Back contact solar cell and preparation method thereof, and battery assembly

Abstract

The present invention relates to the technical field of solar cells, and in particular to a back-contact solar cell and a preparation method thereof, as well as a battery assembly. By adopting a mixed metal electrode structure, the part of the fine grid electrode in the overlapping area of ​​the main grid electrode and the fine grid electrode is removed, and a metal composite layer under the fine grid electrode is used to replace the traditional fine grid electrode, thereby avoiding the spatial cross structure between the fine grid electrode and the main grid electrode, reducing the short circuit caused by insufficient effective insulation thickness, and being beneficial to improving the yield of the battery. At the same time, the discontinuity length of the fine grid electrode and the width of the main grid electrode are limited, providing a more ample error range for welding of welding strips, and by limiting the ratio of the thickness of the composite conductive layer to the width of the composite conductive layer in the first direction, it is beneficial to ensure the line resistivity of the composite conductive layer and avoid excessive power loss caused by excessive resistivity; the fine grid electrode is replaced by a flat composite conductive layer, so that the thickness of the insulating layer is greatly reduced, saving the material cost of the insulating layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and in particular relates to a back-contact solar cell and a preparation method thereof, and a cell assembly. Background Art

[0002] At present, the N electrode and P electrode of the back-contact heterojunction solar cell are both located on the back of the cell, and the electrode pattern is often distributed alternately in a forked shape (for example, the main gate is located at the end of the fine gate, and no insulating glue is required to insulate the main gate electrode and the fine gate electrode), or the main gate electrode and the fine gate electrode are distributed vertically (the main gate is located in the middle of the fine gate, and insulating glue is required to insulate the main gate electrode and the fine gate electrode). Among them, the vertical distribution of the main gate electrode and the fine gate electrode can flexibly arrange the number and position of the main gate electrodes, the current transmission distance on the fine gate electrode is the shortest, and there is almost no loss in the uncovered area at the end of the fine gate electrode, which can achieve the highest efficiency.

[0003] However, the connection of back-contact cells made in this way has the following disadvantages: the fine gate electrode and the main gate electrode are completely insulated by insulating glue. In actual production, due to the difference in the height of the fine gate electrode and the height of the insulating glue layer, the effective insulation thickness (effective insulation thickness = insulating glue thickness ~ fine gate electrode thickness) will be insufficient, which can easily cause a short circuit. In addition, if the thickness of the insulating glue is increased to ensure the effective insulation thickness, the consumption of insulating ink materials will increase.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention and does not necessarily constitute prior art or known technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the technical problem of insufficient effective insulation thickness between a fine grid electrode and a main grid electrode in existing back contact solar cells.

[0006] In order to achieve the above objectives, in a first aspect, an embodiment of the present invention provides a back-contact solar cell, comprising:

[0007] Battery cell substrate;

[0008] A transparent conductive layer is arranged on the back side of the cell substrate;

[0009] A composite conductive layer is arranged on a side of the transparent conductive layer away from the cell substrate;

[0010] A fine grid electrode, the fine grid electrode being arranged on a side of the composite conductive layer away from the battery cell substrate;

[0011] A main gate electrode and an insulating layer, wherein the main gate electrode and the fine gate electrode are vertically overlapped in different planes, and the fine gate electrode is intermittently arranged in the area where the fine gate electrode is vertically overlapped in different planes, and the intermittent length of the fine gate electrode is 0.1-10 mm, and the insulating layer at least fills the intermittent area of ​​the fine gate electrode to isolate the composite conductive layer from the main gate electrode;

[0012] The ratio between the thickness of the composite conductive layer and the width of the composite conductive layer along the first direction satisfies the formula ρ l =ρ0 / (b*h), where ρ l is the line resistivity of the composite conductive layer along the second direction, ρ0 is the volume resistivity of the composite conductive layer, b is the width of the composite conductive layer along the first direction, h is the thickness of the composite conductive layer, and the line resistivity ρ l The range is 0.5~3.5Ω / cm; wherein the first direction is the length extension direction of the main gate electrode, and the second direction is the length extension direction of the fine gate electrode;

[0013] The thickness of the composite conductive layer is 70nm~550nm; the composite conductive layer includes: a first conductive layer and / or a second conductive layer stacked, the thickness of the first conductive layer is 50nm~450nm, and the thickness of the second conductive layer is 20~100nm; the first conductive layer is closer to the transparent conductive layer than the second conductive layer; wherein the first conductive layer is a metal conductive layer, and the second conductive layer is a metal protective layer.

[0014] Optionally, the composite conductive layer is disposed on the transparent conductive layer.

[0015] Optionally, the back side of the cell substrate is provided with alternately arranged N-type conductive areas and P-type conductive areas, the transparent conductive layer and the composite conductive layer are stacked on the N-type conductive areas and the P-type conductive areas and separated by an isolation groove, and the isolation groove is realized by etching the composite conductive layer and the transparent conductive layer;

[0016] The ratio of the width of the composite conductive layer to the width of the isolation trench is 3:1-10:1.

[0017] Optionally, the material of the first conductive layer is one of copper, tin or silver; when the first conductive layer is tin or silver, the second conductive layer is not provided;

[0018] The material of the second conductive layer includes at least one of tin, silver, and nickel; or the second conductive layer is one of an indium oxide film layer, a doped tin oxide film layer, or a doped zinc oxide film layer.

[0019] Optionally, the thickness of the transparent conductive layer is 10nm~200nm; the thickness of the composite conductive layer is 70nm~550nm, the thickness of the first conductive layer is 50nm~450nm, and the thickness of the second conductive layer is 20~100nm

[0020] And / or, the material of the transparent conductive layer includes at least one of a doped indium oxide film layer, a tungsten-doped indium oxide film layer, a doped tin oxide film layer or a doped zinc oxide film layer.

[0021] Optionally, the material of the fine gate electrode includes low-temperature silver paste or silver-copper paste; or, the fine gate electrode is an electroplated copper gate metal electrode;

[0022] The material of the main gate electrode is low-temperature silver paste or silver-copper paste.

[0023] Optionally, the material of the insulating layer is insulating glue; and / or the thickness of the insulating layer is 5 μm-50 μm.

[0024] In a second aspect, an embodiment of the present invention further provides a method for preparing a back-contact solar cell, which is used to prepare the back-contact solar cell as described in the first aspect, comprising:

[0025] A battery cell substrate is provided; the back side of the battery cell substrate is provided with N-type conductive areas and P-type conductive areas arranged alternately;

[0026] Sequentially preparing a transparent conductive layer and a composite conductive film layer on the back side of the cell substrate;

[0027] Removing the transparent conductive layer and the composite conductive film layer at the junction of the N-type conductive region and the P-type conductive region by a patterning process, thereby forming an isolation groove and the transparent conductive layer and the composite conductive layer stacked on the N-type conductive region and the P-type conductive region;

[0028] A fine gate electrode, an insulating layer and a main gate electrode are sequentially manufactured on a cell substrate formed with an isolation groove.

[0029] Optionally, the step of sequentially manufacturing a fine gate electrode, an insulating layer and a main gate electrode on the cell substrate having the isolation groove formed therein comprises:

[0030] A fine gate electrode made of a low-temperature silver paste material is made by screen printing or pad printing, or a fine gate electrode is made by electroplating a copper fine gate; wherein, when the polarity of the main gate electrode is the same as that of the fine gate electrode, the fine gate electrode is kept continuous; when the polarity of the main gate electrode is different from that of the fine gate electrode, the fine gate electrode is pre-disconnected in the area where it will overlap with the main gate electrode, and the disconnection length of the fine gate electrode is 0.1 mm to 10 mm;

[0031] An insulating layer is formed in the region where the fine gate electrode is disconnected by screen printing, pad printing or inkjet printing, wherein the size of the insulating layer along the second direction is 1.1 to 1.5 times the disconnected length of the fine gate electrode; and the size of the insulating layer along the first direction is 1.1 to 1.5 times the width of the composite conductive layer;

[0032] The main gate electrode is manufactured on the insulating layer by screen printing or pad printing. The main gate electrode covers the insulating layer and is connected to the fine gate electrodes of the same polarity.

[0033] In a third aspect, an embodiment of the present invention further provides a method for preparing a back-contact solar cell, which is used to prepare the back-contact solar cell as described in the first aspect, comprising:

[0034] A battery cell substrate is provided; the back side of the battery cell substrate is provided with N-type conductive areas and P-type conductive areas arranged alternately;

[0035] Sequentially preparing a transparent conductive layer and a composite conductive film layer on the back side of the cell substrate;

[0036] An isolation groove is made at the junction of the N-type conductive area and the P-type conductive area on the back side of the cell substrate by a graphic process to form a transparent conductive layer and a composite conductive layer separated by the isolation groove;

[0037] Sequentially forming a fine gate electrode and an insulating layer on the battery substrate having the isolation groove formed therein;

[0038] The main gate electrode is formed in a direction perpendicular to the fine gate electrode.

[0039] In a fourth aspect, an embodiment of the present invention further provides a battery assembly, which includes a back-contact solar cell as described in the first aspect.

[0040] The embodiments of the present invention have at least the following beneficial effects:

[0041] The present invention adopts the above-mentioned technical scheme and adopts a mixed metal electrode structure to remove the part of the fine gate electrode in the overlapping area of ​​the main gate electrode and the fine gate electrode, and uses the metal composite layer under the fine gate electrode to replace the traditional fine gate electrode, so as to avoid the spatial cross structure between the fine gate electrode and the main gate electrode, reduce the short circuit caused by insufficient effective insulation thickness, and help improve the yield of the battery. At the same time, the discontinuity length of the fine gate electrode and the width of the main gate electrode are limited to provide a more ample error range for welding of the welding strip, and by limiting the ratio between the thickness of the composite conductive layer and the width of the composite conductive layer in the first direction, it is beneficial to ensure the line resistivity of the composite conductive layer and avoid excessive power loss caused by excessive resistivity. In addition, by replacing the fine gate electrode with a flat composite conductive layer, the thickness of the insulating layer can be greatly reduced, saving the material cost of the insulating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 A schematic diagram of the internal structure of a back-contact solar cell from a top view provided by an embodiment of the present invention;

[0044] Figure 2 A partial cross-sectional schematic diagram of a back-contact solar cell provided by an embodiment of the present invention;

[0045] Figure 3 A cross-sectional view of a back-contact solar cell along the direction of a fine grid electrode provided by an embodiment of the present invention;

[0046] Figure 4 A cross-sectional view of a back-contact solar cell along the main grid electrode direction provided by an embodiment of the present invention;

[0047] Figure 5 A cross-sectional view of another back-contact solar cell along the main grid electrode direction provided by an embodiment of the present invention;

[0048] Figure 6 A schematic flow chart of a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0049] Figure 7 A schematic diagram of the process structure along the first direction and the second direction of step S100 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0050] Figure 8 A schematic diagram of the process structure along the first direction and the second direction of step S200 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0051] Fig. 9 A schematic diagram of the process structure along a first direction of step S300 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0052] Fig.10 A schematic diagram of the process structure along a first direction of steps S400 and S500 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0053] Fig.11A schematic diagram of the process structure along the second direction of steps S400 and S500 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0054] Fig.12 A schematic flow chart of another method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0055] Fig.13 A schematic diagram of the process structure along the first direction and the second direction of step S1 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0056] Fig.14 A schematic diagram of the process structure along the first direction and the second direction of step S2 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0057] Fig.15 A schematic diagram of the process structure along a first direction of step S3 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0058] Fig.16 A schematic diagram of the process structure along a first direction of step S4 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0059] Fig.17 A schematic diagram of the process structure along the second direction of step S4 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0060] Fig.18 A schematic diagram of the process structure along a first direction of step S5 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0061] Fig.19 A schematic diagram of the process structure along the second direction of step S5 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0062] Fig. 20 A schematic diagram of the process structure along a first direction of step S51 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0063] Fig.21 A schematic diagram of the process structure along a first direction of step S6 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0064] Fig. 22 A schematic diagram of the process structure along the second direction of step S6 in a method for preparing a back-contact solar cell provided by an embodiment of the present invention;

[0065] Fig.23It is a schematic diagram of a slice cross section of a conventional back contact solar cell;

[0066] Fig.24 A schematic cross-sectional view of a slice of a back-contact solar cell provided in an embodiment of the present invention.

[0067] Description of Figure Numbers.

[0068] 1-cell substrate; 2-transparent conductive layer; 2n-transparent conductive layer of N-type conductive area; 2p-transparent conductive layer of P-type conductive area; 2g-isolation area; 3-composite conductive layer; 31-first conductive layer; 32-second conductive layer; 4a-fine gate electrode; 4b-main gate electrode; 5-insulating layer. DETAILED DESCRIPTION

[0069] In the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0070] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0071] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Among them, the terms "optional" and "optional" all mean that they may be included or not included (or may be present or not).

[0072] First, combining Figures 1 to 4 An embodiment of the present invention provides a back-contact solar cell, comprising: a cell substrate 1, a transparent conductive layer 2, a composite conductive layer 3, a fine grid electrode 4a, an insulating layer 5 and a main grid electrode 4b.

[0073] Specifically, the cell substrate 1 has a front side and a back side; the front side refers to the light-receiving side of the cell substrate 1, and the back side is the opposite back side of the light-receiving side. In the embodiment of the present invention, the side close to the cell substrate 1 is generally considered as the inner side, and the side far from the cell substrate 1 is considered as the outer side. The back side of the cell substrate 1 is distributed with alternating N-type conductive areas and P-type conductive areas. Specifically, the N-type conductive areas and the P-type conductive areas are arranged along the Figure 1 The N-type conductive region and the P-type conductive region are alternately arranged in the first direction, an isolation region 2g is formed between the N-type conductive region and the P-type conductive region, and the length extension direction of the N-type conductive region and the P-type conductive region is the second direction, which is perpendicular to the first direction.

[0074] The transparent conductive layer 2 is arranged on the back of the cell substrate 1. The transparent conductive layer 2 can be made of ITO (Indium Tin Oxide). ITO has good light transmittance and conductivity, which is conducive to improving the photoelectric conversion efficiency. The composite conductive layer 3 is arranged on the side of the transparent conductive layer away from the cell substrate 1, that is, the composite conductive layer 3 and the transparent conductive layer 2 are stacked on the back of the cell and separated by the isolation groove. The isolation groove is located in the area where the isolation area 2g is located, and is mainly used to separate the N-type conductive area and the P-type conductive area to form a semiconductor structure with a PN junction. The ratio of the width of the composite conductive layer 3 to the width of the isolation groove is 3:1~10:1. The transparent conductive layer 2 and the composite conductive layer 3 are separated by corrosion to avoid the connection between the N-type conductive area and the P-type conductive area. In principle, the smaller the width of the isolation groove, the better. The empirical value is that the ratio of the width of the composite conductive layer 3 (the fine gate disconnection position) to the width of the isolation groove is between 3:1~10:1. If the width of the isolation groove is too small, the process yield will be reduced. If the width of the isolation groove is too large, the conductive layer will be narrow, which will increase the power loss of current transmission. The transparent conductive layer 2 located in the N-type conductive area is represented as the transparent conductive layer 2n of the N-type conductive area, and the transparent conductive layer located in the P-type conductive area is represented as the transparent conductive layer 2p of the N-type conductive area, so as to facilitate the distinction in the figure.

[0075] The fine gate electrode 4a is arranged on the side of the composite conductive layer 3 away from the cell substrate 1; the main gate electrode 4b and the fine gate electrode 4a are approximately in skew lines and are distributed perpendicularly to each other. The fine gate electrode 4a is intermittently arranged in the mutually perpendicular distribution area, that is, the fine gate electrode 4a in this part of the mutually perpendicular distribution area is not arranged, and the intermittently arranged fine gate electrode 4a is electrically connected through the underlying composite conductive layer 3. The insulating layer 5 at least fills the intermittent area of ​​the fine gate electrode 4a to isolate the composite conductive layer 3 and the main gate electrode 4b in this area.

[0076] The composite conductive layer 3 includes: a first conductive layer 31 and / or a second conductive layer 32 which are stacked; the first conductive layer 31 is closer to the transparent conductive layer 2 than the second conductive layer 32; wherein the first conductive layer 31 is a metal conductive layer, which mainly provides a conductive main layer and should be as thick as possible, and the second conductive layer 32 is a metal protective layer, which is mainly used to protect the first conductive layer 31 below and can prevent the first conductive layer 31 from being oxidized, and has a relatively thin thickness. Optionally, the thickness of the composite conductive layer is 70nm~550nm, the thickness of the first conductive layer 31 is 50nm~450nm, and the thickness of the second conductive layer 32 is 20~100nm.

[0077] The transparent conductive layer and the composite conductive layer 3 are manufactured by physical vapor deposition (PVD) or reactive plasma deposition (RPD).

[0078] When the transparent conductive layer and the composite conductive film layer are prepared, the substrate temperature ranges from 100°C to 250°C, preferably, the substrate temperature ranges from 180°C to 220°C.

[0079] The relationship between the width of the composite conductive layer 3 along the first direction and its thickness in this embodiment is: the ratio between the thickness of the composite conductive layer 3 and the width of the composite conductive layer 3 in the first direction satisfies the formula ρ l =ρ0 / (b*h), where ρ l is the line resistivity of the composite conductive layer 3 along the second direction, ρ0 is the volume resistivity of the composite conductive layer 3, b is the width of the composite conductive layer 3 along the first direction, h is the thickness of the composite conductive layer 3, and the line resistivity ρ l The range is 0.5~3.5Ω / cm; wherein the first direction is the length extension direction of the main gate electrode 4b, and the second direction is the length extension direction of the fine gate electrode 4a.

[0080] Optionally, the line resistivity ρ l The range is 1.0~2.5Ω / cm, which ensures that the resistivity of the composite conductive layer 3 replacing the fine grid line is within an appropriate range to avoid additional transmission power loss caused by excessive resistance in this area and reduce the battery efficiency; if the resistivity is too small, there will be a smaller resistance, but it will not have a significant effect on improving the efficiency, but will increase the cost.

[0081] The back-contact solar cell provided in the embodiment of the present invention adopts a mixed metal electrode structure to remove the part of the fine gate electrode 4a in the vertical division area between the main gate electrode 4b and the fine gate electrode 4a, and uses the metal composite layer under the fine gate electrode 4a to replace the traditional fine gate electrode 4a, thereby avoiding the spatial cross structure between the fine gate electrode 4a and the main gate electrode 4b, thereby increasing the effective insulation thickness and reducing the short circuit caused by insufficient effective insulation thickness, which is beneficial to improving the yield of the battery. At the same time, the discontinuity length of the fine gate electrode 4a and the width of the main gate electrode 4b are limited to provide a more ample error range for welding of the welding strip, and by limiting the ratio between the thickness of the composite conductive layer 3 and the width of the composite conductive layer 3 in the first direction, it is beneficial to ensure the line resistivity of the composite conductive layer 3 and avoid excessive power loss caused by excessive resistivity; in addition, by replacing the fine gate electrode 4a with a flat composite conductive layer 3, the thickness of the insulating layer 5 can be greatly reduced, saving the material cost of the insulating layer 5.

[0082] In some embodiments, see Figure 5 , the composite conductive layer 3 is not provided in the area not covered by the fine grid electrode 4a, the insulating layer 5 and the main grid electrode 4b, that is, the composite conductive layer 3 in the area not covered by the fine grid electrode 4a, the insulating layer 5 and the main grid electrode 4b on the transparent conductive layer 2 is removed, and only the composite conductive layer 3 in the area covered by the fine grid electrode 4a, the insulating layer 5 and the main grid electrode 4b is retained, so that the absorption of sunlight by this part of the composite conductive layer 3, especially the absorption of the near-infrared band, can be reduced, thereby increasing the reflectivity of light and increasing the short-circuit current of the back-contact solar cell. The specific mechanism is that the solar cell with a metal layer provided on the back of the cell substrate 1, especially when the metal layer is used on the back, has obvious absorption of the infrared and near-infrared bands, resulting in a significant reduction in the reflection of the infrared and near-infrared bands on the back of the cell, thereby reducing the short-circuit current of the solar cell. Removing this redundant part of the composite conductive layer and retaining the transparent conductive layer 2 can reduce the loss of this part.

[0083] Optionally, the material of the first conductive layer 31 is copper, which is beneficial to improving the conductive performance.

[0084] Optionally, the material of the second conductive layer 32 includes at least one of tin, silver, and nickel. When the material of the second conductive layer 32 is silver, since silver can contact the covering silver paste, on the one hand, it prevents the copper underneath from being oxidized, and on the other hand, silver has better compatibility with the material of the fine gate electrode 4a (for example, silver paste), which is conducive to improving the bonding force between the film layers.

[0085] Optionally, when the first conductive layer 31 is tin or silver, the composite conductive layer 3 may not be provided with the second conductive layer 32 .

[0086] In some other embodiments, the second conductive layer is one of an indium oxide film layer (such as tin-doped indium oxide ITO, tungsten-doped indium oxide IWO, IZO, etc.), a doped tin oxide film layer (such as FTO, ATO, etc.) or a doped zinc oxide film layer (such as GZO, AZO, etc.).

[0087] Optionally, the material of the transparent conductive layer 2 includes at least one of a doped indium oxide film layer, a tungsten-doped indium oxide film layer, a doped tin oxide film layer or a doped zinc oxide film layer.

[0088] In some embodiments, the material of the fine gate electrode 4a includes low-temperature silver paste or silver-copper paste. Optionally, the fine gate electrode 4a is an electroplated copper gate metal electrode.

[0089] In some embodiments, the insulating layer 5 is made of insulating glue. Optionally, the insulating layer 5 has a thickness of 5 μm to 50 μm.

[0090] In some embodiments, the material of the main gate electrode 4 b is low-temperature silver paste or silver-copper paste.

[0091] The second aspect, such as Figure 6 As shown, an embodiment of the present invention provides a method for preparing a back-contact solar cell, which is used to prepare the back-contact solar cell described in the first aspect, comprising the following steps:

[0092] S100, providing a cell substrate 1; the back side of the cell substrate 1 is provided with N-type conductive areas and P-type conductive areas arranged alternately, such as Figure 7 shown.

[0093] S200, sequentially preparing a transparent conductive layer and a composite conductive film layer on the back side of the cell substrate 1, such as Figure 8 shown.

[0094] S300, removing the transparent conductive layer and the composite conductive film layer at the junction of the N-type conductive region and the P-type conductive region by a graphic process, thereby forming an isolation groove and a transparent conductive layer 2 and a composite conductive layer 3 stacked in the N-type conductive region and the P-type conductive region, such as Fig. 9 and Figure 8 shown.

[0095] S400, a fine gate electrode 4a, an insulating layer 5 and a main gate electrode 4b are sequentially formed on the cell substrate 1 with the isolation groove formed thereon, such as Fig.10 and Fig.11 shown.

[0096] Specifically, firstly, a low-temperature silver paste fine gate electrode 4a is made by screen printing or pad printing, or a copper fine gate is electroplated to make the fine gate electrode 4a. Its characteristics are: the fine gate electrode 4a is designed as follows at the position reserved for the main gate electrode 4b: when the polarity of the main gate electrode 4b is the same as that of the fine gate electrode 4a, the fine gate electrode 4a needs to be kept continuous; when the polarity of the main gate electrode 4b is different from that of the fine gate electrode 4a, the fine gate electrode 4a is pre-disconnected in the area where it will overlap with the main gate electrode 4b, and its disconnection length is 0.1mm~10mm. The disconnection length of the fine gate electrode 4a is 1.2~10 times the width of the main gate electrode 4b, preferably 1.2~5 times.

[0097] Then, the insulating layer 5 is manufactured by screen printing, pad printing, inkjet printing or the like. The length of the insulating layer 5 (i.e., the dimension along the second direction) needs to be greater than the length of the fine gate electrode 4a being disconnected, preferably 1.1 to 1.5 times the length of the fine gate electrode 4a being disconnected; the width of the insulating layer 5 (i.e., the dimension along the first direction) needs to be greater than the width of the composite conductive layer 3, preferably 1.1 to 1.5 times the width of the composite conductive layer 3.

[0098] Finally, a main gate electrode 4b made of a low-temperature silver paste material is manufactured by screen printing, pad printing, etc., which is characterized in that it covers the insulating layer 5 and is connected to the fine gate electrode 4a of the same polarity.

[0099] Optionally, after step S400, the method further includes:

[0100] S500, removing the composite conductive layer 3 not covered by the fine gate electrode 4a, the insulating layer 5 and the main gate electrode 4b. Fig.10 and Fig.11 The composite conductive layer 3 can be removed by a step-by-step etching method. First, a hydrochloric acid solution with a weight ratio of 0.05-0.5% is used to remove the second conductive layer 32 on the surface of the composite conductive layer 3. Then, an alkaline etching solution, such as a mixed solution of copper chloride, ammonium chloride, ammonia water, and hydrogen peroxide, with a weight ratio of 10%-15% copper chloride, 5%-10% ammonium chloride, 10%-50% ammonia water, 1%-20% hydrogen peroxide, and the remainder being water, is used to remove the exposed portion of the composite conductive layer 3.

[0101] Optionally, in the process of removing the composite conductive layer 3 by step-by-step etching, when the first conductive layer 31 is copper, the solution for removing the uncovered area of ​​the first conductive layer 31 can also be replaced by a trivalent iron ion solution, such as a ferric chloride solution or a ferric sulfate solution. The concentration is set according to the actual corrosion rate, and this embodiment does not impose any specific restrictions.

[0102] In addition, the present embodiment can also use a solution method to remove the composite conductive layer 3, and an acidic corrosive solution can be used to remove the exposed part of the composite conductive layer 3 at one time, such as a sulfuric acid and hydrogen peroxide mixed solution, wherein the weight ratio of sulfuric acid is 0.05%~5%, and the weight ratio of hydrogen peroxide is 0.01%~5%. However, the acidic solution also has a strong corrosive ability to the transparent conductive layer 2, and the difference in corrosion rate needs to be controlled to control the time window.

[0103] Optionally, the transparent conductive layer and the composite conductive layer 3 may be deposited by a process such as PVD, reactive plasma deposition (RPD) or evaporation.

[0104] Optionally, the isolation groove is manufactured by an etching paste etching method or a solution etching method.

[0105] Specifically, the etching paste corrosion method is as follows: the etching paste is applied at the junction of the N-type conductive area and the P-type conductive area for corrosion, and the coating method is screen printing, inkjet printing, dispensing, etc.; the composite conductive layer 3 and the transparent conductive layer 2 in the coated area are corroded and removed by baking; and the residual etching paste is then removed by cleaning.

[0106] The solution etching method is as follows: a mask layer is made on the surface of the cell substrate 1, the mask pattern exposes the bottom composite conductive layer 3 and the transparent conductive layer at the junction of the N-type conductive area and the P-type conductive area, and covers other areas; then the composite conductive layer 3 and the transparent conductive layer are corroded by the etching solution; finally, the mask layer is removed. The material of the mask layer is photosensitive glue, dry film, protective ink, and the mask layer is made by spin coating / filming, exposure, development; or screen printing, inkjet printing, dispensing.

[0107] Optionally, the etching solution includes an acidic etching solution and / or an alkaline etching solution. A single acidic etching solution or an alkaline etching solution may be used for etching, or a combination of an acidic etching solution and an alkaline etching solution may be used for etching, which can be flexibly selected according to different configurations of the composite conductive layer. The acidic etching solution includes at least one of hydrochloric acid, sulfuric acid, nitric acid, sodium hypochlorite, hydrogen peroxide, and ferric chloride; the alkaline etching solution includes at least one of cupric chloride, ammonia water, and ammonium chloride.

[0108] Optionally, after step S400, the method further includes: the composite conductive layer 3 not covered by the fine gate electrode 4a, the insulating layer 5 and the main gate electrode 4b may also be retained in the battery to save process steps.

[0109] The third aspect, such as Fig.12 As shown, an embodiment of the present invention provides another method for preparing a back-contact solar cell, which is used to prepare the back-contact solar cell described in the first aspect, comprising the following steps:

[0110] S1, providing a cell substrate 1; the back side of the cell substrate 1 is provided with N-type conductive areas and P-type conductive areas arranged alternately, such as Fig.13 shown.

[0111] S2, sequentially preparing a transparent conductive layer and a composite conductive film layer on the back side of the cell substrate 1, such as Fig.14 shown.

[0112] S3, an isolation groove is made on the back side of the cell substrate 1 at the junction of the N-type conductive area and the P-type conductive area by a graphic process to form a transparent conductive layer 2 and a composite conductive layer 3 separated by the isolation groove, such as Fig.15 shown.

[0113] S4, forming fine gate electrodes 4a in sequence on the battery substrate where the isolation grooves have been formed, such as Fig.16 and Fig.17 shown.

[0114] S5, an insulating layer 5 is provided at the discontinuous position of the fine gate metal electrode, such as Fig.18 and Fig.19 shown.

[0115] Specifically, the method for preparing the fine gate electrode 4 a is the same as the method of step S400 in the aforementioned embodiment, and will not be described in detail here.

[0116] S6, forming the main gate electrode 4b along the direction perpendicular to the fine gate electrode 4a, such as Fig.21 and Fig. 22 shown.

[0117] Specifically, the preparation method of the main gate electrode 4 b is the same as the method of step S400 in the aforementioned embodiment, and will not be described in detail here.

[0118] Optionally, between steps S5 and S6, the following steps are further included:

[0119] S51, removing the composite conductive layer 3 not covered by the fine gate electrode 4a and the insulating layer 5, and continue to refer to Fig. 20 (first direction) and Fig.19 (Second direction) Schematic diagram of the process structure shown.

[0120] In this embodiment, the composite conductive layer 3 not covered by the fine gate electrode 4a and the insulating layer 5 is removed, which can reduce the free carrier absorption effect (FCA) of the metal layer to reduce the infrared absorption loss of the back metal film layer; at the same time, it can also increase the bifaciality of the battery and increase the back power generation efficiency. In addition, it should be noted that the specific process method for removing the composite conductive layer 3 not covered by the fine gate electrode 4a and the insulating layer 5 can refer to step S500 in the above embodiment, and will not be described in detail here.

[0121] The back-contact solar cell obtained by the preparation method of the back-contact solar cell provided by this embodiment does not have a metal conductive layer in the area other than the fine grid electrode 4a, the insulating layer 5 and the main grid electrode 4b, which can avoid the metal layer from absorbing sunlight, improve the reflectivity of light and increase the short-circuit current of the back-contact solar cell. The specific mechanism is that the solar cell with a metal layer on the back of the cell substrate 1, especially when the copper metal layer is used on the back, has obvious absorption of infrared and near-infrared bands, resulting in a significant reduction in the infrared band reflection on the back of the cell, thereby reducing the short-circuit current of the solar cell. Removing this redundant part of the composite conductive layer and retaining the transparent conductive layer 2 can reduce the loss of this part.

[0122] In a fourth aspect, an embodiment of the present invention provides a battery assembly, including the back-contact solar cell in the aforementioned embodiments. The back-contact solar cell included in the battery assembly adopts a mixed metal electrode structure, removes the part of the fine grid electrode in the overlapping area of ​​the main grid electrode and the fine grid electrode, and uses a metal composite layer under the fine grid electrode to replace the traditional fine grid electrode, thereby avoiding the spatial cross structure between the fine grid electrode and the main grid electrode, reducing the short circuit caused by insufficient effective insulation thickness, and is conducive to improving the yield of the battery; at the same time, the fine grid electrode is replaced by a flat composite conductive layer, so that the thickness of the insulation layer can be greatly reduced, saving the material cost of the insulation layer.

[0123] like Fig.23 As shown, in a conventional back-contact battery that uses an insulating layer to insulate and isolate the main gate electrode and the fine gate electrode, in the overlapping area of ​​the main gate electrode and the fine gate electrode, the fine gate electrode and the main gate electrode are continuous. Therefore, the fine gate electrode and the main gate electrode are cross-distributed in space, and the insulation in the middle is completely achieved by filling the insulating layer material. This results in the actual effective insulation thickness (i.e., the spatial spacing between the main gate electrode and the fine gate electrode) being equal to the difference between the insulation layer thickness and the fine gate electrode thickness. For example: the insulation layer thickness is 30μm (the insulation layer is printed on the back of the battery substrate, covering the fine gate electrode, and its thickness is measured from the distance from the substrate surface to the highest point of the insulation layer), and the fine gate thickness is 20μm, then the effective insulation thickness is 10μm. In particular, when the fine gate electrode is a screen-printed silver paste electrode, since the screen-printed electrode always has an undulating shape, for example, a 20μm thick silver paste electrode may have a thickness of less than 15μm at the lowest point and a thickness of up to 25μm at the highest point. When the highest point of the fine gate electrode undulation happens to be at the main gate electrode position, the effective insulating thickness of the insulating layer is 5μm.

[0124] like Fig.24As shown, the embodiment of the present invention proposes to use a composite conductive layer to replace the fine gate electrode. The composite conductive layer made by plating is almost as flat as the substrate (there is no fine gate electrode on its surface either). Therefore, the actual thickness of the insulating layer is equal to the effective thickness of the insulating layer (equivalent to increasing the thickness of the effective insulating layer). Taking the above insulating layer thickness of 30μm as an example, after using a flat composite conductive layer structure, the thickness of the insulating layer is reduced to 15μm, which can greatly reduce the insulating material. At the same time, the insulating layer thickness of 15μm is the effective insulating thickness, which is also greater than the effective insulating thickness of the fine gate continuous structure.

[0125] The embodiments of the present invention are described in detail below, which are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0126] Example 1

[0127] A back contact solar cell having a structure as Figures 1 to 4 As shown, it includes: a cell substrate; a transparent conductive layer arranged on the back of the cell substrate; a composite conductive layer arranged on the side of the transparent conductive layer away from the cell substrate; a fine gate electrode arranged on the side of the composite conductive layer away from the cell substrate; a main gate electrode and an insulating layer, the main gate electrode and the fine gate electrode are vertically overlapped in different planes, and the fine gate electrode is intermittently arranged in the area of ​​vertical overlap in different planes, the peak height of the fine gate electrode is 15μm, and the insulating layer at least fills the intermittent area of ​​the fine gate electrode to isolate the composite conductive layer from the main gate electrode. Among them, the thickness of the transparent conductive layer is 60nm, the thickness of the composite conductive layer is 300nm, and the thickness of the insulating layer is 20μm. At the same time, the width of the composite conductive layer ranges from 500μm. Such thickness setting has an effective insulating thickness equal to the thickness of the insulating layer of 20μm.

[0128] Furthermore, the composite conductive layer includes a first conductive layer 31 and a second conductive layer 32 which are stacked, and the first conductive layer 31 is closer to the transparent conductive layer than the second conductive layer 32; wherein the first conductive layer 31 is a metal copper conductive layer, and the second conductive layer 32 is an ITO protective layer, and the thickness of the first conductive layer 31 is 250nm, and the thickness of the second conductive layer 32 is 50nm. Such a configuration can ensure that the regional conductivity of the composite conductive layer is appropriate, and can replace the metal fine gate electrode for conduction to avoid large power loss.

[0129] Example 2

[0130] Referring to the back-contact solar cell structure of Example 1, the difference is that the thickness of the first conductive layer 31 is increased to 350nm, and the width of the composite conductive layer is adjusted to 300μm. Example 2 is an example of increasing the thickness of the conductive layer and reducing the width of the conductive area. This will result in an increase in the isolation groove area and a decrease in the short-circuit current Isc, but a slight increase in FF due to the increase in the number of conductive areas.

[0131] Example 3

[0132] Referring to the back contact solar cell structure of Example 1, the difference is that the thickness of the composite conductive layer is reduced to 150nm, and the width of the composite conductive layer is adjusted to 700μm. Example 3 is an example of reducing the thickness of the conductive layer and increasing the width of the conductive area, which will result in a reduction in the number of conductive areas and a higher current density in each conductive area, increasing power loss, resulting in low Isc and low FF.

[0133] Example 4

[0134] Referring to the back contact solar cell structure of Example 1, the difference is that, without changing the total thickness of the composite conductive layer, the thickness of the first conductive layer 31 is adjusted to 200nm, and the thickness of the second conductive layer 32 is adjusted to 100nm. Example 4 is an example of reducing the thickness of the first conductive layer 31, which will increase the resistance of the conductive layer and increase the power loss, increase Rs and reduce FF.

[0135] Example 5

[0136] Referring to the back-contact solar cell structure of Example 1, the difference is that, without changing the total thickness of the composite conductive layer, the thickness of the first conductive layer 31 is adjusted to 280nm, and the thickness of the second conductive layer 32 is adjusted to 20nm. Example 5 is an example of increasing the thickness of the first conductive layer 31 and reducing the thickness of the protective layer. The conductive layer is oxidized due to insufficient protection, which increases the transmission resistance and increases the power loss. Its FF is slightly better than Example 4, but lower than Example 1.

[0137] Example 6

[0138] Referring to the back-contact solar cell structure of Example 1, the difference is that the thickness of the first conductive layer 31 is kept unchanged, and the thickness of the second conductive layer 32 is reduced to 20nm. Example 6 is an example of reducing the thickness of the protective layer. The conductive layer is oxidized due to insufficient protection, which increases the transmission resistance and increases the power loss. Its FF is slightly better than Example 4, but lower than Example 1.

[0139] Example 7

[0140] Referring to the back contact solar cell structure of Example 1, the difference is that the thickness of the first conductive layer 31 is kept unchanged, and the thickness of the second conductive layer 32 is increased to 100nm. Example 7 increases the thickness of the protective layer (ITO here). The increase in thickness will lead to an increase in the longitudinal transmission distance and increase the series resistance, and the FF is slightly lower.

[0141] Example 8

[0142] Referring to the back contact solar cell structure of Example 1, the difference is that the fine gate electrode and the composite conductive layer outside the insulating layer coverage area are retained, and Example 8 retains the metal layer outside the coverage area, which will result in a significant decrease in Isc, but an increase in FF.

[0143] Comparative Example 1

[0144] Referring to the back-contact solar cell structure of Example 1, the difference is that no composite conductive layer is set, and the entire fine grid electrode is directly set on the transparent conductive layer. Comparative Example 1 adopts a silver paste fine grid through-design, and the effective insulation thickness is insufficient, resulting in a low Rsh and a significant decrease in the reverse dark current yield.

[0145] Comparative Example 2

[0146] Referring to the back-contact solar cell structure of Example 1, the difference is that the thickness of the first conductive layer 31 is 40 nm, while in the composite conductive layer of Example 2, the first conductive layer 31 is set too thin, resulting in a significant increase in Rs, a significant decrease in FF, and a significant decrease in efficiency, but Rsh and reverse dark current are normal.

[0147] Comparative Example 3

[0148] Referring to the back-contact solar cell structure of Example 1, the difference is that the width of the composite conductive layer is 1000 μm. In Comparative Example 3, the composite conductive layer is too wide (i.e., the conductive area is too wide), and the cell has a significantly low FF and a decreased efficiency due to carrier transmission losses, but Rsh and reverse dark current are normal.

[0149] Comparative Example 4

[0150] Referring to the back-contact solar cell structure of Comparative Example 1, the difference is that the thickness of the insulating layer is set to 30μm, and the entire fine grid electrode is directly set on the transparent conductive layer. Comparative Example 4 refers to Comparative Example 1. While adopting the silver paste fine grid through-design, the thickness of the insulating ink is increased. In this way, although the efficiency can reach a higher level and to a certain extent can alleviate the problems of low Rsh and low reverse dark current yield, the yield cannot reach a higher level due to the random changes in the thickness of the insulating ink.

[0151] The performance data of the back contact solar cell obtained in the above examples and comparative examples are shown in the following table:

[0152] Table 1 Comparison of battery performance data of different embodiments and comparative examples

[0153]

[0154] From the above results, it can be seen that, compared with the comparative example, the embodiment scheme of the present invention can effectively avoid the battery short circuit caused by poor insulation of the insulating layer, which is reflected in the significant improvement of the parallel resistance Rsh and the reverse dark current yield compared with the conventional scheme, which is beneficial to improve the yield of battery production. Further, according to Examples 1 and 2 to 7, it can be seen that the preferred thickness and width of the composite conductive film of the present invention can further reduce the power loss of the composite conductive layer, which is more conducive to further improving the battery efficiency.

[0155] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A back contact solar cell, characterized in that: include: Battery cell substrate; A transparent conductive layer is arranged on the back side of the cell substrate; A composite conductive layer is arranged on a side of the transparent conductive layer away from the cell substrate; A fine grid electrode, the fine grid electrode being arranged on a side of the composite conductive layer away from the battery cell substrate; A main gate electrode and an insulating layer, wherein the main gate electrode and the fine gate electrode are vertically overlapped in different planes, and the fine gate electrode is intermittently arranged in the area where the fine gate electrode is vertically overlapped in different planes, and the intermittent length of the fine gate electrode is 0.1-10 mm, and the insulating layer at least fills the intermittent area of ​​the fine gate electrode to isolate the composite conductive layer from the main gate electrode; The ratio between the thickness of the composite conductive layer and the width of the composite conductive layer along the first direction satisfies the formula ρ l =ρ0 / (b*h), where ρ l is the line resistivity of the composite conductive layer along the second direction, ρ0 is the volume resistivity of the composite conductive layer, b is the width of the composite conductive layer along the first direction, h is the thickness of the composite conductive layer, and the line resistivity ρ l The range is 0.5~3.5Ω / cm; wherein the first direction is the length extension direction of the main gate electrode, and the second direction is the length extension direction of the fine gate electrode; The thickness of the composite conductive layer is 70nm~550nm; the composite conductive layer includes: a first conductive layer and / or a second conductive layer stacked, the thickness of the first conductive layer is 50nm~450nm, and the thickness of the second conductive layer is 20~100nm; the first conductive layer is closer to the transparent conductive layer than the second conductive layer; wherein the first conductive layer is a metal conductive layer, and the second conductive layer is a metal protective layer.

2. The back contact solar cell according to claim 1, characterized in that: The back side of the cell substrate is provided with alternately arranged N-type conductive areas and P-type conductive areas, the transparent conductive layer and the composite conductive layer are stacked on the N-type conductive areas and the P-type conductive areas and separated by an isolation groove, and the isolation groove is realized by etching the composite conductive layer and the transparent conductive layer; The ratio of the width of the composite conductive layer to the width of the isolation trench is 3:1-10:

1.

3. The back contact solar cell according to claim 1, characterized in that: The material of the first conductive layer is one of copper, tin or silver; when the first conductive layer is tin or silver, the second conductive layer is not provided; The material of the second conductive layer includes at least one of tin, silver, and nickel; or the second conductive layer is one of an indium oxide film layer, a doped tin oxide film layer, or a doped zinc oxide film layer.

4. The back contact solar cell according to claim 1, characterized in that: The thickness of the transparent conductive layer is 10nm~200nm; the thickness of the composite conductive layer is 70nm~550nm, the thickness of the first conductive layer is 50nm~450nm, and the thickness of the second conductive layer is 20~100nm And / or, the material of the transparent conductive layer includes at least one of a doped indium oxide film layer, a tungsten-doped indium oxide film layer, a doped tin oxide film layer or a doped zinc oxide film layer.

5. The back contact solar cell according to claim 1, characterized in that: The material of the fine gate electrode includes low-temperature silver paste or silver-copper paste; or, the fine gate electrode is an electroplated copper gate metal electrode; The material of the main gate electrode is low-temperature silver paste or silver-copper paste.

6. The back contact solar cell according to claim 1, characterized in that: The material of the insulating layer is insulating glue; and / or the thickness of the insulating layer is 5 μm-50 μm.

7. A method for preparing a back-contact solar cell, for preparing the back-contact solar cell according to any one of claims 1 to 6, characterized in that: include: Providing a battery cell substrate; The back side of the cell substrate is provided with N-type conductive areas and P-type conductive areas arranged alternately; Sequentially preparing a transparent conductive layer and a composite conductive film layer on the back side of the cell substrate; Removing the transparent conductive layer and the composite conductive film layer at the junction of the N-type conductive region and the P-type conductive region by a patterning process, thereby forming an isolation groove and the transparent conductive layer and the composite conductive layer stacked on the N-type conductive region and the P-type conductive region; A fine gate electrode, an insulating layer and a main gate electrode are sequentially manufactured on a cell substrate formed with an isolation groove.

8. The method for preparing a back contact solar cell according to claim 7, characterized in that: The method of sequentially manufacturing a fine gate electrode, an insulating layer and a main gate electrode on the cell substrate having the isolation groove formed therein comprises: A fine gate electrode made of a low-temperature silver paste material is made by screen printing or pad printing, or a fine gate electrode is made by electroplating a copper fine gate; wherein, when the polarity of the main gate electrode is the same as that of the fine gate electrode, the fine gate electrode is kept continuous; when the polarity of the main gate electrode is different from that of the fine gate electrode, the fine gate electrode is pre-disconnected in the area where it will overlap with the main gate electrode, and the disconnection length of the fine gate electrode is 0.1 mm to 10 mm; An insulating layer is formed in the region where the fine gate electrode is disconnected by screen printing, pad printing or inkjet printing, wherein the size of the insulating layer along the second direction is 1.1 to 1.5 times the disconnected length of the fine gate electrode; and the size of the insulating layer along the first direction is 1.1 to 1.5 times the width of the composite conductive layer; The main gate electrode is manufactured on the insulating layer by screen printing or pad printing. The main gate electrode covers the insulating layer and is connected to the fine gate electrodes of the same polarity.

9. A method for preparing a back-contact solar cell, for preparing the back-contact solar cell according to any one of claims 1 to 6, characterized in that: include: Providing a battery cell substrate; The back side of the cell substrate is provided with N-type conductive areas and P-type conductive areas arranged alternately; Sequentially preparing a transparent conductive layer and a composite conductive film layer on the back side of the cell substrate; An isolation groove is made at the junction of the N-type conductive area and the P-type conductive area on the back side of the cell substrate by a graphic process to form a transparent conductive layer and a composite conductive layer separated by the isolation groove; Sequentially forming a fine gate electrode and an insulating layer on the battery substrate having the isolation groove formed therein; The main gate electrode is formed in a direction perpendicular to the fine gate electrode.

10. A battery assembly, characterized in that: It comprises a back-contact solar cell as claimed in any one of claims 1 to 6.

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