KR20090010498A - Bulk silicon solar cell having improved high temperature characteristics and manufacturing method thereof - Google Patents

Abstract

The bulk type silicon solar cell and manufacturing method thereof are provided to improve the stability for temperature and to achieve the reliability of the high quality. The bulk type silicon solar cell comprises the semiconductor layer having doping concentration gradient; the active layer formed on the semiconductor layer; the semiconductor layer. The low concentration becomes the high concentration based on the interlayer junction surface. The semiconductor layer includes a plurality of semiconductor layers having various doping concentration. The reliability of device can be improved.

Description

Bulk silicon solar cell with improved high temperature characteristics and method for manufacturing same {BULK SILICON SOLAR CELL HAVING IMPROVED HIGH TEMPERATURE CHARACTERISTICS AND MANUFACTURING METHOD THEREOF}

The present invention relates to a bulk silicon solar cell and a method of manufacturing the same, and more particularly, a semiconductor layer having a gradient of doping concentration gradient from low to high concentrations based on the interlayer junction surface, an active layer sequentially formed on the semiconductor layer, and the By providing a solar cell including a semiconductor layer and a semiconductor layer in a different region, the conventional solar cell or solar cell module improves the drop in stability to temperature when the temperature increases under conditions of generating power and the adhesion between semiconductor layers The present invention relates to a bulk silicon solar cell having an increased thickness and a method of manufacturing the same.

Solar cells have been researched for decades as clean energy sources that produce energy by converting light energy transmitted from the sun to the earth. The severity of the oil fluctuations in the 70's and the greenhouse effect caused by carbon dioxide in the early 90's, and the international agreement on the regulation of carbon dioxide emissions to prevent global warming in the late 90's, conveyed the necessity of clean energy such as solar cells to mankind. It has been an important instrument, and until now, researches on solar cell materials include group IV materials such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, amorphous SiC, amorphous SiN, amorphous SiGe, amorphous SiSn, or gallium arsenide (GaAs), Compound semiconductors of group III-V such as aluminum gallium arsenide (AlGaAs) and indium phosphorus (InP), and group II-VI such as CdS, CdTe, Cu ₂ S, and the like have been studied. The pn structure including the back electric field type, the pin structure, the heterojunction structure, the Schottky structure, the multijunction structure including the tandem type or the vertical junction type have been studied.

In general, the characteristics and research and development required for solar cells are proceeding from the viewpoint of improving photoelectric conversion efficiency, reducing manufacturing cost, reducing the number of years of energy recovery and increasing the area.

The photoelectric conversion efficiency is evaluated at a temperature of about 25 ° C for a general solar cell or module. When power is generated in a real solar cell, the temperature is increased by about 70 ° C to 75 ° C, and the photoelectric conversion efficiency is affected by the temperature. .

The change in photoelectric conversion efficiency with temperature is as shown in FIG. 1.

Referring to Figure 1, it can be seen that the efficiency at room temperature of about 20 ℃ to 25 ℃ is significantly reduced at a high temperature of 70 ℃ to 75 ℃. It can be observed that the efficiency of a typical crystalline solar cell is reduced by about 25%, and the efficiency of the HIT solar cell of Sanyo of Japan is reduced by about 20%.

The reason why the efficiency of the solar cell decreases as the temperature increases is that the decrease in Voc increases with increasing temperature, whereas Isc increases slightly as the current-voltage characteristic curve of FIG. 2 increases.

The Voc decreases with increasing temperature because the band gap energy of the bulk crystalline silicon decreases with temperature, and the slight increase of Isc with increasing temperature causes the band gap energy with increasing temperature. It is known that the light absorbance increases because it decreases with the increase.

After all, as the temperature increases, the efficiency of the solar cell decreases because the bandgap energy between the conduction band and the valence band decreases. Therefore, reducing the decrease of the bandgap energy becomes a key to improving the efficiency of the solar cell.

Therefore, in order to develop a solar cell having improved stability to temperature, it is necessary to study the conditions for reducing the reduction of the bandgap energy and to solve the problems caused therefrom.

An object of the present invention is to solve the problem that the general solar cell is less efficient according to the temperature, the bulk type that reduces the bandgap energy decrease with temperature increase and thereby improves the problem of wavelength response To provide a silicon solar cell.

Another object of the present invention is to provide a manufacturing method of a solar cell in which the stability of the solar cell is improved by increasing the temperature through a simple process without changing the original structure in the manufacturing of the conventional solar cell, the manufacturing cost is reduced and economical The present invention also provides a bulk silicon solar cell manufacturing method with improved quality characteristics.

In order to achieve the above object, the bulk silicon solar cell of the present invention may include a semiconductor layer having a doping concentration gradient, an active layer sequentially formed on the semiconductor layer, and a semiconductor layer in a region different from the semiconductor layer.

The doping concentration gradient in the present invention may be characterized in that it is gradient from low concentration to high concentration on the basis of the interlayer bonding surface.

The semiconductor layer may be an n-type or p-type semiconductor layer, and thus may be a solar cell having a structure sequentially stacked with an n-i-p-type or p-i-n-type semiconductor layer.

The semiconductor layer having the doping concentration gradient may be formed by including a plurality of semiconductor layers having different doping concentrations from low to high concentrations based on the interlayer bonding surface.

In order to achieve the above object, a method of manufacturing a bulk silicon solar cell of the present invention is a method of manufacturing a bulk silicon solar cell including semiconductor layers of different regions, and at a high concentration at a low concentration based on a junction surface of any one of the semiconductor layers. Forming a doping concentration gradient.

In the present invention, since the semiconductor layer may be an n-type or p-type semiconductor layer, an n-type semiconductor layer having an doping concentration gradient, an active layer, and a p-type semiconductor layer are stacked in this order, or a p-type semiconductor layer having an doping concentration gradient and an active layer. and laminating in order of the n-type semiconductor layer.

The slope of the doping concentration may be formed by applying an electric field after using any one of ion implantation, thermal diffusion, and phosphorus oxychloride (POCl ₃ ) diffusion method.

The method of manufacturing a bulk silicon solar cell of the present invention for achieving the above object comprises the steps of forming a plurality of semiconductor layers having different doping concentrations and an active layer and a semiconductor layer having a different region from the semiconductor layer on top of the semiconductor layer. Laminating may be included.

In the present invention, the semiconductor layer may be formed by forming a plurality of semiconductor layers doped at a low concentration to a high concentration based on the bonding surface with the active layer.

In the present invention, since the high temperature stability of the solar cell decreases with increasing temperature, the band gap energy is decreased, so that the doping concentration profile of the semiconductor layer is adjusted to reduce the decrease of the band gap energy.

In other words, the higher the doping concentration, the greater the bandgap energy when doping impurities to form an n-type or p-type semiconductor layer on the wafer.

As can be seen with reference to FIG. 3, which is a graph showing an energy state according to temperature, the higher the doping concentration is, the larger the difference in the bandgap energy is. It can be seen that the difference in the bandgap energy decreases as the temperature increases, but the higher the doping concentration, the higher the doping concentration, and the relatively higher the bandgap energy when the doping concentration is lower.

The present invention improves the stability according to the temperature of the solar cell by using the bandgap energy increases as the doping concentration is high.

In the solar cell, the dopant concentration of the impurity semiconductor layer is increased to reduce the band gap energy as much as possible.

The p-type semiconductor layer is formed by adding a valence trivalent element such as boron, gallium, or indium as a doping material to a crystalline silicon wafer, and the n-type semiconductor layer is a valence 5 such as phosphorus, arsenic, and antimony as a doping material to a crystalline silicon wafer. It is formed by adding an additional element.

The slope of the doping concentration of the present invention is to vary the concentration of these impurity element materials.

However, the higher the doping concentration, the lower the efficiency due to the increase in the temperature can be improved, but the sensitivity of the short wavelength at the time of light absorption has a problem that the present invention can be filtered by the short wavelength in the front of the wafer A solar cell including a semiconductor layer having a slope of a doping concentration is provided.

Therefore, in the step of doping the wafer to form an impurity semiconductor layer, a doping concentration gradient is performed such that the doping profile of the wafer is adjusted so that the semiconductor layer on the side of the bonding surface is lightly doped and the remaining portions are doped at high concentration.

To this end, a semiconductor layer having a doping concentration gradient may be formed by stacking a semiconductor layer doped with a relatively low concentration of impurities on a semiconductor layer doped with a high concentration of impurities.

In addition, it can be formed by injecting at a high concentration to a low concentration by varying the doping concentration with respect to one wafer layer, and to be injected at a lower concentration toward the bonding surface on which the active layer or another type of semiconductor layer is laminated.

The doping concentration for forming the concentration gradient in the semiconductor layer may be sufficient to form a relative impurity concentration difference, but preferably, the high doping concentration may be 10 to 100 times higher than the low doping concentration.

More preferably, the doping concentration of the semiconductor layer formed on the junction surface is 10 ¹⁶ cm ^-3 to 10 ¹⁷ cm ^-3 , and the doping concentration of the remaining highly doped semiconductor layer is 10 ¹⁸ cm ^-3 to 10 ¹⁹ cm ^-3. Can be.

According to the present invention, since the doping concentration of the junction surface of the semiconductor layer in which the active layer and the other types of semiconductor layers are stacked is lower than that of other high concentration semiconductor doping concentrations, short wavelength light is filtered from the front of the wafer, thereby improving short wavelength response.

Specific embodiments of the present invention can be seen with reference to the accompanying FIG. In describing the contents of the drawings, detailed descriptions of well-known functions and configurations determined to unnecessarily obscure the subject matter of the present invention will be omitted.

Referring to FIG. 4, a n-type semiconductor layer 10 is formed by doping a donor impurity in a high concentration on a wafer made of a material such as silicon or germanium. The lightly doped n-type semiconductor layer 11 is formed by doping donor impurities at a relatively low concentration.

The lightly doped n-type semiconductor layer 11 may have a thickness of 0.5 micrometers to several tens of micrometers, but preferably 0.5 μm to 1.5 μm.

The i-type semiconductor layer 12 and the p-type semiconductor layer 13 are sequentially formed thereon to form a solar cell.

In another embodiment, the doping concentration gradient may be formed on the p-type semiconductor layer, and the i-type semiconductor layer and the n-type semiconductor layer may be formed thereon.

Another embodiment of the present invention is to adjust the doping concentration profile inside the wafer so that the pn junction side is a low concentration doping, the remaining portion is a high concentration doping, a lightly doped wafer layer on the high concentration doped wafer Can be formed.

As a method for forming a bulk silicon solar cell having improved high temperature characteristics of the present invention, a step of adjusting a doping profile of a heavily doped wafer may be performed by applying a high electric field after a doping step.

However, application of high electric field should be carried out under the discharge condition of solar cell.

The doping method of the impurity in the doping step is not limited to a specific method and will be satisfied by a known method known to those skilled in the art, but preferably, ion implantation, thermal diffusion, phosphorus oxychloride ( Phosphorus Oxychloride, POCl ₃ ) diffusion method and the like can be used.

The ion implantation method is used to vacuum trivalent elements such as boron (B), gallium (Ga) and indium (In) or impurities (dopants) which are pentavalent elements such as phosphorus (P), arsenic (As) and antimony (Sb) in a vacuum. After ionization, the surface layer is p-typed or n-typed by being accelerated by an electric field and placed on the silicon wafer surface.

The thermal diffusion method is a method of p-type or n-type surface layer by heating a substrate so that impurity elements are permeated from the surface of a silicon wafer. Usually, thermal diffusion temperature is 850 degreeC-1000 degreeC, and time is suitable for 30 to 150 minutes.

Phosphorus oxychloride (Phosphorus Oxychloride, POCl ₃₎ diffusion method is a method of thermal diffusion 60 minutes to 90 minutes at a temperature 800 ℃ to 900 ℃ using POCl ₃ in a compound liquid as yeolhwak Maternity Hospital (source).

The ion implantation method is suitable for a doping concentration gradient because it can be doped to a desired depth at a desired doping concentration.

Impurities can be doped in parallel with the etching method for selective doping on the crystalline wafer, and the above doping method and the PSG etching method are simultaneously performed to dope a wafer including an insulator layer such as Phospho Silicate Glass (PSG). Can be used.

The present invention has been described above in connection with specific embodiments of the present invention, but this is only an example and the present invention is not limited thereto. Those skilled in the art can change or modify the described embodiments without departing from the scope of the present invention, and such changes or modifications are within the scope of the present invention. In addition, the materials of each component described herein can be easily selected and replaced by a variety of materials known to those skilled in the art. Those skilled in the art can also omit some of the components described herein without adding performance degradation or add components to improve performance. In addition, those skilled in the art may change the order of the method steps described herein according to the process environment or equipment. Therefore, the scope of the present invention should be determined not by the embodiments described, but by the claims and their equivalents.

The present invention solves the problem that the photoelectric conversion efficiency is lowered according to the temperature in the general solar cell has an effect of improving the stability even when the temperature increases.

In addition, by improving the stability to temperature can solve the problem of poor bonding and short wavelength sensitivity can provide a high quality and reliable solar cell.

According to one embodiment of the present invention, a material of five valence elements is doped by using ion implantation on a silicon wafer substrate. Other known methods can be used for the doping.

The wafer doped with n-type impurity forms an n-type semiconductor layer and sequentially forms an active layer and a p-type semiconductor layer thereon.

A high electric field is applied to the formed solar cell to form a lightly doped semiconductor layer of 0.5 micrometers to 1 micrometer from the p-n junction surface. The remaining portions except for these low concentration doped semiconductor layers may be relatively high doped, thereby forming a doping concentration gradient in one semiconductor layer.

Usually, the doping concentration of the lightly doped semiconductor layer is 10 ¹⁶ cm ^-3 to 10 ¹⁷ cm ^{- 3} , and the doping concentration of the remaining heavily doped semiconductor layer is preferably 10 ¹⁸ cm ^-3 to 10 ¹⁹ cm ^{- 3} . .

1 is a graph showing the efficiency distribution of a conventional silicon solar cell with temperature.

Figure 2 is a graph showing the temperature correlation of the current-voltage characteristic curve of the solar cell.

3 is a graph showing a bandgap energy distribution curve with temperature of a solar cell.

Figure 4 is a cross-sectional view showing the structure of a bulk silicon solar cell according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: high concentration doped n-type semiconductor layer 11: low concentration doped n-type semiconductor layer

12 i-type semiconductor layer 13 p-type semiconductor layer

Claims (9)

A semiconductor layer having a doping concentration gradient; And An improved bulk silicon solar cell including an active layer sequentially formed on the semiconductor layer and a semiconductor layer in a region different from the semiconductor layer. The method of claim 1, The doping concentration gradient, the bulk silicon solar cell with improved high temperature characteristics, characterized in that the gradient from low to high concentrations based on the interlayer bonding surface. The method of claim 1, The semiconductor layer is a bulk silicon solar cell with improved high temperature characteristics, characterized in that the n-type or p-type semiconductor layer. The method of claim 1, The semiconductor layer is a bulk silicon solar cell with improved high temperature characteristics, characterized in that it comprises a plurality of semiconductor layers varying the doping concentration from low concentration to high concentration based on the interlayer bonding surface. In the method of manufacturing a bulk silicon solar cell comprising a semiconductor layer of different regions, A method of manufacturing a bulk silicon solar cell having improved high temperature characteristics, comprising the step of forming a doping concentration gradient from a low concentration to a high concentration based on a junction surface in any one semiconductor layer. The method of claim 5, The semiconductor layer is a manufacturing method of the bulk silicon solar cell with improved high temperature characteristics, characterized in that the n-type or p-type semiconductor layer. The method of claim 6, The slope of the doping concentration is formed by applying an electric field after using any one of ion implantation, thermal diffusion, and phosphorus oxychloride (POCl ₃ ) diffusion method. Improved bulk silicon solar cell manufacturing method. Forming a plurality of semiconductor layers having different doping concentrations; And A method of manufacturing a bulk silicon solar cell having improved high temperature characteristics, comprising: laminating an active layer and a semiconductor layer having a region different from that of the semiconductor layer on the semiconductor layer. The method of claim 8, The semiconductor layer is a method of manufacturing a bulk silicon solar cell with improved high temperature characteristics, characterized in that formed as a semiconductor layer doped at a low concentration to a high concentration on the basis of the bonding surface with the active layer.

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