CN104201235A - Plasma texturing method of AZO film of film solar cell - Google Patents

Abstract

The invention relates to the field of semiconductor industry, and in particular relates to a plasma texturing method of an AZO film of a film solar cell. The method is characterized in that the advantages of physical etching and chemical etching of the plasma etching method and high regulation performance of the etching degree and other advantages are utilized to etch the AZO film of the film solar cell. With the adoption of the method, the effect of wet etching can be reached; meanwhile, any corrosive solution is not used, so that the environmental pollution caused by improper handling of reaction solution can be avoided; the heating temperature, flow rate of inlet air, power and frequency of a radio source, and etching time of a substrate rack are controlled to improve the etching controllability; compared with the sputtering-depositing texturing type AZO film of which the particle energy is limited and obvious texturing effect is not reached, the AZO film has the advantage that a good etching effect can be reached; the texturing method of the AZO film of the film solar cell has the advantages of being high in light trapping structure effect, high in etching controllability and free of pollution; therefore, the method can be applied to the technology for improving the converting efficiency of a solar cell.

Description

A method for plasma texturing of AZO films for thin film solar cells

technical field

The invention relates to the field of semiconductor industry, especially solar cells, in particular to a plasma texturing method for AZO thin films of thin-film solar cells.

Background technique

With the intensification of energy shortage and environmental pollution, all countries are stepping up the pace of development of the photovoltaic industry. At present, in order to solve the problems of high cost and low efficiency of solar cells, various new processes and technologies are applied to the preparation of cells. In the technology of improving the conversion efficiency of solar cells, optical optimization is an important optimization technology, and its purpose is to increase the incident light intensity or photon flux inside the solar cell. Increasing photon flux means that solar cells can use incident photons more effectively, increase photogenerated current, achieve higher conversion efficiency, and reduce the cost of photovoltaic power generation. The ways to achieve optical optimization mainly include anti-reflection coatings, light-condensing systems, and light-trapping structures. Among them, the light trapping structure improves the conversion efficiency of solar cells by increasing the optical path length of photons entering the solar cell, that is, the light trapping effect.

Surface texturing is to prepare irregular grooves or inverted pyramid structures on the front or back surface of solar cells to form a light-trapping structure, so that light can be scattered and reflected in solar cells, so that the direction of light propagation is different from that of the surface. The included angle of the normal increases, and the light entering the solar cell can travel through different optical paths, which increases the absorption of photons by the cell.

Aluminum-doped zinc oxide (AZO) film, as a transparent conductive oxide film (TCO), not only has the advantages of high visible light transmittance and low resistivity, but also has the advantages that other TCOs such as ITO and FTO do not have: abundant raw materials Easy to obtain, easy to dope aluminum, environment friendly, and high chemical stability in high temperature hydrogen plasma environment, it is an ideal electrode material for thin film solar cells, and has been widely used, and the research on its surface texture is becoming more and more many. At present, there are two main methods for AZO surface texturing, one is to wet-etch the deposited AZO film, and the other is to directly sputter the textured AZO film on the glass substrate by controlling the process parameters when preparing the AZO film. film. Wet etching mainly uses diluted acid or alkali solution to chemically corrode the surface of AZO to achieve texturing effect. The acid solution mainly includes hydrochloric acid, sulfuric acid, hydrofluoric acid, etc., and the alkali solution mainly includes sodium hydroxide and ammonium chloride solution. wait. Wet etching has the advantages of large-area substrate processing and fast etching speed. However, because the etching speed is too fast, it is not easy to control the etching process. At the same time, the use of acid or alkali solution is likely to cause environmental pollution. For the method of directly preparing textured AZO thin films, the texturing effect is not obvious due to the limited particle energy during sputtering deposition.

Contents of the invention

In view of the above problems, the present invention provides a method for plasma texturing of AZO thin films of thin film solar cells. The principle is: through the inductive coupling of the radio frequency source, power is added to the reaction chamber to ionize the incoming gas to generate plasma, which contains active particles such as ions, electrons, and free radicals; these active particles hit the surface of the AZO film to achieve Physical etching, and chemical reaction with its surface to achieve chemical etching.

The technical solution adopted in the present invention is: a method for plasma texturing of thin film solar cell AZO films, the steps of which include:

Step 1. Clean the AZO glass substrate, and send the cleaned AZO glass substrate to the substrate holder in the reaction chamber of the plasma etching equipment through the sampling chamber;

Step 2, turn on the heating power supply to heat the substrate holder;

Step 3. Vacuum the reaction chamber until the background vacuum degree of the reaction chamber is 1×10 ^-4 -3×10 ^-3 Pa;

Step 4, feed reaction gas nitrogen and hydrogen at the same time, and adjust the working pressure of the reaction chamber to 0.3-15Pa;

Step 5. Turn on the RF power supply, preheat for 5 minutes, set the power, adjust the matching until the glow generates plasma;

Step 6, continue to feed nitrogen and hydrogen, and maintain the heating temperature, and start timing etching at the same time;

Step 7. After the etching time is reached, turn off the radio frequency power supply, turn off the heating power supply, turn off the gas, pump air to the reaction chamber, and after two hours, take out the AZO glass substrate to complete the etching of the AZO glass substrate.

The thickness of the AZO film on the AZO glass substrate is 400nm-2μm.

The step of cleaning the AZO glass substrate in the first step comprises: washing with decontamination powder and clear water until there are no air bubbles, then washing with acetone, washing with 95% ethanol, and ultrasonic cleaning with ethanol solution for 20 minutes. After the final rinse with deionized water, ultrasonically clean with deionized water for another 20 minutes, and then blow dry with high-purity nitrogen.

In the second step, the heating temperature of the substrate holder is 150-300°C.

The flow rate of nitrogen gas introduced in the step four is 5-20 sccm, and the flow rate of hydrogen gas is 1-10 sccm.

The frequency of the radio frequency power supply in the fifth step is 400KHz-13.56MHz, and the power is 300-2000W.

The etching time of the step 6 is 1-20 minutes.

In summary, the present invention has the following beneficial effects:

1. The present invention includes physical etching and chemical etching, which can achieve the effect of wet etching. At the same time, because no corrosive solution is used, environmental pollution caused by improper treatment of the reaction solution is avoided.

2. The present invention can not only produce isotropic etching on the AZO surface, but also have anisotropic etching on the depth of pits on the AZO textured surface, thereby improving the light trapping effect on the AZO textured surface.

3. The present invention can improve the controllability of etching by controlling the heating temperature of the substrate holder, the flow rate of the incoming gas, the power and frequency of the radio frequency source, and the etching time.

Description of drawings

Fig. 1 is the flow chart of the plasma texturing method of a kind of thin-film solar cell AZO film of the present invention;

2 is a schematic diagram of a planar coil inductively coupled plasma etching device for the reactive plasma texturing method of an AZO thin film used for thin film solar cell electrodes in the present invention;

Fig. 3 is the SEM topography figure of the AZO surface that has not been processed by etching in the present invention;

Fig. 4 is the SEM topography figure of the AZO surface of embodiment one of the present invention;

Fig. 5 is the SEM topography figure of the AZO surface of embodiment two of the present invention;

Fig. 6 is the SEM topography figure of the AZO surface of embodiment three of the present invention;

FIG. 7 is the reflectance spectrum of the AZO film before and after etching in the embodiment of the present invention.

Explanation of reference signs:

Figure 2: 201 radio frequency antenna, 202 quartz disk, 203 gas inlet, 204AZO glass substrate, 205 reaction chamber, 206 heatable substrate holder, 207 gas outlet;

Detailed ways

The present invention will be further described below in conjunction with embodiment:

Embodiment one

For the AZO glass substrate, first rinse with decontamination powder and water until there are no air bubbles; then rinse with acetone, then rinse with 95% ethanol, and ultrasonically clean with ethanol solution for 20 minutes; finally rinse with deionized water, and use Ultrasonic cleaning with deionized water for 20 minutes, and then drying with high-purity nitrogen, set aside.

Send the cleaned AZO glass substrate to the sampling chamber, and send the substrate to the substrate holder in the reaction chamber of the plasma etching device through the sampling chamber; turn on the heating power supply, heat the substrate holder, and keep heating The temperature is 200°C; the vacuum degree of the reaction chamber is evacuated to 1.5×10 ^-4 Pa; the flow rates of nitrogen and hydrogen are 8sccm and 2.5sccm respectively; the working pressure of the reaction chamber is adjusted to keep it at 3Pa; the radio frequency power is turned on, Preheat for 5 minutes, set the frequency and power to 456KHz and 1800W respectively; adjust the radio frequency matching until the ignition generates plasma; continue to feed the above-mentioned nitrogen and hydrogen, and keep heating the substrate holder at 200°C, and start timing at the same time; 2 Minutes later, turn off the radio frequency power supply, turn off the heating power supply, turn off the nitrogen gas and hydrogen gas, pump the reaction chamber, and after two hours, take out the AZO glass substrate to complete the etching of the AZO glass substrate.

Use a scanning electron microscope (JEOL JSM-6700F) to characterize the surface morphology of the AZO glass substrate before and after etching. The SEM morphology of the AZO surface without reactive ion etching is shown in Figure 3. There are pits on the surface, and the level of the pits is The average size of the direction is 320nm. The SEM morphology of the AZO surface after reactive ion etching for 2 minutes is shown in Figure 4. The density of pits on the surface increases, and the average size of the pits in the horizontal direction is 290nm. The reflectance spectrum of the AZO glass substrate before and after etching is shown in FIG. 7 , and the reflectance of the AZO glass substrate etched for 2 minutes is 10% lower on average than that of the unetched one.

Embodiment two

The cleaning of the AZO glass substrate adopts the method of embodiment one; the AZO glass substrate cleaned up is sent to the sample introduction chamber, and the substrate is sent to the substrate holder of the reaction chamber of the plasma etching device through the sample introduction chamber; Heating the power supply, heating the substrate rack, and keeping the heating temperature at 200°C; pumping the vacuum of the reaction chamber to 1.5×10 ^-4 Pa; feeding nitrogen and hydrogen, the flow rates are 8sccm and 2.5sccm respectively; adjust the reaction chamber Keep the working pressure at 3Pa; turn on the radio frequency power supply, preheat for 5 minutes, set the frequency and power to 456KHz and 1800W respectively; Heating the substrate rack at 200°C, and start timing at the same time; after 10 minutes, turn off the radio frequency power supply, turn off the heating power supply, turn off the nitrogen and hydrogen gas, and pump the reaction chamber. After two hours, take out the AZO glass substrate, and the AZO glass is completed. Etching of the substrate.

A scanning electron microscope (JEOL JSM-6700F) was used to characterize the surface of the AZO glass substrate etched for 10 minutes, and its SEM image is shown in Figure 5.

Embodiment three

The cleaning of the AZO glass substrate adopts the method of embodiment one; the AZO glass substrate cleaned up is sent to the sample introduction chamber, and the substrate is sent to the substrate holder of the reaction chamber of the plasma etching device through the sample introduction chamber; Heating the power supply, heating the substrate holder, and keeping the heating temperature at 200°C; pumping the vacuum of the reaction chamber to 1.5×10 ^-4 Pa; feeding nitrogen and hydrogen, the flow rates are 7sccm and 3sccm respectively; adjust the working of the reaction chamber Keep the air pressure at 3Pa; turn on the radio frequency power supply, preheat for 5 minutes, set the frequency and power to 456KHz and 1200W respectively; Heating the rack at 200°C, and start timing at the same time; after 10 minutes, turn off the radio frequency power supply, turn off the heating power supply, turn off the nitrogen and hydrogen gas, and pump the reaction chamber. After two hours, take out the AZO glass substrate, and the AZO glass substrate is completed. slice etching. A scanning electron microscope (JEOL JSM-6700F) was used to characterize the surface of the AZO glass substrate etched for ten minutes, and its SEM image is shown in FIG. 6 .

Embodiment Four

The cleaning of the AZO glass substrate adopts the method of embodiment one; the AZO glass substrate cleaned up is sent to the sample introduction chamber, and the substrate is sent to the substrate holder of the reaction chamber of the plasma etching device through the sample introduction chamber; Heating the power supply, heating the substrate rack, and keeping the heating temperature at 200°C; pumping the vacuum of the reaction chamber to 1.5×10 ^-4 Pa; feeding nitrogen and hydrogen, the flow rates are 8sccm and 2.5sccm respectively; adjust the reaction chamber Keep the working pressure at 3Pa; turn on the radio frequency power supply, preheat for 5 minutes, set the frequency and power to 13.56MHz and 450W respectively; adjust the radio frequency matching until the glow generates plasma; continue to feed the above nitrogen and hydrogen, and keep Heat the substrate rack at 200°C and start timing at the same time; after 5 minutes, turn off the radio frequency power, turn off the heating power, turn off the nitrogen and hydrogen, and pump the reaction chamber. After two hours, take out the AZO glass substrate to complete the AZO Etching of glass substrates.

Claims (8)

1. A method for plasma texturing of thin-film solar cell AZO thin film, is characterized in that, comprises the steps: Step 1. Clean the AZO glass substrate, and send the cleaned AZO glass substrate to the substrate holder in the reaction chamber of the plasma etching equipment through the sampling chamber; Step 2, turn on the heating power supply to heat the substrate holder; Step 3. Vacuum the reaction chamber until the background vacuum degree of the reaction chamber is 1×10 ^-4 -3×10 ^-3 Pa; Step 4, feed reaction gas nitrogen and hydrogen at the same time, and adjust the working pressure of the reaction chamber to 0.3-15Pa; Step 5. Turn on the RF power supply, preheat for 5 minutes, set the power, adjust the matching until the glow generates plasma; Step 6, continue to feed nitrogen and hydrogen, and maintain the heating temperature, and start timing etching at the same time; Step 7. After the etching time is reached, turn off the radio frequency power supply, turn off the heating power supply, turn off the gas, pump air to the reaction chamber, and after two hours, take out the AZO glass substrate to complete the etching of the AZO glass substrate. 2 . The plasma texturing method of the AZO thin film of the thin film solar cell according to claim 1 , wherein the thickness of the AZO thin film of the AZO glass substrate is 400 nm-2 μm. 3. the plasma texturing method of thin-film solar cell AZO film as claimed in claim 1, is characterized in that, the cleaning step of described step one AZO glass substrate comprises: add clear water to rinse earlier with decontamination powder, until there is no bubble, Then wash with acetone, rinse with 95% ethanol, then ultrasonically clean with ethanol solution for 20 minutes, finally rinse with deionized water, ultrasonically clean with deionized water for 20 minutes, and then dry with high-purity nitrogen. 4 . The plasma texturing method of AZO thin film of thin film solar cell according to claim 1 , characterized in that: the heating temperature of the substrate frame in the second step is 150-300° C. 5 . The plasma texturing method of AZO thin film for thin film solar cells according to claim 1 , wherein the flow rate of nitrogen gas introduced in the step 4 is 5-20 sccm, and the flow rate of hydrogen gas is 1-10 sccm. 6 . 6 . The plasma texturing method of AZO thin film of thin film solar cell according to claim 1 , characterized in that: the frequency of the radio frequency power supply in the fifth step is 400KHz-13.56MHz, and the power is 300-2000W. 7 . The method for plasma texturing the AZO thin film of the thin film solar cell according to claim 1 , wherein the etching time in the sixth step is 1-20 minutes. 8. The plasma texturing method of AZO thin film of thin film solar cell as claimed in claim 1, characterized in that: the heating temperature of the substrate holder is 200°C, the vacuum degree of the reaction chamber is 1.5×10 ^-4 Pa, nitrogen and hydrogen The flow rates are 8sccm and 2.5sccm, the radio frequency and power are 456KHz and 1800W, respectively, and the etching time is 2 minutes.