WO2006005116A1

WO2006005116A1 - Laser-formed electrodes for solar cells

Info

Publication number: WO2006005116A1
Application number: PCT/AU2005/001006
Authority: WO
Inventors: Jiun-Hua Guo; Peter John Cousins; Jeffrey Ellis Cotter; Malcolm David Abbott
Original assignee: Newsouth Innovations Pty Limited
Priority date: 2004-07-08
Filing date: 2005-07-08
Publication date: 2006-01-19

Abstract

A method of forming electrodes for solar cells, the method comprising: depositing a dielectric layer (300) on a surface of a semiconductor layer (302) of the solar cell, laser ablating the dielectric layer to form a series of openings (304), each opening extending through the entire thickness of the dielectric layer (300), forming doped regions (305) in the semiconductor layer exposed in the openings, forming metal-semiconductor electrical contacts in the respective openings, wherein deposited metal is in contact with the formed doped semiconductor regions (305) through the respective openings (304), and forming a metal contact (306) electrically interconnecting the metal-semiconductor contacts, wherein the metal contact is formed such that the respective openings (304) are filled with metal through the entire thickness of the dielectric layer (300) and the metal interconnects adjacent metal-semiconductor contacts.

Description

Laser-formed Electrodes for Solar Cells

FIELD OF INVENTION

The present invention relates broadly to a method for forming electrodes for solar cells, and to a solar cell.

BACKGROUND

In the design of high-efficiency solar cells, it is desirable to reduce the metal-to- semiconductor interface in the contacting of the semiconductor. It is also desirable to form regions of heavy doping beneath the regions of the metal-to-semiconductor interface. These make the recombination usually associated with the metal-to- semiconductor interface smaller, which in turn leads to higher output voltages to the solar cell.

On the other hand, the contacts need to be sufficiently "large" and continuous to provide good ohmic contacts along the contact grid, which typically includes a grid of conductor fingers for the p-contact and n-contact electrodes.

It is with the knowledge of this trade-off in the design of high-efficiency solar cells that the present invention has been made and is now reduced to practice.

SUMMARY

In accordance with a first aspect of the present invention there is provided a method of forming electrodes for solar cells, the method comprising depositing a dielectric layer on a surface of a semiconductor layer of the solar cell, laser ablating the dielectric layer to form a series of openings, each opening extending through the entire thickness of the dielectric layer, forming doped semiconductor regions in the regions of the underlying semiconductor layer exposed in the openings; forming metal- semiconductor electrical contacts in the respective openings, wherein deposited metal is in contact with the formed doped semiconductor regions through the respective openings and forming a metal contact electrically interconnecting the metal- semiconductor contacts, wherein the metal contact is formed such that the respective openings are filled with metal through the entire thickness of the dielectric layer and the metal interconnects adjacent metal-semiconductor contacts.

The laser ablating may be performed such that portions of the semiconductor layer of the solar cell substantially underneath the openings are ablated to form pits, and the metal-semiconductor electrical contacts are formed such that the pits are filled with metal and the metal is in electrical contact with the sidewalls of the pits adjoining the underlying semiconductor layer of the solar cell.

The laser ablating may be performed such that portions of the semiconductor layer of the solar cell substantially underneath the openings are melted and recrystallised, thereby dissolving or evaporating the dielectric layer, and the metal- semiconductor electrical contact is formed such that the openings are filled with metal and the metal is in electrical contact with the uηderlying semiconductor layer of the solar cell.

An electrical connection may be formed to either an emitter layer or a base layer of the solar cell.

The forming of the doped semiconductor regions may be performed prior to filling the openings or pits with the metal.

The dielectric layer, or a deposited ancillary layer, may comprise dopant atoms, and the doping of the surface regions of the semiconductor layer comprises melting the surface regions of the semiconductor layer during the ablating of the dielectric layer such that portions of the dielectric layer or the ancillary layer containing the dopant atoms dissolve in the molten surface regions and reforms as a doped semiconductor layer upon recrystallisation.

The ancillary layer may comprise dopant atoms and is deposited over the dielectric layer after the formation of the openings and the method further comprises a subsequent thermal heating step to diffuse dopants from the ancillary layer into the underlying semiconductor layer forming either n-type or p-type polarity doped regions.

Dopant atoms may also be introduced by other techniques such as ion implantation or solid state diffusion whereby the dielectric layer forms a barrier against diffusion and confines the introduction of dopant atoms to the exposed areas.

The metal-semiconductor electrical contacts may be formed by a metal plating deposition process comprising utilising the dielectric layer as a mask layer to confine the metal-semiconductor contact area to the openings.

The metal-semiconductor electrical contacts may be formed by a screen or stencil printed metal deposition process.

A different metal may be used for the forming of the metal-semiconductor electrical contacts and the metal contact.

The metal contact interconnecting the metal-semiconductor contacts may form an electrode grid finger, or an electrode grid busbar or an electrode grid pad for connection to other solar cells and solar modules, or an emitter pad of the solar cell.

Prior to the deposition of the dielectric layer, grooves may be formed in the surface of the semiconductor layer, and the subsequently formed openings are formed at the bottoms of the respective grooves.

A light-sensitive activator may be deposited on the dielectric layer prior to deposition of a metal material that forms the metal contact, and the activator is activated utilising the laser after the formation of the openings in the areas between the openings or pits, thereby allowing the deposition of the metal material to form the metal contact.

The semiconductor layer may comprise silicon.

In accordance with a second aspect of the present invention there is provided a solar cell comprising a dielectric layer on a surface of a semiconductor layer of the solar cell, a series of laser-formed openings formed in the dielectric layer, each opening extending through the entire thickness of the dielectric layer, doped semiconductor regions formed in the openings, metal-semiconductor electrical contacts in the respective openings, wherein deposited metal is in contact with the doped semiconductor regions through the respective openings, and a metal contact electrically interconnecting the metal-semiconductor contacts, wherein the metal contact is formed such that the respective openings are filled with metal through the entire thickness of the dielectric layer and the metal interconnects adjacent metal- semiconductor contacts.

The solar cell may further comprise pits in the semiconductor layer of the solar cell substantially underneath the openings, and the metal contact is formed such that the pits are filled with metal.

An electrical connection may be made to either an emitter layer or a base layer of the solar cell.

Either one of an emitter metal electrode and a base metal electrode may be formed on either the top or bottom surfaces of the solar cell or both the emitter and base electrodes are formed on the top surface or on the bottom surface.

The metal contact may be formed according to a method as defined in the first aspect.

The semiconductor layer may comprise silicon. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only and in conjunction with the drawings, in which:

Figure 1 shows a schematic, perspective view of a solar cell design in accordance with an embodiment of the present invention.

Figure 2 shows a schematic rear view of the solar cell design of Figure 1.

Figure 3 (a) is a schematic diagram illustrating processing steps for fabrication of electrodes in an example embodiment.

Figure 3 (b) shows a microscopic image of a pattern of small pits formed in the surface of a silicon solar cell in an example embodiment.

Figure 4 (a) is a schematic diagram illustrating processing steps for fabrication of small-area contacts and grid electrode fingers whereby the doped semiconductor regions are formed automatically during the small-area formation process in an example embodiment.

Figure 4 (b) shows a microscopic image of a series of small-areas formed thusly in a dielectric coating in an example embodiment.

Figure 5 is a schematic view of a solar cell design in another embodiment of the present invention whereby screen or stencil printed metallization is used to form the interconnection of the small-area contacts.

Figure 6 (a) is a schematic drawing illustrating laser-doped emitter contact openings and laser-doped base contacts in an example embodiment. Figure 6 (b) is a schematic drawing illustrating the laser-doped emitter contact and laser-doped base contact finger after metallisation.

Figures 7 (a) to (c) are schematic cross-sectional diagrams illustrating processing steps for a two-step groove formation process in an example embodiment.

Figure 8 show the current-voltage characteristic curve of a prototype device in an example embodiment.

Figure 9 shows a microscopic image of a prototype device in an example embodiment.

DETAILED DESCRIPTION

Figure 1 shows a schematic, perspective view of a solar cell design 100 in an embodiment of the present invention. The solar cell 100 comprises an n-type or p-type Czochralski (Cz) silicon wafer 102, having a passivated, pyramid texture 104 formed on the front and back surfaces thereof and a diffused pn-junction 120 at the rear surface.

The solar cell design 100 further comprises grid electrodes, e.g. 106 for p-type connection, and grid electrodes, e.g. 108 for n-type connection. Small-area p-type diffused regions, e.g. 110 are formed in the n-type silicon wafer 102 near the rear surface thereof, and in electrical contact with the planar emitter layer 122 of the solar cell and the small-area electrodes, of typically about 300 to about 2000 square microns, for p-type connections, e.g. 106. Small-area n-type diffused regions, e.g. 111 are formed in the n-type silicon wafer 102 near the rear surface thereof, and in electrical contact with the base layer of the solar cell - in the example embodiment, the n-type silicon wafer 102 - and the small-area grid finger electrodes for n-type connections, e.g. 108.

Figure 2 shows a schematic rear view of the n-type silicon wafer 102 with the p- contact electrode connections e.g. 106 and n-contact electrode connections e.g. 108. Turning now to Figure 3 (a), there are schematically illustrated processing steps for fabrication of the small-area electrode connections e.g. 106 or 108 (Figure 1) in the example embodiment. Initially, a dielectric coating 300 is deposited on the rear surface of a n-type silicon wafer 302. A series of spaced laser pulses is then utilised to ablate the dielectric coating 300 and underlying portions of the silicon wafer 302. Residual slag and damage to the underlying silicon created during the ablation process is then removed from the pits e.g. 304 using a chemical etching process.

Smaller and more widely spaced laser pulses are used such that the ablated pits e.g. 304 are not contiguous, unlike in previous techniques where a series of larger, closely spaced laser pulses is used to ablate the silicon, forming a contiguous line of pits, which is referred to as a groove.

Figure 3 (b) shows a microscopic image of a serial pattern of small pits e.g. 310 formed in the surface of a silicon solar cell, eg. 312, in an example embodiment.

Returning now to Figure 3 (a), regions of heavy doping, e.g. of a range from about 5 to about 15 ohms per square, of either n-type or p-type polarity, are formed in the surface regions e.g. 305 of the ablated pits e.g. 304 in the example embodiment, allowing electrical contact to either of the emitter layer 307 or the base layer 302 of the solar cell structure. It will be appreciated that for the fabrication of the p-contact (emitter layer 307 in the example embodiment) electrode contacts a heavily doped p-polarity region e.g. 305 is formed in the pits e.g. 304. Similarly for the n-contact (base layer 302 in the example embodiment) electrode contacts a heavily doped n-type polarity region e.g. 309 is formed in the pit e.g. 311. Different known techniques may be used to achieve the p- or n-polarity region accordingly. The formation of the p-type contact in one embodiment of the present invention will be described below with reference to Figures 4 (a) and (b).

A key advantage of this technique in the example embodiment is that the initial laser-formed openings and corresponding pits e.g. 304 lead to a much smaller total metal-semiconductor interface area on the solar cell compared to the previous laser groove technique. Another key advantage of this technique in the example embodiment is that the semiconductor regions under the metal are heavily doped. As such, the recombination usually associated with the metal-to-semiconductor interface is made significantly smaller and this leads to higher output voltages for the solar cell.

Subsequent to.the diffusion process described above, a suitable metal deposition process such as screen printing is applied to fill the pits with metal and interconnect the individual openings to form a contiguous electrode. The pits e.g. 304 are filled with the metal to form electrical contact to the underlying metal-to-semiconductor interface and the printing mask (not shown) is designed to interconnect the openings to form a contiguous electrode finger 306.

In another embodiment, metal is deposited by a plating process, whereby the metal is deposited first inside the small pits e.g. 304, filling the pit completely. Additional metal is also deposited in the regions between the pits e.g. 304, eventually interconnecting them to form a contiguous electrode finger.

It is noted that the same or similar techniques can also be applied to the solar cell's external contact pad. It will be appreciated that this also results in a dramatic decrease in the metal-semiconductor contact area of the contact pads, and further potentially increases in the cell performance.

In Figure 4 (a), in the example embodiment the dielectric coating 400 contains suitable p-dopant atoms. A series of spaced laser pulses is used to melt the dielectric coating 400 in dot type regions e.g. 402, thereby dissolving or evaporating the dielectric coating 400. During that process, some of the dielectric coating 400 material dissolves into regions of molten silicon e.g. 404 underneath the dot 402, and is incorporated into the silicon as it recrystallises, thus forming a p-polarity region e.g. 404 in the n-type wafer 406. Furthermore, by the subsequent application of a different dielectric coating containing n-type dopants, a n-polarity region suitable for the n-type contact is formed by a similar process.

It will be appreciated that in the process described above, the silicon will melt to a depth that is sufficient to extend through a surface diffused region (for example 412) and the heavily diffused region that forms will also extend the through the diffused region to make electrical contact to the underlying semiconductor layer 406. Depending on the polarity of the heavily diffused regions, contact to either one of the surface diffused region or the base layer region, for example semiconductor layer 406, will be facilitated.

In an alternative embodiment, an ancillary layer containing suitable dopant atoms may be deposited on top of the dielectric coating prior to the laser ablating. During the laser ablating, some of the ancillary layer material dissolves into regions of molten silicon and is incorporated into the silicon as it recrystallises.

In an alternative embodiment, an ancillary layer containing suitable dopant atoms may be deposited on top of the dielectric coating after the laser ablating. In a subsequent thermal diffusion step, dopants from the ancillary layer diffuse into the semiconductor layer, thereby forming a heavily doped region in the semiconductor regions exposed in the openings or pits.

In an alternative embodiment, dopant atoms may also be introduced by other techniques such as ion implantation or solid state diffusion whereby the dielectric layer forms a barrier against diffusion and confines the introduction of dopant atoms to the exposed areas.

Figure 4 (b) shows a microscopic image of laser-formed openings e.g. 412 formed in a dielectric coating 414 on a rear surface of an n-type silicon wafer (not shown).

It will be appreciated that in the example embodiment described above with reference to Figures 4 (a) and (b), the solar cell fabrication process is additionally simplified by eliminating two processing steps in the fabrication sequence. In previous techniques, two processing steps are required subsequent to the laser ablation groove formation. The first is a chemical etching process to remove the slag by-product and damage formed during ablation. The second is a solid-state diffusion of dopant atoms into the walls of the groove, forming either p-doped silicon region (for the cathode connection) or and n-doped silicon region (for the anode). The diffused regions are necessary for previous high-performance devices. It is noted that the process illustrated in Figure 4 (a) may also be utilised for dielectric materials which do not contain dopant atoms, for forming a laser dot pattern without ablating the underlying silicon, only melting it slightly. In such embodiments, known techniques may subsequently be used for the doping of the surface regions underneath the openings.

Subsequent to the diffusion process described above, a suitable metal deposition process such as screen printing is applied to fill the pits with metal and interconnect the individual openings to form a contiguous electrode. The openings e.g. 402 are filled with the metal to form electrical contact to the underlying silicon layer and the printing mask is designed to interconnect the metal in the contact openings to form a contiguous electrode finger 410.

As shown in Figure 5, in such an embodiment the screen or stencil printed metallisation 500 is formed over a dielectric layer 502 in which laser-formed openings or contact openings e.g. 504 are formed in a similar manner as described for the previous embodiment with reference to Figures 4 (a) and (b). The contact areas e.g. 506 corresponding to the openings 504 can be separately diffused using known techniques for buried contact solar cells or laser diffused in accordance with the previous embodiments described above with reference to Figures 3 (a) and (b) and 4 (a) and (b).

The use of printed metallisation in this example embodiment has the advantages of allowing the laser-formed contact openings to be spaced at any arbitrary distance. The use of printed metallization in this example embodiment also has the advantage that, by the use of the heavily diffused regions in the openings, the requirements on the metal pastes are relaxed in terms of providing high conductance and low contact resistance, and that both electrodes may be deposited in a single printing step using a single type of metal paste, reducing the cost and complexity of manufacture. Printed metallization is also a well understood and inexpensive metal deposition technique, and application of printed metallization to solar cell contacting can thus provide additional advantages such as reducing costs and reducing complexity of the fabrication process.

The concept of a small-area contact finger can be extended in other embodiments to replace the planar emitter region (e.g. 122, Figure 1) of the solar cell with a series of widely spaced, small-area openings formed by the laser process and with a suitable technique for the diffusion of n-type or p-type dopants, as described above with reference to Figures 3 (a) and 4 (a). As illustrated in Figures 6 (a), the p-type emitter is formed by an array of closely spaced, small-area diffusions e.g. 600 that are subsequently electrically connected together by a screen or stencil printing metal deposition of metal, or by the metal overplating process to form a plurality of interconnected, small-area emitters e.g. 602, as illustrated in Figure 6 (b).

In such an embodiment, the total area of the emitter is reduced, and contributes to reduce the overall recombination in the solar cell, thus improving efficiency. Also illustrated in Figures 6 (a) and (b) are laser-doped, n-type base contacts, e.g. 604 formed in a manner as illustrated in Figure 5 (a). The small-area diffusions e.g. 600 and n-type based contacts e.g. 604 or formed in the diffused surface field (n-type) at the rear surface of the n-type silicon wafer 608 in the example embodiment. As shown in Figure 6 (b), after metallisation, n-type electrode grid fingers e.g. 606 are formed by the overplating process. Also has shown in Figure 6 (b) larger area small-area emitter pads e.g. 610 are formed by the overplating process.

In another embodiment, the laser-formed contact openings can be placed close enough together to form a contiguous laser-line, much like the previous techniques for buried contact solar cells, except that the laser-line does not form a contiguous groove. The laser-formed lines can be separately diffused, using known techniques for buried contact solar cells, or laser diffused as described for the previous embodiments above. The metallisation can be applied using the known techniques for buried contact solar cells, or by aligned screen or stencil printing. If plated metallisation is utilised, in such an embodiment the laser-line has the advantage of not requiring substantial over-plating to form the contiguous metal fingers, and thus can allow very narrow metal fingers to be formed. Such an embodiment has applications for solar cells where one of the metal electrode patterns is formed on the front surface of the solar cell.

The small-area technique may also be implemented as a 2-step groove formation processing. One such example embodiment will now be described, with reference to Figures 7 (a) to (c). Here, two laser processing steps are combined to form an advanced laser groove pattern with many of the benefits mentioned for the previously described embodiments. As illustrated in Figure 7 (a), laser grooves e.g. 700 are initially formed in the silicon wafer 702 by the ablation process previously described. After several standard processing steps to remove the slag by-product and damage from the grooves e.g. 700 and to coat the surface of the grooves e.g. 700 with a dielectric film 704, as illustrated in Figure 7 (b), a second pass of the laser is made to form an opening e.g. 706 at the bottom of the original groove e.g. 700, as illustrated in Figure 7 (c), by the process described above with reference to Figures 4 (a) and (b). The opening e.g. 706 can either be a line along the bottom of the groove e.g. 700 or a string of laser contact openings. In the case of the string of laser openings, the groove e.g. 700 will help to confine the overplating to the direction of the string of openings, aiding in forming the contiguous metal finger 708 and maintaining a narrow electrode finger profile at the same time.

The concept of this embodiment can be applied in several ways, including forming laser lines at the bottom of grooves, forming small-area laser openings at the bottom of the grooves (both as described above) and small-area forming laser openings at the bottom of pits. By taking advantage of a short focal length final objective lens for the laser, it may also be possible to form openings in dielectric coating at the top or bottom of surface features of the solar cell, such as e.g. pyramid textures.

In another embodiment of the present invention, a light-sensitive activator is placed on the surface of the solar cell before the formation of the small-area contacts. In the first pass across the solar cell, the laser forms a string of widely spaced small-area contacts as described for the previous embodiments above. In the subsequent pass, the laser is adjusted so as to activate the surface of the solar cell to allow the subsequent deposition of a layer of metal onto the protective dielectric by a plating process. As in previous solar cell designs, the protective dielectric prevents deposition of the metal except where it has been previously activated.

This embodiment allows the widely spaced small-area contacts to be joined up by the metal deposition step. Activation could be achieved by a number of techniques, including inducing buried charge within the dielectric layer (thereby activating it), by a photo-induced chemical reaction in the activator, and by a photo-induced reaction between the dielectric and a separate activator (e.g. aluminium on silicon dioxide, whereby the aluminium reduces the silicon dioxide, leaving a silicon rich surface after removal of the aluminium and alumina. The silicon-rich layer serves as the nucleation site for plating).

Figure 8 shows the current-voltage characteristic curve 800 of a prototype device embodiment. Open circuit voltages for the first batch of prototype devices were found to be excellent, at around 670 mV and short-circuit current was found to be adequate given the device structure (no texturisation on the front surface, SiO₂ single-layer antireflection coating). It can be expected that with proper texturisation, anti-reflection coating, hydrogen surface passivation, and by minimising the shunt and series parasitic losses, an efficiency of 21% or greater is possible.

Figure 9 shows a microscopic image of one of the working prototypes 900.

Solar cell designs in example embodiments of the invention can incorporate a number of features that lead to high efficiency and low cost:

1. Lightly diffused, well passivated emitter,

2. Minimal emitter area

2. Localized, heavily diffused regions under the metal contacts,

3. Minimal area electrodes, with low optical profiles, 4. Commercially proved high-efficiency technology.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

For example, it will be appreciated that the present invention is not limited to silicon solar cells, but also applies to other suitable semiconductor material solar cells.

Claims

1. A method of forming electrodes for solar cells, the method comprising depositing a dielectric layer on a surface of a semiconductor layer of the solar cell, laser ablating the dielectric layer to form a series of openings, each opening extending through the entire thickness of the dielectric layer, forming doped semiconductor regions in the regions of the underlying semiconductor layer exposed in the openings, forming metal-semiconductor electrical contacts in the respective openings, wherein deposited metal is in contact with the formed doped semiconductor regions through the respective openings and, forming a metal contact electrically interconnecting the metal-semiconductor contacts, wherein the metal contact is formed such that the respective openings are filled with metal through the entire thickness of the dielectric layer and the metal interconnects adjacent metal-semiconductor contacts.

2. The method as claimed in claim 1 , wherein the laser ablating is performed such that portions of the semiconductor layer of the solar cell substantially underneath the openings are ablated to form pits, and the metal-semiconductor electrical contacts are formed such that the pits are filled with metal and the metal is in electrical contact with the sidewalls of the pits adjoining the underlying semiconductor layer of the solar cell.

3. The method as claimed in claims 1 to 2, wherein the laser ablating is performed such that portions of the semiconductor layer of the solar cell substantially underneath the openings are melted and recrystallised, thereby dissolving or evaporating the dielectric layer, and the metal-semiconductor electrical contact is formed such that the openings are filled with metal and the metal is in electrical contact with the underlying semiconductor layer of the solar cell.

4. The method as claimed in any one of claims 1 to 3, wherein an electrical connection is formed to either an emitter layer or a base layer of the solar cell.

5. The method as claimed in any one of claims 1 to 4, wherein the forming of the doped semiconductor regions is performed prior to filling the openings or pits with the metal.

6. The method as claimed in claim 6, wherein the dielectric layer, or a deposited ancillary layer, comprises dopant atoms, and the doping of the surface regions of the semiconductor layer comprises melting the surface regions of the semiconductor layer during the ablating of the dielectric layer such that portions of the dielectric layer or the ancillary layer containing the dopant atoms dissolve in the molten surface regions and reforms as a doped semiconductor layer upon recrystallisation.

7. The method as claimed in claim 6, wherein the ancillary layer comprises dopant atoms and is deposited over the dielectric layer after the formation of the openings and the method further comprises a subsequent thermal heating step to diffuse dopants from the ancillary layer into the underlying semiconductor layer forming either n- type or p-type polarity doped regions.

8. The method as claimed in claim 6, dopant atoms are incorporated by other techniques such as ion implantation or solid state diffusion whereby the dielectric layer forms a barrier against diffusion and confines the introduction of dopant atoms to the exposed areas.

9. The method as claimed in any one of claims 1 to 8, wherein the metal- semiconductor electrical contacts are formed by a screen or stencil printed metal deposition process.

10. The method as claimed in any one of claims 1 to 8, wherein the metal- semiconductor electrical contacts are formed by a metal plating deposition process comprising utilising the dielectric layer as a mask layer to confine the metal- semiconductor contact area to the openings.

11. The method as claimed in any one of claims 1 to 10, wherein a different metal is used for the forming of the metal-semiconductor electrical contacts and the metal contact.

12. The method as claimed in any of claims 1 to 11 , wherein the metal contact interconnecting the metal-semiconductor contacts forms an electrode grid finger, or an electrode grid busbar or an electrode grid pad for connection to other solar cells and solar modules, or an emitter pad of the solar cell.

13. The method as claimed in any one of claims 1 to 12, wherein prior to the deposition of the dielectric layer, grooves are formed in the surface of the semiconductor layer, and the subsequently formed openings are formed at the bottoms of the respective grooves.

14. The method as claimed in any one of claims 1 to 13, wherein a light-sensitive activator is deposited on the dielectric layer prior to deposition of a metal material that forms the metal contact, and the activator is activated utilising the laser after the formation of the openings in the areas between the openings or pits, thereby allowing the deposition of the metal material to form the metal contact.

15. The method as claimed in any one of claims 1 to 14, wherein the semiconductor layer comprises silicon.

16. A solar cell comprising a dielectric layer on a surface of a semiconductor layer of the solar cell a series of laser-formed openings formed in the dielectric layer, each opening extending through the entire thickness of the dielectric layer, doped semiconductor regions formed in the openings, metal-semiconductor electrical contacts in the respective openings, wherein deposited metal is in contact with the doped semiconductor regions through the respective openings, and a metal contact electrically interconnecting the metal-semiconductor contacts, wherein the metal contact is formed such that the respective openings are filled with metal through the entire thickness of the dielectric layer and the metal interconnects adjacent metal-semiconductor contacts.

17. The solar cell as claimed in claim 16, further comprising pits in the semiconductor layer of the solar cell substantially underneath the openings, and the metal contact is formed such that the pits are filled with metal.

18. The solar cell as claimed in claims 16 or 17, wherein an electrical connection is made to either an emitter layer or a base layer of the solar cell.

19. The solar cell as claimed in any one of claims 16 to 18, wherein the metal contact interconnecting the metal-semiconductor contacts forms an electrode grid finger, or an electrode grid busbar or an electrode grid pad for connection to other solar cells and solar modules, or an emitter pad of the solar cell.

20. The solar cell as claimed in any one of claims 16 to 19, wherein either one of an emitter metal electrode and a base metal electrode is formed on either the top or bottom surfaces of the solar cell or both the emitter and base electrodes are formed on the top surface or on the bottom surface.

21. The solar cell as claimed in any one of claims 16 to 20, wherein the metal contact is formed according to a method as defined in any of the claims 1 to 15.

22. The solar cell as claimed in any one of claims 16 to 21 , wherein the semiconductor layer comprises silicon.