TWI398961B - Solar cell manufacturing method comprising at least two gettering steps - Google Patents

Description

Method for manufacturing a solar cell comprising at least two steps of removing harmful impurities

The present invention relates to a solar cell manufacturing method, and more particularly to a solar cell manufacturing method for removing harmful particles in a twinned substrate by using doped impurities.

A conventional solar cell includes a twinned substrate having a P/N interface, and during the manufacturing process of the twinned substrate, particle contamination is apt to occur, which adversely affects the manufacturing yield. The Republic of China Patent Application No. 095139453 discloses a silicon wafer having high gettering capability and high flatness and a method of manufacturing the same. In this method, a uniform stacking fault defects are generated in the high temperature process of the twinned substrate, and the defective layer absorbs metal contamination (harmful particles) in the process into the gettering region ( Gettering sites), thereby reducing harmful metal particles in the twinned substrate. In U.S. Patent No. 5,066,359, the abrasive damage layer is not completely removed during salty etching, leaving a thin layer of abrasive damage for use as a gettering layer. In the Republic of China Patent Application No. 096127007, a polycrystalline germanium region is deposited on a germanium wafer as an impurity trapping region by using a silane gas, so that the germanium wafer includes a germanium slice and a first impurity trapping region.

These prior art, although having the effect of reducing harmful particles in the twinned substrate, have an improved space for manufacturing solar cell fashion.

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. In one embodiment, a method of fabricating a solar cell that utilizes a method of doping phosphorus impurities to reduce harmful impurities in a twinned substrate is provided.

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. A plurality of first impurities of the second type are doped on the first surface of the twinned substrate. The first surface of the twinned substrate is etched for the first time. A plurality of second impurities of the second type are doped on the first surface of the twinned substrate that has been etched for the first time to form a first type region and a second type region. A second etch is performed on the first surface of the twinned substrate. And forming an electrode structure electrically connecting the first type region and the second type region.

In one embodiment, the first type is a P type and the second type is an N type. And preferably, the first impurity and the second impurity are all phosphorus impurities.

In one embodiment, the first etching of the first surface of the twinned substrate may be performed for the first etching of the second surface of the twinned substrate. In addition, the second etching of the first surface of the twinned substrate may be performed for the second etching of the second surface of the twinned substrate.

In one embodiment, the step of doping a plurality of first impurities of the second type on the first surface of the twin crystal substrate is performed at a first predetermined temperature, and the second impurity of the second type is The step of doping on the first surface of the twinned substrate that has been etched for the first time is performed at a second predetermined temperature, and the first predetermined temperature is higher than the second predetermined temperature.

In one embodiment, the step of performing a first etching on the first surface of the twinned substrate, performing a first predetermined period of time, performing a second etching on the first surface of the twinned substrate, and performing a second predetermined step And the first predetermined period is longer than the second predetermined period.

According to the solar cell manufacturing method of an embodiment of the present invention, the step of performing the doping of the phosphorus impurity twice on the twinned substrate and the two etching steps (preferably, the one-pass over-etching step and the one-time etching step) can effectively reduce Harmful impurities in the twinned substrate, thereby increasing the lifetime of minority carriers inside the twinned substrate.

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

In general, semiconductor components can be classified into P-type and N-type. Taking a P-type semiconductor device as an example, a P-type semiconductor device has a large number of holes. Therefore, a majority of a carrier in a P-type semiconductor device refers to a hole, a minority carrier refers to an electron, and an N-type semiconductor device refers to an electron. in contrast.

The inventor of the present invention conducted an experiment to fully test the raw material 矽 wafer of the solar cell, and actually produced the cell sheet, and compared the photoelectric conversion efficiency and the full detection result of the produced solar cell, and found that the wafer was in the wafer. The life cycle of a few carriers (for example, P-type polysilicon wafers, where a few carriers are electrons) affects the photoelectric conversion efficiency of solar cells. During the manufacturing process of the wafer, the harmful metal particles remaining by the particle contamination will reduce the life cycle of the minority carriers in the wafer.

In order to improve the life cycle of a few carriers in the silicon wafer of the solar cell, the inventors of the present invention tried to conduct experiments using the method of doping phosphorus impurities to verify the adsorption of harmful metals by phosphorus impurities, without affecting the quality and process of the solar cell. The effect of particles.

The design of the experiment of the present invention is as follows. In a comparative example, only one surface of the germanium wafer is subjected to a step of doping phosphorus impurities. Since the step of doping the phosphorus impurity forms a trap layer at the surface that hinders the flow of electrons, the surface of the germanium wafer is etched to remove the trap layer after the step of doping the phosphorus impurity. . In an embodiment of the present invention, in order to verify the effect of the phosphorus impurities adsorbing harmful metal particles, a step of second-doping phosphorus impurities and a second etching step are performed. Hereinafter, a method of manufacturing a solar cell according to an embodiment of the present invention, and a step of the above-described secondary doping of phosphorus impurities and a purpose and a function of the second etching step will be described in detail.

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: cleaning or 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.

As shown in FIG. 2C, step S04: a plurality of N-type first 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. In one embodiment, the first impurity may be a phosphorus impurity, and the phosphorus impurity doping is performed on the P-type polycrystalline germanium substrate 110 by using phosphorus oxychloride (POCl ₃ ) at a temperature of about 800 ° C to about 820 ° C. In order to allow the phosphorus impurities to penetrate deeper into the P-type polycrystalline silicon substrate 110, thereby adsorbing more harmful impurities, it is preferable to make the process temperature of the step S04 higher than the process temperature of the step S08 described later.

As shown in FIG. 2D, step S06: the first surface 113 of the P-type polysilicon substrate 110 is first etched. In one embodiment, step S06 is performed for 1.5 hours (which is three times 0.5 hours of step S10 described later). The etching time in step S06 is longer than the etching time in step S10 to be described later, and in addition to the trap layer formed in step S04, at least a part of the N-type region 111 formed in step S04 can be removed. Since the phosphorus impurity has adsorbed a part of the harmful impurities in the P-type polycrystalline germanium substrate 110 in this portion (that is, the step of doping the phosphorus impurity has a function of gettering), the at least a portion of the N-type region 111 is removed. The latter P-type polycrystalline germanium substrate 110 will have less harmful impurities.

As shown in FIG. 2E, step S08: doping a majority of the second impurity of the N-type onto the first surface 113 of the P-type polysilicon substrate 110 that has been etched for the first time, and again making the P-type polysilicon substrate 110 There are an N-type region 111 and a P-type region 112. In one embodiment, the second impurity may be a phosphorus impurity, and the phosphorus impurity doping is performed on the P-type polycrystalline germanium substrate 110 by using phosphorus oxychloride (POCl ₃ ) at a temperature of about 790 ° C to about 810 ° C. The second phosphorus doping step, in addition to being able to form the N-type region 111, also has the function of adsorbing harmful impurities in the P-type polycrystalline germanium substrate 110, achieving the effect of the second gettering. In addition, in an embodiment, the second impurity may not use phosphorus impurities, and only N-type impurities capable of forming an N-type impurity diffusion region may be used.

Step S10: performing a second etching on the first surface 113 of the P-type polysilicon substrate 110, thereby removing the trap layer formed in step S08. In an embodiment, since the step S10 only needs to remove the trap layer formed in step S08, the etching time of step S10 can be set to 0.5 hours according to experimental experience.

As shown in FIG. 2F, step S11: forming an anti-reflection layer 120 on the P-type polysilicon substrate 110.

As shown in FIG. 2G, step S12: forming an electrode structure 130 electrically connecting the N-type region 111 and the P-type region 112.

In an embodiment, the foregoing step S12 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 to form a current loop.

Referring to FIG. 2H, in an embodiment, the solar cell manufacturing method may further include the step 14 of forming at least one separation trench 140 for separating adjacent battery cells. According to the above steps, the solar cell 100 according to an embodiment of the present invention can be obtained.

Table 1 below shows the experimental results of the comparative example (the one-time gettering step) and the one embodiment of the present invention (the second gettering step).

As shown in the above Table 1, the photoelectric conversion efficiency of the solar cell 100 of the embodiment in which the second gettering step was carried out was 16.132%, which was superior to the photoelectric conversion efficiency of the solar cell of the comparative example in which the gettering step was performed, which was 16.076%. The solar cell 100 of the embodiment in which the second gettering step is performed has a voltage (Voc) value of 0.619 and a current (Isc) value of 8.234, which are respectively superior to a voltage (Voc) value of 0.615 of the solar cell of the comparative example in which the gettering step is performed, respectively. The current (Isc) value is 8.230. Among them, the increase of the voltage value is more obvious, and it can be known that the lifetime of a few carriers in the P-type polycrystalline germanium substrate 110 has increased, so that a good photoelectric conversion efficiency can be obtained.

In summary, in the process of the conventional solar cell, a twinned substrate having a P/N interface is formed by doping phosphorus impurities. Based on the above experimental results, it was confirmed that the phosphorus impurity has a function of gettering. Therefore, in the solar cell manufacturing method according to an embodiment of the present invention, the step of performing the doping of the phosphorus impurity twice on the twinned substrate and the two etching steps (preferably, the one-pass over-etching step and the one-time etching step) can be effective. Reduces harmful impurities in the twinned substrate, thereby increasing the lifetime of minority carriers inside the twinned substrate. As a result, the voltage (Voc), current (Isc), and photoelectric conversion efficiency (Ncell) of the solar cell can be improved.

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

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.

Claims (10)

A solar cell manufacturing method comprising: providing a twinned substrate, wherein the twinned substrate is of a first type and having a first surface and a second surface; and doping a plurality of first impurities of the second type On the first surface of the twinned substrate; performing a first etching on the first surface of the twinned substrate; doping a second impurity of the second type into the twinned crystal that has been first etched Forming a first type region and a second type region on the first surface of the substrate; performing a second etching on the first surface of the twin crystal substrate; forming an electrical connection between the first type region and the second An electrode structure of the type region. The method for manufacturing a solar cell according to claim 1, wherein the step of performing the first etching on the first surface of the twinned substrate is performed for the first time on the second surface of the twinned substrate. Etching. The method for manufacturing a solar cell according to claim 2, wherein the step of performing the second etching on the first surface of the twinned substrate is performed a second time on the second surface of the twinned substrate. Etching. The method of manufacturing a solar cell according to claim 1, wherein the first impurity is of the same type as the second impurity. The method for manufacturing a solar cell according to claim 4, wherein the step of doping a plurality of first impurities of the second type on the first surface of the twin crystal substrate is at a first predetermined temperature Performing the step of doping a second impurity of the second type to the first surface of the twinned substrate that has been first etched, at a second predetermined temperature, and The first predetermined temperature is higher than the second predetermined temperature. The method for manufacturing a solar cell according to claim 5, wherein the step of performing the first etching on the first surface of the twinned substrate is performed for a first predetermined period of time, the The step of performing a second etching on the first surface is performed for a second predetermined period, and the first predetermined period is longer than the second predetermined period. The solar cell manufacturing method of claim 6, wherein the first predetermined period is about three times the second predetermined period. The method of manufacturing a solar cell according to claim 6, wherein the first type is a P type and the second type is an N type. The method for manufacturing a solar cell according to claim 8, wherein the step of doping a plurality of first impurities of the second type on the first surface of the twin crystal substrate is at a temperature of about 800 ° C to The twinned substrate was subjected to phosphorus impurity doping at about 820 ° C using phosphorus oxychloride. The method of manufacturing a solar cell according to claim 9, wherein the step of doping a second impurity of the second type onto the first surface of the twinned substrate that has been first etched, The twinned substrate is subjected to phosphorus impurity doping at a temperature of about 790 ° C to about 810 ° C using phosphorus oxychloride.