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• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
  • H10K71/10—Deposition of organic active material
  • H10K71/12—Deposition of organic active material using liquid deposition, e.g. spin coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
  • H01G9/20—Light-sensitive devices
  • H01G9/2027—Light-sensitive devices comprising an oxide semiconductor electrode
  • H01G9/2031—Light-sensitive devices comprising an oxide semiconductor electrode comprising titanium oxide, e.g. TiO2
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/14—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies
  • H10F77/148—Shapes of potential barriers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
  • H10K2102/301—Details of OLEDs
  • H10K2102/331—Nanoparticles used in non-emissive layers, e.g. in packaging layer
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/10—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising heterojunctions between organic semiconductors and inorganic semiconductors
  • H10K30/15—Sensitised wide-bandgap semiconductor devices, e.g. dye-sensitised TiO2
  • H10K30/151—Sensitised wide-bandgap semiconductor devices, e.g. dye-sensitised TiO2 the wide bandgap semiconductor comprising titanium oxide, e.g. TiO2
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/50—Photovoltaic [PV] devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
  • H10K71/20—Changing the shape of the active layer in the devices, e.g. patterning
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/542—Dye sensitized solar cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/549—Organic PV cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the present invention relates to the field of photovoltaic devices, for example organic photovoltaic devices.
• Organic solar cells offer the prospect of many attractive features and advantages over inorganic devices, such as flexibility, transparency, potential for continuous processing and possibility of formation of large area devices, as well as ecological and economic advantages. Further, they are cheaper to manufacture than inorganic solar cells.
• the most important consideration for photovoltaic devices is their conversion efficiency. Typically, commercial silicon based devices have a conversion efficiency of about 15%. Organic devices currently operate with a maximum efficiency of about 5%. In order to create an organic photovoltaic device that is able to compete with silicon based devices, an improvement by a factor of two would be desirable.
• PV organic photovoltaic
• one electrode In order to allow light into the cell, typically one electrode must be transparent and conductive, for example consisting of a thin film coating of indium tin oxide (ITO) or SnO 2 on a glass substrate.
• ITO indium tin oxide
• SnO 2 on a glass substrate.
• organic PV devices operate by combining organic materials which have donor and acceptor properties and providing a heterojunction between two such organic layers, where one layer is an electron transporter (acceptor) and the other is a hole transporter (donor).
• acceptor electron transporter
• donor-acceptor films are typically lOOnm in thickness.
• This exciton must reach a donor- acceptor interface in order to dissociate efficiently into free charge carriers.
• This dissociation is essential in solar cells such that when an exciton reaches an interface between the donor material and acceptor material, the electron of the electron hole pair (exciton) may be transferred to the acceptor material.
• the electron in the acceptor material is transported to the cathode, and the hole, remaining in the donor material, is transported to the anode.
• the diffusion length of an exciton is of the order of 10 to 50nm; for example in copper phthalocyanine (CuPc) it has been found experimentally to be about 30nm. Beyond this length the probability of the electron and hole recombining increases.
• Figure 2 shows a typical planar heteroj unction between a layer of donor material 40 and a layer of acceptor material 42.
• the organic layer is sandwiched between a transparent electrode 44 and a conductor electrode 46.
• the efficiency of devices with such a structure is limited by the diffusion length of the exciton, which is typically much shorter than the thickness of layers needed for useful light absorption.
• a typical example of such a mixed blend device is shown in Figure 3.
• a transparent electrode 48 and a conductor electrode 50 are situated on opposite sides of the mixed blend layer 52 made up of donor material 54 and acceptor material 56.
• the donor and acceptor materials are co- deposited to form a random distributed heterojunction.
• a further variation of such a mixed blend organic device has been developed, having multiple mixed blend layers.
• the composite is arranged in planar layers which are composed of blended donor material and acceptor material.
• the composition of the layers is graded, the composition of the layer nearest one electrode being made of 100 percent acceptor material, the proportion of acceptor materials then decreasing to zero percent acceptor material and 100 percent donor material in the layer adjacent to the second electrode.
• This type of device is, however, extremely difficult to manufacture.
• a 3D corrugated interface structure as shown in a cross sectional view in Figure 4, is desirable.
• Two electrodes 60, 62 are situated on opposite faces of the organic layer 64.
• the organic layer 64 is made up of corrugated 'fingers' of acceptor material 66 and donor material 68.
• the maximum thickness of these fingers should be about two times the exciton diffusion length in that material. All excitons will thus be formed within the diffusion distance of the acceptor-donor material interface and charge transfer to the electrodes is efficient.
• the exciton diffusion path is minimised. This leads to greater probability that the excitons dissociate at a heteroj unction, resulting in a current being generated by the cell, rather than the excitons recombining and the current being lost.
• Such a composite may for example be used in a photovoltaic device or any other semiconductor device, for example a sensor, a photodetector, or a light emitting diode.
• Figures 2, 3 and 4 show schematic cross-sectional views of a planar heterojunction, a distributed heterojunction and an idealised 3D corrugated interface structure, in known types of organic semiconductor devices.
• a nanocomposite organic film comprising a donor phase and acceptor phase in the form of interpenetrating lattices has been engineered, wherein the interfacial area between the phases is maximised.
• Continuous electrically conductive pathways formed by the respective lattices run between each phase and either the top or bottom electrode (substrate).
• one of the two phases is an inorganic material, i.e. a device could comprise an organic donor material and an inorganic acceptor material, or vice versa, the donor phase could be an inorganic material and the acceptor phase could be an organic material.
• an electrode 1 which may consist of any conducting material for example a flexible plastic material, for example an ITO coated transparent material, e.g. ITO coated glass, is coated with a layer of donor or acceptor material 3.
• the donor material might for example be a phthalocyanine, e.g. a metal phthalocyanine, such as copper phthalocyanine, and the acceptor material could for example be a fullerene or a perylene.
• the layer 3 may be an appropriate inorganic material, such as titanium oxide or zinc oxide. This layer of material enables continuous contact with the electrode.
• spheres 5 are then deposited at step 3 on the layer of material 3, for example by controlled self-assembly deposition from a colloid suspension.
• the spheres may be of any monodisperse, removable material, which is able to produce an ordered, hexagonally or cubic or other geometry close-packed structure. As this structure is ordered or structured and not random, each sphere will be in contact with all of its neighbours, and hence be interconnected.
• the removable particles may for example be polystyrene.
• any carrier solvent is then removed, leaving the layers of spheres in contact with each other but with the interstitial space 7 empty.
• the interstitial space 7 is then infiltrated at step 4 with a further amount of the donor or acceptor material 3 used to coat the electrode 1. This may be done for example by solution infiltration, by dipping or by deposition from the vapour phase.
• a sufficient top layer of the material 3 is then removed to allow access to the uppermost layer of spheres 5, if necessary. Due to the controlled nature of the self-assembly of the layers of spheres, this step will usually not be required.
• the spheres 5 are then removed from the structure by a suitable means so as to leave no residue, resulting in empty space where the spheres were. This might be by combustion, or by a low temperature process, preferably room temperature solution processing, for example the spheres may be removed by solvent extraction, or sonication.
• a skeleton of the donor or acceptor material 3 which is a lattice corresponding to and shaped as the interstitial spaces 7 and which is continuous and connected to the electrode 1.
• the voids created by removal of the spheres 5 are interconnected because the spheres were originally in contact with each other.
• the voids form a continuous lattice 9 that interpenetrates the skeleton 3.
• the interconnected lattice 9 comprising the empty space previously occupied by the spheres in the composite structure is then infiltrated at step 6 by the second phase material 11, which will be an acceptor material if material 3 was a donor material, or vice versa.
• the spheres need only be removable if they are 'sacrificial', as described above.
• the spheres may be 'non-sacrificial' in which case removability is not a desirable characteristic of the spheres.
• steps of removing the spheres and filling the resulting empty lattice with either donor or acceptor material as appropriate are omitted.
• Non-sacrificial particles may for example be used in inorganic-organic hybrid devices, wherein one of either the donor or the acceptor material is an inorganic material.
• the deposited particles could for example be titanium oxide or zinc oxide spheres, which are able to conduct.
• the particles could be an organic material, examples of which are given above, which would not be removed.
• the interstitial space 7 is infiltrated at step 4 with a further amount of the donor or acceptor material 3 used to coat the electrode 1.
• a continuous layer 13 of the second phase material 11 is then formed at the upper face of the composite structure and a second electrode 15, which may be of any appropriate material, for example a metal such as aluminium, gold or copper, is then applied to the layer 13 of the composite structure.
• Electrodes are then furnished with suitable electrical connections, by means known in the art.
• Protective coatings and anti-reflective layers may also be applied, as required.
• An additional exciton-, electron-, or hole-blocking layer, depending on the electrode material used, may be deposited to form layers at either or both electrodes to optimise the performance of the device. Such a layer would preferably have a thickness of approximately 10 to lOOnm.
• the composite device thus formed should have sufficient thickness to ensure efficient absorption of light, whilst the interlaced or interpenetrated nature of the structure provided by the topologically interconnected lattices or networks will ensure that excitons are only required to diffuse a short distance before encountering a donor-acceptor heteroj unction (i.e. at the boundary previously defined by a sphere), the interfacial area of which is maximised.
• a donor-acceptor heteroj unction i.e. at the boundary previously defined by a sphere
• the interfacial area of which is maximised.
• a simple, low cost and high throughput process is provided.
• Such a fabrication method can be used to form, for example, a photovoltaic device (solar cell).
• the volume ratio in the composite is approximately 74% spheres to 26% spaces for hexagonally packed structures.
• the volume ratio in the composite depends on the order of infiltration and on the processing methods and conditions, such as temperature. It can be optimised for any particular combination of donor and acceptor materials. If one of the donor or acceptor materials is the more efficient at light absorption for exciton generation, this more efficient material should preferably form the dominant phase, occupying the greater volume.
• three to four layers of spheres may be deposited, depending on the absorption coefficient and the exciton diffusion length of the materials selected.
• the array of spheres will be hexagonally or cubic close packed. Different size spheres may be used in different devices.
• Sphere size should relate to the exciton diffusion length in the material selected. Spheres may typically be approximately between 10 and 500nm in diameter. The smaller the diameter of the spheres used, the more layers may be required to achieve adequate light absorption. Preferably, for currently known materials, spheres may typically be about 50nm in diameter, in which case at least two layers of spheres are required at least for useful light absorption.
• the total film thickness of the composite structure of a typical organic PV device will usually be less than 150nm, in order to accommodate the short diffusion lengths of excitons, as discussed above.
• the optimum thickness of the composite structure will depend on the properties of the specific organic materials used.
• the diameter of the spheres would typically be in the range of 10 to 50nm, and the number of layers of spheres comprised in the composite structure will depend on the thickness of the composite structure.
• a 160nm thick composite structure would require 20 layers of spheres with a IOnm diameter.
• spheres having a diameter of 50nm are used, then four layers of spheres would be required in a 160nm thick composite structure.
• All process steps in fabrication may be carried out at low temperatures, preferably about room temperature, as required by the organic materials used. It will be understood by a person skilled in the art that the initial substrate applied to the first electrode and the subsequent infiltration may use an acceptor material in place of the donor material referred to, and the second infiltration would then be by a donor material
• a composite, as described herein may for example be used in a photovoltaic device, as well as any other electronic device which incorporates heterojunctions between electron donating and electron accepting material (i.e. electron and hole transporting materials), for example photo detection devices.
• electron donating and electron accepting material i.e. electron and hole transporting materials
• one of the acceptor and donor materials may be an organic material and one may be an inorganic material.
• both the acceptor and donor materials may be inorganic materials.
• the monodisperse particles may be any geometric shape which will pack to form a continuous interpenetrable lattice for example non-tessellating shapes or tessellating shapes laid out in a non-tessellating orientation and that any packing geometry may be adopted.
• a further alternative could comprise both larger and smaller, respectively monodisperse particles, where several of the smaller particles would pack together, for example hexagonally close packed, between larger particles, occupying the space that could alternatively be occupied by a larger particle.
• the resulting lattices would still be completely interconnected, as when particles of only one size are used.
• the electrodes may be reversed, that is, the transparent electrode may form the upper substrate as appropriate in the fabrication approach of Figure 1.
• lattice encompasses both regular and non- regular interconnected structures or arrays.
• monodisperse encompasses spheres or particles whose variation in diameter is extremely small.
• close packing will be understood to comprise both perfect close packing and nearly close packing.

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