Electron passivation contact structure, preparation method and solar cell

Abstract

The invention relates to the field of semiconductor manufacturing, in particular to an electron passivation contact structure, a preparation method and a solar cell. The electron passivation contact structure comprises a silicon substrate, a tunneling layer and a titanium dioxide layer which are sequentially stacked, wherein the titanium dioxide layer comprises a first titanium dioxide sub-layer and a second titanium dioxide sub-layer which are arranged along the thickness direction; the titanium dioxide layer is continuously deposited through an atomic layer deposition process to form a first titanium dioxide sub-layer and a second titanium dioxide sub-layer, the first titanium dioxide sub-layer is of an amorphous structure, and the second titanium dioxide sub-layer is of a crystalline structure.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and in particular to an electronic passivation contact structure, a preparation method and a solar cell. Background Art

[0002] As the core device for converting solar energy into electrical energy, the performance optimization and improvement of solar cells is an important research direction in the global photovoltaic industry and scientific research field. In high-efficiency crystalline silicon solar cells, the design of electronic passivation contact structure is very important for improving the open circuit voltage (V OC ), fill factor (FF) and photoelectric conversion efficiency (η) are crucial.

[0003] In the prior art, the passivation contact structure is usually composed of multiple layers of thin films, including a passivation layer, a carrier selection layer, and a transparent conductive oxide (TCO). The synergistic effect of these films can effectively avoid the recombination loss at the metal-silicon interface, thereby improving the efficiency of the device. However, due to the optical absorption characteristics of TCO and the design limitations of the composite film, the parasitic absorption problem is difficult to avoid, resulting in further limitations on the improvement of the photoelectric conversion efficiency.

[0004] To solve the above problems, titanium dioxide is widely used in electron transport layers due to its high dielectric constant, low resistivity and good match with the silicon conduction band position. The low work function of titanium dioxide facilitates the extraction and transmission of electrons, and its chemical stability also provides advantages for the long-term maintenance of device performance. However, the passivation effect and conductivity of existing titanium dioxide films are limited, and only a maximum conversion efficiency of 22.1% is achieved in specific applications, and the open circuit voltage (V OC ) is only 674mV, which is much lower than the theoretical value. Summary of the invention

[0005] The object of the present invention is to provide an electronic passivation contact structure, which can simultaneously achieve enhanced passivation effect and improved electronic transmission performance.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an electronic passivation contact structure, comprising a silicon substrate, a tunneling layer and a titanium dioxide layer stacked in sequence, the titanium dioxide layer comprising a first titanium dioxide sublayer and a second titanium dioxide sublayer arranged along the thickness direction; the titanium dioxide layer is continuously deposited by an atomic layer deposition process to form a first titanium dioxide sublayer and a second titanium dioxide sublayer, wherein the first titanium dioxide sublayer is an amorphous structure and the second titanium dioxide sublayer is a crystalline structure.

[0007] Further, the first titanium dioxide sublayer is an amorphous titanium dioxide layer formed by doping a precursor with magnesium and / or aluminum, and the doping concentration of magnesium and / or aluminum is 1wt%-10wt%; The second titanium dioxide sublayer is a crystalline titanium dioxide layer formed by doping a precursor with zinc and / or gallium, wherein the doping concentration of zinc and / or gallium is 5wt%-20wt%.

[0008] Further, the mass ratio of magnesium and aluminum doped by the precursor in the first titanium dioxide sublayer ranges from 80:20 to 20:80; The mass ratio of zinc to gallium doped by a precursor in the second titanium dioxide sublayer ranges from 70:30 to 30:70.

[0009] Furthermore, the thickness of the first titanium dioxide sublayer is 1 nm-5 nm, and the thickness of the second titanium dioxide sublayer is 5 nm-50 nm.

[0010] Further, the first titanium dioxide sublayer is formed by a single cycle mode in an atomic layer deposition process, wherein the cycle ratio of the main deposition cycle to the doping cycle is (20-100):1; The second titanium dioxide sublayer is formed by a super-cycle mode in an atomic layer deposition process, wherein the cycle ratio of the main deposition cycle to the doping cycle is (10-50):1.

[0011] Furthermore, the electronic passivation contact structure further includes a hydrogen-containing capping layer stacked on the titanium dioxide layer.

[0012] The present application also provides a method for preparing an electronically passivated contact structure, comprising: providing a silicon substrate; forming a tunneling layer on the silicon substrate; The first titanium dioxide sublayer and the second titanium dioxide sublayer are continuously deposited by an atomic layer deposition process to finally form an overall titanium dioxide layer; wherein: the first titanium dioxide sublayer is doped with a magnesium and / or aluminum precursor through a single cycle mode, and the doping concentration is controlled to be 1wt%-10wt% to form an amorphous structure; the second titanium dioxide sublayer is doped with a zinc and / or gallium precursor through a super cycle mode, and the doping concentration is controlled to be 5wt%-20wt% to form a crystalline structure; A hydrogen-containing capping layer is deposited on the titanium dioxide layer.

[0013] Furthermore, the method for preparing the electronic passivation contact structure further includes removing the hydrogen-containing capping layer.

[0014] The present application also provides a solar cell, comprising the above-mentioned electron passivation contact structure, wherein the electron passivation contact structure is located on the light-receiving surface and / or the backlight surface of the solar cell.

[0015] The beneficial effects of the present invention are as follows: the electronic passivation contact structure of the present application utilizes the titanium dioxide layer to simultaneously achieve enhanced passivation effect and improved electron transmission performance. Specifically, the titanium dioxide layer is divided into two layers along the thickness direction, wherein the first titanium dioxide sublayer is an amorphous structure, which can effectively reduce interface defect states and significantly reduce the interface recombination rate, thereby providing excellent interface passivation performance; the second titanium dioxide sublayer is a crystalline structure, which can increase the electron concentration and reduce the film work function, significantly improve the electron transmission performance and mobility, and has higher conductivity, further optimizes the electron selective transmission function, and enhances the efficiency of the overall device. Compared with existing transparent conductive oxides (TCOs), the electronic passivation contact structure of the present application has lower parasitic absorption characteristics in the light absorption band, thereby improving the short-circuit current density (J SC ) and ultimately improve the photoelectric conversion efficiency.

[0016] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of an electronic passivation contact structure according to an embodiment of the present application is shown; Figure 2-1 to Figure 2-3 A comparison diagram of carrier lifetime, electron mobility and work function of titanium dioxide layer under different doping conditions is shown; Figure 3 A schematic flow chart showing a method for preparing an electronic passivation contact structure according to an embodiment of the present invention is shown; Figure 4 A schematic structural diagram of a solar cell shown in an embodiment of the present application is shown; Figure 5 A schematic structural diagram of a solar cell shown in another embodiment of the present application is shown. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0020] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Figure 1 FIG. 2 shows a schematic structural diagram of an electronically passivated contact structure according to an embodiment of the present invention. Figure 1 As shown, the electron passivation contact structure includes a silicon substrate 10, a tunneling layer 20, a titanium dioxide layer 30 and a hydrogen-containing capping layer 40 which are stacked in sequence, and the titanium dioxide layer 30 includes a first titanium dioxide sublayer and a second titanium dioxide sublayer arranged along the thickness direction; the titanium dioxide layer 30 is continuously deposited by an atomic layer deposition process to form a first titanium dioxide sublayer and a second titanium dioxide sublayer, wherein the first titanium dioxide sublayer is an amorphous structure for interface passivation; the second titanium dioxide sublayer is a crystalline structure for increasing electron concentration, mobility and reducing work function.

[0023] The electronic passivation contact structure of the present application utilizes the titanium dioxide layer 30 to simultaneously achieve enhanced passivation effect and improved electron transmission performance. Specifically, the titanium dioxide layer 30 is divided into two layers along the thickness direction, wherein the first titanium dioxide sublayer 31 is an amorphous structure, which can effectively reduce interface defect states and significantly reduce the interface recombination rate, thereby providing excellent interface passivation performance; the second titanium dioxide sublayer 32 is a crystalline structure, which can increase the electron concentration and reduce the film work function, significantly improve the electron transmission performance and mobility, and has higher conductivity, further optimizes the electron selective transmission function, and enhances the efficiency of the overall device. Compared with the existing transparent conductive oxide (TCO), the electronic passivation contact structure of the present application has lower parasitic absorption characteristics in the light absorption band, thereby improving the short-circuit current density (J SC ) and ultimately improve the photoelectric conversion efficiency.

[0024] It should be noted that existing studies have shown that titanium dioxide can achieve interface passivation effects and electron selective transmission performance. The inventors used this property of titanium dioxide and initially tried to uniformly dope a single component (such as magnesium, aluminum, zinc, gallium, hydrogen, and boron) in the titanium dioxide layer 30, hoping to optimize the interface passivation effect and electron transmission performance by adjusting the doping concentration as a whole. However, as known in the art, it is difficult to balance interface passivation and electron transmission performance. Low doping concentration is conducive to interface passivation, but the electron concentration and mobility are insufficient, and the open circuit voltage (V OC ) and fill factor (FF), while high doping concentration can improve the electron transmission performance, but the interface defects increase and the interface recombination rate rises, resulting in an overall decrease in device efficiency. At the same time, when the thickness of the doping layer exceeds a certain value, the accumulation of interface defects and the reduction of material conductivity lead to a significant decrease in transmission efficiency.

[0025] In order to break through the limitation of single doping, the inventors further tried to use a single-layer titanium dioxide layer with gradient doping or composite doping. In the gradient doping scheme, the inventors gradually changed the doping concentration in the titanium dioxide layer (such as from low doping to high doping) to achieve a balance between interface passivation and electron transport performance. However, the preparation process window of gradient doping is narrow, the doping concentration distribution is difficult to control uniformly, and the experiment shows poor reproducibility. In the conformal doping scheme, by simultaneously doping multiple elements (such as magnesium, aluminum, zinc, gallium, hydrogen, and boron) in the titanium dioxide layer, it is hoped that the overall performance will be optimized through the synergistic effect between the doping components. However, multiple doping components are prone to diffusion during high-temperature deposition or annealing, resulting in uneven doping distribution, increased interface state density, and reduced device performance.

[0026] Due to the above problems, the inventors gave up the idea of ​​continuing to rely on the doping optimization or gradient adjustment of single-layer materials. However, through the above experiments and comparison of the experimental results, it was found that the low-doped amorphous structure can provide excellent interface passivation effect, reduce the interface defect density and carrier recombination rate, and the highly doped crystalline structure can increase the electron concentration and mobility, reduce the work function and enhance the electron selective transmission performance. On this basis, the inventors changed their ideas and first tried to deposit the first titanium dioxide layer and the second titanium dioxide layer in sequence. However, this structure has the following problems: Since the first titanium dioxide layer and the second titanium dioxide layer are two independent structures, there are many interface defects and there is a large stress at the interface, resulting in poor interface stability; and due to the stress and interface defects, the electron transmission performance is poor.

[0027] On this basis, attempts were made to divide the titanium dioxide layer into two layers, and to dope different elements into the two titanium dioxide layers to form an amorphous structure in the lower layer and a crystalline structure in the upper layer. At the same time, by trying various processes and data analysis, it was finally confirmed that the use of atomic layer deposition process to continuously deposit the first titanium dioxide sublayer 31 and the second titanium dioxide sublayer 32 can avoid the problem of inconsistent performance caused by edge effects, thereby obtaining an electronic passivation contact structure that can simultaneously achieve enhanced passivation effect and improved electron transmission performance.

[0028] In this scheme, there may be a transition zone using the atomic layer deposition process, and the transition zone may cause uneven performance or interface problems. In order to enhance the independence of the passivation effect and the electron transport performance, in this scheme, a clear interface is formed between the first titanium dioxide sublayer 31 and the second titanium dioxide sublayer 32, and there is no transition zone. In order to achieve this purpose: in the preparation process, a cleaning gas (such as nitrogen and / or hydrogen) is introduced when switching the precursor to remove the precursor residue on the surface of the first sublayer. Of course, if no transition zone is set, there may be a lattice mismatch problem.

[0029] In order to ensure the stability of the layer structure and the optimization of functions while reducing the lattice mismatch problem, in one embodiment, the first titanium dioxide sublayer 31 is an amorphous titanium dioxide layer 30 formed by doping magnesium and / or aluminum by a precursor, and the doping concentration of magnesium and / or aluminum is 1wt%-10wt%, for example, 1wt%, 5wt% or 10wt%; the second titanium dioxide sublayer 32 is a crystalline titanium dioxide layer 30 formed by doping zinc and / or gallium by a precursor, wherein the doping concentration of zinc and / or gallium is 5wt%-20wt%, for example: 5wt%, 10wt%, 13wt%, 15wt% or 20wt%.

[0030] It should be noted that in the present application, the first titanium dioxide sublayer 31 and the second titanium dioxide sublayer 32 are formed into an amorphous titanium dioxide layer 30 and a crystalline titanium dioxide layer 30 respectively by doping a precursor, and the inventors have actually tried to use a solution of doping ions (for example: doping magnesium ions, aluminum ions, zinc ions and gallium ions). Although similar interface passivation effects can be achieved by adjusting the doping amount and changing the manufacturing process, when ion doping is used, the doping amount is usually high, and the doping concentration needs to be increased accordingly to ensure an effect similar to that of precursor doping. In actual operation, the doping amount is not easy to control accurately, and there will be problems of uneven doping and greater control difficulty.

[0031] The present application adopts a precursor doping scheme. Compared with the ion doping scheme, the precursor can usually achieve a better doping effect at a low doping concentration and has better uniformity. In addition, the doping concentration can be accurately controlled by atomic layer deposition (ALD), and the operation difficulty is relatively low. In the precursor doping scheme, annealing can remove possible doping source residues and ensure the quality and doping effect of the titanium dioxide layer 30, thereby optimizing the electronic structure and interface properties of the film. Unlike the ion doping scheme, the deposition of the precursor is usually carried out at a lower temperature (such as 100-200°C), which is conducive to the formation of a thin and uniform titanium dioxide layer 30 on the surface of the silicon substrate without causing excessive thermal impact on the silicon substrate 10.

[0032] In the electronic passivation contact structure, the appropriate thickness helps to balance the interface passivation effect and the electron transmission performance, wherein the thickness of the first titanium dioxide sublayer 31 must be thin enough to maintain good interface passivation while avoiding the obstruction of the electron tunneling effect caused by excessive thickness; the thickness of the second titanium dioxide sublayer 32 needs to ensure that the interface resistance is not increased too much while improving the electron concentration and mobility. However, if the first titanium dioxide sublayer 31 is too thin, the passivation will be incomplete and the interface defect states will increase; if the second titanium dioxide sublayer 32 is too thick, the work function regulation will fail and the electron injection efficiency will decrease. In order to obtain the appropriate thickness, the inventor finally obtained the preferred solution through a large number of experimental adjustments: the thickness of the first titanium dioxide sublayer 31 is 1nm-5nm, for example, the thickness can be 1nm, 3nm, 4nm or 5nm, and the thickness of the second titanium dioxide sublayer 32 is 5nm-50nm, for example, the thickness can be 5nm, 10nm, 25nm, 40nm or 50nm. It should be noted that the setting of the above thickness can also further reduce the lattice mismatch.

[0033] As mentioned above, in the first titanium dioxide sublayer 31, the doping element can be either single magnesium or aluminum, or a combination of magnesium and aluminum; correspondingly, in the second titanium dioxide sublayer 32, the doping element can be either single zinc or gallium, or a combination of zinc and gallium.

[0034] Figure 2-1 , Figure 2-2 , Figure 2-3 A comparison diagram of carrier lifetime, electron mobility and work function of the titanium dioxide layer 30 in the present application under different doping conditions is shown. In the above embodiment, the doping concentration of magnesium and / or aluminum in the first titanium dioxide sublayer 31 is 5wt%, and the mass ratio is 50:50; the doping concentration of zinc and / or gallium in the second titanium dioxide sublayer 32 is 10wt%, and the mass ratio is 70:30. Figure 2-1 This is a comparison chart of carrier lifetimes obtained through μ-PCD testing. It can be seen from the figure that the passivation effect of Mg+Al combined doping is better than that of single element doping; Figure 2-2 This is a comparison diagram of electron mobility obtained through Hall effect testing. It can be seen from the figure that the conductivity of Mg+Al combined doping is better than that of single element doping; Figure 2-3 This is a comparison diagram of the work function obtained through UPS testing. It can be seen from the figure that the work function of Mg+Al combination doping is lower than that of single element doping.

[0035] According to the experimental results, the present application finally selects a combination of magnesium and aluminum doped in the first titanium dioxide sublayer 31, and a combination of zinc and gallium doped in the second titanium dioxide sublayer 32. In one embodiment, for the first titanium dioxide sublayer 31, the mass ratio of magnesium and aluminum introduced by the precursor is preferably set in the range of 80:20 to 20:80, for example, 80:20, 50:50 or 20:80; for the second titanium dioxide sublayer 32, the mass ratio of zinc and gallium introduced by the precursor is preferably set in the range of 70:30 to 30:70, for example, 70:30, 50:50 or 30:70.

[0036] In this embodiment, the first titanium dioxide sublayer 31 is formed by a single cycle mode in an atomic layer deposition process, each single cycle includes several main deposition cycles and doping cycles, wherein the cycle ratio of the main deposition cycle to the doping cycle is (20~100):1, for example, the cycle ratio can be 20:1, 30:1, 50:1, 60:1, 80:1 or 100:1; the second titanium dioxide sublayer 32 is formed by a super cycle mode in an atomic layer deposition (ALD) process, each super cycle includes several main deposition cycles and doping cycles, wherein the cycle ratio of the main deposition cycle to the doping cycle is (10-50):1, for example, the cycle ratio can be 10:1, 20:1, 30:1, 35:1, 40:1 or 50:1. The first titanium dioxide sublayer 31 deposited by adopting a single cycle mode has good passivation performance, can effectively reduce the interface defect density, and provide sufficient electrical uniformity. By adjusting the cycle ratio of the main deposition cycle and the doping cycle by the super cycle mode, the zinc and / or gallium doping concentration can be precisely controlled to avoid excessive doping or uneven distribution. Among them, the high cycle ratio of the main deposition cycle helps to form a high-quality crystalline titanium dioxide substrate structure, while the doping cycle introduces zinc and / or gallium at an appropriate ratio, which improves electron mobility and reduces the work function while ensuring the integrity of the crystal structure. By setting the cycle ratio, it is possible to avoid the problem of doping ion aggregation due to too high a doping cycle ratio, introducing additional defects, and reducing interface performance.

[0037] The tunneling layer 20 is used to provide an efficient tunneling channel for electrons and passivate interface defects to reduce carrier recombination. In the present embodiment, the tunneling layer 20 is silicon dioxide with a thickness of 0.5nm-2nm, for example, the thickness may be 0.5nm, 1nm, 1.5nm or 2nm. In other embodiments, the tunneling layer 20 may also be aluminum oxide or hafnium dioxide, and the corresponding thickness may be 1nm-3nm or 0.3nm-1.5nm, respectively. By setting the thickness of the tunneling layer 20, the carrier passivation effect and the tunneling efficiency can be balanced.

[0038] In this embodiment, the thickness of the hydrogen-containing cap layer 40 is set at 3nm-10nm, for example, the thickness may be 3nm, 7nm or 10nm. In other embodiments, the hydrogen-containing cap layer 40 may also be removed.

[0039] Figure 3 A schematic flow chart of a method for preparing an electronically passivated contact structure according to Embodiment 1 of the present invention is shown. The steps for preparing the electronically passivated contact structure are as follows: Step S10: providing a silicon substrate 10; The silicon substrate 10 is cleaned to remove surface contaminants and a natural oxide layer to ensure uniformity of subsequent deposition.

[0040] Step S20: forming a tunneling layer 20 on the silicon substrate 10; An atomic layer deposition (ALD) process is used, silicon tetrachloride is used as a silicon source precursor, and water is used as an oxidant to deposit silicon dioxide on a silicon substrate 10 to form a tunneling layer 20. The thickness is controlled to be 0.5 nm-2 nm, for example, 0.5 nm, 1.5 nm or 2 nm. In this embodiment, the thickness is 1 nm. The deposition temperature is controlled to be 250° C.-300° C., for example, 260° C., 275° C. or 300° C. In this embodiment, the deposition temperature is controlled to be 250° C. The specific number of cycles is determined according to the deposition rate of the device, and is generally 50-100 cycles, for example, 50 cycles, 80 cycles or 100 cycles.

[0041] Step S30: A first titanium dioxide sub-layer 31 and a second titanium dioxide sub-layer 32 are continuously deposited by an atomic layer deposition (ALD) process, and finally an overall titanium dioxide layer 30 is formed. Step S31: depositing a first titanium dioxide sublayer 31; Atomic layer deposition (ALD) process is used, titanium tetrachloride is used as a titanium source precursor, magnesium acetylacetone and trimethylaluminum are introduced as dopant drivers, and magnesium and aluminum co-doping of titanium dioxide-based films is achieved through a co-deposition process. The doping concentration range is controlled at 1wt%-10wt%, for example, 1wt%, 5wt% or 10wt%. In this embodiment, the doping concentration range is controlled at 5wt%, and the mass ratio of magnesium to aluminum is set to 80:20 to 20:80, for example, 80:20, 40:60, 60:40 or 20:80. In this embodiment, the mass ratio is set to 50:50. The deposition temperature is set to 100°C-200°C, for example, 100°C, 130°C, 170°C or 200°C. In this embodiment, the deposition temperature is set to 150°C. Within this temperature range, the first titanium dioxide sublayer 31 of an amorphous structure is formed by adjusting the number of reaction cycles, and its thickness is controlled within the range of 1nm-5nm, for example, 1nm, 2nm, 3nm, 4nm or 5nm; a single cycle mode is adopted, and the cycle ratio of the main deposition cycle to the doping cycle is (20~100):1, for example, 10:1, 30:1, 50:1, 70:1 or 100:1; Step S32: In the same reaction chamber, the atomic layer deposition (ALD) process is continued. On the basis of titanium tetrachloride as a titanium source precursor, dimethyl zinc and trimethyl gallium are introduced as co-doping precursors, and the simultaneous doping of zinc and gallium is achieved by alternating pulse precursors. The doping concentration range is set to 5wt%-20wt%, for example: 5wt%, 13wt%, 15wt% or 20wt%. In this embodiment, the doping concentration range is set to 10wt%, and the mass ratio of zinc to gallium is set to 70:30 to 30:70, for example, 60:40, 50:50, 40:60 or 30:70. In this embodiment, the mass ratio is set to 70:30. The deposition temperature is set to 100°C-200°C, for example, 100°C, 130°C, or 170°C. In this embodiment, the deposition temperature is set to 200°C. In this temperature range, by regulating the number of reaction cycles, a second titanium dioxide sublayer 32 with a crystalline structure is formed, and its thickness is controlled within the range of 5nm-50nm, for example, 5nm, 15nm, 25nm, 40nm or 50nm. In this embodiment, the thickness is 10nm. In the super cycle mode, the cycle ratio of the main deposition cycle to the doping cycle is (10-50):1, for example, 10:1, 20:1, 40:1 or 50:1. In this embodiment, the cycle ratio is set to 30:1.

[0042] In the above scheme, in order to form a clear interface between the first titanium dioxide sublayer 31 and the second titanium dioxide sublayer 32 without forming a transition zone therebetween, the present embodiment also adopts: before step S32, a cleaning gas (such as nitrogen and / or hydrogen) is introduced when switching the precursor to remove the precursor residue on the surface of the first titanium dioxide sublayer 31. Specifically: a mixed gas of 95% nitrogen + 5% hydrogen is used to remove part of the precursor in step S32, and the cleaning time is set to 3-10 seconds, for example, 3 seconds, 6 seconds, 10 seconds. In the present embodiment, the cleaning time is set to 5 seconds.

[0043] Step S40: depositing a hydrogen-containing capping layer on the titanium dioxide layer; A low-temperature atomic layer deposition (ALD) process is adopted to react dimethylsilane or triethylborane or a silane hydrogen-containing precursor with water or ozone to form a hydroxide-doped silicon or hydroxide-doped boron silicon film, wherein the deposition temperature is set to 100°C-200°C, for example, 100°C, 130°C, 170°C or 200°C. In the present embodiment, the deposition temperature is set to 200°C, and the film thickness is controlled between 3nm-10nm, for example, 3nm, 4nm, 8nm or 10nm. In the present embodiment, the film thickness is controlled to be 5nm.

[0044] Step S50: annealing treatment; Low temperature annealing is performed in an inert atmosphere (nitrogen or argon) to improve interface bonding and doping uniformity. The annealing temperature is 300°C-400°C, for example, 350°C or 400°C. In this embodiment, the temperature is controlled at 300°C, the annealing time is set to 10 minutes, and the gas flow rate is set to 100 sccm.

[0045] The electronic passivation contact structure formed by the above preparation method can simultaneously enhance the passivation effect and improve the electron transmission performance, and at the same time, it can effectively alleviate the lattice mismatch problem. On the basis of the above scheme, in the preparation method, by limiting the deposition temperature, doping mass ratio and deposition mode, it is helpful to form a clear transition interface, so that there is no need to introduce other transition layers, reducing the manufacturing difficulty.

[0046] In another embodiment, the magnesium precursor may also be magnesium dimethylaminoformyl. It should be noted that, in addition to the above precursors, the inventors have also tried to use other precursors instead, such as titanium tetraisobutanol or titanium tetraacetylacetone, magnesium ethoxy compounds or magnesium methyl compounds, diethylaluminum hydride, zinc chloride, triethylgallium, etc., but in the end they were not ideal (such as low volatility and other problems) and were abandoned. The above precursors are relatively excellent in volatility, reactivity, stability and by-products. For example, most by-products are gaseous (such as hydrogen chloride, methane), which reduces the contamination of the film and is easy to remove.

[0047] The embodiment of the invention provides an electronic passivation contact structure. The electronic passivation contact structure can be applied to a battery, and the electronic passivation contact structure is located on the light-receiving surface and / or the backlight surface of the solar cell. The specific structures of two examples of solar cells are described in detail below.

[0048] Embodiment 1 Ginseng Figure 4 The figure shows a schematic diagram of an electronic passivation contact structure applied to a BC battery, which includes a silicon substrate 101, an n-type heavily doped layer 102 (i.e., a tunneling layer), a titanium dioxide layer 103, and a silicon nitride anti-reflection layer 104 (hydrogen-containing cap layer) deposited in sequence on the front side of the silicon substrate 101, and a P+ emitter layer 105, an n+ BSF layer 106, a passivation layer 107, and a metal electrode 108 deposited in sequence on the back side of the silicon substrate 101.

[0049] In other embodiments, the electronic passivation contact structure can also be removed after the hydrogen-containing capping layer is removed. In this case, the titanium dioxide layer serves as the front passivation layer structure in the current BC solar cell structure.

[0050] Embodiment 2 Ginseng Figure 5The figure shows a schematic diagram of an electronic passivation contact structure applied to a BC / perovskite stacked cell, which includes a silicon substrate 201, an n-type heavily doped layer 202 (i.e., a tunneling layer), a titanium dioxide layer 203, a silicon nitride anti-reflection layer 204 (i.e., a hydrogen-containing capping layer) deposited in sequence on the front side of the silicon substrate 201, a composite layer 209, a perovskite hole transport layer 210, a perovskite layer 211, a fullerene C60 layer 212, a tin dioxide layer 213, a transparent conductive layer 214, an anti-reflection layer 215, and a silver electrode 216, and a P+ emitter layer 205, an n+BSF layer 206, a passivation layer 207, and a metal electrode 208 deposited in sequence on the back side of the silicon substrate 201.

[0051] In other embodiments, the electronic passivation contact structure can also be removed after the hydrogen-containing capping layer is removed. In this case, the titanium dioxide layer serves as the front passivation layer structure in the current BC solar cell structure.

[0052] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An electronically passivated contact structure, characterized in that: It includes a silicon substrate, a tunneling layer and a titanium dioxide layer which are stacked in sequence, wherein the titanium dioxide layer includes a first titanium dioxide sublayer and a second titanium dioxide sublayer which are arranged along the thickness direction; the titanium dioxide layer is continuously deposited by an atomic layer deposition process to form the first titanium dioxide sublayer and the second titanium dioxide sublayer, wherein the first titanium dioxide sublayer is an amorphous structure, and the second titanium dioxide sublayer is a crystalline structure.

2. The electronic passivation contact structure according to claim 1, characterized in that: The first titanium dioxide sublayer is an amorphous titanium dioxide layer formed by doping a precursor with magnesium and / or aluminum, and the doping concentration of magnesium and / or aluminum is 1wt%-10wt%; The second titanium dioxide sublayer is a crystalline titanium dioxide layer formed by doping a precursor with zinc and / or gallium, wherein the doping concentration of zinc and / or gallium is 5wt%-20wt%.

3. The electronic passivation contact structure according to claim 1, characterized in that: The mass ratio of magnesium to aluminum doped by a precursor in the first titanium dioxide sublayer ranges from 80:20 to 20:80; The mass ratio of zinc to gallium doped by a precursor in the second titanium dioxide sublayer ranges from 70:30 to 30:

70.

4. The electronic passivation contact structure according to claim 1, characterized in that: The thickness of the first titanium dioxide sublayer is 1nm-5nm; The thickness of the second titanium dioxide sublayer is 5 nm-50 nm.

5. The electronic passivation contact structure according to claim 1, characterized in that: The first titanium dioxide sublayer is formed by a single cycle mode in an atomic layer deposition process, wherein the cycle ratio of the main deposition cycle to the doping cycle is (20-100):1; The second titanium dioxide sublayer is formed by a super-cycle mode in an atomic layer deposition process, wherein the cycle ratio of the main deposition cycle to the doping cycle is (10-50):

1.

6. The electronic passivation contact structure according to claim 1, characterized in that: The electronically passivating contact structure further includes a hydrogen-containing capping layer stacked on the titanium dioxide layer.

7. A method for preparing an electronically passivated contact structure, characterized in that: include: providing a silicon substrate; forming a tunneling layer on the silicon substrate; A first titanium dioxide sublayer and a second titanium dioxide sublayer are continuously deposited by an atomic layer deposition process to finally form an integral titanium dioxide layer; the first titanium dioxide sublayer is an amorphous structure, and the second titanium dioxide sublayer is a crystalline structure; A hydrogen-containing capping layer is deposited on the titanium dioxide layer.

8. The preparation method according to claim 7, characterized in that: The first titanium dioxide sublayer is doped with magnesium and / or aluminum precursors through a single cycle mode, and the doping concentration is controlled to be 1wt%-10wt% to form an amorphous structure; the second titanium dioxide sublayer is doped with zinc and / or gallium precursors through a super cycle mode, and the doping concentration is controlled to be 5wt%-20wt% to form a crystalline structure.

9. The preparation method according to claim 7, characterized in that: The method for preparing the electronic passivation contact structure further includes removing the hydrogen-containing capping layer.

10. A solar cell, characterized in that: The solar cell comprises the electron passivation contact structure according to any one of claims 1 to 6, and the electron passivation contact structure is located on the light-receiving surface and / or the backlight surface of the solar cell.

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