Method for improving conductive contact of N-type battery microcell

Abstract

The invention relates to the technical field of solar cells, and particularly discloses a method for improving conductive contact of a micro-area of an N-type cell, which comprises the following steps of: (1) performing first micro-area conductive treatment on one side of a cell grid line of the N-type cell: scanning a first side edge of the cell grid line through a first pulse laser beam, and applying a first reverse bias voltage to the cell at the same time; and (2) performing second micro-area conductive treatment on the other side of the cell grid line of the N-type cell: scanning a second side edge, opposite to the first side edge, of the cell grid line through a second pulse laser beam, and applying second reverse bias voltage to the cell at the same time. According to the method, the pulse laser beams with more concentrated energy are used for carrying out single-side scanning on the two side edges of the grid line of the battery piece respectively, and precise treatment on the metal electrode on the basis of not damaging the passivation layer of the battery can be realized, so that the contact performance of the battery is optimized, the contact resistance of the battery is greatly reduced, and the performance of the battery piece is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly relates to a method for improving the micro-region conductive contact of N-type cells. Background Art

[0002] N-type cells are cell wafers with N-type silicon wafers as substrates, including TOPCon cells, HJT cells, IBC cells, etc. In the solar cell industry, N-type cells have attracted much attention due to their development potential of high efficiency and low cost. With the continuous progress of technology and further reduction of costs, the market share of N-type cells is expected to be further expanded.

[0003] Optimizing the preparation process of N-type cells is the key way to improve the comprehensive performance of the cells. In the preparation process of TOPcon cells, the P-pole usually adopts a boron diffusion process and combines with Ag-Al paste to reduce the contact resistance of the p+ doping region and improve the cell performance. Although this method effectively reduces the contact resistance of the cell, the use of Ag-Al paste will increase the surface recombination of the cell and increase the bulk resistivity of the paste electrode, which will instead have an adverse effect on the cell performance. In view of the above problems, the SE (selective emitter) doping process is introduced to solve the problems brought by the use of Ag-Al paste.

[0004] The SE doping process forms a larger doping junction depth in the metal contact region through laser doping, effectively shielding the recombination problem caused by Ag-Al spikes. At the same time, a high sheet resistance shallow junction strategy is adopted in the non-contact region to reduce emitter recombination, thereby improving the Voc (open circuit voltage), FF (fill factor) and the overall efficiency of cell conversion. However, the SE doping process also has some limitations. For example, physical damage may be caused to the silicon wafer during the laser doping process, affecting the integrity and performance of the cell wafer; the ability to repair the recombination caused by the Ag-Al paste itself in the contact region is insufficient, and the line resistance of the Ag-Al paste cannot be effectively reduced, thus limiting the improvement of cell performance.

[0005] In order to overcome the above limitations of the SE doping process and further optimize the cell performance, the current technology has widely adopted a laser-assisted sintering process to replace the SE doping process. This process uses a special silver paste to replace the Ag-Al paste, effectively reducing the recombination in the metal region and reducing the loss of cell contact resistance and open circuit voltage. However, with the application and development of the laser-assisted sintering process, some problems also arise. It is difficult to precisely control the high-temperature treatment in the metal grid line region, which limits the reduction effect of the emitter contact resistance; improper laser energy treatment may cause a decline in cell performance. Whether it leads to an increased risk of over-corrosion contact due to over-contact treatment of the back grid line paste or an under-contact phenomenon due to insufficient treatment of the front electrode, it will have an adverse effect on the cell performance.

[0006] In summary, although the preparation process of TOPcon cells has made certain progress in existing technologies, it still faces multiple challenges such as laser damage, high recombination rate, large contact resistance and over-corrosion contact. Therefore, developing a new process that can effectively reduce contact resistance and recombination rate while avoiding laser damage and over-corrosion contact has become a key technical issue that needs to be solved in the current TOPcon cell preparation field. Summary of the invention

[0007] The present invention aims at the above-mentioned problems, makes up for the deficiencies of the prior art, and provides a method for improving the conductive contact of N-type battery micro-areas to solve the problems arising from the above-mentioned background technology.

[0008] Based on this, the present invention discloses a method for improving the conductive contact of an N-type battery micro-area, comprising the following steps:

[0009] (1) performing a first micro-area conductive treatment on one side of the grid line of the cell of the N-type battery: using two laser sources to emit a first pulse laser beam, divided into two workbenches to respectively scan the first side half cell area and the other half cell area of ​​the first side; and applying a first reverse bias voltage to the cell at the same time;

[0010] (2) Performing a second micro-area conductive treatment on the other side of the grid line of the N-type battery: using two laser sources to emit a second pulsed laser beam, divided into two workbenches to respectively scan the second side half-cell area and the other half-cell area of ​​the second side, and at the same time applying a second reverse bias to the battery cell.

[0011] The present invention applies a reverse bias voltage while performing micro-area laser pulses, only forms a local current within the micro-area, generates instantaneous high temperature conditions, promotes the electron exchange between silver and silicon, accelerates the formation of silver-silicon alloy, significantly reduces the contact resistance between metal and silicon, and improves the battery efficiency of N-type batteries. At the same time, because the instantaneous high temperature is generated in the micro-area at the edge of the gate line, it reduces the damage to the passivation layer of the battery, and improves the stability and reliability of the battery.

[0012] Furthermore, the frequency of the first pulse laser beam is 522THz to 609THz, and the scanning speed is 50000mm / s to 60000mm / s.

[0013] Furthermore, the spot of the first pulsed laser beam is 1 μm to 50 μm away from the first side.

[0014] Furthermore, the frequency of the second pulse laser beam is 522THz to 609THz, and the scanning speed is 50000mm / s to 60000mm / s.

[0015] Furthermore, the spot of the second pulsed laser beam is 1 μm to 50 μm away from the second side.

[0016] Further, the first reverse bias voltage is greater than the second reverse bias voltage.

[0017] Further, the first reverse bias voltage is 10V - 15V.

[0018] Further, the second reverse bias voltage is 5V - 10V.

[0019] Further, the pulse time of the first pulsed laser beam is less than the pulse time of the second pulsed laser beam.

[0020] Further, the laser pulse time of the first pulsed laser beam is 1ns - 50ns.

[0021] Further, the laser pulse time of the second pulsed laser beam is 50ns - 100ns.

[0022] Preferably, the first pulsed laser beam uses green laser light.

[0023] Preferably, the second pulsed laser beam uses green laser light.

[0024] Preferably, both the first pulsed laser beam and the second pulsed laser beam use green laser light.

[0025] Further, the laser power of the first pulsed laser beam is greater than the laser power of the second pulsed laser beam.

[0026] Further, the photoinduced current density of the first pulsed laser beam is 200A / cm 2 ~2000A / cm 2 and the photoinduced current density of the second pulsed laser beam is 10A / cm 2 ~200A / cm 2 .

[0027] Compared with the first micro-region conductive treatment, the second micro-region conductive treatment has a longer laser pulse time and a lower added reverse bias voltage. After the first micro-region conductive treatment on the battery surface, the instantaneous high temperature has diffused silver and silicon into each other, forming a silver-silicon alloy. The second micro-region conductive treatment further increases the silver-silicon contact area, controls a lower second reverse bias voltage and a longer laser pulse time, thereby ensuring that on the basis of further reducing the emitter contact resistance, the risk of over-contact of the laser to the battery is reduced, and the bad phenomenon of the battery EL black line caused by over-contact to the back of the battery is avoided.

[0028] Compared with the prior art, the beneficial effects of the present invention:

[0029] (1) Effectively solves the problem of limited optimization of battery contact resistance: The micro-area laser treatment technology of the present invention can instantaneously excite a higher carrier concentration through controlled multi-pass and precisely targeted concentrated energy pulsed laser scanning. This not only enhances the electron transition efficiency inside the battery but also promotes the effective transmission of electrons at the interface, thereby significantly reducing the contact resistance and improving the overall performance and conversion efficiency of the battery.

[0030] (2) Reduces damage to the passivation layer: The micro-area laser treatment technology of the present invention can maximize the integrity of the passivation layer by precisely controlling various laser parameters and the micro-area action range of laser pulses and reverse bias voltages. This avoids damage to the passivation layer caused by laser sintering, thereby ensuring the long-term stability and reliability of the battery and enabling precise treatment of the battery metal electrodes without damaging the passivation layer.

[0031] (3) Improves the yield rate of the battery: The micro-area laser treatment technology of the present invention performs laser micro-area scanning in a partitioned and multi-pass manner. Compared with the full-surface scanning method in the prior art, it has a higher laser energy density and a shorter scanning time. This not only avoids adverse effects on the back of the battery due to over-contact with the battery but also ensures that the front electrode of the battery can be fully treated, thereby improving the yield rate of the battery.

[0032] (4) By applying different magnitudes of reverse bias voltages in a multi-pass manner within a specific range, a micro-scale electric field is formed at the edge of the metal grid lines of the N-type battery, injecting a large number of carriers into a specific area. This improves the mobility of silver ions and the deposition uniformity on the silicon wafer surface during the laser sintering process, shortens the process time, reduces the contact resistance between the metal grid lines and silicon. At the same time, due to controlling the laser scanning within a small range, the probability of damage to the non-metal grid line area is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic diagram of the micro-area conductive contact improvement process for a half-cell N-type battery of the present invention.

[0035] Wherein: 1. Laser scanning half-cell area, 2. Probe pressing position, 3. First side of laser scanning, 4. Second side of laser scanning, 5. The other half area relative to the laser scanning. DETAILED DESCRIPTION OF THE INVENTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the protection scope of the present invention.

[0037] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative position relationship between components in a specific posture (as shown in the attached drawings). If this specific posture changes, the directional indication will also change accordingly.

[0038] In addition, the descriptions involving "first", "second", etc. in the present invention are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly indicate the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of such features.

[0039] The embodiment of the present invention solves the problem in the prior art that it is impossible to balance reducing the battery contact resistance and avoiding laser damage to optimize the battery performance through a method for improving the micro-region conductive contact of N-type batteries.

[0040] Embodiment 1

[0041] A method for improving the micro-region conductive contact of an N-type battery in this embodiment includes the following steps:

[0042] First micro-region conductive treatment: The N-type battery wafer after sintering in the sintering furnace and light injection during the battery production process is laser-scanned in the laser scanning half-piece area 1 where the first side is located (as shown in Figure 1 ) on the first workbench by a first laser source. The scanning speed of the first laser source is 55000 mm / s, the distance between the laser spot and the first side of the fine grid line is 10 um, and the pulse time is 10 ns. At the same time, the probe of an external power supply applying a reverse bias voltage is pressed against the other half-piece area 5 relative to the laser scanning (the probe pressing position 2 is shown in Figure 1 ), the reverse bias voltage V 1 is 12V. The second workbench also uses the first laser source, the laser scanning area is the other half-piece opposite to the first workbench, and the probe pressing area is the other half-piece relative to the laser scanning.

[0043] Second micro-region conductive treatment: For the N-type cell after the first micro-region conductive treatment, on the third workbench, use the second laser source to perform laser scanning on the laser scanning half-region where the second side 4 opposite to the first side 3 is located. The scanning speed of the second laser source is 55000 mm / s, the distance between the laser spot and the first side of the fine grid line is 10 um, and the pulse time is 60 ns; at the same time, press the probe of the external power supply applying a reverse bias voltage onto the other half-region opposite to the laser scanning, and the reverse bias voltage V 2 is 8V. The laser scanning region on the fourth workbench is the other half opposite to the third workbench, and the probe pressing region is the other half opposite to the laser scanning.

[0044] Example 2

[0045] First micro-region conductive treatment: For the N-type cell after sintering in the sintering furnace and light injection during the battery production process, on the first workbench, use the first laser source to perform laser scanning on the laser scanning half-region where the first side is located (as Figure 1 shown). The scanning speed of the first laser source is 55000 mm / s, the distance between the laser spot and the first side of the fine grid line is 30 um, and the pulse time is 30 ns; at the same time, press the probe of the external power supply applying a reverse bias voltage onto the other half-region opposite to the laser scanning, and the reverse bias voltage V 1 is 15V. The laser scanning region on the second workbench is the other half opposite to the first workbench, and the probe pressing region is the other half opposite to the laser scanning.

[0046] Second micro-region conductive treatment: For the N-type cell after the first micro-region conductive treatment, use the second laser source to perform laser scanning on the half-region where the second side opposite to the first side is located. The scanning speed of the second laser source is 55000 mm / s, the distance between the laser spot and the first side of the fine grid line is 30 um, and the pulse time is 80 ns; at the same time, press the probe of the external power supply applying a reverse bias voltage onto the other half-region opposite to the laser scanning, and the reverse bias voltage V 2 is 5V. The laser scanning region on the fourth workbench is the other half opposite to the third workbench, and the probe pressing region is the other half opposite to the laser scanning.

[0047] Example 3

[0048] First micro-region conductive treatment: For the N-type cell after sintering in the sintering furnace and light injection during the battery production process, on the first workbench, use the first laser source to perform laser scanning on the laser scanning half-region where the first side is located (as Figure 1 shown). The scanning speed of the first laser source is 55000 mm / s, the distance between the laser spot and the first side of the fine grid line is 50 um, and the pulse time is 30 ns; at the same time, press the probe of the external power supply applying a reverse bias voltage onto the other half-region opposite to the laser scanning, and the reverse bias voltage V 1It is 15V. The laser scanning area of the second workbench is the other half piece opposite to the first workbench, and the probe pressing area is the other half piece opposite to the laser scanning.

[0049] Second micro-region conductive treatment: For the N-type cell after the first micro-region conductive treatment, use the second laser source to perform laser scanning on the half region where the second side opposite to its first side is located. The scanning speed of the second laser source is 55000mm / s. The distance between the laser spot and the first side of the fine grid line is 50um, and the pulse time is 80ns. At the same time, press the probe of the external power supply applying a reverse bias voltage against the other half region opposite to the laser scanning. The reverse bias voltage V 2 is 8V. The laser scanning area of the fourth workbench is the other half piece opposite to the third workbench, and the probe pressing area is the other half piece opposite to the laser scanning.

[0050] Comparative Example 1

[0051] A method for laser sintering of N-type cells in this comparative example includes the following steps:

[0052] On the first workbench, use the first laser source to perform overall scanning on the half region of the cell. The scanning speed is 55000mm / s, the laser pulse time is 30ns, and at the same time, apply a 15V reverse bias voltage to the cell. The probe pressing position of the external power supply is on the second main grid of the other half region opposite to the laser scanning;

[0053] On the second workbench, use the second laser source to perform overall scanning on the other half region of the cell relative to the half region scanned on the first workbench. The scanning speed is 55000mm / s, the laser pulse time is 30ns, and at the same time, apply a 15V reverse bias voltage to the cell. The probe pressing position of the external power supply is on the second main grid of the other half region opposite to the laser scanning.

[0054] Test the performance parameters of the N-type cells in the above examples and the cells in the comparative example. The performance parameters are specifically the conversion efficiency Eta, open-circuit voltage Uoc, fill factor FF, and contact resistivity of the cell. The test results are shown in Table 1.

[0055] Table 1

[0056] Difference Eta(%) Uoc(mV) FF(%) <![CDATA[Contact resistivity (mΩ.cm 2 )]]> Example 1 - Comparative Example 1 0.036 0.37 0.13 -0.58 Example 2 - Comparative Example 1 0.062 0.36 0.21 -0.92 Example 3 - Comparative Example 1 0.044 0.47 0.17 -0.73

[0057] Through the difference analysis of the conversion rate Eta, open-circuit voltage Uoc, fill factor FF, and contact resistivity of Examples 1-3 and Comparative Example 1, it can be found that the present invention uses laser micro-region scanning in a partitioned and sequential manner and applies a reverse bias voltage during laser scanning, which improves the cell conversion rate, open-circuit voltage, and fill factor of the N-type cell, and reduces the contact resistance between the metal grid line and silicon, thus greatly optimizing the performance of the N-type cell.

[0058] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A method for improving the conductive contact of N-type battery micro-area, characterized in that: The following steps are involved: (1) performing a first micro-area conductive treatment on one side of the grid line of the cell sheet of the N-type battery: using two laser sources to emit a first pulsed laser beam, divided into two workbenches to respectively scan the first side half cell area and the other half cell area of ​​the first side; and applying a first reverse bias voltage to the cell sheet of the N-type battery at the same time; (2) Performing a second micro-area conductive treatment on the other side of the grid line of the N-type battery: using two laser sources to emit a second pulsed laser beam, divided into two workbenches to respectively scan the second side half-cell area and the other half-cell area of ​​the second side, and at the same time applying a second reverse bias to the battery cell.

2. A method for improving the conductive contact of N-type battery micro-areas according to claim 1, characterized in that: The frequency of the first pulse laser beam is 522 THz to 609 THz, the scanning speed is 50000 mm / s to 60000 mm / s, and the spot of the first pulse laser beam is 1 μm to 50 μm away from the first side.

3. A method for improving the conductive contact of N-type battery micro-areas according to claim 1, characterized in that: The frequency of the second pulse laser beam is 522 THz to 609 THz, the scanning speed is 50000 mm / s to 60000 mm / s, and the spot of the second pulse laser beam is 1 μm to 50 μm away from the second side.

4. A method for improving the conductive contact of N-type battery micro-areas according to claim 1, characterized in that: The first reverse bias voltage is greater than the second reverse bias voltage, and a pulse time of the first pulse laser beam is less than a pulse time of the second pulse laser beam.

5. A method for improving the conductive contact of N-type battery micro-areas according to claim 4, characterized in that: The first reverse bias voltage is 10V to 15V, and the pulse time is 1ns to 50ns.

6. A method for improving conductive contact of N-type battery micro-areas according to claim 4, characterized in that: The second reverse bias voltage is 5V to 10V, and the pulse time is 50ns to 100ns.

7. A method for improving the conductive contact of N-type battery micro-areas according to claim 2 or 3, characterized in that: The first pulse laser beam uses a green laser or the second pulse laser beam uses a green laser.

8. A method for improving the conductive contact of N-type battery micro-areas according to claim 2 or 3, characterized in that: The first pulse laser beam and the second pulse laser beam are both green lasers.

9. The method for improving the conductive contact of N-type battery micro-area according to claim 1, characterized in that: The laser power of the first pulsed laser beam is greater than the laser power of the second pulsed laser beam.

10. A method for improving conductive contact of N-type battery micro-areas according to claim 9, characterized in that: The photoinduced current density of the first pulsed laser beam is 200A / cm 2 ~2000A / cm 2 The photoinduced current density of the second pulse laser beam is 10A / cm 2 ~200A / cm 2 .

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