COLLECTORS

Technical Field

The present invention relates to electrical and electronic devices with carbon based current collectors. The invention finds an application in optoelectronic devices and in particular in perovskite based photovoltaic devices.

Background to the Invention

Electricity production from solar energy using electronic devices such as photovoltaic devices holds great promise for a future with less reliance on fossil fuels. Prior art photovoltaic technology is generally based on materials which require large amounts of energy for their production, high processing temperatures, often in excess of 1,000 °C, and high materials purity requiring expensive, energy intensive and relatively slow high vacuum processing for some of the production steps. In order to tap solar power on a massively larger scale than today and to make a significant impact in combating unsustainable combustion of fossil fuels with its ensuing negative impacts such as environmental pollution and climate change, solar power has to become lower in cost and lower in embodied energy than today’s photovoltaic technologies. Over the past decade, organic-inorganic perovskite light absorbers have attracted tremendous interest for application in light harvesting devices due to their superior properties such as a direct band gap, high carrier mobility, large absorption coefficient, and ambipolar charge transport. While laboratory PSCs have achieved certified efficiencies close to 23% on par with the best multicrystalline Si or thin film CdTe and CIGS devices, they are generally based on expensive evaporated current collectors such as gold.

There remains a need to provide improved electrical and electronic devices.

Summary of the Invention

In a first aspect the present invention provides an electrical or electronic device including: a positive side and a negative side; the negative side includes carbon interspersed with an additive which is of an electron donating character.

The device may be an optoelectronic device. The device may be a photovoltaic device.

The additive which is of an electron donating character may include ammonia, amines, pyridines, pyrroles, pyrrolidones, phosphines such as triphenylphosphine and derivatives thereof, tetrathiafulvalene, dihydronicotinamide adenine dinucleotide, viologens such as benzyl viologens, hydrazine, charge-transfer complexes such as metallocenes such as cobaltocenes or ferrocenes, molecules or polymers with amine, oxygen, sulfur or other electron donating moieties such as polyethylene imine (PEI), polyvinyl alcohol (PVA), polysulfide rubbers, fullerenes and derivatives thereof, transition metal compounds such as SnCT. SnCh, ZnO, T1O ₂ , titanium suboxides, non noble metals such as alkali metals, Ti, Zn, Ga, Ge, Y, Zr, In, Sn, Pb, Bi or rare earth metals.

The additive which is of an electron donating character may include polyethylene imine.

The device may include a first carbon-based layer including the at least one additive of an electron donating character and a second layer with higher conductivity than the first layer.

The second layer may include a mixture of any combination of graphite, carbon nanotubes and metallic particles.

The second layer may include copper, aluminium, zinc, or alloys including solder material based on tin and other metals.

In a second aspect the invention provides a method of forming the negative side of an electrical or electronic device including the steps of: applying a layer of carbon interspersed with an additive which is of an electron donating character.

The additive which is of an electron donating character may include ammonia, amines, pyridines, pyrroles, pyrrolidones, phosphines such as triphenylphosphine and derivatives thereof, tetrathiafulvalene, dihydronicotinamide adenine dinucleotide, viologens such as benzyl viologens, hydrazine, charge-transfer complexes such as metallocenes such as cobaltocenes or ferrocenes, molecules or polymers with amine, oxygen, sulfur or other electron donating moieties such as polyethylene imine (PEI), polyvinyl alcohol (PVA), polysulfide rubbers, fullerenes and derivatives thereof, transition metal compounds such as SnCT. SnCh, ZnO, T1O ₂ , titanium suboxides, non noble metals such as alkali metals, Ti, Zn, Ga, Ge, Y, Zr, In, Sn, Pb, Bi or rare earth metals. The additive which is of an electron donating character may include polyethylene imine.

The method may fruther include the step of applying a second layer with higher conductivity than the first layer.

The second layer may include a mixture of any combination of graphite, carbon nanotubes and metallic particles.

The second layer may include copper, aluminium, zinc, or alloys including solder material based on tin and other metals.

Brief Description of the Drawings

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

FIG. 1 shows a schematic cross section through an embodiment of the present invention.

FIG. 2 shows a schematic cross section through an alternative embodiment of the present invention.

FIG. 3 shows 1 sun IV curves for Test.

FIG. 4 shows device MPPT efficiency stabilised over a 20 h illumination period for TestExample 1.

FIG. 5 shows 1 sun IV curve for Test 2.

FIG. 6 shows a schematic cross section through another embodiment of the present invention.

Detailed Description of Preferred Embodiments

An embodiment of an electronic device configuration is schematically shown in FIG. 1, which represents a single cell optoelectronic device in the form of a photovoltaic cell 10 being a subunit of a larger photovoltaic panel and does not show the encapsulation nor any cabling. In the embodiment of FIG. 1, substrate 1 is preferably transparent and consists of glass or polymer, which can be either rigid or flexible, and optionally contain antireflection, antifouling, antisoiling layers or a layer to improve scratch resistance. Device 10 includes a positive side in the form of positive side (p-side) current collector 2 which is in direct or indirect mechanical and electrical contact with the substrate 1, is preferably transparent to visible light and includes materials such as fluorine (FTO) or indium (ITO) doped tin oxide, aluminium-doped zinc oxide (AZO), various forms of carbon, including but not limited to carbon nanotubes, carbon black, graphite, graphene, doped or undoped conductive polymers or thin layers of metals such as Ni, Cu or Ag. An optional hole transport layer 3 is in direct or indirect mechanical and electrical contact with the p-side current collector 2 and contains materials such as NiO, CuO _x , CoO _x , CrO _x , MoO _x , CuMCh (where M includes but is not limited to Al, Ga, Cr), CuSCN, Cul, metal sulfides or selenides such as M0S2, MoSe2, T1S2, WS2 or electron-donor polymers or molecules such as PTAA or P3HT and other p-type materials known to those skilled in the art or any combination of above. A light absorber layer 4 is then in direct or indirect mechanical and electrical contact with optional hole transport layer 3. In a preferred embodiment said light absorber consists of a pervoskite material such as AMX3, wherein A represents Cs, formamidinium, methylammonium, guanidinium, Rb, K, Na or a mixture thereof, wherein M represents preferably Pb, Sn or a mixture thereof and wherein X represents I, Br, Cl, SCN or a mixture thereof. An optional electron transport layer 5 is in direct or indirect mechanical and electrical contact with light absorber layer 4 and contains materials such as SnCh, ZnO, T1O2, f illerenes such as C60, C70, C76 or Cs2, fullerene derivatives such as phenyl-C6l -butyric acid methyl ester (PCBM) or any inorganic or organic n-type material, including polymers, known to those skilled in the art or any combination of above. Finally, device 10 includes a negative side in the form of negative side (n-side) current collector 6 which is in direct or indirect mechanical and electrical contact with optional electron transport layer 5.

Optional hole transport layer 3 and optional electron transport layer 5 can be compact or porous or be a combination of at least one compact and one porous layer. Their doping level can be based on defect doping, e.g. NiOi _-y (y «1) and controlled through processing conditions such as temperature or be based an added dopants known to those skilled in the art.

Additionally, various interlayers between any of 1 to 6 can be applied with specific functions including but not limited to electron or hole blocking, work function adjustment, adjustment of wettability to facilitate deposition of subsequent layers, seed layers to facilitate crystallisation of subsequent layers, planarising layers for reducing surface roughness, mechanical and/or thermal protection from subsequent high-energy processes, buffer layers to minimise lattice mismatch and mechanical stress between various layers, optical coupling between different layers, barrier layers to minimise diffusion of H ₂ 0, O2 or other contaminants as well as ionic species such as halide- or metal-based species. Such interlayers can be based on a large variety of materials, including semiconducting oxides such as SnCh, ZnO, T1O2, insulating oxides such as AI2O3, Ga2C>3, ZrCh, 2D materials such as graphene or M0S2, metallo-organic compounds such as Ti or Zr acetates or acetylacetonates, organic molecules and polymers such as bathocuproine or PTAA.

The n-side current collector 6 is based on electrically conductive carbonaceous material including but not limited to graphite, carbon black, carbon nanotubes of the single wall or multiwall type, graphene, graphene oxide or reduced graphene oxide, a binder and/or surfactant and optionally other additives such as defoaming or levelling agents. Preferred carbon particle size is below 10 pm, at least in one direction in the case of non-spherical, anisotropic particles such as flakes, platelets, fibres, whiskers, nanowires, nanotubes or nanoflakes. Said binder can consist of polystyrene, polystyrene-butadiene, polyvinyl pyrrolidone, polyacrylonitrile, polyvinyl acetate, poly methyl methacrylate, polyvynylidene fluoride, polyvinyl butyral, cellulose or any other binder known to those skilled in the art. Said surfactant includes Triton X-100, sodium dodecylsulfonate, sodium dodecylbenzenesulfonate, Brij S 100, polyvinyl pyridine, polyethers, or any other surfactant or dispersant known to those skilled in the art. Optionally, the polymeric network, connecting the conductive carbon-based particles, can be created through in situ polymerization, optionally induced through light.

Additionally, the n-side current collector 6 contains at least one material with electron donating character, including molecules and moieties as part of a larger chemical structure or as part of a polymer such as ammonia, amines, pyridines, pyrroles, pyrrolidones, phosphines such as triphenylphosphine and derivatives thereof, tetrathiafulvalene, dihydronicotinamide adenine dinucleotide, viologens such as benzyl viologens, hydrazine, charge-transfer complexes such as metallocenes such as cobaltocenes or ferrocenes, molecules or polymers with amine, oxygen, sulfur or other electron donating moieties such as polyethylene imine (PEI), polyvinyl alcohol (PVA), polysulfide rubbers, fullerenes and derivatives thereof, transition metal compounds such as SnCk, SnCh, ZnO, TiCh, titanium suboxides, non-noble metals such as alkali metals, Ti, Zn, Ga, Ge, Y, Zr, In, Sn, Pb, Bi or rare earth metals.

In another embodiment the at least one material with electron donating character can also act as the binder. Examples of such electron donating binders include polyamines, poly(4- vinylpyridine), polyvinylaniline, polyaniline, polypyrroles, and polyethers.

The carbon-based n-side current collector 6 can be applied through different deposition methods, including but not limited to spray coating, ultrasonic spray coating, spin coating, blade coating, slot-die coating, ink-jet printing, screen printing, flexographic printing, lithographic printing, or other solution coating process known to those skilled in the art. Inks and pastes for the deposition of carbon pastes contain a solvent, in addition to aforementioned conductive carbonaceous material, binder, optional surfactant and additive with electron donating character, and other processing additives such as defoamers or levelling aids. Said solvent is preferably non-aqueous and includes solvents such as alcohols, ethers, hydroxylated ethers, ketones, glycol ethers or esters.

Said material with electron donating character can be added to the carbon electrode either by mixing the electron donating material to the carbonaceous material before deposition or through post-treatment of the deposited carbon layer. Alternatively or additionally, a layer of material with electron donating character can be applied in between the electron transport layer and the carbon electrode back contact or optionally between the light absorber and the carbon electrode back contact.

In another embodiment the carbon-based n-side current collector 6 can consist of more than one layer. A first carbon-based layer including at least one material with electron donating character can be applied directly on the electron transport layer or optionally on the light absorber layer followed by a second carbon layer with higher conductivity, such as a mixture of any combination of graphite, carbon nanotubes and metallic particles such as copper, nickel, zinc or any alloy known to those skilled in the art, optionally without a material with electron donating character. In another embodiment the carbon-based n-side current collector 6 with at least one material with electron donating character can be covered by a layer of non-carbonaceous material such as copper, aluminium, zinc, alloys including solder material based on tin and other metals. Said layer of non-carbonaceous material can be applied through any means known to those skilled in the art.

Another embodiment of this invention is schematically shown in FIG. 2, which represents a single cell 20 as a subunit of a larger photovoltaic panel and does not show the encapsulation nor any cabling. In an embodiment according to FIG. 2, substrate 1 consists of glass, polymer, concrete or metal such as steel, aluminium, nickel or copper. Substrate 1 can be either rigid or flexible. In case of a metal substrate, an electrical isolation layer (1A) can optionally be employed. Isolation layer (1A) can be of ceramic of polymeric nature and can be applied to said metal substrate though any coating or joining process known to those skilled in the art. An n-side current collector 6 is then in direct or indirect mechanical and electrical contact with the substrate (1/1A) and is based on conductive carbonaceous material including but not limited to graphite, carbon black, carbon nanotubes of the single wall or multiwall type, graphene, graphene oxide or reduced graphene oxide, a binder and/or surfactant and optionally other additives such as defoaming or levelling agents. An optional electron transport layer 5 is in direct or indirect mechanical and electrical contact with n-side current collector 6. A light absorber layer 4 is then in direct or indirect mechanical and electrical contact with optional electron transport layer 5. An optional hole transport layer 3 is in direct or indirect mechanical and electrical contact with light absorber layer 4. Finally, a p-side current collector 2 is in direct or indirect mechanical and electrical contact with hole transport layer 3, is preferably transparent to visible light and includes materials such as fluorine (FTO) or indium (ITO) doped tin oxide, aluminium-doped zinc oxide (AZO), various forms of carbon, including but not limited to carbon nanotubes, carbon black, graphite, graphene, doped or undoped conductive polymers or thin layers of metals such as Ni, Cu or Ag, including dielectric-metal -dielectric (DMD) multilayers. Alternatively or additionally, at least part of the p-side current collector 2 can be in the shape of a mesh or another array of current collector structures, including current collection fingers. Another embodiment is schematically shown in FIG. 6, which represents a single cell 30 of a battery or a supercapacitor, such as an electric double layer capacitor, and does not show the encapsulation nor any cabling. Device 30 includes a positive side in the form of positive side current collector 2, which is preferably a metal foil, mesh or expanded metal such as aluminium. A layer or zone of positive active mass 7 containing partially lithiated C0O2, FePCri, high surface area carbon or any positive side active material for electrochemical or electric double layer storage material known to those skilled in the art is in direct or indirect mechanical and electrical contact with positive side current collector 2. A layer of porous separator 8 including an electrolyte solution or alternatively polymeric or ceramic solid state ionic conductor 8A is then in direct or indirect mechanical and electrolytic contact with positive active mass 7. Device 30 includes a layer or zone of negative active mass 9 containing partially lithium metal or alloy, lithiated carbon, high surface area carbon or any negative side active material for electrochemical or electric double layer storage material known to those skilled in the art, which is in direct or indirect mechanical and electrolytic contact with porous separator 8 or polymeric or ceramic solid state ionic conductor 8A. Layer or zone of negative active mass 9 contains at least one material with electron donating character and may additionally be in mechanical and electrical contact with negative side substrate 10, which is preferably a metal foil, mesh or expanded metal such as copper.

TEST RESULTS TEST 1 :

A perovskite solar cell based on glass/FTO/NiO/lead halide perovskite/PCBM/bathocuproine was prepared through a sequence of spin coating and thermal annealing processes, followed by spray deposition under normal atmospheric conditions of a carbon ink consisting of 0.75 g graphite, 0.75 g graphitised mesoporous carbon, 0.6 g polyvinyl pyrrolidone and 0.2 g polyethylene imine ultrasonically dispersed in 15 g ethanol. The cell was then encapsulated using a glass cover and edge-sealed by epoxy. FIG. 3 shows the IV curve, recorded at a scan rate 20 mV/s, for this cell under illumination by a calibrated light source maintained at close to 1 sun. As FIG. 3 shows, there is virtually no hysteresis based on a first scan from high to low voltage followed by a scan from low to high voltage. Key performance parameters are summarised in TABLE 1 TABLE 1

The cell was then held under 1 sun illumination for 20 h at maximum power point using a perturb-and-observe tracking algorithm. FIG. 4 shows that the power output was, after a brief transient period, very stable. EXAMPLE 1 shows that photovoltaic cells based on a low-cost carbon-based p-side current collector containing polyethylene imine as the additive with electron donating character and applied under ambient atmosphere does provide a high-efficiency and long term stable photovoltaic device. TEST 2:

A perovskite solar cell based on glass/FTO/NiO/lead halide perovskite/PCBM/bathocuproine was prepared through a sequence of spin coating and thermal annealing processes, followed by spray deposition under normal atmospheric conditions of a carbon ink consisting of 0.75 g graphite, 0.75 g graphitized mesoporous carbon and 0.6 g polyvinyl pyrrolidone ultrasonically dispersed in 15 g ethanol. The cell was then encapsulated using a glass cover and edge-sealed by epoxy. FIG. 5 shows the IV curve, recorded at a scan rate 20 mV/s, for this cell under illumination by a calibrated light source maintained at close to 1 sun. In contrast to TEST1, performance is very poor, also summarised in TABLE 2.

TABLE 2

TEST 2 shows that photovoltaic cells based on a low-cost carbon-based n-side current collector not containing an additive with electron donating character such as polyethylene imine does not provide a high-efficiency photovoltaic device.

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.