WO2014096929A2

WO2014096929A2 - Photovoltaic cell element having a specific electrode configuration

Info

Publication number: WO2014096929A2
Application number: PCT/IB2013/002789
Authority: WO
Inventors: Raymond Yang Ming LIM
Original assignee: REC Solar Pte Ltd
Current assignee: REC Solar Pte Ltd
Priority date: 2012-12-19
Filing date: 2013-12-17
Publication date: 2014-06-26
Anticipated expiration: 2015-06-19
Also published as: WO2014096929A3; TW201444103A; WO2014096929A8; GB2509097A; GB201223019D0; USD741793S1

Abstract

A photovoltaic cell element (100) is presented. The photovoltaic cell element includes a substrate (101) including a front surface (106), a back surface (107) and front surface electrodes over the front surface. The front surface electrodes include a plurality of front surface bus bar electrodes (102) coupled to a plurality of front surface finger electrodes (103). Widths of the front surface bus bar electrodes (102) are between about 0.5 mm and about 2.5 mm. The plurality of front surface bus bar electrodes (102) is substantially parallel to each other and substantially perpendicular to the front surface finger electrodes (103). Widths of the front surface finger electrodes (103) are between about 30 μηι and about 100 μπι. The front surface electrodes also include first front surface redundancy line electrodes (105) between each two adjacent front surface bus bar electrodes (102). The front surface redundancy line electrodes (105) are substantially parallel to the bus bar electrodes (102) and substantially perpendicular to the front surface finger electrodes (103) to couple to the front surface finger electrodes (103). Widths of the first front surface redundancy line electrodes (104) are between about 30 μπι and about 500 μπι.

Description

Photovoltaic cell element having a specific electrode configuration

FIELD OF THE INVENTION

The present invention relates to a photovoltaic cell element having a specific electrode configuration and to a photovoltaic module comprising such photovoltaic cell element.

TECHNICAL BACKGROUND

Photovoltaic cells, sometimes also referred to as solar cells, are electrical devices that convert energy of light into electrical energy by a photovoltaic effect. In order to transport electrical energy generated in a photovoltaic cell to external electrically powered components, it is necessary to provide electrical contacts to the photovoltaic cell. On the light receiving side of a photovoltaic cell, it is common practice to optimize a light receiving area while ensuring acceptable series resistance using a metallic grid with many thin parallel finger electrodes that are connected to two, three or four wider bus bar electrodes extending perpendicular to the finger electrodes and used for collecting the electric current from the finger electrodes. In module assembly, conducting metallic ribbons may be soldered to the bus bar electrodes in order to connect the photovoltaic cells to external module contacts or to interconnect adjacent photovoltaic cells.

SUMMARY OF THE INVENTION

With known values for contact resistivity, metal resistivities, and possible design and process ranges for finger and bus bar electrode dimensions, it is possible to mathematically model an optimal layout of finger and bus bar electrodes. However, in such modeling it is generally assumed that there are no production flaws or flaws being introduced during the operation of the photovoltaic module.

Therefore, there may be a desire to have an electrode pattern design that may strongly reduce an impact of flaws while maintaining an almost optimal electrode design with respect to generation of electrical energy.

Such desire may be met with the subject-matter of the independent claims. Advantageous embodiments are defined in the dependent claims.

In one embodiment, a photovoltaic cell element is presented. The photovoltaic cell element includes a substrate including a front surface, a back surface and front surface electrodes over the front surface. The front surface electrodes include a plurality of front surface bus bar electrodes coupled to a plurality of front surface finger electrodes. Widths of the front surface bus bar electrodes are between about 0.5 mm and about 2.5 mm. The plurality of front surface bus bar electrodes are substantially parallel to each other and substantially perpendicular to the front surface finger electrodes. Widths of the front surface finger electrodes are between about 30 μπι and about 100 μπι. The front surface electrodes also include first front surface redundancy line electrodes between each two adjacent front surface bus bar electrodes. The first front surface redundancy line electrodes are substantially parallel to the bus bar electrodes and substantially perpendicular to the front surface finger electrodes to couple to the front surface finger electrodes. Widths of the first front surface redundancy line electrodes are between about 30 μπι and about 500 μιη. In another embodiment, a photovoltaic module is disclosed. The photovoltaic module includes a plurality of photovoltaic cells electrically interconnected by means of connection members. Each photovoltaic cell includes a substrate including a front surface, a back surface and front surface electrodes over the front surface. The front surface electrodes include a plurality of front surface bus bar electrodes coupled to a plurality of front surface finger electrodes and coupled to the connection members. Widths of the front surface bus bar electrodes are between about 0.5 mm and about 2.5 mm. The plurality of front surface bus bar electrodes are substantially parallel to each other and substantially perpendicular to the front surface finger electrodes. Widths of the front surface finger electrodes are between about 30 μηι and about 100 μηι. The front surface electrodes also include first front surface redundancy line electrodes between each two adjacent front surface bus bar electrodes. The first front surface redundancy line electrodes are substantially parallel to the bus bar electrodes and substantially perpendicular to the front surfaee finger electrodes to couple to the front surface finger electrodes. Widths of the first front surface redundancy line electrodes are between about 30 μιη and about 500 μηι.

These and other objects, along with possible advantages and features of embodiments of the present invention herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

Fig. 1 shows a perspective view of an embodiment of a photovoltaic cell element;

Fig. 2 shows a layout of an embodiment of a photovoltaic cell element; Fig. 3 shows another layout of an embodiment of a photovoltaic cell element; and Fig. 4 shows yet another layout of an embodiment of a photovoltaic cell element. DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments generally relate to devices, for example, devices for converting energy of light into electrical energy. More particularly, the devices may be photovoltaic cell elements or photovoltaic cell modules including a plurality of photovoltaic cell elements. Fig. 1 shows a perspective view of an embodiment of a photovoltaic cell element 100. The photovoltaic cell element 100 includes a substrate 101. The substrate 101 may be e.g. a monoerystalline, multicrystalline, amorphous or compound semiconductor substrate. Other types of substrates may also be useful. In one embodiment, a silicon substrate is used as the semiconductor substrate. In one embodiment, the substrate includes first and second surfaces. The first surface may include a light receiving surface or a front surface 106, while the second surface may include a non-light receiving surface or a back surface 107. In one embodiment, the substrate 101 is doped with a p-type dopant, and a front surface layer 109 in the substrate is doped with an n-type dopant. The front surface layer 109 is commonly referred to as an emitter layer. The p-type dopant may include boron (B) or any other element or combination of elements that acts as a p-type dopant in silicon. The n-type dopant may include phosphorus (P) or any other element or combination of elements that acts as an n-type dopant in silicon. In another embodiment, the substrate 101 is doped with an n-type dopant, and the front surface layer 109 in the substrate is doped with a p-type dopant. In all embodiments, there may be an anti-reflection layer 110 on the front surface. The thickness of the substrate 101 may be from about ΙΟ πι to about 500μπι. The size of the substrate may be about 15.6 x 15.6 cm². Other sizes of the substrate, for example, about 12.5 x 12.5 cm² or about 10 x 10 cm², may also be useful.

In one embodiment, as shown in Fig. 1, the front surface 106 of the substrate 101 includes a plurality of front surface electrodes. The front surface electrodes may include a plurality of front surface bus bar electrodes 102 and a plurality of front surface finger electrodes 103. For example, the front surface electrodes may include three front surface bus bar electrodes 102 and a large number of front surface finger electrodes 103 as shown in Fig. 1. Having other numbers of front surface bus bar electrodes, for example, two or four, may also be useful. The back surface of the substrate includes back surface contacts 108. In one embodiment, the back surface contacts may include one or more conductive layers which fully cover the back surface of the photovoltaic cell. The conductive layers may include a metal, for example, aluminum, molybdenum, silver or a combination thereof. In another embodiment, the back surface of the photovoltaic cell is not fully covered by the back surface contacts. For example, the back surface contacts may have a similar configuration as the front surface electrodes. Having back surface contacts of other configurations or made of other materials may also be useful.

Fig. 2 shows a layout of an embodiment of a photovoltaic cell element 200. Features in this embodiment which are similar to that described in Fig. 1 will not be described or described in detail. The front surface finger electrodes 103 may be electrodes configured to collect photo-induced carriers. A plurality of the front surface finger electrodes 103 may be arranged substantially parallel to each other and parallel to one edge of the substrate and almost throughout the front surface of the substrate. The width of a front surface finger electrode 103 may be between about 30μη and about ΙΟΟμιη, for example about 60μπι. The front surface finger electrodes 103 may or may not have the same width. The front surface finger electrodes may be equally spaced apart. The spacing between two adjacent front surface finger electrodes may be between about 1mm and about 3mm, for example about 2mm. Front surface finger electrodes with uneven spacing may also be useful. The front surface finger electrodes may be made of 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 103 as well as the front surface bus bar electrodes 102 and/or the front surface redundancy line electrodes 104 and 105 may be made using various methods such as industrially applicable production methods as e.g. screen printing, roller printing, ink jet printing, etc.

The front surface bus bar electrodes 102 may be electrodes configured to extract the carriers collected by the finger electrodes 103. In one embodiment, there are three front surface bus bar electrodes 102 arranged over the front surface 106 of the substrate to couple to the front surface finger electrodes 103. Other numbers of bus bar electrodes 102, for example two or four, may also be useful. The front surface bus bar electrodes 102 may be substantially parallel to each other and substantially perpendicular to the front surface finger electrodes 103. The width of a front surface bus bar electrode may be between about 0.5mm and about 2.5mm, for example about 1.5mm. 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 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 40mm for a 15.6 x 15.6 cm² photovoltaic cell element with three front surface bus bar electrodes 102. Front surface bus bar electrodes 102 with uneven spacing may also be useful. The front surface bus bar electrodes 102 may be made of the same materials as the finger electrodes and may be made preferably with a solderable material, and may have the same or a different thickness compared to the finger electrodes.

Front surface redundancy line electrodes 104 and 105 may be electrodes configured to provide low resistance current paths particularly when the cell contains interrupted finger electrodes 103. Preferably, the front surface redundancy line electrodes 104 and 105 are provided such that each finger electrode 103 crosses at least one first front surface redundancy line electrodes 105 when running from one front surface bus bar electrode 102 to an adjacent front surface bus bar electrode 102 and/or furthermore such that each finger electrode 103 is connected to at least one second front surface redundancy line electrodes 104 when running from one front surface bus bar electrode 102 towards an edge of the substrate 101. The front surface redundancy line electrodes 104, 105 may be substantially perpendicular to the finger electrodes 103 and substantially parallel to the bus bar electrode lines 102, but preferably narrower than the bus bar electrode lines 102 in order not to substantially reduce the light receiving area of the photovoltaic cell. The width of a front surface redundancy line electrode 104, 105 may be between 30 μηι and 500 μπι, preferably between 50 μηι and 400 μιη, for example about 60 μιη. For example, the front surface redundancy line electrode 104, 105 may be narrower than half the width, preferably narrower than a quarter the width, and more preferably smaller than 10% of the width of the bus bar electrodes 102. The front surface redundancy line electrodes 104, 105 may or may not have the same width. The front surface redundancy line electrodes 104, 105 may be made of the same materials as the finger electrodes, and may have the same or a different thickness compared to the finger electrodes 103.

In one embodiment, the front surface finger electrodes 103 are continuous between adjacent bus bar electrodes 102. A plurality of redundancy line electrodes 104, 105 substantially parallel to the bus bar electrode lines 102 may be arranged over the front surface 106 of the substrate. In one embodiment, one first redundancy line electrode 105 between each two adjacent bus bar electrodes 102 is included over the front surface 106 of the substrate. For example, the first redundancy line electrodes 105 may be positioned about mid- way between two adjacent front surface bus bar electrodes 102. Including the first redundancy line electrodes 105 in other positions between two adjacent front surface bus bar electrodes 102 may also be useful. The redundancy line electrodes 104, 105 may be of different widths. In an alternative embodiment, there are two or more redundancy line electrodes 104 between each two adjacent bus bar electrodes 102. Other configurations of the redundancy line electrodes 104, 105 may also be useful. For example, there may also be one or more second front surface redundancy line electrodes 104 included between the outermost front surface bus bar electrodes 102 and edges of the photovoltaic cell element. It may also be beneficial to include the second front surface redundancy line electrodes 104 connecting the outermost ends of the finger electrodes 103, substantially parallel to the cell edges.

The redundancy line electrodes 104, 105 connect the finger electrodes 103 to enable current flow to adjacent finger electrodes 103 in the case of finger electrode interruption. When photovoltaic cells with redundancy lines 104, 105 of the described type are used in module production, the production results show that there are fewer produced photovoltaic modules with reduced efficiency. Qualification tests also indicate that the redundancy line electrodes 104, 105 will increase the practical service life of photovoltaic modules after they are installed in power plants. Fig. 3 shows yet another embodiment of a configuration of a photovoltaic cell element 300. Features in this embodiment which are similar to that described in Figs. 1 and 2 will not be described or described in detail. In one embodiment, the front surface finger electrodes 103 are discontinuous between adjacent bus bar electrodes 102. The discontinuity, denoted as "D", may be positioned about mid- way between two adjacent bus bar electrodes 102. The discontinuity may be about equal to the finger electrode spacing. Having discontinuities smaller than the finger electrode spacings may also be useful. The discontinuity "D" may be between about 50 μιη and about 3000 μπι, for example about 100 μιη,. In one embodiment, the front surfaee of the substrate includes first redundancy line electrodes 105 arranged between each two adjacent front surface bus bar electrodes 102 to connect the ends of discontinuous finger electrodes 103, and second redundancy line electrodes 104 included between the outermost front surface bus bar electrodes 102 and edges of the photovoltaic cell element. For example, two or more first redundancy line electrodes 105 may be arranged between each two adjacent front surface bus bar electrodes 102 wherein one of these first redundancy line electrodes 105 connects ends of discontinuous finger electrodes being coupled to one of these front surface bus bar electrodes 102 whereas another one of these first redundancy line electrodes 105 connects ends of discontinuous finger electrodes being coupled to the other one of these front surface bus bar electrodes 102. Therein, the two or more first redundancy line electrodes 105 may enclose the discontinuity D. For example, one or more second redundancy line electrodes 104 may be included to connect the outermost ends of the front surface finger electrodes 103 near the edges of the substrate. The widths of the redundancy line electrodes 104 and 105 may be between about 30 μπι and about 500 μπι, for example about 60 μπι. The redundancy line electrodes 104, 105 may be of different widths. The redundancy line electrodes 104, 105 may be made of the same materials as the finger electrodes 103, and may have the same or a different thickness compared to the finger electrodes 103. In the exemplary embodiment shown in Fig. 3, the front surface of the substrate includes three bus bar electrodes 102, two first redundancy lines 105 between each of two adjacent bus bar electrodes 102 to connect the ends of discontinuous finger electrodes 103 and two second redundancy lines 104 connecting the outermost ends of the finger electrodes 103. The number of redundancy lines 104, 105 may vary with the number of bus bar electrodes 102 and the number of discontinuities of finger electrodes 102.

This configuration allows for electrically separating sections of the cell. The electrical separation of the sections of the cells can be further enhanced by removing the emitter layer e.g. by laser ablation for example in the area of the discontinuity D between the redundancy lines. This may be beneficial for individual electrical characterization of the separated cell segments. Fig. 4 shows another exemplary embodiment of a photovoltaic element 400 having finger electrodes 103, three bus bar electrodes 102, two first redundancy lines 105 between each of two adjacent bus bar electrodes 102 to connect the ends of discontinuous finger electrodes 103 and two second redundancy lines 104 connecting the outermost ends of the finger electrodes 103. Other numbers of bus bar electrodes 102, for example, 4 or 5, may also be possible. A small gap of width D in a range of between about 50μηι and about 3mm is provided between two adjacent first redundancy lines 105. The bus bar electrodes 102 may have a width of between about 0.5 and about 2.5mm which reduces from a maximum width Wbl to a minimum width Wb2 towards the extremities of the bus bar electrodes 102. The finger electrodes 103 may have a width of between about 30μπι and about Ι ΟΟμηι. The redundancy lines 104, 105 may have a width of between about 30μπι and about 500μπι. The spacings S between finger electrodes 103 may be between about lmm and about 3mm. Ah overall width Wl of the electrode pattern may be approximately 153mm. The width of the photovoltaic element 400 may be approximately 156mm. The widths W2 and W3 in the figure may be e.g. approximately 25 and 52 mm, respectively. All indicated dimensions are exemplary only. A plurality of photovoltaic cell elements as described in Figs. 2 or 3 may be connected to each other by means of connection members, for example, wirings, ribbons or tabs, and encapsulated with polymer and glass layers to form a photovoltaic cell module. In one embodiment, the bus bar electrodes 102 are coupled to the connection members for example by soldering a metal ribbon to each of the bus bar electrodes 102 whereas the redundancy line electrodes 104, 105 preferably are not coupled to any connection members. In one embodiment, bus bar electrodes 102 are electrically interconnected to the back surface contacts of adjacent cells by means of the connection members. The numbers of photovoltaic cell elements in one photovoltaic cell module may be, for example, 10 6 or 12 x 6. Other configurations may also be useful.

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. Terms such as "about" in conj nction 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 20°.

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. LIST OF REFERENCE SIGNS

100 photovoltaic cell element

101 substrate

102 front surface bus bar electrode

103 front surface finger electrode

106 front surface

107 back surface

108 back surface contact

109 front surface layer

110 anti-reflection layer

200 photovoltaic cell element

300 photovoltaic cell element

400 photovoltaic cell element

Claims

1. A photovoltaic cell element (100, 200, 300) comprising:

a substrate (101) including a front surface^'(106) and a back surface (107); and

front surface electrodes over the front surface (106), wherein the front surface electrodes comprise

a plurality of front surface bus bar electrodes (102) coupled to a plurality of front surface finger electrodes (103), wherein widths of the front surface bus bar electrodes (102) are between about 0.5 mm and about 2.5 mm,

the plurality of front surface bus bar electrodes (102) being substantially parallel to each other and substantially perpendicular to the front surface finger electrodes (103), wherein widths of the front surface finger electrodes (103) are between about 30 μπι and about 100 μπι, and

first front surface redundancy line electrodes (105) between each two adjacent front surface bus bar electrodes (102) substantially parallel to the bus bar electrodes (102) and substantially perpendicular to the front surface finger electrodes (103) to couple to the front surface finger electrodes (103 ), wherein widths of the first front surface redundancy line electrodes (105) are between about 30 μπι and about 500 μπι.

2. The photovoltaic cell element in claim 1 comprising second front surface redundancy line electrodes (104) substantially parallel to the bus bar electrodes (102) between the outermost bus bar electrodes and the edges of the photovoltaic cell element to couple to the front surface finger electrodes (103).

3. The photovoltaic cell element in claim 2 wherein the second front surface redundancy line electrodes (104) connect outermost ends of the finger electrodes (103).

4. The photovoltaic cell element in one of claims 1 to 3 wherein

the front surface finger electrodes (103) are discontinuous between two adjacent front surface bus bar electrodes (102), wherein the discontinuity is between about 50 μηι and about 3000 μπι; and

the first front surface redundancy line electrodes (105) connect ends of the discontinuous front surface finger electrodes (103).

5. The photovoltaic cell element in one of claims 1 to 4, wherein the front surface finger electrodes (103) and the first front surface redundancy line electrodes (105) are made of metals.

6. The photovoltaic cell element in claim 2 or 3, wherein the second front surface redundancy line electrodes (104) are made of metals.

7. The photovoltaic cell element in one of claims 1 to 6, wherein the first front surface redundancy line electrodes (105) are positioned about mid-way between two adjacent front surface bus bar electrodes (102).

8. The photovoltaic cell element in one of claims 1 to 7, comprising one or more first front surface redundancy line electrodes (105) between each two adjacent bus bar electrodes (102).

9. The photovoltaic cell element in claim 4 wherein the discontinuity is positioned about mid-way between two adjacent front surface bus bar electrodes (102).

10. The photovoltaic cell element in claim 4 or 9, wherein the discontinuity is about equal to a spacing between two adjacent front surface finger electrodes (103).

11. The photovoltaic cell element in claim 4, 9 or 10, wherein the discontinuity is smaller than a spacing between two adjacent front surface finger electrodes (103).

12. A photovoltaic module comprising :

a plurality of photovoltaic cells electrically interconnected by means of connection members, each photovoltaic cell comprising:

a substrate (101) including a front surface (106) and a back surface (107), and

a plurality of front surface bus bar electrodes (102) coupled to a plurality of front surface finger electrodes (103) and coupled to the connection members, wherein widths of the front surface bus bar electrodes (102) are between about 0.5 mm and about 2.5 mm, the plurality of front surface bus bar electrodes (102) substantially parallel to each other and substantially perpendicular to the front surface finger electrodes (103), wherein widths of the front surface finger electrodes (103) are between about 30 μπι and about 100 μπι, and

first front surface redundancy line electrodes (105) between each two adjacent front surface bus bar electrodes (102) substantially parallel to the bus bar electrodes (102) and substantially perpendicular to the front surface finger electrodes (103) to couple to the front surface finger electrodes (103), wherein widths of the first front surface redundancy line electrodes (105) are between about 30 μπι and about 500 μηι.

13. The photovoltaic module in claim 12, wherein the back surface (107) of the substrate (101) of the photovoltaic cell comprises back surface contacts (108), the front surface bus bar electrodes (102) being electrically interconnected to the back surface contacts (108) of adjacent photovoltaic cells by means of the connection members.

14. The photovoltaic module in claim 12 or 13, wherein the photovoltaic cell comprises second front surface redundancy line electrodes (104) substantially parallel to the bus bar electrodes (102) between outermost bus bar electrodes (102) and edges of the photovoltaic cell to couple to the front surface finger electrodes (103).

15. The photovoltaic module in claim 14 wherein the second front surface redundancy line electrodes (104) of the photovoltaic cell connect the outermost ends of the finger electrodes (103).

16. The photovoltaic module in one of claims 12 to 15, wherein:

the front surface finger electrodes (103) are discontinuous between two adjacent front surface bus bar electrodes (102), wherein the discontinuity is between, about 50 μπι and about 3000 μπι; and