KR101091495B1 - Solar cell and method of fabricating the same - Google Patents

Abstract

Solar cell according to the embodiment, the back electrode layer formed on the substrate; A light absorbing layer formed on the back electrode layer; A buffer layer formed on the light absorbing layer; And a front electrode layer formed on the buffer layer and having a distribution in which the composition of the conductive impurity varies depending on the depth, the charge transport efficiency may be improved.

Solar cell, windows

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

An embodiment relates to a solar cell and a manufacturing method thereof.

Recently, as the demand for energy increases, development of solar cells for converting solar energy into electrical energy is in progress.

In particular, CIGS-based solar cells that are pn heterojunction devices having a substrate structure including a glass substrate, a metal back electrode layer, a p-type CIGS-based light absorbing layer, a high resistance buffer layer, an n-type window layer, and the like are widely used.

Research is underway to improve the power generation efficiency by adjusting the energy band gap in such solar cells.

Embodiments provide a solar cell having an improved power generation efficiency and a method of manufacturing the same.

Solar cell according to the embodiment, the back electrode layer formed on the substrate; A light absorbing layer formed on the back electrode layer; A buffer layer formed on the light absorbing layer; And a front electrode layer formed on the buffer layer and having a distribution in which the composition of the conductive impurity varies depending on the depth.

A method of manufacturing a solar cell according to an embodiment includes forming a back electrode layer on a substrate; Forming a light absorbing layer on the back electrode layer; Forming a buffer layer on the light absorbing layer; And forming a front electrode layer having a composition different from each other on the buffer layer depending on depth.

In the solar cell according to the embodiment, the composition distribution of the conductive impurities in the front electrode layer may vary depending on the position.

In particular, the composition of the conductive impurities in the lower region of the front electrode layer may be low and the composition of the conductive impurities in the upper region may be high.

Accordingly, the band gap energy is increased toward the upper region of the front electrode layer, and the charge transport efficiency may be improved.

Therefore, the solar cell according to the embodiment may have improved power generation efficiency.

In the description of the embodiments, where each substrate, layer, film, or electrode is described as being formed "on" or "under" of each substrate, layer, film, or electrode, etc. , "On" and "under" include both "directly" or "indirectly" formed through other components. In addition, the upper or lower reference of each component is described with reference to the drawings. The size of each component in the drawings may be exaggerated for the sake of explanation and does not mean the size actually applied.

1 to 4 are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment.

Referring to FIG. 1, a back electrode layer 200 is formed on a substrate 100.

The substrate 100 may be glass, and a ceramic substrate, a metal substrate, or a polymer substrate may also be used.

For example, soda lime glass or high strained point soda glass may be used as the glass substrate. As the metal substrate, a substrate including stainless steel or titanium may be used. As the polymer substrate, polyimide may be used.

The substrate 100 may be transparent. The substrate 100 may be rigid or flexible.

The back electrode layer 200 may be formed of a conductor such as metal.

For example, the back electrode layer 200 may be formed by a sputtering process using molybdenum (Mo) as a target.

This is because of high electrical conductivity of molybdenum (Mo), ohmic bonding with the light absorbing layer, and high temperature stability under Se atmosphere.

The molybdenum (Mo) thin film, which is the back electrode layer 200, must have a low specific resistance as an electrode and have excellent adhesion to the substrate 100 so that peeling does not occur due to a difference in thermal expansion coefficient.

Meanwhile, the material forming the back electrode layer 200 is not limited thereto, and may be formed of molybdenum (Mo) doped with sodium (Na) ions.

Although not shown in the drawing, the back electrode layer 200 may be formed of at least one layer. When the back electrode layer 200 is formed of a plurality of layers, the layers constituting the back electrode layer 200 may be formed of different materials.

Referring to FIG. 2, a light absorbing layer 300 is formed on the back electrode layer 200.

The light absorbing layer 300 includes an Ib-IIIb-VIb-based compound.

In more detail, the light absorbing layer 300 includes a copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ , CIGS-based) compound.

Alternatively, the light absorbing layer 300 may include a copper-indium selenide-based (CuInSe ₂ , CIS-based) compound or a copper-gallium-selenide-based (CuGaSe ₂ , CIS-based) compound.

For example, in order to form the light absorbing layer 300, a CIG-based metal precursor film is formed on the back electrode layer 200 using a copper target, an indium target, and a gallium target.

Thereafter, the metal precursor film is reacted with selenium (Se) by a selenization process to form a CIGS-based light absorbing layer 300.

In addition, during the process of forming the metal precursor film and the selenization process, an alkali component included in the substrate 100 passes through the back electrode layer 200, and the metal precursor film and the light absorbing layer 300. Spreads).

An alkali component may improve grain size and improve crystallinity of the light absorbing layer 300.

In addition, the light absorbing layer 300 may form copper, indium, gallium, selenide (Cu, In, Ga, Se) by co-evaporation.

The light absorbing layer 300 receives external light and converts the light into electrical energy. The light absorbing layer 300 generates photo electromotive force by the photoelectric effect.

The bandgap energy Eg of the light absorbing layer 300 may be 0.7 to 1.7 eV.

The bandgap energy of the light absorbing layer 300 may gradually increase as it approaches the back electrode layer 200.

Accordingly, the electron velocity in the light absorbing layer 300 may be improved.

Referring to FIG. 3, a buffer layer 400 and a high resistance buffer layer 500 are formed on the light absorbing layer 300.

The buffer layer 400 may be formed of at least one or more layers on the light absorbing layer 300, and may be formed of cadmium sulfide (CdS).

The energy bandgap of the buffer layer 400 is about 2.2 eV to 2.4 eV.

In this case, the buffer layer 400 is an n-type semiconductor layer, the light absorbing layer 300 is a p-type semiconductor layer. Thus, the light absorbing layer 300 and the buffer layer 400 form a pn junction.

A zinc oxide layer may be further formed on the cadmium sulfide (CdS) by performing a sputtering process targeting the zinc oxide (ZnO).

The high resistance buffer layer 500 may be formed as a transparent electrode layer on the buffer layer 400.

For example, the high resistance buffer layer 500 may be formed of any one of ITO, ZnO, and i-ZnO.

The energy band gap of the high resistance buffer layer 500 is about 3.1 eV to 3.2 eV.

The buffer layer 400 and the high resistance buffer layer 500 are disposed between the light absorbing layer 300 and the front electrode layer 600 formed thereafter.

That is, since the difference between the lattice constant and the energy band gap is large between the light absorbing layer 300 and the front electrode, the buffer layer 400 and the high resistance buffer layer 500 having a band gap in between the two materials are inserted into a good one. A junction can be formed.

In the embodiment, two buffer layers are formed on the light absorbing layer 300, but the present invention is not limited thereto, and the buffer layer may be formed of only one layer.

Referring to FIG. 4, a front electrode layer 600 is formed on the high resistance buffer layer 500.

The front electrode layer 600 may be formed to have a different distribution of conductive impurities depending on its depth.

Specifically, the front electrode layer 600 may have a higher composition of conductive impurities toward its upper surface. Also, the closer the front electrode layer 600 is to the high resistance buffer layer 500, the lower the composition of conductive impurities.

Accordingly, the front electrode layer 600 may have different band gap energy depending on the position.

That is, the upper region of the front electrode layer 600 may have a high band gap energy, and the lower region may have a relatively low band gap energy.

Since the front electrode layer 600 has different band gap energy according to depth, a potential difference is generated in the front electrode layer 600.

Due to such a potential difference, the front electrode layer has a structure in which a potential barrier has a step according to depth, and the mobility of photoganerated electrons generated at the pn junction can be improved.

For example, the front electrode layer 600 is made of zinc-based oxide or ITO (Imdium Tin Oxide) containing impurities such as aluminum (Al), alumina (Al ₂ O ₃ ), magnesium (Mg), gallium (Ga), and the like. Can be formed.

The front electrode layer 600 may be formed to a thickness of 400 ~ 1000nm.

The front electrode layer 600 may be formed by a co-sputtering method.

Specifically, a first target and a second target are disposed at one end of the sputtering chamber to which DC power is applied, and a substrate is disposed to face the first and second targets.

For example, the first target may be ZnO, and the second target may be Al ₂ O ₃ .

An argon (Ar) gas of 150 sccm ± 30 is injected into the sputtering chamber, the process pressure is 5 mtorr ± 3, and the deposition temperature may be 150 ° C. ± 50.

The front electrode layer 600 is formed on the high resistance buffer layer 500 of the substrate 100 by sputtering the first target and the second target.

In this case, power of 3 kW may be applied to the first target, and power of 0.8 kW to 1.5 kW may be applied to the second target.

That is, a constant power is applied to the ZnO target, and the Al ₂ O ₃ Higher power may be applied to the target over time.

For example, an initially deposited film of the front electrode layer 600 is referred to as a lower electrode layer 610, and a later deposited film is referred to as an upper electrode layer 620.

Accordingly, a lower electrode layer 610 doped with a low concentration of conductive impurities may be formed on the high resistance buffer layer 500, and an upper electrode layer 620 doped with a high concentration of conductive impurities may be formed on the lower electrode layer 610. have.

That is, the power applied to the Al ₂ O ₃ target increases with time, so that the composition of the conductive impurity may increase with the surface area of the front electrode layer 600.

Since the composition of the conductive impurities of the upper electrode layer 620 is higher than that of the lower electrode layer 610, the bandgap energy of the upper electrode layer 620 may be relatively higher than that of the lower electrode layer 610.

It can be seen that when the concentration of the conductive impurity increases with depth in the front electrode layer 600, the band gap energy may increase.

5 is a graph showing a composition distribution of conductive impurities according to the depth of the front electrode layer. 6 is a graph showing band gap energy according to the depth of the front electrode layer. 7 is a graph showing a change in band gap energy according to the composition distribution of conductive impurities in the front electrode layer.

As shown in FIG. 5, the front electrode layer 600 may have a higher concentration of conductive impurities toward its surface region.

That is, the conductive impurity composition in the lower region (100 ± 50nm) of the front electrode layer 600 may be 2.0 atmic%. In addition, the composition of the conductive impurity in the upper region (500 ± 50nm) of the front electrode layer 600 may be 2.5 atmic%.

As shown in FIG. 6, the bandgap energy of the front electrode layer 600 may increase as the surface area thereof is increased.

That is, the band gap energy in the lower region (100 ± 50 nm) of the front electrode layer may be 3.3 ± 1.0 eV. In addition, the composition of the conductive impurity in the upper region (500 ± 50nm) of the front electrode layer 600 may be 3.5 ± 1.0eV.

Therefore, as shown in FIG. 7, it can be seen that the bandgap energy increases as the composition of the conductive impurities in the front electrode layer 600 increases.

By changing the bandgap energy of the front electrode layer 600 according to the position, the potential of the front electrode layer 600 may vary depending on the depth.

That is, since the front electrode layer 600 has a stepwise potential distribution, the transport efficiency of the photocharge may be maximized and the power generation efficiency of the solar cell may be improved.

Although described above with reference to the embodiment is only an example and is not intended to limit the invention, those of ordinary skill in the art to which the present invention does not exemplify the above within the scope not departing from the essential characteristics of this embodiment It will be appreciated that many variations and applications are possible. For example, each component specifically shown in the embodiment can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

1 to 4 are cross-sectional views showing a manufacturing process of the solar cell according to the embodiment.

5 is a graph showing a composition distribution of conductive impurities according to the depth of the front electrode layer in the embodiment.

6 is a graph showing bandgap energy according to the depth of the front electrode layer in the embodiment.

FIG. 7 is a graph showing band gap energy according to a composition distribution of conductive impurities in a front electrode layer in an embodiment. FIG.

Claims (6)

A back electrode layer formed on the substrate; A light absorbing layer formed on the back electrode layer; A buffer layer formed on the light absorbing layer; And And a front electrode layer formed on the buffer layer and having a higher composition of conductive impurities toward the upper surface. delete The method of claim 1, The front electrode layer includes a lower electrode layer and an upper electrode layer, The lower electrode layer has a first bandgap energy, The upper electrode layer has a second bandgap energy higher than the first bandgap energy. The method of claim 1, The front electrode layer is formed of a zinc-based oxide containing at least one of aluminum (Al), magnesium (Mg), gallium (Ga), The distribution of the conductive impurities is a solar cell comprising 2 to 2.5 At%. Forming a back electrode layer on the substrate; Forming a light absorbing layer on the back electrode layer; Forming a buffer layer on the light absorbing layer; And Forming a front electrode layer formed on the buffer layer, the composition distribution of the conductive impurities toward the upper surface thereof, comprising the step of forming a solar cell. The method of claim 5, The front electrode layer is formed by a co-sputtering method using a first target containing zinc oxide (ZnO) and a second target containing aluminum (Al), A constant power is applied to the first target, and the power applied to the second target increases over time.

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