SOLAR CELL ASSEMBLY

Abstract

A solar cell assembly (100) comprising: a layered structure (102) comprising a photovoltaic element and a conductive surface (111); and an electrode assembly (101) comprising a plurality of longitudinally extending, laterally spaced conductive elements (104a-104f) arranged side by side, the plurality of conductive elements comprising a first conductive element (104b) having a first cross-sectional area and a second conductive element (104a) having a second cross-sectional area that is larger than the first cross-sectional area, the electrode assembly arranged on the conductive surface of the layered structure such that the conductive elements are in ohmic contact with the conductive surface.

Claims

1. A solar cell assembly comprising: a layered structure comprising a photovoltaic element and a conductive surface; and an electrode assembly comprising a plurality of longitudinally extending, laterally spaced conductive elements arranged side by side, the plurality of conductive elements comprising a first conductive element having a first cross-sectional area and a second conductive element having a second cross-sectional area that is larger than the first cross-sectional area, the electrode assembly arranged on the conductive surface of the layered structure such that the conductive elements are in ohmic contact with the conductive surface.

2. A solar cell assembly according to claim 1 wherein the plurality of conductive elements comprises two outermost conductive elements and a plurality of intermediate conductive elements disposed between the two outermost conductive elements.

3. A solar cell assembly according to claim 2 wherein the second conductive element is an outermost conductive element of the plurality of conductive elements.

4. A solar cell assembly according to claim 2, wherein the first conductive element is an intermediate conductive element.

5. A solar cell assembly according to claim 2 comprising a third conductive element having a third cross-sectional area that is larger than the first cross-sectional area.

6. A solar cell assembly according to claim 5 wherein the third conductive element is an outermost conductive element of the plurality of conductive elements.

7. A solar cell assembly according to claim 2, wherein the two outermost conductive elements each have a cross-sectional area that is larger than that of each of the intermediate conductive elements.

8. A solar cell assembly according to claim 2, wherein a distance between an outermost conductive element of the plurality of conductive elements and an adjacent edge of the layered structure is equal to or larger than a distance between two adjacent conductive elements of the plurality of conductive elements.

9. A solar cell assembly according to claim 1, wherein the plurality of conductive elements are evenly spaced.

10. A solar cell assembly according to claim 1, wherein the first cross-sectional area is between 0.03 mm2 and 0.07 mm2.

11. A solar cell assembly according to claim 1, wherein the second cross-sectional area is between 0.05 mm2 and 0.1 mm2.

12. A solar cell assembly according to claim 1, wherein the second cross-sectional area is between 0.01 mm2 and 0.03 mm2 larger than the first cross-sectional area.

13. A solar cell assembly according to claim 1, wherein each conductive element has a circular transverse cross-sectional shape.

14. A solar cell assembly according to claim 1, wherein the electrode assembly comprises an insulating optically transparent film for retaining the plurality of conductive elements on the conductive surface of the layered structure.

15. A solar cell assembly according to claim 2, wherein the second conductive element has a greater effective served area than the first conductive element, and wherein effective served area is determined for: an intermediate conductive element by summing half of a first area with half of a second area, the first area defined as the area between the intermediate conductive element and a first adjacent conductive element, and the second area defined as the area between the intermediate conductive element and a second adjacent conductive element; and an outermost conductive element by summing half of a third area with a fourth area, the third area defined as the area between the outermost conductive element and an adjacent conductive element, and the fourth area defined as the area between the outermost conductive element and an adjacent edge of the layered structure.

16. An electrode assembly for a solar cell, the electrode assembly comprising: an insulating optically transparent film; and a plurality of longitudinally extending, laterally spaced conductive elements arranged side by side on a surface of the film, the plurality of conductive elements comprising a first conductive element having a first cross-sectional area and a second conductive element having a second cross-sectional area that is larger than the first cross-sectional area.

17. An electrode assembly according to claim 16 wherein the plurality of conductive elements comprises two outermost conductive elements and a plurality of intermediate conductive elements disposed between the two outermost conductive elements.

18. A solar cell assembly according to claim 17 wherein the second conductive element is an outermost conductive element.

19. A solar cell assembly according to claim 17, wherein the first conductive element is an intermediate conductive element.

20. A solar cell assembly according to claim 17, wherein a distance between an outermost conductive element of the plurality of conductive elements and an adjacent edge of the film is equal to or larger than a distance between two adjacent conductive elements of the plurality of conductive elements.

21. A solar cell assembly according to claim 16, wherein the conductive elements are evenly spaced.

22. A solar cell assembly according to claim 16, wherein the second cross-sectional area is between 0.01 mm2 and 0.03 mm2 larger than the first cross-sectional area.

23. A solar cell assembly according to claim 16, wherein each conductive element has a circular transverse cross-sectional shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0093] FIG. 1A is a top view of a solar cell;

[0094] FIG. 1B is a side cross-section view of the solar cell of FIG. 1A; and

[0095] FIG. 2 is a schematic illustrating a layered structure of the solar cell of FIG. 1A.

DETAILED DESCRIPTION

[0096] Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0097] FIGS. 1A and 1B illustrate a solar cell assembly 100 that includes front 101 and rear 101 electrode assemblies arranged on respective front and rear sides of a layered structure 102 comprising a photovoltaic element (not shown) and front 111 and rear conductive surfaces. For brevity only the front electrode assembly 101 is discussed below, but it should be appreciated that the description equally applies to the rear electrode assembly 101 (and for that reason similar reference numerals have been used to label the rear electrode assembly 101).

[0098] The front electrode assembly 101 comprises an electrically insulating optically transparent film 103 and a plurality of laterally spaced conductive elements in the form of wires 104a-104f arranged side by side on a surface of the film 103. As will be described further below, the electrode assembly 101 is configured for arrangement on front conductive surface 111 of the layered structure 102 of the solar cell assembly 100 for extracting electrical current generated by a photovoltaic element of the layered structure 102 (in response to light incident on the solar cell assembly 100).

[0099] Each of plurality of wires 104a-104f has a circular cross-sectional shape (as can be seen from FIG. 1B). The plurality of wires 104a-104f are also evenly spaced, parallel to one another, and extend in a longitudinal direction (the vertical direction in FIG. 1). Although only six wires 104a-104f are shown, it should be appreciated that a number of (intermediate) wires are omitted from the figures for clarity. A first wire 104b of the plurality of wires 104a-104f has a first cross-sectional area and a second wire 104a of the plurality of wires 104a-104f has a second cross-sectional area that is larger than the first cross-sectional area (i.e. the second wire 104a has a greater diameter than the first wire 104b). Again, this is particularly evident from FIG. 1B. The first wire 104b has a diameter of 250 m and the second wire 104a has a diameter of 300 m.

[0100] The second wire 104a, having the larger cross-sectional area, is one of two outermost wires (the other being a third wire 104f) of the plurality of wires 104a-104f. Although not illustrated, these wires 104a-104f are arranged on a plurality of finger electrodes of the front conductive surface 111 of the layered structure, which extend perpendicularly with respect to the wires 104a-104f. The finger electrodes are evenly distributed across the surface and carry current from the layered structure 102 to the wires 104a-104f for extraction of the current from the solar cell assembly 100 by the wires 104a-104f. In general, the amount of current extracted by a particular wire of the plurality of wires 104a-104f is dependent on the proximity of that wire to any adjacent wires and/or adjacent edge of the layered structure 102.

[0101] Accordingly, and as should be apparent from the figures, the second wire 104a is required to extract more current than the first wire 104b. This is because the second wire 104a is an outermost wire of the plurality of wires 104a-104f, which means that all of the current generated in the region between the second wire 104a and an adjacent longitudinal edge 105a of the layered structure is extracted solely by the second wire 104a. This is in contrast to the first wire 104b, which is between two other adjacent wires (the second wire 104a and a fourth wire 104c), such that extraction of current from the regions either side of the first wire 104b is shared with the adjacent wires 104a, 104c.

[0102] In particular, the second wire 104a has a greater effective served area than the first wire 104b. The effective served area for the first wire 104b is determined by summing half of a first area 117a with half of a second area 117b. The first area 117a is defined between the first 104b and second 104a wires, and the second area 117b is defined between the first 104b and fourth 104c wires. The effective served area for the second wire 104b is determined by summing half of the first area 117a with a third area 117c. The third area 117c is defined between the second wire 104a and the adjacent edge 105a of the layered structure 102. Although, for illustrative purposes, the dashed lines indicating the first 117a, second 117b, and third 117c areas are inset from the wires/edges 104a, 104b, 104c, it should be appreciated that these areas 117a, 117b, 117c extend across the entire region between the wires/edges 104a, 104b, 105a.

[0103] The greater cross-sectional area of the second wire 104a helps to minimise power losses that would otherwise occur if, for example, the second wire was undersized (e.g. had the same cross-sectional area as the first wire 104b) with respect to the area that it serves.

[0104] As noted above, the plurality of wires 104a-104f also includes a third wire 104f, which is the second outermost wire of the plurality of wires 104a-104f and is thus disposed at an opposite side of the plurality of wires 104a-104f to the second wire 104a. The third wire 104f has the same diameter (300 m), and thus cross-sectional area, as the second wire 104a.

[0105] The plurality of wires 104a-104f includes a plurality of intermediate wires 104b-104e that are disposed between the outermost wires 104a, 104f. The first wire 104b is one of these intermediate wires 104b-104e. As is evident from FIG. 1B, each of the intermediate wires 104b-104e has the same diameter as the first wire 104b (such that each intermediate wire 104b-104e has the first cross-sectional area). Each of the intermediate wires 104b-104e serves a smaller area (with respect to current extraction) than each of the two outermost wires 104a, 104f. In this respect, the diameters (and thus cross-sectional areas) of the wires 104a-104f correspond to the respective areas they are required to serve (and thus the magnitude of the current they are required to extract). This ensures that both power losses (due to under-sizing of wires) and shading (due to over-sizing of wires) are minimised.

[0106] In addition to minimising power losses, the larger second 104a and third 104f wires allow for better adhesion between the film 103 and the surface of the layered structure 102. This will now be described in more detail.

[0107] As is evident from the figures, a first distance A representative of a spacing between the wires 104a-104f is shorter than a second distance B defined between the second wire 104a and an adjacent edge 105a of the layered structure 102. Likewise, the first distance A is also shorter than a third distance C defined by the third wire 104f and the adjacent edge 105b of the layered structure 102. In the illustrated embodiment, the film 103 has the same width and length dimensions as the layered structure 102. Thus, the second distance B is the same as a fourth distance D defined between the second wire 104a and the adjacent edge 106a of the film 103. Similarly, the third distance C is the same as a fifth distance E defined between the third wire 104f and the adjacent edge 106b of the film 103.

[0108] The second, third, fourth and fifth distances can be longer than the first distance because of the larger cross-sectional areas of the second 104a and third 104f wires (i.e. because these wires 104a, 104f are capable of greater current extraction). The benefit provided by these longer distances results from the fact that the two spaces between the second 104a and third 104f wires and their respective adjacent edges 105a, 105b of the layered structure 102 define regions 107a, 107b that are free of wires. These wire-free regions provide areas within which the film 103 makes direct contact with the front surface of the layered structure 102 (i.e. uninterrupted by the presence of wires). It is desirable to maximise this direct contact because doing so can increase adhesion between the film 103 and the layered structure 102 (and thus can help to ensure the wires 104a-104f are securely held on the layered structure 102).

[0109] FIG. 2 is a sectional view of the layered structure 102 of the solar cell assembly 100 described above. In this view, the layered structure 102 is shown isolated from the front 101 and rear 101 electrode assemblies. The layered structure 102 comprises a multi-layer semiconductor assembly including a photovoltaic element in the form of a semiconductor substrate 108 which is sandwiched between a front collector layer 109 and a back collector layer 110. As such, the front collector layer 109 and the back collector layer 110 are arranged at opposite sides of the substrate 108.

[0110] The front collector layer 109 is arranged towards the front surface 111 of the layered structure 102 and the back collector layer 110 is arranged towards the rear surface 112. When assembled, the front electrode assembly 101 is electrically connected to the front collector layer 109 and the rear electrode assembly 101 is electrically connected to the back collector layer 110. Such an arrangement defines a heterojunction technology (HJT) type solar cell. In other embodiments, the layered structure may take other forms (e.g. the solar cell assembly may not be in the form of a HJT type solar cell). For example, in some other embodiments, one or more layers may be absent, one or more layers may be combined together, and/or additional layers may be added, provided that the layered structure 102 can continue to perform its function of generating electricity from incident radiation (e.g. light).

[0111] The substrate 108 is formed of crystalline silicon (c-Si), which is negatively doped (i.e. an n-type material), with impurities of a group V element, such as phosphor (P), arsenic (As), and antimony (Sb). The front collector layer 109 and the back collector layer 110 are each formed of amorphous silicon (a-Si: H). The amorphous silicon is deposited on the front and rear surfaces of the silicon wafer using PECVD.

[0112] The back collector layer 110 comprises a positively doped semiconductor material (i.e. a p-type material), and the front collector layer 109 comprises an n-type material. The p-type material contains impurities of a group III element such as boron (B), gallium (Ga), and indium (In).

[0113] In this exemplary arrangement of the layered structure 102, the back collector layer 110 defines an impurity region of the layered structure 102 having an opposite conductive type to that of the substrate 108, and thus forms a p-n junction along with the substrate 108.

[0114] The multi-layer semiconductor assembly further comprises first 113 and second 114 intrinsic layers. Both intrinsic layers 113, 114 are formed of intrinsically doped amorphous silicon. The first intrinsic layer 113 is arranged between the front collector layer 109 and the substrate 108 to form a front-side passivation layer. In addition, the second intrinsic layer 114 is arranged between the substrate108 and the back collector layer 110 to form a rear-side passivation layer.

[0115] Finally, the front surface 111 of the layered structure 102 is covered with transparent conductive coating 115, which is formed of indium tin oxide (ITO). An upper surface of the ITO layer is textured to provide anti-reflective characteristics. The anti-reflection layer advantageously reduces the reflectance of light incident on the solar cell assembly 100 and increases selectivity of a predetermined wavelength band, thereby increasing the efficiency of the solar cell assembly 100.

[0116] The rear surface 112 of the layered structure 102 is also covered with a transparent conductive coating 116 formed of indium tin oxide (ITO). The transparent conductive coatings 115, 116 are configured to increase lateral carrier transport to finger electrodes arranged on the respective surfaces of the layered structure 102. The transparent conductive coatings 115, 116 are particularly advantageous in heterojunction type devices which comprise layers formed of amorphous silicon which exhibit poor carrier mobility.

[0117] During operation of the solar cell assembly 100 light is incident upon the layered structure 102, as shown by the arrows at the top of FIG. 2. A plurality of electron-hole pairs are produced through the absorption of the incident photons. The electron-hole pairs are then separated into electrons and holes by a built-in potential difference resulting from the p-n junction. The separated electrons move to the n-type semiconductor in the substrate 108, and the separated holes move to the p-type semiconductor in the back collector layer 110. Accordingly, the electrons become major carriers in the substrate 108, and the holes become major carriers in the back collector layer 110. Each of these majority carriers are extracted from the layered structure 102 by the respective electrode assemblies 101, 101.

[0118] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.