Interdigitated back contact solar cell

Abstract

The invention relates to a screen printing-based patterning method for producing interdigitated back contact (IBC) solar cells.

Description

[0001] DESCRIPTION

[0002] INTERDIGITATED BACK CONTACT SOLAR CELL

[0003] Technical Field

[0004] The invention relates to a screen printing-based patterning method for producing interdigitated back contact (IBC) solar cells.

[0005] State of the Art

[0006] The interdigitated back contact solar cell is an innovative approach in solar energy collection and conversion technology. The interdigitated back contact (IBC) is a structure in which the emitter and BSF field located on the front and back surface of the Si slice in a standard solar cell are both placed on the back surface, and the entire structure is silicon. It uses the same spectrum as a standard silicon cell. The IBC has a higher yield potential as there are no reflection / shading losses due to metal contacts at the front. This technology contributes to clean and sustainable energy sources by increasing efficiency in solar energy conversion.

[0007] There are various patent, utility model applications related to the production methods of interdigitated back contact solar cells in the current system. One of them is the application with the number "CN101523615A". The application discloses an improved method for the front surface of single-sided, embedded contact type cells. More specifically, the present invention relates to a photovoltaic device comprising a monocrystalline silicon or a multicrystalline silicon semiconductor material. It is stated here that an ohmic contact and a back surface area formation behind the cell are obtained by screen printing. This method is based on adding more of the cavities opened using the laser on the front surface of the doped Si slice compared to the previously doped field. On the other hand, this method has been developed for back surface area (BSF) type cell production, and the production of the IBC structure in which the n-type and p-type doped fields are interdigitated is not mentioned.

[0008] CN102610686B relates to the back contact crystal silicon solar cell and its production process. The invention provides a back contact crystalline silicon solar cell and its manufacturing process using a basic front gateless back contact cell design, process improvement to provide intensive doping to the contact surface, and a thermal oxide layer passivation process at the same time. The glue used as a kind of mask in the invention is applied directly on the Si slice and subjected to a high temperature diffusion process with the glue layer on the Si slice. Such production will create serious pollution both in the diffusion furnaces used and on the Si slice. Therefore, both the performance of the produced samples will remain at very low levels and the production output is not stable and reproducible due to furnace pollution. In the proposed method, AZO layers were coated for the contact of the n- type doped field and CuA102 layers were coated for the contact of the p-type field, and the metal contacts of these layers were formed in two separate stages. Considering all these, it does not seem possible to use the proposed production method in production lines or pilot facilities.

[0009] EP2581951B1 relates to the method and apparatus for the formation of solar cells with selective emitters. In particular, the invention relates to methods for aligning selective emitter fields and a screen-printing model for making crystalline silicon-based solar cells. It comprises at least one first patterned heavy doped field with a first additive concentration defining the selective emitters formed on the surface and the second doped emitter field with a second additive concentration lower than the first additive concentration. The first additive atoms and the second additive atoms are each selected from a group of elements comprising phosphorus, arsenic, antimony, boron, aluminum, and gallium.

[0010] As seen in the current system, unlike other photovoltaic cell types, there is no known production method for the production of IBC type cells. However, photolithography-based patterning methods are mostly used to create the interdigitated structure on the back surface. The use of photolithography not only increases the production cost, but also limits the size of the produced cell. Since the patterning process is performed using photolithography in the vast majority of the studies carried out, both cell sizes and production output remain very small compared to industrial scales.

[0011] IBC cell costs produced by the methods used in the present art are quite high compared to other cell technologies. Apart from this, since the design and process details in the existing industrial production lines are protected by patents, large area IBC cell production cannot be performed outside the facilities of the two existing companies. An alternative method is needed for the production of IBC cells, which are produced industrially by only a few companies worldwide and whose design and production details are very closely protected by patents. As a result, there is a need for an IBC cell and production method whose production is simplified due to the above-mentioned and the inadequacy of existing solutions.

[0012] Brief Description and Objects of the Invention

[0013] The invention relates to a screen printing-based patterning method for producing interdigitated back contact (IBC) solar cells. The object of the invention is to ensure the production of interdigitated back contact (IBC) solar cells, which are very complex to produce, at industrial sizes with high product output. For this purpose, a screen printing-based patterning method has been developed. The developed screen printing-based patterning method allows the production of large area cells and keeps the production costs of IBC type cells close to the costs of existing cell technologies thanks to its high product output. In addition, this method can be easily adapted without bringing an extra investment to existing production n-type cell production lines.

[0014] Another object of the invention is that it can be used not only in the production of IBC type cells but also in the production of high efficiency potential cell structures such as selective emitter PERC and TOPCon. The invention can be used not only in the production of IBC type cells but also in the production of high efficiency potential cell structures such as selective emitter PERC and TOPCon.

[0015] Another object of the invention is that it does not require an extra investment cost to be applied. This method, which does not require an extra investment cost, will enable IBC cell production with industrial size and product output in existing production lines.

[0016] Descriptions of the Figures

[0017] Figure 1 : Post-pattern view of the coated silicon slice with abrasion barrier coated on it for boron doping (left), phosphor doping (right) processes.

[0018] Figure 2: A view of the production flow chart of interdigitated back contact (IBC) solar cells using the screen printing-based patterning method.

[0019] Element Numbers Specified in the Figures

[0020] In order to better explain the IBC cell developed by this invention, the parts and elements in the figures are numbered and the corresponding numbers are given below:

[0021] 1. Silicon slice

[0022] 2. Silicon nitride layer

[0023] 3. Boron doped field 4. Phosphorus doped field

[0024] 5. Passivation

[0025] 6. Ink

[0026] 7. Metal contact

[0027] Detailed Description of the Invention

[0028] The invention relates to a screen printing-based patterning method for producing interdigitated back contact (IBC) solar cells. The patterning method developed within the scope of the invention allows the production of interdigitated back contact (IBC) solar cells, which are very complex to produce, at industrial sizes with high product output.

[0029] The biggest difference of the invention compared to the current systems is that it can be easily applied for large area cells. In the invention, a screen printing-based patterning method was developed and successfully applied in the production of IBC cells designed during the studies within the scope of this invention. This developed method allows high efficiency IBC cell production without the need for new equipment in n-type cell production lines.

[0030] For the screen printing-based patterning method developed within the scope of the invention, an ink (6) with high chemical resistance and which can be printed by screen printing is used as an abrasion barrier (mask). The ink (6) is a material that can resist the abrasive effect of the chemicals. The silicon nitride layer (2) ( 'x), which is used as a barrier in the doping stages, is patterned in accordance with the pattern to be used first in the boron and then in the phosphorus diffusion stages with the help of this abrasion barrier. During this patterning, the fields of the silicon nitride layer (2) ('’“' ) under the abrasion barrier are protected, while the abrasion barrier is made ready for the regional doping process by abrading the uncoated fields. Figure 1 shows the image of the silicon nitride layer (2) (before and after patterning) on which the abrasion barrier is coated.

[0031] After the doping processes, the interdigitated cell structure is obtained on the back surface of the silicon (Si) slice (1). Then, IBC cell production is completed by passivation, metallization and burning of the anterior and posterior surfaces. The process steps of the production method are shown in Figure 2 and are as follows:

[0032] • During the texturing and cleaning of the silicon slice (1), the crystal silicon (Si) is textured at a temperature of 65-80°C using the slice of potassium hydroxide solution. After this process, 1-5 pm high randomly distributed pyramids are obtained on the surface of the silicon slice (1). After the texturing process, Radio Corporation of America (RCA)-l and Radio Corporation of America (RCA)-2 cleaning are performed to clean the surface from organic and inorganic impurities. Instead of RCA-1 and RCA-2 cleaning, ozone (O3) cleaning can be done in industrial lines. In RCA-1 cleaning, a cleaning solution containing ammonium hydroxide, hydrogen peroxide and water is generally used. It is effective for the removal of organic contaminants, particles, and some metal ions. RCA-2, on the other hand, is used to remove metallic pollutants and other wastes remaining after RCA-1 cleaning and a different solution is generally used than used in RCA-1 containing hydrochloric acid, hydrogen peroxide and water. RCA-2 further purifies the surface to provide the higher level of cleanliness required for semiconductor production.

[0033] • Coating the surface to be patterned with a silicon nitride layer (2) with a thickness between 50-200 nm.

[0034] At this stage, the silicon nitride layer (2) to be used as a barrier in the doping process is coated on the silicon slice (1) at a temperature between 350-400°C using plasma- enhanced chemical vapor deposition (PECVD).

[0035] • Laying the ink (6) on the coated silicon nitride layer (2) in the desired pattern.

[0036] • After the ink (6) is laid on the surface with the desired pattern by screen printing, the silicon slice (1) is abraded with the help of the dilute hydrofluoric acid (HF) solution. During this process, the silicon slices (1) on which the silicon nitride layer (2) and ink (6) are coated are immersed in the HF solution. While the fields of the silicon nitride layer (2) under the ink (6) are protected against abrasion in the solution, the uncoated fields are abraded in the HF solution. Thus, the desired doping pattern is obtained. After this patterning process, the RCA-1 and RCA-2 or ozone cleaning processes described in the first process step are repeated.

[0037] • Boron doping process.

[0038] In this process, samples with a patterned diffusion barrier on their surfaces are obtained from the boron doped field (3) between 800-950°C, using BCh or BBn , with a depth between 100-1500 nm and a surface concentration between IxlO19and 5xlO20cm'3.

[0039] • Following boron doping, the surface to be patterned for phosphorus doping is coated with a silicon nitride layer (2). The surface to be patterned is coated with a silicon nitride layer (2) with a thickness between 50-200 nm, as mentioned in the second process step of the method. At this stage, the silicon nitride layer (2) to be used as a barrier in the doping process is coated on the silicon slice (1) at a temperature between 350-400°C using plasma-enhanced chemical vapor deposition (PECVD).

[0040] • Laying the ink (6) on the coated silicon nitride layer (2) in the desired pattern.

[0041] • Making the silicon nitride layer (2), whose surfaces are coated with ink (6), ready to add phosphorus using hydrofluoric acid (HF).

[0042] At this stage, as described in the 4th process step of the method, samples with SiNxand ink layer on them are immersed in hydrofluoric acid (HF) solution. While the fields of the SiNxlayer under the ink are protected against abrasion in the solution, the uncoated fields are abraded in the HF solution. Thus, the desired doping pattern is obtained. After this patterning process, the RCA-1 and RCA-2 or ozone cleaning processes described in step 1 of the method are repeated.

[0043] • Phosphorus doping process.

[0044] In this process, samples with a patterned diffusion barrier on their surfaces are obtained from the phosphorus doped field (4) between 750-900°C, using phosphoryl chloride (POCh), with a depth between 100-1500 nm and a surface concentration between IxlO19and 5xl021cm'3.

[0045] Following the 5th and 9th process steps of the method, the boron and phosphorus doped rear surfaces of the silicon slice (1), respectively, can be protected with the silicon nitride layer (2) and doped with boron or phosphorus to have the doping depth and surface concentration mentioned in the 5th and 9th process steps of the front surface. However, IBC type cells, in which the front surface is left undoped, can easily be adapted to the production method mentioned in this invention.

[0046] • Cleaning and surface passivation (5).

[0047] At this stage, after completing the doping processes, surface passivation (5) is provided by using SiCh or SiNxor SiCh / SiNx or AhCL / SiNx layers of RCA-2 or ozone cleaned slices.

[0048] • Metallization.

[0049] In the metallization stage, which is the last step of the designed IBC cell production, it is the stage where aluminum-silver and silver-containing high-temperature metallization pastes are laid on the silicon slice (1) by screen printing using a metal contact (7) and activated at high temperature (750-925°C) using a conveyor oven.

Claims

CLAIMS1. A production method of an interdigitated back contact (IBC) solar cell, characterized in comprising steps of;• Texturing and cleaning silicon slice (1),• Coating the surface of silicon slice (1) to be patterned with a silicon nitride layer (2) with a thickness between 50-200 nm,• Laying the ink (6) on the coated silicon nitride layer (2) in the desired pattern,• Abrading silicon slice (1) by immersing it in the dilute hydrofluoric acid solution,• Boron doping of the abraded silicon slice (1),• Coating the surface to be patterned for phosphorus doping with a silicon nitride layer (2),• Laying ink (6) on the coated silicon nitride layer (2) in the desired pattern,• Preparing of silicon nitride layer (2), whose surfaces are coated with ink (6), for phosphorus doping using hydrofluoric acid,• Phosphorus doping of the silicon nitride layer (2).

2. A production method according to claim 1, characterized in that, in the step of texturing and cleaning the silicon slice (1), said texturing is carried out at a temperature of 65-80°C using crystalline silicon (Si) slice potassium hydroxide solution.

3. A production method according to claim 1, characterized in that, in the step of texturing and cleaning the silicon slice (1), the cleaning process comprises ozone (O3) cleaning or RCA-1 and RCA-2 cleaning.

4. A production method according to claim 1, characterized in that, in the step of coating the surface to be patterned with a silicon nitride layer (2) having a thickness between 50-200 nm, the temperature is between 350°C and 400°C.

5. A production method according to claim 3, characterized in that it comprises the step of abrading the silicon slice (1) with a dilute hydrofluoric acid (HF) solution after the ink is laid on the surface with the desired pattern by screen printing, followed by the step of ozone (O3) cleaning or RCA-1 and RCA-2 cleaning.

6. A production method according to claim 1, characterized in that BCh or BBn is used in the boron doping process at 800-950°C.

7. A production method according to claim 1, characterized in that the step of coating the surface to be patterned for phosphor doping with the silicon nitride layer (2) comprises coating the silicon nitride layer (2) with a thickness between 50-200 nm on the silicon slice (1) at a temperature between 350-400°C using plasma-enhanced chemical vapor deposition (PECVD).

8. A production method according to claim 1, characterized in that in the step of preparing the silicon nitride layer (2), whose surfaces are coated with ink (6), for phosphorus doping using hydrofluoric acid, followed by the process step of ozone (O3) cleaning or RCA-1 and RCA-2 cleaning.

9. A production method according to claim 1, characterized in that, in the step of phosphorus doping, phosphoryl chloride is used at 750-900°C.

10. A production method according to claim 1, characterized in that, in the step of cleaning and surface passivation, said cleaning process is RCA-2 or ozone cleaning.

11. A production method according to claim 1, characterized in that, in the step of cleaning and surface passivation, said surface passivation treatment comprises using SiCh or SiNxor SiCh / SiNx or AI2O3 / SiNxlayers.

12. A production method according to claim 1, characterized in that the step of performing the metallization process comprises process of laying aluminum-silver and silver- containing, high temperature metallization pastes on the silicon slice (1) by screen printing and activating them at a temperature between 750-925°C using a conveyor oven.

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