KR20160134112A

KR20160134112A - Manufacturing method of light trapping structrure using anodizing process and light trapping structure

Info

Publication number: KR20160134112A
Application number: KR1020150067578A
Authority: KR
Inventors: 최기운; 안치원; 강일석; 박재홍
Original assignee: 한국과학기술원
Priority date: 2015-05-14
Filing date: 2015-05-14
Publication date: 2016-11-23
Also published as: KR101700240B1

Abstract

The present invention relates to a method of manufacturing a light capturing structure using an anodization process capable of forming a nanostructure layer on one side of anode and forming a micro structure layer on the nanostructure layer. The method of manufacturing a light capturing structure using an anodization process comprises: a step (S10) of stacking aluminum layers and then performing heat treatment of the aluminum layers; a step (S20) of performing an electro-polishing process on the heat-treated aluminum layer; a step (S40) of performing a first anodization process on a surface of the electro-polished aluminum layer; a step (S50) of selectively etching oxides formed through the anodization process; a step (S60) of performing a second anodization process on the electively etched aluminum layer; and a step (S70) of performing isotropic etching on the second anodized aluminum layer.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing an optical trapping structure and an optical trapping structure using the anodic oxidation process,

The present invention relates to a method of manufacturing an optical trapping structure and an optical trapping structure using an anodic oxidation process, and more particularly, to an optical trapping structure which can obtain an optical trapping structure The present invention relates to a method of manufacturing a light trapping structure and a light trapping structure using the same.

Recently, interest in renewable energy has been increasing due to rising oil prices, global environmental problems, depletion of fossil energy, disposal of nuclear power generation facilities, and location of new power plants. Among them, the research and development of solar cells which are pollution-free energy are being actively carried out

A solar cell is a device that converts light energy into electric energy by using photovoltaic effect. Depending on the constituent material, a solar cell, a thin film solar cell, a dye-sensitized solar cell, and an organic polymer solar cell . These solar cells are independently used as main power sources for electronic clocks, radios, unmanned lighthouses, satellites, and rockets. In particular, as the need for alternative energy is increasing, interest in solar cells is increasing.

Until now, materials of the solar cell such as single crystal silicon, polycrystalline silicon, amorphous SiC, amorphous SiGe, amorphous SiSn and other Group IV materials or gallium arsenide (GaAs), aluminum gallium arsenide (Al GaAs), indium phosphorus And Group II-VI compound semiconductors such as CdS, CdTe, and Cu2S.

In order to improve the efficiency of the crystalline silicon solar cell in the trend of commercialization, researches on the structure and process of the solar cell have been variously carried out. In particular, light trapping, electrode formation with improved contact resistance, There is a need to develop a technique for controlling the recombination of electron hole pairs, but the development of the technology for the optical trapping structure has not been completed yet.

Patent Document 10-2010-0107258 (a solar cell and its manufacturing method) also provides a solar cell including a metal wrap through (MWT) structure and a manufacturing method thereof as a back contact silicon solar cell, There has been no study on the direction of improvement of the optical trapping structure using the anodic oxidation process.

SUMMARY OF THE INVENTION The present invention is directed to a method of fabricating a light trapping structure capable of forming a nanostructure layer on one side of an anode and forming a microstructure layer on the nanostructure layer, And to provide a light trapping structure.

According to an embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, including: depositing and annealing an aluminum layer (S10); performing an electrolytic polishing process on the heat-treated aluminum layer (S20) A step (S40) of performing a first anodizing process on the surface of the aluminum layer (S40); a step (S50) of selectively etching the oxide formed through the anodizing process; A step (S60) of performing a car anodizing process, and a step (S70) of performing isotropic etching on the surface of the aluminum layer on which the second-order anodizing process has been performed, to manufacture a light trapping structure using an anodizing process &Lt; / RTI >

In one embodiment of the present invention, the light trapping structure comprises a nanostructure layer having a gap of 100-600 nm formed on the photoactive layer and a microstructure layer having a gap of 10-100 mu m formed on the nanostructure layer Wherein the microstructure layer is formed of a nanofiber bundle.

In one embodiment of the present invention, a method of manufacturing a solar cell includes the steps of: (a) forming a photoactive layer (S110); (b) forming an aluminum layer on the photoactive layer and performing heat treatment (S120); (c) electrolytically polishing the aluminum layer (S130); (d) performing a first anodization process on the surface of the electrolytically polished aluminum layer (S140); (e) (F) selectively performing a second anodizing process on the selectively etched aluminum layer (S160); (g) forming a second anode And performing isotropic etching on the surface of the aluminum layer on which the oxidation process has been performed (S170).

According to the light trapping structure according to an embodiment of the present invention, the light trapping structure can be formed on the photoactive layer, thereby increasing the light collection efficiency.

According to the method of fabricating a light trapping structure according to an embodiment of the present invention, the distance between the pores can be controlled by applying different voltage conditions according to the electrolyte material.

It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

FIG. 1 is a flowchart showing a manufacturing process of a light trapping structure according to an embodiment of the present invention.
2 is a graph showing the relationship between the lattice constant and the diameter of the pores fabricated according to an embodiment of the present invention.
3 is a photograph schematically showing the result obtained when an etching process is performed after anodization proceeds according to an embodiment of the present invention.
4 is a diagram schematically showing the shape of a light trapping structure according to an embodiment of the present invention.
5 is a top plan view of the microstructure layer 130 of the light trapping structure fabricated according to an embodiment of the present invention.
6 is a photograph showing a nanostructured layer in a light trapping structure according to an embodiment of the present invention.
7 is a graph showing photoelectric conversion efficiency of a solar cell according to an embodiment of the present invention.
8 and 9 are graphs showing the depth of pores and the diameter of pores according to the etching time according to anodizing time in the light trapping structure according to an embodiment of the present invention, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Anodic oxidation is one of the surface treatment techniques for metal. It has been widely used to prevent corrosion by forming an oxide film on the surface of metal, or to color metals. Recently, however, nanostructures such as nano dots, nanowires, nanotubes, and nanorods Or a method for producing a template for forming a burr structure. Al, Ti, Zr, Hf, Ta, Nb, W and the like are known as metals capable of forming a nanostructure by such anodic oxidation. Unlike other metals that use fluorine ions, dual aluminum anodic oxide membranes are relatively easy to manufacture and handling electrolytes relatively easily, and nanocrystals and thickness control are easy to control, and aluminum has been widely used in nanotechnology research. When electrochemically polarized in an aqueous solution containing an electrolyte such as phosphoric acid, a thick anodic oxide film is formed on the surface. The anodic oxide film has a structure in which the pores having regular intervals are grown from the outer surface toward the inner metal, and the structure of the boundary layer, ie, pore spacing, pore size, and boundary layer thickness, Are largely irrelevant and are dominantly determined by the applied voltage.

The self-alignment of the nanopores is determined by specific voltage and temperature depending on the electrolyte. Anodic oxidation at the self-aligning condition can produce a nanotemplate in which nanopores are densely arranged. In particular, the anodic alumina nanotemplate is relatively easy and economical to control the nanopore, and thus it is used in various fields as nanotemplate manufacturing technology.

The anodic alumina nanotemplates can be divided into two processes: hard anodization (HA) and soft anodization (MA). Unlike the MA process, the HA process is capable of growing nanotemplates in a short time due to the high current density by applying a high voltage. However, in the HA process, alignment occurs only in the voltage range of 110-150 V in oxalic acid aqueous solution, and the disorder requirement may be large. In the case of nanotemplates having a known degree of alignment, the pore interval is limited to about 280 nm at 140 V. In order to produce a nanotemplate having a larger pore interval, the MA method in an aqueous solution of phosphoric acid has to be applied. In the MA method, It has a disadvantage that the growth is very slow, about 2-3 탆.

FIG. 1 is a view illustrating a method of manufacturing an optical trapping structure using anodization according to an embodiment of the present invention. FIG. 1 is a cross-sectional view of a light trapping structure using anodic oxidation according to an embodiment of the present invention. (S30) performing a first anodization process on the surface of the electrolytically polished aluminum layer (120A), performing an electro-polishing (S30) on the surface of the electrolytically polished aluminum layer A step (S50) of performing a second anodization process on the selectively etched aluminum layer; a step (S50) of forming a surface of the aluminum layer (120A) And etching (S60).

The nanostructure thus formed will be described in detail as follows. A nanostructure refers to a structure in which nano-sized particles are arranged with regular regularity. The biggest feature of nano-sized particles is that the surface area of particles in a certain volume is much larger than that of conventional materials. Therefore, since the atoms constituting the material are present on the surface or interface rather than the inside of the particle, new physical properties which can not be expected in the conventional materials are revealed. Moreover, since the state of the material is very unstable, it easily reacts with the surrounding environment or easily changes. For example, gold generally has a golden yellow color in a bulk state and has low reactivity to maintain its color and shape. However, when the dimension is less than 20 nm, Reaction. Nanotechnology refers to all the technologies that make use of the physicochemical properties of materials at these nanoscale materials to study useful materials.

Until now, various nano processes such as self-assembly, nanoimprint, lithography, chemical vapor deposition and the like have been introduced. Recently, research for manufacturing nanostructures based on a porous template has attracted attention. The porous structure is made by an electrochemical method (anodic oxidation, etching), and the manufacturing process is simple and economical, and regularly arranged regular diameter (10 nm-2 μm) pores exist on the surface. By filling these pores with various materials and removing the porous structure, a nanostructure having a quantum wire or a quantum tube shape can be manufactured.

There are various methods for manufacturing such nanostructures depending on the object. Since the metal material is excellent in electrical conductivity, it can be relatively easily filled through an electrochemical deposition method. Since the electrical conductivity of the ceramic material is worse than that of the metal, a vacuum deposition method, a sol-gel method, This is being preferred. Most of the polymers, such as conductive polymers, are also poor in electrical properties. Therefore, polymerization reaction may occur in the porous material, or may be filled by applying a high pressure to the polymer in a molten state from the outside to the inside of the porous material, A method of directly wetting using a high surface energy is used.

Although nanoprocesses using porous templates have been reported so far, materials are limited depending on the process, or nanostructures produced are constant, and thus, in order to manufacture nanostructures required for various materials, I have a sense that I need it.

2 is a graph showing the relationship between the lattice constant and the diameter of the pores fabricated according to an embodiment of the present invention.

Referring to FIG. 2, a) shows the diameter of the pores when 19 V is applied in a 1 M aqueous sulfuric acid solution (H ₂ SO ₄ ). b) shows the results when a voltage of 25 V was applied in a 0.3 M aqueous solution of sulfuric acid (H ₂ SO ₄ ). c) shows the results when a voltage of 40 V was applied in a 0.3 M oxalic acid aqueous solution. d) shows the results when a voltage of 160 V was applied in a 1.0 M aqueous solution of phosphoric acid (H ₃ PO ₄ ). e) shows the results when a voltage of 195 V was applied in a 0.1 M aqueous solution of phosphoric acid (H ₃ PO ₄ ).

In order to control the diameter of the pores from the above relationships, the respective electrolyte solutions were selected, and the relationship between the voltage and the pore size as shown in the following equation (1) was obtained.

[Equation 1]

L _c (nm) = 15.8 + 2.17 (V)

Referring to Equation (1), it can be seen that the lattice constant of the nanostructure layer 120 can be controlled according to the kind of the electrolyte and the voltage applied to the anodic oxidation. The nanostructure layer 120 formed at this time may have a hexagonal crystal structure.

Table 1 shows the comparison of the difference in voltage between the porous alumina (Al ₂ O ₃ ) and the electrolyte used in the present invention.

Electrolyte Applied voltage Pore diameter The lattice constant (L _c ) Aqueous solution of sulfuric acid 19V ~ 14 nm ~ 50 nm Aqueous solution of sulfuric acid 25V ~ 19 nm ~ 65 nm Oxalic acid aqueous solution 40V ~ 35 nm ~ 100 nm Aqueous solution of phosphoric acid 160V ~ 120 nm ~ 400 nm Aqueous solution of phosphoric acid 195V ~ 180 nm ~ 500 nm

When the secondary anodizing process is performed, as shown in Table 1, if the distribution of the pores not aligned through the first anodizing process is subjected to the second anodizing process, the pore diameter of the pores can be aligned, The aligned porous alumina may have a pore uniformity of less than or equal to 8%.

The purity of the applied voltage, electrolyte, temperature, and aluminum (Al) influences the self-ordering of the porous alumina structure when anodizing the self-aligned porous alumina structure. It goes crazy.

In general, the applied voltage can be an important factor in determining the alumina lattice constant of the hexagonal crystal structure. Depending on the type and concentration of the electrolyte, the range of voltage that can be applied can vary, as shown in [Table 1]. In general, sulfuric acid (H ₂ SO ₄ ) can be used as an electrolyte at a voltage of 40 V or less, oxalic acid at a voltage of 40-100 V, and phosphoric acid at a voltage of 100 V or more.

As shown in FIG. 1, the aluminum layer 120A may be subjected to ultrasonic cleaning as a first step of the two-step anodization process, and annealing may be performed in a reducing atmosphere at 300-500 ° C. S10). An electro-polishing process may be performed on the heat-treated aluminum layer 120A (S20). At this time, the polishing rate may vary depending on the current density. The alumina formed on the aluminum layer 120A can be removed through the electrolytic polishing process. Such a process may be a condition for inducing a constant current density on the surface of the aluminum layer 120A during an anodizing process. The first anodizing step (S30) can be performed by hanging the anode on the pretreated aluminum layer 120A. The electrolyte may be any one selected from the above-mentioned sulfuric acid, oxalic acid, and aqueous phosphoric acid solution. The first anodization process may be conducted at a temperature of 35 DEG C or higher. The anodization process is possible at a temperature of 35 ° C or less, but it has been experimentally confirmed that it is suitable to proceed at a temperature of 35 ° C or more in terms of kinetics.

A selective etching process may be performed on the thus formed porous structure (S40). Selective etching can be performed in a phosphoric acid aqueous solution (H ₃ PO ₄ ) to which chromia (Cr ₂ O ₃ ) is added.

3 is a photograph schematically showing the result obtained when an etching process is performed after anodization proceeds according to an embodiment of the present invention.

Referring to FIG. 3, as the etching process proceeds, the pores formed in the alumina layer gradually increase, and the etching proceeds continuously in the longitudinal direction.

The secondary anodizing process may be performed on the aluminum layer on which the first anodizing and etching processes have been performed (S50). The second anodizing process may also be performed under the same conditions as the first anodizing process. Through the anodic oxidation process, the depth of the light trapping structure can be deepened.

The isotropic etching process can be performed on the light trapping structure thus formed (S60). For isotropic etching, an aqueous oxalic acid solution may be used. Through the isotropic etching process, the diameter of the pores can be controlled.

4 is a diagram schematically showing the shape of a light trapping structure according to an embodiment of the present invention.

Referring to FIG. 4, (b) of FIG. 4 shows that the nanostructured layer 120 and the microstructured layer 130 are formed on the photoactive layer 110 of FIG. 4 (a). The nanostructure layer 120 and the microstructure layer 130 may be formed during the first and second anodization and etching processes.

The nanostructure layer 120 may be an anti-reflective structure (ARS). Such a light trapping structure can proceed to the nanostructure layer 120 by changing the traveling path of light incident on the micro bundle through reflection or refraction. Thus, light passing through the nanostructure layer 120 can be incident on the photoactive layer 110 in an anti-reflection condition.

The pore size and lattice constant of the light trapping structure may be controlled according to the voltage applied during the anodic oxidation process with the electrolyte solution.

Hereinafter, a method of manufacturing a solar cell including a light trapping structure will be described in detail. (B) forming an aluminum layer (120A) on the photoactive layer and performing a heat treatment (S120); (c) forming a photoactive layer on the photoactive layer; (c) electrolytically polishing the aluminum layer (S130); (d) performing a first anodization process on the surface of the electrolytically polished aluminum layer (S140); (e) (F) selectively performing a second anodizing process on the selectively etched aluminum layer (S160); (g) forming a second anode And performing isotropic etching on the surface of the aluminum layer on which the oxidation process has been performed (S170).

More specifically, a method of manufacturing a solar cell includes the steps of preparing a substrate, forming a rear electrode layer on the substrate, forming a photoactive layer 110 on the rear electrode layer, Forming a capture structure.

The photoactive layer 110 may be a CIGS photoactive layer 110 formed of copper (Cu), indium (In), gallium (Ga), or selenium (Se). As the light trapping structure is formed, the traveling distance of the light incident on the photoactive layer 110 can be increased.

The absorption (A) of the light (L) in the medium can be expressed as shown in Equation (2).

&Quot; (2) "

A = ecL

In Equation (2), e is the medium extinction coefficient, c is the density of the medium, and L is the traveling distance of the light in the medium. In the light trapping structure according to an embodiment of the present invention, the travel distance of the light incident on the photoactive layer 110 can be increased.

5 is a top plan view of the microstructure layer 130 of the light trapping structure fabricated according to an embodiment of the present invention.

Referring to FIG. 5, it can be seen that bundles of nanofibers are intertwined.

FIG. 5B is an enlarged view of portion A of FIG. 5A, and FIG. 5C is an enlarged view of portion B of FIG. 5B.

As shown in FIGS. 5 (a), 5 (b) and 5 (c), it can be seen that the nanofibers are entangled with bundles and large pores are formed between the nanofiber bundles.

6 is a photograph showing a nanostructured layer in a light trapping structure according to an embodiment of the present invention.

Referring to FIG. 6, the nanostructured layer 120 of the light trapping structure may have an inclined porous structure.

A solar cell including a light trapping structure according to an embodiment of the present invention includes a photoactive layer 110, a nanostructure layer 120 formed on the photoactive layer 110, a microstructure formed on the nanostructure layer 130, and the microstructure layer 130 may include a nanofiber bundle.

The current density curve according to the applied voltage for the solar cell was measured.

7 is a graph showing photoelectric conversion efficiency of a solar cell according to an embodiment of the present invention.

Referring to FIG. 7, when comparing the pre-coating (w / o) and post-coating (w), the efficiency can be calculated from the J-V curve. From these results, it was found that the power conversion efficiency was improved by 12.98% from 8.61% to 9.73%.

Table 2 shows the characteristics of the solar cell according to (w / o) and (w) after formation of the light trapping structure.

V _oc (V) J _sc (mA / cm 2) FF (%) PCE (%) w / o 0.774 17.10 65.02 8.61 w 0.791 18.42 66.73 9.73

In Table 2, V _oc represents the open-circuit voltage of the solar cell and J _sc represents the short-circuit current. The short-circuit current means the current flowing when the voltage of both terminals of the solar cell is zero. Since the short-circuit current depends on the generation and collection of carriers generated by the incident light, in the case of an ideal solar cell, the short-circuit current and the photogeneration current are the same, so that the short-circuit current can be the maximum current that can be drawn from the solar cell. In this state, the intensity of the incident light is preferentially changed according to the wavelength distribution. However, in such a condition, electrons and holes excited by light absorption are recombined and not lost, Or to the external circuitry. The loss due to electron recombination can occur either inside the photoelectrode or at each interface. In order to increase the short-circuit current, the reflectance of the sunlight must be reduced as much as possible. The open-circuit voltage (V _oc ), when the incident light is received with the Gibbs free energy, that is, the infinite impedance, obtained from the battery as the optical voltage generated when the photocurrent does not flow due to a large resistance in the circuit, And may be a potential difference formed at both ends.

FF is a Curve Fill Factor which can be defined as the ratio of the output to the product of the open-circuit voltage and the short-circuit current. It may correspond to the maximum rectangular area in FIG. In other words, the curve factor is an important factor that affects the efficiency of the battery with the optimum operation current and the optimal operating voltage in addition to J _sc (short circuit current) and V _oc (open circuit voltage).

8 and 9 are graphs showing the depth of pores and the diameter of pores according to the etching time according to anodizing time in the light trapping structure according to an embodiment of the present invention, respectively.

The depth of the pores formed in FIG. 8 can be expressed by Equation (3).

&Quot; (3) "

D _p (nm) = 66 x t _a (min) + 20

Referring to Equation (3), it can be seen that the depth of the pores, that is, the length of the light trapping structure, increases with the anodization time t _a .

It can be seen that the diameter of the pores formed in FIG. 9 varies according to the etching time (te) according to Equation (4).

&Quot; (4) "

D _p (nm) = 0.219 x t _e (min) +33 (at 30 ° C)

From the results described above, it was confirmed that the shape of the light trapping structure can be controlled by controlling the etching time and conditions and the anodization time.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

100: light trapping structure, 110: photoactive layer
120: nano structure layer, 120A: aluminum layer
130: microstructure layer L: light

Claims

In the method for manufacturing a light trapping structure,
(a) stacking and heat-treating an aluminum layer (S10);
(b) performing (S20) an electrolytic polishing process on the heat-treated aluminum layer;
(c) performing a first anodization process on the surface of the electrolytically polished aluminum layer (S40);
(d) selectively etching the oxide formed through the anodizing process (S50);
(e) performing a second anodizing process on the selectively etched aluminum layer (S60); And
(f) performing an isotropic etching on the surface of the aluminum layer subjected to the second anodizing process (S70).

The method according to claim 1,
Wherein the first and second anodic oxidation processes (S40 and S60) are performed at a temperature of 35 DEG C or more.

The method according to claim 1,
Wherein the isotropic etching step (S70) is performed with an aqueous oxalic acid solution.

The method according to claim 1,
And the electrolytic polishing (S20) removes alumina formed on the aluminum layer.

The method according to claim 1,
Wherein the step (S50) of selectively etching the oxide uses an aqueous phosphoric acid solution (H3PO4) to which chromium oxide (CrO3) is added.

The method according to claim 1,
The length of the light trapping structure is,
Wherein the first and second anodic oxidation process times (t _a (min)) are adjusted.

The method according to claim 6,
The length (D _p ) of the light trapping structure is preferably,
D _p (nm) = 66 x t _a (min) + 20
Wherein the light trapping structure is formed on the substrate.

The method according to claim 1,
The electrolyte used in the first and second anodization processes is
Sulfuric acid (H ₂ SO ₄ ), oxalic acid, and phosphoric acid (H ₃ PO ₄ ).

The method according to claim 1,
Wherein the diameter of the pores formed in the light trapping structure is controlled by a secondary etching process.

In the light trapping structure,
A nanostructured layer comprising pores having a diameter of 10-50 nm and
And a microstructure layer having a lattice constant of 300-600 nm formed on the nanostructured layer,
Wherein the microstructure layer is spaced apart from a nanofiber bundle.

11. The method of claim 10,
In the light trapping structure,
Wherein the pore size and the lattice constant are controlled according to an applied voltage during the anodic oxidation process with the electrolyte solution.

11. The method of claim 10,
Wherein the light trapping structure has a hexagonal crystal structure.

11. The method of claim 10,
Wherein the nanostructure layer in the light trapping structure is a non-reflective layer.

A method of manufacturing a solar cell,
(a) forming a photoactive layer (S110);
(b) forming and annealing an aluminum layer on the photoactive layer (S120);
(c) electrolytically polishing the aluminum layer (S130);
(d) performing (S140) a first anodization process on the surface of the electrolytically polished aluminum layer;
(e) selectively etching the oxide formed by performing the first anodizing process (S150);
(f) performing (S160) a second anodization process on the selectively etched aluminum layer;
(g) performing isotropic etching on the surface of the aluminum layer on which the second anodizing process has been performed (S170).

15. The method of claim 14,
Wherein the first and second anodic oxidation and etching processes are performed to form a nanostructure layer on the interface between the photoactive layer and the light trapping structure and a microstructure layer on the nanostructure layer.

1. A solar cell comprising a light trapping structure,
A photoactive layer;
A nanostructure layer formed on the photoactive layer;
And a microstructure layer formed on the nanostructured layer,
Wherein the microstructure layer comprises a nanofiber bundle. &Lt; RTI ID = 0.0 > 11. < / RTI >