CN101764170A - Aluminized emitter N-type solar battery and production method thereof - Google Patents

Abstract

The invention discloses an aluminized emitter N-type solar battery. The aluminized emitter N-type solar battery mainly comprises six parts of an N-type semiconductor substrate, a heavily doped N-type semiconductor layer, a medium film, an aluminum electrode, a metal front electrode and a P-type semiconductor layer, wherein the heavily doped N-type semiconductor layer only exists in a local region below the metal front electrode; other regions on the front surface of the solar battery is covered by the medium film; and the metal front electrode passes through the medium film and is contacted with the heavily doped N-type semiconductor layer on the front surface of the solar battery. The invention also discloses a production method for the aluminized emitter N-type solar battery. Compared with the aluminized emitter N-type solar battery in the conventional structure, the aluminized emitter N-type solar battery ensures that good ohmic contact is formed between the metal front electrode and a semiconductor substrate, reduces the average doping concentration of the front surface, and contributes to increasing a short circuit current and an open circuit voltage of the battery so as to obtain higher photoelectric transformation efficiency.

Description

A kind of aluminum back-emitter N-type solar cell and its manufacturing method

technical field

The invention belongs to the field of solar photovoltaic power generation, and in particular relates to an aluminum back emitter N-type solar cell and a manufacturing method thereof.

Background technique

A solar cell is a semiconductor device that uses the photovoltaic effect to directly convert solar energy into electrical energy. Structurally speaking, a solar cell consists of a p-n junction, dielectric film and metal electrodes on the surface of a semiconductor substrate.

According to the different conductivity types of the substrate, solar cells can be divided into P-type and N-type solar cells. P-type solar cells have a mature technology and occupy a dominant position in the solar cell market. However, P-type solar cells have obvious light-induced attenuation characteristics, which makes many research institutions and manufacturers turn their attention to N-type solar cells. Since the boron content of N-type crystalline silicon is small, the light-induced attenuation phenomenon caused by the boron-oxygen pair is not obvious. In addition, since N-type crystalline silicon has better tolerance to transition metals such as iron than P-type crystalline silicon, generally speaking, N-type crystalline silicon has a higher minority carrier lifetime. This is very beneficial for making high-efficiency solar cells. The A300 series solar cells of Sunpower Corporation of the United States and the HIT solar cells of Sanyo Corporation of Japan adopt a unique N-type solar cell structure and obtain the highest conversion efficiency of commercial solar cells.

In addition to A300 series and HIT solar cells, the aluminum back-emitter structure is another N-type solar cell structure that has attracted attention. The structure of a traditional aluminum back-emitter N-type solar cell is shown in Figure 1, which mainly consists of an N-type semiconductor substrate 1, a P-type semiconductor layer 7, a heavily doped N-type semiconductor layer 2, a dielectric film 3, an aluminum electrode 4 and The metal front electrode 6 consists of six parts. The main feature of aluminum back-emitter N-type solar cells is that N-type semiconductor materials (such as N-type crystalline silicon) are used as the substrate, and the back surface of the substrate is alloyed with aluminum electrodes to form a p-n junction. Traditional aluminum back-emitter N-type solar cells also form high-low junctions on the front surface of the substrate through phosphorus diffusion, which serves as the front surface field of the solar cell to reduce front surface recombination and increase the collection probability of photogenerated carriers. The manufacturing process of this aluminum back-emitter N-type solar cell is shown in Figure 3. Its manufacturing process is fully compatible with the P-type solar cell manufacturing process and can be produced with existing equipment. Therefore, aluminum back-emitter N-type solar cells have good industrialization prospects.

For aluminum back-emitter N-type solar cells, the effect of front surface recombination rate on cell efficiency is quite obvious. This is because most of the sunlight is absorbed in the very thin area of the front surface, however, the photogenerated carriers generated near the front surface must migrate to the p-n junction on the back surface of the cell to be collected. During this diffusion process, photogenerated carriers are easily recombined on the front surface of the cell, thereby reducing the conversion efficiency of the solar cell. A low front surface recombination rate is a prerequisite for ensuring the efficiency of aluminum back-emitter solar cells.

Reducing the doping concentration of the front surface can reduce the recombination rate of the front surface of the solar cell, but this will also lead to an increase in the contact resistance between the semiconductor substrate and the metal front electrode. The higher the contact resistance, the worse the performance of the solar cell. Because the front surface of traditional aluminum back-emitter N-type solar cells uses a phosphorus diffusion layer with uniform doping concentration as the front surface field, the front surface recombination rate and metal-semiconductor contact resistance are a pair of competing factors. High surface doping concentration means low contact resistance and high surface recombination rate; low surface doping concentration means high contact resistance and low surface recombination rate.

Contents of the invention

An object of the present invention is to propose an aluminum back-emitter N-type solar cell with a localized front surface field, which can simultaneously achieve a low front surface recombination rate and a low metal-semiconductor contact resistance, which is conducive to improving the aluminum Efficiency of back-emitter N-type solar cells.

Another object of the present invention is to propose a method for making the above-mentioned aluminum back-emitter N-type solar cell, which has a simple process, can use existing P-type solar cell production equipment for large-scale production, and has good industrialization prospects.

An aluminum back-emitter N-type solar cell provided by the present invention is mainly composed of six parts: an N-type semiconductor substrate, a heavily doped N-type semiconductor layer, a dielectric film, an aluminum electrode, a metal front electrode and a P-type semiconductor layer. Part of the positional relationship from top to bottom is the metal front electrode, dielectric film, heavily doped N-type semiconductor layer, N-type semiconductor substrate, P-type semiconductor layer and aluminum electrode, characterized in that the heavily doped N-type The semiconductor layer, that is, the front surface field of the solar cell, only exists in a local area under the metal front electrode, and the other areas of the solar cell front surface are covered by a dielectric film, and the metal front electrode penetrates the dielectric film and connects with the heavily doped N-type on the front surface of the solar cell. semiconductor layer contacts.

The heavily doped N-type semiconductor layer in the present invention is an N-type semiconductor layer heavily doped with donor impurities such as phosphorus, arsenic or antimony.

The dielectric film of the present invention is a single-layer dielectric film or a multi-layer dielectric film.

The composition of the single-layer dielectric film in the present invention is silicon nitride, silicon oxide, amorphous silicon, aluminum oxide, titanium oxide, silicon carbide or magnesium fluoride.

The multi-layer dielectric film of the present invention is any combination of single-layer dielectric films of silicon nitride, silicon oxide, amorphous silicon, aluminum oxide, titanium oxide, silicon carbide or magnesium fluoride.

The main component of the metal front electrode in the present invention is silver, copper, nickel, aluminum, tin or an alloy composed of these metal elements.

The p-n junction of the solar cell is formed by the N-type semiconductor substrate and the P-type semiconductor layer on the back surface of the cell. The p-n junction is located on the back surface of the solar cell and is used to collect photo-generated carriers of the solar cell. For aluminum back-emitter N-type solar cells, generally N-type crystalline silicon and aluminum-doped P-type regions formed during the Al-Si alloying process are used to form p-n junctions.

For the aluminum back-emitter N-type solar cell of the present invention, the heavily doped N-type semiconductor layer is only located in a local area under the metal front electrode of the solar cell. The heavily doped N-type semiconductor layer may be an N-type semiconductor thin layer region heavily doped with donor impurities such as phosphorus, arsenic, and antimony, such as a phosphorus-doped crystalline silicon thin layer. Its function is to form a local n ⁺⁺ n-type high-low junction on the front surface of the solar cell. The built-in electric field generated by the high-low junction is conducive to reducing the recombination of photogenerated carriers on the front surface of the cell, thereby improving the short-circuit current of the solar cell and open circuit voltage. The built-in electric field mentioned above is called the front surface field. In addition to forming a local front surface field, another function of the heavily doped N-type semiconductor layer is to reduce the contact resistance between the metal front electrode and the N-type semiconductor substrate, thereby improving the fill factor of the solar cell.

For the aluminum back-emitter N-type solar cell of the present invention, the dielectric film covers the entire area of the front surface of the solar cell except the metal front electrode. On the one hand, the dielectric film reduces the reflection of light on the front surface of the solar cell; on the other hand, it plays the role of surface passivation and reduces the recombination of the front surface. There are two kinds of dielectric films commonly used in production, silicon nitride and silicon oxide. In addition, amorphous silicon, aluminum oxide, silicon carbide, and a variety of multilayer dielectric films composed of the above-mentioned single-layer dielectric films have also shown good surface passivation performance in research.

For the aluminum back-emitter N-type solar cell of the present invention, the aluminum electrode covers the entire or most of the back surface of the solar cell. On the one hand, the aluminum electrode plays the role of collecting holes, and on the other hand, it provides the acceptor impurities required for doping the P-type semiconductor layer. As mentioned earlier, the p-n junction of aluminum back-emitter N-type solar cells is formed in the process of aluminum-silicon alloying. At high temperature, the interface between the aluminum electrode and the N-type silicon substrate forms a molten aluminum-silicon alloy phase, and then as the temperature drops, the molten aluminum-silicon alloy begins to recrystallize and precipitate excess aluminum, and finally forms on the back surface of the silicon substrate A thin layer of recrystallized silicon doped with aluminum. This area is the P-type semiconductor layer in the aluminum back-emitter N-type solar cell.

For the aluminum back emitter N-type solar cell of the present invention, the metal front electrode penetrates the dielectric film and is located on the heavily doped N-type semiconductor layer. Its main components are silver, copper, nickel, aluminum, tin or alloys of these elements. The role of the metal front electrode is mainly to collect electrons generated by the solar cell. For a method of manufacturing the above-mentioned aluminum back-emitter N-type solar cell involved in the present invention, the metal front electrode also plays the role of providing the donor impurity needed for the heavily doped N-type semiconductor layer.

The present invention also proposes a method for making the above-mentioned aluminum back-emitter N-type solar cell, which is characterized in that a heavily doped N-type semiconductor layer is formed at a local position on the front surface of the cell by using N-type heavily doped silicon paste, and A metal front electrode is fabricated on the heavily doped N-type semiconductor layer. Specifically, the following two methods are included:

Method 1: includes the following steps:

(a) Texturing and chemically cleaning the surface of the N-type semiconductor substrate;

(b) preparing a dielectric film on the surface of the N-type semiconductor substrate;

(c) preparing an aluminum electrode on the back surface of the battery;

(d) Print N-type heavily doped paste on a local area of the front surface of the battery and dry it;

(e) printing metal electrode paste on the area of N-type heavily doped paste printed on the front surface of the battery and drying;

(f) high temperature sintering.

Method 2: includes the following steps:

(a) Texturing and chemically cleaning the surface of the N-type semiconductor substrate;

(b) preparing a dielectric film on the surface of the N-type semiconductor substrate;

(c) preparing an aluminum electrode on the back surface of the battery;

(d) After mixing the N-type heavily doped paste and the metal electrode paste, it is simultaneously printed on a local area of the front surface of the battery and dried;

(e) High temperature sintering.

For the manufacturing method of the aluminum back-emitter N-type solar cell described in the present invention, wherein said surface texturing and chemical cleaning steps refer to making pyramids or pits on the surface of the N-type semiconductor substrate with acid or alkali Light-trapping structure, and clean its surface with chemical cleaning agent.

Regarding the manufacturing method of an aluminum back-emitter N-type solar cell according to the present invention, the dielectric film is mainly a single-layer or multi-layer dielectric film composed of silicon nitride, silicon oxide or aluminum oxide thin films. It covers the front surface or the entire surface of the N-type semiconductor substrate. The dielectric film mainly plays the role of reducing reflection and surface passivation.

Regarding the manufacturing method of the aluminum back-emitter N-type solar cell of the present invention, the aluminum electrode is prepared by screen printing aluminum paste, sputtering aluminum metal film or evaporating aluminum metal film.

Regarding the manufacturing method of an aluminum back-emitter N-type solar cell according to the present invention, the main component of the N-type heavily doped paste is phosphorus-doped, arsenic-doped or antimony-doped silicon particles. The N-type heavily doped paste has certain fluidity and can be coated on the surface of the solar cell by screen printing or other printing methods.

Regarding the manufacturing method of the aluminum back-emitter N-type solar cell described in the present invention, the sintering step refers to a high temperature (500-1000° C.) treatment process for the solar cell. During the sintering process, on the one hand, the N-type heavily doped paste is fused with the N-type semiconductor substrate to form a local heavily doped N-type layer on the surface of the N-type semiconductor; on the other hand, the aluminum electrode and the N-type semiconductor substrate The interface forms an aluminum-silicon alloy at high temperature, and forms a P-type semiconductor layer during the cooling process, forming a p-n junction with the N-type semiconductor substrate.

Compared with the traditional aluminum back-emitter N-type solar cell structure, the aluminum back-emitter N-type solar cell structure proposed by the present invention has a heavily doped N-type layer that only exists in the semiconductor region near the front electrode of the solar cell, and the front surface of the solar cell The rest of the position is covered by a dielectric film. This structure is beneficial to reduce the average doping concentration of the front surface of the solar cell, thereby reducing the recombination of the front surface. The heavily doped N-type layer under the front electrode of the solar cell not only makes a good ohmic contact between the metal front electrode and the semiconductor substrate, but also provides a local front surface field for the solar cell. These improvements all increase the short-circuit current and open-circuit voltage without reducing the fill factor of the solar cell, thereby improving the cell efficiency.

Compared with the manufacturing method of the traditional aluminum back-emitter N-type solar cell (as shown in Figure 3), the manufacturing method of the novel aluminum back-emitter N-type solar cell proposed by the present invention avoids the phosphorus diffusion process and greatly reduces the high temperature of the solar cell. The processing time, on the one hand, shortens the production cycle and reduces production energy consumption, and on the other hand, avoids performance degradation of the semiconductor substrate during high-temperature processing. The manufacturing method proposed by the invention also avoids the process of removing the heavily doped N-type layer on the back surface, further simplifying the manufacturing process.

Description of drawings

Figure 1 is a schematic diagram of the structure of a traditional aluminum back-emitter N-type solar cell

Fig. 2 is the structural representation of aluminum back-emitter N-type solar cell of the present invention

Figure 3 is a process flow chart for making a traditional aluminum back-emitter N-type solar cell

Fig. 4 is the process flow chart (embodiment one) of making aluminum back-emitter N-type solar cell of the present invention

Fig. 5 is the process flow chart (embodiment two) of making aluminum back-emitter N-type solar cell of the present invention

In Figures 1 to 5, 1. N-type semiconductor substrate, 2. Heavily doped N-type semiconductor layer, 3. Dielectric film, 4. Aluminum electrode, 5. Metal electrode paste, 6. Metal front electrode, 7, P 8. N-type heavily doped paste, 9. Metal electrode paste mixed with N-type heavily doped paste.

Detailed ways

As shown in Figure 2, the aluminum back emitter N-type solar cell of the present invention mainly consists of an N-type semiconductor substrate 1, a heavily doped N-type semiconductor layer 2, a dielectric film 3, an aluminum electrode 4, a metal front electrode 6 and a P-type solar cell. The semiconductor layer 7 consists of six parts, and the positional relationship of each part from top to bottom is the metal front electrode 6, the dielectric film 3, the heavily doped N-type semiconductor layer 2, the N-type semiconductor substrate 1, the P-type semiconductor layer 7 and the aluminum Electrode 4, wherein the heavily doped N-type semiconductor layer 2, that is, the front surface field of the solar cell only exists in a local area under the metal front electrode 6, and other areas of the front surface of the solar cell are covered by a dielectric film 3, and the metal front electrode 6 penetrates the medium The film 3 is in contact with the heavily doped N-type semiconductor layer 2 on the front surface of the solar cell.

The above-mentioned heavily doped N-type semiconductor layer 2 is an N-type semiconductor layer heavily doped with donor impurities such as phosphorus, arsenic or antimony; the dielectric film 3 is a single-layer dielectric film or a multi-layer dielectric film, and the composition of the single-layer dielectric film is nitride Silicon, silicon oxide, amorphous silicon, aluminum oxide, titanium oxide, silicon carbide or magnesium fluoride, the multilayer dielectric film is silicon nitride, silicon oxide, amorphous silicon, aluminum oxide, titanium oxide, silicon carbide or magnesium fluoride Any combination of single-layer dielectric films; the main component of the metal front electrode 6 is silver, copper, nickel, aluminum, tin or alloys composed of these metal elements.

Figure 4 shows one of the manufacturing processes of the aluminum back-emitter N-type solar cell proposed by the present invention, and the specific steps include:

(a) Texturing and cleaning the surface of the N-type semiconductor substrate 1: For the N-type single crystal silicon substrate, a pyramid-shaped light-trapping structure is fabricated on the substrate surface using dilute sodium hydroxide or potassium hydroxide solution; For the N-type polysilicon substrate, a light-trapping structure with pits is made on the surface of the substrate by using a mixed solution of nitric acid and hydrofluoric acid. Subsequently, the substrate is cleaned with diluted hydrochloric acid and hydrofluoric acid, respectively.

(b) Preparation of a dielectric film 3 on the surface of the N-type semiconductor substrate 1: a silicon nitride film of about 76 nm in thickness is deposited on the front surface of the substrate by plasma enhanced chemical vapor deposition (PECVD). It is also possible to deposit a thin layer of silicon oxide film on the surface of the substrate by thermal oxygen oxidation method, and then use PECVD to deposit a layer of silicon nitride film on the silicon oxide film.

(c) Prepare the aluminum electrode 4 on the back surface of the N-type semiconductor substrate 1: Print a layer of aluminum electrode paste with a thickness of about 20 μm on the back surface of the solar cell by screen printing and dry it. Alternatively, a thin aluminum electrode may be deposited by evaporation or magnetron sputtering.

(d) Print N-type heavily doped paste 8 on a local area of the front surface of the cell and dry it: use screen printing, spraying or inkjet printing to print grid-shaped N-type heavily doped silicon on the front surface of the solar cell paste and dry.

(e) Print the metal electrode paste 5 on the area where the N-type heavily doped paste 8 is printed on the front surface of the battery and dry it: use screen printing, spraying or inkjet printing to print on the area where the silicon paste is printed Silver electrode paste.

(f) High-temperature sintering: the solar cell is sintered at high temperature (500-1000°C) in a chain-type sintering furnace.

What Fig. 5 shows is another kind of manufacturing process of the aluminum back-emitter N-type solar cell proposed by the present invention, and the specific steps include:

(a) Texturing and cleaning the surface of the N-type semiconductor substrate 1: For the N-type single crystal silicon substrate, a pyramid-shaped light-trapping structure is fabricated on the substrate surface using dilute sodium hydroxide or potassium hydroxide solution; For the N-type polysilicon substrate, a light-trapping structure with pits is made on the surface of the substrate by using a mixed solution of nitric acid and hydrofluoric acid. Subsequently, the substrate is cleaned with diluted hydrochloric acid and hydrofluoric acid, respectively.

(b) Preparation of a dielectric film 3 on the surface of the N-type semiconductor substrate 1: a silicon nitride film of about 76 nm in thickness is deposited on the front surface of the substrate by plasma enhanced chemical vapor deposition (PECVD). It is also possible to deposit a thin layer of silicon oxide film on the surface of the substrate by thermal oxygen oxidation method, and then use PECVD to deposit a layer of silicon nitride film on the silicon oxide film.

(c) Prepare the aluminum electrode 4 on the back surface of the N-type semiconductor substrate 1: Print a layer of aluminum electrode paste with a thickness of about 20 μm on the back surface of the solar cell by screen printing and dry it. Alternatively, a thin aluminum electrode may be deposited by evaporation or magnetron sputtering.

(d) Print the metal electrode paste 9 mixed with N-type heavily doped paste on the front surface of the solar cell and dry it: use screen printing, spraying or inkjet printing methods to print a grid-like pattern on the front surface of the solar cell Silver paste mixed with N-type heavily doped paste and dried.

(e) High-temperature sintering: the solar cell is sintered at a high temperature (500-1000° C.) in a chain-type sintering furnace.

In conclusion, the present invention exemplifies the above-mentioned preferred embodiments, but it should be noted that various changes and modifications can be made by those skilled in the art. Therefore, unless such changes and modifications deviate from the scope of the present invention, they should all be included in the protection scope of the present invention.

Claims (10)

1. An aluminum back-emitter N-type solar cell, mainly composed of an N-type semiconductor substrate (1), a heavily doped N-type semiconductor layer (2), a dielectric film (3), an aluminum electrode (4), and a metal front electrode (6) and P-type semiconductor layer (7) are composed of six parts, and the positional relationship of each part is metal front electrode (6), dielectric film (3), heavily doped N-type semiconductor layer (2), N-type semiconductor substrate (1), P-type semiconductor layer (7) and aluminum electrode (4), it is characterized in that, described heavily doped N-type semiconductor layer (2) namely solar cell front surface field only exists in front of metal The local area below the electrode (6), other areas on the front surface of the solar cell are covered by a dielectric film (3), and the metal front electrode (6) penetrates the dielectric film (3) and is connected to the heavily doped N-type semiconductor on the front surface of the solar cell Layer (2) contacts. 2. The aluminum back emitter N-type solar cell according to claim 1, characterized in that, the heavily doped N-type semiconductor layer (2) is an N-type semiconductor heavily doped with donor impurities such as phosphorus, arsenic or antimony layer. 3. The aluminum back-emitter N-type solar cell according to claim 1, characterized in that the dielectric film (3) is a single-layer dielectric film or a multi-layer dielectric film. 4. The aluminum back-emitter N-type solar cell according to claim 3, wherein the composition of the single-layer dielectric film is silicon nitride, silicon oxide, amorphous silicon, aluminum oxide, titanium oxide, silicon carbide or magnesium fluoride. 5. The aluminum back-emitter N-type solar cell according to claim 3, wherein the multilayer dielectric film is silicon nitride, silicon oxide, amorphous silicon, aluminum oxide, titanium oxide, silicon carbide or fluorine Any combination of MgO monolayer dielectric film. 6. The aluminum back emitter N-type solar cell according to claim 1, characterized in that the main component of the metal front electrode (6) is silver, copper, nickel, aluminum, tin or an alloy composed of these metal elements . 7. the manufacture method of aluminum back-emitter N-type solar cell described in claim 1 is characterized in that, adopts N-type heavily doped silicon slurry to form heavily doped N-type semiconductor layer at the local position of battery front surface, and A metal front electrode is fabricated on the heavily doped N-type semiconductor layer. 8. the manufacture method of aluminum back-emitter N-type solar cell according to claim 7, is characterized in that, comprises the following steps: (a) Texturing and chemically cleaning the surface of the N-type semiconductor substrate; (b) preparing a dielectric film on the surface of the N-type semiconductor substrate; (c) preparing an aluminum electrode on the back surface of the battery; (d) Print N-type heavily doped paste on a local area of the front surface of the battery and dry it; (e) printing metal electrode paste on the area of N-type heavily doped paste printed on the front surface of the battery and drying; (f) high temperature sintering. 9. The manufacture method of aluminum back emitter N-type solar cell according to claim 7, is characterized in that, comprises the following steps: (a) Texturing and chemically cleaning the surface of the N-type semiconductor substrate; (b) preparing a dielectric film on the surface of the N-type semiconductor substrate; (c) preparing an aluminum electrode on the back surface of the battery; (d) After mixing the N-type heavily doped paste and the metal electrode paste, it is simultaneously printed on a local area of the front surface of the battery and dried; (e) High temperature sintering. 10. according to the manufacture method of claim 8 or 9 described aluminum back-emitter N-type solar cells, it is characterized in that, the surface texturing described in step (a) and chemical cleaning step refer to with acid or alkali in N Make a pyramid or pit-like light-trapping structure on the surface of the N-type semiconductor substrate, and clean its surface with a chemical cleaning agent; The dielectric film described in step (b) covers the front surface or the entire surface of the N-type semiconductor substrate; Step ( c) the aluminum electrode is prepared by screen printing aluminum paste, sputtering aluminum metal film or evaporating aluminum metal film; the main component of the N-type heavily doped paste described in step (d) is Silicon particles doped with phosphorous, arsenic or antimony.

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