Back contact solar cell, method of manufacturing the same, and photovoltaic module

Abstract

The application provides a back contact solar cell, a preparation method thereof and a photovoltaic module, and relates to the technical field of photovoltaics. The back contact solar cell comprises a silicon substrate; the surface of a first conductive region and / or a second conductive region is provided with a contact opening penetrating through a passivation film and extending into the conductive region; and a composite diffusion barrier layer and a copper electrode are sequentially and laminatedly arranged in the contact opening in a direction away from the silicon substrate. The application arranges two kinds of conductive regions alternately on the back of the silicon substrate, forms a contact opening penetrating through a passivation film and extending into each conductive region, so that the copper electrode can be directly and selectively electrically connected with semiconductor regions of different conductive types; the composite diffusion barrier layer is located at the interface between the copper electrode and the silicon substrate, and can effectively inhibit the diffusion of copper atoms into the silicon body, so that high conversion efficiency, low-cost metallization and long-term operation reliability can be considered without relying on an inert atmosphere or an additional barrier layer process.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and in particular to a back-contact solar cell, its preparation method, and a photovoltaic module. Background Technology

[0002] Back-contact solar cells have become one of the mainstream technologies for next-generation high-efficiency cells due to their lack of front-side grid shading and high conversion efficiency. However, their metallization cost remains high, mainly due to the extensive use of expensive silver paste. Copper, with its excellent conductivity (resistivity of about 1.7 μΩ·cm) and low price (about 1 / 100th that of silver), is an ideal alternative material.

[0003] However, copper readily diffuses rapidly into the silicon substrate at high temperatures, forming deep recombination centers, which leads to a sharp decline in minority carrier lifetime and severe degradation of battery performance. To avoid copper diffusion, existing technologies generally employ: (1) nitrogen or inert gas protected sintering, which results in high equipment investment and maintenance costs; (2) physical vapor deposition (PVD) or chemical vapor deposition (CVD) to pre-deposit barrier layers (such as TiW, Mo, Ni, etc.), which increases process steps and equipment investment; (3) screen printing a thin silver seed layer first, and then printing copper paste to form a silver / copper composite electrode, but still cannot get rid of the dependence on silver.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a back-contact solar cell to at least solve one of the technical problems existing in the prior art.

[0006] The second objective of this invention is to provide a method for preparing a back-contact solar cell.

[0007] The third objective of this invention is to provide a photovoltaic module.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a back-contact solar cell, comprising a silicon substrate, wherein the back side of the silicon substrate is provided with alternating first conductive regions and second conductive regions; The surface of the first conductive region and / or the second conductive region is provided with a contact opening that penetrates the passivation film and extends into the conductive region. A composite diffusion barrier layer and a copper electrode are sequentially stacked in the contact opening along the direction away from the silicon substrate.

[0009] Furthermore, the composite diffusion barrier layer includes a doped transition layer and a copper oxide layer stacked together, wherein the doped transition layer and the copper oxide layer are sequentially disposed in a direction away from the silicon substrate; Preferably, the thickness of the copper oxide layer is 5~30 nm; Preferably, the thickness of the doped transition layer is 10~30 nm; Preferably, the doping element of the doped transition layer includes at least one of phosphorus, boron and manganese. Preferably, the peak concentration of the dopant element is ≥1×10⁻⁶. 18 atoms / cm 3 .

[0010] Furthermore, the copper electrode comprises a plurality of copper particles, each copper particle having a metallic copper core and a copper oxide layer covering the surface of the metallic copper core; Preferably, the copper electrode has a thickness of 5~15 μm, a linewidth of 30~80 μm, and a volume resistivity of <10 μΩ·cm.

[0011] Furthermore, the copper electrode is formed by sintering a copper conductive paste; Preferably, the copper conductive paste comprises copper powder, copper oxide powder, diffusion inhibitor, glass powder, and organic carrier; Preferably, the copper conductive paste comprises, by weight percentage: 70%~90% copper powder, 1%~8% copper oxide powder, 0.1%~5% diffusion inhibitor, 1%~8% glass powder, and the balance being an organic carrier; Preferably, the viscosity of the copper conductive paste is 30~60 Pa·s; the solid content of the copper conductive paste is ≥80 wt%. Preferably, the copper powder has a particle size of 0.5~5 μm; Preferably, the copper oxide powder comprises CuO and / or Cu2O; the particle size of the copper oxide powder is 5~100 nm; Preferably, the diffusion inhibitor comprises one or more of boron phosphate, phosphosilicate glass, strontium manganate, and manganese phosphate; Preferably, the weight ratio of the copper oxide powder to the diffusion inhibitor is 2~5:1; Preferably, the glass powder comprises a low-melting-point glass containing a TeO2-Bi2O3-SiO2 system; the softening point of the glass powder is 450~600℃; Preferably, the organic carrier includes one or more of organic solvents, resins, and additives; Preferably, the organic solvent includes one or more of terpineol, butyl carbitol, diethylene glycol butyl ether acetate, and tributyl citrate; Preferably, the resin includes one or more of ethyl cellulose, acrylic resin, and phenolic resin; Preferably, the additives include one or more of dispersants, leveling agents, defoamers, and thixotropic agents.

[0012] Secondly, the present invention provides a method for preparing a back-contact solar cell, comprising: (a) On a silicon substrate where back-side doping and passivation film deposition have been completed, a contact opening is formed that penetrates the passivation film and exposes a first conductive region and / or a second conductive region; (b) Print copper conductive paste onto the passivation film inside and around the contact opening, and then dry it to remove organic components; (c) Sintering to obtain the back contact solar cell.

[0013] Furthermore, in step (b), copper conductive paste is printed onto the passivation film inside and around the contact opening using screen printing. Preferably, the screen printing stencil has a mesh count of 250-400; the wire diameter is 15-30 μm; the latex thickness is 10-20 μm; and the printing wet weight is 5-20 mg / cm³. 2 The corresponding wet film thickness is 15~35 μm; Preferably, the drying temperature is 150~200℃; the drying time is 5~10 min.

[0014] Furthermore, the sintering process includes: placing the dried silicon wafer in a continuous belt sintering furnace, sintering it in an air atmosphere, and then naturally cooling it to room temperature; Preferably, the peak temperature of the sintering is 550~650℃, and the peak holding time is 5~20 s; Preferably, the heating rate of the sintering is 20~40℃ / s, and the cooling rate is 10~30℃ / s; Preferably, the air flow rate inside the furnace is 10~50 L / min, and the oxygen volume concentration is 15~25%.

[0015] Furthermore, the doping concentration of the first conductive region and the second conductive region are each independently 1×10⁻⁶. 19 ~1×10 20 atoms / cm 3 The junction depths are independently 0.5~2 μm.

[0016] Furthermore, in step (a), a laser grooving process is used to form the contact opening; Preferably, the contact opening depth formed by the laser grooving is 50~150 nm.

[0017] Thirdly, the present invention provides a photovoltaic module, including the back-contact solar cell or a back-contact solar cell prepared by the preparation method described above.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The back-contact solar cell provided by this invention, by setting alternating P-type and N-type regions on the back side of a silicon substrate and forming contact openings that penetrate the passivation film and extend into their respective doped regions, enables the copper electrode to achieve selective electrical connection with semiconductor regions of different conductivity types. The composite diffusion barrier layer is generated in situ at the interface between the copper electrode and the silicon substrate, effectively suppressing the diffusion of copper atoms into the silicon bulk. Thus, without relying on an inert atmosphere or additional barrier layer process, it achieves high conversion efficiency, low-cost metallization, and long-term operational reliability. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 A schematic cross-sectional view of the back electrode of the back contact solar cell provided by the present invention; Figure 2 This is an enlarged schematic diagram of the diffusion barrier layer structure of a back-contact solar cell.

[0021] Icons: 1-Silicon substrate; 2-Passivation film; 3-Contact opening; 4-First conductive region; 5-Second conductive region; 6-Composite diffusion barrier layer; 61-Doped transition layer; 62-Copper oxide layer; 7-Copper electrode. Detailed Implementation

[0022] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1As shown, the first aspect of the present invention provides a back-contact solar cell, including a silicon substrate 1, wherein the back side of the silicon substrate 1 is provided with alternating first conductive regions 4 and second conductive regions 5; the surface of the first conductive regions 4 and / or the second conductive regions 5 is provided with contact openings 3 that penetrate a passivation film 2 and extend into the conductive regions, and a composite diffusion barrier layer 6 and a copper electrode 7 are sequentially stacked in the contact openings 3 in a direction away from the silicon substrate.

[0025] Specifically, the silicon substrate has a light-receiving front side and a back side, the back side comprising alternating first and second conductive regions, wherein when the first conductive region is a P-type region, the second conductive region is an N-type region; or, when the first conductive region is an N-type region, the second conductive region is a P-type region. A copper electrode is located above the P-type and N-type regions, filling the interior of the contact opening and extending to cover the passivation film surrounding the opening.

[0026] The back-contact solar cell provided by this invention achieves a balance between excellent electrical performance and high reliability. The optimized cell device exhibits outstanding photoelectric conversion characteristics, with an excellent ohmic contact formed between the copper electrode and the silicon substrate, resulting in extremely low contact resistance. At the same time, the resistivity of the copper electrode itself is much lower than that of conventional electrodes, effectively ensuring the efficient transport and collection of photogenerated carriers. After 1000 hours of humid heat aging at 85℃ / 85%RH, the efficiency decay is minimal, and the weld pull retention rate is excellent, fully demonstrating the long-term stability of the composite diffusion barrier layer.

[0027] In some preferred embodiments, such as Figure 2 As shown, the composite diffusion barrier layer 6 includes a doped transition layer 61 and a copper oxide layer 62 stacked together, wherein the doped transition layer and the copper oxide layer are arranged sequentially in a direction away from the silicon substrate.

[0028] Specifically, the composite diffusion barrier layer consists of a doped transition layer embedded within the semi-finished battery containing the P / N region and a copper oxide layer situated on top of the doped transition layer. The copper oxide layer is not in direct contact with the silicon substrate. The copper oxide layer is a continuous or semi-continuous dense film, covering ≥80% of the interface area between the copper electrode and the silicon substrate, serving as a barrier to prevent copper from diffusing into the silicon.

[0029] Preferably, the thickness of the copper oxide layer is 5~30 nm, for example, it can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, etc.

[0030] Preferably, the doped transition layer is embedded inside the semi-finished battery with the P / N region, and the thickness of the doped transition layer is 10~30 nm, for example, it can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, etc.

[0031] Preferably, the doping element of the doped transition layer includes at least one of phosphorus (P), boron (B) and manganese (Mn).

[0032] Specifically, the doped transition layer is a silicon-based doped interface transition layer, formed in situ by phosphorus, boron, or manganese elements released from the decomposition of diffusion inhibitors migrating to the silicon substrate surface and bonding with silicon atoms. This interface phase is amorphous or a mixture of nanocrystalline and amorphous states. The peak concentration of the doped elements is ≥1×10⁻⁶. 18 atoms / cm 3 The dopant elements in the doped transition layer form chemical bonds with silicon atoms, resulting in an interface state density between the silicon substrate and the recombination diffusion barrier layer of ≤1×10⁻⁶. 11 cm -2 eV -1 .

[0033] In some preferred embodiments, the copper electrode comprises a plurality of copper particles, each copper particle having a metallic copper core and a copper oxide layer covering the surface of the metallic copper core.

[0034] Specifically, each copper particle has a core-shell structure with an internal metallic copper core and a thin layer of copper oxide on the surface, and adjacent copper particles form a direct, conductive metallurgical connection.

[0035] Preferably, the copper electrode thickness is 5~15 μm, for example, 5 μm, 10 μm, 15 μm, etc.; the linewidth is 30~80 μm, for example, 30 μm, 55 μm, 80 μm, etc.; and the bulk resistivity is <10 μΩ·cm.

[0036] In some preferred embodiments, the copper electrode is formed by sintering a copper conductive paste, wherein the viscosity of the copper conductive paste is 30-60 Pa·s; and the solid content of the copper conductive paste is ≥80 wt%. This invention overcomes the traditional technical bias that copper paste must be absolutely protected against oxidation. Through the synergistic effect of the paste formulation and the air sintering process, the nano-oxide layer formed on the surface of the copper particles has the dual function of blocking copper diffusion and maintaining the conductive path, while the interior of the copper particles remains in a metallic state, thus solving the technical problem that copper inevitably fails during air sintering.

[0037] In detail, the composition of copper conductive paste is as follows: The copper conductive paste, by weight, comprises the following components: The copper powder contains 70% to 90% copper powder, for example, 70%, 75%, 80%, 85%, 90%, etc.; preferably, the particle size of the copper powder is 0.5 to 5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0038] The copper oxide powder is 1% to 8%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc., and more preferably 2% to 5%; preferably, the copper oxide powder includes CuO and / or Cu2O; the particle size of the copper oxide powder is 5 to 100 nm.

[0039] The diffusion inhibitor is 0.1% to 5%, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.; preferably, the diffusion inhibitor includes one or more of boron phosphate (BPO4), phosphosilicate glass (PSG), strontium manganate (SrMnO3) or manganese phosphate (Mn3(PO4)2); the weight ratio of the copper oxide powder to the diffusion inhibitor is 2 to 5:1, for example, it can be 2:1, 3:1, 4:1, 5:1, etc.

[0040] 1%~8% glass powder, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.; the glass powder includes low melting point glass containing the TeO2-Bi2O3-SiO2 system; the softening point of the glass powder is 450~600℃, for example, it can be 450℃, 500℃, 550℃, 600℃, etc.

[0041] The organic carrier comprises, in particular, an organic carrier in the remaining amount; preferably, the organic carrier comprises one or more of an organic solvent, a resin, and an additive; the organic solvent comprises one or more of terpineol, butyl carbitol, diethylene glycol butyl ether acetate, and tributyl citrate; the resin comprises one or more of ethyl cellulose, acrylic resin, and phenolic resin; and the additive comprises one or more of a dispersant, a leveling agent, a defoamer, and a thixotropic agent.

[0042] Optionally, the dispersant is selected from one or more of fatty alcohol polyoxyethylene ether, sodium stearate, polyacrylamide, or polyvinyl alcohol; the leveling agent is selected from one or more of polyether-modified polydimethylsiloxane or acrylate copolymer; the defoamer is selected from one or more of dimethyl silicone oil or polyether defoamers; and the thixotropic agent is selected from one or more of organobentonite, hydrogenated castor oil, or fumed silica.

[0043] A second aspect of the present invention provides a method for fabricating a back-contact solar cell, comprising: (a) On a silicon substrate where back-side doping and passivation film deposition have been completed, a contact opening is formed that penetrates the passivation film and exposes a first conductive region and / or a second conductive region; (b) Print copper conductive paste onto the passivation film inside and around the contact opening, and then dry it to remove organic components; (c) Sintering to obtain the back contact solar cell; wherein, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ. During the high-temperature sintering, the P / B / Mn elements released by the decomposition of the diffusion inhibitor preferentially migrate to the silicon interface and bond with silicon atoms to generate a doped transition layer embedded in the silicon surface in situ. Subsequently, the surface of the copper particles undergoes controllable oxidation, forming a continuous and dense copper oxide layer on the doped transition layer. The two together constitute the composite diffusion barrier layer.

[0044] This invention provides a method for fabricating back-contact solar cells that allows for direct sintering of copper electrodes in air without the need for a protective atmosphere, additional deposited barrier layers, or printed seed layers. This solves the technical problem of existing back-contact solar cells using copper electrodes, which require a protective atmosphere or additional deposited barrier layers or printed seed layers, resulting in complex processes and high costs. This invention utilizes air sintering to generate a composite structure of a doped transition layer and a copper oxide layer embedded in silicon at the copper electrode-silicon interface, effectively suppressing copper diffusion, achieving low cost, and producing a highly reliable back-contact cell.

[0045] Specifically, during the sintering process, the diffusion inhibitor in this invention decomposes and releases elements such as P, B, and Mn, forming a doped transition layer embedded in the surface of the silicon substrate in situ (peak concentration ≥ 1 × 10⁻⁶). 18 atoms / cm 3 Interface state density ≤ 1×10 11 cm -2 eV -1 Combined with the copper oxide layer on the surface, the double barrier effectively locks copper atoms within 50 nm of the interface, thus protecting the PN junction.

[0046] This invention does not require nitrogen-protected sintering equipment or additional deposition barrier layers such as PVD / CVD, and can be completed directly in existing air sintering furnaces. Optionally, the 2-10 nm oxide layer on the surface of the copper electrode can be effectively removed under the action of standard flux, with a welding pull force ≥1.0 N. It is fully compatible with existing component stringing and lamination processes, and the metallization cost is reduced by more than 70% compared to silver paste.

[0047] In some preferred embodiments, in step (b), copper conductive paste is printed onto the passivation film inside and around the contact opening using screen printing.

[0048] Preferably, the screen printing stencil has a mesh count of 250-400; the wire diameter is 15-30 μm, for example, 15 μm, 20 μm, 25 μm, 30 μm, etc.; the latex thickness is 10-20 μm, for example, 10 μm, 15 μm, 20 μm, etc.; and the printing wet weight is 5-20 mg / cm³. 2 For example, it could be 5 mg / cm2 10 mg / cm 2 15 mg / cm 2 20 mg / cm 2 The corresponding wet film thickness is 15~35 μm, for example, it can be 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, etc.

[0049] In some preferred embodiments, the drying temperature is 150~200℃, for example, 150℃, 175℃, 200℃, etc.; the drying time is 5~10 min, for example, 5 min, 7.5 min, 10 min, etc.

[0050] In some preferred embodiments, the sintering process includes: placing the dried silicon wafer in a continuous belt sintering furnace, sintering it in an air atmosphere, and then naturally cooling it to room temperature.

[0051] Specifically, the peak temperature of the sintering is 550~650℃, for example, 550℃, 600℃, 650℃, etc., and the peak holding time is 5~20 s, for example, 5 s, 10 s, 15 s, 20 s, etc.

[0052] Preferably, the heating rate of the sintering is 20~40℃ / s, for example, 20℃ / s, 30℃ / s, 40℃ / s, etc.; the cooling rate is 10~30℃ / s, for example, 10℃ / s, 20℃ / s, 30℃ / s, etc.

[0053] Preferably, the air flow rate inside the furnace is 10~50 L / min, for example, 10 L / min, 20 L / min, 30 L / min, 40 L / min, 50 L / min, etc., and the oxygen volume concentration is 15~25%, for example, 15%, 20%, 25%, etc.

[0054] In some preferred embodiments, the doping concentration of the first conductive region and the second conductive region is each independently 1 × 10⁻⁶. 19 ~1×10 20 atoms / cm 3 The junction depths are independently 0.5~2 μm.

[0055] In some preferred embodiments, the contact opening is formed in step (a) using a laser grooving process.

[0056] Preferably, the contact opening depth formed by the laser grooving is 50~150 nm, for example, it can be 50 nm, 100 nm, 150 nm, etc.

[0057] A third aspect of the present invention provides a photovoltaic module, comprising the aforementioned back-contact solar cell or a back-contact solar cell prepared by the aforementioned method. Optionally, the back-contact solar cells are string-welded, stacked, laminated, and framed to obtain the back-contact solar cell module.

[0058] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0059] Example 1 This embodiment provides a back-contact solar cell, the fabrication process of which is as follows: Step 1: Provide a semi-finished back contact battery with front texturing, passivation, and back P-region (boron diffusion) / N-region (phosphorus diffusion) doping and coating. Then, use a laser grooving process to selectively remove the passivation film along the back electrode pattern area, forming contact openings that penetrate the passivation film and expose the surfaces of the P-type and N-type conductive regions; wherein, the P-region doping concentration is 1.5 × 10⁻⁶. 19 atoms / cm 3 The junction depth is 1.25 μm; the N-region doping concentration is 1.5 × 10⁻⁶. 19 atoms / cm 3 The junction depth is 1.25 μm; the laser grooving depth is 120 nm.

[0060] Step 2, Preparation of copper conductive paste (by weight percentage): 80 wt% copper powder, 7 wt% copper oxide powder, 3.5 wt% diffusion inhibitor, 4 wt% glass powder, and the balance organic carrier were mixed and dispersed evenly using a three-roll mill to obtain a copper conductive paste with a fineness of 8 μm. The viscosity of the copper conductive paste was 45 Pa·s, and the solid content was 94.5 wt%. The copper powder has a particle size of 2.5 μm; the copper oxide powder is CuO with a particle size of 50 nm; the diffusion inhibitor is boron phosphate (BPO4); the glass powder is a low-melting-point glass containing the TeO2-Bi2O3-SiO2 system with a softening point of 550℃; and the organic carrier includes terpineol, ethyl cellulose and fatty alcohol polyoxyethylene ether in a weight ratio of 1:1:1.

[0061] Step 3: Screen printing and drying The copper conductive paste is printed onto the electrode patterns of the P-type and N-type regions on the back side using a screen printing process, and then dried to remove organic solvents. The screen printing used a 350-mesh stencil, a 25 μm wire diameter, and a 15 μm latex thickness; the wet weight of the printed material was 12.5 mg / cm³. 2The corresponding wet film thickness is 25 μm; the drying temperature is 180℃ and the drying time is 8 min.

[0062] Step 4: High-temperature sintering The dried silicon wafers are placed in a continuous belt sintering furnace and sintered at high temperature in an air atmosphere. After natural cooling to room temperature, a back contact solar cell is obtained. The peak sintering temperature is 600℃, and the peak holding time is 12 s. The heating rate for sintering is 30℃ / s, and the cooling rate is 20℃ / s. The air flow rate inside the furnace is 30 L / min, and the oxygen volume concentration is 20%.

[0063] The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising an 18 nm thick copper oxide layer and a 20 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 3.0 × 10⁻⁶. 18 atoms / cm 3 .

[0064] Example 2 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that the diffusion inhibitor is strontium manganate (SrMnO3). In step 4, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a copper oxide layer with a thickness of 18 nm and a doped transition layer with a thickness of 20 nm. In the doped transition layer, the peak concentration of manganese dopant is 3.2 × 10⁻⁶. 18 atoms / cm 3 .

[0065] Example 3 This embodiment provides a back-contact solar cell, the difference in its fabrication process from that of Embodiment 1 is that the diffusion inhibitor is phosphosilicate glass (PSG). In step 4, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a copper oxide layer with a thickness of 18 nm and a doped transition layer with a thickness of 20 nm. In the doped transition layer, the peak concentration of phosphorus dopant is 3.5 × 10⁻⁶. 18 atoms / cm 3 .

[0066] Example 4 This embodiment provides a back-contact solar cell, the fabrication process of which differs from that of Embodiment 1 in that: In step 2, 80 wt% copper powder, 2 wt% copper oxide powder, 1 wt% diffusion inhibitor, 4 wt% glass powder, and the balance organic carrier are mixed and dispersed evenly using a three-roll mill to obtain a copper conductive slurry with a fineness of 8 μm; the viscosity of the copper conductive slurry is 35 Pa·s, and the solid content of the copper conductive slurry is 87 wt%. In step 4, the copper electrode formed after high-temperature sintering has a thickness of 9 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising an 18 nm thick copper oxide layer and a 15 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 2.8 × 10⁻⁶. 18 atoms / cm 3 .

[0067] Example 5 This embodiment provides a back-contact solar cell, the fabrication process of which differs from that of Embodiment 1 in that: In step 2, 80 wt% copper powder, 5 wt% copper oxide powder, 1 wt% diffusion inhibitor, 4 wt% glass powder, and the remaining organic carrier are mixed and dispersed evenly using a three-roll mill to obtain a copper conductive slurry with a fineness of 8 μm; the viscosity of the copper conductive slurry is 38 Pa·s, and the solid content of the copper conductive slurry is 90 wt%. In step 4, the copper electrode formed after high-temperature sintering has a thickness of 8 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising an 18 nm thick copper oxide layer and a 16 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 2.9 × 10⁻⁶. 18 atoms / cm 3 .

[0068] Example 6 This embodiment provides a back-contact solar cell, the fabrication process of which differs from that of Embodiment 1 in that: In step 2, 70 wt% copper powder, 8 wt% copper oxide powder, 5 wt% diffusion inhibitor, 8 wt% glass powder, and the remaining organic carrier are mixed and dispersed evenly using a three-roll mill to obtain a copper conductive slurry with a fineness of 8 μm; the viscosity of the copper conductive slurry is 52 Pa·s, and the solid content of the copper conductive slurry is 91 wt%. In step 4, the copper electrode formed after high-temperature sintering has a thickness of 7 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 20 nm thick copper oxide layer and a 22 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 4.2 × 10⁻⁶. 18 atoms / cm3 .

[0069] Example 7 This embodiment provides a back-contact solar cell, the fabrication process of which differs from that of Embodiment 1 in that: In step 2, 90 wt% copper powder, 1 wt% copper oxide powder, 0.1 wt% diffusion inhibitor, 1 wt% glass powder, and the balance organic carrier are mixed and dispersed evenly using a three-roll mill to obtain a copper conductive slurry with a fineness of 8 μm; the viscosity of the copper conductive slurry is 48 Pa·s, and the solid content of the copper conductive slurry is 92 wt%. In step 4, the copper electrode formed after high-temperature sintering has a thickness of 8 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 10 nm thick copper oxide layer and a 12 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 1.5 × 10⁻⁶. 18 atoms / cm 3 .

[0070] Example 8 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that: in step 4, the peak sintering temperature is 550℃ and the peak holding time is 20 s; The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 10 nm thick copper oxide layer and a 13 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 1.8 × 10⁻⁶. 18 atoms / cm 3 .

[0071] Example 9 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that: in step 4, the peak sintering temperature is 650℃ and the peak holding time is 5 s; The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 20 nm thick copper oxide layer and a 22 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 3.8 × 10⁻⁶. 18 atoms / cm 3 .

[0072] Example 10 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that in step 4, the sintering heating rate is 20℃ / s and the cooling rate is 30℃ / s. The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 16 nm thick copper oxide layer and an 18 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 2.9 × 10⁻⁶. 18 atoms / cm 3 .

[0073] Example 11 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that in step 4, the sintering heating rate is 40℃ / s and the cooling rate is 10℃ / s. The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 15 nm thick copper oxide layer and a 17 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 2.7 × 10⁻⁶. 18 atoms / cm 3 .

[0074] Example 12 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that: in step 4, the peak sintering temperature is 540℃ and the peak holding time is 30 s; The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 13 nm thick copper oxide layer and a 10 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 1.2 × 10⁻⁶. 18 atoms / cm 3 .

[0075] Example 13 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that: in step 4, the peak sintering temperature is 660℃ and the peak holding time is 3 s; The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 22 nm thick copper oxide layer and a 23 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 4.2 × 10⁻⁶. 18 atoms / cm3 .

[0076] Example 14 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that in step 4, the sintering heating rate is 15℃ / s and the cooling rate is 35℃ / s. The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 14 nm thick copper oxide layer and a 13 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 2.5 × 10⁻⁶. 18 atoms / cm 3 .

[0077] Example 15 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that in step 4, the sintering heating rate is 45℃ / s and the cooling rate is 5℃ / s. The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a 14 nm thick copper oxide layer and a 14 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 2.6 × 10⁻⁶. 18 atoms / cm 3 .

[0078] Example 16 This embodiment provides a back-contact solar cell, the difference in its preparation process from that of Embodiment 1 is that the copper oxide powder in the copper conductive paste is replaced with an equal amount of copper powder; In step 4, the copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Simultaneously, during the high-temperature sintering process, a composite diffusion barrier layer is generated in situ, comprising a non-uniformly thick copper oxide layer (locally reaching 35 nm, locally only 10 nm) and a 12 nm thick doped transition layer. In the doped transition layer, the peak concentration of boron dopant is 1.2 × 10⁻⁶. 18 atoms / cm 3 .

[0079] Comparative Example 1 This comparative example provides a back-contact solar cell whose preparation process differs from that of Example 1 in that: the copper conductive paste used does not contain copper oxide powder and diffusion inhibitors, and the remaining amount is made up to 100% using an organic carrier. The copper electrode formed after high-temperature sintering has a thickness of 10 μm, the copper particles are unevenly oxidized (the oxide layer thickness is 10~40 nm, with a large number of defects), and a doped transition layer cannot be formed, and the composite diffusion barrier layer is completely missing.

[0080] The remaining steps are the same as in Example 1.

[0081] Comparative Example 2 This comparative example provides a back-contact solar cell, the fabrication process of which differs from that of Example 1 in that: First, a copper oxide film with a thickness of about 50 nm is deposited on the back side of the silicon substrate by magnetron sputtering as a physical barrier layer. Then, conventional copper paste (without copper oxide powder and diffusion inhibitor) is printed onto the copper oxide layer by screen printing. After drying, it is sintered at a peak temperature of 620°C for 10 seconds under a nitrogen atmosphere to form a copper electrode.

[0082] Comparative Example 3 This comparative example provides a back-contact solar cell, the difference in its preparation process from Example 1 being that: in step 4, sintering is performed under nitrogen atmosphere (oxygen concentration <10 ppm). The copper electrode formed after high-temperature sintering has a thickness of 10 μm and a linewidth of 50 μm. Meanwhile, during the high-temperature sintering process, due to the lack of oxygen, a copper oxide layer cannot be formed on the surface of the copper particles. At the same time, the doping elements released by the diffusion inhibitor failed to form an effective doping transition layer at the silicon interface because there was no oxide layer as an enrichment substrate.

[0083] The back-contact solar cells prepared in the above embodiments and comparative examples were used as samples for testing.

[0084] The battery cells used in this invention are of G12R size (182mm × 210mm, diagonal length 295mm), with a single cell area of ​​approximately 382cm². 2 This specification is one of the mainstream large-size specifications in the photovoltaic industry, and the test results are representative of the industry.

[0085] Test method: (1) Contact resistivity test: Contact resistivity was measured using the transmission line method. A set of parallel copper electrode strips with unequal spacing were prepared on the back of the battery. The total resistance between adjacent electrodes was measured using the four-probe method. The contact resistivity was calculated after linear fitting. Five sets of data were measured for each sample, and the average value was taken (mΩ·cm). 2 ).

[0086] (2) Electrical performance testing: A standard solar simulator (AM1.5G, 1000 W / m²) was used. 2 The IV characteristic curve of the battery was measured at 25℃ to obtain the open circuit voltage (Voc), fill factor (FF), and photoelectric conversion efficiency (Eta).

[0087] (3) Reliability testing The solar cells were placed in a constant temperature and humidity chamber at 85°C and 85% relative humidity for 1000 hours of continuous aging before being removed. The photoelectric conversion efficiency of the module before and after aging was tested using a solar simulator, and the efficiency degradation rate was calculated. At the same time, the peeling tensile force of the electrode solder strip was tested in a 180° direction using a tensile testing machine, and the tensile force retention rate before and after aging was compared.

[0088] Efficiency decay rate = initial efficiency Efficiency after aging × 100%; Tensile retention rate = Initial tensile force × Tensile force after aging × 100%.

[0089] The test results are shown in Table 1.

[0090] Table 1

[0091] As shown in Table 1, considering all aspects of performance, Examples 1-3 exhibit the best results, with photoelectric conversion efficiencies reaching 25.5%-25.8%, open-circuit voltages of 734-738 mV, and contact resistances as low as 1.36-1.45 mΩ·cm. 2 The aging efficiency decay was ≤1.1%, and the tensile strength retention rate was ≥92.4%; all three diffusion inhibitors (BPO4, SrMnO3, PSG) achieved an efficiency of >25.5%.

[0092] The parameters in Examples 4-11 deviated slightly, but were still within the preferred range. Their performance decreased slightly, but was still better than the comparative example, indicating that the system has good process stability. The important process parameters in Examples 12-16 were not within the preferred range of the present invention, resulting in a significant decrease in battery performance.

[0093] The efficiency of Comparative Examples 1-3 was only 8.8%-18.4%, with the absence of key components or improper processes leading to complete failure of electrical performance.

[0094] As demonstrated by Examples 1 and 1 (Comparative Example 1), both copper oxide powder and diffusion inhibitor are indispensable. The absence of either component or both components leads to a sharp drop in performance. In Comparative Example 1, the barrier layer was completely absent, resulting in an efficiency of only 8.8%, demonstrating a significant synergistic effect between the two. Examples 1 and 2 (Comparative Example 2) show that while Comparative Example 2 involved pre-deposited CuOx and nitrogen sintering, resulting in an artificial copper oxide layer, the lack of an in-situ doped transition layer limited the physical barrier effect. Examples 1 and 3 (Comparative Example 3 used a nitrogen atmosphere, preventing copper oxidation and resulting in neither a copper oxide layer nor a doped transition layer forming) failed to form the composite diffusion barrier layer of this invention, verifying the necessity of the synergistic combination of copper oxide powder, diffusion inhibitor, and air atmosphere.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A back-contact solar cell, characterized in that, Includes a silicon substrate, wherein the back side of the silicon substrate is provided with alternating first conductive regions and second conductive regions; The surface of the first conductive region and / or the second conductive region is provided with a contact opening that penetrates the passivation film and extends into the conductive region. A composite diffusion barrier layer and a copper electrode are sequentially stacked in the contact opening along the direction away from the silicon substrate.

2. The back-contact solar cell according to claim 1, characterized in that, The composite diffusion barrier layer includes a doped transition layer and a copper oxide layer stacked together, wherein the doped transition layer and the copper oxide layer are sequentially disposed in a direction away from the silicon substrate; Preferably, the thickness of the copper oxide layer is 5~30 nm; Preferably, the thickness of the doped transition layer is 10~30 nm; Preferably, the doping element of the doped transition layer includes at least one of phosphorus, boron and manganese. Preferably, the peak concentration of the dopant element is ≥1×10⁻⁶. 18 atoms / cm 3 .

3. The back-contact solar cell according to claim 1, characterized in that, The copper electrode comprises a plurality of copper particles, each copper particle having a metallic copper core and a copper oxide layer covering the surface of the metallic copper core; Preferably, the copper electrode has a thickness of 5~15 μm, a linewidth of 30~80 μm, and a volume resistivity of <10 μΩ·cm.

4. The back-contact solar cell according to claim 1, characterized in that, The copper electrode is formed by sintering a copper conductive paste. Preferably, the copper conductive paste comprises copper powder, copper oxide powder, diffusion inhibitor, glass powder, and organic carrier; Preferably, the copper conductive paste comprises, by weight percentage: 70%~90% copper powder, 1%~8% copper oxide powder, 0.1%~5% diffusion inhibitor, 1%~8% glass powder, and the balance being an organic carrier; Preferably, the viscosity of the copper conductive paste is 30~60 Pa·s; the solid content of the copper conductive paste is ≥80 wt% Preferably, the copper powder has a particle size of 0.5~5 μm; Preferably, the copper oxide powder comprises CuO and / or Cu2O; the particle size of the copper oxide powder is 5~100 nm; Preferably, the diffusion inhibitor comprises one or more of boron phosphate, phosphosilicate glass, strontium manganate, and manganese phosphate; Preferably, the weight ratio of the copper oxide powder to the diffusion inhibitor is 2~5:1; Preferably, the glass powder comprises a low-melting-point glass containing a TeO2-Bi2O3-SiO2 system; the softening point of the glass powder is 450~600℃; Preferably, the organic carrier includes one or more of organic solvents, resins, and additives; Preferably, the organic solvent includes one or more of terpineol, butyl carbitol, diethylene glycol butyl ether acetate, and tributyl citrate; Preferably, the resin includes one or more of ethyl cellulose, acrylic resin, and phenolic resin; Preferably, the additives include one or more of dispersants, leveling agents, defoamers, and thixotropic agents.

5. The method for preparing a back-contact solar cell according to any one of claims 1-4, characterized in that, include: (a) On a silicon substrate where back-side doping and passivation film deposition have been completed, a contact opening is formed that penetrates the passivation film and exposes a first conductive region and / or a second conductive region; (b) Print copper conductive paste onto the passivation film inside and around the contact opening, and then dry it to remove organic components; (c) Sintering to obtain the back contact solar cell.

6. The preparation method according to claim 5, characterized in that, In step (b), copper conductive paste is printed onto the passivation film inside and around the contact opening using screen printing. Preferably, the screen printing uses a screen with a mesh count of 250-400; a wire diameter of 15-30 μm; a latex thickness of 10-20 μm; and a printing wet weight of 5-20 mg / cm³. 2 The corresponding wet film thickness is 15~35 μm; Preferably, the drying temperature is 150~200℃; the drying time is 5~10 min.

7. The preparation method according to claim 5, characterized in that, The sintering process includes: placing the dried silicon wafer in a continuous belt sintering furnace, sintering it in an air atmosphere, and then naturally cooling it to room temperature. Preferably, the peak temperature of the sintering is 550~650℃, and the peak holding time is 5~20 s; Preferably, the heating rate of the sintering is 20~40℃ / s, and the cooling rate is 10~30℃ / s; Preferably, the air flow rate inside the furnace is 10~50 L / min, and the oxygen volume concentration is 15~25%.

8. The preparation method according to claim 5, characterized in that, The doping concentration of the first conductive region and the second conductive region is each independently 1×10⁻⁶. 19 ~1×10 20 atoms / cm 3 The junction depths are independently 0.5~2 μm.

9. The preparation method according to claim 5, characterized in that, In step (a), the contact opening is formed using a laser grooving process; Preferably, the contact opening depth formed by the laser grooving is 50~150 nm.

10. A photovoltaic module, characterized in that, This includes the back-contact solar cell according to any one of claims 1-4 or the back-contact solar cell prepared by the preparation method according to any one of claims 5-9.

Images