CN100399584C - A tin dioxide/silicon heterojunction solar cell - Google Patents

Abstract

The invention relates to a tin dioxide/silicon heterojunction solar cell in the field of semiconductor technology. The invention includes grid line electrodes on the light facing surface of the battery, fluorine-doped tin dioxide layer, silicon dioxide layer, n-type silicon substrate, intrinsic amorphous silicon film, phosphorus-doped amorphous silicon film and aluminum back electrode. The grid electrode on the light-facing side of the battery is on the fluorine-doped tin dioxide layer, and a layer of silicon dioxide is sandwiched between the fluorine-doped tin dioxide layer and the front side of the n-type silicon substrate, and the back side of the n-type silicon substrate is sequentially Intrinsic amorphous silicon film and phosphorus-doped amorphous silicon film and aluminum back electrode are deposited. The invention reduces the series resistance of the film, the intrinsic amorphous silicon film on the back, the phosphorus-doped amorphous silicon film and the silicon chip form a high-low junction, improves the electric output performance of the battery, has simple technology, and low industrialization cost. Under the standard light intensity of AM1.5 and 100mW/cm ² , the efficiency of the solar cell is over 13%.

Description

A tin dioxide/silicon heterojunction solar cell

technical field

The invention relates to a battery in the technical field of semiconductors, in particular to a tin dioxide/silicon heterojunction solar battery.

Background technique

Since the first practical silicon solar cell was born in Bell Laboratories in the United States, crystalline silicon (including monocrystalline silicon and polycrystalline silicon) solar cells have been developed for more than half a century, and their shortcomings have also been highlighted in the development. First, the material The loss is large, the available silicon thickness is only 1% of the thickness of the silicon wafer, and the silicon material also increases the weight of the battery; second, the energy consumption is high, and the preparation of silicon ingots and the processing of bulk silicon batteries must be at a high temperature close to 1000 degrees The cost of crystalline silicon solar cells is still high. People have been discussing the technical route of thin film, because thin film solar cells have obvious advantages over crystalline silicon solar cells in terms of material utilization and energy consumption. In order to achieve the goal of thin film solar cells, people first consider the use of heterojunction solar cells. The technology first reduces energy consumption, that is, still uses silicon wafers as the substrate, and replaces the high-temperature homojunction process with a low-temperature heterojunction process, such as the HIT solar cell developed by Japan's Sanyo Electric Co., Ltd.; using metal oxides The production process of solar cells with a heterojunction formed by thin film and silicon wafer is not only simpler than that of traditional crystalline silicon diffused junction solar cells, but also the equipment is simpler than that used in HIT solar cells, and the manufacturing cost is lower.

After searching the literature of the prior art, it is found that U.S. pat. No. 4.366.335 of the United States introduces a solar cell using a heterojunction formed by an indium oxide film and silicon. However, this solar cell has the following disadvantages: first, indium is a noble metal, and the cost of the indium oxide thin film formed therefrom is high; second, because the passivation problem of the back electrode of the battery is not well resolved, the efficiency is not high.

Invention content:

The object of the invention is to overcome the deficiencies in the prior art, provide a kind of tin dioxide/silicon heterojunction solar cell, make it deposit _SnO on the n-type silicon substrate : F thin film, make tin dioxide and silicon Compared with indium oxide thin film and silicon heterojunction solar cells, the cost of heterojunction solar cells is greatly reduced because it does not have indium; secondly, by doping the semiconductor oxide SnO ₂ , the series resistance of the cell is improved, Its photoelectric conversion efficiency exceeds 13%.

The present invention is achieved through the following technical solutions. The invention includes grid line electrodes on the light facing surface of the battery, fluorine-doped tin dioxide layer, silicon dioxide layer, n-type silicon substrate, intrinsic amorphous silicon film, phosphorus-doped amorphous silicon film and aluminum back electrode. The grid electrode on the light facing surface of the battery is arranged on the light facing surface of the battery, the grid line electrode on the light facing surface of the battery is on the fluorine-doped tin dioxide layer, between the fluorine-doped tin dioxide layer and the front surface of the n-type silicon substrate A layer of silicon dioxide is sandwiched, and an intrinsic amorphous silicon film, a phosphorus-doped amorphous silicon film, and an aluminum back electrode are sequentially deposited on the back of the n-type silicon substrate.

The grid electrode on the light-facing side of the battery is a front photocurrent collecting electrode.

The fluorine-doped tin dioxide layer is a fluorine-doped tin dioxide film with a thickness of about 70nm-90nm, so the film is not only a part of the heterojunction but also plays the role of an optical anti-reflection film.

The silicon dioxide layer has a thickness ranging from 1 to 3 nm, and acts as a passivation between the front fluorine-doped tin dioxide layer and silicon.

The intrinsic amorphous silicon thin film, phosphorus-doped amorphous silicon thin film and aluminum back electrode constitute the back of the battery, and the intrinsic amorphous silicon thin film, phosphorus-doped amorphous silicon thin film and n-type silicon substrate form a high-low junction back buffer layer, which not only increases the open circuit voltage of the battery but also facilitates the formation of an ohmic contact with the aluminum electrode on the back.

The n-type silicon substrate can be a single crystal silicon substrate or a polycrystalline silicon substrate, the thickness is between 240-350nm, and the resistivity is 0.5-10Ω/□.

The applicable thickness range of the silicon dioxide layer is 1-3nm, which can be obtained by heating in an electric furnace at high temperature, and the oxidation under natural conditions can also meet the requirements.

The intrinsic amorphous silicon thin film has a thickness of 2nm-5nm.

The phosphorus-doped amorphous silicon film has a thickness of 10-30nm.

As an anti-reflection coating, the thickness and refractive index of the film have strict requirements. Usually: the thickness of the film is an integer multiple of λ/4. (λ is the wavelength of light). The refractive index of the AR coating should be the square root of the substrate's refractive index. Fluorine-doped tin dioxide films meet these requirements as anti-reflection coatings. The substrate used in the present invention and the fluorine-doped tin dioxide thin film have a refractive index of 4 and 2 respectively. At the same time, the thickness of the film is about 70nm-90nm, and the interference color is blue.

The sheet resistance of the fluorine-doped tin dioxide thin film of the invention is reduced to 90Ω/□, and there is no atomization, and the visible light transmittance of the obtained thin film can reach more than 85%. Common _SnO2 films have poor electrical conductivity. If _SnO2 films and silicon are used to form a heterojunction solar cell, it can be found that the series resistance will be large, resulting in a decrease in the output efficiency of the solar cell. The fluorine-doped tin dioxide film itself And the heterojunction formed with silicon has a strong ability to resist environmental corrosion, and the stability of the device is also greatly improved.

The front side of the silicon solar cell is the light-receiving side, and the positive electrode must be able to lead out the photo-generated current without blocking too much sunlight so as to reduce the area irradiated by light. The front side adopts a grid structure. It has been proven to not only optimize the surface coverage, but also reduce the series resistance of the battery.

The fluorine-doped tin dioxide layer of the present invention plays the role of optical anti-reflection and at the same time forms a heterojunction with silicon. The fluorine-doped tin dioxide layer is deposited by ultrasonic atomization technology, and the tin dioxide film is doped with fluorine ions, reducing the The series resistance of the film is improved; the intrinsic amorphous silicon film and phosphorus-doped amorphous silicon film on the back are prepared by hot wire chemical vapor deposition or plasma enhanced chemical vapor deposition technology, and they are combined with n-type silicon substrate The high-low junction is formed, the electric output performance of the battery is improved, the process is simple, and the industrialization cost is low. Under the standard light intensity of AM1.5 and 100mW/cm ² , the efficiency of the solar cell of the present invention reaches more than 13%.

Description of drawings

Fig. 1 is a structural representation of the present invention

Detailed ways

As shown in Fig. 1, the present invention comprises: grid line electrode 1 on the light-facing side of the battery, fluorine-doped tin dioxide layer 2, silicon dioxide layer 3, n-type silicon substrate 4, intrinsic amorphous silicon film 5 and phosphorus-doped Amorphous silicon thin film 6 and aluminum back electrode 7. The grid line electrode 1 on the light-facing surface of the battery is arranged on the light-facing surface of the battery, the grid line electrode 1 on the light-facing surface of the battery is on the fluorine-doped tin dioxide layer 2, and the fluorine-doped tin dioxide layer 2 and the n-type silicon substrate A silicon dioxide layer 3 is sandwiched between the front surfaces of the n-type silicon substrate 4 , and an intrinsic amorphous silicon film 5 , a phosphorus-doped amorphous silicon film 6 and an aluminum back electrode 7 are deposited in sequence on the back of the n-type silicon substrate 4 .

The grid line electrode 1 on the light-facing side of the battery is a front photocurrent collecting electrode.

The fluorine-doped tin dioxide layer 2 is a fluorine-doped tin dioxide film with a thickness of about 70nm-90nm and a refractive index of 2. The film is not only a part of the heterojunction but also functions as an optical anti-reflection film.

The silicon dioxide layer 3 has a thickness ranging from 1 to 3 nm, and acts as a passivation between the front fluorine-doped tin dioxide layer and silicon.

The n-type silicon substrate 4 is a single crystal silicon substrate or a polycrystalline silicon substrate with a thickness of 240-350 nm and a resistivity of 0.5-10 Ω/□.

The n-type silicon substrate 4 has a refractive index of 4.

The intrinsic amorphous silicon thin film 5 and phosphorus-doped amorphous silicon thin film 6 and n-type silicon substrate 4 form a high-low junction back buffer layer, which not only increases the open circuit voltage of the battery but also facilitates the formation of an ohmic contact with the back aluminum electrode 7 .

The intrinsic amorphous silicon thin film 5 has a thickness of 2 nm to 5 nm.

The phosphorus-doped amorphous silicon film 6 has a thickness of 10-30 nm.

The solar cell of the present invention consists of a heterojunction between the fluorine-doped tin dioxide layer 2 and the n-type silicon substrate 4, which provides a built-in electric field for separating photo-generated carriers. An intrinsic amorphous silicon film 5 and a phosphorus-doped amorphous silicon film 6 are added between the electrodes 7, which not only passivate the silicon back surface, but also form a back surface field with the n-type silicon substrate 4, thereby increasing the open circuit voltage of the battery , but also make the rear aluminum electrode 7 form an ohmic contact with silicon. The doped tin dioxide layer 2 on the front reduces the series resistance of the battery, and the design on the back is conducive to efficient electric power output.

example

The n-type silicon substrate 4 is an n-type Czochralski single-crystal silicon wafer with a resistivity of 1Ωcm. The silicon wafer is (100) oriented, polished on one side, and has a thickness of 250 μm. The effective area of the obtained solar cell is 2×2cm ² , doped with fluorine The thickness of the tin dioxide layer 2 is 76nm, the thicknesses of the intrinsic amorphous silicon film 5 and the phosphorus-doped amorphous silicon film 6 are 3nm and 30nm respectively, and the thickness of the silicon dioxide layer 3 is 2nm. The performance test results of the battery are: under the irradiation of AM1.5, 100mW/cm ² standard light intensity, the efficiency of the heterojunction solar cell prepared by this process reaches 14.2%, the open circuit voltage reaches 590mV, the short circuit current reaches 36mA, the fill factor up to 67%.

Claims (8)

1. tin ash/silicon heterojunction solar battery, comprise: battery side to light gate line electrode (1), mix the tin ash layer (2) of fluorine, silicon dioxide layer (3), n type silicon base (4), intrinsic amorphous silicon film (5) and phosphorus doping amorphous silicon membrane (6) and aluminum back electrode (7), it is characterized in that, battery side to light gate line electrode (1) is being mixed on the tin ash layer (2) of fluorine, mix between the front of the tin ash layer (2) of fluorine and n type silicon base (4) and pressed from both sides layer of silicon dioxide layer (3), the back side of n type silicon base (4) is deposition intrinsic amorphous silicon membrane (5) successively, phosphorus doping amorphous silicon membrane (6) and aluminum back electrode (7).

2. tin ash/silicon heterojunction solar battery according to claim 1 is characterized in that, the described tin ash layer (2) of mixing fluorine is the fluorine-doped tin dioxide film of thickness at 70nm～90nm.

3. according to claim 1 or 2 described tin ash/silicon heterojunction solar batteries, it is characterized in that described refractive index of mixing the tin ash layer (2) of fluorine is 2.

4. tin ash/silicon heterojunction solar battery according to claim 1 is characterized in that, described silicon dioxide layer (3), thickness range are 1～3nm.

5. tin ash/silicon heterojunction solar battery according to claim 1 is characterized in that, described n type silicon base (4) is monocrystal silicon substrate, perhaps polysilicon substrate, and thickness is between 240～350nm, and resistivity is 0.5～10 Ω/.

6. according to claim 1 or 5 described tin ash/silicon heterojunction solar batteries, it is characterized in that the refractive index of described silicon base (4) is 4.

7. tin ash/silicon heterojunction solar battery according to claim 1 is characterized in that, described intrinsic amorphous silicon film (5), thickness are 2nm～5nm.

8. tin ash/silicon heterojunction solar battery according to claim 1 is characterized in that, described phosphorus doping amorphous silicon membrane (6), thickness are 10～30nm.

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