Heterojunction ITO film annealing method and HJT battery

Abstract

The invention relates to the technical field of heterojunction batteries, in particular to an annealing method for a heterojunction ITO film and an HJT battery, slurry drying and ITO film annealing are performed on a battery piece subjected to screen printing, the annealing temperature is 190-230 DEG C, the annealing pressure is 500-1000 Pa, nitrogen is filled for protection, and the nitrogen flow is 2000-3000 sccm. On the basis of an original heterojunction manufacturing process, a drying mode of filling dry gas at normal pressure in silk-screen printing is changed into a low-pressure nitrogen filling protection annealing mode, and a mode of annealing the ITO thin film by filling nitrogen at low pressure is utilized, so that the photoelectric characteristic of the ITO thin film is further improved, and the conversion efficiency of a heterojunction battery piece is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heterojunction batteries, and in particular to an annealing method for a heterojunction ITO thin film and an HJT battery. Background Art

[0002] At present, HJT cells (Homojunction Solar Cell cells, heterojunction solar cells) are divided into impurity gettering, texturing and cleaning, PECVD coating, PVD and screen printing processes. Except for impurity gettering and light injection, the temperature of the heterojunction process is within 230°C. After CVD coating, the subsequent process strictly controls the temperature. Overheating will damage the CVD film structure, resulting in a decrease in the open circuit voltage and fill factor of the electrical performance, thereby causing a loss in the conversion efficiency of the heterojunction cell.

[0003] In the process of heterojunction battery manufacturing, the screen printing section oven and curing furnace not only have the function of drying the slurry, but also anneal the ITO film. The principle of ITO annealing is a method of heating the ITO film to remove surface impurities and combine oxygen atoms with defects to obtain a more stable crystal structure, thereby enhancing its conductive properties. The annealing temperature of normal ITO film is between 450-500℃, and it is carried out under the condition of passing dry compressed air. Due to the limitations of the CVD film structure, the PVD process temperature and the annealing temperature of the ITO single film are severely limited. The low-temperature annealing of the ITO single film (200℃ annealing) is not enough to achieve the optimal annealing conditions of the ITO film, so that its optimal photoelectric performance is not enough to achieve. A new low-temperature annealing technology is urgently needed to increase the photoelectric performance of the ITO film, improve the short-circuit current and fill factor of the heterojunction battery cell, and thus achieve efficiency improvement. Summary of the invention

[0004] The purpose of the present invention is to provide a method for annealing a heterojunction ITO film and an HJT battery, so as to solve the technical problem that the low-temperature annealing (200°C annealing) of an ITO single film in the prior art is not enough to achieve the optimal annealing conditions of the ITO film, so that its optimal photoelectric performance cannot be achieved.

[0005] The invention discloses a method for annealing a heterojunction ITO film, comprising the following steps:

[0006] The screen-printed cell is placed in a curing furnace under vacuum conditions for slurry drying and ITO film annealing. The annealing temperature is 190-230°C. Nitrogen flow is used as a protective gas on the one hand, and the annealing pressure is adjusted to 500Pa-1000Pa on the other hand. The nitrogen flow is 2000sccm-3000sccm.

[0007] Furthermore, the annealing pressure is 500Pa-900Pa.

[0008] Furthermore, the preparation of the battery cell also includes the following steps:

[0009] S1. Pre-clean and getter the incoming silicon wafers;

[0010] S2 is then cleaned and velveted to form a pyramid velvet surface;

[0011] S3. Sequentially depositing an intrinsic layer, a non-crystalline / microcrystalline layer and an ITO film;

[0012] S4. Perform screen printing.

[0013] Furthermore, the ITO film is plated by a PVD process.

[0014] Furthermore, the ITO film is double-sided coated.

[0015] Furthermore, the ITO film has a thickness of 95-110 nm.

[0016] Furthermore, the cell after the ITO film annealing is light injected, and finally tested and sorted, and packaged for storage.

[0017] Furthermore, the gettering treatment temperature is 700-750°C.

[0018] Furthermore, the texturing temperature is 80-100°C.

[0019] Furthermore, the intrinsic layer is coated using PECVD.

[0020] Furthermore, the PECVD temperature is 190-230°C.

[0021] Furthermore, the PVD temperature is 160-200°C.

[0022] Furthermore, the light injection temperature is 220-250°C.

[0023] A HJT battery is prepared using the above method.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Based on the original process of heterojunction, the drying method of screen printing by filling dry gas at normal pressure is changed to low-pressure nitrogen protection annealing method. The annealing method of ITO film by low-pressure nitrogen filling can improve the crystallization rate of ITO film under this annealing condition, further improve the photoelectric properties of ITO film, thereby improving the conversion efficiency of heterojunction solar cells. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0027] Example 1

[0028] A method for annealing a heterojunction ITO thin film using the above device in this embodiment includes the following steps:

[0029] S1. The incoming silicon wafer is pre-cleaned and treated with impurities, and the impurity treatment temperature is 795°C;

[0030] S2. The cell after impurity gettering is cleaned and textured to form a pyramid texture surface, and the texture temperature is 95°C;

[0031] S3. The cell after texturing is plated with an intrinsic non-crystalline / microcrystalline layer by PECVD to form a passivation and built-in electric field. The PECVD-N layer process temperature is 220°C and the P layer process temperature is 190°C.

[0032] S4. The heterojunction cell after the non- / microcrystalline silicon film is plated is plated with an ITO film by PVD, the thickness of the front and back films is between 95-110nm, and the PVD temperature is 165°C;

[0033] S5. Screen printing the double-sided TCO-coated cell;

[0034] S6. After printing the grid lines, the cell enters a curing furnace under vacuum conditions to dry the slurry and anneal the ITO film. The annealing temperature is 210°C, the annealing pressure of the curing furnace is 900Pa, and the nitrogen flow rate is 3000sccm;

[0035] S7. After the solidified cell, light is injected, and the light injection temperature is 220-250°C;

[0036] S8. Finally, test and sort, then pack and put into storage.

[0037] Example 2

[0038] In this embodiment, as a comparative example of the present invention, a method for annealing a heterojunction ITO thin film is provided. The only changes to Example 1 are that the annealing pressure in the curing furnace is 500 Pa and the nitrogen flow rate is 2000 sccm.

[0039] Comparative Example 1

[0040] In this embodiment, as a comparative example of the present invention, a method for annealing a heterojunction ITO thin film is provided. The only change on the basis of Example 1 is that the annealing temperature is 210° C. and the annealing is performed under dry compressed air at normal pressure.

[0041] Comparative Example 2

[0042] In this embodiment, as a comparative example of the present invention, a method for annealing a heterojunction ITO thin film is provided. The only changes to Example 1 are that the annealing pressure in the curing furnace is 300 Pa and the nitrogen flow rate is 1500 sccm.

[0043] Table 1

[0044]

[0045] Table 2

[0046]

[0047]

[0048] As can be seen from Table 1 and Table 2, compared with atmospheric pressure dry annealing, 500-1000Pa low-pressure nitrogen annealing has lower square resistance, higher mobility and higher transmittance. Below 500Pa, there will be the opposite effect, and the photoelectric performance of the ITO film and the electrical performance of the battery cell will decrease. Annealing under 500-1000Pa low-pressure nitrogen gas conditions has significantly improved the characteristics of the ITO film; from the perspective of the IV characteristics of the battery cell, compared with atmospheric pressure dry gas annealing, annealing under 500-1000Pa low-pressure nitrogen conditions has increased the short-circuit current by 6mA, the fill factor by 0.11, and the overall efficiency by 0.035%.

[0049] The above are the implementation methods listed in this embodiment, but this embodiment is not limited to the above optional implementation methods. Those skilled in the art can arbitrarily combine the above methods to obtain other various implementation methods. Anyone can derive other various forms of implementation methods under the inspiration of this embodiment. The above specific implementation methods should not be understood as limiting the scope of protection of this embodiment. The scope of protection of this embodiment shall be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A method for annealing a heterojunction ITO thin film, characterized in that: The following steps are involved: The screen-printed cell is subjected to slurry drying and ITO film annealing under vacuum conditions, the annealing temperature is 190-230° C., the annealing pressure is 500Pa-1000Pa, and nitrogen protection is provided, and the nitrogen flow rate is 2000sccm-3000sccm.

2. A method for annealing a heterojunction ITO thin film according to claim 1, characterized in that: The annealing pressure is 500Pa-900Pa.

3. A method for annealing a heterojunction ITO thin film according to claim 1, characterized in that: The preparation of the battery cell also includes the following steps: S1. Pre-clean and getter the incoming silicon wafers; S2 is then cleaned and velveted to form a pyramid velvet surface; S3. Sequentially depositing an intrinsic layer, a non-crystalline / microcrystalline layer and an ITO film; S4. Perform screen printing.

4. A method for annealing a heterojunction ITO thin film according to claim 3, characterized in that: The ITO film is plated by a PVD process.

5. A method for annealing a heterojunction ITO thin film according to claim 3, characterized in that: The ITO film is double-sided coated.

6. A method for annealing a heterojunction ITO thin film according to claim 3, characterized in that: The thickness of the ITO film is 95-110 nm.

7. A method for annealing a heterojunction ITO thin film according to claim 3, characterized in that: The cell after the ITO film annealing is light injected, and finally tested and sorted, and packaged for storage.

8. A method for annealing a heterojunction ITO thin film according to claim 4, characterized in that: The PVD temperature is 160-200°C.

9. A method for annealing a heterojunction ITO thin film according to claim 7, characterized in that: The light injection temperature is 220-250°C.

10. A HJT battery, characterized in that: The method is prepared by using the annealing method for heterojunction ITO thin film described in any one of claims 1 to 9.

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