according to the manufacturing method described above, the paste printed on the main surface of the photoelectric conversion unit 11 is pressed and compressed, so that the unevenness on the upper surface of the paste is reduced and a flattened electrode is formed. Can do. Such an electrode has a variation coefficient of electrode height of 15% or less over a length of 1 mm or more, preferably over the entire length.

In the solar cell 10, by pressing the

pastes

50 a and 50 b to be the first electrode 20 and the second electrode 30 before curing, for example, the electrode material is strongly compressed and the fillers are in strong contact with each other, and a good conductive path is obtained. Can be formed. For this reason, the resistance of the electrode itself can be reduced. In addition, the adhesion between the electrode and the photoelectric conversion unit 11 can be improved, and the contact resistance between the electrode and the photoelectric conversion unit 11 can be reduced. Alternatively, the manufacturing cost can be reduced by reducing the amount of conductive paste used while maintaining low resistance loss. Further, the finger electrode can be further thinned while maintaining a low resistance loss, thereby reducing a light shielding loss.

In the solar cell 10, since the variation in the electrode height is small and the flatness of the upper surface of the electrode is high, for example, the connectivity with the wiring material attached when modularizing is improved. For example, the contact area between the electrode and the wiring material is increased, the adhesion between the electrode and the wiring material is improved, and the contact resistance between the two is also reduced. Furthermore, although the wiring material is thermocompression bonded to the electrode, the influence of the stress generated at that time can be reduced. When the unevenness of the upper surface of the electrode is large, pressure is likely to be applied to the convex portion, and stress concentrates on a part of the photoelectric conversion portion 11, and damage such as cracks or cracks may occur in the photoelectric conversion portion 11. On the other hand, in the solar cell 10, since the flatness of the upper surface of the electrode is high, the stress applied to the photoelectric conversion unit 11 can be dispersed, and damage to the photoelectric conversion unit 11 can be suppressed.

The solar cell 10 exhibits good photoelectric conversion characteristics due to, for example, a synergistic effect thereof.

The above embodiment can be appropriately changed in design without departing from the object of the present invention.
For example, as illustrated in FIG. 11, the photoelectric conversion unit 11 includes an n-type amorphous silicon layer 101 and an n-type amorphous silicon film 102 formed on the light-receiving surface side of an n-type single crystal silicon substrate 100. A p-type region composed of an i-type amorphous silicon layer 103, a p-type amorphous silicon layer 104, and a transparent conductive layer 105, and an i-type amorphous silicon layer A structure having an n-type region composed of the n-type amorphous silicon layer 107, the transparent conductive layer 108, and an insulating layer 111 provided between the p-type region and the n-type region may be employed. . In this case, an electrode is provided only on the back side of n-type single crystal silicon substrate 100. The electrodes include a p-side collector electrode 109 formed on the p-type region and an n-side collector electrode 110 formed on the n-type region.
12, the photoelectric conversion unit 11 includes a p-type polycrystalline silicon substrate 120, an n-type diffusion layer 121 formed on the surface side of the p-type polycrystalline silicon substrate 120, and a p-type polycrystalline. A structure having an aluminum metal film 122 formed on the back surface of the silicon substrate 120 may be used.

10 solar cell, 11 photoelectric conversion unit, 12 intermediate, 20 first electrode, 21, 31 finger electrode, 22, 32 bus bar electrode, 23, 24, 25, 33, 34, 35, 53a, 53b upper surface, 30 second Electrode, 40, 40a, 40b screen plate, 41 mesh, 42, 42a, 42b mask material, 43, 43a, 43b opening, 44 squeegee, 45 flattening screen plate, 50, 50a, 50b paste, 51 table, 52 Press plate.

Claims

A photoelectric conversion unit;
An electrode provided on a main surface of the photoelectric conversion unit, including a binder and a filler;
With
At least a part of the electrode is a solar cell having a coefficient of variation of electrode height of 15% or less over a length of 1 mm or more.
The solar cell according to claim 1,
The electrode includes a light receiving surface electrode provided on a light receiving surface and a back electrode provided on a back surface of the main surface of the photoelectric conversion unit,
The coefficient of variation of the back electrode is 15% or less and smaller than the coefficient of variation of the light receiving surface electrode.
The solar cell according to claim 2,
The coefficient of variation of the light receiving surface electrode is 15% or less.
The solar cell according to any one of claims 1 to 3,
The electrode includes a finger electrode;
The coefficient of variation of the finger electrode is 15% or less.
The solar cell according to any one of claims 1 to 4,
The electrode includes a bus bar electrode,
The coefficient of variation of the bus bar electrode is 15% or less.
A method for manufacturing a solar cell including an electrode on a main surface of a photoelectric conversion unit,
Printing a paste for forming the electrode on the main surface, pressing at least a part of the printed paste in a height direction to flatten the upper surface of the paste, and then curing the paste. A method for manufacturing a solar cell.
It is a manufacturing method of the solar cell according to claim 6,
The electrode includes a first electrode provided on one surface of the main surface and a second electrode provided on the other surface,
In the step, after printing the paste for forming the first electrode on the one surface, the paste is pressed onto a flat surface to flatten the upper surface, and the second surface is formed on the other surface. The paste forming the electrode is printed.
It is a manufacturing method of the solar cell of Claim 7, Comprising:
In the step, the paste is used to form the second electrode on the other surface while pressing the paste printed on the one surface by the printing pressure using the screen printing method on the plane. To print.
It is a manufacturing method of the solar cell according to claim 6,
In the step, a paste for forming the electrode is printed on the main surface, and then a press tool is placed on the paste to flatten the upper surface.
It is a manufacturing method of the solar cell according to claim 9,
The press device includes a plate making without an opening and a squeegee,
In the step, the plate making is placed on the paste printed on the main surface, and the upper surface is flattened by sliding the squeegee on the surface of the plate making opposite to the surface in contact with the paste. .
A method for manufacturing a solar cell according to any one of claims 6 to 10,
The electrode includes a light receiving surface electrode provided on the light receiving surface of the main surface, and a back electrode including a metal film provided on the back surface of the main surface and a bus bar electrode provided on the metal film. ,
In the step, the paste for forming the bus bar electrode is printed and planarized on the metal film, and then the paste is printed on the light receiving surface.
A method for manufacturing a solar cell according to any one of claims 6 to 11,
In the step, before pressing the paste printed on the main surface, the solvent contained in the paste is removed within a range where the upper surface can be flattened.