A method for preparing silicon heterojunction solar cell

Abstract

A method for preparing a silicon heterojunction solar cell comprises the following steps: 1) forming a plasma containing oxygen active group energy with carbon dioxide to form an oxide layer on the surface of a silicon wafer for passivating dangling bonds on the surface of the silicon wafer during PECVD chemical deposition; 2) continuing to deposit the silicon wafer with dangling bonds on the surface of the silicon wafer passivated in a gas atmosphere with a low hydrogen dilution ratio to provide abundant hydrogen for interface passivation; 3) bombarding the silicon wafer with argon plasma to break and reorganize silicon-silicon or silicon-hydrogen weak bonds in amorphous silicon, allowing free hydrogen atoms to diffuse to the interface and combine with dangling bonds on the surface of the silicon wafer, thereby reducing interface defect density and improving photosensitivity; and 4) introducing carbon dioxide as an oxygen source to continue deposition in a gas atmosphere with a high hydrogen dilution ratio to increase the bandgap width of amorphous silicon, reduce parasitic light absorption, and improve the photocurrent density of the solar cell, thereby effectively reducing the parasitic light absorption problem of intrinsic amorphous silicon and solving the problem of reduced photocurrent of heterojunction solar cells.

Description

Technical Field

[0001] The invention relates to a method for preparing a silicon heterojunction solar cell, and belongs to the field of preparation of solar cells. Background Art

[0002] With the changes in the global environment, energy transformation has become an inevitable trend. Traditional fossil energy can no longer meet the needs of sustainable development. Therefore, all countries are vigorously developing new energy technologies for sustainable development. Among them, solar energy is favored among various new energy sources due to its unique advantages. At present, the mainstream photovoltaic solar cells on the market include PERC, PERT, Topcon and HJT and other structural cells. Among them, silicon-based heterojunction solar cells (HJT) HJT solar cells are increasingly favored by the photovoltaic industry due to the good surface passivation effect of amorphous silicon, high conversion efficiency, simple process steps, low preparation process temperature and no light-induced degradation (LID) and other excellent performance.

[0003] Intrinsic amorphous silicon has an excellent chemical passivation effect on the dangling bonds on the surface of silicon wafers, and can usually reduce the recombination rate on the surface of silicon wafers to below 10cm / s, which is the key to the high conversion efficiency of HJT cells. The following two methods are usually used in the prior art: ① Using silane and hydrogen as source gases, a layer of amorphous silicon is deposited on both sides of the textured silicon wafer as a passivation layer under certain power, air pressure and other conditions; ② Using pure silane as the source gas, a first layer of amorphous silicon is deposited on both sides of the textured silicon wafer under certain power, air pressure and other conditions; Using silane and hydrogen as source gases, a second layer of amorphous silicon is deposited on both sides of the textured silicon wafer as a passivation layer under certain power, air pressure and other conditions. The two-step method deposits a stacked amorphous silicon passivation layer to improve the passivation effect. The first layer of amorphous silicon is mainly used to prepare a hydrogen-rich amorphous silicon layer to prevent epitaxial growth at the interface, and the second layer of amorphous silicon has the characteristics of low structure factor and high density to improve the passivation effect. However, both of the above two prior arts have technical defects, for example, the parasitic light absorption of intrinsic amorphous silicon is serious, which reduces the photocurrent of heterojunction solar cells. In addition, the first prior art also has the defect that the passivation effect of the single-layer passivation layer is poor and epitaxial growth is easy to occur at the silicon wafer interface. Summary of the invention

[0004] In order to solve the defects of the prior art, the present invention provides a method for preparing a silicon heterojunction solar cell, which can effectively reduce the parasitic light absorption problem of intrinsic amorphous silicon, thereby solving the problem of reduced photocurrent of heterojunction solar cells.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a silicon heterojunction solar cell, wherein a double-sided textured silicon wafer is deposited by PECVD chemical deposition, and the following methods are used in sequence during the deposition process:

[0006] ① Carbon dioxide is converted into a plasma containing oxygen active group energy, and an oxide layer is formed on the surface of the silicon wafer to passivate the dangling bonds on the surface of the silicon wafer. This oxide layer can also effectively avoid the interface epitaxial phenomenon that occurs during the thickness deposition process;

[0007] ② Continue to deposit the silicon wafer with dangling bonds on the surface of the passivated silicon wafer in a gas atmosphere with a low hydrogen dilution ratio to provide abundant hydrogen for interface passivation, which can enhance the interface passivation effect;

[0008] ③ Use argon plasma to bombard silicon wafers, so that the weak silicon-silicon or silicon-hydrogen bonds in amorphous silicon break and reorganize, so that free hydrogen atoms diffuse to the interface and combine with the dangling bonds on the surface of the silicon wafer, reduce the interface defect density, and improve photosensitivity. The local heating effect during argon plasma bombardment can be used to reduce the interface defect density and improve photosensitivity;

[0009] ④ In a gas atmosphere with a high hydrogen dilution ratio, carbon dioxide is introduced as an oxygen source to continue deposition, which increases the bandgap width of amorphous silicon, reduces parasitic light absorption, and improves the photocurrent density of solar cells. At the same time, the low R (microstructure factor) amorphous silicon film improves the film quality and reduces the contact resistance;

[0010] ⑤ Continue deposition in a gas atmosphere with a higher hydrogen dilution ratio to reduce the contact resistance of the doped amorphous silicon, while reducing the defect density of the overall amorphous silicon film and improving the conversion efficiency of the heterojunction battery. DETAILED DESCRIPTION

[0011] To further illustrate the present invention, specific implementation methods are listed below.

[0012] 1. Perform conventional texturing and cleaning process on silicon wafers to obtain a clean and hydrophobic silicon wafer surface with a certain pyramid light-trapping structure. The size of the pyramid is 0.5-10um and the height is 0.5-10um. Place the double-sided texturing and cleaning silicon wafer in a PECVD chamber for PECVD chemical deposition.

[0013] 2. Introduce 100-10000sccm of CO2 into the PECVD chamber, maintain the pressure at 10Pa-1000Pa, maintain the chamber temperature at 10-300℃, the power density at 1mW.cm-2-100mW.cm-2, and the process time at 1s-60s. The purpose of this step is to form a plasma with CO2 gas under external power. The oxygen-containing active groups in the plasma can react with the surface of the silicon wafer to form a very thin and dense oxide layer with a thickness of 0.1nm-1.5nm. This oxide layer can effectively passivate the dangling bonds on the surface of the silicon wafer and can well avoid the interface epitaxial phenomenon that occurs during the thickness deposition process;

[0014] 3. SiH4 and H2 are passed into the PECVD chamber, with a flow rate range of 100-10000scm, a flow ratio of SiH4 to H2 of 1:0-1:3, a gas pressure of 10Pa-1000Pa, a chamber temperature of 10-300°C, a power density of 1mW.cm-2-100mW.cm-2, a process time of 1s-60s, a film thickness of 0.5nm-10nm, and a film refractive index of 3.3-4.0; this film is prepared in a gas atmosphere with a low hydrogen dilution ratio, mainly to provide abundant hydrogen for interface passivation to enhance the interface passivation effect;

[0015] 4. Ar is passed into the PECVD chamber with a flow rate of 100-10000scm, a pressure of 10Pa-1000Pa, a chamber temperature of 10-300℃, a power density of 1mW.cm-2-100mW.cm-2, and a process time of 1s-60s. This step is to perform argon plasma treatment on the first layer of intrinsic amorphous silicon. The purpose is to break and reorganize the silicon-silicon or silicon-hydrogen weak bonds in the amorphous silicon through the bombardment of argon plasma, so as to reduce the internal defects of the film and improve the photosensitivity of amorphous silicon; at the same time, the bombardment of argon plasma has a local heating effect. Under this thermal effect, the free hydrogen atoms inside the film diffuse to the interface and combine with the dangling bonds on the surface of the silicon wafer, reducing the interface defect density, and finally achieving the passivation effect.

[0016] 5. SiH4, H2 and CO2 gases are passed into the PECVD chamber, with a flow rate range of 100-10000scm, a flow rate ratio of SiH4 and H2 of 1:5-1:30, wherein the CO2 flow rate accounts for 5%-50% of the total gas, the gas pressure is maintained at 10Pa-1000Pa, the chamber temperature is maintained at 10-300℃, the power density is 1mW.cm-2-100mW.cm-2, the process time is 1s-60s, the thickness of the film is 0.5nm-10nm, and the refractive index of the film is 2.5-3.5; the film is prepared in a gas atmosphere with a high hydrogen dilution ratio, and CO2 is introduced as an oxygen source to provide oxygen elements to prepare intrinsic hydrogenated amorphous silicon oxide (a-SiOx:H). The introduction of oxygen into the film is mainly to increase the bandgap width of amorphous silicon, reduce the parasitic light absorption of the amorphous silicon layer, and increase the photocurrent density of the solar cell;

[0017] 6. SiH4 and H2 are passed into the PECVD chamber with a flow rate range of 100-10000scm, a flow ratio of SiH4 to H2 of 1:10-1:50, a gas pressure of 10Pa-1000Pa, a chamber temperature of 10-300°C, a power density of 1mW.cm-2-100mW.cm-2, a process time of 1s-60s, a film thickness of 0.5nm-10nm, and a film refractive index of 3.8-4.5. This film is prepared in a gas atmosphere with a relatively high hydrogen dilution ratio, mainly to reduce the defect density of the overall amorphous silicon film and reduce the contact resistance with the subsequent doped amorphous silicon, so as to achieve good electrical properties and ultimately improve the conversion efficiency of the heterojunction battery.

[0018] Obviously, the above implementation is only one example of the present invention, and any simple improvement on the principle provided by the present invention belongs to the protection scope of the present invention.

Claims

1. A method for preparing a silicon heterojunction solar cell, wherein a double-sided textured silicon wafer is deposited by a PECVD chemical deposition method, characterized in that The following methods are used in sequence during the deposition process: ① Carbon dioxide is used to form a plasma containing oxygen active group energy to form an oxide layer on the surface of the silicon wafer to passivate the dangling bonds on the surface of the silicon wafer; ② The silicon wafer with the dangling bonds on the surface of the passivated silicon wafer is further deposited in a gas atmosphere with a low hydrogen dilution ratio of SiH4 and H2 flow ratio of 1:0-1:3 to provide abundant hydrogen for interface passivation; ③ Argon plasma is used to bombard the silicon wafer to break and reorganize the silicon-silicon or silicon-hydrogen weak bonds in the amorphous silicon, so that free hydrogen atoms diffuse to the interface and combine with the dangling bonds on the surface of the silicon wafer, thereby reducing the interface defect density and improving the photosensitivity; ④ In a gas atmosphere with a high hydrogen dilution ratio of SiH4 and H2 flow ratio of 1:5-1:30, carbon dioxide is introduced as an oxygen source to continue deposition, thereby increasing the band gap width of amorphous silicon, reducing parasitic light absorption, and improving the photocurrent density of the solar cell. After step ④, ⑤ Deposition is continued in a gas atmosphere with a relatively high hydrogen dilution ratio of SiH4 and H2 flow ratio of 1:10-1:50 to reduce the contact resistance with the doped amorphous silicon.

2. The method for preparing a silicon heterojunction solar cell according to claim 1, characterized in that The deposition conditions are as follows: the pressure in the PECVD chamber is maintained at 10Pa-1000Pa, the temperature is maintained at 10-300℃, and the power density is maintained at 1mW.cm 2 -100mW.cm 2 .

3. The method for preparing a silicon heterojunction solar cell according to claim 2, characterized in that Carbon dioxide is introduced into the PECVD chamber at a flow rate of 100-10000 sccm to form a plasma containing oxygen active radical energy.

4. The method for preparing a silicon heterojunction solar cell according to claim 2, characterized in that A gas mixture of SiH4 and H2 with a flow rate ranging from 100 to 10000 scm is introduced into the PECVD chamber to form a gas atmosphere with a low hydrogen dilution ratio.

5. The method for preparing a silicon heterojunction solar cell according to claim 2, characterized in that A mixed gas of SiH4 and H2 with a flow rate range of 100-10000scm is introduced into the PECVD chamber to form a gas atmosphere with a high hydrogen dilution ratio. The flow rate of carbon dioxide introduced under the high hydrogen dilution ratio gas atmosphere accounts for 5%-50% of the total gas in this step.

6. The method for preparing a silicon heterojunction solar cell according to claim 2, characterized in that A mixed gas of SiH4 and H2 with a flow rate ranging from 100 to 10000 scm is introduced into the PECVD chamber to form a gas atmosphere with a high hydrogen dilution ratio.