Integrated film for electrode assembly of solar cells

Abstract

A monolithic film for an electrode assembly of a solar cell, the monolithic film being disposed on a surface of the solar cell in use, with a plurality of conductive elements of the electrode assembly being interposed between the monolithic film and the surface of the solar cell, the monolithic film being formed from a polymeric material and characterized by satisfying at least one of a first criterion and a second criterion, the first criterion requiring that the polymeric material have at least two endothermic peaks in the temperature range of 40°C to 200°C as measured by differential scanning calorimetry using the following method, the method comprising: and identifying and determining a first endothermic peak and a second endothermic peak in the temperature range of 40°C to 200°C in each of the first and second heating traces; and a second criterion requiring that the integral film have a peel strength of at least 5N per 10mm width of the integral film, the peel strength being determined by a 180 degree peel test according to the following method, the method being: thermally bonding the integral film to a surface of a substrate; peeling the integral film from the surface according to standard test method ASTM D903 to provide a peel force trace; and determining from the peel force trace that the integral film has a peel strength of at least 5N per 10mm width of the integral film.

Description

[Technical field]

[0001] The present disclosure relates to an integral film for an electrode assembly of a solar cell. [Background technology]

[0002] A solar module for providing electrical energy from sunlight comprises an array of cells, each of which comprises a photovoltaic element or substrate. The solar cells are typically connected such that electrical current can be sent from the front surface of one solar cell to the back surface of a second solar cell, or vice versa, via electrical connectors. Each of the electrical connectors comprises a number of conductive elements (e.g., interconnect wires) that form electrical connections with electrodes disposed on the front and back surfaces of each of the solar cells.

[0003] A common objective for solar cell development is to achieve high conversion efficiency balanced with the need for reduced production costs. Efforts to achieve this have focused on the electrical connections between the solar cells.

[0004] One approach has been to provide foil wire electrodes that connect directly to finger electrodes placed on the surface of each solar cell. An example of a foil wire electrode is the SmartWire® solar cell connector. The foil wire electrodes reduce electrical losses by minimizing the impact of cell damage on the performance of the solar module. Furthermore, the use of foil wire electrodes can also lead to a significant reduction in module production costs and optical losses resulting from light shading caused by configuring the surface of the solar cell with conventional printed busbar electrodes.

[0005] The foil of the foil wire electrode is a multi-layer transparent film. The foil comprises a support layer that provides a support structure for the foil and an adhesive layer that attaches the foil to the wire connector and the solar cell surface. When the foil wire electrode is placed on the front side of the solar cell, the foil can be configured to have a front side facing away from the solar cell and a back side facing towards the solar cell. The support layer is placed on the front side of the foil and the adhesive layer is placed on the back side of the foil opposite the front side.

[0006] The foil is constructed by laminating together a support layer and an adhesive layer, the adhesive layer being made, for example, of a polymeric material that can be heated to form a thermal bond with the connecting wires.

[0007] During construction of the foil electrode, the foil is laid over the connecting wires such that the adhesive layer is in contact with the connecting wires. Heat and pressure are applied to the foil to thermally bond the foil to the connecting wires.

[0008] The two solar cells are electrically connected together by the foil electrode to form a solar cell assembly. A first end of the foil wire electrode is overlaid on the surface of the first solar cell such that the connecting wire is interposed between the foil and the solar cell surface. Heat and pressure are applied to the foil causing the adhesive layer to thermally bond the foil to the solar cell surface. A second end of the foil wire is connected to the surface of the second solar cell in the same manner. The foil wire electrode thus provides a means of forming an electrical connection between the solar cells of the solar cell assembly.

[0009] Despite these developments, a need remains for improved electrical connections between solar cells in a solar cell assembly. Summary of the Invention

[0010] According to a first aspect, there is provided a monolithic film for an electrode assembly (e.g., a foil-wire electrode assembly) of a solar cell. The monolithic film is disposed, in use, on a surface of the solar cell, with a plurality of conductive elements of the electrode assembly interposed between the monolithic film and the surface of the solar cell. Here, the monolithic film is formed from a polymeric material and is characterized by satisfying at least one of a first criterion and a second criterion.

[0011] The first criterion requires that the polymeric material have at least two endothermic peaks (e.g., endothermic melting peaks) in the temperature range of 40° C. to 200° C. as measured by differential scanning calorimetry using the following method: sequentially heating the integral film through a first thermal cycle and a second thermal cycle in accordance with standard test method ASTM D3418 to produce a first heating trace and a second heating trace, respectively; and The first and second endothermic peaks in the temperature range of 40° C. to 200° C. are identified and determined in the first and second heating traces, respectively.

[0012] The second criterion requires that the integral film have a peel strength of at least 5 N per 10 mm width of the integral film. Peel strength is determined (e.g., measured) by a 180 degree peel test according to the following method, which includes: thermally bonding the integral film to a surface (e.g., a receiving surface) of a substrate; Peeling the integral film from the substrate in accordance with standard test method ASTM D903 to provide a peel force trace; and From the peel force trace, it is determined that the integral film has a peel strength of at least 5 N per 10 mm width of the integral film.

[0013] It should be appreciated that a monolithic film may define a film that forms a single or uniform entity (eg, does not include multiple layers formed from different materials).

[0014] It should be appreciated that the first and second criteria each include methods for identifying and determining the physical properties of the material of the homogenous film, and that these methods do not necessarily limit the claimed integral film, rather, they merely provide a manner of determining whether an integral film has one or more of the characteristic physical properties according to the present disclosure.

[0015] The first criterion refers to standard test method ASTM D3418, which is a standard test method for transition temperature and enthalpy of fusion and crystallization of polymers by differential scanning calorimetry. As characterized by the first criterion, the technical advantage of the integral film is that it exhibits an advantageous phase transition temperature range, which is useful for preventing instability in the integral film during use. For example, in situations where the integral film is thermally bonded to a conductive element (e.g., to form an electrode assembly) or where the integral film is thermally bonded to the surface of a solar cell (e.g., to form a solar cell assembly). The first criterion refers to a method for identifying and determining at least one temperature of the endothermic peak of the polymeric material of the integral film. Using this test method, it can be identified and determined whether a candidate polymeric material exhibits an endothermic phase transition in the required temperature range to fall within the scope of the present disclosure.

[0016] The second criterion refers to standard test method ASTM D903, which is the standard test method for peel (or peeling) strength of adhesive bonds. Peel strength represents the average load per unit width at the bond line between the film and the substrate, which is the requirement for progressively separating the integral film from the substrate at an angle of approximately 180° and a separation speed of 152 mm / min. Peel strength can be expressed as force per unit width (e.g., Newtons (or kilograms) per millimeter of the width of the integral film). The bond line extends parallel to the width of the integral film and defines the contact line between the film and the surface of the substrate.

[0017] As characterized by the second criterion, the technical advantage of the integral film is that it exhibits an advantageous range of peel strengths associated with the improved adhesive properties of the integral film. For example, the test method of the second criterion can be used to identify and determine whether a candidate polymer film exhibits a peel strength in the range required to fall within the scope of the present disclosure (e.g., at least 5 N per 10 mm width of the integral film).

[0018] Peel strength represents a standard measure of the adhesive properties of a film as determined by standard test method ASTM D903. It should be noted that the width direction of the integral film is substantially perpendicular to the direction in which the peel force is applied to the integral film during the 180 degree peel test. Adhesion properties can also be defined by the peel strength of the integral film, which is expressed in units of kg per mm width of the integral film.

[0019] An integral film that meets the requirements of the first and / or second criteria provides increased adhesion between the multiple conductive elements and the integral film, and / or between the solar cell and the integral film during use. Furthermore, the integral nature of the film means that it exhibits substantially uniform physical and thermal properties (e.g., compared to a multi-layer film that includes separate backing and adhesive layers that may have different properties). For example, an integral film is less susceptible to delamination. Thus, an integral film is more stable and easier to handle during fabrication of a solar cell assembly, which can result in improved efficiency of the fabrication process.

[0020] The following are optional features, which can be applied alone or in any combination with any aspect.

[0021] It should be appreciated that the integral film may be defined by at least one or both of a first and a second criterion (eg, a first criterion and a second criterion).

[0022] As noted above, the first standard DSC test method involves identifying at least two endothermic peaks in a trace (e.g., a heating or cooling trace) generated by differential scanning calorimetry. The trace may be generated by a differential scanning calorimeter configured to determine the temperature and heat flow associated with a thermal transition of the material under investigation. Generally, a thermal transition may be characterized by the absorption or release of energy by the sample, resulting in a corresponding endothermic or exothermic peak or baseline shift in the trace. For example, the area under a crystallization exotherm or fusion endotherm of the test material may be compared to the corresponding area of ​​a trace obtained by testing a well-characterized standard.

[0023] To obtain the trace, a material (e.g., a sample of a polymeric material) may be placed in a calorimeter test cell coupled to an empty reference cell. The calorimeter monitors the heat flow between the two cells as they are heated. If the material is not undergoing a phase transition, the heat flow between the cells is usually constant. As the temperature increases (e.g., in the case of a heating trace), the material may, at some temperature, undergo a transition (e.g., an endothermic transition) that requires heat to be transferred from the reference cell to the test cell.

[0024] The calorimeter may be configured to output a trace (i.e., a test trace) corresponding to the flow of heat directed toward or away from the test cell. A separate trace is also generated corresponding to a reference cell (i.e., a reference trace), which is typically a flat line. The difference between the test trace and the reference trace represents the change in heat flow into the test cell with a change in temperature. Such a change may correspond to a transformation of the material under test.

[0025] It should be appreciated that the calorimetric data can be evaluated to determine characteristic properties of the material under investigation. The data can be presented as a graph of temperature (°C) and / or heat flow (W / g) plotted against time. The heat flow value represents the power per unit mass conducted between the cells of the calorimeter. The temperature value corresponds to the measured temperature of the cells. The time value represents the rate at which the temperature of the cells increases during the test.

[0026] A peak may appear on the resulting graph as an area of ​​the test trace that deviates from the substantially linear reference trace. In the case of an endothermic transition, the resulting peak may appear in the test trace as a negative peak or trough.

[0027] As discussed above, a first standard differential scanning calorimetry test method includes identifying and determining the presence of a first endothermic peak and a second endothermic peak in each of the first and second heating traces, and determining that the first and second endothermic peaks in each of the first and second heating traces are at temperatures between 40° C. and 200° C. According to an exemplary arrangement, the first and / or second heating traces may only include two endothermic peaks within a defined temperature range (e.g., 40° C. to 200° C.).

[0028] In situations where two or more peaks are identified in a heating trace (e.g., a first and a second endothermic peak), the first peak may be defined as the peak having a minimum temperature (e.g., a first peak temperature) and the second peak may be defined as the peak having a peak temperature (e.g., a second peak temperature) greater (e.g., higher) than the temperature of the first peak. It should be appreciated that in certain exemplary arrangements, there may be one or more peaks positioned between the first and second peaks of the trace. If the trace has three peaks, the third peak may be defined as the peak exhibiting a peak temperature (e.g., a third peak temperature) greater than the first and second peak temperatures.

[0029] The first heating trace may be measured during a first thermal cycle performed by a differential scanning calorimeter, while the second heating trace may be measured during a second thermal cycle, and the first and second thermal cycles may be performed sequentially according to standard test method ASTM D3418.

[0030] The temperature of the endothermic peak (e.g., the first endothermic peak or the second endothermic peak) may define the peak temperature (Tp) of the endothermic peak (e.g., the first endothermic peak or the second peak temperature, respectively). The peak temperature may represent a characteristic temperature of an endothermic transition (e.g., an endothermic melt).

[0031] The peak temperature may be calculated from a trace (e.g., the first or second heating trace) plotted on a graph of heat flow versus temperature. The peak temperature may be calculated by identifying the minimum value of the peak, i.e., a value less than its nearest neighbors. For such polymeric materials, the minimum temperature may indicate the average melting temperature of the crystals in the material. For a second subsequent phase transition (e.g., a glass transition), the minimum temperature may be the characteristic temperature of the phase transition.

[0032] The first peak temperature may define the temperature of the lowest point of the test trace (e.g., the first or second heating trace) in the region corresponding to the first endothermic peak. The first peak temperature may therefore define the local minimum heat flow value of the trace (e.g., measured in power per unit mass, W / g).

[0033] At least one or each of the first and second endothermic peaks of the first heating trace may be between 80° C. and 160° C. Alternatively or additionally, at least one or each of the first and second endothermic peaks of the second heating trace may be between 80° C. and 160° C. According to an exemplary arrangement, the first and / or second heating trace may only include two endothermic peaks (e.g., the first and second peaks) within a defined temperature range (e.g., 80° C. to 160° C.).

[0034] The first endothermic peak of at least one of the or each of the first and second heating traces may be between 40°C and 130°C.

[0035] The first endothermic peak in the second heating trace may be between 80°C and 130°C.

[0036] The second endothermic peak of at least one or each of the first and second heating traces may be between 100°C and 160°C.

[0037] The second endothermic peak of at least one or each of the first and second heating traces may be between 100°C and 145°C.

[0038] According to an exemplary embodiment of the monolithic film, the second endothermic peak in the first heat trace (e.g., only the first heat trace) may be at a temperature between 100° C. and 135° C. According to a further exemplary embodiment, the second endothermic peak in the first and second heat traces may be at a temperature between 100° C. and 145° C., optionally between 100° C. and 135° C.

[0039] The first reference differential scanning calorimetry method may include identifying a third endothermic peak of at least one or each of the first and second heating traces. The method may further include determining that the third endothermic peak (e.g., at least one or each of the first and second heating traces) is at a temperature between 130°C and 200°C. The third endothermic peak of at least one or each of the first and second heating traces may be between 130°C and 160°C. According to an exemplary embodiment, the first and / or second heating traces may include up to three endothermic peaks (e.g., first, second, and third peaks) within a defined temperature range (e.g., 80°C to 160°C).

[0040] Therefore, the integral film may have a third endothermic peak in the temperature range of 130°C to 200°C in the first and second heating traces.

[0041] The first reference differential scanning calorimetry may include measuring the cooling of the polymeric material during a first thermal cycle (e.g., a cooling phase of the first thermal cycle) to generate a cooling trace according to standard test method ASTM D3418.

[0042] Similar to the heating trace, the cooling trace may be constructed to have heat flow (W / g) plotted against temperature (°C) and / or time (sec), except in this case the trace is recorded as the sample material is cooling.

[0043] The integral film may include an exothermic peak (e.g., an exothermic crystallization peak) at a temperature in the range of 0°C to 200°C. The exothermic peak may be measured by differential scanning calorimetry (e.g., according to standard test method ASTM D3418). The method may further include measuring the cooling of the polymeric material during a first thermal cycle by differential scanning calorimetry to generate a cooling trace and identifying and determining an exothermic peak at a temperature between 0°C and 200°C. The exothermic peak may be between 40°C and 130°C.

[0044] A thermal cycle (e.g., a first and / or second thermal cycle) may include a heating phase in which the test and reference materials are heated over time. During the heating phase, the calorimeter may be controlled to continuously monitor (e.g., with a temperature sensor) the difference in heat input between the reference and test materials to generate heating traces. For example, the heating phase of the first thermal cycle may generate a first heating trace and the heating phase of the second thermal cycle may generate a second heating trace.

[0045] The thermal cycles (e.g., the first and / or second thermal cycles) may also include a cooling phase, which may follow the heating phase, during which the test and reference materials are allowed to cool over time. During the cooling phase, the temperatures of the reference and test materials may be continuously monitored to generate a cooling trace. For example, the cooling phase of the first thermal cycle may follow the heating phase of the first thermal cycle and generate a cooling trace. The cooling trace indicates the release of thermal energy from the test material that was absorbed during the heating phase.

[0046] At least one or each of the thermal cycles (e.g., the first and second thermal cycles) may include heating and / or cooling the test material at a controlled rate (e.g., controlled heating and / or cooling rate). For example, the heating rate of the thermal cycle may be 10°C / min. The rate of change of the sample temperature may be maintained within an error range of ±0.1°C / min. The cooling rate may be substantially the same as the heating rate (e.g., 10°C / min). At the end of the heating stage (e.g., midway through the thermal cycle), the sample may be held at a first holding temperature (e.g., about 300°C) for about 5 minutes. Similarly, at the end of the cooling stage (e.g., at the end of the thermal cycle), the sample may be held at a second holding temperature (e.g., about -50°C) for about 5 minutes.

[0047] Differential scanning calorimetry may be performed in an inert atmosphere (e.g., under a purge or flow of an inert gas). The test environment (e.g., containing the test and / or reference samples) may be purged with an inert gas at a purge flow rate of 50 mL / min. The inert gas may be nitrogen.

[0048] As noted above, the test method of the second standard includes peeling the integral film from the substrate to provide a peel force trace according to standard test method ASTM D 903. The method may also include determining from the peel force trace that the integral film has a peel strength of at least 5 N per 10 mm width of the film.

[0049] It should be appreciated that the peel test can be used to determine (e.g., measure) the adhesion between the integral film and a substrate thermally bonded together. A peel test apparatus may be used to perform the peel test. The peel test apparatus may include a motorized tensile meter configured to apply a tensile force between the integral film and the substrate. The aparat may include a tensile force measuring sensor (e.g., a load cell) for determining the tensile load applied during the test. The peel test apparatus may include a set of grips or grippers configured to hold the integral film and the substrate. The peel test apparatus may include a controller configured to operate the motorized tensile meter to perform the test method. In particular, the controller may be capable of controlling the force applied by the tensile meter to the grippers, thereby determining the force (e.g., "peel force") applied to the integral film.

[0050] In an exemplary form, the peel test method may include determining from the peel force trace that the peel strength of the integral film is at least 10 N. Alternatively, the peel strength may be at least 15 N per 10 mm width of the integral film. The peel strength of the integral film may be up to 30 N per 10 mm width of the integral film.

[0051] As mentioned above, the second criterion is also characterized by thermally bonding the integral film to the substrate. This method step may include heating the integral film to at least 40° C. The peel test may include cooling the integral film (e.g., to room temperature (e.g., about 20° C.)) for a predetermined period of time (e.g., at least 30 minutes) before performing a peel force analysis of the integral film (e.g., before peeling the film from the substrate).

[0052] The peel test method of the second standard may include placing the integral film substantially flat on a receiving surface of a substrate. This may be done before the film is thermally bonded (e.g., laminated) to the substrate. Only a portion of the integral film may be thermally bonded to the substrate. Thus, the film may be configured to have a free end (e.g., a non-bonded end) that can be easily coupled to the grippers of a peel test apparatus.

[0053] The integral film may be arranged in a longitudinal strip. A plurality of longitudinal strips may be arranged (e.g., parallel to each other) on a surface of a substrate. The longitudinal strip may have a width of about 10 mm. The length of the longitudinal strip may have a length of at least 100 mm. The longitudinal strip may be arranged on the substrate such that the width of the strip is substantially perpendicular to the direction in which the peel force is applied.

[0054] The peel test may be applied over a distance (e.g., strain) of about 100 mm. The integral film may be peeled from the substrate at a peel speed of about 100 mm / min. The peel force is continuously monitored. For example, the peel force may be measured at 10 μm intervals until the maximum peel distance (e.g., 100 mm) is reached.

[0055] Peel strength may be determined by taking the average of the data recorded in the peel force trace. The average peel force may be determined by averaging the data recorded after a minimum peel distance or strain (e.g., 20 mm). Data taken before the peel distance may be ignored to prevent distortion of the measurement caused by noise in the data present at the beginning of each test run.

[0056] The substrate may be formed from a rigid material such as glass or metal (eg, a metal alloy). The substrate may comprise a solar cell (eg, a crystalline silicon solar cell).

[0057] The integral film may be configured to be mechanically attached (e.g., thermally bonded) to a plurality of conductive elements (e.g., conductive wires or conductive wire portions) during use. The integral film may be configured to have a surface (e.g., an element-receiving surface) for receiving the elements. Once the elements are disposed on a surface of the integral film, they may be mechanically secured in place to form an electrode assembly.

[0058] The integral film may be configured to be insulating and / or optically transparent. The polymeric material may be formed from a polymeric resin including at least one of polyolefin elastomer (POE), polyvinyl butyral (PVB) hydrocarbon ionomer, thermoplastic organosilicon, silicone rubber, polyurethane, thermoplastic silicone elastomer (TPSE), and ethylene-vinyl acetate (EVA).

[0059] The integral film may be formed from a polymeric material having at least one of the following characteristics: high ductility, low electrical conductivity, high optical transparency, thermal stability, and resistance to shrinkage.

[0060] The integral film may be configured to have a haze parameter of less than 35%, optionally at most 18%, and further optionally at most 25%. It should be appreciated that the haze parameter of a polymeric material may be defined as a measure of the percentage of incident light that is scattered beyond 2.5°. It should be appreciated that the haze parameter of a material may be measured using a haze meter or a spectrophotometer.

[0061] The integral film may be configured to transmit at least 70% of incident light having a wavelength between 280 nm and 1100 nm. Alternatively, the film may be configured to transmit at least 85% of incident light having a wavelength between 280 nm and 1100 nm. The integral film may have a thickness of at least 25 μm. The thickness of the integral film may be between 55 μm and 180 μm.

[0062] In a second aspect of the present disclosure, an electrode assembly is provided, comprising a solar cell and an electrode assembly according to any one of the preceding statements. A plurality of conductive elements are disposed on a surface (e.g., a conductive element receiving surface) of the monolithic film such that the electrode assembly can be disposed on the surface of the solar cell, such that the plurality of conductive elements are interposed between the monolithic film and the surface of the solar cell. Due to the advantageous physical properties of the monolithic film (e.g., as characterized by the first and / or second criteria), the electrode assembly is effectively configured to form a robust and conductive electrical connection with the surface of the solar cell.

[0063] According to a third aspect of the present disclosure, there is provided a solar cell assembly comprising at least one solar cell and an electrode assembly according to any one of the preceding statements. A plurality of conductive elements may be interposed between the integral film and a surface (e.g., an electrode assembly receiving surface) of the solar cell. The solar cell assembly may be manufactured according to the method according to any one of the preceding statements. As described above, the electrode assembly comprises an integral film and a plurality of conductive elements.

[0064] According to an exemplary arrangement, the solar cell assembly may include a first solar cell and a second solar cell. At least one or each of the solar cells may include a layered structure including a photovoltaic element capable of absorbing light and generating charge carriers, as will be understood by one skilled in the art. The electrode assembly may be configured to form an electrical connection with a conductive surface (or a conductive portion of a surface) of the solar cell to extract the photogenerated charge carriers from the solar cell.

[0065] At least one or each of the solar cells may comprise a front surface and a back surface. The front surface may define a surface of the solar cell on which light is incident when the solar cell assembly is in use (e.g., the front-most surface of the solar cell). The back surface may define a surface of the solar cell opposite the front surface (e.g., the back-most surface of the solar cell). The back surface of the solar cell may not be directly exposed to incident light during use. The solar cell assembly may be configured such that light that is transmitted through the solar cell from the front to the back (e.g., not absorbed) is then reflected towards the back surface of the solar cell, thereby providing further opportunity for light to be absorbed.

[0066] At least one or each of the conductive elements may comprise an elongated form, such as a wire or a portion of a wire. The conductive element may comprise a single integrally formed element (e.g., a wire). Configuring the conductive elements in this manner eliminates the need to provide separate connections (such as copper ribbons) between adjacent solar cells, thereby reducing the number and complexity of manufacturing steps required to fabricate a solar cell assembly.

[0067] At least one or each of the conductive elements may comprise a width, an axial length, and a depth. Each of the conductive elements may be configured such that its axial length is substantially greater than its width and / or depth. The width and axial length of the conductive element may be measured in a perpendicular direction aligned with the plane of the surface of the solar cell in which the conductive element is disposed (e.g., the front or back surface of the solar cell). The depth may be measured in a direction perpendicular to the same plane of the solar cell.

[0068] At least one, or each, of the conductive elements may be formed from a conductive material, such as a metal or metal alloy material, which may include at least one of Ag, Al, Au, and Cu.

[0069] At least one or each of the conductive elements may be connectable to a solar cell surface by applying heat and pressure to a coating on the conductive element to form a mechanical and electrical connection with the surface of the solar cell. The coating (e.g., a solderable coating) may include a conductive material having a melting point lower than the melting point of the conductive elements. The coating may include a metal alloy formed from at least two or more components.

[0070] As described above, the solar cell assembly may include a first solar cell and a second solar cell, and the plurality of conductive elements are configured to electrically couple the front surface of the first solar cell to the back surface of the second solar cell. During construction of the solar cell assembly, an electrode assembly may be connected (e.g., stacked) on the front and back surfaces of each of the first and second solar cells. At least one of the first and second solar cells may be inverted such that their front surfaces are arranged to face substantially downward (e.g., substantially vertically downward) and their back surfaces are arranged to face substantially upward (e.g., substantially vertically upward).

[0071] When the electrode assembly is in use, a first surface of the at least one conductive element may be arranged to contact the front surface of the first solar cell and face away from the back surface of the second solar cell. Thus, a second surface of the at least one conductive element may be arranged to contact the back surface of the second solar cell and face away from the front surface of the first solar cell.

[0072] The first and second surfaces may define upper and lower surfaces, respectively, of the conductive element. At least one or each of the first and second surfaces may extend longitudinally along a length of the conductive element. The first surface may be disposed diametrically opposite the second surface of the conductive element.

[0073] A first portion of the electrode assembly contacting the front side of the first solar cell may define a front connecting portion or connector of the electrode assembly, and a second portion of the electrode assembly contacting the back side of the second solar cell may define a back connecting portion or connector of the electrode assembly.

[0074] A first portion of each of the plurality of conductive elements may define a front connector of the electrode assembly. A second portion of each of the plurality of conductive elements may define a back connector of the electrode assembly. Thus, at least one, or each, of the plurality of conductive elements may extend from the front connector to the back connector of the electrode assembly.

[0075] The conductive element may be configured to bend along an axial direction of the conductive element to enable the electrode assembly to be coupled between the front and back surfaces of each of the first and second solar cells (i.e., to enable the conductive element to provide an electrical connection between the front and back connectors).

[0076] A first surface of the conductive element of the rear connector may be positioned to define a rear (i.e., rearmost) surface of the electrode assembly. A second surface of the conductive element of the front connector may be positioned to define a front (i.e., frontmost) surface of the electrode assembly.

[0077] As described above, the conductive elements of the front and back connectors may define a first and second portion of the plurality of conductive elements, respectively. The first portion of the plurality of conductive elements may be disposed in or on a first integral film (e.g., an insulating and / or optically transparent film). The second portion of the plurality of conductive elements may be disposed in or on a second integral film (e.g., an insulating and / or optically transparent film). Thus, the first surface may be exposed from the first integral film to form electrical contact with the front surface of the first solar cell, and / or the second surface may be exposed from the second integral film to form electrical contact with the back surface of the second solar cell.

[0078] A third portion of the plurality of conductive elements may be disposed between the first and second portions of the plurality of conductive elements. The third portion may be configured to be disposed between the first and second solar cells when the electrode assembly is connected therebetween. The third portion may be configured such that the conductive elements of this portion are not disposed within the integral film (i.e., in contrast to the first and second portions).

[0079] At least one, or each, of the conductive elements may be disposed on a surface of each of the first and second integral films. Alternatively, or in addition, at least one of the conductive elements may be at least partially disposed within the integral film. In this manner, at least one conductive element may be embedded within the integral film such that a surface of the conductive element protrudes beyond a surface of the integral film.

[0080] When used, the first integral film of the front connector may define the front integral film of the electrode assembly. Similarly, the second integral film of the rear connector may define the rear integral film of the electrode assembly. The front integral film may be configured such that at least a portion of a first surface of the conductive element of the front connector is exposed. The rear integral film may be configured such that at least a portion of a second surface of the conductive element of the rear connector is exposed.

[0081] The integral film of the front connector may have a back surface (i.e., facing toward the solar cell) and a front surface (i.e., facing away from the solar cell) opposite the back surface. At least one conductive element of a first portion of the plurality of conductive elements may be disposed on the back surface of the front integral film.

[0082] The integral film of the back connector may have a front surface (i.e., facing toward the solar cells) and a back surface opposite the front surface (i.e., facing away from the solar cells). At least one conductive element of the second portion of the plurality of conductive elements may be disposed on the front surface of the integral film.

[0083] Each of the first and second solar cells may have a length, a width, and a depth. The length of the solar cell may be less than its width, and the depth may be less than both its width and length. The longitudinal and lateral directions across the front and back surfaces of the solar cell may be parallel to the length and width directions of the solar cell, respectively. Thus, the plurality of conductive elements may be configured to extend across the length of the solar cell and be spaced apart along its width.

[0084] Each conductive element may be configured to extend longitudinally, vertically, relative to a surface of the solar cell on which it is overlaid. Each conductive element may be spaced laterally, relative to the solar cell surface, to define longitudinally extending spaces between the conductive elements. The conductive elements may be parallel to one another, or substantially parallel. The conductive elements may be equally or substantially equally spaced laterally. Thus, the plurality of conductive elements may form an array of parallel laterally spaced (e.g., equally spaced) conductive elements.

[0085] As described above, the conductive element may be configured to form electrical contact with a conductive surface (e.g., a conductive portion of a surface) of the solar cell. The conductive surface may comprise one or more finger electrodes disposed (e.g., printed) on the front and back surfaces of the layered structure. The one or more finger electrodes may be configured to conduct charge carriers generated by the layered structure.

[0086] Each of the conductive surfaces of the solar cell may include a plurality of finger electrodes extending across the respective solar cell surface, as will be appreciated by those skilled in the art. The finger electrodes may be formed using a printed material that allows them to be conveniently deposited on the surface of the solar cell.

[0087] The solar cell of the solar cell assembly may comprise multiple layers, or elements, including a photovoltaic element, at least one of the layers being formed from a semiconductor material. The photovoltaic element (or layer) may be formed from a crystalline silicon wafer.

[0088] It should be appreciated that the solar cell may be configured to define any type of solar cell structure. For example, the solar cell may define a heterojunction solar cell. Alternatively, the solar cell may define a tandem junction solar cell.

[0089] The surface of the solar cell may be textured to form a textured surface that corresponds to an uneven surface or has uneven characteristics, as will be understood by one of ordinary skill in the art. The textured surface may define an anti-reflective layer or coating disposed on the front and / or back surface of the solar cell.

[0090] The solar cell may include a transparent conductive oxide coating disposed on a front and / or back surface of the solar cell, the transparent conductive oxide coating may be configured to increase lateral carrier transport to finger electrodes disposed on each surface of the solar cell.

[0091] According to an exemplary embodiment, the conductive element may at least partially form an electrode assembly that is applied to the first and second solar cells to define a solar cell assembly. Further, one or more solar cell assemblies according to the present invention may be electrically coupled together and disposed within a housing to define a solar module.

[0092] According to an exemplary embodiment, a second electrode assembly may be provided for coupling the front surface of the second solar cell to the back surface of the third solar cell. The conductive elements in the second electrode assembly may be as described above for the first electrode assembly. In this situation, the second and third solar cells may be combined with the second electrode assembly to define a second solar cell assembly. The conductive elements of the back connector of the first electrode assembly may be aligned with the conductive elements of the front connector of the second electrode assembly, with the second solar cell interposed therebetween.

[0093] The solar module may comprise a frame for housing the plurality of solar cell assemblies. The frame may comprise a front plate and a back plate disposed on the front and back sides of the plurality of solar cell assemblies, respectively. At least one or each of the front plate and the back plate may be formed from glass (e.g., a glass sheet). The solar module may comprise an encapsulant configured to provide adhesion between the front plate and the back plate and the plurality of solar cell assemblies. In this manner, the encapsulant may be disposed between the glass sheet of the solar module and the insulating optically transparent integral film of one of the plurality of solar cell assemblies. The encapsulant may also be disposed between the back sheet of the solar module and the insulating optically transparent integral film of one of the plurality of solar cell assemblies. The encapsulant may be configured to prevent ingress of moisture into the solar module. Thus, the encapsulant may be formed from ethylene vinyl acetate (EVA), or any other suitably moisture resistant material.

[0094] In a fourth aspect, the electrode assembly of the second aspect may be formed according to a manufacturing method of the present disclosure. The method includes thermally bonding a monolithic film to a plurality of conductive elements. The monolithic film is formed from a polymeric material according to any one of the preceding statements (e.g., characterized by the first criterion and / or the second criterion, as described above).

[0095] According to a fifth aspect of the present disclosure, there is provided a method of manufacturing a solar cell assembly according to the third aspect, the method comprising interposing a plurality of conductive elements between the monolithic film and a surface of the solar cell, the method further comprising thermally bonding the monolithic film to the plurality of conductive elements and / or the surface of the solar cell.

[0096] A method of thermally bonding the integral film to a surface of the plurality of elements and / or solar cells may include heating the integral film using at least one of an infrared lamp, a convection heating element, a hot air blower, or an induction heating element.

[0097] The method may include a first method step of thermally bonding the integral film to a plurality of conductive elements, and a second method step of thermally bonding the integral film to a solar cell (e.g., a surface of the solar cell).

[0098] The method may include heating the monolithic film to a pre-bonding temperature corresponding to a temperature of the first endothermic peak prior to thermally bonding the monolithic film to the plurality of conductive elements.

[0099] As described above, at least one or each of the plurality of conductive elements may be thermally bonded to the integral film during use. The integral film may be further configured to attach the conductive elements to the solar cell surface (e.g., to provide a mechanical connection between the conductive elements and the solar cell). The integral film may be configured to maintain the lateral spacing of the conductive elements so that the conductive elements are properly aligned on the solar cell surface. In an exemplary arrangement, the integral film may not cover the entire front and / or back surface of each of the solar cells over which it is stacked.

[0100] The method may include heating and / or applying pressure to (e.g., laminating) the integral film to adhere it to a surface of the conductive element and / or the solar cell. The method may include attaching the integral film to the conductive element before overlaying and / or attaching the conductive element to the solar cell. The method of attaching the integral film to the conductive element may be performed during the method of bonding the associated conductive element to the surface of the solar cell. In this manner, the method of attaching the film to the conductive element (e.g., applying heat and / or pressure to the film) may also include attaching the film to the associated surface of the solar cell.

[0101] During fabrication of the solar cell assembly, heat and / or pressure may be applied to the monolithic film to soften the polymeric material to allow adhesion of the monolithic film to the conductive elements by application of force. In this manner, the conductive elements may be at least partially embedded in the monolithic film. At least a portion of a surface of each conductive element may remain exposed to allow for forming an electrical connection with a respective surface of the solar cell.

[0102] The integral film may be configured to provide structural support to the conductive elements when they are being handled, e.g., prior to being placed on a solar cell. The integral film may be configured such that at least a portion of at least one of the conductive elements is exposed from the film to form electrical contact with a respective surface of the solar cell.

[0103] When the electrode assembly is placed on the solar cell surface, the monolithic film may deform to conform to the shape of the conductive element sandwiched between the monolithic film and the solar cell. In other words, the surface of the monolithic film may form ridges / protrusions on the conductive elements and may be substantially flat in areas without the conductive elements. In this way, the monolithic film may include conductive element contact areas with a non-planar profile.

[0104] According to an exemplary embodiment, a solar cell assembly may include a first solar cell and a second solar cell. The electrode assembly may be configured to electrically connect the first solar cell to the second solar cell. Specifically, the at least one conductive element may be configured to electrically couple a front surface of the first solar cell to a back surface of the second solar cell.

[0105] The method may include placing the second solar cell such that its back surface faces substantially upward (e.g., vertically upward). The method may further include overlaying a first section of the electrode assembly onto the back surface of the second solar cell such that a second surface of the at least one conductive element is disposed in contact with the back surface. The method may further include connecting (e.g., electrically and / or mechanically) the second surface of the at least one conductive element onto the back surface of the second solar cell. The method may include overlaying a front surface of the first solar cell onto the second section of the electrode assembly such that a first surface of the at least one conductive element is disposed in contact with the front surface. The method may further include connecting (e.g., electrically and / or mechanically) the first surface of the at least one conductive element onto the front surface of the first solar cell.

[0106] The solar cells may each include a back surface (e.g., a back surface) and a front surface (e.g., a front surface) opposite the back surface. Thus, the method may include disposing a portion of the electrode assembly on the back surface of the second solar cell to define a back connector. The method may further include disposing another portion of the electrode assembly on the front surface of the first solar cell to define a front connector.

[0107] The conductive elements may be coated with a solderable material that has a lower melting point than the material from which the conductive elements are formed.

[0108] The method may include applying heat and / or pressure (e.g., soldering) to a first portion of the conductive element (i.e., at the front connector) to form electrical contact with a conductive surface (e.g., a finger electrode) of a first solar cell overlying the conductive element. The method may include applying heat and / or pressure (e.g., soldering) to a second portion of the conductive element (i.e., at the back connector) to form electrical contact with a conductive surface (e.g., a finger electrode) of a second solar cell overlying the conductive element.

[0109] The method may include first attaching one of the front and back connectors to the respective first and second solar cells, and then attaching the other of the front and back connectors to the other of the respective first and second solar cells.

[0110] The method may further include disposing (e.g., depositing) a plurality of finger electrodes on at least one, or each, of the front and back surfaces of the first and second solar cells. It should be understood that the method of disposing the finger electrodes may be performed prior to connecting the electrode assembly to the solar cells. The finger electrodes may be formed using a printing material that allows it to be conveniently deposited on the surface of the solar cells. The printing material may be formed using a printable precursor, such as a conductive paste, which may include a mixture of metal powders (e.g., Ag, Al, Au powders) and an organic binder (such as an epoxy). The printable precursor / conductive paste may be fired or cured to form the printed finger electrodes. Alternatively, the finger electrodes may be deposited by a variety of other methods, including evaporation, plating, printing, and the like. The front finger electrodes and the back finger electrodes may be deposited simultaneously (i.e., using a single deposition process) or they may be deposited separately.

[0111] It should be understood that the terms "conductive" and "insulating" as used herein are expressly intended to mean electrically conductive and electrically insulating, respectively. The meaning of these terms should be particularly clear when considering the technical context of this disclosure, i.e., the context of a photovoltaic solar cell device. It should also be understood that the term "electrical contact" is intended to mean a non-rectifying electrical junction (i.e., a junction between two conductors that exhibits a substantially linear current-voltage (IV) characteristic).

[0112] Those skilled in the art will appreciate that, unless mutually exclusive, a feature or parameter described in connection with any one of the above embodiments may be applied to any other embodiment. Furthermore, unless mutually exclusive, any feature or parameter described herein may be applied to any embodiment and / or may be combined with any other feature or parameter described herein. [Brief description of the drawings]

[0113] Embodiments will now be described, by way of example only, with reference to the drawings in which:

[0114] [Figure 1] 1 is an enlarged cross-sectional side view of a solar module including a solar cell assembly, the solar cell assembly comprising a first solar cell coupled to a second solar cell by an electrode assembly. [Figure 2A] 1A and 1B are plan views of the top (front) and bottom (back) surfaces of the first and second solar cells, respectively, as shown in FIG. 1 (1). [Figure 2B] 2A and 2C are cross-sectional views (1) taken through a first solar cell and a second solar cell, respectively. [Figure 2C] 2A and 2B are plan views of the top (front) and bottom (back) surfaces of the first and second solar cells, respectively, as shown in FIG. 1. [Figure 2D] 2A and 2C are cross-sectional views (2) taken through the first and second solar cells as shown in FIGS. 2A and 2C, respectively. [Diagram 3] FIG. 1 is a side view of a solar cell assembly (1) showing different stages of a method for manufacturing the solar cell assembly. [Figure 4] 2 is a side view of a solar cell assembly showing different stages of a method for manufacturing the solar cell assembly; FIG. [Diagram 5] 3 is a side view of a solar cell assembly showing different stages of a method for manufacturing the solar cell assembly (3). [Figure 6] 4 is a side view of a solar cell assembly showing different stages of a method for manufacturing the solar cell assembly (4). [Figure 7] 1 is a side view (5) of a solar cell assembly showing different stages of a method for manufacturing the solar cell assembly. [Figure 8] 6 is a side view of a solar cell assembly showing different stages of a method for manufacturing the solar cell assembly (6). [Figure 9] 9 is a flow chart illustrating a method of manufacturing a solar cell assembly as shown in FIGS. 3-8. [Figure 10] FIG. 1 is a schematic diagram of a differential scanning calorimeter for determining thermal transitions in materials. [Figure 11] 1 is a flow chart illustrating a method for determining a characteristic property of a polymer material of an integral film for an electrode assembly of a solar cell. [Figure 12] 10 and 11 are differential scanning calorimeter traces (1) of different polymeric materials determined using a calorimeter according to the method shown in FIG. [Figure 13] 11 is a differential scanning calorimeter trace (2) of different polymeric materials determined using a calorimeter as shown in FIG. 10 and according to the method shown in FIG. [Figure 14] 11 is a differential scanning calorimeter trace (3) of different polymeric materials determined using a calorimeter as shown in FIG. 10 and according to the method shown in FIG. [Figure 15]11 are differential scanning calorimeter traces (4) of different polymeric materials determined using a calorimeter as shown in FIG. 10 and according to the method shown in FIG. [Figure 16] 11 are differential scanning calorimeter traces (5) of different polymeric materials determined using a calorimeter as shown in FIG. 10 and according to the method shown in FIG. [Figure 17] 11 are differential scanning calorimeter traces (6) of different polymeric materials determined using a calorimeter as shown in FIG. 10 and according to the method shown in FIG. [Figure 18] FIG. 1 is a schematic diagram of a 180-degree peel tester for determining the peel strength of polymer integral films (1). [Figure 19] FIG. 2 is a schematic diagram of a 180-degree peel tester for determining the peel strength of polymer integral films (2). [Figure 20] 1 is a flowchart illustrating a method for determining the peel strength of an integral film of an electrode assembly of a solar cell. [Figure 21] As shown in FIG. 18 and FIG. 19, peel force traces (1) of different polymeric materials determined using a 180 degree peel tester according to the method shown in FIG. [Figure 22] As shown in FIG. 18 and FIG. 19, peel force traces (2) of different polymeric materials determined using a 180 degree peel tester according to the method shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0115] Aspects and embodiments of the present disclosure will now be described with reference to the accompanying drawings. Further aspects and embodiments will be apparent to those skilled in the art.

[0116] An exemplary solar cell assembly 10 manufactured according to the method of the present disclosure is described with reference to Figures 1 and 2A-2D. In the drawings, thicknesses of layers, films, elements, etc. are exaggerated for clarity. Furthermore, when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it should be understood that it may be directly on the other element, or that intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0117] 1 shows a solar cell assembly 10 disposed within a support assembly 102 of a solar module 100 (e.g., a solar panel). The solar cell assembly 10 includes a first solar cell 20, a second solar cell 30, and an electrode assembly 12 disposed to electrically couple a front surface 22 of the first solar cell 20 to a back surface 34 of the second solar cell 30.

[0118] The electrode assembly 12 also includes a plurality of conductive elements that are configured to provide an improved electrical path between the first solar cell 20 and the second solar cell 30 while simultaneously enhancing light scattering and absorption conditions at the front surface 22 of the first solar cell 20.

[0119] A first portion of the electrode assembly 12 is positioned to contact the front surface 22 of the first solar cell 20 to define a front connection portion or front connector 12a of the electrode assembly 12. A second portion of the electrode assembly 12 contacts the back surface 34 of the second solar cell 30 to define a back connection portion or back connector 12b of the electrode assembly 12. The first connector 12a and the second connector 12b are electrically coupled together by a third interconnect portion 12c that bends between the front surface 22 and the back surface 34 of each of the adjacently positioned solar cells 20, 30 of the solar cell assembly 10.

[0120] The solar cell assembly 10 is one of a plurality of solar cell assemblies arranged within a support assembly 102. For example, the front surface 32 of the second solar cell 30 is electrically coupled to the back surface of a third solar cell (not shown) by a second electrode assembly 14. Also, a third electrode assembly 16 is provided to couple the back surface 24 of the first solar cell 20 to the front surface of a fourth solar cell (not shown).

[0121] For example, it will be appreciated that the second and third solar cells in this arrangement are electrically coupled together by the second electrode assembly 14 to define a second solar cell assembly, whereby a plurality of solar cells 20, 30 are coupled together by the electrode assemblies 12, 14, 16 to define a single string.

[0122] The front plate 104 of the support assembly 102 comprises a transparent (e.g., glass) sheet configured to allow light to pass through to a central chamber 106 in which the solar cell assembly 10 rests. The arrows at the top of Figure 1 indicate the direction of solar radiation incident on the solar cell assembly 10.

[0123] A back plate 108 of the support assembly 102 is positioned to enclose the solar cell assembly 10 within a central chamber 106. The back plate 108 includes a reflective sheet configured to reflect any light incident on its top surface toward the solar cell assembly 10. The central chamber 106 is filled with an encapsulant material (shaded area shown in FIG. 1 ) that prevents outside liquids from entering or gases from entering.

[0124] Figures 2A and 2C illustrate top (front) and bottom (back) views, respectively, of the first solar cell 20 and the second solar cell 30 of the solar cell assembly 10. Figures 2B and 2D show cross-sectional views of the first solar cell 20 and the second solar cell 30 taken along dashed lines AA and BB, respectively, as shown in Figures 2A and 2C.

[0125] Each of the solar cells 20, 30 has a length, which is the vertical dimension in Figures 2A and 2C, and a width, which is the horizontal dimension in Figures 2A and 2C. The first solar cell 20 and the second solar cell 30 are arranged in a common cross-section (as shown in Figure 1) with their width and length dimensions parallel to one another. Each of the front surfaces 22, 32 of each solar cell defines a surface onto which light is incident when the solar cell assembly 10 is in use. Each of the back surfaces 24, 34 defines a surface opposite the respective front surface 22, 32, as shown in Figures 2B, 2D.

[0126] Each solar cell 20, 30 includes a layered structure (not shown) disposed between its respective front and back surfaces. The layered structure is a multi-layer semiconductor assembly including photovoltaic elements (or layers) configured to generate charge carriers from the absorption of incident radiation. The front and back finger electrodes 26, 36, 28, 38 are each configured to conduct the charge carriers generated by the respective solar cell 20, 30.

[0127] The first solar cell 20 includes a first plurality of finger electrodes 26 (i.e., front finger electrodes) disposed on its front surface 22 and a second plurality of finger electrodes 28 (i.e., back finger electrodes) disposed on its back surface 24. Similarly, the second solar cell 30 includes a first plurality of finger electrodes 36 disposed on its front surface 32 and a second plurality of finger electrodes 38 disposed on its back surface 34.

[0128] The electrode assembly 12 includes a plurality of conductive elements 18, as shown in Figures 2A-2D. The conductive elements 18 are configured to form electrical contact with finger electrodes 26, 38 disposed on the front surface 22 and back surface 34 of the first and second solar cells, respectively. The conductive elements 18 each have an integral elongated form, such as a wire, formed from a conductive material. For example, the conductive elements 18 include a metal alloy material including at least one of Ag, Al, Au, and Cu. The conductive elements 18 are each disposed within an optically transparent insulating film 40, as shown most clearly in Figures 2B and 2D.

[0129] A first portion 18a of the plurality of conductive elements 18 defines a front connector 12a of the electrode assembly 12. A second portion 18b of the plurality of conductive elements 18 defines a back connector 12b of the electrode assembly 12. Thus, each of the plurality of conductive elements 18 extends from the front connector 12a to the back connector 12b of the electrode assembly 12. A third portion 18c of the plurality of conductive elements 18 is configured to electrically couple the respective first and second portions 12a, 12b together.

[0130] Each of the conductive elements 18 defines a current collector for the electrode assembly 12. Moreover, the conductive elements 18 are configured to collect charge carriers from the front finger electrode 26 of the first solar cell 20 and transfer them to the back finger electrode 38 of the second solar cell 30, or vice versa. Each of the conductive elements 18 comprises a width, a length, and a depth. The length of each conductive element 18 defines an axial length that is substantially greater than its width and depth.

[0131] Next, the configuration of each of the plurality of finger electrodes 26, 28, 36, 38 and the conductive element 18 will be described in more detail with reference to FIGS. 2A to 2D.

[0132] A plurality of front and back finger electrodes 26, 28, 36, 38 are arranged to extend laterally (horizontally in FIGS. 2A, 2C) across the solar cell 20, 30 and are equally spaced apart longitudinally (vertically in FIGS. 2A, 2C). The dimensions of each finger electrode 26, 28, 36, 38 are substantially the same as the dimensions of every other finger electrode 26, 28, 36, 38. Furthermore, each of the finger electrodes has a rectangular cross-section (measured perpendicular to the length of the electrode).

[0133] The finger electrodes disposed on each of the front 26, 36 and back 28, 38 sides of the solar cell 20, 30 are aligned parallel to each other and to corresponding finger electrodes on the opposite side of the solar cell. As shown in Figures 2A and 2C, each of the plurality of front and back finger electrodes 26, 28, 36, 38 includes 12 finger electrodes.

[0134] The finger electrodes 26, 28, 36, 38 are formed from a conductive material, which is formed from a metal alloy including Ag. It should be appreciated that the conductive material is a printing material that allows the finger electrodes to be conveniently deposited on each surface of the solar cell.

[0135] First and second portions 18a, 18b of the plurality of conductive elements 18 are parallel to and extend lengthwise relative to the front and back surfaces 22, 34 of the solar cell in a longitudinal direction (vertical in FIG. 2A). The conductive elements 18 are also equally spaced laterally relative to the front and back surfaces 22, 34 (horizontal in FIG. 2A) so as to define longitudinally extending spaces between the conductive elements 18. Each one of the first and second portions 18a, 18b thus defines an array of parallel, laterally spaced conductive elements 18.

[0136] Each of the first portions 18a of the plurality of conductive elements 18 is axially aligned with a corresponding second portion 18b of the conductive element 18 of the same electrode assembly 12. Also, the second portion 18b of the conductive element 18 of the first electrode assembly 12 is axially aligned with the first portion 18a of the conductive element 18 of the second electrode assembly 14, with the second solar cell 30 therebetween. Thus, as shown in Figures 2A and 2C, the plurality of front finger electrodes 26 and back finger electrodes 38 are disposed perpendicular to the first portions 18a and second portions 18b of the plurality of conductive elements 18.

[0137] The number of conductive elements 18 in the electrode assembly 12 is between 4 and 20. According to embodiments described herein, the first electrode assembly 12 has 16 conductive elements 18, as shown in Figures 2A-2D. It should be appreciated that in some other embodiments, there may be a different number of conductive elements and / or finger electrodes without departing from the scope of the present invention.

[0138] Conductive elements 18 each have a circular cross-sectional shape (i.e., transverse to the axial length of conductive element 18) as shown in Figures 2B and 2D. However, conductive elements 18 may be configured to have different cross-sectional shapes without departing from the scope of the present invention.

[0139] Each of the conductive elements 18 includes a first surface 50 configured to make electrical contact with the front surface 22 of the first solar cell 20, as shown in FIGURE 1. Each conductive element 18 also includes a second surface 52 configured to make electrical contact with the back surface 34 of the second solar cell 30, as shown in FIGURE 1.

[0140] Each of the conductive elements 18 is formed from a single wire portion (i.e., the first portion 18a and the second portion 18b of each conductive element 18 are integrally formed with one another). In this manner, the conductive elements 18 provide a direct electrical connection between the first solar cell 20 and the second solar cell 30 to facilitate the flow of electrical current therebetween. The plurality of conductive elements 18 are covered with a coating (not shown) that is configured to, in use, solder the respective first and second surfaces 50, 52 to the respective surfaces of the solar cells 20, 30 over which they are stacked. The coating is a conductive material that has a melting point lower than the melting point of the conductive elements 18.

[0141] It should be seen that Figures 2A and 2B show a first portion 18a of the conductive element 18 (i.e., the front connector 12a of the electrode assembly 12) on the front side 22 of the first solar cell 20, while Figures 2C and 2D show a second portion 18b of the same conductive element 18 (i.e., the back connector 12b of the electrode assembly 12) on the back side 34 of the second solar cell 30.

[0142] As mentioned above, the electrode assembly 12 includes an insulating, optically transparent film 40 that is thermally bonded to the conductive element 18. Generally, the film has a monolithic construction (i.e., formed from a single layer of material rather than multiple separate layers) and is formed from a polymeric material. Certain characteristic properties of the polymeric material that determine how the monolithic film 40 adheres to the conductive element and / or solar cell surface can be determined using differential scanning calorimetry (DSC) analysis, as described in more detail below.

[0143] The polymeric material may be formed from a polymeric resin including at least one of polyolefin elastomers (POE), polyvinyl butyral (PVB) hydrocarbon ionomers, thermoplastic organosilicones, silicone rubbers, polyurethanes, thermoplastic silicone elastomers (TPSEs), and ethylene-vinyl acetate (EVA). The polymeric material is selected to encompass the following characteristics: high ductility, low electrical conductivity, high optical transparency, thermal stability, and resistance to shrinkage.

[0144] The integral film is configured to have a haze parameter of less than 35%, alternatively at most 25%, optionally at most 18%.

[0145] It should be appreciated that the haze parameter of a polymeric material may be defined as a measure of the percentage of incident light that is scattered beyond 2.5° as measured by a spectrophotometer.

[0146] The monolithic film is configured to transmit at least 85% of incident light having wavelengths between 280 nm and 1100 nm.

[0147] The integral film has a thickness of at least 25 μm, optionally at least 55 μm, and / or at most 180 μm. The front film portion 42 and the back film portion 44 are thinner than the conductive element 18. For example, the conductive element 18 has a thickness of 200 μm to 300 μm.

[0148] The first and second portions 18a, 18b of the plurality of conductive elements 18 are each disposed in separate film portions that are disposed on the front and back surfaces 22, 34 of the respective solar cells. For example, the front connector 12a includes a first film portion that defines a front film portion 42, and the back connector 12b includes a second film portion that defines a back film portion 44. Note, however, that the conductive elements 18 in the third portion 18c are not covered by either film.

[0149] According to an exemplary configuration of the solar cell assembly 10, each of the first portion 18a and second portion 18b of the conductive element 18 is attached to a surface of its respective integral film 42, 44 that faces the solar cell. Thus, the "solar cell facing" surface of each integral film portion 42, 44 is thermally bonded to the surfaces 22, 34 of the first solar cell 20 and second solar cell 30, respectively.

[0150] 2B and 2D, for front connector 12a, film 42 is positioned to contact the front surface 22 of the solar cell in the area between the conductive element 18 and the front finger electrode 26. Back film portion 44 is configured in the same manner for back connector 12b. Each of films 42, 44 is configured to at least partially (e.g., completely) surround or encircle a respective conductive element 18 and respective finger electrode 26, 38, as shown in FIG. 2B and 2D.

[0151] The front film portion 42 and the back film portion 44 are positioned to provide adhesion between the solar cell and the conductive element 18, and to ensure that the conductive element is properly positioned on the solar cell (i.e., aligned with the finger electrodes). In an exemplary embodiment, the front film portion 42 and the back film portion 44 may not completely cover their respective surfaces of the solar cell.

[0152] In contrast, the front film portion 42 and back film portion 44 shown in the drawings include substantially flat bottom and top surfaces, respectively. It should be appreciated that the film may be configured to conform to the structural components of the solar cells and / or conductive elements. For example, film 40 may be configured with elongated channels recessed toward the solar cells in areas of the solar cell surface between the conductive elements on the back surface 34, or may form ridges / protrusions on the structural electrodes (e.g., finger electrodes and conductive elements), if present.

[0153] An exemplary method for manufacturing the solar cell assembly 10 will now be described with reference to Figures 3 to 8, which illustrate the steps of the manufacturing method, and with reference also to Figure 9, which shows a flow chart of the corresponding method steps.

[0154] The method begins with a first method step 202 in which a plurality of conductive elements 18 are thermally bonded to a one-piece film 40 to form the electrode assembly 12. As described above, the one-piece film 40 comprises separate first and second film portions 40a and 40b. As shown in Figures 3 and 4, the method includes disposing a first portion 18a of the plurality of conductive elements 18 on the first one-piece film portion 40a to define a front connector 12a of the electrode assembly 12. The method further includes disposing a second one-piece film portion 42 on a second portion 18b of the plurality of conductive elements 18 to define a back portion 12b of the electrode assembly 12.

[0155] Heat and pressure are applied to the integral film portions 42, 44, as shown in FIG. 4, softening the polymeric material of the film and thereby adhering the film portions to the conductive elements 18. This causes the conductive elements 18 to be at least partially embedded in the integral film portions 42, 44 such that at least a portion of each conductive element remains exposed to form electrical contact with the respective solar cells 20, 30. The integral film 40 is heated using infrared lamps (not shown). Alternatively, the required heat may be applied by any suitable heating means, such as convection heating elements, hot air blowers, or induction heating elements. The heating means can be configured to control the temperature of the integral film 40 during the bonding process, as described in more detail below.

[0156] It should be appreciated that the first portion 18a and the second portion 18b of the plurality of conductive elements 18 can be attached to the respective integral film portions 42, 44 simultaneously or during separate processes. When the electrode assembly 12 is in use, the first portion 18a of the plurality of conductive elements defines the front connector 12a of the electrode assembly 12, while the second conductive element portion 18b defines the back connector 12a. Similarly, the first integral film portion 42 and the second integral film portion 44 define front and back integral film portions, respectively.

[0157] In a second method step 204, the first solar cell 20 is thermally bonded to the front connector 12a of the electrode assembly 12. The first portion 18a of the conductive element is brought into contact with the front surface 22 of the first solar cell 20, as shown in FIG. 5. The conductive elements of the front connector 12a are superimposed on the front surface 22 of the first solar cell 22 such that they lie perpendicular to the front finger electrodes, as shown in FIG. 2A. The method further involves heating and / or applying pressure to the conductive elements 18 of the front connector 12a to physically bond them to the front surface 22 of the first solar cell under a compressive force, as illustrated in FIG. 6. The application of heat and pressure also laminates the front integral film portion 42 onto the front surface 22 of the first solar cell 20.

[0158] In a third method step 206, the second solar cell 30 is thermally bonded to the back connector 12b of the electrode 12, as shown in Figures 7 and 8. The method includes stacking the back connector 12b on the back surface 34 of the second solar cell 30 so that it is positioned perpendicular to the finger electrodes 38, as shown in Figure 2D. The third method step 206 further involves heating and / or applying pressure to the conductive element 18 in the second connector 12b to bond the electrode assembly 12 to the back surface 34 of the second solar cell under a compressive force, as illustrated in Figure 8. The application of heat and pressure also laminates the back surface integral film portion 44 onto the back surface 34 of the second solar cell 30.

[0159] The application of heat and pressure during second method step 204 and third method step 206 causes the coating on the conductive elements 18 to melt and flow toward the finger electrodes on each surface of the solar cells 20, 30. As the coating cools and solidifies, it forms electrical contact with the underlying finger electrodes 38, as shown in Figures 2B and 2D.

[0160] As a result of the above-described method, the front connector 12a and the back connector 12b of the electrode assembly 12 are both mechanically and electrically coupled to the respective first solar cell 20 and second solar cell 30 to form the solar cell assembly 10 according to the present invention.

[0161] It should be appreciated that at least some of the above method steps may be performed simultaneously or in any order. For example, the front connector 12a and the back connector 12b may also be simultaneously connected to the front surface 22 and the back surface 34 of the first solar cell 20 and the second solar cell 30, respectively.

[0162] Prior to at least the second method step 204, the solar cells are fabricated in a conventional manner, as would be understood by one skilled in the art. In particular, the method includes configuring each of the solar cells with a conductive surface (or conductive portion) on the respective front and back surfaces, for example to form a plurality of front finger electrodes 36 and back finger electrodes 38, respectively. The finger electrodes 36, 38 are deposited on their respective surfaces using a screen printing process, as would be understood by one skilled in the art. Once the plurality of finger electrodes 36, 38 are deposited on the surfaces of the first solar cell 20 and the second solar cell 30, the electrode assembly 12 can be connected to the solar cells 20, 30 to define the solar assembly 10.

[0163] As mentioned above, the material of the integral film 40 (e.g., the front and back integral film portions 42, 44) is a polymeric material. The polymeric material of the integral film 40 is characterized by determining its physical properties according to a set of criteria. In particular, a first criterion and a second criterion, respectively, can be used to determine the thermal properties and peel force properties of the integral film 40.

[0164] The first standard for integrated films The first criterion is used to determine that the polymeric material has at least two endothermic peaks at temperatures between 40° C. and 200° C. as measured by differential scanning calorimetry (DSC).

[0165] The first standard DSC test method involves heating and / or cooling a sample of a polymeric material and measuring the heat flow towards (and / or away from) the material over time to identify and measure endothermic peaks. The analysis is performed using a differential scanning calorimeter 60, as shown in Figure 10. The endothermic peaks should be found to correspond to thermal transitions in the polymeric material.

[0166] An exemplary DSC test method 210 according to the first criteria for the integral film 40 will now be described with reference to Figure 11, which shows a flow chart of the corresponding method steps. Reference is also made to Figure 10, which shows a schematic diagram of the calorimeter 60 used to test the polymeric materials, and Figures 12-17, which show heating and cooling traces for a variety of different polymeric materials under investigation. The DSC test method 210 is used to identify and determine whether a polymeric material meets the required thermal properties for the integral film 40.

[0167] The DSC test method 210 incorporates standard test method ASTM D3418, which is a standard test method for transition temperatures and enthalpies of fusion and crystallization of polymers by differential scanning calorimetry. The DSC test method 210 includes a first method step 212 that involves performing a first thermal cycle and a second thermal cycle on a sample of the polymeric material 66 of the integral film 40. The first and second thermal cycles are performed sequentially according to standard test method ASTM D3418.

[0168] The first thermal cycle includes a heating stage where the sample is gradually heated from 0°C to 300°C at a heating rate of 10° / min. The heating stage of the first thermal cycle removes any thermo-mechanical history of the sample that may result from the manufacturing process used to make the film. After the heating stage of the first thermal cycle is complete, the material sample 66 is held by the calorimeter 60 at a holding temperature of 300°C for 5 minutes.

[0169] Method step 212 involves placing a polymeric material sample 66 in a test cell 62 that is thermally coupled to an empty reference cell 64 by a connector 70. A control module 68 of the calorimeter 60 is configured to control a pair of electrical heating elements 72 to control the temperature and heating rate of the test cell 62 and the reference cell 64.

[0170] During the DSC analysis, the control module 68 monitors the heat flow between the test cell 62 and the reference cell 64 as both cells are heated. The measured DSC data is output in the form of a trace (e.g., a heating trace) of heat flow (W / g) plotted against either temperature (° C.) and / or time (sec), as shown in FIG.

[0171] Heat flow represents the power per unit mass (W / g) flowing between the test cell 62 and the reference cell 64. It should be noted that in Figures 12-15 the y-axes have been normalized to show multiple traces on the same set of axes, but in Figures 16 and 17 the heat flow values ​​are shown in units of W / g. The temperature values ​​on the lower x-axis shown in Figures 12-17 correspond to the temperatures (°C) of the test cell 62 and the reference cell 64. The time values ​​shown on the upper x-axis represent the duration of the DSC analysis measured in seconds.

[0172] The first thermal cycle also includes a cooling step that follows consecutively from the heating step. The cooling step involves cooling the polymeric material sample 66 at a rate of 10° / min to a temperature of 300°C to -50°C. During the cooling step, the control module 68 monitors the heat flow between the test cell 62 and the reference cell 64 and outputs a cooling trace of heat flow (W / g) versus temperature (°C) and / or time (sec), as shown in Figure 13. Once the cooling step is complete, the material sample 66 is held by the calorimeter 60 at a holding temperature of -50°C for 5 minutes.

[0173] Once the five minutes have elapsed, method step 212 begins by performing a second thermal cycle on the sample 66. The second thermal cycle includes a heating phase in which the sample 66 is gradually heated from -50°C to 300°C at a heating rate of 10° / min. As with the first thermal cycle, the control module 68 monitors the test cell 62 and reference cell 64 throughout the second heating phase and outputs a second heating trace, as shown in Figures 14 and 15.

[0174] Thus, a first heating trace is measured during a heating phase of a first thermal cycle and a second heating trace is determined during a heating phase of a second thermal cycle.

[0175] Throughout the various DSC analyses (e.g., the heating and cooling stages of the first and second thermal cycles), the polymeric material sample 66 is maintained in an inert atmosphere (e.g., a nitrogen atmosphere) to prevent the material sample 66 from reacting with the atmosphere (e.g., oxidizing). According to an exemplary method, the calorimeter 60 is purged with nitrogen gas at a purge flow rate of 50 mL / min.

[0176] DSC traces of six exemplary polymeric materials (PM1-6) are shown in Figures 12-17. The traces shown in Figures 12 and 16 correspond to the heating stage of the first thermal cycle (i.e., samples are heated from 0°C to 300°C at a heating rate of 10° / min). The traces shown in Figure 13 correspond to the cooling stage of the first thermal cycle (i.e., samples PM1-PM5 are cooled from 300°C to -50°C at a cooling rate of 10° / min). The traces shown in Figures 14, 15, and 17 correspond to the heating stage of the second thermal cycle (i.e., samples are heated from -50°C to 300°C at a heating rate of 10° / min).

[0177] Each of the materials PM1-6 is analyzed to generate a composite DSC trace including a test trace (i.e., corresponding to the test cell 62) and a reference trace 64 (i.e., corresponding to the reference cell 64). Since nothing is contained within the reference cell 64, the reference trace is substantially flat. Phase transitions of the sample materials PM1-6 appear as peaks in the test trace that deviate from the reference trace. In the case of an endothermic transition, the peak appears as a negative peak due to the heat flow absorbed by the material sample 66 in the test cell 62 as it melts.

[0178] A further method step 214 includes identifying the presence of two endothermic peaks in the first and second heating traces corresponding to the polymeric material sample 66. In particular, method step 214 includes identifying the presence of a first endothermic peak and a second endothermic peak in each of the first and second heating traces, and determining that the first and second endothermic peaks in each of the first and second heating traces are at temperatures between 40°C and 200°C.

[0179] Identifying the presence of a peak (e.g., an endothermic peak) in a DSC trace involves identifying an area of ​​the test trace that deviates from the reference trace to form a local minimum (i.e., a negative peak). In the case of an endothermic peak, the peak falls below the reference trace because it corresponds to an endothermic transition in the polymeric material that directs heat flow toward the test cell 62.

[0180] Once an endothermic peak has been identified, it can be characterized to determine the associated peak temperature (Tp). The peak temperature is determined by identifying the minimum heat flow value of the melting peak, i.e., a value that is smaller than its nearest neighbor. The peak temperature of the first endothermic peak (i.e., the first peak temperature) represents the characteristic temperature of the endotherm corresponding to the polymeric material under investigation.

[0181] As can be seen in each of the traces shown in Figures 12 and 14, there are no peaks below 40°C and above 200°C. From this, it can be determined that there is no endothermic transition in this temperature range. Also, note that, as expected, the reference trace for each sample remains substantially constant over the entire temperature range.

[0182] From the DSC traces shown in Figure 12, it is apparent that PM1, PM2, PM3, PM4, and PM5 each have at least two endothermic peaks (e.g., first and second endothermic peaks) with corresponding first and second peak temperatures between 40° C. and 200° C. In contrast, PM6 has only one endothermic peak that falls within the required temperature range (i.e., 40° C. and 200° C.), as shown by the trace in Figure 16.

[0183] In situations where multiple peaks are identified in a heating trace (e.g., a first and a second endothermic peak), the first peak corresponds to the peak having the lowest peak temperature, and the second peak represents the peak exhibiting a higher peak temperature. Similarly, if a trace has three peaks, the third peak may be identified as having a peak temperature greater than the peak temperatures of the first and second peaks.

[0184] Thus, each of the polymeric materials PM1-5 meets the first criterion as determined by DSC test method 210 and would therefore, if so, fall within the scope of an integral film 40 according to an embodiment of the present disclosure. Moreover, such an integral film 40 would be suitable for use in an electrode assembly and / or solar cell assembly according to an embodiment of the present disclosure.

[0185] In contrast, the PM6 material does not fall within the scope of embodiments of the present disclosure because the polymeric material does not meet the first criterion, as determined by DSC test method 210.

[0186] A summary of the results of the DSC analysis of method step 214 for polymeric materials PM1-6 is shown in Table A. Note that materials PM1-5 each have at least two endothermic peaks within the 40° C. to 200° C. range in each of the first and second heating traces, while the PM6 material has only one peak within the required range (e.g., in both the first and second heating traces).

[0187] The first and second endothermic peaks are clearly visible in the first and second heating traces of materials PM1-3 and PM5, respectively, and in the first heating trace of material PM4. A close-up of the second heating trace of material PM4 is shown in FIG. 15, highlighting the two distinct endothermic peaks at 105.39° C. and 122.70° C., respectively. [Table 1]

[0188] According to an alternative exemplary form of the integral film 40, the first criterion requires the presence of two distinct peaks (e.g., a first and a second endothermic peak) in the first heating trace within the temperature range of 80° C. to 160° C. As can be seen from Table A (and FIG. 12), each of the materials PM1-5 meets this criterion since each of the traces exhibits two distinct endothermic peaks within the required temperature range. Thus, integral films 40 formed from these polymeric materials will exhibit particularly beneficial adhesive properties when used as foils in solar cell electrode assemblies 12.

[0189] A further condition of the first criterion is that the second heating trace has two distinct endothermic peaks (e.g., a first endothermic peak and a second endothermic peak) within the temperature range between 80° C. and 160° C. Again, as shown in Table A above, each of materials PM1-5 meets this criterion. However, material PM6 does not meet the criterion (e.g., because it has only one endothermic peak, 145.45° C., within the required range).

[0190] A further requirement of the first criterion is that at least one (e.g., the first endothermic peak) in each of the first and second heating traces is between 40° C. and 130° C. This is true for each of the materials PM1-5, but not PM6. Thus, PM6 does not meet the condition and does not fall within the scope of the integral film 40 according to the present disclosure.

[0191] An additional exemplary condition of the first criterion is that the second heating trace has an endothermic peak (e.g., the first endothermic peak described above) at a temperature between 80° C. and 130° C. Additionally, each of the first heating trace and the second heating trace may be required to include at least one additional endothermic peak (e.g., the second and / or third endothermic peaks as described above) between 100° C. and 160° C. A further requirement of the first criterion may be that the at least one additional endothermic peak of the first heating trace is between 100° C. and 145° C. Each of materials PM1-5 would meet each of these conditions and thus fall within the scope of the integral film 40 according to the present disclosure.

[0192] According to an alternative exemplary condition of the first criterion, the further endothermic peak in the first heating trace is between 100°C and 135°C. Each of the materials PM1, PM2, PM4, and PM5 meets this condition. According to a further exemplary condition of the first criterion, each of the first heating trace and the second heating trace may be required to include at least one further endothermic peak (e.g., the second and / or third endothermic peaks described above) at a temperature between 100°C and 145°C. Each of the materials PM1, PM2, PM4, and PM5 meets these conditions.

[0193] The DSC test method 210 includes further means for determining that the polymeric material (e.g., PM1-5) has the desired thermal properties for use as the integral film 40. According to an exemplary method, method step 214 includes identifying a third endothermic peak in each of the first and second heating traces (e.g., the third peak present in the DSC traces of PM2, as shown in Figures 12 and 14). This also includes determining that the peak temperature of the third endothermic peak (e.g., the third peak temperature) is within the required temperature range of 130°C to 200°C. As shown in Table A, material PM2 is the only sample that exhibits a third endothermic peak in each of its first and second heating traces. Further, note that each of the third endothermic peaks of PM2 is within the required temperature range. Thus, material PM2 meets the requirements of the standard and should preferably be suitable for use in an integral film 40 according to an exemplary embodiment of the present disclosure.

[0194] According to a further exemplary embodiment of the DSC test method 210, method step 212 includes monitoring heat flow between the test cell 62 and the reference cell 64 during a cooling phase of the first thermal cycle and outputting a cooling trace (as described above). Method step 214 may then include identifying and determining an exothermic peak at a temperature between 0° C. and 200° C.

[0195] A series of cooling traces for polymeric materials PM1-5 are shown in Figure 13 and a summary of the results is provided below in Table B. From this, it is clear that each of materials PM1-5 exhibits an exothermic peak within the required temperature range and therefore meets the criteria. [Table 2]

[0196] A further condition of the first criterion may be that the exothermic peak is between 40° C. and 130° C. Again, each of materials PM1-5 meets this requirement. Similar to the analysis of the first and second heating traces, the cooling trace DSC analysis may include identifying at least a second (and third) endothermic peak having a peak temperature within the required temperature range.

[0197] The results of the DSC test method 210 can be used to optimize a method of manufacturing a solar cell assembly 200, as shown in Figure 9. In particular, the manufacturing method 200 is adapted to heat the integral film 40 to a pre-bonding temperature (e.g., a pre-bonding heating step) based on the DSC test method 210 prior to thermally bonding the integral film 40 to the plurality of conductive elements 18. The introduction of a pre-bonding heating step to the manufacturing method 200 improves the adhesion of the integral film 40 to the plurality of conductive elements 18. The pre-bonding temperature is determined based on a first endothermic peak temperature of a first heating trace (i.e., corresponding to a heating stage of a first thermal cycle) as determined by the DSC test method step 210.

[0198] The second standard for integral films According to the second criterion, the polymeric material of the integral film 40 is determined to have a peel strength of at least 5 N per 10 mm width of the integral film 40 as measured by a 180 degree peel test. The peel test is used to determine (e.g., measure) the adhesion between the integral film 40 that is thermally bonded to a surface of a substrate (e.g., a receiving surface of a solar cell). The peel test is performed according to standard test method ASTM D903 to provide a peel force trace for each sample film under test.

[0199] The peel test method is carried out using a 180 degree peel test apparatus 80, as shown in Figures 18 and 19. The peel test apparatus 80 includes a motorized tensile meter (not shown) equipped with a tensile force measuring sensor (e.g., a load cell) to determine the tensile load applied during the test method. The peel test apparatus 80 also includes a pair of grips 84 (or grippers) configured to hold the integral film 40 and the substrate 82 during testing.

[0200] The peel test apparatus 80 also includes a controller (not shown) configured to operate the motorized tensometer to move the grippers (e.g., vertically as shown by the direction of the arrows in FIGS. 18 and 19 ). The controller is configured to control the movement of the grippers 84, thereby determining the peel force applied to peel the integral film 40 from the substrate 82.

[0201] An exemplary peel test method 410 according to the second standard for monolithic films 40 will now be described with reference to Fig. 20, which shows a flow chart of the corresponding method steps. Reference is also made to Figs. 18 and 19, which show a schematic diagram of the test apparatus 80 used to test several polymeric materials (PM1-PM6), and Figs. 21 and 22, which show peel force (per 10 mm width of monolithic film) traces for the different polymeric films under investigation.

[0202] In a first method step 412, the uniform film 40 is thermally bonded to a substrate 82. The substrate 82 is formed of a substantially rigid material such as glass or metal (e.g., a metal alloy). Alternatively, the substrate 82 can be a solar cell (e.g., a crystalline silicon solar cell). Results of the method described herein (shown in Figures 21 and 22 and summarized in Table C below) were produced by peeling the integral film 40 from the surface of a crystalline solar cell.

[0203] Method step 412 begins by cutting the uniform film 40 into a number of longitudinal strips. One end of a strip (e.g., about half of its total length) is placed on an upwardly facing surface of a substrate 82. Multiple longitudinal strips may be placed simultaneously on a single substrate surface (e.g., to form an array of substantially parallel strips). Each longitudinal strip is placed on the substrate such that the width of the strip is substantially perpendicular to the direction in which the peel force is applied.

[0204] Each strip has a width of about 10 mm and a length of about 200 mm. Each strip has a thickness of at least 25 μm (e.g., about 100 μm), which is measured to within a tolerance of + / - 6 μm. Each integral film strip is attached to a backing sheet that provides structural support to the film during the peel test. The backing sheet has a thickness of at least 175 μm (e.g., about 185 μm), which is measured to within a tolerance of + / - 17 μm. The combined thickness of the film and backing sheet is 200 μm to 500 μm (e.g., about 285 μm), which is measured to within a tolerance of + / - 6.

[0205] Once the strip is placed on the surface of the substrate 82, a heat resistant sheet (e.g., formed from PTFE) is interposed between the opposing free ends of the film strip and the substrate 82. The sheet is configured to prevent adhesion between the substrate 82 and the free ends of the strip during subsequent bonding method steps.

[0206] Once the strips are in place on the substrate surface, they are placed into a laminator and heated to at least 50° C. Once the strips are bonded to surface 82, they are allowed to cool for a predetermined period of time (e.g., at least 30 minutes) before performing a peel force analysis (e.g., prior to peeling the film from substrate 82).

[0207] It should be appreciated that only a portion of each strip is thermally bonded to the substrate 82. Thus, each strip is configured to have a free end (e.g., a non-bonded end) that can be readily coupled to the gripper 84 of the peel test apparatus 80.

[0208] In a second method step 314, the strips of film are loaded into a peel test apparatus and analyzed to determine the characteristic peel strength of each material. Method step 314 first involves loading the strip and substrate 82 into the peel test apparatus 80. The strip is loaded into the upper gripper and the substrate is clamped in the lower gripper 84, as shown in FIG. 18. A peel test is then performed according to standard test method ASTM D903 to generate a peel force trace that corresponds to the particular integral film 40 being analyzed.

[0209] The peel test is applied over a distance (e.g., strain) of 100 mm. The integral film 40 is peeled from the substrate 82 at a peel speed of 100 mm / min. Throughout the peel test, the peel force exerted by the tensile meter on the film strip is continuously monitored by the controller. For example, the peel force is measured at intervals of 10 μm until the maximum peel distance (e.g., 100 mm) is reached. The peel speed used for the peel test is optimized to ensure experimental results for such polymer integral films. The peel speed is a balance between a slower speed that increases the duration of the peel test and a faster speed that may cause damage to the integral film.

[0210] The peel force of the material is determined by taking the average of the data recorded in the peel force trace. In particular, the average peel force is calculated using only the data recorded after a minimum peel distance (e.g., 20 mm) is reached to prevent distortion of the measurements caused by noise in the data present at the beginning of each test run.

[0211] Once the peel test is completed, the strip is removed from the gripper 84 and a different strip is loaded ready for testing. The peel test is repeated for each of the strips that are placed and bonded to the substrate 82.

[0212] In a third method step 316, the peel force trace for each of the strips is analyzed to determine the peel strength for each of the corresponding sample films. For a polymeric film material to meet the second criterion and thereby fall within the scope of integral film 40 according to the present disclosure, the material must exhibit a peel strength of at least 5 Newtons (N) per unit width (e.g., 10 mm) of integral film 40.

[0213] A summary of the results of the peel test analysis for each of the polymeric materials PM1-6 is presented in Table C below. Each of the peel test measurements was performed on a strip of integral film 40 having a width of 10 mm. Each of the materials PM1-6 has a peel strength that is within the range required to meet the second criterion (e.g., 5 N per 10 mm width of integral film 40). Figures 20 and 21 show the peel force traces of materials PM3 and PM6, respectively. As shown in Table C, the average peel force of material PM3 is 30 N and the average peel force of material PM6 is 11 N. Thus, material PM3 defines a (relative) high peel strength material, while PM6 defines a (relative) low peel strength material. [Table 3]

[0214] According to a further exemplary condition of the second criterion, the peel strength must be at least 15 N per 10 mm width of the integral film 40. Thus, only materials PM1-3 meet this condition of the second criterion, but materials PM4-6 do not. According to an exemplary embodiment of the present disclosure, the integral film 40 formed from materials PM1-3 is particularly suitable for use in the solar cell electrode assembly 12 because the integral film 40 provides improved adhesion to the conductive element 18 and / or solar cell surface of the solar cell assembly.

[0215] According to the exemplary peel test method 310, the peel strength is required to be in the range of 15N to 30N per 10 mm width of integral film 40 in order to meet the second criterion. Again, each of materials PM1-3 meets this exemplary condition of the second criterion.

[0216] The integral films 40 characterized according to the first and / or second criteria are advantageously configured to have good adhesive properties (e.g., to ensure a mechanical connection between the film and the solar cell and / or conductive elements of the solar cell assembly). Each film is also advantageously configured not to form an excessively or uncontrollably strong bond with another element. In this manner, the integral films 40 help ensure that the manufacturing of the electrode and / or solar cell assembly is not interrupted.

[0217] It will be understood that the present invention is not limited to the embodiments described above, and various modifications and improvements can be made without departing from the concepts described herein. Any feature can be used separately or in combination with any other feature, except where mutually exclusive, and the present disclosure extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

1. An integral film for an electrode assembly of a solar cell, the integral film being disposed on a surface of the solar cell in use, and a plurality of conductive elements of the electrode assembly being interposed between the integral film and the surface of the solar cell; the monolithic film is formed from a polymeric material and is characterized by satisfying at least one of a first criterion and a second criterion; The first criterion requires that the polymeric material have at least two endothermic peaks in the temperature range of 40°C to 200°C as measured by differential scanning calorimetry using the following method: sequentially heating the integral film through a first heat cycle and a second heat cycle according to standard test method ASTM D3418 to produce a first heat trace and a second heat trace, respectively; and identifying and determining a first endothermic peak and a second endothermic peak in the temperature range of 40°C to 200°C in each of the first heating trace and the second heating trace; The second criterion requires that the monolithic film have a peel strength of at least 5 N per 10 mm width of the monolithic film, the peel strength being determined by a 180-degree peel test according to the following method: thermally bonding the integral film to a surface of a substrate; Peeling the integral film from the surface according to standard test method ASTM D903 to provide a peel force trace; and determining from the peel force trace that the monolithic film has a peel strength of at least 5 N per 10 mm width of the monolithic film.

2. 10. The monolithic film of claim 1, wherein at least one of the first endothermic peak and the second endothermic peak in at least one of the first heating trace and the second heating trace is between 80°C and 160°C.

3. 2. The monolithic film of claim 1, wherein the first endothermic peak in each of the first heating trace and the second heating trace is between 40°C and 130°C.

4. 4. The monolithic film of claim 3, wherein the first endothermic peak in the second heating trace is between 80°C and 130°C.

5. 2. The monolithic film of claim 1, wherein the second endothermic peak in each of the first heating trace and the second heating trace is between 100°C and 160°C.

6. 6. The monolithic film of claim 5, wherein the second endothermic peak in each of the first and second heating traces is between 100°C and 145°C.

7. 7. The monolithic film of claim 6, wherein the monolithic film has a third endothermic peak in the temperature range of 130°C to 200°C in the first and second heating traces.

8. 8. The monolithic film of claim 7, wherein the third endothermic peak in the first and second heating traces is between 130°C and 160°C.

9. The monolithic film has an exothermic peak in a temperature range of 0°C to 200°C as measured by the differential scanning calorimetry method, and the differential scanning calorimetry method is measuring the cooling of the polymeric material during the first thermal cycle to produce a cooling trace according to standard test method ASTM D3418; and identifying and determining the exothermic peak at a temperature in the range of 0°C to 200°C.

10. 10. The monolithic film according to claim 9, wherein the exothermic peak is from 40°C to 130°C.

11. 10. The monolithic film of claim 1, wherein the peel force trace of the monolithic film is at least 15N.

12. 10. The integral film of claim 1, wherein the peel force trace of the integral film is up to 30N.

13. 10. The integral film of claim 1, wherein thermally bonding the integral film to the substrate comprises heating the integral film to at least 50°C.

14. The monolithic film of claim 1 , wherein the monolithic film satisfies both the first criterion and the second criterion.

15. 10. The integral film of claim 1, wherein the polymeric material is formed from a polymeric resin comprising at least one of polyolefin elastomer (POE), polyvinyl butyral (PVB) hydrocarbon ionomer, thermoplastic organosilicon, silicone rubber, polyurethane, thermoplastic silicone elastomer (TPSE), and ethylene-vinyl acetate (EVA).

16. The monolithic film of claim 1 , wherein the monolithic film is configured to have a haze parameter of less than 35%.

17. 10. The monolithic film of claim 1, wherein the monolithic film is configured to transmit at least 70% of incident light having a wavelength between 280 nm and 1100 nm.

18. 10. The monolithic film of claim 1, wherein the monolithic film has a thickness of at least 25 μm.

19. 19. An electrode assembly comprising a plurality of conductive elements and the integral film of claim 1, wherein the plurality of conductive elements are disposed on a surface of the integral film.

20. 20. A solar cell assembly comprising the solar cell and electrode assembly of claim 19, wherein the plurality of conductive elements are interposed between the integral film and a surface of the solar cell.

21. 20. A method for manufacturing an electrode assembly for a solar cell, the electrode assembly comprising a plurality of conductive elements and the integral film of claim 1, the method comprising thermally bonding the integral film to the plurality of conductive elements.

22. 20. A method for manufacturing a solar cell assembly comprising a solar cell and the electrode assembly of claim 19, comprising: interposing the plurality of conductive elements between the integral film and a surface of the solar cell; and thermally bonding the integral film to the surfaces of the plurality of conductive elements and / or the solar cells.

23. 22. The method of claim 21, wherein the method comprises substantially simultaneously thermally bonding the integral film to the surfaces of the plurality of conductive elements and the solar cells.

24. 23. The method of claim 22, wherein the method comprises substantially simultaneously thermally bonding the integral film to the surfaces of the plurality of conductive elements and the solar cells.

25. 23. The method of claim 22, wherein thermally bonding the integral film to the surface of the plurality of conductive elements and / or the solar cells comprises heating the integral film to a temperature that is substantially the same as the first endothermic peak of the second heating trace.

26. 23. The method of claim 22, wherein the method comprises heating the monolithic film to a pre-bonding temperature that is substantially the same as the temperature of the first endothermic peak of the first heating trace before thermally bonding the monolithic film to the surface of the plurality of conductive elements and / or the solar cell.

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