Photon Multiplication Film

Abstract

A photon multiplication film comprises a first organic semiconductor, a luminescent agent and a light collecting material, wherein the light collecting material has a band gap, which provides that an exciton state formed in the light collecting material by absorption of light can be energy transferred to the first organic semiconductor, and the luminescent agent has a band gap, which provides that a triplet exciton state formed in the first organic semiconductor can be energy transferred to the luminescent agent; and wherein at least one of the first organic semiconductor and the light collecting material is capable of singlet fission.

Description

[0001] The present invention relates to a photon multiplying film and an opto-electronic device, such as a solar cell or a photovoltaic cell, comprising the same.

[0002] Low-bandgap solar cells like monocrystalline and multicrystalline silicon represent more than 90% of the global solar photovoltaic market. The highest efficiency (26.3%) using monocrystalline silicon is close to the theoretical limit of 29.4%. Improvements aimed at reducing optical losses and charge recombination are difficult and costly to achieve.

[0003] Therefore, much recent work is directed toward approaches that can exceed the theoretical limit. These approaches can be categorized as single-junction solar cells with carrier multiplication (maximum theoretical efficiency of about 39%); tandem solar cells, in which a combination of different materials with and without carrier multiplication is provided (theoretical efficiencies in the range of 39% to 47%); and spectral (up and down) conversion with or without photon multiplication.

[0004] Since around 2006, the use of singlet fission materials (eg, organic semiconductors) in photovoltaics has been actively investigated due to the material's potential to generate twice as many photons or charges across the spectrum.

[0005] Singlet fission in organic semiconductors is a spin-allowed process in which a singlet exciton (S1) formed upon light absorption is converted into two triplet excitons (T1).

[0006] For singlet fission to occur, the triplet exciton level must be close to half the energy of the singlet exciton, e.g. For single crystal silicon (band gap E g The singlet fission material needs to have an S1 energy level (blue-green light absorption) of 2.3 eV to 2.6 eV and a T1 energy level of 1.2 eV to 1.3 eV.

[0007] Note that singlet fission can be classified as endothermic or exothermic. In exothermic fission, the energy of the lowest singlet exciton (S1) is greater than twice the energy of the lowest triplet state (T1), ie, S1>2T1.

[0008] In endothermic fission, the energy of the lowest singlet exciton (S1) is less than twice the lowest triplet energy (T1), i.e., S1 < 2T1. In this case, the singlet exciton is initially converted into a correlated triplet pair state (TT state) whose energy is close to that of the singlet exciton. The TT state then splits into free triplet excitons (T1) via thermal activation.

[0009] WO 2014 / 001817 A1 discloses a solar cell in which an organic semiconductor layer capable of generating multiple excitons is provided on an inorganic semiconductor layer.

[0010] Photovoltaic efficiency enhancement via singlet fission spectral conversion has also been studied in solar cells. Purely optical coupling between a photon multiplier film and the underlying low-bandgap solar cell is advantageous because it places fewer demands on the singlet fission material functionality, e.g., no need to generate and conduct current. Furthermore, the photon multiplier film can be developed independently of well-optimized commercial cell production.

[0011] WO 2014 / 052530 A1 discloses a singlet fission photon multiplier film, which is used as an organic sensitizing window layer deposited on a silicon cell. The organic sensitizing window layer is composed of a singlet fission host material containing a phosphorescent emitter dopant, wherein the singlet fission host material has a triplet energy greater than or equal to the triplet energy of the phosphorescent emitter dopant.

[0012] The singlet state generated after the absorption of a high-energy photon by the singlet fission host undergoes fission into two triplet states, and each triplet state is transferred to a separate phosphorescent emitter dopant. This process results in two near-infrared photons being emitted from the phosphorescent emitter dopant, which are subsequently absorbed into the adjacent silicon cell, generating two electron-hole pairs.

[0013] US 2014 / 0224329 A1 and WO 2016 / 009203 A1 each disclose a photon multiplying film having a double layer including acene and / or lead chalcogenide quantum dots.

[0014] In these films, non-emissive triplet excitons are transferred to infrared-emitting quantum dots via Dexter energy transfer, which relies on orbital overlap between excited donors and excited acceptors.

[0015] The present invention relates to a photon multiplying film having a novel structure, the photon multiplying film comprising a light collecting material.

[0016] The light harvesting material in the present invention increases the range of light available to the organic semiconductor because it efficiently absorbs at wavelengths of light shorter than the absorption wavelength of the organic semiconductor and then transfers the energy to the organic semiconductor via a non-radiative transfer mechanism.

[0017] Light harvesting materials are well known and described in the literature. They generally include luminescent materials such as organic dyes, organic pigments or quantum dots. In particular, they may include more than one organic dye, organic pigment or quantum dot, which may be arranged in close proximity to each other, for example in a polymer matrix.

[0018] A light-collecting material includes polystyrene microspheres containing six different dyes, and shows efficient excitation energy transfer among the dyes. In the case of re-emission of light, the five dyes with the highest first excited state energy levels transfer their excitation to the sixth dye with the lowest energy level (see Roberts, DV et al., "Efficient Excitation Energy Transfer Among Multiple Dyes in Polystyrene Microspheres", Journal of Luminescence, 1988, (79), 225 to 231).

[0019] Another light-harvesting material includes a monolayer of different quantum dots, in which Förster resonance energy transfer between quantum dots is observed ( Resonance Energy Transfer) (FRET). The concentration of quantum dots in a monolayer and the overlap of quantum dot emission and absorption peaks can be used to control the efficiency of energy transfer among quantum dots (see Lunz, M. et al., "Influence of Quantum Dot Concentration on Forster Resonant Energy Transfer in Monodispersed Nanocrystal Quantum Dot Monolayers", in Physical Review, 2010, (B81), 205316).

[0020] Luminescent solar concentrators (LSCs) are planar sheets of material doped with luminescent materials (such as dyes) that emit light and propagate it in a waveguide mode toward the edge of the sheet. Because the surface area at the edge of the planar sheet is significantly smaller than the surface area of ​​the planar sheet that intercepts incident light, a concentrating effect is created.

[0021] Studies of photon trapping and energy transfer in multiple-dye plastic matrices have shown that energy transfer between dyes is caused by two competing non-radiative processes (see Swartz, BA et al., "Photon Trapping and Energy Transfer in Multiple-Dye Plastic Matrices: An Efficient Solar-Energy Concentrator", in Optics Letters, 1977, (1), 73).

[0022] Energy transfer from light harvesting materials to organic semiconductors capable of singlet fission and without subsequent re-emission of light has hardly been described in the literature.

[0023] An example is found in "Enhanced External Quantum Efficiency in an Organic Photovoltaic Cell via Singlet Fission Exciton Sensitizer" by Reusswig. PD et al., Applied Physics Letters, 2012, 101, 113304. Here, an enhanced external quantum efficiency in a double-layer organic photovoltaic cell is obtained when a singlet exciton donor layer is paired with a singlet exciton fission layer so that the singlet state generated in the donor layer can undergo singlet exciton fission. The triplet excitons generated by the singlet fission are separated into charges at the heterojunction of the photovoltaic cell and collected as photocurrent.

[0024] In a first aspect, the present invention provides a photon multiplying film comprising a first organic semiconductor, a luminescent agent and a light collecting material, wherein the light collecting material has a band gap, which provides that an exciton state formed in the light collecting material by absorption of light can be energy transferred to the first organic semiconductor, and the luminescent agent has a band gap, which provides that a triplet exciton state formed in the first organic semiconductor can be energy transferred to the luminescent agent, and wherein at least one of the first organic semiconductor and the light collecting material is capable of singlet fission.

[0025] The exciton state formed in the light harvesting material may be a singlet exciton state or a singlet-like exciton state, or a triplet exciton state or a triplet-like exciton state.

[0026] The triplet exciton state formed in the first organic semiconductor may be generated by singlet fission in the first organic semiconductor or by energy transfer of the triplet exciton state or triplet-like exciton state from the light harvesting material to the first organic semiconductor.

[0027] The first organic semiconductor capable of singlet fission is an organic semiconductor that supports singlet fission upon irradiation of the film with light of an appropriate wavelength.

[0028] Similarly, a light-collecting material capable of singlet fission is a material that collects light and supports singlet fission after irradiating the film with light of an appropriate wavelength. The light-collecting material may include a second organic semiconductor and optionally a luminescent material that supports singlet fission after irradiating the film with light of an appropriate wavelength.

[0029] In some embodiments, the first organic semiconductor is capable of singlet fission and the light-collecting material is not capable of singlet fission. In other embodiments, the light-collecting material is capable of singlet fission and the first organic semiconductor is not capable of singlet fission. Of course, each of the first organic semiconductor and the light-collecting material may be capable of singlet fission.

[0030] In one embodiment, the photon multiplying film comprises a layer of a first organic semiconductor in which a luminescent agent and a light collecting material are provided.

[0031] In this embodiment, the luminescent agent and the light collecting material comprise discrete entities distributed within the layer of the first organic semiconductor.

[0032] In another embodiment, the photon multiplying film comprises a layer of a host material in which a first organic semiconductor, a luminescent agent, and a light collecting material are provided.

[0033] In one such embodiment, the first organic semiconductor and the luminescent agent are discrete entities distributed within a layer of host material with sufficient proximity between the first organic semiconductor and the luminescent agent for energy transfer of exciton triplet states from the first organic semiconductor to the luminescent agent.

[0034] In another such embodiment, the first organic semiconductor is chemically attached to the luminescent agent.The density of the first organic semiconductor ligands on the luminescent agent may or may not provide sufficient proximity between the ligands for singlet fission to occur.

[0035] In both embodiments, the light harvesting material is provided as a discrete entity within a layer of host material with sufficient proximity between the light harvesting material and the first organic semiconductor for energy transfer of exciton states formed in the light harvesting material to the first organic semiconductor.

[0036] In international patent application WO 2018 / 189527 A1, which is incorporated herein by reference in its entirety, a photon multiplying film is described, which includes a layer of a host material in which an organic semiconductor capable of singlet fission and a luminescent agent are provided as discrete materials within the layer.

[0037] In some embodiments, the first organic semiconductor is chemically attached to the luminescent agent through a linking group that maintains a distance between the first organic semiconductor and the luminescent agent under the condition that triplet exciton states formed in the first organic semiconductor can be energy transferred to the luminescent agent.

[0038] In particular, the distance between the first organic semiconductor and the luminescent agent may be less than 2.0 nm, preferably less than 1.0 nm, and more preferably less than 0.5 nm.

[0039] In one embodiment, the first organic semiconductor is chemically attached to the luminescent agent and is capable of singlet fission. In this embodiment, the linking group and band gap of the luminescent agent provide that the exciton triplet formed by the singlet fission in the attached first organic semiconductor can be energy transferred to the luminescent agent.

[0040] In international patent application WO 2019 / 110971 A1, which is incorporated herein by reference in its entirety, a photon multiplying film is described, which includes a layer of a host material in which an organic semiconductor is chemically attached to a luminescent agent as a ligand and undergoes singlet fission.

[0041] In these embodiments, the light collecting material may not be capable of singlet fission, and in particular, may include a luminescent material.

[0042] The distribution of the light emitting material within the host material provides sufficient proximity between the light emitting material and the first organic semiconductor so that singlet excitons formed in the light emitting material by absorption of light can be energy transferred to the first organic semiconductor.

[0043] In particular, energy transfer between the light harvesting material and the first organic semiconductor may occur via Forster Resonance Energy Transfer (FRET).

[0044] In other embodiments, the first organic semiconductor is chemically attached to the luminescent agent and is not capable of singlet fission. In this embodiment, the linking group and band gap of the luminescent agent provide that the exciton triplet formed in the attached first organic semiconductor can be energy transferred to the luminescent agent.

[0045] In these embodiments, the light harvesting material is capable of singlet fission.The light harvesting material may include or may consist of a second organic semiconductor capable of singlet fission.

[0046] In one such embodiment, the light harvesting material comprises a light emitting material and a second organic semiconductor capable of singlet fission. In this embodiment, singlet exciton states formed in the light emitting material can be energy transferred to the second organic semiconductor.

[0047] The distribution of the light emitting material and the second organic semiconductor within the host material provides sufficient proximity between the light emitting material and the second organic semiconductor for energy transfer of a singlet exciton state formed in the light emitting material to the second organic semiconductor.

[0048] The distribution of the first organic semiconductor and the second organic semiconductor within the host material provides sufficient proximity between the first organic semiconductor and the second organic semiconductor for energy transfer to the first organic semiconductor from triplet exciton states formed in the second organic semiconductor by singlet fission.

[0049] The energy transfer between the light harvesting material and the first organic semiconductor may occur via Dexter Energy Transfer (DET).The energy transfer between the light emitting material and the second organic semiconductor of the light harvesting material may occur via Forster Resonance Energy Transfer (FRET).

[0050] In yet another embodiment, the light harvesting material is composed of a second organic semiconductor, and triplet exciton states formed in the second organic semiconductor by singlet fission can be energy transferred to the first organic semiconductor.

[0051] In this embodiment, the distribution of the first organic semiconductor and the second organic semiconductor within the host material provides sufficient proximity between the first organic semiconductor and the second organic semiconductor so that triplet exciton states formed in the second organic semiconductor by singlet fission can be energy transferred to the first organic semiconductor.

[0052] Energy transfer between the light harvesting material and the first organic semiconductor may occur via Dexter Energy Transfer (DET).

[0053] In all of these embodiments, energy transfer between the first organic semiconductor and the luminescent agent may also occur via Dexter Energy Transfer (DET).

[0054] Note that the distribution of the first organic semiconductor, the luminescent agent, and the light harvesting material within the host material can be controlled, at least in part, by the selection of the mass concentrations of the first organic semiconductor, the luminescent agent, the light harvesting material, and the host material.

[0055] When the film is prepared by solution processing, the distribution can also be controlled by the choice of solvent for one or more of the first organic semiconductor, luminescent agent, light harvesting material and host material and the processing conditions.

[0056] The choice of mass concentration, choice of solvent and processing conditions are such that the structure (or morphology) of the film supports one or more of the distances required for energy transfer mentioned above (typically less than or equal to 4 nm in the case of FRET and less than or equal to 1 nm in the case of DET).

[0057] Note that varying the mass concentration of the host material provides for tuning of the photon multiplying film by varying the proximity of the first organic semiconductor, the luminescent agent, and the light harvesting material to each other within the film.

[0058] The mass concentration of the host material may range between 0.0% and 99.9% of the mass of the membrane. In some cases, it may be less than 20.0% of the mass of the membrane, for example, less than 10% or less than 5%.

[0059] The mass concentration of the light harvesting material may generally exceed the mass concentration of the first organic semiconductor in the host material.

[0060] The ratio of the mass concentration of the light collecting material to the mass concentration of the first organic semiconductor (whether or not chemically attached to the luminescent agent) can vary greatly depending on the choice of the light collecting material and the first organic semiconductor. In one embodiment, the ratio can be, for example, between 2:1 and 100:1, in particular between 10:1 and 80:1, for example between 10:1 and 50:1, but in other embodiments, it can differ by an order of magnitude or more.

[0061] As mentioned above, the light collecting material may comprise or may consist of a luminescent material and / or a second organic semiconductor capable of singlet fission.

[0062] The luminescent material may include or consist of one or more of organic dyes, organic pigments, or colloidal inorganic nanocrystals such as quantum dots (and mixtures thereof).

[0063] In particular, the luminescent material may include or may consist of one or more (eg, two, three or four) of the organic dyes.

[0064] In one embodiment, the luminescent material consists of a 50:50 mixture of 1,3,6,8(2H,7H)-tetraone, 2,7-dicyclohexylbenzo[1mn][3,8]-phenanthroline and N,N'-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic acid diimide.

[0065] Organic dyes can be usually separated from each other, but can be combined or associated with each other when they are arranged together in a host material. They can be covalently bound to each other or to a matrix material such as a polymer or oligomer.

[0066] The luminescent material may include a polymer or oligomer, or may consist of a polymer or oligomer, wherein one or more of an organic dye, an organic pigment or a quantum dot is covalently bound within a long chain of polymer or oligomer molecules and is covalently bound to the long chain, or is covalently bound to the long chain as a side group.

[0067] Alternatively or additionally, the light emitting material may include, or may consist of, one or more of high bandgap quantum dots.

[0068] Suitable high bandgap quantum dots include those having a core structure comprising CdSe, CdS, ZnTe, ZnSe, HgS, HgSe, HgTe, HgCdTe, CdTe, CZTS, ZnS, CuInS2, CuInGaSe, CuInGaS, Si, InAs, InP, InSb, SnS2, CuS, graphene, and metal halide perovskites such as CsPbBr3, CsPbCl3, CsPbBr 3-x Cl x One or more of .

[0069] The diameter of the quantum dots may be 50 nm or less, preferably 20 nm or less, preferably 10 nm or less and more preferably 5 nm or less.

[0070] In any case, the luminescent material can provide more than one luminescent entity, each of which has a band gap different from any other luminescent entity, so that light can be absorbed by any of the luminescent entities and the exciton singlet states generated therein can be energy transferred from the luminescent entity to a luminescent entity having an adjacent lower band gap.

[0071] The singlet energy transfer can be repeated on multiple light-emitting entities with adjacent lower band gaps until the light-emitting entity with the most suitable or lowest energy band gap is reached.

[0072] In any case, the light collecting material may comprise at least one luminescent entity having a band gap in the energy range of 1.4 eV to 4.5 eV, preferably 2.0 eV to 4.5 eV and more preferably 2.2 eV to 4.0 eV.

[0073] The host material may include any organic material that changes the morphology of the organic semiconductor, luminescent agent, and light collecting material to improve photon multiplication. The host material may or may not be combined with one or the other of the first organic semiconductor, luminescent agent, or light collecting material. It may include small molecules, oligomers, homopolymers, copolymers, macromolecules, dendrimers, or three-dimensional networks of organic molecules.

[0074] The host material may be synthetic or natural in origin. It may include a variety of chemical structures that provide uniform dispersion of organic semiconductors, luminescent materials, and light collecting materials. These chemical structures may include functional groups such as alcohols, carboxylic acids, thiols, primary, secondary or tertiary amines, phosphines, phosphonic acids, urethanes, imides, and silanols that provide hydrogen bonding to at least one of the organic semiconductors, luminescent materials, and light collecting materials.

[0075] In a preferred embodiment, the host material provides a film that is substantially transparent to visible and infrared light.

[0076] In particular, the main body material may include an organic polymer. The polymer may be selected from a variety of polymers and their derivatives, including polybutyral, polyamide, polyurethane, polythiol, polyester, polymethacrylate, polymethyl methacrylate, epoxy resin, polycarbonate, polyolefin, EVA, silicone.

[0077] The host material may also be selected from suitable macromolecules of natural origin, including carbohydrates, proteins, nucleic acids, and lipids.

[0078] The first organic semiconductor may be selected such that it has a triplet energy greater than the band gap of the luminophore. Preferably, the triplet energy of the first organic semiconductor is + / - 0.4 eV, preferably + / - 0.3 eV and more preferably + / - 0.2 eV of the band gap of the luminophore.

[0079] In some embodiments, the first organic semiconductor has a band gap in the range of 1.4 eV to 4.0 eV, preferably 2.0 eV to 3.0 eV, and more preferably 2.3 eV to 2.6 eV.

[0080] The first organic semiconductor and the second organic semiconductor capable of singlet fission may be selected from any organic material in which multi-exciton generation can occur.

[0081] For example, the first organic semiconductor and the second organic semiconductor may be small molecules, oligomers, homopolymers, copolymers, macromolecules, dendrimers, or organometallic complexes.

[0082] The first organic semiconductor and the second organic semiconductor can be designed to have a wide range of variations in chemical structure. They can include or consist of one or more of acene, perylene, rylene, diketopyrrolopyrrole, fluorene, carotenoid or benzofuran moieties or molecules, phenazinothiadiazole, molecules containing isoindigo moieties or isoindigo (such as in the isoindigo-based polymer IIDDT-Me), zethrene (diradicals), and bithiophene (e.g., tetracyanomethylenequinolinebithiophene).

[0083] These parts or molecules may be unsubstituted or substituted with substituents. In particular, the substituents may include C1 to C 10 (e.g., C1 to C4) alkyl group, alkenyl group or alkynyl group.

[0084] In particular, the first organic semiconductor capable of singlet fission may be 6,11-bis-((triisopropylsilyl)ethynyl)tetracene or a ligand derived from a substituted tetracene, such as 6,11-bis-((triisopropylsilyl)ethynyl)tetracene-2-carboxylic acid.

[0085] In particular, the second organic semiconductor capable of singlet fission may be 6,11-bis-((triisopropylsilyl)ethynyl)tetracene.

[0086] The luminescent agent may be selected from any luminescent material to which excitation can be transferred from the first organic semiconductor and emit at a lower energy.

[0087] In particular, the luminescent agent can be an organic transition metal phosphorescent, thermally activated delayed fluorescence (TADF), quantum dots (metal chalcogenides, III-V, II-VI, Si, Ge, graphene, graphene oxide, metal halide perovskites), emitter small molecules, oligomers, dendrimers, polymers or macromolecules or 2D-materials.

[0088] The quantum dots may have a core structure comprising CdSe, CdS, ZnTe, ZnSe, PbS, PbSe, PbTe, HgS, HgSe, HgTe, HgCdTe, CdTe, CZTS, ZnS, CuInS2, CuInSe x S 2-x , CuGaS2, AgInSe2, CuInGaSe, CuInGaS, silicon, InAs, InP, InSb, SnS2, CuS, graphene, graphene oxide, metal halide perovskite, germanium and Fe2S3.

[0089] The diameter of the quantum dots may be 50 nm or less, preferably 20 nm or less, preferably 10 nm or less and more preferably 5 nm or less.

[0090] In a preferred embodiment, the luminescent agent has an energy band gap in the range of 0.6 eV to 2.0 eV, preferably 0.8 eV to 1.7 eV, more preferably 0.9 eV to 1.4 eV.

[0091] In embodiments where the luminophore is not chemically attached to the organic semiconductor, the quantum dots can be sterically passivated with organic ligands, for example, with ligands including short to medium chain thiols such as 1-octanethiol or hydrocarbon carboxylic acids such as octanoic acid.

[0092] In embodiments where the luminophore is chemically attached to the organic semiconductor, the quantum dots may include passivating ligands, such as those described above, as well as those ligands that include semiconducting portions derived from organic semiconductor molecules.

[0093] The photon multiplying film may absorb light at a first wavelength (eg, visible light) and re-emit the light at a second wavelength (eg, infrared light) that is lower than the first wavelength.

[0094] Note that the photoluminescence quantum efficiency (PLQE) of the film may or may not be greater than 100%. In particular, it may be between 1% and 200% or between 5% and 200%.

[0095] In a second aspect, the present invention provides a photon multiplying film, which includes a light-collecting material, a first organic semiconductor capable of singlet fission, and a luminescent agent, wherein the light-collecting material includes a luminescent material having a band gap, which provides a singlet exciton state formed in the light-collecting material by absorption of light and can be energy transferred to the first organic semiconductor, and the luminescent agent has a band gap, which provides a triplet exciton state formed in the first organic semiconductor by singlet fission and can be energy transferred to the luminescent agent.

[0096] The first organic semiconductor may be attached to the luminescent agent via a chemical linking group.Alternatively, the first organic semiconductor and the luminescent agent may be provided as discrete entities within the film.

[0097] In a third aspect, the present invention provides a photon multiplying film, which includes a light-collecting material, a first organic semiconductor and a luminescent agent, wherein the light-collecting material includes a second organic semiconductor capable of singlet fission and having a band gap, which provides a triplet exciton state formed by singlet fission through absorption of light in which energy can be transferred from the second organic semiconductor to the first organic semiconductor, and the luminescent agent has a band gap, which provides a triplet exciton state formed in the first organic semiconductor by energy transfer to the luminescent agent.

[0098] The first organic semiconductor may or may not be capable of singlet fission.

[0099] In a fourth aspect, the present invention provides a photon multiplying film, which includes a light-collecting material, a first organic semiconductor and a luminescent agent, wherein the light-collecting material includes a luminescent material and a second organic semiconductor, the second organic semiconductor being capable of singlet fission, and wherein the luminescent material has a band gap that provides that a singlet exciton state formed in the luminescent material by absorption of light can be energy transferred to the second organic semiconductor, and has a band gap that provides that a triplet exciton state formed on energy transfer of a singlet exciton from the luminescent material to the second organic semiconductor by singlet fission can be energy transferred from the second organic semiconductor to the first organic semiconductor, and the luminescent agent has a band gap that provides that a triplet exciton state formed in the first organic semiconductor can be energy transferred to the luminescent agent.

[0100] The first organic semiconductor may or may not be capable of singlet fission.

[0101] In a fifth aspect, the present invention provides an exciton multiplication film. The exciton multiplication film may comprise substantially the same components as described for the films of the first to fourth aspects of the present invention.

[0102] In a sixth aspect, the present invention provides an optoelectronic device comprising a photon multiplying film or an exciton multiplying film according to the first aspect or the fifth aspect, wherein the photon multiplying film or the exciton multiplying film is optically connected to an optoelectronic element such as a solar cell, a photodetector, a light-emitting diode, a field effect transistor, a display, a sensor or a biological imaging device.

[0103] Embodiments of the second to sixth aspects of the invention will be apparent from those described with respect to the first aspect.

[0104] The present invention also provides the following items:

[0105] 1. A photon multiplication film, comprising:

[0106] A first organic semiconductor; a light collecting material and a luminescent agent, wherein the light collecting material has a band gap, which provides that an exciton state formed in the light collecting material by absorption of light can be energy transferred to the first organic semiconductor, and the luminescent agent has a band gap, which provides that a triplet exciton state formed in the first organic semiconductor can be energy transferred to the luminescent agent; and wherein at least one of the first organic semiconductor and the light collecting material is capable of singlet fission.

[0107] 2. The film according to item 1, wherein the first organic semiconductor, the luminescent agent and the light collecting material are disposed within a host material.

[0108] 3. A film according to item 1 or item 2, wherein the first organic semiconductor is chemically attached to the luminescent agent via a linking group, and the linking group of the luminescent agent and the band gap provide that the exciton triplet formed in the attached first organic semiconductor can be energy transferred to the luminescent agent.

[0109] 4. The film according to item 1 or item 2, wherein the first organic semiconductor is capable of singlet fission and is not attached to the luminescent agent.

[0110] 5. The film according to item 3 or item 4, wherein the light collecting material comprises a luminescent material and provides that exciton states formed therein by absorption of light can be energy transferred to the first organic semiconductor.

[0111] 6. The film according to item 3, wherein the light collecting material comprises a luminescent material and a second organic semiconductor capable of singlet fission, wherein an exciton state formed in the luminescent material can be energy transferred to the second organic semiconductor.

[0112] 7. The film according to item 6, wherein a triplet exciton state formed in the second organic semiconductor by singlet fission can be energy-transferred to the first organic semiconductor.

[0113] 8. The film according to item 3, wherein the light collecting material comprises a second organic semiconductor capable of singlet fission, and wherein a triplet exciton state formed in the second organic semiconductor by singlet fission can be energy transferred to the first organic semiconductor.

[0114] 9. The film according to any one of items 5 to 7, wherein the luminescent material comprises one or more of an organic dye, an organic pigment or quantum dots.

[0115] 10. A film according to item 9, wherein the luminescent material comprises more than one luminescent entity, wherein each luminescent entity has a band gap different from any other luminescent entity, so that light can be absorbed by any of the luminescent entities and excitons generated therein can be energy transferred from the luminescent entity to an adjacent luminescent entity with a lower band gap.

[0116] 11. The film according to item 9 or item 10, wherein the luminescent material has at least one band gap in the energy range of 1.4 eV to 4.5 eV, preferably 2.0 eV to 4.5 eV and more preferably 2.2 eV to 4.0 eV.

[0117] 12. The film according to any preceding item, wherein the luminescent agent has a band gap in the range of 0.6 eV to 2.0 eV, preferably 0.8 eV to 1.7 eV and more preferably 1.0 eV to 1.5 eV.

[0118] 13. The film according to any preceding item, wherein the triplet energy of the first organic semiconductor is within 0.4 eV, preferably within 0.3 eV, and more preferably within 0.2 eV of the band gap of the luminescent agent.

[0119] 14. The film according to any preceding item, wherein the first organic semiconductor has a band gap in the range of 1.4 eV to 4.0 eV, preferably 2.0 eV to 3.0 eV and more preferably 2.3 eV to 2.6 eV.

[0120] 15. A film according to any of the preceding items, wherein the first organic semiconductor comprises one or more of acene, perylene, rylene, diketopyrrolopyrrole, fluorene, carotenoid or benzofuran, phenazine thiadiazole, isoindigo moiety or isoindigo-containing molecule (such as in isoindigo-based polymer IIDDT-Me), anthracene (diradical class) and bithiophene (e.g., tetracyanomethylenequinolinebithiophene).

[0121] 16. A film according to any one of items 6 to 15, wherein the second organic semiconductor comprises one or more of acene, perylene, rylene, diketopyrrolopyrrole, fluorene, carotenoid or benzofuran, phenazine thiadiazole, isoindigo moiety or isoindigo-containing molecules (such as in the isoindigo-based polymer IIDDT-Me), anthracene (diradical class) and bithiophene (e.g., tetracyanomethylenequinolinebithiophene).

[0122] 17. A film according to any preceding item, wherein the luminescent agent is an organic transition metal phosphor, a thermally delayed phosphor, a colloidal nanocrystal such as a quantum dot, or an emitter small molecule, oligomer, dendrimer, polymer, macromolecule or 2-D material.

[0123] 18. The film of item 17, wherein the quantum dots have a core structure comprising CdSe, CdS, ZnTe, ZnSe, PbS, PbSe, PbTe, HgS, HgSe, HgTe, HgCdTe, CdTe, CZTS, ZnS, CuInS2, CuGaS2, CuInSe x S 2-x , AgInSe2, CuInGaSe, CuInGaS, silicon, InAs, InP, InSb, SnS2, CuS, graphene, graphene oxide, metal halide perovskite, germanium and Fe2S3.

[0124] 19. A film according to item 17 or item 18, wherein the quantum dots have a diameter of 50 nm or less, preferably 20 nm or less, preferably 10 nm or less and more preferably 5 nm or less.

[0125] 20. The film of any one of items 2 to 19, wherein the host material is an organic material selected from the group consisting of small molecules, oligomers, homopolymers, copolymers, macromolecules, dendrimers, or three-dimensional networks of organic molecules.

[0126] 21. A film according to any one of items 2 to 20, wherein the host material is selected from the group consisting of polybutyral, polyamide, polyurethane, polythiol, polyester, polymethacrylate, polymethyl methacrylate, epoxy resin, polycarbonate, polyolefin, EVA, silicone, carbohydrate, protein, nucleic acid and lipid.

[0127] 22. An optoelectronic device comprising a photon multiplying film according to any preceding clause in optical communication with an optoelectronic element such as a solar cell, a photodetector, a light emitting diode, a field effect transistor, a display, a sensor or a bio-imaging device.

[0128] The invention will now be described in more detail, by way of example only, and in view of the following description and accompanying drawings, in which:

[0129] Figure 1 is a scheme illustrating the absorption, emission and energy transfer processes involved in some embodiments of the present invention;

[0130] Figure 2 is a scheme showing the absorption, emission and energy transfer processes involved in other embodiments of the present invention;

[0131] Figure 3 is a schematic diagram of a photon multiplication film according to one embodiment of the present invention;

[0132] Figure 4 is a schematic diagram of a photon multiplication film according to another embodiment of the present invention;

[0133] Figure 5 is a graph showing the emission spectrum of a light-harvesting material (including two organic dyes) and the absorbance of PbS-Tet;

[0134] Figure 6 The absorption spectra of other films are compared with the Figure 4 A graph of the absorption spectrum of the photon multiplying film of the illustrated embodiment at wavelengths of incident light between 300 nm and 600 nm;

[0135] Figure 7 Shown according to Figure 4 A graph of normalized photoluminescence quantum efficiency (PLQE) of a photon multiplying film of an embodiment illustrated in FIG. 5 at excitation wavelengths of 405 nm, 520 nm, and 785 nm;

[0136] Figure 8 A graph showing the photoluminescence quantum efficiency (PLQE) of a photon multiplication film according to another embodiment of the present invention at excitation wavelengths of 520 nm and 658 nm of incident light;

[0137] Fig. 9 shows normalized absorbance and emission spectra of a photon multiplying film according to yet another embodiment of the present invention at wavelengths between 300 nm and 700 nm of incident light; and

[0138] Fig.10 Absorption spectra of a photon multiplying film according to yet another embodiment of the present invention compared to other films are shown, as well as a graph of the photoluminescence quantum yield (PLQE) of the photon multiplying film at excitation wavelengths of 450 nm, 532 nm, and 658 nm.

[0139] Now refer to Figure 1 , a photon multiplying film according to the invention, generally designated 10, comprises a light collecting material 11 (harvester H), an organic semiconductor 12 (SF) capable of singlet fission and a luminescent agent 13 (L).

[0140] In the film, the organic semiconductor 12 (SF) and the luminescent agent 13 (L) may be discrete entities (SF+L) or chemically attached to each other ([SF+L]).

[0141] Figure 1 The incident light (hv) is shown after the film is absorbed by the light harvesting material 11 (H), thereby generating an exciton state which is energy transferred to an exciton singlet state in the organic semiconductor 12 (SF) via FRET.

[0142] Singlet fission of the exciton singlet state in the organic semiconductor 12 (SF) generates a triplet exciton state, which is efficiently and sequentially transferred to the luminescent agent 13 (L) through DET.

[0143] The electron-hole pairs generated in the luminescent agent 13 (L) by triplet energy transfer recombine with emission of light (hv).

[0144] Thus, the film may provide for the emission of two lower energy photons for each high energy photon absorbed by the light collecting material 11 (H).

[0145] Now refer to Figure 2 , a photon multiplying film generally designated as 20 according to the present invention comprises a first organic semiconductor 21 and a luminescent agent (L) 22 .

[0146] In this film, the first organic semiconductor 21 is chemically attached to the light emitting agent ([(SF)+L]), but may not undergo singlet fission.

[0147] In this case, the light collecting material (H) consists of a light emitting material (LM) 23 and a second organic semiconductor capable of singlet fission (SF) 24 .

[0148] Optionally, the light harvesting material (H) consists of a second organic semiconductor capable of singlet fission (SF) 24 .

[0149] Figure 2 It shows incident light (hv) after being absorbed by the light emitting material (LM) 23 in the film (LM+SF+[SF'+L]), thereby generating an exciton singlet state which is transferred to the second organic semiconductor (SF) 24 via FRET.

[0150] Alternatively, light incident on the system (SF+[SF′+L]) is absorbed by the second organic semiconductor (SF) 24 .

[0151] Singlet fission of the exciton singlet state in the second organic semiconductor (SF) 24 generates a triplet exciton state, which is transferred to the first organic semiconductor ((SF)) 21 by DET.

[0152] The triplet exciton state transferred to the first organic semiconductor ((SF)) 21 is efficiently transferred to the light emitting agent (L) through DET.

[0153] The electron-hole pairs generated in the luminescent agent (L) 22 by the transfer of triplet excitons recombine with the emission of light (hv).

[0154] Thus, the film may also provide for the emission of two lower energy photons for each high energy photon absorbed by the light collecting material (H).

[0155] Now refer to Figure 3 , a photon multiplying film generally designated as 30 according to an embodiment of the present invention includes a poly(methyl methacrylate) (PMMA) film 31 in which an organic semiconductor (SF) capable of singlet fission, bis((triisopropylsilyl)ethynyl)tetracene (TIPS-Tet) 32, a light collecting material (H) composed of an organic dye 1,3,6,8(2H,7H)-tetraone, 2,7-dicyclohexyl-benzo[1mn][3,8]phenanthroline 33 and N,N'-bis(2,6-diisopropyl-phenyl)-3,4,9,10-perylenetetracarboxylic acid diimide 34, and a luminescent agent (L) including lead sulfide (PbS) quantum dots 35 are dispersed.

[0156] In this embodiment (H+SF+L), PbS quantum dots 35 and organic dyes 33, 34 are uniformly dispersed in the PMMA film 31 so that the distance between the quantum dots 35 and the organic dyes 33, 34 is less than or equal to the Forster transfer radius of these materials (about 4 nm).

[0157] The organic semiconductor (TIPS-Tet) 32 is dispersed in the PMMA film 31 so that the distance between the organic semiconductor (TIPS-Tet) 32, quantum dots 35 and organic dyes 33, 34 is close enough for diffusion of singlet excitons and triplet excitons through the film and for triplet transfer to the quantum dots 35 without inhibiting singlet fission or aggregation of the quantum dots 35.

[0158] Now refer to Figure 4, a photon multiplying film generally designated as 40 according to another embodiment of the present invention comprises a polymethyl methacrylate (PMMA) film 41 in which a photon multiplying material 42 and a light collecting material are dispersed, the photon multiplying material 42 comprising a luminescent agent of PbS quantum dots 42a having an outer coating, the outer coating comprising an organic semiconductor (ligand) 42b derived from 6,11-bis((triisopropylsilyl)ethynyl)-tetracene-2-carboxylic acid (PbS / TIPS-Tet-CA quantum dots), the light collecting material consisting of two organic dyes 1,3,6,8(2H,7H)-tetraone, 2,7-dicyclohexylbenzo[1mn][3,8]phenanthroline 43 and N,N'-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic acid diimide 44.

[0159] In this embodiment (H+[SF+L]), PbS / TIPS-Tet-CA quantum dots 42a and organic dyes 43, 44 are uniformly dispersed in the PMMA film 41, so that the distance between the quantum dots 42a and the organic dyes 43, 44 is less than or equal to the Forster transfer radius (about 4nm) of these materials. The distance between the organic semiconductor 42b and the quantum dots 42a is determined by the linking group and is generally less than or equal to 1nm to enable DET to occur.

[0160] Example 1 - Photon Multiplication Film (H+[SF+L])

[0161] Preparation of passivated quantum dots

[0162] Passivated lead sulfide quantum dots were synthesized according to a modification of the literature method of Hines, MA and Scholes, GD, Advanced Materials, 2003, 15(21), 1844-1849.

[0163] Lead oxide (PbO, 0.62 g, 2.8 mmol), oleic acid (8 ml, 22.4 mmol, 7.2 g) (acceptor) and octadecene (25.0 ml, 76.3 mmol, 19.5 g) were stirred together in a three-necked reaction flask and placed under vacuum (10 -2 mbar or better) at 110°C.

[0164] After two (2) hours, the reaction flask was flushed with nitrogen and the solution was heated to 115°C. 18 H 36A solution of bis(trimethyl-silyl) sulfide (TMS, (Me3Si)2S, 286 μl, 1.4 mmol) in 4% paraformaldehyde (2% paraformaldehyde, 13.9 ml, 42.4 mmol, 10.8 g) was quickly added to the flask, and the reaction was immediately quenched by placing the reaction flask in an ice-water bath.

[0165] Lead sulfide (PbS) quantum dots passivated by hydrocarbon ligands from oleic acid (OA) were isolated from the reaction mixture by flocculation to turbidity with a mixture of hexane as solvent and 1-butanol / ethanol / octane as antisolvent.

[0166] After filtration, the passivated (PbS-OA) quantum dots were washed and redispersed in octane or toluene at a concentration of about 10 mg to 100 mg per ml. The dispersion was stored under an atmosphere of argon at standard temperature and standard pressure.

[0167] Note that the band gap of the passivated QDs can be tuned by adjusting the oleic acid (OA) concentration in the reaction mixture or by adjusting the temperature of the reaction.

[0168] Preparation of Photon Multiplication Quantum Dots [SF+L]

[0169] Ligand exchange reactions were performed on passivated quantum dots (PbS-OA) using 6,11-bis-((triisopropylsilyl)ethynyl)tetraphenyl-2-carboxylic acid (TIPS-Tet-CA) for the new ligand according to the procedure in Garakyaraghi, S. et al., Journal of Physical Chemistry Letters, 2017, 8(7), 1458-1463.

[0170] To a stirred solution of passivated quantum dots (20 mg) in toluene (1 ml) was added TIPS-Tet-CA (excess). The resulting solution was stirred in the dark for 16 hours and acetone was added to precipitate PbS / TIPS-Tet-CA quantum dots.

[0171] PbS / TIPS-Tet-CA quantum dots were collected by centrifugation at 4000 rpm for 5 minutes and (after removing the supernatant) dispersed in toluene (1 ml).

[0172] The quantum dots were purified by repeating (e.g., six or more times) the precipitation, dispersion, and centrifugation steps until no free TIPS-Tet-CA was detected in the solution. Finally, the PbS / TIPS-Tet-CA quantum dots were dispersed in toluene (1 mL) and stored at -20°C under nitrogen in the dark.

[0173] Note that the ligand exchange reaction can also be performed by adding the sodium salt of TIPS-Tet-CA to a solution of passivated quantum dots (20 mg) in a mixture of toluene and tetrahydrofuran (THF).

[0174] Choice of light collecting material (H)

[0175] Now refer to Figure 5 , the normalized absorption spectrum of PbS quantum dots with attached tetracene ligands (labeled as PbS-Tet) shows strong oscillations caused by the absorption of the tetracene ligands in the "overlap region". The normalized absorption spectrum (thin solid line) and emission spectrum (thin dashed line) of each of the organic dye molecules N,N'-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic acid diimide and 1,3,6,8(2H,7H)-tetraone, 2,7-dicyclohexyl-benzo[1mn][3,8]phenanthroline (labeled as blue or B and green or G, respectively) show good overlap with the absorption of the tetracene ligands of PbS / TIPS-Tet-CA quantum dots, indicating the possibility of FRET between the organic dye and the Tet ligands on the quantum dots.

[0176] Preparation of Photon Multiplication Film (H+[SF+L])

[0177] Poly (methyl methacrylate) (PMMA) and organic dyes 1,3,6,8 (2H, 7H) -tetraketone, 2,7-dicyclohexylbenzo [1mn] [3,8] phenanthroline and N, N'-bis (2,6-diisopropylphenyl) -3,4,9,10-perylene tetracarboxylic acid diimide were dissolved in toluene or chloroform, and the solution was sealed and heated to 100 ° C with stirring overnight. After cooling and opening to an inert atmosphere, PbS / TIPS-Tet-CA quantum dots were added to the solution at room temperature with stirring. After 30 minutes, the resulting suspension was spread onto a glass substrate and the solvent was allowed to dry in air at room temperature.

[0178] The dye amount and quantum dot amount are milligram amounts, which result in a mass concentration of the dye and quantum dots in the PMMA film between 0.1% and 5.0% of the PMMA film.

[0179] Performance of Photon Multiplication Film (H+[SF+L])

[0180] The absorbance and emission spectra of the photon multiplying film (PbS-TetBG film) were studied in comparison with the absorbance and emission spectra of a PMMA film containing PbS / TIPS-Tet-CA quantum dots (PbS-Tet film), a PMMA film containing PbS / TIPS-Tet-CA quantum dots and 1,3,6,8(2H,7H)-tetraone, 2,7-dicyclohexylbenzo[1mn][3,8]phenanthroline (PbS-Tet G), and a PMMA film containing PbS / TIPS-Tet-CA quantum dots and N,N'-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic acid diimide (PbS-Tet B film).

[0181] The absorption spectrum of each of the films was measured using a Shimadzu UV 600 spectrometer with an attached integrating sphere at wavelengths between 300 nm and 600 nm.

[0182] Now refer to Figure 6 , the absorption spectrum of the PbS-Tet BG film and the absorption spectrum of the PbS-TetG film both show increased absorbance in the region between 450 nm and 550 nm compared to the absorption spectrum of the PbS-Tet film.

[0183] In this regard, it is noted that in the absorption spectrum of the PbS-Tet film, the wavelengths at 475 nm, 510 nm and about 545 nm (which corresponds to Figure 5 The peak shown in the overlapping region of is barely visible.

[0184] However, in the region between 350 nm and 400 nm, the absorption spectra of the PbS-Tet G film, the PbS-Tet B film, and the PbS-Tet BG film all showed increased absorbance compared to the absorption spectrum of the PbS-Tet film.

[0185] The photoluminescence emission spectra of each film were measured using an Edinburgh Instruments FLS90 fluorometer. The film samples were excited in an integrating sphere by front illumination with a continuous wave laser at wavelengths of 405 nm, 520 nm and 785 nm (for exciting blue dyes, mainly green dyes and quantum dots, respectively) and at an angle of 45 ° to the surface. The emission was detected using a calibrated Andor iDusDU490AInGaAs detector at an angle of 90 ° to the excitation angle and at an angle of 45 ° to the surface. Note that the integrated flux of these measurements was kept low in order to avoid two-photon absorption.

[0186] The photoluminescence quantum efficiency (PLQE) of the film was calculated according to the method of de Mello, J. et al., "An Improved Experimental Determination of External Photoluminescence Quantum Efficiency", Advanced Materials, 1997, 9 (3) 230-232. This method takes into account photons absorbed by direct excitation, indirect excitation after scattering in an integrating sphere, and emission by the sample.

[0187] Now refer to Figure 7 , a graph of the normalized photoluminescence quantum efficiency (PLQE) of the film at three different wavelengths (405 nm, 520 nm and 785 nm) is superimposed on the normalized absorption spectra of the dyes (B and G) and PbS-Tet-CA quantum dots.

[0188] As can be seen, the PLQE value of the PbS-Tet film at 520 nm is greater than the PLQE value of the PbS-Tet BG film at 785 nm and the PLQE value of the PbS-Tet film at 405 nm, because singlet fission is occurring in the Tet ligand, and the Tet ligand does not absorb at 405 nm and 785 nm. The PLQE value of the PbS-Tet BG film at 785 nm and the PLQE value of the PbS-Tet film at 405 nm are similar because only direct excitation of the PbS quantum dots occurs at these wavelengths.

[0189] The PLQE value of the PbS-Tet B film is larger at 405 nm compared to the excitation of the PbS-Tet BG film at 785 nm because FRET between the blue dye and the Tet ligands in the PbS-Tet B film enables singlet fission to occur, while at 785 nm only direct excitation of the PbS QDs occurs.

[0190] The PLQE values ​​of the PbS-Tet G film are higher at both 405 nm and 520 nm compared to the PLQE value of the film at 785 nm because of FRET between the green dye and the Tet ligand and because the green dye absorbs light at both 405 nm and 520 nm.

[0191] The PLQE value of the PbS-Tet BG film at 405 nm excitation is higher than that of both the PbS-Tet B film and the PbS-Tet G film, indicating that the singlet excitons generated in the blue dye are transferred to the green dye via FRET, and that the green dye transfers the excitons to the Tet ligand more efficiently than the blue dye alone. Figure 5Consistently, a better overlap of the emission spectrum of the green dye with the absorption spectrum of the Tet pair is seen compared to the overlap of the emission spectrum of the blue dye with the absorption spectrum of the Tet ligand.

[0192] Example 2—Photon Multiplication Film (H=SF and [(SF)+L])

[0193] Preparation of photon multiplying films (H=SF and [(SF)+L])

[0194] The ligand exchange reaction was performed on the passivated quantum dots (PbS-OA) as described in Example 1, except that the excess 6,11-bis-((triisopropylsilyl)ethynyl)tetraphenyl-2-carboxylic acid (TIPS-Tet-CA) used did not provide sufficient ligand density on the quantum dots for singlet fission (indicated by (SF)).

[0195] The PbS / TIPS-Tet-CA quantum dots thus obtained showed an emission wavelength peak at 1300 nm and a mass ratio of oleic acid ligand to 6,11-bis-((triisopropylsilyl)ethynyl)tetracene-2-carboxylic acid ligand of 10 to 1.

[0196] Toluene solutions of these quantum dots ([(SF)+L]), 5,12-bis-((triisopropylsilyl)ethynyl)tetracene (TIPS-Tet, SF) and polystyrene with a molecular weight greater than 500 KD were composed into an equivalent mass ratio of PbS / TIPS-Tet-CA quantum dots to polystyrene of 2 to 1.

[0197] The toluene solution was knife coated onto a glass substrate and the coated substrate was dried in an inert (nitrogen) atmosphere. The resulting substrate, which carried a film comprising a dispersion of PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) and 5,12-bis-((triisopropylsilyl)ethynyl)tetracene (TIPS-Tet, SF) in a polystyrene matrix (PS), was edge-capped with a transparent and inert polyisobutylene polymer so that the material did not contact a portion of the coating to be measured.

[0198] A toluene solution containing only PbS / TIPS-Tet-CA quantum dots ([(SF)+L]), 5,12-bis-((triisopropylsilyl)ethynyl)tetracene (TIPS-Tet, SF) was knife coated onto another glass substrate, and the coated substrate was dried in an inert (nitrogen) atmosphere. The resulting substrate carrying a film comprising a dispersion of PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) in 5,12-bis-((triisopropylsilyl)ethynyl)tetracene (TIPS-Tet, SF) was edge encapsulated with a transparent polymer barrier material.

[0199] Performance of Photon Multiplication Films (H=SF and [(SF)+L])

[0200] Photoluminescence quantum efficiency (PLQE) measurements of the encapsulated substrates were performed in an integrating sphere with a continuous wave laser at excitation wavelengths of 520 nm and 658 nm.

[0201] Now refer to Figure 8 (where PbS / TIPS-Tet-CA quantum dots ([(SF)+l]) are indicated as TIPS Tc:ALQD), at an excitation wavelength of 520nm, more than 95% of the light absorbed by each substrate produces excitation on TIPS-Tet, with the remainder absorbed by PbS / TIPS-Tet-CA quantum dots. At an excitation wavelength of 658nm, there is no absorption by TIPS-Tet in each substrate and 100% absorption by PbS / TIPS-Tet-CA quantum dots.

[0202] Therefore, the PLQE measurement at 658 nm represents the intrinsic PLQE of PbS / TIPS-Tet-CA quantum dots ([(SF)+L]), and the difference in the PLQE measurement at 520 nm must be due to exciton multiplication in the film through singlet fission in TIPS-Tet(SF), followed by efficient triplet exciton transfer from TIPS-Tet(SF) to PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) in the film.

[0203] Example 3 - Photon Multiplication Film (H = LM + SF and [(SF) + L])

[0204] Preparation of photon multiplying films (H = LM + SF and [(SF) + L])

[0205] The solution of PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) obtained in Example 2 is composed of one or the other or both of TIPS anthracene (TIPS-An, LM) and TIPS tetracene (TIPS-Tet, SF) in a mass ratio of 5:1 between the organic semiconductor and PbS / TIPS-Tet-CA quantum dots.

[0206] The solutions were each scraped onto the corresponding glass substrates and the substrates were dried in an inert (nitrogen) atmosphere. The coated glass substrates carrying the film of PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) dispersed in organic semiconductors (LM and SF) were sealed with a transparent and inert polyisobutylene polymer by a strong edge seal, ensuring no contact between the polymer and the film.

[0207] Performance of Photon Multiplication Films (H = LM + SF and [(SF) + L])

[0208] Now refer to Fig. 9 , shows a graph of normalized absorbance and normalized emission for each of the (three) coated substrates.

[0209] As can be seen, the absorption spectrum of the film including PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) in TIPS-An(LM) shows multiple peaks between 350nm and 450nm. These peaks correspond to the absorbance transitions occurring in TIPS-An(LM).

[0210] In contrast, the films comprising PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) and TIPS-Tet (SF) showed strong absorbance between 450 nm and 500 nm. The films comprising PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) and both TIPS-An (LM) and TIPS-Tet (SF) showed broad absorbance between 350 nm and 550 nm.

[0211] The emission spectrum (centered at 1300 nm) of the film including PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) in TIPS-An(LM) shows excitations that reflect only moderate energy transfer from TIPS-An(LM) to PbS / TIPS-Tet-CA quantum dots ([(SF)+L]), indicating low energy transfer efficiency that does not involve singlet fission.

[0212] In contrast, the corresponding emission spectrum of the film including PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) in TIPS-Tet(SF) shows a substantial increase in the intensity of the PbS / TIPS-Tet-CA quantum dot emission, again indicating rapid singlet fission in TIPS-Tet(SF) and efficient energy transfer from TIPS-Tet(SF) to PbS / TIPS-Tet-CA quantum dots ([(SF)+L]) in the film.

[0213] In addition, the corresponding excitation spectra of the films including PbS / TIPS-Tet-CA quantum dots ([(SF)+L]), TIPS-Tet (SF) and TIPS-An (LM) showed a relative increase in emission between 350 nm and 450 nm, indicating efficient energy transfer from TIPS-An (LM) to TIPS-Tet (SF) within the films.

[0214] Note here that if this energy transfer is inefficient, substantially reduced emission between 350 nm and 450 nm will be observed due to the absorbance of TIPS-An(LM) at these wavelengths.

[0215] Example 4 - Photon Multiplication Film (H = LM and SF and L)

[0216] Preparation of photon multiplying films (H = LM and SF and L)

[0217] The first solution of passivated quantum dots PbS-OA (L) obtained in Example 1 is composed of TIPS anthracene (TIPS-An, LM) and TIPS tetracene (TIPS-Tet, SF) with a mass ratio of TIPS-Tet (SF) to TIPS-An (LM) to PbS-OA (L) of 10 to 2.5 to 1.

[0218] The second solution of passivated quantum dots PbS-OA was composed of TIPS-Tet (SF) with a mass ratio of TIPS-Tet (SF) to PbS-OA quantum dots (L) of 5:1.

[0219] The solution was scraped onto a glass substrate and dried in an inert (nitrogen) atmosphere. The coated glass substrates carrying films of PbS-OA quantum dots (L) dispersed in TIPS-Tet (SF) or dispersed in TIPS-Tet (SF) and TIPS-An (SF and LM) were sealed in a transparent and inert polyisobutylene polymer by a robust edge encapsulation, ensuring no contact between the polymer and the polymer film.

[0220] Performance of Photon Multiplication Films (H = LM and SF and L)

[0221] Now refer to Fig.10 , shows a graph of the absorption spectrum of the encapsulated substrate compared to the absorption spectrum of PbS-OA quantum dots and the PLQE measurements on the substrate of the film comprising PbS-OA quantum dots (L) dispersed in TIPS-Tet (SF).

[0222] As can be seen, the absorption spectra of the films including PbS / TIPS-Tet-OA quantum dots (L), TIPS-Tet (SF), and TIPS-An (LM) show a clear contribution from TIPS-An between 350 nm and 450 nm.

[0223] The PLQE measurement for excitation at 658 nm (◆) represents the intrinsic PbS / TIPS-OA quantum dot emission yield (since organics do not absorb above 600 nm) and shows 25% of the excitation-derived (infrared) emission.

[0224] Excitation of the film at 520 nm showed a measured PLQE value of 19% (◆), indicating that the TIPS-Tet(SF) in the film undergoes rapid singlet fission to generate triplet excitons.

[0225] Since the absorbance at this wavelength is dominated by TIPS-Tet (SF), the PLQE yield, which far exceeds the expected yield caused by excitation of PbS-OA QDs (L) alone (shown by the X at 520 nm), indicates that energy transfer of triplet excitons to PbS-OA QDs (L) is occurring within the film.

[0226] Note here that if energy transfer of triplet excitons to PbS-OA quantum dots (L) does not occur, only the absorbance by PbS-OA can contribute to the PLQE and the PLQE of the film will be less than 2%.

[0227] The excitation of the film at 450 nm is shared approximately equally between TIPS-An (LM) and the combined absorption of TIPS-Tet (SF) and PbS-OA quantum dots (L) (as evidenced by the absorption spectrum). The PLQE measurement (◆) of the film shows a PLQE of 14%, indicating that the excitation on TIPS-An (LM) is transferred to TIPS-Tet (SF) within the film before being transferred from TIPS-Tet (SF) to PbS-OA quantum dots (L).

[0228] Note here that if there is no energy transfer between the organic semiconductor and the PbS-OA quantum dots (L), the PLQE of the film may not exceed about 3% (shown by the X at 450 nm, QD-only limit). In addition, if there is no energy transfer between TIPS-An (LM) and TIPS-Tet (SF), the PLQE of the film may not exceed about 10% (shown by the O at 450 nm, TIPS Tc:QD limit).

[0229] This study demonstrates photon multiplying films with PLQE that is enhanced by the presence of light harvesting materials, and in particular the collection of light from substantially the entire visible spectrum and its injection into an organic semiconductor capable of singlet fission via non-radiative energy transfer.

[0230] Although some of the embodiments show photon multiplying films with a PLQE of less than 100%, each of these films clearly demonstrates the functional elements of the photon multiplying film, namely, collection of visible light by absorption in the luminescent material, transfer of singlet excitons generated by FRET to a singlet fission material, exciton multiplication in the singlet fission material to produce triplet exciton states in excess of the number of singlet exciton states, diffusion and Dexter transfer of triplet exciton states to quantum dots, and emission of (infrared) photons from the quantum dots.

[0231] Note here that the emission of light from the PbS / TIPS-Tet-CA quantum dots is inefficient (significantly less than 50% in the example, which means that the photon multiplication quantum efficiency for the entire system cannot be greater than 100%, even if all components except the quantum dots are performing perfectly). However, quantum dots with optimized core size and structure (potentially other than PbS) can be expected to provide much higher intrinsic PLQE.

[0232] The present invention may provide significant advantages over the photon multiplication films described in international patent applications WO 2018 / 189527 A1 and WO 2019 / 110971 A1.

[0233] Light-harvesting materials including organic dyes can mean that photon multiplying films require fewer quantum dots per unit volume, especially when they are coupled with organic semiconductors, thereby reducing direct and unwanted absorption and re-emission in the quantum dots.

[0234] The light harvesting material absorbs in regions where the singlet fission molecules do not absorb well thereby increasing the overall absorption of the photon multiplying film.

[0235] Because the dye can transfer energy to the singlet fission material, there is less need for a relatively thick coating of Tet ligands on the quantum dots to absorb light.

[0236] The present invention can reduce the complexity of manufacturing photon multiplying films (and optoelectronic devices using the films) because photon absorption and singlet fission can be independently separated and managed.

[0237] Note that, unless the context requires otherwise, references herein to the "energy band gap" or "band gap" of a particular material or entity are references to the optical band gap of that material or entity.

Claims

1. A photon multiplication material comprising: a first organic semiconductor, a light-harvesting material, and a luminescent agent, wherein the light-harvesting material has a band gap that provides for an exciton state formed in the light-harvesting material by absorption of light to be energy-transferred to the first organic semiconductor, and the luminescent agent has a band gap that provides for a triplet exciton state formed in the first organic semiconductor to be energy-transferred to the luminescent agent; and wherein at least one of the first organic semiconductor and the light-harvesting material is capable of singlet fission; and Either of the following: i) wherein the light harvesting material comprises a light emitting material and a second organic semiconductor capable of singlet fission, wherein an exciton state formed in the light emitting material is capable of being energy transferred to the second organic semiconductor; or ii) wherein the light harvesting material comprises a second organic semiconductor capable of singlet fission, and wherein a triplet exciton state formed in the second organic semiconductor by singlet fission is capable of being energy transferred to the first organic semiconductor; and Also includes either of the following: a) the first organic semiconductor is chemically attached to the luminescent agent via a linking group, and the linking group of the luminescent agent and the band gap of the luminescent agent provide that a triplet exciton state formed in the attached first organic semiconductor can be energy transferred to the luminescent agent; or b) The first organic semiconductor is capable of singlet fission and is not attached to the luminescent agent. 2 . The photon multiplying material according to claim 1 , wherein the first organic semiconductor, the luminescent agent and the light collecting material are disposed within a host material.

3. The photon multiplying material according to claim 1, wherein the light collecting material comprises a luminescent material and provides that an exciton state formed therein by absorption of light can be energy transferred to the first organic semiconductor.

4. The photon multiplying material according to claim 2, wherein the light collecting material comprises a luminescent material and provides that an exciton state formed therein by absorption of light can be energy transferred to the first organic semiconductor. 5 . The photon multiplying material according to claim 1 , wherein a triplet exciton state formed in the second organic semiconductor by singlet fission can be energy-transferred to the first organic semiconductor.

6. The photon multiplying material according to any one of claims 3 to 5, wherein the luminescent material comprises one or more of an organic dye, an organic pigment or a quantum dot.

7. The photon multiplying material of claim 6 , wherein the luminescent material comprises more than one luminescent entity, wherein each luminescent entity has a band gap different from any other luminescent entity, such that light can be absorbed by any one of the luminescent entities and excitons generated therein can be energy transferred from that luminescent entity to an adjacent luminescent entity having a lower band gap.

8. The photon multiplying material of claim 7, wherein the luminescent material has at least one band gap in the energy range of 1.4 eV to 4.5 eV.

9. The photon multiplying material of claim 8, wherein the luminescent material has at least one band gap in the energy range of 2.0 eV to 4.5 eV.

10. The photon multiplying material of claim 8, wherein the luminescent material has at least one band gap in an energy range of 2.2 eV to 4.0 eV.

11. The photon multiplying material according to any one of claims 1 to 5, and 7 to 10, wherein the luminescent agent has a band gap in the range of 0.6 eV to 2.0 eV.

12. The photon multiplying material of claim 11, wherein the luminescent agent has a band gap in the range of 0.8 eV to 1.7 eV.

13. The photon multiplying material of claim 11, wherein the luminescent agent has a band gap in the range of 1.0 eV to 1.5 eV.

14. The photon multiplying material of any one of claims 1 to 5, 7 to 10, and 12 to 13, wherein the triplet energy of the first organic semiconductor is within + / - 0.4 eV of the band gap of the luminescent agent.

15. The photon multiplying material of claim 14, wherein the triplet energy of the first organic semiconductor is within + / - 0.3 eV of the band gap of the luminescent agent.

16. The photon multiplying material of claim 14, wherein the triplet energy of the first organic semiconductor is within + / - 0.2 eV of the band gap of the luminescent agent.

17. The photon multiplying material of any one of claims 1 to 5, 7 to 10, 12 to 13, and 15 to 16, wherein the first organic semiconductor has a band gap in the range of 1.4 eV to 4.0 eV.

18. The photon multiplying material of claim 17, wherein the first organic semiconductor has a band gap in the range of 2.0 eV to 3.0 eV.

19. The photon multiplying material of claim 17, wherein the first organic semiconductor has a band gap in the range of 2.3 eV to 2.6 eV.

20. The photon multiplying material of any one of claims 1 to 5, 7 to 10, 12 to 13, 15 to 16, and 18 to 19, wherein the first organic semiconductor comprises one or more of an acene, a perylene, a rylene, a diketopyrrolopyrrole, a fluorene, a carotenoid or a benzofuran, a phenazine thiadiazole, a molecule containing an isoindigo moiety or isoindigo, anthracene, and a bithiophene.

21. The photon multiplying material of claim 20, wherein the isoindigo moiety or isoindigo-containing molecule is in an isoindigo-based polymer IIDDT-Me, the anthracene is a diradical, and the bithiophene is tetracyanomethylenequinolinebithiophene.

22. The photon multiplying material of any one of claims 1 to 5, 7 to 10, 12 to 13, 15 to 16, 18 to 19, and 21, wherein the second organic semiconductor comprises one or more of an acene, a perylene, a rylene, a diketopyrrolopyrrole, a fluorene, a carotenoid or a benzofuran, a phenazine thiadiazole, a molecule containing an isoindigo moiety or isoindigo, anthracene, and a bithiophene.

23. The photon multiplying material of claim 22, wherein the isoindigo moiety or isoindigo-containing molecule is in an isoindigo-based polymer IIDDT-Me, the anthracene is a diradical, and the bithiophene is tetracyanomethylenequinolinebithiophene.

24. The photon multiplying material of any one of claims 1 to 5, 7 to 10, 12 to 13, 15 to 16, 18 to 19, 21 and 23, wherein the luminescent agent is an organic transition metal phosphor, a thermally delayed phosphor, a colloidal nanocrystal, or an emitter small molecule, macromolecule or 2-D material.

25. The photon multiplying material of claim 24, wherein the colloidal nanocrystals are quantum dots.

26. The photon multiplying material of any one of claims 1 to 5, 7 to 10, 12 to 13, 15 to 16, 18 to 19, 21 and 23, wherein the luminescent agent is a polymer.

27. The photon multiplying material of claim 26, wherein the polymer comprises an oligomer or a dendrimer.

28. The photon multiplying material of claim 25, wherein the quantum dots have a core structure comprising CdSe, CdS, ZnTe, ZnSe, PbS, PbSe, PbTe, HgS, HgSe, HgTe, HgCdTe, CdTe, CZTS, ZnS, CuInS2, CuGaS2, CuInSe x S 2-x , AgInSe2, CuInGaSe, CuInGaS, silicon, InAs, InP, InSb, SnS2, CuS, graphene, graphene oxide, metal halide perovskite, germanium and Fe2S3.

29. A photon multiplying material according to claim 25 or claim 28, wherein the quantum dots have a diameter of 50 nm or less.

30. The photon multiplying material of claim 29, wherein the quantum dots have a diameter of 20 nm or less.

31. The photon multiplying material of claim 29, wherein the quantum dots have a diameter of 10 nm or less.

32. The photon multiplying material of claim 29, wherein the quantum dots have a diameter of 5 nm or less.

33. The photon multiplying material of claim 2, wherein the host material is an organic material selected from the group consisting of small molecules, oligomers, homopolymers, copolymers, macromolecules, dendrimers, or three-dimensional networks of organic molecules.

34. The photon multiplying material of claim 2 or claim 33, wherein the host material is selected from the group consisting of polybutyral, polyamide, polyurethane, polythiol, polymethacrylate, epoxy resin, polycarbonate, polyolefin, EVA, silicone, carbohydrate, protein, nucleic acid and lipid.

35. An optoelectronic device comprising a photon multiplying material according to any preceding claim in optical communication with an optoelectronic element, a light emitting diode, a field effect transistor, a display, a sensor or a bio-imaging device.

36. The photovoltaic device of claim 35, wherein the photovoltaic element is a solar cell.

37. An optoelectronic device comprising a photon multiplying material according to any one of claims 1 to 34, the photon multiplying material being in optical communication with a photodetector.

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