Method for pvd deposition of films

Abstract

The application provides a PVD deposition film method, and belongs to the technical field of PVD deposition films. The PVD deposition film method comprises the following steps: circulating N groups of carrier plates to carry substrates and depositing films; when a first preset condition is met, replacing a group of carrier plates with the largest number of circulation times in a process cavity with a new group of carrier plates; and the like, so that the total number of circulation times of the N groups of carrier plates in the process cavity is always within the range of [M×(N-1) / 2+a]×N. The material of the film can absorb water, N is a natural number greater than or equal to 2, a is 0 to M times, M is a natural number greater than or equal to 30, and the first preset condition is that the water vapor value in the process cavity is greater than a preset water vapor value, or / and the circulation times of the new carrier plate reaches M times. The method can make the film deposited in a relatively stable water vapor range through the carrier plate in the process cavity, so that the film deposition of different batches is more uniform, and the performance of the film of different batches is also more stable.

Description

Technical Field

[0001] This application relates to the field of PVD deposition film technology, and more specifically, to a method for PVD deposition film. Background Technology

[0002] In existing methods for fabricating solar cells, an ITO (indium tin oxide) film is typically deposited on the cell using PVD (Physical Vapor Deposition), followed by electrode printing to form the solar cell.

[0003] During ITO film deposition, the solar cells are typically placed on a carrier plate, which is then placed in the process chamber of a PVD (PVD) equipment for ITO film deposition. After deposition, the carrier plate is removed, the solar cells are removed from the carrier plate, new solar cells are placed on the carrier plate, and the process is repeated. During ITO film deposition, an ITO film inevitably accumulates on the carrier plate. As the number of carrier plate cycles increases, the deposited ITO film gradually thickens. When the carrier plate is removed to replace the solar cells, the ITO film on the carrier plate inevitably absorbs moisture. This moisture is then transferred to the process chamber, causing changes in the moisture content within the chamber. Ultimately, this results in significant differences in conversion efficiency between different batches of solar cells.

[0004] To keep the moisture level in the process chamber within a relatively stable range, existing methods typically use moisture emitters to control the moisture level, but these emitters are expensive. Summary of the Invention

[0005] This application provides a method for PVD deposition of films. This method can use a carrier plate in the process chamber to allow the film deposition on the substrate to be carried out in a relatively stable water vapor range, thereby making the film deposition of different batches more uniform and the film performance of different batches more stable.

[0006] In a first aspect, this application provides a method for PVD deposition of a film. N sets of carrier plates are placed in the PVD deposition process chamber, and the N sets of carrier plates are recycled a times, a+M times, ..., a+(N-1)×M times, respectively. The method includes: cyclically using the N sets of carrier plates to support the substrate and deposit the film; when a first preset condition is reached, replacing the set of carrier plates with the most recycled times in the process chamber with a new set of carrier plates, and so on, so that the total number of recycled times of the N sets of carrier plates in the process chamber is always within the range of [M×(N-1) / 2+a]×N. Wherein, the film material is a water-absorbing material, N is a natural number ≥2, a is 0 to M times, M is a natural number ≥30, and the first preset condition is that the water vapor value in the process chamber is greater than a preset water vapor value, or / and the new carrier plate has been recycled M times.

[0007] In the above technical solution, the process chamber contains N sets of carrier plates, each with a different number of cycles. Through the above method, the total number of cycles for the N sets of carrier plates is always within the range of [M×(N-1) / 2+a]×N. The moisture content in the process chamber is also generally around a preset moisture content, thus ensuring that the film deposition on the substrate on the carrier plates occurs within a relatively stable moisture range. This results in more uniform film deposition across different batches and more stable film performance across different batches. There is no need to use a moisture emitter to control the moisture range in the process chamber, making control more convenient and cost-effective.

[0008] In some embodiments, a method comprising placing N sets of carrier plates in a process chamber for forming PVD deposition, wherein each set of carrier plates is used a times, a+M times, ..., a+(N-1)×M times, includes: cyclically using N sets of unused carrier plates to support the substrate and deposit a film; when a second preset condition is reached, replacing the used set of carrier plates with a new set of carrier plates; then continuing to cyclically use N sets of carrier plates to deposit a film; when the second preset condition is reached, replacing the used but unreplaced set of carrier plates with a new set of carrier plates, and so on, until all N sets of carrier plates are completely replaced; wherein the second preset condition is that the moisture value in the process chamber is greater than a preset moisture value, or the sum of the number of times all carrier plates in the process chamber are used is greater than [M×(N-1) / 2+a]×N times.

[0009] In the above technical solution, adjusting the number of cycles of the N sets of carrier plates in the process chamber by this method can make the adjustment more convenient, and the film deposition can be more uniform during the adjustment process, thereby obtaining a film material with more stable performance.

[0010] In some embodiments, the preset water vapor value is a range, and the preset water vapor value has an upper limit and a lower limit. The first preset condition is that the water vapor value in the process chamber is greater than the upper limit, and the second preset condition is that the water vapor value in the process chamber is greater than the upper limit.

[0011] In the above technical solution, the upper limit of the preset water vapor value is used to determine whether to replace the carrier plate. After replacing the carrier plate, it is highly likely that the water vapor value will be within the preset range, which can stabilize the water vapor value in the process chamber within the preset range.

[0012] In some embodiments, after replacing a used set of carriers with a new set of carriers, the moisture content in the process chamber is greater than the lower limit.

[0013] In the above technical solution, when adjusting the water vapor range in the process chamber, the water vapor value in the process chamber will not decrease excessively, and the water vapor range can be made to fluctuate between the upper and lower limits of the preset water vapor value, and it is easier to perform film deposition in a relatively stable water vapor range.

[0014] In some embodiments, the number of carrier plates N is 12 to 14, each group of carrier plates is a single carrier plate, and each carrier plate carries 100 to 300 substrates.

[0015] In the above technical solution, each time a carrier plate is replaced, the water vapor value in the process chamber changes only slightly, which can reduce the fluctuation of the water vapor range and thus improve the uniformity of membranes from different batches.

[0016] In some embodiments, the substrate is a heterojunction solar cell, and the deposited film is an ITO film.

[0017] In some embodiments, the method for determining the preset moisture value includes: placing N sets of carrier plates in a process chamber and depositing an ITO film on the solar cells placed on the carrier plates to obtain blue films, wherein different cycles of the carrier plates correspond to different blue films and different moisture values ​​in the process chamber. Electrodes are printed on different blue films to obtain solar cells, and the conversion efficiency of different solar cells is measured. A solar cell with a high conversion efficiency is selected, and the cycle count of the carrier plate used for the corresponding blue film is determined. The moisture value in the process chamber is obtained based on the cycle count as the preset moisture value.

[0018] In the above technical solution, the preset water vapor value is determined by the conversion efficiency of the solar cell when the cell is deposited with ITO film in the process chamber. The subsequent adjustment of the cell around the preset water vapor value for ITO film deposition can result in a solar cell with high conversion efficiency and relatively stable conversion efficiency for different batches of solar cells.

[0019] In some embodiments, different blue films are corresponding to different number of times the carrier plate is used, including: different blue films are respectively corresponding to N groups of blue films obtained by the number of times the carrier plate is used, a+M times...a+(N-1)×M times; where M is 50 to 150 times and a is 0 to M times.

[0020] In the above technical solution, the number of times the carrier plate is used is 50 to 150 times, which can cause a fluctuation in the water vapor range value in the process chamber, thereby causing a fluctuation in the conversion efficiency of different batches of solar cells. This allows for the selection of fewer blue films to obtain a more accurate preset water vapor range value, making it easier to obtain the preset water vapor range value.

[0021] In some embodiments, the method for obtaining the conversion efficiency of a solar cell includes: selecting 50 to 150 blue films with consistent number of substrate cycles to print electrodes to obtain a solar cell, and the conversion efficiency is the average value of the conversion efficiencies of the 50 to 150 solar cells tested.

[0022] In the above technical solution, the conversion efficiency of 50 to 150 solar cells is tested in parallel each time and the average value is calculated, which can make the test value of conversion efficiency more accurate.

[0023] In some embodiments, the preset moisture value is a range, and the method for determining the preset moisture value includes: obtaining the highest value of the conversion efficiency, and calculating a range of conversion efficiencies with a difference of less than 0.05% based on the highest value; determining the range of the number of cycles of the carrier plate based on the range of the number of cycles, and obtaining the range of the preset moisture value in the process chamber based on the range of the number of cycles.

[0024] In some embodiments, the preset moisture value is a fixed value, and the method for determining the preset moisture value includes: obtaining the highest value of the conversion efficiency, and obtaining the preset moisture value in the process chamber based on the number of cycles of the carrier plate corresponding to the highest value.

[0025] Of the above technical solutions, this method is simpler and easier to implement.

[0026] In some embodiments, the method for determining the value of M includes: placing N sets of carrier plates in a process chamber and depositing an ITO film on the solar cells placed on the carrier plates to obtain blue films, wherein different cycles of the carrier plates correspond to different blue films. Electrodes are printed on different blue films to obtain solar cells, and the conversion efficiency of different solar cells is measured. A solar cell with a high conversion efficiency is selected, and the cycle count Q of the carrier plate used for the corresponding blue film is determined, where N×Q=[M×(N-1) / 2+a]×N.

[0027] Based on this information, the value of M is calculated, which shows that replacing the substrate with a new one under suitable preset conditions can make the substrate replacement more convenient and eliminate the need for water vapor monitoring, thus ensuring more uniform membrane deposition. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0029] Figure 1 This is a schematic diagram of the layer structure of a heterojunction solar cell provided in some embodiments of this application;

[0030] Figure 2 This is a schematic diagram of the structure of the carrier plate provided in some embodiments of this application;

[0031] Figure 3 This is a first process flow diagram of a method for PVD deposition of films provided in some embodiments of this application;

[0032] Figure 4This is a second process flow diagram of a method for PVD deposition of films provided in some embodiments of this application;

[0033] Figure 5 The graphs show the conversion efficiency curve of the solar cell and the water vapor value curve of the deposited blue film when the preset water vapor value is determined in Embodiment 1 of this application.

[0034] Figure 6 The conversion efficiency curve of the solar cell provided in Example 1 of this application and the water vapor value curve of the blue film deposited during the fabrication of the solar cell;

[0035] Figure 7 This is a conversion efficiency curve of the solar cell in Embodiment 2 of this application;

[0036] Figure 8 The conversion efficiency curve of the solar cell provided in Example 2 of this application and the water vapor value curve of the blue film deposited during the fabrication of the solar cell are shown.

[0037] Icons: 10 - n-type silicon wafer; 11 - front intrinsic amorphous silicon layer; 12 - back intrinsic amorphous silicon layer; 13 - n-type doped amorphous silicon layer; 14 - p-type doped amorphous silicon layer; 15 - front ITO film; 16 - back ITO film; 17 - front electrode; 18 - back electrode;

[0038] 20-Carrier plate; 21-Mounting frame; 22-Carrier plate body. Detailed Implementation

[0039] Figure 1 For schematic diagrams of the layer structure of heterojunction solar cells provided in some embodiments of this application, please refer to [link / reference]. Figure 1 The heterojunction solar cell includes: an n-type silicon wafer 10, a front intrinsic amorphous silicon layer 11, an n-type doped amorphous silicon layer 13, a front ITO film 15 and a front electrode 17 sequentially disposed on the front side of the n-type silicon wafer 10, and a back intrinsic amorphous silicon layer 12, a p-type doped amorphous silicon layer 14, a back ITO film 16 and a back electrode 18 sequentially disposed on the back side of the n-type silicon wafer 10.

[0040] When fabricating heterojunction solar cells, the process typically involves first forming a cell (including an n-type silicon wafer 10, an intrinsic amorphous silicon layer 11 and an n-type doped amorphous silicon layer 13 sequentially disposed on the front side of the n-type silicon wafer 10, and an intrinsic amorphous silicon layer 12 and a p-type doped amorphous silicon layer 14 sequentially disposed on the back side of the n-type silicon wafer 10), then simultaneously depositing ITO films on both the front and back sides of the cell, and finally printing the electrodes.

[0041] In order to mass-produce solar cells at the same time, the usual practice is to carry the cells on a carrier plate in batches. Figure 2 For schematic diagrams of the carrier plate provided in some embodiments of this application, please refer to... Figure 2 The carrier plate 20 has multiple mounting frames 21, each mounting frame 21 supporting a solar cell. The edge of the solar cell is fixed to the frame of the mounting frame 21, and the solar cell is perforated in the mounting frame 21 to allow for the simultaneous deposition of ITO film on both surfaces of the solar cell. After the solar cells are fixed on each mounting frame 21 of the carrier plate 20, a portion of the carrier plate body 22 (including the edge of the carrier plate 20 and the frame of the mounting frame 21, etc.) is exposed. When the carrier plate is placed in the process chamber of the PVD equipment for ITO film deposition, at least a portion of the carrier plate body 22 will inevitably be deposited with ITO film. As the number of cycles of the carrier plate 20 increases, the ITO film deposited on the carrier plate body 22 gradually thickens. When the carrier plate 20 is removed to replace the solar cell, the ITO film on the carrier plate body 22 will inevitably absorb moisture. After this moisture is transferred to the process chamber, the moisture content in the process chamber changes, ultimately leading to differences in the ITO film deposited in different batches, resulting in significant differences in conversion efficiency between different batches of solar cells.

[0042] To keep the moisture level in the process chamber within a relatively stable range, existing methods typically use moisture emitters to control the moisture level, but these emitters are expensive.

[0043] Therefore, this application provides a method for PVD deposition of a film. The PVD deposition process chamber contains N sets of carrier plates, each set of carrier plates being recycled a times, a+M times, ..., a+(N-1)×M times. The method includes: cyclically using the N sets of carrier plates to support the substrate and deposit the film; when a first preset condition is reached, replacing the set of carrier plates with the most recycled times in the process chamber with a new set of carrier plates, and so on, so that the total number of recycled times of the N sets of carrier plates in the process chamber always falls within the range of [M×(N-1) / 2+a]×N. Wherein, the film material is a water-absorbing material, N is a natural number ≥2, a is 0 to M times, M is a natural number ≥30, and the first preset condition is that the water vapor value in the process chamber is greater than a preset water vapor value, or / and the new carrier plate has been recycled M times.

[0044] In the above technical solution, the process chamber contains N sets of carrier plates, each with a different number of cycles. Through the above method, the total number of cycles for the N sets of carrier plates is always within the range of [M×(N-1) / 2+a]×N. The moisture content in the process chamber is also generally around a preset moisture content, thus ensuring that the film deposition on the substrate on the carrier plates occurs within a relatively stable moisture range. This results in more uniform film deposition across different batches and more stable film performance across different batches. There is no need to use a moisture emitter to control the moisture range in the process chamber, making control more convenient and cost-effective.

[0045] The substrate in this application can be a solar cell, or other substrates requiring coating, such as metal substrates, ceramic substrates, etc.; the deposited film can be an ITO film, or other water-absorbing film materials, such as an AZO film (zinc aluminum oxide film) or a VTTO film (indium tin oxide film). The following explanation uses a solar cell as the substrate and an ITO film as the film material.

[0046] Figure 3 For a first process flow diagram of the PVD deposition film method provided in some embodiments of this application, please refer to [link / reference]. Figure 3 The preset conditions of this method are based on preset water vapor values, and the method includes:

[0047] S110, determine the preset water vapor value in the process chamber.

[0048] S111, N sets of carrier plates are placed in the process chamber and ITO films are deposited on the solar cells placed on the carrier plates to obtain blue films. The number of times the carrier plates are used corresponds to different blue films and different water vapor values ​​in the process chamber.

[0049] In other words, solar cells (including an n-type silicon wafer 10, with an intrinsic amorphous silicon layer 11 and an n-type doped amorphous silicon layer 13 sequentially disposed on the front side of the n-type silicon wafer 10, and an intrinsic amorphous silicon layer 12 and a p-type doped amorphous silicon layer 14 sequentially disposed on the back side of the n-type silicon wafer 10) are carried on N sets of carriers. Then, the N sets of carriers are placed in the process chamber for ITO film deposition. When the carrier is used for the first time, the first batch of blue films is obtained. The deposition of the first batch of blue films corresponds to the first moisture value in the process chamber. When the carrier is used for the second time, the second batch of blue films is obtained. The deposition of the second batch of blue films corresponds to the second moisture value in the process chamber. And so on. When the carrier is used for the Qth time, the Qth batch of blue films is obtained. The deposition of the Qth batch of blue films corresponds to the Qth moisture value in the process chamber.

[0050] In some embodiments, different blue films correspond to different numbers of carrier plate cycles, including: different blue films corresponding to N sets of blue films obtained by carrier plate cycles of a times, a+M times, ..., a+(N-1)×M times; where a is 0 to M times. It is not necessary to select the corresponding blue film and water vapor value for each carrier plate cycle, thus reducing the number of blue film detections and making it simpler to obtain the preset water vapor value range.

[0051] In other words, solar cells are carried on N sets of carriers, and then the N sets of carriers are placed in the process chamber for ITO film deposition. The carriers are recycled a times to obtain the a-th batch of blue films. The a-th water vapor value in the process chamber corresponds to the deposition of the a-th batch of blue films. The carriers are recycled a+M times to obtain the a+M-th batch of blue films. The a+M-th batch of blue films corresponds to the deposition of the a+M-th water vapor value in the process chamber. And so on, the carriers are recycled a+(N-1)×M times to obtain the a+(N-1)×M-th batch of blue films. The a+(N-1)×M-th batch of blue films corresponds to the deposition of the a+(N-1)×M-th water vapor value in the process chamber.

[0052] In some embodiments, N is in the range of 10 to 14, each group of carriers has one carrier, and each carrier can carry 100 to 300 solar cells. Typically, the process chamber can hold 10 to 14 carriers, and each carrier can carry 100 to 300 solar cells. In other embodiments, other numbers of carriers and carriers carrying other numbers of solar cells can be selected according to the size of the process chamber, and this application does not limit this.

[0053] S112, electrodes were printed on different blue films to obtain solar cells, and the conversion efficiency of different solar cells was tested.

[0054] Optionally, in step S111, the a-th batch of blue films, the a+M-th batch of blue films, ... and the a+(N-1)×M-th batch of blue films are obtained respectively. Electrodes are printed on these blue films to obtain solar cells, and the conversion efficiency of each solar cell is then detected.

[0055] In some embodiments, 50 to 150 blue films with the same number of cycles of carrier plate are selected to print electrodes to obtain solar cells, and the conversion efficiency is the average value of the conversion efficiency of the 50 to 150 solar cells tested.

[0056] Optionally, 50 to 150 blue films are selected from the first batch a, 50 to 150 blue films are selected from the second batch a+M, and so on, until 50 to 150 blue films are selected from the third batch a+(N-1)×M. Electrodes are printed on these blue films to obtain solar cells, and the conversion efficiency of each solar cell is then measured. The conversion efficiency of the first batch a is the a-th average of the conversion efficiencies of the solar cells formed from 50 to 150 blue films; the conversion efficiency of the second batch a+M is the a+M-th average of the conversion efficiencies of the solar cells formed from 50 to 150 blue films; and so on, until the conversion efficiency of the third batch a+(N-1)×M is the a+(N-1)×M-th average of the conversion efficiencies of the solar cells formed from 50 to 150 blue films.

[0057] S113, Select a solar cell with high conversion efficiency and know the number of cycles of the carrier plate used for the blue film corresponding to the solar cell. Based on the number of cycles, obtain the preset water vapor value in the process chamber.

[0058] In other words, the a-th cycle of the carrier plate corresponds to the a-th batch of blue films. The deposition of the a-th batch of blue films corresponds to the a-th moisture value in the process chamber. After the a-th batch of blue films forms a solar cell, the conversion efficiency of the solar cell is measured, yielding the a-th average value. There is a one-to-one correspondence between the number of times the carrier plate is used, the batch of blue films, the moisture value of the deposited blue films, and the conversion efficiency of the solar cell formed by the blue films. A conversion efficiency curve is formed with conversion efficiency as the ordinate and the number of times the carrier plate is used as the a-axis; similarly, a moisture value curve is formed with the moisture value in the process chamber as the ordinate.

[0059] In some embodiments, the preset water vapor value is a point value. The preset water vapor value is determined by: knowing the highest value of the conversion efficiency, and obtaining the preset water vapor value in the process chamber based on the number of cycles of the carrier plate corresponding to the highest value.

[0060] Select the point value of conversion efficiency that can be satisfied from the above conversion efficiency curve. For example, the highest value of conversion efficiency in the conversion efficiency curve is x. Obtain the horizontal axis of the conversion efficiency curve (number of times the carrier plate is used). The number of times the carrier plate is used is also the number of times the carrier plate is used in the water vapor value curve. Based on the water vapor value curve, determine the vertical axis of the curve, which is the optimal water vapor value.

[0061] In another embodiment, the preset water vapor value is a range. The range of the preset water vapor value is determined as follows: Select the range that the conversion efficiency can satisfy from the above conversion efficiency curve. For example, if the highest value of the conversion efficiency in the conversion efficiency curve is x, then the range that the conversion efficiency can satisfy may be 0.9×x (which may have some fluctuation). That is to say, the conversion efficiency in the range of 0.9×x to x is sufficient for the production of the solar cell of this application. In the conversion efficiency curve, 0.9×x is used as the vertical axis. There will be two intersection points with the curve to obtain the horizontal axis range value, which is the range value of the number of times the carrier plate can be used. Using this range value as the horizontal axis, find the corresponding vertical axis in the water vapor value curve to obtain the range of the preset water vapor value.

[0062] For example: Select a solar cell with high conversion efficiency and know the range of the number of cycles of the carrier plate used for the corresponding blue film of the solar cell; including: knowing the highest value of conversion efficiency, and calculating the range of conversion efficiency within 0.05% of the highest value (conversion efficiency in the range of 0.95×x to x); determining the range of the number of cycles of the carrier plate based on the range of the range of the number of cycles; and then obtaining the range of the preset water vapor value based on the range of the number of cycles.

[0063] S120, First stage of film deposition: N sets of unused carrier plates are used repeatedly to support the substrate and deposit the film. When the second preset condition is reached, a new set of carrier plates is used to replace the used set of carrier plates. Then, the N sets of carrier plates are used repeatedly to deposit the film. When the second preset condition is reached, a new set of carrier plates is used to replace the used set of unreplaced carrier plates, and so on, until all N sets of carrier plates are completely replaced. The second preset condition is that the moisture value in the process chamber is greater than the preset moisture value. After replacement, N sets of carrier plates are placed in the PVD deposition process chamber. The N sets of carrier plates are used a times, a+M times, ..., a+(N-1)×M times, respectively, where N is a natural number ≥2, and a is 0 to M times.

[0064] In one embodiment, N sets of carrier plates each carry a solar cell, and then the N sets of carrier plates are placed in a process chamber for ITO film deposition. The first use of the carrier plate yields the first batch of blue films, with the deposition of the first batch corresponding to a first moisture content in the process chamber. The second use of the carrier plate yields the second batch of blue films, with the deposition of the second batch corresponding to a second moisture content in the process chamber. This process continues until the Wth use of the carrier plate yields the Wth batch of blue films, with the deposition of the Wth batch corresponding to a Wth moisture content in the process chamber. When the Wth moisture content is higher than the preset moisture content obtained in step S110... When a new set of carrier plates is used to replace a set of used carrier plates, since the new carrier plate body 22 has not yet deposited an ITO film, it will not absorb water and will not easily bring more moisture into the process chamber, thus reducing the moisture content in the process chamber. Then, N sets of carrier plates (including new carrier plates and unreplaced carrier plates) are used to deposit the ITO film. After the carrier plates are recycled E times, the moisture content in the process chamber corresponds to the Eth moisture content when the Eth batch of blue film is deposited. When the Eth moisture content is higher than the preset moisture content obtained in step S110, a new set of carrier plates is used to replace a set of used carrier plates. This process is repeated until all N sets of carrier plates are completely replaced. At this point, the moisture content in the process chamber is within a stable range, and this range is basically around the preset moisture content.

[0065] Optionally, the preset moisture value is a range, with an upper and lower limit. When the monitored moisture value exceeds the upper limit, a new set of carrier plates replaces a set of used but not replaced carrier plates. After replacing the carrier plates, the moisture value in the process chamber monitored during the first use of the carrier plates to deposit the film exceeds the lower limit.

[0066] The carrier plate used for each replacement is not limited to one; it can be two or three. Optionally, after replacing the carrier plate, the moisture value in the process chamber monitored during the first use of the carrier plate for film deposition should be greater than the lower limit of the preset moisture value range. When adjusting the moisture range in the process chamber, the moisture value in the process chamber will not decrease excessively, making the adjustment of the moisture range more convenient and making it easier to perform film deposition within a relatively stable moisture range.

[0067] In other embodiments, each set of carrier plates is a single carrier plate, and one carrier plate is replaced at a time when a new carrier plate is used to replace a used one. The moisture content in the process chamber varies only slightly, resulting in smaller fluctuations in the moisture content range and thus better uniformity between different batches of membrane.

[0068] In some embodiments, N is in the range of 10 to 14, each set of carrier plates is one carrier plate, and each carrier plate can carry 100 to 300 substrates. A new carrier plate is replaced each time. This allows the moisture content to fluctuate within a small range so that the first stage of film deposition can be carried out within a relatively stable moisture range.

[0069] S130, Second stage of film deposition: N sets of carrier plates are used cyclically to support the substrate and deposit the film. When the first preset condition is reached, a new set of carrier plates is used to replace the set of carrier plates that have been used the most times in the process chamber. This process is repeated to ensure that the total number of times the N sets of carrier plates in the process chamber are used is always within the range of [M×(N-1) / 2+a]×N. Wherein, N is a natural number ≥2, a is 0 to M times, and the first preset condition is that the water vapor value in the process chamber is greater than the preset water vapor value.

[0070] At this point, the number of times the carrier plates in the process chamber are used is a times, a+M times, ..., a+(N-1)×M times. After the carrier plates continue to be used for a period of time, the moisture level in the process chamber exceeds the upper limit of the preset moisture level range. At this time, the carrier plates with the most cycles are replaced with a new set of carrier plates, and the number of cycles of the carrier plates in the process chamber becomes a times, a+M times, ..., a+(N-1)×M times again. After the carrier plates are used for a period of time, the moisture level in the process chamber exceeds the preset moisture level. At this time, the carrier plates with the most cycles are replaced with a new set of carrier plates, and so on, for ITO film deposition. This makes the deposition of ITO films in different batches more uniform, makes the performance of blue film sheets in different batches more stable, and thus makes the conversion efficiency of solar cells in different batches more stable.

[0071] Figure 4 For a second process flow diagram of the PVD deposition film method provided in some embodiments of this application, please refer to [link / reference]. Figure 4 The method is based on the premise that the new carrier board is used M times. The method includes:

[0072] S210, determine the value of M.

[0073] S211, N sets of carrier plates are placed in the process chamber and ITO films are deposited on the solar cells placed on the carrier plates to obtain blue films. The number of times the carrier plates are recycled corresponds to different blue films.

[0074] In other words, solar cells (including an n-type silicon wafer 10, with an intrinsic amorphous silicon layer 11 and an n-type doped amorphous silicon layer 13 sequentially disposed on the front side of the n-type silicon wafer 10, and an intrinsic amorphous silicon layer 12 and a p-type doped amorphous silicon layer 14 sequentially disposed on the back side of the n-type silicon wafer 10) are carried on N sets of carriers. Then, the N sets of carriers are placed into the process chamber for ITO film deposition. The first time the carrier is used, the first batch of blue films will be obtained. The second time the carrier is used, the second batch of blue films will be obtained. And so on, the Qth time the carrier is used, the Qth batch of blue films will be obtained.

[0075] In some embodiments, different blue films correspond to different numbers of carrier plate cycles, including: different blue films corresponding to N sets of blue films obtained by carrier plate cycles of a times, a+M times, ..., a+(N-1)×M times; where a is 0 to M times. It is not necessary to select the corresponding blue film and water vapor value for each carrier plate cycle, thus reducing the number of blue film detections and making it simpler to obtain the preset water vapor value range.

[0076] In other words, solar cells are carried on N sets of carriers, and then the N sets of carriers are placed into the process chamber for ITO film deposition. The carriers are recycled a times to obtain the a-th batch of blue films. The carriers are recycled a+M times to obtain the a+M-th batch of blue films. And so on, the carriers are recycled a+(N-1)×M times to obtain the a+(N-1)×M-th batch of blue films.

[0077] In some embodiments, N is in the range of 10 to 14, each group of carriers has one carrier, and each carrier can carry 100 to 300 solar cells. Typically, the process chamber can hold 10 to 14 carriers, and each carrier can carry 100 to 300 solar cells. In other embodiments, other numbers of carriers and carriers carrying other numbers of solar cells can be selected according to the size of the process chamber, and this application does not limit this.

[0078] S212, electrodes were printed on different blue films to obtain solar cells, and the conversion efficiency of different solar cells was tested.

[0079] Optionally, in step S111, the a-th batch of blue films, the a+M-th batch of blue films, ... and the a+(N-1)×M-th batch of blue films are obtained respectively. Electrodes are printed on these blue films to obtain solar cells, and the conversion efficiency of each solar cell is then detected.

[0080] In some embodiments, 50 to 150 blue films with the same number of cycles of carrier plate are selected to print electrodes to obtain solar cells, and the conversion efficiency is the average value of the conversion efficiency of the 50 to 150 solar cells tested.

[0081] Optionally, 50 to 150 blue films are selected from the first batch a, 50 to 150 blue films are selected from the second batch a+M, and so on, until 50 to 150 blue films are selected from the third batch a+(N-1)×M. Electrodes are printed on these blue films to obtain solar cells, and the conversion efficiency of each solar cell is then measured. The conversion efficiency of the first batch a is the a-th average of the conversion efficiencies of the solar cells formed from 50 to 150 blue films; the conversion efficiency of the second batch a+M is the a+M-th average of the conversion efficiencies of the solar cells formed from 50 to 150 blue films; and so on, until the conversion efficiency of the third batch a+(N-1)×M is the a+(N-1)×M-th average of the conversion efficiencies of the solar cells formed from 50 to 150 blue films.

[0082] S213, Select a solar cell with high conversion efficiency and find out the number of cycles of the carrier plate used for the blue film corresponding to the solar cell.

[0083] In other words, the a-th cycle of the carrier plate corresponds to the a-th batch of blue film sheets. After the a-th batch of blue film sheets forms a solar cell, the conversion efficiency of the solar cell is measured, and the a-th average value is obtained. There is a one-to-one correspondence between the number of times the carrier plate is used, the batch of blue film sheets, and the conversion efficiency of the solar cell formed by the blue film sheets. A conversion efficiency curve is formed by plotting the conversion efficiency on the ordinate and the number of times the carrier plate is used on the a-axis.

[0084] In one embodiment, the highest conversion efficiency is selected as a point value. The value of M is determined as follows: The highest conversion efficiency is obtained, and the number of carrier cycles corresponding to the highest efficiency is Q, which is the point value. Here, N×Q=[M×(N-1) / 2+a]×N, the value of M can be calculated. Optionally, N is 12~14, each group of carriers is one carrier, and a is 0~M.

[0085] For example: when N is 12 and a = 0, based on the conversion efficiency curve, Q is determined to be 400, 400 = [M × (12-1) / 2], M = 72; when N is 12 and a = M, based on the conversion efficiency curve, Q is determined to be 400, 400 = [M × (12-1) / 2 + M], M = 61, and M is in the range of 61 to 72.

[0086] For example: when N is 12 and a = 0, based on the conversion efficiency curve, Q is determined to be 500, 500 = [M × (12-1) / 2], M = 90; when N is 12 and a = M, based on the conversion efficiency curve, Q is determined to be 400, 400 = [M × (12-1) / 2 + M], M = 76, and M is in the range of 76 to 90.

[0087] In another embodiment, the highest selected conversion efficiency is a range value. The value of M is determined as follows: The highest conversion efficiency is obtained, and based on this highest value, a range of conversion efficiencies with a difference within 0.05% is calculated. Based on this range, the range of the number of cycles Q of the carrier plate is determined, where N×Q=[M×(N-1) / 2+a]×N, from which the value of M can be calculated. Optionally, N is 12~14, each group of carrier plates is one carrier plate, and a is 0~M.

[0088] For example: When N is 12 and a = 0, based on the conversion efficiency curve, Q is determined to be in the range of 350 to 550, where 350 = [M × (12-1) / 2] and M = 63; when N is 12 and a = M, based on the conversion efficiency curve, Q is determined to be 350, where 350 = [M × (12-1) / 2 + M] and M = 53; 550 = [M × (12-1) / 2] and M = 100; when N is 12 and a = M, based on the conversion efficiency curve, Q is determined to be 550, where 550 = [M × (12-1) / 2 + M] and M = 84; therefore, M is in the range of 53 to 100.

[0089] S220, First stage of film deposition: N sets of unused carrier plates are used repeatedly to support the substrate and deposit film. When the second preset condition is reached, a new set of carrier plates is used to replace the used set of carrier plates. Then, the N sets of carrier plates are used repeatedly to deposit film. When the second preset condition is reached, a new set of carrier plates is used to replace the used but unreplaced set of carrier plates, and so on, until all N sets of carrier plates are completely replaced. The second preset condition is that the sum of the number of times all carrier plates in the process chamber are used is greater than [M×(N-1) / 2+a]×N times. After replacement, the PVD deposition process chamber contains N sets of carrier plates, and the number of times the N sets of carrier plates are used are a times, a+M times, ..., a+(N-1)×M times, where N is a natural number ≥2, and a is 0 to M times.

[0090] In one embodiment, solar cells are carried on N sets of carrier plates, and then the N sets of carrier plates are placed in the process chamber for ITO film deposition. The first use of the carrier plate yields the first batch of blue films. The second use of the carrier plate yields the second batch of blue films, and so on. The Wth use of the carrier plate yields the Wth batch of blue films. When N×W is greater than [M×(N-1) / 2+a]×N times, a new set of carrier plates is used to replace a set of used carrier plates. Since the carrier plate body 22 of the new carrier plate has not yet deposited ITO film, it will not absorb water and will not easily bring more moisture into the process chamber, thus reducing the moisture content in the process chamber. Then, the N sets of carrier plates (including new carrier plates and unreplaced carrier plates) are used to deposit ITO film. After the carrier plates continue to be used for a period of time, the sum of the number of times all carrier plates in the process chamber are used is greater than [M×(N-1) / 2+a]×N times, and a new set of carrier plates is used to replace a set of used carrier plates. This process continues until all N sets of carrier plates are completely replaced. At this point, the moisture content in the process chamber is within a stable range, resulting in a better deposition film effect.

[0091] Each set of carrier plates consists of one carrier plate. When replacing a used carrier plate with a new one, one carrier plate is replaced at a time. The moisture content in the process chamber varies only slightly, which can minimize fluctuations in the moisture content range and thus improve the uniformity of membranes from different batches.

[0092] In some embodiments, N is in the range of 10 to 14, each set of carrier plates is one carrier plate, and each carrier plate can carry 100 to 300 substrates. A new carrier plate is replaced each time. This allows the moisture content to fluctuate within a small range so that the first stage of film deposition can be carried out within a relatively stable moisture range.

[0093] S230, Second stage of film deposition: N sets of carrier plates are used repeatedly to support the substrate and deposit the film. When the first preset condition is reached, a new set of carrier plates is used to replace the set of carrier plates that have been used the most times in the process chamber. This process is repeated to ensure that the total number of times the N sets of carrier plates in the process chamber are used is always within the range of [M×(N-1) / 2+a]×N. Wherein, N is a natural number ≥2, a is 0 to M times, M is a natural number ≥30, and the first preset condition is that the new carrier plate has been used M times.

[0094] At this point, the number of times the carrier plates in the process chamber are used are *a* times, *a+M* times, ..., *a+(N-1)×M* times. After the carrier plates have been used *M* times, the set of carrier plates with the most uses is replaced with a new set of carrier plates, and the number of times the carrier plates in the process chamber are used again becomes *a* times, *a+M* times, ..., *a+(N-1)×M* times. This process is repeated, and by depositing the ITO film, the deposition of ITO films in different batches can be made more uniform, the performance of blue film sheets in different batches is more stable, and thus the conversion efficiency of solar cells in different batches is also more stable.

[0095] In other embodiments, the need to replace the carrier plate can be determined by simultaneously using a preset moisture value and the number of times the carrier plate is used. These can be mutually corrected to make the moisture value range in the process chamber more stable, so that the performance of the deposited film is also more stable.

[0096] Example 1

[0097] A method for fabricating a solar cell includes the following steps:

[0098] (1) A double-sided texturing process was performed on an N-type silicon wafer with a thickness of 20 μm and a side length of 166.1 mm to obtain a pyramidal texturing surface with a height of 3 μm.

[0099] (2) A first intrinsic amorphous silicon layer with a thickness of 5 nm is formed on the front side of the N-type silicon wafer, and a second intrinsic amorphous silicon layer with a thickness of 10 nm is formed on the back side.

[0100] (3) Continue to form an N-type doped amorphous silicon layer with a thickness of 5 nm on the first intrinsic amorphous silicon layer.

[0101] (4) Continue to form a P-type doped amorphous silicon layer with a thickness of 10 nm on the second intrinsic amorphous silicon layer to obtain a solar cell.

[0102] (5) Determine the preset moisture value in the process chamber: Each of the 12 carrier plates carries the solar cells obtained in step (4) (150 solar cells on each carrier plate). Place the 12 carrier plates carrying the solar cells in the process chamber of the PVD equipment. Deposit the ITO film for the first time to obtain the first batch of blue films, and record the first moisture value in the process chamber corresponding to the deposition of the first batch of blue films. After the deposition is completed, remove the 12 carrier plates from the process chamber, remove the blue films, and then place new solar cells on the carrier plates. The substrate is then placed into the process chamber of a PVD equipment for a second ITO film deposition. This process is repeated 100 times to obtain the 100th batch of blue films. The 100th moisture content in the process chamber corresponding to the deposition of the 100th batch of blue films is recorded. This process is repeated to obtain the 1100th batch of blue films, and the 1100th moisture content in the process chamber corresponding to the deposition of the 1100th batch of blue films is recorded. The curves showing the number of substrate cycles, the batches of blue films, and the corresponding moisture content during blue film deposition are shown below. Figure 5 .

[0103] Solar cells were obtained by printing electrodes on blue film sheets (the first batch, the 100th batch, ... the 1100th batch). Each batch of blue film sheets yielded 150 solar cells. The conversion efficiency of the solar cells was measured and the average value was calculated. The curves showing the batch number of the blue film sheets (the number of times the carrier plate was used) and the corresponding solar cell conversion efficiency are shown below. Figure 5 .

[0104] from Figure 5 It can be seen that the highest conversion efficiency of the solar cell is 24.13%. The blue film of this solar cell is from the 400th batch, and the corresponding preset water vapor value is 5×10. -4 Pa.

[0105] (6) First stage of film deposition: The solar cells obtained in step (4) are carried in the mounting frames of 12 carrier plates (150 solar cells are carried on each carrier plate). The 12 carrier plates carrying the solar cells are placed in the process chamber of the PVD equipment. The first ITO film is deposited to obtain the first batch of blue films, and the first water vapor value in the process chamber corresponding to the deposition of the first batch of blue films is recorded. After the deposition is completed, the 12 carrier plates are removed from the process chamber, the blue films are removed, and then new solar cells are placed on the carrier plates and put back into the process chamber of the PVD equipment for the second deposition of ITO film. This cycle continues until the first batch of blue films is deposited. If the moisture level in the process chamber exceeds the preset moisture level, a new carrier plate is used to replace a carrier plate that has already been circulated 400 times. The cycle continues, and when the moisture level in the process chamber exceeds the preset moisture level, a new carrier plate is used to replace a carrier plate that has not been replaced. This process continues until all carrier plates have been replaced once. At this point, the number of cycles for the 12 carrier plates in the process chamber are 0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, and 1100, respectively.

[0106] (7) Second stage of film deposition: Continue to use the carrier plate. When the water vapor value in the process chamber is greater than the preset water vapor value, replace the carrier plate that has been used the most times in the process chamber with a new carrier plate. Continue in this way to deposit the ITO film and obtain the blue film.

[0107] (8) Fabrication of solar cells: Electrodes are printed on the blue film obtained in step (7) to form a solar cell, and the conversion efficiency of the solar cell is tested.

[0108] The conversion efficiency curve of the solar cell provided in Example 1 and the water vapor value curve of the blue film deposited during the fabrication of the solar cell are shown in the figure below. Figure 6 .from Figure 6 It can be seen that the conversion efficiency of the solar cell provided in this application embodiment fluctuates within the range of 24.2% to 24.26%, with a very small fluctuation range; in the preparation method of the solar cell provided in this application embodiment, the water vapor value in the process chamber is 3.9 × 10⁻⁶ during the deposition of the ITO film. -4 Pa ~ 4.8 × 10 -4 The water vapor range fluctuates within the Pa range, and the fluctuation range is very small, so there is no need to use a water vapor emitter to adjust the water vapor range in the process chamber.

[0109] Example 2

[0110] The difference between Example 2 and Example 1 is as follows:

[0111] (5) Determine the value of M: Each of the 12 carrier plates carries the solar cells obtained in step (4) (150 solar cells are carried on each carrier plate). Place the 12 carrier plates carrying the solar cells in the process chamber of the PVD equipment and deposit the ITO film for the first time to obtain the first batch of blue film sheets. After the deposition is completed, remove the 12 carrier plates from the process chamber, remove the blue film sheets, and then place new solar cells on the carrier plates and put them back into the process chamber of the PVD equipment for the second deposition of ITO film. Repeat this process 100 times to obtain the 100th batch of blue film sheets. Continue in this manner to obtain the 1100th batch of blue film sheets.

[0112] Solar cells were obtained by printing electrodes on blue film sheets (the first batch, the 100th batch, ... the 1100th batch). Each batch of blue film sheets yielded 150 solar cells. The conversion efficiency of the solar cells was measured and the average value was calculated. The curves showing the batch number of the blue film sheets (the number of times the carrier plate was used) and the corresponding solar cell conversion efficiency are shown below. Figure 7 .

[0113] from Figure 7 It can be seen that the highest conversion efficiency of the solar cell is 24.12%. The blue film of this solar cell is the 500th batch of blue film, and the value of Q is 500. 12×500=[M×(12-1) / 2+a]×12, where a is 0~M. The value of M is calculated to be 76~90, and the value of M is taken as 80.

[0114] (6) First stage of film deposition: The solar cells obtained in step (4) are carried in the mounting frames of 12 carrier plates (150 solar cells are carried on each carrier plate). The 12 carrier plates carrying the solar cells are placed in the process chamber of the PVD equipment, and the first ITO film is deposited to obtain the first batch of blue film sheets. After the deposition is completed, the 12 carrier plates are removed from the process chamber, the blue film sheets are removed, and then new solar cells are placed on the carrier plates and put back into the process chamber of the PVD equipment for the second ITO film deposition. This process is repeated 500 times to obtain the 500th batch of blue film sheets. A new carrier plate is used to replace a carrier plate that has been cycled 500 times. Then the process continues. The cycle continues. When the new carrier plate has been circulated 80 times and the other unreplaced carrier plates have been circulated 580 times, a new carrier plate replaces a carrier plate that has been circulated 580 times. Then the cycle continues. When the new carrier plate has been circulated 80 times and the other unreplaced carrier plates have been circulated 660 times, a new carrier plate replaces a carrier plate that has been circulated 660 times, and so on, until all carrier plates have been replaced once. The number of cycles for the 12 carrier plates in the process chamber are 0, 80, 160, 240, 320, 400, 480, 560, 640, 720, 800, and 880 times, respectively.

[0115] (7) Second stage of film deposition: The carrier plate is recycled 80 times. A new carrier plate is used to replace the carrier plate with the most recycling times in the process chamber. This process is repeated to deposit an ITO film to obtain a blue film. During the film deposition process, the 12 carrier plates in the process chamber are recycled for (0-79) times, (80-159) times, (160-239) times, (240-319) times, (320-399) times, (400-479) times, (480-559) times, (560-639) times, (640-719) times, (720-799) times, (800-879) times, and (880-959) times, respectively.

[0116] (8) Fabrication of solar cells: Electrodes are printed on the blue film obtained in step (7) to form a solar cell, and the conversion efficiency of the solar cell is tested.

[0117] The conversion efficiency curve of the solar cell provided in Example 2 and the water vapor value curve of the blue film deposited during the fabrication of the solar cell are shown in the figure below. Figure 8 .from Figure 8 It can be seen that the conversion efficiency of the solar cell provided in this application embodiment fluctuates within the range of 24.2% to 24.26%, with a very small fluctuation range; in the preparation method of the solar cell provided in this application embodiment, the water vapor value in the process chamber is 3.8 × 10⁻⁶ during the deposition of the ITO film. -4 Pa ~ 4.8 × 10 -4 The water vapor range fluctuates within the Pa range, and the fluctuation range is very small, so there is no need to use a water vapor emitter to adjust the water vapor range in the process chamber.

[0118] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for PVD deposition of a film, characterized in that, The PVD deposition process chamber contains N sets of carrier plates, which are recycled a times, a+M times, ..., a+(N-1)×M times, respectively; the method includes: The N sets of carrier plates are used repeatedly to support the substrate and deposit a film. When the first preset condition is reached, a new set of carrier plates is used to replace the set of carrier plates that have been used the most times in the process chamber. This process is repeated so that the total number of times the N sets of carrier plates in the process chamber are used is always within the range of [M×(N-1) / 2+a]×N. Wherein, the membrane is made of a water-absorbing material, N is a natural number ≥2, a is 0 to M times, and the first preset condition is that the water vapor value in the process chamber is greater than the preset water vapor value, or the new carrier plate is recycled M times.

2. The method according to claim 1, characterized in that, The process chamber for forming the PVD deposition contains N sets of carrier plates, and the N sets of carrier plates are recycled a times, a+M times, ..., a+(N-1)×M times, respectively. The method includes: The substrate is deposited using N sets of unused carrier plates. When a second preset condition is reached, a new set of carrier plates is used to replace the used set of carrier plates. Then, the N sets of carrier plates are used to deposit the film. When the second preset condition is reached, a new set of carrier plates is used to replace the used but unreplaced set of carrier plates. This process is repeated until all N sets of carrier plates are completely replaced. The second preset condition is that the moisture content in the process chamber is greater than a preset moisture content, or the sum of the number of times all carrier plates in the process chamber are used is greater than [M×(N-1) / 2+a]×N times.

3. The method according to claim 2, characterized in that, The preset water vapor value is a range, and the preset water vapor value has an upper limit and a lower limit. The first preset condition is that the water vapor value in the process chamber is greater than the upper limit. The second preset condition is that the water vapor value in the process chamber is greater than the upper limit.

4. The method according to claim 3, characterized in that, After replacing the used set of carrier plates with a new set, the moisture content in the process chamber is greater than the lower limit.

5. The method according to claim 4, characterized in that, The number of carrier plates N is 12 to 14, each group of carrier plates is one carrier plate, and each carrier plate carries 100 to 300 substrates.

6. The method according to any one of claims 1 to 5, characterized in that, The substrate is a heterojunction solar cell, and the deposited film is an ITO film.

7. The method according to claim 6, characterized in that, The method for determining the preset water vapor value includes: N sets of carrier plates are placed in the process chamber and the ITO film is deposited on the battery cells placed on the carrier plates to obtain blue films. The number of times the carrier plates are used corresponds to different blue films and different water vapor values ​​in the process chamber. Solar cells were obtained by printing electrodes on different blue films, and the conversion efficiency of the different solar cells was tested. Select the solar cell with high conversion efficiency, and know the number of cycles of the carrier plate used by the blue film corresponding to the solar cell. Based on the number of cycles, obtain the water vapor value in the process cavity as the preset water vapor value.

8. The method according to claim 7, characterized in that, The preset water vapor value is a range, and the method for determining the preset water vapor value includes: The highest value of the conversion efficiency is determined, and a range of conversion efficiencies with a difference of less than 0.05% is calculated based on the highest value. Based on the range value, the range of the number of times the carrier plate can be used is determined, and based on the range of the number of times it can be used, the range of the preset moisture value in the process chamber is obtained.

9. The method according to claim 7, characterized in that, The preset water vapor value is a constant, and the method for determining the preset water vapor value includes: The highest conversion efficiency is determined, and based on the number of carrier cycles corresponding to the highest efficiency, the preset moisture value in the process chamber is obtained based on the number of cycles.

10. The method according to claim 6, characterized in that, The method for determining the value of M includes: N sets of carrier plates are placed in the process chamber and the ITO film is deposited on the battery cells placed on the carrier plates to obtain blue films. The number of times the carrier plates are recycled corresponds to different blue films. Solar cells were obtained by printing electrodes on different blue films, and the conversion efficiency of the different solar cells was tested. Select the solar cell with high conversion efficiency and know the number of cycles Q of the carrier plate used by the blue film corresponding to the solar cell, where N×Q=[M×(N-1) / 2+a]×N.

Images