A boron diffusion process for N-type solar cells

Abstract

This invention provides a boron diffusion process for N-type solar cells, belonging to the field of photovoltaic technology. In this invention, a furnace tube is first used for preliminary deposition to precisely control the composition and thickness of the BSG layer deposited on the silicon surface from the boron source, accompanied by a certain depth of pre-progression. Then, a rapid thermal processing technique is used to complete the boron diffusion. After diffusion, the surface concentration of the boron-doped layer is 5 x 10⁻⁶. 18 ~3x10 20 atoms / cm 3 The doping depth can be adjusted arbitrarily within the range of 0.20~1.5μm; after the process, a boron doped layer with higher surface concentration or deeper diffusion depth can be obtained, which has great practical application value.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic technology, specifically relating to a boron diffusion process for N-type solar cells. Background Technology

[0002] As market demands for higher solar cell efficiency increase, N-type solar cells are attracting more and more attention due to their advantages such as high minority carrier lifetime, no light-induced degradation, and low temperature coefficient. The production process of N-type solar cells requires the diffusion formation of a PN junction, and boron diffusion is a crucial step in this process. Current technology uses boron tribromide (BBr3) or boron trichloride (BCl3) as the boron source, depositing it onto the surface of the N-type solar cell using a furnace tube diffusion process. High-temperature propulsion and oxidation steps are then used to create the desired diffusion junction. However, in conventional diffusion processes, a thin layer of silicon oxide forms at the interface between the borosilicate glass layer and the silicon. Since boron has a high segregation coefficient in the silicon oxide layer, it directly affects the boron distribution at the interface. The direct effect is a decrease in boron concentration in the silicon layer near the silicon oxide / silicon interface. The highest concentration of the boron-doped layer is often not at the interface, but rather exhibits a Gaussian distribution, with the peak concentration varying depending on the specific boron diffusion process. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a boron diffusion process for N-type solar cells. In this invention, a furnace tube is first used for preliminary deposition to precisely control the composition and thickness of the BSG layer deposited on the silicon surface from the boron source, accompanied by a pre-progression to a certain depth. Then, a rapid thermal processing technique is used to complete the boron diffusion, resulting in a boron doping layer surface concentration of 5 x 10⁻⁶. 18 ~3x10 20 atoms / cm 3 The doping depth can be adjusted arbitrarily within the range of 0.20~1.5μm; after the process, a boron doped layer with higher surface concentration or deeper diffusion depth can be obtained, which has great practical application value.

[0004] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0005] A boron diffusion process for an N-type solar cell, the process comprising:

[0006] After wet texturing, the solar cells are placed in a diffusion furnace and deposited at 840~920℃. Then, they are pre-diffused at 900~980℃. After the pre-diffusion is completed, the solar cells are removed. The removed solar cells are then subjected to rapid heat treatment at 800~1200℃. After the treatment, the temperature is reduced to 100~600℃ to complete the boron diffusion of the solar cells.

[0007] The deposition conditions are as follows: boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, O2 flow rate of 100~3000 sccm, and deposition time of 100~1000 s.

[0008] Preferably, the deposition process includes: first heating to 840℃~890℃, and depositing for 100~600s under the conditions of boron source flow rate of 50~300sccm, N2 flow rate of 100~3000sccm, and O2 flow rate of 100~3000sccm; then heating to 890℃~920℃, and depositing for 100~600s under the conditions of boron source flow rate of 50~300sccm, N2 flow rate of 100~3000sccm, and O2 flow rate of 100~3000sccm.

[0009] Preferably, the deposition process includes: first, heating to 840℃~870℃ and depositing for 100~500s under conditions of boron source flow rate of 50~300sccm, N2 flow rate of 0~3000sccm, and O2 flow rate of 0~3000sccm; then heating to 870℃~890℃ and depositing for 100~500s under conditions of boron source flow rate of 50~300sccm, N2 flow rate of 100~3000sccm, and O2 flow rate of 100~3000sccm; finally, heating to 890℃~920℃ and depositing for 100~500s under conditions of boron source flow rate of 50~300sccm, N2 flow rate of 100~3000sccm, and O2 flow rate of 100~3000sccm.

[0010] Preferably, in the pre-diffusion stage, the flow rate of N2 is 100~3000 sccm, the flow rate of O2 is 100~3000 sccm, and the diffusion time is 10~1000 s.

[0011] Preferably, after the pre-diffusion is completed, the temperature is lowered to 600~800℃, and the O2 flow rate is adjusted to 100~10000 sccm.

[0012] Preferably, in the rapid heat treatment process, the temperature is raised to 800-1200℃ at a heating rate of 10-200℃ / s, then kept at a constant temperature for 1-300s, and after the treatment, the temperature is lowered to 100-600℃ at a cooling rate of 100℃ / s-1℃ / s.

[0013] Preferably, during the rapid heat treatment and cooling process, the oxygen flow rate is 100~10000 sccm and the argon flow rate is 100~10000 sccm.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] This invention employs Rapid Thermal Processing (RTP) technology, which, through rapid heating and cooling combined with atmosphere matching, results in a very thin silicon oxide layer formed at the interface between the borosilicate glass layer and silicon during diffusion. This effectively alters the segregation characteristics of boron at the interface, thereby significantly changing the surface concentration of boron diffused within the silicon wafer.

[0016] This invention adjusts the flow ratio of boron source, N2, and O2 in the BSG deposition process and uses multi-stage deposition to regulate the content and distribution of B, N, and O in the BSG deposition. Furthermore, it fine-tunes the boron doping surface concentration and doping depth through a pre-propellant process, and finally achieves the target doping concentration and depth through a rapid thermal treatment process. Moreover, due to the extremely short diffusion time in this invention, the oxide layer formed on the surface has almost no impact on the boron concentration after diffusion. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. In the following embodiments, the boron source includes compounds or mixtures of boron-containing compounds that can be obtained by reactions such as BCl3 or BBr3 method, APCVD method, spin coating method, and ion implantation method.

[0018] Example 1:

[0019] The solar cells, after wet texturing, are added to a diffusion furnace for deposition. The deposition process is as follows: the diffusion furnace is first heated to 870°C, and boron source, N2 and O2 are introduced, wherein the flow rate of boron source is 100 sccm, the flow rate of N2 is 1000 sccm, the flow rate of O2 is 200 sccm, and the boron source deposition time is 480 s.

[0020] After deposition, the diffusion furnace was heated to 920°C with an O2 flow rate of 200 sccm for pre-diffusion, which lasted 300 s. After pre-diffusion, the temperature was lowered to 800°C, with an O2 flow rate of 5000 sccm introduced during the cooling process. Next, the solar cell was removed and subjected to a rapid processing method, heated to 950°C at a heating rate of 120°C / s and held at that temperature for 20 s. Then, it was cooled to 300°C at a rate of 30°C / s with an O2 flow rate of 2000 sccm to complete the boron diffusion of the solar cell.

[0021] The solar cell was tested, and the boron doping concentration was 8.9 x 10. 18 atoms / cm 3 The doping depth is 0.32 μm.

[0022] Example 2:

[0023] The solar cells, after wet texturing, are added to a diffusion furnace for deposition. The deposition process is as follows: the diffusion furnace is first heated to 885°C, and boron source, N2 and O2 are introduced, wherein the flow rate of boron source is 150 sccm, the flow rate of N2 is 500 sccm, the flow rate of O2 is 500 sccm, and the boron source deposition time is 500 s.

[0024] After deposition, the diffusion furnace was heated to 920°C with an N2 flow rate of 200 sccm for pre-diffusion, which lasted 150 s. After pre-diffusion, the temperature was lowered to 800°C, with an O2 flow rate of 5000 sccm introduced during the cooling process. Next, the solar cell was removed and subjected to a rapid processing method, heated to 1050°C at a heating rate of 50°C / s and held at that temperature for 50 s. Then, it was cooled to 400°C at a rate of 30°C / s with an O2 flow rate of 2500 sccm to complete the boron diffusion of the solar cell.

[0025] The solar cell was tested, and the boron doping concentration was 8.2 x 10. 19 atoms / cm 3 The doping depth is 0.68 μm.

[0026] Example 3:

[0027] The solar cells, after wet texturing, are added to a diffusion furnace for deposition. The deposition process is as follows: first, the diffusion furnace is heated to 880°C, and boron source, N2, and O2 are introduced, wherein the flow rate of boron source is 150 sccm, the flow rate of N2 is 0 sccm, the flow rate of O2 is 300 sccm, and the boron source deposition time is 300 s; then, the diffusion furnace is heated to 900°C, and the flow rate of boron source is adjusted to 180 sccm, the flow rate of N2 is 1000 sccm, and the flow rate of O2 is 500 sccm.

[0028] After deposition, the diffusion furnace was heated to 920°C with an N2 flow rate of 500 sccm for pre-diffusion, which lasted 400 s. After pre-diffusion, the temperature was lowered to 800°C, with an O2 flow rate of 2000 sccm introduced during the cooling process. Next, the solar cell was removed and subjected to a rapid processing method, heated to 1070°C at a heating rate of 50°C / s and held at that temperature for 20 s. Then, it was cooled to 400°C at a rate of 50°C / s with an O2 flow rate of 2000 sccm to complete the boron diffusion of the solar cell.

[0029] The solar cell was tested, and the boron doping concentration was 2.5 x 10. 19 atoms / cm 3 The doping depth is 0.62 μm.

[0030] Example 4:

[0031] The solar cells, after wet texturing, are added to a diffusion furnace for deposition. The deposition process is as follows: first, the diffusion furnace is heated to 860°C, and boron source, N2, and O2 are introduced, wherein the flow rate of boron source is 120 sccm, the flow rate of N2 is 0 sccm, the flow rate of O2 is 200 sccm, and the boron source deposition time is 500 s; then, the diffusion furnace is heated to 880°C, and the flow rate of boron source is adjusted to 150 sccm, the flow rate of N2 is 0 sccm, and the flow rate of O2 is 300 sccm.

[0032] After deposition, the diffusion furnace was heated to 930°C with an N2 flow rate of 800 sccm for pre-diffusion, which lasted 300 s. After pre-diffusion, the temperature was lowered to 800°C, with O2 introduced at a flow rate of 2000 sccm during the cooling process. Next, the solar cell was removed and subjected to a rapid processing method, heated to 1130°C at a heating rate of 50°C / s and held at that temperature for 80 s. Then, it was cooled to 400°C at a rate of 10°C / s, with O2 and argon introduced during the cooling process, at a flow rate of 2000 sccm for O2 and 5000 sccm for argon, thus completing the boron diffusion of the solar cell.

[0033] The solar cell was tested, and the boron doping concentration was 1.2 x 10. 19 atoms / cm 3 The doping depth is 0.85 μm.

[0034] Example 5:

[0035] The solar cells, after wet texturing, are added to a diffusion furnace for deposition. The deposition process is as follows: First, the diffusion furnace is heated to 850°C, and a boron source, N2, and O2 are introduced, with the boron source flow rate at 150 sccm, the N2 flow rate at 2000 sccm, and the O2 flow rate at 300 sccm, and the boron source deposition time at 300 s; then, the diffusion furnace is heated to 880°C, and the boron source flow rate is adjusted to 150 sccm, the N2 flow rate at 1000 sccm, and the O2 flow rate at 350 sccm; then, the diffusion furnace is heated to 890°C, and the boron source flow rate is adjusted to 150 sccm, the N2 flow rate at 500 sccm, and the O2 flow rate at 400 sccm.

[0036] After deposition, the diffusion furnace was heated to 940°C with an N2 flow rate of 500 sccm for pre-diffusion, which lasted 450 s. After pre-diffusion, the temperature was lowered to 700°C, with O2 introduced at a flow rate of 6000 sccm during the cooling process. Next, the solar cell was removed and subjected to a rapid processing method, heated to 1050°C at a heating rate of 50°C / s and held at that temperature for 120 s. Then, it was cooled to 400°C at a rate of 20°C / s, with O2 introduced at a flow rate of 6000 sccm during the cooling process, completing the boron diffusion of the solar cell.

[0037] The solar cell was tested, and the boron doping concentration was 1.2 x 10. 20 atoms / cm 3 The doping depth is 1.15 μm.

[0038] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A boron diffusion process for an N-type solar cell, characterized in that, The process includes: After wet texturing, the solar cells are placed in a diffusion furnace and deposited at 840~920℃. Then, they are pre-diffused at 900~980℃. After the pre-diffusion is completed, the solar cells are removed. The removed solar cells are then subjected to rapid heat treatment at 800~1200℃. After the treatment, the temperature is reduced to 100~600℃ to complete the boron diffusion of the solar cells. The deposition conditions are as follows: boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, O2 flow rate of 100~3000 sccm, and deposition time of 100~1000 s; The deposition process includes: first, heating to 840℃~890℃, and depositing for 100~600s under conditions of boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, and O2 flow rate of 100~3000 sccm; then heating to 890℃~920℃, and depositing for 100~600s under conditions of boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, and O2 flow rate of 100~3000 sccm. During the pre-diffusion stage, the flow rate of N2 is 0~3000 sccm, the flow rate of O2 is 0~3000 sccm, and the diffusion time is 10~1000 s; After the pre-diffusion is completed, the temperature is lowered to 600~800℃, and the O2 flow rate is adjusted to 100~10000 sccm; During the rapid heat treatment process, the temperature is raised to 800-1200℃ at a heating rate of 10-200℃ / s, then kept at a constant temperature for 1-300s, and after the treatment, the temperature is lowered to 100-600℃ at a cooling rate of 100℃ / s-1℃ / s. During the rapid heat treatment and cooling process, the oxygen flow rate is 100~10000 sccm and the argon flow rate is 100~10000 sccm.

2. A boron diffusion process for an N-type solar cell, characterized in that, The process includes: After wet texturing, the solar cells are placed in a diffusion furnace and deposited at 840~920℃. Then, they are pre-diffused at 900~980℃. After the pre-diffusion is completed, the solar cells are removed. The removed solar cells are then subjected to rapid heat treatment at 800~1200℃. After the treatment, the temperature is reduced to 100~600℃ to complete the boron diffusion of the solar cells. The deposition conditions are as follows: boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, O2 flow rate of 100~3000 sccm, and deposition time of 100~1000 s; The deposition process includes: first, heating to 840℃~870℃ and depositing for 100~500s under conditions of boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, and O2 flow rate of 100~3000 sccm; then heating to 870℃~890℃ and depositing for 100~500s under conditions of boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, and O2 flow rate of 100~3000 sccm; finally, heating to 890℃~920℃ and depositing for 100~500s under conditions of boron source flow rate of 50~300 sccm, N2 flow rate of 100~3000 sccm, and O2 flow rate of 100~3000 sccm. During the pre-diffusion stage, the flow rate of N2 is 0~3000 sccm, the flow rate of O2 is 0~3000 sccm, and the diffusion time is 10~1000 s; After the pre-diffusion is completed, the temperature is lowered to 600~800℃, and the O2 flow rate is adjusted to 100~10000 sccm; During the rapid heat treatment process, the temperature is raised to 800-1200℃ at a heating rate of 10-200℃ / s, then kept at a constant temperature for 1-300s, and after the treatment, the temperature is lowered to 100-600℃ at a cooling rate of 100℃ / s-1℃ / s. During the rapid heat treatment and cooling process, the oxygen flow rate is 100~10000 sccm and the argon flow rate is 100~10000 sccm.