WO2009033215A1

WO2009033215A1 - An array of solar cells

Info

Publication number: WO2009033215A1
Application number: PCT/AU2008/001341
Authority: WO
Inventors: Sylvia Tulloch; Paul Murray; Andrew Thein; Renai Platts; Paul Moonie; Johann Desilvestro; Gavin Tulloch; Tony Maine; Matthew Holding; Ben Jausnik
Original assignee: Dyesol Industries Pty Ltd
Priority date: 2007-09-10
Filing date: 2008-09-10
Publication date: 2009-03-19

Abstract

Embodiments of solar cell arrays are described which involve a design of a solar cell array and a method for the processing of individual cells into an array comprised of multiple cells interconnected in series and/or parallel to achieve any desired electrical output and to provide for a non-uniform appearance of colour.

Description

AN ARRAY OF SOLAR CELLS

Technical Field

This invention relates to solar cell arrays and methods and materials used to manufacture arrays. The invention has particular application to portable photoelectrochemical cell arrays and in particular dye solar cell arrays.

Background to the Invention

Solar cells are devices which perform two main functions, the first being the photo generation in light absorbing material/s of electron and hole charge carriers, and the second being the subsequent separation of these charge carriers to a conductive contact to facilitate electron transfer.

The colour of a solar cell influences the light absorbing properties and thus the performance of the cell. Arrays of solar cells have been provided in panels which have a generally uniform appearance of colour across the array. It would be advantageous to provide arrays of non-uniform colour.

In the case of portable arrays, such as might be used to charge portable electronic devices such as mobile phones or GPS devices, it would be advantageous to provide arrays that are rugged, compact and lightweight.

Summary of the Invention

In a first aspect the present invention provides an array of solar cells, wherein the array exhibits variations in colour across the array.

The cells may be located on a substrate.

The solar cells may be of varying dimensions or areas.

The solar cells may be provided in a range of shapes including circles, trapezoids, rectangles, or squares. The array may be flexible.

The solar cells may be photoelectrochemical cells.

The cells may be dye solar cells.

The cells may be electrically interconnected by a printed circuit board (PCB) or a continuous substrate such as the working electrode (WE) or counter electrode (CE). The PCB may be flexible.

The PCB design may allow for inclusion of diodes.

The array may include an external connection point which is attached to the PCB via a knitted, solder paste adhered, rivet, pin, eyelet and/or soldered positive and negative contact/s or a combination thereof.

The array may be formed by joining cells via any one of conductive adhesive coated tape, wire, cable, metal braid, polyimide strip, rivets, eyelets, pins, spade clips, crimp terminals or a combination thereof.

The cells may utilise metal substrates for one of their electrodes.

The substrate may include any one of titanium, steel, coated steel, aluminium or alloys thereof.

At least one of the cells may be flexible. The substrate may utilise a camouflage pattern which is achieved by either a pattern of colours or areas of varying reflectivity.

The array may be encapsulated in a substantially transparent cover which is of low light reflectivity.

The array may be encapsulated by hot lamination, cold lamination and/or vacuum sealing or a combination thereof.

The surface and/or bulk absorption and reflection characteristics of the transparent cover may be non-uniform.

There may be a colour variation between cells in the array.

There may be a colour variation within cells in the array. The colour variation may be achieved by variations in dyes between cells.

The colour variation may be achieved by variations in the characteristics of the particles of the semiconductor between cells.

The colour variation may be achieved by variations in the composition of redox electrolyte between cells. The colour variation may be achieved by variations in the amount and/or concentration of the catalyst deposited as the counter-electrode between cells.

The colour variation may be achieved by the addition of a pigment to the electrolyte or to the dye of at least one of the cells.

The pigment may include an inorganic pigment. The colour variation may be achieved by variations in the reflectivity of the working electrode between cells.

The colour variation may give rise to an overall camouflage appearance.

In a second aspect the present invention provides a portable charging device formed from a multiplicity of arrays according to any preceding claim which are connected together and may be folded in a concertina-like manner for storage.

In a third aspect the present invention provides a method of forming an array of cells according to the first aspect of the invention including the steps of testing and matching the electrical performance of each cell prior to assembly based on measurement of short circuit current per area.

In a fourth aspect the present invention provides an array of solar cells, wherein the cells are physically and electrically connected in the array at one edge of the cell.

The cells may include tabs and may be physically and electrically connected by way of the tabs.

The connected edges of the cells may be oriented towards a centre line of the array. The cells may be physically and electrically connected in the array by way of a support structure.

The support structure may include a printed circuit board (PCB).

In a fifth aspect the present invention provides an array of solar cells wherein the cells are located on a substrate.

Brief Description of the Drawings

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows an example array according to an embodiment of the invention consisting of 32 cells;

Figure 2A shows a large array consisting of multiple interconnected arrays of figure 1;

Figure 2B shows the large array of figure 2A partially folded;

Figure 2C shows the large array of figure 2A completely folded up for storage, Figure 3 shows the front side of the PCB used in the array of figure 1 ;

Figure 4 shows the back side of the PCB of figure 3;

Figure 5 is a graph which illustrates the performance of an array according to the invention when exposed to various light conditions including tree shading at a distance of 1 and 3 metres from the shade source; Figure 6 shows the front and back side view of an alternative series array embodiment utilising a continuous counter electrode which is mechanically or laser isolated instead of the PCB for electrical and mechanical connection;

Figure 7 shows a further embodiment of an array formed by directly joining individually formed cells; Figure 8 is an underside view of the array of figure 7 ;

Figure 9 shows one of the cells from the array of figure 7; and

Figure 10 shows the PCB of the array of figure 7. Detailed Description of the Preferred Embodiment

The embodiment of the invention described below involves a design of a solar cell array and a method for the processing of individual cells into an array comprised of multiple cells interconnected in series and/or parallel to achieve any desired electrical output and to provide for a non-uniform appearance of colour. The design involves the specification of individual cells of a suitable size to have low sensitivity to common shading patterns. The design avoids potential problems of reverse bias arising from a series of cells deposited on a single substrate and avoids the need for integrated interconnects and series isolation while still ensuring a high active area. The design can be applied to cells of any shape or size.

The array manufacture method provides for ease of automation and comprises the steps of: series and/or parallel connecting the cells together on either a printed circuit board (usually flexible), solder secured insulated conductive wire or other backing substrate, followed by encapsulation by lamination with or without a filling encapsulant. This invention is suitable to produce flexible dye solar cell arrays which operate under any solar or artificial light conditions without the need for diode protection. The invention allows for ease of matching of cells of different electrical and electrochemical characteristics. In embodiments of the invention, maximum power point voltage (Vmpp) is maintained irrespective of light conditions. Performance results are presented for an array according to an embodiment of the invention (See Figure 5).

Dye solar cells manufactured according to embodiments of the invention can utilise a metallic substrate while still not requiring any diode protection to maintain operating maximum power point.

The invention involves a design of an array of solar cells that is resistant to reverse bias that would normally result in significant changes to the maximum power point and greatly reduced output of the array. The design is particularly applicable to photoelectrochemical solar cells and applies to any substrate material. The design provides for both flexible and rigid applications. One of the most attractive applications is in flexible solar cells, and that example is explained in more detail herein.

Referring to figure 1, a flexible array 10 consists of a flexible printed circuit board (PCB) 12 with a series electrical design consisting of a positive (CE) and negative (WE) contact for each individual cell. It is noted that a series/parallel electrical layout is also contemplated in other embodiments. The PCB 12 in this example is based on 200 um thickness FR4 PCB though any flexible or rigid PCB material would suit. In the embodiment shown in Figure 1, 32 cells 14 are assembled into an array. An inorganic yellow pigment has been added to each of the cells at the time of producing the cells to provide for variations in colour between cells, and for variations in colour across a single cell. These variations in colour endow the array with a camouflage appearance. The invention allows for the electrical connection of a multiplicity of arrays to achieve a desired output. Additionally a multiplicity of arrays when not in use can be folded and stored in the area of an individual array. Referring to figure 2A, a large array 100 is shown intended for military use which is formed from nine of the modules 10 of figure 1. The modules 10 are mounted along a sheet of fabric 102 which has a camouflage effect finish. A cable 104 facilitates electrical connection of the large array 100. The camouflage effect of the fabric continues the camouflage effect of the cells themselves, thus further enhancing the camouflage effect.

Referring to figure 2B, the large array 100 of figure 2A is shown partially folded for storage in a concertina like manner. At figure 2C, the large array is shown totally folded up for storage.

Referring to Figures 3 and 4, the track layout of the PCB 12 of Figure 1 is shown in more detail. The front side of the PCB is shown in Figure 3 and the contacts for the working electrode and the counter electrodes can be seen set out in contact pairs 16, 18. This embodiment utilises a single sided wrap around design which can be applied to rigid and flexible PCBs. The use of alternative through-hole double sided PCB substrates facilitates the inclusion of protection diodes between interconnected cells to aid array robustness in the hard partial shade for extended periods (such as the permanent shading from a item situated on the array).

In figure 4, the PCB is shown from the reverse side. The PCB is largely transparent, and is shown populated with cells 14 which are visible through the PCB 12.

The cells 14 may be provided in various colours including brown, black, yellow and green applied to the flexible PCB 12 substrate to achieve electrical interconnection and encapsulated with a camouflage pattern laminate finish to provide for excellent blending of cell and substrate colouration and environmental encapsulation.

Actual performance is demonstrated in Figure 5. This plot shows current (I_sc (mA) primary y- axis) and maximum power (Pmax (mW) secondary y- axis) versus voltage ((V) x-axis) for an example 32 solar cell array prepared according to figure 1 when exposed to various illumination levels including tree shading at a distance of 1 and 3 metres from the shade source. These results show very similar current and maximum power results irrespective of degree of incurred shading. This highlights the achievable robustness of solar cell arrays made according to the invention. The accuracy of the PCB layout provides for high active area of cells in each array. The size, flexibility and number of independent solar cells may vary both within each array and between arrays. In the case of photoelectrochemical solar cells, cells of different colours or reflectivity can be utilised and matched by surface area modification to obtain common current for series interconnection. The changes in shape, reflectivity and colour produce a camouflage effect. There is no requirement to maintain the same shape of cell. The design allows for changes of size and shape of the cells by modifications to the PCB layout. For the same photoelectrochemical couple, the requirement is to maintain a common area for each cell. This requirement is relaxed when more than one photoelectrochemical couple is utilised. In the case of a dye solar cell a camouflage effect can be achieved by modification to the semiconductor, dye and/or electrolyte to achieve colour variations between and within the cells. When the assembled cells are combined with a camouflage patterned background as seen in figure 2A the camouflage effect is further enhanced. The use of low mass substrates for the cells and thin flexible PCB such as polyimide allows for creation of a lightweight flexible and durable solar cell array. The design allows for inclusion or exclusion of protection diodes for use with solar cells that suffer significant reverse bias when series connected and subjected to exposure to variable light. Solar cells can be applied manually and/or automatically using pick and place automation equipment. The cells achieve electrical contact to the PCB via ultrasonically applied low temperature solder wire, low-temperature solder paste, low- temperature Silver paste or alternative low-temperature conductive ink applied by screen printing or needle/jet dispenser to WE, CE and/or PCB. This electrical design results in a solar cell array with consistent electrical properties irrespective of illumination conditions. These include maintained high charging voltage (Maximum power point voltage (Vmp)) at all light levels including dappled shading conditions whereby individual cells are exposed to zero direct illumination at the same time as a neighbouring cell is under full sun illumination. Effective electrical and mechanical connection between the cell busbar and

PCB substrate can be achieved via various means including solder secured Copper wires, pins, eyelets, spade clips, crimps, rivets, conductive adhesive coated conductive tape or a combination thereof. All can be applied and secured either manually or automatically using pick and place equipment. Referring to figures 7 & 8, another embodiment of array 50 is shown which is further reduced in weight due largely to a significant reduction in size of the PCB. The cells in the array are attached to the array both physically and electrically at one edge of each cell to a support structure in the form of PCB 56. In this embodiment, the individual cells 54 are formed with tabs 58, 59 (see figure 9) protruding from one end. The tabs are continuations of the working electrode and counter electrodes substrates and thus are electrically connected to the respective working and counter electrodes within the cell. The modules 54 are connected in series or in parallel with a conductive material such as Cu tape in combination with mechanical fastening means in the form of spade connectors 52. The tabs are sandwiched between PCB 56 and the spade connector. The track layout of the PCB is shown in figure 10. Tracks 60 are defined on the PCB substrate 62. The tracks 60 form interconnects between the cells. This embodiment is assembled by laying out the spade connectors 52, placing the cells 54 with their tabs 58,59 overlaying the spade connectors 52, then laying the PCB 56 on top. The spade connectors are then pressed into a closed position by way of a machine. In other embodiments the mechanical fastening means may include eyelets, rivets, pins or a heat activated closure. The array 10 may be encapsulated in a protective cover. The encapsulation of the array is carried out by hot or cold lamination or vacuum sealing with an encapsulant such as polyurethane. The outer polymeric layer may be textured or otherwise modified to enhance camouflage capability or to maximise light transmission. The resultant arrays have lower sensitivity to angle or quality of the light, have shade tolerance and have lower sensitivity to temperature fluctuations.

The cells in an array may be of differing colours as well as differing shapes and sizes. The dimensions and colours of the cells can be selected to give an overall camouflage effect. In particular, colour variations between cells may be achieved by way of any or all of the following techniques:

• variations in dyes between cells

• variations in the characteristics of the particles of the semiconductor between cells

• variations the composition of redox electrolyte between cells • variations in the amount and/or concentration of the catalyst deposited as the counter-electrode between cells

• addition of a pigment to the electrolyte or to the dye of at least one of the cells

• variations in the reflectivity of the working electrode between cells

An overall camouflage appearance may also be contributed to by making the surface and/or bulk absorption and reflection characteristics of the transparent cover to be non-uniform. Further the substrate may utilise a camouflage pattern which is achieved by either a pattern of colours or areas of varying reflectivity.

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated. Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.

Claims

CLAIMS:

I. An array of solar cells, wherein the array exhibits variations in colour across the array. 2. An array of solar cells according to claim 1 wherein the cells are located on a substrate.

3. An array of solar cells according to either of claim 1 or claim 2 wherein the solar cells are of varying dimensions or areas.

4. An array according to claim 3 wherein the solar cells are provided in a range of shapes including circles, trapezoids, rectangles, or squares.

5. An array according to any preceding claim which is flexible.

6. An array according to any preceding claim wherein the solar cells are photoelectrochemical cells.

7. An array of solar cells according to claim 6 wherein the cells are dye solar cells.

8. An array according to any preceding claim wherein the cells are electrically interconnected by a printed circuit board (PCB) or a continuous substrate such as the working electrode (WE) or counter electrode (CE).

9. An array according to claim 8 wherein the PCB is flexible. 10. An array according to either of claims 8 or 9 wherein the PCB design allows for inclusion of diodes.

I 1. An array according to any one of claims 8 to 10 which includes an external connection point which is attached to the PCB via a knitted, solder paste adhered, rivet, pin, eyelet and/or soldered positive and negative contact/s or a combination thereof. 12. An array according to any one of claims 8 to 11 wherein the array is formed by joining cells via any one of conductive adhesive coated tape, wire, cable, metal braid, polyimide strip, rivets, eyelets, pins, spade clips, crimp terminals or a combination thereof.

13. An array according to any preceding claim wherein the cells utilise metal substrates for one of their electrodes.

14. An array according to claim 13 wherein the substrate includes any one of titanium, steel, coated steel, aluminium or alloys thereof.

15. An array according to any preceding claim wherein at least one of the cells is flexible. 16. An array according to any preceding claim wherein the substrate utilises a camouflage pattern which is achieved by either a pattern of colours or areas of varying reflectivity.

17. An array according to any preceding claim wherein the array is encapsulated in a substantially transparent cover which is of low light reflectivity.

18. An array according to claim 17 which is encapsulated by hot lamination, cold lamination and/or vacuum sealing or a combination thereof. 19. An array according to either of claims 17 or 18 wherein the surface and/or bulk absorption and reflection characteristics of the transparent cover are non-uniform.

20. An array according to any preceding claim wherein there is a colour variation between cells in the array.

21. An array according to any preceding claim wherein there is a colour variation within cells in the array.

22. An array according to either of claim 20 or 21 wherein the colour variation is achieved by variations in dyes between cells.

23. An array according to either of claims 20 or 21 wherein the colour variation is achieved by variations in the characteristics of the particles of the semiconductor between cells.

24. An array according to either of claims 20 or 21 wherein the colour variation is achieved by variations in the composition of redox electrolyte between cells.

25. An array according to either of claims 20 or 21 wherein the colour variation is achieved by variations in the amount and/or concentration of the catalyst deposited as the counter-electrode between cells.

26. An array according to either of claims 20 or 21 wherein the colour variation is achieved by the addition of a pigment to the electrolyte or to the dye of at least one of the cells.

27. An array according to claim 26 wherein the pigment includes an inorganic pigment.

28. An array according to either of claims 20 or 21 wherein the colour variation is achieved by variations in the reflectivity of the working electrode between cells.

29. An array according to either of claims 20 or 21 wherein the colour variation gives rise to an overall camouflage appearance. 30. A portable charging device formed from a multiplicity of arrays according to any preceding claim which are connected together and may be folded in a concertina- like manner for storage.

31. A method of forming an array of cells according to any one of claims 1 to 29 including the steps of testing and matching the electrical performance of each cell prior to assembly based on measurement of short circuit current per area.

32. An array of solar cells, wherein the cells are physically and electrically connected in the array at one edge of the cell.

33. An array according to claim 32 wherein the cells include tabs and are physically and electrically connected by way of the tabs.

34. An array according to either of claims 32 or 33 wherein the connected edges of the cells are oriented towards a centre line of the array. 35. An array according to either of claims 32 or 33 wherein the cells are physically and electrically connected in the array by way of a support structure.

36. An array according to claim 35 wherein the support structure includes a printed circuit board (PCB).

37. An array of solar cells wherein the cells are located on a substrate.