KR20110101698A

KR20110101698A - Solar cell and method for manufacturing the same

Info

Publication number: KR20110101698A
Application number: KR1020100020902A
Authority: KR
Inventors: 이창재
Original assignee: 이창재
Priority date: 2010-03-09
Filing date: 2010-03-09
Publication date: 2011-09-16

Abstract

A solar cell using an N-type substrate and a method of manufacturing the same are disclosed. The greatest feature of the present invention is to provide a solar cell having excellent electrical characteristics and high efficiency by minimizing the contact resistance between the electrode of the battery and the substrate by selectively doping a high concentration of N-type impurities only in the region where the electrode of the battery is to be placed. Is that. In other words, by using the N-type substrate rather than the P-type substrate, the characteristics and advantages of the N-type substrate solar cell are utilized, and the phosphorous doping concentration of the FSF layer formed on the front surface of the cell to which the sunlight is incident is lowered so that the FSF layer and the Lowers the recombination of photo-generated electron-hole pairs on the cell surface, improving the blue response of the solar cell, and also improving the Al-doped P + diffusion layer (Emi). The present invention provides a solar cell and a method of manufacturing the same, which can achieve high light conversion efficiency even at a long wavelength.

Description

Solar cell and method for manufacturing the same {Solar cell and method for manufacturing the same}

The present invention relates to a solar cell using an N-type substrate and a method of manufacturing the same, and more particularly, to a low phosphorus doping concentration of a front surface field (FSF) layer formed on a front surface of a cell into which sunlight is incident. This reduces the recombination rate of the photo-generated carriers on the FSF layer and the surface, increasing cell efficiency and selectively increasing the concentration of phosphorus in the region where the electrode is placed, which prevents sunlight from penetrating into the substrate. (Phosphorus) The present invention relates to a solar cell capable of lowering contact resistance between a battery electrode and a substrate (base region) by doping, and a method of manufacturing the same.

Over the past few years, global solar cell production has grown at a level of 30% annually and has increased dramatically. The main materials used in solar cell production are bulk crystalline P-type CZ (Czochralski) monocrystalline silicon and polycrystalline silicon, accounting for more than 80% of all solar cell production. However, in general, a solar cell made of a boron-doped CZ-type silicon substrate is exposed to light or has a problem in that the performance of the solar cell is degraded during long time storage even in a dark place. Many scientists are interested in this problem and are analyzing the cause of the problem. The representative cause is the combination of boron (oxygen), which is a dopant of P-type substrate when the solar cell is exposed to light. It is known to form compounds and to destroy photo-generated carriers.

Therefore, in order to solve the problem of deterioration of solar cell performance by light, the use of a CZ substrate having a high oxygen concentration using boron as a dopant should be avoided. Therefore, when using a P-type substrate, a low oxygen concentration FZ (floating zone) wafer or a gallium doped wafer should be used. These substrates have a disadvantage in that the manufacturing cost of the crystal ingot is expensive. In recent years, the use of N-type CZ wafers doped with phosphorus has been considered.

The advantages of using an N-type CZ silicon substrate in solar cell manufacturing are as follows.

a. Avoiding the problem of deterioration of solar cell performance by the formation of compounds of boron and oxygen

b. Minority carrier life time higher than P type

c.Easy surface passivation by silicon thermal oxide film

d. High conductivity at same substrate concentration

e. Good current linearity

Due to the above advantages, the research and development of N-type crystalline silicon solar cell is actively underway, but the substrate and manufacturing technology of P-type solar cell have also been developed so that N-type solar cell is still compared with P-type solar cell. This did not achieve a high efficiency improvement. Therefore, P-type solar cells are becoming the mainstream of solar cells.

1A to 1G are cross-sectional views illustrating a solar cell manufacturing process using crystalline silicon of a representative P-type substrate, that is, a P-type substrate.

First, as shown in Fig. 1A, a P-type silicon substrate 100 of 0.5 to 3.0 Ω · cm is prepared. Subsequently, as shown in FIG. 1B, the P-type silicon substrate 100 is etched in a KOH / IPA mixed solution at 80 ° C. to form a texturing structure for minimizing reflectance of incident light on the surface. Thereafter, POCl ₃ gas is reacted with oxygen (O ₂ ) in an electric furnace (furnace) in front of the substrate surface as shown in FIG. 1C to thermally diffuse phosphorus (phosphorus) as a pentavalent element (˜10 ²¹ / cm ³ PN junction is formed by forming the N + diffusion layer 110 of the above), and then the PSG (phosphor-silicate-glass) film 120 formed during N + diffusion is immersed in liquid hydrofluoric acid (HF aqueous solution) to remove the structure of FIG. 1D. Get

Next, as shown in FIG. 1E, an anti-reflection film 130 for minimizing reflectance is formed on the surface of the silicon substrate 100, that is, the surface on which the sunlight is incident. As the anti-reflection film 130, a SiNx film formed by PECVD is used. Thereafter, as shown in FIG. 1F, a rear electrode 140, such as an aluminum (Al) electrode, and a front electrode 150, such as an silver (Ag) electrode, are formed on a front surface where sunlight is incident and heat treated to form a rear electric field layer. The back surface field 160 is formed and the front Ag electrode 150 is electrically connected to the N + type layer (emitter of the battery) through the antireflection film 130. The back surface field layer 160 is formed by doping Al atoms to a silicon substrate during firing in a belt furnace. Finally, as shown in FIG. 1G, the edge of the battery is etched and removed to cause the emitter electrode (negative electrode) and the base electrode (plus electrode) to be electrically disconnected, thereby completing the manufacture of the solar cell.

2A to 2G are cross-sectional views illustrating a solar cell manufacturing process using crystalline silicon of a representative N-type substrate, that is, an N-type substrate.

First, as shown in FIG. 2A, a 0.5-3.0 Ω · cm N-type silicon substrate 200 doped with phosphorus (Phosphorus) cut to a predetermined size is prepared. Thereafter, as shown in FIG. 2B, a texturing structure for minimizing the reflectance of sunlight on the surface of the silicon substrate 200 using a KOH / IPA mixed solution such as a base solution or an acid solution such as 80 ° C. is used. To form.

Next, as shown in FIG. 2C, a high concentration for forming a front surface field in a furnace using a POCl ₃ compound as an N-type impurity source on the surface of the substrate. (10 ²¹ / cm ³ N + diffusion layer 210). Subsequently, as illustrated in FIG. 2D, the PSG layer 220 formed on the surface of the POCl ₃ is etched and removed by hydrofluoric acid. Next, as shown in FIG. 2E, the surface silicon nitride (SiNx: H) is formed by the plasma chemical vapor deposition (PECVD) with the antireflection film 230 on the entire surface of the substrate. Next, as illustrated in FIG. 2F, Ag paste and Al paste are printed on the front and rear surfaces by using a screen printer or the like, so that the front electrode 250 and the front and rear surfaces of the substrate are printed. Each of the rear electrodes 240 is formed and heat treated to allow the metal electrode to be electrically connected to the substrate, and the Al-doped P-type diffusion layer 260 is formed directly on the Al electrode at the rear surface where the Al paste is printed. Here, the P type diffusion layer 260 becomes an emitter of the solar cell. Finally, as shown in FIG. 2G, the N / P + junction diode is electrically disconnected by removing the phosphorus diffusion layer (N-type diffusion layer) at the edge of the substrate, thereby completing the N-type substrate-based solar cell manufacturing.

In manufacturing the solar cell as described above, when using the N-type substrate to emphasize again has the following advantages.

That is, it is possible to avoid the problem of deterioration of solar cell performance by the generation of boron-oxygen compound, higher survival time of minority carriers than P-type substrate, easy surface passivation by silicon thermal oxide film, high conductivity at the same substrate concentration, Advantages such as good current linearity can be taken. However, in spite of these advantages, it is inevitable to obtain higher efficiency and commercialization than the solar cell of the P-type substrate in order to lower the contact resistance of the FSF layer subjected to sunlight as shown in FIG. 2C to the metal electrode. It is formed by doping high concentration of Phosphorus, which shortens the life time of electron-hole pairs generated in the short wavelength range of solar light (e.g. 4000 ~ 5000kW) and is easily recombined. It is because it cannot contribute effectively to the output improvement of a battery. Also, as shown in FIG. 2G, the Al-doped P + diffusion layer (emitter), which is formed during heat treatment from the Al electrode on the rear surface of the substrate, is formed by absorbing and inverting a high concentration of Phosphorus diffusion layer (ie, N + diffusion layer). The emitter will contain many Phosphorus impurities and thus will not be able to produce a good P + diffusion layer. When the P + diffusion layer (emitter) has many impurities and crystal defects, the life time of the photo-generated electrons or holes is short even in the long wavelength range (e.g., 9000 1 to 11000 Å) that reaches deep into the substrate. As a result, the recombination rate of electron-holes increases, and sunlight itself does not contribute to the formation of electron-hole pairs.

Accordingly, the problem to be solved by the present invention is to utilize the characteristics and advantages of the N-type substrate-based solar cell described above using an N-type substrate rather than a P-type substrate, Low phosphorus doping concentration minimizes recombination of photo-generated electron-hole pairs on the FSF layer and cell surface, improving the blue response of solar cells In addition, by providing a high quality Al-doped P + diffusion layer (emitter) at the same time to provide a solar cell and a method of manufacturing the same that can obtain a high light conversion efficiency even at long wavelengths.

Another object of the present invention, by selectively doping a high concentration of phosphorous (Phosphorus) only in the region where the electrode of the battery will be placed to minimize contact resistance between the electrode of the battery and the substrate (base region) to excellent electrical properties And to provide a highly efficient crystalline solar cell and its manufacturing method.

The solar cell of the present invention for solving the above problems: an N-type substrate having a front and back; A front electrode formed on the front surface of the N-type substrate; An N diffusion layer formed by doping an N-type impurity of a first concentration under the front electrode; And an N + diffusion layer formed to be in contact with the front electrode by doping an N-type impurity having a second concentration higher than the first concentration at a position covered by the front electrode.

The front electrode may be a recessed electrode formed in the recessed portion of the N-type substrate.

In addition, it is preferable that the first concentration has a value of 10 ¹⁹ / cm ³ or less, and the second concentration has a value of 10 ²⁰ / cm ³ or more.

In the case of the N + diffusion layer, it is preferable to have a deeper depth inside the substrate than the N diffusion layer.

The method of the present invention for manufacturing the solar cell comprises: a first step of etching an N-type substrate having a front surface and a back surface to have a texturing structure; An N diffusion layer is formed by doping N-type impurities of a first concentration on the entire surface of the N-type substrate, and a N-type impurity having a second concentration higher than the first concentration is doped only in a portion that is covered by the front electrode. Forming a diffusion layer; A third step of forming an anti-reflection film on the entire surface of the N-type substrate resulting from the second step; And a fourth step of forming a front electrode on the anti-reflection film and a rear electrode on the rear surface of the N-type substrate and heat treatment.

Here, before the forming of the N + diffusion layer, a recess may be formed only in a portion that is covered by the front electrode so that the front electrode becomes a recessed electrode.

In summary, in the present invention, a phosphor-doped N-type substrate is used as a substrate to be a base of a solar cell, and a front surface field (FSF) layer (ie, N) of a base surface on which light is incident The diffusion layer) and the contact region (that is, the N + diffusion layer) to be connected to the electrode were formed by diffusing phosphors (Phosphorus) having different concentrations. For example, the FSF layer forms a diffusion layer at a concentration of 10 ¹⁹ / cm ³ or less and the diffusion layer of the contact region at a concentration of 10 ²⁰ / cm ³ or more. Here, the method of selectively forming a diffusion layer of a high concentration of contact region is a method of thermal diffusion by injecting a gas containing Phosphorus in a furnace in a conventional manner, or a spin-on dopant containing phosphorus ) And then partially heated with a laser. In addition, as shown in FIG. 4, when the contact region is etched with a laser or the like, a diffusion layer is formed and an electrode having a line width smaller than that of the horizontal electrode as shown in FIG. At the same time, the light receiving area of the battery can be widened, thereby making solar cells with excellent electrical characteristics and high efficiency.

According to the present invention described above, the contact resistance between the electrode and the substrate is minimized, thereby manufacturing a solar cell having excellent electrical characteristics and high efficiency.

1A to 1G are cross-sectional views illustrating a solar cell manufacturing process using crystalline silicon of a representative P-type based, ie, P-type substrate;
2A to 2G are cross-sectional views illustrating a solar cell manufacturing process using crystalline silicon of an exemplary N-type based, ie, N-type substrate;
3A to 3H are cross-sectional views showing a solar cell manufacturing method according to an embodiment of the present invention;
4 is a cross-sectional view showing the structure of a solar cell manufactured by a solar cell manufacturing method according to another embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are only presented to understand the content of the present invention, and those skilled in the art will be capable of many modifications within the technical spirit of the present invention. Therefore, the scope of the present invention should not be construed as limited to these examples.

3A to 3H are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment of the present invention. Referring to FIG. 3A, an N-type silicon substrate 200 of 0.5 to 3.0 Ω · cm doped with phosphorus (Phosphorus) cut to a predetermined size is prepared. Thereafter, a basic or acidic solution is used to form a texturing structure for minimizing the reflectance of sunlight on the surface of the silicon substrate. The texturing structure can be formed by etching using a known etching method. For example, basic etching solutions such as tetramethy lammonium hydroxide (TMHA), potassium hydroxide (KOH), or sodium hydroxide (NaOH) to which a surfactant (surfactact) such as IPA (Iso Propyl Alcohol) or IPE (Iso PropylEthanol) are added, The texturing structure may be formed by dipping the N-type silicon substrate 200 in an acid solution mixed with hydrofluoric acid and nitric acid. The texturing structure can be formed in a pyramid shape (alkaline etching) or irregular irregularities (acidic etching), etc., and diffuses the solar light incident on the solar cell so that the maximum light can be absorbed into the solar cell. This increases the efficiency of the solar cell. Next, as shown in FIG. 3C, POCl ₃ is used as an N-type impurity source on the surface of the N-type silicon substrate 200. The compound is used to form a low concentration (10 ¹⁹ / cm ³ or less) N diffusion layer 212 for forming a front surface field in an electric furnace. Subsequently, as illustrated in FIG. 3D, the PSG layer Phosphorus Silicate Glass (220) formed on the surface during the diffusion of POCl _{3 is} removed by etching with hydrofluoric acid. The descriptions of FIGS. 3A to 3D are substantially the same as the descriptions of FIGS. 2A to 2D of the prior art except for the impurity concentration for forming the N diffusion layer 212. Next, as shown in FIG. 3e, a P-doped paste pattern is formed by screen printing a paste containing phosphorus at the same position where the front grid electrode is to be formed on the front surface, and then heat-processing the paste pattern. The high concentration (10 ²⁰ / cm ³ or more) N + diffusion layer 214 is formed deeper than the depth of the N diffusion layer 212, which is the entire electric field layer, by the diffusion method. At this time, the step of forming the low concentration N diffusion layer 212 for the front surface field layer (FSF layer) and the step of forming the high concentration N + diffusion layer 214 for contacting the front grid electrode of the solar cell may be reversed. In addition, a method of selectively forming a high concentration N + diffusion layer 214 in a contact region is a method of thermally diffusing phosphorus-containing gas in a furnace in a conventional manner, or a spin-on dopant containing phosphorus. ) Can be formed by partial heating with a laser. Meanwhile, in the above description, "the same position where the front grid electrode is to be formed" refers to a position that is covered by the front electrode when viewed from the front side of the substrate. Next, as shown in FIG. 3F, the surface silicon nitride (SiNx: H) is formed by the plasma chemical vapor deposition with the anti-reflection film 230 on the entire surface of the substrate. Subsequently, Ag paste and Al paste are printed on the front and rear surfaces by using a screen printer or the like, as shown in FIG. 3G, and the front electrode 250 and the rear electrode on the front and rear surfaces of the substrate. Each 240 is formed and subjected to a heat treatment, so that the metal electrode is electrically connected to the substrate, and the Al-doped P-type diffusion layer 260 is formed directly on the Al electrode at the rear surface where the Al paste is printed. Here, the P type diffusion layer 260 becomes an emitter of the solar cell. When printing the front electrode 250, care must be taken in the alignment between the substrate and the electrode pattern so that the front Ag electrode does not deviate from the high concentration N + diffusion layer 214. Finally, the N / P + junction diode is electrically disconnected by removing the phosphorus diffusion layer (N-type diffusion layer) at the edge of the substrate, thereby completing the manufacture of the solar cell of the N-type substrate.

Another embodiment of the present invention is to form a trench by etching the contact region with a laser or the like, as shown in Figure 4 to form a high concentration N + diffusion layer 216 in the trench to form a general horizontal type such as Figure 3h A method of configuring the recessed front electrode 252 having a smaller line width than the electrode is provided. By using such a structure, the electrode surface area shading disturbing the sunlight can be made small, and the thickness (depth of depression) of the electrode can be made thick to lower the series resistance of the battery as a whole. Therefore, more sunlight can be received than when the horizontal electrode is employed, and the series resistance of the battery can be lowered, thereby ensuring higher light conversion efficiency than the battery of the horizontal electrode structure.

200: N-type silicon substrate
212 low diffusion N diffusion layer
214: high concentration of N + diffusion layer
216: high concentration N + diffusion layer formed in the depression structure
220: Phosphor-Silicate-Glass layer
230: antireflection film
240: rear electrode
250: front electrode
252: recessed front electrode
260: P type diffusion layer

Claims

An N-type substrate having a front side and a rear side;
A front electrode formed on the front surface of the N-type substrate;
An N diffusion layer formed by doping an N-type impurity of a first concentration under the front electrode;
An N + diffusion layer formed to be in contact with the front electrode by doping an N-type impurity having a second concentration higher than the first concentration at a position covered by the front electrode;
Solar cell having a.

The solar cell of claim 1, wherein the front electrode is a recessed electrode formed in a recess of the N-type substrate.

The solar cell of claim 1, wherein the first concentration has a value of 10 ¹⁹ / cm ³ or less, and the second concentration has a value of 10 ²⁰ / cm ³ or more.

The solar cell of claim 1, wherein the N + diffusion layer is formed deeper in the substrate than the N diffusion layer.

In the manufacturing method for manufacturing the solar cell of Claim 1,
Etching a N-type substrate having a front surface and a back surface to have a texturing structure;
An N diffusion layer is formed by doping N-type impurities of a first concentration on the entire surface of the N-type substrate, and a N-type impurity having a second concentration higher than the first concentration is doped only in a portion that is covered by the front electrode. Forming a diffusion layer;
A third step of forming an anti-reflection film on the entire surface of the N-type substrate resulting from the second step;
A fourth step of forming a front electrode on the anti-reflection film and a rear electrode on a rear surface of the N-type substrate and heat-treating them;
Method for manufacturing a solar cell having a.

6. The solar cell of claim 5, further comprising: forming a recess only in a portion of the N + diffused layer that is covered by the front electrode so that the front electrode becomes a recessed electrode. Manufacturing method.