Patent Description:
A photovoltaic device generates electrical power by converting light into electricity using semiconductor materials that exhibit the photovoltaic effect. Certain semiconductor materials are more efficient at absorbing particular ranges of the electromagnetic spectrum. To improve the overall efficiency of photovoltaic devices, the devices can incorporate stacked submodules, also referred to as subcells, utilizing semiconductor materials with differing absorptive properties to form a tandem photovoltaic device.

In an example tandem photovoltaic device, solar radiation or light enters through a top submodule and a portion of the radiation passes through the top submodule to a bottom submodule. The top submodule can absorb more higher-energy photons having a shorter wavelength, while the bottom submodule can absorb lower energy photons having a longer wavelength. An interlayer can be positioned between the top submodule and the bottom submodule. <CIT> and <CIT> describe an interlayer suitable for use in tandem photovoltaic devices.

Laboratory experiments measuring absorption efficiency at relevant spectral ranges for separate submodules have shown that there are promising submodules that might be used together to absorb a greater proportion of incident radiation. However, with the increased complexity of a tandem architecture, it can also be challenging to close the gap between actual and theoretical performance. A substantial challenge for producing tandem photovoltaic devices, with good efficiency and manufacturability, is in providing an interlayer having desired electrical, optical, physical, and thermal properties.

Accordingly, a need exists for alternative interlayer structures for use in tandem photovoltaic devices and for processes and materials useful in assembling tandem photovoltaic device architecture.

The present invention discloses a tandem photovoltaic device according to claim <NUM> and a method of making a tandem photovoltaic device according to claim <NUM>.

Tandem photovoltaic devices are provided that can include a first submodule, a second submodule, and an interlayer disposed between the first submodule and the second submodule. The interlayer can permit a portion of light to pass therethrough. The interlayer can include a first conformal layer, a second conformal layer, and a core layer. The first conformal layer can directly contact and conform to a portion of a surface of the first submodule. The first conformal layer can include a first polymer having a melting point less than about <NUM> degrees C. The second conformal layer can directly contact and conform to a portion of a surface of the second submodule. The second conformal layer can include a second polymer having a melting point less than about <NUM> degrees C. The core layer can be disposed between and in direct contact with the first conformal layer and the second conformal layer. The core layer can include a third polymer having a melting point greater than about <NUM> degrees C. Solar radiation or light can hence enter through the first submodule and a portion of the radiation can then pass through the first submodule and the interlayer to the second submodule. The interlayer can maintain a desired dielectric resistance between the first and second submodules. The interlayer can minimize voids or imperfections between surfaces of the first and second submodules to optimize an optical interface therebetween.

Ways of making and using tandem photovoltaic devices are provided that employ the interlayer of the present technology. A portion of a surface of a first submodule can be directly contacted with the first conformal layer. The first conformal layer can then be conformed to the portion of the surface of the first submodule. Likewise, a portion of a surface of a second submodule can be directly contacted with the second conformal layer. The second conformal layer can then be conformed to the portion of the surface of the second submodule. Various ways of contacting and conforming the interlayer with the first and second submodules are provided.

The following description of technology is merely exemplary in nature of the subject matter, manufacture and use of one or more inventions, and is not intended to limit the scope, application, or uses of any specific invention claimed in this application or in such other applications as may be filed claiming priority to this application, or patents issuing therefrom. Regarding methods disclosed, the order of the steps presented is exemplary in nature, and thus, the order of the steps can be different in various embodiments, including where certain steps can be simultaneously performed, unless expressly stated otherwise. "A" and "an" as used herein indicate "at least one" of the item is present; a plurality of such items may be present, when possible. Except where otherwise expressly indicated, all numerical quantities in this description are to be understood as modified by the word "about" and all geometric and spatial descriptors are to be understood as modified by the word "substantially" in describing the broadest scope of the technology. "About" when applied to numerical values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by "about" and/or "substantially" is not otherwise understood in the art with this ordinary meaning, then "about" and/or "substantially" as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters.

Unless otherwise specified, values for material properties correspond to conditions at normal temperature and pressure, <NUM> degrees C and <NUM> atmosphere pressure.

Unless specified otherwise, values for provided ranges are inclusive of endpoints and include all distinct values and further divided ranges within the entire range.

When an element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it may be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present.

These terms may be only used to distinguish one element, component, region, layer or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments.

The term "light" can refer to various wavelengths of the electromagnetic spectrum such as, but not limited to, wavelengths in the ultraviolet (UV), infrared (IR), and visible portions of the electromagnetic spectrum. "Sunlight," as used herein, refers to light emitted by the sun. As used herein, near-infrared (NIR) refers to wavelengths in a range of about <NUM> to <NUM>.

The term "layer" can refer to a thickness of material provided upon a surface. The layer can cover all or a portion of the surface. A layer may include sublayers and can have compositional gradients within a layer. A layer can include one or more functional layers of material.

The present technology relates to tandem photovoltaic devices that include a first submodule and a second submodule; however, it should be recognized that such tandem photovoltaic devices can include additional submodules as well as additional arrangements of submodules. In construction of the tandem photovoltaic devices, as provided herein, an interlayer is disposed between the first submodule and the second submodule, where the interlayer permits a portion of light to pass therethrough. In this way, a portion of light passing through the first submodule can further pass through the interlayer to the second submodule. The interlayer can be transparent to near-infrared wavelengths of light. Near-infrared light, incident on the front surface of the tandem device, can pass through the first submodule and interlayer for absorption in the second submodule. The interlayer can operate to maintain a desired dielectric resistance between the first and second submodules. The interlayer can further minimize voids or imperfections between surfaces of the first and second submodules to optimize an optical interface therebetween.

The tandem photovoltaic device can generate electrical power by converting light into direct current electricity using semiconductor materials that exhibit the photovoltaic effect. The photovoltaic effect generates electrical power upon exposure to light as photons are absorbed within the semiconductor material to excite electrons to a higher energy state. These excited electrons can move within the material, resulting in an electrical current. Semiconductor materials suitable for use in photovoltaic devices can include, for example, type II-VI materials - including cadmium telluride alloys, type III-V materials - including GaAs and InGaN, type I-III-VI materials - including CIGS and CIS materials, as well as silicon, and perovskites.

Tandem photovoltaic devices can achieve higher total conversion efficiency than single photovoltaic devices by capturing a larger portion of the solar spectrum. Tandem devices can be formed with more than one p-n junction and with materials having different band-gap properties responsive to different ranges of the electromagnetic spectrum, including infrared, visible, and ultraviolet light. In a device for which the primary light source is from above, a light-incident top cell, or upper submodule, can have a large band gap to capture energetic short wavelengths, such as visible and uv, while a bottom cell, or lower submodule, can use absorber materials having a smaller band gap to capture longer wavelengths and reflected photons, including near-infrared. A tandem device can have two or more stacked sub-cells or submodules, and each submodule can include active regions formed from semiconductor materials having different absorptive properties, including different types of semiconductor materials.

Submodules in a tandem photovoltaic device, as described herein, can be stacked and separated by the interlayer. Incident electromagnetic radiation, or light, enters the device through a front or top surface and enters the upper submodule. Light that is not absorbed by the upper submodule, reaches the interlayer. The interlayer can be configured to reflect some light energy, or photons, back into the upper submodule, and also transmit photons of the light to the back cell or lower submodule. In most tandem devices, it is beneficial for interlayer structures to be substantially transparent to spectral radiation wavelengths configured to be absorbed by the lower submodule. In photovoltaic devices having a plurality of stacked submodules, additional interlayers can be provided between each submodule. Tandem photovoltaic devices can include bifacial devices, configured to receive incident radiation through both front and rear surfaces. Bifacial tandem devices can be configured to receive direct solar radiation on a top or front surface and receive radiation reflected from external surfaces, including visible and infrared light, on a back or rear surface.

Interlayer structures can be exposed to stresses including high temperatures, ultraviolet radiation, mechanical stresses, and temperature fluctuations. Undesirably, in certain photovoltaic devices, these stresses can cause shorting between submodules across an interlayer, and can result in damage to the photovoltaic device. To prevent shorting, it is desirable for interlayer structures to have a suitable dielectric breakthrough strength to electrically separate the first and second submodules. To design efficient and reliable tandem photovoltaic devices, it is also desirable to prevent gaps or bubbles between the interlayer structure and bordering surfaces of the first and second submodules. In some tandem architectures, it can be desirable for the interlayer to have a refractive index suitable to transmit photons to the second submodule and/or reflect some photons back into the first submodule.

In a tandem photovoltaic module, the risk of shorting from one active surface of one submodule to an active surface of the other submodule is important. Electrical isolation between the active surfaces of the submodules maintains a minimum dielectric breakdown distance. At the same time, to make good contact for light transmission and to protect submodules from degradation, an encapsulant can be formed between the first and second submodules and around other system components. An interlayer structure that can both isolate and encapsulate surfaces of adjacent submodules is desirable. To achieve the desired properties, a method and structure is provided for an interlayer formed of a multilayered film having outer layers which provide the desired adhesion and encapsulation and a central core layer which maintains the desired dielectric and structural properties.

In certain embodiments, an interlayer is provided that includes a plurality of layers. The interlayer includes one or more core layers that each can have a high dielectric strength and be non-flowable at expected operating conditions of the tandem photovoltaic device, where the material of each core layer can have a high melting point. The interlayer structure includes an outer layer or a first conformal layer that is flowable with a low melting point. The interlayer structure can also include another outer layer or a second conformal layer, with the first and second conformal layers positioned on opposite sides of the core layer. The conformal layers can include layers of flowable polymer with a melting point less than <NUM> degrees C to conform to system components during lamination and operation at higher temperatures. The core layer comprises a non-flowable polymeric material with a melting point greater than <NUM> degrees C to sustain a dielectric and physical barrier that resists deformation and a narrowing of the dielectric breakdown distance. The interlayer structure, comprising a multi-layered film, provides dielectric resistance across a wide operating temperature range. The interlayer can therefore be configured as a transparent multilayered film for mechanically stacked multijunction solar cells that provides transparency, thermal stability, adhesive strength, moisture protection, prevents shorting, and maintains minimum dielectric breakdown distance between submodules separated by the interlayer. The interlayer can also prevent moisture permeation and can be used to or cooperate with other portions of the tandem photovoltaic device to electrically connect different system components.

Tandem photovoltaic devices constructed in accordance with the present technology can include a first submodule, a second submodule, and an interlayer disposed between the first submodule and the second submodule. The interlayer can permit a portion of light to pass therethrough. The interlayer can include a first conformal layer, a second conformal layer, and a core layer. The first conformal layer can directly contact and conform to a portion of a surface of the first submodule, where the first conformal layer includes a first polymer having a melting point less than about <NUM> degrees C. The second conformal layer direct contacts and conforms to a portion of a surface of the second submodule, where the second conformal layer includes a second polymer having a melting point less than about <NUM> degrees C. The core layer is disposed between and directly contacts the first conformal layer and the second conformal layer, where the core layer includes a third polymer having a melting point greater than about <NUM> degrees C. In certain embodiments, the third polymer can have a melting point greater than about <NUM> degrees C.

Interlayers, as provided herein, can include various aspects. For example, the interlayer can have a refractive index from about <NUM> to about <NUM>. In some embodiments, the interlayer has a refractive index greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In some embodiments, the interlayer has a refractive index in a range of <NUM> to <NUM>, a range of <NUM> to <NUM>, a range of <NUM> to <NUM>, or a range of <NUM> to <NUM>, for wavelengths in a range of <NUM> to <NUM>. Certain embodiments include where the interlayer has a refractive index of about <NUM>. Still further embodiments include where the interlayer has a refractive index of greater than about <NUM>. In this way, the interlayer can provide an optical interface allowing effective transmission of light passing through one submodule to another submodule. The interlayer can also exhibit a dielectric strength greater than <NUM> kV/mm. The opportunity for any electrical shorting between submodules is therefore minimized. Embodiments of the interlayer can have a thickness from about <NUM> to about <NUM>, which can include the total thickness of the first and second conformal layers and the core layer. The interlayer can permit a portion of near-infrared light to pass therethrough. The interlayer can be configured to transmit at least <NUM>% of light having a wavelength from <NUM> to <NUM>. The interlayer can be configured to transmit at least <NUM>% of light having a wavelength from about <NUM> to about <NUM>. In some embodiments, the interlayer can permit a portion of visible light to pass therethrough. The interlayer can be further configured to transmit at least <NUM>% of light having a wavelength from about <NUM> to about <NUM> that passes therethrough. Certain embodiments of the interlayer can have a light transmission of at least <NUM>% for wavelengths from <NUM> to <NUM>. Still further embodiments of the interlayer can have a light transmission of at least <NUM>% at <NUM>.

Polymers used in forming the first and second conformal layers and core layer of the interlayer can include various aspects. The first polymer and the second polymer of the respective first and second conformal layers can independently include one or more of: polyethylene; ethylene-vinyl acetate; polyolefin elastomer (POE); pressure sensitive adhesive; hot-melt adhesive; polyvinyl butyral; thermoplastic polyurethane; silicone; silicone/polyurethane hybrid; ionomer; UV-curable resin; ethylene tetrafluoroethylene (e.g., Tefzel), polyvinyl fluoride (e.g., Tedlar), fluoroplastic of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (e.g., THV220); and polyethylene naphthalate. Certain embodiments include where the first polymer and the second polymer comprise the same material. The third polymer of the core layer can include one or more of oriented polyethylene terephthalate, polytetrafluoroethylene, polycyclooctene, biaxially-oriented polyethylene terephthalate (boPET), and polyimide.

Various layers of the interlayer can have various thicknesses. The first conformal layer and the second conformal layer can have different thicknesses. The conformal layers can operate as adhesives as well as encapsulants. When the polymers of the conformal layers are substantially at their respective melting points, the conformal layers can flow and spread across portions of the surfaces of the respective submodules.

The core layer can include various aspects. The core layer can have a thickness from about <NUM> to about <NUM>. Embodiments of the core layer can also have a dielectric strength greater than about <NUM> kV/mm. The one or more polymers of the core layer can be selected to have melting points above the expected operating temperature of the tandem photovoltaic device. In this way, integrity of the core layer can be maintained during operation of the tandem photovoltaic device, including where the core layer maintains a desired thickness and provides a desired dielectric strength between submodules during operation of the tandem photovoltaic device.

Certain embodiments of the interlayer can include where the first and second conformal layers have thicknesses of <NUM>, the core layer has a thickness of <NUM>, and the third polymer of the core layer includes biaxially-oriented polyethylene terephthalate.

Certain embodiments of the tandem photovoltaic device include a first submodule, a second submodule, and an interlayer disposed between the first submodule and the second submodule. The interlayer is configured to permit a portion of light to pass therethrough, have a refractive index from about <NUM> to about <NUM>, a dielectric strength greater than about <NUM> kV/mm, and a thickness from about <NUM> to about <NUM>. The interlayer includes a first conformal layer, a second conformal layer, and a core layer. The first conformal layer directly contacts and conforms to a portion of a surface of the first submodule, where the first conformal layer includes a first polymer having a melting point less than about <NUM> degrees C, and the first polymer includes a member selected from a group consisting of: polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof. The second conformal layer directly contacts and conforms to a portion of a surface of the second submodule, where the second conformal layer includes a second polymer having a melting point less than about <NUM> degrees C, and the second polymer includes a member selected from a group consisting of: polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof. The core layer is disposed between and directly contacts the first conformal layer and the second conformal layer, where the core layer has a dielectric strength greater than about <NUM> kV/mm and includes a third polymer having a melting point greater than about <NUM> degrees C. The third polymer includes a member selected from a group consisting of: polyethylene terephthalate (PET), oriented polyethylene terephthalate; polytetrafluoroethylene; polycyclooctene; biaxially-oriented polyethylene terephthalate; polyimide; and combinations thereof.

The present technology further provides various methods of making a tandem photovoltaic device. Such methods include providing an interlayer as described herein. A portion of a surface of a first submodule can be directly contacted with the first conformal layer of the interlayer. The first conformal layer can be conformed to the portion of the surface of the first submodule. A portion of a surface of a second submodule can be directly contacted with the second conformal layer of the interlayer. The second conformal layer can be conformed to the portion of the surface of the second submodule. In this way, the core layer can electrically connect two submodules, in certain embodiments, along with preventing moisture ingress into the tandem photovoltaic device.

Provision of the interlayer can take various forms. Certain embodiments include where the core layer is laminated between the first conformal layer and the second conformal layer to provide the interlayer. Likewise, the core layer can be extruded between the first conformal layer and the second conformal layer to provide the interlayer. Other means by which to form the interlayer include hot melt, deposition of one or more layers, and coextrusion of more than one layer thereof.

The methods of making tandem photovoltaic devices can include various aspects. Conforming the first conformal layer to the portion of the surface of the first submodule can include heating the first conformal layer to at least the melting point of the first polymer. Conforming the second conformal layer to the portion of the surface of the second submodule can also include heating the second conformal layer to at least the melting point of the second polymer. It is also possible that one of the portion of the surface of the first submodule and the first conformal layer can be heated to at least the melting point of the first polymer prior to directly contacting the portion of the surface of the first submodule with the first conformal layer, and one of the portion of the surface of the second submodule and the second conformal layer can be heated to at least the melting point of the second polymer prior to directly contacting the portion of the surface of the second submodule with the second conformal layer.

Certain methods can include where conforming the first conformal layer to the portion of the surface of the first submodule and conforming the first conformal layer to the portion of the surface of the first submodule can include simultaneously heating the first submodule, the interlayer, and the second submodule to at least the melting point of the first polymer and at least the melting point of the second polymer following directly contacting the portion of the surface of the first submodule with the first conformal layer and directly contacting the portion of the surface of the second submodule with the second conformal layer. It is also possible to have conforming of the first conformal layer to the portion of the surface of the first submodule to include pressing the interlayer and the first submodule together, or to have conforming the second conformal layer to the portion of the surface of the second submodule to include pressing the interlayer and the second submodule together. Embodiment of methods can further include where conforming the first conformal layer to the portion of the surface of the first submodule and conforming the first conformal layer to the portion of the surface of the first submodule include pressing the interlayer between the first submodule and the second submodule.

In certain embodiments, a precursor to the interlayer can be formed as a contiguous sheet having a plurality of layers including a core layer disposed between a first conformal layer and second conformal layer. The precursor can be placed between a first submodule and a second submodule to form an unbonded tandem photovoltaic device. The unbonded tandem photovoltaic device is subjected to a lamination heat treatment sufficient for the first conformal layer and second conformal layer to flow and bond with the respective adjacent submodules and form a bonded tandem photovoltaic device. At least portions of the respective conformal layers melt during lamination to achieve desired wettability and adhesion of the interlayer to the respective submodules, while the core layer does not melt during lamination and maintains a physical and electrical barrier between the submodules. After the lamination, the interlayer physically and electrically isolates the active surfaces of the submodules in the tandem photovoltaic device. The bonded tandem photovoltaic device can be subjected to finishing processing steps, such as adding further encapsulation layers, bussing, etc. to produce a finished tandem photovoltaic device.

Aspects of the present technology can apply in various combinations, interdependencies, and multiple dependencies, as set forth in the following instances, examples, and embodiments.

In an embodiment, a tandem photovoltaic device comprises a first submodule; a second submodule; and an interlayer disposed between the first submodule and the second submodule, wherein the interlayer permits a portion of light to pass therethrough, the interlayer including: a first conformal layer directly contacting and conforming to a portion of a surface of the first submodule, the first conformal layer including a first polymer having a melting point less than about <NUM> degrees C; a second conformal layer directly contacting and conforming to a portion of a surface of the second submodule, the second conformal layer including a second polymer having a melting point less than about <NUM> degrees C; a core layer disposed between and directly contacting the first conformal layer and the second conformal layer, the core layer including a third polymer having a melting point greater than about <NUM> degrees C.

In some instances, the interlayer has a refractive index from about <NUM> to about <NUM>.

In some instances, the interlayer has a dielectric strength greater than about <NUM> kV/mm.

In some instances, the interlayer has a thickness from about <NUM> to about <NUM>.

In some instances, the interlayer is configured to transmit at least <NUM>% of incident light having a wavelength from <NUM> to <NUM>.

In the invention, the first polymer and the second polymer independently include a member selected from a group consisting of: polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof. In some instances, the first polymer consists essentially of polyolefin elastomer.

In some instances, the first polymer and the second polymer comprise the same material. In some instances, the first polymer and the second polymer consist essentially of, or consist of, the same material.

In the invention, the third polymer includes a member selected from a group consisting of: polyethylene terephthalate, oriented polyethylene terephthalate; polytetrafluoroethylene; polycyclooctene; biaxially-oriented polyethylene terephthalate; polyimide; and combinations thereof. In some instances, the core layer consists essentially of polyethylene terephthalate.

In some instances, the core layer has a thickness from <NUM> to <NUM>.

In some instances, the core layer has a dielectric strength greater than <NUM> kV/mm.

In some instances, the first conformal layer and the second conformal layer have different thicknesses.

In some instances, the first conformal layer has a thickness of about <NUM>, the second conformal layer has a thicknesses of <NUM>, the core layer has a thickness of <NUM>, and the third polymer of the core layer includes biaxially-oriented polyethylene terephthalate.

According to the embodiments provided herein, a tandem photovoltaic device can include a first submodule; a second submodule; an interlayer disposed between the first submodule and the second submodule, wherein the interlayer permits a portion of light to pass therethrough, has a refractive index from about <NUM> to about <NUM>, a dielectric strength greater than about <NUM> kV/mm, a thickness from about <NUM> to about <NUM>, the interlayer including: a first conformal layer directly contacting and conforming to a portion of a surface of the first submodule, the first conformal layer including a first polymer having a melting point less than about <NUM> degrees C, wherein the first polymer includes a member selected from a group consisting of: polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof; a second conformal layer directly contacting and conforming to a portion of a surface of the second submodule, the second conformal layer including a second polymer having a melting point less than about <NUM> degrees C, wherein the second polymer includes a member selected from a group consisting of: polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof; a core layer disposed between and directly contacting the first conformal layer and the second conformal layer, the core layer having a dielectric strength greater than about <NUM> kV/mm, the core layer including a third polymer having a melting point greater than about <NUM> degrees C, wherein the third polymer includes a member selected from a group consisting of: oriented polyethylene terephthalate; polytetrafluoroethylene; polycyclooctene; biaxially-oriented polyethylene terephthalate; polyimide; and combinations thereof.

According to the embodiments of the present disclosure, a method of making a tandem photovoltaic device, can include: providing an interlayer, wherein the interlayer permits a portion of light to pass therethrough, the interlayer including: a first conformal layer including a first polymer having a melting point less than about <NUM> degrees C; a second conformal layer including a second polymer having a melting point less than about <NUM> degrees C; a core layer disposed between and directly contacting the first conformal layer and the second conformal layer, the core layer including a third polymer having a melting point greater than about <NUM> degrees C; directly contacting a portion of a surface of a first submodule with the first conformal layer; conforming the first conformal layer to the portion of the surface of the first submodule; directly contacting a portion of a surface of a second submodule with the second conformal layer; and conforming the second conformal layer to the portion of the surface of the second submodule.

In some instances, the method further comprises laminating the core layer between the first conformal layer and the second conformal layer to provide the interlayer.

In some instances, the method further comprises coextruding the core layer between the first conformal layer and the second conformal layer to provide the interlayer.

In some instances, the step of conforming the first conformal layer to the portion of the surface of the first submodule includes heating the first conformal layer to at least the melting point of the first polymer. In some instances, the step of conforming the second conformal layer to the portion of the surface of the second submodule includes heating the second conformal layer to at least the melting point of the second polymer.

In some embodiments, one of the portion of the surface of the first submodule and the first conformal layer is heated to at least the melting point of the first polymer prior to directly contacting the portion of the surface of the first submodule with the first conformal layer; and one of the portion of the surface of the second submodule and the second conformal layer is heated to at least the melting point of the second polymer prior to directly contacting the portion of the surface of the second submodule with the second conformal layer.

In some embodiments, methods can include conforming the first conformal layer to the portion of the surface of the first submodule and conforming the second conformal layer to the portion of the surface of the second submodule, and simultaneously heating the first submodule, the interlayer, and the second submodule to at least the melting point of the first polymer and at least the melting point of the second polymer following directly contacting the portion of the surface of the first submodule with the first conformal layer and directly contacting the portion of the surface of the second submodule with the second conformal layer.

In some embodiments, methods can include conforming the first conformal layer to the portion of the surface of the first submodule includes pressing the interlayer and the first submodule together; or conforming the second conformal layer to the portion of the surface of the second submodule includes pressing the interlayer and the second submodule together.

In some embodiments, methods can include conforming the first conformal layer to the portion of the surface of the first submodule and conforming the second conformal layer to the portion of the surface of the second submodule include pressing the interlayer between the first submodule and the second submodule.

Example embodiments of the present technology are provided with reference to the several figures enclosed herewith.

With reference to <FIG> & <FIG>, an embodiment of a tandem photovoltaic device <NUM> is shown. The tandem photovoltaic device <NUM> can be configured to receive light and transform light into electrical energy, as photons are absorbed from the light and transformed into electrical current via the photovoltaic effect. For sake of discussion and clarity, the tandem photovoltaic device <NUM> can define a front side <NUM> configured to face a primary light source such as, for example, the sun. Additionally, the tandem photovoltaic device <NUM> can also define a back side <NUM> offset from the front side <NUM> such as, for example, by a plurality of functional layers of material.

The tandem photovoltaic device <NUM> can have a first submodule <NUM>, a second submodule <NUM>, and an interlayer <NUM> therebetween. The first submodule <NUM> can also be termed a top cell or upper submodule. The second submodule <NUM> can also be termed a bottom cell or lower submodule. The interlayer <NUM>, can also be termed an interlayer stack, a dielectric stack, or a transparent coupling layer. Each of the first submodule <NUM>, the second submodule <NUM>, and the interlayer <NUM> can comprise a plurality of layers. Each of the first and second submodules <NUM>, <NUM> of the tandem photovoltaic device <NUM> can include one or more absorber layers for converting light into charge carriers, and conductive layers for collecting the charge carriers.

The first submodule <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the tandem photovoltaic device <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the photovoltaic device <NUM>. The interlayer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the photovoltaic device <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the photovoltaic device <NUM>. The second submodule <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the photovoltaic device <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the photovoltaic device <NUM>.

As depicted in <FIG>, incident light (hv) <NUM> can enter the front side <NUM> of the tandem photovoltaic device <NUM> through the first submodule <NUM> and a first portion <NUM> of light energy can be absorbed by the first submodule <NUM> and a remaining portion <NUM> of light energy can pass through the first submodule <NUM> to the interlayer <NUM>. At the interlayer <NUM>, reflected light <NUM> can be directed back toward the absorptive region of the first submodule <NUM> and transmitted light <NUM> can pass to the second submodule <NUM>. Optionally, in a bifacial tandem device, back side light energy <NUM> can enter the back side <NUM> of the tandem photovoltaic device <NUM> toward the second submodule <NUM>. In many implementations, back side light energy <NUM> can include externally reflected visible light and near infrared light. The first submodule can absorb the first portion <NUM> of light energy, which can include an absorbed combination of the incident light <NUM> and the reflected light <NUM>. The second submodule can absorb a second portion <NUM> of light energy comprising the transmitted light <NUM> and, optionally, the back side light energy <NUM>.

Referring now to <FIG> & <FIG>, an example embodiment of the first submodule <NUM> of the tandem photovoltaic device <NUM> is shown. The first submodule <NUM> can include a plurality of layers disposed between the front side <NUM> and the back side <NUM>. In some embodiments, the layers of the first submodule <NUM> can be divided into an array of photovoltaic cells <NUM>. For example, the first submodule <NUM> can be scribed according to a plurality of serial scribes <NUM> and a plurality of parallel scribes <NUM>. The serial scribes <NUM> can extend along a length Y of the first submodule <NUM> and demarcate the photovoltaic cells <NUM> along the length Y of the first submodule <NUM>. Neighboring cells of the photovoltaic cells <NUM> can be serially connected along a width X of the first submodule <NUM>. In other words, a monolithic interconnect of the neighboring cells <NUM> can be formed; e.g., adjacent to the serial scribe <NUM>. The parallel scribes <NUM> can extend along the width X of the first submodule <NUM> and demarcate the photovoltaic cells <NUM> along the width X of the first submodule <NUM>. Under operation, current <NUM> can predominantly flow along the width X through the photovoltaic cells <NUM> serially connected by the serial scribes <NUM>. Under operation, parallel scribes <NUM> can limit the ability of current <NUM> to flow along the length Y. Parallel scribes <NUM> are optional and can be configured to separate the photovoltaic cells <NUM> that are connected serially into groups <NUM> arranged along length Y.

With particular reference to <FIG>, the parallel scribes <NUM> can electrically isolate the groups <NUM> of photovoltaic cells <NUM> that are serially connected. In some embodiments, the groups <NUM> of the photovoltaic cells <NUM> can be connected in parallel such as, for example, via electrical bussing. Optionally, the number of parallel scribes <NUM> can be configured to limit a maximum current generated by each group <NUM> of the photovoltaic cells <NUM>. In some embodiments, the maximum current generated by each group <NUM> can be less than or equal to about <NUM> milliamps (mA) such as, for example, less than or equal to about <NUM> mA in one embodiment, less than or equal to about <NUM> mA in another embodiment, or less than or equal to about <NUM> mA in a further embodiment.

With particular reference to <FIG>, the layers of the first submodule <NUM> can include a thin film stack provided over a substrate <NUM>. The substrate <NUM> can be configured to facilitate the transmission of light into the first submodule <NUM>. The substrate <NUM> can be disposed at the front side <NUM> of the first submodule <NUM>. Referring collectively to <FIG> & <FIG>, the substrate <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. One or more layers of material can be disposed between the first surface <NUM> and the second surface <NUM> of the substrate <NUM>.

Referring now to <FIG>, the substrate <NUM> can include a transparent layer <NUM> having a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. In some embodiments, the second surface <NUM> of the transparent layer <NUM> can form the second surface <NUM> of the substrate <NUM>. The transparent layer <NUM> can be formed from a substantially transparent material such as, for example, glass. Suitable glass can include soda-lime glass, or any glass with reduced iron content. The transparent layer <NUM> can have any suitable transmittance range, including about <NUM> to about <NUM>,<NUM>, in some embodiments. The transparent layer <NUM> can also have any suitable transmittance percentage, including, for example, more than about <NUM>% in one embodiment, more than about <NUM>% in another embodiment, more than about <NUM>% in yet another embodiment, more than about <NUM>% in a further embodiment, or more than about <NUM>% in still a further embodiment. In one embodiment, transparent layer <NUM> can be formed from a glass with about <NUM>% transmittance, or more. Optionally, the substrate <NUM> can include a coating <NUM> applied to the first surface <NUM> of the transparent layer <NUM>. The coating <NUM> can be configured to interact with light or to improve durability of the substrate <NUM> such as, but not limited to, an antireflective coating, an antifouling coating, or a combination thereof.

Referring again to <FIG>, the first submodule <NUM> can include a barrier layer <NUM> configured to mitigate diffusion of contaminants from the substrate <NUM>, which could result in degradation or delamination of other layers of the photovoltaic stack. The barrier layer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. In some embodiments, the barrier layer <NUM> can be provided adjacent to the substrate <NUM>. For example, the first surface <NUM> of the barrier layer <NUM> can be provided upon the second surface <NUM> of the substrate <NUM>.

Generally, the barrier layer <NUM> can be substantially transparent, thermally stable, with a reduced number of pin holes, have high sodium-blocking capability, and good adhesive properties. Alternatively, or additionally, the barrier layer <NUM> can be configured to apply color suppression to light. The barrier layer <NUM> can include one or more layers of suitable material, including, but not limited to, tin oxide, silicon dioxide, aluminum-doped silicon oxide, silicon oxide, silicon nitride, or aluminum oxide. The barrier layer <NUM> can have any suitable thickness bounded by the first surface <NUM> and the second surface <NUM>, including, for example, more than about <NUM> nanometers in one embodiment, more than about <NUM> in another embodiment, or less than about <NUM> in a further embodiment.

With continuing reference to <FIG>, the first submodule <NUM> can include a transparent conductive oxide (TCO) layer <NUM> configured to provide electrical contact to transport charge carriers generated by the first submodule <NUM>. The TCO layer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. In some embodiments, the TCO layer <NUM> can be provided adjacent to the barrier layer <NUM>. For example, the first surface <NUM> of the TCO layer <NUM> can be provided upon the second surface <NUM> of the barrier layer <NUM>. Generally, the TCO layer <NUM> can be formed from one or more layers of n-type semiconductor material that is substantially transparent and has a wide band gap. Specifically, the wide band gap can have a larger energy value compared to the energy of the photons of the light, which can mitigate undesired absorption of light. The TCO layer <NUM> can include one or more layers of suitable material, including, but not limited to, tin dioxide, doped tin dioxide (e.g., F-SnO<NUM>), indium tin oxide, or cadmium tin oxide (Cd<NUM>SnO<NUM>). In embodiments where the TCO layer <NUM> comprises cadmium stannate, the cadmium stannate can be provided in a crystalline form. For example, the cadmium stannate can be deposited as a film and then subjected to an annealing process, which transforms the thin film into a crystallized film.

The first submodule <NUM> can include a buffer layer <NUM> configured to provide an insulating layer between the TCO layer <NUM> and any adjacent semiconductor layers. The buffer layer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. In some embodiments, the buffer layer <NUM> can be provided adjacent to the TCO layer <NUM>. For example, the first surface <NUM> of the buffer layer <NUM> can be provided upon the second surface <NUM> of the TCO layer <NUM>. The buffer layer <NUM> can include material having higher resistivity than the TCO later <NUM>, including, but not limited to, intrinsic tin dioxide, zinc magnesium oxide (e.g., Znl-xMgxO), silicon dioxide (SiO<NUM>), aluminum oxide (Al<NUM>O<NUM>), aluminum nitride (AlN), zinc tin oxide, zinc oxide, tin silicon oxide, or any combination thereof. In some embodiments, the material of the buffer layer <NUM> can be configured to substantially match the band gap of an adjacent semiconductor layer (e.g., an absorber). The buffer layer <NUM> can have a suitable thickness between the first surface <NUM> and the second surface <NUM>, including, for example, more than about <NUM> in one embodiment, between about <NUM> and about <NUM> in another embodiment, or between about <NUM> and about <NUM> in a further embodiment.

Referring still to <FIG>, the first submodule <NUM> can include an absorber layer <NUM> configured to cooperate with another layer and form a p-n junction within the first submodule <NUM>. Accordingly, absorbed photons of the light can free electron-hole pairs and generate carrier flow, which can yield electrical energy. The absorber layer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. A thickness of the absorber layer <NUM> can be defined between the first surface <NUM> and the second surface <NUM>. The thickness of the absorber layer <NUM> can be between about <NUM> to about <NUM> such as, for example, between about <NUM> to about <NUM> in one embodiment, or between about <NUM> to about <NUM> in another embodiment.

The absorber layer <NUM> can be formed from a p-type semiconductor material having an excess of positive charge carriers, i.e., holes or acceptors. In an example, the absorber layer <NUM> can comprise a Group I-III-VI absorber material, such as, for example, copper indium gallium sulfide/selenide (CIGS), copper gallium sulfide/selenide (CGS), or CuInSe<NUM> (CIS), and can be provided as a thin film. The absorber layer <NUM> can include a suitable p-type semiconductor material such as Group II-VI semiconductors, for example, cadmium and tellurium (CdTe) or cadmium selenide (CdSe). Further examples of Group II-VI absorber materials include, but are not limited to, semiconductor materials comprising cadmium, zinc, tellurium, selenium, or any combination thereof. In some embodiments, the absorber layer <NUM> can include ternaries of cadmium, selenium, and tellurium (e.g., CdSexTe<NUM>-x), or a compound comprising cadmium, selenium, tellurium, and one or more additional element (e.g., CdZnSeTe). The absorber layer <NUM> can further include one or more dopants. The first submodule <NUM> provided herein can include a plurality of absorber materials.

In embodiments where the absorber layer <NUM> comprises tellurium and cadmium, the average atomic percent of the tellurium in the absorber layer <NUM> can be greater than or equal to about <NUM> atomic percent and less than or equal to about <NUM> atomic percent such as, for example, greater than about <NUM> atomic percent and less than about <NUM> atomic percent in one embodiment, greater than about <NUM> atomic percent and less than about <NUM> atomic percent in a further embodiment, or greater than about <NUM> atomic percent and less than about <NUM> atomic percent in yet another embodiment. Alternatively, or additionally, average atomic percent of the tellurium in the absorber layer <NUM> can be greater than about <NUM> atomic percent such as, for example, greater than about <NUM> atomic percent in one embodiment. It is noted that the average atomic percent described herein is representative of the entirety of the absorber layer <NUM>, the atomic percentage of material at a particular location within the absorber layer <NUM> can be graded through the thickness compared to the overall composition of the absorber layer <NUM>. For example, the absorber layer <NUM> can have a graded composition.

In embodiments where the absorber layer <NUM> comprises selenium and tellurium, the average atomic percent of the selenium in the absorber layer <NUM> can be greater than <NUM> atomic percent and less than or equal to about <NUM> atomic percent such as, for example, greater than about <NUM> atomic percent and less than about <NUM> atomic percent in one embodiment, greater than about <NUM> atomic percent and less than about <NUM> atomic percent in another embodiment, or greater than about <NUM> atomic percent and less than about <NUM> atomic percent in a further embodiment. It is noted that the concentration of tellurium, selenium, or both can be graded through the thickness of the absorber layer <NUM>. For example, when the absorber layer <NUM> includes a compound including selenium at a mole fraction of x and tellurium at a mole fraction of <NUM>-x (SexTe<NUM>-x), x can vary in the absorber layer <NUM> with distance from the first surface <NUM> of the absorber layer <NUM>.

Referring still to <FIG>, the absorber layer <NUM> can be doped with a dopant configured to manipulate the charge carrier concentration. In some embodiments, the absorber layer <NUM> can be doped with a Group VA (group <NUM>) dopant such as, for example, arsenic, phosphorous, antimony, or a combination thereof. Alternatively, or additionally, the absorber layer <NUM> can be doped with a Group IB (group <NUM>) dopant such as, for example, copper, silver, gold, or a combination thereof. The total density of the dopant within the absorber layer <NUM> can be controlled. Moreover, the amount of the dopant can vary with distance from the first surface <NUM> of the absorber layer <NUM>.

<FIG> shows an example layer structure and compositions have been described with examples including Group II-VI materials. In other embodiments, the first submodule <NUM> of the tandem photovoltaic device <NUM> can use other photovoltaic materials in alternate layer structures to produce a photovoltaic submodule. In an example, the first submodule <NUM> can comprise a Group I-III-VI absorber material, such as, for example, copper indium gallium sulfide/selenide (CIGS) or CuInSe<NUM> (CIS), and can be provided as a thin film. In another example, the first submodule <NUM> can comprise a perovskite absorber. In a further example, the first submodule <NUM> can include a silicon absorber, which can comprise amorphous, polycrystalline, crystalline, or thin film silicon.

According to the embodiments provided herein, the p-n junction can be formed by providing the absorber layer <NUM> sufficiently close to a portion of the first submodule <NUM> having an excess of negative charge carriers; e.g., electrons or donors. In some embodiments, the absorber layer <NUM> can be provided adjacent to n-type semiconductor material. Alternatively, one or more intervening layers can be provided between the absorber layer <NUM> and n-type semiconductor material. In some embodiments, the absorber layer <NUM> can be provided adjacent to the buffer layer <NUM>. For example, the first surface <NUM> of the absorber layer <NUM> can be provided upon the second surface <NUM> of the buffer layer <NUM>.

The first submodule <NUM> can include a back contact layer <NUM> configured to mitigate undesired alteration of the dopant and to provide electrical contact to the absorber layer <NUM>. The back contact layer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. A thickness of the back contact layer <NUM> can be defined between the first surface <NUM> and the second surface <NUM>. The thickness of the back contact layer <NUM> can be between about <NUM> to about <NUM> such as, for example, between about <NUM> to about <NUM> in one embodiment.

In some embodiments, the back contact layer <NUM> can be provided adjacent to the absorber layer <NUM>. For example, the first surface <NUM> of the back contact layer <NUM> can be provided upon the second surface <NUM> of the absorber layer <NUM>. In some embodiments, the back contact layer <NUM> can include combinations of materials from Groups I, II, VI, such as for example, one or more layers containing zinc and tellurium in various compositions. Further suitable materials include, but are not limited to, a bilayer of cadmium zinc telluride and zinc telluride, or zinc telluride doped with a Group V (group <NUM>) dopant such as, for example, nitrogen. A thin film junction <NUM> can be defined as the thin film stack primarily contributing to the photovoltaic effect. For example, in some embodiments, the thin film junction <NUM> can include the transparent conductive oxide layer <NUM>, the buffer layer <NUM>, the absorber layer <NUM>, the back contact layer <NUM>, or combinations thereof.

Referring to <FIG>, the first submodule <NUM> can include a conducting layer <NUM>, which can be transparent and configured to provide electrical contact with the back contact layer <NUM>, the absorber layer <NUM>, or both. In some embodiments, the conducting layer <NUM> can be formed towards a back side of the first submodule <NUM> with respect to the absorber layer <NUM>. In single junction devices, or when provided as a part of a lower or rear submodule (e.g., second submodule <NUM>), the conducting layer <NUM> can be disposed at the back side of the submodule (e.g., second submodule <NUM>) and can use opaque, non-transparent metal layers as constituents. However, non-transparent layers can be unsuitable for use as the conducting layer <NUM> of the first submodule <NUM>, disposed between junctions in multi-junction photovoltaic devices or tandem photovoltaic devices. The conducting layer <NUM> can have a first surface <NUM> substantially facing the front side <NUM> of the first submodule <NUM> and a second surface <NUM> substantially facing the back side <NUM> of the first submodule <NUM>. In some embodiments, the conducting layer <NUM> can be provided adjacent to the back contact layer <NUM> or the absorber layer <NUM>. For example, the first surface <NUM> of the conducting layer <NUM> can be provided upon the second surface <NUM> of the back contact layer <NUM> or the second surface <NUM> of the absorber layer <NUM>. A thickness of the conducting layer <NUM> can be defined between the first surface <NUM> and the second surface <NUM>. The thickness of the conducting layer <NUM> can be less than about <NUM> such as, for example, between about <NUM> and about <NUM> in one embodiment, or between about <NUM> and about <NUM>.

The first submodule <NUM> can have a back layer <NUM> at the back side <NUM> of the first submodule <NUM>. The back surface of the back layer <NUM> defines the back surface <NUM> of the front submodule. In some embodiments, the back layer <NUM> is a region of the conducting layer <NUM>. In some embodiments, the back layer <NUM> comprises an electron reflector layer. In some embodiments, the back layer <NUM> comprises a tunnel junction having a p+ subregion and an n+ subregion. In some embodiments, the back layer <NUM> comprises a tunnel junction having a p++ subregion and an n++ subregion.

Materials such as semiconductors and transparent conductive oxides can be doped with impurities to alter their electrical and optical properties. Dopants can be incorporated into functional layers to modify n-type or p-type charge carrier concentrations. Charge densities of greater than about <NUM> x <NUM><NUM> cm-<NUM> can be considered to be "+" type. Although the boundaries are not rigid, a material can be considered n-type if electron donor carriers are present in the range of about <NUM> x <NUM><NUM> cm-<NUM> to about <NUM> x <NUM><NUM> cm-<NUM>, and n+ type if donor carrier density is greater than about <NUM> × <NUM><NUM> cm-<NUM>. Similarly, a material is generally considered p-type if electron acceptor carriers (i.e., "holes") are present in the range of about <NUM> x <NUM><NUM> cm-<NUM> to about <NUM> x <NUM><NUM> cm-<NUM>, and p+ type if acceptor carrier density is greater than about <NUM>×<NUM><NUM> cm-<NUM>. The boundaries are not rigid and can overlap because a layer can be p+ relative to a layer that is p-type (or n+ relative to a layer that is n-type) if the carrier concentration is at least two orders of magnitude (i.e., <NUM>-fold) higher, regardless of the absolute carrier density. Additionally, charge densities of greater than about <NUM> x <NUM><NUM> cm-<NUM> can be considered to be "++" type; and thus a layer of either n-type or p-type can be "++" relative to a layer of the same type that is itself "+" relative to yet a third layer, if the ++ layer has a same-type carrier density more than <NUM> fold that of the + layer.

Referring now to <FIG> and <FIG>, the tandem photovoltaic device <NUM> includes a second submodule <NUM>. The second submodule <NUM> can be disposed below or under the first submodule <NUM>, referencing the front side <NUM> of the tandem photovoltaic device <NUM> as the primary light-facing top surface. The photovoltaic device submodule <NUM> can include a plurality of layers disposed between a first surface <NUM> on the front side of the second submodule <NUM> and a second surface on a back side of the second submodule <NUM>. One or more of the plurality of layers can include a photovoltaic absorber material. In some embodiments, the layers of the photovoltaic device submodule <NUM> can be divided into a plurality of photovoltaic cells.

The second submodule <NUM> of the tandem photovoltaic device <NUM> can include one or more absorber materials in a layer structure. In an example, the second submodule <NUM> can comprise a silicon absorber, which can include amorphous, polycrystalline, crystalline, or thin film silicon. In another example, the second submodule <NUM> can comprise a perovskite absorber material. In a further example, the second submodule <NUM> can comprise a Group I-III-VI absorber material, such as CIGS, and can be provided as a thin film. In another example, the second submodule <NUM> can comprise a Group II-VI absorber material, such as, for example, CdTe, CdZnTe, HgCdTe, or CdSeTe.

The second submodule <NUM> can share various aspects with the first submodule <NUM>. The second submodule <NUM> can have a front layer <NUM> at the front side <NUM> of the second submodule <NUM>. The front surface of the front layer <NUM> can define the front surface <NUM> of the second submodule <NUM>. In some embodiments, the front layer <NUM> is a buffer layer. In some embodiments, the front layer <NUM> is a conductive layer. In some embodiments, the front layer <NUM> includes a conductive metallic grid. In some embodiments, the front layer <NUM> comprises a transparent conductive oxide. In certain embodiments, a remainder or the entirety of the second submodule <NUM> can be configured identically or substantially identically to the first submodule <NUM>. Embodiments of the second submodule <NUM> can include portions that are identical or substantially identical in function and structure to portions of the first submodule <NUM>. In some embodiments, the tandem photovoltaic device <NUM> includes a second interlayer and back-sheet at the second surface <NUM> of the second submodule. In some embodiments the second interlayer comprises a material that includes the same matrix polymer as the second conformal layer <NUM>. In some embodiments, the second interlayer is fused to the second conformal layer <NUM> at a peripheral edge of the device. In some embodiments the back-sheet comprises a material that includes the same material as the core layer <NUM>. In other embodiments the back-sheet comprises glass. In some embodiments the second submodule is substantially encapsulated by a polymer comprising the second conformal layer <NUM> with electrical connectors, such as bussing wires passing therethrough. Encapsulation of the submodule by the interlayer and second interlayer can contribute to improve robustness of a tandem module.

With continued reference to <FIG> & <FIG>, the tandem photovoltaic device <NUM> includes an interlayer <NUM>. As shown, the interlayer structure is positioned between the first submodule <NUM> and the second submodule <NUM>. An example of an interlayer <NUM> structure is schematically depicted in a cross-section segment in <FIG>. According to the embodiments provided herein, the interlayer <NUM> can include a first conformal layer <NUM> and a core layer <NUM>, where the first conformal layer <NUM> is disposed between the core layer <NUM> and the back layer <NUM> of the first submodule <NUM>. In some embodiments, the core layer <NUM> can be provided between the first conformal layer <NUM> and a second conformal layer <NUM>. In some embodiments, the core layer <NUM> can be provided adjacent to the first conformal layer <NUM> and adjacent to the second conformal layer <NUM>. For example, the first surface <NUM> of the core layer <NUM> can be provided upon the second surface <NUM> of the first conformal layer <NUM>, and the first surface <NUM> of the second conformal layer <NUM> can be provided upon the second surface <NUM> of the core layer <NUM>. Thus, in some embodiments, the first surface <NUM> of the interlayer <NUM> can be formed by the first surface <NUM> of the first conformal layer <NUM> and the second surface <NUM> of the interlayer <NUM> can be formed by a second surface <NUM> of the second conformal layer <NUM>.

According to the embodiments provided herein, thickness of the interlayer <NUM> can be defined between the first surface <NUM> and the second surface <NUM>. The interlayer <NUM> thickness can be contiguous and substantially uniform, in certain embodiments, with a thickness deviation across the interlayer <NUM> of less than <NUM>%. In an example, the thickness of the interlayer <NUM> can be about <NUM> microns (<NUM>). In some embodiments, the thickness is in a range of <NUM> to <NUM>, such as, for example, between about <NUM> to <NUM>, or between about <NUM> to <NUM>.

In some embodiments, interlayer <NUM> thickness can be contiguous and irregular. In an example, the core layer is substantially uniform, while one or both of the first and second conformal layers <NUM>, <NUM>, are substantially irregular in thickness. In an example, an interlayer comprises a substantially uniform core layer combined with a substantially irregular conformal layer; this combination confers benefits from the electrical isolation and mechanical strength of the core material combined with the flowability and adhesion of the conformal layers to fill-in and ameliorate surface irregularities of an adjacent module surface. The conformal layer adheres contiguously to directly adjacent surfaces of the submodule and core layer. In some embodiments, a uniform layer deviates from an average thickness by no more than <NUM>%, or in a range of <NUM>% to <NUM>%. In some embodiments, an irregular or non-uniform layer includes thickness deviation of more than <NUM>%, more than <NUM>%, or more than <NUM>% of its average thickness. In some embodiments, an irregular or non-uniform layer includes thickness deviation up to a range of <NUM>% to <NUM>%, a range of <NUM>% to <NUM>%, a range of <NUM>% to <NUM>%, a range of <NUM>% to <NUM>%, or a range of <NUM>% to <NUM>% of the average thickness of the irregular layer.

Certain embodiments of the interlayer <NUM> can include where an entirety of the interlayer <NUM> or one or more layers of the interlayer <NUM> has a refractive index from about <NUM> to about <NUM> (e.g., about <NUM>) for light having a wavelength of <NUM>. In some embodiments, at least one of the first conformal layer <NUM>, the second conformal layer <NUM>, and the core layer <NUM> can have a refractive index from about <NUM> to about <NUM>, where certain embodiments include one or more layers having a refractive index of greater than <NUM> for light having a wavelength of <NUM>. In some embodiments, at least one of the first conformal layer <NUM>, the second conformal layer <NUM>, and the core layer <NUM> can have a refractive index in a range of <NUM> to <NUM> for <NUM> light.

The interlayer <NUM> can have an average transmittance greater than <NUM>% for light having a wavelength between <NUM> and <NUM>. Optionally, the interlayer <NUM> can have an average transmittance greater than about <NUM>% for light having a wavelength <NUM> to <NUM> such as, for example, greater than about <NUM>% in one embodiment, or greater than about <NUM>% in another embodiment, or greater than about <NUM>% in a further embodiment.

Without being bound to theory, the interlayer <NUM> provided herein provides synergistic advantages for tandem photovoltaic devices. Providing an interlayer <NUM> with a core layer <NUM> between conformal layers <NUM>, <NUM> confers advantages, both for manufacturability and operation. The core layer <NUM> can prevent shorting and can provide physical and electrical separation. The conformal layers <NUM>, <NUM> can provide good contact to the core layer <NUM> and to the respective submodules <NUM>, <NUM>, which can minimize irregularities, such as voids and bubbles, to provide reliable optical properties between the submodules <NUM>, <NUM>. Additionally, the interlayer <NUM> encapsulates and prevents intrusion of moisture into the submodules <NUM>, <NUM>, mitigating corrosion, degradation, and decreased performance that can be associated with humid environments.

The core layer <NUM> of the interlayer <NUM> can provide a dielectric and physical barrier that resists deformation and a narrowing of the dielectric breakdown distance. The core layer <NUM> can have a melting point above <NUM> degrees C. In certain embodiments, the core layer <NUM> can have a melting point above <NUM> degrees C, while other embodiments include where the core layer <NUM> has a melting point in a range of about <NUM> degrees C to about <NUM> degrees C. In some embodiments, the core layer <NUM> can have a dielectric breakthrough strength of greater than <NUM> kV/mm, greater than <NUM> kV/mm, greater than <NUM> kV/mm, in a range of <NUM> kV/mm to <NUM> kV/mm, or in a range of <NUM> kV/mm to <NUM> kV/mm.

The core layer <NUM> can comprise a polymer sheet. In certain embodiments, the core layer <NUM> can have a thickness in a range of <NUM> to <NUM>. In some embodiments, the core layer <NUM> can have a thickness greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>. In some embodiments, the core layer <NUM> can have a thickness less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>. In some embodiments, the core layer <NUM> can have a thickness of about <NUM> to <NUM>. In some embodiments, the material forming the core layer <NUM> is a thermoplastic polymer resin. In some embodiments, the material forming the core layer <NUM> can include one or more of: oriented polyethylene terephthalate (OPET), polytetrafluoroethylene (PTFE), polycyclooctene (PCO), or biaxially-oriented polyethylene terephthalate (boPET).

Generally, each of the conformal layers <NUM>, <NUM> can be formed by a material comprising a flowable polymer with a melting point less than <NUM> degrees C to conform to system components during lamination with the submodules <NUM>, <NUM> and operation at higher temperatures. In some embodiments, the conformal layers <NUM>, <NUM> are formed by a material with a melting point less than <NUM> degrees C. In some embodiments, one or both of the conformal layers <NUM>, <NUM> has a melting point in a range of about <NUM> degrees C to about <NUM> degrees C, in a range of <NUM> degrees C to <NUM> degrees C, in a range of <NUM> degrees C to <NUM> degrees C, in a range of <NUM> degrees C to <NUM> degrees C, or in a range of <NUM> degrees C to <NUM> degrees C. In some embodiments, one or both of the conformal layers <NUM>, <NUM> has a melting point less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, or less than <NUM> degrees C.

Materials for first conformal layer <NUM> can include polyethylene (PE), ethylene-vinyl acetate (EVA), and/or polyolefin elastomer (POE). Other materials suitable for use in the layer include various optically compatible adhesives.

The thickness of each of the conformal layers <NUM>, <NUM> can be from about <NUM> to about <NUM>. In some embodiments, the first conformal layer <NUM> has a thickness greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In some embodiments, the first conformal layer <NUM> has a thickness less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>. In some embodiments, the second conformal layer <NUM> has a thickness greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In some embodiments, the second conformal layer <NUM> has a thickness less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>.

The conformal layers <NUM>, <NUM> can be configured to conform to irregularities of an adjoining surface, including surface roughness of either the second surface <NUM> of the first submodule <NUM> or the first surface <NUM> of the second submodule <NUM>, respectively. In some embodiments, a ratio between an average surface roughness of the adjoining surface to the thickness of the respective adjacent conformal layer is between <NUM>:<NUM> and <NUM>:<NUM>. In some embodiments, the ratio between the average surface roughness of the adjoining surface to the thickness of the conformal layer is greater than <NUM>:<NUM>, greater than <NUM>:<NUM>, greater than <NUM>:<NUM>, greater than <NUM>:<NUM>, or greater than <NUM>:<NUM>. In some embodiments, the ratio between the average surface roughness of the adjoining surface to the thickness of the conformal layer is less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, or less than <NUM>:<NUM>. The flowable composition of the conformal layer at processing temperatures during manufacturing provides beneficial wettability and adhesion despite surface irregularities.

With reference now to <FIG>, an embodiment of a method of making a tandem photovoltaic device is shown at <NUM>. A first step at <NUM> can include providing an interlayer <NUM> as described herein, where the interlayer <NUM> permits a portion of light to pass therethrough. A second step at <NUM> can include directly contacting a portion of a surface (e.g., second surface <NUM>) of the first submodule <NUM> with the first conformal layer <NUM>. A third step at <NUM> can include conforming the first conformal layer <NUM> to the portion of the surface (e.g., second surface <NUM>) of the first submodule <NUM>. A fourth step at <NUM> can include directly contacting a portion of a surface (e.g., first surface <NUM>) of the second submodule <NUM> with the second conformal layer <NUM>. A fifth step at <NUM> can include conforming the second conformal layer <NUM> to the portion of the surface (e.g., first surface <NUM>) of the second submodule <NUM>.

The interlayer <NUM> can be formed in various ways. In certain embodiments, the core layer <NUM>, the first conformal layer <NUM>, and the second conformal layer <NUM> can be laminated together in a prebonding step to form the interlayer <NUM>. The core layer <NUM> can be laminated between the first conformal layer <NUM> and the second conformal layer <NUM> to provide the interlayer <NUM>. In certain embodiments, one or more layers of the interlayer are co-extruded as a single sheet or layer. The core layer <NUM> can be coextruded between the first conformal layer <NUM> and the second conformal layer <NUM> to provide the interlayer <NUM>.

Whereas <FIG> depicts steps of the method <NUM> sequentially, it is understood that certain steps can be performed simultaneously and/or certain steps can be performed in a different order than depicted. For example, the first conformal layer <NUM> can be conformed to the portion of the surface of the first submodule <NUM> by heating the first conformal layer <NUM> to at least the melting point of the first polymer. Likewise, the second conformal layer <NUM> can be conformed to the portion of the surface of the second submodule <NUM> by heating the second conformal layer <NUM> to at least the melting point of the second polymer. One of the portion of the surface of the first submodule <NUM> and the first conformal layer <NUM> can be heated to at least the melting point of the first polymer prior to directly contacting the portion of the surface of the first submodule <NUM> with the first conformal layer <NUM>. Likewise, one of the portion of the surface of the second submodule <NUM> and the second conformal layer <NUM> can be heated to at least the melting point of the second polymer prior to directly contacting the portion of the surface of the second submodule <NUM> with the second conformal layer <NUM>. Certain embodiments include where conforming the first conformal layer <NUM> to the portion of the surface of the first submodule <NUM> and conforming the second conformal layer <NUM> to the portion of the surface of the second submodule <NUM> includes simultaneously heating the first submodule <NUM>, the interlayer <NUM>, and the second submodule <NUM> to at least the melting point of the first polymer and at least the melting point of the second polymer following directly contacting the portion of the surface of the first submodule <NUM> with the first conformal layer <NUM> and directly contacting the portion of the surface of the second submodule <NUM> with the second conformal layer <NUM>. It is further possible to conform the first conformal layer <NUM> to the portion of the surface of the first submodule <NUM> by pressing the interlayer <NUM> and the first submodule <NUM> together and to conform the second conformal layer <NUM> to the portion of the surface of the second submodule <NUM> by pressing the interlayer <NUM> and the second submodule <NUM> together. Conforming the first conformal layer <NUM> to the portion of the surface of the first submodule <NUM> and conforming the second conformal layer to the portion of the surface of the second submodule <NUM> can include pressing the interlayer <NUM> between the first submodule <NUM> and the second submodule <NUM>.

In some embodiments, a method of forming a tandem photovoltaic device includes: directly contacting a back or second surface <NUM> of a first submodule <NUM> with a first surface <NUM>, <NUM> of a first conformal layer <NUM>; directly contacting a front or first surface <NUM> of a second submodule <NUM> with a second surface <NUM>, <NUM> of a second conformal layer <NUM>; providing a core layer <NUM> between the first conformal layer <NUM> and the second conformal layer <NUM>. The method can comprise conforming the first conformal layer to the surface of the first submodule; and conforming the second conformal layer to the surface of the second submodule.

The method can be performed at a processing temperature below a melt temperature of the core layer. The processing temperature can be near, at, or above a melt temperature of a conformal layer. In some instances, the processing temperature is within <NUM> degrees C above or below the melt temperature of a first polymer. In some instances, the processing temperature is within <NUM> degrees C above or below the melt temperature of a second polymer. In some instances, the processing temperature is above the melt temperature of a first and second polymer. In some embodiments of the method of bonding the interlayer to the first and second submodules, the processing temperature is <NUM> to <NUM> degrees below the melt temperature of a third polymer comprising the core layer. In some instances, the processing temperature is in a range of <NUM> to <NUM> degrees C. In some instances, the processing temperature is less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, less than <NUM> degrees C, or less than <NUM> degrees C.

By controlling the thicknesses and composition of the sublayers of the interlayer, material heat capacity and heat transfer during manufacturing can be controlled to prevent damage to temperature-sensitive components of an adjacent module at processing temperatures suitable to meld and adhere the conformal layer to a surface of the adjacent module. During a laminating or bonding process at processing temperatures, the core layer can be a solid, contiguous sheet, while simultaneously, one or both of the conformal layers are heated to a flowable, viscous state. The methods produce a durable interlayer with good adhesion, robust electrical breakthrough strength, and high transparency for near infrared wavelengths.

Claim 1:
A tandem photovoltaic device (<NUM>) comprising:
a first submodule (<NUM>);
a second submodule (<NUM>);
an interlayer (<NUM>) disposed between the first submodule (<NUM>) and the second submodule (<NUM>), wherein the interlayer (<NUM>) permits a portion of light to pass therethrough, the interlayer (<NUM>) including:
a first conformal layer (<NUM>) directly contacting and conforming to a portion of a surface of the first submodule (<NUM>), the first conformal layer (<NUM>) including a first polymer having a melting point less than <NUM> degrees C;
a second conformal layer (<NUM>) directly contacting and conforming to a portion of a surface of the second submodule (<NUM>), the second conformal layer (<NUM>) including a second polymer having a melting point less than <NUM> degrees C;
a core layer (<NUM>) disposed between and directly contacting the first conformal layer (<NUM>) and the second conformal layer (<NUM>), the core layer (<NUM>) including a third polymer having a melting point greater than <NUM> degrees C; characterized in that
the first polymer includes a member selected from a group consisting of:
polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof;
the second polymer includes a member selected from a group consisting of:
polyethylene; ethylene-vinyl acetate; polyolefin elastomer; and combinations thereof; and
the third polymer includes a member selected from a group consisting of:
oriented polyethylene terephthalate; polytetrafluoroethylene; polycyclooctene; biaxially-oriented polyethylene terephthalate; polyimide; and combinations thereof.