KR101640815B1 - Thin film solar cell and method for fabricaitng the same - Google Patents

Abstract

The present invention relates to a thin film solar cell and a method of manufacturing the same, wherein the thin film solar cell according to the present invention comprises: a p-type front electrode formed on a transparent substrate; A semiconductor layer formed on the front electrode and composed of a p-type semiconductor layer, an i-type semiconductor layer, and an n-type semiconductor layer; A rear reflective layer formed on the semiconductor layer; And a rear electrode formed on the rear reflective layer. The method of fabricating a thin film solar cell according to the present invention includes the steps of: forming a p-type front electrode on a transparent substrate; Forming a semiconductor layer composed of a p-type semiconductor layer, an i-type semiconductor layer, and an n-type semiconductor layer on the front electrode; Forming a rear reflective layer on the semiconductor layer; And forming a rear electrode on the rear reflective layer.

A front electrode, a semiconductor layer, a rear reflective layer, a Schottky barrier,

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a thin film solar cell,

The present invention relates to a solar cell, and more particularly, to a thin film solar cell capable of preventing a reduction in efficiency due to a shottkey barrier formed at a junction between an n-type transparent electrode layer and a p- And a manufacturing method thereof.

In general, solar cells are a core element of solar power generation that converts sunlight directly into electricity, and its application range from space to home is very wide.

This solar cell is basically a diode composed of a pn junction and its operation principle will be described as follows.

When sunlight having an energy larger than the energy bandgap of the semiconductor is incident on the pn junction of the solar cell, an electron-hole pair is generated. The electric field formed in the pn junction of the electrons- , The photovoltaic power is generated between the pn. At this time, when both ends of the solar cell are connected to each other, a current flows to generate power.

Solar cells are variously classified according to materials used as a light absorbing layer, and silicon type solar cells using silicon as a light absorbing layer are typical.

The silicon-based solar cell is classified into a substrate-type (single crystal, poly crystal) solar cell and a thin film (amorphous, poly crystal) solar cell.

Other types of solar cells include compound thin film solar cells of CdTe, CIS (CuInSe ₂ ), III-V solar cells, dye-sensitized solar cells, and organic solar cells.

Monocrystalline silicon substrate type solar cells have the advantage of higher conversion efficiency than other types of solar cells, but they have a disadvantage of high manufacturing cost due to the use of single crystal silicon wafers.

Polycrystalline silicon substrate type solar cells can also be less expensive than monocrystalline silicon substrate type solar cells. However, since the point of making solar cells from bulk raw materials is not different from monocrystalline silicon substrate type solar cells, the raw material cost is high and the process itself There is a limit to the reduction of manufacturing cost due to the complexity.

As a method for solving the problems of such a substrate type solar cell, a thin film type silicon solar cell which is capable of significantly lowering a manufacturing cost by using a thin film of silicon as a light absorbing layer on a substrate such as glass is attracting attention.

Thin-film silicon solar cells can be manufactured with a thickness much smaller than the thickness of a substrate-type silicon solar cell.

Amorphous silicon thin film type solar cell was developed for the first time among thin film type silicon solar cells and started to be widely used in residential area. Amorphous silicon solar cells can be formed by chemical vapor deposition (CVD), which is suitable for mass production and low cost. However, instead of dangling bond ), There is a problem that the conversion efficiency is too low as compared with the substrate type silicon solar cell.

In addition, the amorphous silicon solar cell has a problem that the lifetime is comparatively short and deterioration phenomenon in which efficiency is reduced when used.

In order to solve the problems of such an amorphous silicon solar cell, it is a solar cell having a so-called tandem structure in which a plurality of cells having different optical band gaps are stacked in two or three stages. The silicon solar cell having a tandem structure can improve the photoelectric conversion efficiency by receiving a wide optical spectrum region by dividing it, and it is possible to prevent the deterioration of the photoelectric conversion characteristic due to the photo deterioration phenomenon to some extent.

As a material of the transparent conductive film used as a lower layer in the fabrication of a thin film solar cell having a two or three layer stacked structure having such characteristics, it is preferable to dope a substance which can be made into n-type into zinc oxide (ZnO) A technique has been proposed which utilizes a substance having high transmittance so that light can be incident on the absorption layer as much as possible.

A conventional thin film solar cell using zinc oxide (ZnO) as a transparent conductive film and a manufacturing method thereof will be described with reference to FIGS. 1 and 2. FIG.

1 is a schematic cross-sectional view of a thin film solar cell structure using zinc oxide (ZnO) according to the prior art as a transparent conductive film.

2 is a graph schematically showing an energy band diagram at an interface between a transparent conductive film (TCO) composed of zinc oxide and a p-type silicon layer according to the prior art.

1, a conventional thin film solar cell includes a front electrode 13 formed on a transparent substrate 11, and an amorphous silicon (a-Si: H And a back electrode 19 laminated on the semiconductor layer 15. The semiconductor layer 15 is formed on the semiconductor layer 15,

Here, the front electrode 13 is formed of a transparent conductive oxide (TCO) thin film for transmitting sunlight incident from the transparent substrate 11 side. At this time, zinc oxide (ZnO), which is an n-type material, is mainly used for the transparent conductive oxide thin film.

The semiconductor layer 15 is formed by sequentially stacking a p-type semiconductor layer 15p, an intrinsic semiconductor layer 15i and an n-type semiconductor layer 15n from the front electrode 13, . Here, the intrinsic semiconductor layer 15i serves as a light absorbing layer for increasing the efficiency of the thin film solar cell, and may be referred to as an active layer.

The rear electrode 17 is formed by depositing a transparent conductive oxide (TCO) thin film in the same manner as the front electrode 13.

In a conventional thin film solar cell having such a structure, zinc oxide (ZnO) used as a transparent conductive oxide thin film as a front electrode is doped with aluminum (Al) or germanium (Ga) Physical properties are n-type.

Therefore, in the thin film solar cell according to the prior art, as shown in FIG. 2, by using n-type zinc oxide (ZnO) as the transparent conductive oxide thin film, The bending of the energy band gap is severely caused by the schottkey barrier.

This increases the height of the barrier layer when the hole is moved from the p-type semiconductor layer 15p to the front electrode 13, which is a transparent conductive oxide (TCO) thin film, Occurs.

Therefore, due to such a problem, the front electrode made of the n-type zinc oxide (ZnO) material contacts with the p-type semiconductor layer, thereby increasing the internal resistance and causing a decrease in light efficiency.

SUMMARY OF THE INVENTION The present invention has been made in order to solve all the problems of the prior art described above, and it is an object of the present invention to provide a p-type semiconductor light- a thin film solar cell capable of preventing a reduction in efficiency due to a Schottky barrier by lowering the height of a shottkey barrier, and a method of manufacturing the same.

According to an aspect of the present invention, there is provided a thin film solar cell comprising: a p-type front electrode formed on a transparent substrate; A semiconductor layer formed on the front electrode and composed of a p-type semiconductor layer, an i-type semiconductor layer, and an n-type semiconductor layer; A rear reflective layer formed on the semiconductor layer; And a rear electrode formed on the rear reflective layer.

According to an aspect of the present invention, there is provided a method of fabricating a thin film solar cell including: forming a p-type front electrode on a transparent substrate; Forming a semiconductor layer composed of a p-type semiconductor layer, an i-type semiconductor layer, and an n-type semiconductor layer on the front electrode; Forming a rear reflective layer on the semiconductor layer; And forming a rear electrode on the rear reflective layer.

The thin film solar cell according to the present invention and its manufacturing method have the following effects.

A thin film solar cell and a method of manufacturing the same according to the present invention are characterized by using transparent p-type zinc oxide (ZnO) doped with copper as a front electrode, thereby forming a schottky barrier with energy By decreasing the bending of the bandgap, the collection ratio of the holes can be improved and the photoelectric efficiency can be increased.

The thin film solar cell and the method of manufacturing the same according to the present invention can be fabricated by using a transparent p-type zinc oxide (ZnO) doped with copper as a front electrode to increase the photoelectric efficiency, The present invention is also applicable to a thin film transistor (TFT)

In addition, the thin film solar cell according to the present invention and the manufacturing method thereof can increase efficiency by back reflection by using a back-reflector composed of zinc oxide on the n-type semiconductor layer.

Below. The structure of a thin film solar cell according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

3 is a schematic cross-sectional view of a thin film solar cell structure using p-type zinc oxide (ZnO) according to the present invention as a transparent conductive oxide thin film (TCO).

4 is a graph schematically showing an energy band diagram at an interface between a transparent conductive oxide thin film (TCO) composed of p-type zinc oxide and a p-type semiconductor layer according to the present invention.

3, the thin-film solar cell according to the present invention includes a front electrode 103 formed on a transparent substrate 11, an amorphous silicon (a-Si: H And a backside reflective layer 107 and a backside electrode 109 stacked on the semiconductor layer 105. The backside reflective layer 107 is formed on the semiconductor layer 105,

Here, the front electrode 103 is formed of a transparent conductive oxide (TCO) thin film for transmitting sunlight incident on the transparent substrate 101 side. In this case, p-type zinc oxide (ZnO) doped with copper may be used for the transparent conductive oxide thin film, or ZnO: B, ZnO: Al, SnO ₂ : F, (Transparent Conductive Oxide) thin film such as ITO, and is formed to a thickness of about 700 nm to 2000 nm. In particular, for the transparent conductive oxide thin film, any material may be used as long as it is a transparent conductive oxide material having a p-type property in addition to p-type zinc oxide (ZnO). At this time, the front electrode 103 is made of p-type zinc oxide (ZnO) containing 1 to 5% of copper (Cu) dopant.

On the surface of the front electrode 103, a plurality of pointed irregularities 103a are formed. At this time, the surface of the transparent substrate 101 may be textured in order to improve the efficiency of the solar cell. Here, texturing is a technique for preventing a phenomenon of deterioration of characteristics due to optical loss due to reflection of light incident on a substrate surface of a solar cell, and is a method of roughing the surface of a substrate used in a solar cell, 101 is a pattern of unevenness 103a on the surface. When the surface of the transparent substrate is roughened by the texture ring, the reflected light is reflected again, thereby reducing the reflectance of the incident light. Thus, the optical trapping amount is increased and the optical loss is reduced.

The semiconductor layer 105 is formed by sequentially stacking a p-type semiconductor layer 105p, an intrinsic semiconductor layer 105i and an n-type semiconductor layer 105n from the front electrode 103, . Here, the intrinsic semiconductor layer 105i serves as a light absorbing layer for increasing the efficiency of the thin film solar cell, and may be referred to as an active layer.

At this time, it is preferable that the solar cell is made incident on the i-type semiconductor layer through the p-type semiconductor layer in view of the efficiency of the solar cell. This is due to the difference in drift mobility between the electrons and holes generated by the sunlight. Since the hole mobility of holes is lower than that of electrons, in order to maximize the efficiency of collection of carriers by the sunlight, type semiconductor layer at the interface between the p-type semiconductor layer and the i-type semiconductor layer to minimize the movement distance of the holes.

In the present invention, the i-type semiconductor layer is not necessarily doped between the p-type semiconductor layer and the n-type semiconductor layer. However, the present invention is not limited thereto, It is also possible to arrange an amorphous silicon layer which is insulative (i.e., low in electrical conductivity). For example, it is also possible to arrange a semiconductor layer in which a p-type semiconductor layer and an n-type semiconductor layer are high-doped and an n-type or p-type impurity is doped low therebetween.

The n-type backside reflective layer 107 is made of n-type zinc oxide (ZnO) and functions to increase the efficiency by back reflection. At this time, the n-type back reflective layer 107 in addition to the n-type zinc oxide (ZnO), ZnO: B, ZnO: Al, SnO _2: F, ITO, such as a transparent conductive oxide; formed in a (TCO Transparent Conductive Oxide) thin film, And is formed to a thickness of about 700 nm to 2000 nm.

The rear electrode 109 is formed by depositing a transparent conductive oxide (TCO) thin film or a metal material in the same manner as the front electrode 103.

As described above, n-type zinc oxide (ZnO) is doped with copper (Cu) to form a transparent p-type front electrode 103, so that the n-type front electrode 103 and the p- The height of the Schottky barrier at the interface of the layer 105p decreases, that is, the bending of the energy band gap decreases, thereby increasing the collection ratio of the holes, thereby increasing the photoelectric efficiency.

Further, since the photoelectric efficiency is increased by using p-type zinc oxide (ZnO) doped with copper (Cu) as the front electrode 103, it can be applied to an LED or a thin film transistor (TFT) device having a high mobility .

In addition, a back-reflector 107 made of n-type zinc oxide is deposited on the n-type semiconductor layer 105n to increase the efficiency by back reflection.

A method of manufacturing a thin film solar cell according to the present invention having the above structure will be described with reference to FIGS. 5A to 5D.

5A to 5D are cross-sectional views illustrating a manufacturing process of a thin film solar cell according to the present invention.

5A, a p-type front electrode 103 is formed of a transparent conductive oxide (TCO) material for transmitting sunlight incident on the transparent substrate 101 side on the transparent substrate 101 . As the transparent conductive oxide, p-type zinc oxide (ZnO) doped with copper may be used or ZnO: B, ZnO: Al, SnO ₂ : F, ITO (Transparent Conductive Oxide) thin film, and is formed to a thickness of about 700 nm to 2000 nm. In particular, as the transparent conductive oxide material, any material may be used as long as it is a transparent conductive oxide material having a p-type property other than p-type zinc oxide (ZnO). At this time, the front electrode 103 is made of p-type zinc oxide (ZnO) containing 1 to 5% copper (Cu) dopant. At this time, the front electrode 103 is deposited by physical vapor deposition (PVD) such as chemical vapor deposition (CVD) or sputtering.

Then, as shown in FIG. 5B, a plurality of pointed irregularities 103a are formed on the front electrode 103 surface. At this time, the surface of the transparent substrate 101 may be textured in order to improve the efficiency of the solar cell. Here, texturing is a technique for preventing a phenomenon of deterioration of characteristics due to optical loss due to reflection of light incident on a substrate surface of a solar cell, and is a method of roughing the surface of a substrate used in a solar cell, 101) having a concave and convex pattern on its surface. When the surface of the transparent substrate is roughened by texturing, the reflected light is reflected again to reduce the reflectance of the incident light, thereby increasing the amount of trapped light, thereby reducing the optical loss.

An anti-reflection layer (not shown) may be formed on the transparent substrate 101 before the front electrode 103 is formed. At this time, the antireflection layer prevents sunlight incident through the substrate from being absorbed by the silicon layer and is reflected directly to the outside, thereby preventing the efficiency of the solar cell from deteriorating. For example, silicon oxide (SiO _x ) Silicon nitride (SiN _x ). The formation of the antireflection layer may include low pressure chemical vapor deposition (LPCVD) and PECVD.

5B, a p-type first semiconductor layer 105p, an i-type intrinsic semiconductor layer 105i, and an n-type semiconductor layer (not shown) constituting the semiconductor layer 105 are formed on the front electrode 103 The p-type semiconductor layer 105p is first formed. At this time, the p-type semiconductor layer 105p is doped with p-type boron. In addition, the p-type semiconductor layer 105p is doped with SiH ₄ (not shown) into a vacuum chamber The gas and the boron gas are injected at a proper flow rate and are deposited. At this time, the p-type semiconductor layer 105p may be deposited by chemical vapor deposition (CVD) such as LPCVD, PECVD, hot wire chemical vapor deposition, or the like. At this time, the p-type semiconductor layer 105p is a p-type silicon layer doped with boron ions and has a thickness of about 5 to 20 nm.

Next, as shown in Fig. 5C, an i-type intrinsic semiconductor layer 105i and an n-type semiconductor layer 105n are sequentially formed on the p-type semiconductor layer 105p. At this time, the i-type intrinsic semiconductor layer 105i and the n-type semiconductor layer 105n may be deposited by the same LPCVD, PECVD, hot wire chemical chemical vapor deposition (CVD) such as vapor deposition (CVD) and the like. The n-type semiconductor layer 105n is doped with phosphorus, which is an n-type impurity.

At this time, the semiconductor layer 105 is formed by sequentially stacking a p-type semiconductor layer 105p, an intrinsic semiconductor layer 105i, and an n-type semiconductor layer 105n from the front electrode 103, . Here, the intrinsic semiconductor layer 105i serves as a light absorbing layer for increasing the efficiency of the thin film solar cell, and may be referred to as an active layer.

At this time, it is preferable that the solar light is incident on the i-type semiconductor layer 105i through the p-type semiconductor layer 105p in view of the efficiency of the solar cell. This is due to the difference in drift mobility between the electrons and holes generated by the sunlight. Since the hole mobility of holes is lower than that of electrons, in order to maximize the efficiency of collection of carriers by the sunlight, type semiconductor layer at the interface between the p-type semiconductor layer and the i-type semiconductor layer to minimize the movement distance of the holes.

In the present invention, the i-type semiconductor layer is not necessarily doped between the p-type semiconductor layer and the n-type semiconductor layer. However, the present invention is not limited thereto, It is also possible to arrange an amorphous silicon layer which is insulative (i.e., low in electrical conductivity). For example, it is also possible to arrange a semiconductor layer in which a p-type semiconductor layer and an n-type semiconductor layer are high-doped and an n-type or p-type impurity is doped low therebetween.

Next, as shown in FIG. 5D, the n-type rear reflective layer 107 is deposited using zinc oxide, which is the same as the material of the front electrode 103. At this time, the rear reflective layer 107 functions to increase the efficiency by back reflection. Further, the n-type back reflective layer 107 in addition to the n-type zinc oxide (ZnO), ZnO: B, ZnO: Al, SnO _2: F, a transparent conductive oxide such as ITO; to form a (TCO Transparent Conductive Oxide) material, And is formed to a thickness of about 700 nm to 2000 nm.

Then, a metal material is deposited on the rear reflective layer 107 to deposit the rear electrode 109. At this time, it is preferable that the rear electrode 109 is made of a conductive material such as aluminum or the like, and a physical vapor deposition method such as a thermal deposition method or a sputtering method is used.

As described above, the n-type zinc oxide (ZnO) is doped with copper (Cu) to form a transparent p-type front electrode 103, so that the p-type front electrode 103 and the p- The height of the schottky barrier at the interface between the layers 105p decreases, that is, the bending of the energy band gap decreases, so that the collection ratio of holes increases and the photoelectric efficiency is increased.

Further, the front electrode 103 is formed in a p-type using zinc oxide (ZnO) doped with copper (Cu), thereby forming a Schottky barrier layer at the interface between the p-type front electrode 103 and the p- Since the height of the schottkey barrier is reduced to increase the photoelectric efficiency, the present invention can be applied to an LED or a thin film transistor (TFT) device having a high mobility.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Various modifications and variations are possible. Such variations and modifications are to be considered as falling within the scope of the invention and the appended claims.

1 is a schematic cross-sectional view of a thin film solar cell structure using zinc oxide (ZnO) according to the prior art as a transparent conductive film.

2 is a graph schematically showing an energy band diagram at an interface between a transparent conductive film (TCO) composed of zinc oxide and a p-type silicon layer according to the prior art.

3 is a schematic cross-sectional view of a thin film solar cell structure using p-type zinc oxide (ZnO) according to the present invention as a transparent conductive oxide thin film (TCO).

4 is a graph schematically showing an energy band diagram at an interface between a transparent conductive oxide thin film (TCO) composed of p-type zinc oxide and a p-type semiconductor layer according to the present invention.

5A to 5D are cross-sectional views illustrating a manufacturing process of a thin film solar cell according to the present invention.

Description of the Related Art [0002]

101: transparent substrate 103: front electrode

103a: unevenness 105: semiconductor layer

105p: a p-type semiconductor layer 105i: an i-type intrinsic semiconductor layer

105n: n-type semiconductor layer 107: rear reflective layer

109: Rear electrode

Claims (11)

A p-type front electrode formed on a transparent substrate; A semiconductor layer formed on the p-type front electrode and composed of a p-type semiconductor layer, an i-type intrinsic semiconductor layer, and an n-type semiconductor layer; An n-type rear reflection layer formed on the n-type semiconductor layer of the semiconductor layer and made of n-type zinc oxide (ZnO); And And a back electrode formed on the n-type back reflection layer, Wherein the p-type front electrode is made of zinc oxide containing 1 to 5% copper (Cu) dopant. delete delete delete The thin film solar cell according to claim 1, wherein a plurality of concavities and convexities are formed on the surface of the front electrode. Forming a p-type front electrode on the transparent substrate; Forming a semiconductor layer composed of a p-type semiconductor layer, an i-type intrinsic semiconductor layer, and an n-type semiconductor layer on the p-type front electrode; Forming an n-type n-type back reflection layer made of n-type zinc oxide (ZnO) on the n-type semiconductor layer of the semiconductor layer; And And forming a rear electrode on the n-type rear reflection layer, Wherein the p-type front electrode is made of zinc oxide containing 1 to 5% of copper (Cu) dopant. delete delete delete 7. The method of claim 6, further comprising forming a plurality of projections and depressions on the surface of the front electrode. The method according to claim 6, wherein the front electrode is formed by chemical vapor deposition (CVD) or sputtering (PVD).

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