Back contact solar cell and method for preparing the same

Abstract

The present invention provides a back contact solar cell and a preparation method thereof, belonging to the technical field of solar cells, comprising: after depositing a tunneling oxide layer and a doped polysilicon layer on the back of an n-type silicon wafer, first sintering a high-temperature silver paste in a pre-designed interdigital region in the N region on the back of the silicon wafer to form a first electrode; then ablating the tunneling oxide layer, the doped polysilicon layer and the mask layer in the interdigital region in the P region on the back by laser; then depositing an amorphous silicon layer and a TCO layer on the back of the n-type silicon wafer; then sintering a low-temperature silver paste on the TCO layer in the P region to form a second electrode; finally, by laser scanning a gate line formed after sintering the high-temperature silver paste, ablate the amorphous silicon layer, the TCO layer and the mask layer on and around the gate line to isolate the first electrode from the second electrode. Since the high-temperature silver paste is partially replaced by the low-temperature silver paste, the use cost of the paste is reduced; by laser scanning the gate line ablation, there is no need to make a gap area separately, which simplifies the manufacturing process and reduces the manufacturing cost.

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. Background Art

[0002] HTBC cells are heterojunction tunnel oxide passivated contact hybrid passivated back contact photovoltaic cells (HTBC), also known as back contact solar cells. They use n-type crystalline silicon as the substrate, doped amorphous silicon / nanocrystalline silicon film as the PN emitter junction in the back P region, and tunneling silicon oxide and N-type polycrystalline silicon in the N region to achieve passivation contact, combined with transparent conductive film and metal electrodes.

[0003] At present, the back-contact solar cell can improve the cell conversion efficiency because there is no grid line on the front. However, the positive and negative electrodes of the HTBC solar cell need to deposit low-temperature silver paste to realize the metallization of the cell. There is a huge demand for low-temperature silver paste, and the high cost, difficult transportation and strict environmental requirements of low-temperature silver paste will lead to higher cell manufacturing costs. At the same time, since the two electrodes of the HTBC solar cell are made on the back, in order to prevent the short circuit between the two electrodes, it is necessary to prepare a gap area on the back to prevent the two electrodes from short-circuiting directly. Not only is the process complicated, but if the gap area process is not handled well, short circuit problems may occur. Summary of the invention

[0004] The embodiment of the present invention provides a back-contact solar cell and a method for preparing the same, aiming to solve the problems of high production cost, complicated process flow and easy occurrence of positive and negative electrode short circuit in current HTBC solar cells.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for preparing a back contact solar cell, the method comprising the following steps:

[0006] Step 1, single-sided or double-sided texturing of the n-type silicon wafer;

[0007] Step 2: depositing a tunneling oxide layer and a doped polysilicon layer in sequence on the back of the n-type silicon wafer after texturing;

[0008] Step 3, depositing a passivation layer on the front side of the n-type silicon wafer;

[0009] Step 4, depositing mask layers on the passivation layer on the front side of the n-type silicon wafer and on the doped polysilicon layer on the back side respectively;

[0010] Step 5, sintering high-temperature silver paste on the N region on the back side of the n-type silicon wafer to form a first electrode;

[0011] Step 6, laser ablating the P region on the back side of the n-type silicon wafer where the high-temperature silver paste is not sintered, to expose the n-type silicon wafer;

[0012] Step 7, depositing an amorphous silicon layer on the entire back side of the n-type silicon wafer;

[0013] Step eight, depositing a TCO layer on the amorphous silicon layer;

[0014] Step nine, sintering low-temperature silver paste on the TCO layer of the P region on the back side of the n-type silicon wafer to form a second electrode;

[0015] Step ten, laser ablating the TCO layer and the amorphous silicon layer on the top and surrounding of the high-temperature silver paste, so that the sintered high-temperature silver paste forms an island, constituting the first electrode that is not connected to the second electrode.

[0016] In combination with the first aspect, in one achievable manner, in step five, the sintering temperature of the high temperature silver paste is 500°C-1000°C.

[0017] In combination with the first aspect, in one achievable manner, in step nine, the sintering temperature of the low-temperature silver paste is ≤200°C.

[0018] In combination with the first aspect, in one feasible method, in step six, a 532nm green light or ultraviolet laser with a laser power of 3-20W is used to open the mask layer of the P region, ablate the tunneling oxide layer and the doped polysilicon layer of the P region, and expose the back side of the n-type silicon wafer.

[0019] In combination with the first aspect, in one achievable manner, in step 2, vapor deposition is used to first deposit a tunneling oxide layer on the back side of the n-type silicon wafer, passivate the surface of the n-type silicon wafer, and then dope a polysilicon layer.

[0020] In combination with the first aspect, in one achievable manner, in step 2, the doped polysilicon layer is phosphorus-doped.

[0021] In combination with the first aspect, in one achievable manner, in step three, the passivation layer is an AlOx layer.

[0022] In combination with the first aspect, in one achievable manner, in step four, the mask layer is a SiNx layer.

[0023] In combination with the first aspect, in one achievable manner, in step seven, the amorphous silicon layer includes an intrinsic amorphous silicon layer and a doped amorphous silicon layer.

[0024] In a second aspect, an embodiment of the present invention further provides a back-contact solar cell, which is prepared by the method for preparing a back-contact solar cell, and includes an n-type silicon wafer, on which a tunneling oxide layer and a doped polysilicon layer are deposited in sequence from the inside to the outside in the N region on the back side of the n-type silicon wafer, and a first electrode is sintered at high temperature on the doped polysilicon layer; on the doped polysilicon layer in the P region and the N region on the back side of the n-type silicon wafer, an amorphous silicon layer and a TCO layer are deposited in sequence from the inside to the outside, and the amorphous silicon layer and the TCO layer around the first electrode are laser ablated to form an isolation ring groove around the first electrode; and a second electrode is sintered at low temperature on the TCO layer in the P region.

[0025] Compared with the prior art, the back-contact solar cell and the preparation method thereof provided by the present invention have the following beneficial effects: it is an improvement on the HTBC cell. The design idea is to first sinter high-temperature silver paste, then deposit an amorphous silicon layer and a TCO layer, then sinter low-temperature silver paste, and finally laser ablate to isolate the two electrodes, which can reduce the consumption of low-temperature silver paste, simplify the process steps and reduce the manufacturing cost of solar cells.

[0026] Specifically, after depositing a tunneling oxide layer and a doped polysilicon layer on the back side of an n-type silicon wafer, a high-temperature silver paste is first sintered in a pre-designed interdigitated region in the N region on the back side of the silicon wafer to form a first electrode; then the tunneling oxide layer, the doped polysilicon layer and the mask layer in the interdigitated region in the P region on the back side are ablated by laser; then an amorphous silicon layer and a TCO layer are deposited on the back side of the n-type silicon wafer; then a low-temperature silver paste is sintered on the TCO layer in the P region to form a second electrode; finally, a gate line formed after sintering the high-temperature silver paste is scanned by laser, and the amorphous silicon layer, the TCO layer and the mask layer on and around the gate line are ablated to isolate the first electrode from the second electrode.

[0027] Compared with the current HTBC structure, the preparation method provided by the present invention uses different silver pastes for the two electrodes. The first electrode is sintered with high-temperature silver paste, which greatly reduces the use of low-temperature silver paste, thereby reducing the cost of transporting and storing low-temperature silver paste, and significantly reducing the investment cost of low-temperature silver paste, thereby reducing the manufacturing cost of the battery.

[0028] Compared to the process of first making a gap area isolation groove on the back of the silicon wafer, the present invention does not require additional preparation of the gap area. Instead, the high-temperature silver paste is directly deposited on the doped polysilicon layer. After sintering the low-temperature silver paste, an annular groove is formed around the high-temperature silver paste by laser ablation, so that the amorphous silicon layer and the TCO layer are isolated from the high-temperature silver paste, thereby achieving isolation of the two electrodes, reducing the process steps, and saving the manufacturing cost of the battery to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structure of a back-contact solar cell provided by an embodiment of the present invention;

[0030] Figure 2 A schematic structural diagram of step 1 of a back contact solar cell provided by an embodiment of the present invention;

[0031] Figure 3 A schematic structural diagram of step 2 of a back contact solar cell provided by an embodiment of the present invention;

[0032] Figure 4 A schematic diagram of the structure of steps three and four of a back contact solar cell provided by an embodiment of the present invention;

[0033] Figure 5 A schematic structural diagram of step five of a back contact solar cell provided by an embodiment of the present invention;

[0034] Figure 6 A schematic structural diagram of step six of a back contact solar cell provided by an embodiment of the present invention;

[0035] Figure 7 A schematic structural diagram of step seven of a back contact solar cell provided by an embodiment of the present invention;

[0036] Figure 8 A schematic structural diagram of step eight of a back contact solar cell provided by an embodiment of the present invention;

[0037] Fig. 9 A schematic structural diagram of step nine of a back contact solar cell provided by an embodiment of the present invention;

[0038] Description of reference numerals:

[0039] 1. n-type silicon wafer; 2. tunneling oxide layer; 3. doped polysilicon layer; 4. mask layer; 5. amorphous silicon layer; 6. TCO layer; 7. first electrode; 8. isolation ring groove; 9. second electrode; 10. passivation layer. DETAILED DESCRIPTION

[0040] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] Please also read Figure 1 and Figure 2 Now, the preparation method of the back contact solar cell provided by the present invention is described.

[0042] Example 1

[0043] The present invention provides a method for preparing a back-contact solar cell, the method comprising the following steps:

[0044] Step 1: single-sided texturing of the n-type silicon wafer 1 is performed, see Figure 2 ;

[0045] Step 2: Using vapor deposition, a tunneling oxide layer 2 is first deposited on the back of the n-type silicon wafer 1 to passivate the surface of the n-type silicon wafer 1, and then a polysilicon layer 3 is doped. Figure 3 ;

[0046] Step 3: depositing an AlOx layer as a passivation layer 10 on the front side of the n-type silicon wafer 1, see Figure 4 ;

[0047] Step 4: depositing SiNx layers as mask layers 4 on the passivation layer 10 on the front side of the n-type silicon wafer 1 and on the doped polysilicon layer 3 on the back side, respectively. Figure 4 ;

[0048] Step 5: A high-temperature silver paste is sintered at 900° C. on the interdigitated region of the N region on the back side of the n-type silicon wafer 1 to form a first electrode 7; the high-temperature silver paste is sintered on the doped polysilicon layer 3, see Figure 5 ;

[0049] Step 6: Use 532nm green light or ultraviolet laser with a laser power of 15W to open the mask layer 4 in the P region, ablate the tunnel oxide layer 2 and the doped polysilicon layer 3 in the P region on the back of the n-type silicon wafer 1, and expose the n-type silicon wafer 1. Figure 6 ;

[0050] Step 7: depositing an amorphous silicon layer 5 composed of intrinsic amorphous silicon and a doped amorphous silicon layer 5 on the back side of the n-type silicon wafer 1, see Figure 7 ;

[0051] Step 8: depositing a TCO layer 6 on the amorphous silicon layer 5, see Figure 8 ;

[0052] Step 9: sinter low-temperature silver paste at 200° C. on the TCO layer 6 in the P region on the back side of the n-type silicon wafer 1 to form a second electrode 9, see Fig. 9 ;

[0053] Step 10: laser ablation of the high-temperature silver paste to sinter the TCO layer 6 and the amorphous silicon layer 5 on the top and around the electrode, so that the electrode formed by the sintered high-temperature silver paste forms an isolated island, forming a first electrode 7 that is not connected to the second electrode 9, see Figure 1 .

[0054] Compared with the prior art, the back-contact solar cell and the preparation method thereof provided by the present invention have the following beneficial effects: it is an improvement on the HTBC cell. The design idea is to first sinter high-temperature silver paste, then deposit the amorphous silicon layer 5 and the TCO layer 6, and then sinter low-temperature silver paste, and finally laser ablation to isolate the two electrodes, which can reduce the consumption of low-temperature silver paste, simplify the process steps and reduce the manufacturing cost of solar cells.

[0055] Specifically, after the tunneling oxide layer 2 and the doped polysilicon layer 3 are deposited on the back side of the n-type silicon wafer 1, a high-temperature silver paste is first sintered in a pre-designed interdigitated region in the N region on the back side of the silicon wafer to form a first electrode 7; then the tunneling oxide layer 2, the doped polysilicon layer 3 and the mask layer 4 in the interdigitated region in the P region on the back side are ablated by laser; then an amorphous silicon layer 5 and a TCO layer 6 are deposited on the back side of the n-type silicon wafer 1; then a low-temperature silver paste is sintered on the TCO layer 6 in the P region to form a second electrode 9; finally, a gate line formed after sintering the high-temperature silver paste is scanned by laser, and the amorphous silicon layer 5, the TCO layer 6 and the mask layer 4 on and around the gate line are ablated to isolate the first electrode 7 from the second electrode 9.

[0056] Compared with the current HTBC structure, the preparation method provided by the present invention uses different silver pastes for the two electrodes, and the first electrode 7 is sintered with high-temperature silver paste, which greatly reduces the use of low-temperature silver paste, and can reduce the cost of transporting and storing low-temperature silver paste, and can significantly reduce the investment cost of low-temperature silver paste, thereby reducing the manufacturing cost of the battery.

[0057] Compared to the process of first making a gap area isolation groove on the back of the silicon wafer, the present invention does not require additional preparation of the gap area, but directly deposits the high-temperature silver paste on the doped polysilicon layer 3. After sintering the low-temperature silver paste, an annular groove is formed around the high-temperature silver paste by laser ablation, so that the amorphous silicon layer 5 and the TCO layer 6 are isolated from the high-temperature silver paste, thereby achieving isolation of the two electrodes, reducing the process steps, and saving the manufacturing cost of the battery to a certain extent.

[0058] In particular, it is pointed out that:

[0059] The method for preparing a back-contact solar cell provided by the present invention has the following characteristics:

[0060] (1) There is no Gap area on the back side. High-temperature silver paste and low-temperature silver paste are used respectively. The high-temperature silver paste contacts the doped polysilicon layer 3, and the low-temperature silver paste contacts the TCO film layer.

[0061] (2) Sintering the high-temperature silver paste first and then the low-temperature silver paste can save half of the low-temperature silver paste and save the silver paste cost.

[0062] (3) The first electrode 7 is exposed by laser scanning a part of the high-temperature slurry area, without the need to separately form a gap area.

[0063] (4) A mask layer 4 is first formed in the laser ablation area and then sintered at high temperature, which can prevent the ablation area from being oxidized during the high-temperature sintering process.

[0064] Example 2

[0065] The difference between Example 2 and Example 1 is that:

[0066] The n-type silicon wafer 1 is textured on both sides; the temperature for sintering the high-temperature silver paste is 650°C; the temperature for sintering the low-temperature silver paste is 150°C.

[0067] For ease of understanding, the relevant terms are explained as follows:

[0068] N-type silicon wafer 1: It is a single crystal / polycrystalline silicon wafer doped with Group V elements.

[0069] Tunneling oxide layer 2: composed of SiOx, it can effectively prevent the recombination of electrons and holes, thereby improving the efficiency of current collection and transmission.

[0070] Doped polysilicon layer 3: Polysilicon doped with group III elements (such as boron) or group V elements (such as phosphorus) can induce energy band bending and provide field passivation.

[0071] TCO layer 6: is a conductive film layer having high conductivity, high visible light transmittance, high mechanical hardness and good chemical stability.

[0072] In some embodiments, in step five, the sintering temperature of the high temperature silver paste is 500°C-1000°C.

[0073] In some embodiments, in step nine, the sintering temperature of the low-temperature silver paste is ≤200°C.

[0074] In some embodiments, in step 2, the doped polysilicon layer 3 is phosphorus-doped.

[0075] In some embodiments, in step 3, the passivation layer 10 is an AlOx layer. The AlOx layer is a film layer deposited by a gas such as trimethylaluminum, which can play a role of chemical passivation.

[0076] In some embodiments, in step 4, the mask layer 4 is a SiNx layer. SiNx layer: a deposited protective film layer that can play a role in chemical passivation and field passivation.

[0077] In some embodiments, in step seven, the amorphous silicon layer 5 includes intrinsic amorphous silicon and doped amorphous silicon layer 5. Intrinsic amorphous silicon layer 5: an undoped amorphous silicon layer 5; doped amorphous silicon layer 5: an amorphous silicon layer 5 doped with a group III element (such as boron) or a group V element (such as phosphorus).

[0078] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0079] Based on the same inventive concept, the embodiment of the present invention further provides a back-contact solar cell, which is prepared by the method for preparing a back-contact solar cell, see Figure 1, comprising an n-type silicon wafer 1, on the N region on the back side of the n-type silicon wafer 1, a tunneling oxide layer 2 and a doped polysilicon layer 3 are sequentially deposited from the inside to the outside, and a first electrode 7 is sintered at high temperature on the doped polysilicon layer 3; on the doped polysilicon layer 3 in the P region and the N region on the back side of the n-type silicon wafer 1, an amorphous silicon layer 5 and a TCO layer 6 are sequentially deposited from the inside to the outside, and the amorphous silicon layer 5 and the TCO layer 6 around the first electrode 7 are laser ablated to form an isolation ring groove 8 around the first electrode 7; a second electrode 9 is sintered at low temperature on the TCO layer 6 in the P region.

[0080] The back-contact solar cell provided by the present invention uses high-temperature silver paste to partially replace low-temperature silver paste, thereby reducing the cost of using the paste; through laser scanning grid line ablation, there is no need to separately produce a gap area, which simplifies the production process of the solar cell. The entire process does not require surface cleaning, is environmentally friendly and saves manufacturing costs, and improves the use efficiency of the solar cell.

[0081] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a back contact solar cell, characterized in that: The method comprises the following steps: Step 1, performing single-sided or double-sided texturing on the n-type silicon wafer (1); Step 2: depositing a tunneling oxide layer (2) and a doped polysilicon layer (3) in sequence on the back side of the textured n-type silicon wafer (1); Step three, depositing a passivation layer (10) on the front side of the n-type silicon wafer (1); Step 4: depositing a mask layer (4) on the passivation layer (10) on the front side of the n-type silicon wafer (1) and on the doped polysilicon layer (3) on the back side; Step 5, sintering high-temperature silver paste in the N region on the back side of the n-type silicon wafer (1); Step 6, laser ablating the P region on the back side of the n-type silicon wafer (1) where the high-temperature silver paste has not been sintered, to expose the n-type silicon wafer (1); Step seven, depositing an amorphous silicon layer (5) entirely on the back side of the n-type silicon wafer (1); Step eight, depositing a TCO layer (6) on the amorphous silicon layer (5); Step nine, sintering low-temperature silver paste on the TCO layer (6) in the P region on the back side of the n-type silicon wafer (1) to form a second electrode (9); Step ten: laser ablating the TCO layer (6) and the amorphous silicon layer (5) on the top and surrounding of the high-temperature silver paste, so that the sintered high-temperature silver paste forms an island to form a first electrode (7).

2. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step five, the sintering temperature of the high temperature silver paste is 500°C-1000°C.

3. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step nine, the sintering temperature of the low-temperature silver paste is ≤200°C.

4. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step six, a 532nm green light or ultraviolet laser with a laser power of 3-20W is used to open the mask layer (4) in the P region, ablate the tunneling oxide layer (2) and the doped polysilicon layer (3) in the P region, and expose the back side of the n-type silicon wafer (1).

5. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step 2, a tunnel oxide layer (2) is first deposited on the back of the n-type silicon wafer (1) by vapor deposition, the surface of the n-type silicon wafer (1) is passivated, and then a polysilicon layer (3) is doped.

6. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step 2, the doped polysilicon layer (3) is doped with phosphorus.

7. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step three, the passivation layer (10) is an AlOx layer.

8. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step 4, the mask layer (4) is a SiNx layer.

9. The method for preparing a back contact solar cell according to claim 1, characterized in that: In step seven, the amorphous silicon layer (5) includes intrinsic amorphous silicon and doped amorphous silicon layer (5).

10. A back-contact solar cell, prepared by the method for preparing a back-contact solar cell according to any one of claims 1 to 9, characterized in that: The invention comprises an n-type silicon wafer (1), wherein a tunneling oxide layer (2) and a doped polysilicon layer (3) are sequentially deposited from the inside to the outside in an N region on the back side of the n-type silicon wafer (1), and a first electrode (7) is sintered at high temperature on the doped polysilicon layer (3); an amorphous silicon layer (5) and a TCO layer (6) are sequentially deposited from the inside to the outside on the doped polysilicon layer (3) in the P region and the N region on the back side of the n-type silicon wafer (1), and the amorphous silicon layer (5) and the TCO layer (6) around the first electrode (7) are laser ablated to form an isolation ring groove (8) around the first electrode (7); and a second electrode (9) is sintered at low temperature on the TCO layer (6) in the P region.

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