TW201806168A - N-type bifacial solar cell - Google Patents

Abstract

The instant disclosure provides an n-type bifacial solar cell comprising an n-type substrate, a p-type front emitter layer, an n-type back surface field layer, front and rear function layers, at least one tunnel layer, at least one front electrode and at least one rear electrode. The p-type front emitter layer and the n-type back surface field layer are disposed on the upper surface and the lower surface of the n-type substrate respectively, and the front and rear function layers are disposed on the p-type front emitter layer and the n-type back surface field layer. The tunnel layer is disposed at least one of between the p-type front emitter layer and the front function layer, and between the n-type back surface field layer and the rear function layer. The front and rear electrodes are punched through the front and rear function layers respectively for being electrically connected to the p-type front emitter layer and the n-type back surface field layer via carrier tunneling through the tunnel layer.

Description

N-type double-sided solar cell

The present invention relates to a solar cell, and more particularly to an n-type double-sided solar cell.

In general, the structure of an existing n-type double-sided solar cell includes a front emitter (typically p-type), a back surface electric field (typically n-type), a passivation layer structure, and an electrode structure. The front emitter and the back surface electric field can be formed by doping the n-type germanium substrate or depositing a doped germanium film. The passivation layer structures are respectively disposed on the front surface and the back surface of the n-type double-sided solar cell to directly passivate the front emitter and the back surface electric field, and the passivation layer structure can simultaneously have an anti-reflection function. The electrode structure includes a front electrode and a back electrode which are directly in contact with the front surface and the back surface electric field, respectively, and are subjected to electroplating by passing through the passivation layer structure by metal paste fire through or dielectric layer opening or the like. Therefore, the structure of the passivation layer under the electrode is broken, resulting in metal induced recombination between the electrode structure and the germanium material, thereby greatly limiting the performance of the n-type double-sided solar cell.

In response to the above problems, the industry has developed a tunnel oxide passivated contact (TOPCon) solar cell structure, which replaces the original with a passivation contact structure composed of tunneling oxide and heavily doped germanium film. Full area doped back surface region. Specifically, in the passivation contact structure, a tunneling oxide layer is formed on the surface of the germanium substrate, and the heavily doped germanium film (ie, the back electric field layer) can be covered by tunneling through plasma assisted chemical vapor deposition (PECVD). The surface of the oxide layer. With this, TOPCon The solar cell structure can combine the advantages of existing heterojunction structures as well as conventional polycrystalline junction structures, namely, high carrier selectivity and high temperature stability.

However, in the foregoing TOPCon solar cell structure, since a tunneling oxide layer is disposed between the back surface electric field layer and the germanium substrate, that is, the back surface structure of the solar cell sequentially includes a germanium substrate and a tunneling oxide from the inside to the outside. The layer and the heavily doped germanium film, compared to the existing n-type double-sided solar cell process, the TOPCon solar cell process must be adjusted for the order of the existing process. Specifically, a tunneling oxide layer must be formed on the surface of the germanium substrate, and a heavily doped germanium film is formed by deposition on the surface of the tunnel oxide layer. As a result, in order to manufacture the TOPCon solar cell, it is necessary to adopt a process and equipment different from the existing n-type double-sided solar cell, resulting in an increase in production cost.

Furthermore, in the TOPCon solar cell structure, the heavily doped germanium film is formed on the tunnel oxide layer after the tunnel oxide layer is formed. Specifically, heavy doping is carried out in an in-situ manner in the formation of a hafnium film, or in an ex-situ manner by ion diffusion or gas diffusion after the formation of a hafnium film. However, no matter how the heavy doping process is performed, the conditions and parameters of the heavy doping process must be precisely controlled in the process to avoid damage to the tunnel oxide layer. For example, it is desirable to avoid dopants (Dopant) from passing through the tunneling oxide layer, or subsequent high temperature diffusion processes to disrupt the tunneling oxide layer passivation capability. Therefore, the existing TOPCon solar cell structure still has the disadvantages of high process difficulty and low process reliability. In addition, in the TOPCon solar cell structure, the heavily doped germanium film will block light from entering the solar cell body due to its light absorbing property, and therefore, it is practically applicable only to the back surface structure of the solar cell.

Therefore, there is still a need to provide a solution to reduce the effect of metal induced recombination on the performance of an n-type double-sided solar cell without substantially increasing the complexity of the process, thereby ensuring n-type double sided Solar cell conversion efficiency.

In order to solve the above technical problem, according to one of the solutions of the present invention, An n-type double-sided solar cell comprising an n-type germanium substrate, a p-type front emitter layer, an n-type back surface field layer, a front functional layer, a back functional layer, at least one tunneling layer, and at least one front surface An electrode and at least one back electrode. The germanium substrate has an upper surface and a lower surface, and the p-type front emitter layer and the n-type back surface electric field layer are respectively disposed on the upper surface and the lower surface of the n-type germanium substrate. The front functional layer and the back functional layer are respectively disposed on the surface of the p-type front emitter layer and the n-type back surface electric field layer. At least one tunneling layer is disposed between the p-type front emitter layer and the front functional layer and at least one of two states disposed between the n-type back surface electric field layer and the back surface functional layer. The front electrode passes through the front functional layer, is electrically connected to the p-type front emitter layer via the tunneling layer, the back electrode passes through the back surface functional layer, and is electrically connected to the n-type back surface electric field layer via the tunneling layer.

The main technical means of the present invention is to pass the position setting of at least one of "between the p-type front emitter layer and the front functional layer" and "between the n-type back surface electric field layer and the back functional layer". The tunneling layer can avoid direct contact between the electrode structure metal and the front emitter layer and the back surface electric field layer without changing the existing n-type double-sided solar cell processing sequence, thereby avoiding the occurrence of metal induced recombination. Improve the life of solar cells and conversion efficiency.

For a better understanding of the features and technical aspects of the present invention, reference should be made to the accompanying drawings.

S‧‧‧Double-sided solar cells

1‧‧‧n type test substrate

11‧‧‧ upper surface

12‧‧‧ Lower surface

2‧‧‧p type front emitter layer

3‧‧‧n type back electric field layer

4‧‧‧ Positive functional layer

5‧‧‧Back functional layer

6‧‧‧Front electrode

7‧‧‧Back electrode

8‧‧‧Through tunnel

1 is a schematic cross-sectional view of an n-type double-sided solar cell according to an embodiment of the present invention; FIG. 2 is a cross-sectional view of an n-type double-sided solar cell according to another embodiment of the present invention; and FIG. A schematic cross-sectional view of an n-type double-sided solar cell provided by the embodiment.

The embodiments of the "n-type double-sided solar cell" disclosed in the present invention are described below by specific specific examples, and those skilled in the art can understand the advantages and effects of the present invention from the contents disclosed in the specification. The present invention can be implemented or applied in various other specific embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention. In addition, the drawings of the present invention are merely illustrative and are not intended to be described in terms of actual dimensions. The following embodiments will further explain the related technical content of the present invention, but the disclosure is not intended to limit the technical scope of the present invention.

First, please refer to Figure 1. 1 is a schematic cross-sectional view of an n-type double-sided solar cell according to an embodiment of the present invention. The n-type double-sided solar cell S provided by the embodiment of the invention comprises an n-type germanium substrate 1, a p-type front emitter layer 2, an n-type back surface electric field layer 3, a front functional layer 4, a back functional layer 5, a front electrode 6, The back electrode 7, and the tunneling layer 8.

Furthermore, as shown in FIG. 1, the n-type germanium substrate 1 has an upper surface 11 and a lower surface 12. In the embodiment of the present invention, the direction of the upper surface 11 is defined as the front surface of the n-type double-sided solar cell S, and the direction of the lower surface 12 is defined as the back surface of the n-type double-sided solar cell S. Since the n-type double-sided solar cell S provided by the embodiment of the present invention can receive light on both sides, both the front side and the back side are light receiving surfaces.

Further, the p-type front emitter layer 2 and the n-type back surface electric field layer 3 are respectively provided on the upper surface 11 and the lower surface 12 of the n-type germanium substrate 1. The p-type front emitter layer 2 can be formed in a variety of ways. For example, the p-type front emitter layer 2 can be formed on the upper surface 11 of the n-type germanium substrate 1 by diffusion. After the p-type front emitter layer 2 is formed by a diffusion method (for example, a high-temperature diffusion process), the upper surface 11 serves as an interface between the p-type front emitter layer 2 and the undoped n-type germanium substrate 1. Alternatively, the p-type front emitter layer 2 is formed by Atmospheric pressure chemical vapor deposition (APCVD). Further, the p-type front emitter layer 2 can also be formed by ion implantation. For example, the p-type front emitter layer 2 is a boron doped emitter layer.

Further, like the p-type front emitter layer 2, the n-type back surface electric field layer 3 can be formed by gas diffusion, ion implantation, vapor deposition, or other doping methods. For example, the n-type back surface electric field layer 3 is an electric field layer doped with phosphorus. In the present invention, the formation manner of the p-type front emitter layer 2 and the n-type back surface electric field layer 3 is not limited thereto.

Furthermore, the front functional layer 4 is disposed on the surface of the p-type front emitter layer 2, and the back functional layer 5 is disposed on the surface of the n-type back surface electric field layer 3. The front functional layer 4 and the back functional layer 5 are selected from the group consisting of cerium oxide (SiO _x ), cerium oxynitride (SiON), aluminum oxide (AlO _x ), aluminum nitride (AlN), and tantalum nitride (SiN _x ). And a combination of materials such as a combination of materials. In the present invention, the manner in which the front functional layer 4 and the back functional layer 5 are formed is not limited. A functional layer is provided on the front surface and the back surface of the n-type double-sided solar cell S to passivate the material of the p-type front emitter layer 2 and the n-type back surface field layer 3, and to exhibit an anti-reflection effect.

Specifically, in one embodiment, the front functional layer 4 and the back functional layer 5 may each be a material layer that simultaneously functions as a passivation and anti-reflection function. At this time, the front functional layer 4 and the back functional layer 5 are made of the foregoing materials, and the front functional layer 4 is a front material layer, and the back functional layer 5 is a back material layer, and the front material layer and the back material layer. Both have passivation and anti-reflection effects. Alternatively, in other embodiments, the front functional layer 4 includes a front passivation layer (not shown) and a front anti-reflective coating (not shown), and the back functional layer 5 includes a back passivation layer (not shown). Shown) and a back anti-reflective coating (not shown). In this case, the front and back passivation layers and the front and back anti-reflective coatings each have a passivation and anti-reflection effect. In summary, the front functional layer 4 and the back functional layer 5 may be a single layer material structure or a laminated structure including different material layers.

In detail, the aforementioned anti-reflective coating and passivation layer may be sequentially formed using different materials in the same process procedure. When the solar cell S comprises a first anti-reflective coating and a second anti-reflective coating, the first anti-reflective coating is conformally formed on the front passivation layer. Similarly, a second anti-reflective coating is conformally formed on the back passivation layer. The first and second anti-reflective coatings are used to reduce the amount of photon reflection to increase the solar cell The effectiveness of S. Alternatively, the anti-reflective coating can also achieve the effect of passivating the carrier recombination zone by selecting an anti-reflective coating material.

For example, the first anti-reflective coating and the second anti-reflective coating may be formed of a material selected from the group consisting of: silicon nitride, titanium dioxide (TiO ₂ ), indium tin oxide. (ITO), a transparent conductive oxide, cerium oxide (SiO ₂ ), cerium oxynitride (SiNx: H), and the like. In addition, the first and second anti-reflective coatings may be formed by, for example, atmospheric pressure vapor deposition, thermal oxidation. However, materials and methods for forming the first and second anti-reflective coatings are not limited thereto.

Further, the front electrode 6 and the back electrode 7 are formed on the front functional layer 4 and the back functional layer 5, respectively. The front electrode 6 passes through the front functional layer 4 and is electrically connected to the p-type front emitter layer 2 via the tunneling layer; the back surface electrode 7 passes through the back surface functional layer 5, and is electrically connected to the n through the tunneling layer. Type back surface electric field layer 3. For example, before the front surface electrode 7 and the back surface electrode 8 are formed, a through hole may be formed on the surface of the front functional layer 4 and/or the back surface functional layer 5 through the opening process, so that the subsequently formed front electrode 6 and back surface electrode The material of 7 can be electrically connected to the p-type front emitter layer 2 and the n-type back surface electric field layer 3 through the through holes. The technical means of the opening process include laser opening, use of an Etching paste, and formation of an etching mask, etc., but the invention is not limited thereto.

In the above, for example, the front electrode 6 and the back electrode 7 may have a grid electrode structure and have a main electrode structure as a bus bar and a sub-electrode structure as a finger electrode. The front electrode 6 and the back electrode 7 can be formed by screen printing, vapor deposition, sputtering, or electroplating. However, the invention is not limited thereto. The front electrode 6 and the back electrode 7 may be formed of a screen printing metal paste. For example, the metal paste for forming the front electrode 6 and the back electrode 7 may include silver, aluminum, copper, or the like and a mixture thereof. The front electrode 6 and the back electrode 7 may be formed by plating, for example, by plating a metal layer such as titanium/palladium/silver or plating a metal layer such as nickel/copper/silver/tin and any stacked metal layer. The front electrode 6 and the back electrode 7 may be formed by evaporation or sputtering. For example, a metal layer such as silver or aluminum is formed. It should be noted that the n-type double-sided solar cell S provided by the embodiment of the present invention further includes a tunneling layer 8. In the embodiment shown in FIG. 1, the tunneling layer 8 is disposed between the n-type back surface electric field layer 3 and the back surface functional layer 5. Therefore, the back surface electrode 7 passes through the back surface functional layer 5 and is blocked by the tunneling layer 8 to be isolated from the n-type back surface electric field layer 3. The tunneling layer 8 has an important effect on the n-type double-sided solar cell S provided by the embodiment of the present invention. Specifically, the tunneling layer 8 can avoid direct contact with the n-type back surface electric field layer 3 through the back surface electrode 7 of the back surface functional layer 5. However, in the process of photoelectric conversion using a solar cell, electrons or carriers can still pass through the tunneling layer 8, and therefore, although there is no direct physical contact between the back surface electrode 7 and the n-type back surface electric field layer 3, the back surface electrode 7 remains The n-type back surface electric field layer 3 is electrically connected by a carrier tunneling effect.

The metal back surface electrode 7 of the n-type double-sided solar cell S and the silicon-based material constituting the n-type back surface electric field layer 3 are provided by the design of the tunneling layer 8. Because there is no physical contact between the based materials, not only metal induced recombination is avoided, but also the tunneling layer 8 provides electrical connection and good passivation effect. Therefore, the n-type double-sided solar cell S provided by the embodiment of the present invention can have excellent conversion performance.

For example, the tunneling layer 8 is formed of a stacked structure of tantalum oxide (SiO _x ), aluminum oxide (AlO _x ), or the like. The thickness of the tunneling layer 8 must also be controlled. If the thickness is too thin, the effectiveness of the metal-induced recombination between the back surface electrode 7 and the n-type back surface electric field layer 3 is lowered, and if the thickness is too thick, the thickness is too thick. Will adversely affect the carrier tunneling effect. Therefore, the thickness of the tunneling layer 8 is preferably between 0.5 and 16 nm, preferably between 1 and 4 nm. The tunneling layer 8 may be a tantalum oxide and formed by a Wet-chemical method or a UV/O ₃ growth method; or, the tunneling layer 8 may be aluminum. Oxide, and can be formed by atomic layer chemical vapor deposition (ALD method). However, the invention is not limited thereto.

Next, a tunneling layer 8 formed of aluminum oxide (AlO _x ) will be taken as an example to illustrate a mechanism by which aluminum oxide has a passivation effect on a material mainly composed of n-type germanium. Aluminum oxide can produce field-effect passivation effects on n-type germanium. The high density negative charge (between 10 ¹² -10 ¹³ cm ^-2 ) at the interface of the aluminum oxide layer and its n-type germanium is sufficient to form a strong inversion electric field near the surface of the n-type germanium. The inverted electric field in this region has a good surface passivation effect for n-type germanium with a low doping concentration. For n-type germanium with a moderate doping concentration, the negatively charged aluminum oxide layer can still form a weak inverted electric field near the n-type germanium surface. Therefore, although for the n-type germanium having a moderate doping concentration, the passivation effect obtained by using the aluminum oxide layer is not as good as that of the n-type germanium having a low doping concentration, and the aluminum oxide is still sufficient to produce a passivation effect.

In view of the above, the tunneling layer 8 formed using aluminum oxide has a significant effect on the lifetime of the carrier in the n-type double-sided solar cell S, but does not affect the structure of the emitter or the structure of the electric field and the electrode. Ohmic Contact. For example, by using an aluminum oxide layer as the tunneling layer 8, the lifetime of the carrier in the n-type double-sided solar cell S can be increased by about three times compared to a solar cell that does not use any tunneling layer.

Next, please refer to Figure 2. 2 is a cross-sectional view of an n-type double-sided solar cell according to another embodiment of the present invention. Comparing FIG. 2 with FIG. 1, it can be seen that the difference between FIG. 1 and FIG. 2 is that the arrangement positions of the tunneling layers 8 are different. The tunneling layer 8 is disposed between the p-type front emitter layer 2 and the front functional layer 4 in FIG. Therefore, the front electrode 6 is blocked by the tunneling layer 8 to be isolated from the p-type front emitter layer. In particular, the tunneling layer 8 can avoid direct contact between the front side electrode 6 passing through the front functional layer 4 and the p-type front emitter layer 2. However, in the process of photoelectric conversion using a solar cell, electrons or carriers can still pass through the tunneling layer 8, and therefore, there is no direct physical contact between the front electrode 6 and the p-type front emitter layer 2, and the front electrode 6 The electrical connection is still formed with the p-type front emitter layer 2 by the carrier tunneling effect.

In the structure of the n-type double-sided solar cell S shown in Fig. 2, the structure other than the tunneling layer 8 is the same as that shown in Fig. 1. Therefore, for other structures, ie n The details of the germanium substrate, the p-type front emitter layer 2, the n-type back surface electric field layer 3, the front functional layer 4, the back surface functional layer 5, the front surface electrode 6, and the back surface electrode 7 will not be described again.

Finally, please refer to Figure 3. 3 is a schematic cross-sectional view showing an n-type double-sided solar cell according to still another embodiment of the present invention.

Comparing FIG. 3 with FIG. 1 and FIG. 2, the difference between FIG. 3 and FIGS. 1 and 2 is the installation position of the tunneling layer 8. Specifically, the tunneling layer 8 is disposed between the n-type back surface electric field layer 3 and the back surface functional layer 5 in FIG. 1, and the tunneling layer 8 is disposed between the p-type front emitter layer 2 and the front functional layer 4 in FIG. The tunneling layer 8 is provided between the n-type back surface electric field layer 3 and the back surface functional layer 5 of FIG. 3 and between the p-type front emitter layer 2 and the front functional layer 4. In other words, in the embodiment shown in FIG. 3, the front and back surfaces of the n-type double-sided solar cell S are provided with a tunneling layer 8. 3, the manufacturing method of the tunneling layer 8, the selection of materials, and the relationship with other structures are the same as those shown in FIG. 1 and FIG. 2, and will not be described again. In addition, in the structure of the n-type double-sided solar cell S shown in FIG. 3, other structures than the tunneling layer 8 are the same as those shown in FIGS. 1 and 2. Therefore, for the other structures, that is, the details of the n-type germanium substrate, the p-type front emitter layer 2, the n-type back surface electric field layer 3, the front functional layer 4, the back functional layer 5, the front surface electrode 6, and the back surface electrode 7, This is not explained again.

In summary, the present invention has an advantageous effect that the n-type double-sided solar cell provided by the embodiment of the present invention can pass “between the p-type front emitter layer and the front functional layer” and “in the n-type”. The tunneling layer is disposed at a position of at least one of the two states between the back electric field layer and the back surface functional layer, and the metal used for forming the electrode structure can be avoided without changing the processing sequence of the existing n-type double-sided solar cell. Direct contact with the tantalum material forming the front emitter layer and the back surface electric field layer causes metal induced recombination, thereby improving the life and conversion efficiency of the solar cell.

In particular, the double-sided solar cell provided by the embodiments of the present invention can utilize a variety of existing technologies (ie, not limited to deposition techniques) above or below the germanium substrate. A doped emitter structure or an electric field structure is formed in the material, and an oxide layer is formed on the emitter structure or the electric field structure as a tunneling layer. Compared with the existing TOPCon solar cell structure process, the present invention can form a double-sided solar cell through a less difficult and highly reliable process, and can overcome the existing TOPCon solar cell structure and can only be used on the back side of the solar cell. Disadvantages.

The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Therefore, equivalent technical changes made by using the present specification and the contents of the drawings are included in the protection scope of the present invention. .

S‧‧‧Double-sided solar cells

1‧‧‧n type test substrate

11‧‧‧ upper surface

12‧‧‧ Lower surface

2‧‧‧p type front emitter layer

3‧‧‧n type back electric field layer

4‧‧‧ Positive functional layer

5‧‧‧Back functional layer

6‧‧‧Front electrode

7‧‧‧Back electrode

8‧‧‧Through tunnel

Claims (11)

An n-type double-sided solar cell comprising: an n-type germanium substrate having an upper surface and a lower surface; a p-type front emitter layer disposed on the upper surface of the n-type germanium substrate; An n-type back surface electric field layer disposed on the lower surface of the n-type germanium substrate; a front functional layer disposed on a surface of the p-type front emitter layer; and a back functional layer disposed On the surface of the n-type back surface electric field layer; at least one tunneling layer disposed between the p-type front emitter layer and the front functional layer and disposed on the n-type back surface electric field layer and At least one of two states between the back functional layers; at least one front electrode, at least one of the front electrodes passing through the front functional layer to be electrically connected to the p-type front emitter layer; and at least one back electrode And at least one of the back electrodes passes through the back surface functional layer to be electrically connected to the n-type back surface electric field layer. The n-type double-sided solar cell of claim 1, wherein at least one of the tunneling layers is disposed between the n-type back surface electric field layer and the back surface functional layer, and at least one of the back electrodes is A barrier of at least one of the tunneling layers is isolated from the n-type back surface electric field layer. The n-type double-sided solar cell of claim 1, wherein at least one of the tunneling layers is disposed between the p-type front emitter layer and the front functional layer, and at least one of the front electrodes Blocking from at least one of the tunneling layers to be isolated from the p-type front emitter layer. The n-type double-sided solar cell of claim 1, wherein at least one of the tunneling layers is disposed between the p-type front emitter layer and the front functional layer, and at least one of the front electrodes Blocking from at least one of the tunneling layers to be isolated from the p-type front emitter layer; wherein at least one of the tunneling layers is disposed between the n-type back surface electric field layer and the back functional layer And at least one of the backsides The barrier layer is separated from the n-type back surface electric field by at least one of the tunneling layers. The n-type double-sided solar cell according to claim 1, wherein at least one of the tunneling layers is formed of a stacked structure of tantalum oxide, aluminum oxide or the like. The n-type double-sided solar cell according to claim 1, wherein the front functional layer is a front material layer having both passivation and anti-reflection functions, and the back functional layer has both passivation and anti-reflection functions. The back layer of material. The n-type double-sided solar cell of claim 1, wherein the front functional layer comprises a front passivation layer and a first anti-reflective coating formed on the front passivation layer, the front passivation layer and The first anti-reflective coating exposes at least one of the front electrodes, and the back functional layer comprises a back passivation layer and a second anti-reflective coating formed on the back passivation layer, the back passivation layer and The second anti-reflective coating exposes at least one of the back electrodes. The n-type double-sided solar cell according to claim 1, wherein the front functional layer and the back functional layer are selected from the group consisting of niobium oxide, tantalum nitride, hafnium oxynitride, aluminum oxide, and nitriding. A material composed of a group of aluminum and the like is formed. The n-type double-sided solar cell according to claim 1, wherein the p-type front emitter layer and the n-type back surface electric field layer are formed by gas diffusion, ion implantation or atmospheric vapor deposition. The n-type double-sided solar cell according to claim 1, wherein at least one of the front electrode and at least one of the back electrodes are formed of a metal glue or a metal layer, and the metal glue comprises silver, aluminum, A mixture of copper or the like, and the metal layer comprises a combination of titanium, palladium, silver, nickel, copper, tin, aluminum, or the like. The n-type double-sided solar cell according to claim 10, wherein the plurality of the front electrodes and the plurality of the back electrodes are formed by screen printing, vapor deposition, sputtering, or electroplating.