KR20140099981A - Solar cell - Google Patents

Abstract

A solar cell, according to an embodiment of the present invention, comprises a substrate; a first electrode formed on the substrate; a photoelectric conversion section which includes a conversion portion including a first conductive type semiconductor layer, an intrinsic semiconductor layer, and a second conductive type semiconductor layer sequentially formed on the first electrode; and a second electrode formed on the photoelectric conversion section, wherein the intrinsic semiconductor layer includes silicon-germanium (SiGe). The photoelectric conversion layer further includes a buffer layer located between the first conductive type semiconductor layer and the intrinsic semiconductor layer or between the intrinsic semiconductor layer and the second conductive type semiconductor layer. The buffer layer includes a first surface adjacent to the intrinsic semiconductor layer and a second surface opposite to the first surface. The hydrogen (H) contents of the first surface and the second surface of the buffer layer are different from each other.

Description

Solar cell {SOLAR CELL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell, and more particularly, to a solar cell including amorphous or microcrystalline silicon.

With the recent depletion of existing energy sources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar cells are attracting attention as a next-generation battery that converts solar energy into electric energy.

In such solar cells, various layers and electrodes can be fabricated by design. However, solar cell efficiency can be determined by the design of these various layers and electrodes. In order to commercialize the solar cell, it is required to overcome the low efficiency and to design the electrode area and various layers so as to maximize the efficiency of the solar cell.

The present invention provides a solar cell capable of maximizing efficiency.

A solar cell according to an embodiment of the present invention includes a substrate; A first electrode formed on the substrate; A photoelectric conversion section including a first conductivity type semiconductor layer, an intrinsic semiconductor layer and a second conductivity type semiconductor layer sequentially formed on the first electrode; And a second electrode formed on the photoelectric conversion portion, wherein the intrinsic semiconductor layer includes silicon germanium (SiGe). The photoelectric conversion unit may further include a buffer layer located between the first conductive semiconductor layer and the intrinsic semiconductor layer, and / or between the intrinsic semiconductor layer and the second conductive semiconductor layer. Wherein the buffer layer includes a first surface adjacent to the intrinsic semiconductor layer and a second surface opposite to the first surface, and the first surface and the second surface of the buffer layer have different hydrogen (H) contents .

According to this embodiment, a buffer layer in which the germanium content and the hydrogen content are controlled is located between the intrinsic semiconductor layer composed of silicon-germanium and the first and / or second conductivity type semiconductor layers. Thus, by controlling the content of germanium in the buffer layer, it is possible to prevent the defect caused by germanium by controlling the hydrogen content while eliminating the discontinuity of the energy band gap. Accordingly, the open-circuit voltage (Voc) and the fill factor can be improved by controlling the discontinuity, and the current density (Jsc) can be improved by controlling the defects. Therefore, the efficiency of the solar cell can be improved.

1 is a cross-sectional view illustrating a solar cell according to an embodiment of the present invention.
2 is a graph showing the germanium content of a portion of a second conversion portion of a solar cell according to an embodiment of the present invention.
3 is a view showing an energy band gap of a part of the second conversion portion of the solar cell according to the embodiment of the present invention.
4 is a graph showing the hydrogen content of the second conversion portion of the solar cell according to the embodiment of the present invention.
5 is a view schematically showing the microstructure according to the content of germanium.
6 is a photograph for explaining the microstructure according to the content of hydrogen.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it is needless to say that the present invention is not limited to these embodiments and can be modified into various forms.

In the drawings, the same reference numerals are used for the same or similar parts throughout the specification. In the drawings, the thickness, the width, and the like are enlarged or reduced in order to make the description more clear, and the thickness, width, etc. of the present invention are not limited to those shown in the drawings.

Wherever certain parts of the specification are referred to as "comprising ", the description does not exclude other parts and may include other parts, unless specifically stated otherwise. Also, when a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, it also includes the case where another portion is located in the middle as well as the other portion. When a portion of a layer, film, region, plate, or the like is referred to as being "directly on" another portion, it means that no other portion is located in the middle.

Hereinafter, a solar cell according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view illustrating a solar cell according to an embodiment of the present invention.

Referring to FIG. 1, a solar cell 100 according to the present embodiment includes a first substrate 10 (hereinafter referred to as a "front substrate") 10, A photoelectric conversion unit 30 and a second electrode 40, which are formed on the lower surface of the substrate 10, as shown in FIG. A sealing material 50 and a second substrate (hereinafter referred to as "rear substrate") 60 may be further formed on the second electrode 40. This will be explained in more detail.

The front substrate 10 may be made of a material capable of supporting the first and second electrodes 20 and 40 and the photoelectric conversion unit 30 having light transmittance and formed on the front substrate 10. For example, the transparent substrate may be a transparent substrate made of glass, polymer, or the like.

A first electrode 20 is formed on the front substrate 10 and the first electrode 20 is separated into a plurality of unit cells 30a, 30b, and 30c by the first separator 22 .

The first electrode 20 is located on one surface of the photoelectric conversion unit 30 between the front substrate 10 and the photoelectric conversion unit 30 and charges generated by the photoelectric conversion unit 30 flow. Although the first electrode 20 is illustrated as being in contact with the front substrate 10 and the photoelectric conversion unit 30, the present invention is not limited thereto. Thus, at least one other layer may be located between the first electrode 20 and the front substrate 10 and / or between the first electrode 20 and the photoelectric conversion unit 30. [

The surface of the first electrode 20 may have irregularities by texturing. As described above, when the surface roughness of the first electrode 20 is increased to form irregularities, the reflectance of the incident light can be reduced. Accordingly, the amount of light reaching the photoelectric conversion portion 30 can be increased, and the optical loss can be minimized.

The first separator 22 exposes the front substrate 10 between the plurality of first electrodes 20. The first separator 22 may have a long line shape, for example, so that the plurality of first separators 22 may have a stripe shape. This takes into consideration that it takes a long time to change the moving direction of the laser when forming the first separator 22 using a laser or the like. That is, in this embodiment, the first separator 22 has a line shape, so that the process time can be reduced in the process of forming the first separator 22. However, the present invention is not limited thereto. Accordingly, it is needless to say that the first separator 22 may have various shapes that can divide the first electrode 20 into various shapes.

In this embodiment, the first electrode 20 may include a transparent conductive material having optical transparency and electrical conductivity. For example, the first electrode 20 may be formed of zinc oxide (ZnO), indium tin oxide (ITO), tin oxide (SnO ₂ ), or a metal oxide and one or more impurities Boron (B), fluorine (F), aluminum (Al), etc.). However, the present invention is not limited thereto, and the first electrode 20 may be formed of various transparent conductive materials.

The first electrode 20 is formed by forming a layer made of a transparent conductive material on the front substrate 10 by a sputtering method, a chemical vapor deposition method, a spray method in which a sol-gel solution is sprayed, And by forming the separating portion 22. However, the present invention is not limited thereto. Accordingly, it is needless to say that a plurality of first electrodes 20 partitioned by the first separator 22 can be formed by various methods.

The photoelectric conversion portion 30 is located on the first electrode 20. The photoelectric conversion portion 30 is formed with a second separation portion 32 opened to connect the electrodes of the adjacent unit cells 30a, 30b, and 30c.

The second separator 32 separates the first electrode 20 of one of the unit cells 30a, 30b and 30c from the first separator 22 and the second electrode of the unit cell adjacent thereto (40) overlap each other. The second separator 32 is formed to expose the first electrode 20 and the second electrode 40 is filled in the second separator 32 when the second electrode 40 is formed, The first electrode 20 and the second electrode 40 of the unit cells 30a, 30b, and 30c are electrically connected.

The second separating portion 32 may have a long line shape, for example, so that the plurality of second separating portions 32 may have a stripe shape. This takes into consideration that it takes a long time to change the moving direction of the laser when forming the second separation part 22 by using a laser or the like. That is, in this embodiment, the second separator 32 has a line shape so that the process time can be reduced in the process of forming the second separator 32. However, the present invention is not limited thereto. Therefore, it is needless to say that the second separator 32 may have various shapes that can connect the first electrode 20 and the second electrode 40.

The photoelectric conversion section 30 may include a first conversion section 310 and a second conversion section 320 as shown in the enlargement circle of FIG. At this time, the first conversion portion 310 has a larger energy band gap than the second conversion portion 320. Accordingly, electrons and holes are generated by photoelectric conversion by absorbing a short wavelength in the first conversion portion 310, and electrons and holes are generated by photoelectric conversion by absorbing a long wavelength in the second conversion portion 320. Accordingly, both the long wavelength and the short wavelength can be used, and the efficiency of the solar cell 100 can be improved. For this purpose, the intrinsic semiconductor layer 314 of the first transducer portion 310 may comprise amorphous or microcrystalline silicon and the intrinsic semiconductor layer 324 of the second transducer portion 320 may comprise amorphous or fine Crystalline silicon. This will be explained in more detail.

The first conversion portion 310 includes a first conductivity type semiconductor layer 312 having a first conductivity type, an intrinsic semiconductor layer 314 formed on the first conductivity type semiconductor layer 312, And a second conductive semiconductor layer 316 formed on the first conductive semiconductor layer 314 and having a second conductive type. The second conversion portion 320 includes a first conductivity type semiconductor layer 322 having a first conductivity type, an intrinsic semiconductor layer 324 formed on the first conductivity type semiconductor layer 322, And a second conductive semiconductor layer 326 formed on the first conductive semiconductor layer 324 and having a second conductive type. The first buffer layer 327 is located between the first conductivity type semiconductor layer 322 and the intrinsic semiconductor layer 324 and the intrinsic semiconductor layer 324 and the second conductivity- The second buffer layer 329 may be located between the first buffer layer 326 and the second buffer layer 329.

The first conductivity type may be n-type or p-type, and the second conductivity type may be a p-type or n-type conductivity type opposite to the first conductivity type. Thus, the first and second conversion portions 310 and 320 of the photoelectric conversion portion 30 have a pin junction structure. In the present embodiment, the first and second conversion parts 310 and 320 having a pin junction structure constitute the photoelectric conversion part 30, but the present invention is not limited thereto.

The first conductivity type semiconductor layer 312 of the first conversion portion 310 may include microcrystalline or amorphous silicon having the first conductivity type impurity. At this time, the first conductive semiconductor layer 312 may include amorphous silicon to increase the band gap. And the first conductive semiconductor layer 312 may include carbon or oxygen so as to have a large bandgap. The impurity of the first conductivity type may include a p-type impurity including a Group 3 element such as boron (B), aluminum (Al), gallium (Ga), or indium (In).

Accordingly, the first conductive semiconductor layer 312 may be composed of amorphous silicon carbide or amorphous silicon oxide having a p-type impurity. In addition, hydrogen for passivating defects may be included at a certain ratio. However, the present invention is not limited thereto, and the first conductive semiconductor layer 312 may be formed of various materials.

The intrinsic semiconductor layer 314 of the first conversion portion 310 has an energy band gap larger than the energy band gap of the intrinsic semiconductor layer 324 of the second conversion portion 320. [ For example, the intrinsic semiconductor layer 314 of the first conversion portion 310 may include undoped microcrystals or amorphous silicon such as a separate impurity (e.g., germanium) or the like in order to have a relatively large energy bandgap can do. In this case, the intrinsic semiconductor layer 314 may include amorphous silicon to increase the energy band gap.

The second conductivity type semiconductor layer 316 of the first conversion portion 310 may include microcrystalline or amorphous silicon having a second conductivity type impurity. At this time, the second conductive semiconductor layer 316 may include amorphous silicon to further reduce the energy band gap. At this time, the impurity of the second conductivity type may include an n-type impurity including a Group 5 element such as phosphorus (P), arsenic (As), bismuth (Bi), and antimony (Sb).

Accordingly, the second conductivity type semiconductor layer 316 may be composed of microcrystalline silicon having an n-type impurity. In addition, hydrogen for passivating defects may be included at a certain ratio. However, the present invention is not limited thereto, and the second conductive semiconductor layer 316 may be formed of various materials.

The first conductivity type semiconductor layer 322 of the second conversion portion 320 may include microcrystalline or amorphous silicon having the first conductivity type impurity. At this time, the first conductive semiconductor layer 322 may include amorphous silicon to increase the energy band gap. And the first conductivity type semiconductor layer 322 may include carbon or oxygen so as to have a large energy bandgap. The impurity of the first conductivity type may include a p-type impurity including a Group 3 element such as boron (B), aluminum (Al), gallium (Ga), or indium (In).

Accordingly, the first conductive semiconductor layer 312 may be composed of amorphous silicon carbide or amorphous silicon oxide having a p-type impurity. In addition, hydrogen for passivating defects may be included at a certain ratio. However, the present invention is not limited thereto, and the first conductive semiconductor layer 322 may be formed of various materials.

The intrinsic semiconductor layer 324 of the second conversion portion 320 has an energy band gap smaller than the energy band gap of the intrinsic semiconductor layer 314 of the first conversion portion 310. In one example, the intrinsic semiconductor layer 324 of the second conversion portion 320 may comprise amorphous or microcrystalline silicon (i.e., amorphous or microcrystalline silicon-germanium) comprising germanium. The intrinsic semiconductor layer 324 of the second conversion portion 320 may include amorphous silicon-germanium in consideration of the energy bandgap difference between the first conversion portion 310 and the intrinsic semiconductor layer 314. When the content of germanium is increased in the intrinsic semiconductor layer 324, the energy band gap becomes smaller. If the intrinsic semiconductor layer 324 contains silicon-germanium, the energy band gap can be easily controlled by controlling the content of germanium.

The second conductivity type semiconductor layer 326 of the second conversion portion 320 may include microcrystalline or amorphous silicon having a second conductivity type impurity. At this time, the second conductivity type semiconductor layer 326 may include amorphous silicon to further reduce the energy band gap. At this time, the impurity of the second conductivity type may include an n-type impurity including a Group 5 element such as phosphorus (P), arsenic (As), bismuth (Bi), and antimony (Sb).

Accordingly, the second conductivity type semiconductor layer 326 may be composed of microcrystalline silicon having an n-type impurity. In addition, hydrogen for passivating defects may be included at a certain ratio. However, the present invention is not limited thereto, and the second conductivity type semiconductor layer 326 may be composed of various materials.

In this embodiment, the first buffer layer 327 is located between the first conductivity type semiconductor layer 322 and the intrinsic semiconductor layer 324 of the second conversion portion 320, A second buffer layer 329 is positioned between the layer 324 and the second conductivity type semiconductor layer 326. The first and second buffer layers 327 and 329 are located between the intrinsic semiconductor layer 324 including amorphous or microcrystalline silicon-germanium and the first and second conductivity type semiconductor layers 322 and 326, Thereby improving the characteristics of the semiconductor device 100.

The first and second buffer layers 327 and 329 of the present embodiment are formed of the same or similar material as the first and second conductivity type semiconductor layers 322 and 326 and the intrinsic semiconductor layer 324 Silicon material). Thus, stability can be maintained. In one example, the first and second buffer layers 327 and 329 include amorphous or microcrystalline silicon, and may further include germanium, hydrogen, and the like. At this time, the first and second buffer layers 327 and 329 may include intrinsic or undoped amorphous or microcrystalline silicon containing no p-type or n-type impurity. Accordingly, it is possible to minimize the discontinuity of the energy band gap that may be caused by the p-type or n-type impurity. The first and second buffer layers 327 may further include germanium, hydrogen, and the like.

In this embodiment, the characteristics of the solar cell 100 are improved by controlling the germanium content and the hydrogen content of the first and second buffer layers 327 and 329, which will be described in more detail with reference to FIGS. 2 to 6 do.

FIG. 2 is a graph showing the germanium content of a portion of the second conversion portion of the solar cell according to the embodiment of the present invention, and FIG. 3 is a graph showing the energy band gap of a portion of the second conversion portion of the solar cell according to the embodiment of the present invention Fig. 4 is a graph showing the hydrogen content of the second conversion portion of the solar cell according to the embodiment of the present invention.

Referring to FIG. 2 together with FIG. 1, a first buffer layer 327 formed between the first conductive semiconductor layer 322 and the intrinsic semiconductor layer 324 includes a first conductive semiconductor layer 322, The germanium content (for example, at%) is larger on the first surface adjacent to the intrinsic semiconductor layer 324 than on the first surface. Similarly, the second buffer layer 329 formed between the intrinsic semiconductor layer 324 and the second conductivity type semiconductor layer 326 may be more intrinsic to the intrinsic semiconductor layer 324 than the second surface adjacent to the second conductivity type semiconductor layer 326 (For example, at%) on the first surface adjacent to the first surface (i.e., the first surface). This is because the germanium content of the intrinsic semiconductor layer 324 is high and the germanium content of the first and second conductivity type semiconductor layers 322 and 326 is low.

For example, the germanium content of the intrinsic semiconductor layer 324 may be between 30 at% and 50 at%. The germanium content is determined so that the intrinsic semiconductor layer 324 can have an energy bandgap capable of efficiently using light of a long wavelength. In this case, the first surface of the first buffer layer 327 may have a germanium content (i.e., 30 at% to 50 at%) similar to the intrinsic semiconductor layer 324, and the second surface of the first buffer layer 327 may have a 0 Germanium content (e. G., 0at% to 3at%) of the germanium content. Similarly, the first side of the second buffer layer 327 may have a germanium content (i. E., 30at% to 50at%) similar to the intrinsic semiconductor layer 324 and the second side of the second buffer layer 329 may have a germanium content Germanium content (e. G., 0at% to 3at%) of the germanium content. However, the present invention is not limited thereto, and the germanium content of the intrinsic semiconductor layer 324 may have different values. At this time, the content of germanium on the first surface of the first and second buffer layers 327 and 329 also has a value similar to that of the germanium semiconductor layer 324.

The germanium content of the first buffer layer 327 may gradually increase from the second surface adjacent to the first conductivity type semiconductor layer 322 toward the first surface adjacent to the intrinsic semiconductor layer 324. Similarly, the germanium content of the second buffer layer 329 may gradually increase from the second surface adjacent to the second conductivity type semiconductor layer 326 toward the first surface adjacent to the intrinsic semiconductor layer 324. For example, the first and second buffer layers 329 may gradually increase the germanium content toward the intrinsic semiconductor layer 324 within a range of 0 at% to 50 at%.

As described above, when the content of germanium is increased, the energy bandgap is lowered. Accordingly, the energy band gaps of the first buffer layer 327, the intrinsic semiconductor layer 324, and the second buffer layer 329 have the same shape as shown in FIG. That is, in the first buffer layer 327, the energy band gap from the first surface adjacent to the first conductivity type semiconductor layer 322 to the second surface adjacent to the intrinsic semiconductor layer 324 gradually decreases. In the intrinsic semiconductor layer 324, a low energy band gap is maintained constant. In the second buffer layer 329, the energy band gap from the first surface adjacent to the intrinsic semiconductor layer 324 to the second surface adjacent to the second conductivity type semiconductor layer 326 gradually increases. Accordingly, even when the intrinsic semiconductor layer 324 is made of silicon-germanium, discontinuity of the energy band gap is not caused, so that carriers such as electrons or holes generated by photoelectric conversion can be easily moved.

At this time, in this embodiment, the hydrogen content of the first and second buffer layers 327 and 329 can be controlled to prevent a problem caused by the germanium content, thereby improving the characteristics of the solar cell 100. This will be described in more detail with reference to FIG. 4 and FIG. 5 and FIG. FIG. 5 is a schematic view showing the microstructure according to the content of germanium, and FIG. 6 is a photograph for explaining the microstructure according to the content of hydrogen.

Referring to FIG. 4, the first buffer layer 327 may have a hydrogen content (for example, at%) on the first surface adjacent to the intrinsic semiconductor layer 324 rather than the second surface adjacent to the first conductivity type semiconductor layer 322 It is bigger. Similarly, the second buffer layer 329 is greater in hydrogen content (for example, at%) on the first surface adjacent to the intrinsic semiconductor layer 324 than on the second surface adjacent to the second conductivity type semiconductor layer 326 . And the hydrogen content of the first buffer layer 327 may gradually increase from the second surface adjacent to the first conductivity type semiconductor layer 322 toward the first surface adjacent to the intrinsic semiconductor layer 324. [ Similarly, the germanium content of the second buffer layer 329 may gradually increase from the second surface adjacent to the second conductivity type semiconductor layer 326 toward the first surface adjacent to the intrinsic semiconductor layer 324. This considers that the germanium content in the first and second buffer layers 327 and 329 gradually increases toward the first surface adjacent to the intrinsic semiconductor layer 324.

In other words, germanium differs in atomic size from silicon, so increasing the content of germanium increases dangling bond defects. As shown in FIG. 5 (a), when the content of germanium is small, dangling bonds are small, whereas when the content of germanium is increased as shown in FIG. 5 (b), dangling bonds are also increased.

Accordingly, in the present embodiment, the content of hydrogen is also increased in a portion where the content of germanium is large, so that dangling bonds by germanium are effectively passivated. Thus, generation of defects can be minimized. However, if the content of hydrogen excessively increases, the internal stress may increase and other types of defects such as microcracks may increase, and in this case, the efficiency again drops. That is, as shown in FIG. 6 (a), microcracks did not occur when the hydrogen content was appropriate, but when the hydrogen content was excessive as shown in FIG. 6 (b), microcracks occurred in the vertical direction . Therefore, the hydrogen content of the first and second buffer layers 327 and 329 must be appropriately controlled in consideration of the germanium content of the first and second buffer layers 327 and 329.

For example, the germanium content of the first buffer layer 327 on the second surface (that is, the surface adjacent to the first conductivity type semiconductor layer 322, the surface opposite to the first surface) is 0 at% to 3 at% The hydrogen content on the second surface of the first buffer layer 327 is 8 at% to 13 (%) when the germanium content of the first surface (that is, the surface adjacent to the intrinsic semiconductor layer 324) at% and the hydrogen content on the first side may be from 15 at% to 20 at%. The hydrogen content can be gradually increased in the range between 8 at% and 20 at% while being directed from the second surface of the first buffer layer 327 to the first surface.

Similarly, the germanium content in the second surface (i.e., the surface adjacent to the first conductivity type semiconductor layer 322) of the second buffer layer 329 is 0 at% to 3 at% and the first surface The hydrogen content on the second surface of the second buffer layer 329 may be 8 at% to 13 at% when the germanium content of the second buffer layer 329 is 30 at% to 50 at% The hydrogen content on one side may be from 15 at% to 20 at%. The hydrogen content may gradually increase in a range between 8 at% and 20 at% while being directed from the second surface of the second buffer layer 329 to the first surface.

The hydrogen content of the first and second buffer layers 327 and 329 is determined to be within a range capable of minimizing dangling bond defects due to germanium and preventing the occurrence of another defect due to internal stress. Therefore, the hydrogen content of the first and second buffer layers 327 and 329 may vary according to the change in the germanium content in the intrinsic semiconductor layer 324, and thus the change in the first and second buffer layers 327 and 329 Of course.

Here, the hydrogen content can be measured by using a secondary ion mass spectrometer (SIMS), elastic recoil detection (ERD), nuclear reaction analysis (NRA), Fourier-transformed infrared transmittance ) And the like.

The first buffer layer 327 located between the p-type first conductivity type semiconductor layer 322 and the i-type intrinsic semiconductor layer 324 has an i-type intrinsic semiconductor layer 324 and an n-type second conductivity type semiconductor layer 324, May be less than the thickness of the second buffer layer 329 located between the first buffer layer 326 and the second buffer layer 329. This is to make the carrier movement more smooth considering the energy band gap. For example, the first buffer layer 327 may have a thickness of 5 nm to 30 nm, and the second buffer layer 329 may have a thickness of 50 nm to 150 nm. This thickness takes into account the energy band gap, process time, and material cost. However, the present invention is not limited thereto, and it goes without saying that the thicknesses of the first and second buffer layers 327 and 329 may have different ranges.

The surface of the plurality of layers constituting the photoelectric conversion portion 30 may have irregularities corresponding to the irregularities of the first electrode 20. [ If the surface roughness of the layers constituting the photoelectric conversion unit 30 is increased to form irregularities, the reflectivity of the incident light can be reduced. Accordingly, the amount of light reaching the photoelectric conversion portion 30 can be increased, and the optical loss can be minimized.

The third separator 42 is formed in the photoelectric conversion unit 30. The third separator 42 forms the second electrode 40 and then the photoelectric conversion unit 30 and the second electrode 40, As shown in FIG. Therefore, the third separator 42 will be described in more detail after the second electrode 40 is described.

The second electrode 40 is positioned on the first electrode 20 and the photoelectric conversion portion 30. [ Specifically, the second electrode 40 fills the second separator 32 on the first electrode 20 and the photoelectric converter 30, and the third separator 42 separates the unit cells 30a, 30b, 30c ).

The second electrode 40 is disposed on the other surface of the photoelectric conversion portion 30 between the photoelectric conversion portion 30 and the sealing material 50 (or the rear substrate 60) Charge flows. Although the second electrode 40 is illustrated as being formed in contact with the photoelectric conversion unit 30 and the sealing material 50, the present invention is not limited thereto. Accordingly, at least one other layer may be located between the photoelectric conversion unit 30 and the second electrode 40 and / or between the second electrode 40 and the sealant 50. For example, a transparent electrode layer (not shown) or the like may be further formed between the photoelectric conversion portion 30 and the second electrode 40 to improve the bonding property.

The third separator 42 is formed to expose the first electrode 20 between the plurality of second electrodes 40. That is, the third separator 42 is formed to penetrate through the photoelectric conversion unit 30 and the second electrode 40 and serves to separate them corresponding to the unit cells 30a, 30b, and 30c. The third separator 42 may have a long line shape, for example, so that the plurality of third separators 42 may have a stripe shape. This is considered to take a long time when changing the moving direction of the laser when forming the third separator 42 by using a laser or the like. That is, in this embodiment, the third separator 42 has a line shape so that the process time can be reduced in the process of forming the third separator 42. However, the present invention is not limited thereto. Accordingly, it is needless to say that the third separator 42 may have various shapes that can divide the second electrode 40 into various shapes.

The second electrode 40 may include a material having a lower light transmittance than the first electrode 20 and having excellent conductivity. The second electrode 40 may have a better reflection characteristic than the first electrode 20. Then, light incident through the front substrate 10 can be reflected and reused.

The second electrode 40 may include a metal material to satisfy such a characteristic. In one example, the second electrode 40 may comprise a single or multiple layers comprising silver, aluminum, gold, nickel, chromium, titanium, palladium, or alloys thereof.

The second electrode 40 may be formed by forming a layer made of a metallic material by various methods such as sputtering, screen printing, inkjet, dispensing, and plating, and then forming a third separator 42 ). ≪ / RTI > However, the present invention is not limited thereto. Therefore, it is needless to say that a plurality of second electrodes 40 partitioned by the third separator 42 can be formed by various methods.

By this structure, a plurality of unit cells 30a, 30b, and 30c are connected in series with each other. However, the present invention is not limited thereto, and a plurality of unit cells 30a, 30b, and 30c may be connected in various ways such as parallel, serial, and so on.

The sealing member 50 and the rear substrate 60 may be further disposed on the first electrode 20, the photoelectric conversion unit 30, and the second electrode 40.

The sealing material 50 is adhered by lamination to cut off moisture and oxygen which may adversely affect the solar cell 100, so that the respective elements of the solar cell 100 can be chemically bonded. As the sealing material 50, ethylene-vinyl acetate copolymer resin (EVA), polyvinyl butyral (PVB), silicon resin, ester resin, olefin resin and the like can be used. However, the present invention is not limited thereto. Therefore, the sealing material 50 may be formed by a method other than lamination using various other materials.

The rear substrate 60 serves to support the photoelectric conversion unit 30 and protect it from an external impact. The rear substrate 60 may have the form of a substrate, a film, a sheet, or the like, and may be made of glass, polymer, or the like. However, the present invention is not limited thereto, and it is also possible that the rear substrate 60 is not provided separately.

As described above, according to the present embodiment, a first buffer layer 327 having controlled germanium and hydrogen content is formed between the intrinsic semiconductor layer 324 and the first conductivity type semiconductor layer 322 of the second conversion portion 320 composed of silicon- ). As described above, by controlling the content of germanium in the first buffer layer 327, it is possible to control the hydrogen content while eliminating the discontinuity of the energy band gap, thereby preventing defects caused by germanium. Similarly, a second buffer layer 329 in which germanium and hydrogen content are controlled is positioned between the intrinsic semiconductor layer 324 and the second conductivity type semiconductor layer 326 of the second conversion portion 320 composed of silicon-germanium. As described above, by controlling the content of germanium in the second buffer layer 329, it is possible to prevent the defect caused by germanium by controlling the hydrogen content while eliminating the discontinuity of the energy band gap. Accordingly, the open-circuit voltage (Voc) and the fill factor can be improved by controlling the discontinuity, and the current density (Jsc) can be improved by controlling the defects. Therefore, the efficiency of the solar cell 100 can be improved.

In this embodiment, both the first and second buffer layers 327 and 329 are provided, and the germanium and hydrogen contents in the first and second buffer layers 327 and 329 are controlled, respectively. However, the present invention is not limited thereto. Only one of the first and second buffer layers 329 may be formed, or any one of the germanium and the hydrogen content may be controlled. In addition, although the photoelectric conversion unit 30 includes the first and second conversion units 310 and 320, it is also possible to include only the second conversion unit 320. Alternatively, in the case where the intrinsic semiconductor layer of another conversion portion includes germanium, it is also possible to include other conversion portions other than the first and second conversion portions 310 and 320, The corresponding first and second buffer layers 327 and 329 may be located respectively.

Hereinafter, the present invention will be described in more detail with reference to experimental examples of the present invention. The following experimental examples are presented for the purpose of illustration of the present invention, but the present invention is not limited thereto.

Experimental Example

A solar cell was manufactured by sequentially forming a first electrode, a photoelectric conversion portion, and a second electrode on a front substrate made of a transparent substrate, and then placing a sealing material and a rear substrate portion thereon.

At this time, the photoelectric conversion portion includes a first conversion portion including an intrinsic semiconductor layer composed of amorphous silicon and a second conversion portion including an intrinsic semiconductor layer composed of amorphous silicon-germanium. At this time, the first buffer layer was located on one side of the intrinsic semiconductor layer and the second buffer layer was located on the other side. The germanium content of the intrinsic semiconductor layer was 40 at%, and the content of germanium in the first and second buffer layers increased from 0 at% to 40 at% while being directed from the surface located away from the intrinsic semiconductor layer to the surface adjacent to the intrinsic semiconductor layer. The hydrogen content of the intrinsic semiconductor layer was 8 at%, and the content of germanium in the first and second buffer layers increased from 8 at% to 20 at% while being directed from the surface far from the intrinsic semiconductor layer toward the surface adjacent to the intrinsic semiconductor layer .

Comparative Example

A solar cell was fabricated in the same manner as in Experimental Example 1 except that the hydrogen content of the first and second buffer layers was uniformly set to 8 at% as a whole.

The efficiency, current density, open-circuit voltage and fill density of the solar cells according to Experimental Examples and Comparative Examples were measured and the results are shown in Table 1 below.

Experimental Example Comparative Example efficiency[%] 10.0 9.6 Current density [mA / cm ² ] 7.75 7.60 Open-circuit voltage [V] 1.672 1.671 Filling density [%] 0.770 0.756

Referring to Table 1, the solar cell according to the experimental example has a current density of 0.05 mA / cm ² , an open voltage of 0.001 V, and a fill density of 0.014% larger than the solar cell according to the comparative example. Accordingly, the solar cell according to the experimental example has an excellent efficiency of 0.4% as compared with the solar cell according to the comparative example. Thus, it can be seen that the solar cell according to the experimental example can improve the current density, the open-circuit voltage, and the filling density, thereby improving the efficiency.

Features, structures, effects and the like according to the above-described embodiments are included in at least one embodiment of the present invention, and the present invention is not limited to only one embodiment. Further, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

100: Solar cell
10: front substrate
20: first electrode
30: Photoelectric conversion section
40: second electrode
50: Seal material
60: rear substrate
310: first conversion portion
312: first conductivity type semiconductor layer
314: intrinsic semiconductor layer
316: a second conductivity type semiconductor layer
320: second conversion portion
322: a first conductivity type semiconductor layer
324: intrinsic semiconductor layer
326: second conductivity type semiconductor layer
327: first buffer layer
329: Second buffer layer

Claims (20)

Board;
A first electrode formed on the substrate;
A photoelectric conversion portion including a conversion portion including a first conductivity type semiconductor layer, an intrinsic semiconductor layer, and a second conductivity type semiconductor layer sequentially formed on the first electrode; And
A second electrode formed on the photoelectric conversion unit,
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Wherein the intrinsic semiconductor layer includes silicon germanium (SiGe)
Wherein the photoelectric conversion portion further comprises a buffer layer located in at least one of the first conductivity type semiconductor layer and the intrinsic semiconductor layer and between the intrinsic semiconductor layer and the second conductivity type semiconductor layer,
Wherein the buffer layer includes a first surface adjacent to the intrinsic semiconductor layer and a second surface opposite to the first surface,
Wherein the first surface and the second surface of the buffer layer have different hydrogen (H) contents. The method according to claim 1,
Wherein the buffer layer gradually increases the hydrogen content from the second surface to the first surface. 3. The method of claim 2,
And the hydrogen content of the buffer layer is 8 at% to 20 at%. 3. The method of claim 2,
Wherein the hydrogen content in the second surface of the buffer layer is 8 at% to 13 at%, and the hydrogen content in the first surface of the buffer layer is 15 at% to 20 at%. The method according to claim 1,
Wherein the first surface and the second surface of the buffer layer have different germanium (Ge) contents. 6. The method of claim 5,
Wherein the buffer layer gradually increases the germanium content from the second surface to the first surface. 6. The method of claim 5,
And the germanium content of the buffer layer is 0 at% to 50 at%. 6. The method of claim 5,
Wherein the germanium content in the second surface of the buffer layer is 0 at% to 3 at%, and the germanium content in the first surface of the buffer layer is 30 at% to 50 at%. The method according to claim 1,
Wherein the buffer layer is made of a silicon material. 10. The method of claim 9,
Wherein the buffer layer comprises intrinsic amorphous or microcrystalline silicon. The method according to claim 1,
Wherein the buffer layer comprises: a first buffer layer located between the first conductivity type semiconductor layer and the intrinsic semiconductor layer; And a second buffer layer positioned between the intrinsic semiconductor layer and the second conductive type semiconductor layer,
The hydrogen content of the first buffer layer increases from the second surface of the first buffer layer adjacent to the first conductive semiconductor layer toward the first surface of the first buffer layer adjacent to the intrinsic semiconductor layer,
Wherein the hydrogen content of the second buffer layer increases from a second surface of the second buffer layer adjacent to the second conductive semiconductor layer to a first surface of the second buffer layer adjacent to the intrinsic semiconductor layer. 12. The method of claim 11,
Wherein the first buffer layer gradually increases in germanium content from the second surface of the first buffer layer to the first surface of the first buffer layer,
Wherein the second buffer layer gradually increases in germanium content from the second surface of the second buffer layer to the first surface of the second buffer layer. 12. The method of claim 11,
Wherein the hydrogen content of the first and second buffer layers is 8 at% to 20 at%
Wherein the germanium content of the first and second buffer layers is 0 at% to 50 at%. 12. The method of claim 11,
Wherein the hydrogen content in the second surface of the first and second buffer layers is 8 at% to 13 at%, the hydrogen content in the first surface of the first and second buffer layers is 15 at% to 20 at% Lt;
Wherein the germanium content in the second surface of the first and second buffer layers is 0 at% to 3 at% and the germanium content in the first surface of the first and second buffer layers is 30 at% to 50 at% battery. 12. The method of claim 11,
Wherein the first conductivity type semiconductor layer has a p-type conductivity,
Wherein the second conductivity type semiconductor layer has an n-type conductivity,
Wherein a thickness of the first buffer layer is smaller than a thickness of the second buffer layer. 16. The method of claim 15,
Wherein the first buffer layer has a thickness of 5 nm to 30 nm,
And the thickness of the second buffer layer is 50 nm to 150 nm. 12. The method of claim 11,
Wherein at least one of the first and second buffer layers is made of a silicon material. 18. The method of claim 17,
Wherein at least one of the first and second buffer layers comprises intrinsic amorphous or microcrystalline silicon. The method according to claim 1,
Wherein the first conductivity type semiconductor layer includes amorphous or microcrystalline silicon, and further comprises at least one of oxygen and carbon. The method according to claim 1,
Wherein the photoelectric conversion unit further includes a separate conversion unit positioned between the first electrode and the conversion unit,
Wherein the intrinsic semiconductor layer of the separate conversion portion includes amorphous or microcrystalline silicon.

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