阅读说明：本技术 N型电池正面se结构的制备方法 (Preparation method of positive SE structure of N-type battery ) 是由 瞿辉 曹玉甲 杨松波 张强 袁玲 杨三川 于 2020-07-01 设计创作，主要内容包括：本发明涉及一种N型电池正面SE结构的制备方法,具体为在制绒后的N型硅片上生长一层氧化层,然后按照细栅线的图形位置在氧化层上利用激光进行开槽,再进行硼扩散,后续则进行常规电池制备流程后,在开槽处印刷金属电极。由于氧化层对于硼扩散具有一定的阻挡作用,因此在硼扩散过程中,氧化层覆盖区掺杂浓度较低,可形成浅掺杂区；而开槽处则无氧化层或氧化层极薄,则形成重掺杂区,从而形成硼扩散面SE结构。(The invention relates to a preparation method of an SE structure on the front surface of an N-type battery, which particularly comprises the steps of growing an oxide layer on a textured N-type silicon wafer, then slotting on the oxide layer by utilizing laser according to the pattern position of a fine grid line, then carrying out boron diffusion, and then printing a metal electrode at the slotting after carrying out a conventional battery preparation process. Because the oxide layer has a certain barrier effect on boron diffusion, the doping concentration of the oxide layer covering area is low in the boron diffusion process, and a shallow doping area can be formed; and no oxide layer or extremely thin oxide layer is formed at the groove, and a heavily doped region is formed, so that a boron diffusion surface SE structure is formed.)

1. A preparation method of an N-type battery front SE structure is characterized by comprising the following steps:

s1: texturing;

s2: and (3) oxidation: growing an oxide layer with the thickness of 60-80nm on the surface of the silicon wafer;

s3: laser grooving: laser grooving is carried out on the oxide layer according to the pattern position of the fine grid line, so that the corresponding oxide layer is ablated, and meanwhile, a thermal oxide layer with the thickness of 5-7nm is formed on the ablated silicon surface under the action of laser heat;

s4: and (4) boron diffusion.

2. The method for preparing the SE structure on the front surface of the N-type battery as claimed in claim 1, wherein the method comprises the following steps: the thickness of the oxide layer in step S2 is 70-75 nm.

3. The method for preparing the SE structure on the front surface of the N-type battery as claimed in claim 1, wherein the method comprises the following steps: in the step S3, the laser grooving is carried out by adopting a laser, and the power of the laser is controlled to be 12-14W.

4. The method for preparing the SE structure on the front surface of the N-type battery as claimed in claim 1, wherein the method comprises the following steps: the diffusion temperature of the boron diffusion in the step S4 is controlled to be 950-980 ℃.

Technical Field

The invention belongs to a solar cell production technology, and particularly relates to a preparation method of an N-type cell front surface SE structure.

Background

Solar energy is a clean, safe and inexhaustible energy. The development and utilization of solar energy can effectively solve the problems of environmental pollution, energy crisis and the like in the prior art. Solar cells are devices that convert solar energy directly into electrical energy. At present, the conversion efficiency and the mass production scale of solar cells in China are in the leading position all over the world. The N-type solar cell has the characteristics of high minority carrier lifetime, insensitivity to certain metal impurities and the like, so that the N-type solar cell has higher efficiency and stability. In addition, the N-type solar cell has the advantages of good weak light response, low temperature coefficient and the like, can improve the utilization efficiency of sunlight, and becomes one of the research hotspots in the photovoltaic industry.

A Selective Emitter (SE) solar cell, which is formed by high-concentration doping at and near the contact portion of the metal gate line and the silicon wafer, and low-concentration doping at the region except the electrode, is shown in fig. 1. SE structure solar cells have several advantages: firstly, the non-SE region can be doped with low concentration, and the carrier recombination rate is inversely proportional to the square of the concentration of the impurities, so that the low-concentration doping of SE can effectively reduce the transverse flow of carriers in the diffusion layer, reduce the carrier recombination rate and improve the open-circuit voltage and the current of the battery. According to the metal-semiconductor contact resistance theory, the contact resistance is related to the metal barrier and the surface doping concentration, the higher the doping concentration is, the smaller the contact resistance is, and the higher the filling factor is, so that the high-concentration doping of the B-plane-expanded SE structure can effectively improve the filling factor of the battery.

At present, the manufacturing technology of SE mainly comprises the following methods: 1. the laser method SE is to secondarily drive a doping source in the PSG or BSG by using laser energy to form a heavily doped region, and a non-laser region forms a shallow doped region. The method has few process steps, does not need to add other equipment except laser, is adopted by most PERC battery manufacturers at present, but has the defects that the required laser power is higher, the damage to a silicon wafer is larger, the battery efficiency is not obviously improved, and the production yield is lower because a B source in BSG is difficult to promote. 2. And (3) a reverse etching method, namely printing an organic material mask as same as the pattern of the front grid line on the wafer after the re-diffusion to be used as a corrosion barrier layer, and then corroding the re-diffusion area outside the mask by using a corrosion liquid to form a shallow junction. The method has the advantages of high yield, low fragment rate and easy industrialization, but the reverse etching step is difficult to control, and more process equipment is added. 3. And printing a boron source by a single-step diffusion method, namely screen printing the boron source, performing diffusion by high-temperature heating, forming heavy doping at the contact position with the grid line, and forming shallow doping at other positions. The method has simple process and does not need to increase equipment. However, the diffusion process is difficult to adjust, and the boron source is easily introduced by screen printing, so that the battery and the diffusion furnace tube are polluted.

Disclosure of Invention

In order to overcome the above defects, an object of the present invention is to provide a method for manufacturing an N-type cell front SE structure, which has a simple process and effectively forms a high-concentration doped region and a low-concentration doped region on the cell surface, thereby improving the conversion efficiency of a solar cell.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a preparation method of an N-type battery front SE structure comprises the following steps:

s1: texturing;

s2: and (3) oxidation: growing an oxide layer with the thickness of 60-80nm on the surface of the silicon wafer;

s3: laser grooving: laser grooving is carried out on the oxide layer according to the pattern position of the fine grid line, so that the corresponding oxide layer is ablated, and meanwhile, a thermal oxide layer with the thickness of 5-7nm is formed on the ablated silicon surface under the action of laser heat;

s4: and (4) boron diffusion.

As a further improvement of the invention: the thickness of the oxide layer in step S2 is 70-75 nm.

The thickness of the oxide layer is crucial, and if the thickness of the oxide layer is thinner, the barrier effect on boron diffusion is weaker, and an effective shallow doped region cannot be formed; if the oxide layer is thicker, the barrier effect on boron diffusion is too strong, so that the boron source cannot be doped into the silicon wafer or the doping process time is too long, and the battery performance is influenced.

In the invention, the laser grooving in the step S3 is carried out by adopting a laser, and the power control of the laser is related to the ablation of an oxide layer and the thickness of the formed oxide layer; when the laser power is too low, the ablation thickness of the oxide layer is relatively thin, and the slotted region cannot form an effective heavily doped region after diffusion. When the laser power is too high, the thickness of the oxide layer grown by self-heating is thicker, and meanwhile, the silicon wafer is easily damaged, the recombination of carriers is aggravated, and the efficiency of the battery is influenced. (ii) a According to theoretical calculations and experiments, as a preferred embodiment of the invention: the laser power is controlled at 10-15W, preferably 12-14W.

In the invention, because an oxide layer is pre-grown before boron diffusion, the subsequent boron diffusion temperature is controlled to be 950-980 ℃, and if the temperature is too low, the propulsion time is longer or a boron source cannot propel a silicon wafer; and the crystal lattice damage to the silicon wafer can be caused by overhigh temperature.

The principle of the invention is as follows: growing an oxide layer on the textured N-type silicon wafer, then slotting on the oxide layer by using laser according to the pattern position of the fine grid line, then carrying out boron diffusion, and then printing a metal electrode and the like at the slotting position according to the conventional battery preparation flow. Because the oxide layer has a certain barrier effect on boron diffusion, the doping concentration of the oxide layer covering area is low in the boron diffusion process, and a shallow doping area can be formed; and no oxide layer or extremely thin oxide layer is formed at the groove, and a heavily doped region is formed, so that a boron diffusion surface SE structure is formed.

The invention has the beneficial effects that:

1. the preparation method can carry out local high-concentration doping on the contact area of the metal grid line of the N-type battery and the silicon wafer, and carry out low-concentration doping on the area except the electrode. The low-concentration doping of the SE structure can effectively reduce the transverse flow of carriers in the diffusion layer, reduce the carrier recombination rate and improve the open-circuit voltage and the current, and the high-concentration doping of the SE structure can effectively improve the filling factor, so that the conversion efficiency of the solar cell is improved. In addition, the oxide layer grown before B diffusion can also improve the uniformity of B diffusion resistance.

2. And boron diffusion is carried out on the basis of growing the oxide layer, so that the uniformity of boron diffusion sheet resistance is improved.

3. The preparation method provided by the invention is simple, the compatibility of the required equipment and process with the existing PERC production equipment is high, the large-scale mass production is favorably realized, and the production cost is greatly reduced.

Drawings

FIG. 1 is a conventional N-type cell structure;

fig. 2 is an N-type boron extended surface SE cell structure.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.