WO2017020690A1

WO2017020690A1 - Back-contact solar cell based on p-type silicon substrate

Info

Publication number: WO2017020690A1
Application number: PCT/CN2016/089963
Authority: WO
Inventors: 吕欣; 崇锋
Original assignee: 王能青
Priority date: 2015-08-06
Filing date: 2016-07-14
Publication date: 2017-02-09
Also published as: CN204834653U

Abstract

Disclosed is a back-contact solar cell based on a P-type silicon substrate. The back-contact solar cell comprises a P-type silicon substrate (10). A light receiving surface (10a) of the P-type silicon substrate (10) is provided with a boron-doped p+ doping layer (20) and a first anti-reflective and passivation film (30) thereon. A back surface of the P-type silicon substrate (10) is provided with multiple boron-doped p+ doping regions (40) and multiple phosphorus-doped n+ doping regions (50). Each of the p+ doping regions (40) is provided with a p++ heavy doping region (60) therein, and each of the n+ doping regions (50) is provided with an n++ heavy doping region (70) therein. A second anti-reflective and passivation film (80) is provided on the back surface. First electrodes (91) and second electrodes (92) insulated from each other are provided on the second anti-reflective and passivation film (80), and are respectively electrically connected to the p++ heavy doping regions (60) and n++ heavy doping regions (70). The present invention employs a P-type silicon wafer as a substrate of a back-contact solar cell, and has a significant cost advantage because of the mature P-type silicon wafer technique.

Description

Back contact solar cell based on P type silicon substrate

Technical field

The invention relates to the field of manufacturing new structure solar cells, in particular to a back contact solar cell based on a P-type silicon substrate and a preparation method thereof.

Background technique

With the global energy shortage and climate warming, renewable energy such as solar power is replacing traditional thermal power generation, which has become a hot spot and development trend in the field of energy research. In the history of solar cell development, amorphous silicon thin film solar cells and crystalline silicon solar cells have experienced nearly half a century of development. Crystalline silicon solar cells are more efficient, while amorphous silicon thin film solar cells are less expensive to manufacture. In a conventional P-type silicon substrate solar cell, the PN junction is formed by a high-temperature diffusion method, the PN junction is on the front side and the electrodes are respectively on both sides of the solar cell, and the light-receiving surface is blocked by the electrode to lose part of the sunlight, resulting in partial efficiency damage. At the same time, the conversion efficiency of conventional P-type solar cells has almost reached the bottleneck, and people are gradually shifting to solar cell research with low cost, high efficiency, new structure and new technology.

Since the area of the conventional solar cell receiving surface is about 3.5% to 4% blocked by the front metal grid electrode, in order to reduce or remove the conversion efficiency damage caused by the front electrode shielding, the positive and negative electrodes are disposed on the back of the battery. That is, the back contact type solar cell, the most representative of which is an IBC (Interdigitated back contact) battery.

At present, the base of the IBC battery mainly adopts N-type crystalline silicon, and the P-type emitter is mainly prepared by a high-temperature boron source diffusion process, that is, a method of carrying boron tribromide by high-purity nitrogen. This method mainly has the following problems: 1. BBr ₃ reacts to form B ₂ O ₃ , which has a high boiling point and is still liquid at high temperature, and the surface coverage of the silicon wafer is poor, which is easy to cause poor diffusion uniformity; 2. Boron diffusion The temperature is higher, generally between 900 °C and 1000 °C, which has a great influence on the P-type silicon wafer, which is likely to cause serious decline in the life of the minority carrier; 3. The limitation of the current N-type silicon rod rod technology, its resistivity distribution range (1 Ω·cm ~12 Ω · cm) is much larger than P-type silicon wafer (0.5 Ω · cm ~ 3 Ω · cm), battery process control is more complicated, and the cost of N-type silicon wafer is also an important factor limiting its large-scale application.

Summary of the invention

In view of the above, the present invention provides a P-type silicon substrate-based back contact solar cell and a preparation method thereof, wherein the P-type silicon wafer is used as a substrate material of a back contact solar cell in the solar cell. Its silicon technology is mature and has obvious cost advantages. At the same time, combined with laser non-destructive doping technology, its preparation method is more simplified and easy to implement, which is conducive to large-scale industrial application.

In order to achieve the above object, the present invention adopts the following technical solutions:

A back contact solar cell based on a P-type silicon substrate, comprising a P-type silicon substrate having opposite light-receiving surfaces and a back surface, the light-receiving surface being textured Processing the formed pile surface, the back surface is a plane formed by a planarization process; the light-receiving surface of the P-type silicon substrate is provided with a p+ doped layer doped with boron, and the first lightening surface is disposed on the light receiving surface a passivation film; a back surface of the P-type silicon substrate is provided with a plurality of boron-doped p+ doped regions and a plurality of doped phosphorus n+ doped regions, each of which is disposed in each p+ doped region a p++ heavily doped region, wherein each n+ doped region is provided with an n++ heavily doped region, the back surface is provided with a second anti-passivation film, and the second anti-passivation film is provided with mutual insulation a first electrode and a second electrode, the first electrode being connected to the p++ heavily doped region through the second anti-passivation film electrode, and the second electrode passing through the second anti-passivation passivation The membrane is electrically connected to the n++ heavily doped region.

Wherein, the first electrode and the second electrode are both metal fingers of an interdigitated shape.

Wherein, the first anti-passivation film and the second anti-passivation film are one or more films.

The material of the first anti-passivation film and the second anti-passivation film is SiO ₂ , SiN _x , TiO ₂ , AlO _x or MgF 2 .

Compared with the prior art, the invention adopts a P-type silicon wafer as a substrate material, which is low in cost and universally applied. The backside flattening process, that is, the backside polishing, facilitates the formation of a uniform PN junction and a PP+ high and low junction on the back side, while reducing the surface specific surface area and reducing surface recombination. The doping source is liquid or solid, safe and reliable, and is conducive to laser processing. Compared with conventional thermal diffusion, the laser doping high temperature has a short acting time, and it is easy to accurately position doping and differential doping; the back positive and negative electrode design reduces The front gate line occlusion causes current loss while the metal electrode forms a good ohmic contact with the heavily doped region.

Among them, the laser scanning process is used to process the doping source, mainly by utilizing the thermal effect of the laser, the short effect of the thermal effect, and the precise positioning, so as to form a specific region doping without causing significant damage to the surface of the silicon wafer. Avoiding the side effects of high temperature on P-type silicon wafers, the process is simple, the operation is convenient, the solar cell preparation process is greatly simplified, and the industrial application is more favorable.

DRAWINGS

FIG. 1 is a schematic structural view of a solar cell according to an embodiment of the present invention.

2 is a schematic view showing the structure of a back electrode in an embodiment of the present invention.

3 is a process flow diagram of a method of fabricating a solar cell according to an embodiment of the present invention.

4a-4i are exemplary illustrations of various steps in a method of fabricating a solar cell of the present invention.

detailed description

The technical solutions in the embodiments of the present invention are described in detail below with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the present invention, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

As shown in FIG. 1, this embodiment first provides a P-type silicon substrate-based back contact solar cell including a P-type silicon substrate 10 having a relatively light-receiving light. The surface 10a and the back surface 10b are the suede surface formed by the texturing process, and the back surface 10b is a plane formed by the planarization process. The light-receiving surface 10a of the P-type silicon substrate 10 is provided with a boron-doped p+ doping layer 20, and the light-receiving surface 10a is provided with a first anti-passivation film 30. The back surface 10b of the P-type silicon substrate 10 is provided with a plurality of boron-doped p+ doping regions 40 and a plurality of doped phosphorus n+ doping regions 50 alternately arranged in sequence, each of which is disposed in the p+ doping region 40. There is a p++ heavily doped region 60 with an n++ heavily doped region 70 disposed in each n+ doped region 50. A second anti-passivation film 80 is disposed on the back surface 10b, and the second anti-passivation film 80 is provided with a first electrode 91 and a second electrode 92 insulated from each other, and the first electrode 91 passes through The second anti-passivation film 80 is electrically connected to the p++ heavily doped region 60, and the second electrode 92 is electrically connected to the n++ re-doping through the second anti-passivation film 80. Miscellaneous area 70.

Wherein, the sheet resistance of the p+ doped layer 20 is not more than 60 Ω/□, the sheet resistance of the p+ doped region 40 is not more than 60 Ω/□, and the sheet resistance of the p++ heavily doped region 60 is not more than 40 Ω/□. The n+ doping region 50 has a sheet resistance of not more than 50 Ω/□, and the n++ heavily doped region 70 has a sheet resistance of not more than 30 Ω/□.

As shown in FIG. 2, the first electrode 91 and the second electrode 92 are both metal fingers of an interdigitated shape.

The first anti-passivation film 30 and the second anti-passivation film 80 are one or more thin films, and the materials thereof are SiO ₂ , SiN _x , TiO ₂ , and AlO _x . For example, the first anti-passivation film 30 and the second anti-passivation film 80 may be a SiO ₂ film; or, the first anti-passivation film 30 and the second anti-passivation film 80 include a layer A SiO ₂ film and a SiN _x film coated on the SiO ₂ film.

The method for preparing a solar cell as described above is described below. As shown in FIG. 3, the method includes the steps of:

(a) A P-type silicon substrate is provided, a light-receiving surface of the P-type silicon substrate is textured to form a pile surface, and a back surface of the P-type silicon substrate is planarized to form a plane.

(b) coating or depositing a boron source material on the light receiving surface, applying a laser doping process to diffuse boron in the boron source material into the P-type silicon substrate, and obtaining boron doping on the light receiving surface p+ doped layer. Wherein, the boron source material is selected from the group consisting of a boric acid solution, a borosilicate glass, a boron-containing silicon nitride, a boron-containing silicon oxide or a boron-containing amorphous silicon.

(c) coating or depositing a boron source material on the back surface, applying a laser doping process to diffuse boron in the boron source material into the P-type silicon substrate, and obtaining a plurality of boron doped on the back surface The p+ doped regions form a p++ heavily doped region in each p+ doped region. Wherein, the boron source material is selected from the group consisting of a boric acid solution, a borosilicate glass, a boron-containing silicon nitride, a boron-containing silicon oxide or a boron-containing amorphous silicon.

(d) coating or depositing a phosphorus source material on the back surface, applying a laser doping process to diffuse phosphorus in the phosphorus source material into the P-type silicon substrate, and obtaining a plurality of phosphorus-doped layers on the back surface The n+ doped regions form an n++ heavily doped region in each n+ doped region. The phosphorus source material is selected from the group consisting of a phosphoric acid solution, a phosphosilicate glass, a phosphorus-containing silicon nitride, a phosphorus-containing silicon oxide, or a phosphorus-containing amorphous silicon.

(e) preparing a first anti-passivation film on the light-receiving surface, and preparing a second anti-passivation film on the back surface.

(f) preparing a first electrode and a second electrode on the second anti-passivation film. The first electrode and the second electrode may be prepared by a process such as screen printing, photoinduced plating, chemical plating, or the like, and subjected to a sintering treatment.

It should be noted that the three steps (b), (c) and (d) in the above preparation method are not limited in any order. For example, it may be in the order of (b), (c), or (d), or may be in the order of (d), (b), or (c), or may be sequentially (c), (b). , (d) order.

Wherein, in the laser doping process, the laser light-emitting mode may be pulsed, continuous, quasi-continuous, etc., the laser wavelength may be selected from 355 to 1064 nm, the power may be selected from 5 to 100 W, and the spot diameter may be selected from 30 to 200 μm. When a pulsed laser is selected, the range of the laser pulse width can be selected from 30 to 300 ns.

Steps (c) and (d) in the above preparation method can be prepared in the following manner for the p++ heavily doped region and the n++ heavily doped region:

In the first step, taking the p++ heavily doped region in the step (c) as an example, the process parameters are automatically switched by setting a laser scanning system, and the p+ doping region is obtained by a laser doping process, and the p+ is The p++ heavily doped region is formed in the doped region. Specifically, when scanning is started, the laser scanning system The process parameters are parameters for preparing the p+ doped region. When scanning to the position where the p++ heavily doped region is prepared, the laser scanning system automatically switches to the process parameters for preparing the p++ heavily doped region, and the scanning preparation completes the p++ heavily doped region. Thereafter, the laser scanning system automatically switches to the parameters for preparing the p+ doped region until the p+ doped region is finally completed. Similarly, the preparation of the n++ heavily doped region in step (d) is also carried out in the manner previously described.

In the second method, the p+ doped region is prepared by the laser doping process, and then the p+ doped region is prepared in the p+ doped region. The position is subjected to a secondary laser doping process to form the p++ heavily doped region. Similarly, the preparation of the n++ heavily doped region in step (d) is also carried out in the manner previously described.

Example 1

1. As shown in FIG. 4a, a P-type silicon substrate 10 is first provided, which includes opposite light-receiving faces 10a and back faces 10b. The surface of the light-receiving surface 10a of the P-type silicon substrate 10 is subjected to surface texturing treatment: specifically, a mixed solution of potassium hydroxide or sodium hydroxide, IPA and a texturing additive may be used for surface treatment, and the surface has a pyramid-shaped pile. Surface structure; the silicon substrate 10 is chemically cleaned after the texturing process is completed. The back surface 10b of the P-type silicon substrate 10 is planarized: specifically, first, a protective dielectric film of SiO ₂ , SiN _x or the like is used on the light-receiving surface 10a, and then directly in a potassium hydroxide or sodium hydroxide alkali solution (10% by mass). Back etching is performed in the fraction), or back etching is performed using a HF/HNO ₃ mixed acid solution, and the silicon substrate 10 is chemically cleaned after the etching is completed.

2. As shown in Fig. 4b, a boron source material 10c is applied to the light-receiving surface 10a and the back surface 10b, respectively, and a boric acid solution or other boron-containing organic solvent may be used. In a further embodiment, the boron source material 10c of the borosilicate glass, the boron-containing silicon nitride, the boron-containing silicon oxide or the boron-containing amorphous silicon to form a thin film layer may also be deposited by a CVD deposition process. After drying the boron source material 10c, as shown in FIGS. 4c and 4d, a p+ doped layer (PP+ high and low junction) 20 is formed by laser scanning on the light receiving surface 10a, and a laser is locally scanned on the back surface 10b to obtain a plurality of boron doped p+. A doped region (PP+high and low junction) 40 is formed and a p++ heavily doped region 60 is formed in each p+ doped region 40, and then the residual boron doping source is removed by chemical cleaning and blown dry. The sheet resistance of the p+ doped layer 20 of the light receiving surface 10a is not higher than 60 Ω/□, and the sheet resistance of the p+ doping region 40 of the back surface 10b is not higher than 60 Ω/□, and a green light pulse having a wavelength of 532 nm may be used, continuous or quasi- The continuous laser has a power of 18 W, a scanning speed of 1.2 m/s, and a spot diameter of 50 μm. The sheet resistance of the P++ heavily doped region 60 is not higher than 40 Ω/□, and a green pulse with a wavelength of 532 nm, a continuous or quasi-continuous laser, a power of 20 W, a scanning speed of 1 m/s, and a spot diameter of 50 μm can be used. In other embodiments, a 355 nm ultraviolet pulse, continuous or quasi-continuous laser may be used, with a power selection of 5 to 15 W, a scanning speed of 1 to 1.2 m/s, and a spot diameter of 40 μm for laser scanning. It is also possible to use a 1064 nm infrared pulse, continuous or quasi-continuous laser with a power selection of 10 to 35 W, a scanning speed of 1 to 1.2 m/s, and a spot diameter of 60 μm for laser scanning.

3. As shown in Fig. 4e, a phosphorus source material 10d is coated on the back surface 10b, and a phosphoric acid solution or other phosphorus-containing organic solvent may be used. In other embodiments, the phosphorus source material 10d may be deposited by a CVD deposition process to form a thin film layer of phosphosilicate glass, phosphorus-containing silicon nitride, phosphorus-containing silicon oxide or phosphorus-containing amorphous silicon. After drying the phosphor source material 10d, as shown in FIGS. 4f and 4g, a plurality of phosphorus-doped n+ doped regions 50 (forming a PN junction with the substrate) are formed by laser scanning in respective regions, and each n+ doping An n++ heavily doped region 70 is formed in region 50, and the residual phosphorus doping source is removed by chemical cleaning and blown dry. Wherein, the plurality of boron-doped p+ doping regions 40 and the plurality of doped phosphorus n+ doping regions 50 are alternately arranged. The square resistance of the n+ doped region 50 is not higher than 50 Ω/□, and a 532 nm green pulse, continuous or quasi-continuous laser can be used, the power is 12 W, the scanning speed is 1.2 m/s, and the spot diameter is 50 μm. The block resistance of the n++ heavily doped region 70 is not higher than 30 Ω/□, and a 532 nm green pulse, continuous or quasi-continuous laser can be used, the power is 18 W, the scanning speed is 1.2 m/s, and the spot diameter is 50 um. In other embodiments, a 355 nm ultraviolet pulse, continuous or quasi-continuous laser may be used, with a power selection of 5 to 15 W, a scanning speed of 1 to 1.2 m/s, and a spot diameter of 40 μm for laser scanning. It is also possible to use a 1064 nm infrared pulse, continuous or quasi-continuous laser with a power selection of 10 to 35 W, a scanning speed of 1 to 1.2 m/s, and a spot diameter of 60 μm for laser scanning.

4. As shown in FIG. 4h, a first anti-passivation film 30 is formed on the light-receiving surface 10a, and a second anti-passivation film 80 is formed on the back surface 10b. Specifically, first, on the light-receiving surface 10a and the back surface 10b, a low-temperature oxidation of the furnace tube is used to form a SiO ₂ film layer, and the laser thermal damage is repaired. The SiO ₂ film has a thickness of about 10 nm, an oxidation temperature of 600 to 800 ° C, and a time of 20 to 30 min. Then, a SiNx film is prepared on the SiO ₂ film layer by a PECVD process. Finally, the first anti-passivation film 30 and the second anti-passivation film 80 are respectively composed of a SiO ₂ film layer and a SiNx film. In some other embodiments, the first anti-passivation film 30 and the second anti-passivation film 80 may also include only one film layer, for example, only a SiO ₂ film layer. In other embodiments, it is also possible to deposit an aluminum oxide passivation film instead of the above SiO ₂ film layer by PECVD or ALD, and then deposit a layer of SiNx film.

5. As shown in FIG. 4i, a first electrode 91 and a second electrode 92 (positive and negative electrodes) are formed by screen printing on the second anti-passivation film 80 and sintered, and the first electrode 91 and the second electrode 92 are formed. The second anti-passivation film 80 is electrically connected to the p++ heavily doped region 60 and the n++ heavily doped region 70, respectively. That is, the entire battery preparation process is completed.

Among them, the above steps involve a chemical cleaning process, which may be a cleaning method such as RCA, SPM, HF/O ₃ , HCl/HF.

Example 2

This embodiment differs from Embodiment 1 in that Step 2 and Step 3 in Embodiment 1 are used in this embodiment. The order is reversed, that is, after the P-type silicon substrate 10 is processed, the n+ doping region 50 and the n++ heavily doped region 70 are first prepared on the back surface 10b, see step 3 in the embodiment 1, and then on the light receiving surface 10a. The p+ doped layer 20, the p+ doped region 40, and the p++ heavily doped region 60 are prepared on the back side 10b, see step 2 in Example 1. The remaining steps are the same as those in Embodiment 1, and are not described herein again.

Compared with the prior art, the invention adopts a P-type silicon wafer as a substrate material, which is low in cost and universally applied. The backside flattening process, that is, the backside polishing, facilitates the formation of a uniform PN junction and a PP+ high and low junction on the back side, while reducing the surface specific surface area and reducing surface recombination. The doping source is liquid or solid, safe and reliable, and is conducive to laser processing. Compared with conventional thermal diffusion, laser doping has a short action time, easy to accurately position doping, differential doping, and reduce frontal gate line occlusion. The current is lost while the metal electrode forms a good ohmic contact with the heavily doped region.

Among them, the laser non-destructive doping process is used to treat the doping source, mainly by utilizing the advantages of laser thermal effect, short thermal effect time, and precise positioning, and forming a specific region without causing obvious damage to the surface of the silicon wafer. Miscellaneous, avoiding the side effects of high temperature on P-type silicon wafer, simple process, convenient operation, greatly simplifying the preparation process of solar cells, and is more conducive to industrial application.

The above description is only a specific embodiment of the present application, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present application. It should be considered as the scope of protection of this application.

Claims

A back contact solar cell based on a P-type silicon substrate, comprising: a P-type silicon substrate having opposite light-receiving surfaces and a back surface, the light-receiving surface being textured The formed suede surface is a plane formed by a planarization process; the light-receiving surface of the P-type silicon substrate is provided with a boron-doped p+ doped layer, and the light-receiving surface is provided with a first subtraction a reverse passivation film; a back surface of the P-type silicon substrate is provided with a plurality of boron-doped p+ doped regions and a plurality of doped phosphorus n+ doped regions, which are arranged alternately in each p+ doped region a p++ heavily doped region, each n+ doped region is provided with an n++ heavily doped region, the back surface is provided with a second anti-passivation film, and the second anti-passivation film is provided with mutual insulation a first electrode and a second electrode, the first electrode is electrically connected to the p++ heavily doped region through the second anti-passivation film, and the second electrode passes through the second reversal A passivation film is electrically connected to the n++ heavily doped region.
The solar cell according to claim 1, wherein the first electrode and the second electrode are both interdigitated metal electrodes.
The solar cell according to claim 1, wherein the first anti-passivation film and the second anti-passivation film are one or more films.
The solar cell according to claim 3, wherein the material of the first anti-passivation film and the second anti-passivation film is SiO 2 , SiN x , TiO 2 , AlO x or MgF 2 .