Preparation method of p-type amorphous silicon thin film for heterojunction cell, thin film and application

Abstract

The application provides a preparation method of a P-type amorphous silicon thin film of a heterojunction cell, a thin film and application, relates to the technical field of solar cell preparation, and comprises the following steps: placing a silicon wafer on a carrier plate and entering a film plating cavity, wherein the film plating cavity forms a channel from an inlet to an outlet; control parameters of the film plating cavity are set, and a gas pump arranged at one end of the film plating cavity is enabled to form a certain directional gas flow in the film plating cavity; the carrier plate moves on the channel of the film plating cavity, and special gas with different input parameters is introduced into multiple positions of the film plating cavity, wherein the special gas comprises borane, hydrogen and silane, and the input parameters comprise the ratio, content and power of the borane, hydrogen and silane; under the directional gas flow, the silicon wafer is enabled to form a continuously gradient-doped P-type amorphous silicon thin film through ion deposition during movement from the inlet to the outlet of the film plating cavity, so that the problem of complicated film preparation operation and high cost in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of solar cell fabrication technology, and in particular to a method for preparing P-type amorphous silicon thin films for heterojunction solar cells, the thin films, and their applications. Background Technology

[0002] Traditional HJT cell structures first deposit very thin intrinsic amorphous silicon films (ia-Si:H) and N-type amorphous silicon films (na-Si:H) on the front side of an N-type monocrystalline silicon wafer (c-Si), then deposit very thin intrinsic amorphous silicon films (ia-Si:H) and P-type amorphous silicon films (pa-Si:H) on the back side of the silicon wafer to form a back surface field; then deposit transparent oxide conductive films (TCO) on both sides of the cell, and finally fabricate metal electrodes on the TCO.

[0003] To obtain high-efficiency heterojunction solar cells, boron doping on the P-side is crucial. Boron doping on the P-side forms Pa-Si:H, which then forms a PN junction with the silicon substrate. The PN junction is the core of solar cell power generation. The PN junction creates a built-in electric field. Under the influence of this field, electrons drift towards the N-type region, and holes drift towards the P-type region, thus generating current. The boron doping concentration is key to a successful PN junction, and gradient doping of P is necessary to increase the strength of the built-in electric field. The doping concentration in the P-region can be indirectly represented by dark conductivity; higher dark conductivity corresponds to higher doping concentration and a stronger built-in electric field in the PN junction.

[0004] In HJT (heterojunction) solar cells, boron doping on the P-side and an N-type silicon substrate form a PN junction, and the doping concentration determines the quality of the PN junction. High doping concentration and high dark conductivity on the P-side can improve cell efficiency. Current common P-side doping techniques involve introducing B₂H₆ (borane), H₂, and S into the cavity. i H4 (silane) is used for deposition with the RF power supply turned on. The carrier plate remains stationary during the deposition process. After one layer of P is deposited, the gas in the chamber is evacuated, and the carrier plate enters the next chamber to continue deposition using the same method. Because the P-side requires gradient doping to increase the built-in electric field of the PN junction, the doping of B2H6 needs to increase in subsequent fabrication steps. Therefore, the operation is cumbersome, and the subsequent processes require a large amount of borane, silane, and hydrogen, resulting in high costs. Summary of the Invention

[0005] In order to overcome the above-mentioned technical defects, the purpose of this invention is to provide a method for preparing P-type amorphous silicon thin films for heterojunction solar cells, thin films and their applications, in order to solve the problems of cumbersome and costly thin film preparation operations in the past.

[0006] This invention discloses a method for preparing a P-type amorphous silicon thin film for heterojunction solar cells, comprising:

[0007] A silicon wafer is placed on a carrier plate and enters a coating cavity, wherein the coating cavity forms a channel from the inlet to the outlet;

[0008] Set the control parameters of the coating chamber and make the air pump arranged at one end of the coating chamber work to form a certain airflow in the coating chamber;

[0009] The carrier plate moves along the channel of the coating chamber, while special gases with different input parameters are introduced at multiple locations in the coating chamber. The special gases include borane, hydrogen, and silane. The input parameters include the ratio and content of borane, hydrogen, and silane, and the power supply. Under the directional airflow, the silicon wafer moves from the inlet to the outlet of the coating chamber and forms a continuously gradient-doped P-type amorphous silicon thin film through ion deposition.

[0010] Preferably, the temperature inside the coating cavity is controlled at 200-300℃ and the pressure at 90Pa.

[0011] Preferably, the carrier plate moves within the coating cavity via rollers mounted on the bottom wall.

[0012] Preferably, positions for introducing different special gases are sequentially arranged along the moving direction of the silicon wafer, and the borane, hydrogen, and silane in the special gases introduced along the moving direction of the silicon wafer under directional airflow are continuously superimposed.

[0013] Preferably, the prepared P-type amorphous silicon thin film is subjected to conductivity testing or EVC curve testing, and the ratio and content of borane, hydrogen, and silane in the special gas and the power supply are adjusted according to the test results at different positions.

[0014] Preferably, positions for introducing different special gases are evenly spaced along the moving direction of the silicon wafer.

[0015] Preferably, the following special gases are introduced at five locations along the direction of movement of the silicon wafer:

[0016] First special gas: Hydrogen 9000 sccm, Borane 7 sccm, Silane 70 sccm;

[0017] Second special gas: Hydrogen 2000 sccm, Borane 9 sccm, Silane 90 sccm;

[0018] Third special gas: hydrogen 1500 sccm, silane 100 sccm;

[0019] Fourth special gas: Hydrogen 1500 sccm, Borane 6 sccm, Silane 200 sccm;

[0020] Fifth special gas: hydrogen 1000 sccm, borane 60 sccm, silane 100 sccm.

[0021] The present invention also provides a P-type amorphous silicon thin film for heterojunction solar cells, which is prepared by any of the above-described methods for preparing amorphous silicon thin films.

[0022] This invention also provides an application of a heterojunction P-type amorphous silicon thin film in solar cells.

[0023] Compared with existing technologies, the above technical solution has the following advantages:

[0024] The method, thin film, and application for preparing P-type amorphous silicon thin films for heterojunction solar cells provided in this application utilize an integral coating chamber in which a carrier plate continuously moves and coats the film. Simultaneously, the airflow direction within the coating chamber is controlled to gradually increase the amount of process gas along the directional airflow direction. This causes the silicon wafer to move along the directional airflow direction during the thin film preparation process, thereby achieving gradient doping of the thin film. This method saves gas consumption, reduces operational complexity, lowers costs, and solves the problems of cumbersome and costly existing thin film preparation operations. Attached Figure Description

[0025] Figure 1 This is a flowchart of Example 1 of the method for preparing P-type amorphous silicon thin films for heterojunction solar cells according to the present invention, the thin film, and its applications;

[0026] Figure 2 This is a schematic diagram illustrating the input of a special gas during the preparation process of the heterojunction solar cell P-type amorphous silicon thin film preparation method, thin film, and application according to Example 1 of the present invention.

[0027] Figure label:

[0028] 1-Carrier plate; 2-Roller; 3-Door valve; 4-Air pump. Detailed Implementation

[0029] The advantages of the present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments.

[0030] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0031] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0032] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0033] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] Example 1: This example discloses a method for preparing a P-type amorphous silicon thin film for heterojunction solar cells. In this embodiment, the thin film is prepared using PECVD plasma deposition, where the silicon wafer moves within the deposition chamber. Simultaneously, the airflow direction within the deposition chamber is controlled, gradually increasing the amount of process gas along the directional airflow direction. This allows the silicon wafer to move along the directional airflow direction during the thin film preparation process, achieving gradient doping of the thin film and significantly reducing equipment costs. It also reduces process gas consumption and processing time, increases production capacity, and produces a thin film with higher dark conductivity. (See reference...) Figure 1 and Figure 2 The specific preparation methods include the following:

[0035] S10: The silicon wafer is placed on a carrier plate and enters the coating cavity, wherein the coating cavity forms a channel from the inlet to the outlet; for illustration, the silicon wafer is the substrate for preparing the thin film. The coating cavity in this embodiment can be configured with multiple coating cavities as in the existing system. The existing system usually requires the silicon wafer to enter and exit multiple different coating cavities, while in this solution, it moves within one coating cavity.

[0036] Specifically, the carrier plate moves within the coating cavity via rollers mounted on the bottom wall. As a further supplement, other devices can be provided, such as a control component that automatically controls the speed and direction of the carrier plate movement, or other moving devices can be used instead of rollers, so that the carrier plate can move along the channel within the coating cavity without affecting the ion deposition of the silicon wafer on it.

[0037] S20: Set the control parameters of the coating chamber and make the air pump arranged at one end of the coating chamber work to form a certain airflow in the coating chamber;

[0038] Specifically, the temperature inside the coating chamber can be controlled at 200-300℃, and the pressure at 90Pa. The pressure can also be controlled by the aforementioned air pump. Compared with the prior art where silicon wafers need to enter and exit multiple coating chambers, and each coating chamber is equipped with an air pump, thus requiring multiple air pumps in the preparation process, this application only requires the use of one air pump. Specifically, in this solution, it is set on the outlet side of the coating chamber (or can be arranged on the inlet side, and the airflow direction can be adjusted), which can realize the control of the coating chamber, thereby reducing the complexity of operation and the occupation of equipment.

[0039] It should also be noted that the solution of this application uses an air pump to form a directional airflow. The air pump is arranged near the outlet of the coating chamber. This directional airflow runs from the inlet to the outlet of the coating chamber, covering the channel inside the coating chamber and forming an airflow along the channel. This can control the direction of the gas inside the coating chamber, thereby controlling the distribution or movement direction of the process gas (i.e., the reactive gas participating in ion deposition, the following special gases: borane, hydrogen, silane) inside the coating chamber. When the silicon wafer moves to different positions inside the coating chamber, it can be surrounded by process gases of different degrees, thereby depositing a thin film with gradient changes without having to enter and exit multiple different coating chambers. The thin film can be prepared within the current coating chamber, reducing the cumbersome operation caused by entering and exiting multiple different coating chambers, as well as the problems of more equipment and higher costs.

[0040] S30: The carrier plate moves on the channel of the coating cavity, and at the same time, special gases with different input parameters are introduced at multiple positions in the coating cavity. The special gases include borane, hydrogen and silane. The input parameters include the ratio and content of borane, hydrogen and silane, and power supply. Under the directional airflow, the silicon wafer is deposited with ion to form a continuously gradient doped P-type amorphous silicon thin film during the process of moving from the inlet to the outlet of the coating cavity.

[0041] As described above, the gas flow direction within the coating chamber is controlled by the aforementioned air pump. Furthermore, to achieve variations in process gas at different locations within the coating chamber, process gases of different concentrations (ratios, contents) are introduced at different positions within the coating chamber. Specifically, positions for introducing different specialty gases are sequentially set along the silicon wafer's movement direction. Under directional airflow, borane, hydrogen, and silane in the specialty gases introduced along the silicon wafer's movement direction continuously accumulate. Therefore, due to the effect of this directional airflow, the thin film deposited along the silicon wafer's movement direction forms a continuous gradient doping. Simultaneously, the required amount of borane, hydrogen, and silane in the specialty gases introduced further along the silicon wafer's movement direction should gradually decrease, because some of the borane, hydrogen, and silane in the earlier specialty gases will move backward under the action of the air pump, thereby further reducing process gas loss and lowering costs.

[0042] As a further supplement, and as an option, a special gas can be introduced only at the inlet of the coating chamber, and the borane, hydrogen, and silane in the special gas can be accumulated at different positions in the coating chamber under the action of the air pump. It is even possible to set multiple air pumps at different positions in the coating chamber to adjust the airflow direction in the coating chamber. However, this may result in poor doping effect of the prepared thin film or excessive equipment usage. Therefore, as a preferred option, the above-mentioned scheme of introducing gas at different positions in the coating chamber is adopted, but the aforementioned scheme can also be selected according to the actual application scenario.

[0043] In this embodiment, in order to fabricate a continuously gradient-doped thin film, positions for introducing different specialty gases are evenly spaced along the moving direction of the silicon wafer, and different specialty gases are introduced at different positions. Specifically, the following specialty gases are introduced at five positions along the moving direction of the silicon wafer:

[0044] Special Gas ①: Hydrogen 9000 sccm, Borane 7 sccm, Silane 70 sccm, Power supply 500W;

[0045] Second special gas ②: Hydrogen 2000 sccm, Borane 9 sccm, Silane 90 sccm, Power supply 1700W;

[0046] Third special gas ③: Hydrogen 1500 sccm, Silane 100 sccm, Power supply 1700W;

[0047] Fourth Special Gas ④: Hydrogen 1500 sccm, Borane 6 sccm, Silane 200 sccm, Power Supply 1700W;

[0048] Fifth Special Gas ⑤: Hydrogen 1000 sccm, Borane 60 sccm, Silane 100 sccm, Power Supply 1700W.

[0049] It should also be noted that in the preparation method provided in this embodiment, it is necessary to keep the silicon wafer moving and simultaneously depositing ions after introducing special gases at each position to form a thin film with a continuous gradient change that moves out of the coating chamber outlet. Similar to existing preparation methods, the coating chamber needs to be kept in a vacuum and have a shortcut so that no other gases besides the process gas will affect the quality of the prepared thin film. That is, after introducing special gases in different ratios, the RF power supply is turned on to perform deposition.

[0050] In this embodiment, as mentioned above, the doping concentration of the P-region can be indirectly represented by the dark conductivity, i.e., the higher the dark conductivity, the higher the doping concentration. Therefore, as an option, conductivity testing or EVC curve testing is performed on the prepared P-type amorphous silicon thin film. Based on the test results, the ratio and content of borane, hydrogen, and silane in the special gas at different positions, as well as the power supply, are adjusted. In this application, a continuous gradient thin film is prepared by adjusting the different contents of the input special gas at predetermined positions. As an option, a specific gradient range can also be set according to the test results, and the input special gas can be quantitatively adjusted accordingly. In some implementation scenarios, the position of the input special gas can also be adjusted, which is beneficial to the preparation of a continuous gradient thin film.

[0051] Based on steps S10-S30 above, using the aforementioned special gas, and after coating, the dark conductivity is measured. The dark conductivity of the P-side is >2 Scm. -1 Compared to existing methods that require multiple deposition chambers or multiple gate valves for control during multiple depositions, this method is more effective. As an explanation, to obtain good P-surface conductivity, S... i H4: H2 generally needs to be above 100, which leads to the need for a large amount of H2 gas. However, this solution adds a gas pump (process pump) at the tail end of a large cavity to control the airflow direction and pressure, allowing H2 to flow backward and be used for subsequent coatings. This way, much less H2 is used in the later stages. The same applies to B2H6. Currently, the utilization rate of B2H6 in each coating cavity is low. This solution allows the excess B2H6 at the front to drift to the rear cavity and participate in the doping coating of the rear cavity, which greatly saves gas consumption.

[0052] This solution utilizes a single, integrated coating chamber where the substrate continuously moves and is coated. Existing multi-chamber / multi-cavity coating processes require the substrate to remain stationary, and after each coating cycle, air must be evacuated and valves opened before the next chamber can be moved in. This solution significantly reduces processing time. Furthermore, existing solutions require individual air pumps and valves for each coating chamber, whereas this solution uses a single air pump at the chamber outlet to control airflow direction and pressure, eliminating the need for intermediate valves and greatly reducing equipment costs.

[0053] Example 2: This embodiment also provides a heterojunction P-type amorphous silicon thin film, which is prepared by any of the amorphous silicon thin film preparation methods described in the above embodiments. A coating chamber is used, and an air pump is set at the outlet of the coating chamber. At the same time, special gases with different input parameters are introduced at multiple positions in the coating chamber. Under a specific gas flow direction (from the inlet to the outlet of the coating chamber), borane, hydrogen, and silane are gradually accumulated to generate a thin film with a continuous gradient based on PECVD ion deposition.

[0054] Example 3: This embodiment also provides an application of a heterojunction P-type amorphous silicon thin film in solar cells. Specifically, the application includes, but is not limited to, heterojunction cells, thereby simplifying the operation in the solar cell manufacturing process, reducing costs, and reducing equipment and process gas consumption. Other steps in preparing heterojunction cells are consistent with existing methods, but can be adjusted according to actual application scenarios. It can also be selectively applied to the manufacturing process of other cells under solar cell ground.

[0055] It should be noted that the embodiments of the present invention have better implementability and are not intended to limit the present invention in any way. Any person skilled in the art may use the above-disclosed technical content to change or modify it into equivalent effective embodiments. However, any modifications or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a P-type amorphous silicon thin film for heterojunction solar cells, characterized in that, include: A silicon wafer is placed on a carrier plate and enters a coating cavity, wherein the coating cavity forms a channel from the inlet to the outlet; Set the control parameters of the coating chamber and make the air pump arranged at one end of the coating chamber work to form a directional airflow in the coating chamber. The directional airflow runs from the inlet to the outlet of the coating chamber, covers the channel in the coating chamber and forms an airflow along the channel. The silicon wafer moves along the direction of the directional airflow. The air pump is arranged on the outlet side of the coating chamber. The carrier plate moves along the channel of the coating chamber, while special gases with different input parameters are introduced at multiple locations within the coating chamber. These special gases include borane, hydrogen, and silane. The input parameters include the ratio and content of borane, hydrogen, and silane, and the power supply. Under the directional gas flow, the silicon wafer moves from the inlet to the outlet of the coating chamber, where it undergoes ion deposition to form a continuously gradient-doped P-type amorphous silicon thin film. The dark conductivity of the continuously gradient-doped P-type amorphous silicon thin film is >2 Scm. -1 ; The temperature inside the coating chamber is controlled at 200-300℃, and the pressure is 90Pa. Positions for introducing different specialty gases are sequentially set along the moving direction of the silicon wafer, and borane, hydrogen, and silane in the specialty gases introduced along the moving direction of the silicon wafer under directional airflow continuously accumulate.

2. The method for preparing amorphous silicon thin films according to claim 1, characterized in that: The carrier plate moves within the coating cavity via rollers mounted on the bottom wall.

3. The method for preparing amorphous silicon thin films according to claim 1, characterized in that: Conductivity or EVC curve tests were performed on the prepared P-type amorphous silicon thin film. Based on the test results, the ratio and content of borane, hydrogen, and silane in the special gas, as well as the power supply, were adjusted at different locations.

4. The method for preparing amorphous silicon thin films according to claim 1, characterized in that: Positions for introducing different special gases are evenly spaced along the moving direction of the silicon wafer.

5. The method for preparing amorphous silicon thin films according to claim 1, characterized in that, The following special gases are introduced at five locations along the direction of silicon wafer movement: First special gas: Hydrogen 9000 sccm, Borane 7 sccm, Silane 70 sccm; Second special gas: Hydrogen 2000 sccm, Borane 9 sccm, Silane 90 sccm; Third special gas: hydrogen 1500 sccm, silane 100 sccm; Fourth special gas: Hydrogen 1500 sccm, Borane 6 sccm, Silane 200 sccm; Fifth special gas: hydrogen 1000 sccm, borane 60 sccm, silane 100 sccm.

6. A P-type amorphous silicon thin film for a heterojunction solar cell, characterized in that, The amorphous silicon thin film is prepared using any one of the methods described in claims 1-5.

7. The application of the heterojunction P-type amorphous silicon thin film as described in claim 6 in solar cells.

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