Back structure of IBC battery, IBC battery and preparation method of IBC battery

Abstract

The invention discloses a back surface structure of an IBC battery, the IBC battery and a preparation method of the IBC battery. The back contact structure of the IBC battery provided by the invention comprises a base region silicon wafer which is provided with a back surface, a first dielectric layer and a second dielectric layer, the first dielectric layer and the second dielectric layer are arranged on the back face of the base region silicon wafer, the first emitting electrode is arranged between the first dielectric layer and the second dielectric layer, and the first metal electrode penetrates through the second dielectric layer and is in contact with the first emitting electrode. An emitting electrode of the second emitting electrode is formed in the base region silicon wafer; the second metal electrode penetrates through the second dielectric layer and is in contact with the second emitting electrode; wherein the contact surface between the second metal electrode and the second emitting electrode is provided with a discontinuous dielectric layer, so that the contact recombination can be greatly reduced, and meanwhile, the lower contact resistance is ensured.

Description

Technical Field

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

[0002] IBC cells (Interdigitated Back Contact), or interdigitated full back contact cells, are a type of back junction back contact solar cell technology that involves the diffusion of phosphorus and boron on the back of silicon wafers to form interdigitated p+ and n+ regions. At the same time, the positive and negative metal electrodes are also arranged in an interdigitated manner on the backlight side of the cell. One of the core technologies of IBC cells is the design of the back electrode, because it not only affects the performance of the cell, but also directly determines the manufacturing process of the IBC components.

[0003] The most notable feature of IBC solar cells is that the PN junction and metal contact are both on the back of the solar cell, and the front side completely avoids the shielding of the metal grid electrode. Combined with the pyramid velvet structure on the front side and the light trapping structure composed of the anti-reflection layer, it can maximize the use of incident light, reduce optical losses, and have a higher short-circuit current. At the same time, the back side uses an optimized metal grid electrode to reduce the series resistance.

[0004] Although IBC cells have many advantages, they also face many challenges. Among them, the typical and prominent problem is that conventional IBC solar cells have a large metal area recombination problem, which limits their efficiency improvement. Specifically, IBC cells are usually composed of N-type doped regions and P-type doped regions. In order to reduce the recombination of the metal area in the N-type doped region, a tunneling oxide layer / polysilicon structure is usually introduced to reduce the recombination of its metal area. However, if a tunneling oxide layer / polysilicon structure is also introduced into the P-type doped region, its process is very complicated, and the graphical technology requirements are relatively high, which increases the technical difficulty and cost. Therefore, a simpler way is to form a P-type doped region by direct doping. Although this method can greatly reduce its production cost and technical difficulty, it is currently necessary to use aluminum-containing silver paste in the P-type doped region to form a better ohmic contact. Due to the generation of aluminum spikes during the sintering process and the large amount of damage to the passivation layer under the metal electrode, the metal area recombination is extremely large, often with 1000fA / cm 2 This greatly limits the improvement of battery conversion efficiency. Summary of the invention

[0005] 1. Problem to be solved One of the purposes of the present invention is to provide a back contact structure of an IBC cell, aiming to improve the conversion efficiency of the solar cell; At the same time, the present invention also provides an IBC battery, a back contact structure of the IBC battery, and a preparation process of the IBC battery.

[0006] 2. Technical solution In order to solve the above problems, the technical solution adopted by the present invention is as follows: According to the purpose of the present invention, a first aspect of the present invention provides a back contact structure of an IBC battery, the back contact structure comprising: a base silicon wafer, the base silicon wafer having a back side; A first dielectric layer, wherein the first dielectric layer is disposed on the back side of the base silicon wafer; A second dielectric layer, wherein the second dielectric layer is disposed on the back side of the base silicon wafer; A first emitter and a first metal electrode, wherein the first emitter is disposed between the first dielectric layer and the second dielectric layer, and the first metal electrode passes through the second dielectric layer and contacts the first emitter; a second emitter and a second metal electrode, wherein the second emitter is formed in the base silicon wafer and has a polarity opposite to that of the first emitter, and the second metal electrode passes through a second dielectric layer and contacts the second emitter; Wherein, the contact surface between the second metal electrode and the second emitter has a discontinuous dielectric layer.

[0007] According to the back contact structure of the IBC cell of any embodiment of the first aspect of the present invention, the first emitter is doped polysilicon containing a first doping element; The second emitter is doped single crystal silicon containing a second doping element.

[0008] According to the back contact structure of the IBC cell of any embodiment of the first aspect of the present invention, the first emitter is doped polysilicon containing a first doping element; The second emitter is doped single crystal silicon containing a second doping element.

[0009] According to the back contact structure of the IBC cell of any embodiment of the first aspect of the present invention, the doping type of the first emitter is different from the doping type of the second emitter; The doping concentration of the first emitter is 0.5E20~8E20 cm -3 ; The doping concentration of the second emitter is: 1E18 cm -3 ~1E20 cm -3 .

[0010] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the thickness of the first emitter is 20-300 nm.

[0011] According to the back contact structure of the IBC cell of any embodiment of the first aspect of the present invention, the doping depth of the second emitter does not exceed (ie, is less than or equal to) 0.7 um.

[0012] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the doping type of the first emitter is N-type doping; the doping concentration of the first emitter is 0.5E20-8E20 cm -3 ; The doping type of the second emitter is P-type doping; the doping concentration of the second emitter is 1E18 cm -3 ~1E20 cm -3 .

[0013] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the doping type of the first emitter is N-type doping; the doping concentration of the first emitter is 0.5E20~8E20cm -3 ; The doping type of the second emitter is P-type doping; the doping concentration of the second emitter is 1E18 cm -3 ~1E20 cm -3 .

[0014] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the first dielectric layer includes any one or two or more of oxides (such as aluminum oxide) and silicides (such as silicon dioxide, silicon nitride, silicon carbide).

[0015] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the thickness of the first dielectric layer is 0.5-3 nm.

[0016] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the second dielectric layer includes any one or two or more of oxide (such as aluminum oxide) and silicide (such as silicon dioxide, silicon nitride, silicon oxynitride).

[0017] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the second dielectric layer includes any one or two or more layers of an oxide layer and a silicide layer.

[0018] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the thickness of the second dielectric layer is 50-120 nm.

[0019] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the discontinuous dielectric layer includes any one or two or more of oxides (such as aluminum oxide) and silicides (such as silicon dioxide, silicon nitride, silicon carbide).

[0020] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the discontinuous dielectric layer includes any one or two or more layers of an oxide layer and a silicide layer.

[0021] According to the back contact structure of an IBC battery of any embodiment of the first aspect of the present invention, the thickness of the discontinuous dielectric layer is less than the thickness of the second dielectric layer.

[0022] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the thickness of the discontinuous dielectric layer is 1 to 120 nm.

[0023] As described herein, the optimal cell efficiency can be regulated by controlling the thickness of the discontinuous dielectric layer present on the contact surface between the second metal electrode and the second emitter and the proportion of the coverage area S1.

[0024] According to the back contact structure of an IBC cell of any embodiment of the first aspect of the present invention, the surface of the non-continuous dielectric layer has a glass layer.

[0025] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the area of ​​the contact surface between the second metal electrode and the second emitter is S; The coverage area of ​​the discontinuous dielectric layer is S1; Calculated by S, the proportion of S1 is 5-99%; preferably, the proportion of S1 is 10-99%; more preferably, the proportion of S1 is 50-99%.

[0026] According to the back contact structure of the IBC cell of any embodiment of the first aspect of the present invention, the surface where the second metal electrode contacts the second emitter has a metal point.

[0027] According to the back contact structure of an IBC battery of any embodiment of the first aspect of the present invention, the metal dots contain silver and silicon.

[0028] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the size of the metal dots is 50-800 nm.

[0029] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the embedding depth of the metal dots in the base silicon wafer is 50-500 nm.

[0030] According to the back contact structure of the IBC cell of any embodiment of the first aspect of the present invention, the surface of the second metal electrode in contact with the second emitter has a glass layer.

[0031] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the surface where the second metal electrode contacts the second emitter has a glass layer, and the thickness of the glass layer is 2-800 nm; Alternatively, the area of ​​the contact surface between the second metal electrode and the second emitter is S; The coverage area of ​​the glass layer is S2; Calculated by S, the proportion of S2 is 2-100%; preferably, the proportion of S2 is 20-100%.

[0032] According to the back contact structure of the IBC battery of any embodiment of the first aspect of the present invention, the contact surface between the second metal electrode and the second emitter further includes metal particles (or may also be referred to as metal granules).

[0033] According to the back contact structure of an IBC cell of any embodiment of the first aspect of the present invention, the metal particles are present in the glass layer.

[0034] According to the purpose of the present invention, the second aspect of the present invention provides a method for preparing a back contact structure of an IBC battery as described in any embodiment of the first aspect of the present invention, comprising the steps of: STEP1, polish the surface of the base silicon wafer; STEP2, depositing a first dielectric layer on the surface treated in step STEP1, depositing doped polysilicon or depositing intrinsic polysilicon and then doping to form a doped polysilicon layer to form a first emitter; STEP 3, removing the first dielectric layer and the doped polysilicon layer covering the area not corresponding to the first emitter to expose the base silicon wafer; STEP 4: doping is performed on the partially exposed base silicon wafer to form a second emitter; STEP 5, depositing a second dielectric layer on the back of the base silicon wafer; STEP 6: Use electrode slurry to form the first and second metal electrodes on the back side of the base silicon wafer, and sinter them.

[0035] STEP 7: applying a reverse voltage between the first metal electrode and the second metal electrode and being smaller than the breakdown voltage of the silicon solar cell, and illuminating the back side of the silicon solar cell in the presence of the voltage, thereby inducing a current within the illumination range, wherein the induced current has a current of 10 A / cm2 with respect to the illumination range. 2 Up to 1000A / cm 2 The current density is 10ns to 10ms, guiding the illumination light source until it covers the entire width of the cell.

[0036] According to the method for preparing the back contact structure of an IBC battery of any embodiment of the second aspect of the present invention, the step 6 comprises: wherein the amount of glass powder contained in the second metal electrode slurry does not exceed 3wt%; Furthermore, the second metal electrode paste does not contain aluminum powder; Furthermore, the content of PbO in the glass powder is 20-45% by mole percentage; In this step, the glass powder in the slurry slightly corrodes the second dielectric layer at a high temperature to form a structure in which the second dielectric layer is partially retained, namely, the discontinuous dielectric layer.

[0037] According to the method for preparing the back contact structure of an IBC battery of any embodiment of the second aspect of the present invention, STEP 7 includes, through voltage and current, at the place where the second dielectric layer is completely corroded, the silver ions in the slurry diffuse with the silicon to form metal points.

[0038] According to the purpose of the present invention, the third aspect of the present invention provides an IBC battery, the battery comprising: Base silicon wafer; A back contact structure disposed on the back side of the base silicon wafer, the back contact structure being a back contact structure of an IBC battery according to any embodiment of the first aspect, or a back contact structure of an IBC battery prepared by a method according to any embodiment of the second aspect; A passivation anti-reflection layer is arranged on the front side of the base silicon wafer. According to the IBC cell of any embodiment of the third aspect of the present invention, the thickness of the passivation anti-reflection layer is 50-150 nm.

[0039] According to the IBC battery of any embodiment of the third aspect of the present invention, the passivation layer includes any one or two or more of oxide (such as aluminum oxide) and silicide (such as silicon dioxide, silicon nitride, silicon carbide).

[0040] According to the IBC cell of any embodiment of the third aspect of the present invention, the anti-reflection layer includes any one or two or more of oxides (such as aluminum oxide) and silicides (such as silicon dioxide, silicon nitride, silicon carbide).

[0041] According to the purpose of the present invention, the fourth aspect of the present invention provides a method for preparing an IBC battery as described in any embodiment of the third aspect of the present invention, comprising the steps of: A1. Polishing the base silicon wafer; A2, depositing a first dielectric layer on the back side of the base silicon wafer processed in step A1, depositing doped polysilicon or depositing intrinsic polysilicon and then doping to form a doped polysilicon layer to form a first emitter; A3, removing the first dielectric layer and the doped polysilicon layer covering the area not corresponding to the first emitter to expose the base silicon wafer; A4, doping the back side of the partially exposed base silicon wafer to form a second emitter; A5, performing texturing treatment on the front side of the silicon wafer; A6, depositing a second dielectric layer on the back of the base silicon wafer; A7, depositing a passivation anti-reflection layer on the front side of the base silicon wafer; A8. Using electrode slurry, form the first and second metal electrodes on the back side of the base silicon wafer, and sinter them.

[0042] A9. A reverse voltage that is less than the breakdown voltage of the silicon solar cell is applied between the first metal electrode and the second metal electrode, and in the presence of the voltage, the back side of the silicon solar cell is illuminated, thereby inducing a current within the illumination range, wherein the induced current has a current of 10 A / cm2 with respect to the illumination range. 2 Up to 1000A / cm 2 The current density is 10ns to 10ms, guiding the illumination light source until it covers the entire width of the cell.

[0043] According to the method for preparing an IBC battery of any embodiment of the third aspect of the present invention, the A8 comprises, wherein the amount of glass powder contained in the second metal electrode slurry does not exceed 3wt%; Furthermore, the second metal electrode paste does not contain aluminum powder; Furthermore, the content of PbO in the glass powder is 20-45% by mole percentage; In this step, the glass powder in the slurry slightly corrodes the second dielectric layer at a high temperature to form a structure in which the second dielectric layer is partially retained, namely, the discontinuous dielectric layer.

[0044] According to the method for preparing an IBC battery of any embodiment of the third aspect of the present invention, A9 includes, through voltage and current, where the second dielectric layer is completely corroded, silver ions in the slurry diffuse with silicon to form metal points.

[0045] Beneficial Effects (1) In the back contact structure of the existing IBC battery, the passivation layer under the metal electrode in the second emitter region is completely corroded, and the Al element in the slurry forms spikes in the junction area, so the recombination of the metal area is relatively large. Based on this, the back contact structure of the IBC battery provided by the present invention has a non-continuous dielectric layer on the contact surface between the second metal electrode and the second emitter, and no spikes are generated due to the Al element, which can effectively reduce the contact recombination between the second metal electrode and the second emitter and improve the conversion efficiency of the IBC battery.

[0046] (2) The back contact structure of the IBC battery provided by the present invention, wherein the surface where the second metal electrode of the structure contacts the second emitter also has metal points, wherein the metal points are mainly an alloy of silver and silicon. The presence of the metal points effectively increases the conductive path between the second metal electrode and the second emitter, and can reduce the contact resistance between the second metal electrode and the second emitter, thereby improving passivation and ensuring a low contact resistance at the interface; Furthermore, the optimal cell efficiency is controlled by controlling the size of the metal dots existing on the contact surface between the second metal electrode and the second emitter, and the embedding depth of the metal dots in the base silicon wafer.

[0047] (3) In the back contact structure of the IBC battery provided by the present invention, the surface where the second metal electrode contacts the second emitter also has a glass layer. By controlling the thickness of the glass layer and the coverage area of ​​the glass layer, and in combination with the discontinuous dielectric layer, the open circuit voltage of the battery is effectively improved to reach an ideal value. In summary (1) to (3), the back contact structure of the IBC battery provided by the present invention can reduce the recombination between the second metal electrode and the second emitter to 100 fA / cm 2 Within, thereby improving the efficiency of the structural battery.

[0048] (4) The IBC battery provided by the present invention has the back contact structure as described above, and the battery has the advantages of low recombination, low contact resistance and high conversion efficiency.

[0049] (5) The present invention provides a method for preparing a back contact structure of an IBC battery, and a method for preparing an IBC battery. Compared with the glass powder of the silver-aluminum paste for the traditional P-type emitter, the glass powder of the second metal electrode slurry has a lower total content of glass powder. The reduction of the glass powder in the slurry can achieve the control of the corrosion degree of the second dielectric layer at high temperature, so that it can be retained to form a non-continuous dielectric layer; the slurry has increased contents of B and Si elements, reduced contents of Pb elements, and does not contain Al powder, so that the formation of AgAl spikes is avoided at the contact surface between the second metal electrode and the second emitter, thereby avoiding the problem of increased contact recombination caused by AgAl spikes; in addition, metal points can also be formed at the contact surface between the second metal electrode and the second emitter, and the metal points mainly include an alloy of silver and silicon. The presence of the metal points effectively increases the conductive path between the second metal electrode and the second emitter, and can reduce the contact resistance between the second metal electrode and the second emitter, thereby improving passivation while ensuring a low contact resistance at the interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of the back contact structure of an IBC battery provided in Example 1 of the present invention; Figure 2 A schematic structural diagram of the contact surface between the second emitter and the second metal electrode of the back contact structure of the IBC battery provided in Example 1 of the present invention; Figure 3 Schematic diagram of the overall structure of the IBC battery provided in Example 2 of the present invention; In the figure: 100, base silicon wafer; 110, back side of base silicon wafer; 120, first dielectric layer; 130, first emitter; 140, second dielectric layer; 150, first metal electrode; 160, second metal electrode; 170, second emitter; 180, contact surface between second emitter and second metal electrode (hereinafter referred to as contact surface); 181, metal point; 182, non-continuous dielectric layer; 183, glass layer; 184, metal particles; 190. Front side of base silicon wafer; 191. Front side passivation layer; 192. Front side anti-reflection layer. DETAILED DESCRIPTION

[0051] The present disclosure may be more easily understood by reference to the following description in conjunction with the accompanying drawings and examples, all of which constitute a part of the present disclosure. It should be understood that the present disclosure is not limited to the specific products, methods, conditions or parameters described and / or shown herein. Further, the terms used herein are only used for the purpose of describing specific embodiments by way of example and are not intended to be limiting unless otherwise stated.

[0052] It should also be understood that, for the sake of clarity, certain features of the present disclosure may be described herein in the context of separate embodiments, but may also be provided in combination with each other in a single embodiment. That is, unless clearly incompatible or specifically not included, each separate embodiment is considered to be combinable with any other embodiment, and the combination is considered to represent another different embodiment. Conversely, for the sake of simplicity, the various features of the present disclosure described in the context of a single embodiment may also be provided individually or in any sub-combination. Finally, although a particular embodiment may be described as part of a series of steps or part of a more general structure, each step or sub-structure itself may also be considered to be an independent embodiment.

[0053] Unless otherwise indicated, it should be understood that each individual element in a list and each combination of individual elements in the list will be interpreted as a different embodiment. For example, a list of embodiments expressed as "A, B, or C" should be interpreted to include embodiments "A", "B", "C", "A or B", "A or C", "B or C", or "A, B, or C".

[0054] In the present disclosure, the singular forms of the articles "a", "an", and "the" also include the corresponding plural references, and references to a specific value include at least that specific value unless the context clearly indicates otherwise. Thus, for example, reference to "a substance" is a reference to at least one of that substance and its equivalents.

[0055] The terms including ordinal numbers such as "first" and "second" can be used to explain various layers or structures, but these layers and structures are not limited by these terms. Therefore, without departing from the teachings of the present disclosure, these terms are only used to distinguish the layer / structure from another layer / structure.

[0056] When items are described by using conjunction terms such as “… and / or…”, the description should be understood to include any one of the associated listed items and all combinations of one or more thereof; for example, A and / or B should be interpreted as an embodiment including “A” but not including “B”, an embodiment including “B” but not including “A”, and an embodiment including “A” and “B”.

[0057] Throughout the specification of this application document, when a certain part is described as “including” a certain constituent element, unless otherwise clearly described to the contrary, it does not mean that other constituent elements are excluded but that other constituent elements may also be included.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs; the terms used herein and / or include any and all combinations of one or more of the listed items. In order to make the technical solutions and advantages of the present invention clear, the technical solutions in the embodiments of the present invention will be fully described below.

[0059] Example 1 This embodiment provides a back contact structure of an IBC battery. For the sake of convenience, only the parts related to the embodiment of the present invention are shown. Figure 1 shown.

[0060] The back contact structure of the IBC battery provided by the embodiment of the present invention includes: A base silicon wafer 100, a first dielectric layer 120 and a second dielectric layer 140 arranged on the back side 110 of the base silicon wafer, a first emitter 130 arranged between the first dielectric layer 120 and the second dielectric layer 140, a first metal electrode 150 passing through the second dielectric layer 140 and contacting the first emitter 130, a second emitter 170 formed in the body of the base silicon wafer 100, and a second metal electrode 160 passing through the second dielectric layer 140 and contacting the second emitter 170.

[0061] like Figure 1 As shown, the first emitter 130 is stacked on the first dielectric layer 120 on the back side 110 of the base silicon wafer, and a second dielectric layer 140 is stacked on the top of the first emitter 130, and the first metal electrode 150 passes through the second dielectric layer 140 and contacts the first emitter 130. Among them, for the first emitter 130, it is a "doped polysilicon layer" containing a first doping element; there are two main methods for forming the "doped polysilicon layer": the first is to directly deposit the doped polycrystalline layer using the LPCVD method, and this method can complete the deposition and doping of the polysilicon layer at one time; the second is to first use PECVD or LPCVD to deposit the intrinsic polysilicon layer, and then use ion implantation, diffusion and other processes for doping, and the various doping methods have little difference in process effects. In some preferred embodiments of the present invention, the doping type of the first emitter 130 is N-type doping; the thickness of the first emitter 130 is 20~300 nm, and the doping concentration is 0.5E20~8E20 cm -3 .

[0062] The second emitter 170 is a "doped single crystal silicon layer" containing a second doping element. Based on this, a specific situation is that the second emitter 221 is a diffusion layer formed by a part of the base silicon wafer 100 body; the formation methods of the "second emitter 170" mainly include thermal diffusion, ion implantation, laser doping, etc. A second dielectric layer 140 is stacked above the second emitter 170, and the second metal electrode 160 passes through the second dielectric layer 140 to contact the second emitter 170, and forms a contact surface 180 between the second metal electrode and the second emitter (hereinafter referred to as the contact surface). Regarding the second emitter 170, in some preferred embodiments of the present invention, the doping type of the second emitter 170 is P-type doping.

[0063] In addition, the first dielectric layer 120 mainly includes an ultra-thin layer of any one or two or more materials of oxide (such as aluminum oxide) and silicide (such as silicon dioxide, silicon nitride, silicon carbide), such as an ultra-thin "tunneling oxide layer", which has an important influence on the properties of the passivation contact, and good contact comes from the defect-assisted tunneling mechanism or the micropores on the oxide layer. In some preferred embodiments of the present invention, the ultra-thin oxide layer is an ultra-thin silicon oxide layer. Regarding the formation of the ultra-thin silicon oxide layer, there are currently mainly thermal oxidation methods (including dry oxygen oxidation, wet oxygen oxidation), chemical vapor deposition (CVD) methods (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method), room temperature wet oxidation method, etc., preferably thermal oxidation method. More specifically, the coverage area of ​​the first dielectric layer 120 on the back side 110 of the base silicon wafer basically corresponds to the area of ​​the first emitter 130. In some embodiments of the present invention, the first dielectric layer 120 has a thickness of 1.6nm.

[0064] The second dielectric layer 140 mainly includes any one or two or more materials selected from oxide (such as aluminum oxide) and silicide (such as silicon dioxide, silicon nitride, silicon carbide). As some examples of the present invention, for example, the second dielectric layer 140 can be an oxide layer of a single material, a silicide layer of a single material, or a combination of any layers of oxide layer and silicide layer. It can be understood that the specific structure of the second dielectric layer 140 includes but is not limited to the several methods listed above, and the second dielectric layer 140 can be set accordingly according to actual use needs, and no specific limitation is made here. In some preferred embodiments of the present invention, the thickness of the second dielectric layer 140 is 50~120nm. The formation of the second dielectric layer 140 mainly includes thermal oxidation method (including dry oxygen oxidation, wet oxygen oxidation), chemical vapor deposition (CVD) method (including plasma chemical vapor deposition (PECVD) method, room temperature wet oxidation method, or atomic layer deposition (ALD) method, which are prepared according to actual use needs and are not specifically limited here; the silicon nitride layer can be prepared by plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method and magnetron sputtering technology, which are prepared according to actual use needs. If conditions permit, it is preferred to use plasma chemical vapor deposition (PECVD) method to prepare silicon nitride film; the aluminum oxide layer can be prepared by atomic layer deposition (ALD) method, plasma assisted ALD method PECVD method and other methods, which are prepared according to actual use needs and are not specifically limited here. Silicon nitride and aluminum oxide will contain a certain amount of hydrogen generated during the deposition of the thin film, which can form good hydrogen passivation.

[0065] It is further explained that the base silicon wafer 100 has a front side facing the sun during normal operation and a back side opposite to the front side, wherein the front side is a light-receiving side, and the back side is arranged on the other side of the base silicon wafer 100 relative to the front side; wherein, the base silicon wafer 100 can be a P-type or N-type silicon wafer, and can be a single crystal silicon wafer or a quasi-single crystal silicon wafer, and the corresponding type of base silicon wafer 100 can be selected according to actual use needs.

[0066] Furthermore, if Figure 2As shown, there is a discontinuous dielectric layer 182, a glass layer 183, metal particles 184 and scattered metal dots 181 between the surface 180 where the second metal electrode contacts the second emitter. The basic material composition and formation method of the discontinuous dielectric layer 182 can be the same as those of the second dielectric layer 140. In addition, the "discontinuity" described herein only means that the discontinuous dielectric layer 182 is not required to completely cover the surface 180 where the second metal electrode contacts the second emitter. For example, in some preferred embodiments of the present invention, the area of ​​the surface where the second metal electrode contacts the second emitter is S, and the coverage area of ​​the discontinuous dielectric layer 182 is S1. Calculated by S, the proportion of S1 is 5-99%. In addition, the thickness of the discontinuous dielectric layer 182 is less than the thickness of the second dielectric layer 140, which is generally 1-120 nm. The glass layer 183 has a thickness of 2-800 nm. In addition, the coverage area of ​​the glass layer is S2. Calculated by S, the proportion of S2 is 2-100%, preferably 20-100%. The size of the metal dot 181 is 50-800 nm, and the embedding depth in the base silicon wafer is 50-500 nm.

[0067] The method for preparing the back contact structure of the IBC battery specifically comprises the following steps: In this embodiment, the thickness is 130um, the resistivity is 10ohm·cm, and the doping concentration is 4.5E14m -3 A CZ-type single crystal silicon wafer is used as the base silicon wafer 100 , but it should be noted that when the resistance is above 2 ohmcm, the battery performance requirements can be met, and no limitation or requirement is made here, and the final battery performance of various resistivities is not much different.

[0068] STEP 1. First, the surface of the base silicon wafer is polished. In this embodiment, KOH alkaline liquid is used to react with the base silicon wafer 100 to remove the surface damage layer and form a polished mirror surface. However, it should be noted that the operation of this step can actually be performed in any existing manner, and the various methods have little difference in process effects.

[0069] STEP 2. First, the LPCVD method is used to oxidize the back side 110 of the base silicon wafer to form a first dielectric layer 120 of SiO2 with a thickness of 1.5 nm, and a polysilicon layer with a thickness of 150 nm is deposited; then the polysilicon layer is crystallized by diffusion process to form an N-type doped polysilicon layer with a doping concentration of 5E20cm -3 , that is, Figure 1 As shown, a first emitter 130 is formed on the surface of the first dielectric layer 120 on the back side 110 of the base silicon wafer; STEP3. Remove the dielectric layer formed on the surface of the polysilicon by laser, and use an alkali solution mixed with a polishing additive having a protective oxide layer function and a temperature of 80°C and a mass fraction of 15% to etch away the first dielectric layer 120 and the doped polysilicon layer outside the first emitter region, exposing the base silicon wafer; STEP 4. Deposit a boron-doped silicon oxide layer by PECVD, and form a locally diffused second emitter 170 by laser doping. The doping concentration of the second emitter 170 is 5E19cm -3 , doping depth is 0.6um; It should be further explained that, as described herein, the position and size of the doping area can be controlled by the above-mentioned laser doping patterning method, and a typical formation is as follows: Figure 1 The second emitter 170 of the overlapping area is shown, and it can be seen that there is an isolation area between the first emitter 130 and the second emitter 170 .

[0070] STEP5. An Al2O3 layer having a thickness of 5 nm is deposited on the back side of the base silicon wafer 110 by an ALD method, and a SiNx layer having a thickness of 75 nm is deposited by a PECVD method, and the two constitute a second dielectric layer 140; It should be pointed out that after a series of treatments from STEP1 to STEP3, the texture of the area outside the first emitter region on the back side of the base silicon wafer forms a morphology including any one, two or three of a pyramid, an inverted pyramid or a tower base structure; in terms of the size of the texture, its depth is 0~3μm.

[0071] STEP 6. Using electrode slurry, a first metal electrode 150 and a second metal electrode 160 are formed on the back side of the base silicon wafer 100, and sintered. During the sintering process, the glass powder in the slurry in the second metal electrode slightly corrodes the second dielectric layer 140 to form a discontinuous second dielectric layer (i.e., a discontinuous dielectric layer 182), and a glass layer 183 is simultaneously formed on the second dielectric layer; The reference sintering temperature is 700-800°C and the time is 1-2 minutes. In addition, compared with the traditional silver-aluminum paste for P-type emitter (such as DuPont's PV3N2, Shanghai Silver Paste's 995PFB, Dico DK71A), the amount of glass powder contained in the second metal electrode paste used in this embodiment does not exceed 3wt%; and the second metal electrode paste does not contain aluminum powder; and the content of PbO in the glass powder is 20-45% calculated by molar fraction.

[0072] STEP 7. A reverse voltage of 10 V is applied between the first metal electrode and the second metal electrode, and the reverse voltage is less than the breakdown voltage of the silicon solar cell, 15 V. In the presence of the voltage, the back side of the silicon solar cell is illuminated, thereby inducing a current within the illumination range, wherein the induced current has a current of 200 A / cm2 with respect to the illumination range. 2 The current density is 1 ms, and the illumination light source is guided until the entire width of the cell is covered. Through voltage and current, the silver ions in the slurry diffuse with silicon to form AgSi alloy metal points (i.e., metal points 181) at the place where the second dielectric layer 140 is completely corroded, forming a conductive channel for Si and Ag. At the same time, metal particles 184 are formed at the glass layer 183.

[0073] Based on the above, it is possible to prepare Figure 1 The back contact structure of the IBC battery (IBC-1) shown in FIG. Figure 2 As shown, between the surface 180 where the second metal electrode of the back contact structure of the IBC cell contacts the second emitter, there is a discontinuous dielectric layer 182, a glass layer 183, and dispersed metal particles 184. The basic material of the discontinuous dielectric layer 182 is the same as that of the second dielectric layer 140, but the thickness of the discontinuous dielectric layer 182 is 40nm, which is less than the thickness of the second dielectric layer 140. Taking the area of ​​the surface 180 where the second metal electrode contacts the second emitter as S, the coverage area S1 of the discontinuous dielectric layer 182 accounts for 95%. The thickness of the glass layer is 100nm, and the coverage area S2 accounts for 80% when calculated by S. The size of the metal dot 181 is 450nm, and the embedding depth in the base silicon wafer is 400nm.

[0074] Comparative Example 1 This comparative example provides a back contact structure of an IBC battery prepared with a conventional slurry. As mentioned above, the preparation process is basically the same as that of Example 1, except that the slurry is replaced with the conventional slurry DK71A.

[0075] Specifically speaking of the battery structure, the structure is basically the same as that of Example 1, with the only difference being that the back contact structure of the IBC battery of this comparative example does not have the non-continuous dielectric layer 182 and the metal point 181 as described in Example 1, and an AgAl spike is formed between the contact surface 180 between the second metal electrode and the second emitter of the back contact structure of the IBC battery.

[0076] Example 2 The second embodiment of the present invention further provides an IBC battery. For the sake of convenience, only the parts related to the embodiment of the present invention are shown. Figure 1 ,2 and Figure 3 shown.

[0077] like Figure 3 The IBC cell shown includes: a base silicon wafer 100; A back contact structure as described in the above embodiment disposed on the back side 110 of the base silicon wafer; A passivation anti-reflection layer with a total thickness of 75 nm is disposed on the front side 190 of the base silicon wafer (a front passivation layer 191 with a thickness of 5 nm and a front anti-reflection layer 192 with a thickness of 70 nm); The front passivation layer 191 includes one or more combinations of an oxide layer (such as aluminum oxide) and a nitride layer (such as silicon dioxide, silicon nitride, silicon carbide). As some examples of the present invention, for example, the front passivation layer 191 can be an oxide layer of a single material, a silicon nitride layer of a single material, or a combination of an oxide layer and a silicon nitride layer. It can be understood that the specific structure of the front passivation layer 191 includes but is not limited to the several methods listed above, and the back passivation layer 130 can be set accordingly according to actual use needs, which is not specifically limited here. Furthermore, the oxide layer is preferably composed of an aluminum oxide layer (AlO x layer); therefore, the back passivation layer 130 may also be a combination of an aluminum oxide layer and a silicon nitride layer.

[0078] Regarding the formation of the front passivation layer 191, the aluminum oxide layer can be prepared by chemical vapor deposition (CVD), plasma chemical vapor deposition (PECVD), or atomic layer deposition (ALD), which is prepared according to actual use needs and is not specifically limited here; the silicon nitride layer can be prepared by chemical vapor deposition (CVD), plasma chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD) and magnetron sputtering technology, which is prepared according to actual use needs. If conditions permit, chemical vapor deposition (CVD), plasma chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) are preferably used to prepare SiN film; the aluminum oxide layer can be prepared by atomic layer deposition (ALD), plasma-assisted ALD, pyrolysis deposition, delocalized PECVD, molecular beam epitaxy, deposition A1 plus oxidation, etc., which is prepared according to actual use needs and is not specifically limited here. Silicon nitride and aluminum oxide will generate a large amount of hydrogen during film deposition, which can form good hydrogen passivation.

[0079] The front anti-reflection layer 192 includes an oxide layer, a silicon nitride layer (SiN xThe front anti-reflection layer 192 can be formed by chemical vapor deposition (CVD) method (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method) and magnetron sputtering technology, etc., which is prepared according to actual use needs. If conditions permit, it is preferred to use chemical vapor deposition (CVD) method (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method) to prepare the silicon nitride layer.

[0080] Regarding the preparation of the IBC battery in this embodiment: The preparation method of the IBC battery specifically comprises the steps of: A1~A4 are the same as steps STEP1~STEP4 of Example 1.

[0081] A5, performing alkaline liquid texturing on the front side 190 of the base silicon wafer to form a structure with a pyramid morphology; A6. A second dielectric layer 140 with a thickness of 75 nm is deposited on the back side 110 of the base silicon wafer by ALD and PECVD methods. Specifically, this step is the same as step STEP5 of Example 1.

[0082] A7, forming a front passivation layer 191 of Al2O3 with a thickness of 5 nm and a front anti-reflection layer 192 of SiNx with a thickness of 70 nm on the front side of the base silicon wafer 100 by ALD and PECVD; A8~A9 are the same as steps STEP6~STEP7 of Example 1 or Comparative Example 1.

[0083] Based on the back contact structure of the IBC battery described in this embodiment and the above-mentioned embodiment 1 and comparative example 1, the following two types of IBC batteries are prepared in this embodiment: The first IBC battery (label: IBC-1), such as Figure 1 , 2 , 3, having the front structure as described in this embodiment, and the back structure as described in embodiment 1; The second IBC battery (labeled: IBC-D1) has the front structure as described in this embodiment and the back structure as described in comparative example 1; Table 1. Performance comparison parameters of various solar cells

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The back contact structure of the IBC battery is characterized by: The back contact structure comprises: a base silicon wafer, wherein the base silicon wafer has a back side; A first dielectric layer, wherein the first dielectric layer is disposed on the back side of the base silicon wafer; A second dielectric layer, wherein the second dielectric layer is disposed on the back side of the base silicon wafer; A first emitter and a first metal electrode, wherein the first emitter is disposed between the first dielectric layer and the second dielectric layer, and the first metal electrode passes through the second dielectric layer and contacts the first emitter; a second emitter and a second metal electrode, wherein the second emitter is formed in the base silicon wafer and has a polarity opposite to that of the first emitter, and the second metal electrode passes through a second dielectric layer and contacts the second emitter; Wherein, the first emitter is doped polysilicon containing a first doping element; The second emitter is doped single crystal silicon containing a second doping element; The contact surface between the second metal electrode and the second emitter has a discontinuous dielectric layer.

2. The back contact structure of the IBC battery according to claim 1, characterized in that: The surface where the second metal electrode contacts the second emitter has a metal point.

3. The back contact structure of the IBC battery according to claim 2, characterized in that: The doping concentration of the first emitter is 0.5E20~8E20cm -3 ; The doping concentration of the second emitter is 1E18~1E20 cm -3 .

4. The back contact structure of the IBC battery according to claim 2, characterized in that: The thickness of the discontinuous dielectric layer is smaller than the thickness of the second dielectric layer.

5. The back contact structure of the IBC battery according to claim 4, characterized in that: The thickness of the discontinuous dielectric layer is 1-120 nm.

6. The back contact structure of an IBC battery according to any one of claims 1 to 5, characterized in that: The area of ​​the contact surface between the second metal electrode and the second emitter is S; The coverage area of ​​the discontinuous dielectric layer is S1; Calculated by S, the proportion of S1 is 5~99%.

7. The back contact structure of the IBC battery according to claim 6, characterized in that: The surface of the discontinuous dielectric layer has a glass layer.

8. The back contact structure of an IBC battery according to any one of claims 2 to 5, characterized in that: The metal dots contain silver and silicon.

9. The back contact structure of the IBC battery according to claim 8, characterized in that: The size of the metal dots is 50-800 nm.

10. The back contact structure of the IBC battery according to claim 8, characterized in that: The embedding depth of the metal dots in the base silicon wafer is 50-500 nm.

11. The back contact structure of the IBC battery according to claim 10, characterized in that: The doping depth of the second emitter does not exceed 0.7 um.

12. IBC battery, characterized in that The battery comprises: Base silicon wafer; A back contact structure of an IBC cell according to any one of claims 1 to 11 disposed on the back side of the base silicon wafer; and A passivation layer and an anti-reflection layer are arranged on the front side of the base silicon wafer.

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