Photovoltaic device

Abstract

A photovoltaic device 20 comprises an electrode layer 21 in electrical contact with a photovoltaic component 22; a first metallic array 23 connectable to an electric circuit and being arranged across

Description

Field The present invention relates to a photovoltaic device for converting light energy into electrical energy, photovoltaic modules, methods for manufacture thereof, and uses of photovoltaic devices and modules in various applications. Background Solar energy conversion is one of the most promising technologies to provide renewable energy. One class of photovoltaic materials that has attracted significant recent interest is organic-inorganic halide perovskites. Materials of this type have a perovskite crystal structure with general formula ABX3. These materials have been found to exhibit favourable band gaps, high absorption coefficients and long diffusion lengths, rendering such compounds ideal as an absorber in photovoltaic devices. During the last decade, organic-inorganic halide perovskites have demonstrated efficiencies as high as 25.2% in a single junction photovoltaic device configuration, and as high as 33.9% in a tandem multijunction photovoltaic device system in combination with silicon. These perovskite materials can be made with a range of band-gaps, which makes them suitable for integration in single junction and multijunction solar cells, such as tandem cells. A tandem solar cell is a solar cell comprising two sub-cells, each tailored to harvest photons at different wavelengths, maximising the energy generated. Photovoltaic modules are made of a number of electrically connected photovoltaic devices (i.e. solar cells) that are laminated between two sheets of glass or a flexible material. Between the photovoltaic devices and the glass sheets / flexible material, an encapsulant material is used to ensure lamination and therefore protect the system from environmental impacts, such as moisture, and mechanical impacts. The selection of the laminating materials depends on the application, with the most common choice being two sheets of glass, also known as glass / glass encapsulation. This kind of encapsulation is a “rigid approach” and is used for protecting modules where a longer lifetime is desired. This rigid approach is also compatible with back-sheet / front glass encapsulation. Other type of applications, where a less rigid approach is desirable, uses flexible sheets of plastic, or polymers. For example (but not restricted to), the panels integrated in electric vehicles (EV). Photovoltaic devices are usually finished with a metal array connected to an external electronic circuit. Figure 1 shows a schematic cross-sectional view of a prior art photovoltaic device(10). The photovoltaic device shown in Figure 1 comprises an electrode layer (11), a photovoltaic component (12) and a metallic array (13). The electrode layer is for receiving electrical energy and is in electrical contact with the photovoltaic component comprising photovoltaic material. The electrode layer comprises a first surface (11 a) in contact with the photovoltaic component and a second surface (11 b) opposite to the first surface. The metallic array (13) is connectable to an electric circuit and is arranged across the second surface of the electrode layer, and thus is arranged to receive electrical energy from the electrode layer (which in turn is arranged to receive electrical energy from the photovoltaic component). In the embodiment of the invention shown in Figure 2a, an Intermediate barrier layer (IBL) (24) is deposited by covering all, or substantially all of the electrode layer (21) and a first metallic array (23), and is further topped by a second metallic array (25), which finishes the device. The I BL (24) comprises a first surface (24a) in contact with the electrode layer and the metallic array. The I BL (24) also comprises a second surface (24b) opposite to the first surface (24a) which is in contact with a second metallic array (25), which second metallic array finishes the device. The described configuration can be defined as a “sandwich printing” where two metallic arrays are deposited and in contact through an I BL which can have different functions depending on the properties of the material used and the deposition method utilised. In the prior art, the photovoltaic devices which do not contain an IBL can be directly connected via a metallic array to an electric circuit. However, in forming an IBL layer across the surface of the photovoltaic device according to the present invention, the first metallic array is completely covered. As a result it is not possible to directly connect this first metallic array to an electric circuit for the purposes of extracting electrical current from the photovoltaic device. By careful selection of the IBL and addition of the second metallic array in the present invention, the electric connection is secured. The integration of an IBL layer in a photovoltaic device achieves a dual purpose, on the one hand it serves as an effective barrier layer preventing moisture ingress to the underlying photovoltaic component, and on the other hand it provides optimised optical, mechanical and / or protective properties that can be tuned based on the desired final application, once the solar cells are integrated in a module. In other words the IBL can be optimised optically to achieve higher efficiencies. The IBL can also be designed with extra protection against high energy radiation environments so it is suitable for space applications, or, it can be configured to have higher flexibility properties so it is suitable for integration in flexible modules. Hence, the IBL of the present invention can be tailored for use in photovoltaic devices in: high proton radiation environments, aerospace, terrestrial applications, extra-terrestrial applications, rigid applications, or flexible applications. Newly developed photoelectronic devices, such as those based on perovskites, are known to be more sensitive to external elements, and the higher complexity of their compositions also requires a more advanced optical design to achieve the higher device performance with longer lifetimes. The present invention provides an improved photovoltaic device which features an IBL layer, capable of providing in one unit better protection and enhanced properties. The seamless integration of the encapsulation layer into the device prior to module assembly provides ease of integration and protects the device immediately after fabrication. Summary of Invention Aspects and / or embodiments seek to provide an improved photovoltaic device. According to a first aspect, there is provided a photovoltaic device (20) comprising: an electrode layer (21) for receiving electrical energy, the electrode layer (21) being in electrical contact with a photovoltaic component (22) comprising photovoltaic material, the electrode layer (21) comprising a first surface (21a) in contact with the photovoltaic component (22) and a second surface (21b) opposite to the first surface; a first metallic array (23) connectable to an electric circuit and being arranged across the second surface of the electrode layer (21b); and an intermediate barrier layer (IBL) (24) provided across and covering all or substantially all of the electrode layer (21) and the first metallic array (23), wherein the IBL (24) comprises a first surface (24a) in contact with the electrode layer (21) and the first metallic array (23) and a second surface (24b) opposite to the first surface; further comprising a second metallic array (25) connectable to an electric circuit, the second metallic array being arranged across the second surface of the IBL (24b) and being electrically connected to the first metallic array (23). This configuration can be described as sandwich printing. According to a second aspect of the invention, there is provided a photovoltaic module comprising a plurality of photovoltaic devices as described above in relation to the first aspect of the invention, wherein the plurality of photovoltaic devices are electrically connected to each other. According to the third aspect of the invention, there is provided a photovoltaic array comprising a plurality of photovoltaic modules as described in relation to the second aspect of the invention, wherein the photovoltaic modules are encapsulated and are electrically connected to each other. According to a fourth aspect of the invention, there is provided a method of manufacturing a photovoltaic device, the method comprising: providing an electrode layer in contact with a photovoltaic component comprising photovoltaic material on its first surface; applying a first metallic array across a second surface of the electrode layer wherein the first metallic array is connectable to an electric circuit; encapsulating the surface of the electrode layer and the first metallic array by depositing an I BL across all or substantially all the second surface of the electrode layer and the first metallic array; and arranging a second metallic array across the surface of the IBL and electrically connecting the second metallic array to the first metallic array, wherein the second metallic array is connectable to an electric circuit. According to a fifth aspect of the invention is the use of the photovoltaic device according to aspect 1, a photovoltaic module according to aspect 2, or a photovoltaic array according to aspect 3 of the invention for various applications of solar photovoltaics, including high proton radiation environments, aerospace, extra-terrestrial applications or flexible applications. The second metallic array as described in the first aspect of the invention facilitates easy attachment (e.g. via soldering or gluing) of electrical wires / ribbons to the photovoltaic device which is desirable because the IBL prevents adhesion (e.g. via soldering or an electrically conductive adhesive) directly onto the first metallic array. Without the second metallic array, it would not be possible to have an adhesive interconnection to the photovoltaic device. Meanwhile, without the first metallic array, it would not be possible to have an electrical contact to the photovoltaic component. Directly overlapping the first and second metallic arrays does not introduce any additional shading to incident light. As such, according to the present invention, cell protection, anti-reflection, and electrical contact can advantageously all be achieved together. Furthermore, cell encapsulation can be carried out immediately during the cell fabrication process without the need to wait until the later modularisation step. The photovoltaic device of the first aspect of the invention comprises an electrode layer for receiving electrical energy. The electrode layer acts as an electrical conductor and is in direct contact with the photovoltaic component. When the photovoltaic device is converting light energy to electrical energy, the electrode layer receives electrical energy in the form of electrical current from the photovoltaic component. Optionally, the electrode is formed from a transparent conducting oxide (TOO), a type of optically transparent material which is electrically conductive, or a metal. Suitable TCOs include, but are not limited to, indium oxide or zinc oxide, which may optionally be doped with a dopant, said dopant being a non-metal, such as hydrogen, or a metal selected from aluminium, copper, silver, gallium, magnesium, cadmium, indium, tin, scandium, yttrium, cobalt, manganese, chrome, boron, nickel and platinum, or Fluorine-doped Tin Oxide (FTO). The most preferred TCOs are FTO and Indium Tin Oxide (ITO). Preferably the electrode layer comprises greater than or equal to 60 wt% of a TCO or a metal. Preferably the electrode layer has a thickness of from 10 nm to 1000 nm. The photovoltaic device of the first aspect of the invention further comprises a photovoltaic component comprising photovoltaic material. The photovoltaic material can include any material that is photoactive, in that it is capable of physical or chemical change in response to illumination from a source of light energy. More particularly, the photovoltaic material should be capable of converting light energy into electrical energy when used in the photovoltaic device of the present invention. Suitable types of material include, but are not limited to, the following: crystalline silicon (c-Si), amorphous silicon (a-Si), perovskites, copper-indium-gallium-selenide (CIGS), cadmium-telluride (CdTe), copper-zinc-tin-selenide (CZTSe) and organic conductive polymers. Preferably, the photovoltaic material comprises one or more of crystalline-Si (c-Si), perovskite, CIGS, CdTe, or any combination thereof. Optionally, the photovoltaic device comprises a multi-junction structure. In this regard, a multijunction photovoltaic device comprises multiple separate sub-cells (i.e. each with their own photoactive region) that are ‘stacked’ on top of each other and that together convert more of the solar spectrum into electricity, thereby increasing the overall efficiency of the device. To do so, each photoactive region of each sub-cell is selected so that the band gap of the photoactive region ensures that it will efficiently absorb photons from complementary regions of the solar spectrum. This has two important advantages over conventional single-junction photovoltaic devices. Firstly the combination of multiple sub-cells having multiple photoactive regions with different band gaps ensures that a wider range of incident photons can be absorbed by a multi-junction device, and secondly each sub-cell / photoactive region will be more effective at extracting energy from the photons within the relevant part of the spectrum. In particular, the lowest band gap of a multi-junction photovoltaic device will be lower than that of a typical single junction device, such that a multi-junction device will be able to absorb photons that possess less energy than those that can be absorbed by a single junction device. Furthermore, for those photons that would be absorbed by both a multijunction device and a single junction device, the multi-junction device will absorb those photons more efficiently, as having band gaps closer to the photon energy reduces thermalisation losses. Preferably when the photovoltaic device is a multi-junction structure, the first sub-cell is formed from perovskite and the second sub-cell is formed from any of a second perovskite material, c-Si, CdTe, CZTSe, or CIGS. Optionally, the second perovskite material has different light absorption properties to the first perovskite material. The photovoltaic device of the first aspect of the invention further comprises a first metallic array connectable to an electric circuit and being arranged across the second surface of the electrode layer. The first metallic array is arranged over the surface of the electrode layer for the purpose of receiving the flow of current from the electrode layer. The first metallic array is thus arranged to maintain electrical contact with the electrode layer. Preferably the first metallic array is formed from silver, copper, bismuth, lead or combinations of any of these materials; one such combination would be copper-plated silver, though the skilled person would appreciate that other such plating / combinations are achievable. Most preferably the first metallic array is formed of silver, as silver demonstrates improved current conductivity while simultaneously reducing oxidisation of the first metallic array. Preferably, the first metallic array is arranged in a grid configuration, as this arrangement optimises the collection of electrical current from the photovoltaic component into the electrical circuits of the first metallic array. Such a grid configuration is formed by fingers (i.e. a grid of parallel lines), or by fingers and busbars (a grid of criss-crossing lines). Other types of geometric arrangements are also possible provided the first metallic array has a reasonable coverage over the surface of the electrode layer so that electrical current can effectively be collected from the underlying photovoltaic device. In the embodiment where a grid configuration is utilised, preferably the grid configuration is in the form of finger-like arrangement, more preferably a busbar finger configuration, as this arrangement further optimises the amount of electrical current that is able to flow into the electrical circuits of the first metallic array. A busbar finger configuration is where thin rectangular-shaped strips are formed across the surface of the photovoltaic device, the main contact strips are referred to as the busbars whereas the thinner strips running perpendicular to these are the contact fingers. In an embodiment, the busbar and fingers together form an even coverage, such that the number of busbars and fingers per unit area is approximately identical. In another embodiment, there may be more busbars than fingers, or more fingers than busbars, per unit area. The photovoltaic device of the first aspect of the invention further comprises an intermediate barrier layer (I BL). The I BL forms a layer between the underlying layers of the photovoltaic device (including the photovoltaic component, the electrode layer and the first metallic array) and the second metallic array which tops to the photovoltaic device (i.e. the second metallic array is the uppermost layer when the photovoltaic device is in use). Preferably the I BL is formed from a material that is an electrical insulator, that is a material through which conventionally electrical current would not flow easily or at all. The I BL provides both a barrier to moisture ingress and it forms an encapsulant layer over the layers of the photovoltaic device formed beneath (i.e. the electrode layer and the photovoltaic component).The IBL is generally formed of materials providing refractive and anti-reflective properties which optimises the amount of light energy penetrating through to the layers of the photovoltaic device formed beneath. Preferably the IBL is formed from a metal oxide, metal nitride or a metal oxynitride or a combination of both. The formula for the metal oxynitride is preferably MOxNy. Metal oxides have many advantages, such as being fabricated using simple methods such as deposition via sputtering. The introduction of nitrogen (to make an oxynitride) allows the refractive index (RI) to be tailored and optimised. Preferred metals for the metal oxynitride are Al, Ti, W, Mo, Hf, Ta, Nb, Zr, Cr and V, which form the following oxynitrides: AIOxNy, TiOxNy, WOxNy, MoOxNy, HfOxNy, TaOxNy, NbOxNy, ZrOxNy, CrOxNy, VOxNy. Preferably, the IBL comprises one or more metal oxides selected from aluminium oxide, silicon dioxide, germanium oxide, magnesium oxide and lanthanum oxide or any combination thereof or a metal oxynitride selected from silicon oxynitride and aluminium oxynitride or a combination of both. Optionally, the IBL may comprise one or more polymeric materials, preferably polymeric organosilane materials. Preferably, these polymeric organosilanes are deposited via Chemical Vapour Deposition (CVD). Even more preferably, the precursors for these materials deposited via CVD are selected from one or more of: bis-[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur), SiH4, tetraethyl orthosilicate, hexamethyldisiloxane, or aminosilanes such as 3-aminopropyldiisopropylethoxysilane, 3-aminopropyltriethoxysilane, 3- aminopropyldimethylethoxysilane. By tuning the deposition parameters of the CVD process, these films can advantageously be deposited on nm-thick scales. Preferably, these deposited materials have a final thickness of less than 100 nm. Optionally, the I BL is formed from an alloy (also known as a ‘blend’) of two or more metal oxides and / or metal oxynitrides. Such alloys are preferred materials for components of the I BL, as alloys can enable fine control of the properties of the I BL. In one embodiment, the IBL may comprise one of more polymeric organosilane materials in combination with any other IBL materials described herein. For example the IBL may comprise organosilane materials and one or more of metal oxides, metal nitrides, metal oxynitrides, and alloys of metal oxides and / or metal nitrides. Forming the IBL from one or more of these metal oxides, metal oxynitrides, blend of metal oxides and / or metal nitrides, polymers, organosilanes, or combinations thereof, provides a layer with optimal refractive and anti-reflective properties as these materials have an RI between that of ambient air and the underlying electrode interface which forms the neighbouring layer, preferably the RI of the material used for this purpose has an RI of between 1.0 and 1.8. The Ris of suitable materials for the IBL are given in Table 1 and Table 2 below. Such suggested materials are exemplary and other materials may also be suitable for this purpose. The suggested materials can also be selected based on properties beyond just the optical considerations, such as their tolerance to high radiation environments, weight (e.g. there may be a preference for lightweight materials in some applications) and mechanical properties. Table 1 - Examples of metal oxides suitable for use in the intermediate barrier layer Metal oxide RI Aluminium oxide 1.55-1.70 Silicon oxide 1.40-1.50 Aluminium oxide and silicon oxide blend 1.40-1.70 Germanium oxide 1.40-1.50 Silicon oxide and germanium oxide blend 1.40-1.50 Magnesium oxide 1.70-1.75 Lanthanum oxide 1.70-2.00 Table 2 - Examples of oxynitrides suitable for use in the intermediate barrier layer Metal oxynitride RI Silicon oxynitride Aluminium oxynitride 1.40-1.85 1.50-1.85 An I BL made from one or more of these materials is able to provide excellent barrier properties, while at the same minimising top surface reflection which would otherwise reduce the overall efficiency of the photovoltaic device. By minimising the amount of top surface reflection, the photovoltaic device has improved efficiency since more light energy is able to reach the photovoltaic component part of the device where light energy is converted into electrical energy. An I BL made from one or more of the materials disclosed herein is also able to deliver excellent barrier properties. In particular, the I BL may act as a barrier layer, thereby preventing moisture ingress affecting the layers of the photovoltaic device beneath the I BL. Avoiding moisture ingress in turn improves the overall efficiency of the photovoltaic device. In addition, or alternatively, the IBL when acting as a barrier layer may prevent the egress of species from the photovoltaic device. This can be useful both from an efficiency standpoint, as more components of the device remain in place, and from a reliability perspective, as it extends the lifetime of the device. The material for the IBL may be chosen based on the required properties of the device, in particular to ensure anti-reflective properties. Advantageously, no resistance is added from the configuration according to the invention, despite the presence of an insulating layer between conductive materials. Optionally, the material forming the IBL is selected to have a band gap of more than 4 eV. Materials with bandgaps of more than 4 eV are preferable for optical transparency and electrical insulation since photovoltaic devices will utilise photons of less than 4 eV, such that introducing a layer with more than 4 eV ensures there are no absorption losses. The RI of a material can be determined by methods known in the art, for example by spectroscopy ellipsometry. Optionally, the material forming the IBL is selected to have a refractive index of 1.4 to 1.8. This is the preferred RI range for the refractive and ani-reflective properties of the IBL where it is used in a photovoltaic device such that the amount of light energy propagating through the device to the photovoltaic component is optimised. A particularly preferred RI range for this purpose is 1.6 to 1.7, or alternatively, 1.4 to 1.5, or alternatively 1.5 to 1.6. Some examples of a material that have refractive index in this most preferred range are shown in Table 3. In an embodiment, the k-value (the extinction coefficient) of the material forming the I BL is selected to be approximately 0. Optionally, the IBL is formed from multiple deposited layers. These can be combinations of some of the metal oxides and metal oxynitrides described above, but other materials are also possible provided they have a suitable refractive index and are also suitable for use in encapsulating the underlying layers (i.e. the electrode layer and the photovoltaic component). Optionally, the IBL comprises a multi-layer laminate stack comprising a bilayer configuration (AB)n, wherein A is a first material formed from a metal oxide or a metal oxynitride, B is a second material formed from a metal oxide or a metal oxynitride and n is the number of layers, and wherein the first material is formed from a different metal oxide or metal oxynitrate to the second material. Preferably, A and B are also functionally different materials, n is an integer, preferably ranging from 1-100, preferably ranging from 1-30, further preferably ranging from 1-20, and most preferably ranging from 1-10, 1-7, 1-5, 1-4, or 1-2. In one preferred embodiment, n=2. Examples of suitable combinations of materials in a bilayer configuration are given in Table 3 below - other combinations are possible. The skilled person would be aware that multi-layer stacks provide additional benefits, such as improved resistance to the ingress of moisture, and the ability to tune optical and other properties by carefully arranging two materials with different optical properties to achieve an overall ‘average’ optical property value. Table 3 - Examples of bilayer combinations for use in the intermediate barrier layer, where the intermediate barrier layer is a multi-layer stack. Bilayer first material (A) RI of material A Bilayer second material (B) RI of material B Silicon oxide 1.40-1.50 Aluminium oxide 1.55-1.70 Silicon oxide 1.40-1.50 Silicon nitride approx. 1.85 Silicon oxide 1.40-1.50 Magnesium oxide 1.70-1.75 Optionally, the IBL is from 5 nm to 100 nm in thickness (i.e. width dimension from the initial substrate to the top of the layer wherein the width dimension is in the direction perpendicular to the plane of the initial substrate). Optionally the IBL is from 5 to 80 nm in thickness or 10 to 80 nm or 20 to 80 nm or 5 to 50 nm or 5 to 30 nm in thickness. Preferably, the IBL is from 10 to 25 nm in thickness. More preferably the IBL is 10 to 20 nm in thickness. Such thicknesses are optimal for providing the desired barrier function (e.g. preventing moisture ingress) while at the same time still allowing light to penetrate unimpeded through the layer to the underlying photovoltaic component. When the I BL is a multi-layer such that it comprises one or more sublayers, the thickness of each sub-layer is preferably 1-50 nm, or preferably 1-25 nm, or preferably 1-20 nm, or preferably 1-15 nm, or preferably 1-10 nm, or preferably 1-5 nm, or preferably 1-3 nm. The photovoltaic device of the first aspect of the invention further comprises a second metallic array connectable to an electric circuit, the second metallic array being arranged across the second surface of the I BL and being electrically connected to the first metallic array. The second metallic array is electrically connected to the first metallic array via an electrical connection. This electrical connection is generally achieved by diffusion of the second metallic array through the I BL. This diffusion effect arises because when the second metallic array is deposited, the pressure resulting from said deposition allows some diffusion into the IBL and further permits contact of the first metallic array with the second metallic array without breaking the IBL. Optionally, the surfaces of the photovoltaic components on which the IBL and metallic array are deposited on may be flat or rough textured. In some embodiment the surfaces are flat, such that they have a roughness average (Ra) of less than 100 nm. In some embodiments, the surfaces are textured with a roughness average (Ra) of less than 500 nm, preferably between 100 and 400 nm. Such surface textures typically comprise one of pyramids and inverted pyramids. The pyramid features typically range in height from 50 nm to 30 pm, are more typically between 500 nm and 20 pm, and are often in the range of 1 pm to 10 pm. The second metallic array provides a mechanism for directly connecting the photovoltaic device to an electric circuit as it provides contact points on the upper surface of the IBL for this purpose, but at the same time the second metallic array is still able to receive electric current from the underlying layers of the photovoltaic device as a result of the electrical connection via diffusion through the I BL. By providing a photovoltaic device with this second metallic array arranged across the surface of the IBL, the device is capable of being directly connected to an electric circuit. Preferably the second metallic array is formed from silver, copper, bismuth, lead or combinations of any of these materials. Most preferably the second metallic array is formed of copper plated with silver as this combination has improved current conductivity at the same time as reducing oxidisation of the second metallic array. Preferably, the second metallic array is arranged in spatial alignment with the first metallic array. This configuration prevents shading when the photovoltaic device is in use. By having the second metallic array in spatial alignment with the first metallic array blocking of the light path when travelling through the photovoltaic device is minimised and so prevents shading and this in turn optimises the amount of light energy being received in the underlying photovoltaic component. The spatial alignment between the first metallic array and the second metallic array is also important the ensure a good electrical connection exists between the two arrays. Preferably the second metallic array is in the form of interspersed contact points (as shown by reference numeral 35 in Figure 3b). This further minimises shading caused by the second metallic array blocking the light path into the photovoltaic device. Unlike the first metallic array, which needs to optimise the surface coverage of the electrode layer to maximise receiving the flow of electrical current, the second metallic array does not need to perform this same function, and so a preferred arrangement is in the form of interspersed contact points. This has the advantage of allowing electrical connection while minimising the area of the device which is occluded. Optionally, the first metallic array and second metallic array are formed from a metal selected from silver, copper, bismuth, lead or any combination thereof. These metals have good electrical conductivity characteristics and are also resistant to oxidisation. Optionally, the photovoltaic module of the second aspect of the invention further comprises an encapsulation material arranged to cover the plurality of photovoltaic devices. This encapsulation layer which covers the plurality of photovoltaic devices provides an additional barrier layer to the ingress of moisture and additional protection against ambient conditions. The materials forming such an encapsulation layer are known in the art, and can for example be selected from one or more of: a polyolefin elastomer (POE) material, an ethyl vinyl acetate (EVA) material, PVB (poly vinyl butyral), silicone, TPO (thermoplastic polyolefin), PU (polyurethane), ionomer, and resin or composite materials. These materials may further be laminated. Upon lamination of the module, the layer configuration comprises the encapsulation layer material being positioned and sealed within two opposing sheets, where the opposing sheets may comprise glass, polymer, or a mixture thereof. In a preferred embodiment the encapsulation layer material is laminated between two sheets of glass, or between glass-polymer backsheet. The first metallic array is arranged across the second surface of the electrode layer and the second metallic array is arranged across the surface of the IBL. The first metallic array and the second metallic array may be applied to these surfaces by known techniques such as printing techniques (including screen printing, inkjet printing gravure or offset printing), premetered extrusion deposition, stencilling, soldering, electroplating and vapour deposition techniques. The second metallic array can be placed by using electrically conductive adhesive (EGA). Preferably, the ECA materials are isotropic or anisotropic (e.g. pastes or tapes). Preferably, the ECA materials include cross-linkable polymers loaded with conductive particles, such as metals. For example, the ECA may be selected from one or more of: epoxies, acrylates or silicones loaded with metal conductive particles, preferably wherein the conductive particles are silver or silver-plated. Preferably, the ECA has a resistivity between 0.5 x 10'4 and 50 x 10' 4 Q cm through the thickness of the material, ideally allowing peel strengths above 0.5 N / mm to be achieved. Typically, the thickness of the ECA material ranges from 20 to 300 pm, preferably 30 to 200 pm. Interconnection between the photovoltaic device and metallic array can be achieved by using one of the techniques to directly connect tabbing wire, as shown in Figures 8-9. According to the second aspect of the invention, by providing an IBL to each and every photovoltaic device in a module, each device has an IBL prior to modularisation when multiple photovoltaic devices are strung (linked) together to form a photovoltaic module. The photovoltaic device according to the first aspect of the invention is manufactured by depositing each layer of the device in turn, such that they are formed on top of each other. The different deposition techniques to manufacture the various layers that form the device are well known in the art, and are suitable for this invention. Suitable deposition techniques for the IBL include Atomic Layer Deposition (ALD), Plasma-enhanced ALD, Chemical Vapour Deposition (CVD) and Plasma-enhanced CVD, and initiated CVD. For example, each layer in a multi-layer configuration of the IBL may be deposited by the same or different deposition process. In a preferred embodiment, all layers in the multi-layer configuration are deposited via ALD. In the fifth aspect of the invention is the use of the photovoltaic device according to aspect 1, a photovoltaic module according to aspect 2, or a photovoltaic array according to aspect 3 of the invention or manufactured according to aspect 4, for various applications of solar photovoltaics . In particular, the I BL can be adapted so that it is suitable for different kinds of solar PV applications, e.g. integrated in flexible systems, space applications, BIPV, etc. For example, the mechanical properties of the photovoltaic devices may be customised by composition engineering and / or adapting the deposition process to tailor the density and crystallinity of the IBL so that the device is suitable for flexible applications (e.g. flexible solar panels for built-in integration onto different shaped objects). Such applications may therefore require the intermediate barrier layer(s) to comprise polymeric containing IBL layers, or alternatively they could be tailored from any of the materials from tables 1-3 when the material can be designed based on the selected deposition process. Another application of the photovoltaic devices according to the present invention is in space and / or extra-terrestrial applications. Radiation in space is highly severe, due to the abundance of high energy particles such as protons, electrons and gamma rays present in the solar cosmic, galactic cosmic and radiation belts, such as the Van Allen Radiation belt. Such penetrating particles are known to cause damage to semiconductors as they transfer and deposit their own momentum and energy onto the material, triggering defects in the internal structure through ionization and atomic displacement. Accordingly, the materials for the IBL can be selected to be resistant to certain types of radiation. For example, tuning the bandgap of the IBL material so that it is lower may aid in blocking out some UV radiation. Preferably, the materials as listed in Tables 1 to 3 of this application are used for applications in space. More preferably an SiOx intermediate barrier layer is used for applications in space. Brief Description of Drawings Embodiments will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which: Figure 1 shows a schematic cross-sectional view of a prior art photovoltaic device which does not feature an intermediate layer (as described above). Figure 2a shows a schematic cross-sectional view of a photovoltaic device according to the first aspect of the invention; The schematic shows the sandwich printing comprising the first and second metallic arrays with the IBL deposited between both. Figure 2b shows an embodiment of the invention where the photovoltaic device also includes a wire connection electrically connected to the second metallic array; the photovoltaic device shown in Figure 2b is shown as a schematic cross-sectional view. Figure 3a shows an overhead view of a photovoltaic device including a first metallic array. Figure 3b shows an overhead view of a photovoltaic device according to an embodiment of the invention including a second metallic array. Figure 4 shows an overhead view of a photovoltaic module or panel according to the second aspect of the invention. Figure 5 shows the shows the average fraction of optical images with discolouration over time without the I BL and with 20 nm AI2O31 BL. Figure 6 shows a boxplot of the Fill Factor % and power conversion efficiency (“Efficiency”) without the I BL and with 20 nm AI2O31 BL. Figure 7 shows a diagram of a sandwich printed device with an I BL according to the invention. Figure 8 shows a diagram of a sandwich printed device with an IBL according to the invention wherein there is direct connection of metal wire with an electrically conductive adhesive. Figure 9 shows a diagram of a sandwich printed device with an IBL according to the invention, further wherein the IBL is deposited between two metallic arrays to allow a solder connection of metal wire. Specific Description Referring to Figures 2a to 5, various embodiments of the invention will now be described. Figure 2a shows a schematic cross-sectional view of a photovoltaic device (20) according to the first aspect of the invention. The photovoltaic device shown in Figure 2a comprises an electrode layer (21), a photovoltaic component (22), a first metallic array (23; 23a; 23b; 23c; 23d; 23e), and an intermediate barrier layer (24). The electrode layer is for receiving electrical energy and is in electrical contact with the photovoltaic component comprising photovoltaic material. The electrode layer comprises a first surface (21a) in contact with the photovoltaic component and a second surface (21b) opposite to the first surface. The first metallic array (23) is connectable to an electric circuit and is arranged across the second surface of the electrode layer, and thus is arranged to receive electrical energy from the electrode layer (which in turn is arranged to receive electrical energy from the photovoltaic component). The I BL (24) is provided across and encapsulates all, or substantially all of the electrode layer and the first metallic array; in the embodiment of the invention shown in Figure 2a the IBL encapsulates all of the electrode layer, or substantially all of the electrode layer, such that the first metallic array is fully covered by the IBL. The IBL (24) comprises a first surface (24a) in contact with the electrode layer and the first metallic array (23). The IBL (24) also comprises a second surface (24b) opposite to the first surface (24a). The photovoltaic device shown in Figure 2a further comprises a second metallic array (25; 25a; 25c; 25e) connectable to an electric circuit, the second metallic array (25) is arranged across the second surface (24b) of the IBL (24) and is electrically connected to the first metallic array (23) such that electrical current can flow between the first metallic array and the second metallic array. Electrical current is able to flow between the first metallic array and the second metallic array via an electrical connection through the IBL. This electrical connection can be provided by diffusion of the second metallic array through the IBL, or by mechanical deformation of the IBL. In the embodiment of the invention shown in Figure 2a the individual contact pads of the second metallic array (25a, 25c and 25e) are in spatial alignment with the individual strands of the first metallic array (23a, 23c, 23e). Having the individual strands of the second metallic array in spatial alignment with the individual strands of the first metallic array is the preferred configuration as this prevents shading when the photovoltaic device is in use. When the light reaches the photovoltaic device it passes through the IBL and the electrode layer into the photovoltaic component where the light energy is converted into electrical energy, by having the individual strands of the second metallic array in spatial alignment with the strands of the first metallic array relative to the source of light this minimises the blocking of the light path when travelling through the photovoltaic device and so prevents shading. Having the individual strands of the second metallic array in spatial alignment with the strands of the first metallic array therefore optimises the amount of light energy being received in the photovoltaic component part of the photovoltaic device and thus optimises the amount of energy that can be produced by the photovoltaic device in any given light conditions as the photovoltaic device is positioned to face towards the source of light energy during normal use. In the embodiment of the invention shown in Figure 2a the first metallic array (23) has more individual strands (23a, 23b, 23c, 23d and 23e) than the second metallic array (25a, 25c and 25e). The first metallic array having more individual strands than the second metallic array is a preferred embodiment as the first metallic array needs more in order to have coverage over a substantial part of the surface area of the electrode layer in order to optimise the amount of electrical current that can flow into the electrical circuits of the first metallic array. Preferably the individual strands of the first metallic array are arranged in a grid configuration across the second surface of the electrode layer. Preferably the grid configuration is in the form of fingerlike arrangement, more preferably a Busbar finger configuration, as this arrangement further optimises the amount of electrical current that is able to flow into the electrical circuits of the first metallic array. By contrast the strands of the second metallic array are not for the purpose of extracting electrical current directly from the electrode layer and so do not need to cover so much of the surface area of the photovoltaic device (in the case of the second metallic array this being across the second surface of the I BL). The second metallic array is capable of being connected to an electrical circuit external and separate from the photovoltaic device and so the individual strands of the second metallic array are for conveying electrical current away from the photovoltaic device when it is connected to an electrical circuit. The second metallic array is electrically connected to the first metallic array, preferably this is achieved by diffusion of the second metallic array through the I BL, or by mechanical deformation of the I BL between the two metallic arrays. Figure 2b shows an embodiment of the invention where the photovoltaic device (20) also includes a wire connection (26) electrically connected to the second metallic array (25); the photovoltaic device shown in Figure 2b is shown as a schematic cross-sectional view. The embodiment of the invention shown in Figure 2b is the same as that shown in Figure 2a but with the wire connections (26) shown in Figure 2b. In embodiments of the invention which include wire connections these provide a mechanism for connecting the second metallic array to an electrical circuit external and separate to the photovoltaic device. Alternatively, the wire connections may be used to electrically connect the photovoltaic device to one or more neighbouring photovoltaic devices, for example where a plurality of photovoltaic devices are arranged in an array and are electrically connected to each other thus forming a photovoltaic module. The skilled person is aware of other methods of forming a photovoltaic module, for example via overlapping photovoltaic devices (a ‘shingled connection’ wherein solar cells in a panel are connected to each other by bus bars and ribbons under a high temperature soldering process). Figures 3a and 3b show an overhead view of a photovoltaic device (30) according to an embodiment of the invention. Figure 3a shows an overhead view of the photovoltaic device (30) where the IBL and second metallic array have been stripped away and so are not shown. In the embodiment of the invention shown in Figure 3a, the first metallic array (33) is shown arranged across the surface of the electrode layer (31). In the embodiment of the invention shown in Figure 3a, the first metallic array is arranged in the form of a grid-like arrangement with the individual busbars and fingers of the first metallic array criss-crossing across the second surface (31b) of the electrode layer. Figure 3b shows an overhead view of a photovoltaic device (30) according to an embodiment of the invention, the photovoltaic device is shown in an orientation when it is in use. The upper surface of the photovoltaic device is the IBL (34) and more specifically the second surface (34b) of the IBL. Also shown in Figure 3b is the second metallic array (35). In the embodiment of the invention shown in Figure 3b the second metallic array is formed across the surface of the IBL in a series of interspersed contact points, which are also known as contact pads. The second metallic array is capable of being connected to an electric circuit which allows electric energy produced in the photovoltaic device to flow out of the photovoltaic device as electric current. Preferably the second metallic array is formed in a series of interspersed contact points (i.e. contact pads), as this arrangement minimises shading to the layers of photovoltaic device beneath the IBL, while at the same providing the capability to connect the photovoltaic device to an electric circuit. Figure 4 shows an overhead view of a photovoltaic module (400) according to the second aspect of the invention. Figure 4 shows a photovoltaic module comprising a plurality of photovoltaic devices (40) as described above, wherein the plurality of photovoltaic devices are arranged in an array and are electrically connected to each other. The embodiment of the invention shown in Figure 4 depicts a photovoltaic module comprising 72 separate photovoltaic devices, however the photovoltaic module of the second aspect of the invention can comprise any number of photovoltaic devices. The photovoltaic devices are capable of being electrically connected in series or in parallel and arranged side by side in rows and to provide a photovoltaic module. Preferably the photovoltaic module further comprises an encapsulation material arranged to cover the plurality of photovoltaic devices to protect the photovoltaic module from external environmental conditions such as moisture ingress which can affect the performance of the underlying photovoltaic devices. One or more photovoltaic modules (sometimes called ‘photovoltaic panels’) can be arranged side by side to form a row of photovoltaic modules, or can be arranged in rows and columns to form a photovoltaic array. Such a photovoltaic array might comprise only a low number of modules, for example when employed as a rooftop fixture. Alternatively, the array can be expansive, for example when prepared as part of a ‘solar farm’. Figure 5 shows a comparison of the average fraction of optical images with discolouration of a photovoltaic device with 20 nm AI2O31 BL and without any I BL, measured across a time span of 200 hours. The results of Figure 5 are further discussed in the Examples section. Figure 6 similarly shows a comparison of the efficiency and fill factor results for device with a 20 nm AI2O3IBL against a device without any I BL. The results of Figure 6 are further discussed in the Examples section. Figures 7-9 show the sandwich printing technique further wherein the metal wide is connected to an electrically conductive adhesive (Figure 8) and wherein an additional second metallic grid is printed to allow solder connection of metal wire (Figure 9). Any device feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure. Any feature in one aspect may be applied to other aspects, in any appropriate combination. In particular, method aspects may be applied to device aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspects can be implemented and / or supplied and / or used independently. Definitions The term “photoactive”, as used herein, refers to a region, layer or material that is capable of responding to light photoelectrically. A photoactive region, layer or material is therefore capable of absorbing the energy carried by photons in light that then results in the generation of electricity (e.g. by generating either electron-hole pairs or excitons). The photoactive region includes a photosensitizing material which generates the electron-hole pairs or excitons, and further includes an electron-transporting layer and a hole-transporting layer which sandwich the photosensitizing material. The term “semiconductor”, as used herein, refers to a material with electrical conductivity intermediate in magnitude between that of a conductor and a dielectric. A semiconductor may be an n-type semiconductor, a p-type semiconductor or an intrinsic semiconductor. Typically, the semiconductor used in the present invention is a photosensitizing material, i.e. a material which is capable of performing both photogeneration and charge transportation. The term “bandgap”, as used herein, refers to the energy difference between the top of the valence band and the bottom of the conduction band in a material. The skilled person may readily measure the band gap of a material without undue experimentation. The term “photovoltaic device” as used herein is also interchangeable with the term “photovoltaic cell”. A photovoltaic device / cell comprises at least one photoactive region and at least one of a top and bottom electrode, wherein the cell can convert solar energy into electricity. The term “sub-cell” is part of a device or cell and as used herein refers to a photoactive component when it is connected to one or more photoactive components of other sub-cells. For example, two sub-cells may be connected to each other via a recombination layer (also known as a tunnel junction) in a 2-terminal arrangement or in a 4-terminal arrangement in series. The term “photovoltaic component” as used herein refers to a part of the photovoltaic device other than the electrodes. For example the component may preferably be the part of the photovoltaic device which comprises the photoactive material, layer or region in a photovoltaic device, wherein the device may be single-junction or multi-junction. The term “photovoltaic module” as used herein refers to one or more photovoltaic devices which are electrically connected. The term “module” or “photovoltaic module” may be used interchangeably with the terms “panel” or “solar panel”. The term “photovoltaic array” as used herein refers to one or more photovoltaic modules electrically connected to each other. The term “roughness”, as used herein, refers to the texture of a surface or edge and the extent to which it is uneven or irregular (and therefore lacks smoothness or regularity). The roughness of a surface can be quantified by any measure of the deviations of the surface in a direction that is typically normal to the average surface. As a measure of roughness, the roughness average or mean roughness (Ra) is the arithmetical mean of the absolute values of all deviations from a straight line within a specified reference or sampling length of the surface profile. As an alternative measure of roughness, the root mean square roughness (Rrms or Rq) is the root mean square of the values of all deviations from a straight line within a specified reference or sampling length of the surface profile. The term “textured” refers to a surface of a device on which an artificial uneven surface profile has been intentionally created, e.g. using an etching process. The term “metallic array” as used herein refers to an ordered arrangement of individual busbars and fingers in a photovoltaic device or module. For example, the metallic array may comprise a grid-like arrangement with the individual busbars and fingers of the first metallic form a criss-cross pattern across a surface, usually wherein said surface is an electrode layer. The term “IBL or intermediate barrier layer” as used herein refers to a functional layer of a photovoltaic device which covers and encapsulates all or substantially all of the first electrode layer. It provides a barrier to moisture and forms an encapsulant layer such that it acts as an “integrated barrier layer”. Therefore it provides protection of the photovoltaic device against environmental conditions, preserving the device efficiency and improving lifespan of the device. It may, for example, be formed of materials providing refractive and anti-reflective properties so as to enhance short-circuit current in the underlying photovoltaic components. The layer can also be made to be flexible so that it is suitable for a wide variety of photovoltaic applications. The term “Sandwich printing” refers to the combination of the two metallic arrays with the intermediate barrier layer between them. Examples A device configuration according to the present invention was fabricated and the device characteristics and IBL properties assessed and compared against a device without an IBL. Method A first metallic array was deposited via screen printing a paste through the defined array pattern atop the electrode of a photovoltaic device, followed by a thermal curing process. Following this, an IBL was deposited using atomic layer deposition (ALD), whereby ‘cycles’ of trimethylaluminium (TMA) and Cb-plasma exposures were used to sequentially deposit ~0.1nm of AI2O3 each cycle. The IBLs listed in Table 4 below were each deposited and examined: Intermediate barrier layer Thickness tested (nm) 5 AI2O3 20,40 and 80 AhOs / SiOx / AhOs / SiOx 5 / 5 / 5 / 5 As can be seen, three thicknesses of 20, 40 and 80 nm were used for AI2O3 - the desired thicknesses were achieved by selecting the appropriate number of TMA / 02-plasma cycles. In the multi-layer AhCWSiOx / AhOs / SiOx configuration, each layer was deposited by ALD. The AI2O3 sections used the same process as for the AI2O3 single layer, and the SiOx sections used cycles of a Si-precursor and 02-plasma exposures, with a SiOx growth rate per cycle of ~0.05nm (e.g. for the 5nm / 5nm / 5nm / 5nm process, a cycle sequence of AI2O3-50cycles / SiOx-100cycles / AhOs-SOcycles / AhOa-IOOcycles is performed). Both AI2O3 and AhOa / SiOx / AhOs / SiOx ALD depositions were carried out using a substrate temperature of 100°C. Following this the second metallic array was deposited via screen-printing, using the same process as for the first metallic array. Results All of the IBLs generally showed excellent stability. Figure 5 shows that the 20 nm AI2O3 intermediate barrier layer reduced the number of discoloured pixels taken from optical microscopy images by over 1 order of magnitude. Hence, the intermediate barrier layer is clearly preferable over a configuration without said layer. Figure 6 further supports the advantages of having an I BL. Figure 6 shows that the average efficiency and fill factor are significantly higher for the device with the I BL versus without.

Claims

1. A photovoltaic device (20) comprising:an electrode layer (21) for receiving electrical energy, the electrode layer being in electrical5 contact with a photovoltaic component (22), the electrode layer comprising a first surface (21a) in contact with the photovoltaic component (22) and a second surface (21 b) opposite to the first surface(21a);a first metallic array (23) connectable to an electric circuit and being arranged across the second surface (21b) of the electrode layer; andio an intermediate barrier layer (24) provided across and encapsulating all or substantially all of the electrode layer and the first metallic array, wherein the intermediate barrier layer comprises a first surface (24a) in contact with the electrode layer (21) and the first metallic array (23) and a second surface (24b) opposite to the first surface (24a);further comprising a second metallic array (25) connectable to an electric circuit, theis second metallic array (25) being arranged across the second surface of the intermediate barrier layer (24b) and being electrically connected to the first metallic array (23).

2. The photovoltaic device of claim 1, wherein the material forming the intermediate barrier layer has a band gap of greater than 4 eV.

203. The photovoltaic device of claim 1 or 2, wherein the material forming the intermediate barrier layer has a refractive index of 1.4 to 1.8.

4. The photovoltaic device of any preceding claim, wherein the intermediate barrier layer 25 comprises multiple deposited layers.

5. The photovoltaic device of claim 4, wherein the intermediate barrier layer comprises a multi-layer laminate stack comprising a bilayer configuration (AB)n, wherein A is a first material formed from a metal oxide or a metal oxynitride, B is a second material formed30 from a metal oxide or a metal oxynitride and n is the number of layers, and wherein the first material is formed from a different metal oxide or metal oxynitride to the second material.

6. The photovoltaic device according to any preceding claim, wherein the intermediate barrier layer comprises one or more metal oxides selected from aluminium oxide, silicon dioxide, 35 germanium oxide, magnesium oxide and lanthanum oxide or any combination thereof or a metal oxynitride selected from silicon oxynitride and aluminium oxynitride or a combination of both.

7. The photovoltaic device of any preceding claim, wherein the intermediate barrier layer is formed from an alloy of two or more metal oxides and / or metal oxynitrides.5 8. The photovoltaic device of any preceding claim, wherein the intermediate barrier layer isfrom 5 nm to 100 nm in thickness, preferably 5 to 80 nm in thickness, more preferably 10 to 80 nm in thickness, further preferably 20 to 80 nm in thickness, and most preferably 5 to 50 nm in thickness.io 9. The photovoltaic device according to any preceding claim wherein the intermediate barrier layer further comprises organosilane polymeric materials.

10. The photovoltaic device of any preceding claim, wherein the first metallic array is arranged in a grid configuration.1511. The photovoltaic device of any preceding claim, wherein the second metallic array is arranged in spatial alignment with the first metallic array.T— 12. The photovoltaic device of any preceding claim, wherein the first metallic array and the '1““ 20 second metallic array are formed from a metal selected from silver, copper, bismuth, leador any combination thereof.

13. The photovoltaic device of any preceding claim, wherein the photovoltaic device comprises a multi-junction structure.2514. The photovoltaic device of any proceeding claim, wherein the photovoltaic material comprises one or more of crystalline-Si (c-Si), perovskite, Copper-lndium-Gallium-selenide (CIGS), Copper zinc tin selenide (CZTSe), Cadmium-Telluride (CdTe) or any combination thereof.3015. A photovoltaic module comprising a plurality of photovoltaic devices according to any proceeding claim, which are electrically connected to each other.

16. A photovoltaic array comprising a plurality of photovoltaic modules as defined in claim 15,35wherein the photovoltaic modules are electrically connected to each other.

17. A method of manufacturing a photovoltaic device, the method comprising: providing an electrode layer, wherein the electrode layer comprises a first surface, in contact with a photovoltaic component comprising photovoltaic material on the first surface of the electrode layer;5 arranging a first metallic array across a second surface of the electrode layer wherein the first metallic array is connectable to an electric circuit;encapsulating the surface of the electrode layer and the first metallic array by depositing an intermediate barrier layer across all or substantially all the second surface of the electrode layer and the first metallic array; andio arranging a second metallic array across the surface of the intermediate barrier layer and electrically connecting the second metallic array to the first metallic array, wherein the second metallic array is connectable to an electric circuit.152025303518. A method according to claim 17 wherein the second metallic array is arranged across the surface of the intermediate barrier layer via one or more electrically conductive adhesive materials.

19. A method according to claim 18, wherein the electrically conductive adhesive material is isotropic or anisotropic, preferably wherein the electrically conductive adhesive material materials include cross-linkable polymers loaded with conductive particles, further preferably wherein the electrically conductive adhesive material is selected from one or more of epoxides, acrylates and silicones.

20. A method according to claim 19, wherein the conductive particles are metals, preferably wherein the conductive particles are silver or silver-plated.

21. A method according to claim 19, wherein the second metallic array is arranged across the surface of the intermediate barrier layer by a technique selected from: printing techniques, pre-metered extrusion deposition, stencilling, soldering, electroplating and vapour deposition techniques, preferably wherein the printing techniques are selected from screen printing, inkjet gravure or offset printing.

22. A method according to claim 19, wherein the second metallic array is arranged across the surface of the intermediate barrier layer via an electrically conductive pad, preferably wherein the electrically conductive pad includes solders.CM23. Use of a multi-junction photovoltaic device according to any of claims 1 to 14 or a photovoltaic module according to claim 15 or a photovoltaic array according to claim 16 in: high proton radiation environments, aerospace, terrestrial applications, extra-terrestrial applications, rigid applications, or flexible applications.

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