Preparation method of battery piece and photovoltaic module

Abstract

The embodiment of the invention relates to the photovoltaic field, and discloses a preparation method of a battery piece and a photovoltaic module, and the method comprises the steps: providing a substrate, placing the substrate in a diffusion furnace tube, raising the temperature in the diffusion furnace tube from a preheated first temperature to a second temperature, carrying out pre-oxidation treatment on the surface of the substrate at the second temperature; keeping the temperature in the diffusion furnace tube at the second temperature, and introducing a doping source into the diffusion furnace tube for multiple times so as to perform diffusion deposition for multiple times; raising the temperature in the diffusion furnace tube to a third temperature, and performing high-temperature propulsion for multiple times at the third temperature; reducing the temperature in the diffusion furnace tube to the second temperature, and performing low-temperature propulsion at the second temperature; and reducing the temperature in the diffusion furnace tube to a fourth temperature so as to form a semiconductor doping layer on the surface of the substrate. According to the scheme, an ideal diffusion model of a low-surface-concentration shallow junction can be obtained, and the performance of the solar cell is improved.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the field of photovoltaics, in particular to a preparation method of a cell piece and a photovoltaic module. BACKGROUND

[0002] As a new generation of high-tech, the passivated contact technology is applied to the silicon-based solar cell, and is widely promoted due to the high compatibility of product production equipment and the emitter back passivation technology. The passivated contact solar cell adopts high-quality ultra-thin silicon oxide and doped polysilicon layer to realize the full back high-efficiency passivation and carrier selective collection. The introduction of the passivated contact technology further improves the passivation performance, thereby improving the open-circuit voltage and short-circuit current of the cell, and realizing the goal of high-efficiency cell.

[0003] However, the high surface concentration shallow junction or the low surface concentration deep junction generated by different front boron expansion processes will affect the saturation dark current and the contact resistance in the cell piece, and further affect the filling, open voltage and current in the electrical performance of the passivated contact solar cell, and affect the performance of the solar cell. SUMMARY

[0004] The purpose of the embodiment of the present application is to provide a preparation method of a cell piece and a photovoltaic module, which adopts a step-by-step doping source feeding, pressure and temperature changing mode to promote the diffusion and junction forming method in the cell piece preparation process, obtains a low surface concentration, shallow junction and uniform doped emitter, achieves the ideal diffusion model of low surface concentration shallow junction, and improves the performance of the solar cell.

[0005] In order to solve the above problems, the embodiment of the present application provides a preparation method of a cell piece, comprising:

[0006] A substrate is provided; the substrate is placed in a diffusion furnace tube, the temperature in the diffusion furnace tube is increased from a first preheating temperature to a second temperature, and the surface of the substrate is pre-oxidized at the second temperature; the temperature in the diffusion furnace tube is kept at the second temperature, and a doping source is fed into the diffusion furnace tube multiple times to perform multiple diffusion and deposition; the temperature in the diffusion furnace tube is increased to a third temperature, and multiple high-temperature promotions are performed at the third temperature; the temperature in the diffusion furnace tube is decreased to the second temperature, and low-temperature promotion is performed at the second temperature; and the temperature in the diffusion furnace tube is decreased to a fourth temperature to form a semiconductor doped layer on the surface of the substrate.

[0007] The embodiment of the present application further provides a photovoltaic module, comprising: a cell piece prepared by the preparation method of the cell piece.

[0008] The embodiment of the present application increases the temperature in the diffusion furnace tube from a first preheating temperature to a second temperature, and pre-oxidizes the substrate surface at the second temperature; keeps the temperature in the diffusion furnace tube at the second temperature, and introduces the doping source into the diffusion furnace tube for multiple times to carry out multiple diffusion deposition; increases the temperature in the diffusion furnace tube to a third temperature, and carries out multiple high-temperature pushing at the third temperature; decreases the temperature in the diffusion furnace tube to the second temperature, and carries out low-temperature pushing at the second temperature; decreases the temperature in the diffusion furnace tube to a fourth temperature to form a semiconductor doped layer on the substrate surface. Namely, the embodiment puts the substrate into the diffusion furnace tube, and carries out stepwise increasing and decreasing of the temperature in the diffusion furnace tube for multiple times, and pre-oxidizes the substrate, introduces the doping source, carries out high-temperature pushing and low-temperature pushing at different temperatures in sequence, so as to form a semiconductor doped layer on the substrate surface, and form a uniform doped emitter with low surface concentration and shallow junction depth on the semiconductor doped layer. BRIEF DESCRIPTION OF DRAWINGS

[0009] One or more embodiments are illustrated by way of example in the figures that form a part of this patent document, and which do not limit the scope of the embodiments.

[0010] Figure 1 is a flow of a preparation method of a battery piece provided by an embodiment of the present application Figure 1 ;

[0011] Figure 2 is a flow of a preparation method of a battery piece provided by an embodiment of the present application Figure 2 ;

[0012] Figure 3 is a flow of a preparation method of a battery piece provided by an embodiment of the present application Figure 3 ;

[0013] Figure 4 is a flow of a preparation method of a battery piece provided by an embodiment of the present application Figure 4 ;

[0014] Figure 5 is a flow of a preparation method of a battery piece provided by an embodiment of the present application Figure 5 ;

[0015] Figure 6 is a comparison chart of ECV test results of an implementation group and a control group provided by an embodiment of the present application. DETAILED DESCRIPTION

[0016] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the embodiments of the present application will be described in detail below with reference to the drawings. However, those skilled in the art can understand that, in the embodiments of the present application, many technical details are presented in order to make the readers better understand the present application. However, the technical solutions claimed by the present application can be implemented even without these technical details and based on various changes and modifications of the following embodiments. The division of the following embodiments is for the convenience of description, and should not constitute any limitation on the specific implementation modes of the present application, and the embodiments can be combined with each other and referred to each other without contradiction.

[0017] In the description of the embodiments of the present application, the technical terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple times" is more than twice, unless otherwise explicitly and specifically limited.

[0018] An embodiment of the present application relates to a preparation method of a battery piece. The preparation method in the embodiment mainly refers to a boron diffusion step in the preparation process of the battery piece, as shown in the following figure. Figure 1 The preparation method of the battery piece in the embodiment specifically includes the following steps:

[0019] Step 101: providing a substrate, placing the substrate into a diffusion furnace tube, increasing the temperature in the diffusion furnace tube from a first preheating temperature to a second temperature, and performing pre-oxidation treatment on the surface of the substrate at the second temperature.

[0020] Specifically, a substrate is provided for the preparation of the battery piece, and the substrate is generally a silicon substrate. The substrate can be put into a boat only after the surface organic matter, metal ions and particles are removed by chemical cleaning (such as RCA cleaning). After cleaning, the substrate is placed on a quartz boat in the diffusion furnace tube to prepare for the start of the preparation. Before formally starting to heat and raise the temperature of the diffusion furnace tube, the diffusion furnace tube needs to be vacuumed and leak tested, etc. Among them, the vacuuming is to extract the gas in the diffusion furnace tube by a mechanical pump, a molecular pump, etc., to adjust the gas pressure of the diffusion furnace tube to the required gas pressure, to avoid the residual gas in the furnace tube from reacting with the substrate at the subsequent high temperature, to interfere with the boron diffusion, and to ensure the uniformity of the boron diffusion. Small molecule gas such as helium is then filled into the diffusion furnace tube, and whether small molecule gas has penetrated into the diffusion furnace tube is detected by an instrument to complete the leak test.

[0021] After the preparation work is completed, the diffusion furnace tube is heated. The heating of the diffusion furnace tube is generally performed by winding resistance heating wires or using infrared heating elements on the outside of the diffusion furnace tube. The specific heating method is not limited in the present embodiment. The diffusion furnace tube is first preheated, i.e., the temperature in the diffusion furnace tube is raised to a first temperature. The feeding is started only after the temperature in the diffusion furnace tube reaches the first temperature. The first temperature can be 805-835°C, which is not limited in the present embodiment. When the preparation is formally started, the temperature in the diffusion furnace tube is raised from the first temperature to a second temperature, and the surface of the substrate is pre-oxidized at the second temperature. The second temperature can be 850-870°C. It should be noted that the temperature in the diffusion furnace tube in the present embodiment refers to the average temperature from the furnace mouth to the furnace tail, which will not be described hereinafter. The pre-oxidation in the present embodiment refers to the introduction of a small amount of oxygen (not enough for complete oxidation) into the diffusion furnace tube, so that a very thin silicon oxide film is formed on the surface of the substrate. The pre-oxidation can clean the surface of the substrate, establish a uniform diffusion interface, form an oxidation transition layer, provide an oxidation atmosphere, improve the diffusion conditions, and protect the silicon wafer, thereby laying a foundation for the efficient and uniform diffusion of boron atoms in the subsequent process, and finally ensuring that the semiconductor doped layer has precise concentration and depth.

[0022] In one example, after the temperature in the diffusion furnace tube is raised to the second temperature in step 101, the method of the present embodiment further includes, before the pre-oxidation of the surface of the substrate:

[0023] The diffusion furnace tube is kept heated so that the temperature in the diffusion furnace tube is maintained at the second temperature for a fourth preset time, and the third flow of nitrogen is continuously introduced for the fourth preset time.

[0024] After the fourth preset time, the heating is paused for a third interval time. After the third interval time ends, the diffusion furnace tube is heated again so that the temperature in the diffusion furnace tube is maintained at the second temperature for a sixth preset time.

[0025] Specifically, after the temperature in the diffusion furnace tube is heated from the first temperature to the second temperature in step 101, the heating is not immediately stopped, but is maintained, and the temperature in the diffusion furnace tube is monitored, the heating effect on the diffusion furnace tube is adjusted by adjusting the power of the heating element outside the diffusion furnace tube, and the temperature in the diffusion furnace tube is controlled to be maintained at the second temperature. The time for maintaining is the fourth preset time from the time when the temperature in the diffusion furnace tube reaches the second temperature, and the fourth preset time is 780-820 seconds. In the fourth preset time for maintaining the heating of the diffusion furnace tube, the third flow rate of nitrogen gas is continuously introduced into the diffusion furnace tube. The third flow rate can be 3000-5000 sccm (standard cubic centimeter per minute). The third flow rate of nitrogen gas introduced in this embodiment can be impurities and water vapor that may be generated during the temperature rising process of the diffusion furnace tube, and can stabilize the gas pressure in the furnace tube. The timing starts from the time when the temperature in the diffusion furnace tube reaches the second temperature, and after the fourth preset time, the heating of the diffusion furnace tube is suspended. The suspension time can be a third interval time from the time when the heating is stopped. The third interval time is generally very short, and this embodiment does not make specific limitations. As long as the temperature of the diffusion furnace tube is not lower than the second temperature within the set third interval time, the specific value can be determined according to actual needs and processes. After the third interval time ends, the heating of the diffusion furnace tube is started again, and the temperature of the diffusion furnace tube is still monitored to maintain the second temperature within a sixth preset time from the time when the heating is started again. The sixth preset time is 380-420 seconds. Stabilizing the temperature of the diffusion furnace tube within the sixth preset time can stabilize the atmosphere in the diffusion furnace tube and ensure that the subsequently introduced gas can be distributed more uniformly.

[0026] Correspondingly, the pre-oxidation treatment of the substrate surface at the second temperature in step 101 in this embodiment can include:

[0027] After the sixth preset time, the heating of the diffusion furnace tube is maintained, the temperature in the diffusion furnace tube is maintained at the second temperature within an eighth preset time, and the fourth flow rate of oxygen and the fifth flow rate of nitrogen are continuously introduced within the eighth preset time.

[0028] Specifically, after the sixth preset time ends, the heating state of the diffusion furnace tube is maintained, the eighth preset time is restarted from the time when the sixth preset time starts, the temperature in the diffusion furnace tube is controlled to be maintained at the second temperature within the eighth preset time, and the fourth flow rate of oxygen and the fifth flow rate of nitrogen are continuously introduced within the eighth preset time. The eighth preset time is 180-220 seconds, the fourth flow rate is 720-780 sccm, and the fifth flow rate is 2150-2300 sccm. This embodiment does not make limitations on specific values. The pre-oxidation establishes a uniform diffusion interface and an oxidation atmosphere for subsequent boron diffusion, and promotes uniform decomposition of the subsequent boron source.

[0029] Step 102: maintaining the temperature in the diffusion furnace tube as the second temperature, and introducing the doping source into the diffusion furnace tube for multiple times to perform multiple diffusion deposition.

[0030] Specifically, in the process of preparing the battery piece, the doping concentration of boron element in the silicon substrate is required to be extremely accurate, different devices have different requirements for the boron doping concentration, and the single introduction of the doping source can hardly accurately control the distribution and concentration of boron in silicon due to the uneven distribution of the doping source in the furnace tube, the difference in silicon wafer surface adsorption and other problems. Therefore, the embodiment introduces the doping source into the diffusion furnace tube at the second temperature for multiple times, so that the doping source and the substrate perform multiple diffusion deposition. The multiple introduction of the doping source can better control the boron atom concentration in the substrate and improve the uniformity of boron diffusion, thereby improving the uniformity of sheet resistance distribution and the efficiency of the battery.

[0031] In one example, the doping source includes oxygen and a boron source; on this basis, as shown in Figure 2 Step 102 specifically includes the following steps:

[0032] Step 1021: maintaining heating of the diffusion furnace tube to maintain the temperature in the diffusion furnace tube as the second temperature, and continuously introducing the doping source into the diffusion furnace tube for the first time within the first preset time to perform the first diffusion deposition.

[0033] Specifically, diffusion deposition refers to a process of introducing a boron source into a furnace tube at high temperature, boron atoms generated by decomposition of the boron source enter the inside of a silicon substrate through diffusion, and occupy a certain position in the silicon lattice, thereby changing the electrical properties of the silicon substrate. After the pre-oxidation step is completed, the heating state of the diffusion furnace tube is still maintained to maintain the temperature in the diffusion furnace tube as the second temperature, the first timing starts from the time when the pre-oxidation step is completed, the timing time is the first preset time, the temperature in the diffusion furnace tube is controlled to maintain at the second temperature within the first preset time, and oxygen and the boron source (doping source) are introduced synchronously. The embodiment does not make specific limitation on this. The simultaneous introduction of the boron source and oxygen can make the oxygen and the boron source react in the furnace to generate an oxide of boron (such as B2O3), the oxide of boron is more likely to contact with the silicon surface and release boron atoms at the second temperature, accelerating the diffusion process, and at the same time, the participation of oxygen in the reaction can maintain an oxidizing atmosphere in the furnace tube, avoiding “silicon evaporation” or surface damage of the silicon substrate due to lack of oxygen at high temperature. At the second temperature, boron atoms generated by decomposition in the diffusion furnace tube will be adsorbed on the surface of the substrate, thereby forming a certain concentration distribution on the surface of the substrate. Since the boron atoms adsorbed on the surface of the silicon wafer have a certain energy, under the driving of the high temperature of the second temperature, the boron atoms adsorbed on the surface of the substrate will overcome the resistance of the silicon lattice and diffuse into the silicon. After the first preset time is over, the introduction of the doping source is stopped, and the second introduction is performed after a preset time is paused, so that the boron source introduced for the first time fully performs the first diffusion deposition in the substrate within the time of pausing the introduction.

[0034] Step 1022: After the first time of continuously introducing the doping source into the diffusion furnace tube ends, the doping source is continuously introduced into the diffusion furnace tube for a second time within a first preset time to perform a second diffusion deposition.

[0035] After the first time of continuously introducing the doping source into the diffusion furnace tube ends, the timing is started again after a preset time elapses, the timing time is still the first preset time, the temperature in the diffusion furnace tube is kept at the second temperature, and the oxygen and the boron source are continuously introduced into the diffusion furnace tube within the first preset time to perform a process similar to the first diffusion deposition. After the first preset time ends, the introduction of the doping source is stopped, and a third time of introducing the doping source is performed after a preset time elapses, so that the boron source introduced for the second time fully performs the second diffusion deposition in the substrate during the time when the introduction is suspended.

[0036] Step 1023: After the second time of continuously introducing the doping source into the diffusion furnace tube ends, the doping source is continuously introduced into the diffusion furnace tube for a third time within the first preset time to perform a third diffusion deposition.

[0037] After the second time of continuously introducing the doping source into the diffusion furnace tube ends, the timing is started again after a preset time elapses, the timing time is still the first preset time, the temperature in the diffusion furnace tube is kept at the second temperature, and the oxygen and the boron source are continuously introduced into the diffusion furnace tube within the first preset time to perform a process similar to the first diffusion deposition and the second diffusion deposition to perform the third diffusion deposition. After the first preset time ends, the introduction of the doping source is stopped. It should be noted that the value of the first preset time in the first diffusion deposition, the second diffusion deposition, and the third diffusion deposition in the embodiment is between 160 seconds and 200 seconds, that is, the time of introducing the doping source in the three diffusion depositions is only required to be within the range of the first preset time, and the time of introducing the doping source each time can be the same or different, which is not limited in the embodiment. In addition, the doping source introduced into the diffusion furnace tube for the first time, the doping source introduced into the diffusion furnace tube for the second time, and the doping source introduced into the diffusion furnace tube for the third time are all the same, and specifically can be a boron source with a first flow rate and an oxygen source with a second flow rate. The boron source can be boron trichloride (BCl3), the first flow rate can be 180-220 sccm, and the second flow rate can be 620-680 sccm, and the embodiment does not limit the specific value.

[0038] In another example, after the first time of continuously introducing the doping source into the diffusion furnace tube ends in step 1021, before the second time of continuously introducing the doping source into the diffusion furnace tube in step 1022, the method of the embodiment further includes the following steps:

[0039] The diffusion furnace tube is kept heated to keep the temperature in the diffusion furnace tube at the second temperature, and the boron source with the first flow rate is continuously introduced into the diffusion furnace tube within a second preset time to perform a first purge.

[0040] Specifically, at the end of the first preset time of the first timing, a new timing is started, and the timing time is a second preset time, which can be 120-180 seconds. The diffusion furnace tube is kept heated in the second preset time to keep the temperature in the diffusion furnace tube at the second temperature, and at the moment when the second preset time starts timing, the input of oxygen in the doping source is paused, and the input of the first flow rate of boron source into the diffusion furnace tube is continued to perform the first purging. Since the doping source input in step 1021 includes boron trichloride (B2O3) and oxygen (O2), the reaction in the diffusion furnace tube at the second temperature will produce boron oxide (B2O3) and chlorine (Cl2), and the oxygen in the first input doping source may not be completely consumed after the first diffusion deposition is completed. Therefore, the embodiment sets a purging step after the first input of the doping source ends and before the second input of the doping source, which can remove the residual O2 and Cl2 from the furnace tube by purging BCl3, so that the gas composition in the furnace tube reaches a uniform state before the next input of the doping source, avoids uneven boron doping due to uneven gas distribution, and ensures that the reaction of BCl3 and O2 under the preset conditions (second temperature, ratio of first flow rate of BCl3 to second flow rate of O2) is uniform.

[0041] Similarly, after the second input of the doping source in step 1022 ends, before the third input of the doping source in step 1023, a purging step is also included, which specifically includes:

[0042] The diffusion furnace tube is kept heated to keep the temperature in the diffusion furnace tube at the second temperature, and the first flow rate of boron source is continuously input into the diffusion furnace tube in the second preset time to perform the second purging.

[0043] Specifically, at the end of the first preset time of the second timing, a new timing is started, and the timing time is a second preset time, and the diffusion furnace tube is kept heated in the second preset time to keep the temperature in the diffusion furnace tube at the second temperature, and at the moment when the second preset time starts timing, the input of oxygen in the doping source is paused, and the first flow rate of BCl3 is continuously input into the diffusion furnace tube to perform the second purging.

[0044] Step 103: The temperature in the diffusion furnace tube is raised to a third temperature, and multiple high-temperature pushes are performed at the third temperature.

[0045] Specifically, it is difficult to accurately control the target junction depth in a single push during a conventional boron diffusion process, and in order to obtain a low-concentration shallow junction, the temperature in the diffusion furnace tube is raised to a third temperature, and multiple high-temperature pushes are performed at the third temperature, that is, the diffusion depth and concentration are controlled by step pushing, so that the boron atoms in the B2O3 deposited on the surface of the substrate after step 102 begin to diffuse into the interior of the substrate. Multiple pushes can achieve "concentration redistribution", avoid "lattice distortion" or "impurity agglomeration" caused by too high boron atom concentration on the surface of the substrate during a single push, and make the diffusion progress of the edge and center regions of the substrate more consistent, thereby reducing the within-wafer variation of sheet resistance.

[0046] In one example, as shown in Figure 3 Step 103 can specifically include the following steps:

[0047] Step 1031: heating the diffusion furnace tube, and raising the temperature in the diffusion furnace tube from the second temperature to the third temperature within a third preset time.

[0048] Specifically, after the doping source is introduced, the diffusion furnace tube can be heated by adjusting the heating power of the heating element outside the diffusion furnace tube, and the temperature in the diffusion furnace tube is raised from the second temperature to the third temperature within a third preset time. Since the diffusion speed of boron in the substrate is related to the temperature, the temperature in the diffusion furnace tube is adjusted to the third temperature suitable for boron diffusion. The third preset time is 90-120 seconds, and the third temperature is 880-920°C.

[0049] Step 1032: maintaining heating of the diffusion furnace tube, and controlling the temperature in the diffusion furnace tube to remain at the third temperature within a fourth preset time to perform a first high-temperature push.

[0050] Specifically, after the temperature of the diffusion furnace tube reaches the third temperature, the heating state of the diffusion furnace tube is maintained, and the heating effect is adjusted so that the temperature of the diffusion furnace tube remains at the third temperature within the fourth preset time from the moment when the third temperature is reached. That is, within the fourth preset time, boron on the surface of the substrate will spontaneously diffuse into the interior of the substrate under the action of the high temperature of the third temperature to complete the first high-temperature push. The fourth preset time can be 780-820 seconds.

[0051] Step 1033: after the first high-temperature push is completed, heating of the diffusion furnace tube is suspended within a first interval time, and the diffusion furnace tube is heated again after the first interval time to maintain the temperature in the diffusion furnace tube at the third temperature within a third preset time to perform a second high-temperature push.

[0052] Specifically, after the fourth preset time is counted, the heating of the diffusion furnace tube is stopped, and the time for stopping the heating is the first interval time. The embodiment does not limit the specific value of the first interval time, as long as the temperature of the diffusion furnace tube is not lower than the third temperature in the first interval time. That is, the temperature of the diffusion furnace tube is maintained at the third temperature in the fourth preset time and the first interval time, and the difference is that the diffusion furnace tube is in the heating state in the fourth preset time, but is in the non-heating state in the first interval time. Although the temperature in the diffusion furnace tube is at the third temperature in the heating state and the non-heating state, the microscopic reactions of boron diffusion in the diffusion furnace tube are different in the heating state and the non-heating state. In the heating state, the heat flow in the furnace tube is maintained stable, the silicon lattice of the substrate continuously obtains energy, and the boron atom is in a high kinetic energy state. At this time, the diffusion of boron is mainly substitutional diffusion, which shows a rapid increase in the longitudinal depth of boron diffusion. In the non-heating state, the temperature in the diffusion furnace tube is maintained by the residual temperature of the diffusion furnace tube itself, the heat flow is reduced, the kinetic energy of the boron atom is reduced, the boron atom slowly migrates from the high-concentration region to the low-concentration region, and the transverse diffusion (along the surface of the substrate) and the longitudinal diffusion rate tend to be balanced. That is, by pausing the heating, the embodiment can make the diffusion of boron atoms in the first interval time more inclined to be uniformly distributed in the surface layer of the silicon wafer, thereby reducing the concentration difference between the edge and the center. After the first interval time, the third preset time is restarted, and the heating is started again, while monitoring the temperature of the diffusion furnace tube and controlling the temperature of the diffusion furnace tube to be maintained at the third temperature, and the boron atoms on the surface of the substrate are subjected to a second high-temperature push similar to the first high-temperature push. Through two-step pushing, a more appropriate junction depth can be achieved, and in addition, the gettering capacity generated during the boron diffusion process can be further increased, effectively reducing the recombination of carriers, to improve the efficiency of the battery sheet.

[0053] Step 104: cooling the temperature in the diffusion furnace tube to a second temperature, and performing low-temperature pushing at the second temperature.

[0054] Specifically, the temperature of the diffusion furnace tube is cooled from the third temperature to the second temperature, and low-temperature pushing is performed at the second temperature. Since the diffusion coefficient of boron is high at the third temperature, the diffusion is mainly longitudinal diffusion relative to the surface of the substrate, and the boron diffusion concentration difference between the four edges of the substrate and the center is large. Therefore, after the high-temperature pushing of step 103 is performed, the temperature of the diffusion furnace tube is cooled to the second temperature in the embodiment, and low-temperature pushing is performed. Since the second temperature range is 850-870°C, at the second temperature, the diffusion coefficient of boron is significantly reduced, the longitudinal diffusion rate is slowed down, and the transverse diffusion becomes dominant relative to the longitudinal diffusion, thereby improving the problem that the boron diffusion concentration difference between the four edges of the substrate and the center is large, and improving the uniformity of boron doping.

[0055] In one example, the step 104 specifically comprises: reducing the temperature in the diffusion furnace tube from the third temperature to the second temperature within a third preset time; heating the diffusion furnace tube so that the temperature in the diffusion furnace tube is maintained at the second temperature within a fifth preset time to perform low-temperature pushing.

[0056] Specifically, the diffusion furnace tube is cooled within the third preset time, and after the temperature in the diffusion furnace tube reaches the second temperature, heating of the diffusion furnace tube is started and timing is started, and the timing time is the fifth preset time, wherein the fifth preset time can be 480-520 seconds. Within the fifth preset time, the temperature of the diffusion furnace tube is maintained at the second temperature, so that low-temperature pushing of boron atoms in the diffusion furnace tube is performed at the second temperature, and the boron atoms are diffused in the substrate mainly in the lateral direction.

[0057] Step 105: reducing the temperature in the diffusion furnace tube to a fourth temperature to form a semiconductor doped layer on the surface of the substrate.

[0058] Specifically, after multiple temperature pushing, the boron in the substrate reaches a relatively ideal low-surface-concentration shallow-junction diffusion model through diffusion, and a corresponding semiconductor doped layer is formed.

[0059] In one example, the step 105 specifically comprises: reducing the temperature in the diffusion furnace tube from the second temperature to the fourth temperature; heating the diffusion furnace tube so that the temperature in the diffusion furnace tube is maintained at the second temperature within a sixth preset time; pausing heating within a second interval time, and after the second interval time, heating the diffusion furnace tube again so that the temperature in the diffusion furnace tube is maintained at the second temperature within a seventh preset time to form a semiconductor doped layer on the surface of the substrate.

[0060] Specifically, after the temperature of the diffusion furnace tube is lowered to the fourth temperature, the diffusion furnace tube is heated and timing is started at the same time, the timing duration is the sixth preset time, and the temperature in the diffusion furnace tube is controlled to be the second temperature during the heating process within the sixth preset time. The sixth preset time can be 380-420 seconds. After the sixth preset time is timed, the heating of the diffusion furnace tube is suspended, and the suspension time is the second interval time. The specific value of the second interval time is not limited in the embodiment, as long as the temperature of the diffusion furnace tube is not lower than the second temperature within the second interval time. After the second interval time ends, the diffusion furnace tube is heated again, so that the temperature in the diffusion furnace tube is maintained at the second temperature within the seventh preset time, to form a semiconductor doped layer on the surface of the substrate, and then the temperature is lowered. After the diffusion furnace tube is broken, the boat is taken out, and the boron diffusion is completed. The seventh preset time is 280-320 seconds, and the specific value is not limited in the embodiment. It should be noted that the diffusion furnace tube is at the second temperature in the sixth preset time, the second interval time and the seventh preset time, which still has a certain promoting effect on the boron in the substrate. In addition, the two-cycle temperature lowering in the embodiment can repair defects on the surface of the substrate and improve the quality of the battery piece.

[0061] Compared with the related art, the above-mentioned embodiment of the present application completes boron diffusion by the preparation method of step-by-step source, variable pressure and variable temperature, realizes multi-dimensional precise control of junction depth, impurity distribution, crystal integrity and process compatibility in the boron diffusion process, achieves a relatively ideal low-surface-concentration shallow-junction diffusion model in the substrate, significantly improves the resistance uniformity, and thus improves the performance of the prepared battery piece.

[0062] Another embodiment of the present application relates to a preparation method of a battery piece, which is an additional embodiment of the above-mentioned embodiment. The preparation method of the battery piece in the embodiment focuses on the heat treatment of the substrate after the boron diffusion is completed and the semiconductor doped layer is formed. The heat treatment can repair the lattice defects generated due to high temperature in the boron diffusion process of the above-mentioned embodiment, improve the thickness of silicon oxide on the surface of the substrate to improve the passivation effect, thereby improving the reliability and resistance adaptation of the battery piece, so that the ideal diffusion model of the low-surface-concentration shallow-junction obtained by the above-mentioned embodiment can maximize the efficiency of the passivated contact solar cell.

[0063] As shown in Figure 4 The preparation method of the battery piece in the embodiment includes the following steps:

[0064] Step 201: The temperature in the diffusion furnace tube is raised to the fifth temperature, and the substrate is annealed multiple times at the fifth temperature.

[0065] Specifically, before the temperature is raised, similar preparation steps as performed before step 101 are required, i.e. boat loading, vacuum pumping and leak checking preparation steps, to maintain the clean, constant pressure and constant temperature in the furnace tube. It should be noted that the substrate loaded here refers to the substrate after the formation of the semiconductor doped layer in step 105. After the preparation is completed, the temperature in the diffusion furnace tube is raised to the fifth temperature, and the substrate is annealed multiple times at the fifth temperature to repair the lattice defects generated in the substrate during high temperature.

[0066] In one example, as shown in FIG. 2, step 201 can specifically include the following steps: Figure 5

[0067] Step 2011: heating the diffusion furnace tube to raise the temperature in the diffusion furnace tube to the fifth temperature.

[0068] Step 2012: after the temperature in the diffusion furnace tube reaches the fifth temperature, the diffusion furnace tube is kept heated to maintain the temperature in the diffusion furnace tube at the fifth temperature for a ninth preset time, and the sixth flow rate of oxygen is continuously introduced into the diffusion furnace tube for the first time to perform annealing.

[0069] Specifically, the diffusion furnace tube is heated by starting the heating element outside the diffusion furnace tube to raise the temperature in the diffusion furnace tube to the fifth temperature. The fifth temperature can be 1000-1050°C, and the specific value is not limited in the embodiment. After the temperature in the diffusion furnace tube reaches the fifth temperature, the diffusion furnace tube is kept heated and the first timing is started at the same time, and the timing duration is the ninth preset time. The temperature in the diffusion furnace tube is controlled to maintain the fifth temperature for the ninth preset time, and the sixth flow rate of oxygen is continuously introduced into the diffusion furnace tube for the ninth preset time. The ninth preset time can be 460-500 seconds, and the sixth flow rate can be 18500-19500 sccm. Since a large amount of oxygen is introduced, the annealing in this step should be more specifically called oxidation annealing. That is, the step of maintaining the fifth temperature for the ninth preset time and introducing the sixth flow rate of oxygen has the dual functions of annealing and oxidation, but considering that the substrate is first subjected to the dual action of the fifth temperature and oxygen, the annealing effect is more obvious at this time, so this step is called annealing. Under the action of the fifth temperature and oxygen for the ninth preset time, the interstitial boron atoms in the substrate are combined with vacancies to promote the increase of substitutional atom ratio, reduce carrier recombination centers, and repair the vacancies, dislocations and other crystal defects in the substrate caused by high temperature boron diffusion.

[0070] ​Step 2013: After the ninth preset time, the heating is paused for a fourth interval time, and after the fourth interval time, the heating is performed again on the diffusion furnace tube so as to keep the temperature in the diffusion furnace tube at the fifth temperature for a seventh preset time, and the oxygen gas with the sixth flow rate is continuously introduced into the diffusion furnace tube for the seventh preset time to perform the second annealing.

[0071] Specifically, similar to the reasons for the aforementioned multiple times of introducing the doping source and the multiple times of high-temperature pushing, in order to improve the uniformity of diffusion, after the ninth preset time of step 2012, the heating is paused for a fourth interval time, and after the fourth interval time, the heating is performed again on the diffusion furnace tube, and the timing is started at the same time, the timing lasts for a seventh preset time, the temperature in the diffusion furnace tube is controlled to keep at a fifth temperature for the seventh preset time, and the oxygen gas with a sixth flow rate is continuously introduced into the diffusion furnace tube for the seventh preset time to perform the second oxidation annealing. The seventh preset time can be 280-320 seconds.

[0072] Step 2014: After the seventh preset time, the heating is paused for a fourth interval time, and after the fourth interval time, the heating is performed again on the diffusion furnace tube so as to keep the temperature in the diffusion furnace tube at the fifth temperature for a tenth preset time, and the oxygen gas with the sixth flow rate is continuously introduced into the diffusion furnace tube for the tenth preset time to perform the third annealing.

[0073] Specifically, after the seventh preset time of step 2013, the heating is paused for a fourth interval time, and after the fourth interval time, the heating is performed again on the diffusion furnace tube, and the timing is started at the same time, the timing lasts for a tenth preset time, the temperature in the diffusion furnace tube is controlled to keep at a fifth temperature for the tenth preset time, and the oxygen gas with a sixth flow rate is continuously introduced into the diffusion furnace tube for the tenth preset time to perform the third oxidation annealing. The tenth preset time can be 520-560 seconds.

[0074] Step 2015: After the tenth preset time, the heating is paused for a fourth interval time, and after the fourth interval time, the heating is performed again on the diffusion furnace tube so as to keep the temperature in the diffusion furnace tube at the fifth temperature for an eleventh preset time, and the oxygen gas with the sixth flow rate is continuously introduced into the diffusion furnace tube for the eleventh preset time to perform the fourth annealing.

[0075] Specifically, after the tenth preset time of step 2014, the heating is suspended, and the suspension time is a fourth interval time. After the fourth interval time, the diffusion furnace tube is heated again, and the timing is started synchronously. The timing time is an eleventh preset time, and the temperature in the diffusion furnace tube is controlled to be kept at a fifth temperature within the eleventh preset time. Meanwhile, the oxygen gas with the sixth flow rate is continuously introduced into the diffusion furnace tube within the eleventh preset time, so that the fourth oxidation annealing is performed. The eleventh preset time can be 640-700 seconds. It should be noted that the fourth interval time is generally very short, and the embodiment does not make a specific limitation on this. As long as the temperature of the diffusion furnace tube is not lower than the range of the fifth temperature within the set fourth interval time, the specific value can be determined according to actual needs and processes. Through the above four times of annealing, the crystal lattice defects generated due to high temperature in the boron diffusion process in the foregoing embodiment can be basically repaired. Meanwhile, the oxidation annealing makes the crystal lattice thermal expansion uniform through uniform heating, and reduces the silicon-oxide layer interface stress through slow oxidation when the oxygen gas is introduced, so as to avoid the warping or cracking of the silicon wafer.

[0076] Step 202: keeping the fifth temperature, and performing multiple oxidations on the substrate.

[0077] Specifically, the temperature in the diffusion furnace tube is kept unchanged at the fifth temperature. After the crystal lattice defects in the substrate are repaired, the thickness and uniformity of the silicon oxide on the surface of the substrate are further improved through oxidation.

[0078] In one example, step 202 can specifically include the following steps:

[0079] The diffusion furnace tube is kept heated, so that the temperature in the diffusion furnace tube is kept at the fifth temperature within a twelfth preset time, and the oxygen gas with the sixth flow rate is continuously introduced into the diffusion furnace tube within the twelfth preset time, so as to perform the first oxidation.

[0080] After the twelfth preset time, the heating is suspended within a fifth interval time. After the fifth interval time, the diffusion furnace tube is heated again, so that the temperature in the diffusion furnace tube is kept at the fifth temperature within a thirteenth preset time, and the oxygen gas with the sixth flow rate is continuously introduced into the diffusion furnace tube within the thirteenth preset time, so as to perform the second oxidation.

[0081] The twelfth preset time is 280-300 seconds, and the thirteenth preset time is 850-900 seconds.

[0082] Specifically, it is not difficult to find that the oxidation step in the embodiment is similar to the annealing step in the foregoing embodiment, because the step of maintaining the fifth temperature and introducing the sixth flow of oxygen in the twelfth preset time and the thirteenth preset time has the dual functions of annealing and oxidation, but considering that the lattice repair is mainly performed between steps 2012-2015, the annealing function is realized, therefore, the step of maintaining the fifth temperature and introducing the sixth flow of oxygen in the twelfth preset time and the thirteenth preset time in the embodiment is called oxidation. After the fourth annealing is completed, the heating of the diffusion furnace tube is maintained, and the timing for the twelfth preset time is started at the same time, the temperature in the diffusion furnace tube is controlled to maintain the fifth temperature in the twelfth preset time, and the sixth flow of oxygen is continuously introduced into the diffusion furnace tube in the twelfth preset time to perform the first oxidation. After the first oxidation is completed, that is, after the twelfth preset time, the heating is stopped, and the stopping time is the fifth interval time, after the fifth interval time, the diffusion furnace tube is heated again, and the timing is started at the same time, the timing time is the thirteenth preset time, and the temperature in the diffusion furnace tube is controlled to maintain the fifth temperature in the thirteenth preset time, and the sixth flow of oxygen is continuously introduced into the diffusion furnace tube in the thirteenth preset time to perform the second oxidation. It should be noted that the fifth interval time in the embodiment is generally very short, and the embodiment does not make specific limitations, as long as the temperature of the diffusion furnace tube is not lower than the fifth temperature within the set fifth interval time, and the specific value can be determined according to actual needs and process steps.

[0083] Because the formation of a thick oxide layer by introducing a large amount of oxygen at one time is easy to increase the surface roughness and stress concentration, in the embodiment, the oxygen is introduced in multiple times, each time a thin oxide layer is formed, and the stepwise oxidation is realized under the action of annealing, so as to realize the linear accumulation of the thickness of the oxide layer and improve the surface flatness.

[0084] Step 203: The temperature in the diffusion furnace tube is lowered to a sixth temperature to obtain a heat-treated substrate.

[0085] Specifically, after the annealing and oxidation are completed, the diffusion furnace tube is cooled to the sixth temperature, and after the cooling, the boat is taken out after the furnace tube is broken vacuum, and the heat treatment is completed.

[0086] In one example, the temperature in the diffusion furnace tube is lowered to the sixth temperature in step 203, which includes:

[0087] The temperature in the diffusion furnace tube is lowered from the fifth temperature to the sixth temperature; the diffusion furnace tube is heated so that the temperature in the diffusion furnace tube maintains the sixth temperature in a fourteenth preset time; after the fourteenth preset time, the heating is stopped in a sixth interval time, and the diffusion furnace tube is heated again after the sixth interval time so that the temperature in the diffusion furnace tube maintains the sixth temperature in a fifteenth preset time.

[0088] Specifically, the heating elements outside the diffusion furnace tube are turned off, the temperature in the diffusion furnace tube is lowered from the fifth temperature to a sixth temperature, after the temperature in the diffusion furnace tube reaches the sixth temperature, the diffusion furnace tube is heated and the timing for the fourteenth preset time is started at the same time, so that the temperature in the diffusion furnace tube is maintained at the sixth temperature within the fourteenth preset time. Wherein, the sixth temperature can be: 820-840℃, the fourteenth preset time can be 1400-1600 seconds. After the fourteenth preset time, the heating is suspended within the sixth interval time, and the diffusion furnace tube is heated again to maintain the sixth temperature within the fifteenth preset time. Wherein, the fifteenth preset time can be 400-440 seconds.

[0089] The process of lowering the temperature to the sixth temperature twice in this embodiment can optimize the interface characteristics of the oxide layer and the silicon wafer, provide a stable surface state for the subsequent possible low-temperature process (such as metallization and photoresist curing), ensure the compatibility between processes, and thus improve the electrical performance and reliability of the battery sheet.

[0090] In order to further illustrate the effect of the present application, the low surface concentration shallow junction produced by the method of the above embodiment is the ideal model to be achieved by boron diffusion process. The low surface concentration shallow junction produced by the method of the embodiment is taken as the implementation group, and the conventional high surface concentration shallow junction boron diffusion process is taken as the control group, and the electrochemical differential capacitance voltage (ECV) test results are shown in the following table. Figure 6 As can be seen, after ECV test, the junction depth and surface doping concentration corresponding to the method of the embodiment all meet the requirements of the ideal diffusion model, and the diffusion sheet resistance is higher than that of the comparative process, and the uniformity is better.

[0091] Another embodiment of the present application relates to a photovoltaic module, comprising: a battery sheet prepared by the preparation method of the battery sheet according to any one of the above embodiments.

[0092] It is not difficult to find that the present embodiment is a product embodiment corresponding to the above-mentioned method embodiments. The details described in the above-mentioned method embodiments still apply to the present embodiment, which will not be repeated here.

[0093] Those skilled in the art can understand that the above-mentioned embodiments are specific embodiments for implementing the present application, and in actual application, various changes can be made in form and details without departing from the spirit and scope of the present application.

Claims

1. A method for preparing a battery cell, characterized in that, include: A substrate is provided, the substrate is placed inside a diffusion furnace tube, the temperature inside the diffusion furnace tube is raised from a first preheating temperature to a second temperature, and the surface of the substrate is pre-oxidized at the second temperature; The temperature inside the diffusion furnace tube is maintained at the second temperature, and a dopant source is repeatedly introduced into the diffusion furnace tube to perform multiple diffusion depositions. The temperature inside the diffusion furnace tube is raised to a third temperature, and multiple high-temperature propulsion processes are performed at the third temperature. The temperature inside the diffusion furnace tube is lowered to the second temperature, and cryogenic propulsion is performed at the second temperature; The temperature inside the diffusion furnace tube is lowered to a fourth temperature to form a semiconductor doped layer on the substrate surface.

2. The method according to claim 1, characterized in that, The doping source includes oxygen and boron sources; Maintaining the temperature inside the diffusion furnace tube at the second temperature and repeatedly introducing a doping source into the diffusion furnace tube includes: The diffusion furnace tube is kept heated to maintain the temperature inside the diffusion furnace tube at the second temperature. The dopant source is continuously introduced into the diffusion furnace tube for the first time within a first preset time to perform the first diffusion deposition. After the first introduction of the doping source is completed, the doping source is continuously introduced into the diffusion furnace tube for a second time within the first preset time period to perform a second diffusion deposition. After the second introduction of the doping source is completed, the doping source is introduced into the diffusion furnace tube for the third time within the first preset time period to perform the third diffusion deposition.

3. The method according to claim 2, characterized in that, The doping source introduced into the diffusion furnace tube for the first time is the same as the doping source introduced into the diffusion furnace tube for the second time and the doping source introduced into the diffusion furnace tube for the third time. The doping source first introduced into the diffusion furnace tube is a boron source with a first flow rate and an oxygen source with a second flow rate.

4. The method according to claim 2, characterized in that, After the first introduction of the doping source is completed and before the second introduction of the doping source, the method further includes: The diffusion furnace tube is kept heated to maintain the temperature inside the diffusion furnace tube at the second temperature, and the boron source of the first flow rate is continuously introduced into the diffusion furnace tube for a second preset time to perform the first purging. After the second introduction of the doping source is completed and before the third introduction of the doping source, the method further includes: The diffusion furnace tube is kept heated to maintain the temperature inside the diffusion furnace tube at the second temperature, and the boron source at a first flow rate is continuously introduced into the diffusion furnace tube for a second purging within the second preset time.

5. The method according to claim 1, characterized in that, The process of raising the temperature inside the diffusion furnace tube to a third temperature, and then performing multiple high-temperature propulsion operations at that third temperature, includes: The diffusion furnace tube is heated, and the temperature inside the diffusion furnace tube is raised from the second temperature to the third temperature within a third preset time. The diffusion furnace tube is kept heated, and the temperature inside the diffusion furnace tube is controlled to be maintained at the third temperature for a fourth preset time, so as to carry out the first high-temperature propulsion. After the first high-temperature propulsion is completed, heating is paused during the first interval. After the first interval, the diffusion furnace tube is heated again to maintain the temperature inside the diffusion furnace tube at the third temperature for the third preset time, so as to carry out the second high-temperature propulsion.

6. The method according to claim 1, characterized in that, The step of cooling the temperature inside the diffusion furnace tube to the second temperature, and performing cryogenic propulsion at the second temperature, includes: Within a third preset time period, the temperature inside the diffusion furnace tube is cooled from the third temperature to the second temperature, and the diffusion furnace tube is heated so that the temperature inside the diffusion furnace tube is maintained at the second temperature within a fifth preset time period for low-temperature propulsion.

7. The method according to claim 1, characterized in that, The step of cooling the temperature inside the diffusion furnace tube to a fourth temperature to form a semiconductor doped layer on the substrate surface includes... The temperature inside the diffusion furnace tube is reduced from the second temperature to the fourth temperature; The diffusion furnace tube is heated to maintain the temperature inside the diffusion furnace tube at the second temperature for a sixth preset time period; heating is paused for a second interval period, and after the second interval period, the diffusion furnace tube is heated again to maintain the temperature inside the diffusion furnace tube at the second temperature for a seventh preset time period, so as to form a semiconductor doped layer on the substrate surface.

8. The method according to claim 1, characterized in that, After the temperature inside the diffusion furnace tube is raised to the second temperature, and before the substrate surface is pre-oxidized, the method further includes: The diffusion furnace tube is kept heated so that the temperature inside the diffusion furnace tube is maintained at the second temperature for a fourth preset time, and nitrogen gas with a third flow rate is continuously introduced during the fourth preset time. After the fourth preset time, heating is paused during the third interval. After the third interval ends, the diffusion furnace tube is heated again so that the temperature inside the diffusion furnace tube remains at the second temperature for the sixth preset time.

9. The method according to claim 8, characterized in that, The pre-oxidation treatment of the substrate surface at the second temperature includes: After the sixth preset time, the diffusion furnace tube is kept heated so that the temperature inside the diffusion furnace tube remains at the second temperature for an eighth preset time, and oxygen at a fourth flow rate and nitrogen at a fifth flow rate are continuously introduced during the eighth preset time.

10. The method according to claim 1, characterized in that, After forming a semiconductor doped layer on the substrate surface, the method further includes: The temperature inside the diffusion furnace tube is raised to a fifth temperature, and the substrate is annealed multiple times at the fifth temperature; The substrate is oxidized multiple times while maintaining the fifth temperature; The temperature inside the diffusion furnace tube is lowered to a sixth temperature to obtain the heat-treated substrate.

11. The method according to claim 10, characterized in that, The step of raising the temperature inside the diffusion furnace tube to a fifth temperature and annealing the substrate formed at the fifth temperature includes: The diffusion furnace tube is heated to raise the temperature inside the diffusion furnace tube to a fifth temperature. After the temperature inside the diffusion furnace tube reaches the fifth temperature, the diffusion furnace tube is kept heated so that the temperature inside the diffusion furnace tube remains at the fifth temperature for a ninth preset time. During the ninth preset time, oxygen of a sixth flow rate is continuously introduced into the diffusion furnace tube to perform the first annealing. After the ninth preset time, heating is paused during the fourth interval. After the fourth interval, the diffusion furnace tube is heated again to maintain the fifth temperature within the seventh preset time. During the seventh preset time, oxygen at a sixth flow rate is continuously introduced into the diffusion furnace tube for a second annealing. After the seventh preset time, heating is paused during the fourth interval. After the fourth interval, the diffusion furnace tube is heated again to maintain the fifth temperature within the tenth preset time. During the tenth preset time, oxygen at a sixth flow rate is continuously introduced into the diffusion furnace tube for a third annealing. After the tenth preset time, heating is paused during the fourth interval. After the fourth interval, the diffusion furnace tube is heated again to maintain the fifth temperature during the eleventh preset time. During the eleventh preset time, oxygen at a sixth flow rate is continuously introduced into the diffusion furnace tube for the fourth annealing.

12. The method according to claim 10, characterized in that, Maintaining the fifth temperature and performing multiple oxidation processes on the substrate includes: The diffusion furnace tube is kept heated so that the temperature inside the diffusion furnace tube is maintained at the fifth temperature for a twelfth preset time, and oxygen of a sixth flow rate is continuously introduced into the diffusion furnace tube for the twelfth preset time to carry out the first oxidation. After the twelfth preset time, heating is paused during the fifth interval. After the fifth interval, the diffusion furnace tube is heated again to maintain the fifth temperature during the thirteenth preset time. During the thirteenth preset time, oxygen at a sixth flow rate is continuously introduced into the diffusion furnace tube for a second oxidation.

13. The method according to claim 10, characterized in that, The step of cooling the temperature inside the diffusion furnace tube to the sixth temperature includes: The temperature inside the diffusion furnace tube is reduced from the fifth temperature to the sixth temperature; The diffusion furnace tube is heated so that the temperature inside the diffusion furnace tube is maintained at the sixth temperature for a fourteenth preset time. After the fourteenth preset time, heating is paused for a sixth interval. After the sixth interval, the diffusion furnace tube is heated again so that the temperature inside the diffusion furnace tube is maintained at the sixth temperature for a fifteenth preset time.

14. A photovoltaic module, characterized in that, include: The battery cell prepared by the method of any one of claims 1-13.

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