WO2013039349A2

WO2013039349A2 - Solar cell and method of fabricating the same

Info

Publication number: WO2013039349A2
Application number: PCT/KR2012/007370
Authority: WO
Inventors: Chin Woo Lim
Original assignee: LG Innotek Co Ltd
Current assignee: LG Innotek Co Ltd
Priority date: 2011-09-16
Filing date: 2012-09-14
Publication date: 2013-03-21
Anticipated expiration: 2014-03-16
Also published as: WO2013039349A3; KR20130030122A

Abstract

Disclosed is a solar cell. A solar cell includes a back electrode layer on a support substrate; a light absorbing layer on the back electrode layer; nano-alloy protrusions formed on the light absorbing layer and including a first metal and a second metal; and a front electrode covering the light absorbing layer and the nano-alloy protrusions.

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

The embodiment relates to a solar cell and a method of fabricating the same.

Recently, as energy consumption is increased, a solar cell has been developed to convert solar energy into electrical energy.

In particular, a CIGS-based solar cell, which is a PN hetero junction apparatus having a substrate structure including a glass substrate, a metallic back electrode layer, a P type CIGS-based light absorbing layer, a high resistance buffer layer, and an N type window layer, has been extensively used.

The embodiment provides a solar cell which has improved photoelectric conversion efficiency and durability.

According to the embodiment, there is provided a solar cell including a back electrode layer on a support substrate; a light absorbing layer on the back electrode layer; nano-alloy protrusions formed on the light absorbing layer, and including a first metal and a second metal; and a front electrode covering the light absorbing layer and the nano-alloy protrusions.

According to the embodiment, there is provided a method for fabricating a solar cell including the steps of forming a back electrode layer on a support substrate; forming a light absorbing layer on the back electrode layer; forming nano-alloy protrusions on the light absorbing layer; and forming a front electrode layer on the light absorbing layer and the nano-alloy protrusions.

In a solar cell according to the embodiment, nano-alloy protrusions are provided between a light absorbing layer and a front electrode layer.

The nano-alloy protrusions can change a path of light incident from the sun to the solar cell. That is, the nano-alloy protrusions can reduce the amount of the incident light reflected from the front electrode layer and can induce the incident light to the light absorbing layer. Accordingly, an amount of light induced into the light absorbing layer is increased so that the solar cell may have improved photoelectric conversion efficiency. That is, the solar cell according to the embodiment can efficiently absorb light incident from solar energy so that the photoelectric conversion efficiency can be improved.

Further, the nano-alloy protrusions may include a metallic material having excellent electric properties. Accordingly, electric conductivity and photoelectric conversion efficiency in the solar cell including the nano-alloy protrusions can be improved as compared with a solar cell including only a front electrode layer according to the related art. Moreover, formation of the front electrode layer is easily and a deposited thickness of the front electrode layer can be reduced by laminating the nano-alloy protrusions on the light absorbing layer.

Further, mechanical or chemical durability of the nano-alloy protrusions can be improved as compared with that of metal protrusions. Accordingly, the durability of the solar cell including the nano-alloy protrusions can be improved.

FIGS. 1 to 3 are sectional views showing a section of a solar cell according to the embodiment.

FIGS. 4 to 8 are sectional views showing a method of fabricating a solar cell according to the embodiment.

In the description of the embodiments, it will be understood that, when a substrate, a layer, a film, or an electrode is referred to as being “on” or “under” another substrate, another layer, another film, or another electrode, it can be “directly” or “indirectly” on the other substrate, the other layer, the other film, or the other electrode, or one or more intervening layers may also be present. Such a position of each component has been described with reference to the drawings. The thickness and size of each component shown in the drawings may be exaggerated, omitted or schematically drawn for the purpose of convenience or clarity. In addition, the size of elements does not utterly reflect an actual size.

The term “nano-alloy protrusion” used in the specification refers to at least one region having a size less than about 500 nm, for example, about 100 nm, about 50 nm, about 10 nm, or about 5 nm or a structure having a specified size. For example, the “nano-alloy protrusion” includes a nano-wire, a nano-rod, a nano-dot, a quantum dot, and a nano-particle. A “nano-alloy protrusion” according to one embodiment may be substantially homogenous or heterogeneous (for instance, hetero structure) in terms of material characteristics.

FIGS. 1 to 3 are sectional views showing a section of a solar cell according to the embodiment. Referring to FIGS. 1 to 3, the solar cell includes a support substrate 100, a back electrode layer 200, a light absorbing layer 300, a buffer layer 400, a high resistance buffer layer 500, nano-alloy protrusions 600, and a front electrode layer 700.

The support substrate 100 has a plate shape and supports the back electrode layer 200, the light absorbing layer 300, the buffer layer 400, the high-resistance buffer layer 500, the nano-alloy protrusions 600, and the front electrode layer 700.

The support substrate 100 may be transparent, and may be rigid or flexible.

The support substrate 100 may be an insulator. For example, the support substrate 100 may be a glass substrate, a plastic substrate or a metal substrate. In detail, the support substrate 100 may be a soda lime glass substrate.

In contrast, the support substrate 100 may include a ceramic substrate including alumina, stainless steel, or polymer having a flexible property.

The back electrode layer 200 is provided on the support substrate 100. The back electrode layer 200 is a conductive layer. The back electrode layer 200 may include one selected from the group consisting of molybdenum (Mo), gold (Au), aluminum (Al), chrome (Cr), tungsten (W), and copper (Cu). Among them, since the molybdenum (Mo) makes a less thermal expansion coefficient with the support substrate 100 when comparing with other elements, the Mo represents a superior adhesive property to prevent the delamination phenomenon and generally satisfies characteristics required in the back electrode layer 200.

The back electrode layer 200 may include two or more layers. In this case, respective layers may be formed by the same metal or different metals.

The light absorbing layer 300 is provided on the back electrode layer 200. The light absorbing layer 300 includes a group I-III-VI compound. For example, the light absorbing layer 300 may have the CIGSS (Cu(IN,Ga)(Se,S)2) crystal structure, the CISS (Cu(IN)(Se,S)2) crystal structure or the CGSS (Cu(Ga)(Se,S)2) crystal structure.

The buffer layer 400 is provided on the light absorbing layer 300. The buffer layer 400 may include CdS, ZnS, InXSY or InXSeYZn(O, OH). The buffer layer 400 may have a thickness in the range of about 50 ㎚ to about 150 ㎚. The energy bandgap of the buffer layer 400 may be in the range of about 2.2eV to about 2.4eV.

The high resistance buffer layer 500 is provided on the buffer layer 400. The high resistance buffer layer 500 includes i-ZnO which is not doped with impurities. The energy bandgap of the high resistance buffer layer 500 may be in the range of about 3.1eV to about 3.3eV. In addition, the high resistance buffer layer 500 may be omitted.

The nano-alloy protrusions 600 are provided on the light absorbing layer 300. In more detail, the nano-alloy protrusions 600 may be provided between the light absorbing layer 300 and the front electrode layer 700. For example, the nano-alloy protrusions 600 may directly make contact with the high resistance buffer layer on the light absorbing layer 300.

The nano-alloy protrusions 600 may include a metallic material having excellent electric properties. Accordingly, electric conductivity and photoelectric conversion efficiency in the solar cell according to the embodiment can be improved as compared with a solar cell including only a front electrode layer according to the related art. The nano-alloy protrusions 600 may improve the photoelectric conversion efficiency and reduce a thickness of the front electrode layer 700. That is, the nano-alloy protrusions 600 having excellent electric conductivity may be used as an electrode so that the front electrode layer 700 may have a thinner thickness.

The nano-alloy protrusions 600 include a first metal and a second metal. The first metal may include zinc (Zn), silver (Ag), gold (Au), palladium (Pd), platinum (Pt), calcium (Ca), chrome (Cr), iron (Fe), Nickel (Ni), copper (Cu), molybdenum (Mo), ruthenium (Ru), titanium (Ti), or tungsten (W). The second metal may include a group Ⅲ element. For instance, the second metal may include boron (B), aluminum (Al), gallium (Ga), indium (In), or thallium (TI). For example, the nano-alloy protrusions 600 may be a zinc-aluminum alloy.

The nano-alloy protrusions 600 and the front electrode layer 700 may include at least identical metal. For example, the nano-alloy protrusions 600 may include a zinc (Zn)-aluminum (Al) alloy and the front electrode layer 700 may include aluminum (Al) doped zinc oxide (AZO). That is, each of the nano-alloy protrusions 600 and the front electrode layer 700 may include zinc (Zn) in common, but the embodiment is not limited thereto.

Referring to FIGS. 1 and 3, the nano-alloy protrusions 600 may include various forms such as nano-dot (see, FIG. 1), nano-wire, nano-rod, nano-tube, and nano-roughness (FIG. 3). The nano-alloy protrusions 600 may be optionally arranged. For instance, the nano-alloy protrusions may be regularly aligned or irregularly arranged.

The term “nano-rod” used in the specification includes a nano-structure having a main axis longer than one axis of a nano-rod section. When the nano-alloy protrusions 600 have the nano-rod form, the nano-alloy protrusions 600 may have the aspect ratio of about 1.5 to about 10, but the embodiment is not limited thereto. The “nano-wire” includes a longer nano-rod, for example, a nano-structure having the aspect ratio greater than 10.

As shown in FIGS. 1 and 2, the nano-alloy protrusions may be spaced apart from each other. In contrast, the nano-alloy protrusions 600 may be structures which are integrally connected to each other as illustrated in FIG. 3. For example, the nano-alloy protrusions 600 may be a nano-roughness structure.

The nano-alloy protrusions 600 may change a path of light incident from the sun to the solar cell. That is, the nano-alloy protrusions 600 may reduce the amount of incident light reflected from the front electrode layer 700 and induce the reflected light to the light absorbing layer 300. Accordingly, an amount of the light induced into the light absorbing layer 300 is increased and accordingly the solar cell may have improved photoelectric conversion efficiency. That is, the solar cell according to the embodiment may have improved photoelectric conversion efficiency by efficiently absorbing light incident from solar energy by the nano-alloy protrusions 600.

Since nucleation easily occurs during deposition of the front electrode layer 700 by laminating the nano-alloy protrusions 600 on the light absorbing layer 300, the deposition rate of the front electrode layer 700 can be increased so that the front electrode layer 700 can be easily formed.

The front electrode layer 70 may be provided on the light absorbing layer 300. For example, the front electrode layer 700 may directly make contact with the high resistance buffer layer 50 on the light absorbing layer 300. In more detail, the front electrode layer 700 may cover the high resistance buffer layer 500 and the nano-alloy protrusions 600.

The front electrode layer 700 may include a transparent conductive material. In addition, the front electrode layer 700 may have the characteristics of an N type semiconductor. In this case, the front electrode layer 700 forms an N type semiconductor with the buffer layer 30 to make PN junction with the light absorbing layer 400 serving as a P type semiconductor layer. For example, the front electrode layer 700 may include aluminum (Al) doped zinc oxide (AZO).

The front electrode layer 700 may have a thickness in the range of about 100 nm to about 500 nm. In detail, the front electrode layer 700 may have a thickness in the range of about 100 nm to about 300 nm. The thickness of the front electrode layer 700 may be reduced by providing the nano-alloy protrusions 600 on the high resistance buffer layer 500.

FIGS. 4 to 8 are sectional views showing a method of fabricating a solar cell according to the embodiment. A description of the method of fabricating the solar cell will be based on the foregoing description of the solar cell. The foregoing description of the solar cell may be incorporated herein by reference.

Referring to FIG. 4, the back electrode layer 200 may be formed on the support substrate 100. The back electrode layer 200 may be deposited using molybdenum (Mo). The back electrode layer 200 may be formed by physical vapor deposition (PVD) or a plating method.

An additional layer such as a diffusion barrier layer may be interposed between the support substrate 100 and the back electrode layer 200.

Referring to FIG. 5, the light absorbing player 300 may be formed on the back electrode layer 200.

. The light absorbing layer 300 is formed by a method of forming a CIGSS (Cu(IN,Ga)(Se,S)2) light absorbing layer 300 while simultaneously or separately evaporating copper (Cu), indium (In), gallium (Ga), and Selenium (Se) and a method of performing a solemnization process after formation of a metal precursor layer.

In detail, the metal precursor layer is formed on the back electrode 200 by performing a sputtering process using a copper (Cu) target, an indium (In) target, and a gallium (Ga) target.

After that, the metal precursor layer is subject to the selenization process so that the CIGSS (Cu(IN,Ga)(Se,S)2) light absorbing layer 300 is formed.

In contrast, a sputtering process using the copper target, the indium target, and the gallium target and the solemnization process may be simultaneously performed.

In addition, a CIS or CIG light absorbing layer 300 may be formed by sputtering process using only the copper target and the indium target or only the copper target or the gallium target and the solemnization process.

Referring to FIG. 6, a buffer layer 40 and a high resistance buffer layer 500 are sequentially formed on the light absorbing layer 300.

The buffer layer 400 may be formed by depositing cadmium sulfide on the light absorbing layer 30 through chemical bath deposition (CBD).

After that, zinc oxide is deposited on the buffer layer 400 through a sputtering process and then the high resistance buffer layer 500 on the deposited zinc oxide.

Referring to FIG. 7, the nano-alloy protrusions 600 are formed on the light absorbing layer 300. In detail, the nano-alloy protrusions 600 may directly make contact with the high resistance buffer layer 500 on the light absorbing layer 300.

The nano-alloy protrusions 600 may be formed by various processes. For example, the nano-alloy protrusions 600 may be fabricated through electroplating, a roll to roll process, a sol-gel process, vacuum evaporation, spray pyrolysis, or a combination thereof.

Hereinafter, a method of forming zinc-aluminum alloy protrusions will be described in detail as one example of the method of forming the nano-alloy protrusions 600.

For example, the zinc-aluminum alloy protrusions 700 may be fabricated by vacuum plating of forming zinc-aluminum alloy under vacuum by simultaneously evaporating a zinc source and an aluminum source under vacuum. In this case, the zinc source and the aluminum source may use two independent evaporation sources and the vacuum plating may be performed in a vacuum chamber at pressure of about 10-5 Torr.

Meanwhile, the zinc-alloy protrusions 700 may be formed by an electrolytic plating process. In detail, an aqueous zinc nitride solution Zn(NO3)2?xH2O having zinc may be used as a first precursor solution. For example, the aqueous zinc nitride solution may use zinc nitrate hexahydrate. An aqueous aluminum nitride solution Al(NO3)3?xH2O may be used as the second precursor solution.

After that, a working electrode and a counter electrode of the working electrode are immersed in the mixing precursor solution. The working electrode may use a composite substrate including the back electrode 200 and the light absorbing layer 300 sequentially provided on the substrate 100. After that, a zinc-aluminum alloy may be formed by applying a voltage the electrodes. In the electrolytic plating process, the zinc-aluminum alloy may have various shapes other than a shape of a thin film by a bonding force between aluminum and zinc. For example, the zinc-aluminum alloy may include various shapes such as nano-dot, nano-wire, nano-rod, nano-tube, or nano-roughness, but the embodiment is not limited thereto.

Referring to FIG. 8, the front electrode layer 700 is formed on the high resistance buffer layer 500. In detail, the front electrode layer 700 covers the high resistance buffer layer 500 and the nano-alloy protrusion 600 on the high resistance buffer layer 500. To form the front electrode layer 700, a transparent conductive material is laminated on the high resistance buffer layer 500. For example, the transparent conductive material may include aluminum (Al) or boron (B) doped zinc oxide. A process of forming the front electrode layer 600 may be performed at a temperature in the range of a room temperature to 300℃.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Claims

A solar cell comprising:

a back electrode layer on a support substrate;

a light absorbing layer on the back electrode layer;

nano-alloy protrusions on the light absorbing layer, the nano-alloy protrusions including a first metal and a second metal; and

a front electrode covering the light absorbing layer and the nano-alloy protrusions.
The solar cell of claim 1, wherein a buffer layer and a high resistance buffer layer are further provided on the light absorbing layer, and the nano-alloy protrusions directly make contact with the high resistance buffer layer.
The solar cell of claim 1, wherein the first metal includes zinc (Zn), silver (Ag), gold (Au), palladium (Pd), platinum (Pt), calcium (Ca), chrome (Cr), iron (Fe), Nickel (Ni), copper (Cu), molybdenum (Mo), ruthenium (Ru), titanium (Ti), or tungsten (W).
The solar cell of claim 1, wherein the second metal includes a group Ⅲ element.
The solar cell of claim 1, wherein the second metal includes boron (B), aluminum (Al), gallium (Ga), indium (In), or thallium (TI).
The solar cell of claim 1, wherein the nano-alloy protrusion and the front electrode layer include at least one same metal.
The solar cell of claim 1, wherein the nano-alloy protrusions change a path of light incident from a sun to the solar cell.
The solar cell of claim 1, wherein the nano-alloy protrusions are spaced apart from each other.
The solar cell of claim 1, wherein the nano-alloy protrusions have a shape of nano-dot, nano-wire, nano-rod, nano-tube, or nano-roughness.
The solar cell of claim 1, wherein the front electrode layer has a thickness in a range of 100 nm to 300 nm.
A method of fabricating a solar cell, the method comprising:

forming a back electrode layer on a support substrate;

forming a light absorbing layer on the back electrode layer;

forming nano-alloy protrusions on the light absorbing layer; and

forming a front electrode layer on the light absorbing layer and the nano-alloy protrusions.
The method of claim 11, wherein the forming of the nano-alloy protrusions is performed through vacuum plating, electrolytic plating, a roll to roll process, a sol-gel process, or vacuum evaporation.
The method of claim 12, wherein the forming of the nano-alloy protrusions comprises:

forming a mixed solution by mixing a first metal precursor and a second metal precursor with water or a buffer solution; and

forming nano-alloy protrusions including the first metal and the second metal on the light absorbing layer by applying a voltage to the mixed solution.
The method of claim 12, wherein the nano-alloy protrusions comprise a first metal and a second metal, and

the forming of the nano-alloy protrusions comprises forming the nano-alloy protrusions by simultaneously evaporating a first metal source and a second metal source.