A crystalline silicon solar cell with a localized plasmonic structure and a method of manufacturing the same

Abstract

The application provides a crystalline silicon solar cell with a localized plasmonic structure and a preparation method thereof, which comprises the following steps of texturing, diffusion, single surface cleaning, polishing, junction preparation, annealing, BOE cleaning, ALD, film plating, localized plasmonic structure and metallization in sequence. The structure of the crystalline silicon solar cell comprises a crystalline silicon substrate, wherein the front surface of the crystalline silicon substrate is provided with a carrier selective layer, a first passivation layer and an anti-reflection layer, and the back surface of the crystalline silicon substrate is provided with a second passivation layer composed of a tunneling layer and a heavily doped polysilicon layer, an anti-reflection layer and a localized plasmonic structure. The localized plasmonic structure is embedded in the anti-reflection layer of the back surface of the crystalline silicon substrate and is composed of a plurality of nanometer metal particles. The application increases the localized plasmonic structure on the back surface of the cell by adopting the laser film opening and the electroplating or screen printing mode on the basis of the conventional anti-reflection of the crystalline silicon cell, so that more light is left in the crystalline silicon, and the efficiency of the solar cell is improved.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a crystalline silicon solar cell with a localized plasmon structure and its fabrication method. Background Technology

[0002] Crystalline silicon solar cells are microelectronic devices that directly convert light energy into electrical energy. To ensure sufficient conversion efficiency, the cell must absorb as many photons as possible. With the increasing trend towards thinner wafers, the proportion of transmitted light in crystalline silicon solar cells is gradually increasing.

[0003] To ensure light absorption, traditional solar cells typically have light-trapping structures and anti-reflection films fabricated on their front surface. Common structures include: (1) textured structures, which enhance light scattering and reduce reflection loss through multiple reflections. For example, Chinese patent CN113540268A discloses a solar cell, a textured structure, and its fabrication method, utilizing selectively distributed textured structures to bring better electrical performance to the cell; (2) black silicon structures, such as Chinese patent CN105226114A, which discloses a black silicon passivation structure and its fabrication method, utilizing metal ionization... The method of sub-assisted etching is used to further prepare more complex microporous structures on the textured surface of silicon cells to increase light absorption. However, the surface defect state density of this textured structure is large, which leads to a decrease in the open circuit voltage and fill factor of the cell. (3) Anti-reflection film, such as SiNx, uses the principle of interference cancellation to reduce light reflection. For example, Chinese patent with patent number CN102185006A discloses a method for preparing anti-reflection film of polycrystalline silicon solar cell and a polycrystalline silicon solar cell. The anti-reflection film formed can effectively improve the photoelectric conversion efficiency of polycrystalline silicon solar cell and increase the maximum power of the cell.

[0004] In order to ensure the passivation performance of the back surface and reduce surface recombination, conventional fabrication methods generally make the back surface a polished surface. The smooth surface ensures the preparation effect of the passivation layer, but this also makes it impossible to use traditional light-trapping structures on the back surface, resulting in optical loss. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a crystalline silicon solar cell with a localized plasmon structure and its preparation method. By preparing metal nanoparticles to excite localized plasmons, the light absorption of the crystalline silicon solar cell is further increased without introducing additional damage, thereby improving the efficiency of the solar cell.

[0006] This invention provides a crystalline silicon solar cell with a localized plasmon structure and its fabrication method, the technical solution of which is as follows:

[0007] Step 1: Texturing: The surface of the crystalline silicon substrate is treated with an alkaline solution to form a pyramid-shaped light-trapping structure on the surface of the crystalline silicon substrate;

[0008] Step 2, Diffusion: A boron / phosphorus doping source is used to dop and diffuse one side of the crystalline silicon substrate to prepare a P-type or N-type emitter on the front side of the crystalline silicon substrate.

[0009] Step 3, Single-sided cleaning: A chain machine is used, and an HF aqueous solution is used to remove the oxide layer on the back and sides of the doped silicon wafer;

[0010] Step 4: Polishing: Polish the back side of the crystalline silicon substrate using an alkaline solution;

[0011] Step 5, Junction Formation: A SiO2 tunneling layer is prepared on the back side of a crystalline silicon substrate, and then an N- or P-type doped amorphous silicon thin layer is deposited on the surface of the tunneling layer.

[0012] Step 6, Annealing: Activate the doped atoms in the amorphous silicon thin layer from Step 5 and convert them into doped polycrystalline silicon. The annealing temperature is 800-1000℃ and the annealing time is not less than 1-1.5h.

[0013] Step 7, BOE cleaning: Use hydrogen peroxide and HF to clean the native oxide layer and organic contaminants on the surface of the crystalline silicon substrate;

[0014] Step 8, ALD: Prepare an Al2O3 passivation film on the surface of the P-type emitter;

[0015] Step 9, Coating: A silicon nitride thin film is prepared using SiH4 and NH3 as precursor gases to reduce light reflection of the SiNx thin film and to passivate the silicon substrate with hydrogen by releasing atomic H from the precursor gases.

[0016] Step 10: Prepare an array of dots on the antireflection film surface on the back surface of a crystalline silicon substrate to form a localized plasmon structure composed of several nano-metal particles.

[0017] Step 11, Metallization: Apply metal paste to the front and back sides of the crystalline silicon substrate by screen printing, and then sinter at high temperature to form front and back metal electrodes to collect photogenerated carriers.

[0018] In one embodiment, in step ten: a pulsed laser is used to open an antireflection film layer on the back surface of a crystalline silicon substrate according to the position of the nano-metal particles to be prepared, so as to expose the heavily doped polycrystalline silicon layer. An electroplating process is then used to deposit metal cations on the surface of the polycrystalline silicon layer to form a localized plasmon structure.

[0019] In another embodiment, in step ten: a pulsed laser is used to open the antireflection film layer on the back surface of the crystalline silicon substrate according to the position of the nano-metal particles to be prepared, so that the heavily doped polycrystalline silicon layer is exposed. Solder paste is printed on the back of the battery by screen printing and after being treated with an appropriate temperature, since the tin does not wet the silicon, the tin condenses into individual metal particles at the position where the antireflection film layer is opened, thereby forming a local plasmon structure.

[0020] The volume ratio of the alkaline solution used in step one is KOH:deionized water:ADD = 40:5:1.

[0021] In step three, the ratio of HF aqueous solution used is HF:deionized water = 1:5.

[0022] In step four, the alkaline solution used is a KOH solution with a volume ratio of 1:18-25. The polishing time is 200-350 seconds, and the polishing temperature is 45-65°C.

[0023] This invention also provides a crystalline silicon solar cell with a localized plasmonic structure, the specific technical solution of which is as follows:

[0024] The battery includes a crystalline silicon substrate. The front surface of the crystalline silicon substrate is sequentially provided with a carrier selective layer, a first passivation layer, and an antireflection layer. The back surface of the crystalline silicon substrate is sequentially provided with a second passivation layer composed of a tunneling layer and a heavily doped polycrystalline silicon layer, an antireflection layer, and a localized plasmon structure. The carrier selective layer is a homogeneous structure or a passivated contact structure. The conductivity type of the carrier selective layer is N-type or P-type. An ohmic contact metal electrode is formed on the carrier selective layer on the front surface. An ohmic contact metal electrode is formed on the back surface after the second passivation layer is prepared.

[0025] The local plasmon structure is embedded in the antireflection layer on the back surface of the crystalline silicon substrate and is composed of several nano-sized metal particles.

[0026] Wherein, when the carrier selective layer is a homogeneous structure, the homogeneous structure is a single-crystal doped layer prepared by thermal diffusion or ion implantation, and the sheet resistance of the single-crystal doped layer is 50 to 300 Ω / sq and the junction depth is 0.3 to 3 μm.

[0027] Wherein, when the carrier selective layer is a passivated contact structure: the carrier selective layer on the front surface of the crystalline silicon substrate includes a heavily doped layer and an aluminum oxide passivation layer; the carrier selective layer on the rear surface of the crystalline silicon substrate includes a tunneling oxide layer and a heavily doped polycrystalline silicon layer stacked on the surface of the tunneling oxide layer.

[0028] The heavily doped polycrystalline silicon layer has an N-type or P-type conductivity, a thickness of 50–200 nm, and a doping concentration of 1.0–5.0E+20 cm⁻¹. -3 .

[0029] The implementation of this invention has the following technical effects:

[0030] The crystalline silicon solar cell provided by this invention features a localized plasmonic structure. This structure is achieved by using laser-based film cutting combined with electroplating or screen printing on the back surface of the cell, based on the traditional antireflection technology of crystalline silicon cells. This allows more light to remain inside the crystalline silicon, thereby improving the efficiency of the solar cell.

[0031] The solar cells prepared by the method of this invention also have the following advantages: ① For silicon cells with good interface passivation performance, no additional damage is introduced after laser, sintering and other processes due to H passivation and other factors; ② The nanoscale metal materials form local plasmons, and the surface free electrons will generate collective oscillations under the excitation of incident light. This collective oscillation significantly increases the light scattering path, which can allow light that would otherwise be transmitted to return to the inside of the cell, increasing the final light absorption of the cell, especially for crystalline silicon solar cells that originally transmit strong long-wavelength light. Attached Figure Description

[0032] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0033] Figure 1 This is a schematic diagram of the process flow for fabricating a crystalline silicon solar cell with a localized plasmonic structure according to the present invention.

[0034] Figure 2 This is a simplified structural schematic diagram of the crystalline silicon solar cell prepared according to Embodiments 1 and 2 of the present invention;

[0035] Figure 3 These are several PL brightness diagrams during the localized plasmon structure preparation process in step ten of the preparation method of this invention.

[0036] Figure 4 This is a comparison chart of battery efficiency data for Example 1, Example 2, and conventional batteries. Detailed Implementation

[0037] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1:

[0039] This embodiment describes a method for fabricating a crystalline silicon solar cell with a localized plasmon structure, referring to... Figure 1 As shown, the steps are performed sequentially as follows:

[0040] Step 1: Texturing: The surface of the crystalline silicon substrate is treated with an alkaline solution to form a pyramid-shaped light-trapping structure on the surface of the crystalline silicon substrate. The volume ratio of the solution used is: KOH:DI Water (deionized water):ADD (additive) = 40:5:1.

[0041] Step 2, Diffusion: A boron / phosphorus doping source is used to dop and diffuse one side of the crystalline silicon substrate to prepare a P-type or N-type emitter on the front side of the crystalline silicon substrate.

[0042] Step 3, Single-sided cleaning: A chain machine is used, and an HF aqueous solution is used to remove the oxide layer on the back and sides of the doped silicon wafer. The ratio of HF to deionized water used is 1:5.

[0043] Step 4: Polishing: Polish the back side of the crystalline silicon substrate with an alkaline solution KOH. The volume ratio of the KOH solution is 1:18-25. The polishing time is 200-350 seconds and the polishing temperature is 45-65℃.

[0044] Step 5: Junction Formation: A SiO2 tunneling layer is prepared on the back side of a crystalline silicon substrate, and then an N- or P-type doped amorphous silicon thin film (a-Si) is deposited on the surface of the tunneling layer.

[0045] Step 6, Annealing: Activate the doped atoms in the a-Si thin layer from Step 5 and convert them into doped polycrystalline silicon (poly-Si). The annealing temperature is 800-1000℃ and the annealing time is not less than 1-1.5h.

[0046] Step 7, BOE cleaning, BOE buffered oxide etching: Use hydrogen peroxide and HF to clean the native oxide layer and organic contaminants on the surface of the crystalline silicon substrate.

[0047] Step 8, ALD: Prepare an Al2O3 passivation film on the surface of the P-type emitter.

[0048] Step 9, Coating: A silicon nitride thin film is prepared using SiH4 and NH3 as precursor gases to reduce light reflection and to passivate the silicon substrate with hydrogen by releasing atomic H from the precursor gases.

[0049] Step 10: Prepare an array of dots on the antireflection film surface on the back surface of the crystalline silicon substrate to form a localized plasmon structure composed of several nano-metal particles.

[0050] Step 11, Metallization: Apply metal paste to the front and back sides of the crystalline silicon substrate by screen printing, and then sinter at high temperature to form front and back metal electrodes to collect photogenerated carriers.

[0051] like Figure 2 As shown, the structure of the crystalline silicon solar cell in this embodiment includes a crystalline silicon substrate 1. A P+ emitter 12, an aluminum oxide passivation layer 13, and a front surface antireflection film 14 are sequentially formed on the front surface of the crystalline silicon substrate 1. A tunneling oxide layer 15, an N-type heavily doped polycrystalline silicon layer 16, and a back surface antireflection film 17 are sequentially formed on the back surface of the crystalline silicon substrate. Localized plasmons 18 are also prepared in the back surface antireflection film 17.

[0052] The aluminum oxide passivation layer 13 has a thickness of 0.5–1.5 nm, the front surface antireflective film 14 has a thickness of 60–80 nm, the back surface tunneling oxide layer 15 has a thickness of 0.5–3.0 nm, the back surface antireflective film 18 has a thickness of 80–100 nm, and the nano-metal particles that generate plasmons have a diameter of approximately 50–200 nm, a height of 10–50 nm, and a particle spacing of 0.5–2 μm.

[0053] In this embodiment, the homogeneous emitter is a single-crystal doped layer prepared by thermal diffusion or ion implantation. The sheet resistance of the single-crystal doped layer is 50–300 Ω / sq and the junction depth is 0.3–3 μm.

[0054] It should be noted that the passivation contact structure in this embodiment includes a tunneling oxide layer and a heavily doped polysilicon layer stacked on the surface of the tunneling oxide layer (the surface of the tunneling oxide layer can refer to the front surface and / or the back surface of the tunneling oxide layer). The tunneling oxide layer is made of silicon oxide, titanium oxide, or aluminum oxide, and its thickness is 0.5–3.0 nm. The heavily doped polysilicon layer is N-type or P-type, and its thickness is 100–250 nm with a doping concentration of 1.0–5.0E+20cm. -3 .

[0055] In detail, a tunneling oxide layer, a heavily doped polycrystalline silicon layer, and an antireflection film are prepared on the polished back surface. Preferably, an intrinsic silicon thin layer is formed by physical vapor deposition (PVD) using magnetron sputtering, thermal evaporation, and electron beam deposition, followed by annealing at 500–750°C for 1 hour to form a heavily doped polycrystalline silicon layer; preferably, an 80–100 nm SiNx thin film is prepared by PECVD as the antireflection film.

[0056] Specific implementation methods for forming local plasmon structures:

[0057] A pulsed laser is used to open the anti-reflection coating on the back surface of the solar cell according to the positions of the desired nano-metal particles, exposing a heavily doped polycrystalline silicon layer so that metal cations can be deposited on the polycrystalline silicon surface during electroplating. Preferably, the laser power is within 0.1 to 0.5 W, the laser frequency is 0.5 to 2.0 MHz, and the laser operating speed is determined according to the plasmon spacing, typically 500 to 2000 m / min.

[0058] The preferred electroplating process uses a 5,5-dimethylhydantoin (DMH) cyanide-free silver plating system, employing direct current electrodeposition. The plating bath composition is: silver nitrate 15–40 g / L, DMH 80–200 g / L, potassium carbonate 50–80 g / L, and potassium pyrophosphate 20–50 g / L. The relevant electroplating parameters are: temperature 30–45℃, plating bath pH 10–12, and current density 0.2–0.8 A / dm³. 3 .

[0059] In addition, the applicant discovered through testing that during the preparation of the antireflective coating, the presence of a large amount of [H] in the carrier gas makes the final antireflective coating, such as SiNx, a natural [H] storage structure. When these [H] are excited by an external field, they will release the stored [H] and passivate the dangling bonds on the silicon surface, which is called hydrogen passivation.

[0060] Example 2:

[0061] The preparation method of the crystalline silicon solar cell in this embodiment is roughly the same as that in Example 1, the only difference being the formation method of the local plasmon structure in step ten.

[0062] The structure of the crystalline silicon solar cell in this embodiment also includes a crystalline silicon substrate 1. A P+ emitter 12, an aluminum oxide passivation layer 13, and a front surface antireflection film 14 are sequentially formed on the front surface of the crystalline silicon substrate 1. A tunneling oxide layer 15, an N-type heavily doped polycrystalline silicon layer 16, a back surface antireflection film 17, and a localized plasmon polariton 18 prepared in the back surface antireflection film 17 are sequentially formed on the back surface of the crystalline silicon substrate 1.

[0063] The aluminum oxide passivation layer 13 has a thickness of 0.5–1.5 nm, the front surface antireflective film has a thickness of 60–80 nm, the back surface tunneling oxide layer 15 has a thickness of 0.5–3.0 nm, the back surface antireflective film 18 has a thickness of 80–100 nm, and the nano-metal particles that generate plasmons have a diameter of approximately 50–200 nm, a height of 50–150 nm, and a particle spacing of 0.5–2 μm.

[0064] Regarding the specific implementation method for forming the local plasmon structure in this embodiment:

[0065] Using a pulsed laser, the antireflective coating on the back surface of the solar cell is opened at the positions of the desired nano-metal particles, exposing a heavily doped polycrystalline silicon layer. Screen printing is then used, preferably with solder paste as the printing material. The entire surface is printed with a thickness of about 1 μm. After being treated at a temperature of 250–400°C, the melting point of metallic tin is 231.89°C. Since metallic tin does not wet silicon, at the preferred temperature in this invention, the molten metallic tin will not combine with silicon to form an alloy, but will condense into individual metal particles at the opened positions of the antireflective coating, thereby forming the desired localized plasmons.

[0066] Using lasers may damage the silicon wafer surface, thus affecting battery efficiency. However, in both Embodiment 1 and Embodiment 2 of this invention, laser-induced film opening combined with electroplating or screen printing effectively eliminates laser damage. Figure 3 As shown, (a) represents the PL brightness diagram before laser film opening, (b) represents the PL brightness diagram during laser processing, and (c) represents the PL brightness diagram after obtaining the local plasmon structure. It can be seen that the battery prepared by the method of the present invention can basically repair the damage caused by the laser, thus ensuring the battery efficiency.

[0067] The products prepared according to the methods in Examples 1 and 2 were compared with those of a conventional battery (a TOPcon battery without plasmon resonance) in terms of battery efficiency. The results are as follows: Figure 4 The efficiency comparison diagram shown shows that Example 1 has an efficiency improvement of about 0.21% compared to the conventional battery, and Example 2 has an efficiency improvement of about 0.17% compared to the conventional battery, both showing significant efficiency improvements.

[0068] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for producing a crystalline silicon solar cell having a localized plasmon structure, characterized by, The method comprises the following steps: Step one, texturing: using alkali solution to treat the surface of the crystalline silicon substrate, so that the surface of the crystalline silicon substrate forms a pyramid-shaped light-trapping structure; Step two, diffusion: using boron source / phosphorus source doping source to dope and diffuse one side of the crystalline silicon substrate, so as to prepare P or N type emitter on the front surface of the crystalline silicon substrate; Step three, single-side cleaning: using a chain machine and using HF aqueous solution to remove the oxide layer on the back surface and side surface of the doped silicon wafer; Step four, polishing: using alkali solution to polish the back surface of the crystalline silicon substrate; Step five, junction preparation: preparing SiO2 tunnel layer on the back surface of the crystalline silicon substrate, and then depositing N or P type doped amorphous silicon thin layer on the surface of the tunnel layer; Step six, annealing: activating the doping atoms in the amorphous silicon thin layer prepared in step five, and converting them into doped polysilicon, the annealing temperature is 800-1000℃, and the annealing time is 1-1.5h; Step seven, BOE cleaning: using hydrogen peroxide and HF to clean the native oxide layer and organic contaminant on the surface of the crystalline silicon substrate; Step eight, ALD: preparing Al2O3 passivation film on the surface of the P type emitter; Step nine, film plating: using SiH4 and NH3 as the precursor gas for reaction to prepare silicon nitride thin film, so that the SiNx thin film reduces light reflection and the precursor gas releases atomic H to hydrogen passivate the silicon substrate; Step ten, preparing array type dot matrix on the back surface of the crystalline silicon substrate to form a local plasmonic structure composed of a plurality of nanometer metal particles; Step eleven, metallization: applying metal paste to the front / back surface of the crystalline silicon substrate in a screen printing manner, and then forming front / back surface metal electrodes to collect photo-generated carriers after high-temperature sintering; In step ten, a pulse laser is used to open the anti-reflection film layer on the back surface of the crystalline silicon substrate according to the position of the nanometer metal particles to be prepared, so that the heavily doped polysilicon layer is exposed, and an electroplating process is used to deposit metal cations on the surface of the polysilicon layer to form a local plasmonic structure; Or, A pulse laser is used to open the anti-reflection film layer on the back surface of the crystalline silicon substrate according to the position of the nanometer metal particles to be prepared, so that the heavily doped polysilicon layer is exposed, tin paste is printed on the back surface of the cell in a screen printing manner, and after temperature treatment at 250-400℃, the metal tin does not infiltrate with silicon, and the metal tin condenses into one by one metal particles at the position where the anti-reflection film layer is opened, thereby forming a local plasmonic structure.

2. The method of claim 1, wherein the method further comprises: The volume ratio of the alkali solution used in step one is KOH: deionized water: ADD = 40:5:

1.

3. The method of claim 1, wherein the method further comprises forming a metal layer on the surface of the substrate. The ratio of the HF aqueous solution used in step three is HF: deionized water = 1:

5.

4. The method of claim 1, wherein the method further comprises forming a local plasmonic structure on the surface of the crystalline silicon solar cell. The alkali solution used in step four is KOH solution, and the volume ratio of the solution in the KOH solution is 1:18-25, wherein the polishing time is 200-350s, and the polishing temperature is 45-65℃.

5. A crystalline silicon solar cell with a localized plasmonic structure, characterized in that, The battery is manufactured by the method of any one of claims 1-4, and the battery comprises a crystalline silicon substrate, a front surface of the crystalline silicon substrate is sequentially provided with a carrier selective layer, a first passivation layer and an anti-reflection layer, and a back surface of the crystalline silicon substrate is sequentially provided with a second passivation layer composed of a tunneling layer and a heavily doped polysilicon layer, an anti-reflection layer and a localized surface plasmon structure; the carrier selective layer is a homogenous structure or a passivated contact structure, and the carrier selective layer is of an N-type or a P-type, and a metal electrode with an ohmic contact is formed on the carrier selective layer. The localized surface plasmon structure is embedded in the anti-reflection layer of the back surface of the crystalline silicon substrate, and is composed of a plurality of nanometer metal particles.

6. The crystalline silicon solar cell with localized plasmonic structures of claim 5, wherein, When the carrier selective layer is a homogenous structure, the homogenous structure is a single-crystal doped layer prepared by thermal diffusion or ion implantation, the sheet resistance of the single-crystal doped layer is 50-300 Ω / sq, and the junction depth is 0.3-3 μm.

7. The crystalline silicon solar cell with localized plasmonic structures of claim 5, wherein, When the carrier selective layer is a passivated contact structure, the carrier selective layer on the front surface of the crystalline silicon substrate comprises a heavily doped layer and an aluminum oxide passivation layer.

8. The crystalline silicon solar cell with localized plasmonic structures of claim 5, wherein, The conductivity type of the heavily doped polysilicon layer is N type or P type, the thickness of the heavily doped polysilicon layer is 50-200 nm, and the doping concentration is 1.0-5.0E+20 cm -3 .

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