TW201347220A - Structure of solar cell and texturing method thereof - Google Patents

Abstract

The present invention provides a texturing method for the surface of solar cells. First, a first substrate is provided, which has at least a first light receiving face. Next, a plurality of parallel wire saws is provided and directly in contact with the first light receiving face. Finally, wire saws are moved along their own long axial direction to concurrently form a plurality of first recessed structure on the first receiving face.

Description

Solar cell structure and surface roughening method thereof

The present invention relates to a solar cell structure and a surface roughening method thereof, and more particularly to a method of roughening a surface structure of a solar cell using a wire saw machine.

With the depletion of consumable energy, the development of alternative energy sources such as solar energy has long been an important development direction. In general, the solar module works by using solar cells containing PN junctions to receive radiant energy from sunlight, and converting radiant energy into electrical energy. The main materials of the solar cells include semiconductors. Materials such as single crystal germanium, polycrystalline germanium, amorphous germanium germanium or III-V compound semiconductor materials. In order to further increase the photocurrent generated by the solar cell, a surface texturing process is first performed on the light receiving surface of the solar cell in the process to reduce the reflectance of the light source on the front side of the light receiving surface.

At present, a variety of feasible surface roughening procedures have been disclosed. The surface roughening procedures include wet etching, sandblasting, anodic oxidation, plasma etching, laser dicing, and optical lithography, among which processes are performed, among which the wet etching process includes wet etching, sandblasting, anodic oxidation, plasma etching, laser dicing, and optical lithography. Under the consideration of cost and convenience, wet etching is still the most widely used process in the industry. In general, to achieve the desired degree of roughening through a wet etching process, it is generally necessary to use a corresponding etching solution for a semiconductor substrate of different composition or properties. For example, a polycrystalline germanium substrate generally requires an acidic etching solution; and a single crystal germanium substrate is an alkaline etching solution. Therefore, it is not possible to satisfy the etching requirements of various semiconductor materials with a single etching solution. In addition, the wet etching process usually involves multiple processing procedures, such as rinsing, acid-base neutralization, drying, and waste liquid recovery, which, in addition to being disadvantageous to manufacturing costs, can also cause serious environmental pollution.

Therefore, it is necessary to provide a solar cell structure and a method of roughening the surface thereof. In addition to the simultaneous roughening step for semiconductor materials of different compositions, the roughening process can be further simplified, so that the production cost of the solar cell can be reduced.

It is an object of the present invention to provide a solar cell structure and a surface roughening method thereof to simplify the roughening process and save manufacturing costs.

In order to achieve the above object, a method for roughening a surface of a solar cell according to an embodiment of the present invention includes providing a first substrate having at least one first light receiving surface, and providing a plurality of wire saws parallel to each other, and The wire saw directly contacts the first light receiving surface; finally, the wire saw is moved along the long axis square line of the wire saw, so that the first light receiving surface simultaneously forms a plurality of first grooves.

According to another embodiment of the present invention, a solar cell structure includes a substrate having at least one light receiving surface, and a plurality of grooves on the light receiving surface, wherein the grooves have a grid arrangement to form A roughened structure.

The present invention utilizes a physical roughening process to form a roughened structure on the surface of the solar cell. In addition to the same roughening step for different semiconductor materials, it is possible to further simplify time and cost, and reduce environmental impact.

The above described objects, features and advantages of the present invention will become more apparent from the description of the appended claims. However, the following preferred embodiments and drawings are for illustrative purposes only and are not intended to limit the invention.

Referring first to FIG. 1A, FIG. 1A is a top plan view of a solar cell surface roughening structure according to an embodiment of the invention. As shown in FIG. 1A, a substrate 10 is provided having at least one light receiving surface 12 that accepts an external source of radiation. For example, the source of radiation may be sunlight or other electromagnetic band that is absorbing by the semiconductor layer. A roughened structure 1 is formed on the light receiving surface 12, and the roughened structure 1 includes a plurality of grooves 16, 18. In this first embodiment, the grooves 16, 18 are arranged in a rectangular lattice arrangement such that adjacent grooves 16 and 18 parallel to each other have a first spacing a and a second spacing b, respectively. And according to different product requirements, the values of the first spacing a may be the same or different from the second spacing b. Further, in the present embodiment, the grooves 16, 18 which are parallel to each other have the same depth and width, respectively.

Please refer to FIG. 1B and FIG. 1C. FIG. 1B and FIG. 1C are top views of a surface roughening structure of a solar cell according to another embodiment of the present invention. Different from the rectangular grid layout shown in FIG. 1A, FIG. 1B and FIG. 1C respectively disclose that the roughened structure 1 can be a diamond lattice arrangement or a triangular lattice arrangement. Similar to FIG. 1A, the roughened structure 1 shown in FIG. 1B also includes a plurality of grooves 16, 18, and the grooves 16, 18 parallel to each other have the same depth and width, respectively. The difference from the first embodiment is that the grooves 16, 18 are arranged in a rhombic lattice arrangement, that is, the angle between the two grooves 16, 18 is not a right angle but an acute or obtuse angle. Similarly, the roughened structure 1 in FIG. 1C is similar to the structure shown in FIG. 1A, however the roughened structure 1 of the third embodiment additionally includes a recess 20 such that the grooves 16, 18, 20 are presented. The layout of the triangular lattices has a third spacing c between the grooves 20 adjacent to each other in parallel. Depending on the requirements of the different products, the values of the third spacing c may be the same or different from the values of the first spacing a and/or the second spacing b. Other technical features of the first to third embodiments are substantially the same except for the main differences described above, and will not be described again for the sake of brevity. It should be particularly noted here that in the above first to third embodiments, the light receiving surface 12 in the grooves 16, 18, 20 and/or between the grooves 16, 18, 20 may additionally have a microstructure. The features of this microstructure will be detailed below.

The surface roughening method of the solar cell structure of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the scope of the invention, and may be modified and retouched without departing from the spirit and scope of the invention. The details of some of the conventional process steps will not be disclosed herein, as defined by the scope of the appended claims.

2A and 2B, FIG. 2A is a schematic diagram of forming a plurality of roughened structures on a light receiving surface by using a wire saw according to an embodiment of the present invention, and FIG. 2B is a diagram A partial enlarged view of the 2A diagram. As shown in FIGS. 2A and 2B, at least one substrate 10 is provided at an initial stage of the process, and the substrate 10 may be a single crystal germanium wafer, a polycrystalline silicon wafer, or other conventional semiconductor substrate. Next, the substrate 10 is placed in or in contact with a wire saw table 30 such that at least one light receiving surface 12 of the substrate 10 is in direct contact with a wire web 36. The wire saw row 36 is composed of a plurality of wire saws 34 that are parallel to each other, and the wire saw 34 can be moved along the long axis direction of the wire saw 34 by the rotation of the drive roller 32, for example, a first direction X. Thereafter, the wire saw row 36 is reciprocated or unidirectionally moved along the long axis direction of the wire saw 34 such that the light receiving surface 12 is pressed against the wire saw 36 and subjected to a third direction Z. Subsequently, please refer to FIG. 2B, in which a partial enlarged view of the wire saw 34 is illustrated. It can be seen that the wire saw surface 34a has a plurality of abrasive grains 34b, which may be diamond, diamond-like or tantalum carbide, etc., having a hardness greater than that of the substrate 10, and as the roughening process proceeds, the abrasive particles 34b are continuously ground and contacted. The light receiving surface 12 is formed until the first groove 38 is formed. Each of the first grooves 38 are simultaneously formed and parallel to each other, and the opening width substantially corresponds to the diameter of the wire saw 34, that is, the thicker wire saw 34 can obtain the first groove 38 having a larger opening width. Features will be detailed below. It should be noted here that the wire saw 34 described above can also be replaced with a wire without the abrasive particles 34b. Further, the wire sawing machine 30 described above is not necessarily a machine for cutting a singe ingot, and it may be equally replaced with any device having a wire saw row 36.

Referring to FIGS. 3A and 3B, FIG. 3A is a schematic diagram of a substrate having a roughened structure, and FIG. 3B is a schematic cross-sectional view of the roughened structure taken along a line I-I of FIG. 3A. As shown in FIGS. 3A and 3B, after the above-described roughening process, the light receiving surface 12 of the substrate 10 has a plurality of first grooves 38 extending along the first direction X. The adjacent first grooves 38 have a spacing s therebetween, and each of the first grooves 38 has the same first depth D and first width w. In addition, since the abrasive particles 34b have a specific roughness, the surface within each of the first grooves 38 has a microstructure 42 at the same time in the roughening process.

4 is a cross-sectional view showing a roughened structure according to an embodiment of the invention. The structure of FIG. 4 is similar to the structure of FIG. 3B. However, following the process of FIG. 3B, a conventional roughening process is further performed, so that the surface of the inner surface 8 of each of the first grooves 3 forms the first microstructure 44, and at the same time The light receiving surface 12 between the first grooves 38 forms a second microstructure 46. Preferably, the roughness of the first microstructure 44 is greater than the roughness of the second microstructure 46, but is not limited thereto. At this time, the adjacent first grooves 38 have a spacing s, and each of the first grooves 38 has the same second depth D' and second width w', and preferably, the second depth D' And the second width w' may be slightly larger than the first depth D and the first width w before the conventional roughening process, but is not limited thereto. In addition, according to other embodiments, the conventional roughening process may be performed followed by the wire saw roughening process, that is, the present invention may be combined with other conventional roughening processes. It should be noted here that the conventional roughening process described above includes a wet etching, a plasma etching or a heat treatment, and the like, but is not limited thereto. Therefore, the first microstructure 44 and the second microstructure 46 can further increase the surface area of the light receiving surface 12 and reduce the reflectance thereof, thereby improving the short circuit current (I _sc ) of the solar cell.

So far, the roughened structure of one embodiment of the present invention has been completed. The present invention mainly forms a plurality of first grooves 38 parallel to each other on the light receiving surface 12 of the substrate 10 by physical polishing. Compared with the general wet roughening process, this physical grinding method can avoid the cost of time and has better process stability. In addition, since the present invention utilizes the wire saw row 36 of the wire saw machine table 30 for the roughening process, the wire saw diameter, the abrasive grain roughness, the abrasive grain hardness, the wire saw column pitch, and the wire saw lower pressure path can be adjusted. To define the required groove pitch, depth, width and microstructure roughness.

In addition to the above embodiments, the present invention can further integrate two or more substrates of different materials, perform roughening procedures under the same wire sawing machine 30, and can further perform a continuous roughening process. The steps are described below, with reference to similar FIGS. 2A to 4. First, similar to FIG. 2A, a first substrate and a second substrate are provided, wherein the first substrate is similar to the substrate 10 described in the above embodiment, and the composition of the second substrate is different from that of the first substrate. Then, the wire saw row 36 is continuously pressed against the light receiving surface 12 of the first substrate and the second substrate, and the wire saw row 36 is reciprocated or unidirectionally moved along the long axis direction (the first direction X) of the wire saw 34. The light receiving surface 12 is subjected to a force in a third direction Z until the first substrate and the light receiving surface 12 of the second substrate simultaneously form a plurality of first grooves 38. Like FIG. 3A, the first grooves 38 are parallel to each other and extend along the first direction X. The adjacent first grooves 38 have a spacing s therebetween, and each of the first grooves 38 has the same first depth D and first width w. The subsequent steps are similar to the embodiments as described above, and will not be described again here.

Referring to FIG. 5A, FIG. 5A is a schematic diagram of a surface roughening structure having a rectangular lattice arrangement according to another embodiment of the present invention. As shown in FIG. 5A and in conjunction with FIG. 1A, another roughening process may be selectively performed using the same or different sawing rows, and a plurality of Y-shaped extending along the second direction Y are formed on the light-receiving surface 12 of the substrate 10. The second groove 40. The distance between the second grooves 40 is the same as the s', depth, width and microstructure roughness, and is also affected by the saw line. In addition, the distance between the second groove 40 and the first groove 38 may be the same or different from the s', s, depth, width and microstructure roughness, and the selection of the saw wire row and the process parameters of the roughening process are selected. It should be noted that the arrangement of the first groove 38 and the second groove 40 in FIG. 5A can replace the arrangement layout as shown in FIG. 1B and FIG. 1C, because it is a simple equal transformation. I won't go into details here. A conventional gas phase diffusion process is followed by forming a doped region 48 and a PN junction 49 over the substrate 10. Finally, referring to FIG. 5B, FIG. 5B is a plan view of a solar cell having a finger electrode and a bus electrode. Following the formation of the first recess 38 and the second recess 40, at least one finger electrode 54 and one bus electrode 52 are formed on the light receiving surface 12 of the substrate 10, and a solar cell 50 is completed.

In summary, the present invention provides a solar cell structure and a surface roughening method thereof. By the roughening process of the present invention, time cost can be avoided, better process stability can be provided, and plant space can be saved. In addition, since the present invention utilizes a wire saw row of a wire saw machine for roughening, it is possible to adjust the wire saw diameter, the abrasive grain roughness, the abrasive grain hardness, the wire saw column distribution line width, and the wire saw. The pressure channel defines the desired groove pitch, depth, width and microstructure roughness to greatly enhance the flexibility of the roughening process.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

1. . . Roughened structure

10. . . Base

12. . . Light receiving surface

16, 18, 20. . . Groove

30. . . Wire saw machine

32. . . Drive wheel

34. . . Wire saw

34a. . . Wire saw surface

34b. . . Abrasive grain

36. . . Wire saw column

38. . . First groove

40. . . Second groove

42. . . microstructure

44. . . First microstructure

46. . . Second microstructure

48. . . Doped region

49. . . PN junction

50. . . Solar battery

52. . . Bus electrode

54. . . Finger electrode

a. . . First spacing

b. . . Second spacing

c. . . Third spacing

s, s’. . . spacing

D. . . First depth

D’. . . Second depth

w. . . First width

w’. . . Second width

X. . . First direction

Y. . . Second direction

Z. . . Third direction

I-I’. . . Tangent

1A to 1C are top views of a surface roughening structure of a solar cell according to various embodiments of the present invention.

2A-5B are schematic views showing a method of fabricating a solar cell according to various embodiments of the present invention, wherein:

FIG. 2A is a schematic view showing the formation of a plurality of roughened structures on the light receiving surface by using a wire saw;

2B is a partial enlarged view of FIG. 2A;

Figure 3A is a schematic view of a substrate having a roughened structure;

Figure 3B is a schematic cross-sectional view of the roughened structure taken along the line I-I of Figure 3A;

4 is a schematic cross-sectional view showing a roughened structure according to another embodiment of the present invention;

5A is a schematic diagram of a surface roughening structure having a rectangular lattice arrangement according to another embodiment of the present invention;

Fig. 5B is a plan view of a solar cell having a finger electrode and a bus electrode.

10. . . Base

12. . . Light receiving surface

38. . . First groove

44. . . First microstructure

46. . . Second microstructure

D’. . . Second depth

s. . . spacing

w’. . . Second width

Claims (18)

A method for roughening a surface of a solar cell, comprising: providing a first substrate having at least one first light receiving surface; providing a plurality of wire saws parallel to each other, and the wire saws directly contacting the first light receiving surface; The wire saws are moved along the long axis square lines of the wire saws to form a plurality of first grooves simultaneously on the first light receiving surface. The method of claim 1, wherein after forming the first recesses, further comprising: forming a PN junction in the first substrate; and forming at least one surface on the surface of the first substrate Finger electrode and a bus electrode. The method of claim 1, wherein the wire saws continue to press against the first light receiving surface until the first grooves are formed. The method of claim 1, wherein a plurality of microstructures are simultaneously formed on the surface of each of the first grooves when the first grooves are formed. The method of claim 1, wherein after forming the first recesses, further comprising: performing a roughening process, wherein the roughening process comprises wet etching, plasma etching or heat treatment. The method of claim 1, further comprising providing a second substrate, wherein the second substrate has a composition different from the first substrate, and the method further comprises: when providing the wire saws, The wire saws directly contact one of the second light receiving surfaces of the second substrate; and when the wire saws are moved, a plurality of second grooves are simultaneously formed on the second light receiving surface of the second substrate. The method of claim 1, wherein the wire saws arranged in parallel with each other form a line saw. The method of claim 1, wherein the wire saws are reciprocated or unidirectionally moved along each of the long axis lines. The method of claim 1, wherein before providing the wire saws, a plurality of abrasive grains are formed on the surface of the wire saws. The method of claim 1, wherein each of the first grooves has the same depth and width. A solar cell structure comprising: a substrate having at least one light receiving surface; and a plurality of grooves on the light receiving surface, wherein the grooves have a grid arrangement layout to form a roughened structure. The structure of claim 11, wherein the lattice arrangement is a rectangular lattice arrangement. The structure of claim 11, wherein the lattice arrangement is a diamond lattice arrangement. The structure of claim 11, wherein the lattice arrangement is a triangular lattice arrangement. The structure of claim 11, wherein the surface of each of the grooves has a plurality of first microstructures. The structure of claim 15, wherein the light receiving surface between each of the grooves has a plurality of second microstructures. The structure of claim 11, wherein each of the grooves parallel to each other has the same depth and width. The structure of claim 11, wherein the two adjacent grooves that are parallel to each other have a spacing therebetween, and each of the spacings is identical to each other.