Ultrahigh sheet resistance diffusion process for solar single-crystal efficient TOPCon + SE battery piece

Abstract

The invention discloses a solar single-crystal efficient TOPCon + SE battery piece ultrahigh sheet resistance diffusion process which mainly comprises a front boron process, an SE process and a rear oxidation process, and the front boron process comprises high-temperature oxidation before diffusion and a diffusion process composed of three-step diffusion and heating propulsion. According to the invention, a layer of SiO2 can be coated on the surface of the silicon wafer through high-temperature oxidation before diffusion and is used as an anti-reflection film layer; the PN junction is prepared by adopting a step-by-step diffusion method, so that the advantage of good junction uniformity can be realized, boron can be uniformly distributed on the surface of a silicon wafer through a specific boron diffusion method, and meanwhile, boron elements can be better deposited on the surface of the silicon wafer through variable-temperature diffusion and propulsion; by adding the SE process, the square resistance can reach 700-800 ohms, the junction depth in the grid line area is deeper, the increase of ohms becomes better, the cell center recombination is reduced due to the lower surface concentration, and the open-circuit voltage of the cell is improved; and the post-oxidation process has an annealing effect and can repair lattice damage and the like.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to an ultra-high square resistance diffusion process for a solar single crystal high-efficiency TOPCon+SE cell. Background Art

[0002] The core step in producing solar cells is to prepare the PN junction, and the current manufacturing industry still uses the diffusion method to make the PN junction of solar cells. For example, the Chinese patent with the prior art application number 202410474114.3 discloses a method for preparing an N-type TOPCon solar cell, in which the front PN junction is formed by front boron diffusion.

[0003] The diffusion PN junction method uses heating to dope Group V impurities into P-type silicon or Group III impurities into N-type silicon. Impurity elements enter the silicon matrix due to thermal diffusion at high temperatures. Its distribution in the matrix depends on the type of impurity elements, initial concentration, diffusion temperature and time. This different combination will have different battery structures and have very different electrical performance on the battery. At present, the most commonly used Group V impurity elements in silicon solar cells are phosphorus, and the Group III impurity elements are boron.

[0004] However, most current diffusion processes use high-concentration shallow junctions. After the non-SE diffusion process, the block resistance is only 300-400Ω. The lower junction depth at the gate line will inevitably lead to poor ohmic contact and larger resistance in the lateral transmission process. The electrical performance parameters are manifested as lower open-circuit voltage and fill factor. Higher surface concentration will increase the central recombination of the battery, and the electrical performance at the gate line is manifested as a lower open-circuit voltage. Summary of the invention

[0005] In view of this, the object of the present invention is to provide an ultra-high square resistance diffusion process for solar single crystal high-efficiency TOPCon+SE cell to improve cell efficiency.

[0006] To achieve the above object, the present invention adopts the following contents:

[0007] The present invention provides a solar single crystal high efficiency TOPCon+SE cell ultra-high square resistance diffusion process, comprising the following steps:

[0008] S1. Pre-boron process:

[0009] S1.1, high temperature oxidation before diffusion: high temperature oxidation of silicon wafer, pre-grow a layer of nanometer-thick SiO on the surface of silicon wafer 2; The process parameters are: the pressure in the furnace is 50mbar~150mbar, the oxidation time is maintained for 200s~500s, the oxygen flow rate is 100sccm~2000sccm, the nitrogen flow rate is 1000sccm~3000sccm, and the temperature is 750℃~850℃;

[0010] S1.2, Diffusion process: The PN junction is prepared by step-by-step diffusion method. The specific diffusion steps are as follows:

[0011] S1.2.1, the first step of diffusion, the process parameters are: the pressure in the furnace is 50mbar~150mbar, the diffusion temperature is 830℃~850℃, the diffusion time is 100s~300s, the nitrogen flow rate is 1000sccm~3000sccm, the boron trichloride flow rate is 100sccm~300sccm, and the oxygen flow rate is 200sccm~500sccm;

[0012] S1.2.2, the second step of diffusion, the process parameters are: the pressure in the furnace is 50mbar~150mbar, the diffusion temperature is 850℃~880℃, the diffusion time is 100s~300s, the nitrogen flow rate is 1000sccm~2000sccm, the boron trichloride flow rate is 100sccm~300sccm, and the oxygen flow rate is 200sccm~500sccm;

[0013] S1.2.3, the third step of diffusion, the process parameters are: the pressure in the furnace is 50mbar~150mbar, the diffusion temperature is 850℃~880℃, the diffusion time is 100s~300s, the nitrogen flow rate is 1000sccm~3000sccm, the boron trichloride flow rate is 100sccm~300sccm, and the oxygen flow rate is 200sccm~500sccm;

[0014] S1.2.4, temperature rise and advancement, process parameters are: furnace pressure 200mbar~400mbar, advancement temperature 900℃~950℃, advancement time 400s~600s, nitrogen flow rate 7000sccm~10000sccm, oxygen flow rate 0sccm;

[0015] S2, SE process, marking speed 20000mm / s~25000mm / s, power 30~70%;

[0016] S3, post-oxidation process, process parameters are: furnace pressure is 600mbar~950mbar, oxidation time is maintained at 2000s~5000s, oxygen flow rate is 180000sccm~21000sccm, nitrogen flow rate is 0, temperature is 1000℃~1060℃.

[0017] The above-mentioned solar single crystal high-efficiency TOPCon+SE cell is an N-type phosphorus-doped single crystal silicon wafer.

[0018] The resistivity of the selected N-type phosphorus-doped single crystal silicon wafer is 0.6Ω·cm to 1.6Ω·cm, and the thickness is 100μm to 150μm.

[0019] The oxygen is dry oxygen, the nitrogen is high-purity dry nitrogen of 99.9% or more, and the boron trichloride is high-purity 99.999%.

[0020] Compared with the prior art, the invention has the advantages that: high temperature oxidation before diffusion can coat a layer of SiO on the surface of the silicon wafer. 2 , as an anti-reflective film layer, it can effectively reduce the reflection of light and improve the light absorption rate of solar cells; the step-by-step diffusion method is used to prepare the PN junction, which can achieve the advantage of good junction uniformity, that is, it can effectively improve the uniformity of the square resistance of the silicon wafer diffusion area. Through a specific boron diffusion method, boron can be evenly distributed on the surface of the silicon wafer. At the same time, variable temperature diffusion and advancement can better deposit boron elements on the surface of the silicon wafer; by adding the SE (selective emitter, selective emission level) process, the square resistance can be achieved. 700-800Ω, the junction depth is deeper in the gate line area, and increasing the ohm will become better. The lower surface concentration will reduce the recombination in the center of the battery, and the open circuit voltage of the battery cell is improved; the temperature increase in the post-oxidation process has an annealing effect, which can repair lattice damage, etc. DETAILED DESCRIPTION

[0021] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0022] Embodiment 1:

[0023] This embodiment provides a solar single crystal high efficiency TOPCon+SE cell ultra-high square resistance diffusion process, which specifically includes the following steps:

[0024] S1. Pre-boron process:

[0025] S1.1, high temperature oxidation before diffusion: high temperature oxidation of silicon wafer, pre-grow a layer of nanometer-thick SiO on the surface of silicon wafer 2 ; The process parameters are: the pressure in the furnace is 140 mbar, the oxidation time is maintained for 300 s, the oxygen flow rate is 300 sccm, the nitrogen flow rate is 2000 sccm, and the temperature is 800°C;

[0026] S1.2, Diffusion process: The PN junction is prepared by step-by-step diffusion method. The specific diffusion steps are as follows:

[0027] S1.2.1, the first step of diffusion, the process parameters are: furnace pressure 130mbar, diffusion temperature 835℃, diffusion time 130s, nitrogen flow rate 1500sccm, boron trichloride flow rate 120sccm, oxygen flow rate 300sccm;

[0028] S1.2.2, the second diffusion step, the process parameters are: furnace pressure 140mbar, diffusion temperature 860℃, diffusion time 150s, nitrogen flow rate 1500sccm, boron trichloride flow rate 130sccm, oxygen flow rate 350sccm;

[0029] S1.2.3, the third step of diffusion, the process parameters are: furnace pressure 140mbar, diffusion temperature 865℃, diffusion time 110s, nitrogen flow rate 2500sccm, boron trichloride flow rate 130sccm, oxygen flow rate 350sccm;

[0030] S1.2.4, temperature rise and advancement, process parameters are: furnace pressure 300mbar, advancement temperature 910℃, advancement time 500s, nitrogen flow rate 8000sccm, oxygen flow rate 0sccm;

[0031] S2, SE process, marking speed 22000mm / s, power 55%;

[0032] S3, post-oxidation process, process parameters are: furnace pressure is 800mbar, oxidation time is maintained for 3000s, oxygen flow rate is 20000sccm, nitrogen flow rate is 0, temperature is 1050°C.

[0033] Embodiment 2:

[0034] This embodiment provides a solar single crystal high efficiency TOPCon+SE cell ultra-high square resistance diffusion process, which specifically includes the following steps:

[0035] S1. Pre-boron process:

[0036] S1.1, high temperature oxidation before diffusion: high temperature oxidation of silicon wafer, pre-grow a layer of nanometer-thick SiO on the surface of silicon wafer 2 ; The process parameters are: the pressure in the furnace is 140 mbar, the oxidation time is maintained for 300 s, the oxygen flow rate is 300 sccm, the nitrogen flow rate is 2000 sccm, and the temperature is 800°C;

[0037] S1.2, Diffusion process: The PN junction is prepared by step-by-step diffusion method. The specific diffusion steps are as follows:

[0038] S1.2.1, the first step of diffusion, the process parameters are: furnace pressure 130mbar, diffusion temperature 835℃, diffusion time 120s, nitrogen flow rate 1500sccm, boron trichloride flow rate 130sccm, oxygen flow rate 350sccm;

[0039] S1.2.2, the second step of diffusion, the process parameters are: furnace pressure 140mbar, diffusion temperature 860℃, diffusion time 110s, nitrogen flow rate 1500sccm, boron trichloride flow rate 150sccm, oxygen flow rate 490sccm;

[0040] S1.2.3, the third step of diffusion, the process parameters are: furnace pressure 140mbar, diffusion temperature 865℃, diffusion time 100s, nitrogen flow rate 2500sccm, boron trichloride flow rate 110sccm, oxygen flow rate 330sccm;

[0041] S1.2.4, temperature rise and advancement, process parameters are: furnace pressure 300mbar, advancement temperature 910℃, advancement time 500s, nitrogen flow rate 8000sccm, oxygen flow rate 0sccm;

[0042] S2, SE process, marking speed 22000mm / s, power 55%;

[0043] S3, post-oxidation process, process parameters are: furnace pressure is 800mbar, oxidation time is maintained for 3000s, oxygen flow rate is 20000sccm, nitrogen flow rate is 0, temperature is 1050°C.

[0044] Embodiment 3:

[0045] This embodiment provides a solar single crystal high efficiency TOPCon+SE cell ultra-high square resistance diffusion process, which specifically includes the following steps:

[0046] S1. Pre-boron process:

[0047] S1.1, high temperature oxidation before diffusion: high temperature oxidation of silicon wafer, pre-grow a layer of nanometer-thick SiO on the surface of silicon wafer 2 ; The process parameters are: the pressure in the furnace is 140 mbar, the oxidation time is maintained for 300 s, the oxygen flow rate is 300 sccm, the nitrogen flow rate is 2000 sccm, and the temperature is 800°C;

[0048] S1.2, Diffusion process: The PN junction is prepared by step-by-step diffusion method. The specific diffusion steps are as follows:

[0049] S1.2.1, the first step of diffusion, the process parameters are: furnace pressure 130mbar, diffusion temperature 835℃, diffusion time 150s, nitrogen flow rate 1500sccm, boron trichloride flow rate 100sccm, oxygen flow rate 300sccm;

[0050] S1.2.2, the second diffusion step, the process parameters are: furnace pressure 140mbar, diffusion temperature 860℃, diffusion time 130s, nitrogen flow rate 1500sccm, boron trichloride flow rate 130sccm, oxygen flow rate 350sccm;

[0051] S1.2.3, the third step of diffusion, the process parameters are: furnace pressure 140mbar, diffusion temperature 865℃, diffusion time 110s, nitrogen flow rate 2500sccm, boron trichloride flow rate 135sccm, oxygen flow rate 365sccm;

[0052] S1.2.4, temperature rise and advancement, process parameters are: furnace pressure 300mbar, advancement temperature 910℃, advancement time 500s, nitrogen flow rate 8000sccm, oxygen flow rate 0sccm;

[0053] S2, SE process, marking speed 22000mm / s, power 55%;

[0054] S3, post-oxidation process, process parameters are: furnace pressure is 800mbar, oxidation time is maintained for 3000s, oxygen flow rate is 20000sccm, nitrogen flow rate is 0, temperature is 1050°C.

[0055] Comparative group: According to the existing publicly available diffusion process formula, the non-SE diffusion process is completed through a one-time process, including the following steps:

[0056] S1. High temperature oxidation before diffusion: high temperature oxidation of silicon wafers to pre-grow a nanometer-thick SiO layer on the surface of the silicon wafer. 2 ; The process parameters are: the pressure in the furnace is 130mbar, the oxidation time is maintained for 240s, the oxygen flow rate is 2000sccm, the nitrogen flow rate is 1500sccm, and the temperature is 885℃;

[0057] S2, diffusion process: The PN junction is prepared by step-by-step diffusion method. In this step, the boron oxide deposited on the surface of the silicon wafer reacts with silicon to generate B atoms and silicon oxide. The B atoms expand inward to form P-type silicon. The specific diffusion steps are:

[0058] S2.1, the first step of diffusion, the process parameters are: furnace pressure 130mbar, diffusion temperature 885℃, diffusion time 150s, nitrogen flow rate 2700sccm, boron trichloride flow rate 230sccm, oxygen flow rate 600sccm;

[0059] S2.2, the second diffusion step, the process parameters are: furnace pressure 140mbar, diffusion temperature 885℃, diffusion time 150s, nitrogen flow rate 2700sccm, boron trichloride flow rate 235sccm, oxygen flow rate 600sccm;

[0060] S2.3, the third step diffusion, the process parameters are: furnace pressure 150mbar, diffusion temperature 885℃, diffusion time 150s, nitrogen flow rate 2700sccm, boron trichloride flow rate 240sccm, oxygen flow rate 600sccm;

[0061] S2.4, temperature rise and advancement. In this step, the boron oxide deposited on the surface of the silicon wafer reacts with silicon to generate B atoms and silicon oxide, and the B atoms expand inward to form P-type silicon. The process parameters are: furnace pressure of 400 mbar, advancement temperature of 925°C, advancement time of 420 s, nitrogen flow rate of 5000 sccm, and oxygen flow rate of 0 sccm;

[0062] S3, post-oxidation process, oxygen is introduced at high temperature to form an oxide layer; in this step, B atoms will further diffuse into the silicon wafer, further promote activation, and reach the target junction depth. The generated oxide layer has an adsorption effect on the boron on the surface of the silicon wafer, which plays a role in reducing the surface concentration and reducing the dead layer. The process parameters are: the pressure in the furnace is 800mbar, the oxidation time is maintained at 4000s, the oxygen flow rate is 20000sccm, the nitrogen flow rate is 0, and the temperature is 1035℃.

[0063] In the above embodiments 1, 2, and 3, the silicon wafer is divided into equal pieces before texturing. Except for the differences in diffusion time, boron trichloride flow rate, and oxygen flow rate in S1.2.1, S1.2.2, and S1.2.3 in the diffusion process, the parameter conditions of the other processes are ensured to be consistent. The measured electrical performance parameters are as follows

[0064] Table 1:

[0065] Comment Eta(%) Uoc(V) Isc(A) FF(%) Rs(Ω) Rsh(Ω) Comparison group 26.63 0.7440 14.287 85.48 0.0016 5610 Example 1 26.72 0.7462 14.291 85.53 0.0015 5710 Example 2 26.74 0.7465 14.288 85.61 0.0015 5961 Example 3 26.73 0.7463 14.286 85.60 0.0015 5911

[0066] Table 1: Electrical performance test parameters

[0067] Among them, Uoc is the open circuit voltage, Isc is the short circuit current, Rs is the series resistance, Rsh is the parallel resistance, FF is the fill factor, and Eta is the conversion efficiency of the battery cell.

[0068] Compared with the control group, the open circuit voltage of Example 1 is 2.2 mV higher, the short circuit current is 4 mA higher, the FF is 0.05 higher, and the conversion efficiency is improved by 0.09%.

[0069] Compared with the control group, the open circuit voltage of Example 2 is 2.5 mV higher, the short circuit current is the same, the FF is 0.13 higher, and the conversion efficiency is improved by 0.11%.

[0070] Compared with the control group, the open circuit voltage of Example 3 is 2.3 mV higher, the short circuit current is the same, the FF is 0.12 higher, and the conversion efficiency is improved by 0.10%.

[0071] In the above-mentioned embodiments 1, 2, and 3, the silicon wafer is divided into equal pieces before texturing. Except for the differences in diffusion time, boron trichloride flow rate, and oxygen flow rate in the diffusion process S1.2.1, S1.2.2, and S1.2.3, the parameter conditions of the other processes are ensured to be consistent. The measured square resistance parameters are as shown in Table 2 below:

[0072] Comment Square resistance (ave / Ω) Square resistance (min / Ω) Square resistance (max / Ω) Comparison group 373.4 363.9 392.8 Example 1 752.7 760.3 740.3 Example 2 741.7 752.6 719.8 Example 3 755.1 759.1 751.3

[0073] Table 2: Square resistance test parameters

[0074] It can be seen that the block resistance can be made 700-800Ω by the method provided in the embodiment of the present invention. In this way, the junction depth in the gate line area is deeper, and increasing the ohm will be better. The lower surface concentration will reduce the recombination in the center of the battery, and the open circuit voltage of the battery cell will be improved.

[0075] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A solar single crystal high efficiency TOPCon+SE cell ultra-high square resistance diffusion process, characterized in that: The specific steps include: S1. Pre-boron process: S1.1, high temperature oxidation before diffusion: high temperature oxidation of silicon wafer, pre-grow a layer of nanometer-level SiO2 on the surface of silicon wafer; process parameters are: furnace pressure of 50mbar~150mbar, oxidation time of 200s~500s, oxygen flow rate of 100sccm~2000sccm, nitrogen flow rate of 1000sccm~3000sccm, temperature of 750℃~850℃; S1.2, Diffusion process: The PN junction is prepared by step-by-step diffusion method. The specific diffusion steps are as follows: S1.2.1, the first step of diffusion, the process parameters are: the pressure in the furnace is 50mbar~150mbar, the diffusion temperature is 830℃~850℃, the diffusion time is 100s~300s, the nitrogen flow rate is 1000sccm~3000sccm, the boron trichloride flow rate is 100sccm~300sccm, and the oxygen flow rate is 200sccm~500sccm; S1.2.2, the second step of diffusion, the process parameters are: the pressure in the furnace is 50mbar~150mbar, the diffusion temperature is 850℃~880℃, the diffusion time is 100s~300s, the nitrogen flow rate is 1000sccm~2000sccm, the boron trichloride flow rate is 100sccm~300sccm, and the oxygen flow rate is 200sccm~500sccm; S1.2.3, the third step of diffusion, the process parameters are: the pressure in the furnace is 50mbar~150mbar, the diffusion temperature is 850℃~880℃, the diffusion time is 100s~300s, the nitrogen flow rate is 1000sccm~3000sccm, the boron trichloride flow rate is 100sccm~300sccm, and the oxygen flow rate is 200sccm~500sccm; S1.2.4, temperature rise and advancement, process parameters are: furnace pressure 200mbar~400mbar, advancement temperature 900℃~950℃, advancement time 400s~600s, nitrogen flow rate 7000sccm~10000sccm, oxygen flow rate 0sccm; S2, SE process, marking speed 20000mm / s~25000mm / s, power 30~70%; S3, post-oxidation process, process parameters are: furnace pressure is 600mbar~950mbar, oxidation time is maintained at 2000s~5000s, oxygen flow rate is 180000sccm~21000sccm, nitrogen flow rate is 0, temperature is 1000℃~1060℃.

2. According to claim 1, a solar single crystal high efficiency TOPCon+SE cell ultra-high square resistance diffusion process is characterized in that: The solar single crystal high-efficiency TOPCon+SE cell is an N-type phosphorus-doped single crystal silicon cell.

3. The ultra-high square resistance diffusion process of solar single crystal high-efficiency TOPCon+SE cell according to claim 2, characterized in that: The resistivity of the selected N-type phosphorus-doped single crystal silicon wafer is 0.6Ω·cm-1.6Ω·cm, and the thickness is 100μm-150μm.

4. The ultra-high square resistance diffusion process for solar single crystal high-efficiency TOPCon+SE cell according to claim 1, characterized in that: In the ultra-high square resistance diffusion process, the oxygen is dry oxygen, the nitrogen is high-purity dry nitrogen of more than 99.9%, and the boron trichloride is high-purity 99.999%.