TWI430467B - Solar battery with an anti-reflect surface and the manufacturing method thereof - Google Patents

Description

Method for manufacturing solar cell with anti-reflection surface

The invention relates to the manufacture of solar cells, and more particularly to solar cells having an anti-reflective surface.

Solar cell fabrication technology is now almost complete, and in order to pursue higher photoelectric conversion efficiency, one of the methods is to avoid the light being reflected, and roughening the surface is one way to avoid light reflection, so it will develop A method of roughening the surface of a solar cell, and a solar cell having a rough surface.

The manufacture of such a conventional, typical solar cell is generally a process of roughening on a germanium substrate, followed by formation of an N-type germanium layer, followed by an anti-reflective film, and then defining the electrodes in a printed manner. So the solar battery is complete. However, the current roughening on the surface of a solar cell (usually on a germanium substrate), even if it is made by wet etching, has a limited anti-reflection effect due to insufficient roughness. As a result, most of the light is still reflected and leaves the solar cell, thus causing waste.

This technology has been in existence for a long time, but there is no fundamental reform for the key technology of anti-reflection in this technology, that is, the roughening of the surface of the crucible substrate, that is, the roughening action of the conventional technology cannot be achieved. The high aspect ratio requirement, but only the high aspect ratio surface can make the solar cell have better anti-reflection performance. In addition, when the solar cell is used, its temperature rises due to the irradiation of sunlight, resulting in a decrease in output voltage and maximum output power, while conventional solar cells are used. But did not consider the heat issue. Therefore, only by making major innovations in the production of solar cell technology can the efficiency of photoelectric conversion be greatly improved.

Therefore, in the field of current solar cell technology, there is an urgent need for a technique that can solve problems such as insufficient surface roughness and power reduction due to poor heat dissipation.

In view of the fact that the conventional solar cell manufacturing method has extremely limited improvement in anti-reflection performance, the present invention has a high aspect ratio structure on the surface of the ruthenium base, and achieves an anti-reflection effect through a high aspect ratio structure and further enhances photoelectric conversion. s efficiency.

In order to achieve the above object, the present invention provides a method for fabricating a solar cell having an anti-reflective surface, comprising the steps of: (1) providing a germanium substrate having a front side and a back side; and (2) forming a first nitride. a layer of germanium on the front side; (3) laying a nanosphere on the tantalum nitride layer, using a nanosphere as a first etching mask; (4) etching the tantalum nitride layer by a reactive ion etching technique to form Etching the window on the tantalum nitride layer; (5) removing the nanosphere; (6) etching the germanium substrate to form a deep concave structure; and (7) forming a front electrode on the front surface of the germanium substrate, A back electrode is formed on the back surface.

The method as described above, wherein the tantalum nitride layer of the step (2) is fabricated by means of radio frequency sputtering.

The method as described above, wherein the step (1) further comprises a step (1-1): doping a pentavalent element on the front side of the germanium substrate for nitrogen ion diffusion.

The method as described above, wherein the step (5) further comprises the step (5-1): forming a conductive layer on the back surface of the germanium substrate.

The method as described above, wherein the conductive layer of the step (5-1) is used for generating an electric field as photo-assisted electrochemical etching.

The method as described above, wherein the step (6) further comprises a step (6-1): forming a second tantalum nitride layer on the germanium substrate, and forming the exposed portion on the second tantalum nitride layer to make the germanium The substrate is exposed outside the second tantalum nitride.

The method as described above, further comprising a step of forming a tantalum film on the back surface of the tantalum substrate before the step (7).

In the method as described above, the front electrode of the step (7) is disposed at the bare portion and electrically connected to the germanium substrate.

The method as described above, wherein the step (6) further comprises the steps of: (6-1'): forming a heavily doped germanium film on the germanium substrate; and (6-2'): the heavily doped germanium film Forming a second tantalum nitride layer thereon, and forming a bare place on the heavily doped germanium film and the second tantalum nitride layer to expose the germanium substrate to the heavily doped germanium film and the second tantalum nitride .

The method as described above, wherein the front electrode of the step (7) is located at the bare portion and is electrically connected to the germanium substrate through the heavily doped germanium film and the second tantalum nitride layer.

The method as described above, wherein the step (6) etches the tantalum substrate in a photo-assisted electrochemical etching manner.

The method as described above, wherein before the step (6), further comprising the step of pre-etching the pits on the germanium substrate.

The method as described above, wherein the pit is fabricated by anisotropic wet etching.

In order to achieve the above object, the present invention further provides a method for manufacturing a solar cell having an anti-reflection surface, comprising the steps of: (1) providing a substrate having a front side and a back side; and (2) laying a nanosphere on the substrate. On the front side, and the nanosphere is Etching the mask; (4) etching the germanium substrate to form a deep concave structure; (5) removing the nanosphere; and (6) forming a front electrode on the front surface of the germanium substrate, and forming a front electrode on the back surface Back electrode.

The method as previously described, wherein the step (4) etches the tantalum substrate by a high density plasma reactive ion etching (ICP-RIE) technique.

The method as described above, wherein the step (6) further comprises the steps of: (6-a) forming a second tantalum nitride layer on the germanium substrate; (6-b) forming the second tantalum nitride layer Exposing the germanium substrate to the outside of the second tantalum nitride; (6-c) forming the front electrode on the front surface of the germanium substrate, wherein the front electrode is electrically connected to the germanium substrate through the bare portion; -d) forming a tantalum film on the back side of the tantalum substrate; and (6-e) forming the back surface electrode under the tantalum film.

In the method as described above, wherein the tantalum substrate is an N-type tantalum, the tantalum film is a heavily doped P-type tantalum.

In the method as described above, wherein the germanium substrate is a P-type germanium, the germanium film is a heavily doped N-type germanium.

The method of claim 1, wherein the step (6) further comprises the step of: (6-a'): forming a heavily doped germanium film on the germanium substrate; (6-b'): Forming a second tantalum nitride layer on the heavily doped germanium film, and forming a bare portion on the heavily doped germanium film and the second tantalum nitride layer to expose the germanium substrate to the heavily doped germanium film and the first (6-c') forming the front electrode on a front surface of the germanium substrate, wherein the front electrode is electrically connected to the germanium substrate through the bare portion; and (6-d') the germanium substrate The back surface is formed on the back side.

In the method as described above, wherein the germanium substrate is an N-type germanium, the heavily doped germanium film is a P-type germanium.

In the method as described above, wherein the germanium substrate is a P-type germanium, the heavily doped germanium film is an N-type germanium.

1 to 4 are schematic views showing the steps of using the tantalum nitride as an etching mask (etching window) for manufacturing a deep concave structure in the manufacturing method of the present invention. First, referring to FIG. 1, a first tantalum nitride layer 2 is formed on a germanium substrate 1. Generally, one of physical vapor deposition (PVD) or chemical vapor deposition (CVD) is selected as the formation of the first tantalum nitride layer 2. After the first tantalum nitride layer 2 is formed, the nanosphere 3 is placed on the first tantalum nitride layer 2, and the method of setting is applied by spin coating or soaking to attach the nanosphere 3 to the first layer. A layer of tantalum nitride 2 is used. Since the first tantalum nitride layer 2 is to be used as a mask for etching the germanium substrate 1, the first tantalum nitride layer 2 itself needs to be defined which portion is to be hollowed out and which portion is to be retained. Therefore, the nanosphere 3 It is another mask that determines that the first tantalum nitride layer 2 is in a certain mask type, and can be said to be a preliminary mask, which is referred to as a first mask. Since the spherical nanosphere 3 is used as a mask, it is seen that the gap between the ball and the ball is a portion that can be penetrated into a so-called etching window, and therefore, in order to avoid an irregular etching pattern, The gap is large or small, or the upper part of the gap is blocked by other balls. Therefore, the optimal arrangement of the nanosphere 3 is that the single layer is arranged in the closest order to leave a space of approximately equilateral triangle between the ball and the ball for etching. The object reaches the first tantalum nitride layer 2 through the gap.

Referring to FIG. 2, it is revealed that the gap pattern between the nanospheres 3 has been transferred to the first tantalum nitride layer 2, and an etching window 20 is formed on the first tantalum nitride layer 2, thereby enabling the nanometer to be used. Ball 3 is removed.

Referring to FIG. 3, it is disclosed that after the nanosphere 3 has been removed, a conductive layer 4 is formed on the back surface of the germanium substrate 1. The electrical layer 4 acts as a back surface electric field for photo-assisted electrochemical etching to generate an electric field. Further, the conductive layer 4 is formed by forming a metal such as gold, copper or platinum on the back surface of the ruthenium substrate 1 by means of transmission, screen printing, vapor deposition, sputtering or the like.

Referring to FIG. 4, it is disclosed that a deep concave structure 10, that is, a deep concave hole shape or a deep groove shape, is etched on the ruthenium substrate 1 by photo-assisted electrochemical etching. In general, the deep-concave structure 10 has a high aspect ratio, that is, the depth is much larger than the width. Generally, in order to achieve an effective anti-reflection effect, the width is smaller than the wavelength of the incident light, and the depth is greater than The wavelength of the incident light. At this point, the portion of the anti-reflective structure of a solar cell has been substantially completed.

5 to 6, in the manufacturing method of the present invention, a step of directly using a nanosphere as an etching mask (etching window) for manufacturing a deep concave structure. Referring first to FIG. 5, it is disclosed that the nanosphere 3 is disposed on the ruthenium substrate 1, and as described above, the nanosphere 3 is usually attached to the ruthenium substrate 1 by spin coating or immersion. The preferred arrangement of the nanospheres 3 is such that the nanospheres 3 are arranged on the ruthenium substrate 1 in a manner that the single layer is most closely packed.

Referring to FIG. 6, after the nanosphere 3 is stacked, the nanosphere 3 is used as an etch mask, and the germanium substrate 1 is etched by dry etching. Among various dry etching methods, usually high density is used. A plasma reactive ion etching (ICP-RIE) technique is used to etch the germanium substrate 1. Further, the nanosphere 3 described above is made of polystyrene.

7 is a schematic view of a thinned germanium substrate according to the present invention, wherein in the embodiment of FIGS. 1 to 4, the first tantalum nitride layer 2 and the conductive layer 4 on the back surface are first removed, and then The entire back surface of the substrate 1 is etched to reduce the thickness of the ruthenium substrate 1. In the embodiment of FIGS. 5 to 6, the entire back surface of the ruthenium substrate 1 can be etched after the removal of the nanosphere 3. As for the etching liquid for thinning the tantalum substrate 1 in FIG. 7, KOH or TMAH may be used; or the high-density plasma reactive ion etching (ICP-RIE) technique may be used to thin the tantalum substrate 1.

8 to 10 are schematic views showing an embodiment of a method for forming a tantalum material and a configuration of upper and lower electrodes of a solar cell of the present invention. Referring to FIG. 8 , in order to make the anti-reflection effect better, an anti-reflection film is usually disposed on the surface of the crucible substrate 1 , and in FIG. 8 , the second tantalum nitride layer 5 is used as an anti-reflection film. And a second exposed portion 50 is further formed on the second tantalum nitride layer 5, so that the germanium substrate 1 can be exposed outside the second tantalum nitride layer 5. The exposed portion 50 is intended to expose the germanium substrate 1. Generally, a structure such as a via hole, a groove, a hole, or the like is formed on the tantalum nitride layer 5 by a micro-etching process or a precision cutting machine. The material under it can be exposed.

Referring to FIG. 9, it is disclosed that a first germanium film 6 is formed on the back surface of the germanium substrate 1. Since the present invention is a solar cell, the first germanium film 6 and the germanium substrate 1 are different in shape, such as When the ruthenium substrate 1 is a P-type 矽, the first ruthenium film 6 is an N-type 矽, whereas if the ruthenium substrate 1 is an N-type 矽, the first conductive film 6 is a P-type 矽, and in addition, usually the first ruthenium film 6 The material is heavily doped ruthenium. After the first tantalum film 6 is formed, the lower electrode 7a is placed thereon. Referring to FIG. 10 at this time, the upper electrode 7b is disposed on the front surface of the germanium substrate 1, that is, the exposed portion 50 of the tantalum nitride layer 5, and the upper electrode 7b is electrically connected to the germanium substrate 1 through the bare portion 50. So far, an anti-reflective structure The solar battery is complete.

11 to 12 are schematic views showing another embodiment of the formation of the tantalum material and the arrangement of the upper and lower electrodes of the solar cell of the present invention. Referring to FIG. 11, a heavily doped second germanium film 6' is disposed on the front surface of the germanium substrate 1, wherein if the germanium substrate 1 is a P-type germanium, the second germanium film 6' is an N-type germanium, and vice versa. The ruthenium substrate 1 is an N-type ruthenium, and the second ruthenium film 6' is a P-type ruthenium. After the second ruthenium film 6' is formed, a third tantalum nitride layer 5' is formed thereon as an anti-reflection film. In order to expose the germanium substrate 1, a bare place 50 is formed on the third tantalum nitride layer 5' and the second tantalum film 6' by a yellow photolithography or a wafer precision cutter.

Referring to Fig. 12, an upper electrode 7b is formed on the exposed portion 50 of the third tantalum nitride layer 5', and the material of the upper electrode 7b passes through the exposed portion 50 to reach the tantalum substrate 1 and is electrically connected to the tantalum substrate 1. Further, the lower electrode 7a is formed on the back surface of the substrate 1 again. At this point, a solar cell with an anti-reflective structure is completed.

Further, the anti-reflection film described above may be provided with an anti-reflection film in the form of a multilayer film, and generally has two layers, a first anti-reflection film and a second anti-reflection film. The first antireflection film is selected from the group consisting of cerium oxide (SiO ₂ ), diamond-like carbon (DLC), ceria (CcO ₂ ), aluminum oxide (Al ₂ O ₃ ), and tantalum nitride. One of (Si ₃ N ₄ ); and the second antireflective film, the material of which is selected from one of titanium dioxide (TiO) and tantalum oxide (TaO ₅ ), and the refractive index of the selected material of the second layer is greater than The material selected in the first layer.

As for the anti-reflection film described above, it is selected from the group consisting of physical vapor deposition (PVD), chemical vapor deposition (CVD), spin-on deposition, spray deposition, and dip coating. a method of forming on the ruthenium substrate 1 (please Cooperate with Figure 8) or the second film 6' (please match Figure 11). Thereafter, a further heating step can be performed, and it is generally convenient to return the solar cell to the machine for forming the anti-reflection film. This heating step can cause the anti-reflection film material located at the edge of the projection 12 to contract, and the opposite anti-reflection film material located at the intermediate position of the projection 12 is relatively convex, forming a micro lens structure. And can achieve the effect of focusing.

In general, in order to achieve a better anti-reflection effect, the present invention forms a deep concave structure on the surface of the solar cell by means of deep etching, so that the incident light is not easily reflected back to the atmosphere from the middle, and the deep etching is utilized. The method is photo-assisted electrochemical etching or high-density plasma reactive ion etching. As for the mask required for etching, if high-density plasma reactive ion etching, the present invention directly uses nano-sized polyphenylene. A vinyl sphere, referred to as a nanosphere, is used as a mask. When the nanospheres are arranged on the tantalum substrate in the most dense form of a single layer, the gap between the nanospheres can be used as an etching window to make the underlying germanium substrate It is etched, that is, the pattern of holes between the nanospheres is transferred to the ruthenium substrate. Moreover, in the case of photo-assisted electrochemical etching, it is necessary to use tantalum nitride as an etching mask, and the etching window of the tantalum nitride mask is different from the conventional technique by micro-etching, but it is nanometer. The ball is manufactured, that is, through the gap between the nanospheres as an etching window for etching tantalum nitride, also known as a nanosphere etching window, and transferring the hole pattern between the nanospheres to the nitriding through reactive ion etching technology. On the ruthenium layer, the etched window on the tantalum nitride layer is the hole pattern between the nanospheres. After the nanosphere is removed, the tantalum nitride layer is used as a photo-assisted electrochemical technique to etch the ruthenium substrate. Etched mask. In addition, in order to make the light-assisted electrochemical etching proceed smoothly, an anisotropic etching is used before the etching. The substrate is formed into a tapered pit to form a concave cusp, and the three-dimensional structure is like an inverted pyramid.

The advantage of using a sphere as an etch mask is that when they are arranged in the most densely packed manner, each sphere will be arranged in its most dense state in its own shape, so that it will be arranged in three spheres. There is a triangular pattern resembling an equilateral triangle but recessed on three sides. As an etch mask, there is no need for a mask, sensitizer, developing syrup, exposure, etc. like the conventional lithography technique. Etc. Materials and processes, so to some extent it is convenient. Moreover, since the deep concave structure to be manufactured by the present invention itself is merely an effect as a rough surface, a complicated pattern is not required. In addition, since the nanosphere is used in the present invention, in addition to making the deep concave structure denser and more compact, the true sphericity is improved, and the true sphericity is increased, that is, the nanosphere is in the densest single layer. When arranged, the pattern is more uniform and uniform, which can reduce the frequency of occurrence of irregular, unequal etched window patterns. Therefore, for the purpose of manufacturing a deep concave structure on a solar cell for increasing the surface roughness to achieve an anti-reflection effect, it is most desirable and convenient to use the nanosphere as an etching mask for manufacturing the concave structure. The cheapest manufacturing method.

The invention is intended to be modified by those skilled in the art, without departing from the scope of the invention.

1‧‧‧矽 substrate

10‧‧‧Deep concave structure

2‧‧‧First tantalum layer

20‧‧‧etching window

3‧‧‧Nami Ball

4‧‧‧Back surface electrode

5‧‧‧Second tantalum layer

5'‧‧‧ third tantalum layer

50‧‧‧naked places

6‧‧‧ Etched conductive layer

6‧‧‧First film

6'‧‧‧second film

7a‧‧‧ lower electrode

7b‧‧‧Upper electrode

1 to 4 are schematic views showing the steps of using a tantalum nitride as an etching mask (etching window) for manufacturing a deep concave structure in the manufacturing method of the present invention; and FIGS. 5 to 6, in the manufacturing method of the present invention, directly FIG. 7 is a schematic view showing a step of manufacturing an etched mask (etching window) of a deep concave structure; FIG. 7 is a schematic view showing a thinned ruthenium substrate of the present invention; and FIG. 8 to FIG. A schematic diagram of an embodiment of an electrode configuration; and FIGS. 11 to 12 are schematic views of another embodiment of a method of forming a tantalum material and an arrangement of upper and lower electrodes of a solar cell of the present invention.

1‧‧‧矽 substrate

10‧‧‧Deep concave structure

2‧‧‧First tantalum layer

20‧‧‧etching window

3‧‧‧Nami Ball

Claims (13)

A method for manufacturing a solar cell having an anti-reflection surface, comprising the steps of: (1) providing a germanium substrate having a front side and a back side; and (2) forming a first tantalum nitride layer on the front side; Laying a nanosphere on the tantalum nitride layer, using a nanosphere as a first etching mask; (4) etching the tantalum nitride layer by a reactive ion etching technique to form an etching window on the tantalum nitride layer (5) removing the nanosphere; (6) etching the germanium substrate to form a deep concave structure, wherein step (6) further comprises the following steps: (6-1') forming a heavily doped on the germanium substrate a doped film; and (6-2') forming a second tantalum nitride layer on the heavily doped germanium film, and forming a bare place on the heavily doped germanium film and the second tantalum nitride layer The germanium substrate is exposed outside the heavily doped germanium film and the second tantalum nitride; and (7) a front electrode is formed on the front surface of the germanium substrate, and a back electrode is formed on the back surface. The method of claim 1, wherein the tantalum nitride layer of step (2) is fabricated by radio frequency sputtering. The method of claim 1, wherein the step (1) further comprises a step (1-1): doping a pentavalent element on the front side of the germanium substrate for nitrogen ion diffusion. The method of claim 1, wherein the step (5) further comprises the step (5-1): forming a conductive layer on the back side of the germanium substrate. The method of claim 4, wherein the method The conductive layer of (5-1) is used for generating an electric field as a photo-assisted electrochemical etching. The method of claim 1, wherein the front electrode of the step (7) is located at the bare portion and thus passes through the heavily doped germanium film and the second tantalum nitride layer and the germanium substrate Electrical connection. The method of claim 1, wherein the step (6) etches the germanium substrate in a photo-assisted electrochemical etching manner. The method of claim 7, wherein before step (6), further comprising the step of pre-etching the pits on the substrate. The method of claim 8, wherein the pit is fabricated by anisotropic wet etching. A method for manufacturing a solar cell having an anti-reflection surface, comprising the steps of: (1) providing a substrate having a front side and a back side; (2) laying a nanosphere on the front surface and using the nano ball For etching the mask; (3) etching the germanium substrate to form a deep concave structure; (4) removing the nanosphere; (5-a') forming a heavily doped germanium film on the germanium substrate; B') forming a second tantalum nitride layer on the heavily doped germanium film, and forming a bare place on the heavily doped germanium film and the second tantalum nitride layer to expose the germanium substrate to the heavily doped a ruthenium film and the second tantalum nitride; (5-c') forming a front electrode on a front surface of the ruthenium substrate, wherein the front electrode is electrically connected to the ruthenium substrate through the bare portion; (5-d') A back electrode is formed on the back surface of the substrate. The method of claim 10, wherein the step (3) is etching the tantalum substrate by a high density plasma reactive ion etching (ICP-RIE) technique. The method of claim 10, wherein the ruthenium substrate is an N-type ruthenium, and the heavily doped ruthenium film is a P-type ruthenium. The method of claim 10, wherein the germanium substrate is a P-type germanium, and the heavily doped germanium film is an N-type germanium.