A solar cell and metallization process based on low surface depth junction

Abstract

The present invention discloses a solar cell and metallization process based on low surface depth junction, which sequentially include the following steps: pre-process, boat entry, pre-pressure extraction, pressure extraction, leak detection, pre-oxygenation, primary purging, primary source connection, secondary purging, secondary source connection, junction pushing, primary cooling, phosphorus supplementation, secondary cooling, phosphorus laying, tertiary purging, primary back pressure, secondary back pressure, boat exit, and end; wherein, under the condition of increasing the voltage while keeping the sheet resistance unchanged, the junction pushing time is increased in the junction pushing step, thereby increasing the junction depth, and reducing the phosphorus surface concentration in the phosphorus laying step. The present invention increases the junction depth and reduces the phosphorus surface concentration at the same time, thereby achieving the goal of keeping the sheet resistance unchanged while increasing the voltage, thereby improving the conversion efficiency of the solar cell.

Description

Technical Field

[0001] The invention relates to a solar cell based on low surface depth junction and a metallization process, belonging to the technical field of solar cells. Background Art

[0002] With the continuous development of solar cell manufacturing technology, the efficiency improvement of solar cells has reached a bottleneck.

[0003] Chinese patent CN210110794U discloses a low surface concentration deep junction solar cell, comprising a crystalline silicon wafer, a gate electrode arranged on the light-receiving surface of the crystalline silicon wafer, and a back electrode arranged on the backlight surface of the crystalline silicon wafer. The crystalline silicon wafer is composed of a diffusion layer and a base layer distributed up and down, and the diffusion layer is divided into a lightly doped region and a heavily doped region. The heavily doped region is distributed below the gate line of the gate electrode, and the top end surface of the heavily doped region overlaps with the bottom end surface of the gate line of the gate electrode and has the same size. The doping concentration of the heavily doped region is higher than the doping concentration of the lightly doped region, and the junction depth of the heavily doped region is higher than the junction depth of the lightly doped region. By forming a high concentration doping in the area below the gate electrode and forming a low concentration doping in the area outside the gate electrode, surface recombination is reduced and the photoelectric conversion efficiency is improved.

[0004] Chinese patent CN106057982B discloses a method for preparing a low surface concentration assembleable pn crystalline silicon solar cell, comprising the following steps: 1) texturing on the upper surface of P-type silicon; 2) preparing several layers of N-type nano silicon thin films on the surface of the P-type silicon after texturing, and sequentially stacking and covering the surface of the P-type silicon; 3) annealing the P-type silicon covered with several layers of N-type nano silicon thin films; 4) preparing an anti-reflection film; 5) preparing a back electrode and a back electric field on the lower surface of the P-type silicon; 6) making a positive electrode on the upper surface of the N-type nano silicon thin film. Compared with the prior art, the method of the present invention adopts a method of covering a plurality of N-type nano silicon thin films on the P-type silicon to prepare the pn junction, the junction depth of the pn junction is controlled by the number of layers of the N-type nano silicon thin film, and the surface concentration of the N-type nano silicon thin film is low and controllable, so that the pn prepared in this way has a low surface concentration and a controllable junction depth, which can greatly improve the quality of the pn junction and improve the conversion efficiency of the battery.

[0005] Chinese patent CN103715302B discloses a diffusion method with low surface concentration, including the following steps: placing a silicon wafer in a diffusion furnace, and introducing a small N2, N2 and O2 containing a phosphorus source into the diffusion furnace, diffusing phosphorus on the silicon wafer at a temperature of 800℃~820℃; turning off the small N2, maintaining a temperature of 800℃~820℃, introducing N2 and O2 into the diffusion furnace to push the silicon wafer through oxygen for a short time; introducing N2 into the diffusion furnace, and pushing the silicon wafer with high temperature nitrogen at a temperature of 850℃~870℃; introducing N2 into the diffusion furnace, and pushing the silicon wafer with low temperature nitrogen at a temperature of 740℃~780℃; and removing the silicon wafer from the furnace under the protection of N2. The PN junction is made by the diffusion method provided by the present invention, and the junction depth and surface concentration are easier to adjust and control; the surface doping concentration of the silicon wafer is low, and the surface recombination rate is small; the photoelectric conversion efficiency of the solar cell manufactured subsequently is high.

[0006] From the above, it can be seen that in the existing technical solutions, the method of adjusting the surface concentration and junction depth is adopted to achieve the improvement of the conversion efficiency of the solar cell. However, the relationship between the surface concentration and the junction depth, and how to adjust them to better achieve the improvement of the conversion efficiency of the solar cell are not disclosed in the existing technology. Summary of the invention

[0007] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a solar cell and metallization process based on a low surface depth junction, which increases the junction depth while reducing the phosphorus surface concentration under the premise of increasing the voltage while keeping the square resistance unchanged, thereby achieving the goal of keeping the square resistance unchanged while increasing the voltage, thereby improving the conversion efficiency of the solar cell.

[0008] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A solar cell metallization process based on low surface depth junction comprises the following steps in sequence: pre-process, boat entry, pre-pressure extraction, pressure extraction, leak detection, pre-oxygenation, primary purging, primary source connection, secondary purging, secondary source connection, junction pushing, primary cooling, phosphorus supplementation, secondary cooling, phosphorus laying, tertiary purging, primary back pressure, secondary back pressure, boat exit and end; wherein, under the condition of increasing voltage and keeping square resistance unchanged, the junction depth is increased and the phosphorus surface concentration is reduced.

[0010] Preferably: the temperature is increased in the pre-oxygen, primary purge, primary source, secondary purge, and secondary source steps, the knot pushing time is increased in the knot pushing step, the temperature is lowered, and the knot depth is increased.

[0011] Preferably, the phosphorus surface concentration is reduced by lowering the temperature during the phosphorus plating step.

[0012] Preferably: in the secondary back-pressure step, the back-pressure time is reduced, and the magnitude of the reduced back-pressure time is close to the magnitude of the increased pushing time.

[0013] Preferably, the pushing time is increased to 160-180s in the pushing step.

[0014] Preferably, the temperature is reduced to 10-18 degrees Celsius during the phosphorus plating step.

[0015] Preferably, the back pressure time is reduced to 160-180s in the secondary back pressure step.

[0016] The temperature is increased by 1-16 degrees Celsius in the steps of pre-oxygenation, primary purge, primary source connection, secondary purge, and secondary source connection.

[0017] Preferably: preferably: in the pushing step, the pushing time is increased to 170 seconds. In the phosphorus-laying step, the temperature is reduced to 15 degrees Celsius. In the secondary back-pressing step, the back-pressing time is reduced to 180 seconds.

[0018] A solar cell comprises a substrate and a metallized solar cell produced by a solar cell metallization process based on a low surface depth junction, wherein the metallized solar cell is arranged on the substrate.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] By increasing the temperature before pushing the junction, increasing the pushing time and lowering the temperature during the pushing step, thereby increasing the junction depth, and lowering the temperature during the phosphorus plating step to reduce the phosphorus surface concentration, the square resistance can be kept unchanged while increasing the voltage, thereby improving the conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the surface concentration versus junction depth curve in the ECV curve when the surface concentrations of samples A and B are basically the same.

[0022] Figure 2 This is the current-voltage curve in the ECV curve when the surface concentrations of samples A and B are basically the same.

[0023] Figure 3 This is the surface concentration versus junction depth curve in the ECV curve when the junction depths of samples C and D are basically the same.

[0024] Figure 4 This is the current-voltage curve in the ECV curve when the junction depths of samples C and D are basically the same.

[0025] Figure 5 This is the relationship between junction depth and surface concentration under the condition of constant square resistance in simulation software.

[0026] Figure 6This is the relationship between voltage and surface concentration under the condition of constant square resistance in the simulation software.

[0027] Figure 7 This is the relationship between voltage and junction depth under the condition of constant square resistance in simulation software.

[0028] Figure 8 This is the relationship between voltage, junction depth and surface concentration under the condition of constant square resistance in simulation software. DETAILED DESCRIPTION

[0029] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0030] Example 1

[0031] A solar cell metallization process based on low surface depth junction includes the following steps in sequence: pre-process, boat entry, pre-pressure extraction, pressure extraction, leak detection, pre-oxygenation, primary purge, primary source connection, secondary purge, secondary source connection, junction pushing, primary cooling, phosphorus supplementation, secondary cooling, phosphorus laying, tertiary purge, primary back pressure, secondary back pressure, boat exit, and end; wherein, under the condition of increasing voltage while keeping the square resistance unchanged, the junction depth is increased and the phosphorus surface concentration is reduced. In the pre-oxygenation, primary purge, primary source connection, secondary purge, and secondary source connection steps, the temperature is increased, and in the junction pushing step, the junction pushing time is increased, the temperature is reduced, and the junction depth is increased. In the phosphorus laying step, the temperature is reduced to reduce the phosphorus surface concentration, and the square resistance is kept unchanged while the voltage is increased, thereby improving the conversion efficiency of the solar cell. In the secondary back pressure step, the back pressure time is reduced, and the size of the back pressure time is reduced to the vicinity of the increased junction pushing time, so as to achieve the stability of the overall diffusion time.

[0032] like Figure 1 , 2 As shown in the figure, through the simulation software, it can be known that when the surface concentrations of samples A and B are basically the same, the ECV curve of sample A shows that its junction depth is significantly greater than that of sample B, and the voltage calculated by the ECV curve of sample A is smaller than the voltage calculated by the ECV curve of sample B. This shows that the smaller the advancement depth, the higher the voltage.

[0033] like Figure 3 , 4 As shown in the figure, except for the different surface concentrations, the other information including junction depth of the ECV curves of samples C and D are basically the same. The voltage calculated from the ECV curve of sample C is significantly higher than the voltage calculated from the ECV curve of sample D. This shows that reducing the surface concentration can increase the battery voltage.

[0034] like Figure 5 As shown in the figure, through simulation software, it can be known that under the condition of constant square resistance, the junction depth and surface concentration show a certain functional relationship. Figure 6 As shown in , when the sheet resistance remains unchanged, the higher the surface concentration, the lower the voltage. Figure 7 As shown in the figure, the deeper the junction depth, the higher the voltage when the square resistance remains unchanged. Figure 8 As shown, while keeping the square resistance unchanged, it moves towards the direction of low surface concentration and high junction depth.

[0035] The above illustrates that increasing the junction depth and reducing the phosphorus surface concentration can ensure that the voltage is increased while keeping the square resistance unchanged, thereby improving the efficiency of the solar cell.

[0036] The process parameters of each step of the solar cell metallization process based on low surface depth junction of this embodiment 1 are shown in Table 1.

[0037] Table 1 Process parameters of Example 1

[0038]

[0039]

[0040] Among them, T1, T2, T3, T4, T5, and T6 refer to the temperature of each step, in degrees Celsius. Large nitrogen and small nitrogen refer to the nitrogen flow rates of two different pipelines. The one with a large flow rate is large nitrogen, and the one with a small flow rate is small nitrogen. The unit is sccm. Small oxygen refers to the flow rate of oxygen introduced, in sccm. Pressure refers to the pressure of each step, in mbar. Fan refers to the switch of the source bottle. 0 means closed and no phosphorus source is introduced. 4 means open and phosphorus source is introduced. Furnace mouth nitrogen refers to the nitrogen flow rate at the furnace mouth, in sccm.

[0041] A solar cell comprises a substrate and a metallized solar cell produced by a solar cell metallization process based on a low surface depth junction, wherein the metallized solar cell is arranged on the substrate.

[0042] Example 2

[0043] The process parameters of each step of the solar cell metallization process based on low surface depth junction of this embodiment 2 are shown in Table 2.

[0044] Table 2 Process parameters of Example 2

[0045]

[0046]

[0047] It can be seen from the above table that the differences between this embodiment and Embodiment 1 are as follows: the pushing time is increased in the pushing step, the temperature is lowered in the phosphorus plating step, and the back pressure time is reduced in the secondary back pressure step.

[0048] Example 3

[0049] The process parameters of each step of the solar cell metallization process based on low surface depth junction of this embodiment 3 are shown in Table 3.

[0050] Table 3 Process parameters of Example 3

[0051]

[0052]

[0053] It can be seen from the above table that the differences between this embodiment and Embodiment 1 are as follows: the pushing time is increased in the pushing step, the temperature is lowered in the phosphorus plating step, and the back pressure time is reduced in the secondary back pressure step.

[0054] Example 4

[0055] The process parameters of each step of the existing solar cell metallization process of this embodiment 4 are shown in Table 4.

[0056] Table 4 Process parameters of Example 4

[0057]

[0058]

[0059]

[0060] Table 5 Differences in parameters between Example 1 and Example 4

[0061]

[0062]

[0063] It can be seen from Table 5 that the difference between Example 1 and Example 4 is as follows: the temperature is increased in the pre-oxygen, primary purge, primary source, secondary purge, and secondary source steps; the push junction time is increased in the push junction step, the temperature is lowered, and the junction depth is increased; the temperature is lowered in the phosphorus plating step, and the phosphorus surface concentration is lowered, thereby achieving the goal of increasing the voltage while maintaining the square resistance unchanged. The reduction of the back pressure time in the secondary back pressure step is different. In Example 1 and Example 4, the temperature is increased by 1-12 degrees Celsius before pushing the junction. In the low-surface deep junction metallization diffusion process, the push junction time is increased by 170s, and the temperature is reduced by 3-9 degrees Celsius at the same time to achieve deep junction diffusion; the temperature is reduced by 10-18 degrees Celsius in the phosphorus plating step to achieve low surface concentration diffusion. The overall extra time is subtracted by 180s in the secondary back pressure step to achieve the stability of the overall diffusion time.

[0064] As can be seen from the above, the temperature is controlled at 787-792°C in the pre-oxygen step, 787-792°C in the first purge step, 787-792°C in the first source step, 792-797°C in the second purge step, 792-797°C in the second source step, and 910-930s and 842-848°C in the push-junction step, thereby increasing the junction depth. In the phosphorus-laying step, the temperature is controlled at 768-772°C to achieve low surface concentration diffusion. In the second back pressure step, the time is controlled at 0-20s to achieve the stability of the overall diffusion time.

[0065] Table 6 Electrical performance data of Example 1 and Example 4

[0066]

[0067] It can be seen from Table 6 that compared with Example 4, the conversion efficiency Eta of Example 1 is increased by 0.024, the open circuit voltage Uoc is increased by 0.0006v, the short circuit current Isc is increased by 0.001A, and the fill factor is increased by 0.005. Therefore, compared with Example 4, the overall battery efficiency of Example 1 is greatly improved.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A solar cell metallization process based on low surface deep junction, characterized in that: The following steps are included in sequence: Pre-process, entering the boat, pre-pressure extraction, pressure extraction, leak detection, pre-oxygenation, primary purge, primary source connection, secondary purge, secondary source connection, junction pushing, primary cooling, phosphorus supplementation, secondary cooling, phosphorus laying, tertiary purge, primary back pressure, secondary back pressure, leaving the boat, and ending; wherein, under the condition of increasing the voltage while keeping the square resistance unchanged, the junction depth is increased and the phosphorus surface concentration is reduced; In the steps of pre-oxygenation, primary purge, primary source connection, secondary purge, and secondary source connection, the temperature is increased by 1-16 degrees Celsius in the steps of pre-oxygenation, primary purge, primary source connection, secondary purge, and secondary source connection; In the knot pushing step, the knot pushing time is increased, the temperature is lowered, and the knot depth is increased; in the knot pushing step, the knot pushing time is increased to 160-180s, and the temperature is lowered to 3-9 degrees Celsius; Reduce the back pressure time to 160-180s in the secondary back pressure step; In the phosphorus-laying step, the temperature is lowered to reduce the phosphorus surface concentration; in the phosphorus-laying step, the temperature is lowered to 10-18 degrees Celsius.

2. The solar cell metallization process based on low surface depth junction according to claim 1, characterized in that: In the pushing step, the pushing time is increased to 170s, in the phosphorus-laying step, the temperature is lowered to 15 degrees Celsius, and in the secondary back-pressure step, the back-pressure time is reduced to 180s.

3. A solar cell, characterized in that: The invention comprises a substrate and a metallized solar cell produced by the solar cell metallization process based on low surface depth junction according to claim 1, wherein the metallized solar cell is arranged on the substrate.

Images