Back contact solar cell and fabrication method thereof

Abstract

The present invention discloses a back contact solar cell comprising: a first conductive type semiconductor substrate having a front surface and a rear surface of a texturing structure; an oxide layer formed on the front surface of the substrate; at least one first conductive type semiconductor region and second conductive type semiconductor region alternatively formed at predetermined intervals on the rear surface of the substrate; an oxide layer formed on the remaining rear surface of the substrate except for the first conductive type semiconductor region and the second conductive type semiconductor region; and electrodes formed on each of the first conductive type semiconductor region and the second conductive type semiconductor region.

Claims

1. A fabrication method of a back contact solar cell having a plurality of different conductive type semiconductor regions on a rear surface of a first conductive type semiconductor substrate, the method comprising: forming a pyramid-shaped front texturing structure and a pyramid-shaped rear texturing structure at front and rear surfaces, respectively, of the substrate via etching by immersing the substrate in an etching solution; forming thermal oxide layers both on the front and rear surfaces, respectively, of the substrate at the pyramid-shaped front and rear texturing structures using a rapid thermal oxidation scheme in a rapid thermal processing furnace or by a sputtering method using silicon oxide as a target material; forming first patterns by locally removing a thermal oxide layer formed on the rear surface of the substrate from among the thermal oxide layers by irradiating a laser light to the thermal oxide layer formed on the rear surface at predetermined intervals, and the pyramid-shaped rear texturing structure is not present where the thermal oxide layer is partially removed; forming first conductive type semiconductor regions on the rear surface of the substrate through the first patterns by thermal diffusion in a high-temperature furnace by flowing a first conductive type material into an inside of the high-temperature furnace to dope the first conductive type material at the first patterns; forming, subsequent to the forming the first conductive type semiconductor regions, second patterns by locally removing the thermal oxide layer formed on the rear surface of the substrate by irradiating a laser light to the thermal oxide layer formed on the rear surface that remains at the predetermined intervals with the first patterns, and the pyramid-shaped rear texturing structure is not present where the thermal oxide layer is partially removed, and the pyramid-shaped rear texturing structure remains only between the first conductive type semiconductor regions and second conductive type semiconductor regions at the rear surface of the substrate; forming the second conductive type semiconductor regions on the rear surface of the substrate through the second patterns by a dopant screen printing to print a second conductive type material to dope the second conductive type material at the second patterns so that the first conductive type semiconductor regions and the second conductive type semiconductor regions are respectively formed by different doping methods; and forming first electrodes being in direct contact with the first conductive type semiconductor regions through the first patterns and second electrodes being in direct contact with the second conductive type semiconductor regions through the second patterns, wherein a thermal oxide layer at the front surface acts as a front protection layer, wherein, in the forming of the first conductive type semiconductor regions by the thermal diffusion, the thermal oxide layer at the rear surface acts as a mask for protecting portions corresponding to the second conductive type semiconductor regions at the rear surface, wherein, after the forming of the second patterns, the thermal oxide layer at the rear surface remains between the first patterns and the second patterns and acts as a rear protection layer, wherein the thermal oxide layer remaining on the rear surface is spaced apart so as not to overlap the first conductivity type regions and the second conductivity type regions in a vertical direction, and wherein the first electrodes are formed so as to cover an entire surface of the first conductive type semiconductor regions and extend over an adjacent portion of the thermal oxide layer at the rear surface, and the second electrodes are formed so as to cover an entire surface of the second conductive type semiconductor regions and extend over an adjacent portion of the thermal oxide layer at the rear surface.

2. The fabrication method of the back contact solar cell according to claim 1, wherein the first electrodes or the second electrodes are formed by a screen printing method.

3. The fabrication method of the back contact solar cell according to claim 1, wherein a laser source used to irradiate the laser light is a green laser source or an Nd/YAG laser source.

4. The fabrication method of the back contact solar cell according to claim 1, the method further comprising forming an anti-reflection coating on an upper surface of the thermal oxide layer formed on the font surface of the substrate from among the thermal oxide layers.

5. The fabrication method of the back contact solar cell according to claim 1, wherein the pyramid-shaped front texturing structure on the front surface of the substrate is entirely formed on the front surface of the substrate.

6. A fabrication method of a back contact solar cell having a plurality of different dopant type semiconductor regions on a rear surface of a p-type semiconductor substrate, the method comprising: forming a pyramid-shaped front texturing structure and a pyramid-shaped rear texturing structure, respectively, of the substrate via etching by immersing the substrate in an etching solution; forming thermal oxide layers on the front and rear surfaces, respectively, of the substrate at the pyramid-shaped front and rear texturing structures using a rapid thermal oxidation scheme in a rapid thermal processing furnace or by a sputtering method using silicon oxide as a target material, forming first patterns by locally removing a thermal oxide layer formed on the rear surface of the substrate from among the thermal oxide layers by irradiating a laser light to the thermal oxide layer formed on the rear surface at predetermined intervals; forming n-type semiconductor regions on the rear surface of the substrate through the first patterns by thermal diffusion in a high-temperature furnace by flowing an n-type conductive material into an inside of the high-temperature furnace to dope the n-type conductive material at the first patterns; forming, subsequent to the forming the n-type semiconductor regions, second patterns by locally removing the thermal oxide layer formed on the rear surface of the substrate by irradiating a laser light to the thermal oxide layer formed on the rear surface that remains at the predetermined intervals with the first patterns, wherein p-type semiconductor regions are partially formed at the rear surface of the substrate to correspond to the second patterns by a dopant screen printing to print a p-type conductive material to dope the p-type conductive material at the second patterns so that the n-type semiconductor regions and the p-type semiconductor regions are respectively formed by different doping methods; and forming first electrodes being in direct contact with the n-type semiconductor regions through the first patterns and second electrodes being in direct contact with the p-type semiconductor regions through the second patterns, wherein the rear surface of the substrate has the pyramid-shaped rear texturing structure for reducing reflectance of incident light at intervals between the n-type semiconductor regions and the p-type semiconductor regions, wherein the pyramid-shaped rear texturing structure is partially formed at the rear surface of the substrate, wherein the pyramid-shaped rear texturing structure is not formed at portions of the substrate corresponding to where the n-type semiconductor regions and the p-type semiconductor regions are positioned, wherein a thermal oxide layer at the front surface acts as a front protection layer, wherein, in the forming of the n-type semiconductor regions by the thermal diffusion, the thermal oxide layer at the rear surface acts as a mask for protecting portions corresponding to the p-type semiconductor regions at the rear surface, wherein, after the forming of the second patterns, the thermal oxide layer at the rear surface remains between the first patterns and the second patterns and acts as a rear protection layer, wherein the thermal oxide layer remaining on the rear surface is spaced apart so as not to overlap the n-type semiconductor regions and the p-type semiconductor regions in a vertical direction, and wherein the first electrodes are formed so as to cover an entire surface of the first conductive type semiconductor regions and extend over an adjacent portion of the thermal oxide layer at the rear surface, and the second electrodes are formed so as to cover an entire surface of the second conductive type semiconductor regions and extend over an adjacent portion of the thermal oxide layer at the rear surface.

7. The fabrication method of the back contact solar cell according to claim 1, wherein the pyramid-shaped rear texturing structure of the rear surface of the substrate is one that remains after the forming of the second patterns.

8. The fabrication method of the back contact solar cell according to claim 6, wherein the rear surface of the substrate has the pyramid-shaped rear texturing structure at the intervals between the n-type semiconductor regions and the p-type semiconductor regions, and wherein the pyramid-shaped rear texturing structure of the rear surface of the substrate is one that remains after the forming of the second patterns.

9. The fabrication method of the back contact solar cell according to claim 1, wherein a first portion of the rear surface of the substrate having the pyramid-shaped rear texturing structure on the rear surface of the substrate is different from a second portion of the rear surface of the substrate that is other than the first portion.

10. The fabrication method of the back contact solar cell according to claim 1, wherein intervals between the first conductive type semiconductor regions and the second conductive type semiconductor regions have portions that are without the pyramid-shaped rear texturing structure of the rear surface of the substrate.

11. The fabrication method of the back contact solar cell according to claim 6, wherein the intervals between the n-type semiconductor regions and the p-type semiconductor regions have portions that are without the pyramid-shaped rear texturing structure of the rear surface of the substrate.

12. The fabrication method of the back contact solar cell according to claim 1, wherein the entire surface of the first conductive type semiconductor regions is equal to an exposed surface formed by an opening formed by the first pattern, and the entire surface of the second conductive type semiconductor regions is equal to an exposed surface formed by an opening formed by the second pattern, and wherein the entire surface of the first conductive type semiconductor regions and the entire surface of the second conductive type semiconductor regions are parallel to the rear surface.

13. The fabrication method of the back contact solar cell according to claim 6, wherein the entire surface of the n type semiconductor regions is equal to an exposed surface formed by an opening formed by the first pattern, and the entire surface of the p-type semiconductor regions is equal to an exposed surface formed by an opening formed by the second pattern, and wherein the entire surface of the n-type semiconductor regions and the entire surface of the p-type semiconductor regions are parallel to the rear surface.

Description

DESCRIPTION OF DRAWINGS

(1) The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a cross-sectional view showing a structure of a conventional crystalline silicon solar cell;

(3) FIGS. 2 to 10 are schematic views showing a fabrication process of a conventional back contact solar cell; and

(4) FIGS. 11 to 17 are schematic views showing a fabrication process of a back contact solar cell according to one embodiment of the present invention.

BEST MODE

(5) Hereinafter, embodiments of the present invention will be described in detail with reference to accompanying drawings.

(6) FIGS. 11 to 17 are schematic views showing a fabrication process of a back contact solar cell according to one embodiment of the present invention. Hereinafter, the fabrication process of the back contact solar cell according to the present invention will be described with reference to FIGS. 11 to 17.

(7) First, as shown in FIG. 11, a texturing structure is formed on at least one of a front surface and a rear surface of a p-type silicon substrate 310. The texturing structure may usually be formed in a pyramid shape, etc, and performs a function of reflecting solar light incident to the solar cell so that maximum light may be absorbed into an inside of the solar cell, thereby raising efficiency of the solar cell.

(8) The texturing structure may be formed by etching using a known etching method. As an example, the texturing structure may be formed by immersing the silicon substrate 310 in a basic etching solution such as tetramethylammonium hydroxide (TMHA), potassium hydroxide (KOH), or sodium hydroxide (NaOH), etc., to which surfactant such as isopropyl alcohol (IPA), isopropyl ethanol (IPE), etc., is added.

(9) After forming the texturing structure, thermal oxide layers 321 and 323 for surface passivation are formed on the front and rear surfaces of the silicon substrate 310. The passivation layers 321 and 323 have a role of stabilizing and protecting the surface and minimizing surface recombination of electron-hole pairs to increase efficiency of the solar cell.

(10) These passivation layers 321 and 323 may be thermal oxide such as silicon oxide (SiO.sub.2), etc., formed by a rapid thermal oxidation (RTO) scheme performed inside a furnace for rapid thermal processing (RTP), as described above. Also, the passivation layers 321 and 323 may be formed by a sputtering method using the silicon oxide (SiO.sub.2) as a target material.

(11) After forming the passivation layers 321 and 323, a pattern for diffusing an n-type material is formed on the rear surface of the silicon substrate 310, as shown in FIG. 12.

(12) The formation of the pattern is to partially remove the oxidation layer 323 already formed on the rear surface of the silicon substrate 310, thereby making it possible to diffuse an n-type material through the removed portion.

(13) A process forming the pattern by partially removing the oxide layer 323 may be performed by irradiating laser light. As a light source of the irradiated laser light, various light sources may be used; by way of example, a green laser source with a wavelength of about 532 nm, an Nd/YAG laser source with a wavelength of about 1064 nm, etc., may be used.

(14) After partially removing the oxide layer 323, an n-type material 330 is diffused into portions at which the oxide layer 323 is removed, as shown in FIG. 13.

(15) As a method diffusing the n-type material 33, a thermal diffusion method, etc., may be used. By way of example, a method performing doping by inserting the p-type silicon substrate 310 into a high-temperature furnace and flowing the n-type material (for example, POCl.sub.3) into an inside of the furnace may be used.

(16) After diffusing the n-type material 330, the oxide layer 323 is removed in order to form a p-type semiconductor region in a region except for the region into which the n-type material is diffused, as shown in FIG. 14. At this time, a certain amount of the oxidation layer 323 is left in a region close to the region into which the n-type material 330 is diffused in order to insulate between the region into which the n-type material 330 is diffused and the p-type semiconductor region.

(17) At this time, the oxide layer 323 may also be removed by irradiating green laser light with the wavelength of about 532 nm, Nd/YAG laser light with the wavelength of about 1064 nm, etc.

(18) The oxide layer 323 left in order to isolate the region into which the n-type material is diffused and the p-type semiconductor region may perform a function of a rear passivation layer of the back contact solar cell. That is, the remaining oxide layer 323 protects the rear surface of the silicon substrate 310 as well as prevents rear surface recombination of electron-hole pairs so as to be able to contribute to improvement in efficiency of the solar cell.

(19) After removing all oxide layer 323 except for a certain amount of the oxide layer 323 for isolating the region into which the n-type material 330 is diffused and the p-type semiconductor region among the oxide layer 323 formed on the rear surface of the silicon substrate 310, the p-type semiconductor region 340 is formed by printing an aluminum (Al) metal, etc. in a region except for the region into which the n-type material is diffused, as shown in FIG. 15. The printing of the aluminum (Al) metal, etc., for forming the p-type semiconductor region 340 may be performed by a screen printing method, etc., which is a well-known printing method.

(20) In fabrication of the back contact solar cell of the present invention, since the removal of oxide layer 323 required for diffusing the n-type material 330 and the removal of the oxide layer 323 required for forming the p-type semiconductor region 340 are performed by irradiating the laser light, it is possible to omit a photolithography process requisitely used to remove the oxide layer on the rear surface of the conventional back contact solar cell. Since the photolithography process, which is a complicated and expensive process, may be omitted, it is possible to simplify the fabrication process of the back contact solar cell and also reduce fabrication costs.

(21) After forming the p-type semiconductor region 340, an anti-reflection coating 370 is formed on an upper surface of the oxide layer 321 formed on the front surface of the p-type silicon substrate 310, as shown in FIG. 16. The anti-reflection coating 370 may be deposited using a deposition method such as a plasma enhanced chemical vapor deposition (PECVD) method, a sputtering method, or a spin coating method, etc., and be made of a material such as silicon nitride (SiN.sub.x) or titanium dioxide (TiO.sub.2), etc. This anti-reflection coating 370 may have a function of minimizing reflectance of the solar cell and at the same time, perform a function of a passivation layer. Accordingly, defects of the back contact solar cell are minimized and recombination of electron-hole pairs is further reduced, so that the efficiency of the solar cell may be improved.

(22) After forming the anti-reflection coating 370, electrodes are printed on each of the regions into which the n-type material is diffused and the p-type semiconductor region 340 to form rear electrodes 390, thereby completing the back contact solar cell, as shown in FIG. 17. As the electrode 390, a metal with a high conductivity such as silver (Ag), etc., may be used.

(23) Although the present invention has been illustrated with regard to specific details such as specific components, etc, limited embodiments, and drawings, the specific details such as specific components, etc, the limited embodiments, and the drawings are only provided in order to assist overall understanding of the present invention. The prevent invention is not limited to the above embodiment, but may be variously modified and altered by those skilled in the art.

(24) Therefore, a technical idea of the present invention is not limited to the above-mentioned embodiment and claims described below and equivalents thereof are within a scope of the technical idea of the present invention.

INDUSTRIAL APPLICABILITY

(25) According to the fabrication method of the back contact solar cell of the present invention, it is possible to simplify a fabrication process, reduce fabrication time, and reduce fabrication costs by using the laser method instead of photolithography in forming the pattern for formation of the p-type semiconductor region and the n-type semiconductor region.

(26) Also, it is possible to obtain effects such as a rise in efficiency due to minimization of the shadowing effect, which is an original advantage of the back contact solar cell, a reduction in recombination of electron-hole pairs due to rear surface passivation, etc.