Patent Application
20150090317
The present invention relates to a solar cell, a solar cell module, and a method of manufacturing a solar cell.
A solar cell comprises a photoelectric conversion unit, and an electrode formed over a primary surface of the photoelectric conversion unit (for example, refer to Patent Document 1). A solar cell module comprises a plurality of solar cells, and a wiring member that is attached over the electrode of the solar cells and that connects the solar cells.
[Patent Document 1] JP 2009-290234 A
In a solar cell, a further improvement of the photoelectric conversion characteristic is desired. In order to improve the photoelectric conversion characteristic, for example, it is important to achieve superior contact properties between the photoelectric conversion unit and the electrode. In addition, in a solar cell module, achieving superior contact properties between the solar cell and the wiring member is also important.
According to one aspect of the present invention, there is provided a solar cell comprising: a photoelectric conversion unit; a transparent conductive layer formed over a primary surface of the photoelectric conversion unit; and a silver or copper plated electrode formed directly over the transparent conductive layer.
According to another aspect of the present invention, there is provided a solar cell module comprising: a plurality of the solar cells; a wiring member that connects the solar cells; and an adhesive that adheres the plated electrode of the solar cell and the wiring member, and that enters into a through hole or a gap in the plated electrode and adheres the wiring member and the transparent conductive layer.
According to another aspect of the present invention, there is provided a method of manufacturing a solar cell, comprising: forming a transparent conductive layer over a primary surface of a photoelectric conversion unit; and, after applying a reduction process to at least a part of an electrode formation region, of a region over the transparent conductive layer in which a silver or copper plated electrode is formed, forming the plated electrode in the electrode formation region.
According to various aspects of the present invention, the photoelectric conversion efficiency of the solar cell can be improved. In addition, superior contact properties between the photoelectric conversion unit and the electrode can be achieved. According to various aspects of the present invention, superior contact properties between the solar cell and the wiring member can be achieved in the solar cell module.
A preferred embodiment of the present invention will now be described in detail with reference to the drawings. The present invention is not limited to the below-described preferred embodiment. In addition, the drawings referred to in the embodiment are schematically described, and the size and ratio of the constituent elements drawn in the drawings may differ from the actual structure. Specific size, ratio, or the like should be determined in consideration of the below description.
In the specification, a description of “a second member (for example, a transparent conductive layer) formed over a first member (for example, a primary surface of a photoelectric conversion unit) ” is not intended to describe only a case where the first and second members are formed in direct contact with each other, unless otherwise particularly stated. In other words, such a description is meant to include a case where another member exists between the first and second members.
The solar cell 11 includes a photoelectric conversion unit that receives solar light and that produces carriers, a transparent conductive layer 31 formed over a light receiving surface of the photoelectric conversion unit 20, a finger portion 32, the bus bar portion 33, and an insulating coating layer 50 formed over the transparent conductive layer 31, a transparent conductive layer 41 formed over aback surface of the photoelectric conversion unit 20, and the metal layer 42 formed over the transparent conductive layer 41. In the solar cell 11, carriers produced in the photoelectric conversion unit 20 are collected by the finger portion 32, the bus bar portion 33, and the metal layer 42. Here, a “light receiving surface” refers to a primary surface through which the solar light primarily enters from the outside of the solar cell, and a “back surface” refers to a primary surface on a side opposite from the light receiving surface. For example, of the solar light entering the solar cell 11, 50%˜100% enters the solar cell 11 from the side of the light receiving surface.
The plurality of solar cells 11 are sandwiched by the first protection member 12 and the second protection member 13, and are sealed by an encapsulant 14. For the first protection member 12 and the second protection member 13, for example, a member having a light transmissive characteristic such as a glass substrate, a resin substrate, a resin film, or the like may be used. For the encapsulant 14, for example, a resin such as ethylene vinyl acetate copolymer (EVA) or the like may be used.
The solar cell module 10 includes a wiring member 15 that connects the plurality of solar cells 11 in series. The wiring member 15 is bent in the thickness direction of the solar cell module 10 between the solar cells 11 placed adjacent to each other, and connects the solar cells 11 in series. The wiring member 15 is attached on the bus bar portion 33 and the metal layer 42 of the solar cell 11 using an adhesive 16. For the adhesive 16, for example, a thermosetting adhesive in which, for example, curing agent is mixed as necessary to an epoxy resin, an acrylic resin, a urethane resin, or the like, is preferably used. In the resin, a conductive filler such as Ag particles may be included, but from the viewpoint of the manufacturing cost and reduction of light blockage loss, a non-conductive thermosetting adhesive is preferable. As a form of the adhesive 16, for example, a film form and a paste form can be exemplified.
The photoelectric conversion unit 20 includes a substrate 21 made of a semiconductor material such as a crystalline silicon (c-Si), gallium arsenide (GaAs), indium phosphide (InP), or the like, an amorphous semiconductor layer 22 formed over the light receiving surface of the substrate 21, and an amorphous semiconductor layer 23 formed over the back surface of the substrate 21. The amorphous semiconductor layers 22 and 23 are formed, for example, over the entire region of the primary surface of the substrate 21. The substrate 21 may be, for example, an n-type monocrystalline silicon substrate. On the light receiving surface and the back surface of the substrate 21, a texture structure (not shown) is preferably formed. The texture structure is an unevenness structure for reducing reflection of light, and has, for example, an unevenness size (diameter of circumscribing circle in a two-dimensional microscopic image) of about 1 μm˜10 μm.
The amorphous semiconductor layer 22 has, for example, a layered structure in which an i-type amorphous silicon layer and a p-type amorphous silicon layer are layered in that order from the side of the substrate 21. The amorphous semiconductor layer 23 has, for example, a layered structure in which an i-type amorphous silicon layer and an n-type amorphous silicon layer are layered in that order from the side of the substrate 21. The photoelectric conversion unit 20 may have a structure in which an i-type amorphous silicon layer and an n-type amorphous silicon layer are formed in that order over the light receiving surface of the substrate 21, and an i-type amorphous silicon layer and a p-type amorphous silicon layer are formed in that order over the back surface of the substrate 21.
The transparent conductive layer 31 is formed over the light receiving surface of the photoelectric conversion unit 20. The transparent conductive layer 31 is formed, for example, from a transparent conductive oxide (hereinafter referred to as “TCO”) in which a metal oxide such as indium oxide (In2O3) and zinc oxide (ZnO) is doped with tin (Sn), antimony (Sb), or the like. The transparent conductive layer 31 may be formed covering the entire region over the amorphous semiconductor layer 22, and in the configuration shown in
A plurality (for example, 50) of the finger portions 32 are formed over the transparent conductive layer 31. The finger portion 32 is a narrow, line-shaped electrode formed over a wide area over the transparent conductive layer 31. A plurality (for example, two) of the bus bar portions 33 extend in a direction intersecting the finger portion 32. The bus bar portion 33 is an electrode which collects the carriers from the finger portions 32, and in the solar cell module 10 the wiring member 15 is attached to the bus bar portion 33. The wiring member 15 preferably has a wider width than the bus bar portion 33, and is preferably connected to the finger portion 32 on both sides in the width direction of the bus bar portion 33.
The bus bar portions 33 are placed approximately parallel to each other with a predetermined spacing therebetween, and the plurality of finger portions 32 are placed approximately perpendicular to the bus bar portions 33. A part of each of the plurality of finger portions 32 extends to an end edge 20z at a side that is further out than a virtual line X of the light receiving surface from each of the bus bar portions 33, and a remaining part of each of the plurality of finger portions 32 connects the bus bar portions 33. The bus bar portions 33 also extend to the end edge 20z of the light receiving surface.
The coating layer 50 is an insulating layer formed over the transparent conductive layer 31. The coating layer 50 is preferably formed over the entire region over the transparent conductive layer 31 other than the region where the collecting electrode is formed. A thickness of the coating layer 50 is, for example, 20 μm˜30 μm. The thickness of the coating layer 50 is preferably approximately the same as the thickness of the collecting electrode, but may be slightly thinner or thicker than the thickness of the collecting electrode. A material forming the coating layer 50 is preferably a thermosetting resin including an epoxy resin or the like, from the viewpoint of productivity, insulating characteristics, contact properties with the encapsulant 14, or the like.
The transparent conductive layer 41 is formed over the back surface of the photoelectric conversion unit 20. The other structures of the transparent conductive layer 41 are similar to those of the transparent conductive layer 31. The metal layer 42 functions as a collecting electrode that collects the carriers via the transparent conductive layer 41, and the wiring member 15 is attached thereon. The metal layer 42 is preferably formed over approximately the entire region of the transparent conductive layer 41 (a range that can be assumed to be substantially the entire region, for example, a region of greater than or equal to 95% over the transparent conductive layer 41). Alternatively, the bus bar portion may be formed over the metal layer 42, or the metal layer 42 may be changed to the finger portion.
The finger portion 32 and the bus bar portion 33 are preferably plated electrodes formed by plating. In the following description, unless otherwise particularly stated, the collecting electrode is a plated electrode. The plated electrode maybe formed, for example, by electroplating. The plated electrode is formed by a metal such as, for example, nickel (Ni), copper (Cu), and silver (Ag). As such a metal, Ag or Cu is preferable from the viewpoint of conductivity and reflection characteristic of light or the like, and Cu is more preferable in consideration of the manufacturing cost.
The plated electrode may have a layered structure with a plurality of metal layers (for example, a first layer of a Ni layer and a second layer of a Cu layer), but preferably has a single layer structure of Ag or Cu, particularly, the single layer structure of Cu. The single layer structure of Cu includes a layer formed by a Cu diffusion prevention layer and a Cu plated electrode. The Ag plated electrode and the Cu plated electrode are preferably formed directly over the transparent conductive layers 31 and 41. In other words, no other layer is provided between the Ag plated electrode and the Cu plated electrode and the transparent conductive layers 31 and 41. Cu has a particularly high reflectance for light of a wavelength in a long wavelength region (for example, greater than or equal to 600 nm), and has a reflectance with respect to light of 600 nm of, for example, about 1.5 times that of Ni.
In the present embodiment, about 100% of the light enters from the side of the light receiving surface of the photoelectric conversion unit 20. As shown in
The bus bar portion 33 shown in
The plurality of blocks 33p are provided, for example, in a straight line shape along a longitudinal direction of the wiring member 15. As described above, the wiring member 15 is attached to the block 33p using the adhesive 16. The adhesive 16 preferably adheres the wiring member 15 and the finger portion 32 on both sides in the width direction of the bus bar portion 33, and more preferably, enters the gap 34 and adheres the wiring member 15 and the coating layer 50. With such a configuration, in the gap 34, the adhesive 16 adheres the wiring member 15 and the transparent conductive layer 31 with the coating layer 50 therebetween. Because contact properties between the adhesive 16 and the coating layer 50 and contact properties between the coating layer 50 and the transparent conductive layer 31 are superior compared to the contact properties between the plated electrode and the transparent conductive layer 31, with the provision of the gap 34, the contact strength between the wiring member 15 and the solar cell 11 can be improved.
The coating layer 50 need not be present in the gap 34. In this case, the adhesive 16 enters the gap 34 and is attached to the transparent conductive layer 31, to adhere the wiring member 15 and the transparent conductive layer 31. Because the contact properties between the adhesive 16 and the transparent conductive layer 31 is superior compared to the contact properties between the plated electrode and the transparent conductive layer 31, in this case also, the contact strength between the wiring member 15 and the solar cell 11 can be improved. Stress tends to be easily applied from the wiring member 15 to the bus bar portion 33, but with the presence of the gap 34, peeling at the boundary between the bus bar portion 33 and the transparent conductive layer 31 can be sufficiently inhibited.
The metal layer 42 shown in
The adhesive 16 preferably enters the through hole 43 so that the adhesive 16 attaches to the transparent conductive layer 41. The adhesive 16 is provided between the wiring member 15 and the metal layer 42, a part thereof adheres the wiring member 15 and the metal layer 42, and another part enters the through hole 43 and adheres the wiring member 15 and the transparent conductive layer 41. As described above, as the contact properties with respect to the transparent conductive layer 41 are such that (adhesive 16>metal layer 42), with the provision of the through hole 43, the contact strength between the wiring member 15 and the solar cell 11 can be improved.
Next, a structure of the transparent conductive layers 31 and 41 will be described in detail with reference to
In the transparent conductive layer 31, preferably, in at least apart of an electrode formation region 31z in which the plated electrode is formed, a surface roughness is greater than a non-electrode formation region which is a region outside of the electrode formation region 31z. In other words, in at least a part of the electrode formation region 31z, the extent of the surface unevenness is greater than in the non-electrode formation region. The size of the surface unevenness is smaller than the texture structure size, and is preferably less than or equal to 1/10 of the texture structure size. By setting the surface roughness in the electrode formation region 31z to be greater, the contact area between the plated electrode and the transparent conductive layer 31 is increased and the contact properties therebetween can be improved. On the other hand, in the non-electrode formation region in which the solar light is received, from the viewpoint of reduction of light blockage loss or the like, the surface unevenness is preferably small and a protrusion 31p to be described later preferably does not exist. In the present embodiment, the electrode formation region 31z is a region, of the surface of the transparent conductive layer 31, not covered by the coating layer 50, and the non-electrode formation region is a region covered by the coating layer 50.
The above-described surface roughness can be evaluated by an arithmetic average roughness Ra. The arithmetic average roughness Ra can be measured, for example, using a scanning electron microscope (SEM), a laser microscope, or the like.
In the example configuration shown in
In the following, a region of the electrode formation region 31z positioned at the end edge 20z will be described as “a region R1”, a region of the electrode formation region 31 corresponding to an area in which the wiring member 15 is attached will be described as “a region R2”, and a region of the electrode formation region 31z other than R1 and R2 will be described as “a region R3”. Similarly, a region of the electrode formation region 41z positioned at the end edge 20z will be described as “a region S1”, a region of the electrode formation region 41z corresponding to an area in which the wiring member 15 is attached will be described as “a region S2”, and a region of the electrode formation region 41z other than S1 and S2 will be described as “a region S3”.
The transparent conductive layer 31 has, for example, a greater surface roughness in the region R1 than in the regions R2 and R3. In the present embodiment, because the plated electrode is formed extending to the end edge 20z, the region R1 is a region positioned at an end in the longitudinal direction of the plated electrode. In other words, for the electrode formation region 31z, at the region positioned at the end in the longitudinal direction of the plated electrode, the surface roughness is greater than a region positioned at a center section in the longitudinal direction of the plated electrode. Because boundary peeling between the plated electrode and the transparent conductive layer 31 tends to occur more at the end than the center section in the longitudinal direction of the electrode, with such a structure, the peeling can be sufficiently inhibited.
As shown in
In the present embodiment, in the region R1, a number of the protrusions 31p is greater than that in the region R3, and the size of the protrusions 31p is also greater (refer to
In an example configuration shown in
The size of the protrusions 31p is preferably greater than or equal to 10 nm and less than or equal to 200 nm, and more preferably, greater than or equal to 10 nm and less than or equal to 100 nm. The size of the protrusions 31p is defined as a diameter of a circumscribing circle of a protrusion 31p in a two-dimensional microscopic image such as the SEM.
In an example configuration of
On the back surface side of the solar cell 11, the metal layer 42 is formed over an approximately entire region of the surface of the transparent conductive layer 41. In the transparent conductive layer 41, protrusions similar to the protrusions 31p may be formed over the entire region of the electrode formation region 41z (a region where the metal layer 42 is formed), that is, approximately the enter region of the surface of the transparent conductive layer 41. Preferably, similar to the electrode formation region 31z, the surface roughness of a part of the electrode formation region 41z is set greater than that in the other parts.
In a configuration shown in
In a configuration shown in
The transparent conductive layer 31 has, for example, a higher sheet resistance corresponding to the electrode formation region 31z than a sheet resistance corresponding to the non-electrode formation region. In particular, the sheet resistance tends to be higher as the surface roughness becomes greater, and the sheet resistance of the region R1 is, for example, about 1.05 times to 5 times the sheet resistance of the non-electrode formation region. The sheet resistance can be measured by a known method (for example, a four-point probe method). In addition, in the transparent conductive layer 31, for example, a portion immediately below the electrode formation region 31z has a non-columnar crystalline structure, and the other portions have a columnar crystalline structure. The columnar crystalline layer refers to a layer in which crystal grain boundaries oriented in the same direction can be confirmed on approximately the entire region of an observation cross section by a cross-sectional observation using the SEM. In the SEM image, dark/light portions of the contrast are repeated in one direction, which appears to be a plurality of columns arranged in the one direction. Alternatively, the image may appear to be a banded shape. The boundary of the dark/light portions of the contract shows the crystal grain boundary. The non-columnar crystalline layer is a layer in which a percentage of crystal grain boundaries oriented in different directions is larger than a percentage of crystal grain boundaries oriented in the same direction, in the cross-sectional observation using the SEM. In the SEM image, a portion in which the dark/light portions of the contrast are repeated in one direction is less than 50%, and in some cases, the portion in which the dark/light portions of the contrast are regularly repeated cannot be observed.
The structure of the photoelectric conversion unit may be suitably changed to a structure other than that described above. For example, as shown in
Next, a manufacturing process of the solar cell 11 having the above-described structure will be described in detail with reference to
In the manufacturing process of the solar cell 11, first, the photoelectric conversion unit 20 is manufactured by a known method (the manufacturing process of the photoelectric conversion unit 20 will not be described in detail). In the example configuration of
The transparent conductive layers 31k and 41k can be formed, for example, through chemical vapor deposition (CVD). The film formation by CVD is preferably executed under a temperature condition of about 200° C.˜300° C., and the TCO is crystallized by the heat and the columnar crystal layer is formed. The transparent conductive layers 31k and 41k may alternatively be formed at a low temperature of less than 200° C., by sputtering. In this case, a separate annealing step is provided to crystallize the TCO. An electrical conductivity of the TCO is improved by the TCO being crystallized.
Then, coating layers 50 and 51 are respectively formed as mask patterns covering the transparent conductive layers 31k and 41k (
The coating layers 50 and 51 can be formed through a known method. For example, after a thin film layer made of a photo-curing resin is formed by spin coating over the transparent conductive layers 31k and 41k, the thin film layer may be patterned using a photolithography process. Alternatively, the coating layers 50 and 51 may be formed with the above-described pattern or the like using a printing method such as screen printing.
Then, the reduction process is applied on the electrode formation regions 31zk and 41zk (
The method of the reduction process is not particularly limited so long as the TCO can be reduced and the protrusions can be formed, and for example, reduction by a hydrogen plasma process or electrolysis reduction maybe employed. The former is a gaseous phase reduction and the latter is a liquid phase reduction. The reduction process steps will now be described exemplifying the electrolysis reduction.
In the electrolysis reduction, for example, ammonium sulfate solution is used as an electrolytic solution, the photoelectric conversion unit 20 is set as a cathode, and a platinum plate is set as an anode. The photoelectric conversion unit 20 and the platinum plate are immersed in the electrolytic solution, and a current is applied between the photoelectric conversion unit 20 and the platinum plate. In this process, for example, a reduction terminal 100 connected to a negative electrode of a power supply device is attached to the photoelectric conversion unit 20, at a part over the exposed electrode formation region 31zk (refer to
In the example configuration shown in
The reduction terminal 100 is preferably attached, in the region R1, to regions corresponding to the finger portion 32 and the bus bar portion 33. In other words, the reduction terminal 100 is preferably attached to regions corresponding to ends in the longitudinal direction of the finger portion 32 and the bus bar portion 33. Because the number of bus bar portions 33 is small, the reduction terminals 100 can be attached to all regions corresponding to the ends in the longitudinal direction (for example, 4 locations). On the other hand, as the number of the finger portions 32 is large, for example, the reduction terminals 100 may be attached to only a part of the finger portions 32 with a predetermined spacing therebetween.
After the reduction process is completed, the coating layer 51 is removed, and the entire region over the electrode formation region 41z is exposed (
Then, the plated electrodes are formed directly over the electrode formation regions 31z and 41z (
a) is a plan view showing a mask pattern when the protrusions 31p are to be formed only in the region R1 (refer to
The reduction process is executed using a coating layer 52 formed covering regions other than the region R1 over the transparent conductive layer 31 as a mask (
The plurality of electroplating terminals 111 are placed in a line form with a spacing therebetween, and a resin 112 is provided around each terminal. When this structure is attached over the transparent conductive layer 41, the plurality of electroplating terminals 111 are aligned in a line form. When the photoelectric conversion unit 20 is immersed in a plating solution 113 in this state, the plating solution 113 enters the region between the resins 112. With this process, the plated electrode can be formed over approximately the entire region, of the surface of the transparent conductive layer 41, for example, except for the region around the electroplating terminals 111 in which the plating solution 113 does not act. At the periphery of the electroplating terminals 111, through holes 43 are formed (refer to
The metal layer 42 having the through hole 43 or the bus bar portion 33 including the plurality of blocks 33p can also be formed using a mask pattern protecting the portions corresponding to the through hole 43 or the gap 34. More specifically, by applying a plating process using, as a mask, the coating layer 50 which exposes only the region, over the transparent conductive layer 31, in which the finger portion 32 and the plurality of blocks 33p are formed, it is possible to form the bus bar portion 33 including the plurality of blocks 33p.
As described, in the solar cell 11, by forming the Ag or Cu plated electrode having a superior reflection characteristic directly over the transparent conductive layers 31 and 41, an amount of reflection and attenuation of light entering the photoelectric conversion unit 20 can be inhibited and the light collecting efficiency can be improved. For example, by using a plated electrode having a single layer structure of Cu, in comparison to a case where a plated electrode having a layered structure of a Ni seed layer and a Cu layer is used, the reflection characteristic, in particular in the long wavelength region, can be improved, and the light collection efficiency can be improved.
The solar cell 11 has a greater surface roughness in at least a part of the electrode formation regions 31z and 41z, and the contact properties between the transparent conductive layers 31 and 41 and the collecting electrode are superior. Because of this, for example, even when the Cu plated electrode is formed directly over the transparent conductive layer 31 without the use of a Ni seed layer, a sufficient contact strength can be maintained.
In addition, the reduction process is applied in a limited manner in the regions where the contact strength between the collecting electrode and the transparent conductive layers 31 and 41 is particularly desired and the surface roughness is locally set greater. Because of this, for example, the contact strength can be efficiently improved without reducing the FF and the reflectance.
Moreover, because the through hole 43 is formed in the area of the metal layer 42 in which the wiring member 15 is attached, the adhesive 16 may enter the through hole 43, and adheres the wiring member 15 and the transparent conductive layer 41. With this configuration, the contact strength between the wiring member 15 and the solar cell 11 can be improved, and a solar cell module 10 with a high reliability can be obtained.
10 Solar Cell Module; 11 Solar Cell; 12 First Protection Member; 13 Second Protection Member; 14 Encapsulant; 15 Wiring Member; 16 Adhesive; 20 Photoelectric Conversion Unit; 20z End Edge; 21 Substrate; 22, 23 Amorphous Semiconductor Layer; 31, 41 Transparent Conductive Layer; 31z, 41z Electrode Formation Region; 32 Finger Portion; 33 Bus Bar Portion; 34 Gap; 42 Metal Layer; 43 Through Hole; 50 Coating Layer.
The present application is a continuation under 35 U.S.C. §120 of PCT/JP2012/066676, filed Jun. 29, 2012, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/066676 | Jun 2012 | US |
| Child | 14564334 | US |
