Transferable photovoltaic device

Abstract

The present invention provides a transferable photovoltaic device arrangement for transferring a thin film photovoltaic device to a bottom photovoltaic sub-cell to produce a series photovoltaic cell, the transferable photovoltaic device arrangement comprising: a flexible release substrate; and a thin film photovoltaic device comprising (i) a first transparent conductive layer over the flexible release substrate and (ii) a photoactive layer over the first transparent conductive layer, where the first transparent conductive layer is a solution treated layer, comprising at least one selected from the group consisting of conductive polymers or polymer composites, activatable binders and organic binders, and wherein the flexible release substrate is separable from the thin film photovoltaic device after adhesion of the thin film photovoltaic device to the bottom photovoltaic sub-cell with the transparent conductive adhesive, thereby exposing the first transparent conductive layer at the outer conductive surface of the thin film photovoltaic device.

Description

[0001] Priority Cross Reference

[0002] This application claims priority to Australian Provisional Patent Application No. 2022900663 filed on March 17, 2022, the contents of which should be understood to be incorporated into this specification by reference. Technical Field

[0003] The present invention relates to a transferable photovoltaic device arrangement for transferring a thin film photovoltaic device to a bottom photovoltaic sub-cell to produce a tandem photovoltaic cell. The transferable photovoltaic device arrangement comprises a flexible release substrate and a thin film photovoltaic device located thereon, the flexible release substrate being separable from the thin film photovoltaic device after the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell with a transparent conductive adhesive. The present invention also relates to a method of producing a transferable photovoltaic device arrangement, and a method of producing a tandem photovoltaic cell using the transferable photovoltaic device arrangement. Background Art

[0004] Silicon-based photovoltaic (PV) cells are currently the dominant photovoltaic technology used in commercial solar panels. The cost of electricity from such solar panels has fallen dramatically in recent decades due to improvements in power conversion efficiency and the benefits of large-scale manufacturing of input and final solar panel modules. However, single-junction PV cells, which comprise a single photoactive layer between a pair of charge-collecting electrodes, have inherent efficiency limitations due to a variety of mechanisms, including low-bandgap spectral losses and energy losses due to band-edge relaxation (thermalization). The power conversion efficiency of state-of-the-art solar panels utilizing single-junction Si-PV cells (<27%) is now close to the maximum that can be expected, and therefore a fundamental change in photovoltaic cell technology is needed to provide further substantial improvements.

[0005] One way to improve the power conversion efficiency of solar panels is to utilize multi-junction PV cells, in which two (or more) PV subcells are physically stacked on top of each other. The photoactive layer of the top subcell is designed to efficiently absorb photons from the high-energy region of the solar radiation spectrum, while the photoactive layer of the bottom subcell captures low-energy photons that pass through the semi-transparent top subcell. Tandem PV cells, in which the two subcells are electrically connected in series via a transparent conductive interlayer (recombination layer or tunnel junction), can therefore achieve power conversion efficiencies of up to 47% under concentrated sunlight. Therefore, in principle, tandem PV cells with Si-PV bottom subcells can provide significantly improved energy conversion efficiencies over single-junction Si-PV cells, while still benefiting from modern Si-PV manufacturing techniques.

[0006] Despite these theoretical advantages, the development of commercially competitive multi-junction PV cells, especially those with Si-PV bottom subcells, remains challenging due to technical and cost-related issues with the fabrication of the top subcell and its integration with the bottom subcell. Vapor deposition methods for fabricating top subcells on Si-PV bottom subcells are not easily adaptable to industrial scale-up. Thin-film top subcells comprising solution-processable photoactive layers such as metal halide perovskite semiconductors are particularly attractive due to the ability to appropriately tune the band gap. However, fabricating top subcells layer by layer directly on Si-PV bottom subcells by solution processing methods remains technically and economically challenging due to the difficulty in forming uniform thin layers on large-area rigid substrates and the high proportion of material waste associated with batch deposition methods.

[0007] It has been proposed previously to address these problems by separately producing a thin film top sub-cell and then laminating this multi-layer device directly onto the bottom sub-cell to produce a tandem PV cell in a single process step. A transparent conductive adhesive is used to physically bond the two devices and provide the required electrical interconnect (as a recombination layer or tunnel junction) between the two sub-cells of the final tandem PV cell. However, thin film devices are not self-supporting and therefore the thin film top sub-cell must be manufactured on a supporting film substrate. After laminating the top and bottom sub-cells together, this substrate will form a relatively thick outer layer of the tandem PV cell, which can potentially absorb a non-negligible portion of the solar radiation, thereby adversely affecting the power conversion efficiency. In addition, the supporting film substrate on which the thin film electronic devices are produced is typically electrically insulating. While an insulating outer layer can be accommodated in small devices, it is undesirable on larger surface area photovoltaic cells where current is typically extracted through the outer surface to minimize internal resistance in solar panels.

[0008] Other reported methods for manufacturing the top subcell (which is subsequently laminated to the bottom subcell) rely on vapor or plasma deposition techniques and / or high temperature processing steps to produce a thin film device architecture. As a result, the top subcell must be produced on a supporting substrate that can withstand such processing conditions, which compromises the transferability of the subcell to the bottom subcell when manufacturing tandem PV cells. It is desirable to produce a thin film top subcell directly on a substrate suitable for transfer to a bottom subcell by a low cost and scalable technique.

[0009] Therefore, there is a continuing need for methods of producing tandem photovoltaic cells, and arrangements for transferring thin film photovoltaic devices to bottom subcells to form tandem photovoltaic cells, which at least partially address one or more of the above-mentioned disadvantages, or provide useful alternatives.

[0010] The reference herein to a patent document or other matter cited as prior art should not be taken as an admission that the document or matter was known or that the information it contained was part of the common general knowledge as at the priority date of any claim. Summary of the invention

[0011] The inventors have now developed a method of producing a tandem photovoltaic cell by transferring a thin film photovoltaic top subcell initially present on a supporting release substrate onto a compatible bottom subcell and then removing the release substrate to provide a tandem PV cell having a transparent conductive layer at the outer surface. The transparent conductive layer is produced on the release substrate by solution processing and comprises organic and usually polymeric conductive and / or binder components, but the interface between the release substrate and the transparent conductive layer is designed to allow selective delamination of the release substrate from the top subcell after bonding of the top and bottom subcells, thereby exposing the transparent conductive layer at the conductive outer surface of the tandem PV cell. This can be achieved in several ways, for example by designing the release substrate to have an inherently weak adhesion to the transparent conductive layer or by formulating the transparent conductive layer to release bond from the release substrate in response to an external stimulus.

[0012] The presence of an organic or polymeric component in the first transparent conductive layer is expected to improve its flexibility and elasticity, thereby ensuring that the physical integrity and conductivity of the first transparent conductive layer remains unchanged despite the bending and compression applied to the layer during transfer of the thin film photovoltaic device to the bottom photovoltaic sub-cell.

[0013] The thin film top subcell is adhered to the bottom subcell via a transparent conductive adhesive layer, which ultimately forms a recombined layer (also called a tunnel junction) in the tandem photovoltaic device. The transparent conductive adhesive layer, which is initially present as an outer layer of the transferable top subcell in some embodiments, can be activated and optionally cured to promote adhesion of the two subcells. Importantly, when the release substrate is to be separated from the thin film top subcell, the resulting adhesive bond between the two subcells is stronger than the bond between the release substrate and the top subcell.

[0014] Advantageously, the methods and apparatus disclosed herein can be used to produce tandem photovoltaic cells having silicon-based photovoltaic (Si-PV) cells and are compatible with both the manufacturing processes of Si-PV cells and the common use of Si-PV cells in solar panel modules. Thus, a thin-film top subcell can be pressed onto and adhered to a bottom subcell (e.g., a Si-PV subcell) in a roll lamination process that includes nearly simultaneous separation and removal of a release substrate. Furthermore, because the resulting tandem photovoltaic cell has a conductive outer surface, this outer surface can also be functionalized with a current collector network (e.g., a printed metal grid) as commonly applied to Si-PV cells.

[0015] In a first aspect, the present invention provides a transferable photovoltaic device arrangement for transferring a thin film photovoltaic device to a bottom photovoltaic sub-cell to produce a tandem photovoltaic cell, the transferable photovoltaic device arrangement comprising: a flexible release substrate; and a thin film photovoltaic device comprising (i) a first transparent conductive layer located on the flexible release substrate and (ii) a photoactive layer located on the first transparent conductive layer, wherein the first transparent conductive layer is a solution-processed layer comprising at least one selected from a conductive polymer or polymer composite, an activatable adhesive, and an organic binder, and wherein after the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell with the transparent conductive adhesive, the flexible release substrate can be separated from the thin film photovoltaic device to expose the first transparent conductive layer at the outer conductive surface of the thin film photovoltaic device.

[0016] In some embodiments, the first transparent conductive layer includes a first activatable adhesive, wherein when the first activatable adhesive is activated, the flexible release substrate can be separated from the thin film photovoltaic device. The first activatable adhesive can be a heat-activatable adhesive polymer. The heat-activatable adhesive polymer can be a thermoplastic polymer, for example, selected from ethylene-vinyl acetate (EVA) copolymer, polyethylene, polyethylene oxide (PEO) and polystyrene (PS).

[0017] In some embodiments, the flexible release substrate comprises a non-stick surface, wherein the flexible release substrate can be separated from the thin film photovoltaic device by delaminating the first transparent conductive layer from the non-stick surface. The non-stick surface can be provided by a low surface energy polymer. The non-stick surface can be the surface of a non-stick coating on the flexible release substrate. The non-stick coating can include a low surface energy polymer, for example selected from a fluorinated polymer and a silicone polymer.

[0018] In some embodiments, the transferable photovoltaic device arrangement includes a low cohesion sacrificial layer between the flexible release substrate and the first transparent conductive layer, wherein the low cohesion sacrificial layer has an inherent low cohesion or has a low cohesion when activated, so that the flexible release substrate can be separated from the thin-film photovoltaic device by destroying the low cohesion sacrificial layer.

[0019] In some embodiments, the low cohesion sacrificial layer comprises a low cohesion organic non-polymer solid. In some embodiments, the low cohesion sacrificial layer comprises a third activatable adhesive, and the flexible release substrate can be separated from the thin film photovoltaic device by (i) activating the third activatable adhesive by heat or radiation and (ii) destroying the low cohesion sacrificial layer. The third activatable adhesive can be a thermoplastic polymer, for example selected from ethylene-vinyl acetate (EVA) copolymers, polyethylene, polyethylene oxide (PEO) and polystyrene (PS), or a photodegradable polymer composition, for example selected from polyphthalaldehyde (PPHA) and photoacid generator (PAG) combination, polyacetal and PAG combination and polylactide (PLA) and TiO2 combination.

[0020] In some embodiments, the low cohesion sacrificial layer is conductive. In some embodiments, the low cohesion sacrificial layer has a thickness of less than 100 nm, or less than 50 nm, or less than 20 nm.

[0021] In some embodiments, the first transparent conductive layer includes a first conductive component selected from metals, metal oxides, conductive polymers or polymer composites, fullerenes or functionalized derivatives thereof, carbon nanomaterials (such as graphene), non-polymer organic semiconductors, organic aromatic compounds, and non-polymer conjugated organic compounds.

[0022] In some embodiments, the thin film photovoltaic device further comprises (iii) a second transparent conductive layer overlying the photoactive layer, wherein the second transparent conductive layer comprises a transparent conductive adhesive for adhering the thin film photovoltaic device to a bottom photovoltaic sub-cell.

[0023] In some embodiments, the transparent conductive adhesive includes a second conductive component, which includes at least one selected from metals, metal oxides, conductive polymers or polymer composites, fullerenes or functionalized derivatives thereof, carbon nanomaterials (such as graphene), non-polymer organic semiconductors, organic aromatic compounds and non-polymer conjugated organic compounds.

[0024] In some embodiments, the transparent conductive adhesive comprises a second activatable adhesive, wherein when the second activatable adhesive is activated, the second transparent conductive layer adheres to the bottom photovoltaic sub-cell. The second activatable adhesive can be activated by heat, radiation, or chemical treatment. In some embodiments, the second activatable adhesive is irreversibly cured by a covalent bond forming reaction when activated.

[0025] In some embodiments, the transparent conductive adhesive is heat activatable at a temperature sufficient to release the flexible release substrate from the thin film photovoltaic device.

[0026] In some embodiments, the first transparent conductive layer includes a first heat-activatable binder polymer and the second transparent conductive layer includes a second heat-activatable binder polymer, wherein the second heat-activatable binder polymer has a higher melting point than the first heat-activatable binder polymer.

[0027] In some embodiments, the thin film photovoltaic device further comprises (iv) a first charge transport layer between the first transparent conductive layer and the photoactive layer and / or (v) a second charge transport layer located above the photoactive layer.

[0028] In some embodiments, the photoactive layer is a photoactive perovskite layer.

[0029] In some embodiments, the transferable photovoltaic device arrangement is configured as a roll for a roll lamination process, wherein the thin film photovoltaic device is pressed onto the bottom photovoltaic sub-cell and the flexible release substrate is separated from the thin film photovoltaic device.

[0030] In some embodiments, each functional layer of the thin film photovoltaic device selected from (i) a first transparent conductive layer, (ii) a photoactive layer, (iv) a first charge transport layer between the first transparent conductive layer and the photoactive layer, and (v) a second charge transport layer located above the photoactive layer is a solution-processed layer formed on a flexible release substrate. In some embodiments, each functional layer of the thin film photovoltaic device is a solution-processed layer formed on a flexible release substrate.

[0031] In a second aspect, the invention provides a tandem photovoltaic cell arrangement comprising a bottom photovoltaic sub-cell and a transferable photovoltaic device arrangement according to any embodiment of the first aspect, wherein the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell via a second transparent conductive layer comprising a transparent conductive adhesive.

[0032] In some embodiments, the bottom photovoltaic sub-cell is a silicon photovoltaic cell.

[0033] In some embodiments, the flexible release substrate is partially separated from the thin film photovoltaic device, exposing the first transparent conductive layer at the outer conductive surface.

[0034] In a third aspect, the present invention provides a method for producing a transferable photovoltaic device arrangement, the method comprising: providing a flexible release substrate; and producing a thin-film photovoltaic device on the flexible release substrate by successively forming (i) a first transparent conductive layer on the flexible release substrate; and (ii) a photoactive layer on the first transparent conductive layer, wherein the first transparent conductive layer is formed by solution processing and comprises at least one selected from a conductive polymer or a polymer composite, an activatable adhesive and an organic binder, and wherein the flexible release substrate can be separated from the thin-film photovoltaic device to expose the first transparent conductive layer at the outer conductive surface of the thin-film photovoltaic device.

[0035] In some embodiments, forming a first transparent conductive layer over a flexible release substrate comprises applying a first fluid composition comprising a first conductive component or a reactive precursor thereof to form a wet film over the flexible release substrate; and curing the wet film to form the first transparent conductive layer on the flexible release substrate.

[0036] In some embodiments, the first fluid composition further includes a solvent, and curing the wet film includes removing the solvent.

[0037] In some embodiments, the first fluid composition includes a first activatable adhesive. The first activatable adhesive can be a heat-activatable adhesive polymer, wherein the flexible release substrate can be separated from the thin film photovoltaic device when the first transparent conductive layer is heated.

[0038] In some embodiments, the flexible release substrate includes a non-stick surface and the first transparent conductive layer is formed directly on the non-stick surface.

[0039] In some embodiments, the flexible release substrate includes a low cohesion sacrificial layer on a surface thereof and the first transparent conductive layer is formed directly on the low cohesion sacrificial layer.

[0040] In some embodiments, forming a photoactive layer on the first transparent conductive layer comprises applying a flowable composition comprising one or more photoactive layer components or precursors thereof dispersed in a solvent to form a wet film on the first transparent conductive layer; and forming the photoactive layer by removing the solvent from the wet film. Optionally, the flowable composition is a perovskite precursor solution.

[0041] In some embodiments, producing a thin film photovoltaic device on a flexible release substrate further comprises forming (iii) a second transparent conductive layer on top of the photoactive layer, wherein the second transparent conductive layer comprises a transparent conductive adhesive for adhering the thin film photovoltaic device to a bottom photovoltaic subcell. Forming the second transparent conductive layer may comprise applying a second fluid composition comprising a second activatable adhesive and a second conductive component or a reactive precursor thereof to form a wet film on top of the photoactive layer; and curing the wet film to form the second transparent conductive layer.

[0042] In some embodiments, producing a thin film photovoltaic device on a flexible release substrate further comprises forming (iv) a first charge transport layer between the first transparent conductive layer and the photoactive layer and / or (v) a second charge transport layer above the photoactive layer.

[0043] In some embodiments, the flexible release substrate is configured as a roll, and the thin film photovoltaic device is produced on the flexible release substrate by coating and / or printing steps in a roll-to-roll process.

[0044] In a fourth aspect, the present invention provides a method for producing a tandem photovoltaic cell, comprising: providing a transferable photovoltaic device arrangement according to any embodiment of the first aspect, or a transferable photovoltaic device arrangement as produced by a method according to any embodiment of the third aspect; adhering a thin-film photovoltaic device of the transferable photovoltaic device arrangement to a bottom photovoltaic sub-cell with a transparent conductive adhesive, thereby electrically coupling the thin-film photovoltaic device to the bottom photovoltaic sub-cell via a second transparent conductive layer; and separating a flexible release substrate of the transferable photovoltaic device arrangement from the thin-film photovoltaic device, thereby producing a tandem photovoltaic cell having a first transparent conductive layer of the thin-film photovoltaic device at the outer conductive surface.

[0045] In some embodiments, the bottom photovoltaic sub-cell is a silicon photovoltaic cell.

[0046] In some embodiments, the thin film photovoltaic device is pressed or compressed onto the bottom photovoltaic sub-cell to promote adhesion prior to separating the flexible release substrate from the thin film photovoltaic device.

[0047] In some embodiments, the transferable photovoltaic device arrangement is configured as a roll, and the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell and the flexible release substrate is separated from the thin film photovoltaic device in a roll lamination process.

[0048] In some embodiments, adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell includes activating the transparent conductive adhesive with heat, radiation, or chemical treatment.

[0049] In some embodiments, adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell comprises activating the transparent conductive adhesive with heat at a temperature sufficient to release the flexible release substrate from the thin film photovoltaic device.

[0050] In some embodiments, the method further comprises creating a metallic current collector network on the outer conductive surfaces of the tandem photovoltaic cells.

[0051] According to a fifth aspect, the present invention provides a tandem photovoltaic cell produced by the method according to any embodiment of the fourth aspect.

[0052] Further aspects of the invention will appear from the detailed description of the invention below. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Embodiments of the present invention will be described herein by way of example only with reference to the accompanying drawings, in which:

[0054] Figure 1 A transferable photovoltaic device arrangement 100 according to the present invention is schematically depicted, as is a method 150 of using such a transferable photovoltaic device arrangement to produce a tandem photovoltaic cell 130 by transferring a photovoltaic device 104 to a bottom photovoltaic sub-cell 112 .

[0055] Figure 2 A transferable photovoltaic device arrangement 200 is schematically depicted, according to an embodiment of the present invention, and a method 250 of using such a transferable photovoltaic device arrangement to produce a tandem photovoltaic cell 230 by transferring a photovoltaic device 204 to a bottom photovoltaic sub-cell 212 .

[0056] Figure 3 A transferable photovoltaic device arrangement 300 is schematically depicted, along with a method 350 of using such a transferable photovoltaic device arrangement to produce a tandem photovoltaic cell 330 by transferring a photovoltaic device 304 to a bottom photovoltaic sub-cell 312 .

[0057] Figure 4 A transferable photovoltaic device arrangement 400 is schematically depicted, along with a method 450 of using such a transferable photovoltaic device arrangement to produce a tandem photovoltaic cell 430 by transferring a photovoltaic device 404 to a bottom photovoltaic sub-cell 412 .

[0058] Figure 5 is a flow chart showing the steps of a method of producing a transferable photovoltaic device arrangement according to the present invention.

[0059] Figure 6 A method of producing tandem photovoltaic cells in a roll lamination process according to an embodiment of the invention is schematically depicted.

[0060] Figure 7 A method of transferring a solution-processed thin film photovoltaic device from a flexible release substrate to a conductive substrate, as performed in Example 3, is schematically depicted. DETAILED DESCRIPTION

[0061] The present invention relates to a transferable photovoltaic device arrangement for transferring a thin film photovoltaic device to a bottom photovoltaic sub-cell to produce a tandem photovoltaic cell. The transferable photovoltaic device arrangement includes a flexible release substrate and a thin film photovoltaic device on the flexible release substrate. The thin film photovoltaic device includes at least a first transparent conductive layer located on the flexible release substrate and a photoactive layer located on the first transparent conductive layer. The first transparent conductive layer is a solution-treated layer and includes at least one selected from a conductive polymer or a polymer composite, an activatable adhesive, and an organic adhesive. In use, after the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell with a transparent conductive adhesive, the flexible release substrate can be separated from the thin film photovoltaic device. Therefore, the resulting tandem photovoltaic cell has the first transparent conductive layer of the thin film photovoltaic device exposed at the outer conductive surface.

[0062] like Figure 1As seen in , the transferable photovoltaic device arrangement 100 includes a flexible release substrate 102, which may include a flexible polymer film. A thin film photovoltaic device 104 is located on the flexible release substrate 102, and an interface 106 is located between the flexible release substrate and the photovoltaic device. As will be explained in more detail below, the interface 106 is designed to release the thin film photovoltaic device 104 once the photovoltaic device 104 is adhered to the bottom photovoltaic sub-cell. The thin film photovoltaic device 104 includes at least a solution-treated transparent conductive layer 108 located on the flexible release substrate and a photoactive layer 110 located on the layer 108. The transparent conductive layer 108 will eventually form the top electrical contact surface of the tandem photovoltaic solar cell, while the photoactive layer 110 is a light absorbing semiconductor layer, such as a perovskite photoactive layer, having a band gap suitable for the top sub-cell photoactive layer of the tandem photovoltaic solar cell. Thin film photovoltaic device 104 may optionally include other layers (not shown), such as charge transport layers (ie, electron selective layers and / or hole selective layers) between transparent conductive layer 108 and photoactive layer 110 and / or above photoactive layer 110 .

[0063] The transferable photovoltaic device arrangement 100 is configured to transfer the thin film photovoltaic device 104 to the bottom photovoltaic sub-cell 112 to produce a tandem photovoltaic cell 130, also as Figure 1 as shown in .

[0064] The present invention therefore also relates to a method for producing a tandem photovoltaic cell. The method comprises providing a transferable photovoltaic device arrangement as disclosed herein, and adhering a thin film photovoltaic device of the transferable photovoltaic device arrangement to a bottom photovoltaic sub-cell with a transparent conductive adhesive. Thereby, the thin film photovoltaic device is functionally coupled to the bottom photovoltaic sub-cell via a second transparent conductive layer. The flexible release substrate of the transferable photovoltaic device arrangement is then separated from the thin film photovoltaic device. The resulting tandem photovoltaic cell has a first transparent conductive layer of the thin film photovoltaic device at the outer conductive surface, and the second transparent conductive layer acts as a recombination layer or tunnel junction between the top and bottom sub-cells.

[0065] Continue to refer Figure 1, the transferable photovoltaic device arrangement 100 is used in this transfer method (indicated by arrow 150) to transfer the thin film photovoltaic device 104 to the bottom photovoltaic sub-cell 112. The bottom photovoltaic sub-cell 112 includes at least a top conductive layer 114, a bottom electrical contact 116, and a photoactive semiconductor layer 118, and in some embodiments is a conventional silicon photovoltaic solar cell. Therefore, the thin film photovoltaic device 104 is adhered to the top conductive layer 114 of the bottom sub-cell by the transparent conductive adhesive 120, so that the thin film photovoltaic device 104 and the bottom photovoltaic sub-cell 112 are functionally coupled by the transparent conductive layer 122. Therefore, the transparent conductive layer 122 formed by the transparent conductive adhesive 120 forms a recombination layer or tunnel junction between the top and bottom sub-cells in the tandem photovoltaic cell 130.

[0066] In some embodiments, transparent conductive layer 122 initially exists as a preformed outer layer of thin film photovoltaic device 104, located on photoactive layer 110. In other embodiments, transparent conductive layer 122 initially exists as a preformed outer layer of bottom photovoltaic sub-cell 112, located on or as top conductive layer 114. In still other embodiments, transparent conductive adhesive 120 can be applied as a coating to the surface of either thin film photovoltaic device 104 or bottom photovoltaic sub-cell 112 as part of the transfer process.

[0067] The transfer method also includes the step of separating the flexible release substrate 102 from the thin film photovoltaic device 104. The separation step, which typically occurs by peeling off the flexible substrate to gradually destroy the interface 106, can occur almost simultaneously with the adhesion of the thin film photovoltaic device 104 to the bottom photovoltaic sub-cell 112, or later as a separate operation. In either case, the separation of the flexible substrate relies on the adhesion or cohesion at the interface 106 being at least weaker at the time of separation than: (i) the adhesion of the thin film photovoltaic device 104 to the bottom photovoltaic sub-cell 112 via the transparent conductive layer 122, and (b) the adhesion and cohesion between and within other functional layers in the tandem photovoltaic cell 130. After the separation step, the tandem photovoltaic cell 130 has a transparent conductive layer 108 at the outer conductive surface 124 through which current can be drawn when the tandem cell is in operation.

[0068] definition

[0069] When the terms "comprise", "comprises" and "comprising" are used in the specification (including the claims), they should be interpreted as specifying stated features, integers, steps or components, but not excluding the presence of one or more other features, integers, steps or components, or groups thereof.

[0070] As used herein, the terms "first", "second", "third", etc., in connection with various features of the disclosed arrangements, devices, and methods, are arbitrarily assigned labels and are used only to distinguish between two or more such features that may be combined in various embodiments. These terms themselves do not indicate any particular orientation or order. Moreover, it should be understood that the presence of a "first" feature does not imply the presence of a "second" feature, the presence of a "second" feature does not imply the presence of the "first" feature, and so on.

[0071] As used herein, the terms "top" and "bottom" are referenced relative to the top light receiving surface of a tandem photovoltaic cell which is the first transparent conductive layer.

[0072] As used herein, the term "above," particularly in relation to functional layers of a transferable photovoltaic device arrangement, indicates a relative position in a multi-layer device structure, including "in direct contact" and "separated by one or more intervening functional layers." Thus, if layer B is above layer A, and layer C is above layer B, then the multi-layer device structure may include the following layer sequences: ABC, AXBC, ABXC, and AXBXC, where X is one or more intervening functional layers.

[0073] As used herein, the term "conductive layer" refers to a thin film having sufficient conductivity to transport photogenerated charges through the layer. The conductive layer can be an electrical conductor or a semiconductor. The "conductive layer" can have a variety of functions, including charge selectivity.

[0074] As used herein, an "activatable" layer, adhesive, or adhesive polymer is adapted to be functionally activated by an external stimulus such as heat, radiation (eg, actinic light), or chemical treatment to bond or debond as desired.

[0075] Transferable photovoltaic device layout

[0076] Flexible release substrate

[0077] The transferable photovoltaic device arrangement includes a flexible release substrate. The flexible release substrate is generally a flexible film, so it can be separated from the thin film photovoltaic device by peeling off the flexible film. In some embodiments, the flexible substrate is in the form of a roll of a film or a tape to facilitate (i) manufacturing a thin film photovoltaic device thereon in a roll-to-roll manufacturing process and / or (ii) transferring the thin film photovoltaic device to a bottom photovoltaic sub-cell in a roll lamination process. Alternatively, the release substrate can be formed as a flat sheet of a flexible film. The flexible release substrate can include a flexible polymer film, such as a polyester (such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN)), a polyolefin (such as polypropylene) or a fluorinated polymer (such as ethylene tetrafluoroethylene (ETFE)), which are typical materials for substrates in a roll manufacturing process. However, it is not excluded that the flexible release substrate can be made of other materials, such as metal foil or paper.

[0078] In some embodiments, the release substrate includes a non-stick surface, so by delaminating the adjacent transparent conductive layer from the non-stick surface, the flexible release substrate can be easily separated from the thin film photovoltaic device. As will be appreciated by those skilled in the art, the non-stick surface is inherently weakly sensitive to adhesion due to the low surface energy composition at its surface, so thermal activation is not required to obtain non-stick properties. Suitable non-stick surfaces can have a surface energy of less than 36 dynes / cm (Dyne / cm), preferably less than 30 Dyne / cm, such as measured according to ASTM D7490-13. The non-stick surface can be provided by a low surface energy polymer, such as a polymer selected from fluorinated polymers (such as polytetrafluoroethylene (PTFE)) and silicone polymers (such as polydimethylsiloxane (PDMS)). The non-stick surface can be the surface of a non-stick coating on a flexible release substrate. Suitable non-stick coatings are generally coatings of low surface energy polymers as described above. Alternatively, the flexible release substrate can include a self-supporting film of a suitable low surface energy polymer, and the non-stick surface is the surface of the film.

[0079] Low cohesion sacrificial layer

[0080] In some embodiments, the transferable photovoltaic device arrangement includes a low cohesion sacrificial layer between the flexible release substrate and the first transparent conductive layer of the thin-film photovoltaic device. As used herein, a low cohesion sacrificial layer is a layer in which the cohesion within the layer is intentionally weaker than the adhesive force between other layers and the cohesion within other layers in the multilayer structure obtained when the thin-film photovoltaic device is adhered to the bottom sub-cell via a transparent conductive adhesive layer. The low cohesion sacrificial layer is either an inherently low cohesion layer (i.e., at room temperature) or has a suitable low cohesion when activated. In either case, the flexible release substrate can be separated from the thin-film photovoltaic device by preferentially destroying the low cohesion sacrificial layer. However, it will be recognized that the low cohesion sacrificial layer still requires sufficient cohesive integrity and adhesive characteristics so that the flexible release substrate can adhere to and support the thin-film photovoltaic device during manufacturing and when the thin-film photovoltaic device is transferred to the bottom sub-cell.

[0081] The transparent low cohesion sacrificial layer is preferably a very thin layer, for example less than 100 nm thick, or less than 50 nm, or less than 20 nm thick. In some embodiments, the low cohesion sacrificial layer is conductive due to the incorporation of a conductive component, such as a metal, a metal oxide, and a conductive polymer or polymer composite material (such as poly (3,4-ethylenedioxythiophene) polystyrene sulfonate, i.e., PEDOT:PSS). If residues of the low cohesion sacrificial layer remain on the first transparent conductive layer after separation and removal of the flexible release substrate, then the inclusion of a conductive component can advantageously mitigate any loss of conductivity through the surface of the first transparent conductive layer.

[0082] In some embodiments, the low cohesion sacrificial layer comprises a low cohesion organic non-polymer solid, such as a wax. In some embodiments, the low cohesion sacrificial layer comprises an activatable adhesive. The activatable adhesive can be activated by any suitable external stimulus (such as heat or radiation) applied on command to fully reduce the cohesion of the sacrificial layer. Therefore, the flexible release substrate can be separated from the thin film photovoltaic device by activating the activatable adhesive by heat or radiation and destroying the low cohesion sacrificial layer.

[0083] In some embodiments, the activatable adhesive in the sacrificial layer is a heat-activatable adhesive, such as a thermoplastic polymer selected from ethylene-vinyl acetate (EVA) copolymers, polyethylene, polyethylene oxide (PEO) and polystyrene (PS). Thermoplastic polymers respond to the application of heat by melting or softening, thereby reducing the cohesion of the sacrificial layer as desired. Preferably, activation occurs at a temperature that can be achieved when the transferable photovoltaic device arrangement is pressed onto the bottom sub-cell and does not damage other layers in the device. In some embodiments, the sacrificial layer is heat-activatable at a temperature of 50°C to 170°C, for example in the range of 90°C to 140°C, to sufficiently reduce its cohesion.

[0084] In other embodiments, the activatable binder in the sacrificial layer is a photodepolymerizable polymer composition, optionally including a suitable photoinitiator or photocatalyst. Examples include polymer compositions selected from the following: a combination of polyphthalaldehyde (PPHA) and a photoacid generator (PAG), a combination of polyacetal and PAG, and a combination of polylactide (PLA) and TiO2. The photodepolymerizable polymer composition responds to irradiation with light of a suitable wavelength by depolymerizing or de-crosslinking, thereby reducing the cohesion of the sacrificial layer as desired.

[0085] Thin-film photovoltaic equipment

[0086] The transferable photovoltaic device arrangement includes a thin film photovoltaic device on a flexible release substrate, wherein the interface is configured to allow separation of the flexible substrate. The thin film photovoltaic device generally has a multilayer architecture formed by a series of thin film functional layers. In some embodiments, each functional layer has a dry layer thickness of less than 50 μm. In an embodiment, each functional layer has a dry layer thickness of less than 10 μm, or less than 5 μm, or less than 2 μm.

[0087] Due to this architecture, thin film photovoltaic devices are generally not self-supporting (i.e., they are not physically stable) and must therefore be fabricated and manipulated on a supporting substrate (here the flexible release substrate itself) by the methods described below. Once transferred to the bottom sub-cell, as disclosed herein, the thin film photovoltaic device will become the top sub-cell in the resulting tandem photovoltaic cell.

[0088] First transparent conductive layer

[0089] The thin film photovoltaic device comprises a first transparent conductive layer, which is a solution processed layer and comprises at least one organic and typically polymeric conductive and / or binder component selected from a conductive polymer or polymer composite, an activatable adhesive and an organic binder. Advantageously, the organic or polymeric component may also improve the flexibility and elasticity of the first transparent conductive layer, thereby ensuring that despite the flexing and compression applied to the layer during the transfer of the thin film photovoltaic device to the bottom photovoltaic sub-cell, its physical integrity and conductivity remain unchanged.

[0090] The first transparent conductive layer is destined to become the outer conductive layer of the top sub-cell in the tandem photovoltaic cell. However, in the transferable photovoltaic device arrangement, the first transparent conductive layer is located on a flexible release substrate and can be directly in contact with the substrate or separated from it by an interposed sacrificial layer. The interface between the flexible release substrate and the solution-treated first transparent conductive layer is designed to facilitate the release and separation of the flexible release layer once the thin-film photovoltaic device is adhered to the bottom sub-cell. In accordance with the preferred production method to be disclosed below, the first transparent conductive layer can be produced on the release substrate by solution processing techniques (such as coating or printing).

[0091] To provide the necessary conductivity, the first transparent conductive layer includes at least one conductive component, optionally held together by a binder (for example, if the conductive component is a specific non-polymer material that requires consolidation). In some embodiments, the first transparent conductive layer includes a conductive component selected from metals, metal oxides, conductive polymers or polymer composites, fullerenes or functionalized derivatives thereof, carbon nanomaterials (such as graphene), non-polymer organic semiconductors, organic aromatic compounds, and non-polymer conjugated organic compounds. In some embodiments, the first transparent conductive layer includes a conductive component selected from metals, metal oxides, and conductive polymers or polymer composites. Suitable metals and metal oxides may include particulate nanomaterials, including metal (such as silver) nanowires, other metal nanoparticles, and nanoparticle transparent conductive oxides (such as indium tin oxide, zinc oxide, tin oxide, and nickel oxide). In some embodiments, the first transparent conductive layer includes or consists of a conductive polymer or polymer composite. A suitable conductive polymer composite is PEDOT:PSS.

[0092] In some embodiments, the first transparent conductive layer is an electrical conductor layer (i.e., has metal-like conductive properties). Suitable electrical conductor layers may include conductive metal compositions such as Au, Ag, Al, Mg, Cu, or suitable alloys thereof. For example, such metal compositions may be present as nanoparticles in a transparent conductive matrix (i.e., a conductive polymer), or may be consolidated by an organic binder.

[0093] In other embodiments, the first transparent conductive layer is a semiconductor charge transport layer, such as an electron selective transport layer or a hole selective transport layer, depending on the intended orientation of the top subcell. When used in a tandem photovoltaic cell, the first transparent conductive layer can thus cooperate with the photoactive layer of the top subcell to selectively extract photovoltaically excited electrons or corresponding holes to the outer conductive surface of the top subcell.

[0094] When the first transparent conductive layer is an electron selective transport layer, it may include a transparent conductive oxide (such as at least one of tin oxide, nickel oxide, zinc oxide, titanium dioxide, tungsten trioxide, etc.), a fullerene derivative (such as [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) or [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM)), a pristine fullerene (such as C 60 , C 70 etc.), or functional polymers (such as polyethyleneimine ethoxylate (PEIE) etc.).

[0095] When the first transparent conductive layer is a hole selective transport layer, it may include a transparent conductive polymer such as 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD), poly[(2,5-bis(2-hexyldecyloxy)phenyl)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole)] (PPDT2FBT), poly(3,4-ethylenedioxythiophene) (PEDOT), a mixture of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS), poly(4,4-dioctylcyclopentadithiophene) (PEDOT:PSS), and poly(4,4-dioctylcyclopentadithiophene). At least one; P3HT, doped P3HT (poly (3-hexylthiophene-2,5-diyl)), poly (triarylamine) (PTAA), poly [N-9 "-heptadecanyl-2,7-carbazole-alt-5,5- (4 ',7 '-di-2-thienyl-2 ',1 ',3 '-benzothiadiazole)] (PCDTBT), poly [2,6- (4,4-bis- (2-ethylhexyl) -4H-cyclopentadienyl [2,1-b; 3,4-b '] dithiophene) -alt-4,7 (2,1,3-benzothiadiazole)] (PCPDTBT), poly (N-alkyl diketopyrrolopyrrole dithienyl thieno [3,2-b] thiophene) (DPP-DTT), etc.

[0096] The first transparent conductive layer may include a transparent conductive adhesive containing an activatable adhesive component, as will be explained in more detail below. However, this is not necessary, as even a non-activatable or non-sticky transparent conductive layer can be appropriately laminated to a non-stick surface of a release substrate or a low cohesion sacrificial layer on the release substrate by a solution processing method. Therefore, separation of the release substrate does not need to rely on debonding triggered by activation of the first transparent conductive layer itself. For example, the inventors have found that a thin film photovoltaic device including a PEDOT:PSS transparent conductive layer can be peeled from either (i) a flexible release substrate having a non-stick silicone coating or (ii) a flexible release substrate having a heat-activated low cohesion sacrificial layer thereon, although there is no activatable adhesive component in the transparent conductive layer.

[0097] In some embodiments, the first transparent conductive layer includes a transparent conductive adhesive or is composed of a transparent conductive adhesive. Therefore, the first transparent conductive layer may include a first activatable adhesive so that when the first activatable adhesive is activated, the flexible release substrate can be separated from the thin film photovoltaic device. As used herein, an activatable adhesive is an adhesive composition, typically an adhesive polymer composition, which can be activated by any applied stimulus (such as heat, radiation or chemical treatment) to allow adhesive bonding and / or debonding. In principle, a transparent conductive layer including an activatable adhesive can be formed on various flexible release substrates because the debonding of the interface is triggered by the activation of the transparent conductive adhesive. Therefore, the interface between the activated first transparent conductive layer and the flexible release substrate preferably becomes the weakest point in the structure after activation, so that the activated transparent conductive layer is completely separated. However, as long as there is still a suitable continuous layer of transparent conductive adhesive on the thin film photovoltaic device after transfer, it is not excluded that some residues of the activated transparent conductive adhesive may remain on the flexible release substrate.

[0098] In some embodiments, the first transparent conductive layer includes a heat-activatable adhesive, such as a heat-activatable adhesive polymer. The heat-activatable adhesive polymer can be a thermoplastic polymer selected from ethylene-vinyl acetate (EVA) copolymers, polyethylene, polyethylene oxide (PEO) and polystyrene (PS). When such an insulating polymer is present as a matrix for the first transparent conductive layer, it will be appreciated that a conductive component is also required to establish the necessary conductivity. Suitable conductive components include particles comprising a conductive metal or metal oxide and a conductive polymer such as PEDOT:PSS, polyaniline (PANI), polyacetylene, polypyrrole, polythiophene-vinyl, polythiophene, polystyrene-vinyl, polyphenylene sulfide. In one such example, the first transparent conductive layer is composed of a thermoplastic EVA copolymer matrix with Ag-coated conductive microspheres as a conductive additive. In another approach, the first transparent conductive layer comprises a heat-activatable conductive polymer composition, for example, a combination of PEDOT:PSS and a polyol such as D-sorbitol (see, for example, J. Ouyang, Y. Yang, Adv. Mater. 2006, 18, 2141).

[0099] A suitable heat-activatable first transparent conductive layer is preferably adapted to be activated at a temperature that can be provided when the transferable photovoltaic device arrangement is pressed onto the bottom subcell without damaging other functional layers in the device. In some embodiments, the first transparent conductive layer is heat-activatable to trigger debonding from the flexible release substrate at a temperature in the range of 50°C to 170°C, such as in the range of 90°C to 140°C.

[0100] Photoactive layer

[0101] The thin film photovoltaic device comprises a photoactive layer destined to become the light absorbing layer of the top subcell in the tandem photovoltaic cell. However, in the transferable photovoltaic device arrangement, the photoactive layer is located above the first transparent conductive layer, either directly in contact with the layer or separated from it by one or more intervening layers (such as charge transport layers). In accordance with the preferred production method to be disclosed below, the photoactive layer can be a solution-processed layer and can be produced on a release substrate.

[0102] The photoactive layer comprises a light absorbing semiconductor having a bandgap higher than the bandgap of the bottom subcell used in the tandem photovoltaic cell. The silicon based bottom subcell has a bandgap of approximately 1.1 eV. The power conversion efficiency of the tandem cell with Si-PV subcells is expected to be highest when the bandgap of the top subcell photoactive layer is between 1.6 and 1.9 eV, but it will be appreciated that bandgaps above and below this preferred range may also be accommodated. Thus, in some embodiments, the bandgap of the photoactive layer in the thin film photovoltaic device is between 1.6 and 1.9 eV.

[0103] In some embodiments, the photoactive layer includes a metal halide semiconductor. In some such embodiments, the metal halide semiconductor is a photoactive perovskite layer. Organic-inorganic hybrid perovskites are considered particularly suitable because the band gap can be adjusted to the desired target by adjusting the composition of the perovskite structure. In addition, the perovskite layer can be manufactured in thin film form by a solution processing method, including on a flexible substrate in a roll-to-roll manufacturing process. Examples of such methods are disclosed in international patent applications published as WO2016 / 115602A1 and WO2020 / 073082A1. The electrical properties of perovskites are highly tolerant to defects that may be caused by solution processing methods. The perovskite photoactive layer typically has a dry layer thickness in the range of 0.5 to 1 μm.

[0104] The photoactive perovskite layer includes a light absorbing perovskite semiconductor, which is mainly composed of crystallites of perovskite. The perovskite material can be represented by the formula AMX3, where A is at least one cation, M is at least one cation and X is at least one anion. When the perovskite includes more than one A cation, different A cations can be distributed in an ordered or disordered manner on the A position. When the perovskite includes more than one M cation, different M cations can be distributed in an ordered or disordered manner on the M position. When the perovskite includes more than one X anion, different X anions can be distributed in an ordered or disordered manner on the X position. The symmetry of a perovskite including more than one A cation, more than one M cation or more than one X cation will be lower than the symmetry of CaTiO3. Perovskite is a crystalline compound. Therefore, a perovskite semiconductor layer without open pores is usually mainly composed of perovskite crystallites. In a perovskite-type photoactive device (such as a photovoltaic cell), the photoactive layer may include an organic-inorganic perovskite structure semiconductor. However, it should be appreciated that in some embodiments, the photoactive layer may be entirely inorganic, for example, CsPb(I n X 1-n )3, wherein X is a non-iodine halide.

[0105] As used herein, the term "perovskite" refers to (a) a material having a three-dimensional crystal structure related to that of CaTiO3 or (b) a material comprising a layer of material, wherein the layer has a structure related to that of CaTiO3. Although both classes of perovskites can be used in devices according to the present invention, in some cases, it is preferred to use perovskites of the first class (a), i.e., perovskites having a three-dimensional (3D) crystal structure. Such perovskites typically include a 3D network of perovskite unit cells without any separation between layers. On the other hand, perovskites of the second class (b) include perovskites having a two-dimensional (2D) layered structure. Perovskites having a 2D layered structure may include layers of perovskite unit cells separated by (embedded) molecules; an example of such a 2D layered perovskite is [2-(l-cyclohexenyl)ethylammonium]2PbBr4. 2D layered perovskites tend to have high exciton binding energies, which facilitates the generation of bound electron-hole pairs (excitons) rather than free charge carriers under photoexcitation. The bound electron-hole pairs may not have sufficient mobility to reach the p-type or n-type contacts, where they can then transfer (ionize) and generate free charges. Therefore, in order to generate free charges, the exciton binding energy must be overcome, which represents the energy cost of the charge generation process and leads to lower voltage and lower efficiency in photovoltaic cells. In contrast, perovskites with 3D crystal structures tend to have much lower exciton binding energies (on the order of thermal energy) and can therefore generate free carriers directly after photoexcitation. Thus, the perovskite semiconductor used in the devices and processes of the present invention is preferably a perovskite of the first category (a), i.e., a perovskite with a three-dimensional crystal structure.

[0106] In some embodiments, the perovskite has AM(I n X 1-n )3, wherein: A is at least one cation, preferably selected from methylammonium ([CH3NH3] + ) and formamidine ([R2N-CH=NR2] + ) and cesium, M is a metal, I is iodine, X is a non-iodine halide, preferably selected from Br and Cl, and n is in the range of 0 to 1. M is preferably selected from Pb, Sn, Ge, Cs, Bi. Advantageously, by replacing iodine with bromine, the band gap of such perovskite semiconductors can be continuously tuned in the range of 1.6 eV and 2.3 eV, as disclosed in the international patent application published as WO2016 / 090179.

[0107] In some embodiments, the photoactive layer comprises an organic photovoltaic active layer, such as used in polymer solar cells. Such photoactive layers generally include an organic polymer electron donor material such as poly(3-hexylthiophene) (P3HT) or poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione) )](PBDB-T)) is combined with a fullerene-based electron acceptor material such as phenyl-C61-butyric acid methyl ester (PCBM) or a non-fullerene acceptor such as 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indan[1,2-b:5,6-b′]dithiophene)(ITIC) or Y6. The organic photoactive layer can also be advantageously modified to be manufactured in thin film form by solution processing methods, including on a flexible substrate in a roll-to-roll manufacturing process. Examples of such methods are disclosed in Na et al. Advanced Functional Materials 2018, 6, 1805825.

[0108] Charge transport layer(s)

[0109] The thin film photovoltaic device may comprise one or more transparent functional layers in addition to the first transparent conductive layer and the photoactive layer. In line with the preferred production method to be disclosed below, the transparent functional layer may be a solution processed layer and may be produced on a release substrate.

[0110] In some embodiments, the thin film photovoltaic device further comprises a first charge transport layer, which is between the first transparent conductive layer and the photoactive layer, for example, sandwiched between these layers and in direct contact with these layers. In some embodiments, the thin film photovoltaic device further comprises a second charge transport layer, which is located above the photoactive layer, for example, in direct contact with the photoactive layer. Such a charge transport layer typically has a thickness of less than 0.2 μm, or less than 0.1 μm.

[0111] The first and second charge transport layers may be electron selective transport layers and hole selective transport layers, or vice versa, depending on the intended orientation of the top subcell. Such charge transport layers may help selectively extract photovoltaically excited electrons and corresponding holes toward the outer conduction surface and recombination layer / tunnel junction of the top subcell, respectively, thereby providing improved photovoltaic performance. However, as will be appreciated by those skilled in the art, charge transport layers are not essential to the solar cell architecture, and thus one or both of the first and second charge transport layers may not be present.

[0112] Suitable electron selective transport layers may include transparent conductive oxides (such as at least one of tin oxide, zinc oxide, titanium dioxide, etc.), fullerene derivatives (such as [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) or [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM)), pristine fullerene mixtures (such as C 60 , C 70 etc.) or transparent conductive polymers (such as polyethyleneimine ethoxylate (PEIE) etc.).

[0113] Suitable hole selective transport layers may include transparent conductive polymers, such as at least one of 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD), poly[(2,5-bis(2-hexyldecyloxy)phenyl)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole)] (PPDT2FBT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene and polystyrene sulfonate mixture (PEDOT:PSS), poly(4,4-dioctylcyclopentadithiophene); 3HT, doped P3HT (poly (3-hexylthiophene-2,5-diyl)), poly (triarylamine) (PTAA), poly [N-9"-heptadecanyl-2,7-carbazole-alt-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT), poly [2,6- (4,4-bis- (2-ethylhexyl) -4H-cyclopentadienyl [2,1-b; 3,4-b'] dithiophene) -alt-4,7 (2,1,3-benzothiadiazole)] (PCPDTBT), poly (N-alkyl diketopyrrolopyrrole dithienylthieno [3,2-b] thiophene) (DPP-DTT), MoO3, etc.

[0114] Second transparent conductive layer

[0115] In some embodiments, the thin film photovoltaic device of the transferable photovoltaic device arrangement includes a second transparent conductive layer. The second transparent conductive layer is located above the photoactive layer, either directly in contact with the photoactive layer or separated from it by one or more intervening layers (such as charge transport layers). The second transparent conductive layer present as an outer layer of the thin film photovoltaic device includes a transparent conductive adhesive for adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell. Advantageously, therefore, the thin film photovoltaic device can be adhered to the bottom sub-cell (such as a silicon-based cell) by simply contacting the two layers under the condition that the transparent conductive adhesive is bonded to the bottom sub-cell.

[0116] Consistent with the preferred production methods disclosed below, the second transparent conductive layer may be a solution processed layer and may be produced on a release substrate.

[0117] Preferred transparent conductive adhesives for the second transparent conductive layer have the following characteristics: (i) the ability to be adhesively bonded to the bottom subcell, optionally after first being activated by an external stimulus, with sufficient bonding strength to allow the flexible release substrate to be peeled from the thin film photovoltaic device; (ii) the ability to form a durable bonding interlayer between the top and bottom subcells to form a monolithic tandem photovoltaic device; (iii) high optical transparency to photons that pass through the top subcell to be absorbed in the photoactive layer of the bottom subcell; and (iv) electronic properties suitable for allowing the hole current from one subcell to recombine with the electron current from the other subcell with low voltage losses.

[0118] The transparent conductive adhesive includes a second conductive component, which may include at least one selected from metals, metal oxides, conductive polymers or polymer composites, fullerenes or functionalized derivatives thereof, carbon nanomaterials (such as graphene), non-polymer organic semiconductors, organic aromatic compounds, and non-polymer conjugated organic compounds. In some embodiments, the second conductive component includes at least one selected from metals, metal oxides, conductive polymers, or polymer composites.

[0119] In some embodiments, the transparent conductive adhesive comprises an activatable adhesive such that when the activatable adhesive is activated, the second transparent conductive layer adheres to the bottom photovoltaic sub-cell. The activatable adhesive may be activated by any applied stimulus such as heat, radiation, or chemical treatment.

[0120] If heat-activatable, the second transparent conductive layer is preferably adapted to be activated at a temperature that can be provided when the transferable photovoltaic device arrangement is pressed onto the bottom sub-cell without damaging other functional layers in the device. In some embodiments, the second transparent conductive layer is heat-activatable at a temperature in the range of 50°C to 170°C, such as in the range of 90°C to 140°C, to promote adhesion to the bottom sub-cell.

[0121] In some embodiments, the transparent conductive layer is heat activatable at a sufficiently high temperature so as to also release the flexible release substrate from the thin film photovoltaic device. For example, as described herein, either the first transparent conductive layer or the low cohesion sacrificial layer may include a first heat activatable adhesive polymer, while the second transparent conductive layer includes a second heat activatable adhesive polymer. The two heat activatable adhesive polymers are selected so that a single heat treatment step results in (i) debonding of the interface between the flexible release film and the thin film photovoltaic device, and (ii) activation and adhesion of the second transparent conductive layer to the bottom photovoltaic sub-cell. For example, the second heat activatable adhesive polymer may have a higher melting point than the first heat activatable adhesive polymer. Therefore, if the transferable photovoltaic device arrangement is heat pressed onto the bottom photovoltaic sub-cell (e.g., in a roller lamination process), then separation of the flexible release substrate can be performed almost simultaneously with adhesion of the thin film photovoltaic device to the bottom photovoltaic sub-cell.

[0122] In some embodiments, the activatable adhesive of the second transparent conductive layer is a thermoplastic polymer selected from ethylene-vinyl acetate (EVA) copolymers, polyethylene, polyethylene oxide (PEO) and polystyrene (PS). When such an insulating polymer is present as a matrix for the second transparent conductive layer, a conductive component is required to establish the necessary conductivity. The conductive component may include a particulate conductive element that establishes a conductive path through the thickness of the second transparent conductive layer. In one such example, a transparent conductive adhesive suitable for the recombinant layer is composed of a thermoplastic EVA copolymer matrix with Ag-coated conductive microspheres as a conductive additive (see TRKlein et al., J. Phys. D: Appl. Phys. 2021, 54, 184002).

[0123] The thermoplastic polymer may form a continuous matrix of the second transparent conductive layer, or may be present in a discontinuous form. For example, the second transparent conductive layer may include a combination of a conductive polymer or composite material (such as PEDOT:PSS) and a particulate thermoplastic polymer. When heat activated in use, the thermoplastic polymer flows and the layer becomes adhered to the bottom photovoltaic sub-cell.

[0124] In other embodiments, the second transparent conductive layer includes a heat-activatable conductive polymer composition, such as a combination of PEDOT:PSS and a polyol such as D-sorbitol (see, eg, J. Ouyang, Y. Yang, Adv. Mater. 2006, 18, 2141).

[0125] In some embodiments, the transparent conductive adhesive comprises a radiation-activatable adhesive such that when the activatable adhesive is illuminated by suitable actinic light, the second transparent conductive layer adheres to the bottom photovoltaic sub-cell.

[0126] The second transparent conductive layer, once activated and adhered to the bottom subcell, can be adapted to cure or harden, thereby forming a durable transparent conductive interlayer between the top and bottom subcells. This can simply involve cooling the heat-activated adhesive to allow it to solidify again. However, in some embodiments, the second transparent conductive layer includes an activatable adhesive that, when activated (e.g., by heat or radiation), irreversibly cures via a covalent bond forming reaction. An example of such a conductive adhesive material is Panacol Elecolit 3065 available from Ulbricht.

[0127] In some embodiments, the transparent conductive adhesive comprises a pressure sensitive adhesive such that when the thin film photovoltaic device is pressed onto its top receiving surface, the second transparent conductive layer adheres to the bottom photovoltaic subcell. For example, the second transparent conductive layer may comprise a combination of PEDOT:PSS and an acrylic microemulsion pressure sensitive adhesive (see, e.g., D. Bryant et al., Adv. Mater. 2014, 26, 7499-7504).

[0128] Configuration

[0129] The transferable photovoltaic device arrangement can be configured as a roll, suitable for a roll lamination process, in which the thin film photovoltaic device is pressed onto the bottom photovoltaic sub-cell and the flexible release substrate is separated from the thin film photovoltaic device. Thus, the flexible release substrate is configured as an elongated film or ribbon when unfolded. The thin film photovoltaic device can be configured as a continuous or discontinuous strip extending along the elongated film, preferably with dimensions suitable for matching a specific bottom photovoltaic sub-cell.

[0130] Method for producing a transferable photovoltaic device arrangement

[0131] The present invention also relates to a method for producing a transferable photovoltaic device arrangement. The method includes providing a flexible release substrate and producing a thin film photovoltaic device on the flexible release substrate. This is achieved by successively forming a series of functional layers, which include at least a first transparent conductive layer on the flexible release substrate and a photoactive layer on the first transparent conductive layer. The first transparent conductive layer is formed by solution processing and includes at least one selected from a conductive polymer or a polymer composite, an activatable adhesive and an organic adhesive. The interface between the flexible release substrate and the first transparent conductive layer produced thereon is designed so that the flexible release substrate can be separated from the thin film photovoltaic device when in use, thereby exposing the first transparent conductive layer at the outer conductive surface of the thin film photovoltaic device.

[0132] A particular advantage of the methods disclosed herein is that low-cost and easily scalable solution processing techniques can be used to produce the functional layers. At least the first transparent conductive layer is formed by solution processing, but in preferred embodiments, at least one other functional layer, at least two other functional layers, or all functional layers in the thin film photovoltaic device are solution processed functional layers.

[0133] Solution-processed functional layers are formed in a manufacturing process in which the materials forming the layer are deposited while in solution (otherwise referred to as "wet" processing methods). This is in contrast to "dry" processing methods in which these materials are deposited while in a gas or vapor phase. Solution-processed functional layers typically include the functional material of the layer and optionally an organic binder. The wet solution used to form the solution-processed functional layer typically includes the functional material or its precursor and an optional binder mixed together in a solvent.

[0134] When one or more functional materials of the solution-treated layer are particulate materials that require consolidation to form suitable bonding and adhesion layers, an organic binder is usually required. Any suitable organic binder can be used. The example of a suitable organic binder comprises one or more of ethyl cellulose, butyl cellulose, nitrocellulose, hydroxy cellulose, cellulose acetate butyrate, alkyd resins, epoxy resins, phenolic resins, acrylic resins, butyl carbitol, butadiene-styrene rubber, polyvinyl pyrrolidone, polyacrylamide and cellulose derivatives. Polymer organic binders are particularly preferred.

[0135] Suitable solvents include, but are not limited to, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile, N-methyl-2-pyrrolidone (NMP), gamma-butyrolactone (GBL), terpineol, dibutyl phthalate, butyl carbitol, dibutyl carbitol, turpentine, butyl glycol ether, butyl carbitol acetate, glycol ether acetate, tributyl citrate and tributyl phosphate, propylene glycol methyl ether acetate toluene, diethylene glycol butyl ether, propanol, benzyl alcohol, isopropanol, ethanol, methanol, chloroform, diethylene glycol derivatives, toluene, xylene isopropanol, ethyl acetate, water, chlorobenzene, or combinations thereof.

[0136] The wet solution for producing each solution-treated functional layer can be applied as a wet film to the immediately preceding layer using any suitable method, such as at least one of the following methods: casting, blade coating, doctor blade coating, rod coating, screen printing, inkjet printing, pad printing, knife coating, meniscus coating, slot die coating, gravure printing, reverse gravure printing, touch coating, micro roller coating, curtain coating, slide coating, spray coating, flexographic printing, offset printing, rotary screen printing, or dip coating. In an exemplary embodiment, at least one, at least two, or all functional layers are produced using at least one of blade coating, screen printing, slot die coating, gravure printing, or reverse gravure coating methods.

[0137] Once the wet film has been produced, the solvent is removed to produce a thin film functional layer. A heat treatment step (also referred to as an annealing step) is typically used to remove the solvent from the wet film, thereby drying the functional layer. The heat treatment step is preferably performed after each layer is applied. However, it should be appreciated that two or more layers may also be applied before the combined layer is heat treated. Various heat treatment schemes may be used, depending on the specific requirements of each functional layer. In some embodiments, the heat treatment comprises heating the wet film to at least 80°C, preferably to at least 100°C, and more preferably to at least 120°C. In an embodiment, the heat treatment scheme is performed for 0 to 10 minutes.

[0138] The solution processed functional layers can advantageously be produced on a flexible substrate by roll-to-roll manufacturing techniques that can be adapted for large-scale low-cost and high-volume production. Thus, in some embodiments, the first transparent conductive layer is produced by roll-to-roll processing. In some embodiments, at least one, at least two, or all functional layers are produced by roll-to-roll processing.

[0139] Now refer to Figure 5 A method for producing a transferable photovoltaic device arrangement is described. The method includes a step 500 of providing a flexible release substrate, which is generally as described herein with respect to a transferable photovoltaic device arrangement. Suitable flexible release substrates can be obtained from commercial sources. In some embodiments, the flexible release substrate is configured as a roll so that a thin film photovoltaic device can be subsequently produced on the flexible release substrate by a series of coating and / or printing steps in a roll-to-roll manufacturing process.

[0140] In some embodiments, the flexible release substrate comprises a non-stick surface, as described above. Then, the first transparent conductive layer will be formed directly on the non-stick surface. In some embodiments, the flexible release substrate comprises a low cohesion sacrificial layer on its surface, as described above in this article.

[0141] Thus, the method may include an optional step 510 of forming a low cohesion sacrificial layer on the flexible release substrate. This may be accomplished by applying a fluid composition comprising components of the sacrificial layer to form a wet film on the flexible release substrate and curing the wet film to form the low cohesion sacrificial layer. The fluid composition may include a solvent that is typically removed from the wet film by heating to form the low cohesion sacrificial layer. Although it has inherent or activatable low cohesion characteristics, the resulting sacrificial layer still has sufficient cohesive integrity and adhesion characteristics that can be used to manufacture and support subsequent layers thereon.

[0142] The method includes a step 520 of forming a first transparent conductive layer on a flexible release substrate by solution processing, as described previously herein. The first transparent conductive layer can be formed directly on the flexible release substrate, or on an inserted low cohesion sacrificial layer (e.g., as formed in optional step 510). The first transparent conductive layer can be formed by applying a fluid composition to form a wet film on the flexible release substrate and curing the wet film to form the first transparent conductive layer on the flexible release substrate. The fluid composition may include a solvent, which is typically removed from the wet film by heating to form the first transparent conductive layer.

[0143] The fluid composition includes the desired conductive component(s) (as described previously herein) or its reactive precursor(s). The reactive precursor may include a reactive metal compound, such as a metal halide or metal alkoxide, which forms a transparent conductive metal oxide in situ by reacting with moisture. Examples of such compositions include titanium chloride, titanium 2-propoxide, and zinc acetate solutions, with or without dopants. The fluid composition may include an organic binder and / or an activatable binder, and if the conductive component itself is not a polymer, at least one such component will be included. A suitable activatable binder (e.g., a heat-activatable binder polymer) adheres the first transparent conductive layer to the underlying layer, but can then be activated to release the flexible release substrate from the thin film photovoltaic device.

[0144] The method may include an optional step 530 of forming one or more transparent functional layers (such as the charge transport layer described previously herein) on the first transparent conductive layer. The electron selective transport layer or the hole selective transport layer may be produced by applying a fluid composition including (one or more) charge transport components or (one or more) reactive precursors thereof to form a wet film on the first transparent conductive layer and curing the wet film to form the charge transport layer. The fluid composition may include a solvent, which is typically removed from the wet film by heating to form the charge transport layer.

[0145] The method includes a step 540 of forming a photoactive layer on top of the first transparent conductive layer, as described previously herein. The photoactive layer can be formed directly on the first transparent conductive layer, or on an intervening transparent functional layer (such as a charge transport layer formed in optional step 530). The photoactive layer can be produced by applying a flowable composition comprising one or more photoactive layer components or precursors thereof dispersed in a solvent to form a wet film on the first transparent conductive layer; and forming the photoactive layer by removing the solvent from the wet film.

[0146] The flowable composition can be a perovskite precursor solution containing dissolved ionic components that crystallize into a photoactive perovskite structure when a wet film of the perovskite precursor solution is concentrated by drying. One way to prepare a suitable perovskite precursor solution is to simply dissolve the desired perovskite composition in a sufficiently volatile polar solvent (e.g., dimethylformamide). Alternatively, the perovskite precursor solution is applied only to a portion of the underlying layer (e.g., a charge transport layer) and allowed to diffuse into the intended coverage in response to the adhesion between the polar perovskite precursor solution and the hydrophilic underlying layer, as disclosed in the international patent application published as WO2020 / 073082.

[0147] The photoactive layer can also be formed by sequentially applying two or more flowable compositions that together form the photoactive layer. An example of such a method in which two perovskite precursor solutions are sequentially applied to form a perovskite photoactive layer is disclosed in the international patent application published as WO2016 / 115602.

[0148] The flowable composition may be used to produce an organic photovoltaic active layer and thus may contain photoactive layer components including an organic polymeric electron donor material and a fullerene or non-fullerene acceptor.

[0149] The method may include an optional step 550 of forming one or more transparent functional layers (such as the charge transport layer described previously herein) on the photoactive layer. An electron selective transport layer or a hole selective transport layer may be produced by applying a fluid composition including (one or more) charge transport components or (one or more) reactive precursors thereof to form a wet film on the photoactive layer and curing the wet film to form the charge transport layer. The fluid composition may include a solvent, which is typically removed from the wet film by heating to form the charge transport layer.

[0150] The method may include an optional step 560 of forming a second transparent conductive layer over the photoactive layer, as described previously herein. The second transparent conductive layer includes a transparent conductive adhesive for adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell. As described previously herein, the second transparent conductive layer can be formed directly on the photoactive layer or on an interposed transparent functional layer (such as a charge transport layer formed in optional step 550). The second transparent conductive layer can be formed by applying a fluid composition to form a wet film over the photoactive layer and curing the wet film to form the second transparent conductive layer. The fluid composition may include a solvent, which is typically removed from the wet film by heating to form the second transparent conductive layer. The fluid composition will also include components of a transparent conductive adhesive (such as an activatable adhesive) and a conductive component or a reactive precursor thereof.

[0151] Method for producing tandem photovoltaic cells

[0152] The present invention also relates to a method for producing a tandem photovoltaic cell. The method includes providing a transferable photovoltaic device arrangement as disclosed herein or produced by the method disclosed herein. The thin-film photovoltaic device of the transferable photovoltaic device arrangement is adhered to the bottom photovoltaic sub-cell with a transparent conductive adhesive. The thin-film photovoltaic device and the bottom photovoltaic sub-cell are thereby functionally coupled via a second transparent conductive layer, which forms a recombination layer or tunnel junction in the tandem photovoltaic cell. The flexible release substrate of the transferable photovoltaic device arrangement is separated from the thin-film photovoltaic device, thereby exposing the first transparent conductive layer. Thus, the resulting tandem photovoltaic cell has the first transparent conductive layer of the thin-film photovoltaic device at the outer conductive surface.

[0153] The bottom photovoltaic subcell can in principle be any type of photovoltaic cell with a suitable bandgap for the bottom subcell of the tandem photovoltaic cell, including silicon photovoltaic cells, copper indium gallium (di) selenide (CIGS) photovoltaic cells, cadmium telluride (CdTe) photovoltaic cells, or perovskite photovoltaic cells. The bottom photovoltaic subcell generally has a conventional architecture, including a photoactive (light absorbing) layer and a bottom electrical contact (which can be opaque). The bottom photovoltaic subcell has a conductive outer layer having a receiving surface to which the thin film photovoltaic device is adhered. The outer layer can be a highly doped Si layer (n-type or p-type) or a transparent conductive oxide layer.

[0154] In some embodiments, the bottom photovoltaic subcell is a silicon photovoltaic cell. The silicon photovoltaic cell can be a conventional pn homojunction cell or a heterojunction silicon photovoltaic cell. In some embodiments, the bottom photovoltaic subcell has a rigid planar structure. In some embodiments, the bottom photovoltaic subcell has a bendable thin planar structure. In some embodiments, the bottom photovoltaic subcell is a textured crystalline silicon (c-Si) solar cell.

[0155] In some embodiments, the transparent conductive adhesive is present as a preformed outer layer of either the thin film photovoltaic device or the bottom photovoltaic sub-cell. In such cases, the thin film photovoltaic device and the bottom photovoltaic sub-cell are contacted to adhere them via the second transparent conductive layer. In other embodiments, the method may include an additional step of applying a transparent conductive adhesive coating to the surface of either the thin film photovoltaic device or the bottom photovoltaic sub-cell before contacting the thin film photovoltaic device with the bottom photovoltaic sub-cell.

[0156] In some embodiments, the transparent conductive adhesive is activated to promote adhesion and / or curing of the second transparent conductive layer.The transparent conductive adhesive may be activated by heat, radiation or chemical treatment before or after contacting the thin film photovoltaic device and the bottom photovoltaic sub-cell.

[0157] In some embodiments, the transparent conductive adhesive is heat activated, optionally at a temperature in the range of 50°C to 170°C, such as in the range of 90°C to 140°C. For example, the transferable photovoltaic device arrangement can be heat pressed onto the bottom photovoltaic sub-cell at a suitable temperature and dwell time to fluidize or soften the heat-activated adhesive polymer in the transparent conductive adhesive. Thus, the activated transparent conductive adhesive becomes tacky and adheres to the receiving surface of the bottom photovoltaic sub-cell. Once the heat press is removed, the adhesive polymer cools and solidifies, thereby providing a permanent adhesive bond.

[0158] In some embodiments, the transparent conductive adhesive is radiation activated. For example, the transferable photovoltaic device arrangement is irradiated with actinic radiation (such as UV light) to promote initial adhesion to the bottom subcell, followed by curing via a covalent bond forming reaction to form a permanent adhesive bond.

[0159] The thin film photovoltaic device may be pressed or compressed onto the bottom photovoltaic sub-cell to promote adhesion. Any suitable compression / pressing process may be used. For example, the compression / pressing process may include roller pressing, such as a calender / laminator, uniaxial pressing, or isostatic pressing. In an embodiment, the thin film photovoltaic device is applied to the bottom photovoltaic sub-cell by compression, preferably by a pressing arrangement, more preferably by a calender.

[0160] In some embodiments, the thin film photovoltaic device is brought into contact with the bottom photovoltaic sub-cell. This can be accomplished, for example, by calendering the thin film photovoltaic device arrangement onto the bottom photovoltaic sub-cell in a roll lamination process.

[0161] Sufficient adhesive bonding is required between the thin film photovoltaic device and the bottom photovoltaic sub-cell to ensure that the flexible release substrate is selectively separated from the flexible release substrate when desired. However, it will be appreciated that the thin film photovoltaic device and the bottom photovoltaic sub-cell do not need to be in contact over the entire intended interface before starting to separate the flexible release film. For example, in a roll lamination process, the thin film photovoltaic device and the bottom photovoltaic sub-cell only need to be in contact and adhered below the separation interface between the flexible release substrate and the thin film photovoltaic device. In addition, the final bonding strength of the interlayer between the thin film photovoltaic device and the bottom photovoltaic sub-cell does not need to be fully formed when the flexible release substrate is separated.

[0162] The flexible release substrate can be separated from the thin film photovoltaic device at any time after the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell below the separation interface. In some embodiments, the flexible release substrate is separated from the thin film photovoltaic device in a subsequent process step, which process step can in principle be performed at a different time and location. For example, the thin film photovoltaic device arrangement can be adhered to the bottom photovoltaic sub-cell on one production line, and the flexible release substrate can be separated and removed on a different production line or even during the assembly of the solar cell module. In other embodiments, the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell and the flexible release substrate is separated from the thin film photovoltaic device in a single process, so that the two steps occur almost simultaneously (i.e., within a few minutes, preferably no more than a few seconds apart from each other).

[0163] As disclosed herein, the separation step includes selectively destroying the interface between the flexible release substrate and the thin film photovoltaic device. In some embodiments, for example when the flexible release substrate has a non-stick surface or an inherently low cohesion sacrificial layer is inserted between the thin film photovoltaic device and the flexible release substrate, once the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell, the flexible release substrate can be separated and removed simply by gradually peeling off the release substrate.

[0164] In other embodiments, for example, when the first transparent conductive layer is activatable or an activatable low cohesion sacrificial layer is interposed between the thin film photovoltaic device and the flexible release substrate, separating the flexible release substrate from the thin film photovoltaic device includes an activation step. The activation step may include, for example, using heat or radiation to activate an activatable adhesive in the first transparent conductive layer or the low cohesion sacrificial layer.

[0165] In some embodiments, the activation step comprises thermally activating the first transparent conductive layer or the low cohesion sacrificial layer at a temperature in the range of 50°C to 170°C (e.g., in the range of 90°C to 140°C). For example, the transferable photovoltaic device arrangement can be hot pressed onto the bottom photovoltaic sub-cell at a suitable temperature and dwell time to fluidize or soften the heat-activated adhesive polymer in the first transparent conductive layer or the low cohesion sacrificial layer. This releases the adhesive bond between the flexible release substrate and the thin film photovoltaic device, thereby allowing the flexible release substrate to be peeled off. In other embodiments, the flexible release substrate is released by irradiating the first transparent conductive layer or the low cohesion sacrificial layer with actinic light to activate the activatable adhesive (e.g., by a depolymerization mechanism).

[0166] In some embodiments, a single activation step is used to (i) release the flexible release layer from the thin film photovoltaic device, thereby allowing it to be separated, and (ii) activate the transparent conductive adhesive to adhere the thin film photovoltaic device to the bottom photovoltaic sub-cell. In some embodiments, the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell by activating the transparent conductive adhesive with heat at a temperature sufficient to release the flexible release substrate from the thin film photovoltaic device. For example, the transferable photovoltaic device arrangement can be heat pressed onto the bottom photovoltaic sub-cell at a suitable temperature and dwell time to (i) heat activate the transparent conductive adhesive to adhere the thin film photovoltaic device to the bottom photovoltaic sub-cell, and (ii) heat activate the first transparent conductive layer or the low cohesion sacrificial layer to release the adhesive bond between the flexible release substrate and the thin film photovoltaic device.

[0167] In some embodiments, the transferable photovoltaic device arrangement is configured as a roll, and the thin film photovoltaic device is transferred to the bottom photovoltaic sub-cell in a roll lamination process.

[0168] Reference Figure 6 A method of producing tandem photovoltaic cells in a roll lamination process is described. A transferable photovoltaic device arrangement 600 includes a flexible release substrate 602 and a plurality of photovoltaic cells disposed thereon as a continuous strip (covering a plurality of photovoltaic cells). Figure 6 The thin film photovoltaic device 604 is a thin film photovoltaic device having an entire invisible bottom side of a flexible release substrate 602 in the middle. The interface between the flexible release substrate 602 and the transparent conductive inner layer of the thin film photovoltaic device 604 is designed to allow separation as disclosed herein. The thin film photovoltaic device 604 includes a transparent conductive adhesive layer on its outer surface.

[0169] A plurality of bottom Si-PV subcells 608 are held on a rigid mobile stage 610, each Si-PV subcell comprising a conductive outer layer having a receiving surface 612 for receiving a thin film photovoltaic device 604. Both the mobile stage 610 and the transferable photovoltaic device arrangement 600 are passed through a calender 614 in the direction indicated by arrow 615. The arrangement 600, initially configured as a roller (not shown), is thus unrolled and brought into contact with the bottom Si-PV subcell 608. The calender roller 616 presses the thin film photovoltaic device 604 onto the receiving surface 612 for a dwell time sufficient to adhere the transparent conductive adhesive layer thereto. Optionally, the calender roller 616 is heated and applies a temperature sufficient to heat activate the transparent conductive adhesive, thereby promoting adhesion.

[0170] After the laminated structure emerges from the opposite side of the calender 614, the flexible release substrate 602 is pulled away from the moving table 610 and optionally rewound onto another roll. Because the interface between the flexible release substrate 602 and the thin film photovoltaic device 604 is the weakest interface after roll lamination, the flexible release substrate 602 is selectively peeled off wherever the thin film photovoltaic device 604 adheres to the bottom Si-PV subcell 608, i.e., from the cutout area 613 of the flexible release substrate 602. The tandem photovoltaic cell 620 is thus formed with (i) a transparent conductive layer (i.e., a transparent conductive adhesive) that forms a recombination layer or tunnel junction between the bottom Si-PV subcell and the transferred thin film photovoltaic device 604a (top subcell), and (ii) the transparent conductive layer 618 of the thin film photovoltaic device 604a exposed at the outer surface. The release of the flexible release substrate 602 from the transparent conductive layer 618 can be facilitated by heat optionally applied by the calendar roller 616, which heats the transparent conductive layer 618 itself or an interposed low cohesion sacrificial layer to thermally activate. Alternatively, the flexible release substrate 602 can have a non-stick surface so that the interface between the flexible release substrate 602 and the transparent conductive layer 618 is inherently separable (i.e., no activation is required).

[0171] The separation of the flexible release substrate from the thin film photovoltaic device exposes the first transparent conductive layer at the outer conductive surface of the tandem photovoltaic cell. The removal of the insulating release substrate advantageously allows current to flow through the outer surface of the tandem cell during operation. However, on large surface area tandem photovoltaic cells, it is still necessary to collect current via a metal current collector network on the external solar receiving surface. Therefore, in some embodiments, the method also includes producing a metal current collector network on the outer conductive surface of the tandem photovoltaic cell, such as a silver metal grid commonly applied to the outer surface of commercial-sized silicon photovoltaic cells. Optionally, one or more additional transparent conductive layers (e.g., a vacuum-treated transparent conductive oxide) can also be produced on the first transparent conductive layer of the tandem photovoltaic cell. The metal current collector network can then be produced on the new conductive surface thus provided.

[0172] Tandem photovoltaic cells

[0173] The present invention also relates to a tandem photovoltaic cell arrangement comprising a bottom photovoltaic sub-cell and a transferable photovoltaic device arrangement as disclosed herein, wherein the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell via a second transparent conductive layer comprising a transparent conductive adhesive. The bottom photovoltaic sub-cell may be as previously disclosed herein, and in some exemplary embodiments is a silicon photovoltaic cell.

[0174] In some embodiments, the flexible release substrate remains unseparated from the thin film photovoltaic device. However, the interface between the flexible release substrate and the thin film photovoltaic device is designed to allow removal by peeling when desired, optionally after first releasing the interface by applying a suitable external stimulus (such as heat or radiation).

[0175] In other embodiments, the flexible release substrate is partially separated from the thin film photovoltaic device, thereby exposing the first transparent conductive layer at the outer conductive surface.Such an arrangement may be an intermediate structure obtained when manufacturing a tandem photovoltaic cell according to the methods disclosed herein.

[0176] Once the flexible release substrate is completely separated, a tandem photovoltaic cell is produced.Thus, the present invention also relates to a tandem photovoltaic cell produced by the method disclosed herein.

[0177] Example

[0178] Reference Figure 2 Embodiments of the present invention are described. A transferable photovoltaic device arrangement 200 includes a flexible release substrate 202 on which a thin film photovoltaic device 204 is located. The thin film photovoltaic device 200 includes the following functional layers in sequence: a first transparent conductive layer 208, a charge transport layer 226, a photoactive layer 210, a charge transport layer 228, and a second transparent conductive layer 222 on the flexible release substrate. The second transparent conductive layer 222 includes a heat-activatable transparent conductive adhesive as disclosed herein. The charge transport layer 226 can be an electron selective transport layer and the charge transport layer 228 is a hole selective transport layer, or vice versa, as required to match the architecture of the bottom subcell.

[0179] The transferable photovoltaic device arrangement 200 includes a low cohesion sacrificial layer 206 between a flexible release substrate 202 and a transparent conductive layer 208. The sacrificial layer 206 includes a heat-activatable adhesive (such as PEO) and optionally a conductive component (such as PEDOT:PSS). When heated, the heat-activatable adhesive fluidizes or softens, so that the sacrificial layer produces a suitable low cohesion. Therefore, in the bonding and separation method step indicated by arrow 250, when the flexible release substrate 202 is separated from the thin film photovoltaic device 204, the sacrificial layer forms an interface that is selectively destroyed.

[0180] In a method of producing a tandem photovoltaic cell, as represented by arrow 250, the thin film photovoltaic device 204 is transferred to the bottom photovoltaic sub-cell 212, which can be a silicon photovoltaic cell. Thus, the thin film photovoltaic device 204 is adhered to the bottom sub-cell 212 by (i) contacting the second transparent conductive layer 222 with the receiving surface of the bottom sub-cell 212, and (ii) thermally activating the transparent conductive adhesive in the second transparent conductive layer 222 to induce bonding. Optionally, this is accomplished by heat pressing the transferable photovoltaic device arrangement 200 onto the bottom photovoltaic sub-cell 212 at a suitable temperature and dwell time to fluidize or soften the heat-activatable adhesive polymer in the transparent conductive adhesive. After the heat-activated bonding step, the thin film photovoltaic device 204 and the bottom photovoltaic sub-cell 212 are functionally coupled via the transparent conductive layer 222, which forms a recombinant layer or tunnel junction between the top and bottom sub-cells in the tandem photovoltaic cell 230.

[0181] The transfer method 250 also includes the step of separating the flexible release substrate 202 from the thin film photovoltaic device 204. The separation step involves (i) thermally activating the heat-activatable adhesive in the sacrificial layer 206 to reduce its cohesive force, and (ii) peeling the flexible release substrate 202 to gradually destroy the activated sacrificial layer. Optionally, the heat activation is performed while the transferable photovoltaic device arrangement 200 is heat pressed onto the bottom photovoltaic sub-cell 212, so that the flexible release substrate 202 is separated almost simultaneously with the thin film photovoltaic device 204 adhering to the bottom photovoltaic sub-cell 212. This can be done in a roll lamination process, as described herein with reference to Figure 6 as described.

[0182] After the separation step, the tandem photovoltaic cell 230 has a transparent conductive layer 208 at the outer conductive surface 224 through which current can be drawn when the tandem photovoltaic cell 230 is in operation. Because the sacrificial layer 206 is a very thin layer (and optionally conductive), any residue 206a remaining on the transparent conductive layer 208 has an acceptably low impact on the conductivity of the outer conductive surface 224.

[0183] Another embodiment of the present invention will refer to Figure 3 300. The transferable photovoltaic device arrangement 300 includes a flexible release substrate 302 on which a thin film photovoltaic device 304 is located. The flexible release substrate 302 includes a flexible polymer film 303 (such as PET) coated with a non-stick coating 306 (a low surface energy polymer such as a siloxane polymer). The thin film photovoltaic device 304 includes the following functional layers in sequence: a first transparent conductive layer 308, a charge transport layer 326, a photoactive layer 310, a charge transport layer 328, and a second transparent conductive layer 322. The second transparent conductive layer 322 includes an activatable transparent conductive adhesive as disclosed herein.

[0184] The first transparent conductive layer 308 is in direct contact with the non-stick coating 306 , thereby forming an interface that is selectively destroyed when the flexible substrate 302 is separated from the thin-film photovoltaic device 304 in the adhesion and separation method step indicated by arrow 350 .

[0185] In a method of producing a tandem photovoltaic cell, thin film photovoltaic device 304 is transferred to bottom photovoltaic sub-cell 312, which may be a silicon photovoltaic cell, as represented by arrow 350. Thus, thin film photovoltaic device 304 is adhered to bottom sub-cell 312 by (i) contacting second transparent conductive layer 322 with a receiving surface of bottom sub-cell 312, and (ii) activating a transparent conductive adhesive in second transparent conductive layer 322 to induce adhesion, such as using heat or radiation. Optionally, activation is performed while pressing transferable photovoltaic device arrangement 300 onto bottom photovoltaic sub-cell 312.

[0186] The transfer method 350 also includes the step of separating the flexible release substrate 302 from the thin film photovoltaic device 304. The separation step simply involves peeling off the flexible substrate 302 to gradually break the interface between the non-stick coating 306 and the first transparent conductive layer 308. The flexible substrate 302 can be separated almost simultaneously with the thin film photovoltaic device 304 being adhered to the bottom photovoltaic sub-cell 312, for example in a roll lamination process, as described herein with reference to Figure 6 as described.

[0187] Another embodiment of the present invention will refer to Figure 4 4. The transferable photovoltaic device arrangement 400 includes a flexible release substrate 402 on which a thin film photovoltaic device 404 is located. The flexible release substrate 402 can be a flexible polymer film, such as PET. The thin film photovoltaic device 404 includes the following functional layers in sequence: a first transparent conductive layer 408, a charge transport layer 426, a photoactive layer 410, a charge transport layer 428, and a second transparent conductive layer 422. The second transparent conductive layer 422 includes a heat-activatable transparent conductive adhesive, as disclosed herein.

[0188] The first transparent conductive layer 408 is in direct contact with the flexible release substrate 402, thereby forming an interface that is selectively destroyed when the flexible substrate 402 is separated from the thin film photovoltaic device 404 in the bonding and separation method steps indicated by arrow 450. The first transparent conductive layer 408 includes a heat-activatable adhesive (e.g., a thermoplastic polymer) and a conductive component, which can be a metal, a metal oxide, or a conductive polymer or polymer composite material (such as, PEDOT:PSS) as appropriate.

[0189] In the method of producing a tandem photovoltaic cell, the thin film photovoltaic device 404 is transferred to the bottom photovoltaic sub-cell 412, which can be a silicon photovoltaic cell, as represented by arrow 450. Thus, the thin film photovoltaic device 404 is adhered to the bottom sub-cell 412 by (i) contacting the second transparent conductive layer 422 with the receiving surface of the bottom sub-cell 412, and (ii) thermally activating the transparent conductive adhesive in the second transparent conductive layer 422 to induce adhesion. Optionally, this is accomplished by heat pressing the transferable photovoltaic device arrangement 400 onto the bottom photovoltaic sub-cell 412 at a suitable temperature and dwell time to fluidize or soften the heat-activatable adhesive polymer in the transparent conductive adhesive.

[0190] The transfer method 450 also includes the step of separating the flexible release substrate 402 from the thin film photovoltaic device 404. The separation step involves (i) thermally activating the heat-activatable adhesive in the first transparent conductive layer 408 to release (debond) the flexible release substrate, and (ii) peeling the flexible release substrate 402 to gradually destroy the interface. Optionally, the heat activation is performed while the transferable photovoltaic device arrangement 400 is heat pressed onto the bottom photovoltaic sub-cell 412, so that the flexible release substrate 402 is separated almost simultaneously with the thin film photovoltaic device 404 adhering to the bottom photovoltaic sub-cell 412. This can be done in a roll lamination process, as described herein with reference to Figure 6 as described.

[0191] Example

[0192] The present invention will be described with reference to the following examples. It should be understood that these examples are only for illustration and not for limiting the invention described herein.

[0193] Materials and processes.

[0194] The solution processed films were made using a custom roll-to-roll slot die coater (slot die equipped with a 50 μm shim). The machine was designed to handle narrow (25 mm wide) films to minimize material usage for the study. The sheet resistance of the films was tested using a Jandel RM3000 four-point probe system.

[0195] Example 1. Transferable photovoltaic devices on non-stick surfaces

[0196] A transparent conductive layer was produced by coating a commercial 1% PEDOT:PSS aqueous solution (S315, Agfa) onto a roll of 25 mm wide, 50 micron thick PET film coated with a non-stick silicone release layer (FRA 319, Fox River) through a roll-to-roll slot die coating. Aqueous solutions (including PEDOT:PSS aqueous solutions) easily dewet on non-stick, low surface energy surfaces, in which case no continuous layer is formed. Therefore, the PEDOT:PSS solution was deposited onto a substrate on a heated stage (80°C) to alleviate the dewetting problem by reducing the surface tension of the solution and accelerating solvent evaporation. An air knife (10 L / min) was also used to promote solvent evaporation before dewetting occurred. The PEDOT:PSS solution was heated at 3.8 μl / cm 2 A loading of 1000 μm (wet film thickness was therefore approximately 38 μm) was deposited in a continuous strip 13 mm wide at a speed of 0.3 m / min and dried at 130° C. for 30 seconds.

[0197] Then, a commercial ZnO solution (2.8% in 2-propanol, InfityPV) was coated on the dried PEDOT:PSS film by roll-to-roll slot die coating to form an electron transport layer on the first transparent conductive layer. The ZnO solution was coated at 0.5 μl / cm 2 A loading of 500 Å (wet film thickness was therefore approximately 5 microns) was deposited in a continuous strip 13 mm wide at a speed of 0.3 m / min on top of the PEDOT:PSS strip and dried at 130° C. for 30 seconds.

[0198] The photoactive layer was then produced by coating the electron transport layer with a solution consisting of 8 mg PBF-QxF and 12 mg Y6 per 1 ml dichlorobenzene by roll-to-roll slot die coating. The solution was deposited on top of the ZnO strips in a continuous strip 7 mm wide while the substrate was placed on a heated stage (130 °C) with a loading of 2 μl / cm 2 (The wet film thickness is therefore approximately 20 microns and the dry film thickness is approximately 260 nanometers) at a speed of 0.3 m / min.

[0199] The separability of the multilayer photovoltaic device including a transparent conductive layer, an electron transport layer, and a photoactive layer from a release substrate was investigated by a simple tape peel test (also known as the Scotch tape test). It was observed that the device selectively separated at the interface between the transparent conductive layer and the non-stick coating of the release layer, so that the multilayer photovoltaic device was transferred to the tape intact.

[0200] Example 2. Transferable Photovoltaic Device with Sacrificial Layer

[0201] The coating composition for preparing the sacrificial layer was prepared by mixing 10 ml of a commercial 1.3-1.7% aqueous PEDOT:PSS solution (Clevios AI 4083, Heraeus), 200 mg of polyethylene oxide (PEO), a water-soluble low melting point polymer (molecular weight 100 000 Dalton, melting point 65°C) and 10 ml of 2-propanol. The sacrificial layer was produced by applying the mixture to a roll of uncoated polyethylene terephthalate (PET) film by roll-to-roll slot die coating. The mixture was deposited in a 25 mm wide continuous strip at room temperature with a solution loading of 1 μl / cm2 (wet film thickness was therefore approximately 10 microns) and then dried at 130°C for 30 seconds. The dried film, which was non-sticky at room temperature, became soft and sticky when heated to above 80°C. In the Scotch tape test, the tape adhered firmly at room temperature but was easily peeled off when heated to 80°C. Based on visual inspection, residual sacrificial layer was still present on the PET film after peeling.

[0202] Then, a commercial 1% PEDOT:PSS aqueous solution (S315, Agfa) was applied to the sacrificial layer by roll-to-roll slot die coating to produce a transparent conductive layer. The PEDOT:PSS solution was heated at 3.8 μl / cm 2 A loading of 1000 Å (wet film thickness was therefore approximately 38 microns) was deposited in a continuous strip 13 mm wide at a speed of 0.3 m / min and dried at 130° C. for 30 seconds. The sheet resistance of the transparent conductive layer was approximately 80 ohm / sq.

[0203] The photoactive layer was then produced by coating the transparent conductive layer with a solution consisting of 8 mg PBF-QxF and 12 mg Y6 per 1 ml dichlorobenzene by roll-to-roll slot die coating. The solution was deposited on top of the PEDOT:PSS strip in a 7 mm wide continuous strip while the substrate was placed on a heated stage (130 °C) with a loading of 2 μl / cm 2 (The wet film thickness is therefore approximately 20 microns and the dry film thickness is approximately 260 nanometers) at a speed of 0.3 m / min.

[0204] The separability of the multilayer photovoltaic device including the transparent conductive layer and the photoactive layer from the release substrate was studied by Scotch tape test at 80°C. The device was easily separated from the PET substrate via the destruction of the heat-activated sacrificial layer. The sheet resistance of the transparent conductive layer exposed after removing the PET film was about 90-100 ohm / sq.

[0205] PEDOT:PSS is included in the sacrificial layer for several reasons. First, it overcomes the dewetting problem encountered when a roll-to-roll slot die coats a PEO-only solution. Second, it is believed that including conductive PEDOT:PSS can mitigate the effects of sacrificial layer residues on the conductivity of the transparent conductive layer.

[0206] Example 3. Transfer of photovoltaic devices by bonding with a transparent conductive adhesive and removal of the release substrate

[0207] A coating composition for preparing a separation sacrificial layer was prepared by dissolving 2 grams of ethylene vinyl acetate in 40 ml of xylene and stirring at 50° C. for 30 minutes. This solution was applied to a roll of uncoated polyethylene terephthalate (PET) film by roll-to-roll slot die coating to produce a sacrificial layer. The mixture was deposited as a 25 mm wide continuous strip at 90° C. with a solution loading of 0.8 μl / cm2 (wet film thickness was therefore approximately 8 microns) and then dried with hot air at 80° C. for 30 seconds. The dry film, which was non-sticky at room temperature, became soft and sticky when heated above 90° C.

[0208] Then, a commercial 1% PEDOT:PSS aqueous solution (S315, Agfa) was applied to the sacrificial layer by roll-to-roll slot die coating to produce a transparent conductive layer. The PEDOT:PSS solution was deposited on a 25 mm wide PET film at a speed of 0.3 m / min at a width of 13 mm with a loading of 3.3 μl / cm2 (the wet film thickness was therefore approximately 33 microns) and dried at 90°C for 2 minutes. The relatively low drying temperature was chosen to avoid melting the sacrificial layer before the conductive layer solidified.

[0209] Then, a commercial ZnO nanoparticle solution (Infinity PV, 2.8 wt% in 2-propanol) was coated at a speed of 0.2 m / min at 0.58 μl / cm 2 A loading of 1000 μm (wet film thickness was therefore approximately 5.8 μm) was applied to the transparent conductive layer to create an electron transport layer. The film was then blow dried with hot air at 90° C. for 2 minutes.

[0210] A coating composition for preparing a perovskite photoactive layer was prepared by mixing 21.5 mg of formamidine iodide, 139.1 mg of methylammonium iodide, 5.6 mg of methylammonium bromide, 507 mg of lead iodide and 1 ml of acetonitrile. Methylamine gas was introduced until the solution became clear. The perovskite precursor solution was then applied to the electron transport layer at a loading of 0.58 μl / cm2 (the wet film thickness was therefore approximately 5.8 microns) at a speed of 0.6 m / min by roll-to-roll slot die coating.

[0211] like Figure 7 As schematically depicted in , the resulting transferable photovoltaic device arrangement 700 includes a PET flexible release substrate 702 , a heat-activatable low cohesion sacrificial layer 704 , a PEDOT:PSS transparent conductive layer 706 , a ZnO electron transport layer 708 , and a perovskite photoactive layer 710 .

[0212] Then use the following method ( Figure 7 The method 701 schematically depicted in FIG. 701 uses a transferable photovoltaic device arrangement 700 to transfer a thin film photovoltaic device to a conductive substrate (Solutia OC50 substrate) comprising a PET film 712 coated with an indium tin oxide (ITO) layer 714. A transparent conductive adhesive (3M, conductive adhesive transfer tape) layer 716 (25 mm wide) is applied to the ITO layer 714 by manual lamination. The ITO-coated PET film is then placed on a hot stage (110° C.) and the transferable photovoltaic device arrangement 700 is manually laminated thereto such that the perovskite photoactive layer 710 adheres to the ITO layer 714 via the transparent conductive adhesive layer 716. Subsequently, the PET flexible release substrate 702 is immediately peeled off, leaving a thin film photovoltaic device comprising layers 706, 708, and 710, which are adhered to the conductive substrate via the transparent conductive interlayer 716, and the PEDOT:PSS transparent conductive layer 706 is exposed at the outer surface. The thin film photovoltaic device is cleanly separated from the PET flexible release substrate 702 via the destruction of the heat activated sacrificial layer 704 .

[0213] Those skilled in the art will appreciate that the invention described herein may have other variations and modifications in addition to those specifically described. It should be understood that the present invention includes all such variations and modifications that fall within the spirit and scope of the present invention.

Claims

1. A transferable photovoltaic device arrangement for transferring a thin film photovoltaic device to a bottom photovoltaic sub-cell to produce a tandem photovoltaic cell, the transferable photovoltaic device arrangement comprising: a flexible release substrate; as well as A thin film photovoltaic device comprising (i) a first transparent conductive layer located on the flexible release substrate and (ii) a photoactive layer located on the first transparent conductive layer, wherein the first transparent conductive layer is a solution-processed layer comprising at least one selected from a conductive polymer or polymer composite, an activatable adhesive and an organic binder, and Wherein after adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell with a transparent conductive adhesive, the flexible release substrate can be separated from the thin film photovoltaic device to expose the first transparent conductive layer at the outer conductive surface of the thin film photovoltaic device.

2. The transferable photovoltaic device arrangement of claim 1, wherein the first transparent conductive layer comprises a first activatable adhesive, wherein the flexible release substrate is detachable from the thin film photovoltaic device when the first activatable adhesive is activated.

3. The transferable photovoltaic device arrangement of claim 2, wherein the first activatable adhesive is a heat-activatable adhesive polymer.

4. The transferable photovoltaic device arrangement of claim 1, wherein the flexible release substrate comprises a non-stick surface, wherein the flexible release substrate is separable from the thin film photovoltaic device by delaminating the first transparent conductive layer from the non-stick surface.

5. The transferable photovoltaic device arrangement of claim 4, wherein the non-stick surface is a surface of a non-stick coating on the flexible release substrate.

6. The transferable photovoltaic device arrangement of claim 5, wherein the non-stick coating comprises a low surface energy polymer selected from the group consisting of fluorinated polymers and silicone polymers.

7. The transferable photovoltaic device arrangement according to claim 1 comprises a low cohesion sacrificial layer between the flexible release substrate and the first transparent conductive layer, wherein the low cohesion sacrificial layer has an inherent low cohesion or has a low cohesion when activated, so that the flexible release substrate can be separated from the thin film photovoltaic device by destroying the low cohesion sacrificial layer.

8. A transferable photovoltaic device arrangement according to claim 6, wherein the low cohesion sacrificial layer comprises a third activatable adhesive, and the flexible release substrate can be separated from the thin film photovoltaic device by (i) activating the third activatable adhesive by heat or radiation and (ii) destroying the low cohesion sacrificial layer.

9. A transferable photovoltaic device arrangement according to claim 7 or 8, wherein the low cohesion sacrificial layer is conductive.

10. A transferable photovoltaic device arrangement according to any one of claims 7 to 9, wherein the low cohesion sacrificial layer has a thickness of less than 100 nm.

11. A transferable photovoltaic device arrangement according to any one of claims 1 to 10, wherein the thin film photovoltaic device further comprises (iii) a second transparent conductive layer located above the photoactive layer, wherein the second transparent conductive layer comprises a transparent conductive adhesive for adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell.

12. The transferable photovoltaic device arrangement of claim 11, wherein the transparent conductive adhesive comprises a second activatable adhesive, wherein the second transparent conductive layer adheres to the bottom photovoltaic sub-cell when the second activatable adhesive is activated.

13. The transportable photovoltaic device arrangement of claim 12, wherein the second activatable adhesive irreversibly cures via a covalent bond forming reaction when activated.

14. The transferable photovoltaic device arrangement of any one of claims 11 to 13, wherein the transparent conductive adhesive is heat activatable at a temperature sufficient to release the flexible release substrate from the thin film photovoltaic device.

15. A transferable photovoltaic device arrangement according to any one of claims 11 to 14, wherein the first transparent conductive layer comprises a first heat-activatable adhesive polymer and the second transparent conductive layer comprises a second heat-activatable adhesive polymer, wherein the second heat-activatable adhesive polymer has a higher melting point than the first heat-activatable adhesive polymer.

16. A transferable photovoltaic device arrangement according to any one of claims 1 to 15, wherein the photoactive layer is a photoactive perovskite layer.

17. The transferable photovoltaic device arrangement according to any one of claims 1 to 16, configured as a roll for a roll lamination process, wherein the thin film photovoltaic device is pressed onto the bottom photovoltaic sub-cell and the flexible release substrate is separated from the thin film photovoltaic device.

18. A tandem photovoltaic cell arrangement comprising a bottom photovoltaic sub-cell and a transferable photovoltaic device arrangement according to any one of claims 1 to 17, wherein the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell via a second transparent conductive layer comprising a transparent conductive adhesive.

19. A method of producing a transferable photovoltaic device arrangement, the method comprising: providing a flexible release substrate; as well as By successively forming (i) a first transparent conductive layer on the flexible release substrate; and (ii) a photoactive layer on top of the first transparent conductive layer to produce a thin film photovoltaic device on the flexible release substrate, wherein the first transparent conductive layer is formed by solution processing and comprises at least one selected from a conductive polymer or polymer composite, an activatable adhesive and an organic binder, and Wherein the flexible release substrate can be separated from the thin film photovoltaic device to expose the first transparent conductive layer at the outer conductive surface of the thin film photovoltaic device.

20. The method of claim 19, wherein forming the first transparent conductive layer on the flexible release substrate comprises applying a first fluid composition comprising a first conductive component or a reactive precursor thereof to form a wet film on the flexible release substrate; and curing the wet film to form the first transparent conductive layer on the flexible release substrate.

21. A method according to claim 19 or claim 20, wherein the first fluid composition comprises a first activatable adhesive.

22. The method of claim 21, wherein the first activatable adhesive is a heat-activatable adhesive polymer, wherein the flexible release substrate is separable from the thin film photovoltaic device when the first transparent conductive layer is heated.

23. The method of claim 19 or claim 20, wherein the flexible release substrate comprises a non-stick surface and the first transparent conductive layer is formed directly on the non-stick surface.

24. The method of claim 19 or claim 20, wherein the flexible release substrate comprises a low cohesion sacrificial layer on a surface thereof and the first transparent conductive layer is formed directly on the low cohesion sacrificial layer.

25. The method of any one of claims 19 to 24, wherein producing the thin film photovoltaic device on the flexible release substrate further comprises forming (iii) a second transparent conductive layer above the photoactive layer, wherein the second transparent conductive layer comprises a transparent conductive adhesive for adhering the thin film photovoltaic device to a bottom photovoltaic sub-cell.

26. The method of claim 25, wherein forming the second transparent conductive layer comprises applying a second fluid composition comprising a second activatable adhesive and a second conductive component or a reactive precursor thereof to form a wet film over the photoactive layer; and curing the wet film to form the second transparent conductive layer.

27. The method according to any one of claims 19 to 26, wherein the flexible release substrate is configured as a roll and the thin film photovoltaic device is produced on the flexible release substrate by coating and / or printing steps in a roll-to-roll process.

28. A method of producing a tandem photovoltaic cell comprising: Providing a transferable photovoltaic device arrangement according to any one of claims 1 to 18, or a transferable photovoltaic device arrangement produced according to the method of any one of claims 19 to 27; adhering the thin film photovoltaic device of the transferable photovoltaic device arrangement to a bottom photovoltaic sub-cell with a transparent conductive adhesive, thereby coupling the thin film photovoltaic device to the bottom photovoltaic sub-cell via a second transparent conductive layer; and The flexible release substrate of the transferable photovoltaic device arrangement is separated from the thin film photovoltaic device, thereby producing a tandem photovoltaic cell having the first transparent conductive layer of the thin film photovoltaic device at an outer conductive surface.

29. The method of claim 28, wherein the bottom photovoltaic sub-cell is a silicon photovoltaic cell.

30. The method of claim 28 or claim 29, wherein the transferable photovoltaic device arrangement is configured as a roll, and wherein the thin film photovoltaic device is adhered to the bottom photovoltaic sub-cell and the flexible release substrate is separated from the thin film photovoltaic device in a roll lamination process.

31. The method of any one of claims 28 to 30, wherein adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell comprises activating the transparent conductive adhesive with heat, radiation, or chemical treatment.

32. The method of any one of claims 28 to 31, wherein adhering the thin film photovoltaic device to the bottom photovoltaic sub-cell comprises activating the transparent conductive adhesive with heat at a temperature sufficient to release the flexible release substrate from the thin film photovoltaic device.

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