CN116193880A - Hybrid tandem solar cell - Google Patents

Hybrid tandem solar cell Download PDF

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Publication number
CN116193880A
CN116193880A CN202211514134.6A CN202211514134A CN116193880A CN 116193880 A CN116193880 A CN 116193880A CN 202211514134 A CN202211514134 A CN 202211514134A CN 116193880 A CN116193880 A CN 116193880A
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solar cell
layer
contact
polarity
tandem
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兰伯特·约翰·吉林斯
吴宇
张栋
约翰尼斯·艾德里安努斯·玛丽亚·万鲁斯马伦
斯蒂芬·利伯图斯·卢森堡
齐格弗里德·克里斯蒂安·维恩斯特拉
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Netherlands Organization For Applied Scientific Research
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Priority claimed from NL2015987A external-priority patent/NL2015987B1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/078—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers including different types of potential barriers provided for in two or more of groups H01L31/062 - H01L31/075
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/043—Mechanically stacked PV cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • H01L31/1868—Passivation
    • H—ELECTRICITY
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/80—Constructional details
    • H10K30/81—Electrodes
    • H10K30/82—Transparent electrodes, e.g. indium tin oxide [ITO] electrodes
    • H10K30/83—Transparent electrodes, e.g. indium tin oxide [ITO] electrodes comprising arrangements for extracting the current from the cell, e.g. metal finger grid systems to reduce the serial resistance of transparent electrodes
    • H—ELECTRICITY
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/50—Organic perovskites; Hybrid organic-inorganic perovskites [HOIP], e.g. CH3NH3PbI3
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/50—Photovoltaic [PV] devices
    • H10K30/57—Photovoltaic [PV] devices comprising multiple junctions, e.g. tandem PV cells
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

The tandem solar cell (3) comprises a top solar cell (210) and a bottom solar cell (230). The top solar cell and the bottom solar cell each have a respective front surface and a rear surface, wherein the respective front surfaces are each adapted to face the radiation source during use. The top solar cell is arranged with its rear surface overlying the front surface of the bottom solar cell. The top solar cell includes a photovoltaic absorber layer (212), the photovoltaic absorber layer (212) having a bandgap greater than that of crystalline silicon. The bottom solar cell includes a crystalline silicon substrate (232). On at least a portion of the front surface of the bottom solar cell, a passivation layer stack (236) is provided, the passivation layer stack (236) comprising a thin dielectric film (238) and an auxiliary layer (240) of a selective carrier extracting material or polysilicon. A thin dielectric film is disposed between the silicon substrate and the auxiliary layer.

Description

Hybrid tandem solar cell
Technical Field
The present invention relates to tandem solar cells. Furthermore, the invention relates to a method for producing such a tandem solar cell. The invention also relates to a solar panel comprising at least one such tandem solar cell.
Background
Tandem solar cells are known to consist of a crystalline silicon bottom cell with an amorphous silicon (a-Si) heterojunction and a higher bandgap (bandgap) top solar cell. While bottom solar cells provide a high open circuit voltage (Voc) due to the a-Si heterojunction, which is advantageous for series performance, such bottom solar cell designs have a number of drawbacks. These drawbacks are for example: i) The low lateral conductivity of amorphous silicon heterojunctions requires the use of Transparent Conductive Oxide (TCO) electrodes, which have a large IR absorption (unless expensive materials such as hydrogen or tungsten doped InOx, indium oxide are used); ii) low thermal robustness of amorphous silicon passivation, which means that the resulting cells cannot be soldered to interconnect frequently, and in the case of a 2-terminal series structure, the handling of the top cell is also thermally limited; iii) Manufacturing a cell in the form of interdigitated back contacts with amorphous silicon heterojunction requires a complex process and high cost.
It is an object of the present invention to overcome or alleviate the disadvantages of the prior art.
Disclosure of Invention
This object is achieved by a tandem solar cell comprising a top solar cell and a bottom solar cell; the top solar cell and the bottom solar cell each have a respective front surface and rear surface; the respective front surfaces are each adapted to face the radiation source during use; the top solar cell is arranged with its rear surface adjacent to (i.e., stacked on or overlying) the front surface of the bottom solar cell; the top solar cell includes a photovoltaic absorber layer having a band gap greater than that of crystalline silicon; the bottom solar cell includes a crystalline silicon substrate; wherein a passivation layer stack is provided on at least a portion of the region of the front surface of the crystalline silicon substrate, the passivation layer stack comprising a thin dielectric such as a thin oxide ("tunnel oxide") film and an auxiliary layer of a selective carrier extracting material or polysilicon, the thin dielectric film being disposed between the silicon substrate and the auxiliary layer.
Advantageously, the present invention provides improved thermal robustness of the bottom solar cell, as compared to prior art amorphous heterojunction layers, as the material in the passivation layer stack may be selected to be a thermally stable structure, and relatively lower production costs than using an amorphous silicon heterojunction cell as the bottom solar cell in a tandem solar cell. This high thermal robustness may allow for the use of relatively high temperature manufacturing processes, such as standard burn-through metallization, and the like.
Furthermore, using a passivation layer stack with a combination of thin passivation dielectric such as tunnel oxide and auxiliary layers can provide a fairly low charge carrier recombination (recombination) rate, which results in higher Voc and FF values, as well as higher tandem solar cell performance. This is especially true when the auxiliary layer provides selective carrier extraction (also described as selective carrier collection) from the silicon substrate, in which case the passivation layer stack is referred to as a passivation contact or passivation contact. This is also especially true when the auxiliary layer is an intrinsic (unintentionally doped, at most lightly doped) polysilicon layer, which does not lead to passivation contacts but provides excellent passivation.
Furthermore, the prior art application of TCO electrodes to compensate for the low lateral conductivity in amorphous heterojunctions may be omitted, as the selective carrier extracting material of the auxiliary layer (such as highly doped polysilicon having a thickness of at least tens of nanometers) may provide lateral conductivity.
In the current scientific understanding, it is argued that good carrier selectivity requires good interface passivation (interface between substrate and carrier collector stack), for example by thin silicon oxide. In this sense, the thin dielectric may be considered part of the selective carrier collection structure, and the auxiliary layer itself is not necessarily very carrier selective without the thin dielectric. However, thin silicon oxide itself does not create selectivity to electrons or holes. This selectivity must be produced by the material provided on the thin silicon oxide. Thus, when referring herein to a selective carrier extraction material or collection material, it is meant a material or layer disposed on a thin silicon oxide or thin dielectric film to cause selective carrier collection properties. Also in the current scientific understanding, thin dielectrics exhibit at least three functions: i) Passivating the interface with the silicon substrate to reduce carrier recombination; ii) reducing minority charge carrier transport from the silicon substrate to the selective carrier extraction material (wherein minority is defined as the polarity or type opposite to the polarity or type of the selective carrier extraction material); and iii) transport of majority charge carriers sufficient to not exceed the small resistive losses of the bottom solar cell.
Thin dielectrics that yield good performance are, for example, silicon oxide (e.g., silicon dioxide) and silicon oxynitride. Other possible thin dielectrics are, for example, aluminum oxide or hafnium oxide. Typical thicknesses of silicon oxide or oxynitride are between 0.5nm and 5nm, preferably about 1nm to 2nm. Thin oxides with a thickness greater than about 1.5nm may achieve the functions required for good passivation and sufficient transport of majority charge carriers and sufficiently low transport of minority charge carriers, depending on process conditions such as an annealing process to form, for example, pinholes in the thin oxide film.
The wide band gap top cell typically consists of an absorber layer (e.g., metal organic perovskite halide, zinc ore such as copper zinc tin sulfide, chalcogenides such as copper indium gallium selenide, thin film silicon, organic absorber layers (organic photovoltaic cells, OPV, dye sensitized solar cells, DSSC), III-V compound semiconductors, cdTe, quantum dot containing layers, etc.), a suitable semitransparent electrode, and possibly an auxiliary layer (e.g., a window layer) to form a p-n heterojunction in the case of applications such as chalcogenides or CdS/CdTe junctions, and/or charge selective layers typically in OPV and metal organic perovskite halide solar cells.
The selective charge transport layer may be composed of a stack of different materials (e.g., having different doping levels or chemically different compounds). Desirably, these auxiliary layers are optically highly transparent and have electronic properties suitable for charge injection and charge transport. The electrodes and charge transport layer are typically located on either side of the absorber layer, however, in the case of back contact cells they may be located on one side of the absorber layer (see for example U.S. bach 2016). A known example is that a single charge selective layer is sufficient to achieve a good working device (Graetzel Science, month 4 2014).
According to one aspect, the present invention provides a tandem solar cell as described above, wherein the stack of thin dielectric layers and auxiliary layers together form a selective carrier collecting contact to the bottom cell.
According to an aspect, the present invention provides a tandem solar cell as described above, wherein the auxiliary layer comprises polysilicon. In general, polysilicon films with a thickness in the range of 5nm-500nm have a relatively high absorption in the visible range of the spectrum, but are transparent in the infrared range, which allows the use of polysilicon as the front layer of the bottom solar cell of a tandem solar cell. Thus, integration in a tandem solar cell structure is the solution to obtain the highest performance from a silicon solar cell with a polysilicon pre-passivation contact or polysilicon pre-passivation layer stack that would otherwise (i.e., be used as a stand-alone single junction) have poor performance. Furthermore, when using a crystalline silicon cell with a polysilicon passivation contact alone, the polysilicon passivation contact is applied only to the back side and additional process steps are required to provide a high quality diffusion junction on the front side, for example, and photolithographic techniques are required to provide contact with very small contact areas on the front side, resulting in high performance. According to an aspect of the invention, polysilicon may advantageously be applied to both the front and back sides of the silicon wafer, and for example the front and back sides polysilicon may be doped with opposite polarity, for example by printing a boron dopant source on one side and implanting a phosphorus dopant on the other side, followed by annealing, resulting in a simple and low cost cell process sequence for the bottom cell, and also in a high performance series cell and module.
The polysilicon is intrinsic polysilicon (meaning low or unintentional doping, e.g. dopant concentration<10 18 cm -3 ) Or polysilicon is doped with impurities of a first conductivity type or a second conductivity type, the second conductivity type being opposite to the first conductivity type. After the polysilicon is doped to a sufficiently high level (typically 10 19 cm -3 Or higher), the passivation layer stack also forms selective carrier-collecting contacts (passivation contacts) to the bottom cell.
The polysilicon thickness may be in the range of 5nm to 500nm, with 10nm to 200nm being more preferred. For so-called burn-through contacts, it is preferable to be 100nm or more to avoid damage to the thin dielectric by contact metals penetrating the polysilicon layer.
Alternatively, the auxiliary layer comprises a metal oxide that produces selective carrier-collecting properties. Such metal oxides are selected from the group comprising: molybdenum oxide, nickel oxide, tungsten oxide, vanadium oxide, aluminum doped zinc oxide for hole contact; or titanium oxide, tantalum oxide, indium tin oxide for electronic contact. In this case, the passivation layer stack is also formed into selective carrier-collecting contact to the bottom cell. Alternatively, the auxiliary layer may comprise an n-type or p-type organic semiconductor material, such as PEDOT: PSS, PCBM, spiral OMeTAD, etc., yielding selective carrier-collecting properties.
According to one aspect, the present invention provides tandem solar cells as described above, wherein the front surface of the bottom solar cell is textured and at least some sharp features of the resulting texture are rounded or smoothed, with an increased radius of curvature of greater than about 25nm to about 1000 nm.
According to an aspect, the present invention provides the tandem solar cell as described above, wherein the textured front surface comprises a tapered shape with intermediate valleys rounded to have a radius of curvature selected from the range of 25nm-1000 nm.
According to an aspect, the present invention provides a tandem solar cell as described above, wherein the top solar cell comprises a thin film photovoltaic layer structure comprising an upper carrier extraction layer, a lower carrier extraction layer and a photovoltaic absorber layer, the photovoltaic absorber layer being arranged between the upper carrier extraction layer and the lower carrier extraction layer and comprising at least a first contact layer arranged in contact with the upper extraction layer; the bottom solar cell comprises a silicon substrate of a basic conductivity type having at least a first contact terminal at its rear surface.
According to an aspect, the present invention provides a tandem solar cell as described above, wherein the top solar cell comprises a second contact layer below the photovoltaic layer structure in contact with the lower carrier extraction layer; the first contact layer has a first polarity and the second contact layer has a second polarity opposite the first polarity; the bottom solar cell includes a second contact terminal having a polarity opposite to that of the first contact terminal, and the second contact terminal is in contact with the auxiliary layer and the second contact layer is electrically connected to the second contact terminal.
Depending on the respective polarities of the second contact terminal and the auxiliary layer, a two-terminal (2T) or three-terminal (3T) tandem solar cell may be constructed.
A four terminal (4T) tandem solar cell may be constructed if an insulating layer or a usual insulating space is arranged between the passivation layer stack and the second contact terminal of the bottom solar cell and the rear surface of the top solar cell.
According to an aspect, the present invention provides the tandem solar cell as described above, wherein one of the lower carrier extraction layer and the second contact layer coincides with one of the auxiliary layer and the second contact terminal.
Alternatively, the lower extraction layer in the top solar cell and the auxiliary layer in the bottom solar cell may overlap if the overlap layer may also extract carriers from the photovoltaic layers of the other cells.
According to an aspect, the present invention provides a tandem solar cell as described above, wherein the tandem solar cell comprises a third contact layer between the bottom solar cell and the top solar cell, the third contact layer being in contact with the lower carrier extraction layer and in contact with the auxiliary layer on the crystalline silicon cell, wherein the polarity of the lower carrier extraction layer is opposite to the polarity of the auxiliary layer.
According to an aspect, the present invention provides the tandem solar cell as described above, wherein one of the lower carrier extraction layer and the lower contact layer is in direct contact with one of the auxiliary layer and the second contact terminal.
According to an aspect, the present invention provides the tandem solar cell as described above, wherein a composite layer is arranged between the auxiliary layer as the selective carrier extraction layer and the lower carrier extraction layer at the rear surface of the top solar cell, the composite layer being in electrical contact with both the auxiliary layer and the lower carrier extraction layer, and the first contact layer of the top solar cell has a first polarity, and the first contact terminal has a second polarity opposite to the first polarity.
In this way, a two-terminal (2T) tandem solar cell can be constructed in which the recombination layer provides for efficient recombination of charge carriers from the lower extraction layer with charge carriers from the auxiliary layer. The composite layer is optional if the interface between the lower extraction layer and the auxiliary layer provides an effective composite.
According to an aspect, the present invention provides the tandem solar cell as described above, wherein the auxiliary layer as the selective carrier extraction layer is in electrical contact with the lower extraction layer at the rear surface of the top solar cell, and the first contact layer of the top solar cell has a first polarity, and the first contact terminal has a second polarity opposite to the first polarity.
According to one aspect, the present invention provides a method for manufacturing tandem solar cells, the method comprising:
providing a bottom solar cell having a front surface and a back surface;
providing a top solar cell having a front surface and a back surface;
arranging the top solar cell with its rear surface on the front surface of the bottom solar cell such that the front surfaces of both the top and bottom solar cells face the radiation source during use;
wherein the top solar cell comprises a photovoltaic absorber layer having a bandgap greater than that of crystalline silicon,
the bottom solar cell includes a crystalline silicon substrate;
on the front surface of the bottom solar cell, the crystalline silicon substrate comprises a passivation layer stack comprising a thin dielectric film and an auxiliary layer, the thin dielectric film being arranged between the silicon substrate and the auxiliary layer; the auxiliary layer is made of a selective carrier extracting material or polysilicon.
Advantageous embodiments are further defined by the dependent claims.
Drawings
The invention will be explained in more detail below with reference to the drawings, in which illustrative embodiments of the invention are shown.
Fig. 1 shows a schematic cross section of a four-terminal tandem solar cell according to an embodiment of the invention;
Fig. 2 shows a schematic cross section of a four-terminal tandem solar cell according to an embodiment of the invention;
fig. 3 shows a schematic cross section of a four-terminal tandem solar cell according to an embodiment of the invention;
fig. 4 shows a schematic cross section of a two terminal tandem solar cell according to an embodiment of the invention;
fig. 5 shows a schematic cross section of a two terminal tandem solar cell according to an embodiment of the invention; and
fig. 6 shows a schematic cross section of a two terminal tandem solar cell according to an embodiment of the invention.
Detailed Description
According to the invention, the tandem solar cell comprises a stack of top solar cells (or top photovoltaic devices) and bottom solar cells (or bottom photovoltaic devices), wherein the top solar cells are arranged on top of the bottom solar cells. The top solar cell and the bottom solar cell are stacked such that the back surface of the top solar cell is stacked on the front surface of the bottom solar cell.
The front surface refers to the surface of the respective solar cell that substantially faces the radiation source (sun) during use. The rear surface refers to the surface of the respective solar cell facing away from the radiation source during use of the solar cell.
The bandgaps of the top solar cell photovoltaic material and the bottom solar cell photovoltaic material are configured such that the top solar cell is substantially transparent to radiation having a wavelength to be absorbed by the bottom solar cell. The top solar cell may be, for example, based on a metal organic perovskite photovoltaic material absorber layer, a Cd-Te photovoltaic material absorber layer, or a CZTS (copper zinc tin sulfide) photovoltaic material absorber layer that absorbs radiation in the visible range of the spectrum (wavelength: 400nm-700 nm) and is relatively transparent to infrared radiation, and the bottom solar cell may be a crystalline silicon-based solar cell that in this configuration utilizes mainly the infrared portion of the spectrum (wavelength: 700-1100 nm) of radiation.
Additional solar cells with a wider band gap may be included on top of such an arrangement, or additional solar cells with a smaller band gap may be included under such an arrangement to form a series cell with more than 2 absorber layers or junctions as known in the art.
Fig. 1 shows a cross section of a tandem solar cell according to an embodiment of the present invention.
The tandem solar cell 1 includes a top solar cell 10 and a bottom solar cell 30.
The top solar cell 10 is stacked on top of the bottom solar cell with the back surface RT of the top solar cell facing the front surface FB of the bottom solar cell.
The top solar cell 10 is a wide bandgap solar cell that is substantially transparent to infrared light. The bandgap of the top solar cell needs to be wider than that of crystalline silicon. About 1.35eV to 2.9eV is allowed for the 4-terminal configuration, and about 1.35eV to 1.9eV is allowed for the 2-terminal configuration, theoretically 35% performance can be achieved using a crystalline silicon bottom cell.
On top of the top solar cell 10, a first contact layer 18 is arranged (i.e. on the front surface FT side of the top solar cell). Further, a second contact layer 20 is arranged on the top solar cell (e.g., on the rear surface RT side of the top solar cell 10). The first contact layer 18 and the second contact layer 20 have different polarities and form a first terminal and a second terminal of the tandem solar cell.
A superstrate 22 is disposed on the front surface FT of the top solar cell 10. Such a superstrate may be a glass layer provided with a textured surface and/or an anti-reflective coating (not shown).
The bottom solar cell 30 is a crystalline silicon substrate 32 based on a base conductivity type with at least a lower contact terminal 34 at its rear surface RB. Between the lower contact terminal and the substrate may be features known in the art of manufacturing silicon solar cells, such as anti-reflective coatings, doped layers at the rear surface of the substrate, e.g. formed by diffusion or deposition, etc.
On the front surface FB of the bottom solar cell 30, the crystalline silicon substrate 32 is provided with a passivation layer stack 36. The passivation layer stack includes a thin dielectric film 38 (e.g., tunnel oxide film) and an auxiliary layer 40. A thin dielectric film 38 is disposed between the crystalline silicon substrate 32 and the auxiliary layer 40.
The bottom solar cell 30 may be a front-to-back contact solar cell with upper contact terminals of one polarity disposed on the front surface FB of the bottom solar cell, as schematically illustrated by the dashed outline 42, and lower contact terminals of opposite polarity on the back surface RB. In this case, the passivation layer stack is a passivation contact that selectively extracts one type of carrier from the substrate. Layer 40 may be, for example, a doped polysilicon layer. Alternatively, the bottom solar cell 30 may be a back contact solar cell having contact terminals of different polarities arranged on the back surface RB of the bottom solar cell. Such back contact solar cells may be Metal Wrap (MWT) solar cells or Interdigitated Back Contact (IBC) solar cells. If it is an IBC cell, the auxiliary layer 40 may be an intrinsic or almost intrinsic (unintentionally doped) polysilicon layer, by means of which the passivation layer stack provides excellent passivation, but no extraction of carriers from the substrate.
The contact terminals 34, 42 of the bottom solar cell form the third and fourth terminals of the tandem solar cell 1.
On the rear surface RT of the top solar cell 10, a spacer layer or spacer layer stack 24 may be provided. The spacer layer 24 forms an intermediate layer between the back surface RT of the top solar cell 10 and the front surface FB of the bottom solar cell 30.
The spacer layer 24 couples the top solar cell 10 to the bottom solar cell 30. The spacer layer 24 may be based on an encapsulation material. The spacer layer 24 (encapsulant) mechanically and optically connects the top solar cell 10 with the bottom solar cell 30.
As described above, the auxiliary layer 40 may be, for example, a polysilicon layer, intrinsic or doped to form a passivation contact, or may be a transparent conductive metal oxide to form a passivation contact.
According to the invention, the auxiliary layer 40 allows the transmission of infrared radiation (or any radiation) not absorbed by the top solar cell 10 to the bottom solar cell 30, i.e. the auxiliary layer 40 is transparent to radiation in the infrared range. As described above, the combination of the thin dielectric such as tunnel oxide 38 and the auxiliary layer 40 of selective carrier extraction material provides a relatively low charge carrier recombination rate, which results in higher Voc and FF values for the bottom solar cell. In addition, transparency in the infrared range of the spectrum allows absorption of infrared radiation in crystalline silicon bottom solar cells.
In an embodiment, crystalline silicon substrate 32 is n-type and auxiliary layer 40 is p-type doped polysilicon.
Fig. 2 shows a schematic cross section of a four-terminal tandem solar cell according to another embodiment of the present invention.
In fig. 2, entities having the same reference numerals as shown in fig. 1 refer to corresponding or similar entities.
The embodiment of fig. 2 shows a tandem solar cell 2 comprising a top solar cell 10 and a bottom solar cell 130 as described above.
The top solar cell 10 is a wide bandgap solar cell, for example, the top solar cell includes a photovoltaic absorber layer 12 sandwiched between an upper carrier extraction layer 14 for carriers of a first polarity (e.g., electrons) and a lower carrier extraction layer 16 for carriers of a second polarity (e.g., holes), the second polarity being opposite the first polarity.
In an embodiment, the photovoltaic absorber layer 12 is a methyl ammonium-lead-triiodide perovskite layer, the upper carrier extraction layer 14 is a layer for extracting electrons, the upper carrier extraction layer 14 includes TiO2, and the lower carrier extraction layer 16 for extracting holes is a spiral ome tad ([ 2,2', 7' -tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9' -spirobifluorene ]).
Other electron and hole extraction layers are known in the art, such as variations of perovskite compositions (e.g., replacing some of the iodine with bromine) to alter the band gap or other properties. The top contact layer is a transparent conductive oxide layer (e.g., indium tin oxide). Similarly, the lower contact layer is a transparent conductive oxide layer (e.g., indium tin oxide). Alternative contact layers for ITO that allow higher transmittance, such as indium hydroxide, are known in the art.
Other thin film solar cells are also possible, such as semitransparent CdTe solar cells known in the art, wherein the top contact layer is CTO/ZTO; the top carrier extraction layer is replaced by a CdS window layer, which together with CdTe forms a p-n junction; the bottom carrier extraction layer may be omitted and the bottom contact layer is for example ZnTe: cu or other suitable translucent back contact layer selected from for CdTe. The structure of the top solar cell may be locally modified to achieve a monolithic interconnection, i.e. a series circuit of solar cell strips, as known in the art, to increase the output voltage and reduce resistive losses.
The bottom solar cell 130 is similar to the silicon-based bottom solar cell 30 of fig. 1 and includes upper contact terminals 42 on the front surface FB and lower contact terminals 34 on the back surface RB.
Further, the front surface FB and the rear surface RB of the crystalline silicon substrate 32 are provided with textures T1, T2.
In this embodiment, the textured front surface FB comprises a passivation layer stack 36, which passivation layer stack 36 is a selective carrier-collecting layer stack (passivation contact) consisting of an auxiliary layer 40 and a thin dielectric 38, such as a tunnel oxide film. The auxiliary layer 40 is covered by an anti-reflective (ARC) coating that also provides hydrogen to the tunnel oxide/silicon interface, such as hydrogen-rich silicon nitride (SiNx: H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD). The upper contact terminal 42 is connected to the auxiliary layer 40 through the ARC coating. This connection of the upper contact terminal 42 to the auxiliary layer 40 may be what is known in the art as a burn-through connection of thick film metal paste.
The textured back surface RB of the bottom solar cell 130 includes a second passivation layer stack 136 comprised of a second thin tunnel oxide film 138 and a back surface auxiliary layer 140. The rear surface auxiliary layer 140 is covered with a SiNx H second anti-reflection coating having a similar function to the front side anti-reflection coating. The lower contact terminal 34 is connected to the rear surface auxiliary layer 140 through a second anti-reflection coating.
The auxiliary layer 40 on the front surface FB may be a doped polysilicon layer of a first conductivity type (e.g., n-type). The auxiliary layer 140 on the rear surface RB has an opposite conductivity type to the first conductivity type For example, a p-type doped polysilicon layer. At a doping level of at least 1X 10 19 cm -3 Or preferably higher, e.g. about 1-3 x 10 20 cm -3 . The thickness of the polysilicon is preferably between 10nm and 300 nm. If a burn-through contact is used, the thickness is preferably at least 100nm to avoid damage to the passivation thin oxide by the metal burn-through contact. Placing the p-type polysilicon layer on the back side and the n-type polysilicon layer on the front side is advantageous because n-type polysilicon is more easily doped to high concentrations and has higher carrier mobility. As it was unexpectedly found that for a given polysilicon layer, when it is placed in the back of a silicon solar cell, the optical Free Carrier Absorption (FCA) is greater than when it is in the front of a silicon solar cell, placing a more highly doped n-type polysilicon in the front reduces FCA. Also due to the lower carrier mobility, it is more advantageous to place p-type polysilicon in the back, where there may be a denser metallization grid, without shadowing losses.
The thickness of the polysilicon on the front and rear portions (if used on the rear portion) is not necessarily the same, but if the polysilicon is deposited uniformly on both sides, for example by Low Pressure Chemical Vapor Deposition (LPCVD), it may be substantially the same, which reduces process complexity. For example, the front side and back side polysilicon may be doped by, for example, printing a boron dopant source on one side and implanting a phosphorus dopant on the other side, followed by annealing, resulting in a simple and low cost cell process sequence for the bottom cell, and also resulting in high performance tandem cells and modules.
According to an embodiment, the texture on the front surface FB and/or the rear surface RB may be rounded after the texturing process. Such rounding or smoothing means that at least some of the sharp features of the texture (especially valleys between texture cones in the case of a conical texture) achieve an increased radius of curvature, e.g. from just a few nanometers (about 25 nm) to about 100nm to about 200nm, or even larger, e.g. up to 1000nm.
Rounding may be performed by etching methods known in the art.
Fig. 3 shows a schematic cross section of a four-terminal tandem solar cell according to an embodiment of the invention.
In the four-terminal tandem solar cell 2a of this embodiment, the front of the bottom solar cell 132 is similar to the front of the silicon-based bottom solar cell 130 of fig. 2 and includes the upper contact terminal 42 on the front surface FB.
Further, the front surface FB of the crystalline silicon substrate 132 is provided with a texture T1.
In this embodiment, the textured front surface FB comprises a passivation layer stack 36, which passivation layer stack 36 is a selective carrier-collecting layer stack (passivation contact), 12 consisting of an auxiliary layer 40 and a thin dielectric 38, such as a tunnel oxide film.
The auxiliary layer 40 is covered by an anti-reflective (ARC) coating that also provides hydrogen to the tunnel oxide region, such as hydrogen-rich silicon nitride (SiNx: H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD). The upper contact terminal 42 is connected to the auxiliary layer 40 through the ARC coating.
This connection of the upper contact terminal 42 to the auxiliary layer 40 may be a so-called burn-through connection of thick film metal paste as known in the art.
The rear surface RB of the bottom solar cell is provided as the rear surface of a so-called PERC (passivation emitter and rear cell) or double-sided PERC cell. This means that the rear surface is set as follows: the back surface is smoothed or polished to a certain extent and comprises a second passivation layer stack consisting of a dielectric layer or a dielectric layer stack 134 as used in PERC solar cells, for example a stack of aluminum oxide and silicon nitride (aluminum oxide between substrate and silicon nitride), or a stack of silicon oxide and silicon nitride (silicon oxide between substrate and silicon nitride). A metal layer 138 or metal layer stack is applied on top of the dielectric stack 134 (the dielectric stack is between the metal layer and the substrate), partially penetrating the dielectric layer stack, and forming a partial back surface field 136 of doped aluminum silicon penetrating the dielectric layer stack. The metal layer may be disposed on substantially the entire rear surface or locally to create a double-sided bottom cell. In fig. 3, the metal layer is shown as being locally disposed.
This embodiment may be produced, for example, as follows. After the texturing process, a polysilicon film and a thin oxide may be applied to at least the front side. The polysilicon may then be doped, if desired, at least on the front side, for example by diffusion in a gaseous POCb environment at high temperature. It may also be doped, for example, by implantation and annealing. If polysilicon is deposited on the rear portion, the polysilicon may be removed from the rear portion and the rear portion may be smoothed or polished by a single-sided etch. In a further process, coatings and metallizations are provided for PERC solar cell processing as known in the art.
Alternatively, in an alternative embodiment, the back surface RB of the bottom solar cell 132 is provided with a texture, or polished, or to the extent that it is in between. The back surface includes a second passivation layer stack of a thin dielectric layer and a polysilicon layer, which may be similar to the front side (e.g., similar in the sense of similar thickness or similar composition), but is substantially undoped. A metal layer or metal layer stack is applied on top of the back layer stack (the back layer stack being between the metal layer and the substrate), locally penetrates the back layer stack, and forms a local back surface field of doped aluminum silicon penetrating the back layer stack. The metal layer may be disposed on substantially the entire rear surface or locally to create a double-sided bottom cell.
This embodiment may be produced, for example, as follows. After texturing and optional post-polishing, oxide and substantially intrinsic polysilicon are applied to the front and back surfaces. The polysilicon is then doped only on the front side, for example by implantation and annealing, or by printing a dopant paste on the front and annealing, or by other methods known in the art for localized doping. If desired, the rear portion may be provided with a diffusion barrier against the front side dopant. In a further process, a coating and metallization are provided. It may be advantageous to apply a hydrogen-rich silicon nitride or other hydrogen-rich coating over the rear polysilicon to enhance its surface passivation. As is known for PERC cells or double sided PERC cells, a metallization on the rear can be provided, for example, first providing holes in the layer stack of the rear, then providing a metal layer, and then providing a high temperature, such as in so-called firing.
According to an embodiment, the texture on the front surface FB may be rounded after texturing. Such rounding or smoothing means that at least some of the sharp features of the texture (especially valleys between texture cones in the case of a conical texture) achieve an increased radius of curvature, e.g. from just a few nanometers (about 25 nm) to about 100nm to about 200nm, or even larger, e.g. up to 1000nm.
Rounding may be performed by etching methods known in the art.
Fig. 4 shows a schematic cross section of a two-terminal tandem solar cell according to an embodiment of the invention.
In fig. 4, entities having the same reference numerals as shown in fig. 1 or fig. 2 or fig. 3 refer to corresponding or similar entities.
The embodiment of fig. 4 shows a series connection of solar cells 3 comprising a top solar cell 210 stacked on a bottom solar cell 230.
The bottom solar cell 230 has a lower contact terminal 234 at its rear surface RB based on a crystalline silicon substrate 232 of the base conductivity type.
On the front surface FB of the bottom solar cell 230, the silicon substrate 232 is provided with a passivation layer stack 236. The passivation layer stack includes a thin dielectric (e.g., tunnel oxide) film 238 and an auxiliary layer 240. A thin dielectric film 238 is disposed between the silicon substrate 232 and an auxiliary layer 240.
The top solar cell 210 is a wide bandgap solar cell that substantially transmits infrared light. On top of the solar cell 210, a top contact layer 218 is arranged (i.e. on the front surface FT side of the top solar cell). On the rear surface RT of the top solar cell 210, a separation layer 250 is arranged between the rear surface layer of the top solar cell and the auxiliary layer 240 of the bottom solar cell 230.
The separation layer 250 comprises at least a composite layer 252 to connect the top solar cell 210 of one polarity with the auxiliary layer 240 of the bottom solar cell (of opposite polarity).
The top contact layer 218 of the top solar cell 210 and the lower contact terminal 234 of the bottom solar cell form a first terminal and a second terminal, respectively, of the tandem solar cell 3.
In an embodiment, the top solar cell 210 includes a photovoltaic absorber layer 212, the photovoltaic absorber layer 212 being sandwiched between an upper carrier extraction layer 214 for carriers of a first polarity (e.g., electrons) and a lower carrier extraction layer 216 for carriers of a second polarity (e.g., holes) that acts as a back surface layer, the second polarity being opposite the first polarity. For example, the photovoltaic absorber layer 212 is a metal organic perovskite halide layer such as methyl ammonium-lead-triiodide perovskite, the upper carrier extraction layer 214 is a layer for extracting electrons, the upper carrier extraction layer 214 includes TiO2, and the lower carrier extraction layer 216 for extracting holes is a helical ome layer. The top contact layer 218 is a transparent conductive oxide layer (e.g., indium tin oxide) combined with a metal grid.
The silicon substrate 232 may be n-type and the auxiliary layer 240 at the interface with the top solar cell may be n-type doped polysilicon to match the opposite polarity of the underlying carrier extraction layer of the top solar cell, and in this case the back surface auxiliary layer of the top solar cell is p-type doped polysilicon (opposite polarity to the front surface).
Fig. 5 shows a schematic cross section of a two-terminal tandem solar cell according to an embodiment of the invention.
In fig. 5, entities having the same reference numerals as those shown in the previous fig. 1 to 4 refer to corresponding or similar entities.
The embodiment of fig. 5 shows a tandem solar cell 4 comprising a bottom solar cell 330 and a top solar cell 210 as described above with reference to fig. 3.
The bottom solar cell 330 is similar to the silicon-based bottom solar cell 230 of fig. 4, except that the front surface FB and the back surface RB of the silicon substrate 32 have textures T1, T2.
In this embodiment, the textured front surface FB includes a passivation layer stack 336, the passivation layer stack 336 consisting of the thin dielectric film 338 and the auxiliary layer 340 as described above with reference to fig. 1-4. The auxiliary layer 340 is covered with an anti-reflection coating. As described previously with respect to fig. 2, the bottom cell may include polysilicon passivation contacts on the front and back sides.
Furthermore, the tandem solar cell comprises a separation layer 350, which separation layer 350 is arranged between the back surface layer of the top solar cell (in an embodiment: the lower carrier extraction layer 216) and the auxiliary layer 340 of the passivation layer stack of the bottom solar cell 330 to provide an electrical connection. The separation layer 350 comprises a composite layer that provides for efficient recombination of carriers extracted by the auxiliary layer 340 and carriers of opposite polarity extracted at the back surface of the top solar cell (in embodiments: through the carrier extraction layer 216).
The separation layer 350 or the lower carrier extraction layer 216 may be adapted as a smoothing layer to form a substantially planar surface on which the lower contact layer of the top solar cell is arranged. This may be accomplished, for example, by: liquid deposition of the materials of these layers (printing, spraying, slot die coating, etc.), which preferably fills valleys between the textural features (such as tapers), and/or an etch back process (e.g., plasma etching, mechanical etching) after deposition of these materials to planarize them. By providing a planar surface, the fabrication of a thin film solar cell comprising a stack of thin film layers is simplified. Such a planarization process is not only advantageous for tandem solar cells according to the present invention, but generally does not degrade the performance of the top cell when the front side of the bottom solar cell should preferably be textured, and when the top solar cell process does not cover the texture features of these bottom cells well conformally.
It should be noted that the lower contact layer 216 of the top solar cell may alternatively or additionally be adapted as a smoothing layer.
It should also be noted that alternatively, separation layer 350 may be omitted if sufficient recombination occurs at the interface between layer 340 and layer 216.
The texture features on the front and/or back may be rounded as described in fig. 2 before the passivation layer stack is arranged.
Fig. 6 shows a schematic cross section of a two-terminal tandem solar cell 4a according to an embodiment of the present invention.
In fig. 6, entities having the same reference numerals as previously shown in fig. 1 to 5 refer to corresponding or similar entities.
In the embodiment shown in fig. 6, the bottom solar cell 132 may be compared to the solar cell 132 as shown and described with reference to fig. 3. The rear surface RB of the bottom solar cell is provided as the rear surface of a PERC cell or a double sided PERC cell. The rear surface is smoothed or polished to a certain extent and comprises a second passivation layer stack consisting of a dielectric layer or a dielectric layer stack 134 used in so-called PERC solar cells, for example a stack of aluminum oxide and silicon nitride (aluminum oxide between substrate and silicon nitride), or a stack of silicon oxide and silicon nitride (silicon oxide between substrate and silicon nitride). A metal layer 138 or metal layer stack is applied on top of the dielectric stack 134 (the dielectric stack is located between the metal layer and the substrate, partially penetrating the dielectric layer stack, and forming a partial back surface field 136 of doped aluminum silicon penetrating the dielectric layer stack). The metal layer may be disposed on substantially the entire rear surface or locally to create a double-sided bottom cell.
It should be noted that similar modifications as shown in fig. 6 may be made to the rear surface RB of the bottom solar cell 230 as shown in fig. 4.
It should also be noted that the invention includes embodiments in which a passivation layer stack is provided on the front surface of the bottom solar cell, the passivation layer stack comprising a thin dielectric film and an auxiliary layer of selective carrier extraction material or polysilicon, the thin dielectric film being arranged between the silicon substrate and the auxiliary layer, wherein the passivation layer stack is provided in a specific partial pattern or is patterned in a specific partial pattern, the specific partial pattern having patterns of different thickness or doping levels or consisting of selective carrier extraction material.
Such a partial pattern may be, for example, a grid pattern that is aligned with a contact metallization grid (e.g., the metallization grid is represented by fingers 42 in fig. 2 and 3). For example, if the passivation layer stack includes a thin oxide and doped polysilicon film, the polysilicon of the front surface FB in the regions between the grid fingers may be thinner or removed entirely. Advantageously, these embodiments of the present invention may be used to provide a greater thickness of selective carrier extraction material (e.g., doped polysilicon having a thickness of 100nm or greater) between the metal grid fingers and the wafer substrate, which may result in reduced recombination caused by the metal grid fingers, and a lesser thickness on FB on the wafer surface area between the grid fingers, which may result in a reduction in free carrier absorption of so-called IR wavelength photons. Therefore, the performance of the bottom solar cell can be improved. This variation in thickness may be achieved, for example, by a localized chemical etchback process of polysilicon as known in the art. Advantageously, the selective carrier extraction material used between the metal grid fingers and the wafer substrate extends laterally from the metal grid fingers a length to provide alignment tolerances during application of the metal grid fingers. For example, the fingers of the selective carrier extraction material under the metal grid fingers may be 100-500 microns wider than the metal grid fingers. It is also advantageous that a doped layer for the same carrier type as the selective carrier extraction material may be provided in the front surface of the wafer substrate of the bottom cell, e.g. between the grid fingers and in the underlying surface, which may reduce the series resistance of the bottom cell.
Tandem solar cells according to embodiments of the present invention may be fabricated from a bottom solar cell based on a silicon substrate and a top solar cell based on a thin film photovoltaic device.
The method for manufacturing such tandem solar cells comprises:
providing a bottom solar cell having a front surface and a back surface;
providing a top solar cell having a front surface and a back surface;
arranging the top solar cell with its rear surface on the front surface of the bottom solar cell such that the front surfaces of both the top and bottom solar cells face the radiation source during use;
wherein the top solar cell comprises a photovoltaic absorber having a bandgap greater than that of crystalline silicon;
the bottom solar cell includes a crystalline silicon substrate;
on the front surface of the bottom solar cell, the silicon substrate comprises a passivation layer stack comprising a thin dielectric film and an auxiliary layer, the auxiliary layer being formed of a selective carrier collecting material or polysilicon, the thin dielectric film being arranged between the silicon substrate and the auxiliary layer.
In the foregoing description of the drawings, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the scope of the invention as outlined in the appended claims.
In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
In particular, specific features of various aspects of the invention may be combined. One aspect of the present invention may be further advantageously enhanced by adding features described with respect to another aspect of the present invention.
It is to be understood that the invention is solely limited by the appended claims and their technical equivalents. In this document and in the claims, the verb "to comprise" and its conjugations is used in its non-limiting sense to mean that items following the word are included, not excluding items not specifically mentioned. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that one and only one of the elements be present. Thus, the indefinite article "a" or "an" generally means "at least one".

Claims (28)

1. A tandem solar cell comprising a top solar cell and a bottom solar cell; the top solar cell and the bottom solar cell each have respective front and back surfaces; the respective front surfaces are each adapted to face the radiation source during use; the top solar cell is arranged such that its rear surface covers the front surface of the bottom solar cell;
The top solar cell includes a photovoltaic absorber layer having a band gap greater than that of crystalline silicon;
the bottom solar cell includes a crystalline silicon substrate;
on the front surface of the bottom solar cell, a passivation layer stack is arranged, the passivation layer stack comprising a thin dielectric film and an auxiliary layer of polysilicon, the thin dielectric film being bonded to the crystalline silicon substrate and arranged between the front surface of the crystalline silicon substrate and the auxiliary layer;
wherein the bottom solar cell is provided with a second passivation layer stack on the rear surface, the second passivation layer stack comprising a dielectric layer or a dielectric layer stack or comprising a thin dielectric layer and a polysilicon layer, and a metal layer on top of the second passivation layer stack, the metal layer locally penetrating the second passivation layer stack and forming a local back surface field of doped aluminum silicon penetrating the second passivation layer stack, and wherein the metal layer is provided on the entire rear surface or locally on the rear surface to create a double sided bottom cell.
2. The tandem solar cell of claim 1 wherein the second passivation layer stack comprises a stack of aluminum oxide and silicon nitride, the aluminum oxide being between the crystalline silicon substrate and the silicon nitride, or the second passivation layer stack comprises a stack of silicon oxide and silicon nitride, the silicon oxide being between the crystalline silicon substrate and the silicon nitride.
3. The tandem solar cell of claim 1 or 2 wherein the auxiliary layer comprises polysilicon doped with impurities of the first conductivity type or the second conductivity type.
4. The tandem solar cell of claim 1 wherein the thin dielectric film has a thickness between 0.5nm and 5 nm.
5. The tandem solar cell of claim 1 wherein the thin dielectric film is a silicon oxide or silicon oxynitride layer having a thickness between 1nm and 2.5 nm.
6. The tandem solar cell of claim 1 wherein the polysilicon has a thickness in the range of 5nm to 500 nm.
7. The tandem solar cell of claim 5 or 6 wherein the doping level of the polysilicon is higher than 1 x 10 19 cm -3 。
8. The tandem solar cell of claim 1 wherein the top solar cell comprises a metal organic perovskite halide layer as a photovoltaic absorber layer.
9. The tandem solar cell of claim 1 wherein the top solar cell includes a CdTe layer as a photovoltaic absorber layer.
10. The tandem solar cell of claim 1 wherein the front surface of the bottom solar cell is textured and at least some sharp features of the texture formed are rounded or smoothed to have an increased radius of curvature of greater than 25nm to 1000 nm.
11. The tandem solar cell of claim 10 wherein the textured front surface includes a tapered shape with intermediate valleys rounded to have a radius of curvature selected from the range of 25nm-1000 nm.
12. The tandem solar cell of claim 1 wherein,
the top solar cell includes:
a thin film photovoltaic layer structure comprising an upper carrier extraction layer, a lower carrier extraction layer, and a photovoltaic absorber layer disposed between the upper carrier extraction layer and the lower carrier extraction layer, an
At least a first contact layer arranged in contact with the upper carrier extraction layer;
the bottom solar cell includes:
and a silicon substrate of a basic conductivity type having at least a first contact terminal on a rear surface thereof.
13. The tandem solar cell of claim 12 wherein the top solar cell includes a second contact layer located below the thin film photovoltaic layer structure in contact with the lower carrier extraction layer; the first contact layer has a first polarity and the second contact layer has a second polarity opposite the first polarity;
The bottom solar cell comprises a second contact terminal having a polarity opposite to the polarity of the first contact terminal, an
The second contact terminal is in contact with the auxiliary layer, and the second contact layer is electrically connected with the second contact terminal.
14. The tandem solar cell of claim 13 wherein one of the lower carrier extraction layer and the second contact layer coincides with one of the auxiliary layer and the second contact terminal.
15. The tandem solar cell of claim 14 wherein the tandem solar cell includes a third contact layer located between the bottom solar cell and the top solar cell, the third contact layer being in contact with the lower carrier extraction layer and with the auxiliary layer on a crystalline silicon cell, wherein the polarity of the lower carrier extraction layer is opposite to the polarity of the auxiliary layer.
16. The tandem solar cell of claim 14 wherein one of the lower carrier extraction layer and lower contact layer is in direct contact with one of the auxiliary layer and the second contact terminal.
17. The tandem solar cell of claim 14 wherein a composite layer is arranged between the auxiliary layer of polysilicon and the lower carrier extraction layer at the rear surface of the top solar cell, the composite layer being in electrical contact with both the auxiliary layer and the lower carrier extraction layer, and
the first contact layer of the top solar cell has a first polarity and the first contact terminal has a second polarity opposite the first polarity.
18. The tandem solar cell of claim 12 wherein the auxiliary layer as a selective carrier extraction layer is in electrical contact with the lower carrier extraction layer at the rear surface of the top solar cell, and
the first contact layer of the top solar cell has a first polarity and the first contact terminal has a second polarity opposite the first polarity.
19. The tandem solar cell of claim 1 wherein the thin dielectric film is a silicon dioxide layer or a silicon oxynitride layer.
20. A method for manufacturing tandem solar cells, comprising:
providing a bottom solar cell having a front surface and a back surface;
Providing a top solar cell having a front surface and a back surface;
disposing the top solar cell with its rear surface on or adjacent to the front surface of the bottom solar cell such that the front surfaces of both the top and bottom solar cells face the radiation source during use;
wherein the top solar cell comprises a photovoltaic absorber layer having a bandgap greater than that of crystalline silicon,
the bottom solar cell includes a crystalline silicon substrate;
on the front surface of the bottom solar cell, the crystalline silicon substrate is arranged with a passivation layer stack comprising a thin dielectric film and an auxiliary layer, the thin dielectric film being bonded to the crystalline silicon substrate and arranged between the front surface of the crystalline silicon substrate and the auxiliary layer; the auxiliary layer is made of polysilicon;
wherein after the texturing step, a thin oxide layer and a polysilicon film are applied to at least the front side of the bottom solar cell; then if the polysilicon film is deposited on the rear portion of the bottom solar cell, removing the polysilicon film from the rear portion and smoothing or polishing the rear portion by single-sided etching; next, a coating and metallization is provided on the rear of the bottom solar cell, or
Applying an oxide layer and an intrinsic polysilicon layer to the front and back surfaces of the bottom solar cell after texturing and polishing the back of the bottom solar cell; then doping the polysilicon layer only on the front side; and further providing a coating and metallization on the back of the bottom solar cell.
21. The method of claim 20, wherein the metallization on the back of the bottom solar cell is provided by: holes are first provided in the layer stack on the rear part, followed by a metal layer and then a high temperature is provided.
22. The method according to claim 20 or 21, wherein,
the metallization forms a localized back surface field of doped aluminum silicon that penetrates the second passivation layer stack.
23. The method of claim 20, comprising:
the top solar cell comprises a second contact layer at its rear surface, the second contact layer being in contact with the lower extraction layer of the photovoltaic layer structure, the first contact layer having a first polarity, and the second contact layer having a second polarity opposite to the first polarity;
the bottom solar cell includes a second contact terminal having a polarity opposite to the polarity of the first contact terminal.
24. The method of claim 23, wherein the method comprises:
an insulating layer is arranged between the auxiliary layer of the bottom solar cell and the rear surface of the top solar cell.
25. The method of claim 23, wherein the second contact layer is in electrical contact with the second contact terminal.
26. The method of claim 20, comprising:
disposing a third contact layer between the auxiliary layer of the bottom solar cell and a lower carrier extraction layer of the top solar cell;
the third contact layer is in electrical contact with both the auxiliary layer and the lower carrier extraction layer, the auxiliary layer and the lower carrier extraction layer having the same polarity.
27. The method of claim 20, comprising:
a composite layer is arranged between the auxiliary layer of the bottom solar cell and a lower carrier extraction layer of the top solar cell.
28. Solar panel comprising at least one tandem solar cell manufactured according to any of the preceding claims 1-19 or according to any of the preceding claims 20-27.
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