CN101794845A - Method for preparing selective emitter by one-time diffusion - Google Patents

Abstract

The invention relates to the technical field of production methods of solar cells, in particular to a method for preparing a selective emitter by primary diffusion. It has the following process steps in sequence: first texture the silicon wafer, then perform uniform re-diffusion, deposit a silicon nitride film on the surface of the silicon wafer after diffusion, and then print the corrosive paste on the non-metal electrode area of the silicon wafer to etch Remove the silicon nitride film at this place, and finally use acid solution or alkali solution to etch away the silicon in the non-metal electrode area to obtain a shallow diffusion area, and the electrode area is the heavy diffusion area. The re-diffusion process can get gettered on both sides, the deposition temperature of the silicon nitride film is low, the whole process is simple, easy to control, the surface has no damage, no dead layer, and the cost is low.

Description

A Method for Preparing Selective Emitter by Primary Diffusion

technical field

The invention relates to the technical field of production methods of solar cells, in particular to a method for preparing a selective emitter by primary diffusion.

Background technique

In order to achieve high efficiency of solar cells, researchers from various countries are developing selective emitter solar cells to prepare perfect p-n junctions and ideal contacts, reducing optical loss and electrical loss in the process.

The existing methods for preparing selective emitters are:

(1) Uniform re-diffusion and selective etching on the surface of the silicon wafer. This process includes two processes: 1) uniform re-diffusion on the surface of the silicon wafer, and the junction is relatively deep; 2) the front electrode is screen-printed, and after metallization, a thin layer is etched with plasma in the non-electrode area, and the selective The emitter is also formed. However, plasma etching in this method requires relatively complex and expensive equipment, and the contact of electrodes will be affected during the etching process.

(2) Diffusion to form a selective emitter after corroding the oxide film. First grow a layer of silicon dioxide film on the surface of the silicon wafer, then print the corrosive paste, etch out the shape of the gate line, and then perform phosphorus diffusion to obtain a heavy diffusion area, then wash off the oxide film, and then perform shallow diffusion. In this way, high-doped and low-doped regions are obtained. This method has been used in industrial production at present, but the process is relatively complicated.

(3) Print high-concentration phosphorous slurry only in the electrode area, and then put it into a diffusion furnace for diffusion. Print the high-concentration phosphorus slurry on the surface of the silicon wafer in the form of electrode grid lines, and then put the silicon wafer into a diffusion furnace for diffusion. The high-concentration phosphorous paste volatilizes and deposits from the printing area to the non-printing area during the diffusion process. Since the phosphorus concentration obtained by volatile deposition is not as high as that in the printing area, high and low concentration doping is formed to obtain a selective emitter structure, but the diffusion junction obtained by this method is very uneven, and it is close to the high-concentration phosphorus slurry. The diffuse concentration is high in places, and the concentration is low in distant places.

Contents of the invention

The technical problem to be solved by the present invention is: in order to solve the complex process, difficult control and high production cost of the existing method for preparing a selective emitter, the present invention provides a method for preparing a selective emitter by one-time diffusion.

The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a selective emitter by one-time diffusion, which has the following process steps in turn: first, the silicon wafer is textured, and then uniformly re-diffused, and after the diffusion, the silicon wafer surface Deposit a silicon nitride film, then print the corrosive slurry on the non-metal electrode area of the silicon wafer to etch the silicon nitride film there, and finally use an acid solution or alkaline solution to etch the silicon in the non-metal electrode area to obtain a shallow The diffusion area, the electrode area is the heavy diffusion area.

The silicon wafer is P-type or N-type single crystal silicon or polycrystalline silicon, and its resistivity is 0.2-10Ωcm.

The thickness of the silicon nitride film is 30-200nm.

The acid solution is a mixed solution of HF acid and _HNO3 , wherein the concentration of HF acid is 20-150g/l, and the concentration of _HNO3 is 20-350g/l; the alkali solution is KOH solution or NaOH solution, and the concentration of KOH solution or NaOH solution is 0.1wt%-5wt%; the corrosion time with acid solution or alkali solution is 1-30min, and the temperature is 5-90°C.

The beneficial effects of the invention are: double-sided gettering in the re-diffusion process, low deposition temperature of the silicon nitride film, simple whole process, easy control, no damage on the surface, no dead layer, and low cost.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a structural schematic diagram of the present invention.

In the figure 1. Heavy diffusion area, 2. Shallow diffusion area, 3. Silicon nitride film.

Detailed ways

The present invention is described in further detail now in conjunction with accompanying drawing. These drawings are all simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, so they only show the configurations related to the present invention.

As shown in Figure 1, a method for preparing a selective emitter by one-time diffusion has the following process steps in turn: first texture the silicon wafer, then perform uniform re-diffusion, and deposit 30-200nm thick nitrogen on the surface of the silicon wafer after diffusion Silicon nitride film 3, and then print the corrosive paste on the non-metal electrode area of the silicon wafer to etch the silicon nitride film 3 there, and then use acid solution or alkali solution to etch the non-metal The silicon in the electrode area obtains the shallow diffusion area 2, and the electrode area is the heavy diffusion area 1, and finally the subsequent solar cell process can be performed. Here, the silicon wafer is P-type or N-type single crystal silicon or polycrystalline silicon, and its resistivity is 0.2-10Ωcm.

The preparation of the shallow diffusion junction here is to slowly etch the heavy diffusion area with an acid solution or an alkali solution, and the shallow diffusion area 2 is obtained by controlling the concentration ratio, time, and temperature of the acid solution or alkali solution. The acid solution here is a mixed solution of HF acid and _HNO3 , wherein the concentration of HF acid is 20-150g/l, and the concentration of _HNO3 is 20-350g/l; the alkali solution is KOH solution or NaOH solution, KOH solution or NaOH solution The concentration is 0.1wt%-5wt%; the corrosion time with acid solution or alkali solution is 1-30min, and the temperature is 5-90°C. In this way, by controlling the solution ratio, reaction temperature and time, the corrosion rate can be controlled at about 0.1um/min.

The structure of the selective emitter prepared by this method has no damage on the surface, the surface concentration of the shallow diffusion zone 2 is lower than that of the two-part diffusion method, and there is no dead layer, which effectively avoids the influence of the damaged layer and the dead layer on the performance of the solar cell. At the same time, the re-expansion process can also achieve the effect of double-sided gettering. In addition, the process is simple and easy to control, saving a high-temperature process and reducing the thermal budget.

Example 1:

Select a P-type single-crystal silicon wafer with a crystal plane (100) and a doping concentration of 2.5Ωcm. The surface of the silicon wafer is textured by normal solar cell technology, and then re-diffused to obtain a sheet resistance of 25ohm/Sq. Plating an 80nm SiN film on the surface, and _then printing a corrosive slurry on the non-electrode area. After washing off the etched product, the process temperature is 5°C, the time is 5min. As the process progresses, the heavy diffusion region 1 not covered by the silicon nitride film 3 will be etched slowly. The total etching thickness is 0.6um, and then pickled with 10% HF Remove the SiN shielding film in the electrode area, and then perform other subsequent processes of normal selective diffusion solar cells such as anti-reflection film coating, front and back electrode printing and sintering according to the process requirements.

Inspired by the above-mentioned ideal embodiment according to the present invention, through the above-mentioned description content, relevant workers can make various changes and modifications within the scope of not departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, but must be determined according to the scope of the claims.

Claims (4)

1. A method for preparing selective emitter by one-time diffusion is characterized in that it has the following process steps successively: earlier, the silicon chip is textured, then carries out uniform heavy diffusion, after the diffusion, the silicon nitride film is deposited on the surface of the silicon chip, and then the The corrosive paste is printed on the non-metal electrode area of the silicon wafer to etch away the silicon nitride film there, and finally the silicon in the non-metal electrode area is etched away with acid solution or alkali solution to obtain a shallow diffusion area, and the electrode area is the heavy Diffusion zone. 2. A method for preparing a selective emitter by primary diffusion according to claim 1, characterized in that: the silicon wafer is P-type or N-type single crystal silicon or polycrystalline silicon, and its resistivity is 0.2～10Ωcm . 3. A method for preparing a selective emitter by primary diffusion according to claim 1, characterized in that: the thickness of the silicon nitride film is 30-200nm. 4. a kind of method for preparing selective emitter by primary diffusion according to claim 1 is characterized in that: described acid solution is HF acid and _HNO Mixed solution, wherein the concentration of HF acid is 20-150g/ l, the concentration of _HNO3 is 20-350g/l; the alkali solution is KOH solution or NaOH solution, and the concentration of KOH solution or NaOH solution is 0.1wt%-5wt%; the corrosion time with acid solution or alkali solution is 1-30min, the temperature 5-90°C.

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