CN102122684B - Electrode preparation method applied to crystalline silicon solar battery - Google Patents

Abstract

The invention discloses an electrode preparation method applied to a crystalline silicon solar battery. The method comprises the following steps of: firstly, uniformly diffusing a silicon sheet and forming a p-n node and an oxidization layer rich in diffusion elements simultaneously; secondly, thinning and optimizing the thickness of the oxidization layer, covering a metal electrode on a part of the oxidization layer and performing thermal treatment, wherein in the thermal treatment process, the oxidization layer has functions of preventing the metal electrode from burning through the p-n node, and reducing the contact resistance of a metal semiconductor; and finally, removing the oxidization layer which is not covered by the metal electrode and a silicon material of which the surface of the silicon sheet is rich in diffusion elements by using chemical solution. By the method, the electrode can be prevented from burning through the p-n node and the contact resistance between the electrode and the silicon sheet can be reduced simultaneously, and the battery conversion efficiency can be improved; and the method has the advantage of low cost, and can be compatible with a process for industrially producing crystalline silicon solar batteries.

Description

A method for preparing electrodes applied to crystalline silicon solar cells

technical field

The invention belongs to the technical field of solar cells, and in particular relates to an electrode preparation method applied to crystalline silicon solar cells.

Background technique

The current manufacturing process of traditional crystalline silicon solar cells in industrial production is: silicon wafer cleaning - texture preparation - high temperature diffusion - removal of phosphosilicate glass - plasma edge etching or etching of the back pn junction - PECVD deposition of SiNx:H Thin films - screen printed front, back electrodes and back aluminum - high temperature co-sintering. During the high-temperature co-sintering process, the electrode will burn through the silicon nitride and form an alloy contact with the emitter. Therefore, in order to form a good metal-semiconductor contact, the contact resistance is small and the leakage of the electrode is avoided when the electrode burns through the emitter. The requirements for the depth and phosphorous doping concentration on the emitter surface are relatively high. Usually, after the silicon wafer used for crystalline silicon solar cells is diffused at high temperature to form a uniform emitter, the concentration of phosphorus atoms or boron atoms doped on the surface is very high, in the range of 10 ²¹ ~ 10 ²² cm ^-3 . In the case of high surface doping concentration, Auger recombination plays a dominant role, resulting in serious electron-hole recombination phenomenon on the surface, poor short-wave response of the battery, and decreased short-circuit current of the battery; at the same time, high surface doping concentration is not conducive to surface Due to the effect of the passivation process, it is difficult to increase the open circuit voltage of the battery. Therefore, the conventional high-temperature diffused uniform emitter structure is not conducive to the further improvement of battery conversion efficiency.

In view of the shortcomings of the uniform emitter structure, the research on the new preparation process of the selective emitter structure has become one of the hotspots in the research of high-efficiency crystalline silicon solar cell technology. In addition, improving the electrode preparation technology is also the research direction to solve the above problems. At present, the preparation process of selective emitter mainly includes the following types: double diffusion method, slurry co-diffusion method, laser heavy doping method and mask anti-etching method, etc. The two-time diffusion method involves two high-temperature diffusion processes, which not only has high production costs, but also reduces the minority carrier lifetime and quality of the silicon wafer; the slurry co-diffusion method effectively avoids the shortage of the two-time diffusion, but the cost of the slurry is very high. High, the dosage is large, and it is lacking in economical considerations; the preparation cost of the laser heavy doping method is high, and the stability and controllability of lasers and other equipment are high; the preparation cost of the mask anti-etching method is low. The process is relatively simple, but involves the use of hydrofluoric acid/nitric acid, which poses a high risk to the environment and operators, and requires high controllability of the corrosion process, and the deposition and removal process of acid-resistant corrosion protection materials is relatively complicated. Therefore, these methods have their own disadvantages. As for the improved electrode preparation technology, it mainly includes Double Printing technology, Aerosol jetting technology and Plating technology. The two-time printing technology can increase the aspect ratio of the electrode through two screen printing processes to effectively reduce the transmission resistance of the electrode, but it does not solve the problems of high contact resistance and easy electrode burn-through; Aerosol jetting technology is a German Fraun The technology developed by Hefei Solar Energy Research Institute, this technology achieves low contact resistance effect on silicon wafers with low surface doping concentration through fine printing, coupled with electroplating technology to increase electrodes, but this technology is very costly and depends on equipment very high.

Therefore, it is particularly important to develop a low-cost electrode preparation technology compatible with existing industrial production equipment to solve the above problems and further improve the efficiency of crystalline silicon solar cells.

Contents of the invention

The object of the present invention is to provide an electrode preparation method applied to crystalline silicon solar cells, which can effectively avoid the phenomenon of electrode burning through the p-n junction, reduce the contact resistance between the electrode and the silicon wafer, improve the conversion efficiency of the battery, and have low The method has cost advantages and is compatible with the industrial production process of crystalline silicon solar cells, and is suitable for large-scale industrial production.

The electrode preparation method applied to crystalline silicon solar cells provided by the present invention is: first, the silicon wafer is uniformly diffused to simultaneously form a p-n junction and an oxide layer rich in diffusion elements, and then the thickness of the oxide layer is thinned and optimized, and then Part of the oxide layer covers the metal electrodes, followed by heat treatment. During the heat treatment, the oxide layer prevents the metal electrodes from burning through the p-n junction and reduces the metal-semiconductor contact resistance. Finally, a chemical solution is used to remove the oxide layer in the area not covered by the metal electrodes. And the silicon material rich in diffusion elements on the surface of the silicon wafer.

The silicon wafer described in the present invention is a p-type or n-type single crystal silicon wafer or polycrystalline silicon wafer, the resistivity of the silicon wafer is 0.1-20 Ω·cm, and the thickness is 50-500 μm.

The diffusion described in the present invention is phosphorus diffusion or boron diffusion, and the sheet resistance of the diffusion is 30-120Ω/□.

The oxide layer rich in diffusion elements in the present invention is a silicon oxide layer rich in phosphorus or boron, with a thickness of 10-80 nm.

The thinning optimization of the thickness of the oxide layer in the present invention adopts the plasma etching method or the corrosion method of hydrofluoric acid solution, ammonia solution or tetramethylammonium hydroxide solution, and the thickness of the oxide layer after thinning is 5-50nm .

The metal electrode of the present invention is a metal material containing one or more of silver, titanium, palladium, copper, aluminum, nickel, tin and lead.

The metal electrode covering method in the present invention is one or a combination of magnetron sputtering, thermal evaporation, electron beam evaporation and screen printing.

The maximum temperature of the heat treatment process in the present invention is 700-1000°C. During the heat treatment process, the diffusion elements rich in the oxide layer will diffuse into the silicon chip again, and at the same time, the metal electrode and the silicon form an alloy structure.

The chemical liquid of the present invention includes acidic chemical liquid and alkaline chemical liquid, wherein the acidic chemical liquid is a hydrofluoric acid solution or a mixed liquid of hydrofluoric acid, hydrochloric acid, and sulfuric acid, and the alkaline chemical liquid is a potassium hydroxide solution, One or a mixture of sodium solution, potassium carbonate solution, sodium carbonate solution, ammonia solution, tetramethylammonium hydroxide solution.

The chemical liquid removal method described in the present invention is to firstly use an acidic chemical liquid to remove the oxide layer in the area not covered by the metal electrode, and then use an alkaline chemical liquid to remove the silicon material that is rich in diffusion elements on the surface, and the depth of the removed silicon material is 5~100nm.

The beneficial effects of the present invention are:

(1) The present invention uses uniform diffusion to simultaneously form a p-n junction and an oxide layer rich in diffusion elements, and optimizes the thickness of the oxide layer so that the oxide layer can effectively prevent the electrode from burning through the p-n junction during high-temperature sintering. Play the role of anti-burn-through protective layer, improve the cell yield rate of industrial production of crystalline silicon solar cells;

(2) The present invention adopts a uniform diffusion to simultaneously form a p-n junction and an oxide layer rich in diffusion elements, utilizes the characteristics of the oxide layer rich in diffusion elements, and adopts a heat treatment process to make the diffusion elements diffuse into the silicon wafer again, thereby effectively reducing the electrode contact with the silicon wafer. The metal-semiconductor contact resistance of silicon improves the photoelectric conversion efficiency of crystalline silicon solar cells;

(3) The electrode preparation method applied to crystalline silicon solar cells provided by the present invention has the advantages of simple process flow and low preparation cost, and is well compatible with industrial production equipment, and is suitable for large-scale industrial production.

Detailed ways

The following specific examples are given to illustrate the present invention. It should be pointed out that the following examples are only used to further illustrate the present invention, and do not represent the protection scope of the present invention. Non-essential modifications and adjustments made by others according to the prompts of the present invention still belong to the protection scope of the present invention.

The electrode preparation method applied to crystalline silicon solar cells mentioned in the following examples is: first, the silicon wafer is uniformly diffused to form a p-n junction and an oxide layer rich in diffusion elements, and then the thickness of the oxide layer is optimized for thinning, Then cover the metal electrode on the part of the oxide layer, and then carry out the heat treatment process. During the heat treatment process, the oxide layer plays the role of preventing the metal electrode from burning through the p-n junction and reducing the metal-semiconductor contact resistance. Finally, chemical liquid is used to remove the metal electrode. The oxide layer and the silicon material on the surface of the silicon wafer are rich in diffusion elements. This method can prevent the electrode from burning through the p-n junction, reduce the contact resistance between the electrode and the silicon wafer, and improve the conversion efficiency of the battery. It has the advantage of low cost and can be used with crystalline silicon solar cells. Compatible with industrial production processes.

Example 1

A method for preparing an electrode applied to a crystalline silicon solar cell mentioned in this embodiment includes the following steps:

(1) Perform high-temperature phosphorus diffusion on the silicon wafer to form a uniform p-n junction and an oxide layer rich in phosphorus;

(2) thinning and optimizing the thickness of the oxide layer;

(3) Partially covering the silver-containing metal electrode in the oxide layer;

(4) carrying out heat treatment process to silicon chip, oxide layer and silver-containing metal electrode;

(5) Chemical solution is used to remove the oxide layer and the phosphorus-rich silicon material in the area not covered by the metal electrode.

The silicon wafer described in this embodiment is a p-type single crystal silicon wafer, the resistivity of the silicon wafer is 1.5Ω·cm, and the thickness of the silicon wafer is 200 μm.

The highest diffusion temperature of the high-temperature phosphorus diffusion described in this embodiment is 870°C.

The optimization of reducing the thickness of the oxide layer described in this embodiment adopts the corrosion method of hydrofluoric acid solution with a weight concentration of 5%, and the thickness of the oxide layer after thinning is about 20 nm.

The local coverage described in this embodiment is to cover the "H"-shaped electrode pattern by screen printing.

The maximum temperature of the heat treatment process described in this embodiment is 850°C.

The chemical liquid described in this embodiment includes hydrofluoric acid solution and tetramethylammonium hydroxide solution.

The chemical solution removal method described in this embodiment is to firstly use a hydrofluoric acid solution with a weight concentration of 5% to remove the oxide layer rich in phosphorus, and then use a solution of tetramethylammonium hydroxide with a weight concentration of 20% to remove the oxide layer with a depth of about 50nm. Phosphorus-rich silicon material.

Example 2

A method for preparing an electrode applied to a crystalline silicon solar cell mentioned in this embodiment includes the following steps:

(1) Perform high-temperature phosphorus diffusion on the silicon wafer to form a uniform p-n junction and an oxide layer rich in phosphorus;

(2) thinning and optimizing the thickness of the oxide layer;

(3) Partially covering the silver-containing metal electrode in the oxide layer;

(4) carrying out heat treatment process to silicon chip, oxide layer and silver-containing metal electrode;

(5) Chemical solution is used to remove the oxide layer and the phosphorus-rich silicon material in the area not covered by the metal electrode.

The silicon wafer described in this embodiment is a p-type polycrystalline silicon wafer, the resistivity of the silicon wafer is 1.5Ω·cm, and the thickness of the silicon wafer is 200 μm.

The highest diffusion temperature of the high-temperature phosphorus diffusion described in this embodiment is 850°C.

The optimization of reducing the thickness of the oxide layer described in this embodiment adopts the corrosion method of hydrofluoric acid solution with a weight concentration of 5%, and the thickness of the oxide layer after thinning is about 20 nm.

The local coverage described in this embodiment is to cover the "H"-shaped electrode pattern by screen printing.

The maximum temperature of the heat treatment process described in this embodiment is 850°C.

The chemical liquid described in this embodiment includes hydrofluoric acid solution and tetramethylammonium hydroxide solution.

The chemical liquid removal method described in this embodiment is to firstly use a hydrofluoric acid solution with a weight concentration of 5% to remove the oxide layer rich in phosphorus, and then use a 20% weight concentration of tetramethylammonium hydroxide solution to remove the phosphorus with a depth of about 30nm. Phosphorus-rich silicon material.

Example 3

A method for preparing an electrode applied to a crystalline silicon solar cell mentioned in this embodiment includes the following steps:

(1) Perform high-temperature boron diffusion on the silicon wafer to form a uniform p-n junction and an oxide layer rich in boron;

(2) thinning and optimizing the thickness of the oxide layer;

(3) Partially covering the silver-containing metal electrode in the oxide layer;

(4) carrying out heat treatment process to silicon chip, oxide layer and silver-containing metal electrode;

(5) Chemical solution is used to remove the oxide layer and boron-rich silicon material in the area not covered by the metal electrode.

The silicon wafer described in this embodiment is an n-type single crystal silicon wafer, the resistivity of the silicon wafer is 1.5Ω·cm, and the thickness of the silicon wafer is 200 μm.

The highest diffusion temperature of the high-temperature boron diffusion described in this embodiment is 870°C.

The optimization of reducing the thickness of the oxide layer described in this embodiment adopts the corrosion method of hydrofluoric acid solution with a weight concentration of 5%, and the thickness of the oxide layer after thinning is about 20 nm.

The local coverage described in this embodiment is to cover the "H"-shaped electrode pattern by screen printing.

The maximum temperature of the heat treatment process described in this embodiment is 850°C.

The chemical liquid described in this embodiment includes hydrofluoric acid solution and tetramethylammonium hydroxide solution.

The chemical solution removal method described in this embodiment is to first use a 5% hydrofluoric acid solution by weight to remove the oxide layer rich in boron, and then use a 20% by weight tetramethylammonium hydroxide solution to remove the boron-rich oxide layer with a depth of about 50nm Boron-rich silicon material.

Example 4

A method for preparing an electrode applied to a crystalline silicon solar cell mentioned in this embodiment includes the following steps:

(1) Perform high-temperature boron diffusion on the silicon wafer to form a uniform p-n junction and an oxide layer rich in boron;

(2) thinning and optimizing the thickness of the oxide layer;

(3) Partially covering the silver-containing metal electrode in the oxide layer;

(4) carrying out heat treatment process to silicon chip, oxide layer and silver-containing metal electrode;

(5) Chemical solution is used to remove the oxide layer and boron-rich silicon material in the area not covered by the metal electrode.

The silicon wafer described in this embodiment is an n-type polycrystalline silicon wafer, the resistivity of the silicon wafer is 2.5Ω·cm, and the thickness of the silicon wafer is 300 μm.

The highest diffusion temperature of the high-temperature boron diffusion described in this embodiment is 850°C.

The thinning optimization of the thickness of the oxide layer described in this embodiment adopts a plasma etching method, and the thickness of the thinned oxide layer is about 30 nm.

The local coverage described in this embodiment is to cover the "H"-shaped electrode pattern by screen printing.

The maximum temperature of the heat treatment process described in this embodiment is 850°C.

The chemical liquid described in this embodiment includes hydrofluoric acid solution and tetramethylammonium hydroxide solution.

The chemical solution removal method described in this embodiment is to firstly use a hydrofluoric acid solution with a weight concentration of 5% to remove the boron-rich oxide layer, and then use a 20% weight concentration tetramethylammonium hydroxide solution to remove the boron with a depth of about 30nm. Boron-rich silicon material.

Example 5

A method for preparing an electrode applied to a crystalline silicon solar cell mentioned in this embodiment includes the following steps:

(1) Perform high-temperature boron diffusion on the silicon wafer to form a uniform p-n junction and an oxide layer rich in boron;

(2) thinning and optimizing the thickness of the oxide layer;

(3) Partially covering the silver-containing metal electrode in the oxide layer;

(4) carrying out heat treatment process to silicon chip, oxide layer and silver-containing metal electrode;

(5) Chemical solution is used to remove the oxide layer and boron-rich silicon material in the area not covered by the metal electrode.

The silicon wafer described in this embodiment is an n-type polycrystalline silicon wafer, the resistivity of the silicon wafer is 2.5Ω·cm, and the thickness of the silicon wafer is 300 μm.

The highest diffusion temperature of the high-temperature boron diffusion described in this embodiment is 870°C.

The thinning optimization of the thickness of the oxide layer described in this embodiment adopts a plasma etching method, and the thickness of the thinned oxide layer is about 30 nm.

The local coverage described in this embodiment is to cover the "H"-shaped electrode pattern by screen printing.

The maximum temperature of the heat treatment process described in this embodiment is 870°C.

The chemical liquid described in this embodiment includes hydrofluoric acid solution and sodium hydroxide solution.

The chemical liquid removal method described in this embodiment is to firstly use a hydrofluoric acid solution with a weight concentration of 5% to remove the oxide layer rich in boron, and then use a sodium hydroxide solution with a weight concentration of 20% to remove the boron-rich oxide layer with a depth of about 30nm. Elemental silicon material.

Claims (9)

1. electrode preparation method that is applied to crystal-silicon solar cell; It is characterized in that; At first silicon chip is evenly spread the oxide layer that forms p-n junction simultaneously and be rich in diffuse elements, then this thickness of oxide layer is carried out attenuate optimization, cover metal electrode in the part of oxide layer again; Then heat-treat process; The maximum temperature of heat treatment process is 700～1000 ℃, and the diffuse elements that in heat treatment process, is rich in the oxide layer diffuses in the silicon chip once more, and metal electrode and silicon form alloy structure simultaneously; Oxide layer plays the barrier metal electrode and burns p-n junction and the effect that reduces the metal semiconductor contact resistance in the heat treatment process, uses chemical liquids to remove not the silicon materials that are rich in diffuse elements by the oxide layer of metal electrode overlay area and silicon chip surface at last.

2. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1 is characterized in that, described silicon chip is p type or n type monocrystalline silicon piece or polysilicon chip, and silicon chip resistivity is 0.1～20 Ω cm, and thickness is 50～500 μ m.

3. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1 is characterized in that, describedly evenly is diffused as phosphorous diffusion or boron diffusion, and the square resistance of diffusion is 30～120 Ω/.

4. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1 is characterized in that, the described oxide layer that is rich in diffuse elements is the silicon oxide layer that is rich in P elements or boron element, and thickness is 10～80nm.

5. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1; It is characterized in that; Describedly oxidated layer thickness is carried out attenuate optimize the using plasma lithographic method or adopt hydrofluoric acid solution, ammonia spirit or tetramethyl ammonium hydroxide solution caustic solution, the thickness of attenuate rear oxidation layer is 5～50nm.

6. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1 is characterized in that, described metal electrode is one or more the metal material that contains in silver, titanium, palladium, copper, aluminium, nickel, tin, the lead;

7. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1 is characterized in that, described metal electrode coverage mode is a kind of mode or the combination of several kinds of modes in magnetron sputtering, hot vapor deposition, electron beam evaporation, the silk screen printing.

8. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1; It is characterized in that; Described chemical liquids comprises acidic chemical liquid and alkali electroless liquid; Wherein acidic chemical liquid is the mixed liquor of hydrofluoric acid solution or hydrofluoric acid and hydrochloric acid or the mixed liquor of hydrofluoric acid and sulfuric acid, and alkali electroless liquid is one or more the mixed liquor in potassium hydroxide solution, sodium hydroxide solution, solution of potassium carbonate, sodium carbonate liquor, ammonia spirit, the tetramethyl ammonium hydroxide solution.

9. the electrode preparation method that is applied to crystal-silicon solar cell according to claim 1; It is characterized in that; Described chemical liquids removing method is to adopt acidic chemical liquid to remove not by the oxide layer of metal electrode overlay area earlier; Adopt alkali electroless liquid to remove the silicon materials that diffuse elements is rich on the surface then, the degree of depth of removed silicon materials is 5～100nm.