CN111378958A - Back film preparation method capable of improving conversion efficiency of single-sided PERC battery - Google Patents

Abstract

The invention relates to a method for preparing a back film which can improve the conversion efficiency of a single-sided PERC cell. It includes preparing an aluminum oxide film, preparing a silicon oxide film on the back side, preparing a silicon oxynitride film on the back side, and preparing a double-layer silicon nitride film on the back side. The silicon wafer back film structure obtained by the existing production process generally only has an aluminum oxide layer and a silicon nitride layer. The method provided by the present invention adds a high-density silicon oxynitride film and a silicon oxide film layer to the back film. The high refractive index silicon oxynitride film can well increase the reflection of the long-wavelength sunlight on the back of the battery, so that the long-wave light enters the silicon wafer again, and increases the absorption of the long-wave light, thereby improving the open voltage and current of the battery to achieve the ultimate conversion efficiency. At the same time, the high refractive index silicon oxynitride film and silicon oxide film added on the back can well block the efficiency attenuation caused by water vapor and metal ions entering the interior of the cell, and improve the quality of the product.

Description

A method for preparing a back film that can improve the conversion efficiency of single-sided PERC cells

technical field

The invention relates to a method for preparing a back film of a single-sided PERC battery, in particular to a method for preparing a back film that can improve the conversion efficiency of a single-sided PERC battery.

Background technique

At present, as environmental issues and energy issues get more and more people's attention, as a clean energy, people's research, development and utilization of solar cells have entered a new stage. In order to reduce the cost of crystalline silicon and adapt to the fiercely competitive photovoltaic industry, the thickness of crystalline silicon cells is getting thinner and thinner. Because crystalline silicon is a gap band material, the light absorption coefficient is small, and the loss caused by transmitted light will decrease with the thickness of the silicon wafer. Therefore, in today's increasingly thin crystalline silicon, high-efficiency battery technology based on thinner crystalline silicon is the research focus of major enterprises and universities. At present, the main research hotspots are HIT cells, WMT cells, N-type double-sided cells, P-type SEPERC cells, etc. Among them, P-type SEPERC cells have become the mainstream battery technology in the market due to their relatively mature technology and low difficulty in mass production.

Therefore, improving the structure of the back film layer and optimizing the coating process, enhancing the back reflection of the cell, increasing the absorption of long-wave light, and improving the photoelectric conversion efficiency of P-type single-sided cells are the focus of research in the solar cell industry.

SUMMARY OF THE INVENTION

The invention provides a method for preparing a back film which can improve the conversion efficiency of a single-sided PERC cell, and solves the problem in the prior art that the thickness of the silicon wafer is reduced and the light absorption coefficient is reduced.

The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: a method for preparing a back film that can improve the conversion efficiency of a single-sided PERC cell, step 1: preparing an aluminum oxide film, loading the cell sheets into a graphite boat, And send it into the deposition furnace tube, firstly prepare the aluminum oxide film on the back of the cell;

Step 2: prepare a silicon oxide film on the back side, and deposit the silicon oxide film in the deposition furnace tube. The deposition temperature of the silicon oxide film is 400℃～500℃, the radio frequency power is 8kw～11kw, and the duty ratio is 1:25～1 :30, the furnace tube pressure is 900-1200mtorr, the deposition gas flow ratio of the silicon oxide film is SiH ₄ :N ₂ O=0.10:1-0.03:1, and the deposition time of the silicon oxide film is 220±30s;

Step 3: prepare a silicon oxynitride film on the back side, and deposit the silicon oxynitride film in the deposition furnace tube. The deposition temperature of the silicon oxynitride film is 400℃～500℃, the radio frequency power is 8kw～11kw, and the duty ratio is 1: 14～1:18, the furnace tube pressure is 1300～1600mtorr, the deposition gas flow ratio of the silicon oxynitride film is SiH ₄ : NH ₃ : N ₂ O=1:3:0.6～1:2:0.4, the silicon oxynitride film is The deposition time is 100±30s;

Step 4: A double-layer silicon nitride film is prepared on the backside, and the silicon nitride film is deposited in the deposition furnace tube. The deposition temperature of the silicon nitride film is 400°C to 500°C, the radio frequency power is 10kw to 15kw, and the duty cycle is 1:10～1:15, the furnace tube pressure is 1400～1800mtorr, the deposition gas flow ratio of the first layer of silicon nitride film is SiH ₄ : NH ₃ =0.3:1～0.25:1, the first layer of silicon nitride film is The deposition time of the second layer of silicon nitride film is 160±30s; the deposition gas flow ratio of the second layer of silicon nitride film is SiH ₄ : NH ₃ =0.18:1～0.13:1, and the deposition time of the second layer of silicon nitride film is 220±30s.

The silicon wafer back film structure obtained by the existing production process generally only has an aluminum oxide layer and a silicon nitride layer. Compared with the existing process, the method provided by the present invention adds a high-density silicon oxynitride film and a silicon oxide film to the back film. The composite film structure composed of silicon oxide film, silicon nitride oxide film and silicon nitride film is a good back reflector. The high refractive index silicon oxynitride film can well increase the reflection of the long-wavelength sunlight on the back of the battery, so that the long-wave light can enter the silicon wafer again, and increase the absorption of the long-wave light, thereby improving the open voltage and current of the battery to achieve the ultimate conversion efficiency. At the same time, the high refractive index silicon oxynitride film and silicon oxide film added on the back can well block the efficiency attenuation caused by water vapor and metal ions entering the interior of the cell, and improve the quality of the product. Meanwhile, the high-density silicon oxide film and the high-refractive-index silicon oxynitride film enhance the anti-potential-induced decay performance of the battery.

Therefore, improving the structure of the back film layer and optimizing the coating process, enhancing the back reflection of the cell, increasing the absorption of long-wave light, improving the photoelectric conversion efficiency of the P-type single-sided cell, reducing the cost of the cell and improving the quality of the cell are worthy of industrialization. application.

Preferably, the silicon oxide film has a thickness of 5±2 nm and a refractive index of 1.5±0.1.

Preferably, the silicon oxynitride film has a thickness of 25±5 nm and a refractive index of 2.4±0.2.

Preferably, the thickness of the first layer of silicon nitride film is 38±5nm and the refractive index is 2.25±0.1, and the thickness of the second layer of silicon nitride film is 46±5nm and the refractive index is 2.15±0.1.

Preferably, the total thickness of the aluminum oxide film, the silicon oxide film, the silicon nitride oxide film and the silicon nitride film is 97 nm to 131 nm, the refractive index is 2.15 to 2.25, and the film color is light yellow.

Therefore, compared with the prior art, the present invention has the following characteristics: 1. The method provided by the present invention adds a high-density silicon oxynitride film and a silicon oxide film to the back film, and the high-refractive-index silicon oxynitride film can be well increased The reflection of the long-wavelength sunlight on the back of the battery allows the long-wave light to enter the silicon wafer again, increasing the absorption of the long-wave light, thereby improving the battery open voltage and current, and finally improving the conversion efficiency. And the silicon oxide film can well block the efficiency attenuation caused by water vapor and metal ions entering the interior of the cell, and improve the quality of the product; 2. At the same time, the high-density silicon oxide film and the high refractive index silicon oxynitride film enhance the battery resistance. Potential-induced decay performance.

Description of drawings

Accompanying drawing 1 is the process flow diagram of the present invention;

2 is a schematic diagram of the structure of the back film of the silicon cell produced according to the present invention.

Detailed ways

The technical solutions of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

Example 1: The first step: prepare the backside aluminum oxide film 2, put the cell 1 into a graphite boat, and send it into the deposition furnace tube, and deposit an aluminum oxide film on the back of the cell in the deposition furnace tube, and the deposition temperature is 250 ° C -350℃, the thickness of the aluminum oxide film is 10nm;

The second step: prepare the silicon oxide film 3 on the backside, after the first step, the temperature is raised to 450 ° C, and the reactive gases SiH ₄ and N2O are introduced, wherein the gas flow rate of SiH ₄ is 150 sccm, N ₂ O is 4500 sccm, and the radio frequency power is 9kw, the duty ratio is 1:30, the furnace tube pressure is 1000mtorr, the deposition time of the silicon oxide film is 220s, the thickness of the silicon oxide is 4nm, and the refractive index is 1.5;

The third step: prepare the silicon oxynitride film 4 on the back side, and after the second step, pass in the reactive gases SiH ₄ , NH ₃ and N ₂ O, wherein the gas flow rate of SiH ₄ is 1000 sccm, NH ₃ is 2500 sccm, and N ₂ O is 500 sccm , the RF power is 9kw, the duty ratio is 1:16, the furnace tube pressure is 1500mtorr, the deposition time of the silicon oxynitride film is 100s, the thickness of the silicon oxynitride is 25nm, and the refractive index is 2.4;

The fourth step: prepare the double-layer silicon nitride film 5 on the back, and after the third step, pass in the reactive gases SiH ₄ and NH ₃ , the radio frequency power is 14kw, the duty ratio is 1:12, and the furnace tube pressure is 1500mtorr; The deposition gas flow rate of one layer of silicon nitride film 51 is _SiH4 is 1000sccm, _NH3 is 3500sccm, the deposition time of the first layer of silicon nitride film is 160s, the thickness of the first layer of silicon nitride film is 38nm, the refractive index is 2.3 ; The deposition gas flow rate of the second layer of silicon nitride film 52 is SiH ₄ is 1000sccm, NH ₃ is 6800sccm, the deposition time of the second layer of silicon nitride film is 220s, the thickness of the second layer of silicon nitride film is 46nm, the refractive index is 2.15.

In this embodiment, the total thickness of the composite film formed by the silicon oxide film, the silicon oxynitride film and the two layers of silicon nitride films is 113 nm, and the refractive index is 2.23. The refractive index of the composite film layer gradually decreases from the silicon oxynitride film to the silicon nitride film, that is, the refractive index of the first layer of silicon nitride film is smaller than that of the silicon oxynitride film, and the refractive index of the second layer of silicon nitride film is smaller than that of the silicon nitride film. The advantage is that the overall film has a higher refractive index and the high-refractive silicon oxynitride film can greatly increase the reflection of the long-band sunlight on the back of the cell. The long-wave light enters the silicon wafer again, and the absorption of the long-wave light is increased, thereby improving the open voltage and current of the battery and finally improving the conversion efficiency. The high refractive index silicon oxynitride film and silicon oxide film added to the back film can well block the efficiency attenuation caused by the entry of water vapor and metal ions into the interior of the cell.

Using the P-type single-sided SEPERC battery produced in Example 1, the subsequent production process also requires backside laser grooving. Since the thickness of the backside film has increased, the backside laser power needs to be increased by 3W at this time to ensure good opening. hole effect.

The test efficiency of the P-type single-sided SEPERC battery produced in Example 1 and the battery produced by the existing production line process is compared, and the results are shown in Table 1:

Table 1

name Uoc(V) Isc (mA) FF Front Eta (%) The new technology of the present invention 0.6800 10.024 81.60 22.236% Production line process 0.6785 10.011 81.59 22.156%

Uoc (open circuit voltage), Isc (short circuit current), FF (fill factor), Eta (photoelectric conversion rate)

According to the experimental data in Table 1 above, the photoelectric conversion efficiency of the P-type single-sided SEPERC cell produced in Example 1 is increased by 0.08% compared with the existing production line process, and the efficiency is significantly improved, which is worthy of industrial application.

It will be apparent to those skilled in the art that the present invention may be modified in various ways and such modifications are not considered to depart from the scope of the present invention. All such modifications obvious to those skilled in the art are intended to be included within the scope of the present claims.

Claims (6)

1. A method for preparing a back film that can improve the conversion efficiency of a single-sided PERC cell, step 1: preparing an alumina film (2), loading the cell sheet (1) into a graphite boat, and sending it into a deposition furnace tube, first in the An aluminum oxide film (2) is prepared on the back of the battery sheet (1); it is characterized in that: Step 2: preparing a silicon oxide film (3) on the back side, and depositing the silicon oxide film (3) in the deposition furnace tube. The duty ratio is 1:25～1:30, the furnace tube pressure is 900～1200mtorr, the deposition gas flow ratio of the silicon oxide film (3) is SiH ₄ : N ₂ O = 0.10:1～0.03:1, the silicon oxide film (3) The deposition time is 220±30s; Step 3: A silicon oxynitride film (4) is prepared on the back side, and the silicon oxynitride film (4) is deposited in the deposition furnace tube. The deposition temperature of the silicon oxynitride film (4) is 400°C to 500°C, and the radio frequency power is 8kw ～11kw, the duty ratio is 1:14～1:18, the furnace tube pressure is 1300～1600mtorr, and the deposition gas flow ratio of the silicon oxynitride film (4) is SiH ₄ : NH ₃ : N ₂ O =1:3: 0.6～1:2:0.4, the deposition time of the silicon oxynitride film (4) is 100±30s; Step 4: A double-layer silicon nitride film (5) is prepared on the back side, and the silicon nitride film (5) is deposited in the deposition furnace tube. The deposition temperature of the silicon nitride film (5) is 400° C. to 500° C. is 10kw～15kw, the duty ratio is 1:10～1:15, the furnace tube pressure is 1400～1800mtorr, and the deposition gas flow ratio of the first layer of silicon nitride film (51) is SiH ₄ : NH ₃ = 0.3:1 ~0.25:1, the deposition time of the first layer of silicon nitride film (51) is 160±30s; the deposition gas flow ratio of the second layer of silicon nitride film (52) is SiH ₄ : NH ₃ = 0.18:1 to 0.13 : 1, the deposition time of the second layer of silicon nitride film (52) is 220±30s. 2 . The method for preparing a back film capable of improving the conversion efficiency of a single-sided PERC cell according to claim 1 , wherein the silicon oxide film ( 3 ) has a thickness of 5±2 nm and a refractive index of 1.5±0.1. 3 . 3. The method for preparing a back film capable of improving the conversion efficiency of a single-sided PERC cell according to claim 1 or 2, wherein the silicon oxynitride film (4) has a thickness of 25±5 nm and a refractive index of 2.4±0.2. 4 . The method for preparing a back film capable of improving the conversion efficiency of a single-sided PERC cell according to claim 3 , wherein the first layer of silicon nitride film ( 51 ) has a thickness of 38±5 nm and a refractive index of 2.25±0.1. 5 . 5 . The method for preparing a back film capable of improving the conversion efficiency of a single-sided PERC cell according to claim 4 , wherein the thickness of the second layer of silicon nitride film ( 52 ) is 46±5 nm and the refractive index is 2.15±0.1. 6 . 6. The method for preparing a back film capable of improving the conversion efficiency of a single-sided PERC cell according to claim 5, characterized in that: an aluminum oxide film (2), a silicon oxide film (3), a silicon oxynitride film (4) and a nitrogen oxide film (4). The total film thickness of the silicon carbide film (5) added is 97 nm to 131 nm, the refractive index is 2.15 to 2.25, and the film color is light yellow.

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