WO2009156321A1

WO2009156321A1 - Method for preparing dye sensitised solar cells

Info

Publication number: WO2009156321A1
Application number: PCT/EP2009/057555
Authority: WO
Inventors: Gerardo Triani; Peter John Evans; Mervyn Alexis Jehan De Borniol
Original assignee: Polymers Crc Ltd.
Priority date: 2008-06-27
Filing date: 2009-06-18
Publication date: 2009-12-30
Also published as: TW201010113A

Abstract

This invention relates to patterning metal oxide layers by atomic layer deposition (ALD) on substrates used in the fabrication of dye-sensitised solar cells (DSSC).

Description

Method For Preparing Dye Sensitised Solar Cells

WO 2009/040499 describes a method of patterning a mesoporous nanoparticulate layer.

The deposition of blocking layers onto substrates for use in DSSC typically requires an etching technique to remove parts of the deposited layer to create the pattern. Light-based patterning techniques such as photolithography utilise resists, solvents and developers to create the outline however these materials may be detrimental to polymer substrate. In addition, photolithography is cumbersome when applied to large area patterning and is not adaptable to continuous reel to reel deposition methods.

More recently, microcontact printing using chemical based templates has been used to create patterns. Self-assembled monolayers (SAM) are transferred onto the surface using polymer pads. SAM layers present non-wetting surfaces having hydrophobic molecules such as alkanethiols that preclude deposition of subsequent printed matter. Although this technique offers good resolution, this method requires chemical treatment to define the pattern and is generally too slow for large scale processing.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

The present invention pertains to a method for forming DSSCs comprising providing a TCO coated transparent substrate, masking one or more regions of the TCO surface; forming metal oxide layer (underlayer) on the masked TCO layer using ALD and removing the masking.

Preferably, the masking provides a plurality of patterned regions of ALD metal oxide layer. For instance, the patterning comprises using a masking agent that inhibits the deposition of the metal oxide on the surface.

The invention relates to patterning selective areas of metal oxides by Atomic Layer Deposition (ALD) of the metal oxide onto the conductive surfaces in fabrication of DSSCs. The conductive layer may be supported on polymer, glass or metal foils and fabrication may be by batch or continuous fabrication. The patterning occurs using a masking agent that excludes the deposition of the metal oxide onto the surface.

Patterning (i.e. by applying the mask) may take place by at least one method selected from the group consisting of: a) application of a non-reacting ink to the surface followed by metal oxide deposition; b) by use of a polymer mask placed close to or on the surface such that the adsorption/desorption occurring during ALD metal oxide deposition creates an area of exclusion in the vicinity of the mask; and c) use of non-contact masking agent where a device located near to but not touching the surface emits a stream of gas that continually flushes the surface thereby preventing the deposition of metal oxide during ALD processing; for instance, method a) is used, for example, method b) is used, for example, method c) is used, for example, whereby the method b) and/or c) are particularly preferred.

In a further embodiment the invention provides a method of preparing a DSSC comprising forming an optical electrode preferably TCO such as ITO on a transparent substrate comprising; preferably subjecting the free surface of the optical electrode to surface modification such as with corona discharge or plasma discharge; masking the one or more regions of modified surface; applying a layer of metal oxide by ALD; and removing the mask to provide a plurality of laterally spaced apart ALD coated regions.

The invention may comprise the additional step of applying a nanoparticulate metal oxide layer to the ALD deposited metal oxide. The nanoparticulate metal oxide layer may be deposited prior to removal of the mask but in the preferred embodiment the nanoparticulate layer is deposited after removal of mask. For instance, a further ALD layer (overlayer) is applied to the particulate metal oxide layer. The preferences and conditions outlined herein for the ALD layer applied to the masked substrate apply also to the further ALD layer applied to the particulate metal oxide layer. As number of cycles for the ALD overlayer is 2-500 particularly preferred. Prior to the application of the ALD overlayer one or more regions of the substrate (i.e. TCO surface, ALD underlayer and/or nanoparticulate metal oxide layer) might be masked as outlined herein for the ALD underlayer and the mask is removed after the application of the ALD overlayer.

There is provided a method for the substantially continuous fabrication of thin film DSSCs by performing, on a substantially continuously moving, elongated, flexible substrate having a transparent conductive oxide film layer, the following steps:

(a) optionally subjecting the TCO substrate to surface modification such as by plasma or corona discharge; (b) masking the one or more regions of the TCO surface;

(c) applying metal oxide film by ALD; and

(d) removing the mask to provide a plurality of laterally spaced ALD coating patterns on the TCO.

The continuous method may comprise the additional step of applying a particulate metal oxide layer over the ALD layer either before or after removing the mask and optionally further applying an ALD coating (overlayer) on the particulate metal oxide layer. The preferences and conditions outlined herein for the ALD layer (underlayer) applied to the masked substrate apply also to the further ALD layer applied to the particulate metal oxide layer. As number of cycles for the ALD overlayer is 2-500 particularly preferred. Prior to the application of the ALD overlayer one or more regions of the substrate (i.e. TCO surface, ALD underlayer and/or nanoparticulate metal oxide layer) might be masked as outlined herein for the ALD underlayer and the mask is removed after the application of the ALD overlayer.

"Metal oxide" is used to designate a compound that comprises at least one metal bound to oxygen. Preferably, the metal is selected from the group consisting of metals of Groups NA, NIB, IVB, VB, VIB, VIII and INA. More preferably, the metal is selected from the group consisting of Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Ni, Cu, and In, Al, Ga. The preferred metal oxide comprises one or more of, for example, titanium oxide, - A -

niobium oxide, tungsten oxide, indium oxide, tin oxide, nickel oxide and zirconium oxide and the like, but is not necessarily limited thereto. These metal oxides may be used alone or in a mixture of two or more. Specific examples of the metal oxide include TiO₂, SnO₂, WO₃, Nb₂O₅, NiO and SrTiO₃, preferably the metal oxide is TiO₂.

The term "transparent" is used herein to refer to materials allowing transmission of at least 50%, preferably at least about 80% visible light (having wavelength of about 400 to about 700nm).

Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps.

"ParticlesTparticulate". Although there is no particular limitation on the particle size of the metal oxides forming the metal oxide particulate layer, the average particle size of primary particles is 5-400 nm and more preferably 5 to 150 nm and most preferably from 5 to 80 nm.

The particle size of the primary particles is preferably measured by dynamic light scattering. It is also possible to use a mixture of at least two metal oxides having different particle sizes to scatter incident light and increase quantum yield. In addition, the metal oxide particulate layer may also be formed to have a two-layer structure using two kinds of metals having different particle sizes. The metal oxides particles form the mesoporous layer to which the dye is adsorbed thus creating a light-absorbing or photo responsive layer. The mesoporous layer has large surface area in order to enable improved dye incorporation. Accordingly, the metal oxides of the light-absorbing layer preferably have a nanostructure selected from the group consisting of: nanoparticles with spherical or platelet morphologies, and mixtures thereof.

The term "low temperature paste" relates to a semiconductor particle precursor formulation which can be processed to volatilize binder at temperatures lower than 200 ⁰C. For example, Peccell PECC-C01-06 may be processed between 100-200⁰C, preferably at about 150 ⁰C.

The term "high temperature paste" relates to a semiconductor particle precursor formulation which can be processed to volatilize binder at temperatures greater than 300 ⁰C. For example, Solaronix 300 is typically processed at about 450 ⁰C. The term "sintering" refers to a process for providing particle interconnectivity that involves heating the sample to a specified temperature.

The invention uses an optical electrode on a light transmissible substrate. The optical electrode may be a conventional transparent conductive oxide (TCO) electrode of the type known for Gratzel DSSCs. The conductive layer is preferably made in the form of a thin layer of the order of 100 to 5000 nanometers in thickness. The conductive layer is advantageously made of a material chosen from the group consisting of fluorine doped tin oxide (FTO), antimony or arsenic or indium doped tin oxide (ITO), aluminum stannate, and zinc oxide doped with aluminium, preferably FTO or ITO. The conductive layer may be deposited by a method known in the art such as sputter coating or the like or may be deposited by ALD.

The light transmissible substrate may be a rigid substrate such as glass or flexible material such as a light transmissible polymeric material. Examples of flexibly suitable polymeric material may include: polycarbonates such as polycarbonate (bisphenol A polycarbonate, or (2,2-bis 4-hydroxyphenylpropane) carbonate) (PC) modified polycarbonate, polycarbonate blended with other polymers, poly(phthalate carbonate) (PPC) and bisphenol A / tetramethylpolycarbonate (PC-TMPC); polyacrylates such as poly(methyl methacrylate) (PMMA) and cycloaliphatic acrylic; polyamides such as transparent polyamide (nylon) (PA-T); polyesters such as poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), polyester copolymer (copolyester) and fluorinated copolyester (O-PET); polyarylates (PAr); styrenics such as polystyrene (PS), high-impact polystyrene (HIPS), styrene-acrylonitrile copolymer (SAN), methyl methacrylateacrylonitrile-butadienestyrene copolymer (MABS) and advanced styrenic copolymers; polyetherimides; sulfone polymers such as polysulfone (PSU), poly(ether sulfone) (PES) and poly(phenyl sulfone) (PPSU); poly(ether imide) (PEI); polyimides, such as Kapton H or Kapton E (made by Dupont) or Upilex (made by UBE Industries, Ltd.); polynorbornenes; olefinics such as cyclo-olefinic copolymer (COC), cyclo- olefinic polymer (COP) and clarified polypropylene; liquid crystal polymers (LCP) such as polyetheretherketone (PEEK); Poly(phenylene ether) (PPE), poly(phenylene oxide) (PPO), Rigid thermoplastic polyurethane (PUR-R); optically transparent thermosetting polymers including: diethylene glycol bis(allyl carbonate) or allyl diglycol carbonate (CR39); other ophthalmic resins based on sulfur containing monomers, urethane monomers, halogenated aromatic diallyl, divinyl or dimethacryl monomers; and other optical polymers such as fluorinated polyimide (Pl-f) and poly(methylpentene) (TPX). Products such as Barix™ barrier film, transparent organic-inorganic hybrid materials, transparent nanocomposite materials and similar materials may also be used. The light transmissible substrate is preferably glass or transparent polymer, most preferably PEN.

In context of the present invention, "an ALD process" generally refers to a process for producing thin films over a substrate in which a thin film is formed by surface-initiated chemical reactions. The general principles of ALD are disclosed, e.g. in U.S. Pat. Nos. 4,058,430 and 5,71 1 ,81 1 , the disclosures of which are incorporated herein by reference. In an ALD process, gaseous reactants, i.e. precursors are conducted into a reaction chamber of an ALD type reactor where they contact a substrate located in the chamber to provide a surface reaction. The pressure, temperature and flow conditions in the reaction chamber are adjusted to a range where physisorption (i.e. condensation of gases) and thermal decomposition of the precursors is minimised. In the process of the present invention temperatures are selected having regard to the nature of the substrate and other materials so as to avoid decomposition and to form an effective semiconductor coating layer without a requirement for high temperature processes. Only up to one monolayer (i.e. an atomic layer or a molecular layer) of material is usually deposited at a time during each metal-oxidant pulsing cycle. The actual growth rate of the thin film typically depends on the number of available reactive surface sites or active sites on the surface and bulkiness of the chemisorbing molecules. Gas phase reactions between precursors and any undesired reactions of by-products are inhibited because precursor pulses are separated from each other by time and the reaction chamber is purged with an inactive gas (e.g. nitrogen or argon) and/or evacuated using, e.g. a pump between precursor pulses to remove surplus gaseous reactants and reaction by-products from the chamber.

The invention involves formation via a process comprising atomic layer deposition of metal oxide film on unmasked areas on the free surface of an optical electrode deposited on a transparent substrate. The free surface at this stage of constructions is the side of the TCO electrode opposite the substrate bonded surface and which forms the optical electrode disposed in the DSSC inboard of the transparent substrate. We have found that atomic layer deposition on the optical electrode provides a good bond with the unmasked areas of the optical electrode particularly where the electrode surface has been subject to surface modification in accordance with the preferred embodiment of the invention. The masking step may be conducted using a range of techniques and masking agents. The mask may be in the form of a coating or ink applied to form a negative pattern prior to application of the positive pattern of metal oxide deposited by ALD.

Alternatively, the masking step may be carried out using a solid negative pattern held touching or adjacent the areas of the optical electrode not to be coated by ALD. In one embodiment the solid negative comprises a material adapted to adsorb and/or absorb the ALD reactant gases. For example, the solid mask may comprise a polyurethane resin optionally retained on a porous support such a carbon support (e.g. carbon fibre) coated with a polyurethane resin. In this embodiment the solid negative pattern may be held adjacent to or touching the areas to be masked.

The masked areas may also be formed by purging the areas to be masked with a gaseous masking agent during the deposition process, for example by flushing the areas of the optical electrode to be masked with a stream of inert gas. This may be done using a perforated lance or other suitable method for directing a stream of gas adjacent or the surface to thereby inhibit the reaction of ALD reagents on the purged surface.

In some preferred embodiments, thin films are deposited from halogen-containing chemicals. Geometrically challenging architectures are also possible due to the surface-initiated nature of ALD.

The invention preferably includes application of metal oxide nanoparticles to the ALD deposited metal oxide. An atomic layer deposition (ALD) type process may additionally be used to deposit a thin film on the surface of the nanoparticulate metal oxide layer. Such a process is described in WO 2009/013285.

In a preferred embodiment of the invention, a substrate having an optical electrode and nanoparticulate layer thereon is placed in a reaction chamber and subjected to alternately repeated surface reactions. In particular, thin films are formed by repetition of surface- initiated ALD cycles. Atomic layer deposition (ALD) is a known method of producing uniform metal oxide thin-films with excellent conformality. ALD is based on two or more separate half-reactions between vapor phase reactants and the deposition surface. Film growth is believed to involve the incoming vapor phase reacting by a process of chemisorption with surface functional groups. The process is continued with the separate introduction of the second vapor phase, which reacts with ligands attached to the precursor species previously deposited on the surface. The first half reaction generally involves deposition of a metal compound. The second precursor may then be reacted to provide modification of the adsorbed metal compound. For example, the growth of TiC>₂ from TiCI₄ and H₂O on a hydroxylated surface commences with the chemisoption of TiCI₄ to form Ti-O bonds together with some unreacted Ti-Cl terminal ligands. The latter ligands then react with H₂O vapor during the second half-reaction cycle to re-hydroxylate the growth surface and form HCI vapor as a reaction by-product. This process is typically repeated for a predetermined number cycles to form a TiO₂ film of the desired thickness. For instance, the number of cycles is 10-1000, preferably 20-500.

In performing ALD, process conditions, including temperatures, pressures, gas flows and cycle timing, are adjusted to meet the requirements of the process chemistry and substrate materials. The temperature and pressure are controlled within a reaction chamber. Typical temperatures used in the process of the invention are less than 300°C (e.g. at no more than 299°C, especially at less than 299°C, for example at no more than 25O⁰C, such as at no more than 200°C, in particular at no more than 15O⁰C, for instance at no more than 12O⁰C) and pressure ranges from about 1 to 10,000 Pascal. Temperatures from 50-400⁰C, preferably 80- 300⁰C can also be used. It is also possible to do sintering/volatile removal and ALD in the one process step. The conditions used should be chosen having regard to the substrate and temperature needed for treating the metal oxide particles to remove any solvent or carrier used as an aid in deposition of the metal oxide particles.

An inert purge gas is introduced to remove any excess of the first vapor and any volatile reaction products. The embodiments of the deposition process are described herein as involving purging with an inert gas. The terms "purging" and "purge" are intended to be construed broadly, to include not only flushing of the reaction space by introduction of a flow of an inert gas or other material, but also more generally to include the removal or cleansing of excess chemicals and reaction by-products from the reaction space. For example, excess chemicals and reaction by-products may be removed from the reaction space by pumping the reaction space and/or by lowering the pressure within the reaction space. Consistent with the broad definition of the term "purge," the removal of excess chemicals from the reaction space need not be perfectly effective, but will typically involve leaving surface bound chemicals and possibly some insignificant amount of non-surface bound chemicals or residual matter within the reaction space.

Moreover, when a purge gas is used to remove chemicals from the reaction space, various inert purge gases may be used. Preferred purge gases include nitrogen (N₂), helium (He), neon (Ne), argon (Ar), and mixtures thereof. A constant or pulsed flow of one or more of these purge gases may also be used to transport the first chemical and the second chemical into the reaction space and/or to adjust the pressure within the reaction space.

A second precursor vapor is introduced into the reaction chamber and reacts with the adsorbed first precursor vapor and creates a film; the second precursor vapor does not react with itself.

Each film growth cycle is typically of the order of a monolayer or less.

The second precursor vapor is purged to remove excess precursor vapor as well as any volatile reaction products. This completes one cycle. This procedure is repeated until the desired thickness of the film is achieved.

Successful ALD growth requires that the precursor vapors be alternately pulsed into the reaction chamber. The ALD process also requires that each starting material be available in sufficient concentration for thin film formation over the substrate area.

Preferred examples of metal reactants for use in the present invention include at least one metal compound selected from the group consisting of: halides (e.g. MX_n where X is a halogen), preferably chlorides, bromides or iodides, particularly TiCI₄ which is liquid at room temperature and particularly useful as a precursor for TiO₂; alkoxides (e.g. M-(OR)_n where R is alkyl), preferably Ci to Ce alkoxides and more preferably C₃ and C₄ alkoxides such as isopropoxide and sec-butoxide and tert-butoxide or a combination thereof. Specific examples of preferred alkoxides include titanium iso-propoxide (Ti(i-OC₃H₇)₄) and zirconium tert-butoxide (Zr(I-OC₄Hg)₄); β-diketonate chelates (e.g. M=(O₂C₃Rs)_n); alkylamides (e.g. M(N R₂)_n where R is independently H or alkyl such as Ci to C₄ alkyl); amidinates (e.g. M(N₂CR₃)_n wherein R is independently H or alkyl such as Ci to C₄ alkyl); and organometallics (that is compounds wherein the metal is bonded directly to carbon) such as alkyls including Ci to C₄ alkyls cyclopentadienyls such as dicyclopentadienyldimethyl metal complexes. A particularly preferred metal reactant is a metal halide, especially TiCI₄. In the above list M is the metal and n is the number of ligands in the complex and is generally the valency of the metal or, in the case of bidentate ligands, half the metal valency.

The ALD layer comprises for instance TiO₂, preferably the ALD layer consists of TiO₂.

The layer of metal oxide nanoparticles is typically in the range of from 0.1 to 100 μm and typically up to 20 μm thick. The nanoparticle layer of metal oxide for deposition on the ALD coated optical electrode may for example be prepared by a sol-gel process. The paste may be a high temperature or low temperature paste. The particulate metal oxide layer may include a polymeric linking agent of the type described in WO 03/065472 assigned to Konarka Technologies, lnc and/or the performance may be enhanced by an ALD coating of a metal oxide onto the metal oxide particulate layer which is for example described in WO 2009/013285.

The metal oxide particulate layer can be deposited onto the optical electrode (e.g. the TCO or TCO plus blocking layer) by doctor blading, screen-printing, spin coating, dip coating and/or by spray coating methods. In a typical example, the TiO₂ nanoparticles are mixed with an organic vehicle as described in J. M. Kroon Prog. Photovolt. Res. Appl. 15, 2007, 1-18.

Typical solids loading are between 5 and 50 weight percent of the nanoparticulate. The paste is applied by one of the film forming methods above to create a continuous film on the optical electrode. Following deposition, the resultant film is heated to remove the organic material. The temperature of this organic binder removal is typically between 5O⁰C and

500°C which is determined by the composition of the binder and the nature of the substrate. With the conventional DSSC procedure a heat treatment step of 400-600⁰C, preferably 430- 500⁰C, for instance at least 440⁰C, for example at least about 45O⁰C would normally be required to sinter the particulates to create both a connective pathway between the semiconducting particles and adhesion to the optical electrode.

With a low temperature paste such that removal of volatiles can be carried out at low temperatures of 100-200°C, for instance 140-160°C, for example less than or equal to 150°C we find that the efficiency can be improved by ALD overcoating of the particulate layer. The ALD procedure may also be conducted at or below such temperatures so that the entire process of cell construction may then be carried out at low temperatures preferably less than or equal to 150⁰C.

Typically the heat treatment step is carried out at the temperature of 100-600⁰C.

As to the dye in the present invention, any material may be used without any particular limitation as long as it is one compatible with use in the photovoltaic cell field.

According to a further embodiment, the photosensitized interconnected nanoparticle material includes a photosensitizing agent that includes a molecule selected from the group consisting of xanthines, cyanines, merocyanines, phthalocyanines, indolines, porphyrins, oligothiophenes, coumarins, perylenes, polyaromatic compounds and pyrroles.

According to another embodiment the photosensitizing agent is a metal complex that includes a metal atom or ion selected from the group consisting of multivalent metals. Preferably this is selected from the group consisting of a ruthenium transition metal complex, an osmium transition metal complex, an iron transition metal complex and rhenium transition metal complex.

In one illustrative embodiment, the photosensitizing agent is adsorbed (e.g. chemisorbed and/or physisorbed) on the interconnected nanoparticles. The photosensitizing agent may be adsorbed on the surfaces of the interconnected nanoparticles throughout the interconnected nanoparticles or both. The photosensitizing agent is selected, for example, based on its ability to absorb photons in a wavelength range of operation, its ability to produce free electrons in a conduction band of the interconnected nanoparticles and its effectiveness in complexing with or adsorbing onto the surface of the interconnected nanoparticles. Suitable photosensitizing agents may include, for example, dyes that include functional groups, such as carboxyl and/or hydroxyl groups, that can chelate to the nanoparticles, e.g. to Ti (IV) sites on a TiC>₂ surface. Examples of suitable dyes include, but are not limited to, anthocyanins, porphyrins, phthalocyanines, merocyanines, cyanines, squarates, eosins, and metal- containing dyes such as, for example, cis-bis (isothiocyanato) bis (2,2'-bipyridyl-4, 4'- dicarboxylato)-ruthenium (II) ("N3 dye"); tris (isothiocyanato)-ruthenium (ll)-2, 2' : 6', 2"- terpyridine-4,4', 4"- tricarboxylic acid; cis-bis (isothiocyanato) bis (2,2'-bipyridyl-4, 4'- dicarboxylato)-ruthenium (II) bis- tetrabutylammonium; cis-bis (isocyanato) (2,2'-bipyridyl-4, 4'dicarboxylato) ruthenium (II) ; and tris (2,2'-bipyridyl-4, 4'-dicarboxylato) ruthenium (II) dichloride, all of which are available from Solaronix SA.

Preferred examples of the dye are ruthenium complexes such as RuL₂(SCN)₂, RuL₂(H.₂O)₂, RuL₃, and RuL₂, wherein L represents 2,2'-bipyridyl-4,4'-dicarboxylate or the like. In addition to the ruthenium complexes, any dye may be used as long as it has a charge separation function and shows photosensitivity.

The DSSC may utilise an electrolyte layer made of a material that has a hole transport function. Examples of a material that can be used to form the electrolyte layer in the present invention include iodide/iodine in a suitable solvent such as acetonitrile or other suitable media.

The DSSC of the invention comprises a charge carrier material which may be of type known in the art. The charge carrier may be a liquid, gel, salt or solid electrolyte. The charge carrier material may be any material that facilitates the transfer of electrical charge from a ground potential or a current source to the interconnected nanoparticles (and/or a photosensitizing agent associated therewith). A general class of suitable charge carrier materials can include, but is not limited to solvent based liquid electrolytes, polyelectrolytes, polymeric electrolytes, solid electrolytes, n-type and p-type transporting materials (e.g. conducting polymers), and gel electrolytes, which are described in more detail below.

Other choices for the charge carrier material are possible. For example, the electrolyte composition may include a lithium salt that has the formula LiX, where X is an iodide, bromide, chloride, perchlorate, thiocyanate, trifluoromethyl sulfonate, or hexafluorophosphate. In one embodiment, the charge carrier material includes a redox system. Suitable redox systems may include organic and/or inorganic redox systems. Examples of such systems include, but are not limited to, Ce³⁺, Ce⁴⁺, sodium bromide/bromine, lithium iodide/iodine, Fe²VFe³⁺, Co²VCo³⁺, and viologens. Furthermore, an electrolyte solution may have the formula M|X_j, where i and j are greater than or equal to: 1. X is an anion, and M is selected from the group consisting of Li, Cu, Ba, Zn, Ni, lanthanides, Co, Ca, Al, and Mg. Suitable anions include, but are not limited to, chloride, perchlorate, thiocyanate, trifluoromethyl sulfonate, and hexafluorophosphate.

In some illustrative embodiments the charge carrier material includes a polymeric electrolyte. In one version, the polymeric electrolyte includes polyvinyl imidazolium halide) and lithium iodide. In another version, the polymeric electrolyte includes polyvinyl pyridinium salts). In still another embodiment, the charge carrier material includes a solid electrolyte. In one version, the solid electrolyte includes lithium iodide and pyridinium iodide. In another version, the solid electrolyte includes substituted imidazolium iodide.

According to some illustrative embodiments, the charge carrier material includes various types of polymeric polyelectrolytes. In one version, the polyelectrolyte includes between about 5% and about 100% (e. g. , 5-60%, 5-40%, or 5-20%) by weight of a polymer, e.g. an ion-conducting polymer, about 5% to about 95%, e.g. about 35-95%, 60-95%, or 80-95%, by weight of a plasticizer and about 0.05 M to about 10 M of a redox electrolyte, e.g., about 0.05 M to about 10 M, e.g. 0.05-2 M, 0.05-1 M, or 0.05-0.5 M, of organic or inorganic iodides, and about 0. 01 M to about 1 M, e.g., 0.05-5 M, 0.05-2 M, or 0.05-1 M, of iodine. The ion- conducting polymer may include, for example, polyethylene oxide (PEO), polyacrylonitrile (PAN), certain acrylics, polyethers, and polyphenols. Examples of suitable plasticizers include, but are not limited to ethyl carbonate, propylene carbonate, mixtures of carbonates, organic phosphates, butyrolactone, and dialkylphthalates.

The solar cells may be based on semiconducting organic materials. Typically, the active component of an organic cell comprises at least two layers of organic semiconducting materials disposed between two conductors or electrodes. At least one layer of organic semiconducting material is an electron acceptor, and at least one layer of organic material is an electron donor. An electron acceptor is a material that is capable of accepting electrons from another adjacent material due to a higher electron affinity of the electron acceptor. An electron donor is a material that is capable of accepting holes from an adjacent material due to a lower ionization potential of the electron donor. The absorption of photons in an organic photoconductive material results in the creation of bound electron-hole pairs, which must be dissociated before charge collection can take place. The separated electrons and holes travel through their respective acceptor (semiconducting material) to be collected at opposite electrodes.

The invention may be used for continuous fabrication of thin film DSSCs by performing, on a substantially continuously moving, elongated, flexible substrate having a transparent conductive oxide film layer, the following steps:

(a) optionally subjecting the TCO substrate to surface modification such as by plasma or corona discharge;

(b) masking the one or more regions of the TCO surface; (c) applying metal oxide film by ALD; and

The masked regions may be used to prepare a multiplicity of longitudinally and/ or laterally spaced regions of ALD deposited metal oxide. In one embodiment the regions are continuously formed and laterally spaced on the elongated flexible substrate.

For instance, the TCO layer is subject to surface modification by plasma discharge.

For example, the layer of metal oxide particles is prepared from a low temperature paste and removal of volatiles from the paste is carried out at a temperature of less than or equal to 150⁰C and the layer of metal oxide particles is overcoated by ALD of a metal oxide.

For example, the layer of metal oxide particles is overcoated with a metal oxide layer applied by ALD.

For example, a photosensitising agent is applied to the layer of metal oxide particles wherein the photosensitizing agent includes one or more agents selected from the group consisting of xanthines, cyanines, merocyanines, phthalocyanines, indolines, porphyrins, oligothiophenes, coumarins, perylenes and pyrroles. For instance, if the particulate metal oxide layer is overcoated with an ALD layer, the photosensitising agent is applied to the ALD overlayer. For instance, the particulate metal oxide layer is applied essentially only over the ALD layer (underlayer), for example, there is essentially no particulate metal oxide applied to the free or masked substrate.

Preferably the particulate metal oxide layer is applied only over the ALD layer, for instance, there is no particulate metal oxide applied to the free or masked substrate.

Brief Description of the Drawings

Referring to the attached drawings:

Figure 1a shows a schematic cross section of a patterned device in accordance with the invention;

Figure 1 b to 1 d show stages used in a process for patterning in accordance with the embodiment shown in 1a, namely Figure 1 b shows a conductive substrate; Figure 1c shows the selective area deposition using a negative pattern to deposit a positive layer;

Figure 1d shows an application of a printed nanoparticulate metal oxide layer to an ALD underlayer;

Figure 2 shows a schematic plan view image of a patterned device in accordance with this invention.

Figures 1 b to 1d show stages of the patterning process. Patterning occurs by use of a masking agent which creates exclusion zones on the surface (1 ) to be coated. A substrate (1 ) having patterned regions with a positive image (2) of the metal oxide film is deposited and printed with nano-particulate matter (3) is applied onto the metal oxide film having a dimension smaller area than the patterned structure. A topcoat (4) is deposited using a masking technique, but not necessarily the same method, is used to create another positive image of the underlying patterned film having the same or larger dimension.

Patterning can be used to create arrays of rectangular ALD metal oxide layers on the substrate of choice. The number of rectangles is limited by the width of the substrate. Fig 2 shows the positive image of the underlayer (2), printed nano-particulate matter (3) and a positive image top-coat (4)

The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

Examples

Example 1 The substrate to be coated is a polymer (PEN) with a conductive surface tin doped indium oxide (ITO). The polymer/ITO substrate is plasma treated in a vacuum chamber. A plasma discharge is induced by applying 4OW of 13.56 MHz RF power to an inductive loop outside the chamber. The water-plasma treatment of the polymer substrate typically takes 6 minutes. Water vapor is introduced from a small reservoir into an evacuated vacuum chamber during plasma discharge.

After removal from surface treatment and prior to ALD coating, a mask containing carbon fibers bound tightly to a metal frame are placed near but not touching the substrate to be deposited. The fixture is located 3mm above the coating surface and held by glass spacers. The carbon fiber is coated with a polyurethane resin having the same linear dimension as the negative. The substrate to be coated and framed fixture are positioned in the hot-zone of the deposition chamber. A thin film of titanium dioxide is deposited using a flow-type hot-walled F-120 ALD reactor from ASM Microchemistry. The chamber is continually flushed with nitrogen gas flowing at 350/200 seem, and pressure is maintained at less than a few mbar. Precursor vapor from titanium tetrachloride (TiCI₄) and water is delivered from Peltier cooled reservoirs maintained at 20⁰C. The pulsing sequence of the precursors is 0.4 seconds exposure of TiCI₄ followed by a 1.0 second nitrogen-only purge, then 1.0 second exposure of water followed by a 1.5 second nitrogen-only purge. Coating process is completed at 120⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. Typically 400 cycles of titanium dioxide are deposited.

A nano-particulate TiO₂ paste formulation from PECELL (product name PECC-C01-06) paste is applied by doctor blading. A nano-particulate film with area of 1 1 mm by 8mm is located in the centre of the substrate. The paste is allowed to dry at room temperature before post- thermal treatment at 150⁰C for 15 minutes.

Following thermal treatment, the substrate with nanoparticle thick-film is prepared for ALD top coating. The fixture is located 2mm or less above the coating surface and held by glass spacers. The carbon fiber, which is coated with a polyurethane resin having the same linear dimension as the negative, is placed over it. The substrate to be coated and framed fixture are positioned in the hot-zone of the deposition chamber. An ALD top coat is applied to the patterned surface with nanoparticulate metal oxide. The precursors and processing conditions are identical to the ALD underlayer. Coating process is completed at 120⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 100 cycles of titanium dioxide are deposited.

Example 2 The substrate to be coated is glass with a conductive FTO. The glass substrate is approximately 1.8cm by 1.6cm. The glass substrate is plasma treated in a vacuum chamber by applying 4OW of 13.56 MHz RF power to an inductive loop outside the chamber. The water-plasma treatment of the substrate is 6 minutes.

A negative image is applied with an organic solvent ink using a felt tipped pen such that a rectangular region remains uncoated. The substrate to be coated is positioned in the hot- zone of the ALD vacuum chamber. A thin film of titanium dioxide is deposited using a flow- type hot-walled F-120 ALD reactor from ASM Microchemistry. The chamber is continually flushed with nitrogen gas flowing at 350/200 seem, and pressure is maintained at less than a few mbar. Precursor vapor from titanium tetrachloride (TiCI₄) and water is delivered from Peltier cooled reservoirs maintained at 20⁰C. The pulsing sequence of the precursors is 0.4 seconds exposure of TiCI₄ followed by a 0.5 second nitrogen-only purge, then 0.5 second exposure of water followed by a 0.5 second nitrogen-only purge. Coating process is completed at 300°C and the thickness of the titania coating is controlled by the number of deposition cycles. 300 cycles are applied in this example.

A nano-particulate TiC>₂ paste formulation from Solaronix (product name Ti-Nanoxide 300) paste is applied by screen-printing using a 200 micron mesh. Nano-particulate metal oxide pad with area of 1 1 mm by 8mm is located in the centre of the substrate coating on top of both the ALD underlayer pattern and the conductive substrate. The paste is allowed to dry at room temperature before thermal de-binding and sintering to 450⁰C for 30 minutes.

Before the application of an ALD topcoat, the area surrounding the thick-film nano-particulate metal oxide is masked having a different design with an organic solvent ink. An ALD topcoat is applied by materials processes described above. Coating process is completed at 300⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 50 cycles of titanium dioxide are deposited.

Example 3

The substrate to be coated is a polymer (PEN) with a conductive tin doped indium oxide (ITO) surface layer. The polymer/ITO substrate is plasma treated in a vacuum chamber. A plasma discharge is induced by applying 4OW of 13.56 MHz RF power to an inductive loop outside the chamber. The water-plasma treatment of the polymer substrate typically takes 6 minutes. Water vapor is introduced from a small reservoir into an evacuated vacuum chamber during plasma discharge.

After removal from surface treatment and prior to ALD coating, a mask comprising an ink is applied to the conductive surface. The masked substrate is positioned in the hot-zone of the deposition chamber. A thin film of titanium dioxide is deposited using a flow-type hot-walled F-120 ALD reactor from ASM Microchemistry. The chamber is continually flushed with nitrogen gas flowing at 350/200 seem, and pressure is maintained at less than a few mbar. Precursor vapor from titanium tetrachloride (TiCI₄) and water is delivered from Peltier cooled reservoirs maintained at 20⁰C. The pulsing sequence of the precursors is 0.4 seconds exposure of TiCI₄ followed by a 1.0 second nitrogen-only purge, then 1.0 second exposure of water followed by a 1.5 second nitrogen-only purge. Coating process is completed at 120⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. Typically 50 cycles of titanium dioxide are deposited.

The inked region is removed by immersion of the sample in methanol to reveal a patterned area on the substrate.

A nano-particulate TiO₂ paste formulation from PECCELL (product name PECC-C01-06) paste is applied by doctor blading onto the patterned underlayer regions. A nano-particulate film with area of 30mm by 8mm is located on top of the patterned underlayer. The paste is allowed to dry at room temperature before post-thermal treatment at 150⁰C for 15 minutes.

Following thermal treatment, the substrate with nanoparticle thick-film is prepared for ALD top coating. An ink is applied to the uncoated regions of the substrate. The substrate to be coated with ink mask is placed in the hot-zone of the deposition chamber. An ALD top coat is applied to the patterned regions with nanoparticulate metal oxide. The precursors and processing conditions are identical to the ALD underlayer. Coating process is completed at

120⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 50 cycles of titanium dioxide are deposited.

Example 4

The substrate to be coated is glass with a conductive FTO layer. The glass substrate is approximately 40mm by 20mm. The glass substrate is plasma treated in a vacuum chamber by applying 4OW of 13.56 MHz RF power to an inductive loop outside the chamber. The water-plasma treatment of the substrate is typically carried out for 6 minutes.

A thin section of polyurethane is suspended above the substrate to be coated. The masked substrate to be coated is positioned in the hot-zone of the ALD vacuum chamber. A thin film of titanium dioxide is deposited using a flow-type hot-walled F-120 ALD reactor from ASM Microchemistry. The chamber is continually flushed with nitrogen gas flowing at 350/200 seem, and pressure is maintained at less than a few mbar. Precursor vapors from titanium tetrachloride (TiCI₄) and water are delivered from Peltier cooled reservoirs maintained at 20°C. The pulsing sequence of the precursors is 0.4 seconds exposure of TiCI₄ followed by a 1.0 second nitrogen-only purge, then 1.0 second exposure of water followed by a 1.5 second nitrogen-only purge. Coating process is completed at 120⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 200 cycles are applied in this example.

A nano-particulate TiO₂ paste formulation from PECCELL (product name PECC-C01-06) paste is applied by doctor blading onto the patterned underlayer regions. A nano-particulate film with area of 20mm by 8mm is located on top of the patterned underlayer. The paste is allowed to dry at room temperature before post-thermal treatment at 150°C for 15 minutes. Before the application of an ALD topcoat, the area surrounding the thick-film nano-particulate metal oxide is masked with a metal mask coated with a thin films of polyurethane. An ALD topcoat is applied by materials processes described above. Coating process is completed at 100⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 50 cycles of titanium dioxide are deposited.

Example 5

The substrate to be coated is glass with a conductive FTO. The glass substrate is approximately 40mm by 20mm. The glass substrate is plasma treated in a vacuum chamber by applying 4OW of 13.56 MHz RF power to an inductive loop outside the chamber. The water-plasma treatment of the substrate is carried out for 6 minutes.

The substrate to be coated is glass with a conductive FTO layer. A metal frame containing fine metal tubes is placed over the substrate to be patterned. The tubes are aligned in the same direction as the conductive rails of the FTO glass. The fixture is not touching the substrate and is located 2mm or less above the coated surface and held by glass spacers. The tubes with fine capillaries face towards the substrate. The tubes are connected to a manifold that is attached to a nitrogen gas source. The substrate to be coated and fixture with fine tubes are positioned in the hot-zone of the deposition chamber. A thin film of titanium dioxide is deposited using a flow-type hot-walled F-120 ALD reactor from ASM Microchemistry. The chamber is continually flushed with nitrogen gas flowing at 350/200 seem, and pressure is maintained at less than a few mbar. Precursor vapors from titanium tetrachloride (TiCI₄) and water are delivered from Peltier cooled reservoirs maintained at 20⁰C. The pulsing sequence of the precursors is 0.4 seconds exposure of TiCI₄ followed by a 0.5 second nitrogen-only purge, then 0.5 second exposure of water followed by a 0.5 second nitrogen-only purge. Coating process is completed at 200⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 100 cycles are applied in this example. A rectangular layer of titanium dioxide deposited by ALD is patterned on the transparent conductive region of the substrate

A nano-particulate layer of TiO₂ using paste formulation from Solaronix (product name Ti- Nanoxide 300) paste which is applied by screen-printing using a 200 micron mesh. The paste is allowed to dry at room temperature before thermal de-binding and sintering to 450°C for 30 minutes. Rectangular thick-films of TiO₂ are spaced at regular intervals to form an array.

Before the application of an ALD topcoat, the area surrounding the thick-film nano-particulate metal oxide is masked with a metal mask coated with a thin film of polyurethane. An ALD topcoat is applied by materials processes described above. Coating process is completed at 120⁰C and the thickness of the titania coating is controlled by the number of deposition cycles. 25 cycles of titanium dioxide are deposited.

Claims

WHAT IS CLAIMED:

1. A method for forming DSSCs comprising providing a TCO coated transparent substrate, masking one or more regions of the TCO surface; forming metal oxide layer on the masked TCO layer using ALD and removing the masking.

2. A method according to claim 1 wherein the masking provides a plurality of patterned regions of ALD metal oxide layer.

3. A method according to claim 1 or 2 wherein the patterning comprises using a masking agent that inhibits the deposition of the metal oxide on the surface.

4. A method according to any one of the previous claims wherein the mask is applied by a method selected from the group consisting of: a) application of a non-reacting ink to the surface followed by metal oxide deposition; b) application of a polymer mask placed adjacent to or touching the surface such that the adsorption/desorption occurring during ALD metal oxide deposition creates an area of exclusion on the surface; and c) application of a non-contact masking gaseous agent where a device located adjacent the surface emits a stream of gas that continually flushes a localised area of the surface thereby preventing the deposition of metal oxide during ALD processing.

5. A method of preparing a DSSC comprising forming an optical electrode such as ITO on a transparent substrate comprising; preferably subjecting the free surface of the optical electrode to surface modification such as with corona discharge or plasma discharge; masking the one or more regions of modified surface; applying a layer of metal oxide by ALD; and removing the mask to provide a plurality of laterally spaced apart ALD coated regions.

6. A method according to any one of the previous claims further comprising the step of applying a nanoparticulate metal oxide layer to the ALD deposited metal oxide.

7. A method according to claim 6 wherein the nanoparticulate metal oxide layer is deposited after removal of the mask.

8. A method according to claim 6 wherein the nanoparticulate layer is deposited and the mask subsequently removed.

9. A method according to any one of claims 1-4 for the substantially continuous fabrication of thin film DSSCs by performing, on a substantially continuously moving, elongated, flexible substrate having a transparent conductive oxide film layer, the following steps: (a) optionally subjecting the TCO substrate to surface modification such as by plasma or corona discharge; (b) masking the one or more regions of the TCO surface;

(c) applying metal oxide film by ALD; and

10. A method according to claim 9 wherein the the TCO layer is subject to surface modification by plasma discharge.

1 1. A method according to claim 9 or 10 further comprising applying a particulate metal oxide layer over the ALD layer either before or after removing the mask.

12. A method according to claim 1 1 further comprising further applying an ALD coating on the particulate metal oxide layer.

13. A method according to claim 12 wherein the layer of metal oxide particles is prepared from a low temperature paste and removal of volatiles from the paste is carried out at a temperature of less than or equal to 150⁰C and the layer of metal oxide particles is overcoated by ALD of a metal oxide.

14. A method according to any one of claims 6-8 or 1 1-13 wherein a photosensitising agent is applied to the layer of metal oxide particles wherein the photosensitizing agent includes one or more agents selected from the group consisting of xanthines, cyanines, merocyanines, phthalocyanines, indolines, porphyrins, oligothiophenes, coumarins, perylenes and pyrroles.

15. A method according to any one of claims 6-8 or 1 1-14, wherein the particulate metal oxide layer is applied essentially only over the ALD layer.