Heterojunction solar cell with back contact structure

Abstract

The utility model provides a heterojunction solar cell with a back contact structure, which is characterized in that intrinsic amorphous silicon, doped amorphous silicon and transparent conductive oxide are adopted to cover the side walls of cell through holes which are distributed in a periodic dot matrix manner, and front electrodes of the cell are connected with electrodes filling the side walls of the through holes and extend to the back surface of the cell; therefore, photon-generated carriers on the front surface of the cell are efficiently conducted to the back surface of the cell through the through holes and then conducted to an external circuit. Moreover, the doped amorphous silicon / intrinsic amorphous silicon on the side wall of the through hole and the n-type silicon substrate can also form a heterojunction, so that photon-generated carriers generated in the cell body can be extracted from the side wall, and the extraction, transmission and collection capabilities of the photon-generated carriers are further enhanced. According to the structural design, on the basis that efficient photon-generated carrier extraction, transmission and collection are achieved, the shading rate of the front electrode can be greatly reduced. According to the heterojunction solar cell, the photo-generated current density of the heterojunction solar cell can be effectively improved, and the photoelectric conversion efficiency of the heterojunction solar cell is further effectively improved.

Description

Technical Field

[0001] The utility model belongs to the field of solar cells, and in particular relates to a heterojunction solar cell with a back contact structure. Background Art

[0002] Photovoltaic power generation is green and environmentally friendly, can be developed sustainably, can solve the energy and environmental crisis of mankind, and has an important strategic position in the future energy development. The development of high-efficiency and low-cost solar cells is the key to promoting the stable and rapid development of the photovoltaic power generation industry. Among all types of solar cells, crystalline silicon solar cells (referred to as crystalline silicon cells) have the fastest development in research and application due to their high photoelectric conversion efficiency, stable performance and low manufacturing cost. The industrialization technology is the most mature and the market share is the highest. At present, industrialized crystalline silicon solar cells mainly include PERC (passivated emitter and rearcell), passivated contact TOPCon (Tunnel oxide and passivated contact) cells, and heterojunction HJT (Silicon Heterojunction) cells. Among them, HJT cells are a highly promising high-efficiency battery industrial technology route. HJT cells can achieve extremely excellent field passivation and interface passivation, selective passage of photogenerated carriers, and one-dimensional efficient collection of photogenerated carriers through the heterojunction composed of doped (boron or phosphorus) amorphous silicon / intrinsic amorphous silicon and substrate silicon, and have very high photoelectric conversion efficiency; moreover, the battery preparation process is very simple.

[0003] At present, HJT cells have not become mainstream in industrialization. HJT cells have very high open circuit voltage, but low photocurrent density, which limits the further improvement of the photoelectric conversion efficiency of heterojunction cells. ph There are two main factors affecting the HJT cell performance: on the one hand, the intrinsic amorphous silicon and doped (boron or phosphorus) amorphous silicon on the front and back of the cell have high optical parasitic absorption coefficients, which affects the utilization of solar photons by HJT cells; on the other hand, HJT cells generally adopt a double-sided cell structure, and the shading loss of the metal electrode on the front of the cell makes the HJT cell's J ph Therefore, improving the photocurrent density of HJT cells - and thus improving their photoelectric conversion efficiency - is of great significance to the further industrial development of HJT cells and the reduction of the cost of electricity in their applications. Utility Model Content

[0004] The utility model proposes a heterojunction solar cell with a back contact structure (referred to as a back contact heterojunction cell). The back contact heterojunction cell has through holes with periodic lattice distribution; the side walls of the through holes are covered with intrinsic amorphous silicon, doped amorphous silicon, transparent conductive oxide and electrodes from the inside to the outside in sequence; the front of the cell has the same intrinsic amorphous silicon, doped amorphous silicon and transparent conductive oxide as the side walls of the through holes; the electrode on the front of the cell is located at the intersection of the through hole and the front of the cell, and is connected to the electrode filling the through hole; the intersection of the back of the cell and the through hole has an electrode connected to the electrode filling the through hole. Through this structural design, the photogenerated carriers collected on the front of the cell can be efficiently transmitted to the back of the cell via the through hole, and conducted to the external circuit; moreover, the doped amorphous silicon / intrinsic amorphous silicon on the side walls of the through holes and the n-type silicon substrate can also form a heterojunction, so that the photogenerated carriers generated in the cell body can be extracted in the side walls, which further enhances the extraction, transmission and collection capabilities of the photogenerated carriers.

[0005] The specific scheme of the utility model is as follows:

[0006] The utility model discloses a heterojunction solar cell with a back contact structure, comprising: an n-type silicon substrate; a first intrinsic amorphous silicon, a first doped amorphous silicon, and a first transparent conductive oxide formed in sequence on the first surface of the silicon substrate; a through hole penetrating the silicon substrate and distributed in a periodic lattice; the sidewall of the through hole is covered in a winding manner by the first intrinsic amorphous silicon, the first doped amorphous silicon, and the first transparent conductive oxide in sequence from the inside to the outside, and is filled with a first electrode unit; a second electrode formed on the first surface of the silicon substrate, the second electrode having a plurality of second electrode units distributed in a periodic lattice, the second electrode unit and the projection of the through hole on the first surface of the silicon substrate having the same shape and geometric center, and the area is equal to the projection area of ​​the through hole on the first surface of the silicon substrate; an electrically insulating isolation region formed on the second surface of the silicon substrate, the electrically insulating isolation region having a plurality of electrically insulating isolation units distributed in a periodic lattice, the electrically insulating isolation unit being an annular region, the overall region included in its outer contour and the through hole on the silicon substrate The projection of the through hole on the second surface of the silicon substrate has the same shape and geometric center, and the area of ​​the whole area is larger than the projection area of ​​the through hole on the second surface of the silicon substrate; a second intrinsic amorphous silicon, a second doped amorphous silicon and a second transparent conductive oxide are sequentially formed in the area of ​​the second surface of the silicon substrate outside the electrically insulating isolation area, and the doping type of the second doped amorphous silicon is opposite to the doping type of the first doped polycrystalline silicon; a third electrode is formed at the intersection of the through hole and the second surface of the silicon substrate, the third electrode has a plurality of third electrode units distributed in a periodic lattice, the projection of the third electrode unit and the through hole on the second surface of the silicon substrate have the same shape and geometric center, and the area is less than or equal to the projection area of ​​the through hole on the second surface of the silicon substrate; the first electrode unit is connected to the second electrode unit and the third electrode unit respectively at the intersection with the first surface and the second surface of the silicon substrate; a fourth electrode is formed in the area outside the electrically insulating isolation area of ​​the second surface of the silicon substrate, and the projection of the fourth electrode and the through hole on the same horizontal plane are completely staggered.

[0007] Optionally, the area percentage of the through holes is 0.05%-0.6%.

[0008] Optionally, the pattern of the periodic lattice distribution of the through holes is rectangular or rhombus; the shape of the through holes is any one of circular, rectangular, rhombus, and elliptical.

[0009] Optionally, the through holes are arranged at a period of 250-5000 microns.

[0010] Optionally, when the through hole is circular in shape, the diameter of the through hole is 10-500 microns, and the diameter of the overall area included in the outer contour of the electrically insulating isolation unit is 100-2000 microns; when the through hole is square, the side length of the through hole is 10-500 microns; the side length of the overall area included in the outer contour of the electrically insulating isolation unit is 100-2000 microns.

[0011] Optionally, the shading rate of the second electrode is 0.05%-0.6%.

[0012] Optionally, the first doped amorphous silicon is p-type doped or n-type doped; the first intrinsic amorphous silicon has a thickness of 1-20nm, and the first doped amorphous silicon has a thickness of 3-50nm; the second intrinsic amorphous silicon has a thickness of 1-50nm, and the second doped amorphous silicon has a thickness of 5-500nm.

[0013] Optionally, the first transparent conductive oxide is any one of tin-doped indium oxide, indium-doped zinc oxide, and aluminum-doped zinc oxide, and has a thickness of 10-150 nm; the second transparent conductive oxide is any one of tin-doped indium oxide, indium-doped zinc oxide, and aluminum-doped zinc oxide, and has a thickness of 10-300 nm.

[0014] Optionally, the first electrode unit is an aluminum electrode or a copper electrode; the second electrode unit and the third electrode unit are silver electrodes.

[0015] Optionally, the fourth electrode is a gate line electrode.

[0016] The utility model has the following beneficial effects:

[0017] 1. The back-contact heterojunction solar cell provided by the utility model uses intrinsic amorphous silicon, doped amorphous silicon and transparent conductive oxide to cover the side walls of the battery through-holes distributed in a periodic lattice. The second electrode unit on the front side of the battery is connected to the first electrode unit filling the side walls of the through-holes and extends to the back side of the battery to form a third electrode unit, thereby conducting the photogenerated carriers on the front side of the battery through the through-holes with low loss and high efficiency to the back side of the battery and then to the external circuit. Furthermore, the doped amorphous silicon / intrinsic amorphous silicon on the side walls of the through-holes can also form a p-type silicon substrate with the n-type silicon substrate. + -in or n +-in heterojunction, the photogenerated carriers generated in the battery body can also be extracted from the side walls, and efficiently transmitted to the back of the battery through the transparent conductive oxide and electrodes on the side walls, which further enhances the extraction, transmission and collection capabilities of the photogenerated carriers. Through this structural design, on the basis of being able to achieve efficient extraction, transmission and collection of photogenerated carriers, the shading rate of the front electrode of the battery can be greatly reduced (typically, less than 0.2%), which significantly increases the area ratio of the battery to receive photons, thereby effectively improving the photogenerated current density of the heterojunction battery. In summary, the back-contact heterojunction battery provided by the utility model can achieve excellent performance in both electrical and optical aspects, thereby effectively improving the photoelectric conversion efficiency.

[0018] 2. The through-holes are filled with copper or aluminum, and the dot-matrix electrode units at the intersection of the through-holes and the front and back sides of the battery are filled with silver. This through-hole metallization solution can not only ensure the efficient transmission and collection of photogenerated carriers in the through-holes, but also significantly save the amount of silver (low-temperature silver paste) used in the metallization of heterojunction batteries. This is because, for the dot-matrix silver electrode at the intersection of the front and back sides of the battery, the area percentage of the dot matrix is ​​significantly lower than the area ratio of the front electrode of the current conventional heterojunction bifacial battery (prepared as a grid-line silver electrode using low-temperature silver paste).

[0019] 3. The back-contact heterojunction solar cell provided by the utility model has a simple structure and can effectively improve the photoelectric conversion efficiency of the heterojunction battery; the preparation method is simple and can be achieved by using the existing battery preparation method, thus effectively reducing the battery manufacturing cost, being suitable for industrialization, and being conducive to the further development of the industrialization of heterojunction batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 .Schematic diagram of the structure of the back contact heterojunction solar cell.

[0021] Among them, 1 is an n-type single crystal silicon substrate, 2 is intrinsic amorphous silicon, 3 is phosphorus-doped amorphous silicon, 4 is boron-doped amorphous silicon, 5 is a transparent conductive oxide on the front of the battery, 6 is a transparent conductive oxide on the back of the battery, 7 is an electrically insulating isolation area adjacent to the intersection of the through hole and the back of the battery, 8 is intrinsic amorphous silicon covering the sidewalls of the through hole, 9 is phosphorus-doped amorphous silicon covering the sidewalls of the through hole, 10 is a transparent conductive oxide covering the sidewalls of the through hole, 11 is the second electrode unit on the front of the battery (located at the intersection of the through hole and the front of the battery), 12 is the first electrode unit filling the through hole, 13 is the third electrode unit at the intersection of the through hole and the back of the battery, 14 is the fourth electrode on the back of the battery; 15 represents the through hole formed in the battery area corresponding to the two vertical dotted lines. Note: Boron-doped amorphous silicon can also be used in the front of the battery and the through hole, and phosphorus-doped amorphous silicon can also be used on the back of the battery.

[0022] Figure 2.Schematic diagram of the through hole lattice distribution pattern of the back contact heterojunction solar cell from the top of the front of the cell. The through hole lattice adopts a periodic square distribution, with square through holes. Among them, 1 is the front of the cell, 2 is the projection of the square through hole on the front of the cell, and is also the second electrode unit on the front of the cell (the two have equal diameters).

[0023] Figure 3 .Schematic diagram of the through hole lattice distribution pattern of the back contact heterojunction solar cell viewed from the back of the cell. The through hole lattice adopts a periodic square distribution, with square through holes. Among them, 1 is the back of the cell, 2 is the doped amorphous silicon / intrinsic amorphous silicon area on the back of the cell, 3 is the electrical insulation isolation area (ring square area) around the intersection of the through hole and the back of the cell, and 4 is the projection of the square through hole on the back of the cell. Note: The third electrode unit at the intersection of the through hole and the back of the cell is within the projection of the through hole on the back of the cell and is not shown in this figure. DETAILED DESCRIPTION

[0024] In order to better understand the utility model, the utility model will be further described below in conjunction with specific embodiments and drawings. Obviously, the embodiments described are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0025] The utility model discloses a heterojunction solar cell with a back contact structure, the cell having the following characteristics:

[0026] The silicon material substrate (referred to as silicon substrate or silicon wafer) used in the battery is n-type (phosphorus-doped) single crystal silicon.

[0027] The battery has through holes distributed in a periodic lattice pattern, and these through holes penetrate the entire battery: starting from the front side of the battery and penetrating to the back side of the battery in a direction perpendicular to the battery surface.

[0028] The front side of the battery has intrinsic amorphous silicon and doped amorphous silicon, the thickness of the intrinsic amorphous silicon is 1-20nm, and the thickness of the doped amorphous silicon is 3-50nm. Among them, the doping type of the doped amorphous silicon can be boron doping or phosphorus doping. For silicon materials, in the utility model, boron doping (acceptor doping, i.e. p-type doping) and phosphorus doping (donor doping, i.e. n-type doping) are defined as "opposite doping conductivity types" to each other.

[0029] The outer side of the doped amorphous silicon on the front of the battery has a layer of transparent conductive oxide (TCO) to enhance charge transfer. The specific choice of transparent conductive oxide is not limited, and can be tin-doped indium oxide (ITO), indium-doped zinc oxide (IZO), aluminum-doped zinc oxide (AZO), etc., and its thickness is 10-150nm.

[0030] The front side of the battery has a second electrode, which is located at the intersection of the through hole and the front side of the battery. The material of the second electrode is not limited, and is generally made of metal, such as silver.

[0031] The through hole is the key structure of the back contact heterojunction battery. The pattern design of the through hole includes the following aspects: the distribution form of the through hole in the periodic lattice on the battery surface, the shape and size of the through hole, and the horizontal spacing between the center points of each adjacent through hole. It can be understood that the through hole pattern design scheme has various forms. Specifically, the through hole can be distributed in a rectangular or rhombus form on the front of the battery, but it is not limited to this. The shape of the through hole is not limited, and can be circular, rectangular, rhombus, elliptical, etc. The size of the through hole, that is, its diameter, side length, and the length of the major and minor axes of the ellipse, is not limited. Typically, taking a circular through hole as an example, its diameter is 10-500 microns; taking a square through hole as an example, its side length is 10-500 microns. Generally, the horizontal spacing (i.e., period) between the center points of each adjacent through hole is 250-5000 microns. The percentage of the total projected area of ​​all through holes on the front of the battery to the battery area is referred to as the through hole area percentage. Generally, the through hole area percentage is between 0.05% and 0.6%, and typically less than 0.2%.

[0032] On the sidewalls of the through-hole, intrinsic amorphous silicon, doped amorphous silicon, and transparent conductive oxide are uniformly covered in sequence from the inside to the outside, and are filled with the first electrode unit. It should be noted that the sidewalls of the through-hole and the front of the battery have the same intrinsic amorphous silicon, doped polycrystalline silicon, and transparent conductive oxide, and their respective thickness ranges are also the same. The intrinsic amorphous silicon on the front of the battery and the intrinsic amorphous silicon on the sidewalls of the through-hole are interconnected, the doped amorphous silicon on the front of the battery and the doped amorphous silicon on the sidewalls of the through-hole are interconnected, and the transparent conductive oxide on the front of the battery and the transparent conductive oxide on the sidewalls of the through-hole are interconnected. Therefore, the coverage of the intrinsic amorphous silicon, doped polycrystalline silicon, and transparent conductive oxide on the sidewalls of the through-hole described in the utility model can be understood as a winding coverage.

[0033] A second electrode on the front of the battery is disposed at the intersection of the through hole and the front of the battery, and the second electrode has a plurality of second electrode units distributed in a periodic lattice. The second electrode unit on the front of the battery and the projection of the through hole on the front of the battery have the same shape, geometric center and size (area). The shading rate of the electrode on the front of the battery (i.e., the second electrode) is between 0.05% and 0.6% (inclusive), and typically less than 0.2%.

[0034] It can be understood that the intrinsic amorphous silicon, doped amorphous silicon and transparent conductive oxide that sequentially cover the side walls of the through holes are all at the nanometer level, while the size of the first electrode unit filled in the through hole is at the micrometer level. Therefore, when comparing the areas, the thickness of other structures on the side walls of the through holes can be ignored, and the area of ​​the second electrode unit can be considered to be equal to that of the first electrode unit.

[0035] It can be understood that the first electrode unit uniformly covers the surface of the transparent conductive oxide and fills the through hole, and the first electrode unit is connected to the second electrode unit on the front side of the battery. The first electrode unit is generally made of metal material, which is not limited to a specific material.

[0036] A third electrode is provided at the intersection of the through hole and the back of the battery, and its function is to conduct the photogenerated carriers collected from the front of the battery to the external circuit. The third electrode has a number of third electrode units with periodic lattice distribution. The projection of the third electrode unit and the through hole on the back of the battery has the same shape and geometric center, and its area is less than or equal to the projection area of ​​the through hole on the back of the battery. It can be understood that in the metallization interconnection and packaging of the back contact heterojunction battery, it is necessary to connect the third electrode units at the projection of the discrete through holes with periodic lattice distribution on the back of the battery to achieve convergence, so as to conduct the photogenerated carriers collected from the front of the battery to the external circuit.

[0037] The first electrode unit filling the through hole, and the second electrode unit and the third electrode unit at the intersection of the through hole and the front and back sides of the battery can be made of the same or different materials. In order to reduce the cost of battery preparation, preferably, the first electrode unit filling the through hole is made of copper or aluminum, and the second electrode unit and the third electrode unit at the intersection of the through hole and the front and back sides of the battery are made of silver.

[0038] The through hole sidewall structure in the utility model has a further function: the doped amorphous silicon / intrinsic amorphous silicon of the through hole sidewall and the n-type silicon substrate also form a p + -in or n + -in heterojunction, so that the photogenerated carriers generated in the cell body can be extracted from the side wall and efficiently transmitted to the back of the cell through the transparent conductive oxide and the first electrode of the side wall. Therefore, this structural design can further enhance the extraction, transmission and collection capabilities of the heterojunction cell.

[0039] The back of the battery, the area around the intersection of the through hole and the back of the battery is an electrically insulating isolation area. The electrically insulating isolation area has a number of electrically insulating isolation units distributed in a periodic lattice. The electrically insulating isolation unit is an annular area, and the overall area contained in its outer contour has the same shape and geometric center as the projection of the through hole on the back of the battery. The area of ​​the overall area is larger than the projection area of ​​the through hole on the back of the battery. Figure 1 and 3As shown. The function of the electrical insulation isolation area is to electrically insulate and isolate the photogenerated carriers derived from the back and front of the battery to avoid shunting or short circuit. On the basis of meeting the electrical insulation isolation performance, the area of ​​this area can be designed to be as small as possible; taking the electrical insulation isolation unit whose overall area included in the outer contour is a square as an example, its side length ranges from 100 to 2000 microns, and the typical side length is 200 to 800 microns.

[0040] The other regions outside the back electrical insulation isolation region are intrinsic amorphous silicon and doped amorphous silicon, where the doped conductivity type of the doped amorphous silicon is opposite to that of the doped amorphous silicon on the front side of the battery. The thickness of the intrinsic amorphous silicon is 1-50nm, and the thickness of the doped amorphous silicon is 5-500nm.

[0041] There is a layer of transparent conductive oxide below the doped amorphous silicon on the back of the cell (the side away from the silicon substrate) to enhance charge transfer. The specific choice of transparent conductive oxide is not limited, and can be tin-doped indium oxide, indium-doped zinc oxide, aluminum-doped zinc oxide, etc., with a thickness of 10-300nm.

[0042] The back of the battery has a fourth electrode with a grid line pattern. The material of the fourth electrode is not limited, and generally metal, such as silver, is used.

[0043] It should be noted that, for the periodic lattice-distributed through holes, when viewed from the normal direction of the battery surface, the projections of the through holes and the fourth electrode unit on the back of the battery on the same horizontal plane should be completely staggered, and preferably have a sufficient horizontal distance to prevent shunting or short-circuiting of photogenerated carriers.

[0044] The above structural design can realize efficient extraction, transmission and collection of photogenerated carriers, and can also significantly reduce the shading rate of the front electrode, and significantly increase the area ratio of the battery receiving photons. Therefore, the back contact heterojunction battery technical solution provided by the utility model can effectively improve the photogenerated current density of the heterojunction battery, and then effectively improve its photoelectric conversion efficiency. The battery structure and preparation process are simple and practical, and can be prepared by conventional technical methods, which is suitable for industrialization.

[0045] The above solution is further illustrated below with reference to a specific embodiment.

[0046] Example 1 provides a back contact heterojunction battery. Figure 1As shown, the back contact heterojunction cell mainly includes: n-type single crystal silicon substrate 1, intrinsic amorphous silicon 2 on the front of the cell, phosphorus-doped amorphous silicon 3 on the front of the cell, boron-doped amorphous silicon 4 on the back of the cell, transparent conductive oxide 5 on the front of the cell, transparent conductive oxide 6 on the back of the cell, electrical insulation isolation area 7 adjacent to the intersection of the through hole and the back of the cell, intrinsic amorphous silicon 8 covering the side wall of the through hole, phosphorus-doped amorphous silicon 9 covering the side wall of the through hole, transparent conductive oxide 10 covering the side wall of the through hole, second electrode unit 11 on the front of the cell (located at the intersection of the through hole and the front of the cell), first electrode unit 12 filling the through hole, third electrode unit 13 at the intersection of the through hole and the back of the cell, and fourth electrode 14 on the back of the cell. The front of the cell and the side wall of the through hole have the same intrinsic amorphous silicon, doped amorphous silicon and transparent conductive oxide.

[0047] The pattern design of through holes on the battery surface, such as Figure 2 As shown, the through-hole dot pattern adopts a periodic square distribution. The projection of the axis of the through-hole on the normal of the back of the battery just falls on the center line between the two adjacent gate wire electrodes metallized on the back of the battery. The horizontal spacing between the axis of each two most adjacent through-holes is 1250μm. The through-hole shape is a square with a side length of 45μm. The first electrode unit on the front of the battery has the same shape, geometric center and area as the projection of the through-hole on the front of the battery. The overall area included in the outer contour of the third electrode unit at the intersection of the through-hole and the back of the battery and the electrically insulating isolation unit on the back of the battery is also a square with side lengths of 35μm and 450μm respectively. Their geometric center is the same as the projection of the through-hole on the back of the battery. The through-hole area percentage and the shading rate of the front electrode of the battery are both 0.13%.

[0048] Then, a method for preparing the back contact heterojunction battery is provided, which specifically comprises the following steps:

[0049] Step 1. Select a 182mm*182mm n-type single crystal silicon wafer with a bulk resistivity of 1Ω·cm.

[0050] Step 2. First, the n-type silicon wafer is textured with a sodium hydroxide solution to form a random pyramid-shaped texture on both sides of the silicon wafer. One side is defined as the front side of the battery, and phosphorus doping is performed later; correspondingly, the other side is defined as the back side of the battery, and boron doping is performed later. Then, a hydrofluoric acid solution is used to etch away the naturally grown thin silicon oxide that may exist on the surface of the silicon wafer. The hydrofluoric acid concentration is 1%, and the cleaning time is 15-30 seconds.

[0051] Step 3. Use VHF-RF-PECVD to prepare intrinsic amorphous silicon and boron-doped amorphous silicon on the back of the battery. The RF frequency is 40.68 MHz and the deposition pressure is 0.2 Torr (1 Torr = 1.33·10 2 Pa), and the deposition temperature is 180°C. The process gases for preparing intrinsic amorphous silicon are SiH4, H2 and CH4, and the process gases for preparing boron-doped amorphous silicon are SiH4, H2, CH4 and TMB (trimethyl boron). The thickness of intrinsic amorphous silicon is 10nm. The thickness of boron-doped amorphous silicon is 30nm, and the square resistance is 50-60Ω / □.

[0052] Step 4. Prepare tin-doped indium oxide (ITO) on the back of the battery by DC magnetron sputtering. The sputtering process parameters are as follows: the target material is a ceramic target of indium tin oxide (In2O3:SnO2=90:10wt%) with a purity higher than 99.999%. The sputtering atmosphere is a mixed gas of Ar and O2 (with a purity higher than 99.999%), and the background vacuum is 1.5·10 -4 Pa, the sputtering gas pressure is 0.1 Pa, and the substrate temperature is 150°C. The thickness of ITO is 120nm, and the sheet resistance is 40-50Ω / □.

[0053] Step 5. Use laser etching technology to prepare through holes. In the etching process, the n-Si substrate, intrinsic amorphous silicon, boron-doped amorphous silicon and ITO need to be etched away in sequence. The through hole pattern is given above. Use a diode-pumped Yb:YAG disk laser with a wavelength of 1030nm, a pulse width of 250-500ns, a repetition frequency of 10-20kHz, and a nitrogen atmosphere. Then, use a dilute hydrochloric acid solution at room temperature to clean the through hole to remove the loss layer of laser etching.

[0054] Step 6. Use a single-sided water-floating hydrofluoric acid solution etching method to etch away the naturally grown thin silicon oxide that may exist on the front side of the battery. The hydrofluoric acid concentration is 1% and the cleaning time is 3-60 seconds.

[0055] Step 7. Use the very high frequency radio frequency inductively coupled PECVD method to prepare intrinsic amorphous silicon and phosphorus-doped amorphous silicon on the front of the battery and the sidewalls of the through-hole. The radio frequency is 110MHz, the deposition pressure is 0.2Torr, and the deposition temperature is 170℃. The process gases for preparing intrinsic amorphous silicon are SiH4, H2 and CH4, and the process gases for preparing phosphorus-doped amorphous silicon are SiH4, H2, CH4 and PH3. The thickness of intrinsic amorphous silicon is 5nm. The thickness of phosphorus-doped amorphous silicon is 10nm, and the square resistance is 90Ω / □.

[0056] Step 8. Prepare ITO on the front of the battery and the side wall of the through hole by DC magnetron sputtering. The sputtering process parameters are as follows: the target material is a ceramic target of indium tin oxide (In2O3:SnO2=90:10wt%) with a purity higher than 99.999%. The sputtering atmosphere is a mixed gas of Ar and O2 (purity higher than 99.999%), and the background vacuum is 1.5·10 -4 Pa, the sputtering gas pressure is 0.1 Pa, and the substrate temperature is 150° C. The thickness of ITO is 80 nm, the sheet resistance is 50-60 Ω / □, and the average light transmittance is 91.5%.

[0057] Step 9. Use low-damage laser etching technology to etch the area around the intersection of the back of the battery and the through hole into an electrically insulating area. Laser etching needs to be able to achieve precise alignment, and the specific pattern design has been given above.

[0058] Step 10. Metallize the sidewall of the through hole by screen printing low-temperature copper paste combined with rapid thermal treatment curing. The copper paste fills the entire through hole to form the first electrode unit. In the screen printing low-temperature copper paste process, it is necessary to align with the through hole formation. The screen printing pattern is the same as the through hole design pattern given above. The drying and curing temperature of the low-temperature copper paste is 120°C, and the time is 7-10 minutes.

[0059] Step 11. Metallize the intersection of the through hole with the front and back of the battery to prepare the second and third electrodes, using screen printing of low-temperature silver paste combined with rapid thermal treatment curing. Screen printing needs to be aligned with the through hole formation, and the screen pattern is consistent with the through hole pattern. The second electrode unit and the third electrode unit are both square, with side lengths of 45μm and 35μm respectively. The drying and curing temperature of the low-temperature silver paste is 170°C, and the time is 15-20 minutes.

[0060] Step 12. The fourth electrode on the back of the battery is prepared by screen printing low-temperature silver paste combined with rapid thermal treatment curing, and its pattern is a grid line type with a line width of 40 μm and a spacing of 1250 μm. The drying and curing temperature of the low-temperature silver paste is 170°C and the time is 15-20 minutes.

[0061] At this point, the preparation of the back-contact heterojunction solar cell is completed. In the metallization interconnection and packaging of the components, a conductive backplane (including a printed circuit board) can be used to connect the third electrode units at the projections of the periodic lattice and discrete through holes on the back of the cell to achieve current convergence, thereby conducting the photogenerated carriers collected by the front of the cell to the external circuit.

[0062] Finally, it should be noted that, although the implementation scheme of the utility model is described above in conjunction with the accompanying drawings, the utility model is not limited to the above-mentioned specific implementation scheme and application field. The above-mentioned specific implementation scheme is only illustrative and instructive, and is used to help understand the method and its core idea of ​​the utility model, but is not restrictive. Under the enlightenment of this specification, ordinary technicians in this field can make many forms of changes, improvements and equivalent implementations in the specific implementation scheme and application scope without departing from the scope of protection of the principles of the utility model and the claims, which should also be regarded as the protection scope of the utility model.

Claims

1. A heterojunction solar cell with a back contact structure, characterized in that: include: n-type silicon substrate; A first intrinsic amorphous silicon, a first doped amorphous silicon, and a first transparent conductive oxide are sequentially formed on the first surface of the silicon substrate; A through hole that penetrates the silicon substrate and is distributed in a periodic lattice; the sidewalls of the through hole are covered in a winding manner from the inside to the outside in sequence by a first intrinsic amorphous silicon, a first doped amorphous silicon, and a first transparent conductive oxide, and are filled with a first electrode unit; A second electrode is formed on the first surface of the silicon substrate, wherein the second electrode has a plurality of second electrode units distributed in a periodic lattice, and the second electrode unit and the projection of the through hole on the first surface of the silicon substrate have the same shape and geometric center, and the area is equal to the projection area of ​​the through hole on the first surface of the silicon substrate; An electrically insulating isolation region is formed on the second surface of the silicon substrate, wherein the electrically insulating isolation region has a plurality of electrically insulating isolation units distributed in a periodic lattice, wherein the electrically insulating isolation unit is an annular region, wherein the overall region included in the outer contour thereof and the projection of the through hole on the second surface of the silicon substrate have the same shape and geometric center, and the area of ​​the overall region is greater than the projection area of ​​the through hole on the second surface of the silicon substrate; A second intrinsic amorphous silicon, a second doped amorphous silicon and a second transparent conductive oxide are sequentially formed in a region of the second surface of the silicon substrate outside the electrically insulating isolation region, wherein the doping type of the second doped amorphous silicon is opposite to the doping type of the first doped polysilicon; A third electrode is formed at the intersection of the through hole and the second surface of the silicon substrate, wherein the third electrode has a plurality of third electrode units distributed in a periodic lattice, and the projection of the third electrode unit and the through hole on the second surface of the silicon substrate have the same shape and geometric center, and the area is less than or equal to the projection area of ​​the through hole on the second surface of the silicon substrate; The first electrode unit is connected to the second electrode unit and the third electrode unit respectively at the intersection with the first surface and the second surface of the silicon substrate; A fourth electrode is formed in an area outside the electrically insulating isolation area on the second surface of the silicon substrate, and projections of the fourth electrode and the through hole on the same horizontal plane are completely offset.

2. The heterojunction solar cell according to claim 1, characterized in that: The area percentage of the through holes is 0.05%-0.6%.

3. The heterojunction solar cell according to claim 2, characterized in that: The pattern of the periodic lattice distribution of the through holes is rectangular or rhombus; the shape of the through holes is any one of circular, rectangular, rhombus and elliptical.

4. The heterojunction solar cell according to claim 3, characterized in that: The arrangement period of the through holes is 250-5000 microns.

5. The heterojunction solar cell according to claim 3, characterized in that: When the through hole is circular in shape, the diameter of the through hole is 10-500 microns, and the diameter of the overall area included in the outer contour of the electrically insulating isolation unit is 100-2000 microns; when the through hole is square, the side length of the through hole is 10-500 microns; the side length of the overall area included in the outer contour of the electrically insulating isolation unit is 100-2000 microns.

6. The heterojunction solar cell according to any one of claims 1 to 5, characterized in that: The light shielding rate of the second electrode is 0.05%-0.6%.

7. The heterojunction solar cell according to any one of claims 1 to 5, characterized in that: The first doped amorphous silicon is p-type doped or n-type doped; the first intrinsic amorphous silicon has a thickness of 1-20nm, and the first doped amorphous silicon has a thickness of 3-50nm; the second intrinsic amorphous silicon has a thickness of 1-50nm, and the second doped amorphous silicon has a thickness of 5-500nm.

8. The heterojunction solar cell according to any one of claims 1 to 5, characterized in that: The first transparent conductive oxide is any one of tin-doped indium oxide, indium-doped zinc oxide, and aluminum-doped zinc oxide, and has a thickness of 10-150nm; the second transparent conductive oxide is any one of tin-doped indium oxide, indium-doped zinc oxide, and aluminum-doped zinc oxide, and has a thickness of 10-300nm.

9. The heterojunction solar cell according to any one of claims 1 to 5, characterized in that: The first electrode unit is an aluminum electrode or a copper electrode; the second electrode unit and the third electrode unit are silver electrodes.

10. The heterojunction solar cell according to any one of claims 1 to 5, characterized in that: The fourth electrode is a gate line electrode.

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