Method for improving crystallization rate of heterojunction cell and heterojunction cell

Abstract

The invention belongs to the technical field of solar photovoltaic cell coating, and particularly relates to a method for improving the crystallization rate of a heterojunction cell and the heterojunction cell, and the method comprises the following steps: introducing a gas mixture into a reaction cavity; applying high-frequency voltage to ionize the gas mixture into plasma; depositing the plasma on the surface of the base material to form a film; wherein the gas mixture comprises precursor gas, diluent gas, process gas and doping gas; the diluent gas comprises argon gas; according to the method, the plasma density of the central area of the heterojunction cell can be effectively improved by introducing the diluted gas argon in the coating stage, so that the ionization efficiency of the central area is improved, the crystallization reaction is more sufficient, in addition, the etching of the amorphous phase of the corner area by H ions and carbon dioxide can also be reduced by the dilution of argon, and the etching efficiency of the amorphous phase is improved. The difference of the overall crystallization rate of the heterojunction cell is reduced, and the uniformity of a deposited coating film is ensured.

Description

Technical Field

[0001] This invention belongs to the field of solar photovoltaic cell coating technology, specifically relating to a method for improving the crystallization rate of heterojunction cells and heterojunction cells. Background Technology

[0002] With the increasing global demand for renewable energy, the solar photovoltaic industry has developed rapidly. Among them, heterojunction (HJT) cells have advantages such as low light decay and low temperature coefficient, which can reduce energy consumption while reducing thermal damage to the silicon substrate. They have become an important direction for the development of high-efficiency cells in the future. Heterojunction cells are mainly formed by depositing intrinsic amorphous silicon thin films on both sides of a silicon substrate, followed by depositing P-type and N-type amorphous or microcrystalline silicon thin films respectively. After preparing corresponding transparent conductive oxide layers (TCO) on the surfaces of the amorphous or microcrystalline silicon thin films on both sides of the silicon substrate, surface metal electrodes are formed by screen printing and curing using low-temperature silver paste.

[0003] Existing heterojunction solar cells typically employ PECVD deposition equipment for intrinsic crystalline silicon deposition, N-type and P-type amorphous or microcrystalline silicon deposition. The process gases used are mainly hydrogen and silane. During the deposition process, carbon dioxide is introduced into the process chamber. Carbon dioxide can adjust the refractive index and band gap of the heterojunction solar cell, thereby increasing the efficiency by increasing the short-circuit current. However, the introduction of carbon dioxide results in significant differences in the crystallinity on the PECVD deposition substrate, leading to uneven deposition.

[0004] Therefore, overcoming the crystallization rate difference caused by the introduction of carbon dioxide is a technical problem that urgently needs to be solved in this field.

[0005] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0006] This disclosure provides at least one method for improving the crystallinity of heterojunction solar cells and a heterojunction solar cell.

[0007] In a first aspect, embodiments of this disclosure provide a method for improving the crystallinity of heterojunction solar cells, comprising: introducing a gas mixture into a reaction chamber; applying a high-frequency voltage to ionize the gas mixture into plasma; and depositing the plasma into a thin film on a substrate surface; wherein the gas mixture comprises a precursor gas, a dilution gas, a process gas, and a dopant gas; and the dilution gas comprises argon.

[0008] In one alternative embodiment, the precursor gas includes any one of silane and ammonia, or a mixture thereof.

[0009] In one alternative embodiment, the process gas includes hydrogen and carbon dioxide.

[0010] In one alternative embodiment, the doping gas includes any one of phosphine and borane or a mixture thereof.

[0011] In one optional embodiment, the dilution ratio of H atoms in the gas mixture to the precursor gas is 200 to 300.

[0012] In one optional embodiment, the doping ratio of carbon dioxide to precursor gas in the gas mixture is 0.8 to 1.6.

[0013] In one optional embodiment, the dilution ratio of argon to precursor gas in the gas mixture is 1 to 50.

[0014] Secondly, this disclosure also provides a heterojunction solar cell, prepared by the method described above, wherein the difference between the edge crystallization rate and the center crystallization rate of the heterojunction solar cell is not greater than 40%.

[0015] In one optional embodiment, the center crystallinity of the heterojunction cell is not less than 10%.

[0016] Thirdly, embodiments of this disclosure also provide a photovoltaic module, including the heterojunction cell as described above.

[0017] The beneficial effects of this invention are that the method for improving the crystallization rate of heterojunction cells, by introducing diluting gas argon during the coating stage, can effectively increase the plasma density in the central region of the heterojunction cell, thereby improving the ionization efficiency in the central region and making the crystallization reaction more complete. In addition, the etching of amorphous phases in the corner regions by H ions and carbon dioxide can also be reduced by the dilution of argon gas, thereby reducing the overall crystallization rate difference of the heterojunction cell and ensuring uniform deposition.

[0018] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 Raman spectra provided for embodiments of this disclosure;

[0022] Figure 2 Parameter diagrams for embodiments numbered 39 and 42 provided in this disclosure;

[0023] Figure 3 A physical image of a heterojunction battery from embodiment number 39 provided in this disclosure;

[0024] Figure 4 A physical image of a heterojunction battery for embodiment number 42 provided in this disclosure;

[0025] Figure 5 Parameter diagrams for embodiments numbered 87, 90, 91, and 92 provided for embodiments of this disclosure. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0028] In this document, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. As used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0029] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0030] In general, in amorphous silicon networks, weak Si-Si bonds are etched away by hydrogen atoms, and the resulting sites are replaced by new growth precursors. Simultaneously, the newly arrived precursors form a stable crystalline structure on the growth surface. The etching effect is not significant in all cases; it only becomes significant when the hydrogen concentration reaches a certain level.

[0031] In plasma, CO2 decomposes into active species (such as CO and O free radicals). These species may exert a weak etching effect on the surface of amorphous silicon (a-Si) thin films, preferentially etching the amorphous phase and amorphous regions (microcrystalline or nanocrystalline silicon), thereby indirectly promoting the improvement of crystallinity.

[0032] The addition of CO2 may alter the decomposition kinetics of hydrogen (H2) in the plasma. Hydrogen radicals (H2) + The etching effect on the amorphous silicon network selectively removes weak bonds (amorphous phase), while oxidizing species of CO2 (such as O) may combine with silicon dangling bonds, inhibiting the growth of amorphous phase and promoting the formation of ordered structures.

[0033] In the PECVD reaction chamber, the electric field intensity at the electrode edge is typically higher than that in the central region (edge ​​effect), resulting in a higher plasma density at the edge. Active species generated by CO2 decomposition (such as O and CO) are more concentrated at the edge, enhancing etching and crystallization.

[0034] Furthermore, the flow of reactive gases (such as SiH4, H2, CO2) within the cavity may lead to higher CO2 concentrations in the edge regions (due to the gas flow boundary layer effect), thereby exacerbating edge crystallization.

[0035] The shortcomings of the above solutions are the result of the inventor's practical experience and careful research. Therefore, the discovery process of the above problems and the solutions proposed in this disclosure below should be considered as the inventor's contribution to this disclosure.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0037] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0038] This disclosure provides a method for improving the crystallinity of heterojunction solar cells, comprising: introducing a gas mixture into a reaction chamber; applying a high-frequency voltage to ionize the gas mixture into plasma; and depositing the plasma into a thin film on a substrate surface; wherein the gas mixture includes a precursor gas, a dilution gas, a process gas, and a dopant gas; and the dilution gas includes argon.

[0039] In some embodiments, specifically, the precursor gas includes either silane or ammonia, or a mixture thereof.

[0040] In some embodiments, specifically, the process gas includes hydrogen and carbon dioxide.

[0041] In some embodiments, specifically, the doping gas includes any one of phosphine and borane or a mixture thereof.

[0042] In some embodiments, specifically, the dilution ratio of H atoms in the gas mixture to the precursor gas is 200 to 300, preferably 275 times.

[0043] In some embodiments, specifically, the doping ratio of carbon dioxide to precursor gas in the gas mixture is 0.8 to 1.6, preferably 1.

[0044] In some embodiments, specifically, the dilution ratio of argon to precursor gas in the gas mixture is 1 to 50.

[0045] Specifically, in this application, high-frequency voltage refers to AC voltage with a frequency significantly higher than that of conventional power systems (50Hz / 60Hz), usually referring to voltage signals in the range of kilohertz (kHz) to megahertz (MHz), and more specifically, high-frequency voltage of 13.56MHz in this application.

[0046] This disclosure also provides a heterojunction solar cell, prepared by the method described above, wherein the difference between the edge crystallization and the center crystallization of the heterojunction solar cell is no greater than 40%.

[0047] In some embodiments, specifically, the central crystallinity of the heterojunction solar cell is not less than 10%.

[0048] Specifically, in this application, in the calculation of the crystallinity ratio of silicon-based thin film materials, we use the phase composition of microcrystalline materials as the standard, and in the fitting of Raman spectra, we use 520 cm⁻¹ as the standard. -1 505cm -1 and the amorphous peak at 480cm -1 The characteristic peak at 520 cm⁻¹ is the fitting center. -1 The location indicates the crystal phase composition, 510 cm⁻¹ -1 Indicates the microcrystalline phase composition, 480 cm⁻¹ -1 The value indicates the amorphous component. The specific calculation formula is as follows:

[0049]

[0050] Among them, I a I c and I m These represent the integrated intensity of the scattering peaks for amorphous, crystalline, and small-grained materials, respectively. Figure 1 This is a typical Raman spectrum, which is mainly calculated by Gaussian fitting. a I c and I m The final crystallization rate is calculated using a formula based on the integral intensities of the three peaks.

[0051] This disclosure also provides a photovoltaic module, including the heterojunction cell as described above.

[0052] Please see Figure 2 ,like Figure 2 The examples shown are numbered 39 and 42, where number 39 represents a gas mixture that does not contain carbon dioxide or argon. Figure 3 As shown, the crystallinity of the edge region and the central region is approximately equal, with an average value of 55%–60%; Serial number 42 represents the case where the gas mixture contains carbon dioxide but no argon, such as… Figure 4As shown, there is a significant difference in crystallinity between the edge region and the central region, with the central region abruptly dropping to 0% and the edge region to 16.25%.

[0053] Please see Figure 5 ,like Figure 5 Examples 87, 90, 91, and 92 are shown. Example 87 is a comparative example where the amount of carbon dioxide added is adjusted from 0.54 slm to 0.4 slm compared to example 42. It can be seen that the decrease in carbon dioxide can improve the crystallization rate of the intermediate region. Based on this, the inventors conducted subsequent example tests with a carbon dioxide flow rate of 0.4 slm.

[0054] As shown in examples 90, 91, and 92, by adjusting the argon flow rate, it was found that the intermediate crystallization rate was highest when the argon flow rate was increased to 20 slm.

[0055] Specifically, Ar acts as an inert gas and a diluent. Ar has a single-atom structure that does not require dissociation, making it easier to ionize and increase plasma density, especially in the central region. Previously, the plasma in the central region might have been limited by gas diffusion, leading to incomplete decomposition of reactants. The addition of Ar can effectively increase plasma density, particularly the ionization efficiency in the central region, resulting in a more complete crystallization reaction.

[0056] Specifically, Ar, as a diluent gas, can increase the turnover rate of the reactant gases, reduce the concentration gradient between the central and peripheral regions, and prevent insufficient reaction in the central region due to excessively high gas flow rate or short residence time.

[0057] Specifically, when Ar ions bombard the substrate, they can enhance the migration rate of surface atoms, promoting the orderly arrangement of silicon atoms into a crystal structure. After adding Ar, the ion energy and flux in the central region may reach a similar level to those in the corner regions, thereby reducing the difference in crystallinity.

[0058] Specifically, the etching effect of H ions on the amorphous phase in the corner regions may be too strong, leading to a higher crystallinity. The addition of Ar dilutes the H2 concentration to some extent.

[0059] In summary, this method for improving the crystallinity of heterojunction solar cells involves introducing argon gas as a dilution gas during the coating stage. This effectively increases the plasma density in the central region of the heterojunction solar cell, thereby improving the ionization efficiency in the central region and making the crystallization reaction more complete. In addition, the etching of amorphous phases in the corner regions by H ions and carbon dioxide can also be reduced by the dilution of argon gas, thereby reducing the overall crystallinity difference of the heterojunction solar cell and ensuring uniform deposition.

[0060] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for improving the crystallinity of heterojunction solar cells, characterized in that, include: The gas mixture is introduced into the reaction chamber; Applying a high-frequency voltage ionizes a gas mixture into plasma; Plasma is deposited on the surface of a substrate to form a thin film; The gas mixture includes precursor gas, dilution gas, process gas, and dopant gas; Furthermore, the diluting gas includes argon.

2. The method as described in claim 1, characterized in that, The precursor gas includes any one of silane and ammonia, or a mixture thereof.

3. The method as described in claim 1, characterized in that, The process gases include hydrogen and carbon dioxide.

4. The method as described in claim 1, characterized in that, The doping gas includes any one of phosphine and borane or a mixture thereof.

5. The method as described in claim 1, characterized in that, The dilution ratio of H atoms to precursor gas in the gas mixture is 200–300.

6. The method as described in claim 3, characterized in that, The doping ratio of carbon dioxide to precursor gas in the gas mixture is 0.8 to 1.

6.

7. The method as described in claim 1, characterized in that, The dilution ratio of argon to precursor gas in the gas mixture is 1 to 50.

8. A heterojunction battery, characterized in that, Prepared using the method described in any one of claims 1-7, the difference between the edge crystallinity and the center crystallinity of the heterojunction solar cell is not greater than 40%.

9. The heterojunction battery as described in claim 8, characterized in that, The central crystallinity of the heterojunction solar cell is not less than 10%.

10. A photovoltaic module, characterized in that, Including the heterojunction battery as described in claim 8.

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