Large area dye cells, and methods of production thereof

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PHOTOVOLTAIC CELL TO CONVERT A LIGHT SOURCE INTO ELECTRICITY, A CELL PRODUCTION METHOD

PHOTOVOLTAIC TO CONVERT A LIGHT SOURCE INTO ELECTRICITY

This application claims priority from Provisional Patent Application series no. 60/990,307, filed on November 27, 2007.

FIELD AND FOUNDATION OF THE INVENTION

The present invention relates to photovoltaic cells, also known as solar batteries, for the production of electricity from sunlight, and more particularly, monolithic solar batteries of the dye-sensitive type, and to methods for producing such cells.

Dye-sensitive photovoltaic cells for producing electricity from sunlight were disclosed by US Patent. 5,350,644 to Graetzel, et al. US Patent 5,350,644 teaches a photovoltaic cell with a light transmitter, an electrically conductive layer deposited on a glass plate or a transparent polymer sheet to a series of layers of titanium dioxide has been applied, in which at least the last layer of titanium dioxide is doped with a metal ion which is selected from a divalent or trivalent metal.

Then the US Patent. 5,350,644, US Patent 6,069,313 to Kay teaches a plurality of serially connected cell elements arranged in distinct, parallel, elongated narrow strips on a common, transparent substrate. Each element includes a light facing the anode containing nanocrystalline titania, a carbon-based counting electrode (cathode) and a porous layer that electrically insulates the intermediate, based on alumina, silica, titania and zirconia, which separates the anode from the cathode. The pores of the middle layer are at least partially filled with a liquid phase, an ion-transferring electrolyte, after coating nanocrystalline titania with a light-sensitive dye. The current collection layer of a tin oxide based on transparent electrically conductive material is situated between the transparent substrate and the anode. The anode and cathode of a given cell provide a direct current voltage when the anode is exposed to light, so that series arrays of cells can be easily constructed. The cathode of each preceding element is related to the intermediate conductive layer of the preceding anode element, along a space separating the respective intermediate layers of

2/17 two elements. The battery pack is then sealed with an organic polymer, primarily ensuring that each individual battery pack is sealed from its neighboring battery pack, and this set is referred to as a monolithic battery pack.

Generally, dye cells from the above prior art disclosures are much closer conceptually to battery cells than conventional photovoltaic cells, since the charge generators are separated by an electrolyte and are not in direct contact. These cells have two electrodes separated by an electrolyte, with one electrode (the photoelectrode or photoanode) facing the light or solar source. Each electrode is supported on its own current collector, usually a sheet that conducts glass, the glass of which is coated on one side with a thin transparent layer (-0.5 micrometer), usually based on electrically conductive tin oxide. The glass-conducting sheets act as the transparent walls of the dye cell.

A clear polymer can be used in place of glass to support the tin oxide. The photoelectrode or photoanode includes a transparent porous layer about 40-20 micrometers thick (in contact with the tin oxide layer), based on titania, with a characteristic nanocrystalline particle size of 90-50 nm, applied by the baking in a conductive glass or transparent polymer and impregnated with a special dye. The roasted titania layer is applied in dispersion form by any of the methods: doctor-blading, rolling, spraying, painting, electrophoresis, gravure printing, coating, screen printing or printing. The cooking step with the best cell performance is normally at least 450°C, requiring the use of conductive glass rather than plastic to support the titania layer. Other treatment processes for the titania layer are viable, such as reduced cooking temperature, or pressure, usually with some sacrifice of efficiency. It is important to note that titania is mainly in contact with tin oxide. The presence of other conductors (such as many metals, coal and the like, even if chemically inert to the electrolyte) in the photoanode can greatly increase the recombination of charge carriers and provide a severe loss of efficiency in the cell. Few materials (among them tin oxide and titanium metal) are applicable for inclusion as conductors as part of the photoanode, due to stringent criteria for the chosen conductor, including chemical inertness of the electrolyte, electrical resistivity below 10'⁴ ohm cm, and characteristically none

3/17 tendency or virtually no tendency to recombination.

For cells that are partially transparent, the other electrode (counter electrode) includes a thin layer of catalyst (usually containing a few micrograms of platinum per cm²) in its respective sheet of tin oxide coated with conductive glass or clear plastic. If cell transparency is not required, the counter electrode can be opaque, for example carbon or graphite based advantageously catalyzed with platinum or another active electrocatalyst. The electrolyte in the cell is usually an organic solvent with dissolved redox species. The electrolyte is usually acetonitrile or a nitrile of reduced volatility and higher molecular weight with redox species in classical dye cells being dissolved in iodine and potassium triiodide essentially potassium iodide. However, other solvents and phases can be used, for example ionic liquids with zero vapor pressure and different redox species.

US Patent 5,350,644 to Graetzel, et al., discloses various cell chemistries of dyes, especially dyes based on ruthenium complexes. Photons falling on the photoelectrode excite the dye (creation of oxidized activated dye molecules), causing electrons to enter the titania conduction band and flow (through an externally charged circuit) to the counter electrode. There, electrons reduce the triiodide to iodide in the electrolyte and the iodide is oxidized by the activated dye in the photoanode back to the triiodide, leaving behind a deactivated dye molecule ready for the next photon. It has been reported that such dye cells can achieve a solar-to-electrical conversion efficiency of 10% and over 11% has been achieved in the small area (typically 0.2 square millimeter) in the champion research cells.

The cells of US Patent 5,350,644 to Graetzel, et al., are based on two sheets of conductive glass sealed with organic adhesive at the ends (the conductive glass designs in addition to the adhesive on each side, allowing for actual removal). These cells operate at a voltage of about 70OmV and a current density of 15mA/cm2 under maximum sunlight with the counterelectron having a positive pole.

Efforts were made to increase the active area and width of cells by establishing parallel tracks of conduction on a conductive glass surface, thus allowing for large-area, large-cell construction. US Patent Application 20050072458 to Goldstein discloses a large area, conductive glass

4/17 or wide conductive plastic for a dye cell. In one embodiment, the parallel conductors are inert strips or wires of titanium, molybdenum, tungsten, chromium or their alloys bonded directly to the conductive glass surface by means of an inert, electrically conductive ceramic adhesive. Large area cells of 10-15 cm on each side, with current removal and better performance are thus allowed.

To date, there has been no real commercialization of dye photovoltaic cells, despite the great technical-economic potential. It would be very advantageous to have a large area of ​​dye photovoltaic cells which is characterized by low ohmic resistance, is low cost and robust and which successfully addresses the various shortcomings of the prior art.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention there is provided a photovoltaic cell for converting a light source into electricity, including: (A) a housing adapted to enclose the cell, including at least one partially transparent cell wall with an interior surface (b) an electrolyte disposed within the cell wall containing a redox species, (c) an at least partially transparent conductive coating disposed on the interior surface; (d) an anode, including: a porous titania film disposed on the conductive coating, and adapted to make intimate contact with the redox species, the film contains a plurality of continuous areas separated by gaps arranged along a length of the film, and (ii) a dye, absorbed in a porous film surface, the dye and the film adapted to convert photons to electrons (e) a cathode disposed within the housing substantially opposite the anode for the purpose of electrolytic communication, through the electrolyte, with the porous film, and (f) at least two conductive structures disposed within spaces, electrically bonded to the anode and the conductive coating, and touching the porous film, each conductive structure including an electrically conductive structural element, at least partially surrounded by a layer of electrically conductive ceramic, each structure forming a ridge that projects above the surface of the porous film by at least 50 micrometers, where, across an entire length of the porous film disposed between the conductive structures, the porous film thickness is within 15 micrometers and/or 50% of the nominal film thickness.

According to another aspect of the present invention there is provided a method

5/17 production of a photovoltaic cell for converting a light source into electricity, including: (a) providing a structure including: (I) a housing adapted to include the photovoltaic cell, and including at least one partially transparent cell wall, such cell wall having an interior surface, (ii) at least one partially transparent conductive coating disposed on such an interior surface of such cell wall within the photovoltaic cell, (iii) an anode disposed in such a conductive coating, such anode including a film of porous titania wherein said porous film is a discontinuous film having at least a first continuous area and a second continuous area separated by a space having an average width of at least 100 micrometers; (b) subsequently, the insertion of an electrically conductive structural element along and within the space between such continuous areas, such a structural element having a small dimension of at least 50 micrometers; (C) introducing an electrically conductive adhesive at least partially surrounding such structural element and for electrically joining such structural element and such space, such structural element and such electrically conductive adhesive forming at least a part of an uncured conductive structure, and 9d ) treating the uncured conductive structure to produce a first cured conductive structure within the anode of the cell.

According to new elements in the described preferred embodiments, in areas within less than 1 mm of the conductive structures, the porous film thickness is within 30%, and preferably within 20%, of the nominal porous film thickness.

According to new elements in the described preferred embodiments, in areas within less than 1 mm of the conductive structures, the porous film thickness is within 10 micrometers, and preferably, within 5 micrometers of the nominal porous film thickness.

In accordance with still further elements of the described preferred embodiments, over the entire width of the porous film disposed between such conductive structures, the thickness of the porous film is within 50%, preferably within 30%, and most preferably within 20 % of the nominal thickness of the porous film.

In accordance with still further elements of the described preferred embodiments, over the entire width of the porous film disposed between such conductive structures, the thickness of the porous film is within 15 micrometers, preferably within 10 micrometers, most preferably within fence

6/17 of 5 micrometers and more preferably about 3 micrometers of the nominal thickness of the porous film.

According to other elements in the described preferred embodiments, and such electrically conductive structural element is selected from the group of electrically conductive structural elements of a metal strip or a metal wire.

In accordance with other elements of the described preferred embodiments, such an electrically conductive structural element has a specific electrical resistivity below 1200 x 10'⁶ ohm cm, preferably below 500 x 10'⁶ohm cm, more preferably below 200 x 10'⁶ ohm cm, and more, preferably less than 50 x W⁶ ohm cm.

In accordance with still other elements in the described preferred embodiments, the anode and cathode are arranged in a monolithic arrangement.

In accordance with other elements in the described preferred embodiments, the conductive ceramic layer is covered by a solid insulating layer with a specific electrical resistivity of at least 10⁶ ohm cm.

According to still further elements in the described preferred embodiments, each of the conductive structures forming the protrusion that projects above the impregnated dye, surface facing the cathode of the porous film of at least 75 micrometers, 100 micrometers, 150 micrometers or 200 micrometers .

In accordance with still other elements in the described preferred embodiments, the redox species includes an iodine-based redox species and the transparent conductive coating includes tin oxide.

According to still further elements in the described preferred embodiments, the conductive structures have a width between 100 and 1200 micrometers, preferably below 1000 micrometers, and more, preferably less than 700 micrometers.

In accordance with still further elements in the preferred embodiments described, the cathode includes: (I) a conductive layer of carbon, and (ii) a catalytic component, associated with the layer of carbon and adapted to catalyze a redox reaction of the redox species, the conductive layer of carbon adapted to transfer electrons from the catalyst element to a current-gathering component of the cathode.

In accordance with other elements of the described preferred embodiments, such a conductive ceramic layer has a specific electrical resistivity below

7/17 of 1.0 ohm cm, preferably below 0.1 ohm cm and most preferably below 0.01 ohm cm.

In accordance with still further elements in the described preferred embodiments, the cathode comes into direct contact with the porous titania film.

In accordance with still further elements in the described preferred embodiments, the cell further includes an insulating spacer layer disposed between the porous titania film and the cathode.

In accordance with other elements of the described preferred embodiments, the second continuous area is separated from a third continuous area of ​​the porous film by a second space having a second cured conductive structure.

In accordance with other elements of the described preferred embodiments, the second continuous area of ​​the porous film is delimited by the first and second cured conductive structures and in which over a full width of the second area between the cured conductive structures, the thickness of the second area is within 50%, preferably within 30% and even more preferably 20% with a nominal thickness of the second area.

In accordance with still further elements of the described preferred embodiments, the method further includes placing the cathode within the housing substantially opposite the anode.

In accordance with still further elements of the described preferred embodiments, the method further includes the step of contacting a porous film surface with a dye, the dye, and the film adapted to convert photons to electrons.

In accordance with still further elements in the described preferred embodiments, the method further includes the step of introducing an electrolyte containing redox species into the cell wall to effect electrolyte communication through the electrolyte between the porous film and the cathode.

In accordance with other elements of the described preferred embodiments, the electrically conductive adhesive, after treatment, has a specific electrical resistivity below 1.0 ohm cm, preferably below 0.1 ohm cm and most preferably below 0 .01 ohm cm.

In accordance with still further elements in the described preferred embodiments, the electrically conductive adhesive includes a ceramic material.

In accordance with other elements in the described preferred embodiments, the electrically conductive adhesive includes an electrically conductive material.

8/17 selected from the group of materials consisting of titanium nitride, zirconium nitride and titanium borate.

In accordance with still further elements in the described preferred embodiments, the electrically conductive adhesive includes tungsten particles.

According to another aspect of the present invention there is provided a photovoltaic cell for converting a light source into electricity, the photovoltaic cell produced by any method described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described herein, by way of example, only with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is important to note that the elements shown are given by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented with the intention of providing what is believed to be the most useful and understandable description of the principles and conceptual aspects of the invention. In this regard, no attempt has been made to show structural details of the invention in greater detail than is necessary for a fundamental understanding of the invention, the description taken from the drawings becoming apparent to those skilled in the art as to the various forms of the invention that may be incorporated into practice. Throughout the designs, characters that are similar are used to designate similar elements.

In the drawings:

Figure 1 is a schematic cross-sectional view of the example of a large area monolithic single cell that can be manufactured based on the prior art;

Figure 2 is a schematic top view of the cell of Figure 1, showing the printed areas in the form of a long strip, where the adjacent printed areas are separated by conductive structures;

Figure 3 provides a schematic cross-sectional view of a part of the structure of the invention, in which separate strips of a titania layer and insulating spacer layer are arranged on a glass substrate so as to leave a space between the strips, and

Figure 4 is a schematic cross-sectional view of an example embodiment of a dye photovoltaic cell of the present invention.

DESCRIPTION OF THE PREFERRED MODALITIES

One aspect of the present invention is an improved monolithic structure of

9/17 wide area single dye cells. In a monolithic dye cell design, there is usually not a single sheet of conductive glass required per cell, with attached cost savings. On such a single sheet of conductive glass a porous titanium photoanode layer, a porous insulating spacer layer and a porous carbon cathode layer (counter electrode) are printed in sequence. After staining the titania dye and adding electrolytes, the cell can be sealed with an outer sheet of glass, polymer, aluminum, metal or laminate. Since the spacer layer between the titania and cathode layers can be very thin, on the order of several micrometers only, this guarantees a low resistance of the electrolyte and, consequently, a lower ohmic resistance of the cell. The result is a much lower resistance cell compared to cells where the cathode element is a separate structure, where such close spacing between photoanode and cathode can be extremely difficult to achieve. The fact that the active cell layers are built on the same support also avoids electrode spacing variations resulting in thermal cycling of the cell, which can be a performance limiting problem in cells with a separate cathode. The large area monolithic single cells according to the present invention additionally have a greater fraction of footprint cells that are optically active, relative to Kay's multi-monolithic cell design of US Patent 6,069,313. Thus, the inactive opaque areas and conductive areas are proportionately reduced for the large area individual cells and the active titania area can more completely approximate the carbon cathode area in the design of the present invention. Both factors positively impact cell efficiency.

Figure 1 shows an exemplary schematic view of a single large area monolithic cell 100 that can be fabricated based on the prior art (elements not drawn to scale). On a sheet of glass 1 with a layer of a conductive surface 4 based on tin oxide, a set of spaced parallel conductor structures 8 is established before printing the layers of titania. Conductive structures 8 project above conductive surface layer 4. In the embodiment shown, each conductive structure 8 includes a substantially chemically inert metal wire 12 bonded in place to the conductive surface layer 4 by an electrically inert, substantially chemically conductive bond 16 and covered with an electrically insulating layer 20 that prevents a electrical reduction of

10/17 conductive structures for the layers subsequently applied.

By way of example, adjacent conductive structures 15 cm long and 1 cm apart preferably have an ohmic drop of less than 0.5 ohms to obtain current collection of cells of suitable dyes in a tin oxide glass. with a surface resistance of 10 ohm/m².

In a monolithic cell construction, the main cell components, which preferably include a titanium photoanode layer 24, a spacer insulating layer 28 and a counter electrode layer 32, are normally built up, layer by layer, over a glass substrate, by successive printing operations, including drying and sintering these layers, to form substantially printed continuous areas 36. Figure 2 is a schematic top view of cell 100 showing continuous printed areas 36 in the form of a long strip, in which adjacent printed areas 36 are separated by conductive structures 8.

When such prints are attempted by screen printing the appropriate pastes, there is not necessarily a lack of uniformity in layer thickness following sintering, due to the presence of the raised features of the conductive structures 8 on the surface of the glass. Conductive structures 8 can protrude above the surface of the conductive surface layer 4. The titania and spacer layers are less prominent, for example only 15 and 10 micrometers thick, respectively, after sintering. However, even conductive structure with a height of only a few tens of micrometers can spoil the print uniformity of the main titania layer. Due to the projection of the conductive structures 8, the mesh or screen through which the paste is applied cannot be made to be placed on the glass surface. The flat arrangement on the glass surface is ideal for optimal orientation for correct mass release by eg squeegee pressure.

Consequently, after drying and sintering is carried out, a significant portion of the photoactive area of ​​the cell is not entirely parallel to the backing glass. As shown in Figure 1, in the central area of ​​each strip, e.g. area A between adjacent conductors 8, the layers are optimally thin, uniform and parallel to the substrate surface, but in areas B and C arranged closely to the structures adjacent conductors 8, the layers (e.g. the titanium photoanode layer 24) are much thicker and not

11/17 fully parallel to the supporting glass. In a normal print, the titanium layer 24 of area A is 15 ± 2 micrometers thick after sintering. However, we found that the titanium dioxide layer 24 from areas B and C can have a maximum thickness of 30-200 micrometers or more. The main result of this lack of homogeneity in the thickness of the layers (typically screen printing) is the reduction of cell performance. Areas close to the conductive structures 8 are effectively inactive, since they may have a much longer ionic path characterized by increased electrolyte resistance, a long diffusion path of ion recombination, and reduced light transmission, due to excess layer thickness. of titania 24. In typical prints, where the width of the printed strips between the conductive structures is about 8 mm, the idle width can be 1 mm (or more) on each side of the conductive structures, so the cell performance loss compared with the case of uniform printing of strips across the width it can approach 20%.

A similar result can be obtained through other methods of applying conductive structures in cells of large areas, for example, the bonding of wires in grooves on the substrate or electrodeposition of conductive metal or metal alloy strips on the substrate, as here also, the conductive structures may be situated well above the surface of the substrate.

In the present invention, a strategy for uniform printing of the active layers is adopted whereby impressions of the active layer are made prior to application of the conductive structures. Figure 3 provides a schematic cross-sectional side view of a portion of a structure of the invention, in which separate strips 45 of a titania layer 40 and insulating spacer layer 44 are arranged (e.g., by screen printing) on ​​a substrate. of glass 48 with a layer of conductive tin oxide 52, leaving at least one space 56 between the strips 45 which can later be at least partially filled by conductive structures. In this case, there is no problem in obtaining active layers with a substantially uniform and homogeneous thickness, even in the areas adjacent to the conductive structures.

The spaces 56 are preferably substantially parallel to each other.

A schematic cross-sectional side view of one embodiment of a monolithic cell 200 of the present invention is provided in Figure 4.

12/17 electrically conductive structural elements or cores such as wires 60 are positioned in spaces (such as spaces 56 shown in Figure 3) between layers and/or impressions (e.g. titania layer 40 and optional insulating spacer layer 44) , or next to an end or end 55 of the prints. Preferably, sufficient tension is applied to the wires 60 to ensure closure and placement substantially parallel to the tin oxide surface. This placement procedure can be performed using a jig or other means known in the art.

The wires 60 are permanently connected in place by an electrically conductive adhesive layer (eg, containing ceramic adhesive), which can be added by a metering dispenser to produce uncured conductive structures. These uncured conductive structures may undergo treatment (e.g. a heat treatment) to produce a cured or at least partially sintered conductive structure as conductive structures 98. Conductive structures 98 may include electrically conductive structural elements, such as wires 60, at least partially surrounded by, and preferably completely surrounded by, an electrically conductive bond layer, such as an electrically conductive bond layer or bond layer 64 formed by treating the adhesive layer. electrically conductive. The binder layer 64 may contain a ceramic material and one or more electrically conductive materials, such as tungsten, titanium nitride, zirconium nitride, and titanium boride.

Conductive structures 98 may also have an electrically insulating layer, such as a ceramic insulating layer 68, which at least partially, and preferably, completely surrounds or surrounds wire 60 and electrically conductive bonding layer 64.

In the photovoltaic cell and the method of the present invention, depending on the application method of the conductor employed, the conductive structures can be between 0.1 mm and 2 mm in width, they can be spaced about 5-20 mm in the conductive glass, and may be at least 50 micrometers to 200 micrometers or higher (or more) above the conductive glass surface. Preferably, the conductive structures may have a width of less than 1 mm, and more, preferably, less than 0.7 millimeters.

The cathodic layer, such as a porous carbon-based cathode 72, optionally catalyzed, can be screen-printed or laid directly on top of an insulating spacer layer 44. Alternatively, a carbon-based cathode

13/17 porous carbon 72 can be screen-printed or laid directly onto the titanium layer 40.

Actual removal of the cathode can be achieved by a variety of means, for example a carbon based cathode bond 72, a graphite sheet 76 carrying a built-in metal mesh or strip guide 80, and the layers below can be well compressed after removal. sealing by the additional inclusion of an optional sponge element (not shown).

The titania layer 40 can be coated with a dye using a dye solution printed on a carbon 72 based cathode, which allows the dye to pierce the titania layer 40, where it chemoabsorbs strongly. After evaporation of the dye solvent, the cell electrolyte is added to the cell by printing on the porous cathode 72. In the exemplary embodiment provided in Figure 4, cell 200 is substantially closed and sealed at the edges with a sealant layer, such as a sealant layer of the polymer layer 84 supported by a housing such as sheet metal 88 (for a lightweight design), in which case, a metallic guide 80 can be brought through the sheet 88 via an insulating ring 92 which can be associated with the sheets 88. Other standard openings, such as a sheet of glass edge-sealed with polymer or adhesive, may also be viable. The actual removal of wired structures from the photoanode or the embedded cathode guide, which pass from inside the cell through the sealed edges of the cell, can be accomplished by welded metal strips that can connect to the adjacent cell in a modular set of cells (not shown).

Thus, in the cell of the present invention, the active layers can have a substantially uniform and homogeneous thickness, even including the areas adjacent to the conductive structures. Over the entire width of the strips arranged between the conductive and adjacent structures (within 1mm) for conductive structures 98 in particular, the thickness of a strip of strips 45 is within 50%, preferably within 30% and more preferably within approximately 20% of the nominal thickness of the strip. Likewise, with respect to each of the individual strip components 45, such as the titania layer 40 and insulating spacer layer, the thickness of a given component is within 50%, preferably within 30%, and more preferably within approximately 20% of the nominal thickness of the strip over the entire width of the strips disposed between the conductive structures and in particular in adjacent areas (within 1 mm) for structures

14/17 conductors 98.

By way of example, in a dye cell of the present invention, and the determined titania layer 40 screen-printed onto a substrate and with a nominal thickness of 15 micrometers, the strip 40 would have a thickness of not more than 22.5 micrometers along the entire width of the strip, including areas adjacent to the conductive structures. Preferably, strip 40 has a thickness of no more than 19.5 micrometers across the entire width of the strip, and more preferably, no more than about 18 micrometers.

Typical printing accuracy of a layer (such as a layer of titania) on flat glass can be about +/- 2 micrometers.

As used herein in the specification and claims section that follows, the term nominal thickness, with respect to a strip such as strip 45, a strip component, or a porous layer, such as a titanium layer, refers to if at an average thickness, within a substantially planar area A, of the strip, component or layer, respectively, which is at least 2.5 mm from any of the conductive structures.

In absolute terms, over the entire width of the strips arranged between the conductive and adjacent structures (within 1mm) for conductive structures 98 in particular, the thickness of a strip of strips 45 is within 15 micrometers, preferably within 10 micrometers and more preferably, within approximately 5 micrometers of the nominal thickness of the strip. Likewise, with respect to each individual component of strips 45, such as the titania layer 40 and insulating spacer layer 44, the thickness of a given component is within 15 micrometers, preferably within 10 micrometers, and more, preferably, within approximately 5 micrometers, of the nominal thickness of the strip along the entire width of the strips arranged between the conductive structures and, in particular, in adjacent areas (within 1 mm) for conductive structures 98.

By way of example, in a dye cell of the present invention, and the determined titania layer 40 screen-printed onto a substrate and with a nominal thickness of 10 micrometers, the strip 40 would have a thickness of not more than 25 micrometers along the entire width. of the strip, including areas adjacent to the conductive structures. Preferably, strip 40 has a thickness of no more than 20 micrometers across the entire width of the strip, and more preferably, no more than about 15 micrometers.

The invention is not limited to the exemplary sequence of operations envisaged

15/17 above, and various modifications will be apparent to those skilled in the art. For example, active layers can be printed onto the substrate in a large print area without separations and spaces cleaned in a subsequent ablation step. Likewise, it is possible to print the carbon layers on the spacer layers prior to the establishment of conductive structures. The sequence can also be adjusted to allow proper coordination of drying and sintering steps in cell preparation, or to better accommodate placement of the conductors in grooves on the substrate or coated surface. Removable mask layers can also be established in order to avoid contamination of previous active layers or electrical circuitry of subsequent layers.

As used herein, the term monolithic and the like, with respect to a dye cell, refers to a cellular structure in which both the cathode and photoanode layers of the cell are supported by a common conductive glass backing. The term monolithic and the like is specifically intended to exclude dye cell structures in which the photoanode is supported by a first glass support and the cathode is supported by a second glass support such that the photoanode and cathode are substantially arranged. Typically, monolithic dye cell structures are produced in a screen printing process, and have an insulating porous spacer layer arranged between the photoanode and cathode layers.

Below we provide a list of various materials that can be used in dye photovoltaic cells, along with their specific electrical resistivity (in ohm cm units), available in the literature.

Specific Electrical Resistivities (ohm cm)

Silver 1.5x10'⁶

Copper 1.5 x 10'⁶

Nickel 6.2 x 10'⁶

Platinum 9.6x10'⁶

Aluminum 2.4 x 10'⁶

Titanium 39 x 10'⁶

Bismuth 107 x 10'⁶

Copper coated titanium ~ 3 x 10-⁶

Molybdenum 4.9 x 10'⁶

Chromium 11.8 x 10'⁶

16/17

Tantalum 12.2x10'⁶

Tungsten 4.8 x 10'⁶

Carbon 3000 x 10'⁶

Graphite 1000 x 10'⁶

Titanium Nitride 25 x 10'⁶

Tin oxide 500 x 10'⁶

Titanium Dioxide ~ 10¹²

Alumina binder ~ 10¹⁴

Synthesizer dye ~ 10⁹

Conductivity is inversely related to resistivity. It is evident from these values ​​that metals such as silver, copper, aluminum, tungsten are intrinsically highly conductive, while other metals such as titanium and some fillers such as titanium nitride are somewhat less conductive. Carbon, graphite and tin oxide are much less conductive. Materials such as titanium dioxide, alumina and sensitizing binder dyes are correctly classified as insulators, with resistivities that are at least 13 times the order of magnitude of materials that are considered true conductors.

Not only is the specific resistivity of an important material important in determining the strength of a layer of material, but also the thickness of the layer, its length and width, and the continuity of the layer's components. Thus, in dye cells, the tin oxide layer on glass is an extremely poor conductor, not only because its specific resistivity is much higher than the specific resistivity of metals, but also because the layer has to be extremely thin (usually 0.5 micrometer) in order to keep the layer transparent and light to be able to enter the cell with adequate transmission. Therefore, the tin oxide layer on the glass is a poor vehicle for transporting the cell along the general plane of the tin oxide layer.

Conductive structures 98, such as metallic wires connected in place to a tin oxide glass by an electrically conductive ceramic adhesive, can be beneficial, as current removing elements on the basis of their intrinsic conductivity. However, other criteria for the structures include low tin oxide surface contact resistance and minimal light shading to the cell. So, for example, we can consider a coloring cell having a square geometry of 15 cm from each

17/17 side, which can generate, the conversion efficiency of 7%, a peak current of about 3 amps. The parallel conductive structures arranged across the face of the device, each 15 cm long, 1 mm wide and 1 cm spacing, yield an acceptably low shading of 10%. For proper current removal in tin oxide glass with a surface resistance of 10 ohm/m². However, the resistance between adjacent conductive structures should preferably not exceed about 0.5 ohms.

Generally speaking, highly electrically conductive structural elements, such as wires 60, arranged in conductive structures 98, have specific electrical resistivity of less than 1,200 x 10 10'⁶ ohm cm, preferably below 500 x 10'⁶ ohm cm, more preferably, below 200x10'⁶ ohm cm, even more, preferably less than 100x10'⁶ cm ohm, and more, preferably less than 50 x 10'⁶ ohm cm.

With respect to the cured layer produced from the conductive paste or adhesive layer 64, the specific electrical resistivity is less than 1.0 ohm cm, preferably less than 0.1 ohm cm, more preferably less than 0.05 ohm cm , and more, preferably, less than 0.01. Some materials suitable for use in or with the conductive adhesive layer 64 may have specific electrical resistivity that are several orders of magnitude lower.

With regard to the electrically insulating layer (such as ceramic layer 68), which generally surrounds the electrically conductive structural element and the conductive ceramic layer, and taking into account the spacer insulating layer 44 as well, the specific electrical resistivity is generally centimeters, at least 10⁶ ohm preferably at least 10⁸ohm cm, and more preferably at least 10¹°-10¹⁴ ohm cm.

While the invention will be described in conjunction with its specific embodiments, it will be apparent that many alternatives, modifications and variations will be apparent to those skilled in the art. In this way, it is intended to include all alternatives, modifications and variations. All publications and patents mentioned in this specification are hereby incorporated in their entirety by reference in the report, to the extent that each individual publication or patent is specifically or individually indicated to be incorporated herein by reference. Furthermore, mention or identification of any reference in this application will not be construed as an admission that such reference is available as in the prior art of the present invention.