BACK CONTACT SOLAR CELL AND FABRICATION METHOD THEREOF

Abstract

The present invention discloses a back contact solar cell. The back contact solar cell includes a semiconductor substrate having a front surface and a rear surface; a first conductive type semiconductor region having a first conductive type and a second conductive type semiconductor region having a second conductive type at an interval on the rear surface of the semiconductor substrate. Furthermore, the rear surface of the semiconductor substrate has a texturing structure at the interval between the first conductive type semiconductor region and the second conductive type semiconductor region.

Claims

1. A back contact solar cell, comprising: a semiconductor substrate including a textured front surface and a partially textured rear surface, the semiconductor having a first conductive type; a first oxide layer formed over the front surface of the substrate; at least one first conductive type region and at least one second conductive type region formed in an alternating pattern at predetermined intervals on the rear surface of the substrate, wherein the at least one first conductive type region each has a second conductive type opposite to the first conductive type, and the at least one second conductive type region each has a first conductive type, wherein the second conductive type region has a doping concentration greater than the substrate; a second oxide layer formed on the partially textured rear surface of the substrate; electrodes formed on each of the at least one first conductive type region and the at least one second conductive type region, wherein portions of the rear surface of the substrate corresponding to the at least one first conductive type region and the at least one second conductive type region are not textured, the entire front surface of the substrate is textured, and an area of textured region on the front surface of the substrate is larger than an area of textured region on the rear surface of the substrate.

2. The back contact solar cell according to claim 1, wherein the substrate is an n-type silicon substrate.

3. The back contact solar cell according to claim 1, wherein the first conductive type region is a p-type region and the second conductive type region is an n-type region.

4. The back contact solar cell according to claim 1, wherein the first oxide layer and the second oxide layer are silicon oxide layers.

5. The back contact solar cell according to claim 1, wherein the first oxide layer is formed over an entire surface of the front surface of the substrate.

6. The back contact solar cell according to claim 1, further comprising an anti-reflection layer formed over a surface of the first oxide layer away from the substrate.

7. The back contact solar cell according to claim 6, wherein the anti-reflection layer comprises silicon nitride.

8. The back contact solar cell according to claim 6, wherein the anti-reflection layer is formed over an entire surface of the first oxide layer.

9. The back contact solar cell according to claim 1, wherein the at least one first conductive type region includes a plurality of first conductive type regions, and the at least one second conductive type region includes a plurality of second conductive type regions, wherein the plurality of first conductive type regions and the plurality of second conductive type regions are formed in an alternating pattern.

10. The back contact solar cell according to claim 1, wherein the electrodes comprises: a first electrode electrically connected to the first conductive type region; and a second electrode electrically connected to the second conductive type region.

11. The back contact solar cell according to claim 1, wherein each of the electrodes has a width greater than first conductive type region or the second conductive type region.

12. The back contact solar cell according to claim 1, wherein the first conductive type region and the second conductive type region have different sizes.

13. The back contact solar cell according to claim 1, wherein textured structures on the front surface and rear surface of the substrate have a pyramidal shape.

14. The back contact solar cell according to claim 1, wherein the second conductive type region extends further into the substrate than the first conductive type region.

15. The back contact solar cell according to claim 1, wherein a surface roughness of the rear surface of the substrate corresponding to the first conductive type region and the second conductive type region is smaller than a surface roughness of the rear surface of the substrate corresponding to the interval between the first conductive type region and the second conductive type region.

16. The back contact solar cell according to claim 1, wherein an average surface roughness of the front surface of the substrate is greater than an average surface roughness of the rear surface of the substrate.

17. The back contact solar cell according to claim 1, wherein a surface of the partially textured portion of the rear surface of the substrate is coplanar with a surface of the first conductive type region and a surface of the second conductive type region.

18. The back contact solar cell according to claim 1, wherein the first conductive type region and the second conductive type region are fabricated in different processing steps with different methods.

19. The back contact solar cell according to claim 1, wherein the at least one first conductive type region includes a plurality of first conductive type regions and the at least one second conductive type region includes a plurality of second conductive type regions, the first conductive type regions and the second conductive type regions are formed on positions of the rear surface of the substrate without the second oxide layer.

20. The back contact solar cell according to claim 19, wherein the second conductive type region is formed between the first conductive type regions with predetermined intervals at both sides.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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:

[0041] FIG. 1 is a cross-sectional view showing a structure of a conventional crystalline silicon solar cell;

[0042] FIGS. 2 to 10 are schematic views showing a fabrication process of a conventional back contact solar cell; and

[0043] 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.

[0044] Hereinafter, embodiments of the present invention will be described in detail with reference to accompanying drawings.

DESCRIPTION OF THE EMBODIMENTS

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 I064 nm, etc., may be used.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Therefore, a technical idea of the present invention is not limited to the abovementioned embodiment and claims described below and equivalents thereof are within a scope of the technical idea of the present invention.

[0064] 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.

[0065] 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.