Method for manufacturing a heterojunction cell

Abstract

The application provides a preparation method of a heterojunction cell, which comprises a plating process for preparing an intrinsic amorphous silicon layer on the upper and lower surfaces of a silicon substrate and a doped layer on the intrinsic amorphous silicon layer in a vacuum environment; the plating process comprises the following steps: firstly, depositing a first intrinsic amorphous silicon layer on the upper and lower surfaces of the silicon substrate at a first deposition rate, wherein the first deposition rate is between 0.4 nm / s and 1.2 nm / s; secondly, depositing a second intrinsic amorphous silicon layer on the first intrinsic amorphous silicon layer at a second deposition rate, wherein the second deposition rate is between 0.03 nm / s and 0.3 nm / s; and thirdly, forming a doped layer with gradually increasing doping concentration on the intrinsic amorphous silicon layer in a direction away from the intrinsic amorphous silicon layer; the method can enhance the passivation effect and improve the photoelectric conversion efficiency of the finally formed heterojunction cell.

Description

Technical Field

[0001] This invention relates to solar cells, and more particularly to a method for preparing a heterojunction solar cell. Background Technology

[0002] With the development of solar cells, the requirements for their conversion efficiency are becoming increasingly stringent. Silicon-based heterojunction solar cells, as one of the development directions for high-efficiency cells, are playing an increasingly important role in the photovoltaic power generation industry.

[0003] The core of silicon-based heterojunction solar cells is the passivation layer on the silicon wafer surface—the intrinsic amorphous silicon layer. Amorphous silicon effectively passivates the silicon wafer surface, significantly reducing the surface recombination rate. Simultaneously, its larger bandgap allows for a larger built-in electric field after forming a pn junction in the same silicon, resulting in a higher open-circuit voltage for the heterojunction cell. Although the intrinsic amorphous silicon layer is very thin (10-20 nm), the requirements for its growth differ depending on the interface (Si / a-Si:H, a-Si:H / TCO). Selecting an appropriate growth rate and doping concentration significantly improves the photoelectric conversion efficiency of the heterojunction cell.

[0004] In view of this, it is necessary to provide a new method for preparing heterojunction solar cells to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing heterojunction solar cells, which can improve the photoelectric conversion efficiency of heterojunction solar cells.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a method for fabricating a heterojunction solar cell, comprising a coating process for fabricating an intrinsic amorphous silicon layer on the upper and lower surfaces of a silicon substrate under vacuum conditions, and a coating process for fabricating a doped layer on the intrinsic amorphous silicon layer; the coating process includes the following steps:

[0007] First, a first intrinsic amorphous silicon layer is deposited on the upper and lower surfaces of a silicon substrate at a first deposition rate between 0.4 nm / s and 1.2 nm / s.

[0008] A second intrinsic amorphous silicon layer is then deposited on the first intrinsic amorphous silicon layer at a second deposition rate, wherein the second deposition rate is between 0.03 nm / s and 0.3 nm / s.

[0009] Along a direction away from the intrinsic amorphous silicon layer, a doped layer with gradually increasing doping concentration is formed on the intrinsic amorphous silicon layer.

[0010] As a further improvement of the present invention, when depositing the first intrinsic amorphous silicon layer, the radio frequency power is 400-1000W and the silane flow rate is 500-2000sccm.

[0011] As a further improvement of the present invention, when depositing the second intrinsic amorphous silicon layer, the radio frequency power is 150-400W and the silane flow rate is 100-800sccm.

[0012] As a further improvement of the present invention, when depositing the second intrinsic amorphous silicon layer, the ratio of silane to hydrogen is between 5:1 and 1:20.

[0013] As a further improvement of the present invention, when depositing the second intrinsic amorphous silicon layer, the ratio of silane to hydrogen gradually decreases along the direction away from the first intrinsic amorphous silicon layer; or, when depositing the second intrinsic amorphous silicon layer, the second deposition rate gradually decreases along the direction away from the first intrinsic amorphous silicon layer.

[0014] As a further improvement of the present invention, the thickness of the second intrinsic amorphous silicon layer is greater than the thickness of the first intrinsic amorphous silicon layer.

[0015] As a further improvement of the present invention, the thickness of the first intrinsic amorphous silicon layer is between 1 nm and 3 nm.

[0016] As a further improvement of the present invention, the thickness of the second intrinsic amorphous silicon layer is between 2nm and 10nm.

[0017] As a further improvement of the present invention, along the direction away from the intrinsic amorphous silicon layer, the ratio between silane and dopant elements gradually increases from 5:1 to 1:3 to 1:1 to 1:6.

[0018] As a further improvement of the present invention, the doped layer includes a p-type doped layer and / or an n-type doped layer. When the doped layer is a p-type doped layer, the doping element is a borane mixed gas with a borane concentration of 2%; when the doped layer is an n-type doped layer, the doping element is a phosphine mixed gas with a phosphine concentration of 1%.

[0019] The beneficial effects of this invention are as follows: In the method for fabricating a heterojunction solar cell, for the intrinsic amorphous silicon layer, a first intrinsic amorphous silicon layer is first formed by high-speed deposition, and then a second intrinsic amorphous silicon layer is formed by low-speed deposition. The first intrinsic amorphous silicon layer is in direct contact with the silicon substrate, which can suppress the epitaxial growth of amorphous silicon on the surface of the silicon substrate and obtain a high-quality second intrinsic amorphous silicon layer, thereby improving the passivation effect of the intrinsic amorphous silicon layer. For the doped layer, the doping concentration of the doped layer gradually increases along the direction away from the intrinsic amorphous silicon layer. The low doping concentration results in a small structural change in the doped amorphous silicon, and when it comes into contact with the intrinsic amorphous silicon, it will not cause a large change in the intrinsic amorphous silicon structure, thus having a small impact on the passivation effect. On the other hand, the interface between the doped layer and the transparent conductive film is the amorphous silicon with the highest doping concentration, which can effectively reduce the contact resistance between the doped layer and the transparent conductive film, reduce the contact resistance of the final heterojunction solar cell, and improve the cell conversion efficiency. Attached Figure Description

[0020] Figure 1 The diagram shows a flowchart of the preparation method of the heterojunction solar cell in this invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. Please refer to the accompanying drawings for further details. Figure 1 The figures shown represent preferred embodiments of the present invention. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent modifications or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0022] Please refer to Figure 1 As shown, the present invention provides a method for fabricating a heterojunction solar cell, comprising the following steps: in a vacuum environment, a process for fabricating an intrinsic amorphous silicon layer on the upper and lower surfaces of a silicon substrate and a coating process for fabricating a doped layer on the intrinsic amorphous silicon layer.

[0023] By preparing intrinsic amorphous silicon layers on the upper and lower surfaces of the silicon substrate, defects on the surface of the silicon substrate are passivated, surface defect states are reduced, and carrier recombination is reduced.

[0024] The doped layer includes a p-type doped layer and an n-type doped layer. The p-type doped layer is formed on the upper surface of the intrinsic amorphous silicon layer to form a pn heterojunction. The n-type doped layer is formed on the lower surface of the intrinsic amorphous silicon layer to form a back surface field.

[0025] Specifically, the aforementioned vacuum environment refers to a pressure of 0.5–0.7 torr. Of course, this is not a limitation and can be adjusted according to the specific needs of the product.

[0026] The coating process includes the following steps:

[0027] First, a first intrinsic amorphous silicon layer is deposited on the upper and lower surfaces of a silicon substrate at a first deposition rate between 0.4 nm / s and 1.2 nm / s.

[0028] A second intrinsic amorphous silicon layer is then deposited on the first intrinsic amorphous silicon layer at a second deposition rate, wherein the second deposition rate is between 0.03 nm / s and 0.3 nm / s.

[0029] Along a direction away from the intrinsic amorphous silicon layer, a doped layer with gradually increasing doping concentration is formed on the intrinsic amorphous silicon layer.

[0030] In this invention, the first intrinsic amorphous silicon layer is in direct contact with the silicon substrate and is deposited at a high speed using a first deposition rate between 0.4 nm / s and 1.2 nm / s, which can suppress the epitaxial growth of amorphous silicon on the surface of the silicon substrate; the second intrinsic amorphous silicon layer is deposited at a slow speed using a second deposition rate between 0.03 nm / s and 0.3 nm / s, which can obtain a high-quality amorphous silicon layer, improve the passivation effect of the intrinsic amorphous silicon layer, and at the same time, prevent the diffusion of dopant elements in the doped layer from affecting the passivation performance of the silicon wafer surface, thereby improving the performance of the final product.

[0031] Meanwhile, in this invention, the doping concentration of the doped layer gradually increases along the direction away from the intrinsic amorphous silicon layer. On the one hand, the interface between the doped layer and the intrinsic amorphous silicon layer has a low doping concentration, which results in minimal structural changes in the doped amorphous silicon. When in contact with the intrinsic amorphous silicon, it does not cause significant changes in the intrinsic amorphous silicon structure, thus having a minimal impact on the passivation effect. On the other hand, the interface between the doped layer and the transparent conductive film has the highest doping concentration of amorphous silicon, which can effectively reduce the contact resistance between the doped layer and the transparent conductive film, thereby reducing the contact resistance of the ultimately formed heterojunction cell and improving the cell conversion efficiency.

[0032] Furthermore, when depositing the first intrinsic amorphous silicon layer, the radio frequency power is 400–1000 W, and the silane flow rate is 500–2000 sccm. That is, in this embodiment, by using a high radio frequency power between 400–1000 W and a high silane flow rate between 500–2000 sccm, the deposition rate when depositing the first intrinsic amorphous silicon layer is relatively high, reaching between 0.4 nm / s and 1.2 nm / s.

[0033] Furthermore, when depositing the second intrinsic amorphous silicon layer, the radio frequency power is 150–400 W, and the silane flow rate is 100–800 sccm. That is, in this embodiment, by using a low radio frequency power between 150–400 W and a low silane flow rate between 100–800 sccm, the deposition rate when depositing the second intrinsic amorphous silicon layer is relatively low, ranging from 0.03 nm / s to 0.3 nm / s.

[0034] Furthermore, during the deposition of the second intrinsic amorphous silicon layer, the ratio of silane gas to hydrogen gas is between 5:1 and 1:20. That is, hydrogen gas is incorporated during the growth of the second intrinsic amorphous silicon layer, and the passivation effect of the second intrinsic amorphous silicon layer is further improved by hydrogen ions.

[0035] Furthermore, during the deposition of the second intrinsic amorphous silicon layer, the ratio of silane to hydrogen gradually decreases along the direction away from the first intrinsic amorphous silicon layer. With the same flow rate of silane introduced into the chamber, a higher relative flow rate of hydrogen within the chamber results in a lower deposition rate. That is, the gradual decrease in the ratio of silane to hydrogen along the direction away from the first intrinsic amorphous silicon layer leads to a gradual decrease in the second deposition rate, which helps improve the passivation effect and effectively prevents the diffusion of dopant elements in the doped layer from affecting the passivation performance of the silicon wafer surface.

[0036] Furthermore, the thickness of the second intrinsic amorphous silicon layer is greater than that of the first intrinsic amorphous silicon layer, which can enhance the passivation effect of the second intrinsic amorphous silicon layer.

[0037] In one specific embodiment, the thickness of the first intrinsic amorphous silicon layer is between 1 nm and 3 nm, and the thickness of the second intrinsic amorphous silicon layer is between 2 nm and 10 nm. Of course, it is not limited to this.

[0038] Furthermore, along the direction away from the intrinsic amorphous silicon layer, the ratio between silane and dopant elements gradually increases from 5:1 to 1:3 to 1:1 to 1:6.

[0039] Specifically, when the doped layer is a p-type doped layer, the doping element is a borane mixture gas with a borane concentration of 2%. The borane mixture gas includes borane gas and hydrogen gas.

[0040] When the doped layer is an n-type doped layer, the doping element is a phosphine gas mixture with a phosphine concentration of 1%. The phosphine gas mixture includes phosphine gas and hydrogen gas.

[0041] Furthermore, after forming the doped layer, the method for fabricating the heterojunction solar cell further includes the following steps:

[0042] A transparent conductive film is disposed on the bottom side of the n-type doped layer and the top side of the p-type doped layer;

[0043] Electrodes are formed on the outer surface of a transparent conductive film to form a heterojunction cell.

[0044] To better illustrate the present invention, some specific embodiments will be provided below to further describe the present invention. Of course, it should be understood that the embodiments of the present invention are not limited to the following embodiments.

[0045] Example 1

[0046] The method for preparing the heterojunction solar cell in this embodiment includes the following steps:

[0047] Texturing and cleaning the silicon substrate;

[0048] First, a first intrinsic amorphous silicon layer is deposited on the upper and lower surfaces of a silicon substrate using pure silane gas at a first deposition rate of 0.7 nm / s. When depositing the first intrinsic amorphous silicon layer, the radio frequency power is 500 W and the silane flow rate is 2000 sccm.

[0049] A second intrinsic amorphous silicon layer is then deposited on the first intrinsic amorphous silicon layer using a silane mixed gas at a second deposition rate of 0.11 nm / s. The ratio of silane to hydrogen in the silane mixed gas is 1:1, the radio frequency power is 150 W, and the silane flow rate is 200 sccm.

[0050] An n-type doped layer and a p-type doped layer are formed. Along the direction away from the intrinsic amorphous silicon layer, the ratio between silane and dopant gradually increases from 1:1 to 1:3, wherein the silane flow rate gradually changes from 200 sccm to 100 sccm with a slope of -10 sccm / s, and the dopant flow rate gradually changes from 200 sccm to 300 sccm with a slope of 10 sccm / s.

[0051] A transparent conductive film is disposed on the bottom side of the n-type doped layer and the top side of the p-type doped layer;

[0052] Electrodes are formed on the outer surface of a transparent conductive film.

[0053] It is understandable that during the formation of n-type and p-type doped layers, the silane flow rate is gradually reduced while the dopant flow rate is gradually increased, so that the ratio between silane and dopant gradually increases from 1:1 to 1:3.

[0054] Specifically, when the doped layer is a p-type doped layer, the doping element is a borane mixture gas with a borane concentration of 2%. The borane mixture gas includes borane gas and hydrogen gas.

[0055] When the doped layer is an n-type doped layer, the doping element is a phosphine gas mixture with a phosphine concentration of 1%. The phosphine gas mixture includes phosphine gas and hydrogen gas.

[0056] The performance of the obtained heterojunction solar cells is shown in Table 1.

[0057] Example 2

[0058] The preparation method of the heterojunction solar cell in this embodiment includes the following steps:

[0059] Texturing and cleaning the silicon substrate;

[0060] First, a first intrinsic amorphous silicon layer is deposited on the upper and lower surfaces of a silicon substrate using pure silane gas at a first deposition rate of 0.7 nm / s. When depositing the first intrinsic amorphous silicon layer, the radio frequency power is 500 W and the silane flow rate is 2000 sccm.

[0061] Along a direction away from the first intrinsic amorphous silicon layer, a second intrinsic amorphous silicon layer is deposited on the first intrinsic amorphous silicon layer using a silane mixed gas at a gradually decreasing deposition rate. The ratio of silane to hydrogen in the silane mixed gas gradually changes from 1:1 to 1:10, the radio frequency power is 150W, the silane flow rate gradually changes from 500sccm to 200sccm with a slope of -10sccm / s, and the hydrogen flow rate gradually changes from 500sccm to 2000sccm with a slope of 50sccm / s.

[0062] An n-type doped layer and a p-type doped layer are formed. Along the direction away from the intrinsic amorphous silicon layer, the ratio between silane and dopant gradually increases from 1:1 to 1:3, wherein the silane flow rate gradually changes from 200 sccm to 100 sccm with a slope of -10 sccm / s, and the dopant flow rate gradually changes from 200 sccm to 300 sccm with a slope of 10 sccm / s.

[0063] A transparent conductive film is disposed on the bottom side of the n-type doped layer and the top side of the p-type doped layer;

[0064] Electrodes are formed on the outer surface of a transparent conductive film.

[0065] It is understandable that during the deposition of the second intrinsic amorphous silicon layer, the ratio of silane to hydrogen in the silane mixture is gradually changed from 1:1 to 1:10 by gradually reducing the silane flow rate and gradually increasing the hydrogen flow rate.

[0066] During the formation of n-type and p-type doped layers, the silane flow rate is gradually reduced while the dopant flow rate is gradually increased, so that the ratio between silane and dopant is gradually increased from 1:1 to 1:3.

[0067] Specifically, when the doped layer is a p-type doped layer, the doping element is a borane mixture gas with a borane concentration of 2%. The borane mixture gas includes borane gas and hydrogen gas.

[0068] When the doped layer is an n-type doped layer, the doping element is a phosphine gas mixture with a phosphine concentration of 1%. The phosphine gas mixture includes phosphine gas and hydrogen gas.

[0069] The performance of the obtained heterojunction solar cells is shown in Table 1.

[0070] Comparative Example 1

[0071] The preparation method of the heterojunction solar cell in Comparative Example 1 includes the following steps:

[0072] Texturing and cleaning the silicon substrate;

[0073] First, a first intrinsic amorphous silicon layer is deposited on the upper and lower surfaces of a silicon substrate using pure silane gas at a first deposition rate of 0.7 nm / s. When depositing the first intrinsic amorphous silicon layer, the radio frequency power is 500 W and the silane flow rate is 2000 sccm.

[0074] A second intrinsic amorphous silicon layer is then deposited on the first intrinsic amorphous silicon layer using a silane mixed gas at a second deposition rate of 0.11 nm / s. The ratio of silane to hydrogen in the silane mixed gas is 1:1, the radio frequency power is 150 W, and the silane flow rate is 200 sccm.

[0075] An n-type doped layer and a p-type doped layer are formed, and the ratio of silane to dopant element is fixed at 1:2 along the direction away from the intrinsic amorphous silicon layer.

[0076] A transparent conductive film is disposed on the bottom side of the n-type doped layer and the top side of the p-type doped layer;

[0077] Electrodes are formed on the outer surface of a transparent conductive film.

[0078] Specifically, when the doped layer is a p-type doped layer, the doping element is a borane mixture gas with a borane concentration of 2%. The borane mixture gas includes borane gas and hydrogen gas.

[0079] When the doped layer is an n-type doped layer, the doping element is a phosphine gas mixture with a phosphine concentration of 1%. The phosphine gas mixture includes phosphine gas and hydrogen gas.

[0080] The performance of the obtained heterojunction solar cells is shown in Table 1.

[0081] Comparative Example 2

[0082] The preparation method of the heterojunction solar cell in Comparative Example 2 includes the following steps:

[0083] Texturing and cleaning the silicon substrate;

[0084] Intrinsic amorphous silicon layers are deposited on the upper and lower surfaces of a silicon substrate using a silane mixed gas at a fixed deposition rate of 0.11 nm / s. During the deposition of the intrinsic amorphous silicon layers, an RF power of 150 W is provided, and the ratio of silane to hydrogen in the silane mixed gas is 1:1.

[0085] An n-type doped layer and a p-type doped layer are formed. Along the direction away from the intrinsic amorphous silicon layer, the ratio between silane and dopant gradually increases from 1:1 to 1:3, wherein the silane flow rate gradually changes from 200 sccm to 100 sccm with a slope of -10 sccm / s, and the dopant flow rate gradually changes from 200 sccm to 300 sccm with a slope of 10 sccm / s.

[0086] A transparent conductive film is disposed on the bottom side of the n-type doped layer and the top side of the p-type doped layer;

[0087] Electrodes are formed on the outer surface of a transparent conductive film.

[0088] It is understandable that during the deposition of the second intrinsic amorphous silicon layer, the ratio of silane to hydrogen in the silane mixture is gradually changed from 1:1 to 1:10 by gradually reducing the silane flow rate and gradually increasing the hydrogen flow rate.

[0089] During the formation of n-type and p-type doped layers, the silane flow rate is gradually reduced while the dopant flow rate is gradually increased, so that the ratio between silane and dopant is gradually increased from 1:1 to 1:3.

[0090] Specifically, when the doped layer is a p-type doped layer, the doping element is a borane mixture gas with a borane concentration of 2%. The borane mixture gas includes borane gas and hydrogen gas.

[0091] When the doped layer is an n-type doped layer, the doping element is a phosphine gas mixture with a phosphine concentration of 1%. The phosphine gas mixture includes phosphine gas and hydrogen gas.

[0092] The performance of the obtained heterojunction solar cells is shown in Table 1.

[0093] Comparative Example 3

[0094] The preparation method of the heterojunction solar cell in Comparative Example 3 includes the following steps:

[0095] Texturing and cleaning the silicon substrate;

[0096] Intrinsic amorphous silicon layers are deposited on the upper and lower surfaces of a silicon substrate using a silane mixed gas at a fixed deposition rate of 0.11 nm / s. During the deposition of the intrinsic amorphous silicon layers, an RF power of 150 W is provided, and the ratio of silane to hydrogen in the silane mixed gas is 1:1.

[0097] An n-type doped layer and a p-type doped layer are formed, and the ratio of silane to dopant element is fixed at 1:2 along the direction away from the intrinsic amorphous silicon layer.

[0098] A transparent conductive film is disposed on the bottom side of the n-type doped layer and the top side of the p-type doped layer;

[0099] Electrodes are formed on the outer surface of a transparent conductive film.

[0100] It is understandable that during the deposition of the second intrinsic amorphous silicon layer, the ratio of silane to hydrogen in the silane mixture is gradually changed from 1:1 to 1:10 by gradually reducing the silane flow rate and gradually increasing the hydrogen flow rate.

[0101] During the formation of n-type and p-type doped layers, the silane flow rate is gradually reduced while the dopant flow rate is gradually increased, so that the ratio between silane and dopant is gradually increased from 1:1 to 1:3.

[0102] Specifically, when the doped layer is a p-type doped layer, the doping element is a borane mixture gas with a borane concentration of 2%. The borane mixture gas includes borane gas and hydrogen gas.

[0103] When the doped layer is an n-type doped layer, the doping element is a phosphine gas mixture with a phosphine concentration of 1%. The phosphine gas mixture includes phosphine gas and hydrogen gas.

[0104] The performance of the obtained heterojunction solar cells is shown in Table 1.

[0105] Table 1

[0106] Test Project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Voc(mV) 743.2 744.7 742.1 740.9 740.3 Jsc(mA / cm2) 38.6 38.55 38.53 38.5 38.47 FF (%) 84.62 84.52 84.16 84.55 84.09 Rs(mΩ) 0.85 0.95 1.72 0.92 1.74 EFF (%) 24.24 24.26 24.06 24.12 23.95

[0107] As can be seen from the comparison between Example 1 and Example 2 in Table 1 above, Example 2 has a slightly higher open-circuit voltage (Voc) and a slightly higher final conversion efficiency (EFF) compared to Example 1. It can be seen that the deposition method of gradually decreasing the deposition rate of the second intrinsic amorphous silicon layer significantly improves the passivation effect, and the resulting solar cell has a higher conversion efficiency.

[0108] As can be seen from the comparison between Example 1 and Comparative Example 1 in Table 1 above, Example 1 has a slightly higher open-circuit voltage (Voc) and a significantly lower contact resistance (Rs) compared to Comparative Example 1, resulting in a 0.46% increase in fill factor (FF) and a 0.17% increase in conversion efficiency (EFF). It can be seen that using a gradual change in the ratio of silane to dopant elements when forming n-type and p-type doped layers can effectively improve the contact between amorphous silicon and the upper ITO layer, thereby improving the fill factor of the solar cell.

[0109] As can be seen from the comparison between Example 1 and Comparative Example 2 in Table 1 above, the open circuit voltage (Voc) of Example 1 is increased by 2.3mV compared with Comparative Example 2, indicating that the use of two deposition rates in the intrinsic layer significantly improves the surface passivation effect compared with a single deposition rate, and the final photoelectric conversion efficiency (EFF) of the solar cell is increased by 0.12%.

[0110] As can be seen from the comparison between Example 1 and Comparative Example 3 in Table 1 above, Example 1 has an open-circuit voltage (Voc) that is 2.9 mV higher and a fill factor (FF) that is 0.53% higher than Comparative Example 3. This shows that Example 1 uses two deposition rates to dop the intrinsic layer while the N / P layer is gradient-doped, which can simultaneously improve the surface passivation effect and the contact between amorphous silicon and the upper ITO layer. Ultimately, the photoelectric conversion efficiency (EFF) of the solar cell is increased by 0.29%, which is a very significant effect.

[0111] In summary, in the heterojunction solar cell fabrication method of this invention, for the intrinsic amorphous silicon layer, a first intrinsic amorphous silicon layer is first formed by high-speed deposition, and then a second intrinsic amorphous silicon layer is formed by low-speed deposition. The first intrinsic amorphous silicon layer is in direct contact with the silicon substrate, which can suppress the epitaxial growth of amorphous silicon on the surface of the silicon substrate and obtain a high-quality second intrinsic amorphous silicon layer, thereby improving the passivation effect of the intrinsic amorphous silicon layer. For the doped layer, the doping concentration of the doped layer gradually increases along the direction away from the intrinsic amorphous silicon layer. On the one hand, the interface between the doped layer and the intrinsic amorphous silicon layer has a low doping concentration, which results in a small change in the structure of the doped amorphous silicon. When in contact with the intrinsic amorphous silicon, it will not cause a large change in the intrinsic amorphous silicon structure, thus having a small impact on the passivation effect. On the other hand, the interface between the doped layer and the transparent conductive film is the amorphous silicon with the highest doping concentration, which can effectively reduce the contact resistance between the doped layer and the transparent conductive film, reduce the contact resistance of the final heterojunction solar cell, and improve the cell conversion efficiency.

[0112] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0113] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a heterojunction cell, comprising a coating process for preparing an intrinsic amorphous silicon layer on the upper and lower surfaces of a silicon-based substrate and a doped layer on the intrinsic amorphous silicon layer in a vacuum environment; characterized in that: The coating process comprises the following steps: a first intrinsic amorphous silicon layer is deposited on the upper and lower surfaces of the silicon substrate at a first deposition rate of 0.4 nm / s to 1.2 nm / s; a second intrinsic amorphous silicon layer is then deposited on the first intrinsic amorphous silicon layer at a second deposition rate of 0.03 nm / s to 0.3 nm / s, and the ratio of silane to hydrogen gradually decreases along a direction away from the first intrinsic amorphous silicon layer during deposition of the second intrinsic amorphous silicon layer; or the second deposition rate gradually decreases along a direction away from the first intrinsic amorphous silicon layer during deposition of the second intrinsic amorphous silicon layer; a doped layer with gradually increasing doping concentration is formed on the intrinsic amorphous silicon layer along a direction away from the intrinsic amorphous silicon layer, and the ratio of silane to doping element gradually increases from 5:1 to 1:3 to 1:1 to 1:6 along a direction away from the intrinsic amorphous silicon layer.

2. The method of producing a heterojunction cell according to claim 1, wherein: The radio frequency power is 400 W to 1000 W, and the silane flow rate is 500 sccm to 2000 sccm during deposition of the first intrinsic amorphous silicon layer.

3. The method of producing a heterojunction cell according to claim 1, wherein: The radio frequency power is 150 W to 400 W, and the silane flow rate is 100 sccm to 800 sccm during deposition of the second intrinsic amorphous silicon layer.

4. The method of producing a heterojunction cell according to claim 1, wherein: The ratio of silane to hydrogen is 5:1 to 1:20 during deposition of the second intrinsic amorphous silicon layer.

5. The method of producing a heterojunction cell according to claim 1, wherein: The thickness of the second intrinsic amorphous silicon layer is greater than the thickness of the first intrinsic amorphous silicon layer.

6. The method of producing a heterojunction cell according to claim 5, wherein: The thickness of the first intrinsic amorphous silicon layer is 1 nm to 3 nm.

7. The method of producing a heterojunction cell according to claim 5, wherein: The thickness of the second intrinsic amorphous silicon layer is 2 nm to 10 nm.

8. The method of producing a heterojunction cell according to claim 1, wherein: The doped layer comprises a p-type doped layer and / or an n-type doped layer, the doping element is borane mixed gas with a borane concentration of 2% when the doped layer is a p-type doped layer, and the doping element is phosphine mixed gas with a phosphine concentration of 1% when the doped layer is an n-type doped layer.

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