CN114695579A - Solar cells and photovoltaic modules - Google Patents

Abstract

The embodiment of the application relates to the field of photovoltaics, in particular to a solar cell and a photovoltaic module, which comprise a substrate, a tunneling layer, a field passivation layer, a first passivation film and a first electrode, wherein the tunneling layer, the field passivation layer and the first passivation film are sequentially arranged on the back surface of the substrate; the doping concentration of the first doping element in the tunneling layer is smaller than that of the first doping element in the field passivation layer, and the doping concentration of the first doping element in the tunneling layer is larger than that of the first doping element in the substrate; the field passivation layer comprises a first doping area and a second doping area, and the slope of the doping curve of the first doping area is larger than that of the doping curve of the second doping area. The doping concentration of the first doping element in the field passivation layer is higher than that in the tunneling layer and the substrate, and the first doping element realizes higher activation rate in the surface layer of the field passivation layer, so that the passivation effect of the solar cell is promoted, and the conversion efficiency of the solar cell is improved.

Description

Solar cells and photovoltaic modules

technical field

The embodiments of the present application relate to the field of photovoltaics, and in particular, to a solar cell and a photovoltaic assembly.

Background technique

Conventional fossil fuels for photovoltaic modules are increasingly being consumed. Among all sustainable energy sources, solar energy is undoubtedly one of the cleanest, most common and most potential alternative energy sources. At present, among all solar cells, crystalline silicon solar cells are one of the solar cells that have been widely commercialized. This is due to the extremely abundant reserves of silicon materials in the earth's crust, and crystalline silicon solar cells are compared with other types of solar cells. Cells have excellent electrical and mechanical properties, therefore, crystalline silicon solar cells occupy an important position in the field of photovoltaics.

With the continuous development of solar cell technology, the recombination loss in the metal contact area has become one of the important factors restricting the further improvement of the conversion efficiency of solar cells. In order to improve the conversion rate of solar cells, the solar cells are often passivated by passivating the contacts to reduce the recombination in the solar cell and on the surface. Commonly used passivated contact cells include Heterojunction with Intrinsic Thin-layer (HIT) cells and Tunnel Oxide Passivated Contact (TOPCon) cells. However, the conversion efficiency of existing passivated contact cells needs to be improved.

SUMMARY OF THE INVENTION

The purpose of the embodiments of the present application is to provide a solar cell and a photovoltaic assembly, which can improve the passivation effect of the solar cell and improve the conversion efficiency of the solar cell.

In order to solve the above problems, an embodiment of the present application provides a solar cell, comprising: a substrate, a tunneling layer sequentially arranged on the back surface of the substrate, a field passivation layer, a first passivation film, and a field penetrating the first passivation film and the field The passivation layer forms a contacted first electrode; wherein the substrate, the tunneling layer and the field passivation layer all include the same first doping element, and the doping concentration of the first doping element in the tunneling layer is smaller than that of the first doping element The doping concentration of the doping element in the field passivation layer, the doping concentration of the first doping element in the tunneling layer is greater than the doping concentration of the first doping element in the substrate; the field passivation layer includes the first doping and the second doping region, the second doping region is close to the tunneling layer relative to the first doping region; wherein, the doping curve slope of the first doping region is greater than the doping curve slope of the second doping region; A doping element is annealed and activated to obtain an activated first doping element; the slope of the doping curve is the slope of the curve of the doping concentration of the activated first doping element changing with the doping depth; direction, the slope of the doping curve of the tunneling layer gradually decreases.

In addition, when the back surface of the substrate faces the interior of the substrate, the slope of the doping curve of the substrate gradually increases and tends to be stable.

In addition, the slope of the doping curve of the substrate is less than or equal to the average value of the slope of the doping curve of the second doping region.

In addition, the doping concentration of the activated first doping element in the field passivation layer is 1×10 ²⁰ atom/cm ³ to 5×10 ²⁰ atom/cm ³ ; the activation rate of the first doping element in the field passivation layer is 50% to 70%; the activation rate is the ratio of the doping concentration of the activated first doping element to the concentration of the total implanted first doping element.

In addition, the slope of the doping curve of the first doped region is 5×10 ¹⁸ to 1×10 ¹⁹ ; the slope of the doping curve of the second doped region is −5×10 ¹⁸ to 5×10 ¹⁸ .

In addition, the slope of the doping curve of the tunnel layer is -2.5×10 ¹⁹ ~-2.5×10 ¹⁸ ; the slope of the doping curve of the substrate is -2.5×10 ¹⁹ ~0.

In addition, in the direction perpendicular to the surface of the substrate, the thickness of the field passivation layer is 60 nm˜130 nm, and the thickness of the tunneling layer is 0.5 nm˜3 nm.

In addition, the above-mentioned solar cell also includes: an emitter electrode, a second passivation film, and a second electrode formed in contact with the emitter electrode through the second passivation film, which are sequentially arranged on the upper surface of the substrate; wherein, the substrate further includes a second dopant element.

In addition, after the second doping element is activated by annealing, an activated second doping element is obtained; the doping concentration of the activated second doping element on the upper surface of the substrate is 5×10 ¹⁸ atom/cm ³ ~1.5×10 ¹⁹ atom /cm ³ ; the concentration of the total implanted doping element of the second doping element on the upper surface of the substrate is 1.5×10 ¹⁹ atom/cm ³ to 1×10 ²⁰ atom/cm ³ .

In addition, in the direction that the upper surface of the substrate points to the back surface of the substrate, the substrate includes a first area, a second area and a third area; wherein, the second area is located between the first area and the third area; the first area is relative to the first area. The second region is close to the upper surface of the substrate, and the third region is closer to the back surface of the substrate than the second region; the doping concentration of the second doping element in the second region and the doping concentration of the second doping element in the third region are both less than the doping concentration of the second doping element in the first region.

In addition, the doping concentration of the activated second doping element in the first region is 5×10 ¹⁸ atom/cm ³ to 1.5×10 ¹⁹ atom/cm ³ .

In addition, the distance between the bottom surface of the first region and the upper surface of the substrate is 350 nm to 450 nm; the distance between the bottom surface of the second region and the upper surface of the substrate is 1000 nm to 1200 nm; the distance between the bottom surface of the third region and the upper surface of the substrate is 1200 nm to 1600 nm.

In addition, the activation probability of the second doping element in the first region is 20%-40%; the activation probability of the second doping element in the second region is 60%-90%; the activation probability of the second doping element in the third region The activation probability is 5% to 90%; the activation probability is the ratio of the doping concentration of the second doping element activated by annealing to the concentration of the total implanted second doping element.

The embodiment of the present application also provides a photovoltaic module, comprising: a battery string, an encapsulation layer and a cover plate, the battery string is formed by connecting the above-mentioned solar cells; the encapsulation layer is used to cover the surface of the battery string; the cover plate is used to cover the encapsulation layer Keep away from the surface of the battery string.

Compared with the prior art, the technical solutions provided in the embodiments of the present application have the following advantages:

Embodiments of the present application provide a solar cell and a photovoltaic assembly, including a substrate, a tunneling layer, a field passivation layer, a first passivation film and a first electrode; wherein the substrate, the tunneling layer and the field passivation layer are all doped with Doping with a first doping element, the doping concentration of the first doping element in the field passivation layer is greater than the doping concentration in the tunneling layer and in the substrate, and with the increase of doping depth, the doping concentration of the first doping element The doping concentration gradually decreases. The doping curve slope of the first doping element presents a gradient distribution with the increase of doping depth; in the first doping region of the field passivation layer, the doping curve slope first decreases, and then the doping curve slope in the second doping region It is stable near 0, indicating that the doping concentration of the first doping element changes greatly at the surface layer of the field passivation layer, and then the change tends to be stable; in the tunneling layer, the doping curve slope of the first doping element is Negative, and greatly decreased, indicating that the doping concentration of the first doping element gradually decreased and the decrease was large; in the substrate, the doping curve slope of the first doping element gradually increased and became stable. The doping concentration of the first doping element in the field passivation layer in the embodiments of the present application is higher than the doping concentration of the first doping element in the tunneling layer and the substrate, and the first doping element is in the surface layer of the field passivation layer A higher activation rate is achieved, which is beneficial to improve the passivation effect of the solar cell and improve the conversion efficiency of the solar cell.

Description of drawings

FIG. 1 is a schematic structural diagram of a solar cell according to an embodiment of the present application;

FIG. 2 is a graph showing a change in doping concentration of a first doping element in a solar cell with doping depth according to an embodiment of the present application;

3 is a distribution diagram of a doping curve slope of a first doping element in a solar cell according to an embodiment of the present application as a function of doping depth;

FIG. 4 is a graph showing the change of the doping concentration of the second doping element in the solar cell with the doping depth according to an embodiment of the present application;

FIG. 5 is a distribution diagram of the activation probability of the second doping element in the solar cell according to an embodiment of the present application as a function of doping depth;

FIG. 6 is a schematic structural diagram of a photovoltaic module according to an embodiment of the present application.

Detailed ways

It can be seen from the background art that at present, tunneling oxide passivation contact (TOPCon) cells have received continuous attention due to their excellent surface passivation effect, high theoretical efficiency and good compatibility with traditional production lines. The most notable feature of TOPCon technology is its high-quality stack structure of ultra-thin silicon oxide and heavily doped polysilicon (poly-Si), so phosphorus diffusion doping is an important part of it, and the excellent passivation contact on the back of TOPCon requires The field effect is achieved by phosphorus diffusion doping.

At present, the research on doping phosphorus elements mainly focuses on the distribution of phosphorus elements in Poly-Si. The research on the concentration change and distribution of phosphorus elements in Poly-Si-SiO _x -Si is not perfect, and it is impossible to essentially optimize the field effect. and passivated contacts, thereby achieving further efficiency improvements of the solar cell.

In order to improve the conversion efficiency of the solar cell and essentially optimize the field effect and the passivation contact, an embodiment of the present application proposes a solar cell in which the doping concentration of the first doping element in the field passivation layer is higher than that of the first doping element The doping concentration in the tunneling layer and the substrate, and the first doping element achieves a high activation rate in the surface layer of the field passivation layer, which is beneficial to improve the passivation effect of the solar cell and improve the conversion efficiency of the solar cell. The embodiment of the present application also analyzes the doping concentration distribution of the phosphorus element in the Poly-Si-SiO _x -Si of the solar cell, thereby providing a basis for improving the phosphorus doping process and improving the efficiency of the battery.

Referring to FIG. 1 , an embodiment of the present application provides a solar cell, including: a substrate 10 , a tunneling layer 121 , a field passivation layer 122 , a first passivation film 123 and a first passivation penetrating layer 121 sequentially disposed on the back surface of the substrate 10 The passivation film 123 forms a first electrode 124 in contact with the field passivation layer 122; wherein, the substrate 10, the tunneling layer 121 and the field passivation layer 122 all include the same first doping element, and the first doping element is in the tunnel The doping concentration in the tunneling layer 121 is lower than the doping concentration of the first doping element in the field passivation layer 122 , and the doping concentration of the first doping element in the tunneling layer 121 is greater than that of the first doping element in the substrate 10 The field passivation layer 122 includes a first doping region and a second doping region, and the second doping region is close to the tunneling layer 121 relative to the first doping region; wherein, the doping region of the first doping region is The doping curve slope is greater than the doping curve slope of the second doping region; the first doping element is annealed and activated to obtain an activated first doping element; the doping curve slope is that the doping concentration of the activated first doping element varies with The slope of the curve of doping depth variation; in the direction of the tunnel layer 121 toward the substrate 10 , the slope of the doping curve of the tunnel layer 121 gradually decreases.

The substrate 10 is used to receive incident light and generate photo-generated carriers. In some embodiments, the back surface and the upper surface of the substrate 10 are disposed opposite to each other, and both the back surface and the upper surface of the substrate 10 can be used to receive incident light or reflected light.

In some embodiments, the substrate 10 may be a silicon substrate, and the material of the silicon substrate may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or microcrystalline silicon. The substrate 10 may be an N-type semiconductor substrate, that is, the substrate 10 is doped with an N-type first dopant element. The first doping element may be any one of phosphorus element, arsenic element or antimony element. Specifically, when the first doping element is phosphorus element, phosphorus diffusion can be performed on the back surface of the substrate 10 through a doping process (eg, thermal diffusion, ion implantation, etc.), so that the tunneling layer 121 and the field passivation are The layer 122 and the substrate 10 are both doped with phosphorus element, and the phosphorus element is activated by annealing treatment, thereby obtaining the activated phosphorus element.

The tunneling layer 121 is used to realize the interface passivation of the back surface of the substrate 10 and facilitate the migration of carriers through the tunneling effect; in some embodiments, the tunneling layer 121 can be formed by a deposition process, for example, chemical vapor can be used to form the tunneling layer 121 deposition process. In other embodiments, the tunneling layer 121 may also be formed by an in-situ generation process. Specifically, the tunneling layer 121 may include a dielectric material that provides passivation and tunneling effects, such as oxides, nitrides, semiconductors, conductive polymers, and the like. For example, the material of the tunneling layer 121 may include silicon oxide, silicon nitride, silicon oxynitride, intrinsic amorphous silicon, intrinsic polysilicon, and the like. In some instances, the tunneling layer 121 may not be a perfect tunneling barrier in effect, as it may, for example, contain defects such as pinholes, which may lead to other charge carrier transport mechanisms (eg, drift, diffusion) relative to tunneling The wear effect dominates.

The field passivation layer 122 is used to form the field passivation. In some embodiments, the material of the field passivation layer 122 may be doped silicon. Specifically, in some embodiments, the field passivation layer 122 and the substrate 10 have the same material Doping elements of conductivity type, doped silicon may include one or more of N-type doped polysilicon, N-type doped microcrystalline silicon or N-type doped amorphous silicon. Preferably, the material of the field passivation layer 122 is a phosphorus-doped polysilicon layer. In some embodiments, the field passivation layer 122 may be formed using a deposition process. Specifically, intrinsic polysilicon may be deposited on the back surface of the tunneling layer 121 away from the substrate 10 to form a polysilicon layer, and the first dopant element may be doped by means of ion implantation and source diffusion to form an N-type doped polysilicon layer to The N-type doped polysilicon layer serves as the field passivation layer 122 . In some embodiments, the N-type doped amorphous silicon can be formed on the back surface of the tunneling layer 121 away from the substrate 10 first, and then the N-type doped polysilicon layer can be formed after a high temperature treatment.

Referring to FIG. 1 , the first passivation film 123 is a backside passivation film and is formed on the side of the field passivation layer 122 away from the back surface of the substrate 10 . In some embodiments, the material of the first passivation film 123 may be one or more of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride or silicon oxycarbonitride. Specifically, in some embodiments, the first passivation film 123 may have a single-layer structure. In other embodiments, the first passivation film 123 may also be a multi-layer structure. In some embodiments, the first passivation film 123 may be formed by a plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical Vapor Deposition, PECVD) method.

The first passivation film 123 passivates the defects existing in the field passivation layer 122 on the back surface of the substrate 10, removes the recombination site of minority carriers, thereby increasing the open circuit voltage of the solar cell. In addition, a first anti-reflection film may also be provided on the side of the first passivation film 123 away from the back surface of the substrate 10, and the first anti-reflection film reduces the reflectivity of light incident on the back surface of the substrate 10, thereby increasing the The amount of light reaching through the substrate 10 and the tunnel junction formed with the penetrating layer 121 increases the short circuit current (Isc) of the solar cell. Therefore, the first passivation film 123 and the first anti-reflection film can increase the open-circuit voltage and short-circuit current of the solar cell, thereby improving the conversion efficiency of the solar cell.

In some embodiments, the first anti-reflection coating may be formed of various materials capable of preventing surface reflection. For example, the material of the first anti-reflection film may be one or more of silicon nitride, hydrogen-containing silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, MgF ₂ , ZnS, TiO ₂ or CeO ₂ . Specifically, in some embodiments, the first anti-reflection film may have a single-layer structure. In other embodiments, the first anti-reflection film can also be a multi-layer structure. In some embodiments, the first anti-reflection film may be formed using a PECVD method.

In some embodiments, the first electrode 124 penetrates the first passivation film 123 to form an electrical connection with the field passivation layer 122 . Specifically, the first electrode 124 is electrically connected to the field passivation layer 122 via an opening formed in the first passivation film 123 (ie, the first electrode 124 penetrates the first passivation film 123 while it is).

In some embodiments, the method of forming the first electrode 124 may include: printing a conductive paste on the surface of the first passivation film 123 in a predetermined area, and the conductive material in the conductive paste may be silver, aluminum, copper, tin, At least one of gold, lead or nickel; sintering the conductive paste, for example, sintering at a peak temperature of 750° C.˜850° C. to form the first electrode 124 .

In some embodiments, for the solar cell described in FIG. 1 , when the first doping element is phosphorus, electrochemical capacitance-voltage (Electrochemical Capacitance Voltage, ECV) and secondary ion mass spectrometry (Secondary ion mass spectrometry) can be used Ion Mass Spectrometry, SIMS) tests the activated phosphorus atom concentration and the total implanted phosphorus atom concentration in the phosphorus diffusion doping process, and obtains the distribution curve of the activated phosphorus atom concentration and the total implanted phosphorus atom concentration with the doping depth, as shown in Figure 2 shown. It can be seen from FIG. 2 that the distribution trend of the doping concentration of the total implanted phosphorus element concentration in the field passivation layer 122 , the tunneling layer 121 and the substrate 10 is that the doping concentration gradually decreases. In the field passivation layer 122 (Poly-Si thin film), the activated phosphorus element concentration is about 3×10 ²⁰ atom/cm ³ , the total implanted phosphorus element concentration is about 5×10 ²⁰ atom/cm ³ , and the activation rate of phosphorus element is about 5×10 20 atom/cm 3 . It is 50%-70%, which achieves a higher probability of phosphorus activation.

Referring to FIG. 2 , the field passivation layer 122 includes a first doping region having a high doping concentration and a second doping region having a lower doping concentration than the first doping region, thereby improving light incidence on the field passivation layer 122 passivation effect. At the same time, the contact resistance between the field passivation layer 122 and the first electrode 124 can also be reduced, thereby improving the conversion efficiency of the solar cell.

As shown in Fig. 2, there is an obvious doping concentration peak in the total implanted phosphorus element concentration spectrum obtained by SIMS test, which is mainly due to the presence of the field passivation layer 122 to the tunneling layer 121 (Poly-Si- _SiOx thin film) On both sides of the interface, the chemical environment of the phosphorus element has changed, which affects the ionization rate of the phosphorus element, especially in the _SiOx thin layer of the tunneling layer 121 There is abundant oxygen element, in the SIMS positive ion test mode The signal intensity of the phosphorus element will be increased under low temperature, resulting in a high doping concentration obtained by the test. When the test depth reaches the single crystal silicon layer where the substrate 10 is located, the signal intensity will gradually stabilize and become stable.

As an example, combined with ECV and SIMS tests, it can be found that the interface depth positions of Poly-Si- _SiOx and _SiOx -Si are about 94 nm and 101 nm, respectively. As shown in FIG. 2 , from the surface layer of the field passivation layer 122 to the position of the tunneling layer 121 (interface depth 0 nm~94 nm), the total injected phosphorus element concentration is about 5×10 ²⁰ atom/cm ³ , and the change trend is stable; At the interface depth of about 94 nm, the total implanted phosphorus concentration begins to fluctuate, and there is a doping concentration peak in the interval between 94 nm and 101 nm at the interface depth; when the interface depth is greater than 101 nm, the total implanted phosphorus concentration gradually It decreases and stabilizes at an interface depth of about 310 nm. When the interface depth is between 310 nm and 500 nm, the total injected phosphorus concentration is between 5×10 ¹⁸ atom/cm ³ and 5×10 ¹⁹ atom/cm ³ . And the activated phosphorus element concentration is about 3×10 ²⁰ atom/cm ³ from the surface layer of the field passivation layer 122 to the position of the tunneling layer 121 (interface depth 0 nm~94 nm), and the change trend is stable; At the interface depth of about 94 nm, the concentration of activated phosphorus element decreases greatly; when the interface depth is greater than 101 nm, the change trend of the activated phosphorus element concentration decreases slowly, and reaches the lowest value near the position of the interface depth of 160 nm.

It should be noted that the doping curve is the relationship between the phosphorus doping concentration (unit atom/cm ³ ) and the doping depth (unit nm). The slope of the doping curve is the slope of the curve of the doping concentration of the phosphorus element activated by annealing as a function of doping depth.

Figure 3 shows the gradient distribution of the slope of the phosphorus element doping curve with the doping depth, which can more clearly analyze the change of the phosphorus element doping concentration in the TOPCon structure. As shown in FIG. 3 , the boundary line between the first doped region and the second doped region is a dashed line D, and the boundary line between the tunneling layer 121 (SiO _x film) and the second doped region is a dashed line E. The boundary line between the layer 121 and the substrate 10 is a dotted line C. In the first doped region of the field passivation layer 122 (Poly-Si thin film), the slope of the phosphorus element doping curve is greatly reduced, and in the second doped region, the slope of the phosphorus element doping curve decreases gradually, and then stabilizes Near 0, it indicates that the phosphorus doping concentration varies greatly in the first doped region of the field passivation layer 122 (which may also be referred to as the Poly-Si surface layer), and then in the first doped region of the field passivation layer 122 The change of the phosphorus doping concentration tends to be stable; in the tunneling layer 121 (SiO _x film), the slope of the phosphorus doping curve is negative and greatly decreases, indicating that the phosphorus doping concentration gradually decreases and the decreasing amplitude gradually increases .

In some embodiments, when the back surface of the substrate 10 faces the interior of the substrate 10 , the slope of the doping curve of the substrate 10 gradually increases and tends to be stable. As shown in FIG. 3 , in the substrate 10 , with the increase of the interface depth, the slope of the doping curve of phosphorus element in the substrate 10 gradually increases and tends to be stable, indicating that the doping concentration of phosphorus element in the substrate 10 decreases The amplitude slows down and gradually stabilizes.

In some embodiments, the slope of the doping curve of the substrate 10 is less than or equal to the average value of the slope of the doping curve of the second doped region. Continuing to refer to FIG. 3 , the slope of the doping curve of the substrate 10 gradually increases and tends to a stable value, which is approximately equal to the average value of the slope of the doping curve of the second doped region.

In some embodiments, the doping concentration of the activated first doping element in the field passivation layer 122 is 1×10 ²⁰ atom/cm ³ to 5×10 ²⁰ atom/cm ³ ; the first doping element is in the field passivation The activation rate in the layer 122 is 50%˜70%; the activation rate is the ratio of the doping concentration of the activated first doping element to the concentration of the total implanted first doping element.

As shown in FIG. 2 , when the first doping element is phosphorus element, the doping concentration of the activated phosphorus element in the field passivation layer 122 may be 1×10 ²⁰ atom/cm ³ , 2×10 ²⁰ atom/cm cm ³ , 3×10 ²⁰ atom/cm ³ , 4×10 ²⁰ atom/cm ³ or 5×10 ²⁰ atom/cm ³ ; preferably, the doping concentration of the activated phosphorus element in the field passivation layer 122 may be 3 ×10 ²⁰ atom/cm ³ , the total implanted phosphorus element concentration is about 5×10 ²⁰ atom/cm ³ , and the activation rate of the first doping element in the field passivation layer 122 is 50% to 70%, which achieves high Probability of elemental phosphorus activation.

In some embodiments, the slope of the doping curve of the first doped region is 5×10 ¹⁸ to 1×10 ¹⁹ ; the slope of the doping curve of the second doped region is −5×10 ¹⁸ to 5×10 ¹⁸ .

As shown in FIG. 3 , the position from the surface layer of the field passivation layer 122 to the interface depth is about 10mn, which is the first doped region, and the slope of the doping curve of the first doped region is greatly reduced; in the second doped region, The slope of the doping curve first decreases gently (the interface depth is about 10nm~20mn), and the slope of the doping curve is stable at the position of the interface depth of about 20nm, and it is in a stable state and lasts until the interface of the Poly-Si- _SiOx film. position (interface depth is about 94mn).

In some embodiments, the slope of the doping curve of the tunneling layer 121 is -2.5×10 ¹⁹ ~-2.5×10 ¹⁸ ; the slope of the doping curve of the substrate 10 is -2.5×10 ¹⁹ ~0.

Please continue to refer to FIG. 3 , within the interface depth range from the tunnel layer 121 to the substrate 10 , that is, within the interface depth range from the SiO _x film to the crystalline silicon layer in FIG. 3 , the slope of the doping curve begins to decrease significantly (as shown in FIG. shown at A), which is greatly reduced from 2.5×10 ¹⁸ to -2.5×10 ¹⁹ . This is mainly because the phosphorus element enters the _SiOx film from the Poly-Si film, and the chemical environment of the phosphorus element changes, which affects the ionization rate of the phosphorus element, resulting in a significant reduction in the doping concentration of the phosphorus element. In the interface depth interval from the back surface of the substrate 10 (Si) to the upper surface of the substrate 10, the slope of the doping curve increases significantly from -2.5×10 ¹⁹ (as shown at B in FIG. 3 ), until 2.5× 10 ¹⁸ , then the slope of the phosphorus doping curve tends to stabilize. It can be seen from FIG. 3 that the slopes of the doping curves on the left and right sides of the SiO _x -Si interface position are approximately symmetrical with respect to the dotted line C in FIG. 3 , and the slopes of the phosphorus doping curves after stabilization in the substrate 10 It is approximately equal to the average value of the slope of the doping curve of the second doping region. It can be seen from FIG. 3 that the center line of the slope of the phosphorus doping curve of the second doping region is the same as the slope of the stabilized phosphorus doping curve in the substrate 10 The centerlines are roughly flush.

In some embodiments, in a direction perpendicular to the surface of the substrate 10 , the thickness of the field passivation layer 122 is 60 nm˜130 nm, and the thickness of the tunneling layer 121 is 0.5 nm˜3 nm.

In some embodiments, in order to provide sufficient passivation and tunneling effects, the thickness of the tunneling layer 121 may be 0.5 nm˜3 nm. When the thickness of the tunneling layer 121 exceeds 3 nm, tunneling cannot be effectively performed, and the solar cell may not work, and when the thickness of the tunneling layer 121 is less than 0.5 nm, passivation performance may be deteriorated. In order to further improve the tunneling effect, the thickness of the tunneling layer 121 may also be 0.5 nm˜2 nm, or the thickness of the tunneling layer 121 may also be 0.5 nm˜1 nm.

In some embodiments, the thickness of the substrate 10 is 130 μm˜250 μm.

The embodiments of the present application provide a solar cell and a photovoltaic module. By analyzing the activation rate and doping curve slope of phosphorus atoms in the phosphorus diffusion doping process of the solar cell, a theoretical basis is provided for optimizing field effects and passivation contacts and improving battery efficiency. Through the above analysis, it is known that the activation rate of phosphorus atoms in the field passivation layer 122 is 50%-70%; in the Poly-Si film, the slope of the phosphorus atom doping curve first decreases, and then stabilizes at 5×10 ¹⁸ to -5× In the range of 10 ¹⁸ , in the SiO _x film, the slope of the phosphorus atom doping curve decreases from about -1×10 ¹⁸ to about -3×10 ¹⁹ , and in the crystalline silicon, the phosphorus atom doping curve gradually increases and stabilizes. In the range of -1×10 ¹⁷ to -1×10 ¹⁸ .

In some embodiments, the above-mentioned solar cell further includes: an emitter electrode 111 , a second passivation film 112 and a second electrode 114 penetrating the second passivation film 112 and forming contact with the emitter electrode 111 , which are sequentially arranged on the upper surface of the substrate 10 . ; wherein, the substrate 10 further includes a second doping element.

Specifically, the above-mentioned preparation process of the solar cell includes: first, depositing a P-type dopant source on the upper surface of the substrate 10 to form a thin film layer. Then, the P-type doping source in the thin film layer in the predetermined area is diffused into the substrate 10 through a doping process, so as to form an emitter 111 inside the substrate 10 in the predetermined area.

In some embodiments, the P-type doping source is a trivalent element-containing element or compound such as boron tribromide or boron trichloride. In some embodiments, when the P-type doping source is a boron source, the second doping element is boron; a simple substance or compound containing a trivalent element such as boron tribromide or boron trichloride can be used as the doping source . Specifically, the second doping element in the predetermined region can be diffused into the upper surface of the substrate 10 through a doping process (eg, a laser doping process, a plasma positioning doping process or an ion implantation process).

In some embodiments, before the film layer is formed on the upper surface of the substrate 10, the upper surface of the substrate 10 is pretreated, including cleaning the substrate 10 and texturing the upper surface of the substrate 10; specifically, chemical etching may be used. A pyramid-like texture structure is formed on the upper surface of the substrate 10 by processes such as etching, laser etching, mechanical method or plasma etching. smaller, thereby increasing the absorption utilization of incident light. On the other hand, compared with the fact that the upper surface of the substrate 1 is a flat surface, the existence of the pyramid-like texture structure increases the surface area of the upper surface of the substrate 10 , so that the upper surface of the substrate 10 can store more The second doping element is beneficial to form the emitter 111 with a higher concentration. In some embodiments, the emitter 111 is a doped layer diffused to the upper surface of the substrate 10 to a certain depth, and a PN junction structure is formed in the substrate 10 .

Referring to FIG. 1 , the second passivation film 112 is a front passivation film formed on the side of the emitter electrode 111 away from the upper surface of the substrate 10 . The material of the second passivation film 112 may be one or more of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride or silicon oxycarbonitride. Specifically, in some embodiments, the second passivation film 112 may have a single-layer structure. In other embodiments, the second passivation film 112 may also be a multi-layer structure. In some embodiments, the second passivation film 112 may be formed using a PECVD method.

In addition, a second anti-reflection film can also be provided on the side of the second passivation film 112 away from the upper surface of the substrate 10, and the second anti-reflection film can reduce the reflectivity of the light incident on the upper surface of the substrate 10, thereby increasing the arrival rate of light passing through the substrate 10. The amount of light in the tunnel junction formed by the substrate 10 and the emitter 111 increases the short circuit current (Isc) of the solar cell. Therefore, the second passivation film 112 and the second anti-reflection film can increase the open-circuit voltage and short-circuit current of the solar cell, thereby improving the conversion efficiency of the solar cell.

In some embodiments, the material of the second AR coating is the same as the material of the first AR coating. For example, the material of the second anti-reflection film may be one or more of silicon nitride, hydrogen-containing silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, MgF ₂ , ZnS, TiO ₂ or CeO ₂ . Specifically, in some embodiments, the second anti-reflection film may have a single-layer structure. In other embodiments, the second anti-reflection film can also be a multi-layer structure. In some embodiments, the PECVD method can be used to form the second anti-reflection film.

In some embodiments, the second electrode 114 penetrates the second passivation film 112 to form an electrical connection with the emitter electrode 111 . Specifically, the second electrode 114 is electrically connected to the emitter electrode 111 via an opening formed in the second passivation film 112 (ie, the second electrode 114 penetrates the second passivation film 112 while it is). Specifically, the method of forming the second electrode 114 may be the same as the method of forming the first electrode 124 , and the material of the second electrode 114 may also be the same as the material of the first electrode 124 .

In some embodiments, for the solar cell shown in FIG. 1 , the activated second doping element is obtained after the second doping element is activated by annealing; the doping concentration of the activated second doping element on the upper surface of the substrate 10 is 5×10 ¹⁸ atom/cm ³ to 1.5×10 ¹⁹ atom/cm ³ ; the concentration of the total implanted doping element of the second doping element on the upper surface of the substrate 10 is 1.5×10 ¹⁹ atom/cm ³ to 1×10 ²⁰ atom/cm ³ .

In some embodiments, the doping concentration of the activated second doping element on the upper surface of the substrate 10 may be, for example, 5×10 ¹⁸ atom/cm ³ , 9×10 ¹⁸ atom/cm ³ , or 1×10 ¹⁹ atom/cm ^3. 1.2×10 ¹⁹ atom/cm ³ or 1.5×10 ¹⁹ atom/cm ³ ; the concentration of the total implanted doping element of the second doping element on the upper surface of the substrate 10 can be, for example, 1.5×10 ¹⁹ atom/cm ³ , 3×10 ¹⁹ atom/cm ³ , 6×10 ¹⁹ atom/cm ³ , 8×10 ¹⁹ atom/cm ³ , 1×10 ²⁰ atom/cm ³ .

Preferably, the doping concentration of the activated second doping element on the upper surface of the substrate 10 is 1×10 ¹⁹ atom/cm ³ ; the concentration of the total implanted doping element of the second doping element on the upper surface of the substrate 10 is 3× 10 ¹⁹ atoms/cm ³ to 5×10 ¹⁹ atoms/cm ³ .

In some embodiments, for the solar cell described in FIG. 1 , the distribution curves of activated boron concentration and total implanted boron concentration with doping depth are obtained through ECV test and SIMS test, as shown in FIG. 4 . It can be seen from Fig. 4 that the total implanted boron concentration in the surface layer of crystalline silicon is about 3×10 ¹⁹ atom/cm ³ , and with the increase of doping depth, the total implanted boron concentration first increases and then decreases. The peak concentration is reached at a depth of 300 nm, which is about 5×10 ¹⁹ atoms/cm ³ . The activated boron concentration showed the same trend as the total implanted boron concentration. The activated boron concentration in the surface layer was about 1×10 ¹⁹ atom/cm ³ and also reached a peak at 300 nm depth.

In some embodiments, the substrate 10 includes a first area, a second area and a third area in a direction from the top surface of the substrate 10 to the back surface of the substrate 10; wherein the second area is located between the first area and the third area ; the first region is close to the upper surface of the substrate 10 relative to the second region, the third region is close to the back surface of the substrate 10 relative to the second region; the doping concentration of the second doping element in the second region and the second doping element The doping concentration in the third region is smaller than the doping concentration of the second doping element in the first region.

In some embodiments, the doping concentration of the activated second doping element in the first region is 5×10 ¹⁸ atom/cm ³ to 1.5×10 ¹⁹ atom/cm ³ .

In some embodiments, the distance between the bottom surface of the first region and the upper surface of the substrate 10 is 350 nm to 450 nm; the distance between the bottom surface of the second region and the upper surface of the substrate 10 is 1000 nm to 1200 nm; the bottom surface of the third region and the upper surface of the substrate 10 The distance is 1200nm~1600nm.

As shown in FIG. 4 , the interface depth of the first region is about 400 nm, and the doping concentration of activated boron element in the surface layer of the first region is 1×10 ¹⁹ atom/cm ³ . As the doping depth increases, The doping concentration of the activated boron element in the first region first increases slowly, increases to the highest point (doping concentration is about 1.5×10 ¹⁹ atom/cm ³ ), and then slowly decreases (doping concentration is about 1.1× 10 ¹⁹ atom/cm ³ ); the doping concentration of activated boron in the second region continued to decrease until around 1×10 ¹⁸ atom/cm ³ ; the doping concentration of activated boron in the third region continued to decrease, reaching The lowest value is around 1×10 ¹⁷ atom/cm ³ .

In some embodiments, the activation probability of the second doping element in the first region is 20%-40%; the activation probability of the second doping element in the second region is 60%-90%; The activation probability of the third region is 5%-90%; the activation probability is the ratio of the doping concentration of the second doping element activated by annealing to the concentration of the total implanted second doping element.

In the surface layer of the substrate 10, due to the high concentration of the total implanted boron element and the low doping concentration of the surface layer, the activation probability of the doping element in the first region is 20%-40%; As the doping depth increases, the total implanted boron concentration decreases and the activation probability increases. When the doping depth is greater than 1100 nm, the activation probability of boron during diffusion reaches the limit at the doping depth of 1100 nm, and continues to increase at the doping depth. , the activation probability drops sharply again.

FIG. 5 shows the gradient distribution curve of the activation probability of boron atoms with the doping depth in the boron diffusion doping process. By measuring the activation probability data of boron atoms at different doping depths, fitting the data to obtain the fitting curve. By fitting the curve, it can be known that the activation probability of boron atoms in the surface layer of crystalline silicon and the shallow junction area (doping depth less than 400nm) is relatively low, about 33%, indicating that the dead layer problem is mainly concentrated in this part of the area, and the diffusion process can be used. Make targeted adjustments. When the doping depth exceeds 400 nm, the activation probability of boron atoms gradually increases, reaching a peak at about 1100 nm, and the peak activation probability is in the range of 60%-90%. When the doping depth is further increased, the activation probability of boron atoms decreases sharply. It can be seen that the activation probability of boron atoms in the surface layer of the substrate 10 (doping depth is 0nm to 400nm) is relatively stable, in the range of 20%-40%; when the doping depth increases from 400nm to 1400nm, the activation probability of boron atoms increases first The peak position is located at the doping depth of 1000nm to 1200nm, and the peak activation probability is in the range of 60%-90%.

Referring to FIG. 6 , an embodiment of the present application further provides a photovoltaic module, comprising: a battery string 101 , an encapsulation layer 102 and a cover plate 103 , the battery string 101 is formed by connecting the solar cells provided in the above-mentioned embodiments; the encapsulation layer 102 is used for Cover the surface of the battery string 101 ; the cover plate 103 is used to cover the surface of the encapsulation layer 102 away from the battery string 101 .

In some embodiments, the solar cells may be electrically connected in the form of a whole piece or a plurality of pieces to form a plurality of battery strings 101, and the plurality of battery strings 101 are electrically connected in series and/or parallel manner.

Specifically, in some embodiments, the plurality of battery strings 101 may be electrically connected through conductive strips 104 . The encapsulation layer 102 covers the front side and the back side of the solar cell. Specifically, the encapsulation layer 102 may be an organic package such as an ethylene-vinyl acetate copolymer (EVA) adhesive film, a polyethylene octene co-elastomer (POE) adhesive film, or a polyethylene terephthalate (PET) adhesive film. film. In some embodiments, the cover plate 103 may be a cover plate 103 with a light-transmitting function, such as a glass cover plate, a plastic cover plate, or the like. Specifically, the surface of the cover plate 103 facing the encapsulation layer 102 may be a concave-convex surface, thereby increasing the utilization rate of incident light.

The embodiment of the present application provides a solar cell and a photovoltaic assembly, by doping the back surface of the substrate 10 with a first doping element and doping the upper surface of the substrate 10 with a second doping element, and the first doping element is field passivated The doping concentration in the passivation layer is higher than the doping concentration in the tunneling layer and the substrate, and the first doping element achieves a higher activation rate in the surface layer of the field passivation layer, which is beneficial to improve the passivation effect of the solar cell , improve the conversion efficiency of solar cells. In addition, by increasing the activation probability of the surface layer of the second doping element on the upper surface of the substrate, the doping distribution of the second doping element in the surface layer of the substrate and the shallow junction region is improved, the influence of the dead layer is reduced, and the solar cell is improved. the overall performance of the solar cell, thereby improving the conversion efficiency of the solar cell.

Those of ordinary skill in the art can understand that the above-mentioned embodiments are specific examples for realizing the present application, and in practical applications, various changes can be made in form and details without departing from the spirit and the spirit of the present application. scope. Any person skilled in the art can make respective changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims.

Claims (14)

1. A solar cell, characterized in that, comprising: base(10); A tunneling layer (121), a field passivation layer (122), a first passivation film (123), and a tunneling layer (121), a field passivation layer (122), and a first passivation film (123) penetrating the first passivation film (123) and the the field passivation layer (122) forms a contacted first electrode (124); Wherein, the substrate (10), the tunneling layer (121) and the field passivation layer (122) all include the same first doping element, and the first doping element is used in the tunneling The doping concentration in the layer (121) is less than the doping concentration of the first doping element in the field passivation layer (122), the first doping element in the tunneling layer (121) The doping concentration of is greater than the doping concentration of the first doping element in the substrate (10); The field passivation layer (122) includes a first doping region and a second doping region, the second doping region is close to the tunneling layer (121) relative to the first doping region; wherein, The doping curve slope of the first doping region is greater than the doping curve slope of the second doping region; the first doping element is annealed and activated to obtain an activated first doping element; the doping The slope of the curve is the slope of the curve in which the doping concentration of the activated first doping element changes with the doping depth; In the direction of the tunneling layer (121) towards the substrate (10), the slope of the doping curve in the tunneling layer (121) decreases gradually. 2. The solar cell according to claim 1, characterized in that in the process that the back surface of the substrate (10) faces the inside of the substrate (10), the slope of the doping curve of the substrate (10) gradually increases large and stable. 3 . The solar cell according to claim 2 , wherein the slope of the doping curve of the substrate ( 10 ) is less than or equal to the average value of the slope of the doping curve of the second doped region. 4 . 4. The solar cell according to claim 1, wherein the doping concentration of the activated first doping element in the field passivation layer (122) is 1×10 ²⁰ atom/cm ³ ~ 5×10 ²⁰ atoms/cm ³ ; The activation rate of the first doping element in the field passivation layer (122) is 50%-70%; the activation rate is the difference between the doping concentration of the activated first doping element and the total implantation. The ratio of the concentrations of the first doping element. 5 . The solar cell according to claim 1 , wherein the doping curve of the first doped region has a slope of 5×10 ¹⁸ to 1×10 ¹⁹ ; the doping curve of the second doped region has a slope of 5×10 18 to 1×10 19 . The slope is -5×10 ¹⁸ to 5×10 ¹⁸ . 6 . The solar cell according to claim 5 , wherein the doping curve slope of the tunneling layer ( 121 ) is -2.5×10 ¹⁹ ~-2.5×10 ¹⁸ ; the doping curve of the substrate (10) is The slope of the hybrid curve is -2.5×10 ¹⁹ ~0. 7. The solar cell according to claim 1, characterized in that, in a direction perpendicular to the surface of the substrate (10), the field passivation layer (122) has a thickness of 60 nm to 130 nm, and the tunnel The thickness of the through layer (121) is 0.5nm~3nm. 8 . The solar cell according to claim 1 , further comprising: an emitter electrode ( 111 ), a second passivation film ( 112 ) arranged on the upper surface of the substrate ( 10 ) in sequence, and a second passivation film ( 112 ) penetrating the substrate ( 10 ). A second passivation film (112) forms a second electrode (114) in contact with the emitter (111); Wherein, the substrate (10) further includes a second doping element. 9 . The solar cell according to claim 8 , wherein the activated second doping element is obtained after the second doping element is activated by annealing; the activated second doping element is in the substrate ( 10) The doping concentration of the upper surface is 5×10 ¹⁸ atom/cm ³ ~1.5×10 ¹⁹ atom/cm ³ ; The concentration of the total implanted doping element of the second doping element on the upper surface of the substrate (10) is 1.5×10 ¹⁹ atom/cm ³ to 1×10 ²⁰ atom/cm ³ . 10. The solar cell according to claim 9, characterized in that, in a direction from the upper surface of the substrate (10) to the back surface of the substrate (10), the substrate (10) comprises a first region, a second A second area and a third area; wherein the second area is located between the first area and the third area; the first area is close to the upper surface of the substrate (10) relative to the second area a surface, the third region is close to the back surface of the substrate (10) relative to the second region; The doping concentration of the second doping element in the second region and the doping concentration of the second doping element in the third region are both smaller than those of the second doping element in the first region doping concentration. 11 . The solar cell according to claim 10 , wherein the doping concentration of the activated second doping element in the first region is 5×10 ¹⁸ atom/cm ³ to 1.5×10 ¹⁹ atom 11 . /cm ³ . 12 . The solar cell according to claim 10 , wherein the distance between the bottom surface of the first region and the upper surface of the substrate ( 10 ) is 350 nm to 450 nm; 12 . The distance between the bottom surface of the second region and the upper surface of the substrate (10) is 1000nm˜1200nm; The distance between the bottom surface of the third region and the upper surface of the substrate (10) is 1200 nm˜1600 nm. 13 . The solar cell according to claim 10 , wherein the activation probability of the second doping element in the first region is 20%˜40%; 13 . The activation probability of the second doping element in the second region is 60%-90%; The activation probability of the second doping element in the third region is 5% to 90%; The activation probability is the ratio of the doping concentration of the activated second doping element to the total implanted concentration of the second doping element. 14. A photovoltaic module, comprising: A battery string (101), the battery string (101) is formed by connecting a plurality of solar cells according to any one of claims 1 to 13; an encapsulation layer (102), the encapsulation layer (102) is used to cover the surface of the battery string (101); A cover plate (103), the cover plate (103) is used to cover the surface of the encapsulation layer (102) away from the battery string (101).

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