Solar cell and preparation method thereof

Abstract

The invention relates to the technical field of solar cells, in particular to a solar cell and a preparation method thereof.The solar cell comprises a substrate, a front passivation layer, a back passivation layer, an N-type doping layer and a P-type doping layer; the front passivation layer is formed on the front surface of the substrate; the back passivation layer is formed on the back; the N-type doping layer is formed on the front passivation layer; the P-type doping layer comprises an in-situ doping layer and a gradient doping layer, the in-situ doping layer is formed on the back passivation layer, and the gradient doping layer is formed on the in-situ doping layer; the doping concentration of the in-situ doping layer is smaller than the doping concentration of the gradient doping layer. According to the solar cell, unexpected tunneling current or interface recombination current can be weakened, the problem of reverse breakdown risk of a PN junction under a high electric field is solved, the problem of damage to a passivation layer of the cell is further solved, the performance of the passivation layer and a doping layer of a cell piece is improved, the reliability of the solar cell is improved, and the yield of the solar cell is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular to a solar cell and a preparation method thereof. BACKGROUND

[0002] In the preparation method of the solar cell provided by the related art, a grid line is prepared by printing. In addition, the related art adopts a copper interconnection process to replace the process of preparing the grid line by printing. The copper interconnection process is a process of organically integrating the preparation of the solar cell and metal plating technology.

[0003] The power generation mechanism of the solar cell includes a photovoltaic voltage caused by the built-in electric field of the PN junction. When the solar cell is superimposed with the plating process, an additional electric field is introduced due to the existence of the plating electrolytic cell. Thus, a double electric field superposition effect of the additional electric field and the built-in electric field of the PN junction is formed, and unintended tunneling current or interface recombination current is generated, which causes damage to the P surface of the solar cell after plating, increases the defect rate of the solar cell, and reduces the reliability of the solar cell. SUMMARY

[0004] The present application aims to provide a solar cell and a preparation method thereof. The solar cell prepared by the preparation method of the present application can weaken unintended tunneling current or interface recombination current, reduce the risk of reverse breakdown of the PN junction under a high electric field, improve the damage to the passivation layer of the solar cell (such as amorphous silicon layer corrosion or grain boundary defects), improve the performance of the passivation layer and the doped layer of the solar cell, and thus improve the reliability of the solar cell and increase the yield of the solar cell.

[0005] The present application is implemented as follows: In a first aspect, the present application provides a solar cell, comprising: a substrate, the substrate having a front surface and a back surface; a front passivation layer formed on the front surface; a back passivation layer formed on the back surface; an N-type doped layer formed on the front passivation layer; a P-type doped layer, wherein the P-type doped layer comprises an in-situ doped layer and a gradient doped layer, the in-situ doped layer is formed on the back passivation layer, and the gradient doped layer is formed on the in-situ doped layer; the doping concentration of the in-situ doped layer is less than the doping concentration of the gradient doped layer.

[0006] In an optional embodiment, the gradient doped layer comprises at least two sub-doped layers arranged in sequence, the doping concentration of the at least two sub-doped layers increases in sequence, and the doping concentration of the sub-doped layer formed on the in-situ doped layer is greater than the doping concentration of the in-situ doped layer.

[0007] In optional embodiments, the difference between the doping concentrations of two adjacent sub-doped layers is greater than or equal to 0.05*10 19 cm -3 ; and / or, the difference between the doping concentrations of two adjacent sub-doped layers is less than or equal to 0.15*10 19 cm -3 .

[0008] In optional embodiments, the doping concentration of the in-situ doped layer is 0.30*10 19 cm -3 ~0.70*10 19 cm -3 ; and / or, the doping concentration of any one of the sub-doped layers is 0.75*10 19 ~1.20*10 19 cm -3 .

[0009] In optional embodiments, the gradient doped layer comprises five sub-doped layers arranged in sequence; from the back passivation layer to the in-situ doped layer, the concentrations of the five sub-doped layers are in sequence: 0.75*10 19 cm -3 ~0.80*10 19 cm -3 , 0.85*10 19 cm -3 ~0.90*10 19 cm -3 , 0.95*10 19 cm -3 ~1.00*10 19 cm -3 , 1.05*10 19 cm -3 ~1.10*10 19 cm -3 , 1.15*10 19 ~1.20*10 19 cm -3 .

[0010] In optional embodiments, the thickness of at least one of the front passivation layer and the back passivation layer is 2-7nm.

[0011] In a second aspect, the present application provides a method for preparing the solar cell according to any one of the preceding embodiments, comprising: texturing the front side and the back side of the substrate; forming a front passivation layer on the front side and a back passivation layer on the back side; forming an N-type doped layer on the front passivation layer; The in-situ doped layer and the gradient doped layer are formed in sequence on the back passivation layer; wherein the volume ratio of SiH4 and H2 and the atomic ratio concentration of B are controlled so that the doping concentration of the in-situ doped layer is less than the doping concentration of the gradient doped layer.

[0012] In optional embodiments, when forming the in-situ doped layer and the gradient doped layer, the volume ratio of SiH4 and H2 is controlled to be 1:7±0.2~1:12±0.2, and the volume ratio of SiH4 and H2 for forming the in-situ doped layer is less than the volume ratio of SiH4 and H2 for forming the gradient doped layer; and / or, When forming the in-situ doped layer and the gradient doped layer, the atomic ratio concentration of B is controlled to be 0.5±0.2~3±0.2%, and the atomic ratio concentration of B for forming the in-situ doped layer is less than the atomic ratio concentration of B for forming the gradient doped layer.

[0013] In optional embodiments, when forming the gradient doped layer in sequence with at least two sub-doped layers, the volume ratio of SiH4 and H2 decreases layer by layer; and / or, When forming the gradient doped layer in sequence with at least two sub-doped layers, the atomic ratio concentration of B increases layer by layer.

[0014] In optional embodiments, the temperature for forming the gradient doped layer is 180-220℃.

[0015] In optional embodiments, the method for preparing the solar cell further comprises: forming a transparent conductive layer on the N-type doped layer and the gradient doped layer, respectively; forming a seed layer on the transparent conductive layer; electroplating to form a grid line on the seed layer; wherein, the concentration of copper ions in the electrolyte used for electroplating is 15-35 g / L; and / or, the voltage for electroplating is less than 3V.

[0016] In optional embodiments, the process of electroplating comprises an initial stage, a deposition stage and a termination stage, the initial stage comprises maintaining a first set voltage for a first set time; the deposition stage comprises performing under pulse conditions; the termination stage comprises maintaining a second set voltage for a second set time; wherein, the first set voltage, the voltage of the pulse and the second set voltage are all less than 3V.

[0017] In optional embodiments, the first set voltage is a forward voltage of 0.5±0.1V; and / or, the pulse conditions comprise a forward voltage of 0.3±0.1V with a duty cycle of 80±5%, and a reverse voltage of 0.5±0.1V with a duty cycle of 20±5%; and / or, The second set voltage is a forward voltage of 0.1±0.05V.

[0018] The present application includes the following advantages: The P-type doped layer of the solar cell of the present application includes an in-situ doped layer and a gradient doped layer, and the doping concentration of the in-situ doped layer is less than that of the gradient doped layer. In this way, the built-in electric field can be weakened by the in-situ doped layer with low doping concentration, the carrier tunneling induced by high electric field can be reduced, the accumulation of electrons on the HJT (heterojunction) surface caused by the applied electric field during electroplating can be compensated, the width of the depletion region of the PN junction can be compressed, the recombination loss can be reduced by the low defect density of the in-situ doped layer with low doping concentration, and the Voc can be improved; at the same time, the conductivity can be improved by the gradient doped layer with high doping concentration, the contact resistance can be reduced, and the problem of the increase of the contact resistance caused by the in-situ doped layer with low doping concentration can be balanced, so as to realize the seesaw effect of balancing the conductivity and passivation quality. In other words, the solar cell of the present application can weaken the unintended tunneling current or interface recombination current, reduce the risk of reverse breakdown of the PN junction under high electric field, and further reduce the damage of the passivation layer of the cell (such as amorphous silicon layer corrosion or grain boundary defects), improve the performance of the passivation layer and the doped layer of the cell, and thus improve the reliability of the solar cell and improve the yield of the solar cell.

[0019] The preparation method of the solar cell of the present application can prepare the above-mentioned solar cell, which can weaken the unintended tunneling current or interface recombination current, reduce the risk of reverse breakdown of the PN junction under high electric field, and further reduce the damage of the passivation layer of the cell (such as amorphous silicon layer corrosion or grain boundary defects), improve the performance of the passivation layer and the doped layer of the cell, and thus improve the reliability of the solar cell and improve the yield of the solar cell. Moreover, the preparation method of the present application is simple and easy to operate. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0021] Figure 1 Fig. 1 is a structural schematic diagram of a solar cell; Figure 2 Fig. 3 is a schematic diagram of electroplating of a solar cell. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] Please refer to Figure 1 The process of copper electroplating to prepare solar cells typically includes: texturing and cleaning an N-type monocrystalline silicon wafer (substrate); depositing intrinsic amorphous silicon (i.e., front passivation layer) and an N-type amorphous silicon thin film (i.e., N-type doped layer) on the front side of the silicon wafer; depositing intrinsic amorphous silicon (i.e., back passivation layer) and a P-type amorphous silicon thin film (i.e., P-type doped layer) on the back side of the silicon wafer; depositing transparent conductive films (TCO conductive layers) on both the N-type and P-type amorphous silicon films; depositing a copper seed layer on the transparent conductive film; growing copper grid lines in the electroplating solution by utilizing the good conductivity of the copper seed layer; and finally depositing a layer of metallic tin on the copper grid lines to protect them and use them as welding metal for module soldering.

[0024] It should be noted that after the copper seed layer is prepared and before the gate lines are formed by electroplating, the process may include steps such as edge wrapping, coating, printing, and development; the specific process parameters are similar to those of related technologies and will not be elaborated here.

[0025] When preparing intrinsic amorphous silicon, N-type amorphous silicon thin films, P-type amorphous silicon thin films, transparent conductive films, and seed layers, the silicon wafer needs to be placed on a special carrier plate. The opposite ends of the back side of the silicon wafer are in contact with the carrier plate. Therefore, the positions on the back side of the silicon wafer that are in contact with the carrier plate are blocked by the carrier plate and will not grow and form intrinsic amorphous silicon, P-type amorphous silicon thin films, transparent conductive films, and seed layers. Only the areas not blocked by the carrier plate can grow intrinsic amorphous silicon, N-type amorphous silicon thin films, P-type amorphous silicon thin films, transparent conductive films, and seed layers.

[0026] The inventors discovered that when a solar cell to be electroplated is connected to an electrolytic cell as a cathode, the cell acts as the cathode, forming a current loop with the electrolyte and anode. For example, the PN junction of an HJT cell is composed of amorphous silicon (a-Si:H) and crystalline silicon (c-Si) heterostructures. The PN junction of the solar cell is on the P-plane, and the built-in electric field exists on the P-plane, with the direction of the electric field pointing from the N-plane to the P-plane (i.e., from the a-Si:H(n) / c-Si(p) interface to the back electrode). Figure 2 From left to right; simultaneously, in the electrolytic cell, the applied electric field points from the anode to the cathode ( Figure 2 (From right to left); when built-in electric fields and external electric fields in opposite directions interact, they will produce a superposition effect.

[0027] Wherein, when there is no external voltage (i.e., when electroplating has not started), a depletion region is formed at the PN junction, the energy band tilts (about 0.8-1.0 eV), which can prevent the diffusion of most carriers and maintain dynamic balance. When the external voltage is turned on (i.e., when electroplating), the external voltage makes the HJT cathode at a negative potential, forming an electric field from the electrolyte to the surface of the HJT (i.e., driving cations such as H + , Cu 2+ , migrate to the cathode surface and be reduced). In the electrolyte, the main task of the HJT cell cathode is to participate in the reduction reaction (metal copper deposition) as an electron donor, but the built-in electric field in the PN junction attempts to block the flow of electrons from the P surface to the N surface. Here, due to the reverse bias of the electrolytic voltage (i.e., the voltage of the applied electric field), the electrolytic electric field forces the accumulation of electrons on the surface of the HJT, which compresses the depletion region width of the PN junction (i.e., carrier tunneling induced by a high electric field), resulting in a local carrier multiplication effect. This process is unstable and can cause a thermal effect, resulting in unintended tunneling current or interface recombination current. Therefore, under the high electric field of electroplating, the PN junction has a risk of reverse breakdown, causing damage to the passivation layer of the cell (such as corrosion of the amorphous silicon layer or grain boundary defects).

[0028] In other words, the inventors have found that the process for preparing a grid line by electroplating provided by the related art is difficult to improve the carrier competition between the PN junction and the electrolyte and the risk of PN junction breakdown or damage caused by the reverse voltage of the electrolytic cell, ultimately resulting in a dark PL sheet for the cell sheet or a black EL sheet for the component after LID aging.

[0029] To improve the above problems, the present application provides a solar cell, which comprises a substrate, a front passivation layer, a back passivation layer, an N-type doped layer and a P-type doped layer; the substrate has a front surface (i.e., an N surface) and a back surface (i.e., a P surface); the front passivation layer is formed on the front surface of the substrate; the back passivation layer is formed on the back surface; the N-type doped layer is formed on the front passivation layer; wherein the P-type doped layer comprises an in-situ doped layer and a gradient doped layer, the in-situ doped layer is formed on the back passivation layer, and the gradient doped layer is formed on the in-situ doped layer; the doping concentration of the in-situ doped layer is less than the doping concentration of the gradient doped layer.

[0030] The built-in electric field is weakened by the in-situ doping layer with a low doping concentration, the carrier tunneling induced by a high electric field is reduced, the accumulation of electrons on the surface of the HJT caused by the applied electric field is compensated during electroplating, the width of the depletion region of the PN junction is compressed, the recombination loss is reduced by the low defect density of the in-situ doping layer with a low doping concentration, and the Voc is improved; meanwhile, the conductivity is improved by the gradient doping layer with a high doping concentration, the contact resistance is reduced, the problem of the increase of the contact resistance caused by the in-situ doping layer with a low doping concentration is balanced, and the seesaw effect of balancing the conductivity and the passivation quality is realized; in other words, the solar cell of the present application can weaken the unintended tunneling current or interface recombination current, reduce the risk of reverse breakdown of the PN junction under a high electric field, and thus reduce the damage to the passivation layer of the cell (such as amorphous silicon layer corrosion or grain boundary defects), improve the performance of the passivation layer and the doping layer of the cell, and thus improve the reliability of the solar cell and improve the yield of the solar cell.

[0031] Optionally, the solar cell of the present application refers to a heterojunction cell. Of course, in other embodiments, the solar cell can also refer to a perovskite cell and the like, which is not specifically limited here.

[0032] Optionally, the gradient doping layer comprises at least two sub-doping layers arranged in sequence, the doping concentrations of the at least two sub-doping layers increase in sequence, and the doping concentration of the sub-doping layer formed on the in-situ doping layer is greater than the doping concentration of the in-situ doping layer.

[0033] The at least two sub-doping layers with a gradient increase in doping concentration can effectively improve the conductivity and reliably balance the problem of the increase of the contact resistance caused by the low concentration doping of the in-situ doping layer; at the same time, the risk of reverse breakdown of the PN junction under a high electric field can be more reliably reduced, and the damage to the passivation layer can be caused.

[0034] Optionally, the difference between the doping concentrations of the two adjacent sub-doping layers is greater than or equal to 0.05*10 19 cm -3 , for example, 0.05*10 19 cm -3 , 0.06*10 19 cm -3 , 0.07*10 19 cm -3 , and the like, which is not specifically limited here.

[0035] Optionally, the difference between the doping concentrations of the two adjacent sub-doping layers is less than or equal to 0.15*10 19 cm -3 , for example, 0.15*10 19 cm -3 , 0.14*10 19 cm -3, 0.13x10 19 cm -3 , etc., which are not specifically limited herein.

[0036] Optionally, the doping concentration of the in-situ doped layer is 0.30x10 19 cm -3 ~0.70x10 19 cm -3 , for example: 0.30x10 19 cm -3 , 0.40x10 19 cm -3 , 0.50x10 19 cm -3 , 0.60x10 19 cm -3 , 0.70x10 19 cm -3 , etc., which are not specifically limited herein. Within the above doping concentration range, the built-in electric field can be reliably weakened to reduce high electric field induced carrier tunneling, compensate for the case that the depletion region width of the PN junction is compressed when the electrolytic electric field forces electrons to accumulate on the surface of the HJT, and facilitate the improvement of Voc.

[0037] Optionally, the doping concentration of any one of the sub-doped layers is 0.75x10 19 ~1.20x10 19 cm -3 . Within the above doping concentration range, the conductivity and passivation quality seesaw effect can be effectively balanced.

[0038] Optionally, the gradient doped layer comprises five sub-doped layers arranged in sequence; from the back passivation layer to the in-situ doped layer, the concentrations of the five sub-doped layers are in sequence: 0.75x10 19 cm -3 ~0.80x10 19 cm -3 (for example: 0.75x10 19 cm -3 , 0.78x10 19 cm -3 , 0.80x10 19 cm -3 , etc., which are not specifically limited herein), 0.85x10 19 cm -3 ~0.90x10 19 cm -3 (for example: 0.85x10 19 cm -3 , 0.88x10 19 cm -3, 0.90 x 10 19 cm -3 , 0.95 x 10 19 cm -3 , 1.00 x 10 19 cm -3 , 1.05 x 10 19 cm -3 , 1.10 x 10 19 cm -3 , 1.15 x 10 19 cm -3 , 1.20 x 10 19 cm -3 , 1.25 x 10 19 cm -3 , 1.30 x 10 19 cm -3 , 1.35 x 10 19 cm -3 , 1.40 x 10 19 cm -3 , 1.45 x 10 19 , 1.50 x 10 19 cm -3 , 1.55 x 10 19 cm -3 , 1.60 x 10 19 cm -3 , 1.65 x 10 19 cm -3 , 1.70 x 10 .

[0039] Optionally, the thickness of the P-type doped layer is 5-15 nm, for example, 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, etc.

[0040] Optionally, the thickness of the in-situ doped layer is 3-5 nm, for example, 3 nm, 4 nm, 5 nm, etc.

[0041] Optionally, the thickness of each sub-doped layer can be uniform or non-uniform, for example, the gradient doped layer includes five sub-doped layers arranged in sequence; from the back passivation layer to the in-situ doped layer, the thickness of the five sub-doped layers is 1-2 nm, 1-2 nm, 2-3 nm, 2-3 nm, 2-3 nm, respectively.

[0042] The inventors have further found that the thickness of the passivation layer is also not appropriate and can also cause an increase in recombination loss.

[0043] To improve the above problems, the thickness of at least one of the front passivation layer and the back passivation layer is 2-7 nm, for example: 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, etc. By so setting, the interface recombination rate (SRV<10 cm / s) can be reduced, and the effective injection of electrons into the electrolyte can be enhanced.

[0044] The present application also provides a preparation method for preparing the above solar cell, which comprises: Texturing the front surface and the back surface of the substrate; forming a front passivation layer on the front surface and a back passivation layer on the back surface; forming an N-type doped layer on the front passivation layer; forming an in-situ doped layer and a gradient doped layer on the back passivation layer in sequence; wherein the doping concentration of the in-situ doped layer is less than that of the gradient doped layer by controlling the volume ratio of SiH4 and H2 and the atomic ratio concentration of B.

[0045] In the formation of the in-situ doped layer and the gradient doped layer of the P-type doped layer, the preparation of the in-situ doped layer and the gradient doped layer with different doping concentrations is realized by controlling the volume ratio of SiH4 and H2 and the atomic ratio concentration of B, which not only can weaken the unintended tunneling current or interface recombination current of the prepared solar cell, reduce the risk of reverse breakdown of the PN junction under high electric field, and further reduce the problem of damage to the passivation layer of the cell (such as amorphous silicon layer corrosion or grain boundary defects, etc.), improve the performance of the passivation layer and the doped layer of the cell, thereby improving the reliability of the solar cell and improving the yield of the solar cell. Moreover, the preparation method is simple and easy to operate.

[0046] It should be noted that the raw material doped with B element can be B2H6, etc., which is not specifically limited here.

[0047] It should be further noted that the atomic ratio concentration of B refers to the total percentage of boron (B) atoms in the total number of atoms (including silicon Si and hydrogen H) in the amorphous silicon layer, i.e.: .

[0048] Optionally, in the formation of the in-situ doped layer and the gradient doped layer, the volume ratio of SiH4 and H2 is controlled to be 1:7±0.2~1:11±0.2, and the volume ratio of SiH4 and H2 in the formation of the in-situ doped layer is less than that in the formation of the gradient doped layer. In this way, the in-situ doped layer and the gradient doped layer with different doping concentrations can be formed.

[0049] Optionally, when forming the in-situ doped layer and the gradient doped layer, the atomic ratio concentration of B is controlled to be 1.5-3%, and the atomic ratio concentration of B when forming the in-situ doped layer is less than that when forming the gradient doped layer. In this way, the in-situ doped layer and the gradient doped layer with different B doping concentrations can be formed.

[0050] Optionally, when sequentially forming the at least two sub-doped layers of the gradient doped layer, the volume ratio of SiH4 and H2 decreases layer by layer, and the atomic ratio concentration of B increases layer by layer. In this way, the at least two sub-doped layers with the atomic ratio concentration of B increasing sequentially can be formed.

[0051] For example, when forming the in-situ doped layer, the volume ratio of SiH4 and H2 is 1:(7±0.2), and the atomic concentration ratio of B is 3±0.2%; the gradient doped layer includes five sub-doped layers, and the five sub-doped layers are sequentially defined as P1 layer, P2 layer, P3 layer, P4 layer and P5 layer from the direction of the substrate to the back passivation layer. When forming the P1 layer, the volume ratio of SiH4 and H2 is 1:(8±0.2), and the atomic concentration ratio of B is 2.5±0.2%; when forming the P2 layer, the volume ratio of SiH4 and H2 is 1:(9±0.2), and the atomic concentration ratio of B is 2±0.2%; when forming the P3 layer, the volume ratio of SiH4 and H2 is 1:(10±0.2), and the atomic concentration ratio of B is 1.5±0.2%; when forming the P4 layer, the volume ratio of SiH4 and H2 is 1:(11±0.2), and the atomic concentration ratio of B is 1±0.2%; and when forming the P5 layer, the volume ratio of SiH4 and H2 is 1:(12±0.2), and the atomic concentration ratio of B is 0.5±0.2%.

[0052] Optionally, the temperature when forming the in-situ doped layer is 180±5℃, for example, 175℃, 180℃, 185℃, etc., which is not limited herein.

[0053] Optionally, the temperature when forming the gradient doped layer is 180-220℃, for example, 180℃, 190℃, 200℃, 210℃, 220℃, etc. In this way, the problem of damage to the crystalline silicon substrate (i.e., the substrate) caused by excessively high temperature can be improved.

[0054] Optionally, the preparation method further includes: forming a transparent conductive layer on the N-type doped layer and the gradient doped layer, respectively; forming a seed layer on the transparent conductive layer; and electroplating to form a grid line on the seed layer.

[0055] Optionally, the concentration of copper ions (Cu 2+ ) in the electrolyte used for electroplating is 15-35 g / L. Reducing the concentration of copper ions in the electrolyte is conducive to dynamic control, i.e., ensuring the balance between adsorption and desorption and inhibiting the growth of dendrites.

[0056] Optionally, the pH of the electrolyte can be 3.5-4.5 (e.g., 3.5, 3.8, 4.0, 4.3, 4.5, etc.); electroplating in an acidic environment can ensure adsorption-desorption equilibrium and inhibit dendrite growth.

[0057] Optionally, the electrolyte contains additives, including but not limited to: accelerators 10-20 ml / L, leveling agents 7-15 ml / L, and inhibitors 5-10 ml / L; wherein the accelerators include but are not limited to thiourea, sodium polydithiopropane sulfonate, sodium mercaptopropane sulfonate, PEG (polyethylene glycol), leveling agents include but are not limited to polyethyleneimine (PEI), benzotriazole (BTA), quinoline derivatives (such as methyl quinoline salt), gelatin, and inhibitors include but are not limited to polyethylene glycol (PEG), tetrabutylammonium salt (TBA), acetylenic alcohol compounds (such as propargyl alcohol, butynediol).

[0058] Optionally, the voltage during electroplating is less than 3V. Avoiding the application of a high reverse bias voltage can prevent PN junction avalanche breakdown from causing local leakage damage to the thin film structure (i.e., avoid breaking the PN junction), or excessive HJT surface electron accumulation, causing local carrier multiplication effect, weakening the thermal effect to cause unintended tunneling current or interface recombination current, to reduce the risk of damage to the battery passivation layer (such as amorphous silicon layer corrosion or grain boundary defects).

[0059] To better weaken the PN junction barrier and reduce the accumulation of double electric field charges; the electroplating process is divided into an initial stage, a deposition stage, and a termination stage, the initial stage includes maintaining a first set voltage for a first set time; the deposition stage includes being carried out under pulse conditions; the termination stage includes maintaining a second set voltage for a second set time; wherein the first set voltage, the pulse voltage, and the second set voltage are all less than 3V. Through the synergy and modulation between non-pulse voltage and pulse voltage, the PN junction barrier can be weakened, and the accumulation of double electric field charges can be eliminated.

[0060] Optionally, the first set voltage is a forward voltage of 0.5±0.1V (e.g., 0.4V, 0.5V, 0.6V, etc.); the pulse conditions include a forward voltage of 0.3±0.1V (e.g., 0.2V, 0.3V, 0.4V, etc.) with a duty cycle of 80±5% (e.g., 75%, 80%, 85%, etc.) and a reverse voltage of 0.5±0.1V (e.g., 0.4V, 0.5V, 0.6V, etc.) with a duty cycle of 20±5% (e.g., 15%, 20%, 25%, etc.); the second set voltage is a forward voltage of 0.1±0.05V (e.g., 0.05V, 0.1V, 0.15V, etc.). In this way, the PN junction barrier can be weakened by using a forward bias, and the accumulation of double electric field charges can be eliminated by a reverse pulse.

[0061] Optionally, the first set voltage can be a gradient voltage rising from 0V to 0.5±0.1V, and when the first set voltage reaches 0.5±0.1V, the constant voltage is maintained for 30±5s to stimulate the PN junction carrier tunneling.

[0062] Optionally, the pulse voltage of the deposition stage is a bipolar pulse mode, the frequency of the forward voltage and the reverse voltage can both be 500±50Hz (for example: 450Hz, 500Hz, 550Hz, etc.), and the plating time can be determined by the height of the grid line to be prepared, which is not specifically limited here.

[0063] Optionally, the termination stage can be maintained at a constant voltage of 0.1±0.05V for 30±5s to eliminate residual stress.

[0064] The application will be further described in detail below in combination with examples.

[0065] Example 1 Texturing the front side and the back side of the substrate; Forming a front passivation layer (thickness 7nm) on the front side and a back passivation layer (thickness 7nm) on the back side; Forming an N-type doped layer on the front passivation layer; Forming an in-situ doped layer and a gradient doped layer on the back passivation layer in sequence.

[0066] The temperature for forming the in-situ doped layer is 180℃; when forming the in-situ doped layer, the volume ratio of SiH4 and H2 is 1:7, and the atomic ratio concentration of B is 3%. The thickness of the in-situ doped layer is 3nm.

[0067] The temperature for forming each sub-doped layer of the gradient doped layer is 180℃; when forming the P1 sub-doped layer, the P2 sub-doped layer, the P3 sub-doped layer, the P4 sub-doped layer and the P5 sub-doped layer in sequence, the volume ratio of SiH4 and H2 is 1:8, 1:9, 1:10, 1:11 and 1:12 respectively, and the atomic ratio concentration of B is 2.5%, 2%, 1.5%, 1% and 0.5% respectively. The thickness of the five layers of sub-doped layers is 2nm.

[0068] The total thickness of the P-type doped layer is 13nm.

[0069] Plating, the voltage rises from 0 to +0.5V in the initial stage, and is maintained at 0.5V for 30s in the constant voltage; in the deposition stage, the voltage is switched to a bipolar pulse mode, the forward voltage +0.3V accounts for 80% of the duty cycle, the reverse voltage -0.5V accounts for 20% of the duty cycle, and the frequency is 500Hz; in the termination stage, the voltage is reduced to +0.1V, and the constant voltage is maintained for 30s.

[0070] The concentration of copper ions in the electrolyte of the electroplating is 15 g / mL, and the pH of the electrolyte is 3.5; the electrolyte also contains 10 ml / L of an accelerator, 15 ml / L of a leveling agent, and 5 ml / L of an inhibitor.

[0071] The P-type doped layer of the prepared solar cell includes an in-situ doped layer (B doping concentration: 0.30×10 19 cm -3 ) formed on the back passivation layer, and five sub-doped layers (B doping concentration: 0.75×10 19 cm -3 , 0.85×10 19 cm -3 , 0.95×10 19 cm -3 , 1.05×10 19 cm -3 , and 1.15×10 19 ) formed on the in-situ doped layer in sequence.

[0072] Embodiment 2 Texturing is performed on the front side and the back side of the substrate; A front passivation layer (thickness: 2 nm) is formed on the front side, and a back passivation layer (thickness: 2 nm) is formed on the back side; An N-type doped layer is formed on the front passivation layer; An in-situ doped layer and a gradient doped layer are formed on the back passivation layer in sequence.

[0073] The temperature for forming the in-situ doped layer is 185 ℃; the volume ratio of SiH4 and H2 for forming the in-situ doped layer is 1:6.8, and the atomic ratio concentration of B is 3.2%. The thickness of the in-situ doped layer is 5 nm.

[0074] The temperature for forming each sub-doped layer of the gradient doped layer is 220 ℃; the volume ratio of SiH4 and H2 for forming the P1 sub-doped layer, the P2 sub-doped layer, the P3 sub-doped layer, the P4 sub-doped layer, and the P5 sub-doped layer in sequence is 1:7.8, 1:8.8, 1:9.8, 1:10.8, and 1:11.8, respectively; the atomic ratio concentration of B is 2.7%, 2.2%, 1.7%, 1.2%, and 0.7% in sequence. The thickness of the P1 sub-doped layer, the P2 sub-doped layer, the P3 sub-doped layer, the P4 sub-doped layer, and the P5 sub-doped layer is 1 nm, 1 nm, 2 nm, 3 nm, and 3 nm in sequence.

[0075] The total thickness of the P-type doped layer is 15 nm.

[0076] Electroplating, initial stage voltage from 0 to +0.4V, and maintain 0.4V for 35s; deposition stage, switch to bipolar pulse mode, positive voltage +0.2V duty cycle 85%, reverse voltage-0.4V duty cycle 15%, frequency of 550Hz; termination stage, the voltage is reduced to +0.05V, constant voltage for 35s.

[0077] The concentration of copper ions in the electrolyte for electroplating is 35g / mL, and the pH of the electrolyte is 4.5; the electrolyte also contains accelerant 20ml / L, leveling agent 7ml / L and inhibitor 10ml / L.

[0078] The P-type doped layer of the prepared solar cell includes an in-situ doped layer (B doping concentration: 0.70×10 19 cm -3 ) formed on the back passivation layer, and five sub-doped layers (B doping concentration: 0.80×10 19 cm -3 , 0.90×10 19 cm -3 , 1.00×10 19 cm -3 , 1.10×10 19 cm -3 , 1.20×10 19 ) formed on the in-situ doped layer in sequence.

[0079] Example 3 Texturing the front side and the back side of the substrate; Forming a front passivation layer (thickness 5nm) on the front side and a back passivation layer (thickness 5nm) on the back side; Forming an N-type doped layer on the front passivation layer; Forming an in-situ doped layer and a gradient doped layer on the back passivation layer in sequence.

[0080] The temperature for forming the in-situ doped layer is 175℃; the volume ratio of SiH4 and H2 for forming the in-situ doped layer is 1:7.2, and the atomic ratio concentration of B is 2.8%. The thickness of the in-situ doped layer is 4nm.

[0081] The temperature for forming each sub-doped layer of the gradient doping layer is 220℃. The volume ratios of SiH4 and H2 when forming the P1, P2, P3, P4, and P5 sub-doped layers are 1:8.2, 1:9.2, 1:10.2, 1:11.2, and 1:12.2, respectively, and the atomic concentrations of B are 2.3%, 1.8%, 1.3%, 0.8%, and 0.3%, respectively. The thicknesses of the P1, P2, P3, P4, and P5 sub-doped layers are 1.5 nm, 1.5 nm, 3 nm, 2 nm, and 2 nm, respectively.

[0082] The total thickness of the P-type doped layer is 14 nm.

[0083] In the initial stage of electroplating, the voltage is increased from 0 to +0.6V and maintained at a constant voltage of 0.6V for 25s. In the deposition stage, the voltage is switched to bipolar pulse mode, with a forward voltage of +0.4V and a duty cycle of 75% and a reverse voltage of -0.5V and a duty cycle of 25%, both at a frequency of 450Hz. In the final stage, the voltage is reduced to +0.15V and maintained at a constant voltage for 25s.

[0084] The concentration of copper ions in the electroplating electrolyte is 22 g / mL, and the pH of the electrolyte is 4.0. The electrolyte also contains 15 ml / L of accelerator, 10 ml / L of leveling agent, and 8 ml / L of inhibitor.

[0085] The p-type doped layer of the fabricated solar cell includes an in-situ doped layer formed on the back passivation layer (B doping concentration: 0.50 × 10⁻⁶). 19 cm -3 ), and five sub-doped layers formed sequentially in situ doped layers (B doping concentrations are 0.78 × 10⁻⁶ in sequence). 19 cm -3 0.88×10 19 cm -3 0.98×10 19 cm -3 1.09×10 19 cm -3 1.17×10 19 ).

[0086] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the P-type doped layer only includes an in-situ doped layer, and no gradient doped layer is formed. Other process parameters are the same as in Example 1.

[0087] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the volume ratio of SiH4 and H2 for forming the plurality of sub-doping layers is 1:8, and the atomic ratio concentration of B for forming the plurality of sub-doping layers is 2.5%. Other process parameters refer to Example 1.

[0088] The doping concentration of each sub-doping layer prepared is 0.75x10 19 cm -3 .

[0089] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the process parameters for preparing each sub-doping layer are the same as the process parameters for preparing the in-situ doped layer. Other process parameters refer to Example 1.

[0090] The doping concentration of each sub-doping layer is 0.30x10 19 cm -3 .

[0091] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the thickness of the front passivation layer and the back passivation layer is 9 nm. Other process parameters refer to Example 1.

[0092] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the temperature control for forming the sub-doping layer is 240°C. Other process parameters refer to Example 1.

[0093] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that during the deposition stage of electroplating, the pulse mode is not used, and only deposition is performed at a voltage of +0.3V. Other process parameters refer to Example 1.

[0094] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the concentration of copper ions in the electrolyte during electroplating is 40 g / mL. Other process parameters refer to Example 1.

[0095] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the concentration of copper ions in the electrolyte during electroplating is 10 g / mL. Other process parameters refer to Example 1.

[0096] The LID60 EL black sheet failure rate (LID refers to: Light-Induced Degradation) and the degradation power of each example and comparative example were detected, and the detection method refers to IEC TS 62941, IEC 61215-2:2021. The results are shown in Table 1.

[0097]

[0098] According to the results of Table 1, it can be seen from Comparative Examples 1-3 and Comparative Example 1 that, when a gradient doped layer is not prepared in the P-type doped layer during preparation of the solar cell, the solar cell cannot weaken the unintended tunneling current or interface recombination current, and thus it is difficult to reduce the risk of reverse breakdown of the PN junction under high electric field, and it is difficult to reduce the problem of damage to the passivation layer of the cell, and the LID 60 EL black sheet failure rate is increased.

[0099] It can be seen from Comparative Examples 1-3 and Comparative Example 2 that, when a gradient doped layer is not formed in the P-type doped layer during preparation of the solar cell, although other doped layers are added to the in-situ doped layer, the solar cell cannot weaken the unintended tunneling current or interface recombination current, and thus it is difficult to reduce the risk of reverse breakdown of the PN junction under high electric field, and it is difficult to reduce the problem of damage to the passivation layer of the cell, the LID 60 EL black sheet failure rate is increased, and the cell decay is increased.

[0100] It can be seen from Comparative Examples 1-3 and Comparative Examples 2 and 3 that, if the gradient doped layer and the in-situ doped layer do not form a difference in doping concentration, the black sheet failure rate will be further increased, and the cell decay will be further increased.

[0101] It can be seen from Comparative Examples 1-3 and Comparative Example 4 that, if the thickness of the front passivation layer and the back passivation layer is too large, the black sheet failure rate and the cell decay will be increased.

[0102] It can be seen from Comparative Examples 1-3 and Comparative Example 5 that, if the temperature is too high when forming the sub-doped layer, the black sheet failure rate and the cell decay will be increased.

[0103] It can be seen from Comparative Examples 1-3 and Comparative Example 6 that, if a pulse voltage is not used during electroplating, the double electric field charge accumulation cannot be eliminated, and thus the black sheet failure rate and the cell decay will be increased.

[0104] It can be seen from Comparative Examples 1-3 and Comparative Examples 7 and 8 that, if the concentration of copper ions in the electrolyte is too high or too low during electroplating, it is difficult to inhibit the growth of dendrites, and thus the black sheet failure rate and the cell decay will be increased; among them, the adverse effects are more significant when the concentration of copper ions is too high.

[0105] In summary, the solar cell prepared by the preparation method of the present application can weaken the unintended tunneling current or interface recombination current, reduce the risk of reverse breakdown of the PN junction under high electric field, and thus improve the problem of damage to the passivation layer of the cell (such as amorphous silicon layer corrosion or grain boundary defects), improve the performance of the passivation layer and the doped layer of the cell sheet, and thus improve the reliability of the solar cell and increase the yield of the solar cell.

[0106] The above merely describes the preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A solar cell, characterized by, The solar cell comprises: a substrate having a front surface and a back surface; a front passivation layer formed on the front surface; a back passivation layer formed on the back surface; an N-type doped layer formed on the front passivation layer; a P-type doped layer, wherein the P-type doped layer comprises an in-situ doped layer formed on the back passivation layer and a gradient doped layer formed on the in-situ doped layer; the doping concentration of the in-situ doped layer is less than that of the gradient doped layer.

2. The solar cell according to claim 1, characterized in that, The gradient doped layer comprises at least two sub-doped layers stacked in sequence, the doping concentration of at least two sub-doped layers increases in sequence, and the doping concentration of the sub-doped layer formed on the in-situ doped layer is greater than that of the in-situ doped layer.

3. The solar cell according to claim 2, characterized in that, a difference between the doping concentrations of two adjacent sub-doping layers is greater than or equal to 0.05 x 10 19 cm -3 ; and / or, The difference between the doping concentrations of two adjacent sub-doping layers is less than or equal to 0.15 x 10 19 cm -3 .

4. The solar cell according to claim 2 or 3, characterized in that, The in-situ doped layer has a doping concentration of 0.30 x 10 19 cm -3 -0.70 x 10 19 cm -3 ; and / or, The doping concentration of any one of the sub-doped layers is in the range of 0.75xlO 19 1.20xlO 19 cm -3 .

5. The solar cell according to claim 4, characterized in that, The gradient doped layer comprises five sub-doped layers arranged in sequence; from the back passivation layer to the in-situ doped layer, the concentration of the five sub-doped layers is: 0.75*10 19 cm -3 ~0.80*10 19 cm -3 , 0.85*10 19 cm -3 ~0.90*10 19 cm -3 , 0.95*10 19 cm -3 ~1.00*10 19 cm -3 , 1.05*10 19 cm -3 ~1.10*10 19 cm -3 , 1.15*10 19 ~1.20*10 19 cm -3 .

6. The solar cell according to any one of claims 1 to 3, wherein The thickness of at least one of the front passivation layer and the back passivation layer is 2-7 nm.

7. The method of producing a solar cell according to any one of claims 1 to 6, wherein The solar cell comprises: texturing the front surface and the back surface of a substrate; forming a front passivation layer on the front surface and a back passivation layer on the back surface; forming an N-type doped layer on the front passivation layer; forming an in-situ doped layer and a gradient doped layer on the back passivation layer in sequence; wherein the doping concentration of the in-situ doped layer is less than that of the gradient doped layer by controlling the volume ratio of SiH4 and H2 and the atomic ratio concentration of B.

8. The method of producing a solar cell according to claim 7, wherein When forming the in-situ doped layer and the gradient doped layer, the volume ratio of SiH4 and H2 is controlled to be 1:7±0.2-1:12±0.2, and the volume ratio of SiH4 and H2 for forming the in-situ doped layer is less than that for forming the gradient doped layer; and / or, When forming the in-situ doped layer and the gradient doped layer, the atomic ratio concentration of B is controlled to be 0.5±0.2-3±0.2%, and the atomic ratio concentration of B for forming the in-situ doped layer is less than that for forming the gradient doped layer.

9. The method of producing a solar cell according to claim 8, wherein When forming at least two sub-doped layers of the gradient doped layer in sequence, the volume ratio of SiH4 and H2 decreases layer by layer; and / or, When forming at least two sub-doped layers of the gradient doped layer in sequence, the atomic ratio concentration of B increases layer by layer.

10. The method of producing a solar cell according to claim 7, wherein The temperature for forming the gradient doped layer is 180-220°C.

11. The method of producing a solar cell according to claim 7, wherein The preparation method of the solar cell further comprises: forming a transparent conductive layer on the N-type doped layer and the gradient doped layer, respectively; forming a seed layer on the transparent conductive layer; electroplating to form a grid line on the seed layer; wherein, the concentration of copper ions in the electrolyte used in the electroplating is 15-35 g / L; and / or, the voltage during the electroplating is less than 3V.

12. The method of producing a solar cell according to claim 11, wherein The process of the electroplating comprises an initial stage, a deposition stage and a termination stage, the initial stage comprises maintaining a first set voltage for a first set time; the deposition stage comprises performing under pulse conditions; the termination stage comprises maintaining a second set voltage for a second set time; wherein, the first set voltage, the voltage of the pulse, and the second set voltage are all less than 3V.

13. The method of producing a solar cell according to claim 12, wherein the first set voltage is a forward voltage of 0.5±0.1V; and / or, The pulse conditions include a forward voltage of 0.3±0.1V with a duty cycle of 80±5%, a reverse voltage of 0.5±0.1V with a duty cycle of 20±5%; and / or, The second set voltage is a forward voltage of 0.1±0.05V.

Images