A secondary vapor deposition apparatus for bifacial CIGS solar cells

Abstract

This invention relates to a secondary vapor deposition apparatus for bifacial CIGS solar cells, addressing the problem that secondary deposition on the back side of a bifacial CIGS solar cell substrate can easily damage the already deposited coating on the front side. The apparatus includes a vacuum chamber containing an unwinding shaft, a winding shaft, and several conveying rollers. The substrate is sequentially conveyed along the conveying rollers between the unwinding and winding shafts. The middle section of the substrate conveying area is the vapor deposition zone. The key feature is that a lower evaporation source is positioned below the vapor deposition zone, and a heating plate is positioned above the substrate in the vapor deposition zone between adjacent conveying rollers. Selenium replenishment nozzles, pointing downwards and spraying selenium vapor onto the upper surface of the substrate, are located between the heating plates or between the heating plates and the conveying rollers. These nozzles are connected to an upper selenium evaporation source. This invention replenishes selenium on the front side of the substrate during secondary deposition on the back side of the bifacial CIGS solar cell substrate, ensuring that the coating on the front side of the substrate is not damaged during the high-temperature secondary deposition environment.

Description

Technical Field

[0001] This invention belongs to the field of solar cell manufacturing, and relates to the production of CIGS flexible solar cells, particularly to a secondary vapor deposition apparatus for bifacial CIGS cells. Background Technology

[0002] Flexible solar cells are made by depositing solar photovoltaic materials onto a flexible, rollable substrate. Copper indium gallium selenide (CIGS) thin-film solar cells are a type of solar photovoltaic material with high power-to-weight ratio and good stability, and are widely considered to be the most promising flexible solar cell material. The multi-element co-evaporation method is the most widely used CIGS coating method. Deposition is completed in a vacuum environment, utilizing the co-evaporation of copper, indium, gallium, and selenium to react on the substrate surface and form a polycrystalline coating. Vapor deposition is performed in a vacuum, high-temperature, and highly corrosive environment.

[0003] In many applications, CIGS solar cells are stationary, such as in the sound barriers of elevated roads, highways, and high-speed railways. These sound barriers are vertical partitions, fixed and non-rotating. They are made of transparent material, allowing CIGS solar cells to be sandwiched within. Existing CIGS solar cells are generally single-sided coated. However, due to seasonal changes and the daily sun's rising and setting, these fixed single-sided CIGS cells cannot generate electricity for nearly half of the daytime sunlight exposure. In these scenarios, double-sided coating of the substrate can effectively extend the daytime power generation time. Furthermore, existing CIGS solar cells have large gaps between adjacent cells during installation, preventing sunlight passing through these gaps from reaching the ground. With double-sided coating, sunlight reflected off the ground and onto the back of the cells can be utilized, effectively improving power generation efficiency. To obtain bifacial CIGS solar cells with CIGS coatings on both sides of the substrate, CIGS coating needs to be applied to both sides of the substrate. The vacuum CIGS coating process requires the substrate to be coated with the coating side facing down during vapor deposition. Bifacial CIGS solar cells require coating the front and back sides of the substrate separately, necessitating a total of two coating processes. Since CIGS coating is performed in a vacuum and high-temperature environment, coating the front side of the substrate first and then the back side can damage the coating layer. This damage primarily includes: 1. Cracks in the coating layer caused by the reverse bending of the front coating layer after the substrate is switched from forward to reverse winding; 2. Selenium escape from the front coating layer during the high-temperature vapor deposition on the back side; 3. Interdiffusion of elements from the front coating layer with elements from the conveyor roller surface under high-temperature conditions; 4. The diffusion of plumes from the back coating process onto the front side of the substrate, leading to changes in the coating layer. Currently, there is no effective solution to reduce damage to the front coating layer of the substrate during the two-stage coating process. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that the already coated front side of the substrate is easily damaged when a secondary coating is applied to the back side of the substrate for double-sided CIGS solar cells, and to provide a secondary evaporation device for double-sided CIGS solar cells.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a secondary vapor deposition device for double-sided CIGS solar cells, including a vacuum chamber, an unwinding shaft, a winding shaft and several conveying rollers are arranged in the vacuum chamber, the unwinding shaft and the winding shaft sequentially convey the substrate along each conveying roller, the middle section of the substrate conveying is the vapor deposition zone, a lower evaporation source is arranged below the vapor deposition zone, a heating plate is arranged above the substrate in the vapor deposition zone between adjacent conveying rollers, a selenium replenishment nozzle is provided between the heating plates or between the heating plates and the conveying rollers to spray selenium vapor downwards onto the upper surface of the substrate, and the selenium replenishment nozzle is connected to an upper selenium evaporation source.

[0006] CIGS coating is completed in a vacuum chamber, with the substrate temperature around 500 degrees Celsius during the coating process. During the first vapor deposition on the front side of the substrate, there is no film layer on the back side. However, when the substrate is reverse-wound and the back side is facing down for the second vapor deposition, the CIGS film layer already coated on the front side of the substrate is present. The temperature threshold for high-temperature escape of copper indium gallium in the CIGS on the front side of the substrate is around 1000°C, so it can remain stable. Selenium in CIGS will exhibit high-temperature escape at temperatures exceeding 300°C. Moreover, during the reverse roll-up and reverse second vapor deposition process, the conversion of the coating surface on the front side of the substrate from the outer arc surface to the inner arc surface will cause extrusion damage to the film surface. Therefore, this device sets a selenium replenishment nozzle between the heating plate and the conveying roller above the substrate. The selenium replenishment nozzle is connected to the upper selenium evaporation source. The upper selenium evaporation source continuously generates selenium vapor through heating. The vapor pressure in the coating vacuum chamber is lower than that in the upper selenium evaporation source. Using the pressure difference, selenium vapor is sprayed downward from the selenium replenishment nozzle to replenish selenium atoms on the front side of the substrate, compensate for selenium escape, and repair the extrusion damage to the film surface. This device can be easily modified from a traditional CIGS coating device. This device can be used for secondary coating, and primary coating can be done using a traditional CIGS coating device. It can also be used for both primary and secondary coating. The selenium evaporation source is not activated during primary coating.

[0007] Preferably, a selenium vapor conduit is provided between the upper selenium evaporation source and the selenium replenishment nozzle; the upper selenium evaporation source is a built-in selenium source located inside the vacuum chamber; or the upper selenium evaporation source is an external selenium source located outside the vacuum chamber.

[0008] Preferably, each selenium-supplemented nozzle is connected to a separate selenium evaporation source, or all selenium-supplemented nozzles share a single selenium evaporation source.

[0009] Preferably, the conveyor roller is coated with a high-temperature resistant coating, which is either an alumina coating or a boron nitride coating. Currently used conveyor rollers are primarily made of stainless steel, which contains iron. Iron significantly affects battery efficiency in semiconductors and its use should be minimized. Therefore, in this application, the conveyor roller is coated with a smoother, high-temperature resistant, iron-free coating, reducing scratches and abrasions on the film layer from the roller surface, and also reducing Fe diffusion from the traditional iron-containing roller surface on the CIGS film surface, which leads to a decline in CIGS film performance.

[0010] Preferably, the conveyor roller has a built-in heating device, and the operating temperature of the conveyor roller is 300-500℃. The temperature of the conveyor roller is higher than the deposition temperature of selenium, which prevents selenium on the substrate front and selenium vapor in the vacuum chamber from depositing and adhering to the conveyor roller, thus avoiding a decrease in the flatness of the roller surface and damage to the coating surface.

[0011] Preferably, the lower evaporation source includes a lower selenium source and a metal source, wherein the metal source is one or more of copper, indium, and gallium.

[0012] Preferably, an external rewinding device is also included, comprising a rewinding unwinding shaft and a rewinding rewinding shaft, wherein the unwinding direction of the rewinding unwinding shaft and the rewinding direction of the rewinding rewinding shaft are opposite. For the substrate material after the first coating is completed, the rewinding device is used to rewind the substrate from the front side outwards to the back side outwards, so that the back side of the substrate is facing down when unwinding during the second coating.

[0013] Preferably, several reverse winding conveyor rollers are provided between the reverse winding unwinding shaft and the reverse winding rewinding shaft.

[0014] Preferably, a synchronization device is provided between each conveyor roller.

[0015] Preferably, the substrate is a stainless steel substrate.

[0016] Preferably, inclined baffles are provided on both sides of the substrate in the vapor deposition zone. The inclined baffles are inclined with the inner side lower than the outer side, and the inner end of the inclined baffle is flush with the substrate. The inclination of the inclined baffles is 30-60°. In this device, the inclined baffles guide the plume below the substrate outward, preventing the plume deposited below the substrate from flowing around to the upper surface of the substrate from both sides and affecting the existing film layer on the upper surface of the substrate. At the same time, since the selenium replenishment nozzle above the upper surface of the substrate replenishes selenium, a positive pressure zone is formed in the space between the inclined baffles and the upper surface of the substrate, which can also prevent the plume below the substrate from entering through the gap between the inclined baffles and the substrate and reaching the upper surface of the substrate.

[0017] Preferably, a vacuum chamber suction port is provided at intervals on the upper end of the inclined baffle. The vacuum in the vacuum chamber is created by a vacuum pump, which draws suction from the vacuum chamber through the suction ports distributed within the vacuum chamber. In this design, the suction ports of the vacuum chamber are strategically arranged, with some suction ports positioned at the upper end of the inclined baffle. This allows for the suction of the vapor deposition plume from the lower surface of the substrate outside the inclined baffle and the selenium replenishment vapor from the upper surface of the substrate above the inclined baffle, reducing excessive accumulation of the vapor deposition plume and selenium replenishment vapor and minimizing disordered diffusion of the vapor deposition plume and selenium replenishment vapor in the gaps.

[0018] In this invention, when performing a secondary coating on the back side of a double-sided CIGS solar cell substrate, selenium is added to the front side of the substrate to ensure that the coating on the front side of the substrate is not damaged during the high-temperature secondary coating environment. Attached Figure Description

[0019] The invention will now be further described with reference to the accompanying drawings.

[0020] Figure 1 This is a schematic diagram of one structure of the present invention.

[0021] Figure 2 This is a schematic diagram of a rewinding device according to the present invention.

[0022] Figure 3 This is a schematic diagram of the inclined baffle in Embodiment 1 of the present invention.

[0023] Figure 4 This is a schematic diagram of the inclined baffle in Embodiment 2 of the present invention.

[0024] In the diagram: 1. Vacuum chamber, 2. Unwinding shaft, 3. Rewinding shaft, 4. Conveyor roller, 5. Base, 6. Heating plate, 7. Selenium replenishment nozzle, 8. Upper selenium evaporation source, 9. Selenium vapor conduit, 10. Lower evaporation source, 11. Reverse unwinding shaft, 12. Reverse rewinding shaft, 13. Reverse conveyor roller, 14. Inclined baffle, 15. Suction port. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0026] Example 1: A secondary vapor deposition apparatus for bifacial CIGS solar cells, such as... Figure 1 , 3 As shown, a secondary vapor deposition is performed on the back side of the substrate for bifacial CIGS solar cells. In this apparatus, the front side of the substrate for the bifacial CIGS solar cells has already been coated with CIGS film, and then... Figure 2The shown rewinding device rewinds the base roll material from the front side outwards to the back side outwards: the rewinding device includes a rewinding unwinding shaft 11 and a rewinding take-up shaft 12, the unwinding direction of the rewinding unwinding shaft 11 and the take-up direction of the rewinding take-up shaft 12 are opposite. Several rewinding conveyor rollers 13 are arranged between the rewinding unwinding shaft and the rewinding take-up shaft.

[0027] like Figure 1 As shown, this device includes a vacuum chamber 1, within which an unwinding shaft 2, a winding shaft 3, and several conveying rollers 4 are arranged. A substrate 5, made of stainless steel, is conveyed sequentially along each conveying roller between the unwinding and winding shafts. The middle section of the substrate conveying section is a vapor deposition zone. Below the vapor deposition zone, a lower evaporation source 10 is arranged, comprising a lower selenium source and a metal source, wherein the metal source is one or more of copper, indium, and gallium sources. The lower evaporation source is arranged in the same manner as the primary deposition process. Above the substrate 5 in the vapor deposition zone, a heating plate 6 is arranged between adjacent conveying rollers. Between the heating plate 6 and the conveying rollers 5, a selenium replenishment nozzle 7 is provided, pointing downwards and spraying selenium vapor onto the upper surface of the substrate. The selenium replenishment nozzle 7 is connected to an upper selenium evaporation source 8. In this example, the upper selenium evaporation source 8 is an external selenium source, located outside the vacuum chamber. A selenium vapor conduit 9 is provided between the upper selenium evaporation source and the selenium replenishment nozzle. Each selenium replenishment nozzle 7 is synchronously connected to one upper selenium evaporation source 8. The roller face of each conveying roller 4 is coated with a high-temperature resistant alumina coating. The conveyor roller 4 has a built-in heating device, and its operating temperature is approximately 400℃. This prevents selenium from adhering to the conveyor roller, which could worsen the flatness of the roller surface and cause unevenness of the film on the substrate. A synchronization device is installed between each conveyor roller. Figure 3 As shown, inclined baffles 14 are provided on both sides of the base of the vapor deposition zone of this device. The inclined baffles 14 are inclined with the inner side lower than the outer side. The inner end of the inclined baffles 14 is flush with the base 5, and the inclination of the inclined baffles is 45°.

[0028] During the first coating on the front side of the substrate, there is no film layer on the back side. However, when the substrate is reversed and rolled up, and the device performs a second coating with the back side facing down, the copper indium gallium (CIGS) film already has a completed coating on the front side of the substrate. The high-temperature escape temperature threshold of CIGS on the front side of the substrate is around 1000°C, thus maintaining a stable state. Selenium in CIGS will exhibit high-temperature escape at temperatures exceeding 300°C, while the substrate temperature exceeds 500°C during coating. Furthermore, the substrate changes from facing outwards to facing outwards. During the reverse roll and reverse secondary coating process, the transition from the outer arc surface to the inner arc surface of the substrate's front coating surface can cause compression damage to the film surface. Therefore, this device sets up a selenium replenishment nozzle between the heating plate and the conveying roller above the substrate. The selenium replenishment nozzle is connected to an upper selenium evaporation source. The upper selenium evaporation source continuously generates selenium vapor through heating. The vapor pressure in the coating vacuum chamber is lower than that in the upper selenium evaporation source. Using the pressure difference, selenium vapor is sprayed downwards from the selenium replenishment nozzle to replenish selenium atoms on the front surface of the substrate, compensating for selenium escape and repairing the compression damage to the film surface. The inclined baffle guides the plume below the substrate outwards, preventing the plume deposited below the substrate from flowing around to the upper surface of the substrate from both sides, thus affecting the existing film layer on the upper surface of the substrate. At the same time, since the selenium replenishment nozzle above the upper surface of the substrate replenishes selenium, a positive pressure zone is formed in the space between the inclined baffle and the upper surface of the substrate, which can also prevent the plume below the substrate from entering through the gap between the inclined baffle and the substrate and reaching the upper surface of the substrate. The vacuum environment of the entire vacuum chamber is greatly reduced because the vapor deposition plume and selenium replenishment vapor can diffuse and dilute within the vacuum chamber after being guided by the inclined baffle, thus greatly reducing the amount that diffuses to the other side.

[0029] Example 2: A secondary vapor deposition apparatus for bifacial CIGS solar cells, such as... Figure 1 , 4 As shown. Based on Example 1, this example improves the arrangement of the vacuum chamber suction ports by setting a vacuum chamber suction port 14 at intervals on the upper end of the inclined baffle 13. The suction ports are positioned at the upper end of the inclined baffle to suction the vapor deposition plume from the lower surface of the substrate outside the inclined baffle and the selenium replenishment vapor from the upper surface of the substrate above the inclined baffle, reducing excessive accumulation of the vapor deposition plume and selenium replenishment vapor, and reducing disordered diffusion of the vapor deposition plume and selenium replenishment vapor in the gaps.

Claims

1. A secondary vapor deposition apparatus for double-sided CIGS solar cells, comprising a vacuum chamber, an unwinding shaft, a winding shaft, and several conveying rollers arranged within the vacuum chamber, wherein a substrate is sequentially conveyed along each conveying roller between the unwinding shaft and the winding shaft, and the middle section of the substrate conveying is a vapor deposition zone, characterized in that: A lower evaporation source is set below the vapor deposition zone, and a heating plate is set above the substrate of the vapor deposition zone between adjacent conveying rollers. A selenium replenishment nozzle is provided between the heating plates or between the heating plates and the conveying rollers, which sprays selenium vapor downwards onto the upper surface of the substrate. The selenium replenishment nozzle is connected to an upper selenium evaporation source.

2. The secondary evaporation apparatus for double-sided CIGS solar cells according to claim 1, characterized in that: A selenium vapor conduit is provided between the upper selenium evaporation source and the selenium replenishment nozzle; the upper selenium evaporation source is a built-in selenium source set in the vacuum chamber, or the upper selenium evaporation source is an external selenium source set outside the vacuum chamber.

3. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: Each selenium supplement nozzle is connected to a separate selenium evaporation source, or all selenium supplement nozzles share a single selenium evaporation source.

4. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: The conveying roller is coated with a high-temperature resistant coating, which is an alumina coating or a boron nitride coating.

5. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: The conveyor roller is equipped with a heating device, and the working temperature of the conveyor roller is 300-500℃.

6. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: The lower evaporation source includes a lower selenium source and a metal source, wherein the metal source is one or more of copper, indium, and gallium.

7. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: It also includes an external anti-winding device, which includes an anti-winding unwinding shaft and an anti-winding rewinding shaft, wherein the unwinding direction of the anti-winding unwinding shaft and the rewinding direction of the anti-winding rewinding shaft are opposite.

8. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: A synchronization device is installed between each conveyor roller.

9. A secondary vapor deposition apparatus for double-sided CIGS solar cells according to claim 1 or 2, characterized in that: Inclined baffles are provided on both sides of the substrate of the vapor deposition zone. The inclined baffles are inclined with the inner side lower than the outer side. The inner end of the inclined baffle is flush with the substrate. The inclination of the inclined baffle is 30-60°.

10. The secondary evaporation apparatus for a double-sided CIGS solar cell according to claim 9, characterized in that: The upper end of the inclined baffle is provided with a vacuum chamber suction port at intervals.

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