KR100446593B1 - Silicon solar cell and its manufacturing method - Google Patents

Abstract

The present invention provides a silicon solar cell having excellent back reflection effect and a method of manufacturing the same. The silicon solar cell is a p-type silicon substrate; An n ⁺ type semiconductor layer and an oxide film sequentially formed on the entire surface of the textured substrate; A plurality of line type front electrodes formed on the front surface of the substrate to be equally spaced apart at predetermined intervals and made of a conductive metal; P ⁺ on the back of the planarized substrate A semiconductor layer; P ⁺ type A back electrode formed on the semiconductor layer; And a conductive metal layer formed on the rear electrode. According to the present invention, the open circuit voltage and the conversion efficiency are improved by increasing the overall photocurrent due to the formation of extra carriers.

Description

Silicon solar cell and its manufacturing method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon solar cell and a method of manufacturing the same, and more particularly, to a silicon solar cell and a method of manufacturing the same having improved conversion efficiency by improving light reflection effects on the back of the cell.

Currently commercially available silicon solar cells have a structure as shown in FIG. 1.

Referring to this, n ⁺ type is formed on the front surface of the p-type silicon substrate 11 having the inverted pyramid structure formed thereon. The semiconductor layer 12 and the oxide film 13 are sequentially formed.

The front surface of the silicon substrate 11 is formed to be equally spaced apart at predetermined intervals, and a plurality of line type front electrodes 14 made of a conductive metal are formed.

And n ⁺⁺ type for reducing electrical contact resistance between the plurality of line type front electrodes 14 and the silicon substrate 11. The semiconductor layer 12 'is formed.

P ⁺ type on the back of the planarized silicon substrate 11 A semiconductor layer (not shown) and an aluminum layer 15, which is a back electrode, are sequentially formed.

As described above, the silicon solar cell has a back structure consisting of a p ⁺ -type semiconductor layer and a back electrode formed thereon. At this time, the p ⁺ -type semiconductor layer is prepared by vacuum-depositing aluminum on the back of the semiconductor substrate or coating a paste composition containing aluminum, followed by heat treatment, the back electrode is prepared by plating a conductive metal.

When the silicon solar cell having the back structure is irradiated with light, since silicon is an indirect interband transition semiconductor, light of an energy level higher than the band gap of the semiconductor is absorbed to generate a carrier. The energy of the energy level lower than the band gap is transmitted as it is (FIG. 2).

When measuring spectral response or quantum efficiency, which indicates the solar cell's response to the wavelength of light, the solar cell must measure all spectra in this frequency band in order to improve the response efficiency for solar radiation between 400 and 1200 nm. Improvements in properties are required. In addition, since the wavelength of the short wavelength region has high energy, the wavelength of this region is not used because it damages the surface of the solar cell or increases the recombination of carriers on the surface of the solar cell to decrease the efficiency.

In response to this demand, the present inventors have completed the present invention regarding a silicon solar cell having a back structure capable of reflecting light efficiently as shown in FIG.

The technical problem to be achieved by the present invention is to improve the light reflection effect on the back of the silicon substrate, the surface of the carrier by recombining the electrons in the back of the solar cell applied by the metal oxide silicon (MOS) structure by the back metal to the upper layer of the solar cell It is to provide a solar cell that lowers the speed.

Another object of the present invention is to provide a method of manufacturing the silicon solar cell.

The first object of the present invention is a p-type silicon substrate; An n ⁺ type semiconductor layer and an oxide film sequentially formed on the entire surface of the textured substrate; A plurality of line type front electrodes formed on the front surface of the substrate to be equally spaced apart at predetermined intervals and made of a conductive metal; P ⁺ on the back of the planarized substrate A semiconductor layer; P ⁺ type A back electrode formed on the semiconductor layer; And a conductive metal layer formed on the rear electrode.

A second object of the present invention is to form an oxide film on a p-type silicon substrate; (b) forming a photoresist pattern on the oxide film on the entire silicon substrate and etching the oxide film using the photoresist pattern; (c) removing the photoresist pattern and performing texturing; (d) etching the oxide film on the entire surface of the silicon substrate; (e) diffusing phosphorus (P) over the entire silicon substrate to form an n ^{+ `</sup> semiconductor layer, and then forming an oxide film over the n <sup>+`} type semiconductor layer over the silicon substrate; (f) Aluminum (Al) is deposited on the entire backside of the silicon substrate, followed by sintering to form p ⁺ Forming a semiconductor layer; (g) forming a plurality of line type front electrodes by plating a conductive metal on a predetermined region of the front surface of the silicon substrate; (h) forming a rear electrode made of a conductive metal on the back surface of the silicon substrate; And (i) forming a conductive metal layer on the back electrode.

In the present invention, in order to improve light absorption in the long wavelength region, a metal layer that can reflect light reaching the rear surface of the battery is additionally formed. This metal layer not only improves the reflection of light in the long wavelength region of light that reaches the rear surface of the silicon substrate but also serves to lower the series resistance by contacting the silicon region of the heat-treated rear surface.

Hereinafter, the structure of the silicon solar cell according to the present invention will be described with reference to FIGS. 4 and 5.

Referring to this, n ⁺ type is formed on the upper surface of the p-type silicon substrates 41 and 51 on which the inverse pyramid structure is formed. The semiconductor layers 42 and 52 and the oxide films 43 and 53 are sequentially formed.

The front surface of the silicon substrates 41 and 51 is formed to be equally spaced apart at predetermined intervals, and a plurality of line type front electrodes 44 and 54 made of a conductive metal are formed. The front electrodes 44 and 54 collect current generated in the pn junction silicon substrate and contact the external terminals. The front electrodes 44 and 54 are formed by plating a conductive metal by an electroless plating method or an electroplating method capable of selective plating. do.

And n ⁺⁺ type for reducing electrical contact resistance between the plurality of line type front electrodes 44 and 54 and the silicon substrates 41 and 51. The semiconductor layers 42 'and 52' are formed.

In the solar cell shown in FIG. 4, the back side of the planarized silicon substrate 41 is p ⁺ type. A semiconductor layer (not shown), an aluminum (Al) layer 45 as a back electrode, a conductive metal layer 46 and a silver (Ag) layer 47 are sequentially formed. The conductive metal layer may be formed using a metal having high reflectance and low resistance, that is, titanium (Ti), chromium (Cr), or aluminum (Al). The preferred thickness of the conductive metal layer is 200 to 600 nm, and the effect of reflecting light reaching the rear surface is maximized when in this range.

The silver layer 47 is a layer protecting the conductive metal layer 46, and is easily soldered when connected to other solar cells to manufacture a solar cell module. Such a silver layer is preferably formed to a thickness of 0.5 to 5㎛, preferably 0.5 to 1㎛.

In the solar cell shown in FIG. 5, the back side of the planarized silicon substrate 51 is p ⁺ type. A semiconductor layer (not shown), an aluminum layer 55, a silver (Ag) layer 57, and a metal thin film 56, which are back electrodes, are sequentially formed. Here, the silver layer 57 serves to compensate for the aluminum layer 55 etched by the alkali plating solution during plating.

In the solar cell according to the present invention, the operation principle will be described.

Sunlight is essentially composed of light with different wavelengths. Silicon is an indirect band-to-band transition semiconductor and has a low absorption of light. Therefore, in the solar cell which converts light energy into electric energy, only light having energy above the band gap of silicon can generate electron-hole carriers, and light having energy lower than the band gap of silicon passes through the silicon substrate as it is. Done.

However, as in the present invention, when the metal layer is formed using a metal having high reflectance and low electrical resistance on the back surface of the silicon substrate, the light reaching the back surface can be reflected. Light reflected from the back of the substrate may generate extra carriers and reduce series resistance. As the carrier generation increases, the quantum efficiency is increased, and the current density is improved. This improves the filling rate, thereby increasing the overall conversion efficiency.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

<Example 1>

An SiO ₂ film having a thickness of about 1300 μs was formed on the front and rear surfaces of the p-type silicon substrate. Then, a positive photoresist was applied on the SiO ₂ film on the entire surface of the silicon substrate to a thickness of about 1 μm, and only a predetermined portion was exposed using a shadow mask and then developed.

The photoresist pattern formed through this process was used as an etching mask, and the SiO ₂ film was etched for about 2 minutes and 30 seconds using a 7: 1 BHF solution, and then the photoresist was removed.

Thereafter, texturing was performed at 70 ° C. for 8 minutes using about 8% potassium hydroxide (KOH) solution. The SiO ₂ film on the entire silicon substrate was then etched for 2 minutes 30 seconds using a 7: 1 BHF solution.

POCl ₃ was diffused on the entire surface of the silicon substrate at about 840 ° C. for 20 minutes to about 150 to 240 Ω /? N ^{+ `} type with sheet resistance After the semiconductor layer was formed, a SiO ₂ film was formed over the n ⁺ type semiconductor layer on the entire silicon substrate.

Aluminum (Al) was deposited on the entire back surface of the silicon substrate and sintered at 900 to 980 ° C. for 1 to 2 hours to form a p ⁺ semiconductor layer having a thickness of about 2 μm.

By using a lithography process, a plurality of line-type front electrodes were formed by sequentially depositing Ti of about 600 GPa, Pd of about 600 GPa, and Ag of about 600 GPa in a predetermined region on the front surface of the silicon substrate.

Subsequently, aluminum was deposited on the back surface of the silicon substrate to form a back electrode having a thickness of about 1 μm. Then, Ti and Pd were sequentially plated to form a conductive metal layer having a thickness of about 50 nm.

Subsequently, a silicon solar cell was completed by electroplating silver (Ag) on the front electrode and the conductive metal layer on the back surface of the silicon substrate to form a silver layer having a thickness of about 1 μm.

<Example 2>

An SiO ₂ film having a thickness of about 1300 μs was formed on the front and rear surfaces of the p-type silicon substrate. Then, a positive photoresist was applied on the SiO ₂ film on the entire surface of the silicon substrate to a thickness of about 1 μm, and only a predetermined portion was exposed using a shadow mask and then developed.

The photoresist pattern formed through this process was used as an etching mask, and the SiO ₂ film was etched for about 2 minutes and 30 seconds using a 7: 1 BHF solution, and then the photoresist was removed.

Thereafter, texturing was performed at 70 ° C. for 8 minutes using about 8% potassium hydroxide (KOH) solution. The SiO ₂ film on the entire silicon substrate was then etched for 2 minutes 30 seconds using a 7: 1 BHF solution.

POCl ₃ was diffused on the entire surface of the silicon substrate at about 840 ° C. for 20 minutes to about 150 to 240 Ω /? N ⁺ type with sheet resistance After the semiconductor layer was formed, a SiO ₂ film was formed over the n ⁺ type semiconductor layer on the entire silicon substrate.

Aluminum (Al) was deposited on the entire back surface of the silicon substrate and sintered at 900 to 980 ° C. for 1 to 2 hours to form a p ⁺ semiconductor layer having a thickness of about 2 μm.

By using a lithography process, a plurality of line-type front electrodes were formed by sequentially depositing Ti of about 600 GPa, Pd of about 600 GPa, and Ag of about 600 GPa in a predetermined region on the front surface of the silicon substrate.

Subsequently, aluminum was deposited on the back surface of the silicon substrate to form a back electrode having a thickness of about 1 μm. Then, silver (Ag) was electroplated to form a silver layer having a thickness of about 1 μm, and titanium and palladium were sequentially deposited to form a silicon metal cell having a thickness of about 50 nm.

Comparative Example

An SiO ₂ film having a thickness of about 1300 μs was formed on the front and rear surfaces of the p-type silicon substrate. Then, a positive photoresist was applied on the SiO ₂ film on the entire surface of the silicon substrate to a thickness of about 1 μm, and only a predetermined portion was exposed using a shadow mask and then developed.

The photoresist pattern formed through this process was used as an etching mask, and the SiO ₂ film was etched for about 2 minutes and 30 seconds using a 7: 1 BHF solution, and then the photoresist was removed.

Thereafter, texturing was performed at 70 ° C. for 8 minutes using about 8% potassium hydroxide (KOH) solution. The SiO ₂ film on the entire silicon substrate was then etched for 2 minutes 30 seconds using a 7: 1 BHF solution.

POCl ₃ was diffused on the entire surface of the silicon substrate at about 840 ° C. for 20 minutes to about 150 to 240 Ω /? N ⁺ type with sheet resistance After the semiconductor layer was formed, a SiO ₂ film was formed over the n ⁺ type semiconductor layer on the entire silicon substrate.

Aluminum (Al) was deposited on the entire back surface of the silicon substrate and sintered at 900 to 980 ° C. for 1 to 2 hours to form a p ⁺ semiconductor layer having a thickness of about 2 μm.

By using a lithography process, a plurality of line-type front electrodes were formed by sequentially depositing Ti of about 600 GPa, Pd of about 600 GPa, and Ag of about 600 GPa in a predetermined region on the front surface of the silicon substrate.

Thereafter, a lift off process was performed to remove the resist and unnecessary Ti, Pd and Ag layers. Subsequently, aluminum was deposited on the back of the silicon substrate to form a back electrode.

In the solar cell manufactured according to Example 2, the open circuit voltage (V _oc ), the short circuit current density (J _SC ), the fill factor (FF) and the total conversion efficiency (E _ff ) were measured. In this case, the measurement was performed two times after electroplating silver (Ag) on the back surface of the silicon substrate (No. 1) and after forming a conductive metal layer (No. 2), and the results are shown in Table 1 below. It was.

TABLE 1

division V _oc (mV) J _SC (mA / ㎠) FF (%) E _ff (%) No. One 655 37.7 74.4 18.4 No. 2 654 37.9 76.8 19.1

From Table 1, it can be seen that the solar cell according to Example 2 has improved conversion efficiency than that of the solar cell manufactured according to the comparative example.

In addition, Fig. 6 shows the comparative analysis of the quantum efficiency change according to the wavelength of light in the silicon solar cell (dotted line) manufactured according to Example 2 and the solar cell (solid line) manufactured according to the comparative example.

Referring to this, it can be seen that in the solar cell manufactured according to the embodiment, the quantum efficiency was improved compared to the comparative example by generating an extra electron-hole carrier by forming a metal layer serving as a reflective film on the rear surface.

Silicon solar cell according to the present invention has a back structure that can efficiently reflect the light reached to the back of the substrate. Therefore, the open circuit voltage and the conversion efficiency are improved by increasing the overall photocurrent by forming an extra carrier. In addition, the surface recombination rate of the carrier is lowered by pushing electrons from the rear surface applied by the metal oxide silicon (MOS) structure by the rear metal to the upper portion of the solar cell.

1 is a view showing the structure of a conventional silicon solar cell,

2 is a view showing a state in which light is transmitted to the silicon substrate.

3 is a view showing a state in which light is reflected from the back of the silicon substrate,

4 and 5 are views showing the structure of a silicon solar cell according to the present invention,

6 is a graph showing a change in quantum efficiency according to the wavelength change of light in the solar cells manufactured according to the Examples and Comparative Examples.

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

11, 41, 51 ... p-type silicon substrate 12, 42, 52 ... n ⁺ type semiconductor layer

12 ', 42', 52 '... n ⁺⁺ type Semiconductor layers 13, 43, 53 ... oxide film

14, 44, 54 ... Line front electrode 15, 45, 55 ... Rear electrode

46, 56 ... metal thin layer 47, 57 ... silver (Ag) layer

Claims (8)

p-type silicon substrate; An n ⁺ type semiconductor layer and an oxide film sequentially formed on the entire surface of the textured substrate; A plurality of line type front electrodes formed on the front surface of the substrate to be sequentially spaced apart in equilibrium and made of a conductive metal; P ⁺ on the back of the planarized substrate A semiconductor layer; P ⁺ type A back electrode made of aluminum (Al) formed under the semiconductor layer; It is formed under the back electrode, and includes a conductive metal layer made of a material selected from the group consisting of chromium (Cr), titanium (Ti), titanium (Ti) / palladium (Pd), The silicon solar cell, characterized in that a silver (Ag) layer is formed between the back electrode and the conductive metal layer. The silicon solar cell of claim 1, further comprising a silver layer under the conductive metal layer. The silicon solar cell of claim 1, wherein the conductive metal layer has a thickness of 60 nm to 100 nm. The silicon solar cell of claim 1 or 2, wherein the silver (Ag) layer has a thickness of 0.5 to 5 µm. (a) forming an oxide film on the p-type silicon substrate; (b) forming a photoresist pattern over the oxide film on the entire silicon substrate and etching the oxide film using the photoresist pattern; (c) removing the photoresist pattern and performing texturing; (d) etching the oxide film on the silicon substrate; (e) diffusing phosphorus (P) on the entire surface of the silicon substrate to form an n ⁺ -type semiconductor layer, and then forming an oxide film on the n ⁺ -type semiconductor layer over the silicon substrate; (f) Aluminum was deposited on the entire backside of the silicon substrate, followed by sintering to form p ⁺ Forming a semiconductor layer; (g) forming a plurality of line type front electrodes by plating a conductive metal on a predetermined region of the front surface of the silicon substrate; (h) forming a rear electrode made of aluminum (Al) on the back surface of the silicon substrate; (i) forming a silver (Ag) layer by plating silver under the rear electrode, and then chromium (Cr), titanium (Ti), and titanium (Ti) / palladium (Pd) below the silver (Ag) layer. Forming a conductive metal layer made of a material selected from the group comprising the method of manufacturing a silicon solar cell. The method of manufacturing a silicon solar cell further comprising the step of plating silver (Ag) on the lower conductive metal layer on the back of the silicon substrate. The method of manufacturing a silicon solar cell, characterized in that the thickness of the conductive metal layer is 60 to 100nm. The method of claim 6, wherein the silver (Ag) layer has a thickness of 0.5 to 5 μm.

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