CN107665928A - A method for surface passivation of crystalline silicon solar cells - Google Patents

Abstract

The invention discloses a method for passivating the surface of a crystalline silicon solar cell, which comprises the steps of oxidizing and passivating a crystalline silicon substrate in oxygen, cleaning the oxygen by using gas containing hydrogen to enable the crystalline silicon substrate to be in the gas atmosphere of the hydrogen, and finally annealing in the gas atmosphere of the hydrogen.

Description

A method for surface passivation of crystalline silicon solar cells

technical field

The invention relates to the field of solar cells, in particular to a method for passivating the surface of a crystalline silicon solar cell.

Background technique

The passivation effect of the surface of crystalline silicon solar cells is one of the important factors that directly affect the performance of the cells. At present, the commonly used passivation method is silicon nitride passivation. A hydrogen-containing silicon nitride film is prepared on the surface of the battery by PECVD technology. Silicon nitride can saturate the dangling bonds on the surface of the battery, but the silicon nitride film is not dense, and the surface of the battery Dangling keys cannot be completely eliminated either. Another way of passivation is oxidation passivation, which passivates dangling bonds by oxidation, but if the action time is too long, the self-interstitial silicon atoms generated by oxidation will produce some secondary defects in the oxygen precipitation or other defects in the silicon wafer. , reducing the life expectancy of the minority.

Contents of the invention

The purpose of the present invention is to provide a method for passivating the surface of a crystalline silicon solar cell, which solves the problem of secondary defects caused by excessive oxidation and passivation on the surface of the cell, and achieves a better passivation effect.

In order to solve the above technical problems, the present invention provides a method for surface passivation of crystalline silicon solar cells, comprising:

The crystalline silicon substrate is oxidized and passivated in the gas atmosphere of oxygen; the oxygen is cleaned with a gas containing hydrogen, so that the crystalline silicon substrate is in the gas atmosphere of hydrogen; Annealing is performed in a gas atmosphere, and the crystalline silicon substrate is hydrogenated and passivated.

Among them, before the crystalline silicon substrate is oxidized and passivated in an oxygen gas atmosphere, it also includes:

The crystalline silicon substrate is subjected to hydrogenation treatment in a gas atmosphere containing hydrogen, so as to remove impurities on the surface of the silicon substrate, and at the same time, the crystalline silicon substrate is subjected to hydrogenation passivation.

Wherein, the hydrogenation treatment of the crystalline silicon substrate in a gas atmosphere containing hydrogen comprises:

The crystalline silicon substrate is hydrogenated in a first mixed gas, wherein the first mixed gas includes hydrogen and nitrogen.

Wherein, the volume percentage of the hydrogen in the first mixed gas is 9%-11%.

Wherein, the hydrogenation treatment of the crystalline silicon substrate in a gas atmosphere containing hydrogen comprises:

At a temperature of 580°C-620°C, in the first mixed gas with a flow rate of 8slm-12slm, hydrogenation treatment is performed on the crystalline silicon substrate, and the duration of the hydrogenation treatment is 15min-30min.

Wherein, the use of hydrogen-containing gas to clean the oxygen includes:

The oxygen is cleaned by using a second mixed gas, wherein the second mixed gas includes hydrogen and nitrogen.

Wherein, the volume percentage of the hydrogen in the second mixed gas is 3%-5%.

Wherein, the continuing annealing in the hydrogen gas atmosphere includes:

At a temperature of 400° C.-450° C., in a gas atmosphere with a flow rate of the mixed gas of 8 slm-12 slm, annealing is performed for 30 min-60 min.

Wherein, the oxidation passivation of the crystalline silicon substrate in an oxygen gas atmosphere includes:

The crystalline silicon substrate is oxidized for 20min-30min at a temperature of 700°C-800°C, and the oxygen gas flow is 1slm-2slm, to generate SiO ₂ .

In the surface passivation method of crystalline silicon solar cells provided by the present invention, after the crystalline silicon substrate is oxidized and passivated, hydrogen is used to clean the oxygen, and finally annealed in a hydrogen atmosphere. Since there is only one electron in the hydrogen atom, it can Re-passivate the surface of the crystalline silicon substrate, and form an electron pair with a single electron in the outer layer of the silicon atom on the surface of the silicon wafer to eliminate the dangling bond and further improve the passivation effect. The entire passivation process is simple and efficient, and no additional processing equipment is required , and in the annealing process of oxidation passivation, the hydrogenation passivation is directly completed, which improves the passivation efficiency. The passivation method of the present invention improves the passivation efficiency, obtains better passivation effect and improves the open-circuit voltage of the solar cell, so that the solar cell has better service life and performance.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only For some embodiments of the present invention, those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the flowchart of surface passivation method of crystalline silicon solar cell in the embodiment provided by the present invention;

Fig. 2 is a flowchart of a surface passivation method for a crystalline silicon solar cell in another embodiment provided by the present invention.

Detailed ways

The core of the present invention is to provide a method for passivating the surface of a crystalline silicon solar cell. By annealing in a hydrogen atmosphere, the dangling bonds after oxidation and passivation on the surface of a crystalline silicon substrate are eliminated, so that the crystalline silicon substrate has better passivation. effect.

In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. Apparently, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The flow chart of the surface passivation method for crystalline silicon solar cells in the embodiment provided by the present invention is shown in Figure 1, the method may include:

Step S101: performing oxidation passivation on the crystalline silicon substrate in an oxygen gas atmosphere;

Step S102: using hydrogen-containing gas to clean the oxygen, so that the crystalline silicon substrate is in the hydrogen gas atmosphere;

Step S103: continue annealing in the hydrogen gas atmosphere, and perform hydrogenation passivation on the crystalline silicon substrate.

At present, the passivation of crystalline silicon substrates mainly adopts silicon nitride passivation and oxidation passivation. For silicon nitride passivation, since the silicon nitride film is not dense, the crystalline silicon substrate coated with silicon nitride film is used. The bottom is used in the manufacture of solar cells, the working efficiency of the obtained solar cells is relatively low, and the working life will be relatively short; and for the coating method of oxidation passivation, due to the long time of oxidation passivation, it will During the passivation process, interstitial silicon atoms are generated, and they will generate some secondary defects in the oxygen precipitation or other defects in the silicon wafer, thereby generating new recombination centers and reducing the lifetime of minority carriers.

The passivation method of the present invention is based on oxidation passivation, annealing in a hydrogen-containing gas atmosphere, because the hydrogen atom has only one electron in the outermost layer, it is easy to form a chemical bond with the dangling bond on the surface of the crystalline silicon substrate, thereby Neutralize the recombination center on the surface of the crystalline silicon substrate, so that the crystalline silicon substrate can have a better passivation effect, thereby improving the lifetime of the minority carrier, and improving the open circuit voltage of the solar cell prepared with the crystalline silicon substrate. Moreover, the passivation method of the present invention does not need to add new equipment to the original passivation equipment, and the process is simple and easy to operate.

Based on the above-mentioned embodiments, because hydrogen atoms have a good effect of neutralizing the dangling bonds on the surface of the crystalline silicon substrate, therefore, in another specific embodiment of the present invention, it may further include:

Before the crystalline silicon substrate is oxidized and passivated in an oxygen gas atmosphere, the crystalline silicon substrate is hydrogenated in a hydrogen-containing gas atmosphere, so as to remove impurities on the surface of the silicon substrate, and The crystalline silicon substrate was hydrogenated and passivated.

Before oxidizing and passivating the crystalline silicon substrate, hydrogen can be used to clean the impurities on the surface of the crystalline silicon substrate in order to prepare for the subsequent oxidation passivation. At the same time, hydrogen can also suspend the surface of the crystalline silicon substrate in advance. The bond is neutralized, and the hydrogen passivation effect is achieved on the local defects on the surface of the crystalline silicon substrate, which is beneficial to the formation of the subsequent oxide film.

In addition, annealing in a hydrogen atmosphere after oxidation passivation is also beneficial to prevent the escape of hydrogen atoms that neutralize dangling bonds before oxidation passivation, thereby achieving a better passivation effect on the entire crystalline silicon substrate.

Based on the above embodiments, in another specific embodiment of the present invention, before the oxidation passivation in the above embodiments, the hydrogenation treatment of the crystalline silicon substrate may specifically include:

The crystalline silicon substrate is hydrogenated in a first mixed gas, wherein the first mixed gas includes hydrogen and nitrogen.

It should be noted that in the present invention, pure hydrogen can also be directly used to hydrogenate the crystalline silicon substrate, but considering that the cost of pure hydrogen is relatively high, and the chemical properties of nitrogen are inactive, at a relatively low temperature It is difficult to react with other substances under certain conditions and is relatively easy to obtain. Therefore, the crystalline silicon substrate can be passivated in a mixed gas of hydrogen and nitrogen, which can provide a good passivation environment for hydrogenation passivation.

In addition, for the neutralization of the dangling bonds on the surface of the crystalline silicon substrate, pure hydrogen is not required at all, and only a certain concentration of hydrogen in the gas is required to ensure that the dangling bonds on the surface of the crystalline silicon substrate can be absorbed by hydrogen as much as possible. The atoms are neutralized. Therefore, in this embodiment, further improvements can be made, specifically including:

The volume percentage of the hydrogen in the first mixed gas is 9%-11%, specifically 9%, 10%, or 11%. Of course, in the present invention, a mixed gas with a larger proportion of hydrogen can also be used. However, from the perspective of reducing costs, a mixed gas with a relatively low hydrogen content can be used to achieve a better hydrogenation passivation effect. Wherein the percentage of hydrogen should not be less than 9%.

Based on the above embodiments, in another specific embodiment of the present invention, the specific process of hydrogenating the crystalline silicon substrate in a hydrogen-containing gas atmosphere may include:

At a temperature of 580°C-620°C, in the first mixed gas with a flow rate of 8slm-12slm, hydrogenation treatment is performed on the crystalline silicon substrate, and the duration of the hydrogenation treatment is 15min-30min.

It should be noted that the hydrogenation treatment temperature can specifically be 580°C, 590°C, 600°C, 610°C, 620°C, and the more preferred temperature is 600°C; the flow rate of the first mixed gas can be specifically 8slm, 9slm, 10slm , 11slm, 12slm; correspondingly, the duration of hydrogenation treatment should not be less than 15min, specifically 16min 20min 25min, 30min. Generally, after the hydrogenation treatment for 30 minutes, the neutralization of the dangling bonds on the surface of the crystalline silicon substrate by hydrogen has basically reached a saturated state.

Based on the above embodiments, in another specific embodiment of the present invention, after oxidizing and passivating the crystalline silicon substrate, cleaning the oxygen with a gas containing hydrogen may specifically include:

Use the second mixed gas to clean the oxygen, wherein the second mixed gas includes hydrogen and nitrogen, the same as the first mixed gas in the above embodiment, in this embodiment, pure hydrogen can also be used to clean the oxygen Cleaning treatment is carried out, but from the perspective of cost reduction, the use of a mixed gas of hydrogen and nitrogen can reduce costs on the basis of ensuring a good passivation effect.

Considering that before the oxidation passivation, the crystalline silicon substrate has been hydrogenated, in the annealing process, there are relatively fewer dangling bonds that need to be passivated by hydrogen, so the volume percentage of hydrogen in the second mixed gas is relatively The percentage in the first mixed gas can be appropriately reduced, so further improvements can be made in this embodiment, including:

The volume percentage of the hydrogen gas in the second mixed gas is 3%-5%, specifically 3%, 4%, 5%. Of course, the hydrogen gas in the second mixed gas provided in this embodiment The percentage is based on the hydrogenation treatment before oxidation passivation, a more preferred embodiment. If the crystalline silicon substrate is not hydrogenated before oxidation passivation, more dangling bonds need to be neutralized by hydrogen during annealing in a hydrogen atmosphere. At this time, the proportion of hydrogen in the mixed gas should be increased. Volume percentage, the specific ratio can be selected according to the actual application situation, and will not be repeated here.

Based on the above-mentioned embodiments, in another specific embodiment of the present invention, after oxidation and passivation of the crystalline silicon substrate, the specific process of annealing in a hydrogen gas atmosphere may include:

At a temperature of 400° C.-450° C., in a gas atmosphere with a flow rate of the mixed gas of 8 slm-12 slm, annealing is performed for 30 min-60 min.

It should be noted that the annealing temperature should not be too high to avoid the chemical bond formed by the hydrogen atom and the dangling bond being detached from the high temperature during the previous hydrogenation treatment. Specifically, it can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C. In addition, the gas flow of the mixed gas can specifically be 8slm, 9slm, 10slm, 11slm, 12slm. The duration of annealing should not be less than 30 minutes, specifically 30 minutes, 40 minutes, 50 minutes, 60 minutes.

Based on any of the above embodiments, in another specific embodiment of the present invention, the oxidation of the crystalline silicon substrate may include:

The crystalline silicon substrate is oxidized for 20min-30min at a temperature of 700°C-800°C, and the oxygen gas flow is 1slm-2slm, to generate SiO ₂ .

It should be noted that before oxidation passivation, if the crystalline silicon substrate is subjected to hydrogenation treatment, the dangling bonds between hydrogen atoms and dangling bonds may be destroyed during the hydrogenation treatment under the temperature environment of oxidation passivation. After oxidation passivation, due to the annealing in hydrogen, the dangling bonds generated during oxidation passivation can be neutralized by hydrogen again. It can be seen that after oxidation passivation, in the gas atmosphere of hydrogen The importance of annealing.

In addition, the temperature for oxidation passivation may specifically be 700°C, 720°C, 740°C, 760°C, 780°C, or 800°C. Because oxygen needs to form a dense oxide film on the entire surface of the crystalline silicon substrate, the gas flow of oxygen should not be too fast, resulting in insufficient reaction time between oxygen and the crystalline silicon substrate, which will affect the formation of the oxide film. The specific gas flow rate can be 1slm, 1.5slm, 2slm. The duration of oxidation passivation should not be less than 20min, specifically 25min or 30min.

Based on any of the above embodiments, the flow chart of the surface passivation method of crystalline silicon solar cells provided by another embodiment of the present invention is shown in Figure 2, the method may include:

Step S201 : at 600° C., in a gas flow rate of 10 slm, in a mixed gas atmosphere of hydrogen and nitrogen with a hydrogen volume percentage of 10%, the crystalline silicon substrate is hydrogenated for 20 minutes.

Step S202: Oxidize and passivate the crystalline silicon substrate for 25 minutes in an oxygen gas atmosphere with a gas flow rate of 1.5 slm at a temperature of 750° C. to form a uniform oxide film.

Step S203: Use hydrogen-containing gas to clean the oxygen.

Step S204: Annealing at 425° C., in a gas flow rate of 10 slm, in a mixed gas atmosphere of hydrogen and nitrogen with a hydrogen volume percentage of 4%, for a duration of 45 minutes.

It should be noted that each embodiment in this specification is described in a progressive manner, each embodiment focuses on the differences from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A method for surface passivation of a crystalline silicon solar cell, characterized in that, comprising: The crystalline silicon substrate is oxidized and passivated in an oxygen gas atmosphere; Purging the oxygen with hydrogen-containing gas, so that the crystalline silicon substrate is in the hydrogen gas atmosphere; Continue to perform annealing in the hydrogen gas atmosphere, and perform hydrogenation passivation on the crystalline silicon substrate. 2. The method according to claim 1, further comprising: The crystalline silicon substrate is subjected to hydrogenation treatment in a gas atmosphere containing hydrogen, so as to remove impurities on the surface of the silicon substrate, and at the same time, the crystalline silicon substrate is subjected to hydrogenation passivation. 3. The method according to claim 2, wherein the hydrogenation treatment of the crystalline silicon substrate in an atmosphere containing hydrogen comprises: The crystalline silicon substrate is hydrogenated in a first mixed gas, wherein the first mixed gas includes hydrogen and nitrogen. 4. The method according to claim 3, characterized in that the volume percentage of the hydrogen in the first mixed gas is 9%-11%. 5. The method according to claim 4, wherein the hydrogenation treatment of the crystalline silicon substrate in an atmosphere containing hydrogen comprises: At a temperature of 580°C-620°C, in the first mixed gas with a flow rate of 8slm-12slm, hydrogenation treatment is performed on the crystalline silicon substrate, and the duration of the hydrogenation treatment is 15min-30min. 6. The method according to claim 5, wherein said adopting hydrogen-containing gas to sweep said oxygen comprises: The oxygen is cleaned by using a second mixed gas, wherein the second mixed gas includes hydrogen and nitrogen. 7. The method according to claim 6, characterized in that the volume percentage of the hydrogen in the second mixed gas is 3%-5%. 8. The method according to claim 7, wherein the continuing annealing in the hydrogen gas atmosphere comprises: At a temperature of 400° C.-450° C., in a gas atmosphere with a flow rate of the mixed gas of 8 slm-12 slm, annealing is performed for 30 min-60 min. 9. The method according to any one of claims 1 to 7, wherein said performing oxidation passivation of the crystalline silicon substrate in an oxygen gas atmosphere comprises: The crystalline silicon substrate is oxidized for 20min-30min at a temperature of 700°C-800°C, and the oxygen gas flow is 1slm-2slm, to generate SiO ₂ .