SOLAR CELL WITH SPECIFIC FRONT SURFACE ELECTRODE DESIGN

Abstract

A solar cell (104) is disclosed. The solar cell includes a substrate (151) including a front surface (156) and front surface electrodes (153) extending along the front surface (156). Therein, the front surface electrodes comprise a plurality of bus bar electrodes (152) coupled to a plurality of first finger electrodes (153.sub.1) arranged in a parallel finger region (105) and second finger electrodes (153.sub.2) arranged in a palm finger region (106).The first finger electrodes (153.sub.1) are substantially parallel to each other and perpendicular to the bus bar electrodes (152). The second finger electrodes (153.sub.2) originate from end regions of the bus bar electrodes (152) and radially extend at least in portions thereof in directions non-perpendicular to the bus bar electrodes (152). Therein, a palm-like group of neighboring second finger electrodes (153.sub.2) originates from a same associated bus bar electrode (152) and neighboring second finger electrodes (153.sub.2) radially extend at different angles with respect to the bus bar electrodes (152). With such electrode configuration, shading losses as well as electrical resistance losses may be reduced.

Claims

1. A solar cell comprising: a substrate including a front surface; and front surface electrodes extending along the front surface, wherein the front surface electrodes comprise a plurality of elongate bus bar electrodes coupled to a plurality of first elongate finger electrodes arranged in a parallel finger region and second elongate finger electrodes arranged in a palm finger region, the first finger electrodes being substantially parallel to each other and perpendicular to the bus bar electrodes, the second finger electrodes originating from end regions of the bus bar electrodes and radially extending at least in portions thereof in directions non-perpendicular to the bus bar electrodes, wherein a palm-like group of neighboring second finger electrodes originates from a same associated bus bar electrode and neighboring second finger electrodes radially extend at different angles with respect to the bus bar electrodes.

2. The solar cell of claim 1 wherein a width (w) of a single palm-like group of neighboring second finger electrodes of the palm-finger region is between 10% and 100% of a distance (d) between two neighboring bus bar electrodes, the width (w) being measured in a direction perpendicular to a longitudinal direction of the bus bar electrodes.

3. The solar cell of claim 1 wherein a width (w) of a single palm-like group of neighboring second finger electrodes of the palm-finger region is between 25% and 75% of a distance (d) between two neighboring bus bar electrodes, the width (w) being measured in a direction perpendicular to a longitudinal direction of the bus bar electrodes.

4. The solar cell of one of claim 1 wherein the second finger electrodes are configured such that spacings (s) between neighboring second finger electrodes are from 0 to 3 mm.

5. The solar cell of one of claim 1 comprising one side having half or a lower fraction of a length of an adjacent side.

6. The solar cell of one of claim 1 comprising conductive ribbons soldered on the bus bar electrodes.

7. The solar cell of claim 6 wherein the conductive ribbons do not extend into the palm finger region.

8. The solar cell of one of claim 1 wherein the bus bar electrodes have lengths (l.sub.b) of less than 90% of a length of the substrate in a direction parallel to the bus bar electrodes.

9. The solar cell of one of claim 1 wherein the bus bar electrodes have lengths (l.sub.b) of less than 70% of a length of the substrate in a direction parallel to the bus bar electrodes.

10. The solar cell of one of claim 1 wherein second finger electrodes divide into several branches upon extending radially away from an associated bus bar electrode.

11. The solar cell of one of claim 1 wherein end regions opposite to an associated bus bar electrode of second electrode fingers of a palm-like group of neighboring second finger electrodes are interconnected to end regions of second electrode fingers of a neighboring palm-like group of neighboring second finger electrodes via third finger electrodes extending substantially parallel to each other and perpendicular to the bus bar electrodes.

12. The solar cell of one of claim 1 wherein the second finger electrodes have a width smaller than a width of the bus bar electrodes.

13. The solar cell of one of claim 1 wherein at least one of the second finger electrodes extends up to a position less than 3 mm away from an edge of the substrate.

14. The solar cell of one of claim 1 wherein a length of the palm-finger region is between 25% and 75% of distance (d) between two neighboring bus bar electrodes, the lengths being measured in a direction parallel to a longitudinal direction of the bus bar electrodes.

15. The solar cell of one of claim 1 wherein the substrate has a surface area of at least 25 cm.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the drawings, the same reference characters generally refer to same or similar parts throughout the different views. Also, the drawings are only schematically and not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments are described with reference to the following drawings, in which:

[0025] FIG. 1 shows a front surface of a substrate to be cut in two pieces with a conventional electrode design.

[0026] FIGS. 2a, b show a front surface of a substrate with a specific electrode design for forming solar cells according to an embodiment of the invention before and after cutting in two pieces and rearranging, respectively.

[0027] FIGS. 3 shows a front surface of a substrate with another specific electrode design for forming solar cells according to an alternative embodiment of the invention after cutting in two pieces and rearranging, respectively.

[0028] FIG. 4 shows a side view of an assembly with a metal ribbon connecting conventional neighboring conventional solar cells.

[0029] FIG. 5 shows a side view of an assembly with a metal ribbon connecting neighboring solar cells according to an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] Embodiments generally relate to devices, for example, devices for converting energy of light into electrical energy. More particularly, the devices may be solar cell elements or solar cell modules including a plurality of solar cell elements.

[0031] FIG. 1 shows a pair of half-cut solar cells 4.sub.1 and 4.sub.2. They may be obtained by cutting a normal full-size substrate 50 for a solar cell with 15.6×15.6 cm.sup.2 dimensions into two equal portions along a direction substantially perpendicular to bus bars 52, as indicated by a dashed line A-A, thereby forming elongate rectangular solar cell substrates 51.sub.1 and 51.sub.2. Other sizes of the substrate 50, for example, about 12.5×12.5 cm.sup.2 or about 10×10 cm.sup.2, may also be useful. A conventional electrode design with parallel fingers 53 running perpendicular to bus bars 52 is provided on a front surface 56 of the substrate 50.

[0032] FIG. 2a shows an embodiment of a pair of half-cut solar cells 104.sub.1 and 104.sub.2 on substrates 151.sub.1 and 151.sub.2with an electrode configuration with linear first finger electrodes 153.sub.1 in a parallel finger electrode region 105 and with a palm-finger electrode configuration in a palm finger region 106. The two solar cells 104.sub.1 and 104.sub.2 may be provided by generating two electrode configurations on a common square substrate 150 and then cutting the substrate 150 into half substrates 151.sub.1 and 151.sub.2 along the line A-A.

[0033] It is also advantageous to implement the palm-finger electrode design on normal full size cells with square substrates, but the benefit is lower than for cut cells with elongate rectangular substrates due to that the palm-finger region covers a proportionally lower part of the cell area. Solar cells may be cut by laser. Other cutting methods may also be possible. By cutting the solar cells into half, resistive power losses which show a parabolic dependence on the length of the cells, may effectively be reduced. Power output may be improved by about 2%, i.e. cutting cells in elongate rectangular halves may give approximately 2% relative increase in module power over full size square cells with the same cell technology. A design where the solar cells are cut along 3 parallel equidistant lines into 4 parts each with a palm-finger electrode design will have further reduced series resistance.

[0034] In one embodiment, as shown in FIG. 2a, a front surface 156 of a substrate 150 for each of half-cut solar cells 104.sub.1 or 104.sub.2 includes a plurality of front surface electrodes. FIG. 2b shows how the half cut solar cells will be oriented in a solar cell assembly after cutting.

[0035] The front surface electrodes may include many thin parallel finger electrodes 153 connected to a plurality of wider bus bar electrodes 152 extending perpendicular to the finger electrodes 153 and used for collecting the electric current from the finger electrodes 153.

[0036] For example, the front surface electrodes may include four front surface bus bar electrodes 152 and a large number of front surface finger electrodes 153 as shown in FIG. 2a and b or five front surface bus bar electrodes 152 as shown in FIG. 3. Having other numbers of front surface bus bar electrodes, for example 2 or 3 or 6 or more, may also be useful.

[0037] The front surface finger electrodes 153 may be electrodes configured to collect photo-induced carriers. In one embodiment, a plurality of the front surface finger electrodes 153 are arranged substantially parallel to each other and parallel to one long edge of the elongate substrate 151.sub.1 and almost throughout the front surface of the substrate in the parallel finger regions 105, i.e. in the regions without palm-finger electrodes. The width of a front surface finger electrode 153 may be between about 30 μm and about 100 μm, for example about 60 μm. The front surface finger electrodes 153 may or may not all have the same width. The front surface finger electrodes 153 may have a constant width or alternatively the width may vary along the length of a front surface finger electrode and a front surface finger electrode may for example be tapered towards its ends from about 60 μm or above to about 30 μm or below. The front surface finger electrodes in the region without palm-finger electrodes may be equally spaced apart. The spacing between two adjacent front surface finger electrodes may be between about 1 mm and about 3 mm, for example about 2 mm. Front surface finger electrodes with uneven spacing may also be useful.

[0038] In one embodiment, the portion from one end to a fraction of length of a bus bar electrode 152 in FIG. 1 is replaced by the second finger electrode 153.sub.2 in the palm finger region 106. The length of the bus bar electrode to be replaced by the second finger electrode 153.sub.2, i.e. the length l.sub.p of the palm finger region (as shown in FIG. 2b), may be e.g. between about 25% to about 75% of the distance d or spacing between two adjacent bus bar electrodes 152. A width w of a single palm-like group of neighboring second finger electrodes 153.sub.2 of the palm finger region may be e.g. between 10% and 100%, preferably between about 25% to about 75%, of the distance d between two adjacent bus bar electrodes 152.

[0039] In one embodiment, the second finger electrodes 153.sub.2 originate from the ends 160 of the bus bar electrodes 152 and extend to merge with third finger electrodes 153.sub.3. In between, some or each of the second finger electrodes 153.sub.2 may split into branches 154.sub.1, 154.sub.2. The second finger electrodes 153.sub.2 may be configured in such a way that the spacings between the adjacent second finger electrodes 153.sub.2 fall within the range from about 0 to about 3 mm. The finger electrode spacings should be optimized such that the power losses of the emitter and shading losses are kept minimal. The configuration also allows the use of less silver paste per solar cell substrate. One exemplary embodiment of such configurations is shown in FIG. 2a with the second finger electrodes 153.sub.2 radiating from the ends of the bus bar electrodes 160.

[0040] The number of bus bar electrodes may be 4 or 5, as shown in FIG. 2a,b and FIG. 3. Other numbers of bus bar electrodes, for example, 2, 3 or 6 or more, may also be useful.

[0041] The front surface bus bar electrodes 152 are be substantially parallel to each other and substantially perpendicular to the front surface finger electrodes 153 in the regions without palm-finger electrodes. The width of a front surface bus bar electrode may be between about 0.5 mm and about 2.5 mm, for example about 1.5 mm. The front surface bus bar electrodes may have a continuous width or alternatively the width may vary along the length of a front surface bus bar electrode and a front surface bus bar electrode may for example be tapered towards its ends. The front surface bus bar electrodes may or may not have all the same width. The front surface bus bar electrodes may be equally spaced apart. The spacing between two adjacent front surface bus bar electrodes may be dependent on the cell size and number of bus bar electrodes. For example, the spacing between two adjacent front surface bus bar electrodes may be about 39 mm for a 15.6×15.6 cm.sup.2 photovoltaic cell element with four front surface bus bar electrodes 152. Front surface bus bar electrodes 152 with uneven spacing may also be useful. The front surface bus bar electrodes 152 and the finger electrodes 153 may be made of the same or different materials and may be made preferably with a solderable material, and may have the same or a different thickness compared to the finger electrodes.

[0042] The front surface finger electrodes may be made of a paste including copper, silver, an alloy where one of these metals are the major component or any other conducting material. For example, the front surface finger electrodes 153 as well as the front surface bus bar electrodes 152 may be made using various methods such as industrially applicable production methods as e.g. screen printing, roller printing, ink jet printing, etc.

[0043] A plurality of the half-cut cells may be assembled in solar cell units. Every two half-cut cells may be arranged in such a way that the palm-finger structures of one half-cut cell may be adjacent to the bus bar electrodes 152 of the adjacent half-cut cell as shown in FIG. 2b and FIG. 3.

[0044] FIGS. 4 and 5 show side views of a part of a string of solar cells 4.sub.1, 104.sub.1 connected with metal ribbons 21, 121, which are attached to rear side bus bars 23, 123 and front side bus bars 52, 152, respectively.

[0045] This and similar configurations may result in less paste consumption and higher cell efficiency due to less shading losses. Further, the reduction of the front surface bus bar electrodes 152 by replacing portions of them with second finger electrodes 153.sub.2 may reduce stress on the cell substrate 151.sub.1. In addition, as conducting metallic ribbons 121 may be soldered to the front surface bus bar electrodes 152 in module assembly, the ribbons 121 at least may not need to be soldered in the area occupied by the second finger electrodes 153.sub.2 as shown in FIG. 5. Therefore, the reduced front surface bus bar electrodes 152 may also result in reduction in ribbon consumption compared to the standard connection with ribbons as shown in FIG. 4.

[0046] The invention may be embodied in other specific forms without departing from the scope of the invention. The foregoing embodiments, therefore, are to be considered in all respects illustrative rather than limiting the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

[0047] Terms such as “about” in conjunction with a specific distance or size are to be interpreted as not to exclude insignificant deviation from the specified distance or size and may include for example deviations of up to 20%. Furthermore, terms such as “substantially parallel” or “substantially perpendicular” are to be interpreted as not to exclude insignificant deviation from the specified arrangement and may include for example deviations of up to 10° or even up to 20°. Particularly, one skilled in the art will understand that insignificant deviations from a strictly parallel arrangement may be acceptable as long as they do not induce e.g. excessive serial resistance losses which is assumed to be the case as long such deviations do not exceed 10° or 20°.

[0048] Finally, it should be noted that the term “comprising” does not exclude other elements or steps and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.