solar cells
The solar cell design with strip-shaped semiconductor layers and electrode patterns with increased aperture ratios at the ends addresses the cost issue of silver paste by minimizing material usage and maintaining efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KANEKA CORP
- Filing Date
- 2024-11-25
- Publication Date
- 2026-06-04
AI Technical Summary
Silver paste used in forming electrodes for solar cells is expensive, and widening the metal electrode increases the cost of the solar cell.
A solar cell design with strip-shaped semiconductor layers and electrode patterns featuring openings that increase the aperture ratio towards the ends, reducing the amount of conductive material needed while maintaining efficient charge collection.
The design allows for a cost-effective solar cell with minimal material usage and reduced electrical resistance, maintaining high photoelectric conversion efficiency.
Smart Images
Figure 2026091613000001_ABST
Abstract
Description
Technical Field
[0004] ,
[0001] The present invention relates to a solar cell.
Background Art
[0002] Solar cells in which a plurality of semiconductor layers having different conductivity types are laminated on a semiconductor substrate and electrodes for current collection are laminated on these semiconductor layers are widely used. A technique for forming the electrodes of a solar cell by printing and firing a conductive paste is known (see, for example, Patent Document 1). As the conductive paste for forming the electrodes of a solar cell, generally, a silver paste that can form an electrode with low electrical resistance is used. In particular, in the case of a back-contact type solar cell, since the metal electrode exists only on the back side opposite to the light incident surface, there is no need to consider the light shielding loss due to the metal electrode. Therefore, by widening the width of the electrode, the charge transfer distance in the semiconductor substrate can be shortened, and the contact resistance with the printing underlayer can be reduced. Thus, a low-resistance electrode can be easily formed. In addition, a technique for forming a metal electrode by screen printing of a silver paste and etching a transparent electrode layer under the metal electrode using the metal electrode as a mask has also been disclosed (see, for example, Patent Document 2). This is a technique that requires patterning of the transparent electrode layer and makes use of the characteristics of a back-contact type solar cell in which a metal electrode can be formed wider.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0004] Silver paste is relatively expensive, and widening the metal electrode increases the cost of the solar cell, which is a disadvantage. Therefore, the present invention aims to provide a relatively inexpensive solar cell. [Means for solving the problem]
[0005] A solar cell according to one aspect of the present invention comprises a semiconductor substrate, a first semiconductor layer partially laminated on the back side (opposite side from the light-receiving surface) of the semiconductor substrate and having a plurality of strip-shaped first branches, a second semiconductor layer laminated complementary to the first semiconductor layer on the back side of the semiconductor substrate and having a different conductivity type from the first semiconductor layer and having a plurality of strip-shaped second branches extending between the plurality of first branches, a first electrode pattern laminated on the back side of the first semiconductor layer and having a plurality of first finger electrodes extending along each of the first branches, and a second electrode pattern laminated on the back side of the second semiconductor layer and having a plurality of second finger electrodes extending along each of the second branches, wherein the first finger electrodes have a plurality of openings, and the aperture ratio per unit length of the first finger electrodes is larger towards the ends.
[0006] In the solar cell described above, the openings may be formed at equal intervals in the extending direction of the first finger electrode, and may have a larger area towards the end.
[0007] In the solar cell described above, the opening is an elongated hole extending in the direction of extension of the first finger electrode, and may have a wider width towards the end.
[0008] In the solar cell described above, the aperture ratio per unit length at the base end of the longest first finger electrode may be 5% or less.
[0009] In the solar cell described above, the second finger electrode has multiple openings, and the aperture ratio per unit length of the second finger electrode may be larger towards the end.
[0010] In the solar cell described above, the first electrode pattern and the second electrode pattern may be formed from a conductive paste.
[0011] The solar cell described above may further include transparent electrode layers between the first semiconductor layer and the first electrode pattern, and between the second semiconductor layer and the second electrode pattern.
[0012] In the solar cell described above, the transparent electrode layer may have a planar shape that follows the first electrode pattern and the second electrode pattern. [Effects of the Invention]
[0013] According to the present invention, relatively inexpensive solar cells can be provided. [Brief explanation of the drawing]
[0014] [Figure 1] This is a schematic rear view of a solar cell relating to one embodiment of the present invention. [Figure 2] Figure 1 is an enlarged view of a section of the solar cell along line AA. [Modes for carrying out the invention]
[0015] Embodiments of the present invention will be described below with reference to the drawings. Note that the dimensions of various components in the drawings have been adjusted for ease of viewing. Figure 1 is a schematic rear view of a solar cell 1 according to one embodiment of the present invention. Figure 2 is an enlarged section of the solar cell 1 of Figure 1 along line AA.
[0016] The solar cell 1 comprises a semiconductor substrate 10, a first semiconductor layer 20 partially laminated on the back side of the semiconductor substrate 10, a second semiconductor layer 30 complementary to the first semiconductor layer 20 laminated on the back side of the semiconductor substrate 10, a first electrode pattern 40 laminated on the back side of the first semiconductor layer 20, a second electrode pattern 50 laminated on the back side of the second semiconductor layer 30, and a transparent electrode layer 60 laminated between the first semiconductor layer 20 and the first electrode pattern 40 and between the second semiconductor layer 30 and the second electrode pattern 50. In Figure 1, the boundary between the first semiconductor layer 20 and the second semiconductor layer 30 is shown with a dashed line to make it easier to distinguish from the outer edges of the first electrode pattern 40 and the second electrode pattern 50.
[0017] The semiconductor substrate 10 can be formed from a crystalline silicon material such as single-crystal silicon or polycrystalline silicon. It may also be formed from other semiconductor materials such as gallium arsenide (GaAs). The semiconductor substrate 10 is, for example, an n-type semiconductor substrate in which an n-type dopant is doped into a crystalline silicon material. An example of an n-type dopant is phosphorus (P). The semiconductor substrate 10 functions as a photoelectric conversion substrate that absorbs incident light from the light-receiving surface side and generates photocarriers (electrons and holes). By using crystalline silicon as the material for the semiconductor substrate 10, the dark current is relatively small, and relatively high output (stable output regardless of illuminance) can be obtained even when the intensity of incident light is low.
[0018] The first semiconductor layer 20 attracts and extracts one of the photocarriers generated on the semiconductor substrate 10. The first semiconductor layer 20 can be formed from an amorphous silicon material containing a dopant that imparts a desired conductivity type. Examples of p-type dopants include boron (B), and examples of n-type dopants include phosphorus (P) as described above.
[0019] The first semiconductor layer 20 has a plurality of first branch portions 21 formed in a strip shape extending with a substantially constant width respectively, and a first collective portion 22 to which the first branch portions 21 are connected. The widths of the plurality of first branch portions 21 are preferably equal to each other in order to extract charges evenly. The first branch portions 21 extend from other portions of the first semiconductor layer 20. That is, the proximal ends of the first branch portions 21 are connected to the first branch portions 21 or the first collective portion 22. Also, the distal ends of the first branch portions 21 are terminated by the outer edge of the second semiconductor layer 30 or the solar cell 1. Further, the first semiconductor layer 20 may further have a trunk portion (not shown) having a width larger than that of the first branch portions 21 connecting the plurality of first branch portions 21 and the first collective portion 22. The trunk portion is typically formed along one edge of the semiconductor substrate 10.
[0020] The second semiconductor layer 30 has a conductivity type different from that of the first semiconductor layer 20, and attracts and extracts the other of the optical carriers generated in the semiconductor substrate 10. The second semiconductor layer 30 can be formed of an amorphous silicon material containing a dopant that imparts a conductivity type different from that of the first semiconductor layer 20, for example. The second semiconductor layer 30 is laminated on the back surface of the semiconductor substrate 10 in a shape substantially complementary to the first semiconductor layer 20. Similar to the first semiconductor layer 20, the second semiconductor layer 30 has a plurality of second branch portions 31 formed in a strip shape extending with a substantially constant width respectively, and a second collective portion 32 to which the second branch portions 31 are connected, and may further have a trunk portion (not shown) connecting the plurality of second branch portions 31 and the second collective portion 32.
[0021] The first electrode pattern 40 is provided to extract charge from the first semiconductor layer 20. The first electrode pattern 40 has a plurality of first finger electrodes 41 extending along the first branch portions 21 on each first branch portion 21, and a first pad electrode 42 formed on the first assembly portion 22 to which the base ends of the first finger electrodes 41 are connected. If the first semiconductor layer 20 has a trunk, the first electrode pattern 40 may further have an assembly electrode or busbar electrode formed on the trunk and connecting the first finger electrodes 41 and the first pad electrode 42. The first electrode pattern 40 has a planar shape that generally follows the first semiconductor layer 20, but is formed to leave a margin around the outer edge of the first semiconductor layer 20 to prevent short circuits. The first electrode pattern 40 may be formed from a material containing a cured conductive paste such as silver paste, i.e., a plurality of conductive particles and their binder. When the first electrode pattern 40 is formed using a conductive paste, the cost reduction effect due to the reduction in the area of the first electrode pattern 40 according to the present invention is significant.
[0022] The first finger electrode 41 preferably has a substantially constant width, but the base end may be widened or the end may be tapered for smooth connection. The first finger electrode 41 has a plurality of first openings 43. The aperture ratio per unit length of the first finger electrode 41 is larger towards the end of the first finger electrode 41. In other words, the first finger electrode 41 reduces the amount of forming material used by increasing the aperture ratio at the end where the current value is small, and suppresses losses due to electrical resistance by decreasing the aperture ratio at the base end where the current value is large. The "aperture ratio per unit length" of the first finger electrode 41 is calculated as the aperture ratio per length that is sufficiently large relative to the width of the first finger electrode 41 (for example, 30 times the width), excluding the bent and branched portions. Furthermore, the aperture ratio per unit length of the first finger electrode 41 may be locally smaller at the bent portion and branched portion of the first finger electrode 41 (the portion to which other first finger electrodes 41 are connected), etc. For this reason, the first finger electrode 41 may include a portion with a smaller aperture ratio than its proximal end, within a range of 10% or less of its length.
[0023] The first opening 43 may be formed, for example, in a scattered pattern arranged randomly, but it is preferably formed in a regular pattern. Specifically, the first opening 43 is preferably formed to form a row aligned in the extending direction of the first finger electrode 41 in order to form the shortest path through which current flows in the extending direction of the first finger electrode 41. In order to adjust the aperture ratio, the interval of the first openings 43 may be changed, but it is preferable to increase the area of the first openings 43 arranged at equal intervals toward the end side. Thereby, the design becomes easy, and since the current can flow in the extending direction of the first finger electrode 41, an increase in resistance loss can be suppressed. In particular, in order to make the electrical resistance with respect to the aperture ratio of the first finger electrode 41 as small as possible, the plurality of first openings 43 are preferably formed in a long hole shape extending in the extending direction of the first finger electrode 41 and have a larger width toward the end side. By arranging the long hole-shaped first openings 43 with a minimum interval and making the cross-sectional area of the first finger electrode 41 the minimum size corresponding to the flowing current, the volume of the first finger electrode 41, and thus the amount of material used to form the first finger electrode 41 can be minimized, so that the solar cell 1 can be made inexpensive.
[0024] The aperture ratio per unit length at the end portion of the first finger electrode 41 is preferably 20% to 60%, and more preferably 25% to 35%. The maximum aperture width at the end portion of the first finger electrode 41 is preferably 30 μm to 200 μm, and more preferably 50 μm to 160 μm. The aperture ratio per unit length at the base end portion of the longest first finger electrode 41 is preferably 5% or less, and more preferably 3% or less. The lower limit of the aperture ratio is 0%. Furthermore, when forming the first finger electrode by screen printing, the lower limit of the aperture width is preferably 30 μm or more due to the specifications of the printing plate. By optimizing the aperture ratio at the base end portion of the longest first finger electrode 41 where the current value is maximum, the width of the first finger electrode 41 and thus the width of the first branch portion 21 can be reduced, thereby reducing the distance of charge movement within the semiconductor substrate 10 and increasing the photoelectric conversion efficiency of the solar cell 1.
[0025] The second electrode pattern 50, like the first electrode pattern, is provided to extract charge from the second semiconductor layer 30. The second electrode pattern 50 has a plurality of second finger electrodes 51 extending along the second branch portions 31 on each second branch portion 31, and a second pad electrode 52 formed on the first assembly portion 22 and connected to the base ends of the second finger electrodes 51. The second finger electrodes 51 may have a plurality of second apertures 53, similar to the first finger electrodes 41. When the second semiconductor layer 30 has a different conductivity type than the semiconductor substrate 10, the second semiconductor layer 30 becomes the layer that generates the voltage of the solar cell 1. Since the second finger electrodes 51 also serve to protect the second semiconductor layer 30, depending on the module structure, the second finger electrodes 51 may be constructed without a plurality of second apertures 53 in order to ensure long-term reliability. The detailed configuration of the second electrode pattern 50, including the second aperture 53 of the second finger electrode 51, is the same as that described for the first finger electrode 41. This allows for the even and efficient collection of both positive and negative charges.
[0026] The transparent electrode layer 60 improves the mechanical and electrical adhesion between the first semiconductor layer 20 and the first electrode pattern 40, and between the second semiconductor layer 30 and the second electrode pattern 50. The transparent electrode layer 60 can be formed from, for example, ITO (Indium Tin Oxide), zinc oxide (ZnO), etc. To prevent short circuits between the first semiconductor layer 20 and the second semiconductor layer 30, the transparent electrode layer 60 is not laminated in at least the boundary region between the first semiconductor layer 20 and the second semiconductor layer 30. The transparent electrode layer 60 may be patterned by etching using an etching mask before laminating the first electrode pattern 40 and the second electrode pattern 50, or it may be patterned by etching the first electrode pattern 40 and the second electrode pattern 50 using the etching mask. In other words, the transparent electrode layer 60 has a planar shape that follows the first electrode pattern 40 and the second electrode pattern 50, and may be selectively formed only directly beneath the first electrode pattern 40 and the second electrode pattern 50. In this case, the transparent electrode layer 60 has openings that expose the first semiconductor layer 20 or the second semiconductor layer 30, at least directly below the first opening 43 at the tip of the first finger electrode 41 and the second opening 53 at the tip of the second finger electrode 51. The planar shape of the transparent electrode layer 60 may be slightly smaller than the first electrode pattern 40 and the second electrode pattern 50 due to side etching, or slightly larger than the first electrode pattern 40 and the second electrode pattern 50 due to the seepage of binder components from the conductive paste that forms the first electrode pattern 40 and the second electrode pattern 50.
[0027] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. For example, the solar cell according to the present invention may include further components such as a passivation layer formed from, for example, an amorphous silicon material that does not contain dopants, between the semiconductor substrate and the first semiconductor layer and the second semiconductor layer, and an anti-reflective film formed on the light-receiving surface side of the semiconductor substrate. Furthermore, in the solar cell according to the present invention, the transparent electrode layer may be omitted if adhesion between the first semiconductor layer and the first electrode pattern and between the second semiconductor layer and the second electrode pattern can be ensured. [Examples]
[0028] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples.
[0029] As an example, in a solar cell in which a first finger electrode and a second finger electrode with a width of 550 μm are provided on a first branch and a second branch with a width of 700 μm using silver paste, rectangular openings with a length of 500 μm were formed in two rows on the first finger electrode and the second finger electrode, with a spacing of 50 μm in both the extending direction and the width direction. The width of the openings at the ends of the first finger electrode and the second finger electrode was set to 150 μm. As a result, the amount of silver paste used was reduced by 8%.
[0030] The photoelectric conversion efficiency was measured for both the first and second finger electrodes with and without openings. The results showed that the photoelectric conversion efficiency without openings was 23.31%, while the efficiency with openings was 23.44%. Thus, despite a significant reduction in the amount of silver paste used by providing openings in the first and second finger electrodes, there was no significant difference in photoelectric conversion efficiency. [Explanation of symbols]
[0031] 1 solar cell 10 Semiconductor substrates 20 First Semiconductor Layer 21. First branch 22 1st gathering area 30 Second Semiconductor Layer 31. Second branch 32 2nd assembly area 40 First electrode pattern 41 First finger electrode 42 First pad electrode 43. First opening 50 Second electrode pattern 51 Second finger electrode 52 Second pad electrode 53. Second opening 60 Transparent electrode layer
Claims
1. Semiconductor substrate and A first semiconductor layer is partially laminated on the back side of the semiconductor substrate and has a plurality of strip-shaped first branches, A second semiconductor layer is laminated on the back side of the semiconductor substrate in a complementary manner to the first semiconductor layer, has a different conductivity type from the first semiconductor layer, and has a plurality of strip-shaped second branches extending between the plurality of first branches, A first electrode pattern is laminated on the back side of the first semiconductor layer and has a plurality of first finger electrodes extending along each of the first branches, A second electrode pattern is laminated on the back side of the second semiconductor layer and has a plurality of second finger electrodes extending along each of the second branches, Equipped with, The first finger electrode has a plurality of openings, A solar cell in which the aperture ratio per unit length of the first finger electrode is larger towards the end.
2. The solar cell according to claim 1, wherein the openings are formed at equal intervals in the extending direction of the first finger electrode and have a larger area towards the end.
3. The solar cell according to claim 1 or 2, wherein the opening is elongated and extends in the direction of extension of the first finger electrode, and has a wider width towards the end.
4. The solar cell according to claim 1 or 2, wherein the aperture ratio per unit length at the base end of the longest first finger electrode is 5% or less.
5. The solar cell according to claim 1 or 2, wherein the second finger electrode has a plurality of openings, and the aperture ratio per unit length of the second finger electrode is larger towards the end.
6. The solar cell according to claim 1 or 2, wherein the first electrode pattern and the second electrode pattern are formed from a conductive paste.
7. The solar cell according to claim 6, further comprising a transparent electrode layer between the first semiconductor layer and the first electrode pattern and between the second semiconductor layer and the second electrode pattern.
8. The solar cell according to claim 7, wherein the transparent electrode layer has a planar shape that conforms to the first electrode pattern and the second electrode pattern.