TWI469367B - Back-contacted photovoltaic cell - Google Patents

Description

Back contact solar cell

This invention relates to a back-contacted solar cell. In particular, it refers to a back contact solar cell that can avoid leakage of conductive vias.

The so-called back contact solar cell means that the positive electrode and the negative electrode of the solar cell are disposed on the back surface of the solar cell, so that the area of the front side of the solar cell can be increased, and the output current can be increased. In the process of back contact solar cells, metal wrap through (MWT) or emitter wrap through (EWT) techniques are generally used, which provide a plurality of through-light receiving fronts and The conduction hole on the back side is in the substrate. For a metallized cladding penetration technique, it is known to perform a screen printing process and a metallization process after the formation of the conductive holes, so that the bus bar is filled in the conduction hole, so that the bus bar is placed in the conduction hole. The bus electrode on the front side of the light is placed on the back of the solar cell. Since the bus electrode can be electrically connected to the finger electrode on the light receiving front surface, electrons can be transmitted from the finger electrode to the external load via the bus electrode through the electrical connection.

For the metallized cladding penetration technique, in order to avoid the phenomenon that the bus electrode in the conduction hole contacts the P-type and the N-type semiconductor layer at the same time, a short-circuit phenomenon occurs, and before the formation of the bus electrode of the conduction hole, a dopant diffusion process must be fully implemented. The side wall for heavily doping the conductive hole is such that the bus electrode only has to directly contact the second type semiconductor layer, for example, an N type semiconductor layer. However, due to the opening diameter of the conductive hole, for example: 60 μm, the diffusion rate of the dopant gas and the diffusion capacity of the dopant in the substrate are limited, so that after the diffusion process is finished, the re-doping on the sidewall of the conductive hole The junction depth of the interfering regions may still be insufficient, so that the bus electrodes located in the conducting holes may still contact the P-type and N-type semiconductor layers at the same time, resulting in a problem of leakage current.

Therefore, it is necessary to provide a structure of a back contact solar cell to solve the problem of leakage current and improve the shunt resistance of the sidewall of the conductive hole, thereby improving the reliability of the back contact solar cell.

It is an object of the present invention to provide a back contact solar cell which can solve the problem that the back contact solar cell is prone to leakage current in the conduction hole and improve the shunt resistance of the conduction hole sidewall.

In order to achieve the above object, in accordance with a preferred embodiment of the present invention, a back contact solar cell structure includes a substrate having a first conductivity type, and the substrate includes a light receiving front surface and a back surface; at least one finger An electrode is disposed on the front surface of the light receiving portion; a first doped region has a second conductivity type, the first doped region is located on the front surface of the light receiving surface and the back surface, wherein the first doping region has a first doping region a concentration; at least one conductive hole is disposed in the substrate, wherein the conductive hole penetrates the light receiving front surface and the back surface; at least one bus electrode is disposed on the back surface, and the bus electrode is filled in the conductive hole and electrically connected Connected to the finger electrode; a second doped region having a second conductivity type, the first doped region being located on a sidewall of the conductive hole, wherein the second doped region has a second doping concentration, And the second doping concentration is greater than the first doping concentration; and at least one contact electrode is disposed on the back surface and electrically insulated from the bus electrode.

The invention provides a second doping region which is located on one side wall of a conducting hole in the back contact solar cell structure, can solve the problem of leakage current, and improve the shunt resistance of the side wall of the conducting hole, thereby improving the back contact solar cell Reliability.

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

Please refer to FIG. 1 , which is a cross-sectional view showing a structure of a back contact solar cell according to a preferred embodiment of the present invention. As shown in FIG. 1, the back contact solar cell structure 1 comprises a substrate 101 having a first conductivity type, for example, a P type, and the substrate 101 includes a radiation-receiving front surface 101a. And a back surface 101b; at least one finger electrode 107 is disposed on the light receiving front surface 101a; and a first doping region 103a having a second conductivity type, for example, an N type, which has a first A doping concentration. The first doped region 103a is located on the light receiving front surface 101a and the back surface 101b; at least one conductive hole 105 is disposed in the substrate 101, wherein the conductive hole 105 penetrates the light receiving front surface 101a and the back surface 101b; The first bus electrode 109 is disposed on the back surface 101b, and the bus electrode 109 is filled in the conductive hole 105 and electrically connected to the finger electrode 107. The second doping region 103b has a second conductivity type. The second doping region 103b is located on a sidewall of the conductive hole 105, wherein the second doping region 103b has a second doping concentration, and the second doping concentration is greater than the first doping concentration; and at least one The contact electrode 111 is provided on the back surface 101b and is electrically insulated from the bus electrode 109.

Please refer to FIG. 2 to FIG. 9 . FIG. 2 to FIG. 9 are cross-sectional views showing a method for fabricating a back contact solar cell according to a preferred embodiment of the present invention. It is represented by the same symbol. It should be noted that the drawings are for illustrative purposes and are not mapped to the original dimensions.

As shown in FIG. 2, in the initial stage of the process, a substrate 101 is provided. The substrate 101 has a first conductivity type, for example, a P type, and the substrate 101 includes a light receiving front surface 101a and a back surface 101b. The 101 is used to receive sources of radiation, such as sunlight or other electromagnetic bands that are available for absorption by the semiconductor layer. The substrate 101 may be a single crystal germanium wafer or a polycrystalline germanium wafer, but is not limited thereto. Next, at least one conductive hole 105 located in the substrate 101 may be formed via a drilling technique, such as a laser drilling technique, wherein the conductive hole 105 penetrates the light receiving front surface 101a and the back surface 101b. As shown in FIG. 3, since the tantalum wafer is formed by slicing an ingot through a wire saw, a conventional wet etching process must be performed to remove the wire saw defect on the surface of the substrate 101. Next, a conventional surface roughening process is performed on the light-receiving front surface 101a and the back surface 101b of the substrate 101, and the surface roughening is known to reduce the radiation source in the light receiving process. The reflection phenomenon of the front surface 101a increases the photocurrent of the solar cell.

As shown in FIG. 4, next, a dopant source layer 10 having a second conductivity type, for example, an N type, is filled in the conductive hole 105 and covers a peripheral position 13 adjacent to the opening of the conductive hole 105. 13 may correspond to a location of a bus electrode 109 (not shown), and the dopant source layer 10 may be filled in by screen printing or the like, but is not limited thereto. Wherein, the dopant source layer 10 can be any phosphorus-containing slurry or liquid. Next, as shown in FIG. 5, a Phosphorus chloride oxide (POCl ₃ ) gas is supplied by a diffusion furnace, and a first doping region having a first doping concentration is formed on the light receiving front surface 101a and the back surface 101b. 103a, and it has a second conductivity type. While forming the first doping region 103a, the dopants located in the dopant source layer 10, such as phosphorus, thermally diffuse into the sidewalls of the conductive holes 105 and into the corresponding peripheral locations under the high temperature of the diffusion furnace. On the lower surface of the substrate 101, a second doping region 103b having a second conductivity type is formed. The second doped region 103b extends from the sidewall of the conductive via 105 to the back surface 101b of the substrate 101, thereby forming an L-type second doped region 103b. At this time, a PN junction is formed between the substrate 101 and the second doping region 103b, and the depth thereof is between 300 nm and 1000 nm. According to another preferred embodiment of the present invention, the second doped region 103b may be located only on the sidewall of the conductive via 105 and form at least a vertical PN junction with the substrate 101.

The second doping region 103b has a second doping concentration, for example, between 4E21 and 4E22 atoms/cm ³ (resistance value is between 40 and 50 Ω/sq), and the second doping concentration is greater than the first doping region. A doping concentration, for example, less than 4E21 atoms/cm ³ . Still as shown in Fig. 5, finally, the dopant source layer 10 is removed, and hydrofluoric acid (HF) is used to remove the phosphosilicate glass (PSG) on the surface of the substrate 101.

Referring to FIG. 6, an anti-reflective coating (ARC) 100 is formed on the light-receiving front surface 101a. The composition of the anti-reflective coating 100 may include tantalum nitride (SiN _x ) or titanium dioxide (TiO ₂ ), but is not limited thereto. It is known that the anti-reflective coating 100 can be formed in different ways, for example, chemical vapor deposition (CVD), low pressure CVD (LPCVD), plasma enhanced CVD (PECVD). , spray pyrolysis, spin coating, screen printing or other techniques well known in the art. Among them, the anti-reflective coating 100 has the use of anti-reflection and may also provide a surface passivation effect.

As shown in FIG. 7, at least one bus electrode (negative electrode) 109 is formed on the back surface 101b, and the bus electrode 109 is filled or filled in the conductive hole 105 in which the second doping region 103b has been formed, and The two doped regions 103b are in direct contact. As shown in FIG. 8, at least one finger electrode 107 is formed on the light receiving front surface 101a, and at least one contact electrode 111 is formed on the back surface 101b. The method of forming the bus electrode 109, the finger electrode 107, and the contact electrode 111 may be screen printing or other methods, such as inkjet printing, decal transfer, plating, and electroless plating. But it is not limited to this. Further, the metal paste component of the bus electrode 109, the finger electrode 107, and the contact electrode 111 may include silver, aluminum, or other low resistance compound, but is not limited thereto.

Finally, as shown in FIG. 9, the bus electrode 109 is in ohmic contact with the second doping region 103b through a fast firing furnace (FFF), and the silver, aluminum and the substrate 101 in the contact electrode 111 are formed. The ruthenium in the eutectic alloy produces a eutectic alloy which produces a backside field. The back surface electric field is known to reduce the probability of electrons and holes in the substrate 101, and to enhance the carrier. Collection rate. The insulating region 15 is formed by a laser or a cutting process, and the bus electrode 109 and the finger electrode 107 are electrically insulated from the contact electrode 111.

In summary, the present invention provides a back contact solar cell structure 1, as shown in FIG. 1, having a second doped region 103b along the sidewall of the conductive via 105 or further The sidewall of the self-conducting hole 105 extends horizontally to the back surface 101b of the substrate 101 under the bus electrode 109, so that the bus electrode 109 located in the conducting hole 105 can be prevented from simultaneously contacting the P-type and N-type semiconductor layers and the sidewall of the conductive hole 105 can be raised. The shunt resistor solves the phenomenon that leakage current is generated in the conduction hole 105 in the prior art, thereby improving the reliability of the back contact solar cell 1.

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

1‧‧‧Back contact solar cell structure

15‧‧‧Insulated area

100‧‧‧Anti-reflective coating

101‧‧‧Substrate

101a‧‧‧light front

101b‧‧‧Back

103a‧‧‧First doped area

103b‧‧‧Second doped area

105‧‧‧Transfer holes

107‧‧‧ finger electrodes

109‧‧‧Concurrent electrode

111‧‧‧Contact electrode

1 is a cross-sectional view showing the structure of a back contact solar cell in accordance with a preferred embodiment of the present invention.

2 to 9 are cross-sectional views showing a method of fabricating a back contact solar cell in accordance with a preferred embodiment of the present invention.

1. . . Back contact solar cell structure

13. . . Surrounding location

15. . . Insulating area

100. . . Anti-reflective coating

101. . . Substrate

101a. . . Receiving light front

101b. . . back

103a. . . First doped region

103b. . . Second doped region

105. . . Conductive hole

107. . . Finger electrode

109. . . Bus electrode

111. . . Contact electrode

Claims (10)

A back-contacted solar cell structure includes: a substrate having a first conductivity type, and the substrate includes a radiation-receiving front surface and a back surface; At least one finger electrode is disposed on the light receiving front surface; a first doped region has a second conductivity type, the first doping region is located on the light receiving front surface and the back surface, wherein the first doping region has a first a doping concentration; at least one conductive via is disposed in the substrate, wherein the conductive hole penetrates the light receiving front surface and the back surface; at least one bus bar is disposed on the back surface, and the confluence An electrode is filled in the conductive hole and electrically connected to the finger electrode; a second doped region has a second conductivity type, and the second doped region is located on a sidewall of the conductive hole, wherein the second doping The region has a second doping concentration, and the second doping concentration is greater than the first doping concentration; and at least one contact electrode is disposed on the back surface and electrically insulated from the bus electrode. The back contact solar cell structure of claim 1, wherein the second doped region forms a vertical PN junction with the substrate along the sidewall of the conductive hole. The back contact solar cell structure of claim 2, wherein the second doped region further extends horizontally from the sidewall of the conductive hole to the back surface of the substrate below the bus electrode, thereby forming a L-type second doped region. The back contact solar cell structure according to claim 1, wherein the second doping concentration is between 4E21 and 4E22 atoms/cm ³ , and the resistance of the second doping region is between 40 and 50 Ω. /sq. The back contact solar cell structure of claim 1, wherein the first doping concentration is less than 4E21 atoms/cm ³ . The back contact solar cell structure according to claim 1, wherein the first conductivity type is a P type, and the second conductivity type is an N type. The back contact solar cell structure of claim 1, wherein the bus electrode and the second doped region form an ohmic contact. The back contact solar cell structure of claim 1, wherein the contact electrode and the first doped region are sintered to form a backside field. The back contact solar cell structure of claim 1, wherein the first doped region has a junction depth of between 180 nm and 1000 nm. The back contact solar cell structure of claim 1, wherein the second doped region has a junction depth of between 300 nm and 3000 nm.