Heterojunction solar cell

Abstract

The utility model provides a heterojunction solar cell which comprises an n-type silicon wafer, and two opposite side surfaces of the n-type silicon wafer are respectively a front surface and a back surface. A back surface intrinsic amorphous silicon layer, a first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a fourth boron-doped p-type microcrystalline silicon layer, a back surface transparent conductive layer and a back surface metal electrode are sequentially arranged on the back surface; a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer and a front metal electrode are sequentially arranged on the front surface of the substrate; the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is smaller than the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer, and the boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is smaller than the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer. The boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer is greater than that in the second boron-doped p-type microcrystalline silicon layer; and the thickness of the fourth boron-doped p-type microcrystalline silicon layer is less than or equal to 5nm.

Description

Technical Field

[0001] The utility model belongs to the technical field of silicon solar cells, and in particular relates to a heterojunction solar cell. Background Art

[0002] Silicon heterojunction (HJT) solar cells have attracted considerable attention for their advantages, including high turn-on voltage, high conversion efficiency, and low temperature coefficient. Boron-doped amorphous or microcrystalline silicon thin films are a crucial component in achieving high conversion efficiency. By varying the boron doping concentration and adjusting the electrical properties of the emitter, the conversion efficiency of the cell can be directly influenced. High-efficiency HJT cells require the highest possible conductivity to increase field-effect passivation, while also maintaining the lowest possible defect state density to improve film quality and the cell's fill factor (FF). This requires appropriate optimization of the doping concentration to prevent excessive boron incorporation, which would render the boron atoms in the film inactive, affecting the crystallization rate of the microcrystalline film and preventing them from contributing to conductivity. Furthermore, the formation of neutral scattering centers reduces the mobility of carriers within the film, thereby impacting the cell's efficiency.

[0003] Therefore, how to optimize the boron doping concentration in microcrystalline silicon films, improve interface contact, improve the quality of microcrystalline silicon films, enhance carrier mobility, and improve battery efficiency are technical problems that need to be solved urgently. Utility Model Content

[0004] In response to the shortcomings of the prior art, the present invention aims to provide a heterojunction solar cell. The present invention designs four layers of boron-doped p-type microcrystalline silicon, achieves gradient boron doping by controlling each boron-doped p-type microcrystalline silicon layer, and limits the thickness of the fourth boron-doped p-type microcrystalline silicon layer to ≤5nm. This ensures that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. The third and fourth boron-doped p-type microcrystalline silicon layers further enhance hole extraction and improve carrier transport. The four layers work together to significantly reduce back-hole tunneling contact and improve cell efficiency.

[0005] In order to achieve the purpose of this utility model, the utility model adopts the following technical solutions:

[0006] In a first aspect, the utility model provides a heterojunction solar cell, the heterojunction solar cell comprising an n-type silicon wafer, wherein a back surface of the n-type silicon wafer is provided with a back intrinsic amorphous silicon layer, a first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a fourth boron-doped p-type microcrystalline silicon layer, a back transparent conductive layer, and a back metal electrode in sequence along a direction away from the n-type silicon wafer;

[0007] The front surface of the n-type silicon wafer is provided with a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer and a front metal electrode in sequence along a direction away from the n-type silicon wafer;

[0008] The boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is less than the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer, the boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is less than the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer, and the boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer is greater than the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer;

[0009] The thickness of the fourth boron-doped p-type microcrystalline silicon layer is ≤5 nm.

[0010] It should be noted that effective hole collection is a combination of the tunneling effect from c-Si to pa-Si:H (P-type microcrystalline silicon) and the transparent electrode / pa-Si:H interface. Hole extraction from c-Si is primarily related to the work function matching between ia-Si:H (intrinsic amorphous silicon) and pa-Si:H, and between the transparent electrode and pa-Si:H.

[0011] Therefore, the present invention designs four boron-doped p-type microcrystalline silicon layers and achieves a gradient boron doping by controlling each boron-doped p-type microcrystalline silicon layer. Meanwhile, the thickness of the fourth boron-doped p-type microcrystalline silicon layer is limited to ≤5nm, ensuring that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. Under conditions of a high gradient doping ratio, the third and fourth boron-doped p-type microcrystalline silicon layers are enhanced by upward band bending, resulting in more efficient hole tunneling through the ia-Si:H layer, leading to hole accumulation at the transparent electrode / pa-Si:H heterointerface. The accumulated holes can easily recombine with electrons in the transparent electrode through increased trap states, which leads to a reduction in hole tunneling resistivity and an improvement in the cell fill factor (FF). Furthermore, the enhanced upward band bending also causes electrons to be repelled from the c-Si / pa-Si:H interface. Therefore, the above process optimization further enhances the extraction of holes and improves the transport of carriers. The four layers work together to significantly reduce the back hole tunneling contact and improve the battery efficiency.

[0012] The design scheme of the boron-doped p-type microcrystalline silicon layer provided by the utility model is not only applicable to heterojunction solar cells, but also to Topcon, IBC back contact and other batteries.

[0013] In the present invention, the thickness of the fourth boron-doped p-type microcrystalline silicon layer is ≤ 5 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm or 5 nm, etc. If the thickness of the fourth boron-doped p-type microcrystalline silicon layer is too thick, the parasitic absorption of the microcrystalline silicon film will increase.

[0014] Preferably, the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is 1.2E19-5.3E19 atom / cm 3 , for example, it can be 1.2E19atom / cm 3 、1.3E19atom / cm 3 、2E19atom / cm 3 or 5E19atom / cm 3 wait.

[0015] In the present invention, the appropriate boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is beneficial to the nucleation of microcrystalline silicon.

[0016] Preferably, the thickness of the first boron-doped p-type microcrystalline silicon layer is 1-2 nm, for example, 1 nm, 1.5 nm or 2 nm.

[0017] Preferably, the first boron-doped p-type microcrystalline silicon layer is a first boron-oxygen co-doped p-type microcrystalline silicon layer.

[0018] The function of doping oxygen into the first boron-doped p-type microcrystalline silicon layer of the present invention is to facilitate microcrystalline nucleation and improve the crystallization rate of microcrystalline silicon. The same applies to the following.

[0019] Preferably, the oxygen doping concentration in the first boron-oxygen co-doped p-type microcrystalline silicon layer is 1.2E20-2.5E21atom / cm 3 , for example, it can be 1.2E20atom / cm 3 、1.7E20atom / cm 3 、2E20atom / cm 3 、5E21atom / cm 3 、7E21atom / cm 3 、8E21atom / cm 3 、1E21atom / cm 3 、1.5E21atom / cm 3 or 2E21atom / cm 3 wait.

[0020] Preferably, the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer is 1E20-4.5E20 atom / cm 3 , for example, it can be 1E20atom / cm 3 、1.8E20atom / cm 3 、2.5E20atom / cm 3 、3E20atom / cm 3 、3.5E20atom / cm 3or 4E20atom / cm 3 wait.

[0021] In the present invention, the appropriate boron doping concentration in the second boron-doped p-type microcrystalline silicon layer is beneficial to increasing the field effect passivation effect.

[0022] Preferably, the thickness of the second boron-doped p-type microcrystalline silicon layer is 23-28 nm, for example, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm or 28 nm.

[0023] Preferably, the second boron-doped p-type microcrystalline silicon layer is a second boron-oxygen co-doped p-type microcrystalline silicon layer.

[0024] Preferably, the oxygen doping concentration in the second boron-oxygen co-doped p-type microcrystalline silicon layer is 1.2E20-2.5E21atom / cm 3 , for example, it can be 1.2E20atom / cm 3 、1.7E20atom / cm 3 、2E20atom / cm 3 、5E21atom / cm 3 、7E21atom / cm 3 、8E21atom / cm 3 、1E21atom / cm 3 、1.5E21atom / cm 3 or 2E21atom / cm 3 wait.

[0025] Preferably, the boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is 1.5E18-1.5E19 atom / cm 3 , for example, it can be 1.5E18atom / cm 3 、5E18atom / cm 3 、1E19atom / cm 3 or 1.5E19atom / cm 3 wait.

[0026] In the present invention, the appropriate boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is conducive to forming a high concentration gradient with the fourth boron-doped p-type microcrystalline silicon layer.

[0027] Preferably, the thickness of the third boron-doped p-type microcrystalline silicon layer is 1-2 nm, for example, 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm or 2 nm.

[0028] In the present invention, a third boron-doped p-type microcrystalline silicon layer with a low thickness is used, and a lower concentration of boron doping elements is carried at the same time, which can further increase hole accumulation. If the thickness is too large, more holes cannot be accumulated.

[0029] Preferably, the third boron-doped p-type microcrystalline silicon layer is a third boron-oxygen co-doped p-type microcrystalline silicon layer.

[0030] Preferably, the oxygen doping concentration in the third boron-oxygen co-doped p-type microcrystalline silicon layer is 1.2E20-2.5E21atom / cm 3 , for example, it can be 1.2E20atom / cm 3 、1.7E20atom / cm 3 、2E20atom / cm 3 、5E21atom / cm 3 、7E21atom / cm 3 、8E21atom / cm 3 、1E21atom / cm 3 、1.5E21atom / cm 3 or 2E21atom / cm 3 wait.

[0031] Preferably, the boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer is 2E21-8.6E21 atom / cm 3 , for example, it can be 2E21atom / cm 3 、5.2E21atom / cm 3 、6E21atom / cm 3 、6.7E21atom / cm 3 、7E21atom / cm 3 、7.5E21atom / cm 3 、8E21atom / cm 3 、8.5E21atom / cm 3 or 8.6E21atom / cm 3 wait.

[0032] In the present invention, a low-thickness fourth boron-doped p-type microcrystalline silicon layer is used, and a high-concentration boron-doped element is simultaneously carried, which can further enhance the extraction of holes, more effectively improve carrier transport, and significantly improve battery efficiency.

[0033] Preferably, the thickness of the fourth boron-doped p-type microcrystalline silicon layer is 4-6 nm, for example, 4 nm, 4.5 nm, 5 nm, 5.5 nm or 6 nm.

[0034] Preferably, the total thickness of the first boron-doped p-type microcrystalline silicon layer, the second boron-doped p-type microcrystalline silicon layer, the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 30-35nm, for example, it can be 30nm, 31nm, 32nm, 33nm, 34nm or 35nm.

[0035] Preferably, the thickness of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are independently 5-7 nm, for example, 5 nm, 5.5 nm, 6 nm, 6.5 nm or 7 nm.

[0036] Preferably, the back transparent conductive layer and the front transparent conductive layer each independently include an ITO (indium tin oxide) layer.

[0037] Preferably, the thickness of the back transparent conductive layer and the front transparent conductive layer is independently 80-100 nm, for example, 80 nm, 90 nm or 100 nm.

[0038] Preferably, the phosphorus doping concentration in the phosphorus-doped n-type microcrystalline silicon layer is 1.2E21-1.9E21 atom / cm 3 , for example, it can be 1.2E21atom / cm 3 、1.4E21atom / cm 3 、1.6E21atom / cm 3 or 1.8E21atom / cm 3 wait.

[0039] Preferably, the phosphorus-doped n-type microcrystalline silicon layer has a thickness of 25-30 nm, for example, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm or 30 nm.

[0040] Preferably, the back metal electrode and the front metal electrode each independently comprise a silver electrode.

[0041] Preferably, the thickness of the back metal electrode and the front metal electrode is independently 10-20 μm, for example, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm.

[0042] In a second aspect, the present invention provides a method for preparing a heterojunction solar cell, the method comprising the following steps:

[0043] An intrinsic amorphous silicon layer is deposited on the front side and the back side of the n-type silicon wafer, respectively, which are denoted as the front side intrinsic amorphous silicon layer and the back side intrinsic amorphous silicon layer.

[0044] A first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped microcrystalline silicon layer and a fourth boron-doped p-type microcrystalline silicon layer are sequentially deposited on the back intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer.

[0045] Among them, the boron source flow ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:(2.5-3), and the boron source flow ratio for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:(20-30); the thickness of the fourth boron-doped p-type microcrystalline silicon layer is ≤5nm.

[0046] A phosphorus-doped n-type microcrystalline silicon layer is deposited on the front intrinsic amorphous silicon layer, and then a transparent conductive layer is deposited on the phosphorus-doped n-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer respectively. Subsequently, metal electrodes are made on the transparent conductive layers on the front and back sides of the n-type silicon wafer respectively to obtain the heterojunction solar cell.

[0047] In the present invention, the boron source flow ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:(2.5-3), for example, it can be 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3, etc. If the boron source flow ratio is too small, the doping concentration is insufficient; if the boron source flow ratio is too large, Auger recombination is increased.

[0048] In the present invention, the boron source flow ratio for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:(20-30), for example, it can be 1:20, 1:22, 1:24, 1:26, 1:28 or 1:30, etc. If the boron source flow ratio is too small, it will not lead to hole accumulation; if the boron source flow ratio is too large, it will affect passivation.

[0049] Preferably, the deposition method of the intrinsic amorphous silicon layer includes a PECVD method.

[0050] Preferably, the deposition methods of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are both PECVD methods, and the specific parameters independently include:

[0051] The reaction gas includes a silicon source and hydrogen, the reaction gas pressure is 0.4-0.6 Torr, for example, it can be 0.4 Torr, 0.5 Torr or 0.6 Torr, etc., the deposition power is 100-200 W, for example, it can be 100 W, 150 W or 200 W, etc., and the deposition temperature is 160-200 ° C, for example, it can be 160 ° C, 170 ° C, 180 ° C, 190 ° C or 200 ° C, etc.

[0052] Preferably, the flow ratio of the silicon source to the hydrogen is 1:(1-1.5), for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5.

[0053] It should be noted that the present invention does not limit the type of silicon source. For example, it can be silane, etc. The same applies to the following.

[0054] Preferably, the deposition method of the first boron-doped p-type microcrystalline silicon layer includes a PECVD method.

[0055] Preferably, the deposition method of the first boron-doped p-type microcrystalline silicon layer is a PECVD method, and the specific parameters include:

[0056] The reaction gas includes a silicon source, a boron source and hydrogen. The reaction gas pressure is 4-5 Torr, for example, it can be 4 Torr, 4.5 Torr or 5 Torr, etc. The deposition power is 5000-7000 W, for example, it can be 5000 W, 6000 W or 7000 W, etc. The deposition temperature is 145-165°C, for example, it can be 145°C, 150°C, 160°C or 165°C, etc.

[0057] Preferably, the flow rate of the boron source is 25-35 sccm, for example, 25 sccm, 30 sccm or 35 sccm.

[0058] It should be noted that the present invention does not limit the type of boron source. For example, it can be borane, etc. The same applies to the following.

[0059] Preferably, the flow ratio of the silicon source to the hydrogen is 1:(350-380), for example, it can be 1:350, 1:360, 1:370 or 1:380.

[0060] Preferably, the reaction gas further includes carbon dioxide.

[0061] The purpose of adding carbon dioxide into the first boron-doped p-type microcrystalline silicon layer in the present invention is to serve as a raw material for oxygen doping elements, thereby facilitating microcrystalline nucleation and improving the crystallization rate of microcrystalline silicon. The same applies to the following.

[0062] Preferably, the flow rate of the carbon dioxide is 100-200 sccm, for example, 100 sccm, 120 sccm, 140 sccm, 160 sccm, 180 sccm or 200 sccm.

[0063] Preferably, the deposition method of the second boron-doped p-type microcrystalline silicon layer includes a PECVD method.

[0064] Preferably, the deposition method of the second boron-doped p-type microcrystalline silicon layer is a PECVD method, and the specific parameters include:

[0065] The reaction gas includes a silicon source, a boron source and hydrogen. The reaction gas pressure is 4-5 Torr, for example, it can be 4 Torr, 4.5 Torr or 5 Torr, etc. The deposition power is 5000-7000 W, for example, it can be 5000 W, 6000 W or 7000 W, etc. The deposition temperature is 145-165°C, for example, it can be 145°C, 150°C, 160°C or 165°C, etc.

[0066] Preferably, the flow rate of the boron source is 60-80 sccm, for example, 60 sccm, 70 sccm or 80 sccm.

[0067] Preferably, the flow ratio of the silicon source to the hydrogen is 1:(300-350), for example, it can be 1:300, 1:310, 1:320, 1:330, 1:340 or 1:350.

[0068] Preferably, the reaction gas further includes carbon dioxide.

[0069] Preferably, the flow rate of the carbon dioxide is 15-25 sccm, for example, 15 sccm, 20 sccm or 25 sccm.

[0070] Preferably, the deposition method of the third boron-doped p-type microcrystalline silicon layer includes a PECVD method.

[0071] Preferably, the deposition method of the third boron-doped p-type microcrystalline silicon layer is a PECVD method, and the specific parameters include.

[0072] The reaction gas includes a silicon source, a boron source and hydrogen. The reaction gas pressure is 4-5 Torr, for example, it can be 4 Torr, 4.5 Torr or 5 Torr, etc. The deposition power is 5000-7000 W, for example, it can be 5000 W, 6000 W or 7000 W, etc. The deposition temperature is 145-165°C, for example, it can be 145°C, 150°C, 160°C or 165°C, etc.

[0073] Preferably, the flow rate of the boron source is 10-20 sccm, for example, 10 sccm, 15 sccm or 20 sccm.

[0074] Preferably, the flow ratio of the silicon source to the hydrogen is 1:(300-350), for example, it can be 1:300, 1:310, 1:320, 1:330, 1:340 or 1:350.

[0075] Preferably, the reaction gas further includes carbon dioxide.

[0076] Preferably, the flow rate of the carbon dioxide is 15-25 sccm, for example, 15 sccm, 20 sccm or 25 sccm.

[0077] Preferably, the deposition method of the fourth boron-doped p-type microcrystalline silicon layer includes a PECVD method.

[0078] Preferably, the fourth boron-doped p-type microcrystalline silicon layer is deposited by a PECVD method, and specific parameters include:

[0079] The reaction gas includes a silicon source, a boron source and hydrogen. The reaction gas pressure is 4-5 Torr, for example, it can be 4 Torr, 4.5 Torr or 5 Torr, etc. The deposition power is 5000-7000 W, for example, it can be 5000 W, 6000 W or 7000 W, etc. The deposition temperature is 145-165°C, for example, it can be 145°C, 150°C, 160°C or 165°C, etc.

[0080] It should be noted that carbon dioxide is not used for oxygen doping during the deposition of the fourth boron-doped p-type microcrystalline silicon layer, which is beneficial to improving the contact between the fourth boron-doped p-type microcrystalline silicon layer and the transparent conductive layer.

[0081] Preferably, the flow rate of the boron source is 300-400 sccm, for example, 300 sccm, 350 sccm or 400 sccm.

[0082] Preferably, the flow ratio of the silicon source to the hydrogen is 1:(300-350), for example, it can be 1:300, 1:310, 1:320, 1:330, 1:340 or 1:350.

[0083] Preferably, the preparation method comprises the following steps:

[0084] A back intrinsic amorphous silicon layer with a thickness of 5-7 nm is deposited on the back side of an n-type silicon wafer by a PECVD method. The specific steps include: introducing hydrogen and a silicon source as reaction gases into a reaction chamber, wherein the hydrogen flow rate is 800-1200 sccm (for example, it can be 800 sccm, 900 sccm, 1000 sccm, 1100 sccm or 1200 sccm, etc.), the silicon source flow rate is 800-1000 sccm (for example, it can be 800 sccm, 900 sccm or 1000 sccm, etc.), the silicon source and hydrogen flow rate ratio is 1:(1-1.5), the preset deposition power is 100-200 W, the deposition temperature is 160-200 ° C, and the reaction gas pressure is 0.4-0.6 Torr.

[0085] A front intrinsic amorphous silicon layer with a thickness of 5-7 nm is deposited on the front side of an n-type silicon wafer by a PECVD method. The specific steps include: introducing hydrogen and a silicon source as reaction gases into a reaction chamber, wherein the hydrogen flow rate is 800-1200 sccm (for example, it can be 800 sccm, 900 sccm, 1000 sccm, 1100 sccm or 1200 sccm, etc.), the silicon source flow rate is 800-1000 sccm (for example, it can be 800 sccm, 900 sccm or 1000 sccm, etc.), the silicon source and hydrogen flow rate ratio is 1:(1-1.5), the preset deposition power is 100-200 W, the deposition temperature is 160-200 ° C, and the reaction gas pressure is 0.4-0.6 Torr.

[0086] A first boron-doped p-type microcrystalline silicon layer with a thickness of 1-2 nm is deposited on the back intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by a PECVD method. The specific steps include: introducing a silicon source, a boron source, hydrogen and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm (for example, it can be 50 sccm, 60 sccm, 70 sccm or 80 sccm, etc.), the flow rate of the boron source is 25-35 sccm, the flow rate of the hydrogen is 25000-29000 sccm (for example, it can be 25000 sccm, 27000 sccm or 29000 sccm, etc.), the flow rate of the carbon dioxide is 100-200 sccm, the flow ratio of the silicon source to the hydrogen is 1:(350-380), the preset deposition power is 5000-7000 W, the deposition temperature is 145-165° C., and the reaction gas pressure is 4-5 Torr.

[0087] A second boron-doped p-type microcrystalline silicon layer with a thickness of 23-28 nm is deposited on the first boron-doped p-type microcrystalline silicon layer by a PECVD method. The specific steps include: introducing a silicon source, a boron source, hydrogen and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm (for example, it can be 50 sccm, 60 sccm, 70 sccm or 80 sccm, etc.), the flow rate of the boron source is 60-80 sccm, the flow rate of the hydrogen is 15000-28000 sccm (for example, it can be 15000 sccm, 20000 sccm, 25000 sccm or 28000 sccm, etc.), the flow rate of the carbon dioxide is 15-25 sccm, the flow ratio of the silicon source to the hydrogen is 1:(300-350), the preset deposition power is 5000-7000 W, the deposition temperature is 145-165°C, and the reaction gas pressure is 4-5 Torr.

[0088] A third boron-doped p-type microcrystalline silicon layer with a thickness of 1-2 nm is deposited on the second boron-doped p-type microcrystalline silicon layer by a PECVD method. The specific steps include: introducing a silicon source, a boron source, hydrogen and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm (for example, it can be 50 sccm, 60 sccm, 70 sccm or 80 sccm, etc.), the flow rate of the boron source is 10-20 sccm, the flow rate of the hydrogen is 15000-28000 sccm (for example, it can be 15000 sccm, 20000 sccm, 25000 sccm or 28000 sccm, etc.), the flow rate of the carbon dioxide is 15-25 sccm, the flow ratio of the silicon source to the hydrogen is 1:(300-350), the preset deposition power is 5000-7000 W, the deposition temperature is 145-165°C, and the reaction gas pressure is 4-5 Torr.

[0089] A fourth boron-doped p-type microcrystalline silicon layer with a thickness of 4-6 nm is deposited on the third boron-doped p-type microcrystalline silicon layer by a PECVD method. The specific steps include: introducing a silicon source, a boron source and hydrogen into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm (for example, it can be 50 sccm, 60 sccm, 70 sccm or 80 sccm, etc.), the flow rate of the boron source is 300-400 sccm, the flow rate of the hydrogen is 15000-28000 sccm (for example, it can be 15000 sccm, 20000 sccm, 25000 sccm or 28000 sccm, etc.), the flow ratio of the silicon source to the hydrogen is 1:(300-350), the preset deposition power is 5000-7000 W, the deposition temperature is 145-165°C, and the reaction gas pressure is 4-5 Torr.

[0090] A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 25-30 nm (for example, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, or 30 nm, etc.) is deposited on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by a PECVD method. The specific steps include: introducing a silicon source, a phosphorus source, and hydrogen into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the phosphorus source is 300-800 sccm, and the flow rate of the hydrogen is 8000-11000 sccm, the preset deposition power is 4000-6000 W, the deposition temperature is 180-200° C., and the reaction gas pressure is 4-6 Torr.

[0091] An ITO (indium tin oxide) transparent conductive layer is deposited on the phosphorus-doped n-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer by magnetron sputtering, with each layer independently having a thickness of 80-110 nm (for example, 80 nm, 85 nm, 100 nm, or 110 nm).

[0092] Metal electrodes (eg, silver electrodes) are respectively fabricated on the transparent conductive layers on the front and back sides of the n-type silicon wafer by screen printing to obtain the heterojunction solar cell.

[0093] In a third aspect, the present invention provides a silicon solar cell, which includes the heterojunction solar cell as described in the second aspect.

[0094] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0095] Compared with the prior art, the present invention has the following beneficial effects:

[0096] The utility model designs four boron-doped p-type microcrystalline silicon layers. Gradient boron doping is achieved by controlling each boron-doped p-type microcrystalline silicon layer. The thickness of the fourth boron-doped p-type microcrystalline silicon layer is limited to ≤5nm, ensuring that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. Under conditions of high gradient doping ratios, the third and fourth boron-doped p-type microcrystalline silicon layers experience enhanced upward band bending, leading to more efficient hole tunneling through the ia-Si:H layer. This results in hole accumulation at the transparent electrode / pa-Si:H heterointerface. The accumulated holes can easily recombine with electrons in the transparent electrode through increased trap states, resulting in a reduction in hole tunneling resistivity and an improvement in the cell fill factor (FF). Furthermore, the enhanced upward band bending also causes electrons to be repelled from the c-Si / pa-Si:H interface. Therefore, the above process optimization further enhances the extraction of holes and improves the transport of carriers. The four layers work together to significantly reduce the back hole tunneling contact and improve the battery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 This is a schematic structural diagram of the heterojunction solar cell provided in Example 1 of the present utility model.

[0098] Figure 2 This is a schematic structural diagram of the heterojunction solar cell provided in Comparative Example 1 of the present invention.

[0099] Figure 3 This is a schematic structural diagram of a heterojunction solar cell provided in Comparative Example 2 of the present invention.

[0100] Among them, 1-n-type silicon wafer; 2-back intrinsic amorphous silicon layer; 3-front intrinsic amorphous silicon layer; 41-first boron-doped p-type microcrystalline silicon layer; 42-back boron-doped p-type microcrystalline silicon layer; 43-low-concentration boron-doped p-type microcrystalline silicon layer; 51-second boron-doped p-type microcrystalline silicon layer; 52-medium-concentration boron-doped p-type microcrystalline silicon layer; 61-third boron-doped p-type microcrystalline silicon layer; 62-high-concentration boron-doped p-type microcrystalline silicon layer; 7-fourth boron-doped p-type microcrystalline silicon layer; 8-phosphorus-doped n-type microcrystalline silicon layer; 91-back transparent conductive layer; 92-front transparent conductive layer; 101-back metal electrode; 102-front metal electrode. DETAILED DESCRIPTION

[0101] The technical solution of the present invention is further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0102] Example 1

[0103] This embodiment provides a heterojunction solar cell, the structural diagram of which is shown in FIG. Figure 1 As shown, the heterojunction solar cell includes an n-type silicon wafer 1, and a back side of the n-type silicon wafer 1 is provided with a back side intrinsic amorphous silicon layer 2, a first boron-doped p-type microcrystalline silicon layer 41, a second boron-doped p-type microcrystalline silicon layer 51, a third boron-doped p-type microcrystalline silicon layer 61, a fourth boron-doped p-type microcrystalline silicon layer 7, a back side transparent conductive layer 91 and a back side metal electrode 101 in sequence along the direction away from the n-type silicon wafer 1;

[0104] The front surface of the n-type silicon wafer 1 is provided with a front intrinsic amorphous silicon layer 3, a phosphorus-doped n-type microcrystalline silicon layer 8, a front transparent conductive layer 92 and a front metal electrode 102 in sequence along a direction away from the n-type silicon wafer 1;

[0105] The boron doping concentration in the first boron-doped p-type microcrystalline silicon layer 41 is 5.3E19 atom / cm 3 , which is less than the boron doping concentration of 1.8E20atom / cm in the second boron-doped p-type microcrystalline silicon layer 51. 3 The boron doping concentration in the third boron-doped p-type microcrystalline silicon layer 61 is 1.1E19 atom / cm 3 The boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer 7 is 2.1E21atom / cm 3 ;

[0106] The first boron-doped p-type microcrystalline silicon layer 41 is a first boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 2.3E21atom / cm 3The second boron-doped p-type microcrystalline silicon layer 51 is a second boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 2.3E21atom / cm 3 The third boron-doped p-type microcrystalline silicon layer 61 is a third boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 2.3E21atom / cm 3 ;

[0107] The thickness of the first boron-doped p-type microcrystalline silicon layer 41 is 1.5 nm; the thickness of the second boron-doped p-type microcrystalline silicon layer 51 is 26 nm; the thickness of the third boron-doped p-type microcrystalline silicon layer 61 is 1.5 nm; the thickness of the fourth boron-doped p-type microcrystalline silicon layer 7 is 5 nm, and the total thickness is 34 nm.

[0108] The thickness of the front intrinsic amorphous silicon layer 3 and the back intrinsic amorphous silicon layer 2 are both 6nm; the back transparent conductive layer 91 and the front transparent conductive layer 92 are both ITO layers, and the thickness is 95nm; the thickness of the phosphorus-doped n-type microcrystalline silicon layer 8 is 28nm, and the phosphorus doping concentration is 1.9E21atom / cm 3 The back metal electrode 101 and the front metal electrode 102 are both silver grid electrodes, and the thickness is 14 μm.

[0109] This embodiment also provides a method for preparing the above-mentioned heterojunction solar cell, the method comprising the following steps:

[0110] (1) A back intrinsic amorphous silicon layer 2 with a thickness of 6 nm is deposited on the back side of the n-type silicon wafer 1 by a PECVD method. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1000 sccm, the flow rate of silane is 900 sccm, and the flow ratio of silane to hydrogen is 1:1.11. The preset deposition power is 150 W, the deposition temperature is 200°C, and the reaction gas pressure is 0.5 Torr.

[0111] A front intrinsic amorphous silicon layer 3 with a thickness of 6 nm is deposited on the front side of the n-type silicon wafer 1 by PECVD method. The specific steps include:

[0112] Hydrogen and silane were introduced into the reaction chamber as reaction gases, wherein the flow rate of hydrogen was 1000 sccm, the flow rate of silane was 900 sccm, the flow ratio of silane to hydrogen was 1:1.11, the preset deposition power was 150 W, the deposition temperature was 200 ° C, and the reaction gas pressure was 0.5 Torr.

[0113] (2) depositing a first boron-doped p-type microcrystalline silicon layer 41 with a thickness of 1.5 nm on the back intrinsic amorphous silicon layer 2 in a direction away from the n-type silicon wafer 1 by a PECVD method, the specific steps comprising:

[0114] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 75 sccm, the flow rate of borane was 25 sccm, the flow rate of hydrogen was 27000 sccm, the flow rate of carbon dioxide was 150 sccm, the flow ratio of silane to hydrogen was 1:360, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0115] (3) depositing a second boron-doped p-type microcrystalline silicon layer 51 with a thickness of 26 nm on the first boron-doped p-type microcrystalline silicon layer 41 by PECVD, the specific steps comprising:

[0116] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 70 sccm, the flow rate of borane was 70 sccm, the flow rate of hydrogen was 23100 sccm, the flow rate of carbon dioxide was 10 sccm, the flow ratio of silane to hydrogen was 1:330, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0117] The borane flow ratio for depositing the first boron-doped p-type microcrystalline silicon layer 41 and the second boron-doped p-type microcrystalline silicon layer 51 is 1:2.8.

[0118] (4) depositing a third boron-doped p-type microcrystalline silicon layer 61 with a thickness of 1.5 nm on the second boron-doped p-type microcrystalline silicon layer 51 by PECVD, the specific steps comprising:

[0119] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 65 sccm, the flow rate of borane was 15 sccm, the flow rate of hydrogen was 21450 sccm, the flow rate of carbon dioxide was 20 sccm, the flow ratio of silane to hydrogen was 1:330, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0120] (5) Depositing a fourth boron-doped p-type microcrystalline silicon layer 7 with a thickness of 5 nm on the third boron-doped p-type microcrystalline silicon layer 61 by PECVD. The specific steps include:

[0121] Silane, borane and hydrogen were introduced into the reaction chamber, where the flow rate of silane was 65 sccm, the flow rate of borane was 375 ccm, the flow rate of hydrogen was 21450 sccm, the flow ratio of silane to hydrogen was 1:330, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0122] The borane flow ratio for depositing the third boron-doped p-type microcrystalline silicon layer 61 and the fourth boron-doped p-type microcrystalline silicon layer 7 is 1:25.

[0123] (6) Depositing a phosphorus-doped n-type microcrystalline silicon layer 8 with a thickness of 28 nm on the front intrinsic amorphous silicon layer 3 in a direction away from the n-type silicon wafer 1 by a PECVD method, the specific steps comprising:

[0124] Silane, phosphine and hydrogen were introduced into the reaction chamber, wherein the flow rate of silane was 50 sccm, the flow rate of phosphine was 380 sccm, the flow rate of hydrogen was 8000 sccm, the preset deposition power was 4500 W, the deposition temperature was 190° C., and the reaction gas pressure was 4.5 Torr.

[0125] (7) A magnetron sputtering method is used to deposit an ITO transparent conductive layer on the phosphorus-doped n-type microcrystalline silicon layer 8 and the fourth boron-doped p-type microcrystalline silicon layer 7, respectively, with a thickness of 95 nm.

[0126] (8) Silver grid electrodes with a thickness of 14 μm were made on the ITO transparent conductive layers on the front and back sides of the n-type silicon wafer 1 by screen printing to obtain the heterojunction solar cell.

[0127] Example 2

[0128] This embodiment provides a heterojunction solar cell, the heterojunction solar cell comprising an n-type silicon wafer, wherein a back surface of the n-type silicon wafer is provided with a back intrinsic amorphous silicon layer, a first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a fourth boron-doped p-type microcrystalline silicon layer, a back transparent conductive layer, and a back metal electrode in sequence along a direction away from the n-type silicon wafer;

[0129] The front surface of the n-type silicon wafer is provided with a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer and a front metal electrode in sequence along a direction away from the n-type silicon wafer;

[0130] The boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is 1.8E19 atom / cm 3 , which is less than the boron doping concentration of 1.3E20atom / cm in the second boron-doped p-type microcrystalline silicon layer. 3 The boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is 1.1E19atom / cm 3 The boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer is 2.5E21atom / cm 3 ;

[0131] The first boron-doped p-type microcrystalline silicon layer is a first boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 1.5E21atom / cm 3The second boron-doped p-type microcrystalline silicon layer is a second boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 1.5E21atom / cm 3 The third boron-doped p-type microcrystalline silicon layer is a third boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 1.5E21atom / cm 3 ;

[0132] The thickness of the first boron-doped p-type microcrystalline silicon layer is 2 nm; the thickness of the second boron-doped p-type microcrystalline silicon layer is 23 nm; the thickness of the third boron-doped p-type microcrystalline silicon layer is 2 nm; the thickness of the fourth boron-doped p-type microcrystalline silicon layer is 4 nm, and the total thickness is 31 nm;

[0133] The thickness of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are both 5nm; the back transparent conductive layer and the front transparent conductive layer are both ITO layers, and the thickness is 95nm; the thickness of the phosphorus-doped n-type microcrystalline silicon layer is 25nm, and the phosphorus doping concentration is 1.7E21atom / cm 3 ; The back metal electrode and the front metal electrode are both silver grid line electrodes, and the thickness is 14μm.

[0134] This embodiment also provides a method for preparing the above-mentioned heterojunction solar cell, the method comprising the following steps:

[0135] (1) A back intrinsic amorphous silicon layer with a thickness of 5 nm was deposited on the back side of the n-type silicon wafer by a PECVD method. The specific steps included: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen was 800 sccm, the flow rate of silane was 800 sccm, the flow ratio of silane to hydrogen was 1:1, the preset deposition power was 100 W, the deposition temperature was 190°C, and the reaction gas pressure was 0.4 Torr.

[0136] A 5 nm thick intrinsic amorphous silicon layer is deposited on the front side of the n-type silicon wafer by PECVD. The specific steps include:

[0137] Hydrogen and silane were introduced into the reaction chamber as reaction gases, wherein the flow rate of hydrogen was 800 sccm, the flow rate of silane was 800 sccm, the flow ratio of silane to hydrogen was 1:1, the preset deposition power was 100 W, the deposition temperature was 190°C, and the reaction gas pressure was 0.4 Torr.

[0138] (2) depositing a first boron-doped p-type microcrystalline silicon layer with a thickness of 2 nm on the back intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by a PECVD method, the specific steps comprising:

[0139] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 80 sccm, the flow rate of borane was 25 sccm, the flow rate of hydrogen was 28,000 sccm, the flow rate of carbon dioxide was 100 sccm, the flow ratio of silane to hydrogen was 1:350, the preset deposition power was 5,000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4 Torr.

[0140] (3) depositing a second boron-doped p-type microcrystalline silicon layer with a thickness of 23 nm on the first boron-doped p-type microcrystalline silicon layer by a PECVD method, the specific steps comprising:

[0141] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 50 sccm, the flow rate of borane was 62.5 sccm, the flow rate of hydrogen was 15000 sccm, the flow rate of carbon dioxide was 15 sccm, the flow ratio of silane to hydrogen was 1:300, the preset deposition power was 5000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4 Torr.

[0142] The borane flow ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:2.5.

[0143] (4) depositing a third boron-doped p-type microcrystalline silicon layer with a thickness of 2 nm on the second boron-doped p-type microcrystalline silicon layer by a PECVD method, the specific steps comprising:

[0144] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 50 sccm, the flow rate of borane was 10 sccm, the flow rate of hydrogen was 15000 sccm, the flow rate of carbon dioxide was 15 sccm, the flow ratio of silane to hydrogen was 1:300, the preset deposition power was 5000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4 Torr.

[0145] (5) depositing a fourth boron-doped p-type microcrystalline silicon layer with a thickness of 4 nm on the third boron-doped p-type microcrystalline silicon layer by a PECVD method, the specific steps comprising:

[0146] Silane, borane and hydrogen were introduced into the reaction chamber, where the flow rate of silane was 50 sccm, the flow rate of borane was 300 sccm, the flow rate of hydrogen was 15000 sccm, the flow ratio of silane to hydrogen was 1:300, the preset deposition power was 5000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4 Torr.

[0147] Wherein, the borane flow ratio for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:30.

[0148] (6) depositing a phosphorus-doped n-type microcrystalline silicon layer with a thickness of 25 nm on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by a PECVD method, the specific steps comprising:

[0149] Silane, phosphine and hydrogen were introduced into the reaction chamber, wherein the flow rate of silane was 50 sccm, the flow rate of phosphine was 400 sccm, the flow rate of hydrogen was 8000 sccm, the preset deposition power was 3500 W, the deposition temperature was 190° C., and the reaction gas pressure was 4 Torr.

[0150] (7) A magnetron sputtering method is used to deposit an ITO transparent conductive layer on the phosphorus-doped n-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer, respectively, with a thickness of 95 nm.

[0151] (8) Silver grid electrodes with a thickness of 14 μm were made on the ITO transparent conductive layers on the front and back sides of the n-type silicon wafer by screen printing to obtain the heterojunction solar cell.

[0152] Example 3

[0153] This embodiment provides a heterojunction solar cell, the heterojunction solar cell comprising an n-type silicon wafer, wherein a back surface of the n-type silicon wafer is provided with a back intrinsic amorphous silicon layer, a first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a fourth boron-doped p-type microcrystalline silicon layer, a back transparent conductive layer, and a back metal electrode in sequence along a direction away from the n-type silicon wafer;

[0154] The front surface of the n-type silicon wafer is provided with a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer and a front metal electrode in sequence along a direction away from the n-type silicon wafer;

[0155] The boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is 1.5E19 atom / cm 3 , which is less than the boron doping concentration of 1.3E20atom / cm in the second boron-doped p-type microcrystalline silicon layer. 3 The boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is 1.1E19atom / cm 3 The boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer is 2.5E21atom / cm 3 ;

[0156] The first boron-doped p-type microcrystalline silicon layer is a first boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 1.7E21atom / cm 3 The second boron-doped p-type microcrystalline silicon layer is a second boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 1.7E21atom / cm 3The third boron-doped p-type microcrystalline silicon layer is a third boron-oxygen co-doped p-type microcrystalline silicon layer, and the oxygen doping concentration is 1.7E21atom / cm 3 ;

[0157] The thickness of the first boron-doped p-type microcrystalline silicon layer is 1 nm; the thickness of the second boron-doped p-type microcrystalline silicon layer is 27 nm; the thickness of the third boron-doped p-type microcrystalline silicon layer is 1 nm; the thickness of the fourth boron-doped p-type microcrystalline silicon layer is 6 nm, and the total thickness is 35 nm;

[0158] The thickness of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are both 7nm; the back transparent conductive layer and the front transparent conductive layer are both ITO layers, and the thickness is 95nm; the thickness of the phosphorus-doped n-type microcrystalline silicon layer is 30nm, and the phosphorus doping concentration is 1.7E21atom / cm 3 ; The back metal electrode and the front metal electrode are both silver grid line electrodes, and the thickness is 12μm.

[0159] This embodiment also provides a method for preparing the above-mentioned heterojunction solar cell, the method comprising the following steps:

[0160] (1) A back intrinsic amorphous silicon layer with a thickness of 7 nm was deposited on the back side of the n-type silicon wafer by a PECVD method. The specific steps included: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen was 1200 sccm, the flow rate of silane was 800 sccm, and the flow ratio of silane to hydrogen was 1:1.5. The preset deposition power was 200 W, the deposition temperature was 190°C, and the reaction gas pressure was 0.6 Torr.

[0161] A 7nm thick front intrinsic amorphous silicon layer is deposited on the front side of the n-type silicon wafer by PECVD. The specific steps include:

[0162] Hydrogen and silane were introduced into the reaction chamber as reaction gases, wherein the flow rate of hydrogen was 1200 sccm, the flow rate of silane was 800 sccm, the flow ratio of silane to hydrogen was 1:1.5, the preset deposition power was 200 W, the deposition temperature was 190°C, and the reaction gas pressure was 0.6 Torr.

[0163] (2) depositing a first boron-doped p-type microcrystalline silicon layer with a thickness of 1 nm on the back intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by a PECVD method, the specific steps comprising:

[0164] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 78 sccm, the flow rate of borane was 27 sccm, the flow rate of hydrogen was 29000 sccm, the flow rate of carbon dioxide was 200 sccm, the flow ratio of silane to hydrogen was 1:372, the preset deposition power was 7000 W, the deposition temperature was 155°C, and the reaction gas pressure was 5 Torr.

[0165] (3) depositing a second boron-doped p-type microcrystalline silicon layer with a thickness of 27 nm on the first boron-doped p-type microcrystalline silicon layer by a PECVD method, the specific steps comprising:

[0166] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 80 sccm, the flow rate of borane was 80 sccm, the flow rate of hydrogen was 28000 sccm, the flow rate of carbon dioxide was 25 sccm, the flow ratio of silane to hydrogen was 1:350, the preset deposition power was 7000 W, the deposition temperature was 155°C, and the reaction gas pressure was 5 Torr.

[0167] The borane flow ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:3.

[0168] (4) depositing a third boron-doped p-type microcrystalline silicon layer with a thickness of 1 nm on the second boron-doped p-type microcrystalline silicon layer by a PECVD method, the specific steps comprising:

[0169] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 80 sccm, the flow rate of borane was 14 sccm, the flow rate of hydrogen was 28,000 sccm, the flow rate of carbon dioxide was 25 sccm, the flow ratio of silane to hydrogen was 1:350, the preset deposition power was 7,000 W, the deposition temperature was 155°C, and the reaction gas pressure was 5 Torr.

[0170] (5) depositing a fourth boron-doped p-type microcrystalline silicon layer with a thickness of 6 nm on the third boron-doped p-type microcrystalline silicon layer by PECVD, the specific steps comprising:

[0171] Silane, borane and hydrogen were introduced into the reaction chamber, where the flow rate of silane was 80 sccm, the flow rate of borane was 400 sccm, the flow rate of hydrogen was 28000 sccm, the flow ratio of silane to hydrogen was 1:350, the preset deposition power was 7000 W, the deposition temperature was 155°C, and the reaction gas pressure was 5 Torr.

[0172] The borane flow ratio for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:29.

[0173] (6) depositing a phosphorus-doped n-type microcrystalline silicon layer with a thickness of 30 nm on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by a PECVD method, the specific steps comprising:

[0174] Silane, phosphine and hydrogen were introduced into the reaction chamber, wherein the flow rate of silane was 50 sccm, the flow rate of phosphine was 400 sccm, the flow rate of hydrogen was 8000 sccm, the preset deposition power was 3500 W, the deposition temperature was 185° C., and the reaction gas pressure was 4 Torr.

[0175] (7) A magnetron sputtering method is used to deposit an ITO transparent conductive layer on the phosphorus-doped n-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer, respectively, with a thickness of 95 nm.

[0176] (8) Silver grid electrodes with a thickness of 12 μm were made on the ITO transparent conductive layers on the front and back sides of the n-type silicon wafer by screen printing to obtain the heterojunction solar cell.

[0177] Example 4

[0178] The difference between this embodiment and embodiment 1 is that the thickness of the third boron-doped p-type microcrystalline silicon layer is 5 nm.

[0179] The rest of the preparation methods and parameters remained the same as in Example 1.

[0180] Example 5

[0181] The difference between this embodiment and embodiment 1 is that oxygen doping is not performed in the first boron-doped p-type microcrystalline silicon layer, the second boron-doped p-type microcrystalline silicon layer and the third boron-doped p-type microcrystalline silicon layer, that is, carbon dioxide is not introduced in steps (2), (3) and (4).

[0182] The rest of the preparation methods and parameters remained the same as in Example 1.

[0183] Comparative Example 1

[0184] This comparative example provides a heterojunction solar cell, the structural diagram of which is shown in FIG. Figure 2 As shown, it includes a stacked back metal electrode 101, a back transparent conductive layer 91, a back boron-doped p-type microcrystalline silicon layer 42, a back intrinsic amorphous silicon layer 2, an n-type silicon wafer 1, a front intrinsic amorphous silicon layer 3, a phosphorus-doped n-type microcrystalline silicon layer 8, a front transparent conductive layer 92 and a front metal electrode 102;

[0185] The back metal electrode 101 and the front metal electrode 102 are both silver grid electrodes, and the thickness is 12 μm;

[0186] The back transparent conductive layer 91 and the front transparent conductive layer 92 are both ITO layers, and both have a thickness of 95 nm;

[0187] The thickness of the back boron-doped p-type microcrystalline silicon layer 42 is 34 nm, and the boron doping concentration is 1.5E20 atom / cm 3 ;

[0188] The thickness of the front intrinsic amorphous silicon layer 3 and the back intrinsic amorphous silicon layer 2 are both 6 nm;

[0189] The thickness of the phosphorus-doped n-type microcrystalline silicon layer 8 is 28 nm, and the phosphorus doping concentration is 1.3E21 atom / cm 3 .

[0190] This comparative example also provides a method for preparing the above-mentioned heterojunction solar cell, which comprises the following steps:

[0191] (1) A back intrinsic amorphous silicon layer 2 with a thickness of 6 nm is deposited on the back side of the n-type silicon wafer 1 by a PECVD method. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1000 sccm, the flow rate of silane is 900 sccm, and the flow ratio of silane to hydrogen is 1:1.11. The preset deposition power is 150 W, the deposition temperature is 195°C, and the reaction gas pressure is 0.5 Torr.

[0192] A front intrinsic amorphous silicon layer 3 with a thickness of 6 nm is deposited on the front side of the n-type silicon wafer 1 by PECVD method. The specific steps include:

[0193] Hydrogen and silane were introduced into the reaction chamber as reaction gases, wherein the flow rate of hydrogen was 1000 sccm, the flow rate of silane was 900 sccm, the flow ratio of silane to hydrogen was 1:1.11, the preset deposition power was 150 W, the deposition temperature was 195°C, and the reaction gas pressure was 0.5 Torr.

[0194] (2) depositing a back boron-doped p-type microcrystalline silicon layer 42 with a thickness of 34 nm on the back intrinsic amorphous silicon layer 2 in a direction away from the n-type silicon wafer 1 by PECVD, the specific steps comprising:

[0195] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 75 sccm, the flow rate of borane was 60 sccm, the flow rate of hydrogen was 27000 sccm, the flow rate of carbon dioxide was 20 sccm, the flow ratio of silane to hydrogen was 1:360, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0196] (3) Depositing a phosphorus-doped n-type microcrystalline silicon layer 8 with a thickness of 28 nm on the front intrinsic amorphous silicon layer 3 in a direction away from the n-type silicon wafer 1 by a PECVD method, the specific steps comprising:

[0197] Silane, phosphine and hydrogen were introduced into the reaction chamber, wherein the flow rate of silane was 50 sccm, the flow rate of phosphine was 400 sccm, the flow rate of hydrogen was 800 sccm, the preset deposition power was 3500 W, the deposition temperature was 190° C., and the reaction gas pressure was 4 Torr.

[0198] (4) A magnetron sputtering method is used to deposit an ITO transparent conductive layer on the phosphorus-doped n-type microcrystalline silicon layer 8 and the fourth boron-doped p-type microcrystalline silicon layer 7, respectively, with a thickness of 95 nm.

[0199] (5) Silver grid electrodes with a thickness of 12 μm were made on the ITO transparent conductive layers on the front and back sides of the n-type silicon wafer 1 by screen printing to obtain the heterojunction solar cell.

[0200] Comparative Example 2

[0201] This comparative example provides a heterojunction solar cell, the structural diagram of which is shown in FIG. Figure 3 As shown, it includes a stacked back metal electrode 101, a back transparent conductive layer 91, a high-concentration boron-doped p-type microcrystalline silicon layer 62, a medium-concentration boron-doped p-type microcrystalline silicon layer 52, a low-concentration boron-doped p-type microcrystalline silicon layer 43, a back intrinsic amorphous silicon layer 22, an n-type silicon wafer 1, a front intrinsic amorphous silicon layer 3, a phosphorus-doped n-type microcrystalline silicon layer 8, a front transparent conductive layer 92 and a front metal electrode 102;

[0202] The back metal electrode 101 and the front metal electrode 102 are both silver grid electrodes, and the thickness is 12 μm;

[0203] The back transparent conductive layer 91 and the front transparent conductive layer 92 are both ITO layers, and both have a thickness of 95 nm;

[0204] The thickness of the high-concentration boron-doped p-type microcrystalline silicon layer 62 is 22 nm, and the boron doping concentration is 1.8E20 atom / cm 3 The thickness of the medium concentration boron-doped p-type microcrystalline silicon layer 52 is 5nm, and the boron doping concentration is 1.1E20atom / cm 3 The thickness of the low-concentration boron-doped p-type microcrystalline silicon layer 43 is 2nm, and the boron doping concentration is 1.2E19atom / cm 3 ;

[0205] The thickness of the front intrinsic amorphous silicon layer 3 and the back intrinsic amorphous silicon layer 2 are both 6 nm;

[0206] The thickness of the phosphorus-doped n-type microcrystalline silicon layer 8 is 28 nm, and the phosphorus doping concentration is 2.1E20 atom / cm 3 .

[0207] This comparative example also provides a method for preparing the above-mentioned heterojunction solar cell, which comprises the following steps:

[0208] (1) A back intrinsic amorphous silicon layer 2 with a thickness of 6 nm is deposited on the back side of the n-type silicon wafer 1 by a PECVD method. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1000 sccm, the flow rate of silane is 900 sccm, and the flow ratio of silane to hydrogen is 1:1.11. The preset deposition power is 150 W, the deposition temperature is 190°C, and the reaction gas pressure is 0.5 Torr.

[0209] A front intrinsic amorphous silicon layer 3 with a thickness of 6 nm is deposited on the front side of the n-type silicon wafer 1 by PECVD method. The specific steps include:

[0210] Hydrogen and silane were introduced into the reaction chamber as reaction gases, wherein the flow rate of hydrogen was 1000 sccm, the flow rate of silane was 900 sccm, the flow ratio of silane to hydrogen was 1:1.11, the preset deposition power was 150 W, the deposition temperature was 190°C, and the reaction gas pressure was 0.5 Torr.

[0211] (2) depositing a low-concentration boron-doped p-type microcrystalline silicon layer 43 with a thickness of 2 nm on the back intrinsic amorphous silicon layer 2 in a direction away from the n-type silicon wafer 1 by a PECVD method, the specific steps comprising:

[0212] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 75 sccm, the flow rate of borane was 25 sccm, the flow rate of hydrogen was 27000 sccm, the flow rate of carbon dioxide was 20 sccm, the flow ratio of silane to hydrogen was 1:360, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0213] (3) Depositing a medium-concentration boron-doped p-type microcrystalline silicon layer 52 with a thickness of 25 nm on the low-concentration boron-doped p-type microcrystalline silicon layer 43 by PECVD. The specific steps include:

[0214] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 75 sccm, the flow rate of borane was 60 sccm, the flow rate of hydrogen was 27000 sccm, the flow rate of carbon dioxide was 20 sccm, the flow ratio of silane to hydrogen was 1:360, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0215] (4) Depositing a high-concentration boron-doped p-type microcrystalline silicon layer 62 with a thickness of 5 nm on the medium-concentration boron-doped p-type microcrystalline silicon layer 52 by PECVD. The specific steps include:

[0216] Silane, borane, hydrogen and carbon dioxide were introduced into the reaction chamber, where the flow rate of silane was 75 sccm, the flow rate of borane was 90 sccm, the flow rate of hydrogen was 27000 sccm, the flow rate of carbon dioxide was 20 sccm, the flow ratio of silane to hydrogen was 1:360, the preset deposition power was 6000 W, the deposition temperature was 155°C, and the reaction gas pressure was 4.5 Torr.

[0217] (5) Depositing a phosphorus-doped n-type microcrystalline silicon layer 8 with a thickness of 28 nm on the front intrinsic amorphous silicon layer 3 in a direction away from the n-type silicon wafer 1 by a PECVD method, the specific steps comprising:

[0218] Silane, phosphine and hydrogen were introduced into the reaction chamber, wherein the flow rate of silane was 50 sccm, the flow rate of phosphine was 400 sccm, the flow rate of hydrogen was 8500 sccm, the preset deposition power was 3500 W, the deposition temperature was 190° C., and the reaction gas pressure was 4 Torr.

[0219] (6) A magnetron sputtering method is used to deposit an ITO transparent conductive layer on the phosphorus-doped n-type microcrystalline silicon layer 8 and the fourth boron-doped p-type microcrystalline silicon layer 7, respectively, with a thickness of 95 nm.

[0220] (7) Silver grid electrodes with a thickness of 12 μm were made on the ITO transparent conductive layers on the front and back sides of the n-type silicon wafer 1 by screen printing to obtain the heterojunction solar cell.

[0221] Comparative Example 3

[0222] The difference between this comparative example and Example 1 is that by adjusting the flow rate of the borane in step (2) or the flow rate of the borane in step (3), the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is equal to the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer.

[0223] The rest of the preparation methods and parameters remained the same as in Example 1.

[0224] Comparative Example 4

[0225] The difference between this comparative example and Example 1 is that by adjusting the flow rate of the borane in step (2) or the flow rate of the borane in step (4), the boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is equal to the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer.

[0226] The rest of the preparation methods and parameters remained the same as in Example 1.

[0227] Comparative Example 5

[0228] The difference between this comparative example and Example 1 is that by adjusting the flow rate of the borane in step (3) or the flow rate of the borane in step (5), the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer is equal to the boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer.

[0229] The rest of the preparation methods and parameters remained the same as in Example 1.

[0230] Comparative Example 6

[0231] The difference between this comparative example and Example 1 is that the thickness of the fourth boron-doped p-type microcrystalline silicon layer is 10 nm.

[0232] The rest of the preparation methods and parameters remained the same as in Example 1.

[0233] Performance Testing

[0234] The heterojunction solar cells provided in the above embodiments and comparative examples were tested for back hole tunneling contact resistivity and photoelectric performance.

[0235] The test conditions were as follows: a special metal mask was used on glass, electrodes were printed, and then contact was tested. Photoelectric performance was tested using an IV tester under 1 sun. The test results are shown in Table 1.

[0236] Table 1

[0237]

[0238] analyze:

[0239] As shown in the table above, the present invention employs four boron-doped p-type microcrystalline silicon layers. By controlling the boron source flow rate ratio between each layer, the doping gradient is designed. This ensures that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. Under conditions of high gradient doping ratios, the third and fourth boron-doped p-type microcrystalline silicon layers exhibit enhanced band bending, leading to more efficient hole tunneling through the ia-Si:H layer. This results in hole accumulation at the transparent electrode / pa-Si:H heterointerface. These accumulated holes can easily recombine with electrons in the transparent electrode through increased trap states, reducing the hole tunneling resistivity and improving the cell fill factor (FF). Furthermore, the enhanced band bending also results in electrons being repelled from the c-Si / pa-Si:H interface. Consequently, the aforementioned process optimization further enhances hole extraction and improves carrier transport. The synergistic effect of the four layers significantly reduces back-hole tunneling contact and improves cell efficiency.

[0240] It can be seen from Example 1 and Example 4 that if the thickness of the third boron-doped p-type microcrystalline silicon layer is too thick, the passivation performance will be affected.

[0241] It can be seen from Examples 1 and 5 that if oxygen is not doped in the first boron-doped p-type microcrystalline silicon layer, the second boron-doped p-type microcrystalline silicon layer, and the third boron-doped p-type microcrystalline silicon layer, the thin film has poor light transmittance, which affects the current.

[0242] From Example 1 and Comparative Examples 1-2, it can be seen that if the boron-doped p-type microcrystalline silicon layer is a single layer, effective contact cannot be formed. If the boron-doped p-type microcrystalline silicon layer is a three-layer structure consisting of low, medium and high boron concentrations, the hole concentration is low.

[0243] It can be seen from Example 1 and Comparative Example 3 that if the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is equal to the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer, effective field effect passivation cannot be provided.

[0244] It can be seen from Example 1 and Comparative Example 4 that if the boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is equal to the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer, it cannot form a higher concentration gradient with the fourth boron doping, affecting the photoelectric performance of the battery and the back hole tunneling contact resistivity.

[0245] It can be seen from Example 1 and Comparative Example 5 that if the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer is equal to the boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer, it cannot form a higher concentration gradient with the third boron doping, affecting the photoelectric performance of the battery and the back hole tunneling contact resistivity.

[0246] It can be seen from Example 1 and Comparative Example 6 that if the thickness of the fourth boron-doped p-type microcrystalline silicon layer is too thick, the doping is excessive, which affects the passivation performance.

[0247] The applicant declares that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Persons skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A heterojunction solar cell, characterized in that: The heterojunction solar cell comprises an n-type silicon wafer, wherein two opposite surfaces of the n-type silicon wafer are respectively a front surface and a back surface, and the back surface of the n-type silicon wafer is provided with a back intrinsic amorphous silicon layer, a first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a fourth boron-doped p-type microcrystalline silicon layer, a back transparent conductive layer, and a back metal electrode in sequence along a direction away from the n-type silicon wafer; The front surface of the n-type silicon wafer is provided with a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer and a front metal electrode in sequence along a direction away from the n-type silicon wafer; The boron doping concentration in the first boron-doped p-type microcrystalline silicon layer is less than the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer, the boron doping concentration in the third boron-doped p-type microcrystalline silicon layer is less than the boron doping concentration in the first boron-doped p-type microcrystalline silicon layer, and the boron doping concentration in the fourth boron-doped p-type microcrystalline silicon layer is greater than the boron doping concentration in the second boron-doped p-type microcrystalline silicon layer; The thickness of the fourth boron-doped p-type microcrystalline silicon layer is ≤5 nm.

2. The heterojunction solar cell according to claim 1, characterized in that The thickness of the first boron-doped p-type microcrystalline silicon layer is 1-2 nm.

3. The heterojunction solar cell according to claim 1, wherein: The first boron-doped p-type microcrystalline silicon layer is a first boron-oxygen co-doped p-type microcrystalline silicon layer.

4. The heterojunction solar cell according to claim 1, wherein: The thickness of the second boron-doped p-type microcrystalline silicon layer is 23-28 nm.

5. The heterojunction solar cell according to claim 1, characterized in that: The second boron-doped p-type microcrystalline silicon layer is a second boron-oxygen co-doped p-type microcrystalline silicon layer.

6. The heterojunction solar cell according to claim 1, characterized in that: The thickness of the third boron-doped p-type microcrystalline silicon layer is 1-2 nm.

7. The heterojunction solar cell according to claim 1, characterized in that: The third boron-doped p-type microcrystalline silicon layer is a third boron-oxygen co-doped p-type microcrystalline silicon layer.

8. The heterojunction solar cell according to claim 1, characterized in that: The thickness of the fourth boron-doped p-type microcrystalline silicon layer is 4-6 nm.

9. The heterojunction solar cell according to claim 1, characterized in that: The total thickness of the first boron-doped p-type microcrystalline silicon layer, the second boron-doped p-type microcrystalline silicon layer, the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 30-35 nm.

10. The heterojunction solar cell according to claim 1, characterized in that: The thickness of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are independently 5-7 nm; The back transparent conductive layer and the front transparent conductive layer each independently include an ITO layer; The thickness of the back transparent conductive layer and the front transparent conductive layer are independently 80-100 nm; The thickness of the phosphorus-doped n-type microcrystalline silicon layer is 25-30 nm; The back metal electrode and the front metal electrode each independently comprise a silver electrode; The thickness of the back metal electrode and the front metal electrode are independently 10-20 μm.

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