A two-terminal all-silicon-based double-junction solar cell and its manufacturing method

Abstract

The present invention relates to the field of solar cells, and discloses a two-terminal all-silicon-based double-junction solar cell and a preparation method thereof. The two-terminal all-silicon-based double-junction solar cell comprises: an N-type silicon substrate, a pyramid-textured surface and a passivation and antireflection film sequentially arranged on the front surface of the N-type silicon substrate, and a positive electrode region and a negative electrode region arranged on the back surface of the N-type silicon substrate; the positive electrode region comprises an inner boron diffusion layer, a phosphorus diffusion layer, an outer boron diffusion layer and a passivation and antireflection film sequentially arranged on the back surface of the N-type silicon substrate, and a positive electrode arranged on the surface of the outer boron diffusion layer; the negative electrode region comprises a passivation and antireflection film arranged on the back surface of the N-type silicon substrate, and a negative electrode arranged on the back surface of the N-type silicon substrate. The present invention creatively designs a two-terminal all-silicon-based double-junction stacked cell, which can effectively solve the problem of poor stability of conventional stacked cells. In addition, through a clever structural design, the present invention designs all the electrodes on the back surface of the cell, which can effectively reduce the shading damage and is beneficial to improving the cell performance.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and in particular to a two-terminal all-silicon-based double-junction solar cell and a preparation method thereof. Background Art

[0002] Different from conventional single-junction solar cells such as TOPCon cells, a tandem cell is a brand-new multi-junction solar cell. Since such a cell is formed by connecting a top cell and a bottom cell in series, a higher open-circuit voltage can be obtained (for example, the perovskite-silicon tandem cell in Patent CN118414005A). Based on this, a higher conversion efficiency can be achieved, making it a current cutting-edge solar cell technology.

[0003] However, there are still many difficulties with multi-junction tandem cells at present: First, the preparation steps of tandem cells are numerous and complex, resulting in a high cost; second, the stability of the top perovskite cell (ionic crystal) of the tandem cell is poorer than that of the bottom silicon-based cell (atomic crystal), posing a huge challenge to the reliability of the overall cell. Due to the above reasons, the current development of double-junction tandem cells as a whole is still in a situation of "only blooming but not bearing fruit". Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a two-terminal all-silicon-based double-junction solar cell and a preparation method thereof. The present invention creatively designs a two-terminal all-silicon-based double-junction cell, which not only has a simple process but also can effectively solve the problem of poor stability of conventional tandem double-junction cells. In addition, through a clever structural design, the present invention designs all electrodes on the back of the cell, which can effectively reduce shading damage and is beneficial to improving the cell performance.

[0005] The specific technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a two-terminal all-silicon-based double-junction solar cell, which includes:

[0007] An N-type silicon substrate, a pyramid-shaped textured surface, a passivation and antireflection film sequentially disposed on the front surface of the N-type silicon substrate, and a positive electrode region and a negative electrode region disposed on the back surface of the N-type silicon substrate. Among them:

[0008] The positive electrode region includes an inner boron diffusion layer, a phosphorus diffusion layer, an outer boron diffusion layer, and a passivation and antireflection film sequentially disposed on the back surface of the N-type silicon substrate, and a positive electrode disposed on the surface of the outer boron diffusion layer and penetrating through the passivation and antireflection film;

[0009] The negative electrode region includes a passivation and antireflection film disposed on the back surface of the N-type silicon substrate, and a negative electrode disposed on the back surface of the N-type silicon substrate and penetrating through the passivation and antireflection film.

[0010] As described in the background art section, since the structure of current tandem cells is generally a perovskite cell on the top and a silicon-based cell on the bottom, the perovskite cell (ionic crystal) has poorer stability compared to the silicon-based cell (atomic crystal), which leads to insufficient reliability of the overall tandem cell. For this reason, the present invention creatively designs the above-mentioned all-silicon-based tandem cell (both the top and bottom of the cell are silicon-based cells without perovskite cells), effectively solving the problem of poor stability of perovskite cells. In addition, through a clever structural design (the design of the back negative region) in the present invention, the front electrode of the conventional tandem cell is moved to the back (electrodes are provided on both the front and back of the conventional tandem cell), which can effectively reduce shading damage and is beneficial to improving the cell performance.

[0011] Preferably, the boron atom concentration in the inner boron diffusion layer is lower than the phosphorus atom concentration in the phosphorus diffusion layer, and the phosphorus atom concentration in the phosphorus diffusion layer is lower than the boron atom concentration in the outer boron diffusion layer.

[0012] Optionally, the positive electrode region and the negative electrode region are respectively located in two side regions on the back surface of the N-type silicon substrate.

[0013] In a second aspect, the present invention provides a method for manufacturing a two-terminal all-silicon-based tandem solar cell, which includes the following steps:

[0014] S1. Double-sided polishing of the N-type silicon substrate.

[0015] S2. First boron diffusion on the back surface, and an inner boron diffusion layer and a BSG layer are sequentially formed on the back surface of the N-type silicon substrate.

[0016] After the first boron diffusion, a boron diffusion layer that changes the back surface of the silicon substrate from N-type to P-type is formed. Since the subsequent processes of the present invention require phosphorus atom doping (phosphorus diffusion) and boron atom secondary doping (secondary boron diffusion) on the basis of the first boron diffusion, a part of the surface layer of the inner boron diffusion layer is changed into a phosphorus diffusion layer and a high-concentration outer boron diffusion layer; therefore, the surface boron atom doping concentration in the first boron diffusion process needs to be designed to be relatively low (but higher than the phosphorus atom doping amount in the N-type silicon substrate itself, 1E15~1E16 cm -3 ) and the doping depth needs to be relatively deep.

[0017] S3. Chain removal of the BSG layer on the back surface.

[0018] The presence of the BSG layer on the back surface will block the penetration of phosphorus atoms in the subsequent phosphorus diffusion and boron atoms in the secondary boron diffusion into the inner boron diffusion layer, so it needs to be removed in advance.

[0019] S4. Phosphorus diffusion on the back surface to convert the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer and a PSG layer.

[0020] During this process, since a wrap-around coating (boron diffusion layer and BSG layer) will be formed on the front side of the silicon substrate during a single boron diffusion in S2, this BSG layer can block the entry of doping atoms into the front region during subsequent phosphorus diffusion and secondary boron diffusion. In addition, in order to form an ideal phosphorus diffusion layer, the doping concentration of phosphorus atoms after phosphorus diffusion must be higher than that of boron atoms after the first boron diffusion, and the doping depth is shallower than that of the first boron diffusion.

[0021] S5. Chain-remove the PSG layer on the back side.

[0022] The presence of the PSG layer on the back side will block the penetration of boron atoms into the phosphorus diffusion layer during subsequent secondary boron diffusion, so it needs to be removed in advance.

[0023] S6. Perform secondary boron diffusion on the back side to convert the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer.

[0024] Since secondary boron diffusion needs to transform the surface of the phosphorus diffusion layer formed in S4 into a high-concentration outer boron diffusion layer, the doping concentration of boron atoms on the surface needs to be relatively high after secondary boron diffusion, higher than the doping concentration of phosphorus atoms in the phosphorus diffusion layer; in addition, the doping depth during secondary boron diffusion should not be too large (the doping depth is less than the phosphorus doping depth in S4). After secondary boron diffusion, a layered alternating N-P-N-P (double-junction) structure (N-type silicon substrate - P-type inner boron diffusion layer - N-type phosphorus diffusion layer - P-type outer boron diffusion layer) is formed on the entire back side of the silicon substrate.

[0025] S7. Laser pattern to remove the BSG layer in the negative electrode region on the back side.

[0026] S8. Chain-remove the BSG layer on the surface of the front wrap-around coating.

[0027] S9. Clean and texture to remove the deposition layer on the surface of the silicon substrate in the negative electrode region and form a pyramid-shaped texture on the front side.

[0028] S10. Double-sided coating to form a passivation and antireflection film on the front and back sides.

[0029] S11. Screen printing, sintering, and light injection to form a positive electrode and a negative electrode in the positive electrode region and the negative electrode region respectively.

[0030] Preferably, the conditions for the first boron diffusion are: boron diffusion temperature 900 - 950 °C, diffusion time 20 - 80 min, BCl3 flow rate 20 - 100 sccm, O2 flow rate 200 - 1000 sccm; oxidation and push temperature 1000 - 1050 °C, O2 flow rate 1000 - 20000 sccm, push time 60 - 120 min, the thickness of the obtained BSG layer is 30 - 80 nm; the surface doping concentration of boron atoms is 1E17 - 5E18 cm -3 , doping depth 2 - 5 μm.

[0031] As described above, since the subsequent processes of the present invention require phosphorus diffusion and secondary boron diffusion on the basis of primary boron diffusion, a part of the surface layer of the inner boron diffusion layer is transformed into a phosphorus diffusion layer and a high-concentration outer boron diffusion layer; therefore, the surface boron atom doping concentration in the primary boron diffusion process needs to be designed to be relatively low (but higher than the phosphorus atom doping amount in the N-type silicon substrate itself, 1E15~1E16 cm -3 ), and the doping depth needs to be relatively deep. Therefore, in order to achieve the above object, it is necessary to precisely control the process of primary boron diffusion. Finally, the present invention finds that the above object can be achieved under the above boron diffusion conditions (the main characteristics of the primary boron diffusion process of the present invention compared with the conventional boron diffusion process are: relatively less source throughput; longer oxidation and diffusion time).

[0032] Preferably, the phosphorus diffusion conditions are: phosphorus diffusion temperature 750~850 °C, diffusion time 5~30 min, the flow rate of POCl3 carried by nitrogen is 200~500 sccm, and the O2 flow rate is 300~1000 sccm; oxidation and diffusion temperature 850~950 °C, O2 flow rate 500~3000 sccm, diffusion time 30~90 min; the thickness of the obtained PSG layer is 30~70 nm, and the surface phosphorus atom doping concentration is 6E18~1E19 cm -3 , and the doping depth is 1~2 μm.

[0033] In order to convert the surface layer of the inner boron diffusion layer into an N-type phosphorus diffusion layer, the phosphorus atom doping concentration after phosphorus diffusion must be higher than the boron atom concentration after primary boron diffusion, and the doping depth is shallower than that of primary boron diffusion. Similarly, it is necessary to precisely control the process of phosphorus diffusion. Finally, the present invention finds that the above object can be achieved under the above phosphorus diffusion conditions (the main characteristic of the phosphorus diffusion process of the present invention compared with the conventional phosphorus diffusion process is the longer oxidation and diffusion time).

[0034] Preferably, the secondary boron diffusion conditions are: boron diffusion temperature 900~950 °C, diffusion time 20~80 min, BCl3 flow rate 300~800 sccm, O2 flow rate 1000~5000 sccm; oxidation and diffusion temperature 1000~1050 °C, O2 flow rate 5000~80000 sccm, diffusion time 10~50 min, the thickness of the obtained BSG layer is 20~60 nm, and the surface doping concentration is 2E19~1E20cm -3 , and the doping depth is 0.3~1 μm.

[0035] As described above, since the secondary boron diffusion needs to transform the surface of the phosphorus diffusion layer formed by S4 into a high-concentration outer boron diffusion layer, the surface boron atom doping concentration after the secondary boron diffusion needs to be relatively high, higher than the phosphorus atom doping concentration in the phosphorus diffusion layer. In addition, during the secondary boron diffusion process, the doping depth cannot be too large (the doping depth is less than the phosphorus doping depth in S4). In the secondary boron diffusion of the present invention, the boron source flow rate is relatively large, resulting in a relatively high surface boron atom doping concentration; at the same time, the oxidation promotion time is relatively short, so that the doping depth can be precisely controlled.

[0036] In a third aspect, the present invention provides another method for manufacturing a two-terminal all-silicon-based double-junction solar cell, including:

[0037] S1. Double-sided polishing of the N-type silicon substrate.

[0038] S2. Primary boron diffusion to form an inner boron diffusion layer on the back surface of the N-type silicon substrate in sequence.

[0039] S3. Phosphorus diffusion to convert the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer.

[0040] Since no obvious BSG layer is formed on the surface after the primary boron diffusion in S2, during the phosphorus diffusion process, phosphorus atoms can directly enter the low-concentration inner boron diffusion layer, causing part of this layer to be converted into a phosphorus diffusion layer.

[0041] S4. Secondary boron diffusion to convert the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer.

[0042] Since no obvious PSG layer is formed on the surface after the phosphorus diffusion, during the secondary boron diffusion process, boron atoms can enter the phosphorus diffusion layer. In addition, with the effect of the high temperature during the secondary boron diffusion, the inner boron diffusion layer formed by the initial primary boron diffusion and the phosphorus diffusion layer formed by the phosphorus diffusion will be further advanced synchronously, so as to meet the requirements of the process.

[0043] S5. Laser patterning to remove the BSG layer in the negative electrode region.

[0044] S6. Chain removal of the BSG layer plated on the front surface.

[0045] S7. Cleaning and texturing to remove the surface deposition layer in the negative electrode region and form a pyramid-shaped texture on the front surface;

[0046] S8. Double-sided coating to form a passivation and antireflection film on the front and back surfaces.

[0047] S9. Screen printing to form a positive electrode and a negative electrode in the positive electrode region and the negative electrode region respectively, followed by sintering and optical injection.

[0048] Among them, the phosphorus atom concentration in the N-type silicon substrate < the boron atom concentration in the first boron diffusion < the phosphorus atom concentration in the phosphorus diffusion < the boron atom concentration in the second boron diffusion; and the depth of the first boron diffusion > the depth of the phosphorus diffusion > the depth of the second boron diffusion; and both the first boron diffusion and the phosphorus diffusion adopt oxygen-free propulsion, while the second boron diffusion adopts oxygen-containing propulsion; the propulsion time of the first boron diffusion and the phosphorus diffusion is shorter than that of the second boron diffusion.

[0049] The research team of the present invention found that in the preparation method provided in the second aspect of this application, due to the secondary high-temperature effect brought by the high-temperature propulsion process of the second boron diffusion on the boron diffusion layer formed by the first boron diffusion and the phosphorus diffusion layer formed by the phosphorus diffusion, the doping depth of each initial diffusion layer will be further increased, seriously affecting the subsequent evaluation of experimental results (since the temperature during the phosphorus diffusion process is relatively low, the influence on the inner boron diffusion layer is small). Secondly, after the first boron diffusion and the phosphorus diffusion, BSG layer and PSG layer will be formed respectively; separate steps are required to remove them, which not only makes the process cumbersome, but also increases the internal stress of the silicon substrate after multiple rounds of high and low temperature treatments, increasing the probability of silicon substrate fragmentation. Therefore, the present invention further optimizes the processes of the first boron diffusion and the phosphorus diffusion, that is, adopts a continuous high-temperature diffusion process of "no oxygen supply and short propulsion time", which can not only accurately control the doping depth, but also will not generate B / PSG layer, and can significantly shorten the cycle (conventional diffusion process: the first step is diffusion, the second step is oxidation propulsion, and oxygen participates in the oxidation propulsion process, thus forming a B / PSG layer on the surface, and the B / PSG layer is the key to blocking wet alkali etching in the follow-up).

[0050] Preferably, the conditions for the first boron diffusion are as follows: the boron diffusion temperature is 900-950 °C, the diffusion time is 20-80 min, the BCl3 flow rate is 20-100 sccm, and the O2 flow rate is 200-1000 sccm; the propulsion temperature is 1000-1050 °C, and the propulsion time is 40-100 min; the surface boron atom doping concentration is 3E17-7E18 cm -3 (Since the propulsion time is short, most of the surface boron atoms are still in the shallow surface, and the surface doping concentration is relatively higher), and the doping depth is 1.5-4.5 μm (since the propulsion time is short, the doping depth is correspondingly shallower).

[0051] In the above first boron diffusion process, first, no oxygen participates in the high-temperature propulsion process, and almost no BSG layer is generated on the surface, so there is no need to remove the BSG layer in the subsequent steps; secondly, since there will be a secondary high-temperature propulsion in the subsequent second boron diffusion, the high-temperature propulsion time of the first boron diffusion is relatively short, which can shorten the process time and reduce the cost.

[0052] Preferably, the conditions for phosphorus diffusion are as follows: the phosphorus diffusion temperature is 750 - 850 °C, the diffusion time is 5 - 30 min, POCl3 is carried by nitrogen with a flow rate of 200 - 500 sccm, and the O2 flow rate is 300 - 1000 sccm; the driving temperature is 850 - 950 °C, and the driving time is 10 - 50 min; the surface phosphorus doping concentration is 9E18 - 2E19 cm -3 , and the doping depth is 0.8 - 1.5 μm.

[0053] In the above phosphorus diffusion process, there is no oxygen participation during the high-temperature driving process, and almost no PSG layer is generated on the surface. Therefore, there is no need for a subsequent step to remove the PSG layer. In addition, the high-temperature driving time in the phosphorus diffusion process is shorter (the required driving temperature for phosphorus diffusion is lower than that for boron diffusion, so the driving time is shorter than that for one-time boron diffusion). During the subsequent secondary boron diffusion process, the high temperature will synchronously drive the phosphorus diffusion layer to the expected depth position.

[0054] Preferably, the conditions for secondary boron diffusion are as follows: the boron diffusion temperature is 900 - 950 °C, the diffusion time is 20 - 80 min, the BCl3 flow rate is 300 - 800 sccm, and the O2 flow rate is 1000 - 5000 sccm; the oxidation driving temperature is 1000 - 1050 °C, the O2 flow rate is 5000 - 80000 sccm, the driving time is 10 - 50 min, and the obtained BSG layer thickness is 20 - 60 nm; the surface boron doping concentration is 2E19 - 1E20cm -3 , and the doping depth is 0.3 - 1 μm.

[0055] In the above secondary boron diffusion process, since no oxygen is introduced during the high-temperature driving process of phosphorus diffusion, a relatively obvious PSG layer is not formed on the surface. Therefore, boron atoms can enter the phosphorus diffusion layer during the secondary boron diffusion process. In addition, with the action of the high temperature during the secondary boron diffusion, the inner boron diffusion layer formed by the initial primary boron diffusion and the phosphorus diffusion layer formed by phosphorus diffusion will be further advanced synchronously, thus meeting the requirements of the process.

[0056] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0057] (1) The present invention creatively designs the above-mentioned all-silicon-based double-junction stacked cell (both the top and the top of the cell are silicon-based cells, without perovskite cells), effectively solving the problem of poor stability of perovskite cells. In addition, through a clever structural design (the design of the back negative electrode area) of the present invention, the front electrode of the conventional double-junction stacked cell is moved to the back (electrodes are provided on both the front sides of the conventional double-junction stacked cell), which can effectively reduce the shading damage and is beneficial to improving the cell performance.

[0058] (2) The present invention provides two different methods for preparing the above-mentioned all-silicon-based double-junction stacked cell, and the all-silicon-based double-junction stacked cell prepared by the method of the present invention has excellent performance. Description of the Drawings

[0059] Figure 1 It is a schematic structural diagram of the N-type silicon substrate after double-sided polishing in Example 1.

[0060] Figure 2 It is a schematic structural diagram of the N-type silicon substrate after the first boron diffusion in Example 1.

[0061] Figure 3 It is a schematic structural diagram of the N-type silicon substrate after phosphorus diffusion in Example 1.

[0062] Figure 4 It is a schematic structural diagram of the N-type silicon substrate after the second boron diffusion in Example 1.

[0063] Figure 5 It is a schematic structural diagram of the N-type silicon substrate after wet cleaning and texturing in Example 1.

[0064] Figure 6 It is a schematic structural diagram of the two-terminal all-silicon-based double-junction solar cell of the present invention.

[0065] Figure 7 It is a schematic structural diagram of the unit cell B in Example 3 of the present invention.

[0066] Figure 8 It is a schematic diagram of the connection mode of the battery module composed of the unit cell A and the unit cell B in Example 3 of the present invention.

[0067] The reference numerals are: N-type silicon substrate 1, inner boron diffusion layer 2, BSG layer 3, phosphorus diffusion layer 4, PSG layer 5, outer boron diffusion layer 6, pyramid texture 7, passivation and antireflection film 8, positive electrode 9, negative electrode 10, P-type silicon substrate 11, solder strip 12, inner phosphorus diffusion layer 13, boron diffusion layer 14, outer phosphorus diffusion layer 15. Detailed Embodiments

[0068] The present invention will be further described below in conjunction with embodiments.

[0069] (1) A two-terminal all-silicon-based double-junction solar cell, which includes: an N-type silicon substrate, a pyramid texture and a passivation and antireflection film sequentially arranged on the front surface of the N-type silicon substrate, and a positive electrode region and a negative electrode region arranged on the back surface of the N-type silicon substrate. Among them: the positive electrode region includes an inner boron diffusion layer, a phosphorus diffusion layer, an outer boron diffusion layer and a passivation and antireflection film sequentially arranged on the back surface of the N-type silicon substrate, and a positive electrode arranged on the surface of the outer boron diffusion layer and penetrating through the passivation and antireflection film; the negative electrode region includes a passivation and antireflection film arranged on the back surface of the N-type silicon substrate, and a negative electrode arranged on the back surface of the N-type silicon substrate and penetrating through the passivation and antireflection film.

[0070] In some preferred embodiments, the concentration of boron atoms in the inner boron diffusion layer is lower than the concentration of phosphorus atoms in the phosphorus diffusion layer, and the concentration of phosphorus atoms in the phosphorus diffusion layer is lower than the concentration of boron atoms in the outer boron diffusion layer.

[0071] In some preferred embodiments, the positive electrode region and the negative electrode region are respectively located in two side regions on the back surface of the N-type silicon substrate.

[0072] (2) A preparation method of a two-terminal all-silicon-based double-junction solar cell, which comprises the following steps:

[0073] S1. Double-sided polishing of the N-type silicon substrate: Select the N-type silicon substrate after wire sawing, put it into an alkaline polishing tank, maintain the temperature at 75-85 °C, the time is 6-8 min, perform double-sided polishing, the polishing thickness is 3-7 μm, and the thinning amount is 0.35-0.45 g.

[0074] S2. First boron diffusion on the back surface, and an inner boron diffusion layer and a BSG layer are sequentially formed on the back surface of the N-type silicon substrate. After the first boron diffusion, the back surface of the silicon substrate is changed from N-type to a P-type boron diffusion layer. Since the subsequent processes of the present invention require phosphorus atom doping (phosphorus diffusion) and boron atom secondary doping (secondary boron diffusion) on the basis of the first boron diffusion, a part of the surface layer of the inner boron diffusion layer is changed into a phosphorus diffusion layer and a high-concentration outer boron diffusion layer; therefore, the surface boron atom doping concentration in the first boron diffusion process needs to be designed to be relatively low (but higher than the phosphorus atom doping amount in the N-type silicon substrate itself, 1E15-1E16 cm -3 ), and the doping depth needs to be relatively deep.

[0075] In some preferred embodiments, the conditions for the first boron diffusion are: boron diffusion temperature 900-950 °C, diffusion time 20-80 min, BCl3 flow rate 20-100 sccm, O2 flow rate 200-1000 sccm; oxidation promotion temperature 1000-1050 °C, O2 flow rate 1000-20000 sccm, promotion time 60-120 min, the thickness of the obtained BSG layer is 30-80 nm; the surface boron atom doping concentration is 1E17-5E18 cm -3 , and the doping depth is 2-5 μm.

[0076] S3. Chain removal of the back surface BSG layer. The existence of the back surface BSG layer will block the penetration of phosphorus atoms in the subsequent phosphorus diffusion and boron atoms in the secondary boron diffusion into the inner boron diffusion layer, so it needs to be removed in advance.

[0077] In some preferred embodiments, a chain machine is used to remove the BSG layer on the back surface after the first boron diffusion, wherein the concentration of the HF solution in the chain machine is 20-80 wt%, and the belt speed is 0.5-5 m / min.

[0078] S4. Backside phosphorus diffusion is carried out to convert the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer and a PSG layer. During this process, since the S2 primary boron diffusion will simultaneously form a coating layer (boron diffusion layer and BSG layer) on the front side of the silicon substrate, this BSG layer can block the entry of doping atoms into the front region during subsequent phosphorus diffusion and secondary boron diffusion. In addition, in order to form an ideal phosphorus diffusion layer, the doping concentration of phosphorus atoms after phosphorus diffusion must be higher than that of boron atoms after primary boron diffusion, and the doping depth is shallower than that of primary boron diffusion.

[0079] In some preferred embodiments, the conditions for phosphorus diffusion are as follows: the phosphorus diffusion temperature is 750 - 850 °C, the diffusion time is 5 - 30 min, POCl3 is carried by nitrogen with a flow rate of 200 - 500 sccm, and the O2 flow rate is 300 - 1000 sccm; the oxidation promotion temperature is 850 - 950 °C, the O2 flow rate is 500 - 3000 sccm, and the promotion time is 30 - 90 min; the thickness of the obtained PSG layer is 30 - 70 nm, and the surface doping concentration of phosphorus atoms is 6E18 - 1E19 cm -3 , and the doping depth is 1 - 2 μm.

[0080] S5. The backside PSG layer is removed by a chain machine. The presence of the backside PSG layer will block the penetration of boron atoms into the phosphorus diffusion layer during subsequent secondary boron diffusion, so it needs to be removed in advance.

[0081] In some preferred embodiments, for S5, the backside PSG layer after phosphorus diffusion is removed by a chain machine, where the concentration of the HF solution in the chain machine is 20 - 80 wt%, and the belt speed is 0.5 - 5 m / min.

[0082] S6. Backside secondary boron diffusion is carried out to convert the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer. Since the secondary boron diffusion needs to convert the surface of the phosphorus diffusion layer formed in S4 into a high-concentration outer boron diffusion layer, a relatively high surface doping concentration of boron atoms is required after secondary boron diffusion, which is higher than the doping concentration of phosphorus atoms in the phosphorus diffusion layer; in addition, the doping depth during secondary boron diffusion should not be too large (the doping depth is less than the phosphorus doping depth in S4). After secondary boron diffusion, a layered alternating N-P-N-P (double junction) structure (N-type silicon substrate - P-type inner boron diffusion layer - N-type phosphorus diffusion layer - P-type outer boron diffusion layer) is formed on the entire backside of the silicon substrate.

[0083] In some preferred embodiments, the conditions for secondary boron diffusion are as follows: the boron diffusion temperature is 900 - 950 °C, the diffusion time is 20 - 80 min, the BCl3 flow rate is 300 - 800 sccm, and the O2 flow rate is 1000 - 5000 sccm; the oxidation promotion temperature is 1000 - 1050 °C, the O2 flow rate is 5000 - 80000 sccm, and the promotion time is 10 - 50 min. The thickness of the obtained BSG layer is 20 - 60 nm, and the surface doping concentration is 2E19 - 1E20 cm-3 , the doping depth is 0.3~1 μm.

[0084] S7. Laser patterning is used to remove the BSG layer in the negative electrode region on the back side.

[0085] In some preferred implementation cases, the conditions for laser patterning are: laser wavelength 400~600 nm, frequency 500~700 KHz, marking speed 40000~50000 mm / s, power 10~50 W, and processing time 1~5 s.

[0086] S8, chain-remove the BSG layer plated on the front side.

[0087] In some preferred implementation cases, a chain machine is used to remove the BSG layer on the front surface of the silicon substrate, wherein the concentration of the HF solution in the chain machine is 20-80 wt % and the belt speed is 0.5-5 m / min.

[0088] S9, cleaning and texturing to remove the deposited layer on the surface of the silicon substrate in the negative electrode area, and form a pyramid velvet surface on the front side: the silicon substrate is cleaned and texturized in an alkaline solution. Since the BSG layer on the back of the silicon substrate is removed by laser patterning in step S7, the high-concentration outer boron diffusion layer, medium-concentration phosphorus diffusion layer, and low-concentration inner boron diffusion layer at the bottom of the BSG layer can be removed by regulating the wet process conditions during the cleaning and texturing process, all the way to the silicon substrate. In the non-laser patterned area, since the BSG layer still exists on the back surface, the doping layers at the bottom of the area can be protected from being destroyed during the wet texturing process. For the front side of the silicon substrate, since the BSG layer has been removed in step S8, a pyramid velvet surface can be formed on the front side of the silicon substrate during the cleaning and texturing process. The acid (HF / HCl) cleaning tank that comes with the tank body can then remove the BSG layer remaining on the surface.

[0089] In some preferred implementation cases, the wet cleaning and texturing conditions are: 1.7-2.2 wt% KOH, temperature 70-85° C., time 6-10 min.

[0090] S10, double-sided coating, forming a passivation anti-reflection film on the front and back sides: ALD deposition method is used to deposit AlO on the front and back sides of the processed silicon substrate x The film is generated by the reaction of Al(CH3)3 and water vapor, with a thickness of 8~10 nm and a process temperature of 220~280℃. Then, SiN is deposited on the front and back sides using a tubular PECVD device. x Film, including SiN xThe thickness of the thin film is 80 - 120 nm, and the refractive index is 1.9 - 2.1; the reaction gases in the tube cavity are SiH4 and NH3, the working pressure is 1500 - 1700 mTorr, the power is 10000 - 15000 W, the temperature is 400 - 600 °C, the flow rate of SiH4 gas is 900 - 2000 sccm, the flow rate of NH3 gas is 7000 - 12000 sccm, and the deposition time is 5 - 20 min.

[0091] S11, screen printing, sintering, light injection: After coating the silicon substrate, through the screen printing process, the positive electrode is printed on the surface of the high-concentration outer boron diffusion layer, and the negative electrode is printed in the laser-patterned silicon substrate area (negative electrode area). Then, it is sintered at 700 - 800 °C to form an Ag-Si ohmic contact, and finally, the final finished battery is obtained through light injection repair.

[0092] (3)Another preparation method for a two-terminal all-silicon-based double-junction solar cell, including:

[0093] S1, double-sided polishing of the N-type silicon substrate.

[0094] S2, primary boron diffusion, successively forming an inner boron diffusion layer on the back of the N-type silicon substrate.

[0095] In some preferred embodiments, the conditions for primary boron diffusion are: boron diffusion temperature 900 - 950 °C, diffusion time 20 - 80 min, BCl3 flow rate 20 - 100 sccm, O2 flow rate 200 - 1000 sccm; push temperature 1000 - 1050 °C, push time 40 - 100 min; surface boron atom doping concentration 3E17 - 7E18 cm -3 (Since the push time is short, most of the surface boron atoms are still in the shallow surface, and the surface doping concentration is relatively higher), doping depth 1.5 - 4.5 μm (since the push time is short, the doping depth is correspondingly shallower).

[0096] S3, phosphorus diffusion, converting the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer. Since no obvious BSG layer is formed on the surface after S2 primary boron diffusion, during the phosphorus diffusion process, phosphorus atoms can directly enter the low-concentration inner boron diffusion layer, causing part of this layer to transform into a phosphorus diffusion layer.

[0097] In some preferred embodiments, the conditions for phosphorus diffusion are: phosphorus diffusion temperature 750 - 850 °C, diffusion time 5 - 30 min, POCl3 is carried by nitrogen with a flow rate of 200 - 500 sccm, O2 flow rate 300 - 1000 sccm; push temperature 850 - 950 °C, push time 10 - 50 min; surface phosphorus doping concentration 9E18 - 2E19 cm -3 , doping depth 0.8 - 1.5 μm.

[0098] S4. The secondary boron diffusion converts the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer. Since no obvious PSG layer is formed on the surface after phosphorus diffusion, boron atoms can enter the phosphorus diffusion layer during the secondary boron diffusion process. In addition, with the effect of the high temperature of the secondary boron diffusion, the inner boron diffusion layer formed by the initial primary boron diffusion and the phosphorus diffusion layer formed by phosphorus diffusion will be further advanced synchronously, so as to meet the requirements of the process.

[0099] In some preferred embodiments, the conditions for secondary boron diffusion are as follows: the boron diffusion temperature is 900 - 950 °C, the diffusion time is 20 - 80 min, the flow rate of BCl3 is 300 - 800 sccm, and the flow rate of O2 is 1000 - 5000 sccm; the oxidation promotion temperature is 1000 - 1050 °C, the flow rate of O2 is 5000 - 80000 sccm, the promotion time is 10 - 50 min, the thickness of the obtained BSG layer is 20 - 60 nm; the surface boron doping concentration is 2E19 - 1E20 cm -3 , and the doping depth is 0.3 - 1 μm.

[0100] S5. Laser patterning is used to remove the BSG layer in the negative electrode region.

[0101] S6. Chain removal of the BSG layer plated around the front side.

[0102] S7. Cleaning and texturing are performed to remove the deposited layer on the surface of the negative electrode region and form a pyramid-shaped textured surface on the front side;

[0103] S8. Double-sided coating is carried out to form a passivation and antireflection film on the front and back sides.

[0104] S9. Screen printing is carried out to form the positive electrode and the negative electrode in the positive electrode region and the negative electrode region respectively, followed by sintering and light injection.

[0105] Specific examples and comparative examples.

[0106] Example 1

[0107] A preparation method of a two-terminal all-silicon-based double-junction solar cell, which includes the following steps:

[0108] S1. Double-sided polishing of the N-type silicon substrate 1: Select the N-type silicon substrate 1 (the doping amount of phosphorus atoms is 2E15cm -3 ) after being cut by a diamond wire, put it into an alkaline polishing tank, maintain the temperature at 75 °C, and the time is 6 min for double-sided polishing. The polishing thickness is about 4 μm, and the thinning amount is about 0.42 g, as Figure 1 shown.

[0109] S2. Primary boron diffusion on the back side, and an inner boron diffusion layer 2 and a BSG layer 3 are sequentially formed on the back side of the N-type silicon substrate, as Figure 2As shown. After the first boron diffusion, a boron diffusion layer is formed on the back surface of the silicon substrate, which transforms the back surface from N-type to P-type. Specifically, the conditions for the first boron diffusion are as follows: boron diffusion temperature is 930 °C, diffusion time is 25 min, BCl3 flow rate is 40 sccm, and O2 flow rate is 500 sccm; oxidation and push temperature is 1045 °C, O2 flow rate is 5000 sccm, push time is 90 min, and the thickness of the obtained BSG layer is about 50 nm; the doping concentration of surface boron atoms is about 2E18 cm -3 , and the doping depth is about 2.7 μm.

[0110] S3. Use a chain machine to remove the BSG layer on the back surface after the first boron diffusion. The concentration of the HF solution in the chain machine is 40 wt%, and the belt speed is 3 m / min.

[0111] S4. Perform backside phosphorus diffusion to convert the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer 4 and a PSG layer 5, as Figure 3 shown. Specifically, the conditions for phosphorus diffusion are as follows: phosphorus diffusion temperature is 790 °C, diffusion time is 20 min, POCl3 is carried by nitrogen with a flow rate of 300 sccm, and O2 flow rate is 600 sccm; oxidation and push temperature is 890 °C, O2 flow rate is 2000 sccm, push time is 40 min; the thickness of the obtained PSG layer is about 39 nm, and the doping concentration of surface phosphorus atoms is about 9E18 cm -3 , and the doping depth is about 1.2 μm.

[0112] S5. Use a chain machine to remove the PSG layer on the back surface after phosphorus diffusion. The concentration of the HF solution in the chain machine is 20 wt%, and the belt speed is 3 m / min.

[0113] S6. Perform backside secondary boron diffusion to convert the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer 6 and a BSG layer 3, as Figure 4 shown. After the secondary boron diffusion, a layered alternating N-P-N-P (double junction) structure (N-type silicon substrate - P-type inner boron diffusion layer - N-type phosphorus diffusion layer - P-type outer boron diffusion layer) is formed on the back surface of the entire silicon substrate. Specifically, the conditions for the secondary boron diffusion are as follows: boron diffusion temperature is 930 °C, diffusion time is 50 min, BCl3 flow rate is 700 sccm, and O2 flow rate is 4000 sccm; oxidation and push temperature is 1045 °C, O2 flow rate is 20000 sccm, push time is 15 min, the thickness of the obtained BSG layer is about 25 nm, and the surface doping concentration is about 5E19 cm -3 , and the doping depth is about 0.4 μm.

[0114] S7, laser patterning to remove the BSG layer in the negative electrode region on the back side. The conditions for laser patterning are: laser wavelength 532nm, frequency 600KHz, marking speed 45000mm / s, power 50W, and processing time 3s.

[0115] S8. Use a chain machine to remove the BSG layer on the front surface of the silicon substrate, wherein the concentration of the HF solution in the chain machine is 40wt% and the belt speed is 3 m / min.

[0116] S9, cleaning and texturing to remove the deposited layer on the surface of the silicon substrate in the negative electrode region and form a pyramid velvet surface 7 on the front side, such as Figure 5 As shown. The silicon substrate is cleaned and texturized in an alkaline solution. Specifically, the wet cleaning and texturizing conditions are: 1.7 wt% KOH, temperature 75°C, time 8 min. Since the BSG layer on the back of the silicon substrate is removed by laser patterning in step S7, the high-concentration outer boron diffusion layer, medium-concentration phosphorus diffusion layer, and low-concentration inner boron diffusion layer at the bottom of the BSG layer can be removed all the way to the silicon substrate by regulating the wet process conditions during the cleaning and texturizing process. In the non-laser patterned area, since the BSG layer still exists on the back surface, the doping layers at the bottom of the area can be protected from being damaged during the wet texturizing process. For the front side of the silicon substrate, since the BSG layer has been removed in step S8, a pyramid velvet surface can be formed on the front side of the silicon substrate during the cleaning and texturizing process. The acid (HF / HCl) cleaning tank that comes with the tank body can then remove the BSG layer remaining on the surface.

[0117] S10, double-sided coating, forming a passivation anti-reflection film 8 on the front and back sides, such as Figure 6 Figure 2: AlO is deposited on the front and back of the treated silicon substrate using ALD deposition. x The film is generated by the reaction of Al(CH3)3 and water vapor, with a thickness of about 8 nm and a process temperature of 250°C. Then, SiN is deposited on the front and back sides using a tubular PECVD device. x Film, including SiN x The thickness of the film is about 85 nm and the refractive index is about 2.0; the reaction gases in the tubular cavity are SiH4 and NH3, the working pressure is 1600 mTorr, the power is 12000 W, the temperature is 440℃, the SiH4 gas flow rate is 1200 sccm, the NH3 gas flow rate is 9000 sccm, and the deposition time is 12 min.

[0118] S11, the coated silicon substrate is subjected to a screen printing process, and the positive electrode 9 is printed on the surface of the high-concentration outer boron diffusion layer, and the negative electrode 10 is printed on the laser-patterned silicon substrate area (negative electrode area), and then sintered at 700-800°C to form an Ag-Si ohmic contact, and finally the final finished battery is obtained through light injection repair, such asFigure 6 as shown

[0119] Comparative Example 1

[0120] Compared with Example 1, the only difference lies in the different phosphorus diffusion processes:

[0121] S4. Backside phosphorus diffusion, the phosphorus diffusion conditions are: phosphorus diffusion temperature 790 °C, diffusion time 3 min, POCl3 is carried by nitrogen with a flow rate of 150 sccm, O2 flow rate 270 sccm; oxidation and push temperature 870 °C, O2 flow rate 700 sccm, push time 20 min; the obtained PSG layer thickness is about 18 nm, the surface phosphorus atom doping concentration is about 1.6E18 cm -3 , and the doping depth is about 0.3 μm.

[0122] Comparative Example 2

[0123] Compared with Example 1, the only difference lies in the different phosphorus diffusion processes:

[0124] S4. Backside phosphorus diffusion, the phosphorus diffusion conditions are: phosphorus diffusion temperature 790 °C, diffusion time 50 min, POCl3 is carried by nitrogen with a flow rate of 700 sccm, O2 flow rate 2500 sccm; oxidation and push temperature 890 °C, O2 flow rate 5000 sccm, push time 120 min; the obtained PSG layer thickness is about 60 nm, the surface phosphorus atom doping concentration is about 8E18 cm -3 , and the doping depth is about 5.6 μm.

[0125] Comparative Example 3

[0126] Compared with Example 1, the only difference lies in the different secondary boron diffusion processes:

[0127] S6. Backside secondary boron diffusion, the secondary boron diffusion conditions: boron diffusion temperature 890 °C, diffusion time 10 min, BCl3 flow rate 200 sccm, O2 flow rate 3000 sccm; oxidation and push temperature 1010 °C, O2 flow rate 7000 sccm, push time 8 min, the obtained BSG layer thickness is about 13 nm, the surface doping concentration is about 1E18 cm -3 , and the doping depth is about 0.2 μm.

[0128] Comparative Example 4

[0129] Compared with Example 1, the only difference lies in the different secondary boron diffusion processes:

[0130] S6. Secondary boron diffusion on the back side. Conditions for secondary boron diffusion: boron diffusion temperature is 940 °C, diffusion time is 60 min, BCl3 flow rate is 1200 sccm, and O2 flow rate is 8000 sccm; oxidation push temperature is 1050 °C, O2 flow rate is 50000 sccm, push time is 120 min. The thickness of the obtained BSG layer is about 75 nm, and the surface doping concentration is about 2E20 cm -3 , and the doping depth is about 5.7 μm.

[0131] Comparative Example 5

[0132] A preparation method for a conventional single-junction back-contact battery, including:

[0133] S1. Select an N-type monocrystalline silicon wafer after being cut by a diamond wire. Place the cut silicon wafer into an alkaline polishing tank, maintain the temperature at 75 °C, and perform double-sided polishing for 6 min. The polishing thickness is about 4 μm, and the thinning amount is about 0.42 g.

[0134] S2. Then, use the method of high-temperature boron diffusion to transform the back side of the silicon wafer into a boron diffusion layer and a BSG layer. Boron diffusion temperature is 850 °C, diffusion time is 10 min, BCl3 gas flow rate is 200 sccm, O2 gas flow rate is 1200 sccm, oxidation push temperature is 950 °C, O2 flow rate is 7000 sccm, push time is 30 min, and the thickness of the BSG layer is about 45 nm. During this process, a boron diffusion layer and a BSG layer with circumferential diffusion will be formed on the front and side surfaces of the silicon wafer synchronously.

[0135] S3. Use a laser to pattern and groove the BSG layer on the back side of the silicon wafer, and make the grooved position the subsequent negative electrode area. The laser wavelength used is 532 nm, the frequency is 600 KHZ, the marking speed is 45000 mm / s, the power is 50 W, and the processing time is 3 s.

[0136] S4. Use a chain-type acid cleaning machine to remove the BSG layers with circumferential diffusion on the front and side surfaces of the silicon wafer. The concentration of the HF solution in the chain-type machine is 40 wt%, and the belt speed is 3 m / min.

[0137] S5. Subsequently, place the silicon wafer into an alkaline texturing bath for integrated wet cleaning of the back laser grooving area and front texturing. The concentration of the KOH solution in the texturing bath is 1.7 wt%, the temperature is maintained at 82 °C, and the time is 7 min. Since the BSG layer on the front of the silicon wafer has been removed, an effective light-trapping textured surface can be formed during texturing; for the back laser patterned area, the alkaline solution can effectively remove the boron diffusion layer until the N-type silicon substrate is exposed. In addition, since the BSG layer on the side of the silicon wafer has also been removed, the corresponding laterally diffused boron diffusion layer is further cleaned and removed, preventing edge leakage. Subsequently, the subsequent acid (HF / HCl) cleaning tank in the texturing bath can further remove the residual BSG layer on the silicon wafer.

[0138] S6. Double-sided coating to form a passivation and antireflection film on the front and back: Deposit AlO x thin film by ALD deposition method on the front and back of the treated silicon substrate. It is formed by the reaction of Al(CH3)3 with water vapor, with a thickness of about 8 nm, and the process temperature is controlled at 250 °C. Subsequently, deposit SiN x film on the front and back using a tube-type PECVD equipment. The thickness of the SiN x film is about 85 nm, and the refractive index is about 2.0; the reaction gases in the tube cavity are SiH4 and NH3, the working pressure is 1600 mTorr, the power is 12000 W, the temperature is 440 °C, the flow rate of SiH4 gas is 1200 sccm, the flow rate of NH3 gas is 9000 sccm, and the deposition time is 12 min.

[0139] S7. Screen-print the coated wafer to form a metal contact on the back (print the positive electrode on the back boron diffusion layer and the negative electrode on the N-type silicon substrate), then sinter at 770 °C to form an Ag-Si ohmic contact, and finally obtain the final conventional single-junction back-contact finished cell through optical injection repair.

[0140] Example 2

[0141] A preparation method for a two-terminal all-silicon-based double-junction solar cell, comprising:

[0142] S1. Double-sided polishing of the N-type silicon substrate, with the specific process the same as in Example 1.

[0143] S2. First boron diffusion, sequentially forming an inner boron diffusion layer on the back of the N-type silicon substrate. Specifically, the conditions for the first boron diffusion are: boron diffusion temperature 930 °C, diffusion time 25 min, BCl3 flow rate 40 sccm, O2 flow rate 500 sccm; push temperature 1045 °C, push time 75 min; the doping concentration of surface boron atoms is about 3E18 cm -3 , and the doping depth is about 2.3 μm.

[0144] S3. Phosphorus diffusion is carried out to convert the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer. Specifically, the phosphorus diffusion conditions are as follows: the phosphorus diffusion temperature is 790 °C, the diffusion time is 20 min, the POCl3 is carried by nitrogen with a flow rate of 300 sccm, and the O2 flow rate is 600 sccm; the push temperature is 890 °C, and the push time is 20 min; the surface phosphorus doping concentration is about 1E19 cm -3 , and the doping depth is about 1.0 μm.

[0145] S4. Secondary boron diffusion is carried out to convert the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer. Specifically, the secondary boron diffusion conditions are as follows: the boron diffusion temperature is 930 °C, the diffusion time is 50 min, the BCl3 flow rate is 700 sccm, and the O2 flow rate is 4000 sccm; the oxidation push temperature is 1045 °C, the O2 flow rate is 20000 sccm, the push time is 15 min, and the obtained BSG layer thickness is about 25 nm; the surface boron doping concentration is 5E19 cm -3 , and the doping depth is about 0.4 μm.

[0146] S5. Laser patterning is used to remove the BSG layer in the negative electrode area, and the specific process is the same as S7 in Example 1.

[0147] S6. Chain removal of the BSG layer plated around the front side, and the specific process is the same as S8 in Example 1.

[0148] S7. Cleaning and texturing are carried out to remove the deposited layer on the surface of the negative electrode area and form a pyramid-shaped textured surface on the front side. The specific process is the same as S9 in Example 1.

[0149] S8. Double-sided coating is carried out to form a passivation and antireflection film on the front and back sides. The specific process is the same as S10 in Example 1.

[0150] S9. Screen printing is carried out to form a positive electrode and a negative electrode in the positive electrode area and the negative electrode area respectively, followed by sintering and light injection. The specific process is the same as S11 in Example 1.

[0151] Example 3

[0152] A two-terminal all-silicon-based double-junction solar cell module includes unit cells A and B connected in staggered series. Among them, unit cell A is the two-terminal all-silicon-based double-junction solar cell prepared in Example 2.

[0153] Unit cell B is similar in structure to unit cell A, except that the polarities are opposite. The specific structure of unit cell B is as Figure 7As shown in the figure, it includes: a P-type silicon substrate 11, a pyramid-shaped velvet surface and a passivation and antireflection film sequentially arranged on the front of the P-type silicon substrate, a positive electrode region and a negative electrode region arranged on the back of the P-type silicon substrate (the positive electrode region and the negative electrode region are respectively located in the two side regions on the back of the P-type silicon substrate). Among them: the negative electrode region includes an inner phosphorus diffusion layer 13, a boron diffusion layer 14, an outer phosphorus diffusion layer 15 and a passivation and antireflection film sequentially arranged on the back of the P-type silicon substrate, and a negative electrode arranged on the surface of the outer phosphorus diffusion layer and penetrating the passivation and antireflection film; the positive electrode region includes a passivation and antireflection film arranged on the back of the P-type silicon substrate, and a positive electrode arranged on the back of the P-type silicon substrate and penetrating the passivation and antireflection film. Among them, the concentration of phosphorus atoms in the inner phosphorus diffusion layer is lower than the concentration of boron atoms in the boron diffusion layer, and the concentration of boron atoms in the boron diffusion layer is lower than the concentration of phosphorus atoms in the outer phosphorus diffusion layer.

[0154] The positions of the positive and negative electrodes of unit cell A and unit cell B are opposite, as Figure 8 shown. Their connection method is: the negative electrode of unit cell A is connected to the positive electrode of the adjacent unit cell B behind it through a welding strip 12, and the positive electrode of unit cell A is connected to the negative electrode of the adjacent unit cell B in front of it through a welding strip.

[0155] The above connection method of the components can realize the series welding of "one"-shaped positive / negative electrodes in the same direction on the back of the battery, avoiding the cumbersome process problems brought by cross welding (conventional laminated batteries have electrodes on both the front and back, so they must be connected in a Z-shaped series connection with up and down interaction. In this connection method, the welding strips will be interspersed between adjacent silicon wafers, and the up and down interaction between the welding strips and the edges of the silicon wafers will cause greater stress on the silicon wafers, resulting in easy damage and a low yield rate).

[0156] Performance Test

[0157] The electrical performance of the solar cells obtained in each example and comparative example was tested, and the results are shown in Table 1.

[0158] Table 1

[0159]

[0160] First, for Example 1, since the battery adopts a full-silicon-based double-junction back-contact structure, its V oc value is relatively high compared to a conventional single-junction back-contact battery (Comparative Example 5), and the back-contact structure can further reduce the shading loss of the front grid lines of the battery, and the corresponding battery J sc value is also relatively high.

[0161] For Comparative Example 1, due to insufficient phosphorus diffusion during the phosphorus diffusion process (less phosphorus doping), it is impossible to transform the surface layer of the inner boron diffusion layer into a phosphorus diffusion layer, so the so-called back "layered" double-junction structure cannot be formed, resulting in the battery terminal Voc The value is lower than that of Example 1; since the conventional structure of the back-contact battery is basically satisfied, the battery performance has not decreased significantly, but it is lower than that of Example 1.

[0162] For Comparative Example 2, due to the excessive degree of phosphorus diffusion during the phosphorus diffusion process (a large amount of phosphorus doping and a relatively deep doping depth), all of the inner boron diffusion layer is transformed into a phosphorus diffusion layer. After the secondary boron diffusion, the so-called back "layered" double-junction structure cannot be formed at the battery end either. However, it also basically satisfies the conventional structure of the back-contact battery, so the battery performance has not decreased significantly. Due to the large amount of doping during the phosphorus diffusion process, the carrier recombination between its diffusion layers is relatively large, and the V oc value is relatively low, and the overall electrical performance is lower than that of Example 1 and Comparative Example 1.

[0163] For Comparative Example 3, due to the insufficient degree of boron diffusion during the secondary boron diffusion process, the outer layer of the phosphorus diffusion layer cannot be transformed into an outer boron diffusion layer. On the one hand, the back "layered" double-junction structure cannot be formed. On the other hand, the entire back surface of the silicon wafer is the negative electrode region (N-type silicon substrate, phosphorus diffusion layer), resulting in the lowest overall battery performance.

[0164] For Comparative Example 4, due to the relatively large degree of boron diffusion during the secondary boron diffusion process, all of the phosphorus diffusion layer is transformed into a boron diffusion layer. And due to the large amount of surface boron doping, the surface recombination rate is even greater, and the corresponding battery V oc value is very low. However, since it also satisfies the conventional structure of the back-contact battery, the battery performance is higher than that of Comparative Example 3 but lower than that of other groups.

[0165] For Comparative Example 5, since only a single-junction back-contact structure is adopted on the back of the battery, its battery V oc value is lower than that of the double-junction back-contact structure, and the overall electrical performance is also lower than that of Example 1 and Example 2.

[0166] For Example 2, since the preparation process is further optimized and improved on the basis of Example 1, on the one hand, the complexity of the overall process is simplified, and on the other hand, the high and low temperature effects brought about by repeated wet treatments before and after each diffusion process are avoided. This not only reduces the fragmentation rate of the silicon wafers but also indirectly improves the influence of the internal stress of the silicon wafers. Accordingly, the crystal lattice will be more stable. Therefore, the overall electrical performance is the best.

[0167] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0168] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A two-terminal all-silicon-based double-junction solar cell, characterized in that include: An N-type silicon substrate, a pyramid velvet surface and a passivation anti-reflection film are sequentially arranged on the front side of the N-type silicon substrate, and a positive electrode region and a negative electrode region are arranged on the back side of the N-type silicon substrate; wherein: The positive electrode region includes an inner boron diffusion layer, a phosphorus diffusion layer, an outer boron diffusion layer and a passivation anti-reflection film which are sequentially arranged on the back of the N-type silicon substrate, and a positive electrode arranged on the surface of the outer boron diffusion layer; The cathode region includes a passivation anti-reflection film disposed on the back of the N-type silicon substrate, and a cathode disposed on the back of the N-type silicon substrate; The boron concentration in the inner boron diffusion layer is lower than the phosphorus concentration in the phosphorus diffusion layer, and the phosphorus concentration in the phosphorus diffusion layer is lower than the boron concentration in the outer boron diffusion layer.

2. The two-terminal all-silicon-based double-junction solar cell according to claim 1, characterized in that: The positive electrode region and the negative electrode region are respectively located at two side regions of the back side of the N-type silicon substrate.

3. A method for preparing a two-terminal all-silicon-based double-junction solar cell according to claim 1 or 2, characterized in that include: S1, N-type silicon substrate double-sided polishing; S2, a boron diffusion, forming an inner boron diffusion layer and a BSG layer on the back side in sequence; S3, remove the BSG layer; S4, phosphorus diffusion, so that the surface layer of the inner boron diffusion layer is converted into a phosphorus diffusion layer and a PSG layer; S5, removing the PSG layer; S6, secondary boron diffusion, converting the surface of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer; S7, removing the BSG layer in the negative electrode region; S8, removing the BSG layer plated on the front side; S9, cleaning and velveting to remove the surface deposition layer of the negative electrode area and form a pyramid velvet surface on the front side; S10, double-sided coating; S11, screen printing, sintering, light injection.

4. The preparation method according to claim 3, characterized in that: The phosphorus atom concentration of the N-type silicon substrate is less than the boron atom concentration of the first boron diffusion, less than the phosphorus atom concentration of the phosphorus diffusion, and less than the boron atom concentration of the second boron diffusion; and the first boron diffusion depth is greater than the phosphorus diffusion depth and the second boron diffusion depth.

5. The preparation method according to claim 4, characterized in that: The primary boron diffusion conditions are as follows: diffusion temperature 900-950°C, time 20-80 min, BCl3 flow rate 20-100 sccm, O2 flow rate 200-1000 sccm; oxidation push temperature 1000-1050°C, O2 flow rate 1000-20000 sccm, time 60-120 min; surface boron doping concentration 1E17-5E18 cm -3 , doping depth 2~5 μm; Phosphorus diffusion conditions are as follows: diffusion temperature 750-850°C, time 5-30 min, POCl3 flow rate 200-500 sccm, O2 flow rate 300-1000 sccm; oxidation advancement temperature 850-950°C, O2 flow rate 500-3000 sccm, time 30-90 min; surface phosphorus doping concentration 6E18-1E19 cm -3 , doping depth 1~2 μm; Secondary boron diffusion conditions: diffusion temperature 900-950°C, time 20-80 min, BCl3 flow rate 300-800 sccm, O2 flow rate 1000-5000 sccm; oxidation push temperature 1000-1050°C, O2 flow rate 5000-80000 sccm, time 10-50 min; surface boron doping concentration 2E19-1E20 cm -3 , the doping depth is 0.3~1 μm.

6. The preparation method according to claim 5, characterized in that: The BSG layer obtained after the first boron diffusion is 30 to 80 nm thick; The thickness of the PSG layer obtained after phosphorus diffusion is 30 to 70 nm; The thickness of the BSG layer obtained after secondary boron diffusion is 20 to 60 nm.

7. A method for preparing a two-terminal all-silicon-based double-junction solar cell according to claim 1 or 2, characterized in that include: S1, N-type silicon substrate double-sided polishing; S2, a boron diffusion is performed to form an inner boron diffusion layer on the back of the N-type silicon substrate; S3, phosphorus diffusion, so that the surface layer of the inner boron diffusion layer is converted into a phosphorus diffusion layer; S4, secondary boron diffusion converts the surface layer of the phosphorus diffusion layer into an outer boron diffusion layer and a BSG layer; S5, removing the BSG layer in the negative electrode region; S6, removing the BSG layer plated on the front side; S7, cleaning and velveting to remove the surface deposited layer of the negative electrode area and form a pyramid velvet surface on the front side; S8, double-sided coating; S9, screen printing, sintering, light injection.

8. The preparation method according to claim 7, characterized in that: The phosphorus atomic concentration of the N-type silicon substrate is less than the boron atomic concentration of the first boron diffusion, less than the phosphorus atomic concentration of the phosphorus diffusion, less than the boron atomic concentration of the second boron diffusion; and The primary boron diffusion depth > phosphorus diffusion depth > secondary boron diffusion depth; The primary boron diffusion and phosphorus diffusion are both promoted without oxygen, and the secondary boron diffusion is promoted with oxygen; the promotion time of the primary boron diffusion and phosphorus diffusion is shorter than that of the secondary boron diffusion.

9. The preparation method according to claim 8, characterized in that: Primary boron diffusion conditions: diffusion temperature 900-950°C, time 20-80 min, BCl3 flow rate 20-100 sccm, O2 flow rate 200-1000 sccm; push temperature 1000-1050°C, time 40-100 min; surface boron doping concentration 3E17-7E18 cm -3 , doping depth 1.5~4.5 μm; Phosphorus diffusion conditions: diffusion temperature 750-850°C, time 5-30 min, POCl3 flow rate 200-500 sccm, O2 flow rate 300-1000 sccm; push temperature 850-950°C, time 10-50 min; surface phosphorus doping concentration 9E18-2E19 cm -3 , doping depth 0.8~1.5 μm; Secondary boron diffusion conditions: diffusion temperature 900-950°C, time 20-80 min, BCl3 flow rate 300-800 sccm, O2 flow rate 1000-5000 sccm; oxidation push temperature 1000-1050°C, O2 flow rate 5000-80000 sccm, time 10-50 min; surface boron doping concentration 2E19-1E20 cm -3 , doping depth 0.3~1 μm.

10. The preparation method according to claim 7, characterized in that: The thickness of the BSG layer obtained after the secondary boron diffusion is 20 to 60 nm.

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