EP2737549A1

EP2737549A1 - Solar cell and method of fabricating the same

Info

Publication number: EP2737549A1
Application number: EP12820573.9A
Authority: EP
Inventors: Se Han Kwon; Chul Hwan Choi
Original assignee: LG Innotek Co Ltd
Current assignee: LG Innotek Co Ltd
Priority date: 2011-07-29
Filing date: 2012-07-26
Publication date: 2014-06-04
Also published as: EP2737549A4; KR20130014265A; KR101305802B1; WO2013019029A1; CN103843156A

Abstract

Disclosed are a solar cell and a method of fabricating the same. The solar cell includes a back electrode layer on a support substrate; an optical path converting layer on the back electrode layer, the optical path converting layer including a protrusion pattern; a light absorbing layer on the optical path converting layer; and a front electrode layer on the light absorbing layer. The optical path converting layer reflects an incident light toward the light absorbing layer, so that the light efficiency is improved.

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 may be easily fabricated and have improved photoelectric conversion efficiency.

According to the embodiment, there is provided a solar cell including a back electrode layer on a support substrate; an optical path converting layer on the back electrode layer, the optical path converting layer including a protrusion pattern; a light absorbing layer on the optical path converting layer; and a front electrode layer on the light absorbing layer.

A method for fabricating a solar cell according to the embodiment includes the steps of: forming a back electrode layer on a support substrate; forming an optical path converting layer on the back electrode layer and forming a protrusion pattern by etching the optical path converting layer; forming a light absorbing layer including the protrusion pattern on the optical path converting layer; and forming a front electrode layer on the light absorbing layer.

The solar cell according to the embodiment includes an optical path converting layer which includes a protrusion pattern and is disposed on the back electrode layer. The optical path converting layer including the protrusion pattern reflects a light, which is transmitted without being absorbed in the light absorbing layer, toward the light absorbing layer, so that a light absorption rate of the light absorbing layer may be increased. Thus, the solar cell according to the embodiment may have improved efficiency.

That is, since an optical path of an incident light is lengthened about two times due to the optical path converting layer including the protrusion pattern, the light absorption rate of the light absorbing layer may be increased.

Further, according to the solar cell of the embodiment, due to the optical path converting layer including the protrusion pattern 320, the efficiency of the solar cell can be improved even if the light absorbing layer has a thin thickness. Thus, the solar cell according to the embodiment can be fabricated by using the light absorbing layer having the thin thickness, so that a thin film solar cell having a thickness in the range of several nm to several hundreds of nm may be provided. Further, according to the solar cell of the embodiment, the thickness of the light absorbing layer may be reduced due to the protrusion pattern, so that the raw material cost may be reduce and the productivity may be improved.

Further, since the optical path converting layer includes the protrusion pattern, the solar cell may have good physical and chemical interfacial characteristics between the optical path converting layer and the light absorbing layer. Further, the optical path converting layer may include a group V element. Thus, the interfacial characteristic of the optical path converting layer with respect to the light absorbing layer may be more improved.

FIG. 1 is a sectional view showing a solar cell according to the embodiment;

FIG. 2 is a transparent perspective view showing the solar cell according to the embodiment;

FIG. 3 is a sectional view of a protrusion included in an optical path converting layer according to the embodiment;

FIG. 4 is a sectional view showing a solar cell according to another embodiment;

FIG. 5 is a sectional view illustrating a process of converting an optical path of an incident light by the optical path converting layer according to the embodiment; and

FIGS. 6 to 12 are views illustrating a process 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.

FIGS. 1 and 4 are sectional views showing a solar cell according to the embodiment. FIG. 2 is a transparent perspective view showing the solar cell of FIG. 1. FIG. 3 is a sectional view of a protrusion included in an optical path converting layer according to the embodiment. FIG. 5 is a sectional view illustrating a process of converting an optical path of an incident light by the optical path converting layer according to the embodiment.

Referring to FIG. 1, the solar cell according to the embodiment includes a back electrode layer 200 which is formed on a support substrate 100, an optical path converting layer 300 which includes a protrusion pattern and is disposed on the back electrode layer 200, a light absorbing layer 400 which is disposed on the optical path converting layer 300, a buffer layer 500 on the light absorbing layer 400, a high-resistance buffer layer 600 on the buffer layer 500, and a front electrode layer 700 on the high-resistance buffer layer 600.

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

The support substrate 100 may be an insulator. 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. The support substrate 100 may be transparent. Further, the support substrate 100 may be rigid or flexible.

The back electrode layer 200 is disposed on the support substrate 100. The back electrode layer 200 is a conductive layer. For example, a material used for the back electrode layer 200 is metal such as molybdenum (Mo).

Further, the back electrode layer 200 may include two layers or more. The layers may be formed of the same material or different materials, respectively.

The optical path converting layer 300 is disposed on the back electrode layer 200. The optical path converting layer 300 includes the protrusion pattern 320. The optical path converting layer 300 includes a compound selected from the group consisting of zinc oxide, indium tin oxide (ITO), tin oxide and a combination thereof. In detail, the optical path converting layer 300 may be zinc oxide.

Further, the optical path converting layer 300 may be transparent. The optical path converting layer 300 may have a thickness in the range of 10 ㎚ to 100 ㎚.

The optical path converting layer 300 may include a material selected from the group consisting of a group V element, a transition metal element, alkali metal and a combination thereof. The optical path converting layer 300 may be doped with a dopant selected from the group consisting of a group V element, a transition metal element, alkali metal and a combination thereof. In detail, the optical path converting layer 300 may be doped with a compound consisting of a group V element, a transition metal element, alkali metal and a combination thereof. That is, the optical path converting layer 300 may be doped with at least two doping materials. The dopant concentration is in a range of 1.0 × 1016 atoms/㎤ to 1.0 × 1019 atoms/㎤, but the embodiment is not limited thereto.

At this time, the group V element may include one selected from the group consisting of nitrogen, phosphor, arsenic and a combination thereof, but the embodiment is not limited thereto. Further, the transition metal element includes one selected from the group consisting of vanadium (V), chrome (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and a combination thereof, but the embodiment is not limited thereto. Further, the alkali metal may include one selected from the group consisting of lithium (Li), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr) and a combination thereof, but the embodiment is not limited thereto.

The protrusion pattern 320 may have various shapes to the extent that the protrusion pattern 320 has a shape including an inclined surface inclined with respect to the support substrate 100. Further, as shown in FIG, 1, although the protrusion pattern 320 has a regular interval, the shape of the protrusion pattern 320 is not limited thereto, and the protrusion pattern 320 may include protrusions which have various sizes and are spaced apart from each other at irregular intervals.

In detail, the protrusion pattern 320 may have a pyramid shape, a hemisphere shape, or a triangular prism shape. For example, as shown in FIG. 1, the protrusion pattern 320 may have a pyramid shape.

In more detail, the protrusion pattern 320 may include the first and second inclined surfaces 321 and 322 which are opposite to each other. Referring to FIG. 3, the first inclined surfaces 321 are directed in the first direction. The first inclined surfaces 321 may extend in the same direction. The first inclined surfaces 321 are inclined with respect to an upper surface of the back electrode layer 200. Similarly, the second inclined surfaces 322 may extend in the same direction. The second inclined surfaces 322 may be opposite to the first inclined surfaces 321. For example, the second inclined surfaces 322 may be symmetrical to the first inclined surfaces 321.

Gradients (θ1, θ2) of the first and second inclined surfaces about the back electrode layer 200 may be in the range of about 10 degrees to about 90 degrees. Preferably, the gradients (θ1, θ2) of the first and second inclined surfaces may be in the range of about 30 degrees to about 55 degrees. The gradient of the first inclined surface may be equal to or different from the gradient of the second inclined surface.

In contrast, the optical path converting layer 300 according to the embodiment may include a base layer 310 disposed on the back electrode layer 100 and the protrusion pattern 320 on the base layer 310. That is, as shown in FIGS. 1 and 2, the optical path converting layer 300 may be formed only with the protrusion pattern 320, or, as shown in FIGS. 3 and 4, may have the base layer 310 and the protrusion pattern 320 on the base layer 310. The base layer 310 is prepared as a thin film. At this time, the protrusion pattern 320 on the base layer 310 may have a height in the range of 30 ㎚ to 100 ㎚.

Referring to FIG. 5, the surface area of the optical path converting layer 300 may be expanded due to the protrusion pattern 320 and may scatter an incident light. The protrusion pattern 320 may reflect the light incident from the top of the optical path converting layer 300 in several directions.

The light incident into an upper surface of the back electrode layer 200 through the light absorbing layer 400 is scattered by the protrusion pattern 320. The light incident from the top to the bottom is laterally reflected by the protrusion pattern 320 placed over the upper surface of the back electrode layer 200. Thus, the optical path of the reflected light in the light absorbing layer 400 can be increased.

Therefore, according to the solar cell of the embodiment, the optical path of the light passing through the light absorbing layer 400 can be increased, so that the photoelectric conversion efficiency may be improved.

Further, according to the solar cell of the embodiment, due to the optical path converting layer 300 including the protrusion pattern 320, the solar cell may have the improved efficiency even if the light absorbing layer 400 has a thin thickness. Thus, the solar cell according to the embodiment can be fabricated by using the light absorbing layer 400 having the thinner thickness, so that a thin film solar cell having a thickness in the range of several nm to several hundreds of nm may be provided.

Further, the upper surface of the optical path converting layer 300 may represent high roughness. That is, the optical path converting layer 300 may be fully formed with the protrusion pattern 320, or a concavo-convex section such as the protrusion pattern 320 is formed on the upper surface of the base layer 200. Thus, the upper surface of the back electrode has a large surface area. Therefore, the back electrode layer 200 and the light absorbing layer 400 have a large contact area. Accordingly, the back electrode layer 200 and the light absorbing layer 400 have improved physical and electrical contact characteristics.

The light absorbing layer 400 is disposed on the optical path converting layer 300. In detail, the optical path converting layer 300 is coated around the back electrode layer 200 and the light absorbing layer 300. The light absorbing layer 400 includes a group Ⅰ-Ⅲ-Ⅵ compound. For example, the light absorbing layer 400 may have a CIGSS (Cu(IN,Ga)(Se,S)2) crystal structure, a CISS (Cu(IN)(Se,S)2) crystal structure or a CGSS (Cu(Ga)(Se,S)2) crystal structure. The energy band gap of the light absorbing layer 400 may be in the range of about 1 eV to about 1.8 eV.

The buffer layer 500 is disposed on the light absorbing layer 400. The buffer layer 500 directly makes contact with the light absorbing layer 400. For example, cadmium sulfide (CdS) is used as a material of the buffer layer 500. The energy band gap of the buffer layer 500 is in the range of about 1.9 eV to about 2.3 eV.

The high resistance buffer layer 600 is disposed on the buffer layer 500. The high resistance buffer layer 600 includes i-ZnO that is not doped with impurities. The energy band gap of the high resistance buffer layer 600 may be in the range of about 3.1 eV to about 3.3 eV.

The front electrode layer 700 is disposed on the high resistance buffer layer 600. The front electrode layer 700 is a transparent and conductive layer. For example, a material such as Al doped zinc oxide (Al doped ZnO;AZO) may be used for the front electrode layer 700.

FIGS. 6 to 12 are views illustrating a process of fabricating a solar cell according to the embodiment. The fabrication method will be described with reference to the solar cell described above. The description about the solar cell may be basically incorporated herein by reference.

Referring to FIG. 6, the back electrode layer 200 is formed by depositing a metal such as molybdenum (Mo) on the support substrate 100 through a sputtering process. The back electrode layer 200 may be formed by performing processes twice under different conditions.

Referring to FIGS. 7 and 8, the optical path converting layer 300 is formed on the back electrode layer 200 and is etched, such that the protrusion pattern 320 is formed. The protrusion pattern 320 may be formed by wet-etching or dry-etching the optical path converting layer 300. In the case of wet etching, an etching solution generally used in the art, such as a hydrochloric acid or a nitric acid, is used. In detail, the optical path converting layer 300 disposed on the back electrode layer 200 is dipped into an solution including a hydrochloric acid (HCl) by a predetermined % and is reacted for several seconds to several hours, such that the optical path converting layer 300 may be etched.

At this time, for example, the etching degree of the optical path converting layer 300 may be controlled according to the conditions of the etching process such as acidity of the etching solution, concentration of the etching solution, reaction time, reaction temperature, etc. For example, when the etching process is performed under the condition that may sufficiently etch the optical path converting layer 300, as shown in FIG. 1, the optical path converting layer 300 is entirely converted into the protrusion pattern 320. In the etching process, the entire upper surface of the optical path converting layer 300 may not be uniformly etched. That is, the optical path converting layer 300 may be selectively etched naturally. For example, one part of the optical path converting layer 300 is etched too much and the other part is insufficiently etched, such that the optical path converting layer 300 may have the inclined surface inclined with respect to the support substrate 100.

In contrast, referring to FIG. 3, when the etching process time is short, the upper surface of the optical path converting layer 300 is partially etched, such that the protrusion pattern 320 is formed and the optical path converting layer 300, which comes into contact with the back electrode layer 200, may remain in a thin film shape.

Referring to FIG. 9, the light absorbing layer 400 is formed on the back electrode layer 200 and the optical path converting layer 300. The light absorbing layer 400 may be formed through a sputtering process or an evaporation process.

For example, Cu, In, Ga and Se are simultaneously or independently evaporated to form the CIGS-based light absorbing layer, or the light absorbing layer can be formed through the selenization process after forming a metal precursor layer..

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

Then, the selenization process is performed to form the CIGS-based light absorbing layer.

In addition, the sputtering process using the Cu target, the In target, and the Ga target and the selenization process can be simultaneously performed.

Further, the CIS-based or CIG-based light absorbing layer 400 can be formed through the selenization process and the sputtering process using only the Cu and In targets or the Cu and Ga targets.

Referring to FIGS. 10 and 11, the buffer layer 500 and the high resistance buffer layer 600 are formed on the light absorbing layer 400.

The buffer layer 500 may be formed through a CBD (Chemical Bath Deposition) process. For example, after the light absorbing layer 400 is formed, the light absorbing layer 400 is immersed in a solution including materials for forming cadmium sulfide, such that the buffer layer 500 including the cadmium sulfide is formed on the light absorbing layer 400.

Then, i-ZnO that is not doped with impurities is deposited on the buffer layer 500 through the sputtering process and then the high resistance buffer layer 600 is formed.

Referring to FIG. 12, the front electrode layer 700 is formed on the high resistance buffer layer 600. In order to form the front electrode layer 700, transparent conductive materials are laminated on the high resistance buffer layer 700. For example, transparent conductive materials include zinc oxide doped with aluminum, indium zinc oxide or indium tin oxide (ITO).

Therefore, according to the method for fabricating a solar cell of the embodiment, the solar cell having improved efficiency can be fabricated.

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;

an optical path converting layer on the back electrode layer, the optical path converting layer including a protrusion pattern;

a light absorbing layer on the optical path converting layer; and

a front electrode layer on the light absorbing layer.
The solar cell of claim 1, wherein the protrusion pattern includes an inclined surface inclined with respect to the support substrate.
The solar cell of claim 1, wherein the protrusion pattern includes a first inclined surface and a second inclined surface which are opposed to each other.
The solar cell of claim 1, wherein the protrusion pattern includes a plurality of first inclined surfaces and a plurality of second inclined surfaces opposed to the plurality of first inclined surfaces.
The solar cell of claim 1, wherein the protrusion pattern has a pyramid shape.
The solar cell of claim 1, wherein the protrusion pattern has a height in a range of 30 ㎚ to 100 ㎚.
The solar cell of claim 1, wherein the optical path converting layer includes a base layer on the back electrode layer and the protrusion pattern over the back electrode layer.
The solar cell of claim 7, wherein the base layer is prepared as a thin film, and the protrusion pattern is disposed on the base layer.
The solar cell of claim 1, wherein the optical path converting layer includes one selected from the group consisting of zinc oxide, indium tin oxide (ITO), tin oxide and a combination thereof.
The solar cell of claim 1, wherein the optical path converting layer has a thickness in a range of 10 ㎚ to 100 ㎚.
The solar cell of claim 1, wherein the optical path converting layer is doped with a dopant selected from the group consisting of a group V element, a transition metal element, alkali metal and a combination thereof.
The solar cell of claim 11, wherein the group V element includes one selected from the group consisting of nitrogen, phosphor, arsenic and a combination thereof.
The solar cell of claim 11, wherein the transition metal element includes one selected from the group consisting of vanadium (V), chrome (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and a combination thereof.
The solar cell of claim 11, wherein concentration of the dopant is in a range of 1.0 × 1016 atoms/㎤ to 1.0 × 1019 atoms/㎤.
The solar cell of claim 1, wherein the optical path converting layer is transparent.
A method for fabricating a solar cell, the method comprising:

forming a back electrode layer on a support substrate;

forming an optical path converting layer on the back electrode layer and forming a protrusion pattern by etching the optical path converting layer;

forming a light absorbing layer including the protrusion pattern on the optical path converting layer; and

forming a front electrode layer on the light absorbing layer.
The method of claim 16, wherein the forming of the protrusion pattern is performed through wet etching or dry etching.