Coloured photovoltaic devices and methods of formation

Abstract

A photovoltaic module, comprising: a photovoltaic cell; and a luminous material applied to a surface of the photovoltaic cell, or to a surface or an encapsulant of the module, to form a visual modification layer that interacts with at least a portion of the incident light on the photovoltaic cell to generate a coloured appearance to an observer of the module. The luminous material has a photoluminescence quantum yield value of at least 80% and comprises one or more photoluminescent down shifting materials from the group of: (i) semiconductor nano-particles having a particle size of at least 50 nm; (ii) fluorescent or phosphorescent phosphors; and (iii) organic luminogens.

Description

"Coloured photovoltaic devices and methods of formation"Technical Field

[0001] This disclosure relates to photovoltaic devices, and methods of constructing the same, that produce a vivid and stable coloured appearance without significantly reducing the relative power conversion efficiency of the photovoltaic process.Background

[0002] Photovoltaic (PV) technology includes devices and systems that directly convert solar energy into electricity. Recently, the deployment of photovoltaic technology has significantly increased due to factors such as a focus on the development and implementation of renewable energy sources, and the significant cost reduction associated with the installation of photovoltaic modules in locations previously considered to be of marginal value [1], Examples of modem applications of PV technology include Building-integrated photovoltaics (BIPV), which exhibit the potential to both power and decorate urban architecture (i.e., building facades) due to their low space requirements, and vehicle integrated photovoltaics (VIPV) which may be used for example to power electric vehicles (EVs).

[0003] In BIPV, VIPV, and other modem applications of PV technology the PV devices, such as photovoltaic modules (also referred to as “solar panels”), are required to have a high efficiency and also to have an aesthetic appearance that is compatible with the desired design. The dark blue or black appearance of conventional photovoltaic modules is aesthetically dull and incompatible with the appearance of most building facades (e.g., in BIPV). Moreover, aesthetically designed PV technology is also popular in product integrated modules used to power electronics and simultaneously meet the overall visual design of the product (e.g. in VIPV).

[0004] However, it is challenging to improve the visual aesthetics of a photovoltaic module while preserving its power conversion efficiency (PCE). There is a trade-offbetween achieving a coloured appearance of a photovoltaic device and its performance, since a coloured appearance requires the reflection of light from the cell surface which results in less light absorption (and therefore a reduction in the PCE).

[0005] Current solutions for providing coloured photovoltaic modules lead to significant efficiency losses (i.e., around 10% absolute loss [2]). Comparable efficiency losses are realized when attempting to mask or disguise the appearance of the photovoltaic module (i.e. to make it look like a painted surface). This is undesirable and acts as a deterrent to deploying conventionally coloured (or other) photovoltaic modules in applications such as BIPV and VIPV, or in any other application where the modules are generally visible.

[0006] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

[0007] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.Summary

[0008] There is provided a photovoltaic module, comprising: a photovoltaic cell; and a luminous material applied to a surface of the photovoltaic cell, or to a surface or an encapsulant of the photovoltaic module, to form a visual modification layer that interacts with at least a portion of light incident on the photovoltaic cell to generate a coloured appearance to an observer of the photovoltaic module, wherein the luminous material has a photoluminescence quantum yield value of at least 80% and comprisesone or more photoluminescent down shifting materials from the group of: (i) semiconductor nano-particles having a particle size of at least 50 nm; (ii) fluorescent or phosphorescent phosphors; and (iii) organic luminogens.

[0009] In some embodiments, the photovoltaic module has a power conversion efficiency of at least 18%.

[0010] In some embodiments, each photoluminescent downshifting material is configured to absorb a fraction of incident light in a first wavelength range and re-emit light in a second wavelength range that is narrower than the first wavelength range.

[0011] In some embodiments, the first wavelength range extends to an upper wavelength that is determined by an energy bandgap value of the photoluminescent downshifting material.

[0012] In some embodiments, the energy bandgap value and the second wavelength range of each photoluminescent downshifting material is selected according to a desired colour of the coloured appearance of the module.

[0013] In some embodiments, the visual modification layer has an opacity that is determined by a density of the photoluminescent downshifting material(s) within the layer.

[0014] In some embodiments, the semiconductor nano-particles include but are not limited to: CdSe, CdS, ZnSe, hybrid perovskites in the form of ABX3 (A: CH3NH3+, HC(NH2)+, Cs+ ; B: Pb2+, Sn2+; X: I-, Br-, C1-, F-) or other forms.

[0015] In some embodiments, the particle size of the semiconductor nano-particles is between 50 nm and 1 um.

[0016] In some embodiments, the fluorescent or phosphorescent phosphors include host material comprising one or more of: oxides; nitrides; oxynitrides; sulfides;selenides; halides; silicates; aluminate; borate; phosphates; molybdate; and wherein the host material comprises an added activator.

[0017] In some embodiments, the added activator includes one or more of the following: copper (Cu), silver (Ag), zinc (Zn), cadmium (Cd), manganese (Mn), aluminium (Al), chromium (Cr), silicon (Si), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (TM), ytterbium (Yb), lutetium (Lu), yttrium (Y), scandium (Sc), or another rare-earth metal with similar properties.

[0018] In some embodiments, the fluorescent or phosphorescent phosphors are include but are not limited to one or more of the following materials: Garnet-type phosphors; Si3N4-type phosphors; Apatite-type phosphors; Melilite-type phosphors; A3MX5-type phosphors; Ucr4C4-type phosphors; P-K2SO4-type phosphors; [3- Ca3(PO4)2 type phosphors; Phosphors based on lanthanide-doped alkaline earth aluminate; and phosphors based on materials including BaMgA110O17 (BAM), Y2O3, MgA111019, La3Si6Nl l, NaYF4, ZnS, (Sr,Ca)AlSiN3, SrA12O4, Msi2O2N2 (M = Ca, Sr, Ba), K2A12B2O7, MN4(BO3)3 (M = Li, Na, K; N = Ca, Sr), A2MF6 (A = Na, K, Cs, Rb or (NH4); M = Si, Al, Ge, Sn, Ti or Zr), BMF6 (B = Ba and Zn; M = Si, Ge, Sn or Ti), (Ba, Sr, La)SiaAlbOcNd, M2Si5N8 (M = Ca, Sr, Ba), La3Ga5GeO14, ScBO3, ZnGa2O4, (Ga, Sc, Al, In)2O3.

[0019] In some embodiments, the organic luminogens comprise one or more of: Organometallic chelates; conjugated dendrimers; luminescent conductive polymers; phosphorescent organometallic complexes; fluorescent or phosphorescent dyes; and aggregation-induced-emission (AIE) molecules.

[0020] In some embodiments, the AIE molecules include but are not limited to one or more of: tetraphenylethene (TPE) derivatives, tetraphenylbenzene (TPB) derivatives, silole derivatives, triphenylamine (TP A) derivatives, 9,10-distyrylanthracene (DSA)derivatives, pyrrole derivatives, cyanostilbene derivatives, thiophene derivatives, salicylaldehyde derivatives, and 9,10-diheteroarylanthracene (DHA) derivatives.

[0021] In some embodiments, the organic luminogens are dispersed and wrapped in a nano- or micro-powder or a polymer.

[0022] In some embodiments, the nano- or micro-powder comprises one or more of: oxide nanoparticles, nitride nanoparticles, oxynitride nanoparticles, halide nanoparticles, carbide nanoparticles, hydroxide nanoparticles, large-bandgap semiconductor nanoparticles, phosphor nano- / micro-particles, 2D material nano-sheets, organic nano- / micro-spheres, molecular sieves, and metal-organic frameworks.

[0023] In some embodiments, the organic luminogens include but are not limited to one or more of: Xanthene derivatives, Cyanine derivatives, Squaraine derivatives and ring-substituted squaraines, Squaraine rotaxane derivatives, Naphthalene derivatives, Coumarin derivatives, Oxadiazole derivatives, Anthracene derivatives, Pyrene derivatives, Oxazine derivatives, Acridine derivatives, Arylmethine derivatives, Tetrapyrrole derivatives, and Dipyrromethene derivatives.

[0024] In some embodiments, the luminous material, as applied, is industrially stable according to IEC standard 61215 for photovoltaic modules.

[0025] There is also provided a composition for use with a photovoltaic module, the composition comprising a luminous material that, when applied to a surface of a photovoltaic cell of the photovoltaic module, or to a surface or an encapsulant of the photovoltaic module, generates a coloured appearance to an observer of the photovoltaic module, wherein the luminous material has a photoluminescence quantum yield value of at least 80% and comprises one or more photoluminescent down shifting materials from the group of: (i) semiconductor nano-particles having a particle size of at least 50 nm; (ii) fluorescent or phosphorescent phosphors; and (iii) organic luminogens.

[0026] There is also provided a method of forming a coloured photovoltaic module, the method comprising: preparing a composition of a luminous material, the luminous material having a photoluminescence quantum yield value of at least 80% and comprising one or more photoluminescent down shifting materials from the group of: (i) semiconductor nano-particles having a particle size of at least 50 nm; (ii) fluorescent or phosphorescent phosphors; and (iii) organic luminogens; and applying the composition to a surface of a photovoltaic cell of the photovoltaic module, or to a surface or an encapsulant of the photovoltaic module, to form a visual modification layer that generates a coloured appearance to an observer of the photovoltaic module.

[0027] In some embodiments, the visual modification layer is a transparent structure in which the composition is embedded.

[0028] In some embodiments, the composition is applied to the surface of the photovoltaic cell, or to the surface or the encapsulant of the photovoltaic module, with a solution based process.

[0029] In some embodiments, the solution based process is a thin film deposition technique.

[0030] In some embodiments, the solution based process comprises: applying the composition as a gel; and curing the composition following its application onto the surface.

[0031] In some embodiments, the solution based process comprises covering the composition, following its application onto the surface, with a capping layer.Brief Description of Drawings

[0032] Some embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0033] Fig. la is a schematic diagram of a conventional photovoltaic module;

[0034] Fig. lb is a schematic diagram of a first example of a coloured photovoltaic module in accordance with some embodiments;

[0035] Fig. 1c is a schematic diagram of a second example of a coloured photovoltaic module in accordance with some embodiments;

[0036] Fig. Id is a schematic diagram of a third example of a coloured photovoltaic module in accordance with some embodiments;

[0037] Fig. le is a schematic diagram of a fourth example of a coloured photovoltaic module in accordance with some embodiments;

[0038] Fig. 2 is a plot of an ideal absorption curve, and a corresponding emission curve, of a PL DS material in accordance with some embodiments;

[0039] Fig. 3a is a graph set of a tuneable photoluminescent (PL) spectrum of a nanoparticle material used in a coloured photovoltaic module in accordance with some embodiments;

[0040] Fig. 3b is a plot of an absorption curve of a transparent film of a semiconductor nano-particle material used in a coloured photovoltaic module in accordance with some embodiments;

[0041] Fig. 3c is a graphical representation of a coloured appearance of the film of Fig. 3b;

[0042] Fig. 3d is a plot of an I-V characteristic indicating the power efficiency of a coloured photovoltaic module having the film of Fig. 3b, in accordance with some embodiments;

[0043] Fig. 4a is a structural formula of a first example aggregation-induced emission (AIE) molecule used in the luminous material in accordance with some embodiments;

[0044] Fig. 4b is a plot of the absorbance curve of the AIE molecule of Fig. 4a;

[0045] Fig. 4c is a structural formula of a second example aggregation-induced emission (AIE) molecule used in the luminous material in accordance with some embodiments;

[0046] Fig. 4d is a plot of the normalized intensity characteristic of the AIE molecule of Fig. 4c;

[0047] Fig. 5a is a graph of an emission curve of a first example phosphor with a high photoluminescent quantum yield (PLQY) used in the luminous material in accordance with some embodiments;

[0048] Fig. 5b is a graph of an emission curve of a second example phosphor with a high PLQY used in the luminous material in accordance with some embodiments;

[0049] Fig. 5c is a set of graphs of emission curves of a third example phosphor with a high PLQY used in the luminous material in accordance with some embodiments;

[0050] Fig. 5d is a graph of photovoltaic cell efficiencies for the application of yellow, red, and green coloured coatings, as measured after encapsulation used in the luminous material, in accordance with some embodiments;

[0051] Fig. 5e is a photograph of a photovoltaic cell with the yellow, red, and green coloured coatings of Fig. 5d;

[0052] Fig. 6a is an exemplary conventional photovoltaic module with colouring due to its photovoltaic cell;

[0053] Fig. 6b is a coloured photovoltaic module with a coloured appearance due to a luminous material layer in accordance with some embodiments;

[0054] Fig. 6c is a plot of I-V curves of the conventional module and the coloured module of Figs. 6a and 6b respectively in accordance with some embodiments;

[0055] Fig. 6d is a set of pictures of coloured photovoltaic modules having vivid colours that mask the colour of the cell of the conventional photovoltaic module, in accordance with some embodiments;

[0056] Fig. 7 is a flow diagram of a method of forming a coloured photovoltaic module in accordance with some embodiments;

[0057] Fig. 8a is a schematic diagram of a first example coloured coating formed by applying a luminous material composition to, or mixing the luminous material composition in, a covering layer of a coloured photovoltaic module in accordance with some embodiments;

[0058] Fig. 8b is a schematic diagram of a second example coloured coating formed by applying a medium containing the luminous material to a cell of a coloured photovoltaic module in accordance with some embodiments; and

[0059] Fig. 8c is a schematic diagram of a third example coloured coating formed by depositing the luminous material onto a cell, and subsequently covering the material, of a coloured photovoltaic module in accordance with some embodiments.Description of EmbodimentsConventional photovoltaic devices

[0060] Fig. la schematically illustrates a conventional photovoltaic module 10 with a layered arrangement of components including a photovoltaic cell 102, one or more encapsulant layers 104a 104b surrounding the cell 102 within the module 10, a coversheet 106, and a backsheet layer 108.

[0061] Photovoltaic cell 102 is comprised of a semiconductor material configured to generate an electrical current by absorbing photons of light incident on the surface of the cell 102 resulting in the freeing of charge carriers within the semiconductor lattice. The structure and composition of the cell 102 determines its power conversion efficiency. For example, commercial polycrystalline silicon cells can achieve module efficiencies of around to 23-25%.

[0062] Encapsulant layers 104a and 104b surround the photovoltaic cell 102 and act as a binder between the various layers of the module 10. Each encapsulant layer 104a 104b is formed from a polymer such as ethylene vinyl acetate (EVA). Following deposition onto the photovoltaic module 10 the encapsulant layers 104a and 104b transparently incorporate the photovoltaic cell 102 allowing incident light to reach the cell 102 via the coversheet 106.

[0063] Coversheet 106 is formed of glass, acrylic or another transparent and durable material. The coversheet 106 provides robustness to the photovoltaic module 10 while maintaining transparency. In some embodiments, the coversheet 106 has a thickness varying between 2mm to 4mm depending on the type of glass or other material used.

[0064] Backsheet layer 108 is formed from a polymeric material (e.g., EVA, polyester, or fluoropolymer) and provides electrical insulation and protecting the PV cell 102 from moisture and other environmental effects that may otherwise cause degradation to the cell 102.

[0065] Typical examples of photovoltaic module 10 are constructed to maximize transparency such as by optimizing the module components to minimize reflection. However, this leads to a design that is aesthetically monotonous (i.e., since the module has a black and opaque appearance) and limits the utility of the module 10 for some applications such as BIPV and VIPV. Coloured PV modules are favoured for these applications.

[0066] Previous attempts to provide PV modules with a coloured appearance have involved the use of non-luminous materials or structures [2, 4], Nonluminous materials absorb some of the incident light and reflect the rest, leading to visible colour. Examples of techniques that utilize nonluminous materials include: applying antireflection PV cell coatings, using coloured and / or semi-transparent PV-active layers, and using special solar filters as layers, coatings or interlayers. Another method to achieve a coloured PV device with a relatively high efficiency is to limit the reflection band to a minimum using Bragg reflectors [5], Drawbacks of these approaches include that the colour will often change based on viewing angle, and that the application of the material has a relatively high cost per unit area.

[0067] Coloured polymeric encapsulant films provide a coloured appearance from any viewing angle but are generally opaque and reduce the amount of light reaching the PV cells below it substantially, which limits the power conversion efficiency of the module.

[0068] However, there is difficulty providing colour to a module for aesthetic purposes while still maintaining transparency to maximize power generation. One of the major challenges for coloured PV modules is to maintain a high power conversion efficiency (e.g., above 20%) while also providing an appearance of vivid colour that is non-angle dependent, readily customizable (e.g., to enable a selection of the emitted colour), and cost effective to fabricate. Further, there is a need for the coloured appearance of the PV module to be stable (i.e., capable of retaining its colour for prolonged periods of time, and under adverse environmental conditions, both with and without encapsulation). Further, a highly efficient low-cost method for fabricating coloured photovoltaic modules is desired.

[0069] Photoluminescent (PL) downshifting (DS) materials absorb light that has energy above their HOMO-LUMO / band gaps and emit light of energy near their HOMO-LUMO / band gaps. PL DS materials have been previously used in luminescent solar concentrators (LSC). A LSC has at most three purposes, being to provide colour, some transparency, and solar energy conversion to electrical power. However, thecompetition between these three purposes greatly limits its performance, e.g., the highest conversion efficiency is about 7%. As a large portion of the light is used for solar conversion, the coexistence of high transparency and high power conversion has not been achieved for current LSC technology. For at least this reason, existing photoluminescent materials have not been readily applied for the purpose of achieving coloured photovoltaic modules.

[0070] Further, recent attempts to use photoluminescent materials for colour generation within photovoltaic devices have not been able to demonstrate the performance and stability properties needed for real-world applications. For example, quantum dots (QDs) have recently been used in a coloured photovoltaic device [6], however the colour achieved is translucent and unstable. This significantly limits the viability of the module when deployed in BIPV or VIPV products.

[0071] It is therefore desired to devise techniques that ameliorate these drawbacks, or one or more other drawbacks of the prior art, or that at least provide a useful alternative.Overview

[0072] Disclosed herein are photovoltaic modules, and methods for constructing the same, each having a luminous material that, when applied to a surface of a photovoltaic cell of the module, or to a surface or an encapsulant of the module, generates a persistent, vivid, and stable coloured appearance of the module. The luminous material comprises one or more PL DS materials from the group including: (i) semiconductor nano-particles with a large particle size; (ii) fluorescent or phosphorescent phosphors; and (iii) organic luminogens. Accordingly, the luminous material itself has photoluminescent downshifting properties in that it is configured to absorb photons of incident light in a first wavelength range (e.g., short wavelength high energy photons in the UV and lower regions of the visible spectrum), and re-emit light in a second wavelength range that is narrower than the first wavelength range (e.g., in a range corresponding to a desired colour).

[0073] The luminous material proposed herein has a photoluminescent quantum yield (PLQY) value of at least 80%. The PLQY value is a measure of the effectiveness of the downshifting property of the photoluminescent material, and is calculated as the ratio of the number of emitted photons to the number of absorbed photons. The PLQY value of a photoluminescent material therefore determines the relative reduction in power conversion efficiency of a photovoltaic module to which the material is applied. For example, the power conversion efficiency of a proposed coloured photovoltaic module formed by applying the luminous material to a conventional silicon based photovoltaic cell, the cell producing a power conversion efficiency of around 23% in an uncoloured module, is at least 18%.

[0074] Various embodiments of the photoluminescent downshifting materials (i)-(iii) that form the luminous material are described herein. Semiconductor nano-particles (i) of the luminous material include existing nano-particle materials that have not previously been adapted to colour a PV module, and newly developed materials (e.g., hybrid perovskites). Significantly, the semiconductor nano-particles are large-scale particles having a particle size (e.g., a particle diameter) of at least 50nm. In some embodiments, the particle size of the semiconductor nano-particles ranges between 50 nm and 1 um. This enables the generation of colour with increased stability compared to semiconductor nano-particles with a smaller particle size (such as quantum dots).

[0075] In some embodiments, the semiconductor nano-particle materials, as applied to the PV module, are stable for at least months without encapsulation (and for years with encapsulation).

[0076] Fluorescent and phosphorescent phosphors have been used in Light Emitting Diode (LED) devices to downshift short wavelength incident light to other colours. However, the requirements for PL DS in LED devices differ from those of providing PV module colouring. In some embodiments, the fluorescent and phosphorescent phosphors (ii) of the luminous material include but are not limited to: Garnet-type phosphors; Si3N4-type phosphors; Apatite-type phosphors; Melilite-type phosphors; A3MX5-type phosphors; UCr4C4-type phosphors; P-K2SO4-type phosphors; [3-Ca3(PO4)2 type phosphors; and phosphors based on lanthanide-doped alkaline earth aluminate, or similar materials.

[0077] The organic luminogens (iii) of the luminous material include organic dyes, such as fluorescent or phosphorescent dyes, and aggregation-induced-emission (AIE) molecules. For example, the AIE molecules may include but are not limited to derivatives of: tetraphenyl ethene (TPE), tetraphenylbenzene (TPB), silole, triphenylamine (TP A), 9,10-distyrylanthracene (DSA), pyrrole, cyanostilbene, thiophene, salicylaldehyde, 9,10-diheteroarylanthracene (DHA). AIE molecules demonstrate higher PLQY values when aggregated enabling the production of opaque colours, and thereby overcoming issues with standard organic dyes (e.g., aggregation quenching) when used for colouring PV modules. In some embodiments, a diluted dye composition (e.g., <0. lwt%) is used to produce lightly tinted, transparent colours that maintain a high PLQY value.

[0078] In some embodiments, the organic luminogen molecules are dispersed and wrapped into a nano- / micro-powder, or a polymer, so that the molecules are protected and / or isolated from each other. This is advantageous in reducing aggregation-induced- quenching and improves the stability of the organic luminogens (e.g., against the effects of moisture, oxygen and ultraviolet light).

[0079] Various properties of the coloured appearance are controllable based on the PL DS material(s) used for the PV module. A PL DS material may be selected based on its energy bandgap, such as to control the absorption and emission characteristics of the luminous material. In some embodiments, an upper wavelength of the first wavelength range is determined by the energy bandgap value of the photoluminescent DS material (e.g., such that photons with energy above the bandgap value are absorbed). Subsequently re-emitted photons may have energies, and corresponding wavelengths, in a range closely centred on the wavelength corresponding to the energy bandgap. The energy bandgap value of the photoluminescent DS material may therefore be selected according to a desired colour of the coloured appearance (i.e., to control the colour that will be visible when the module is observed).

[0080] In some embodiments, the luminous material is contained within a layer of the photovoltaic module, which is referred to as a visual modification layer. The visual modification layer is customizable or configurable by controlling the composition of the luminous material within the layer. In some embodiments, the opacity of the visual modification layer is determined by the density of the one or more PL DS materials within the layer.

[0081] It is advantageous that the resulting photovoltaic module emits a vivid coloured appearance (i.e., since the emitted photons are downshifted to a narrow wavelength range corresponding to a particular desired colour) without incurring a significant reduction in its power conversion efficiency relative to the efficiency of an uncoloured module (i.e., by maintaining a high optical transparency over the visible spectrum and part of the near-infrared spectrum). Further, the PL DS material(s) described herein have unique stability characteristics that enable the coloured appearance of the PV module to persist with a lifetime comparable to that of the photovoltaic cell (i.e., at least several years).

[0082] Also disclosed herein are methods of forming a coloured photovoltaic module using photolumine scent downshifting material(s) with the above described properties. The methods generally involve the steps of: (1) preparing a composition of one or more photoluminescent downshifting materials as a luminous material; and (2) applying the luminous material composition to a surface of a photovoltaic cell of the photovoltaic module, or to a surface or an encapsulant of the photovoltaic module, to generate a coloured appearance to an observer of the photovoltaic module (e.g., by forming a visual modification layer on the surface or encapsulant). The luminous material composition has a PLQY value of at least 80% and is comprised of at least one of the photoluminescent downshifting materials (i)-(iii) above.

[0083] In some embodiments, the luminous material composition is deposited on the surface of the photovoltaic cell, or on the surface or encapsulant of the module, with a solution based process. Exemplary solution based processes include doctor blade coating, inkjet printing, slot die coating, and other thin-film deposition techniques.Alternatively, the luminous material composition can be deposited separately on a transparent substrate, such as glass or polymer sheets, or mixed into a transparent structure (e.g., resin or silicone) to form a layer. The coloured substrate or matrix structure containing the luminous material is then encapsulated with the photovoltaic cell in the process of forming the coloured photovoltaic module.

[0084] It is advantageous that the proposed methods provide an efficient and low-cost means of constructing a vivid and optically transparent photovoltaic module that is compatible with conventional processes for the manufacturing of photovoltaic devices and products.Photovoltaic module with a coloured appearance

[0085] Figs, lb to le schematically illustrate examples of a proposed photovoltaic module 100 100’ 100” 100’” that generate a coloured appearance while maintaining high optical transparency over the visible and part of the near-infrared spectrum, thereby minimizing relative reductions in power conversion efficiency compared to an uncoloured module 10.

[0086] Referring to Fig. lb, example photovoltaic module 100 comprises a layered arrangement of a photovoltaic cell 102, one or more encapsulant layers 104a and 104b surrounding the cell 102 within the module 100, a coversheet 106, and a backsheet layer 108. Photovoltaic module 100 further comprises a luminous material 110 that is applied, in this example, to a surface of the photovoltaic cell 102. The luminous material 110 forms a visual modification layer 112 that interacts with at least a portion of the incident light on the photovoltaic cell 102 (i.e., light entering the module 100 via the coversheet 106 and passing through the top encapsulant layer 104a) to generate a coloured appearance to an observer of the module 100.

[0087] Figs. 1c to le represent alternative examples of the proposed coloured photovoltaic module 100’ 100” 100’” respectively where the luminous material 110 is applied to a different component of the module. Referring to Fig. 1c, in some embodiments the luminous material 110 is applied to an encapsulant of the module100’ (i.e., to the top encapsulant layer 104a). In an alternative arrangement, the luminous material 110 is applied to the bottom encapsulant layer 104b or to both encapsulant layers 104a and 104b. Referring to Fig. Id, in some embodiments the luminous material 110 is applied to a surface of the module 100” such as for example an outer surface (as shown) and / or an inner surface of the coversheet 106. Referring to Fig. le, in some embodiments the luminous material 110 is embedded within the material of a component of the module 100’”, such as within the top encapsulant layer 107 (e.g., as a protective transparent matrix). In such examples, the embedding of the luminous material 110 enables the component (e.g., the embedded encapsulant layer 107) to act as the visual modification layer 112.

[0088] It will be appreciated that other embodiments of the proposed coloured photovoltaic module exist in which the luminous material 110 is applied to, deposited on, or embedded within, any other surface of the module or cell, or on or in any materials and / or any substrates that are attached to those surfaces, with an equivalent effect to the embodiments explicitly shown in Figs, lb to le.Photoluminescent downshifting materials

[0089] Typically, an object needs to absorb some of any incident light and reflect the rest to show colours, which results in a loss of transparency. Unlike the traditional pigments and dyes used to impart a coloured appearance onto a conventional photovoltaic module 10, PL materials re-emit part of the absorbed light back to the environment, thereby improving transparency. Further, shifting the re-emitted photons to a specific wavelength enables the generation of a corresponding colour to an observer of the module.

[0090] The use of specific PL DS materials described herein within the luminous material 110 results in the material 110 itself having photoluminescent downshifting properties, and thereby enables the coloured photovoltaic module to generate a vivid colour while still achieving high transparency and stability. Each of the photoluminescent DS materials comprising the luminous material 110 are configured toabsorb a fraction of incident light in a first wavelength range and re-emit light in a second wavelength range that is narrower than the first wavelength range.

[0091] Fig. 2 illustrates a plot 200 of an ideal absorption curve 202, and a corresponding emission curve 204, of a PL DS material with an energy bandgap value Eg. In the curves 202 and 204 of Fig. 2, the absorption (and emission) percentage of the incident and emitted photons (y-axis) is plotted against the photon wavelength (x-axis). The PL DS material absorbs photons with energy above the bandgap energy Egand reemits photons near the bandgap energy value Egwith a narrower spectral range. In some embodiments, the first wavelength range extends to an upper wavelength that is determined by an energy bandgap value of the PL DS material. Put another way, the energy bandgap value Egdetermines a corresponding wavelength threshold value Xgwhich sets an upper bound on the wavelength of the incident photons which are absorbed by the PL DS material.

[0092] In the example shown by Fig. 2, the energy bandgap Egis selected such that the second wavelength range corresponds to the green colour (with an emission wavelength value of Xg« 525nm). In other examples, the energy bandgap value Egand / or the emission wavelengthgof the photoluminescent DS material is selected according to a desired colour of the coloured appearance of the module 100. In some embodiments, the luminous material 110 may generate the appearance of a pure colour by including, in the material 110, a single PL DS material that emits light at the desired bandgap energy. Alternatively, the luminous material 110 may comprise a mixture of two or more different PL DS materials at various ratios (i.e., as determined by the energy bandgap value of each material) to achieve an appearance of an arbitrary colour.

[0093] Referring to Fig. 2, inset 220 shows the absorption and emission functions of a luminous material forming a visual modification layer 112 on a substrate 109 of a coloured photovoltaic module. Incident photons 222 arrive onto the surface of the visual modification layer 112 which comprises the luminous material 110. Absorptionoccurs leading to selective emissions 224 and 226 of some of the photons in the second wavelength range.

[0094] The visual modification layer 112 depicted in Fig. 2 is a protective transparent structure that arranged within the module (e.g., as in example modules 100, 100’ and 100”) or embedded within a transparent substrate and then applied to surfaces of the module (as in example module 100’”) including surfaces of the photovoltaic cell 102 or any other component. In some embodiments, the transparent structure is in the form of a matrix made of inorganic materials of large bandgaps, including oxides, nitrides, carbides, etc., and transparent organic materials, like polymers, resins, etc. It will be appreciated that other embodiments of the coloured photovoltaic module 100 may involve the application of the luminous material 110 to a different surface or encapsulant, where the PL DS properties of the material 110 function analogously.

[0095] The ratio between the emitted photons to the absorbed photons is referred to as the photoluminescent quantum yield (PLQY). The luminous material 110 is configured to have a high PLQY value (e.g., > 80%) irrespective of the composition of the material 110 as a single PL DS material, or a mixture of any two or more materials, from (i)- (iii), thereby enabling both high transparency and a vivid coloured appearance of the resulting module 100.Example materials

[0096] The luminous material 110 comprises one or more photoluminescent (PL) down shifting (DS) materials from the groups of: (i) semiconductor nano-particles (NPs) having a particle size of at least 50 nm; (ii) fluorescent or phosphorescent phosphors; and (iii) organic luminogens. Examples of each of the materials (i)-(iii) are discussed below. In some embodiments, the luminous material 110 comprises individual PL DS material(s) from only one of (i)-(iii) i.e., either one or more semiconductor NPs, one or more phosphors, or one or more organic luminogens. In other embodiments, the luminous material 110 comprises individual PL DS material(s) from more than one of groups (i)-(iii) i.e., a combination of semiconductor NPs, phosphors, and / or organic luminogens. In such embodiments, the luminous material110 may be arranged as a plurality of individual sub-layers, where each sub-layer comprises PL DS material(s) from one of the groups (i)-(iii).Semiconductor nano-particles

[0097] Semiconductor nanoparticles (NPs) are nano-size single crystals of semiconductor material (e.g., silicon). Though the PLQY of intrinsic NPs is usually less than 70% the semiconductor NPs of the luminous material 110 are subjected to doping with one or more ions, dyes, or phosphors, and / or to passivation with ligands, or shells, to substantially enhance the PLQY such that it reaches or exceeds 80%.

[0098] A challenge of utilizing NPs to generate a coloured appearance of a photovoltaic module 100 is that the PLQY of NPs drops significantly after application of the luminous material 110, since the surface environment of dried NPs is changed compared to that of their pre-application form.

[0099] The ability of the luminous material 110 to maintain its coloured appearance following application, and in response to environmental conditions faced by the photovoltaic module 100, is referred to as the stability of the luminous material 110. In some embodiments, using the luminous material 110 provides a coloured photovoltaic module 100 that has a stability sufficient to pass the IEC standard 61215 for photovoltaic modules, including but not limited to the UV preconditioning test (MQT 10), Thermal cycling test (MQT 11) and Damp heat test (MQT 13) with less than 5% efficiency reduction.

[0100] The stability may be controlled by the size of the semiconductor nano-particles comprising the luminous material 110. In some embodiments, the luminous material 110 includes semiconductor NPs with a particle size of at least 50 nm. In some embodiments, the particle size (e.g. the diameter of the NP) ranges between 50nm and 1 um depending on the type of particle and its structure (e.g., nanocrystal composition). Semiconductor NPs with small particle sizes (e.g., <10nm) are not suitable to provide the coloured photovoltaic module 100 with the stability characteristics desired for applications in BIPV and VIPV, for example.

[0101] In some embodiments, the semiconductor NPs are comprised of one or more doped or undoped semiconductors that have bandgaps between 1.5 eV to 3 eV, corresponding to the visible light region (e.g., configured to show colours ranging from red to violet). These semiconductor NPs may include but are not limited to: CdSe, CdS, ZnSe, hybrid perovskites in the form of ABX3(A: CH NH3+, HC(NH2)+, Cs+; B: Pb2+, Sn2+; X: I", Br", Cl", F") or other forms.

[0102] Fig. 3a illustrates a graph set 300 of the tuneable PL spectrum of CsPbX NPs, where X denotes I, Br, Cl, or their mixture [7], In graph set 300, the normalized PL intensity is plotted against wavelength for perovskite NPs that exhibit -100% PLQY and a tuneable PL response across the visible spectrum.

[0103] Fig. 3b illustrates a plot 310 of an absorption curve of the transparent film of CsPbBr, NPs. As shown in the absorption curve 310 of Fig. 3b, a thin film of CsPbBr3 NPs on glass shows an average absorption of less than 10% in the visible and NIR-I spectrum. This means that the transparency of the semiconductor NP film can exceed 90% with a suitable antireflection layer when utilized in the photovoltaic module 100.

[0104] Fig. 3c illustrates a graphical representation 320 of the coloured appearance of the film of Fig. 3b under sunlight, and without angular dependence. The vivid green colour decorates the black surface of the photovoltaic cell 102.

[0105] Fig. 3d illustrates a plot 330 of an I-V characteristic indicating the power efficiency of the coloured photovoltaic module 100, where the associated efficiency loss is only 2%. As the efficiency of commercial Si and group IILV photovoltaic cells are above 23% and 34%, respectively, application of a luminous material 110 generally comprised of the NPs described above (i.e., with a PLQY of at least 80%) can produce a coloured photovoltaic module with a power conversion efficiency of at least 18%.Organic luminogens

[0106] Organic luminogens are light-emitting molecules and polymers, such as organic molecules that emit light in the visible light region, e.g., showing coloursranging from red to violet. In some embodiments, the luminous material 110 comprises one or more of: organometallic chelates; fluorescent and phosphorescent dyes; conjugated dendrimers; luminescent conductive polymers (like derivatives of poly (p- phenylene vinylene) and polyfluorene); phosphorescent organometallic complexes (such as Ir(mppy)3) in hosts; and aggregation-induced-emission (AIE) molecules.

[0107] Selection of the organic luminogens of the luminous material 110 may vary based on the desired characteristics of the coloured appearance of the module 100. In some embodiments, fluorescent dyes with high PLQY (i.e., at least 80%), such as the Lumogen F series of dyes of BASF, are used in a dilute composition (<0.1wt%) to obtain transparent colours

[0011] ,

[0108] A drawback of using fluorescent dyes is that their fluorescence is quenched when the dye molecules aggregate. In some embodiments, the luminous material 110 comprises aggregation-induced emission (AIE) dyes. AIE dyes emit light more efficiently in the solid state such as powders and films.

[0109] Various AIE dyes show high PLQY (i.e., at least 80%) with tuneable PL characteristics in the visible spectrum. Fig. 4a illustrates a structural formula 400 of an example AIE molecule in the form of a TPB-AC molecule used in the luminous material. Fig. 4b illustrates a plot 410 of an absorbance curve of the TPB-AC molecule with structural formula 400 of Fig. 4a having a blue PL with PLQY ~ 100%

[0013] , The absorbance (normalized intensity) is plotted against wavelength for absorption (PL emission) of photons. Fig. 4c illustrates a structural formula 420 of an example AIE molecule in the form of a NAI-BiFA molecule used in the luminous material. Fig. 4d illustrates a plot 430 of the normalized intensity of the NAI-BiFA molecule of Fig. 4c with different solvent compositions and having a tuneable PL emission colour with PLQY - 90%

[0014] ,

[0110] In some embodiments, the organic luminogens (such as the AIE molecules) are dispersed and wrapped in a nano- and / or micro-powder, or a polymer, to reduce aggregation-induced-quenching and improve stability. For example, the nano- / micro-powder may comprise one or more of: oxide nanoparticles, nitride nanoparticles, oxynitride nanoparticles, halide nanoparticles, carbide nanoparticles, hydroxide nanoparticles, large-bandgap semiconductor nanoparticles, phosphor nano- / micro- particles, 2D material nano-sheets, organic nano- / micro-spheres, molecular sieves, metal-organic frameworks, or other similar materials.

[0111] In some embodiments, the luminous material 110 comprises other AIE dyes with high PLQY and various colours. For example, the AIE molecules may include, without limitation, one or more of: tetraphenylethene (TPE) derivatives, tetraphenylbenzene (TPB) derivatives, silole derivatives, triphenylamine (TP A) derivatives, 9, 10-di styryl anthracene (DS A) derivatives, pyrrole derivatives, cyanostilbene derivatives, thiophene derivatives, salicylaldehyde derivatives, and 9,10- diheteroarylanthracene (DHA) derivatives.

[0112] Other organic luminogens may be used in various examples, including but not limited to one or more of: Xanthene derivatives, Cyanine derivatives, Squaraine derivatives and ring-substituted squaraines, Squaraine rotaxane derivatives, Naphthalene derivatives, Coumarin derivatives, Oxadiazole derivatives, Anthracene derivatives, Pyrene derivatives, Oxazine derivatives, Acridine derivatives, Arylmethine derivatives, Tetrapyrrole derivatives, and Dipyrromethene derivatives.

[0113] In some embodiments, the luminous material 110 comprises dye-SiO2 coreshell nanoparticles (NP) formed by mixing one or more dyes, Si(OC2H5)4, and ethanol with water of different pH values

[0012] , Organic dyes, such as the dye-SiO2 NP composition, are advantageous in that they avoid aggregation-induced quenching, and thereby enable the formation of a coloured appearance with high transparency and high stability. Further, the organic luminogens may provide enhanced stability against the effects of moisture, oxygen and ultraviolet light.Fluorescent or phosphorescent phosphors

[0114] Fluorescent or phosphorescent phosphors are luminescent downshifting substances, which are typically made from a suitable host material with anadded activator. The fluorescent or phosphorescent phosphors are inorganic compounds that emit light in the visible light region (e.g., configured to show colours ranging from red to violet). The phosphors can be categorized by host crystal structures and / or composition, including but not limited to one or more of the following materials: o Garnet-type phosphors in the chemical formula of A3B2C3O12, where elements A, B, C can be Y, Lu, Ca, Mg, Al, Sc, Si, Ga, Ge, Gd, Zr, Hf, La, etc; o Si3N4-type phosphors P-SiAlON and M-a-SiAlON, where element M can be Li, Mg, Ca and rare-earth metals; o Apatite-type phosphors having a general chemical formula of A10[XO4]6Z2, where elements A can be Ca, Sr, Ba, Mg, Fe, Mn, Pb, Na, K, Ag and rare earth ions; X is P, As, Si, etc.; and Z is denoted by halogen ions, F, Cl, Br, or O, OH, and vacancies; o Melilite-type phosphors having a general chemical formula of A2BC2X7, where element A is a cation of Na, Ca, Sr, Y, La, etc.; B is a cation of Mg, Mn, Fe, Zn, Cd, Al, Ga, etc.; C is also a smaller cation of Al, Si, Fe, Ga, Ge; X is an anion of O, F, S, etc; o A3MX5-type phosphors having elements A (Sr, Ba, Ca and rare earths), M (Al and Si) and X (O and F); o UCr4C4-type phosphors having a chemical formula of A[B3TX4], where A is Sr, Ca, Ba, etc.; B is Al, Mg, S, etc.; T is Li, Si, Al, etc.; and X is N; o P-K2SO4-type phosphors having typical materials like M2SiO4 and ABPO4, where M is Ba, Sr, Ca; A is Li, Na, K; and B is Ca, Sr, Ba; o P-Ca3(PO4)2 type phosphors having two forms of M3(PO4)2 and A8BC(PO4)7, where M is Ca, Sr, Ba etc.; A is Ca and Sr; B and C can be Lu, Y, Gd, La, Sc, Al, Zn, Li, Mg, K, etc; o Phosphors based on lanthanide-doped alkaline earth aluminate; and o Other phosphors based on materials including BaMgAl 10017 (BAM), Y2O3, MgAll 101 , La3Si6Nl l, NaYF4, ZnS, (Sr,Ca)AlSiN3, SrA12O4, Msi2O2N2 (M = Ca, Sr, Ba), K2A12B2O7, MN4(BO3)3 (M =Li, Na, K; N = Ca, Sr), A2MF6 (A = Na, K, Cs, Rb or (NH4); M = Si, Al, Ge, Sn, Ti or Zr), BMF6 (B = Ba and Zn; M = Si, Ge, Sn or Ti), (Ba, Sr, La)SiaAlbOcNd, M2Si5N8 (M = Ca, Sr, Ba), La3Ga5GeO14, ScBO3, ZnGa2O4, (Ga, Sc, Al, In)2O3.

[0115] Despite their luminescence characteristics, until the development of the methods and techniques proposed herein by the inventors, applications and uses of fluorescent or phosphorescent phosphors have not focused on generating vivid coloured appearances for photovoltaic modules.

[0116] In some embodiments of the proposed coloured photovoltaic module 100, the luminous material 110 includes fluorescent or phosphorescent phosphors that are selected to have a high PLQY (i.e., at least 80%) and a high stability when forming the coloured appearance.

[0117] In some embodiments, the luminous material 110 includes phosphors with a host material including an oxide, nitride, oxynitride, sulfide, selenide, halide, silicate, or other similar materials. In some examples, the added activator includes one or more of the following: copper (Cu), silver (Ag), zinc (Zn), cadmium (Cd), manganese (Mn), aluminium (Al), chromium (Cr), silicon (Si), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium ™, ytterbium (Yb), lutetium (Lu), yttrium (Y), scandium (Sc), or another rare- earth metal with similar properties. In some examples, the fluorescent or phosphorescent phosphors are a YAG-based phosphor or a ZnS-based phosphor.

[0118] Figs. 5a to 5c illustrate graphs 500, and 510, and graph set 520 respectively of the emission characteristics (stability) of phosphors of high PLQY in the visible spectrum at different temperatures. Fig. 5a is a graph 500 illustrating the emission curve of a first example phosphor (Sr0 99Bax)2P2O7with PLQY ~ 80% [8], Fig. 5b is a graph 510 illustrating the emission curve of a second example phosphorwith PLQY ~ 100% [9], Fig. 5c is a set of graphs 520 illustratingthe emission characteristics of a third example phosphor Gd3 67EuSi3O13with PLQY ~ 80%

[0010] ,

[0119] Fig. 5d illustrates a graph 530 showing experimental results demonstrating photovoltaic cell efficiencies of around 20% for the application of each of an opaque yellow, red, and green coloured coating, as measured after encapsulation. Fig. 5e illustrates the yellow, red, and green encapsulated coloured solar cells 540, 550, 560 providing the efficiencies show in Fig. 5d.

[0120] Various embodiments of coloured photovoltaic modules may be implemented using one or more of the PL DS materials (i)-(iii) in the luminous material 110. Fig. 6a illustrates an exemplary photovoltaic module 600 which has colouring (i.e., a dark blue) due to the photovoltaic cell 102.

[0121] Fig. 6b illustrates a coloured module 610 having a luminous material layer of a semi-transparent orange PL DS material.

[0122] Fig. 6c is a graph 630 illustrating I-V curves of a conventional module 600 and a coloured module 610, where the coloured module 610 experiences a reduction in efficiency of only 0.12% compared to the conventional module 600.

[0123] Fig. 6d illustrates a set of exemplary coloured photovoltaic modules 620 having vivid colours that mask the colour of the photovoltaic cell of the conventional photovoltaic module, as achieved by yellow phosphors, green perovskite NPs, and red CdSe / ZnS based NPs, having large particle sizes as described above.Methods of construction

[0124] Fig. 7 illustrates a method 700 of forming a coloured photovoltaic module 100 in accordance with some embodiments of the proposed technology. At step 702, a composition of the luminous material 110 is prepared, where the luminous material has a PLQY value of at least 80% and comprises one or more PL DS materials from the group of: (i) semiconductor nano-particles having a particle size of at least 50 nm; (ii)fluorescent or phosphorescent phosphors; and (iii) organic luminogens, as described above.

[0125] At step 704, the composition is applied to a surface within the photovoltaic module 100. In some embodiments, the surface is a surface of the photovoltaic cell 102 of the photovoltaic module 100, or to an encapsulant 104a and 104b or a surface of the photovoltaic module 100 (e.g., a surface of coversheet 106), to form a visual modification layer 112 that generates a coloured appearance to an observer of the photovoltaic module 100.

[0126] In some embodiments, the composition is a solution prepared according to the PL DS materials of the luminous material 110 (e.g., nano / micro powders that are dissolved in a solvent). The solution is applied via a solution based process, such as for example a thin film deposition technique (e.g., dip coating, spin coating, slot-die coating, doctor blading, bar coating, spray coating, inkjet / screen printing, L-B trough, etc.). In other embodiments, the solution is applied via a vacuum and / or gas based coating process.

[0127] The selection of solvent for the composition, and the corresponding deposition process, is based on the PL DS materials of the luminous material 110 and / or the desired characteristics of the coloured appearance. For example, semiconductor NP materials may be dispersed in solvents, such as hexane and octane, and subsequently inkjet printed on substrates or photovoltaic cells of the module 100.

[0128] In some embodiments, a luminous material 110 comprising phosphor powders is mixed with silicone (such as Sylgard 184) at various weight ratios (l-50wt%) according to a target colour transparency. After degassing, the mixture is coated on clean substrates, or photovoltaic cells, of the module 100 by a doctor blade coater and then cured at room temperature.

[0129] In some embodiments, a luminous material 110 comprising organic luminogens (e.g., dyes) is mixed with PMMA or other polymers in a solvent liketoluene, then coated and dried to form a coloured polymer layer. The organic dye based solution may be deposited by inkjet or spray printed on substrates, or photovoltaic cells, of the module 100.

[0130] Various colouration structures are realizable using the method 700 to form the coloured photovoltaic module 100. In some embodiments, applying the composition of the luminous material 110 (i.e., at step 702) involves forming a transparent structure in which the composition is embedded, and subsequently applying the structure to a surface of the cell 102, or to a surface, encapsulant, or other substrate layer of the module 100, to form the visual modification layer 112.

[0131] Fig. 8a illustrates a first exemplary coloured coating 800 formed by depositing the luminous material composition 110 on, and / or mixing the luminous material composition 110 in, a covering layer (e.g., substrate 802 as arranged on top of the photovoltaic cell 102).

[0132] Fig. 8b illustrates a second exemplary coloured coating 810 formed by applying a medium (e.g., a silicon or epoxy gel) 812 containing the luminous material 110 to the photovoltaic cell 102 and then curing the composition following the application.

[0133] Fig. 8c illustrates a third exemplary coloured coating 820 formed by depositing the luminous material 110 directly onto a surface of the photovoltaic cell 102 and subsequently covering the material 110 with a capping layer 822.

[0134] In some embodiments, the gap size and refractive index of encapsulant 104a and 104b between photovoltaic cell 102 and glass / polymer substrates will affect the coupling. In some embodiments, the distribution and density of the PL DS materials of the luminous material 110 (e.g., the NPs, phosphors and / or dyes) will affect the light that is trapped, absorbed, and reflected by the module 100.

[0135] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.References[1] Feldman, D., et al., U.S. Solar Photovoltaic System and Energy Storage Cost Benchmark:Ql 2020. 2020, National Renewable Energy Laboratory.[2] Peharz, G., et al., Application of plasmonic coloring for making building integrated PV modules comprising of green solar cells. Renewable Energy, 2017. 109: p. 542-550.[3] Peacock, B., Australia’s green bank backs flexible, lightweight eArc ‘solar skins’, in pv-magazine-australia. 2020.[4] Liu, W., et al., Advance in photonic crystal solar cells. Renewable & Sustainable Energy Reviews, 2019. 116.[5] Dong, W.J., et al., Efficiency enhancement and angle-dependent color change in see-through organic photovoltaics using distributed Bragg reflectors. Applied Physics Letters, 2016. 108(10).[6] Jiang, C., et al., Colored Silicon Heterojunction Solar Cells Exceeding 23.5% Efficiency Enabled by Luminescent Down-Shift Quantum Dots. Adv Mater, 2023. 35(6): p. e2208042.[7] Lignos, I., et al., Synthesis of Cesium Lead Halide Perovskite Nanocrystals in a Droplet-Based Microfluidic Platform: Fast Parametric Space Mapping. Nano Lett, 2016. 16(3): p. 1869-77.[8] Zhong, Y., et al., Pyrophosphate Phosphor Solid Solution with High Quantum Efficiency and Thermal Stability for Efficient LED Lighting. iScience, 2020. 23(3): p. 100892.[9] Yang, B.B., et al., Optical and reliability properties studies of green YAG phosphors by Ga substitution. Journal of Materials Science-Materials in Electronics, 2016. 27(4): p. 3376-3383.

[0010] Ye, W., et al., High Quantum Yield Gd4.67Si3O13:Eu3+ Red-Emitting Phosphor for Tunable White Light-Emitting Devices Driven by UV or Blue LED. ACS Applied Electronic Materials, 2021. 3(3): p. 1403-1412.

[0011] Alonso-Alvarez, D., et al., Luminescent down-shifting experiment and modelling with multiple photovoltaic technologies. Progress in Photovoltaics, 2015. 23(4): p. 479-497.

[0012] Rutschmann, M. and C. Feldmann, Perylene dye@SiO2 core-shell nanoparticles with intense fluorescence. Journal of Materials Chemistry C, 2023. 11(2): p. 616-621.

[0013] Xu, Z., et al., Highly Efficient Deep Blue Aggregation-Induced Emission Organic Molecule: A Promising Multifunctional Electroluminescence Material for Blue / Green / Orange / Red / White OLEDs with Superior Efficiency and Low Roll-Off. ACS Photonics, 2019. 6(3): p. 767-778.

[0014] Chen, S., et al., Naphthalimide-arylamine derivatives with aggregation induced delayed fluorescence for realizing efficient green to red electroluminescence. Journal of Materials Chemistry C, 2019. 7(10): p. 2886- 2897.

Claims

1. A photovoltaic module, comprising:a photovoltaic cell; anda luminous material applied to a surface of the photovoltaic cell, or to a surface or an encapsulant of the photovoltaic module, to form a visual modification layer that interacts with at least a portion of light incident on the photovoltaic cell to generate a coloured appearance to an observer of the module,wherein the luminous material has a photoluminescence quantum yield value of at least 80% and comprises one or more photoluminescent down shifting materials from the group of:(i) semiconductor nano-particles having a particle size of at least 50 nm;(ii) fluorescent or phosphorescent phosphors; and(iii) organic luminogens.

2. The module of claim 1, wherein the photovoltaic module has a power conversion efficiency of at least 18%.

3. The module of any of claims 1 to 2, wherein each photoluminescent downshifting material is configured to absorb a fraction of incident light in a first wavelength range and re-emit light in a second wavelength range that is narrower than the first wavelength range.

4. The module of claim 3, wherein the first wavelength range extends to an upper wavelength that is determined by an energy bandgap value of the photoluminescent downshifting material.

5. The module of claims 3 to 4, wherein the energy bandgap value and the second wavelength range of each photoluminescent downshifting material is selected according to a desired colour of the coloured appearance of the module.

6. The module of any of claims 1 to 5, wherein the visual modification layer has an opacity that is determined by a density of the photoluminescent downshifting material(s) within the layer.

7. The module of any of claims 1 to 6, wherein the semiconductor nano-particles include but are not limited to: CdSe, CdS, ZnSe, hybrid perovskites in the form of ABX (A: CH3NH3+, HC(NH2)+, Cs+ ; B: Pb2+, Sn2+; X: I; Br, Cl; F’) or other forms.

8. The module of claim 7, wherein the particle size of the semiconductor nanoparticles is between 50 nm and 1 um.

9. The module of any of claims 1 to 8, wherein the fluorescent or phosphorescent phosphors include host material comprising one or more of: oxides; nitrides;oxynitrides; sulfides; selenides; halides; silicates; aluminate; borate; phosphates; molybdate; and wherein the host material comprises an added activator.

10. The module of claim 9, wherein the added activator includes one or more of the following: copper (Cu), silver (Ag), zinc (Zn), cadmium (Cd), manganese (Mn), aluminium (Al), chromium (Cr), silicon (Si), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (TM), ytterbium (Yb), lutetium (Lu), yttrium (Y), scandium (Sc), or another rare-earth metal with similar properties.

11. The module of claim 9 to 10, wherein the fluorescent or phosphorescent phosphors are include but are not limited to one or more of the following materials: Garnet-type phosphors; Si3N4-type phosphors; Apatite-type phosphors; Melilite-type phosphors; A3MX5-type phosphors; Ucr4C4-type phosphors; P-K2SO4-type phosphors; P-Ca3(PO4)2 type phosphors; Phosphors based on lanthanide-doped alkaline earth aluminate; and phosphors based on materials including BaMgAl 10017 (BAM), Y2O3, MgAl 1IO19, La3Si6Nll, NaYF4, ZnS, (Sr,Ca)AlSiN3, SrA12O4,Msi2O2N2 (M = Ca, Sr, Ba), K2A12B2O7, MN4(BO3)3 (M = Li, Na, K; N = Ca, Sr), A2MF6 (A = Na, K, Cs, Rb or (NH4); M = Si, Al, Ge, Sn, Ti or Zr), BMF6 (B = Ba and Zn; M = Si, Ge, Sn or Ti), (Ba, Sr, La)SiaAlbOcNd, M2Si5N8 (M = Ca, Sr, Ba), La3Ga5GeO14, ScB03, ZnGa2O4, (Ga, Sc, Al, In)2O3.

12. The module of any of claims 1 to 11, wherein the organic luminogens comprise one or more of: Organometallic chelates; conjugated dendrimers; luminescent conductive polymers; phosphorescent organometallic complexes; fluorescent or phosphorescent dyes; and aggregation-induced-emission (AIE) molecules.

13. The module of claim 12, wherein the AIE molecules include but are not limited to one or more of: tetraphenylethene (TPE) derivatives, tetraphenylbenzene (TPB) derivatives, silole derivatives, triphenylamine (TPA) derivatives, 9,10-distyrylanthracene (DSA) derivatives, pyrrole derivatives, cyanostilbene derivatives, thiophene derivatives, salicylaldehyde derivatives, and 9,10-diheteroarylanthracene (DHA) derivatives.

14. The module of any of claims 12 to 13, wherein the organic luminogens are dispersed and wrapped in a nano- or micro-powder or a polymer.

15. The module of claim 14, wherein the nano- or micro-powder comprises one or more of: oxide nanoparticles, nitride nanoparticles, oxynitride nanoparticles, halide nanoparticles, carbide nanoparticles, hydroxide nanoparticles, large-bandgap semiconductor nanoparticles, phosphor nano- / micro-particles, 2D material nano-sheets, organic nano- / micro-spheres, molecular sieves, and metal-organic frameworks.

16. The module of any of claims 12 to 15, wherein the organic luminogens include but are not limited to one or more of: Xanthene derivatives, Cyanine derivatives, Squaraine derivatives and ring-substituted squaraines, Squaraine rotaxane derivatives, Naphthalene derivatives, Coumarin derivatives, Oxadiazole derivatives, Anthracenederivatives, Pyrene derivatives, Oxazine derivatives, Acridine derivatives, Arylmethine derivatives, Tetrapyrrole derivatives, and Dipyrromethene derivatives.

17. The module of any of claims 1 to 16, wherein the luminous material, as applied, is industrially stable according to IEC standard 61215 for photovoltaic modules.

18. A composition for use with a photovoltaic module, the composition comprising a luminous material that, when applied to a surface of a photovoltaic cell of the photovoltaic module, or to a surface or an encapsulant of the photovoltaic module, generates a coloured appearance to an observer of the photovoltaic module, wherein the luminous material has a photoluminescence quantum yield value of at least 80% and comprises one or more photoluminescent down shifting materials from the group of:(i) semiconductor nano-particles having a particle size of at least 50 nm;(ii) fluorescent or phosphorescent phosphors; and(iii) organic luminogens.

19. A method of forming a coloured photovoltaic module, the method comprising: preparing a composition of a luminous material, the luminous material having a photoluminescence quantum yield value of at least 80% and comprising one or more photoluminescent down shifting materials from the group of:(i) semiconductor nano-particles having a particle size of at least 50 nm;(ii) fluorescent or phosphorescent phosphors; and(iii) organic luminogens; andapplying the composition to a surface of a photovoltaic cell of the photovoltaic module, or to a surface or an encapsulant of the photovoltaic module, to form a visual modification layer that generates a coloured appearance to an observer of the photovoltaic module.

20. The method of claim 19, wherein the visual modification layer is a transparent structure in which the composition is embedded.

21. The method of claim 19, wherein the composition is applied to the surface of the photovoltaic cell, or to the surface or the encapsulant of the photovoltaic module, with a solution based process.

22. The method of claim 21, wherein the solution based process is a thin film deposition technique.

23. The method of any of claims 21 to 22, wherein the solution based process comprises: applying the composition as a gel; and curing the composition following its application onto the surface.

24. The method of any of claims 21 to 23, wherein the solution based process comprises covering the composition, following its application onto the surface, with a capping layer.

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