CN101673785A - Method for preparing reflection reduction film with surface embedded type porous silicon structure of silicon base solar battery - Google Patents

Abstract

The invention relates to a method for preparing an anti-reflection film with a porous silicon structure embedded on the surface of a silicon-based solar cell, belonging to the technical field of electrochemical corrosion. The main points of the method of the present invention are: first prepare the anode electrode of the metal aluminum film on the back of the silicon chip by the traditional screen printing method, and make the Al and silicon have good ohmic contact, and use the platinum sheet or platinum wire as the cathode electrode in addition. Then place the front side of the silicon wafer in the etching solution of HF:H ₂ O=1:10 (volume ratio) and soak for 1 minute; the temperature of the etching solution is 26°C; In a container under ultrasonic conditions of ~60Hz, electrochemical corrosion treatment is carried out in a mixed solution of electrolyte HF:H ₂ O:C ₂ H ₅ OH=2:1:1 (volume ratio); the temperature of the electrolyte is 40°C. The surface density of the electrolytic corrosion current is 5-10mA/cm ² ; the electrolytic corrosion time is 40-60s; finally, an anti-reflection layer film with embedded porous silicon structure is formed on the front side of the silicon wafer, and its average reflectivity is 1.42%.

Description

Preparation method of porous silicon structure anti-reflection film embedded on the surface of silicon-based solar cells

technical field

The invention relates to a method for preparing an anti-reflection film with a porous silicon structure embedded on the surface of a silicon-based solar cell, belonging to the technical field of electrochemical corrosion.

Background technique

At present, anti-reflection coatings such as TiO ₂ , MgF ₂ , ZnS and Si ₃ N ₄ are often used in the industry for monocrystalline silicon solar cells, and their production costs are high and the process is complicated. How to cheaply and reliably prepare anti-reflective coatings for silicon-based solar cells is one of the key technologies for the continuous improvement of photoelectric conversion efficiency and large-scale industrialization of solar cells. Micron-scale porous silicon has the following advantages as an embedded anti-reflection layer for solar cells:

(1) The surface-embedded porous silicon has a high suede texture density, random orientation, and good uniformity. It can be used to directly "face" the natural light incident from all directions, greatly enhancing the capture probability of light quanta. Improving the internal quantum efficiency of silicon-based semiconductors. In terms of preparation, the traditional NaOH or KOH etching solution can only etch the <100>-oriented monocrystalline silicon surface into a pyramid, which serves as a textured surface for light trapping. However, the preparation of surface-embedded porous silicon has no technical limitation of crystal orientation. Surfaces of monocrystalline, polycrystalline or microcrystalline silicon in any orientation can be prepared as embedded porous silicon. The surface-embedded porous silicon is covered on the surface of the silicon, and its anti-reflection effect can be compared with other complex thin-film structures, and even better than the double-layer film structure.

(2) Surface-embedded porous silicon solar cells have good development prospects. Compared with other methods (such as ion beam sputtering), the preparation of embedded porous silicon is low-cost, easy to operate, and easy to control. Injection, laser ablation patterning technology) is more eye-catching and easy to realize industrial production.

Contents of the invention

The purpose of the present invention is to provide a method for preparing and forming a surface-embedded porous silicon structure anti-reflection layer film by electrochemical corrosion

A method for preparing an anti-reflection film with a porous silicon structure embedded on the surface of a silicon-based solar cell of the present invention is characterized in that it has the following processes and steps:

a. Select solar cell silicon substrate material, which is Czochralski monocrystalline silicon, P type, crystal orientation <100>, thickness 200-240μm, unpolished; first place the silicon wafer as solar cell silicon substrate material on Preliminary corrosion is carried out in the sodium hydroxide magnetic solution, to remove the mechanical damage layer on the surface of the silicon wafer; the preparation of the lye is that the volume ratio of sodium hydroxide and water is 1:5; the temperature of the lye is 80 ° C; The silicon wafer is placed in the alkali solution and corroded for 1 to 2 minutes under the action of ultrasonic waves;

b. Prepare metal aluminum thin film anode electrode with traditional screen printing method on the back side of the silicon wafer, and make the Al thin film have good ohmic contact with the substrate silicon wafer; Cathode electrode platinum sheet or platinum wire;

c. Place the front side of the silicon wafer in hydrofluoric acid solution and soak it for 1 to 2 minutes to remove the natural oxide layer on the surface of the silicon wafer; the preparation of the hydrofluoric acid solution is that the volume ratio of HF and H ₂ O is 1: 10; The temperature of the corrosive solution is 26-30°C;

d. Then place the front side of the silicon chip in a container under ultrasonic conditions with an ultrasonic frequency of 40-60 Hz, and perform electrochemical corrosion treatment in a mixed solution composed of electrolytic hydrofluoric acid, water and ethanol; The electrolyte is a mixture of hydrofluoric acid, water and organic solvent ethanol, and the volume ratio of the three is: HF: _{H 2} O:C ₂ H ₅ OH=2:1:1; the temperature of the electrolyte is 40-50 ℃; then turn on the DC power supply, the surface density of the electrolytic corrosion current is 5-10mA/cm ² ; the electrolytic corrosion time is 40-60s; finally, an anti-reflection layer film with a porous silicon structure embedded in the surface is formed on the front of the silicon wafer, and its reflection The average rate is 1.42%; the thickness of the anti-reflection layer film is 380-1100nm, and has a porous structure.

The characteristics and principle of the inventive method are as follows:

In the process of preparing ultra-low reflectivity surface-embedded porous silicon by electrochemical corrosion method, the platinum sheet is used as the cathode electrode, and the contact between the silicon sheet and Al is used as the anode electrode, and the electrochemical corrosion is carried out in a mixed solution containing HF acid . In the anodizing process, the most important process parameters include ambient temperature, acid concentration in the mixed solution, current surface density, corrosion time, matrix doping type, resistivity, polishing degree, etc., which affect the structure of the surface-embedded porous silicon and Optical properties have a big impact.

The commonly used electrolyte is a mixed solution made of a certain concentration of HF and an organic solvent. Experiments have shown that adding organic solvents in the preparation of porous silicon can increase the wettability of the silicon surface and reduce the surface tension of the electrolyte. In the process of anodizing, a large amount of hydrogen gas is produced, resulting in a large number of bubbles. Water has a high surface tension. When hydrogen is generated, due to the surface tension of water, hydrogen is firmly adsorbed on the surface of silicon and cannot overflow freely, preventing the next electrochemical reaction. The surface tension of the corrosive solution can be reduced by adding organic solvents and ultrasonic waves. The role of organic solvents can be determined by many factors, and the more important point is the solubility of organic solvents in water. The addition of ethanol can keep the porous silicon uniform and consistent in depth, and can also make the surface morphology of the porous silicon uniform.

In the method of the present invention, the electrochemical formation mechanism of surface-embedded porous silicon is as follows:

Silicon is continuously dissolved in HF aqueous solution. Generally, the chemical corrosion rate of Si in HF is extremely slow, and the silicon dangling bonds on the surface are passivated by hydrogen, which can form Si-H and Si-H ₂ bonds. In the electrochemical process, the anode continuously provides holes from the silicon body, and the holes diffused near the surface will repel the hydrogen atoms that have passivated the silicon dangling bonds, weakening the silicon-hydrogen bonds. An F atom can replace an H atom, releasing an electron at the same time. After losing one H atom, another H atom on the silicon atom becomes less stable, and another F atom can take its place and release an electron to the silicon. The two H atoms released form one _H2 molecule. The silicon atoms that have lost the passivation of H atoms are dissolved by HF to produce SiF ₄ . And then combine with F atom to form SiF ₆ group. That is, when holes migrate from the body to the silicon surface, Si-H bonds are broken and Si-F bonds are formed. Thus, the Si-Si bond is dissolved by HF. (See Figure 2)

Electrochemical reaction process:

Si+2HF+2e ⁺ → SiF ₂ +2H ⁺

SiF ₂ +4HF→H ₂ SiF ₆ +H ₂ ↑

Description of drawings

Fig. 1 is a schematic diagram of a device for preparing an anti-reflection film by an electrochemical corrosion method in the present invention.

Fig. 2 is a diagram of the formation mechanism of the surface-embedded porous electrochemical corrosion method in the present invention.

Detailed ways

Specific embodiments of the present invention are described below.

Example

The process and steps of this embodiment are as follows

The device used in this example is shown in Figure 1 of the accompanying drawings. Fig. 1 is a schematic diagram of a device for preparing an anti-reflection film or a low-reflection film by electrochemical corrosion. The device is a commonly used laboratory device.

(1) Select solar cell silicon substrate material, which is Czochralski monocrystalline silicon, P type, crystal orientation <100>, thickness 220 μm, unpolished; first place the silicon wafer as the solar cell silicon substrate material on Preliminary corrosion is carried out in the sodium hydroxide magnetic solution, to remove the mechanical damage layer on the surface of the silicon wafer; the preparation of the lye is that the volume ratio of sodium hydroxide and water is 1:5; the temperature of the lye is 80 ° C; The silicon wafer is placed in the alkali solution and corroded for 1 minute under the action of ultrasonic waves;

(2), on the back side of the silicon chip, i.e. the upper surface, prepare the metal aluminum thin film anode electrode with the traditional screen printing method, and make the Al thin film and the substrate silicon chip have good ohmic contact; The front side of one side, that is, the lower surface, is connected to a cathode electrode platinum sheet or platinum wire through a wire;

(3) Place the front side of the silicon chip in hydrofluoric acid solution and soak it for 1 minute to remove the natural oxide layer on the surface of the silicon chip; the preparation of the hydrofluoric acid solution is that the volume ratio of HF and H ₂ O is 1: 10; The temperature of the corrosive solution is 26°C;

(4), then place the front side of the silicon chip in a container under ultrasonic conditions with an ultrasonic frequency of 40 Hz, and carry out electrochemical corrosion treatment in a mixed solution composed of electrolyte hydrofluoric acid, water and ethanol; The electrolyte is a mixture of hydrofluoric acid, water and organic solvent ethanol, and the volume ratio of the three is: HF: _{H 2} O:C ₂ H ₅ OH=2:1:1; the temperature of the electrolyte is 40°C; Then turn on the DC power supply, and the surface density of the electrolytic corrosion current is 5mA/cm ² ; the electrolytic corrosion time is 40s; finally, an anti-reflection layer film with a surface-embedded porous silicon structure is formed on the front side of the silicon wafer; the anti-reflection layer film has an extremely low The reflectivity is 1.42% on average; the thickness of the anti-reflection layer is 700-900nm and has a porous structure.

Claims (1)

1, a kind of preparation method of reflection reduction film with surface embedded type porous silicon structure of silicon base solar battery is characterized in that having following process and step:

A. select the solar cell silicon substrate material for use, it is pulling of silicon single crystal, P type, crystal orientation＜100 〉, thickness is 200～240 μ m, not polishing; At first will in NaOH magnetic solution, tentatively corrode, to remove the mechanical damage layer of silicon chip surface as the silicon slice placed of solar cell silicon substrate material; The preparation of alkali lye is that the volume proportion of NaOH and water is 1: 5; The temperature of alkali lye is 80 ℃; Described silicon slice placed is placed described alkali lye, and under the ultrasonic wave effect, corrode 1～2 minute;

B. prepare metallic aluminium thin film positive pole electrode at the described silicon chip back side with traditional silk screen print method, and make Al film and silicon substrate have good Ohmic contact; Connect a cathode electrode platinized platinum or a platinum filament in the front of silicon chip opposite side by lead in addition;

C. the silicon chip front is positioned in the etching acid solution corrosion liquid and soaked 1～2 minute, to remove the natural oxidizing layer of silicon chip surface; The preparation of etching acid solution is HF and H ₂The volume proportion of O is 1: 10; The temperature of corrosive liquid is 26～30 ℃;

D. then the silicon chip front is placed in the container that has under the ultrasound condition that ultrasonic frequency is 40～60Hz, and in the mixed liquor that electrolyte etching acid, water and ethanol are formed, carries out electrochemical corrosion and handle; Described electrolyte is the mixed liquor of etching acid, water and organic solvent ethanol, and its three's volume ratio is: HF: H ₂O: C ₂H ₅OH=2: 1: 1; The temperature of electrolyte is 40～50 ℃; Connect DC power supply then, the surface density of electrolytic corrosion electric current is 5～10mA/cm ²The electrolytic corrosion time is 40～60s; Finally at the positive antireflection layer film that forms surface embedded type porous silicon structure of silicon chip, its reflectivity average out to 1.42%; The thickness of this antireflective tunic is 380～1100nm, has loose structure.

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