WO2024091112A1

WO2024091112A1 - Integrated internal heat sink for passively cooling photovoltaic modules

Info

Publication number: WO2024091112A1
Application number: PCT/NL2023/050514
Authority: WO
Inventors: Olindo ISABELLA; Hesan ZIAR; Juan Camilo ORTIZ LIZCANO; Manuwel DAKESSIAN
Original assignee: Technische Universiteit Delft
Priority date: 2022-10-24
Filing date: 2023-10-03
Publication date: 2024-05-02

Abstract

The present invention is in the field of a solar cell, or photovoltaic (PV) cell, for the conversion of light into electrical energy, a process for making such a solar cell, and a PV-module comprising said solar cells. In particular the invention relates to a silicon-based solar cell (100) comprising at least one p-n junction, a substrate (10), wherein the substrate comprises Si and dopants, and at least one electrical contact layer (15), in particular a heterojunction solar cell.

Description

INTEGRATED INTERNAL HEAT SINK FOR PASSIVELY COOLING PHOTOVOLTAIC

MODULES

FIELD OF THE INVENTION

The present invention is in the field of a solar cell, or photovoltaic (PV) cell, for the conversion of light into electrical energy, a process for making such a solar cell, and a PV-module comprising said solar cells. In particular the invention relates to a silicon-based solar cell comprising at least one p-n junction, a substrate, wherein the substrate comprises Si and dopants, and at least one electrical contact layer, in particular a heterojunction solar cell.

BACKGROUND OF THE INVENTION

A solar cell, or photovoltaic (PV) cell, is an electrical device that converts energy of light, typically sun light (hence “solar”), directly into electricity by the so-called photovoltaic effect. The solar cell may be considered a photoelectric cell, having electrical characteristics, such as current, voltage, resistance, and fill factor, which vary when exposed to light and which vary from type of cell to type.

Solar cells are described as being photovoltaic irrespective of whether the source is sunlight or an artificial light. They may also be used as photo detector.

When a solar cell absorbs light it may generate either electron-hole pairs or excitons. In order to obtain an electrical current charge carriers of opposite types are separated. The separated charge carriers are “extracted” to an external circuit, typically providing a DC-current. For practical use a DC-current may be transformed into an AC-current, e.g. by using an inverter. Typically solar cells are grouped into an array of elements. Various elements may form a panel, also referred to as module, and various panels may form a system.

Wafer based c-Si solar cells contribute to more than 90% of the total PV market. According to recent predictions, this trend will remain for the upcoming years towards 2025 and many years beyond. Due to their simplified process, conventional c-Si solar cells dominate a large part of the market. As alternative to the industry to improve the power to cost ratio, the silicon heterojunction approach has become increasingly attractive for PV industry, even though the relatively complicated process to deploy the proper front layers, such as a transparent conductive oxide (TCO) and an inherent low thermal budget of the cells limiting usage of existing production lines and thus result in a negligible market share so far. A heterojunction is the interface that occurs between two layers or regions of dissimilar crystalline semiconductors. These semiconducting materials have unequal band gaps as opposed to a homojunction. A homojunction relates to a semiconductor interface formed by typically two layers of similar semiconductor material, wherein these semiconductor materials have equal band gaps and typically have a different doping (either in concentration, in type, or both). A common example is a homojunction at the interface between an n-type layer and a p-type layer, which is referred to as a p-n junction. In heterojunctions advanced techniques are used to precisely control a deposition thickness of layers involved and to create a lattice-matched abrupt interface. Three types of heterojunctions can be distinguished, a straddling gap, a staggered gap, and a broken gap.

The conversion efficiencies of wafer-based c-Si solar cells typically lie in the range of 20%. Theoretically a single p-n junction crystalline silicon device has a maximum power efficiency of 33.7%. An infinite number of layers may reach a maximum power efficiency of 86%. The highest ratio achieved for a solar cell per se at present is about 44%. For commercial silicon solar cells the record is about 25.6%. In view of efficiency the front contacts may be moved to a rear or back side, eliminating shaded areas. In addition thin silicon films were applied to the wafer. Solar cells also suffer from various imperfections, such as recombination losses, reflectance losses, heating during use, thermodynamic losses, shadow, internal resistance, such as shunt and series resistance, leakage, etc. A qualification of performance of a solar cell is the fill factor (FF). The fill factor may be defined as a ratio of an actual maximum obtainable power to the product of the open circuit voltage and short circuit current. It is considered to be a key parameter in evaluating performance. A typical advanced commercial solar cell has a fill factor > 0.75, whereas less advanced cells have a fill factor between 0.4 and 0.7. Cells with a high fill factor typically have a low equivalent series resistance and a high equivalent shunt resistance; in other words less internal losses occur. Efficiency is nevertheless improving gradually, so every relatively small improvement is welcomed and of significant importance.

In current c-Si solar cell designs the main focus is to achieve a high efficiency. However, efficiency is often hampered by the temperature of the solar cell, which may increase significantly, such as to 60-70 °C. With an increasing temperature the efficiency of a solar cell can drop significantly. Studies have shown that high PV module operating temperatures can significantly increase their degradation rate. Currently, there is a need to control the temperature of PV modules, particularly in remote locations where large-scale projects are expected. Currently, most of the research for passively cooling PV modules has been focused on creating add-on surfaces to the back side of the module. These surfaces usually require a lot of metallic material, which makes them costly.

Incidentally US 2014/332074 Al recites a solar cell module, wherein the solar cell module includes a solar cell device, a first protective film, a second protective film, a cover plate, a back- sheet and a plurality of thermal radiation provided by particles. The solar cell device includes a first surface and a second surface opposite to the first surface. The first protective film is located on the first surface, and the second protective film is located on the second surface. The cover plate is located on the first protective film, and the first protective film is located between the solar cell device and the cover plate. The back-sheet is located on the second protective film, and the second protective film is located between the solar cell device and the back- sheet, and the thermal radiation particles are distributed in the back-sheet.

The present invention relates to an improved silicon-based solar cell and various aspects thereof and a simple process for manufacturing said solar cell which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages. SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a solar cell, in particular a heterojunction solar cell, in a second aspect to a process for making such a solar cell, and in a third aspect to a PV-module comprising said solar cells. Design of prior art solar cells typically prevents heat to be transferred away from the solar cell. The present design relates to an internal heat sink to cool down photovoltaic modules passively. Thereto an internal heat circuit is formed in the solar cell that allows the conduction of heat produced by the cells through the circuit directly towards the outside environment. In this way, inventors prevent some heat from flowing through materials that do not conduct heat efficiently, but are considered necessary for manufacturing the solar cell and/or module in which the cell is incorporated, such as the encapsulant and the polymer used as a back sheet. The present heat sink uses low quantities of metal, and a thermal pad to ensure that there is no electricity running through the thermal circuit. Therewith the additional use of metal is kept to a minimum compared to other alternatives, and the heat dissipation requires no additional component other than the module's frame. The present solar cell provides a good heat sink, heat dissipation, thermal management of the solar cell, temperature control of the solar cell, integration of the present thermal circuit into existing solar cell production technologies and designs, and direct improved thermal connection of the solar cell to the environment. The hermeticity, thermal stability, and degradation rate of the metallic connectors is found to be good. The present operating temperature reduction increases energy yield, lifetime, and bankability of PV projects. The present solution requires little additional material and has been proven to reduce the operating temperature under current environmental conditions. In an exemplary embodiment the present solution creates a direct thermal connection from the cell to the frame of a module.

The term “cooling”, in particular “passive cooling” refers to natural processes and techniques of heat dissipation and modulation without the use of energy. It does typically not include minor and simple mechanical systems, which applications would typically be referred to as ‘hybrid cooling systems’ . The techniques for passive cooling can be grouped in two main categories, preventive techniques and modulation techniques. Preventive techniques typically aim to provide protection and/or prevention of external and internal heat gains, which is more close to the present thermal circuit’s effect. Modulation and heat dissipation techniques typically allow storage and dissipation of heat gain, such as through the transfer of heat from heat sinks, such as may be provided in the present module.

The present solar cell 100, in particular a heterojunction solar cell, comprises a substrate 10, in particular wherein the substrate comprises silicon, more in particular crystalline Si, an electrical circuit comprising at least one P-N junction, in particular a hetero junction, and at least one contact 15 selected from a front contact and a back contact, the at least one contact configured for transporting holes or electrons respectively from the at least one P-N junction to a front side or back side of the solar cell, characterized in an into the solar cell integrated thermal circuit 20, wherein the thermal circuit is in thermal contact with solar cell and configured to transfer heat away from the solar cell, and wherein the thermal circuit is electrically insulated from the electrical circuit, in particular wherein the thermal circuit is a patterned thermal circuit. Particularly such patterned thermal circuit is patterned by applying lithographic patterning, in particular by applying photolithographic patterning. Lithography is a planographic method of printing, typically used in semiconductor processing. In integrated circuit manufacturing, photolithography uses light to produce minutely patterns, typically of thin films of suitable materials, on a substrate, such as a silicon wafer, or previous provided layers, to protect selected areas of it during subsequent etching, deposition, or implantation operations. Typically, light, such as ultraviolet light, is used to transfer a geometric design from an optical mask comprising the to be formed pattern to a light-sensitive chemical coated on e.g. the substrate. The patterned film is then created by removing the softer parts of the coating with appropriate solvents, also known in this case as developers. The obtained pattern in the present patterned thermal circuit has not much to do with materials that could be patterned in themselves, such as foams. The present typically silicon based solar cell comprises at least one p-n junction, a positive PV-generator terminal in electrical contact with the p-n junction, a negative PV-generator terminal in electrical contact with the p-n junction, wherein the terminals may be in direct or indirect electrical contact with the respective side of the p-n junction, wherein the terminal provides a contact opportunity to connect external components, such as other solar cells, a converter, electronics, and the like, a substrate 10, wherein the substrate typically comprises Si and dopants, at least one electrical contact or contact layer 15, wherein the electrical contact layer, or part thereof can function as a terminal, wherein the at least one electrical contact layer covers < 99% of a surface of the solar cell at a respective front-side and/or respective back-side, in particular < 70%, more in particular <50%, wherein the coverage for the front-side contact typically is smaller (e.g. smaller than 50%) than for the back-side (e.g. 75%). It is noted that the electrical contact can be used as electron or hole transport layer, such as an n-type doped Si or p-type doped Si layer. These may have a high dopant concentration, such as 5*1O¹⁴-O.5*1O²⁰ n- or p-type dopants/cm³. In general a terminal may be considered as a point at which an external circuit can be connected, or a point where a first part of the present solar cell electro-magnetically overlaps with another part of the present solar cell. The external terminal typically provides the DC-current of the solar cell. The term “terminal” relates to a part that forms an end, e.g., of the passive component, or of the p-n-junction, that is a physical termination of said part. The terminals provide a point of contact, which may be used as such, or may not be used. The present solar cell is characterized in the integrated thermal circuit. The thermal circuit, connected directly to the solar cell, needs to have an electrical insulation from the electrical circuit of the solar cell, to avoid safety concerns and potential damage. The thermal circuit, or components thereof, in particular thermal pad 21, typically have a thermal conductivity of > 5 W/m*K [ASTM E-1461, @293 K], in particular > 7 W/m*K, such as 8-10 W/m*K, which is relatively high for non-metallic thermal pads. The thermal circuit typically comprises a thermally conductive strip or the like with a thermal conductivity of > 200 W/m*K [ASTM E-1461, @293 K], in particular > 230 W/m*K, more in particular > 300 W/m*K, such 350-430 W/m*K. To this end, commercially available thermal pads can be used. The thermal circuit does not relate to a layer fully covering the present solar cell per se. Therewith heat can flow directly from the solar cell towards an outside environment. Further integration with e.g. a module frame is considered.

Typical solar cells considered are wherein the substrate is covered with at least one intrinsic layer such as one intrinsic layer at the rear side, and one intrinsic layer at the front side, in particular wherein the at least one intrinsic layer each individually is selected from intrinsic Si, such as ia-Si:H and ic-Si:H, from intrinsic Si-dielectrics, such as ia-SiO_x:H, ia-SiC_x:H, and ia- SiNx:H, or dielectric metal oxide passivation layer, and combinations thereof, and/or wherein the thickness of the intrinsic layer each individually is from 0.1 nm-50 nm, in particular 1-20 nm, such as 2-15 nm, and/or wherein the intrinsic layer each individually is textured, in particular with a same texturing as the substrate. The solar cell may comprise at least one doped silicon layer, such as a p-doped silicon layer, and an n-doped silicon layer, in particular comprising a 5* 10¹⁴-0.5* 10²¹ dopants/cm³ n- or p-type doped crystalline Si layer, and/or wherein a doping concentration is preferably spatially constant, and/or wherein n-type dopants are selected from P, As, Bi, Sb and Li, and wherein p-type dopants are selected from B, Ga, and In. The doped silicon layer is typically provided in between the at least one contact and substrate, and/or wherein the doped silicon layer substantially covers the same surface area and the same amount of surface area as the at least one contact. The at least one contact is typically provided on a TCO layer, in particular wherein the material of the transparent conductive layer is selected from Indium Tin Oxide ITO, IOH, ZnO, or doped ZnO, such as Aluminium doped ZnO, doped Tin oxide, such as fluorine doped tin oxide, doped indium oxide, such as Indium Fluor Oxide IFO:H, and Indium Tungsten Oxide IWO, and/or wherein a thickness of the transparent conductive layer is 10-200 nm, in particular 20-170 nm, more in particular 30-50 nm, and/or wherein the refractive index of the transparent conductive layer is <2.2, and/or wherein the work function of the TCO layer is from 2 eV to 8 eV, in particular 3.4 eV to 6.4 eV, and/or wherein the work function of the TCO layer is 3.4 eV to 4.7 eV in case of the TCO-layer mainly transporting electrons, and/or wherein the work function of the TCO layer 12 is 4.7 eV to 6.4 eV in case of the TCO-layer mainly collecting holes, and/or wherein the TCO layer each individually is textured, in particular with a same texturing as the substrate. The contact, in particular a metal contact, more in particular a contact layer, the TCO layer, and optionally the doped silicon layer typically form a stack, in particular a stack of substantially the same shaped layers, more in particular wherein a width of the doped silicon layer > a width of the TCO layer, which width of the TCO layer > width of the contact layer. The at least one contact is typically provided as a strip, more in particular as a strip with a width of 0.01-200 pm, in particular a width of 0.05-50 pm. The at least one light absorbing layer may be surface treated, in particular wherein the treatment is selected from treatment with a gas, and treatment with a plasma, more particular wherein in the treatment hydrogen is used, or wherein in the treatment oxygen is used, even more in particular wherein substantially only hydrogen is used, or wherein substantially only oxygen is used. The substrate 10 may be a single sided or double sided flat substrate 10 surface, and/or the substrate 10 may be a single sided or double sided textured substrate 10 surface ISO 4287:1997, in particular textured with a surface roughness R_a of 1-20 pm, such as 2-10 pm, and/or wherein the textured surface has an aspect ratio heightdepth of a textured structure of 2-10. The substrate typically has a thickness of 1-500 pm, and/or comprising 10¹⁴-10²¹ dopants/cm³ n- or p-type doped substrate 10, and/or wherein the substrate 10 comprises l*10¹²-0.5*10¹⁹ n- or p-type dopants/cm³, in particular 2*10¹⁴-10¹⁷ dopants/cm³, more in particular 5*10¹⁴-10¹⁶ dopants/cm³, such as 8*10¹⁴-3*10¹⁵ dopants/cm³, and/or wherein the substrate 10 has a resistivity of 0.1-1000 ohm*cm at 300K, more in particular 1-100 ohm*cm, such as 5-10 ohm*cm. The at least one contact typically covers less than 5% of the front surface area or back surface area, in particular wherein the at least one contact covers less than 1% of the front surface area or back surface area, more in particular less than 0.5%, and/or wherein the contact comprises a metal, wherein the metal of the contacts independently comprises at least one of Cu, Al, W, Ti, Ni, Cr, Ag, and/or wherein a thickness of said metal contacts is 200 nm-50 pm, in particular 1-25 pm, and/or wherein the metal contact is selected from a metal layer, a metal grid, a metal line, or a combination thereof. An at least one of the front surface and of the back surface may be provided with an anti-reflective coating, in particular an anti-reflective coating on the surface area not covered by the contact. The layer underneath the anti-reflective coating may be surface treated, such as surface treated with H2, with O2, or a combination thereof. Therewith the present solar cell typically has the following characteristics: the VOC is >700 mV, in particular > 725 mV, such as > 730 mV, and/or a J_sc is > 30 mA/cm², in particular > 38 mA/cm², such as > 39 mA/cm², and/or a fill factor FF of >75%, in particular > 80%, such as > 82.5%, and/or an efficiency of > 23%, in particular >23.8%, such as > 23.9%. The solar cell may be a back-contacted solar cell, such as an interdigitated back-contacted solar cell, or the solar cell may be a back and front contacted solar cell.

In a second aspect the present invention relates to a module comprising at least two solar cells according to the invention, in particular n*m solar cells, wherein ne [2-20] and me [2-10], wherein each solar cell individually comprises a separated thermal circuit, and/or wherein thermal circuits of more than two adjacent solar cells are thermally interconnected, in particular wherein 10-90% of thermal circuits of adjacent solar cell are thermally interconnected or wherein all adjacent solar cell are thermally interconnected. Various designs are possible (see figures). A first design connects frame rods to the thermal circuit from the middle cell, acting like fins. This design requires more material for the frame. The frame add-ons may have the same size, in length, as the PV module, and may be built as thin as possible to improve convection on the backside of the module. A second design connects only the thermal circuit to opposite ends of the frame, which makes for a simpler design. The frame add-ons are typically only applied to the extremes of the module, but the principle of design, to be as thin as possible, typically still applies.

In a third aspect the present invention relates to a method of producing a solar cell according to the invention, comprising providing a heterojunction solar cell, comprising a substrate 10, in particular wherein the substrate comprises silicon, more in particular crystalline Si, an electrical circuit comprising (i) at least one P-N junction, in particular a hetero junction, and (ii) at least one contact 15 selected from a front contact and a back contact, the at least one contact configured for transporting holes or electrons respectively from the at least one P-N junction to a front side or back side of the solar cell, depositing a thermal circuit on the solar cell, and providing a support layer. The thermal pad and a copper strip are typically added before the lamination step to secure the direct contact with the solar cell. The optimal indentation of these materials for maximum heat extraction was found to be 0.5-5 cm, in particular 1-2.5 cm, such as 1.7 cm. In an example small cuts are made to the EVA and the Tedlar to create the direct pathway towards the modules frame. The thermal circuit for the solar cells located on the middle columns of a module can be done in various ways (see figures). For instance, they can be interconnected to create a heat flow towards the ends of the module, or they can have their own thermal circuit.

The method may further comprise typical steps as providing a substrate, such as a crystalline Si-substrate, optionally texturing the substrate, such as double-side texturing the substrate, thereafter immersing the substrate into a strong oxidizing solution, thereafter etching the oxidized substrate by dipping the oxidized substrate into an acidic solution, directly thereafter loading the etched substrate into a layer deposition tool, and depositing an intrinsic Si layer on at least one side of the etched substrate, thereafter providing at least one doped silicon layer on the at least one intrinsic Si-layer, in particular a layer that covers less than 20% of the front surface area or back surface area, respectively, thereafter depositing a transparent conductive ox- ide(TCO) layer on the at least one doped Si-layer, in particular after a first alignment of the solar cell, and then depositing metal contacts on the TCO-layer, in particular after a second alignment of the solar cell, more in particular wherein the first and second alignment each individually is with an accuracy of better than 20 pm lateral, such as better than 1 pm lateral, wherein deposition of the TCO-layer and/or the metal contacts and optionally provision of the doped silicon layer a hard mask is used, and/or wherein contacts and/or contact layers are provided by metal deposition and lift off of non-contact areas, screen printing, and electrical plating.

Thereby the present invention provides a solution to one or more of the above-mentioned problems.

Advantages of the present description are detailed throughout the description. References to the figures are not limiting, and are only intended to guide the person skilled in the art through details of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a solar cell, and in a second aspect to a PV-module comprising said solar cell, in a third aspect to a method of producing said solar cell.

In an exemplary embodiment of the present solar cell the thermal circuit is provided substantially at a back side of the solar cell.

In an exemplary embodiment of the present solar cell at least one thermal circuit is configured to be thermally connected to a frame 30 for supporting the solar cell.

In an exemplary embodiment of the present solar cell a thermal conductivity of the thermal circuit is > 5 W/(m*K), in particular > 6 W/(m*K), more in particular > 1 W/(m*K).

In an exemplary embodiment of the present solar cell a melting point of a material of the thermal circuit is > 250 °C, in particular > 400 °C.

In an exemplary embodiment of the present solar cell the material of the thermal circuit is stable between -100 °C and 250 °C, in particular wherein the thermal characteristics are substantially unaltered between -100 °C and 250 °C.

In an exemplary embodiment the present solar cell comprises a support layer 40, such as a polymeric support layer, wherein the thermal circuit is at least partly provided between the substrate of the solar cell and the support layer.

In an exemplary embodiment of the present solar cell the solar cell has a width and a length, wherein the thermal circuit is at least partly provided at an edge of the solar cell, in particular within 20% of the respective length or width of the solar cell, more in particular within 10% of the respective length or width of the solar cell.

In an exemplary embodiment of the present solar cell the thermal circuit comprises a section 26 provided substantially at a central part of the solar cell, wherein the central section is in thermal connection with a remainder of the thermal circuit, in particular a central section covering 5-25% of a surface area of the solar cell, such as a cross -shaped central section, a circular shaped section, a multigonal shaped section, and combinations thereof.

In an exemplary embodiment of the present solar cell the thermal circuit is in thermal contact with 5-60% of a surface area of the solar cell, in particular with 10-30% of the surface area, more in particular with 15-25% of the surface area.

In an exemplary embodiment of the present solar cell the thermal circuit comprises a thermal pad 21, in particular a non-metallic thermal pad, more in particular a polymeric thermal pad, and a thermal connector 22, wherein the thermal connector is adapted to transfer heat away from the solar cell.

In an exemplary embodiment of the present solar cell the thermal pad has a thickness of 10-500 pm, in particular 50-200 pm.

In an exemplary embodiment of the present solar cell each thermal pad individually has a width of 1-50 mm, in particular 5-10 mm, and/or wherein the thermal connector has a thickness of 10-500 pm, in particular 50-200 pm.

In an exemplary embodiment of the present solar cell each thermal connector individually covers the solar cell with a width of 1-50 mm, in particular 5-10 mm.

In an exemplary embodiment of the present solar cell the thermal circuit is internally integrated, and/or wherein the thermal circuit is configured to cool the solar cell passively, in particular wherein the solar cell is thermally connected to at least one passive cooling element 50, such as a fin. In an exemplary embodiment of the present solar cell the thermal circuit has a thickness of 10-300 pm, in particular 20-100 pm.

In an exemplary embodiment of the present solar cell the material of the thermal circuit comprises a material selected from metals, in particular wherein metals are selected from copper, aluminum, gold, silver, silicon, and tungsten, from graphene, from silicon alloys, and combinations thereof.

In an exemplary embodiment of the present solar cell the thermal circuit comprises at least one area with a textured surface, wherein the textured surface is configured to increase the surface area thereof with 10-150% relatively, in particular 30-90% relatively.

In an exemplary embodiment of the present solar cell the thermal circuit comprises open areas, in particular 10-50% open areas.

In an exemplary embodiment the present module comprises a frame for supporting solar cells, wherein at least one thermal circuit is thermally connected to the frame.

In an exemplary embodiment of the present module the frame comprises receivers 60 for receiving at least one thermal connector or a thermal connection of the thermal circuit, in particular a receiver with a surface area > 2 cm², and/or a receiver with a slit.

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art, it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY OF FIGURES

Figures 1, 2a-b, 3, 4a-b, 5a-b and 6a-b show present layouts.

DETAILED DESCRIPTION OF FIGURES

100 solar cell

10 substrate

15 front/back contact

17 dielectric layer or stack of layers

20 thermal circuit

21 thermal pad

22 thermal contact

26 thermal circuit section

30 module frame

40 PV-support layer, e.g. EVA

41 Foil, e.g. Tedlar

50 passive cooling element, e.g. fin

60 frame add-on, e.g. receiver

70 cover, e.g. at least one of glass, transparent foil, typically flexible foil, and cover

The figures are further detailed in the description of the experiments below. Figure 1 shows a top/bottom view of the present solar cell 100. Left: top view, showing the actual PV-cell. Middle: showing a layout of the present thermal circuit, divided over four boundary sections, and electrical contact 15 separated from thermal circuit 20. Right: another layout of thermal circuit, showing boundary and central sections provided with the thermal circuit.

Figure 2a shows a cross-section of the present solar cell, showing the PV-cell, thermal pad 21 and copper connector 22 forming the thermal circuit, and typical support/pro- tection layers, such as an EVA layer 40 and a Tedlar layer 41. Also the size of the indentation of the thermal circuit is shown. Figure 2b shows a similar layout, including thermal dissipation.

Fig. 3 shows a cross-section of a typical stack, including a PV cell with substrate 10 and contacts 15, a pad 21, a connector 22, an EVA layer 40, and a Tedlar layer 41, as well as the indentation of the thermal circuit.

Fig. 4a shows an interconnection of connectors 22 between adjacent solar cells 100 in a bottom view, and fig. 4b in a side view. A heat flow towards a side of the module is generated, if applicable.

Fig. 5a shows thermal circuit sections 26 on adjacent solar cells 100 in a bottom view, and fig. 5b in a side view. A heat flow towards a side of the module is generated, if applicable.

Fig. 6a shows a side view of adjacent solar cells in a module, connected to a frame having fins 50, wherein thermal connectors are in thermal contact with said fins. The module may further comprise frame add-ons. Such is in particular shown in fig. 6b.

Experiments

The following experiments are carried out.

A prototype, as shown in Fig. 5a. was manufactured for long-term testing during the months of June towards August of 2022. P-type thermocouples were attached on the backside of three selected solar cells (top left, center, bottom right). A similar model, without the heat sink, was manufactured for comparison. Electrical test and Electroluminescence tests showed no differences between the two prototypes, confirming characteristics according to standards.

Field tests showed that, under clear sky conditions, the integrated heat sink could reduce the operational temperature of the solar cell up to (-)6 °C relative. On average, during the testing period, an average temperature reduction of 4 °C was observed on the prototype.

A thermal imaging camera was used to find potential inhomogeneities on the solar cells. No significant differences were observed. The thermal behavior of the solar cells with the integrated heat sink was similar in its heat distribution as the standard module, the only difference being a lower value of temperature as indicated before.

Initial hermeticity tests showed no intrusion of humidity on the inside layers of the modules. Further testing in this regard was carried out in a climate chamber during a longer period of time of a few months, and no detrimental effects were found.

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures. It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.

Claims

1. A solar cell (100), in particular a heterojunction solar cell, comprising a substrate (10), in particular wherein the substrate comprises silicon, more in particular crystalline Si, an electrical circuit comprising

(i) at least one P-N junction, in particular a hetero junction, and

(ii) at least one contact (15) selected from a front contact and a back contact, the at least one contact configured for transporting holes or electrons respectively from the at least one P-N junction to a front side or back side of the solar cell, characterized in an into the solar cell integrated thermal circuit (20), wherein the thermal circuit is in thermal contact with solar cell and configured to transfer heat away from the solar cell, and wherein the thermal circuit is electrically insulated from the electrical circuit, in particular wherein the thermal circuit is a patterned thermal circuit, and wherein the thermal circuit comprises a thermal pad (21), in particular a non-metallic thermal pad, more in particular a polymeric thermal pad, and a thermal connector (22), wherein the thermal connector is adapted to transfer heat away from the solar cell.

2. The solar cell according to claim 1, wherein the thermal circuit is provided substantially at a back side of the solar cell.

3. The solar cell according to any of claims 1-2, wherein at least one thermal circuit is configured to be thermally connected to a frame (30) for supporting the solar cell.

4. The solar cell according to any of claims 1-3, wherein a thermal conductivity of the thermal circuit is > 5 W/(m*K), in particular > 6 W/(m*K), more in particular > 1 W/(m*K), and/or wherein a melting point of a material of the thermal circuit is > 250 °C, in particular > 400 °C, and/or wherein the material of the thermal circuit is stable between -100 °C and 250 °C, in particular wherein the thermal characteristics are substantially unaltered between -100 °C and 250 °C.

5. The solar cell according to any of claims 1-4, comprising a support layer (40), such as a polymeric support layer, wherein the thermal circuit is at least partly provided between the substrate of the solar cell and the support layer.

6. The solar cell according to any of claims 1-5, wherein the solar cell has a width and a length, wherein the thermal circuit is at least partly provided at an edge of the solar cell, in particular within 20% of the respective length or width of the solar cell, more in particular within 10% of the respective length or width of the solar cell, and/or wherein the thermal circuit comprises a section (26) provided substantially at a central part of the solar cell, wherein the central section is in thermal connection with a remainder of the thermal circuit, in particular a central section covering 5-25% of a surface area of the solar cell, such as a cross-shaped central section, a circular shaped section, a multigonal shaped section, and combinations thereof, and/or wherein the thermal circuit is in thermal contact with 5-60% of a surface area of the solar cell, in particular with 10-30% of the surface area, more in particular with 15-25% of the surface area.

7. The solar cell according to any of claims 1-6, wherein the thermal pad has a thickness of 10- 500 pm, in particular 50-200 pm, and/or wherein each thermal pad individually has a width of 1-50 mm, in particular 5-10 mm, and/or wherein the thermal connector has a thickness of 10-500 pm, in particular 50-200 pm, and/or wherein each thermal connector individually covers the solar cell with a width of 1-50 mm, in particular 5-10 mm.

8. The solar cell according to any of claims 1-7, wherein the thermal circuit is internally integrated, and/or wherein the thermal circuit is configured to cool the solar cell passively, in particular wherein the solar cell is thermally connected to at least one passive cooling element (50), such as a fin.

9. The solar cell according to any of claims 1-8, wherein the thermal circuit has a thickness of 10-300 pm, in particular 20-100 pm, and/or wherein the material of the thermal circuit comprises a material selected from metals, in particular wherein metals are selected from copper, aluminium, gold, silver, silicon, and tungsten, from graphene, from silicon alloys, and combinations thereof, and/or wherein the thermal circuit comprises at least one area with a textured surface, wherein the textured surface is configured to increase the surface area thereof with 10-150% relatively, in particular 30-90% relatively, and/or wherein the thermal circuit comprises open areas, in particular 10-50% open areas.

10. The solar cell according to any of claims 1-9, wherein the thermal circuit is a patterned thermal circuit obtained by applying lithographic patterning, in particular by applying photolithographic patterning.

11. A module comprising at least two solar cells according to any of claims 1-10, in particular n*m solar cells, wherein ne [2-20] and me [2-10], wherein each solar cell individually comprises a separated thermal circuit, and/or wherein thermal circuits of more than two adjacent solar cells are thermally interconnected, in particular wherein 10-90% of thermal circuits of adjacent solar cell are thermally interconnected or wherein all adjacent solar cell are thermally interconnected.

12. The module according to claim 11, comprising a frame for supporting solar cells, wherein at least one thermal circuit is thermally connected to the frame.

13. The module according to claim 12, wherein the frame comprises receivers (60) for receiving at least one thermal connector or a thermal connection of the thermal circuit, in particular a receiver with a surface area > 2 cm², and/or a receiver with a slit.

14. A method of producing a solar cell according to any of claims 1-10, comprising providing a heterojunction solar cell, comprising a substrate (10), in particular wherein the substrate comprises silicon, more in particular crystalline Si, an electrical circuit comprising (i) at least one P-N junction, in particular a hetero junction, and (ii) at least one contact (15) selected from a front contact and a back contact, the at least one contact configured for transporting holes or electrons respectively from the at least one P-N junction to a front side or back side of the solar cell, depositing a thermal circuit on the solar cell, and providing a support layer.