METHOD OF MANUFACTURING A PHOTOVOLTAIC CELL

Abstract

Method of manufacturing a photovoltaic cell, comprising the steps of: providing a photovoltaic conversion device; providing a transparent conductive oxide layer upon at least a first face of said photovoltaic conversion device; forming a self-assembled monolayer on said transparent conductive oxide layer, said self-assembled monolayer being based on molecules terminated by at least one group F which is chosen from: a phosphonic acid group, a P(O)O.sub.2.sup.−M.sup.+ group, a OPO.sub.3H.sub.2 group, or an OP(O)O.sub.2.sup.−M.sup.+ group, wherein M.sup.+ is a metal cation; patterning said self-assembled monolayer so as to define at least one plateable zone in which said transparent conductive oxide layer is exposed; plating a metal onto said at least one plateable zone.

Claims

1. Method of manufacturing a photovoltaic cell, comprising the steps of: providing a photovoltaic conversion device; providing a transparent conductive oxide layer upon at least a first face of said photovoltaic conversion device; forming a self-assembled monolayer on said transparent conductive oxide layer, said self-assembled monolayer being based on molecules terminated by at least one functional group F which is chosen from: a phosphonic acid group, a PO.sub.2.sup.−M.sup.+ group, a OPO.sub.3H.sub.2 group, or an OP(O)O.sub.2.sup.−M.sup.+ group, wherein M.sup.+ is a metal cation; patterning said self-assembled monolayer so as to define at least one plateable zone in which said transparent conductive oxide layer is exposed; plating a metal onto said at least one plateable zone.

2. Method according to claim 1, wherein said self-assembled monolayer is directly applied over at least 90% of said transparent conductive oxide layer and in contact therewith.

3. Method according to claim 1, wherein no intervening deposition steps are carried out on said transparent conductive oxide layer before forming said self-assembled monolayer.

4. Method according to claim 1, wherein said step of plating a metal is carried out directly upon the exposed transparent conductive oxide layer in said at least one plateable zone, with or without use of a seed layer.

5. Method according to claim 1, wherein said molecules have at least one tail moiety comprising at least one of: a straight alkyl chain comprising at least two carbon atoms; a straight alkyl chain comprising at least two carbon atoms in which at least one hydrogen is substituted by a halogen; a branched alkyl chain comprising at least two carbon atoms; a straight perfluorinated alkyl chain comprising preferably from 1 to 100 atoms of carbon; a branched perfluorinated alkyl chain comprising preferably from 1 to 100 atoms of carbon; one or more aromatic rings; (CF(CF.sub.3)CF.sub.2O).sub.q(CF.sub.2).sub.tCF.sub.3 with q between 0 and 100, and t between 2 and 100; (CF.sub.2CF(CF.sub.3)O).sub.q(CF.sub.2).sub.tCF.sub.3 with q between 0 and 100, and t between 2 and 100; (CF.sub.2CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.tCF.sub.3 with q between 0 and 100, and t between 2 and 100; (CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.tCF.sub.3 with q between 0 and 100, and t between 2 and 100.

6. Method according to claim 1, wherein said molecules are of the general formula:
F—R1-R′—R2 wherein R1 is one of: an alkyl chain, an alkyl chain in which at least one hydrogen atom is substituted with a halogen, an aryl chain, an alkylaryl chain, an aralkyl chain, an aralkyl chain in which at least one hydrogen atom is substituted with a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl chain, an oligothioether chain of formula (CH.sub.2CH.sub.2X).sub.n with X being an O or S atom and n being between 1 and 25, R′ is one of: (CH.sub.2).sub.m with m between 0 and 100, O, S, S—S, NH, O(CO), O(CS), NH(CO), NH(CS), NH(CO)NH, NH—CS—NH, NH(CO)O, NH(CS)O, S(CO), (CO)S, triazolium, R2 is one of: an alkyl chain, an alkyl chain wherein at least one atom of hydrogen is substituted by a halogen, an aryl chain, an alkylaryl, an aralkyl chain, an aralkyl chain wherein at least one atom of hydrogen is substituted by a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.p with X being an O or S atom and p being between 1 and 25, a perfluoroalkyl chain comprising from 1 to 20 carbon atoms, (CF(CF.sub.3)CF.sub.2O).sub.q(CF.sub.2).sub.2CF.sub.3 with q between 0 and 100, (CF.sub.2CF(CF.sub.3)O).sub.q(CF.sub.2)2CF.sub.3 with q between 0 and 100, (CF.sub.2CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.2CF.sub.3 with q between 0 and 100, (CF.sub.2CF.sub.2O).sub.q(CF.sub.2)CF.sub.3 with q between 0 and 100.

7. Method according to claim 6, wherein said molecule is one of: 12,12,13,13,14,14,15,15,15,15-Nonafluoropentadecylphosphonic acid, 12,12,13,13,14,14,15,15,16,16,17,17-Tridecafluoroseptadecylphosphonic acid, 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-Heptadecafluorononadecylphosphonic acid, 10-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyloxy)carbonyl)decylphosphonic acid, 5,7,7-Trimethyl-2-(4,4-dimethylpentan-2-yl)octylphosphonic acid Diethyl-12-pentafluorophenoxydodecylphosphonate, octadecylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octylphosphonic acid.

8. Method according to claim 1, wherein said molecules are of the general formula ##STR00014## wherein: R1 is one of: an alkyl chain, an alkyl chain in which at least one hydrogen is substituted by a halogen, an aryl chain, an alkylaryl, an aralkyl chain, an aralkyl chain in which at least one hydrogen is substituted by a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.n with X being an O or S atom and n being between 1 and 25, R′ is one of: a bond, (CH.sub.2).sub.m with m between 0 and 100, O, S, S—S, NH, O(CO), O(CS), NH(CO), NH(CS), NH(CO)NH, NH—CS—NH, NH(CO)O, NH(CS)O, S(CO), (CO)S, a triazolium bond, R2 is one of: alkyl chain, an alkyl chain in which at least one hydrogen is substituted by a halogen, an aryl chain, an alkylaryl, an aralkyl chain, an aralkyl chain in which at least one hydrogen is substituted by a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.p with X being an O or S atom and p being between 1 and 25, a perfluoroalkyl chain comprising from 1 to 20 carbon atoms, (CF(CF.sub.3)CF.sub.2O).sub.q(CF.sub.2)2CF.sub.3 with q between 0 and 100, (CF.sub.2CF(CF.sub.3)O).sub.q(CF.sub.2).sub.2CF.sub.3 with q between 0 and 100, (CF.sub.2CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.2CF.sub.3 with q between 0 and 100, (CF.sub.2CF.sub.2O).sub.q(CF.sub.2)CF.sub.3 with q between 0 and 100. T is one of: a bond, (CH.sub.2).sub.r with r between 0 and 100, O, S, S—S, NH, O(CO), O(CS), NH(CO), NH(CS), NH(CO)NH, NH—CS—NH, NH(CO)O, NH(CS)O, S(CO), (CO)S, a triazolium bond, R3 is one of: H, an alkyl group, an alkyl group in which at least one hydrogen is substituted by a halogen, an aryl group, a branched alkyl, a branched aryl chain, an aralkyle group, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.s with X being an O or S atom and s being between 1 and 25.

9. Method according to claim 1, wherein said molecules are 10,11-Bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-Heptadecafluorononyl)icosane-1,20-diyldiphosphonic acid.

10. Method according to claim 1, wherein, after said step of plating, said self-assembled monolayer is left in place.

11. Method according to claim 1, wherein said self-assembled monolayer has a thickness or 2 nm to 5 nm, preferably from 3 nm to 4 nm.

12. Method according to claim 1, wherein said self-assembled monolayer is cured in a vacuum oven prior to patterning.

13. Method according to claim 1, wherein said self-assembled monolayer is formed by: a first application of said molecules; a first drying and curing; a second application of said molecules; and a subsequent drying and curing.

14. Method according to claim 1, wherein said patterning is carried out by at least one of: selective laser ablation; reactive ion etching through a mask; selective application of an acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Further details of the invention will appear more clearly upon reading the description below, in connection with the following figures which illustrate:

[0069] FIG. 1: a schematic representation of part of a photovoltaic device according to the invention, this part of a photovoltaic device equally being an intermediate product in the manufacture of said device;

[0070] FIG. 2: a schematic representation of a method according to the invention;

[0071] FIG. 3: photographs of comparative experimental results of the outcome of a first example of a method according to the invention;

[0072] FIG. 4: a confocal microscope image of a nickel track from the experiment of FIG. 3;

[0073] FIG. 5: confocal microscope images of the outcome of a second example of a method according to the invention; and

[0074] FIG. 6: a photograph of experimental results of the outcome of a third example of a method according to the invention.

EMBODIMENTS OF THE INVENTION

[0075] FIG. 1 illustrates schematically a part of a photovoltaic (PV) cell 1 made by the method of the invention as outlined in FIG. 2. This part of a photovoltaic cell 1 constitutes an intermediate product in the manufacture of the final device. It should be noted that only the essential elements have been illustrated, and that further non-illustrated intermediate and outer layers such as passivation layers, substrates, encapsulation layers and so on can also be provided.

[0076] The PV cell 1 comprises a photovoltaic conversion device 3, formed in a first step 101. This PV conversion device 3 comprises at least one photovoltaically active junction (PN, NP, PIN, NIP) based on at least one of thin-film silicon (which may be amorphous, microcrystalline, or micromorph in the case of a tandem cell), crystalline (i.e. monocrystalline) silicon, germanium, Perovskite, quantum dot cells, copper indium gallium selenide, cadmium telluride, dye sensitized cells, plasmonic cells, or any other convenient type. The PV device may be based on single layers of cells, multijunction cells, hybrid cells, etc. The PV conversion device 3 may be patterned as required, and may be front-side contacted, back-side contacted, or bifacially-contacted.

[0077] Upon at least one face of the PV conversion device 3, which may be the light-incident side or the rear side (or both sides in the case of a silicon heterojunction cell), is situated a layer of transparent conductive oxide (TCO) 5, which usually has a thickness in the range of 50 nm to 150 nm, preferably in the range of 80 nm to 120 nm, and is typically also patterned. The most commonly used TCO's are indium tin oxide (ITO), indium zinc oxide (IZO) and aluminium zinc oxide (AZO), although other types such as doped or undoped zinc oxide or tin oxide are also possible. This TCO layer 5 is formed directly or indirectly upon said surface of the PV conversion device 3 in step 102, typically by means of chemical vapour deposition as is generally known.

[0078] On the face of the photovoltaic conversion device 3 opposite to the TCO layer 5 may optionally be situated one or more further layers 7, in function of the cell construction. For instance, this may be one or more of a substrate, one or more encapsulation layers, a further layer of TCO, a further metallic layer, a passivation layer, a transparent or opaque backsheet, a front sheet (e.g. of glass or polymer) or similar, as is generally known.

[0079] The core of the invention is in the manner in which a patterned metallic layer 11 is formed upon the TCO layer 5.

[0080] As noted in the introduction, such layers are typically formed lithographically by means of a photostructured photoresist layer, so as to form metallic features such as electrical tracks, electrical pads and similar, typically from materials such as copper, nickel, nickel phosphor, or silver. This latter can also be directly screen-printed or inkjet-printed as an alternative to a lithographic process.

[0081] According to the present invention, in step 103, a self-assembled monolayer (SAM) 9 is applied to the free surface of the TCO layer 5, for instance by dip coating, spray coating, bar coating, slot-die coating spin coating or similar in a solution of SAM molecules dispersed in a solvent such as ethanol or isopropanol at a suitable concentration of e.g. 1.0 to 20 mmol/L, preferably 2.5 to 10 mmol/L. Coating may take place at room temperature, but also at elevated temperature such as up to 70° C. Although this layer can be selectively applied to the surface, it is typically applied to substantially the whole surface, since this is significantly simpler to carry out while ensuring a uniform thickness, which is typically from 1 nm to 5 nm, preferably from 1.5 nm to 3 nm, further preferably from 1.5 to 2.0 nm. It should be noted that the SAM layer 9 is ideally applied directly to at least 90%, preferably substantially all of the surface of the TCO layer 5, in an unpatterned fashion. This is carried out such that the SAM layer 9 is formed directly on the surface of TCO layer 5, in intimate contact therewith, and prior to any metallisation/plating steps having been carried out.

[0082] SAMs in general are molecular assemblies formed spontaneously on surfaces by adsorption and are organised into more or less large ordered domains, as is generally known from the scientific literature. The SAMs used in the present invention are specially chosen to, on the one hand, bind well to the TCO layer 5, and, on the other hand, to prevent plating where the SAM is present. They also are chemically stable during the subsequent plating process, since such processes are sometimes carried out at high or low pH, as low as pH2, or as high as pH 14, more typically as low as pH 4 or as high as pH 10. Of course, processes at milder pH's such as pH between 5 and 9, preferably between 6 and 8 are also possible, and the present invention is not limited to extreme pH deposition processes.

[0083] To this end, the SAM is based on molecules terminated by at least one functional group F which is one of: a phosphonic acid group, a P(O)O.sub.2.sup.−M.sup.+ group, an OPO.sub.3H.sub.2 group, or an OP(O)O.sub.2.sup.−M.sup.+ group, wherein M.sup.+ is a metal cation such as Na.sup.+ or K.sup.+. This functional group forms a head moiety of the molecule, which binds strongly to the TCO.

[0084] According to one general form, the molecules may have at least one tail moiety comprising one or more of the following: a straight or branched alkyl chain having more than 2 carbon atoms covalently bonded in a chain, a straight or branched perfluorinated alkyl chain comprising preferably from 1 to 100 atoms of carbon, one or more aromatic rings, (CF(CF.sub.3)CF.sub.2O).sub.q(CF.sub.2).sub.tCF.sub.3, (CF.sub.2CF(CF.sub.3)O).sub.q(CF.sub.2).sub.tCF.sub.3, (CF.sub.2CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.tCF.sub.3, (CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.tCF.sub.3 in each case with q between 0 and 100, and t between 2 and 100.

[0085] According to a second general form, the molecules may have the general formula

F—R1-R′—R2

in which F is the head moiety as defined above, and R1-R′—R2 is the tail moiety in which:

[0086] R1 is one of: an alkyl chain, an alkyl chain in which at least one hydrogen atom is substituted with a halogen, an aryl chain, an alkylaryl chain, an aralkyl chain, an aralkyl chain in which at least one hydrogen atom is substituted with a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl chain, an oligothioether chain of formula (CH.sub.2CH.sub.2X).sub.n with X being an O or S atom and n being between 1 and 25. In general, where chains are mentioned, these are typically between 1 and 50 carbons long, preferably between 2 and 50 carbons long, further preferably between 8 to 20 carbons long, and hence also include the smallest group of each category of molecule which comprises only one carbon atom.

[0087] Specific examples of substances falling within this general formula are the following: [0088] 12,12,13,13,14,14,15,15,15,15-Nonafluoropentadecylphosphonic acid

##STR00002## [0089] 12,12,13,13,14,14,15,15,16,16,17,17-Tridecafluoroseptadecylphosphonic acid

##STR00003## [0090] 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-Heptadecafluorononadecylphosphonic acid

##STR00004## [0091] 10-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyloxy)carbonyl)decylphosphonic acid

##STR00005## [0092] 5,7,7-Trimethyl-2-(4,4-dimethylpentan-2-yl)octylphosphonic acid

##STR00006## [0093] Diethyl-12-pentafluorophenoxydodecylphosphonate

##STR00007## [0094] octadecylphosphonic acid,

##STR00008## [0095] decylphosphonic acid,

##STR00009## [0096] dodecylphosphonic acid,

##STR00010## [0097] octylphosphonic acid

##STR00011##

[0098] According to a third general form, said molecules are of the general formula

##STR00012##

[0099] In this formula, F is again a head moiety (of which there are two), and the tail moieties are as illustrated, in which:

[0100] R1 is one of: an alkyl chain, an alkyl chain in which at least one hydrogen is substituted by a halogen, an aryl chain, an alkylaryl, an aralkyl chain, an aralkyl chain in which at least one hydrogen is substituted by a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.n with X being an O or S atom and n being between 1 and 25,

[0101] R′ is one of: a bond, (CH.sub.2).sub.m with m between 0 and 100, O, S, S—S, NH, O(CO), O(CS), NH(CO), NH(CS), NH(CO)NH, NH—CS—NH, NH(CO)O, NH(CS)O, S(CO), (CO)S, a triazolium bond,

[0102] R2 is one of: alkyl chain, an alkyl chain in which at least one hydrogen is substituted by a halogen, an aryl chain, an alkylaryl, an aralkyl chain, an aralkyl chain in which at least one hydrogen is substituted by a halogen, a branched alkyl chain, a branched aryl chain, a branched aralkyl chain, a branched alkylaryl, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.p with X being an O or S atom and p being between 1 and 25, a perfluoroalkyl chain comprising from 1 to 20 carbon atoms, (CF(CF.sub.3)CF.sub.2O).sub.q(CF.sub.2).sub.2CF.sub.3, (CF.sub.2CF(CF.sub.3)O).sub.q(CF.sub.2).sub.2CF.sub.3, (CF.sub.2CF.sub.2CF.sub.2O).sub.q(CF.sub.2).sub.2CF.sub.3, (CF.sub.2CF.sub.2O).sub.q(CF.sub.2)CF.sub.3 with q between 0 and 100.

[0103] T is one of: a bond, (CH.sub.2).sub.r with r between 0 and 100, O, S, S—S, NH, O(CO), O(CS), NH(CO), NH(CS), NH(CO)NH, NH—CS—NH, NH(CO)O, NH(CS)O, S(CO), (CO)S, a triazolium bond,

[0104] R3 is one of: H, an alkyl group, an alkyl group in which at least one hydrogen is substituted by a halogen, an aryl group, a branched alkyl, a branched aryl chain, an aralkyle group, an oligothioether of formula (CH.sub.2CH.sub.2X).sub.s with X being an O or S atom and s being between 1 and 25.

[0105] A specific example of a particularly advantageous molecule fulfilling this general form is: [0106] 10,11-Bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-Heptadecafluorononyl)icosane-1,20-diyldiphosphonic acid

##STR00013##

[0107] After application of the SAM 9, the workpiece can be rinsed if required, e.g. with ethanol, and can then be dried and cured, e.g. in a vacuum oven at e.g. 120° C. for 30 minutes. Other temperatures and times are of course also possible in function of the SAM and solvent used.

[0108] SAM 9 is then subsequently patterned in step 104 to leave plateable zones 9a in which the SAM 9 is removed in order to reveal the underlying TCO layer 5. This patterning can be carried out by various methods such as laser ablation, dry etching through a hard silicon mask by means of oxygen plasma, acid etching, UV-Ozone, corona treatment, mechanical removal, or similar, the patterned SAM layer forming a plating mask. The tail moieties mentioned above are all highly hydrophobic, and the SAM molecules are electrically insulating, and hence plating does not take place where the SAM molecules cover the surface of the TCO layer 5.

[0109] Subsequently, in step 105, the metallic features 11 are plated onto the plateable zones 9a. The metal chosen is typically copper, but nickel, silver, tin, cobalt, titanium, tantalum, tungsten, molybdenum, nickel-phosphor, and alloys of the foregoing and silver are also possibilities. Multiple depositions of the same or different metals are possible, such as a first layer of 2-5 μm of nickel followed by 10-30 μm of copper, capped with 200-300 nm of immersion silver.

[0110] This plating can be carried out using a conventional electroplating bath, a conventional electroless plating (i.e. autocatalytic plating) bath, deposition from aqueous solution of ionic liquids, or similar, by immersing the workpiece therein as is generally known. A seed layer of e.g. a solution or suspension of an appropriate plating catalyst (e.g. a solution or suspension of metal ions, colloid silver, a metal complex or similar) may be applied on the plateable zones 9a prior to plating, as is generally known.

[0111] Subsequently, the PV device 1 can be rinsed and dried.

[0112] Since the SAM layer 9 is very thin and is transparent, it is not always necessary to remove it after plating, removing a significant process step in cases in which this is possible. Indeed, if the formation of the metallic features 11 was the last processing step on the PV device 1 itself, encapsulation and assembly into a module can follow immediately. However, the SAM layer 9 can indeed be removed with an appropriate solvent if required.

[0113] A number of experimental results applying the method are reported below.

Example 1

[0114] A piece of silicon wafer with dimensions 5×5 cm.sup.2 was provided, so as to simulate PV conversion device 3. This was coated with a TCO layer of indium tin oxide with a thickness of 100 nm.

[0115] This workpiece was then rinsed with isopropanol in an ultrasonic bath to remove possible organic contamination, then rinsed in ethanol in an ultrasonic bath and dried. The substrate is then treated with a diffusive oxygen plasma for 15 min at room temperature in order to ensure that the TCO surface is chemically clean.

[0116] The workpiece then immersed in a 5 mmol/L solution of 12,12,13,13,14,14,15,15,15,15-nonafluoropentadecylphosphonic acid in ethanol for 30 minutes at a temperature 70° C. The workpiece was then rinsed in ethanol, and dried. It was then placed for extra curing at 150° C. for 2 hours in a vacuum oven.

[0117] The thus prepared SAM layer 9 of 12,12,13,13,14,14,15,15,15,15-nonafluoropentadecylphosphonic acid was then patterned by covering the sample with a silicon hard mask containing lines of varying width and placed under a reactive ion etching (RIE) oxygen plasma for selective SAM removal. By so doing, plateable zones 9a were created, in which the underlying TCO layer 5 was exposed.

[0118] To create a contact for the electroplating step, the SAM 9 was removed on one edge by dipping in concentrated sulfuric acid (96%) for between 1 and 3 minutes, so as to enable electrical contact with the TCO layer 5. The workpiece and a non-patterned reference workpiece were then placed in an electroplating bath at pH 4 and temperature of 50° C. The electrolyte is chloride free Ni-sulphamate. A constant voltage of 2V was applied during 5 minutes at an electrode contacted with the workpiece or the back side of the workpiece.

[0119] The results of this experiment are shown in FIG. 3. On the left sample, nickel plated lines of various thicknesses (the zones of light coloration) corresponding to the patterning can be seen, whereas there was no nickel deposition on the non-patterned reference sample (the zones of dark coloration) away from the electrical contact zone formed by dipping in sulphuric acid. Furthermore, FIG. 4 illustrates confocal microscope image of one of the nickel lines formed on the patterned sample.

Example 2

[0120] Again, a silicon wafer of dimensions 5×5 cm.sup.2 provided with a TCO layer was used as a workpiece for this experiment, the SAM layer 9 being provided as before.

[0121] In order to pattern the SAM layer 9 so as to define plateable zones 9a in which the surface of the TCO layer 5 is exposed, a Trumpf marking laser was used to laser ablate the SAM along a line.

[0122] The workpiece was then plated as before.

[0123] FIG. 5 illustrates the results of this experiment, the left-hand image being a confocal microscope image of the nickel-plated track, and the right-hand image being a confocal microscope image of an unablated region of the workpiece.

Example 3

[0124] In this example, the substrate is as before, but has dimensions of 15×15 cm2, with a TCO layer 5 on both sides, one of the TCO layers being silver coated with 200 nm thick sputtered silver on the side opposite to the exposed TCO layer 5.

[0125] This workpiece was prepared for SAM coating as before, and was then coated by being manually sprayed with a 5 mmol/L solution of 12,12,13,13,14,14,15,15,15,15-nonafluoropentadecylphosphonic acid. The excess was removed by rinsing in ethanol, and the workpiece was dried. The substrate was then cured at 150° C. for 30 minutes in a vacuum oven. The substrate was then manually sprayed again, rinsed again and placed again at 150° C. in a vacuum oven for 30 minutes.

[0126] The SAM layer 9 was then patterned by forming lines of approximatively 0.5 cm using H.sub.2SO.sub.4 at 96% concentration wt/wt on the surface of the SAM layer 9 for 1 to 2 minutes, and then rinsing.

[0127] The plating was performed using a chloride free nickel sulphamate bath at pH 5.8 and T 42° C. The applied voltage is 2.6V for 2 minutes, the silver backing to the silicon wafer being used as an electrical contact. As can be seen on FIG. 6, the surface outside the conductive lines 11 remains hydrophobic after plating, evidencing the resistance of the SAM to the plating conditions. Some nickel marks are observed where the sample was handled.

[0128] As can be seen from the foregoing it is clear that the method of the invention can be carried out with simple equipment, using a minimum of materials. In particular, the SAM is cheaper, faster and easier to use than a conventional photoresist-based lithography, or printing of masking material. Furthermore, removal of the SAM layer is not necessarily required, reducing the requirements for solvents and the time required to strip the masking material. The lower overall quantities of chemicals used, particularly in respect of the comparatively small amounts of SAM molecules, and the simple, standard solvents used, are highly cost-effective and environmentally friendly.

[0129] Although the invention has been described with reference to specific embodiments, variations are possible without departing from the scope of the invention as defined in the appended claims.