TWI385811B - Solar cell manufacturing method - Google Patents

Description

Solar cell manufacturing method

The present invention relates to a method of fabricating a solar cell, and more particularly to a method of fabricating a solar cell comprising removing harmful particles from a twinned substrate.

Figure 4 shows a cross-sectional view of a conventional solar cell. As shown in FIG. 4, the solar cell 100 includes a twinned substrate 110, an anti-reflective layer 120, a separation trench 140, and an electrode structure 130. The twin substrate 110 includes an N-type region 111 and a P-type region 112 interconnected. The electrode structure 130 includes an upper electrode 131 penetrating the anti-reflection layer 120 and electrically connecting the N-type region 111; and a lower electrode 132 electrically connecting the P-type region 112.

As described above, the conventional solar cell 100 includes a twinned substrate 110 having a P/N interface, and during the manufacturing process of the twinned substrate 110, particle contamination is likely to occur, and the contaminated particles may be, for example, Metals, such metal particles form a recombination center of electrons, reducing the chance of electrons reaching the electrode structure 130, thereby reducing the photoelectric conversion efficiency of the solar cell 100.

There is therefore a need for a solar cell manufacturing method capable of achieving the effect of reducing harmful particles in the twinned substrate 110, thereby improving the photoelectric conversion efficiency of the solar cell 100.

It is an object of an embodiment of the present invention to provide a method of fabricating a solar cell that reduces harmful impurities in a twinned substrate.

According to an embodiment of the invention, a solar cell manufacturing method is provided which comprises the following steps. A twinned substrate is provided, and the twinned substrate is of a first type and has a first surface and a second surface. An impurity trap layer is deposited on the first surface. The impurity trap layer is etched using an acid solution to remove the impurity trap layer. A plurality of impurities of the second type are doped on the first surface of the twinned substrate after the impurity trapping layer is removed to form a first type region and a second type region. An electrode structure electrically connecting the first type region and the second type region is formed.

In one embodiment, the impurity trap layer is a layer of ruthenium dioxide. In an embodiment, the impurity trap layer may comprise a tantalum nitride layer, a non-twisted tantalum nitride layer, a titanium oxide layer or a zinc oxide layer.

In one embodiment, the acid solution comprises a hydrofluoric acid. In addition, the acid solution may further comprise monohydrochloric acid.

In one embodiment, the step of etching the impurity trap layer is performed by an overetching method to further etch a portion of the twinned substrate. .

According to an embodiment of the present invention, after the surface is roughened, the impurity trap layer is deposited in advance and then removed by using an acid solution, and the crystal grains on the surface of the twin crystal substrate can be removed simultaneously by means of impurity adsorption (Gettering). Metal impurities, reducing defects or recombination centers in the twinned substrate, increasing the lifetime of a few carriers, and thus obtaining solar cells with better electrical or electrical properties.

Other objects and advantages of the present invention will become apparent from the technical features disclosed herein. The above and other objects, features, and advantages of the invention will be apparent from

1A to 1B are flow charts showing a method of fabricating a solar cell according to an embodiment of the present invention. 2A to 2H are schematic cross-sectional views showing respective steps of a method of fabricating a solar cell according to an embodiment of the present invention. As shown in FIGS. 1A to 1B and FIGS. 2A to 2H, the solar cell manufacturing method includes the following steps.

As shown in FIG. 2A, step S02: providing a twinned substrate, and the twinned substrate has a first surface 113 and a second surface 114. In this embodiment, the twinned substrate is a P-type polycrystalline germanium substrate 110.

As shown in FIG. 2B, step S03: etching and etching the first surface 113 and the second surface 114 of the P-type polycrystalline silicon substrate 110 with an acid-base solution to roughen the surfaces 113 and 114 of the P-type polycrystalline silicon substrate 110 to reduce sunlight. reflection. In one embodiment, the first surface 113 can be etched using a solution of hydrofluoric acid (HF) and nitric acid (HNO ₃ ). In one embodiment, the second surface 114 can be etched using a potassium hydroxide (KOH) solution.

As shown in FIG. 2C, step S04: depositing a layer 119 of cerium oxide (SiO ₂ ) on the first surface 113. After depositing the yttria layer 119, metal impurities in the P-type polysilicon substrate 110 are absorbed into the ruthenium dioxide layer 119, so that the amount of metal impurities in the P-type polysilicon substrate 110 is reduced. In addition, an impurity trapping layer such as a germanium tantalum nitride (Si ₃ N ₄ ) layer or a non-twisted tantalum nitride (SiN _x ) layer, a titanium oxide (TiO ₂ ) layer, or a zinc oxide (ZnO) layer may be deposited. It is used as a metal impurity remaining in the P-type polycrystalline germanium substrate 110.

As shown in FIG. 2D, step S05: etching the ruthenium dioxide layer 119 with a hydrofluoric acid solution to remove the ruthenium dioxide layer 119. Thereby, the content of the metal impurities remaining in the P-type polycrystalline silicon substrate 110 after the step S05 is smaller than the content of the metal impurities in the P-type polycrystalline silicon substrate 110 provided in the step S02. In one embodiment, a portion of the P-type polysilicon substrate 110 is further etched by over-etching to ensure complete removal of the ceria layer 119 while also removing metal impurities in the portion. In one embodiment, the cerium oxide layer 119 may also be etched using a mixed solution of hydrofluoric acid and hydrochloric acid.

As shown in FIG. 2E, step S06: a plurality of N-type impurities are doped on the first surface 113 of the P-type polysilicon substrate 110. In an embodiment, the first surface 113 may be doped with an N-type impurity by a furnace tube diffusion method or a screen printing, a spin coating method or a spray method, and the N-type impurity may diffuse into the P-type polycrystalline germanium substrate 110 to form an N-type. The impurity diffusion region is such that the P-type polysilicon substrate 110 has an N-type region 111 and a P-type region 112. The N-type impurity may be, for example, a phosphorus impurity, and phosphorus impurity doping is performed on the P-type polycrystalline germanium substrate 110 using phosphorus oxychloride (POCl ₃ ) at a high temperature.

As shown in FIG. 2F, step S07: forming an anti-reflection layer 120 on the P-type polysilicon substrate 110.

As shown in FIG. 2G, step S08: forming an electrode structure 130 electrically connecting the N-type region 111 and the P-type region 112. In an embodiment, the foregoing step S08 may include the following steps. Step S32: forming a first conductive paste on the first surface 113. Step S34: forming a second conductive paste on the second surface 114. Step S36: performing a sintering treatment on the P-type polycrystalline germanium substrate 110 on which the first conductive paste and the second conductive paste are formed, so that the first conductive paste is sintered and penetrates the anti-reflective layer 120 to form the first electrode 131; After the glue is sintered, the second electrode 132 is formed, and the first electrode 131 and the second electrode 132 are electrically connected to each other through a load to form a current loop.

Referring to FIG. 2H, in an embodiment, the solar cell manufacturing method may further include the step of: forming at least one separation trench 140 for cutting off a leakage current path of an electron flowing from the N-type region 111 to the second electrode 132. . According to the above steps, the solar cell 100 according to an embodiment of the present invention can be obtained.

Hereinafter, the principle of an embodiment of the present invention will be further described.

The impurity in the material of the P-type polycrystalline germanium substrate 110 causes uneven diffusion concentration during doping in step S06. To improve the situation, in one embodiment of the present invention, a new procedure for removing impurities is utilized, which utilizes impurity adsorption (Gettering). The method is to reduce crystal grains and metal impurities on the surface of the P-type polycrystalline silicon substrate 110. Metal impurities form a recombination center in a polycrystalline silicon solar cell and affect the lifetime of a few carriers. These metal impurities have many residual forms, including precipitates of replacement ions, interstitial ions, oxides, citrates, tellurides, and the like. The material, which has the greatest influence on the interstitial impurities, such as iron (Fe) or chromium (Cr), and the precipitate of copper (Cu) also affects the P-type polycrystalline silicon substrate 110 (tantalum wafer).

3 is a schematic view showing an atomic arrangement of a P-type polycrystalline germanium substrate on which a hafnium oxide layer is formed. As shown in FIG. 3, the germanium atoms in the P-type polycrystalline germanium substrate 110 are regularly arranged. The cerium oxide (SiO ₂ ) molecule is bonded to each of the germanium atoms (Si) and the four oxygen atoms (O), and each oxygen atom is bonded to two germanium atoms. At the Si/SiO ₂ interface, some of the germanium atoms are not bonded. This incomplete cerium oxide ion Si/SiO ₂ interface is less than 2 nm and is a source of positively fixed oxide charge. There are other interface-trapped oxides on the Si/SiO ₂ interface, which may be positive or negative due to structural defects, oxidation-induced defects, or metal impurities.

According to an embodiment of the present invention, in the process for manufacturing a solar cell, steps S04 and S05 are added, and a hydrofluoric acid solution is used to react with cerium oxide (SiO ₂ ) on the first surface 113 of the P-type polycrystalline germanium substrate 110. Thereafter, a water-soluble product (H ₂ SiF ₆ ) is formed, and H ₂ SiF ₆ is carried away from the surface 113 of the P-type polycrystalline germanium substrate 110 by a solution, as follows:

SiO _2(s) +6HF _2(aq) →H ₂ SiF _6(aq) +2H ₂ O _(g)

Among them, SiO ₂ is a main component of the phosphonic acid glass; and the H ₂ SiF ₆ reaction product is soluble in water, and thus is easily carried away from the surface 113 of the P-type polycrystalline silicon substrate 110 by the solution.

In the dry or wet oxidation mode, cesium atoms are consumed when SiO ₂ is grown. The thickness of the erbium-consuming atoms is 0.46 units of the SiO ₂ layer, that is, the oxide layer of 46 nm is consumed per 100 nm of the oxide layer. When SiO ₂ is removed by hydrofluoric acid, the effect of impurity adsorption (Gettering) is simultaneously caused by the thermal oxidation phenomenon, and the metal impurities or surface defects in which the impurity adsorption phenomenon occurs can be removed. Therefore, the diffusion length of the minority carrier can be effectively increased, and the open circuit voltage (Voc) can be improved. At this time, the wafer state of the P-type polycrystalline germanium substrate 110 is good, so the furnace tube diffusion in step S06 is performed to form the PN diode, and the latter. The solar cell 100 having better electrical performance can be obtained by the process.

In summary, according to an embodiment of the present invention, after the surface roughening, the ruthenium dioxide layer is pre-deposited and removed by using a hydrofluoric acid solution, and the P-type can be removed by means of impurity adsorption (Gettering). The crystal grains and metal impurities on the surface of the polycrystalline germanium substrate 110 reduce defects and recombination centers of the P-type polycrystalline germanium substrate 110, increase the lifetime of a minority carrier, and further obtain a solar cell 100 having a good electric or electric power.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application. In addition, any of the objects or advantages or features of the present invention are not required to be achieved by any embodiment or application of the invention. In addition, the abstract sections and headings are only used to assist in the search of patent documents and are not intended to limit the scope of the invention.

100. . . Solar battery

110. . . Twin crystal substrate

111. . . N-type area

112. . . P-type area

113. . . First surface

114. . . Second surface

119. . . Ceria layer

120. . . Antireflection layer

130. . . Electrode structure

131. . . First electrode

132. . . Second electrode

140. . . Separation ditch

1A to 1B are flow charts showing a method of fabricating a solar cell according to an embodiment of the present invention.

2A to 2H are schematic cross-sectional views showing respective steps of a method of fabricating a solar cell according to an embodiment of the present invention.

3 is a schematic view showing an atomic arrangement of a P-type polycrystalline germanium substrate on which a hafnium oxide layer is formed.

Figure 4 shows a cross-sectional view of a conventional solar cell.

Claims (9)

A method for manufacturing a solar cell, comprising: providing a twinned substrate, wherein the twinned substrate is of a first type and having a first surface and a second surface; depositing an impurity trapping layer on the first surface; An acid solution to etch the impurity trap layer to remove the impurity trap layer; and doping a plurality of impurities of the second type on the first surface of the twin crystal substrate after removing the impurity trap layer Forming a first type region and a second type region; forming an electrode structure electrically connecting the first type region and the second type region. The method for manufacturing a solar cell according to claim 1, wherein before the step of depositing an impurity trap layer on the first surface, the method for manufacturing the solar cell further comprises: etching the solution by using an acid-base solution; The first surface and the second surface of the twinned substrate roughen the first surface and the second surface of the twinned substrate. The method of manufacturing a solar cell according to claim 1, wherein the impurity trap layer is a layer of ruthenium dioxide. The method for producing a solar cell according to claim 1, wherein the acid solution comprises a hydrofluoric acid. The method of manufacturing a solar cell according to claim 4, wherein the acid solution comprises monohydrochloric acid. The method for manufacturing a solar cell according to claim 1, wherein the step of etching the impurity trap layer is performed by an overetching method to further etch a portion of the twinned substrate. The solar cell manufacturing method according to claim 1, wherein the impurity trap layer comprises a twinned tantalum nitride layer, a non-crystalline tantalum nitride layer, a titanium oxide layer or a zinc oxide layer. The method of manufacturing a solar cell according to claim 1, wherein the impurities of the second type are phosphorus impurities. The solar cell manufacturing method according to claim 1, wherein the twinned substrate is a P-type polycrystalline germanium substrate.