Diffusion method and solar cell

Abstract

The present application provides a diffusion method and a solar cell. In the diffusion method provided in the present application, a silicon wafer is first placed in a diffusion furnace, and a pre-oxidation treatment is performed on the silicon wafer for 200 to 240 seconds at a temperature of 820 to 840°C, an oxygen flow rate of 200 to 500 sccm, and a nitrogen flow rate of 2000 to 3000 sccm; then, a pre-deposition treatment is performed on the silicon wafer for 100 to 160 seconds at a temperature of 750 to 860°C and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4; then, a secondary deposition treatment is performed on the silicon wafer for 100 to 160 seconds at a temperature of 840 to 900°C and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4; finally, a push-junction is performed on the silicon wafer at a temperature of 850 to 950°C to obtain a boron diffusion layer; wherein, through the combined effects of the above-mentioned pre-oxidation treatment, pre-deposition, secondary deposition, and push-junction treatment, the doping concentration of the boron source can be reduced, the diffusion is uniform, the diffusion square resistance is increased, and the PN junction distribution becomes shallower.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic cells, and in particular to a diffusion method and a solar cell. Background Art

[0002] Boron diffusion is a commonly used technology in the manufacturing process of photovoltaic cells. This technology is used to introduce boron atoms into silicon wafers to form P-type doped regions.

[0003] Taking N-type TOPCON solar cells as an example, the principle of boron diffusion is that BCl3 reacts with O2 at high temperature to generate Cl2 and B2O3. The generated B2O3 reacts with silicon at the diffusion temperature to generate SiO2 and B atoms to form a layer of borosilicate glass on the surface of the silicon wafer. Then the boron atoms continue to diffuse into the silicon wafer to form a P-type layer with a certain junction depth and impurity gradient distribution, which can form a PN junction at the interface with the N-type silicon substrate.

[0004] However, the boron diffusion layer prepared by the existing boron diffusion process has a high boron doping concentration, a small square resistance and a deep PN junction, which makes the carrier Auger recombination larger and the minority carrier transmission distance longer, which easily causes the open circuit voltage and short circuit current of the photovoltaic cell to be low, affecting the photoelectric conversion efficiency. Summary of the invention

[0005] The technical problem to be solved by the present application is to provide a diffusion method and a solar cell to solve the problems of excessively high concentration, small square resistance and deep PN junction of the boron diffusion layer prepared by the existing diffusion process.

[0006] In order to solve the above problems, the present application is implemented through the following technical solutions:

[0007] The present application proposes a diffusion method, which includes:

[0008] Placing the silicon wafer in a diffusion furnace, and performing a pre-oxidation treatment on the silicon wafer for 200 to 240 seconds under the conditions of a temperature of 820 to 840° C., an oxygen flow rate of 200 to 500 sccm, and a nitrogen flow rate of 2000 to 3000 sccm;

[0009] After the pre-oxidation treatment, the silicon wafer is subjected to a pre-deposition treatment for 100 to 160 seconds at a temperature of 750 to 860° C. and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4;

[0010] After the pre-deposition treatment, the silicon wafer is subjected to a secondary deposition treatment for 100 to 160 seconds at a temperature of 840 to 900° C. and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4;

[0011] After the secondary deposition process, the silicon wafer is pushed and bonded at a temperature of 850-950° C. to obtain a boron diffusion layer.

[0012] Optionally, in the diffusion method, the oxygen flow rate of the pre-deposition treatment is 480-510 sccm, and the boron source flow rate is 160-180 sccm;

[0013] The secondary deposition oxygen flow rate is 480~510sccm and the boron source flow rate is 160~180sccm.

[0014] Optionally, in the diffusion method, the silicon wafer is pushed at a temperature of 850-950° C., comprising:

[0015] The process is carried out for 3 to 10 minutes at a temperature of 870 to 925°C, a nitrogen flow rate of 1000 to 3000 sccm, an oxygen flow rate of 0 to 3000 sccm, and a pressure of 120 to 180 mbar.

[0016] Optionally, before pushing the silicon wafer at a temperature of 850-950° C., the method further comprises:

[0017] The silicon wafer after the secondary deposition process is purged under the conditions of a temperature of 850-950° C., a nitrogen flow rate of 100-800 sccm, and a pressure of 120-180 mbar.

[0018] Optionally, before performing a secondary deposition process on the silicon wafer, the method further includes:

[0019] Under the conditions of a nitrogen flow rate of 2000-3000 sccm and a pressure of 120-180 mbar, the silicon wafer after the pre-deposition treatment is heated to 840-900° C.

[0020] Optionally, in the diffusion method, the boron source includes at least one of boron tribromide and boron trichloride.

[0021] Optionally, before performing pre-oxidation treatment on the silicon wafer, the method further comprises:

[0022] The diffusion furnace is evacuated while controlling the temperature of the diffusion furnace to 750-860° C. and the pressure to 100-200 mbar.

[0023] Optionally, after the silicon wafer is pushed, the method further comprises:

[0024] After the diffusion furnace is controlled to cool to 850-880° C., nitrogen is introduced into the diffusion furnace, and when the internal and external gas pressures are the same, the silicon wafer with the boron diffusion layer formed thereon is taken out.

[0025] Optionally, in the diffusion method, in the process of controlling the diffusion furnace to cool down to 850-880° C., the nitrogen flow rate is 8000-15000 sccm, and the pressure is controlled to be 500-800 mbar.

[0026] The present application also provides a solar cell, comprising a silicon substrate having a first surface and a second surface arranged opposite to each other;

[0027] A diffusion layer, formed by the above diffusion method, located on the first surface and sharing the same top surface with the first surface;

[0028] A passivation layer, disposed on the diffusion layer;

[0029] The anti-reflection layer is disposed on the passivation layer.

[0030] Optionally, in the solar cell, the sheet resistance of the diffusion layer is 150-200Ω / sq.

[0031] Optionally, in the solar cell, along the thickness direction of the silicon substrate, the width of the diffusion layer is 0.65-0.85 um.

[0032] Optionally, in the solar cell, the boron doping concentration on the surface of the diffusion layer is (1E+18) / cm 3 ~(4.0E+20) / cm 3 .

[0033] Compared with the prior art, this application has the following advantages:

[0034] In the diffusion method provided in the present application, a silicon wafer is first placed in a diffusion furnace, and a pre-oxidation treatment is performed on the silicon wafer for 200 to 240 seconds at a temperature of 820 to 840°C, an oxygen flow rate of 200 to 500 sccm, and a nitrogen flow rate of 2000 to 3000 sccm; then, a pre-deposition treatment is performed on the silicon wafer for 100 to 160 seconds at a temperature of 750 to 860°C, a boron source flow rate of 1:3 to 1:4, and then, a pre-deposition treatment is performed on the silicon wafer for 100 to 160 seconds at a temperature of 840 to 900°C, a boron source flow rate of 1:3 to 1:4, and a nitrogen flow rate of 200 to 3000 sccm. Under the conditions of the above-mentioned pre-oxidation treatment, the silicon wafer is subjected to a secondary deposition treatment for 120-140s; finally, the silicon wafer is subjected to a push-junction treatment at a temperature of 850-950°C to obtain a boron diffusion layer; wherein, through the combined effects of the above-mentioned pre-oxidation treatment, pre-deposition, secondary deposition and push-junction treatment, the doping concentration of the boron source can be reduced, the diffusion is uniform, and the diffusion square resistance is increased, and the PN junction distribution becomes shallower, which effectively improves the dead layer caused by the excessive depth of the PN junction in the existing boron diffusion process, the dark aggregation of the recombination center, and the low current and voltage, thereby improving the open circuit voltage, short circuit current and photoelectric conversion efficiency of the battery cell.

[0035] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a diffusion method according to an embodiment of the present application;

[0037] Figure 2 Schematic diagram for comparing the ECV characterization data of Example 1 and Comparative Example 1 in the present application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0039] It should be understood that the references to "one embodiment" or "an embodiment" throughout the specification mean that the specific features, structures, or characteristics associated with the embodiment are included in at least one embodiment of the present application. Therefore, the references to "in one embodiment" or "in an embodiment" appearing throughout the specification do not necessarily refer to the same embodiment. In addition, these specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0040] At present, the main process of boron diffusion is as follows: ①, placing the silicon wafer in a diffusion furnace, heating it to the range of 800-830℃, introducing oxygen into the diffusion furnace to grow a silicon dioxide layer; ②, low-temperature source deposition process, that is, diffusion is carried out at the temperature of step ①; ③, heating process, that is, raising the temperature in the diffusion furnace to a temperature in the range of 870~900℃; ④, high-temperature promotion process, that is, maintaining the temperature after heating in step ③, and introducing oxygen to promote the boron deposited in step ③ to further diffuse into the silicon wafer.

[0041] However, the diffusion layer obtained by the above diffusion process has a low center resistance value (as low as 120Ω) and a high surface concentration (4.5E+20 / cm 3 ) and the PN junction is deep (up to 0.9um), which is a PN junction type with high surface concentration and deep junction, which makes its carrier Auger recombination larger and the minority carrier transmission distance longer, resulting in lower open circuit voltage Voc and short circuit current Isc of the battery, thus affecting the photoelectric conversion efficiency.

[0042] In view of the above problems, the present application provides a diffusion method, such as Figure 1 As shown, it includes steps 101 to 104:

[0043] Step 101, placing a silicon wafer in a diffusion furnace, and performing a pre-oxidation treatment on the silicon wafer for 200-240 seconds under the conditions of a temperature of 820-840° C., an oxygen flow rate of 200-500 sccm, and a nitrogen flow rate of 2000-3000 sccm.

[0044] In this step, the silicon wafer is placed under the conditions of a temperature of 820-840°C, an oxygen flow rate of 200-500sccm, and a nitrogen flow rate of 2000-3000sccm for 200-240s, which can generate a silicon dioxide layer of moderate thickness. The silicon dioxide layer has a masking effect, which can block the effective diffusion of the boron source, achieve the effect of shallow junction, and make the boron source advance more uniformly. The shallow junction direction is clearer, which can improve the uniformity of boron diffusion resistance. At the same time, the PN junction distribution becomes shallower, and the diffusion resistance increases, thereby improving the conversion efficiency.

[0045] The silicon wafer may be an N-type silicon wafer or a P-type silicon wafer.

[0046] Step 102: After the pre-oxidation treatment, the silicon wafer is subjected to a pre-deposition treatment for 100 to 160 seconds at a temperature of 750 to 860° C. and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4.

[0047] In this step, at a temperature of 750-860°C, the boron source and oxygen are introduced at a ratio of 1:3-1:4 for 100-160 seconds, which not only enables effective pre-deposition of the silicon wafer, but also has a low boron source content and a short pre-deposition treatment time, and low surface Auger recombination, which can ensure the doping effect. Further, at a temperature of 820-840°C, the boron source and oxygen are introduced at a ratio of 1:3-1:4 for 120-140 seconds for the above pre-deposition treatment, and the pre-deposition effect is particularly good.

[0048] Wherein, the boron source includes at least one of boron tribromide and boron trichloride.

[0049] Optionally, in one embodiment, the oxygen flow rate of the pre-deposition treatment is 480-510 sccm, and the boron source flow rate is 160-180 sccm, which can effectively reduce the boron doping concentration formed by pre-deposition in the silicon wafer while ensuring doping uniformity, so that the SE post-doping effect is more sufficient. For example, the oxygen flow rate of the pre-deposition treatment can be one of 480 sccm, 490 sccm, 500 sccm, 510 sccm, or a range value between any two of them, and the boron source flow rate can be one of 160 sccm, 170 sccm, 180 sccm, or a range value between any two of them.

[0050] Step 103 , after the pre-deposition treatment, the silicon wafer is subjected to a secondary deposition treatment for 100 to 160 seconds at a temperature of 840 to 900° C. and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4.

[0051] In this step, at a temperature of 840-900°C, a boron source and oxygen are introduced at a ratio of 1:3-1:4 to oxygen flow and continued for 100-160 seconds, thereby performing a secondary deposition treatment on the silicon wafer, wherein the boron source content is low and the pre-deposition treatment time is short, which can effectively reduce the surface Auger recombination, improve the doping effect, increase Uoc, and improve the photoelectric conversion efficiency. Further, at a temperature of 860-880°C, a boron source and oxygen are introduced at a ratio of 1:3-1:4 to oxygen flow and continued for 120-140 seconds for the above-mentioned secondary deposition treatment, and the secondary deposition effect is particularly good.

[0052] Wherein, the boron source includes at least one of boron tribromide and boron trichloride.

[0053] Optionally, in one embodiment, the oxygen flow rate of the secondary deposition process is 480-510sccm, and the boron source flow rate is 160-180sccm, which can effectively reduce the doping concentration of boron in boron diffusion while ensuring doping uniformity. For example, the oxygen flow rate of the secondary deposition process can be one of 480sccm, 490sccm, 500sccm, 510sccm, or a range value between any two of them, and the boron source flow rate can be one of 160sccm, 170sccm, 180sccm, or a range value between any two of them.

[0054] In this step, since the diffusion coefficient of boron atoms in silicon is low, a better doping curve can be obtained by depositing at a temperature of 840-900°C for 100-160s.

[0055] Step 104: After the secondary deposition process, the silicon wafer is subjected to push bonding at a temperature of 850-950° C. to obtain a boron diffusion layer.

[0056] In this step, by pushing the silicon wafer at a temperature of 850-950°C, the boron oxide deposited on the surface of the silicon wafer can react with silicon to generate B atoms and silicon oxide, and the B atoms expand inward to form P-type silicon, further promoting activation to reach the target junction depth. The generated oxide layer has an adsorption effect on the boron on the surface of the silicon wafer, which reduces the surface concentration and the dead layer. At the same time, the oxide layer also acts as a mask in other process routes and can protect the PN junction. Further, pushing the silicon wafer at a temperature of 870-925°C can better achieve the effect of reducing the surface concentration, reducing the dead layer and protecting the PN junction.

[0057] In the embodiments of the present application, through the combined effects of the above-mentioned pre-oxidation treatment, pre-deposition, secondary deposition and junction pushing treatment, the doping concentration of the boron source can be reduced, the diffusion can be uniform, and the diffusion square resistance can be increased. At the same time, the PN junction distribution becomes shallower, which effectively improves the dead layer caused by the excessive depth of the PN junction in the existing boron diffusion process, the dark aggregation of the recombination center, and the low current and voltage, thereby improving the open circuit voltage, short circuit current and photoelectric conversion efficiency of the battery cell.

[0058] The sheet resistance of the diffusion layer is 150~200Ω / sq.

[0059] Along the thickness direction of the silicon substrate, the width of the diffusion layer is 0.65-0.85 um.

[0060] The boron doping concentration on the surface of the diffusion layer is (3.4E+20) / cm 3 ~(4.0E+20) / cm 3 .

[0061] Optionally, in one embodiment, the silicon wafer is pushed at a temperature of 850-950° C., comprising:

[0062] The process is carried out for 3 to 10 minutes at a temperature of 870 to 925°C, a nitrogen flow rate of 1000 to 3000 sccm, an oxygen flow rate of 0 to 3000 sccm, and a pressure of 120 to 180 mbar.

[0063] In this embodiment, under the condition of temperature of 870~925°C, nitrogen is introduced at a flow rate of 1000~3000sccm and oxygen is introduced at a flow rate of 0~3000sccm, and the system pressure is controlled to be 120~180mbar, and then the junction is pushed continuously for 3~10min. This can not only generate an oxide layer of sufficient thickness by oxidizing the silicon wafer with oxygen at high temperature to adsorb boron on the surface of the silicon wafer, but also effectively push the B atoms further into the silicon wafer to a suitable target junction depth.

[0064] Among them, the temperature during the pushing process can be one of 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 925℃ or a range value between any two of them, the nitrogen flow rate can be one of 1000, 1500sccm, 2000sccm, 2500sccm, 3000sccm or a range value between any two of them, the oxygen flow rate can be one of 100sccm, 600sccm, 1000sccm, 2000sccm, 3000sccm or a range value between any two of them, the pressure can be one of 120mbar, 130mbar, 140mbar, 150mbar, 160mbar, 170mbar, 180mbar or a range value between any two of them, and the pushing time can be one of 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min or a range value between any two of them.

[0065] Optionally, in one implementation, before the above step 104, the method provided in the embodiment of the present application further includes step 141:

[0066] Step 141, purging the silicon wafer after the high temperature deposition treatment under the conditions of a temperature of 850-950°C, a nitrogen flow rate of 100-800 sccm, and a pressure of 120-180 mbar.

[0067] In this embodiment, the pressure in the furnace is controlled to be 120-180 mbar at a temperature of 850-950°C, and nitrogen gas with a flow rate of 100-800 sccm is introduced, so that the surface of the silicon wafer after the secondary deposition process can be cleaned with nitrogen gas to ensure the cleanliness of the tube. Furthermore, the silicon wafer after the high-temperature deposition process is purged at a temperature of 870-925°C to better achieve the cleanliness of the tube.

[0068] Among them, the low-pressure environment of 120~180mbar requires only a small nitrogen flow rate to achieve the cleaning process requirements, reducing gas usage costs and environmental pollution.

[0069] Optionally, in one implementation, before the above step 103, the method provided in the embodiment of the present application further includes step 131:

[0070] Step 131, under the conditions of a nitrogen flow rate of 2000-3000 sccm and a pressure of 120-180 mbar, heating the silicon wafer after the pre-deposition treatment to 840-900°C.

[0071] In this embodiment, after the pre-deposition treatment, nitrogen gas with a flow rate of 2000-3000 sccm is introduced and the pressure is controlled to 120-180 mbar and the temperature is raised to 840-900°C to facilitate secondary boron deposition. The above heating method can effectively protect the silicon wafer from reacting with oxygen or boron source during the heating process by nitrogen, thereby affecting the overall uniformity of doping. Further, the silicon wafer after the pre-deposition treatment is heated to 860-880°C to facilitate better secondary boron deposition.

[0072] Optionally, in one implementation, before the silicon wafer is subjected to pre-oxidation treatment, the diffusion method provided in the embodiment of the present application further includes step 100:

[0073] Step 100, the diffusion furnace is evacuated under the condition of controlling the temperature of the diffusion furnace to 820-840°C and the pressure to 100-200 mbar.

[0074] In this embodiment, before pre-oxidation, the diffusion furnace is first evacuated, specifically by heating to 820-840°C and evacuating to 100-200 mbar to remove impurities such as water vapor in the diffusion furnace, thereby facilitating subsequent pre-oxidation of the silicon wafer with oxygen.

[0075] The above-mentioned temperature increase process can be performed by gradient temperature increase with the same or different temperature differences.

[0076] In actual operation, during the emptying process, the diaphragm pump can be turned on first and the diffusion furnace can be evacuated to 600~800mbar, then the temperature can be raised to 820~840℃, and then the vacuum can be continued to be evacuated to 100~200mbar to complete the above emptying process.

[0077] In the embodiment of the present application, before the above-mentioned emptying process is performed, it is necessary to open the furnace door and send the graphite boat carrying the silicon wafer after texturing into the diffusion furnace and then close the furnace door.

[0078] During the process of opening the furnace door, the temperature is set at 780~820℃, the nitrogen flow rate is 3000~5000sccm, the pressure is controlled to be normal pressure such as 850mbar, and the duration is 5~15s.

[0079] During the boat entry process, the temperature was set at 820~840°C, the nitrogen flow rate was 3000~5000sccm, the pressure was controlled at normal pressure, and the duration was 7~10 minutes.

[0080] Optionally, in one implementation, after the diffusion furnace is evacuated and before the silicon wafer is pre-oxidized, the diffusion method provided in the embodiment of the present application further includes step 110:

[0081] Step 110: Perform vacuum leak detection on the diffusion furnace.

[0082] In this embodiment, after the diffusion furnace is evacuated, the diaphragm pump is closed while the temperature of the diffusion furnace is maintained at 820-840°C, and the pressure in the diffusion furnace is maintained at 100-200 mbar for 0.5-5 minutes for leak detection. That is, the airtightness of the diffusion furnace can be confirmed by simulating the low-pressure environment of subsequent deposition processing.

[0083] Optionally, in one implementation, after the silicon wafer is pushed, the diffusion method provided in the embodiment of the present application further includes step 105:

[0084] Step 105 , after controlling the temperature of the diffusion furnace to drop to 850-880° C., nitrogen is introduced into the diffusion furnace, and when the internal and external air pressures are the same, the silicon wafer with the boron diffusion layer formed thereon is taken out.

[0085] In this embodiment, after completing the push-bonding of the quartz boat after the secondary deposition treatment, the temperature of the diffusion furnace is first controlled to drop to 850~880°C, and then nitrogen and other protective gases are introduced to control the back pressure of the diffusion furnace to reach the external air pressure, and then the furnace door is opened to end the diffusion treatment process, thereby obtaining a silicon wafer with a boron diffusion layer.

[0086] Optionally, in a specific embodiment, 5000-20000 sccm nitrogen can be introduced and the pressure in the diffusion furnace can be controlled to normal pressure, such as 850 mbar, so that the furnace reaches the external pressure to open the furnace door and remove the boat, and then the diffusion process can be terminated.

[0087] Optionally, in a specific implementation, in the process of controlling the diffusion furnace to cool down to 850-880° C., the nitrogen flow rate is 8000-15000 sccm, and the pressure is controlled to be 500-800 mbar.

[0088] In this specific embodiment, during the cooling process, nitrogen gas with a flow rate of 8000-15000sccm is continuously introduced to maintain the pressure in the furnace at a low pressure state of 500-800mbar, which can not only achieve cooling treatment to facilitate subsequent boat unloading, but also clean the diffusion furnace and silicon wafers.

[0089] Optionally, the temperature of the diffusion furnace may be controlled to drop to one of 850° C., 860° C., 870° C., 880° C., or a range between any two of them.

[0090] The embodiment of the present application also provides a solar cell, comprising a silicon substrate, wherein the silicon substrate has a first surface and a second surface arranged opposite to each other;

[0091] A diffusion layer, formed by the above diffusion method, located on the first surface and sharing the same top surface with the first surface;

[0092] A passivation layer is disposed on the diffusion layer;

[0093] The anti-reflection layer is disposed on the passivation layer.

[0094] In the embodiment of the present application, the above-mentioned diffusion layer is formed by the above-mentioned diffusion method, and the above-mentioned diffusion method can improve the uniformity of boron source doping and the uniformity of boron diffusion resistance by increasing the oxygen front shorter, and make the PN junction distribution shallower and the diffusion resistance higher; at the same time, in the above-mentioned diffusion method, the source conduction time is short and the flow rate is small, so that the surface Auger recombination is reduced, and the doping effect is further improved, thereby increasing the open circuit voltage and improving the photoelectric conversion efficiency; in addition, in the above-mentioned diffusion method, the junction pushing temperature is low, which can reduce the surface dead layer and reduce recombination, so that the open circuit voltage and short circuit current of the battery cell are effectively improved, thereby improving the photoelectric conversion efficiency of the battery cell.

[0095] Optionally, in the embodiment of the present application, the boron doping concentration on the surface of the diffusion layer is (1E+18) / cm 3 ~(4.0E+20) / cm 3 .

[0096] Furthermore, the boron doping concentration on the surface of the diffusion layer is (3.4E+20) / cm3~(4.0E+20) / cm3.

[0097] In the embodiment of the present application, the sheet resistance of the diffusion layer is 150-200Ω / sq. Through the diffusion method, the sheet resistance of the diffusion layer in the embodiment of the present application is increased to 150-200Ω / sq, for example, it can be one of 150Ω / sq, 160Ω / sq, 170Ω / sq, 180Ω / sq, 190Ω / sq, 200Ω / sq or any range between two values.

[0098] In the embodiment of the present application, the width of the diffusion layer along the thickness direction of the silicon substrate is 0.65~0.85 um, that is, the PN junction depth is 0.65~0.85 um, for example, it is a range value between one of 0.65 um, 0.66 um, 0.7 um, 0.8 um, 0.85 um or any two thereof.

[0099] For the above solar cell embodiment, it includes a diffusion layer, and the above diffusion layer is processed by the above diffusion method and can achieve the same technical effect. In order to avoid repetition, it will not be described here. For relevant parts, please refer to the partial description of the diffusion method embodiment.

[0100] The present application is described in detail below through examples.

[0101] Example 1

[0102] (1) Open the furnace door: set the temperature to 800°C, the nitrogen flow rate to 4000sccm, the atmospheric pressure to 850mbar, and the time to 10s;

[0103] (2) Loading the boat: Load the texturized silicon wafer into the diffusion furnace, set the temperature to 830°C, introduce nitrogen at a flow rate of 4000sccm, and maintain the pressure at 850mbar for 9 minutes;

[0104] (3) Vacuuming: Evacuate the diffusion furnace to 700 mbar, turn on the diaphragm pump, and reduce the tube pressure from 860 mbar to 700 mbar in preparation for the next step;

[0105] (4) Heating and decompression: Heating to 830°C and continuing to evacuate until the pressure in the diffusion furnace tube reaches 140 mbar;

[0106] (5) Constant temperature: The temperature is maintained at 830°C and the constant pressure is ensured at 140 mbar;

[0107] (6) Leak detection: The pressure is maintained at 140 mbar, the diaphragm pump is turned off, and the leak detection process is carried out. The specific pressure change in the furnace tube within one minute;

[0108] (7) Pre-oxidation: The silicon wafer was pre-oxidized for 220 seconds at a temperature of 830°C, an oxygen flow rate of 300 sccm, and a nitrogen flow rate of 2500 sccm;

[0109] (8) Pre-deposition: The temperature was maintained at 830 °C, while oxygen (600 sccm), BCl3 (200 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 140 mbar;

[0110] (9) Heating: The temperature was raised to 870 °C, the nitrogen flow rate was 2500 sccm, and the pressure was controlled at 140 mbar;

[0111] (10) Secondary deposition: The temperature was maintained at 870 °C, while oxygen (600 sccm), BCl3 (200 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 140 mbar;

[0112] (11) Heating and purging: The temperature was raised to 900 °C, nitrogen was introduced at a flow rate of 500 sccm, and the pressure was controlled at 140 mbar;

[0113] (12) Temperature push-in: Push-in for 6.7 min at a temperature of 900 °C, a nitrogen flow rate of 2000 sccm, an oxygen flow rate of 2000 sccm, and a pressure of 140 mbar;

[0114] (13) Constant temperature push-in: the temperature is maintained at 900 °C, the nitrogen flow rate is 2000 sccm, and the pressure is set to 140 mbar;

[0115] (14) Cooling: The temperature was lowered to 860 °C, the nitrogen flow rate was 10000 sccm, the pressure was increased to 700 mbar, and maintained for 20 min;

[0116] (15) Back-pressure: The nitrogen flow rate is 18000 sccm, the pressure rises to normal pressure 850 mbar, and is maintained for 2 min;

[0117] (16) Exiting the boat: The nitrogen flow rate is 1000 sccm, the pressure is maintained at 850 mbar, and the time lasts for 8 min;

[0118] (17) End the process.

[0119] The above-mentioned Example 1 was repeated to obtain 6 silicon wafers with boron diffusion layers.

[0120] Example 2

[0121] (1) Open the furnace door: set the temperature to 800°C, the nitrogen flow rate to 4000sccm, the atmospheric pressure to 850mbar, and the time to 10s;

[0122] (2) Loading the boat: Load the texturized silicon wafer into the diffusion furnace, set the temperature to 820°C, introduce nitrogen at a flow rate of 4000sccm, and maintain the pressure at 850mbar for 7 minutes;

[0123] (3) Vacuuming: Evacuate the diffusion furnace to 700 mbar, turn on the diaphragm pump, and reduce the tube pressure from 860 mbar to 700 mbar in preparation for the next step;

[0124] (4) Heating and decompression: Heating to 820°C and continuing to evacuate until the pressure in the diffusion furnace tube reaches 120 mbar;

[0125] (5) Constant temperature: The temperature is maintained at 820°C and the constant pressure is ensured at 120 mbar;

[0126] (6) Leak detection: Maintain the pressure at 120 mbar, turn off the diaphragm pump, and perform the leak detection process. The specific pressure change in the furnace tube within one minute;

[0127] (7) Pre-oxidation: The silicon wafer was pre-oxidized for 200 s at a temperature of 820 °C, an oxygen flow rate of 200 sccm, and a nitrogen flow rate of 2000 sccm;

[0128] (8) Pre-deposition: The temperature was maintained at 820 °C, while oxygen (480 sccm), BCl3 (160 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 120 mbar;

[0129] (9) Heating: The temperature was raised to 860 °C, the nitrogen flow rate was 2500 sccm, and the pressure was controlled at 120 mbar;

[0130] (10) Secondary deposition: The temperature was maintained at 860 °C, while oxygen (480 sccm), BCl3 (160 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 120 mbar;

[0131] (11) Heating and purging: the temperature was raised to 870 °C, nitrogen was introduced at a flow rate of 100 sccm, and the pressure was controlled at 120 mbar;

[0132] (12) Temperature rise and push-in: push-in for 3 min at a temperature of 870 °C, a nitrogen flow rate of 2000 sccm, an oxygen flow rate of 100 sccm, and a pressure of 120 mbar;

[0133] (13) Constant temperature push-in: the temperature is maintained at 870 °C, the nitrogen flow rate is 2000 sccm, and the pressure is set to 120 mbar;

[0134] (14) Cooling: The temperature was lowered to 850 °C, the nitrogen flow rate was 10000 sccm, the pressure was increased to 700 mbar, and maintained for 20 min;

[0135] (15) Back-pressure: The nitrogen flow rate is 18000 sccm, the pressure rises to normal pressure 850 mbar, and is maintained for 2 min;

[0136] (16) Exiting the boat: The nitrogen flow rate is 1000 sccm, the pressure is maintained at 850 mbar, and the time lasts for 5 min;

[0137] (17) End the process.

[0138] The above-mentioned Example 2 was repeated to obtain 6 silicon wafers with boron diffusion layers.

[0139] Example 3

[0140] (1) Open the furnace door: set the temperature to 800°C, the nitrogen flow rate to 4000sccm, the atmospheric pressure to 850mbar, and the time to 10s;

[0141] (2) Loading the boat: Load the texturized silicon wafer into the diffusion furnace, set the temperature to 840°C, introduce nitrogen at a flow rate of 4000sccm, and maintain the pressure at 850mbar for 10 minutes;

[0142] (3) Vacuuming: Evacuate the diffusion furnace to 700 mbar, turn on the diaphragm pump, and reduce the tube pressure from 860 mbar to 700 mbar in preparation for the next step;

[0143] (4) Heating and decompression: Heating to 840°C and continuing to evacuate until the pressure in the diffusion furnace tube reaches 180 mbar;

[0144] (5) Constant temperature: The temperature is maintained at 840°C and the constant pressure is ensured at 180 mbar;

[0145] (6) Leak detection: The pressure is maintained at 180 mbar, the diaphragm pump is turned off, and the leak detection process is carried out. The specific pressure change in the furnace tube within one minute;

[0146] (7) Pre-oxidation: The silicon wafer was pre-oxidized for 240 seconds at a temperature of 840°C, an oxygen flow rate of 500 sccm, and a nitrogen flow rate of 3000 sccm;

[0147] (8) Pre-deposition: The temperature was maintained at 840 °C, while oxygen (510 sccm), BCl3 (180 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 180 mbar;

[0148] (9) Heating: The temperature was raised to 880 °C, the nitrogen flow rate was 2500 sccm, and the pressure was controlled at 180 mbar;

[0149] (10) Secondary deposition: The temperature was maintained at 860 °C, while oxygen (510 sccm), BCl3 (180 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 180 mbar;

[0150] (11) Heating and purging: The temperature was raised to 925 °C, nitrogen was introduced at a flow rate of 800 sccm, and the pressure was controlled at 180 mbar;

[0151] (12) Temperature rise and push-in: push-in for 10 min at a temperature of 925 °C, a nitrogen flow rate of 3000 sccm, an oxygen flow rate of 3000 sccm, and a pressure of 180 mbar;

[0152] (13) Constant temperature push-in: the temperature is maintained at 925 °C, the nitrogen flow rate is 3000 sccm, and the pressure is set to 180 mbar;

[0153] (14) Cooling: The temperature was lowered to 880 °C, the nitrogen flow rate was 10000 sccm, the pressure was increased to 700 mbar, and maintained for 20 min;

[0154] (15) Inflation back pressure: The nitrogen flow rate is 18000sccm, the pressure rises to normal pressure 850mbar, and is maintained for 2min;

[0155] (16) Exiting the boat: The nitrogen flow rate is 1000 sccm, the pressure is maintained at 850 mbar, and the time lasts for 10 min;

[0156] (17) The process is completed to obtain a silicon wafer having a boron diffusion layer.

[0157] The above-mentioned Example 3 was repeated to obtain 6 silicon wafers with boron diffusion layers.

[0158] Comparative Example 1

[0159] (1) Open the furnace door: set the temperature to 800°C, the nitrogen flow rate to 4000sccm, the atmospheric pressure to 850mbar, and the time to 10s;

[0160] (2) Loading the boat: Load the texturized silicon wafer into the diffusion furnace, set the temperature to 840°C, introduce nitrogen at a flow rate of 4000sccm, and maintain the pressure at 850mbar for 10 minutes;

[0161] (3) Vacuuming: Evacuate the diffusion furnace to 700 mbar, turn on the diaphragm pump, and reduce the tube pressure from 860 mbar to 700 mbar in preparation for the next step;

[0162] (4) Heating and decompression: Heating to 840°C and continuing to evacuate until the pressure in the diffusion furnace tube reaches 140 mbar;

[0163] (5) Heating: Maintain the temperature at 840°C and ensure constant pressure at 180 mbar;

[0164] (6) Leak detection: Set the pressure to 500 mbar, turn off the diaphragm pump, and perform the leak detection process. The specific pressure change in the furnace tube within one minute;

[0165] (7) Heating: Under the conditions of temperature of 840°C, oxygen flow rate of 0 sccm, and nitrogen flow rate of 3100 sccm, the remaining gases in the chamber are evacuated;

[0166] (8) Pre-deposition: The temperature was maintained at 840 °C, while oxygen (600 sccm), BCl3 (200 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 180 mbar;

[0167] (9) Heating: The temperature was raised to 880 °C, the nitrogen flow rate was 2500 sccm, and the pressure was controlled at 180 mbar;

[0168] (10) Secondary deposition: The temperature was maintained at 880 °C, while oxygen (600 sccm), BCl3 (200 sccm) and nitrogen (2600 sccm) were introduced, and the pressure was maintained at 180 mbar;

[0169] (11) Heating and purging: the temperature was raised to 925 °C, nitrogen was introduced at a flow rate of 2000 sccm, and the pressure was controlled at 180 mbar;

[0170] (12) Temperature rise and push-in: push-in for 10 min at a temperature of 925 °C, a nitrogen flow rate of 3000 sccm, an oxygen flow rate of 3000 sccm, and a pressure of 180 mbar;

[0171] (13) Constant temperature push-in: the temperature is maintained at 925 °C, the nitrogen flow rate is 3000 sccm, and the pressure is set to 180 mbar;

[0172] (14) Cooling: The temperature was lowered to 880 °C, the nitrogen flow rate was 10000 sccm, the pressure was increased to 700 mbar, and maintained for 20 min;

[0173] (15) Inflation back pressure: The nitrogen flow rate is 18000sccm, the pressure rises to normal pressure 850mbar, and is maintained for 2min;

[0174] (16) Exiting the boat: The nitrogen flow rate is 1000 sccm, the pressure is maintained at 850 mbar, and the time lasts for 10 min;

[0175] (17) The process is completed to obtain a silicon wafer having a boron diffusion layer.

[0176] The above comparative example 1 was repeated to obtain 6 silicon wafers with boron diffusion layers.

[0177] Sheet resistance tests were performed on different parts of the boron diffusion layer formed in each embodiment and comparative example, and boron doping concentration tests were performed on different parts of the boron diffusion layer formed in one of the embodiments and comparative examples. The results are shown in Table 1.

[0178] The silicon wafers formed with the boron diffusion layer in each embodiment and comparative example are subjected to SE treatment (i.e., heavily doped at the contact portion between the metal gate line and the silicon wafer, and lightly doped at the position between the electrodes), and then subjected to texturing, boron diffusion, SE, removal of the borosilicate glass layer (BSG), alkali polishing, low-pressure chemical vapor deposition (LPCVD), phosphorus diffusion, removal of the phosphorus silicon glass layer (PSG), de-coating, front atomic layer deposition (ALD), coating, printing, light injection, and testing to manufacture an N-type TOPCon cell;

[0179] Among them, the sheet resistance and boron doping concentration of the boron diffusion layer after SE were tested, and the results are shown in Table 1;

[0180] In addition, the boron diffusion layer in Example 1 and Comparative Example 1 was subjected to ECV characterization, and the results are as follows: Figure 2 As shown; wherein a represents the surface concentration curve of the boron diffusion layer in comparative example 1, and b represents the surface concentration curve of the boron diffusion layer in embodiment 1.

[0181] In addition, the electrical performance of each battery was tested and the average value was calculated. The results are shown in Table 2.

[0182] Table 1

[0183]

[0184] Table 2

[0185]

[0186] Based on the comparison of each embodiment and comparative example 1 in Table 1 and Table 2, it can be seen that by adopting the diffusion method of the embodiment of the present application, compared with comparative example 1, the measured square resistance of the boron diffusion layer can reach 182.78Ω, so that the Voc of the solar cell is increased by up to 2.8mV, the short-circuit current is increased by up to 31mA, and the fill factor is increased by up to 0.2%, so that the photoelectric conversion efficiency is increased to 26.245%. It can be seen that the square resistance of the boron diffusion layer and the photoelectric conversion efficiency of the solar cell are greatly improved.

[0187] In addition, based on Figure 2 By comparing Example 1 with Comparative Example 1, it can be seen that by adopting the diffusion method of the embodiment of the present application, the boron doping concentration decreases and the PN junction depth becomes shallower.

[0188] In summary, in this embodiment, the silicon wafer is first placed in a diffusion furnace, and the silicon wafer is pre-oxidized for 200 to 240 seconds at a temperature of 820 to 840°C, an oxygen flow rate of 200 to 500 sccm, and a nitrogen flow rate of 2000 to 3000 sccm; then, the silicon wafer is pre-deposited for 100 to 160 seconds at a temperature of 750 to 860°C, a boron source flow rate of 1:3 to 1:4, and then, the silicon wafer is pre-deposited for 100 to 160 seconds at a temperature of 840 to 900°C, a boron source flow rate of 1:3 to 1:4. The silicon wafer is subjected to secondary deposition treatment for 100-160s; finally, the silicon wafer is subjected to push-junction treatment at a temperature of 850-950°C to obtain a boron diffusion layer; wherein, through the combined effects of the above-mentioned pre-oxidation treatment, pre-deposition, secondary deposition and push-junction treatment, the doping concentration of the boron source can be reduced, the diffusion is uniform, and the diffusion square resistance is increased, while the PN junction distribution becomes shallower, effectively improving the dead layer caused by the excessive depth of the PN junction in the existing boron diffusion process, the dark aggregation of the recombination center, and the low current and voltage, thereby improving the open circuit voltage, short circuit current and photoelectric conversion efficiency of the battery cell.

[0189] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0190] Although the optional embodiments of the present application 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 optional embodiments and all changes and modifications that fall within the scope of the present application.

[0191] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity from another entity, and do not necessarily require or imply any such actual relationship or order between these entities. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that an article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or terminal device. In the absence of further restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the article or terminal device including the elements.

[0192] The technical solution provided by the present application is introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. At the same time, for those skilled in the art, according to the principles and implementation methods of the present application, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A diffusion method, characterized in that: include: Placing the silicon wafer in a diffusion furnace, and performing a pre-oxidation treatment on the silicon wafer for 200 to 240 seconds under the conditions of a temperature of 820 to 840° C., an oxygen flow rate of 200 to 500 sccm, and a nitrogen flow rate of 2000 to 3000 sccm; After the pre-oxidation treatment, the silicon wafer is subjected to a pre-deposition treatment for 100 to 160 seconds at a temperature of 750 to 860° C. and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4; After the pre-deposition treatment, the silicon wafer is subjected to a secondary deposition treatment for 120 to 140 seconds at a temperature of 860 to 880° C. and a ratio of a boron source flow rate to an oxygen flow rate of 1:3 to 1:4; After the secondary deposition process, the silicon wafer is pushed and bonded at a temperature of 850-950° C. to obtain a boron diffusion layer.

2. The diffusion method according to claim 1, characterized in that: The oxygen flow rate for pre-deposition treatment is 480~510sccm, and the boron source flow rate is 160~180sccm; The secondary deposition oxygen flow rate is 480~510sccm and the boron source flow rate is 160~180sccm.

3. The diffusion method according to claim 1, characterized in that: The silicon wafer is subjected to push-junction at a temperature of 850-950° C., comprising: The process is carried out for 3 to 10 minutes at a temperature of 870 to 925°C, a nitrogen flow rate of 1000 to 3000 sccm, an oxygen flow rate of 0 to 3000 sccm, and a pressure of 120 to 180 mbar.

4. The diffusion method according to claim 1, characterized in that: Before pushing the silicon wafer under the temperature condition of 850-950° C., the method further comprises: The silicon wafer after the secondary deposition process is purged under the conditions of a temperature of 850-950° C., a nitrogen flow rate of 100-800 sccm, and a pressure of 120-180 mbar.

5. The diffusion method according to claim 1, characterized in that: Before performing a secondary deposition process on the silicon wafer, the method further comprises: Under the conditions of a nitrogen flow rate of 2000-3000 sccm and a pressure of 120-180 mbar, the silicon wafer after the pre-deposition treatment is heated to 840-900° C.

6. The diffusion method according to claim 1, characterized in that: The boron source includes at least one of boron tribromide and boron trichloride.

7. The diffusion method according to any one of claims 1 to 6, characterized in that: Before performing pre-oxidation treatment on the silicon wafer, the method further comprises: The diffusion furnace is evacuated while controlling the temperature of the diffusion furnace to 820-840° C. and the pressure to 100-200 mbar.

8. The diffusion method according to claim 1, characterized in that: After the silicon wafer is pushed, the method further comprises: After the diffusion furnace is controlled to cool to 850-880° C., nitrogen is introduced into the diffusion furnace, and when the internal and external gas pressures are the same, the silicon wafer with the boron diffusion layer formed thereon is taken out.

9. The diffusion method according to claim 8, characterized in that: In the process of controlling the diffusion furnace to cool down to 850-880° C., the nitrogen flow rate is 8000-15000 sccm, and the pressure is controlled to be 500-800 mbar.

10. A solar cell, characterized in that: The silicon substrate comprises a first surface and a second surface which are arranged opposite to each other; a diffusion layer, formed by the diffusion method according to claim 1, located on the first surface and sharing the same top surface with the first surface; A passivation layer, disposed on the diffusion layer; The anti-reflection layer is disposed on the passivation layer.

11. The solar cell according to claim 10, characterized in that The sheet resistance of the diffusion layer is 150-200Ω / sq.

12. The solar cell according to claim 10, characterized in that: Along the thickness direction of the silicon substrate, the width of the diffusion layer is 0.65-0.85 um.

13. The solar cell according to claim 10, characterized in that: The boron doping concentration on the surface of the diffusion layer is (1E+18) / cm 3 ~(4.0E+20) / cm 3 .

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