Nanometer silicon particle layer assisted laser enhanced contact optimization method and solar cell

Abstract

The invention relates to the technical field of photovoltaics, and discloses a nanometer silicon particle layer-assisted laser enhanced contact optimization method and a solar cell. The method comprises the following steps: pretreating a silicon substrate; preparing a nanometer silicon particle layer on the surface of the pretreated silicon substrate; preparing a first passivation antireflection layer on the surface of the nanometer silicon particle layer; printing electrode slurry on the surface of the first passivation antireflection layer, and sintering to form a first electrode which burns through the first passivation antireflection layer; and a laser enhanced contact optimization technology is adopted for optimization treatment, so that the first electrode can be in ohmic contact with the silicon substrate through the nano silicon particle layer. According to the method, large-volume Ag-Si peaks and Ag-Si lattice defects formed by LECO heat instability can be effectively inhibited, metal recombination can be reduced, the process range of LECO optimization treatment can be widened, contact resistance can be reduced, the electrode conductivity can be improved, the EL cloud and mist phenomenon can be effectively avoided, and the fill factor, the open-circuit voltage and the conversion efficiency of the battery can be further improved.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic technology, and in particular to a method for nano-silicon particle layer assisted laser enhanced contact optimization and a solar cell. Background Art

[0002] With the introduction of laser enhanced contact optimization (LECO) technology, the conversion efficiency of crystalline silicon solar cells (referred to as solar cells) has been further improved. However, recent studies have shown that due to different expansion coefficients and large lattice mismatch, Ag (silver, which is mainly located in the grid lines or electrodes) and Si (silicon, which is mainly located in the P + The direct bonding of the doped layers (such as the emitter and the silicon substrate) under high temperature formed by local high current will inevitably lead to residual stress accumulation, thus forming defects at the silver-silicon interface. In particular, with the gradual increase of reverse bias, the instability of LECO heat formation will aggravate the formation of lattice defects, resulting in defects and metal recombination at the silver-silicon contact interface in the solar cell, so that the cloud phenomenon appears in the electroluminescence (EL) detection, which hinders the further improvement of the conversion efficiency of the solar cell. In addition, the limitations of the coating process will also make the anti-reflection passivation film in the local edge area of ​​the front thicker than the anti-reflection passivation film in other areas of the front. This local thickness difference of the front anti-reflection passivation film causes the LECO process to form a higher temperature in the local edge area, resulting in excessive large-area contact of Ag-Si in the local edge area, thereby aggravating the defects and metal recombination at the silver-silicon contact interface caused by the instability of LECO heat, reducing the fill factor of the battery, and showing a cloud phenomenon in the EL detection image.

[0003] At present, the strategies to solve the clouding problem are often focused on improving the Ag-Si contact during the high-temperature sintering process of preparing electrodes. As shown in publication number CN118866423A, bismuth-silicon-tellurium glass powder is used to inhibit excessive corrosion of silicon wafers by glass powder in the front main grid slurry. As shown in publication number CN117877785A, inert additives such as nano-silicon are added to the front main grid slurry to balance the corrosion of the glass material on the silicon surface.

[0004] However, the existing method of adding inert additives such as nano-silicon to the front main grid paste reduces corrosion while also reducing the volume of the Ag-Si alloy. This reduction in contact volume will reduce the contact performance between the electrode (especially the electrode in the middle area) and the doped layer and the silicon substrate, increase the contact resistance, and is not conducive to improving the fill factor, open circuit voltage and conversion efficiency of the solar cell. In addition, since the conductivity of nano-silicon at room temperature is lower than that of silver, adding nano-silicon to the front main grid paste will also reduce the conductivity of the silver grid line (or silver electrode), which is also not conducive to improving the efficiency of the battery. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a method for nano-silicon particle layer-assisted laser enhanced contact optimization and a solar cell.

[0006] Based on this, the present invention discloses a method for nano-silicon particle layer assisted laser enhanced contact optimization, comprising the following steps:

[0007] Step S1, pre-treating the silicon substrate;

[0008] Step S2, preparing a nano silicon particle layer on the surface of the pretreated silicon substrate;

[0009] Step S3, preparing a first passivation anti-reflection layer on the surface of the nano-silicon particle layer;

[0010] Step S4, printing electrode paste on the surface of the first passivation anti-reflection layer, and sintering to form a first electrode that burns through the first passivation anti-reflection layer;

[0011] Step S5, using laser enhanced contact optimization technology to optimize the silicon substrate processed in step S4, so that the first electrode can make ohmic contact with the silicon substrate through the nano silicon particle layer.

[0012] Preferably, the step S1 specifically comprises: preparing an emitter on the front side of the silicon substrate.

[0013] Preferably, in step S2, the nano silicon particle layer is prepared in a local edge region of the front side of the silicon substrate; the local edge region corresponds to the position of the first electrode located in the edge region in step 4; the first electrode is a silver electrode.

[0014] Further preferably, the nano-silicon particle layer is prepared by a laser induced forward transfer method.

[0015] More preferably, the process conditions for preparing the nano-silicon particle layer by the laser induced forward transfer method include: the transfer material is a 50nm a-Si:H film, the wavelength of the femtosecond laser is 1050nm, the laser energy is 50-100nJ, it is focused by a 10x objective lens, the deposition path is controlled by a laser scanning path, and the diameter of the nano-silicon particles in the deposited nano-silicon particle layer is controlled at 50-400nm.

[0016] In step S2, a laser-induced forward transfer method is used to deposit a nano-silicon particle layer on the local edge area of ​​the front side of the emitter (or silicon substrate). The laser-induced forward transfer method has advantages over other methods in terms of deposition quality, resolution and speed, and can form a nano-silicon particle layer arranged in a periodic array. The deposition path is controlled by a laser scanning path, so that the nano-silicon particle layer can be precisely deposited at the position of the silicon surface (such as the emitter and other doping layers and the silicon substrate) corresponding to the first electrode (such as the front electrode) in the edge area. There is no need for additional processes such as masking and etching, and the process is simpler.

[0017] Further preferably, in the step S5, laser enhanced contact optimization technology is used to perform optimization processing under reverse bias and laser, the reverse bias voltage is 13-19.5V, and the laser power is 20-500w.

[0018] In step S5, the presence of the nano-silicon particle layer below the first electrode (such as the front electrode) in the edge region is beneficial to suppressing the large-volume Ag-Si spikes formed by LECO thermal instability, reducing defects and metal recombination inside the solar cell, and enabling the front electrode to form excellent contact performance with the silicon surface, which is specifically manifested in: a reduction in the probability of EL fogging and a dual improvement in open circuit voltage and fill factor.

[0019] Further preferably, after step S2, the method further comprises preparing a passivation contact structure on the back side of the silicon substrate;

[0020] The passivation contact structure comprises a tunneling oxide layer and a doped polysilicon layer which are sequentially prepared on the back side of a silicon substrate.

[0021] More preferably, in step S3, the first passivation anti-reflection layer is a front passivation anti-reflection layer, and the front passivation anti-reflection layer is located on the entire front side of the silicon substrate;

[0022] The step S3 further includes: preparing a back passivation anti-reflection layer on the back side of the doped polysilicon layer.

[0023] More preferably, in step S4, the first electrode is a front electrode;

[0024] The step S4 specifically includes: printing electrode paste on the surface of the back passivation anti-reflection layer and the front passivation anti-reflection layer, and sintering to form a back electrode and the front electrode; wherein the back electrode is ohmically contacted with the doped polysilicon layer after burning through the back passivation anti-reflection layer.

[0025] The present invention also discloses a solar cell, which is manufactured by using the method for nano-silicon particle layer assisted laser enhanced contact optimization described above in the present invention.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] The method of the present invention further regulates the silver-silicon interface reaction of the crystalline silicon solar cell under the laser enhanced contact optimization technology (LECO) by introducing a nano silicon particle layer at the contact interface between the first electrode (such as the front electrode) and the silicon surface (such as the emitter and other doping layers and the silicon substrate); thus, through the cooperation of preparing the nano silicon particle layer on the silicon surface (the nano silicon particle layer is preferably prepared in the local edge area of ​​the silicon surface) and the LECO optimization treatment, the large volume Ag-Si spikes and Ag-Si lattice defects formed by the thermal instability of LECO can be effectively suppressed, the metal recombination caused by the lattice defects can be further reduced, and the process range of the LECO optimization treatment can be widened (therefore, the voltage and laser power of the LECO optimization treatment can be increased, thereby reducing the contact resistance of the front electrode in the middle area and effectively avoiding excessive etching of the silicon surface by the front electrode slurry in the edge area), reducing the overall contact resistance and improving the electrode conductivity, effectively avoiding the EL fogging phenomenon, and promoting the further improvement of the fill factor, open circuit voltage and conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a top view of the method for nano-silicon particle layer assisted laser enhanced contact optimization of this embodiment after being processed by step 5.

[0029] Figure 2 This is a schematic diagram of the cross-sectional structure of a solar cell manufactured by a method of nano-silicon particle layer assisted laser enhanced contact optimization in this embodiment.

[0030] Figure 3 It is a graph showing the EL test data of the optimized solar cells of the embodiments and comparative examples.

[0031] Description of the accompanying drawings: silicon substrate 11; P + Emitter 12; nano-silicon particle layer 13; passivation contact structure 14; back anti-reflection passivation film 15; front anti-reflection passivation film 16; back electrode 17; front electrode 18. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example

[0034] A method of nano-silicon particle layer assisted laser enhanced contact optimization in this embodiment, see Figure 1-2 , including the following steps:

[0035] Step 1: Use an alkaline solution to perform texturing treatment on the front and back sides of the silicon substrate 11.

[0036] The mass fraction of the alkaline solution is 1-3%, the reaction temperature of the texturing treatment is 65-85° C., and the texturing time is 1-5 minutes.

[0037] Specifically, a preferred example of this embodiment is: the mass fraction of the alkaline solution is 2.5%, the reaction temperature of the texturing treatment is 70° C., and the texturing time is 2 minutes.

[0038] Step 2: Form a P on the front side of the silicon substrate 11 by using a doping diffusion process. + Emitter 12.

[0039] Among them, the doping diffusion process uses BCl3 as the doping boron source, the boron doping diffusion temperature is 800-1100°C, and the square resistance is 100-500Ω / sq.

[0040] Specifically, a preferred example of this embodiment is that the temperature of boron doping diffusion is 890° C. and the sheet resistance is 230Ω / sq.

[0041] Step 3: Use a chain machine to perform single-side HF solution pickling on the silicon substrate 11 to remove the borosilicate glass formed on the back and sides of the silicon substrate 11 due to the boron doping diffusion process.

[0042] The mass fraction of the HF solution is 5-30%, the pickling time is 0.2-2 min, and the pickling temperature is 25-35°C.

[0043] Specifically, a preferred example of this embodiment is: the mass fraction of the HF solution is 8%, the pickling time is 1 min, and the pickling temperature is 30°C.

[0044] Step 4: polishing the back side of the silicon substrate 11 with an alkaline solution (such as KOH solution).

[0045] The mass fraction of the KOH solution is 1-5%, the polishing time is 1-5 minutes, and the polishing temperature is 60-90°C.

[0046] Specifically, a preferred example of this embodiment is: the mass fraction of the KOH solution is 1.5%, the time is 1 minute, and the temperature is 75°C.

[0047] Step 5: Laser induced forward transfer (LIFT) method was used to + A nano-silicon particle layer 13 is deposited on a local edge region of the front side of the emitter 12 .

[0048] Among them, the transfer material is a 50nm a-Si:H film, the wavelength of the femtosecond laser is 1050nm, the laser energy is 50-100nJ, it is focused by a 10x objective lens, and the deposition path is controlled by a laser scanning path. The local edge area of ​​the deposited nano-silicon particle layer 13 corresponds to the front electrode 18 of the edge area of ​​the subsequent step 10, and the diameter of the nano-silicon particles in the nano-silicon particle layer 13 is controlled at 50-400nm.

[0049] Specifically, a preferred example of this embodiment is: the laser energy is 60nJ, and the local edge area of ​​the deposited nano-silicon particle layer 13 is as follows: Figure 1 shown.

[0050] Step 6: depositing a tunneling oxide layer and a phosphorus-doped amorphous silicon layer in sequence on the back side of the silicon substrate 11.

[0051] The thickness of the tunnel oxide layer is 0.2-3 nm, and the thickness of the phosphorus-doped amorphous silicon layer is 20-50 nm.

[0052] Specifically, a preferred example of this embodiment is that the thickness of the tunnel oxide layer is 2 nm, and the thickness of the phosphorus-doped amorphous silicon layer is 30 nm.

[0053] Step 7: annealing to transform the phosphorus-doped amorphous silicon layer into a phosphorus-doped polysilicon layer, thereby obtaining a passivation contact structure 14 composed of a tunnel oxide layer and a phosphorus-doped polysilicon layer.

[0054] The annealing temperature is 700-900°C, and the annealing time is 50-120min.

[0055] Specifically, a preferred example of this embodiment is: the annealing temperature is 850° C., and the annealing time is 55 minutes.

[0056] Step 8: Use NaOH solution and HF solution in sequence to clean the coating layer and doped silicon glass formed by doping on the back of the silicon substrate 11. The cleaning process of step 8 is specifically referred to the prior art, so it is not described in detail here.

[0057] Step 9: Prepare a front anti-reflection passivation film 16 and a back anti-reflection passivation film 15 on the front and back sides of the silicon substrate 11, respectively.

[0058] The front anti-reflection passivation film 16 includes: + The aluminum oxide film on the front of the emitter 12 and the nano-silicon particle layer 13, and the front silicon nitride film deposited on the front of the aluminum oxide film. The back anti-reflection passivation film 15 includes a back silicon nitride film deposited on the back of the passivation contact structure 14. The thickness of the aluminum oxide film is 6-9nm, and the thickness of the front silicon nitride film and the back silicon nitride film are both 70-120nm.

[0059] Specifically, a preferred example of this embodiment is that the thickness of the aluminum oxide film is 6 nm, and the thickness of the front silicon nitride film and the back silicon nitride film are both 70 nm.

[0060] Step 10: Print silver electrode paste on the surface of the front anti-reflection passivation film 16 and the back anti-reflection passivation film 15 to form the front electrode 18 and the back electrode 17 respectively through sintering. After sintering, the front electrode 18 located in the edge area burns through the front anti-reflection passivation film 16 and then contacts with the P through the nano-silicon particle layer 13. + The emitter 12 makes a preliminary ohmic contact; the front electrode 18 located in the middle printing area burns through the front anti-reflection passivation film 16 and directly contacts the P + The emitter 12 makes a preliminary ohmic contact, and the back electrode 17 burns through the back anti-reflection passivation film 15 and makes an ohmic contact with the phosphorus-doped polysilicon layer in the passivation contact structure 14. After the processing in step 10, a solar cell can be manufactured.

[0061] Among them, the sintering temperature is 600-900℃.

[0062] Specifically, a preferred example of this embodiment is that the sintering temperature is 870°C.

[0063] Step 11: Use laser enhanced contact optimization technology to optimize the solar cell so that the front electrode 18 (i.e., the silver electrode) in the edge area is connected to the P through the nano-silicon particle layer 13. + The emitter 12 forms an excellent ohmic contact, and the front electrode 18 (i.e., the silver electrode) in the middle printing area is directly connected to the P + The emitter 12 forms an excellent ohmic contact; thus, the contact performance between the front electrode 18 and the silicon substrate 11 is improved to obtain an optimized solar cell (such as Figure 2 shown).

[0064] Among them, when laser enhanced contact optimization technology is used for optimization processing, the reverse bias voltage is 13-19.5V and the laser power is 20-500w.

[0065] Specifically, a preferred example of this embodiment is: the reverse bias voltage is 16V, and the laser power is 20W.

[0066] Comparative Example 1

[0067] The comparative example provides a method for laser enhanced contact optimization, and its specific steps refer to steps 1-11 of the embodiment, and the difference between the comparative example and the embodiment is that step 5 is omitted in the comparative example.

[0068] Comparative Example 2

[0069] The present comparative example is a method for laser enhanced contact optimization, and its specific steps refer to steps 1-11 of the embodiment. The difference between the present comparative example and the embodiment is that step 5 is omitted in the present comparative example, and the front electrode slurry used in the present comparative example is the existing silver electrode slurry with added nano silicon particles.

[0070] Performance Testing

[0071] 1. The optimized solar cells of the embodiment and the comparative example (the optimized solar cells are prepared by adopting the preferred process conditions of the above steps) were respectively subjected to performance tests, and the test results are shown in Table 1.

[0072] Table 1

[0073] sample Eta / % Voc / mV Isc / A FF / % Example 24.92 739.2 14.09 80.28 Comparative Example 1 24.37 735.2 14.90 78.70 Comparative Example 2 24.76 744.1 14.11 78.93

[0074] In Table 1, Eta is the conversion efficiency, Voc is the open circuit voltage, Isc is the short circuit current, and FF is the fill factor.

[0075] 2. The optimized solar cells of the embodiment and the comparative example (the optimized solar cells are prepared by adopting the preferred process conditions of the above steps) were tested for EL, and the test results are shown in FIG. Figure 3 shown.

[0076] In summary, the prior art such as CN117877785A cannot ensure that the front electrode in the middle area forms excellent contact with the silicon surface through LECO optimization treatment, while solving the problem of excessive etching of the silicon surface by the electrode slurry in the edge area under the high voltage and high laser power of LECO.

[0077] In this regard, the method of the present invention first prepares a nano-silicon particle layer on the silicon surface (such as the emitter and other doping layers and the silicon substrate) (preferably: depositing the nano-silicon particle layer in the local edge area of ​​the silicon surface), and then performs LECO optimization treatment; in this way, under the protection of the nano-silicon particle layer, the LECO process range of the middle area of ​​the solar cell can be broadened, so the LECO voltage and laser power can be increased, thereby reducing the contact resistance of the front electrode in the middle area and effectively avoiding excessive etching of the silicon surface by the front electrode slurry (such as fine grid slurry) in the edge area. Therefore, the method of the present invention can not only improve the open circuit voltage by preventing excessive etching of the silicon surface in the local edge area, but also reduce the contact resistance of the middle area to improve the fill factor, and can effectively avoid the occurrence of clouding in EL detection after LECO treatment (such as Figure 3As shown), the conversion effect of the battery is further improved (see Table 1); moreover, the method of the present invention is further combined with the laser induced forward transfer method, which can also realize the precise deposition of the nano-silicon particle layer, which helps to further improve the fill factor and open circuit voltage of the battery, and increases the improvement of LECO on the conversion efficiency of solar cells.

[0078] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0079] The technical solution provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for laser enhanced contact optimization assisted by a nano-silicon particle layer, characterized in that: The steps include: Step S1, pre-treating the silicon substrate; Step S2, preparing a nano silicon particle layer on the surface of the pretreated silicon substrate; Step S3, preparing a first passivation anti-reflection layer on the surface of the nano-silicon particle layer; Step S4, printing electrode paste on the surface of the first passivation anti-reflection layer, and sintering to form a first electrode that burns through the first passivation anti-reflection layer; Step S5, using laser enhanced contact optimization technology to optimize the silicon substrate processed in step S4, so that the first electrode can make ohmic contact with the silicon substrate through the nano silicon particle layer.

2. The method of claim 1, wherein: The step S1 specifically includes: preparing an emitter on the front side of the silicon substrate.

3. The method of claim 1, wherein: In the step S2, the nano silicon particle layer is prepared in a local edge region of the front side of the silicon substrate; the local edge region corresponds to the position of the first electrode located in the edge region in step 4; the first electrode is a silver electrode.

4. The method for nano-silicon particle layer-assisted laser enhanced contact optimization according to any one of claims 1 to 3, characterized in that: The preparation method of the nano silicon particle layer is a laser induced forward transfer method.

5. The method of claim 4, wherein: The process conditions for preparing the nano-silicon particle layer by the laser-induced forward transfer method include: the transfer material is a 50nm a-Si:H film, the wavelength of the femtosecond laser is 1050nm, the laser energy is 50-100nJ, it is focused by a 10x objective lens, the deposition path is controlled by a laser scanning path, and the diameter of the nano-silicon particles in the deposited nano-silicon particle layer is controlled to be 50-400nm.

6. A method for nano-silicon particle layer assisted laser enhanced contact optimization according to any one of claims 1-3 and 5, characterized in that: In the step S5, the laser enhanced contact optimization technology is used to perform optimization processing under reverse bias and laser, the reverse bias voltage is 13-19.5V, and the laser power is 20-500w.

7. The method of nano-silicon particle layer assisted laser enhanced contact optimization according to claim 1 or 2, characterized in that: After step S2, the method further includes preparing a passivation contact structure on the back side of the silicon substrate; The passivation contact structure comprises a tunneling oxide layer and a doped polysilicon layer which are sequentially prepared on the back side of a silicon substrate.

8. The method of claim 7, wherein: In the step S3, the first passivation anti-reflection layer is a front passivation anti-reflection layer, and the front passivation anti-reflection layer is located on the entire front side of the silicon substrate; The step S3 further includes: preparing a back passivation anti-reflection layer on the back side of the doped polysilicon layer.

9. The method of claim 8, wherein: In the step S4, the first electrode is a front electrode; The step S4 specifically includes: printing electrode paste on the surface of the back passivation anti-reflection layer and the front passivation anti-reflection layer, and sintering to form a back electrode and the front electrode; wherein the back electrode is ohmically contacted with the doped polysilicon layer after burning through the back passivation anti-reflection layer.

10. A solar cell, characterized in that: It is prepared by the method for nano-silicon particle layer assisted laser enhanced contact optimization as described in any one of claims 1-9.

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