Patent Application
20090084434
This application claims the benefit of Korean Patent Application No. 10-2007-0098887, filed on Oct. 1, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a nanocomposite and method of fabricating the same and a dye-sensitized solar cell (DSSC) using the nanocomposite. The present invention is derived from research conducted by Ministry of Information and Communication (MIC) and Institute of Information Technology Advancement (IITA) as part of efforts to develop core technologies as an IT new growth engine (Project No: 2006-S-006-02 “Component Modules for Ubiquitous Terminal”)
2. Description of the Related Art
Much research has been conducted into a dye-sensitized solar cell (DSSC) technology since development of DSSCs in 1991 by a research team led by Michael Gratzel, professor of Swiss Federal Institute of Technology at Lausanne, Switzerland. A DSSC is an electrochemical solar cell that includes an electrode with an oxide layer having dye molecules chemically absorbed onto the surface thereof. The dye molecules absorb visible rays to produce electron-hole pairs and the electrode transfers the produced electrons.
Despite an advantage of lower manufacturing costs over conventional silicon solar cells, DSSCs have low energy conversion efficiency. Since the energy conversion efficiency of the DSSC increases in proportion to the amount of electrons produced by absorbing incoming light, the number of dye molecules being absorbed on the oxide layer must be increased in order to generate more electrons. Thus, in order to increase the concentration of dye molecules absorbed per unit area, it is necessary to reduce the size of particles which form the oxide layer.
The present invention provides a nanocomposite that can be used to fabricate a dye-sensitized solar cell (“DSSC”) as well as materials for other industry sectors and can contain an increased amount of dye molecules and other general molecules absorbed.
The present invention also provides a method of easily fabricating the nanocomposite.
The present invention also provides a DSSC using the nanocomposite as a nano oxide layer having dye molecules absorbed thereon.
According to an aspect of the present invention, there is provided a nanocomposite including: a plurality of nanotubes arranged perpendicular to a substrate and a plurality of nanoparticles dispersed within each of the plurality of nanotubes or between adjacent ones of the plurality of nanotubes. The nanotube and the nanoparticle may be formed of titanium dioxide (TiO2), tin dioxide (SnO2), zinc oxide (ZnO), tungsten trioxide (WO3), or mixtures thereof. The nanoparticle may have a spherical, tubular, or rod-like shape.
According to another aspect of the present invention, there is provided a method of fabricating a nanocomposite. According to the method, a plurality of nanotubes are formed perpendicular to a substrate. A plurality of nanoparticles that will be incorporated into each of the plurality of nanotubes are then synthesized. the nanoparticles may have a diameter of less than an inner diameter of the nanotube or distance between two adjacent nanotubes. The plurality of nanoparticles are subsequently placed within the nanotube or between the adjacent nanotubes.
The nanotube may be obtained by etching the substrate or forming a conducting layer for nanotubes on the substrate and etching the conducting layer. The conducting layer for nanotubes may be formed of Ti, Sn, Zn, W, or a mixture thereof. The nanotube and the nanoparticle may be formed of TiO2, SnO2, ZnO, WO3, or mixtures thereof. The plurality of nanoparticles are disposed within the nanotube or between adjacent nanotubes using electrophoresis, spin coating, or deep coating.
According to another aspect of the present invention, there is provided a DSSC including: a first electrode unit including a nanocomposite and dye molecules absorbed on the nanocomposite, the nanocomposite having a plurality of nanotubes arranged on a first substrate and a plurality of nanoparticles dispersed within each of the plurality of nanotubes or between adjacent ones of the plurality of nanotubes; a second electrode unit formed on a second substrate so as to face the first electrode unit; and an electrolytic solution interposed between the first and second electrode units.
The nanotube and the nanoparticle may be formed of TiO2, SnO2, ZnO, WO3, or mixtures thereof. The nanoparticle has a spherical, tubular, or rod-like shape.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted.
A nanocomposite according to the present invention includes a plurality of nanotubes and a plurality of nanoparticles that are dispersed within each of the plurality of nanotubes or between adjacent ones of the plurality of nanotubes and have a diameter of less than an inner diameter of each nanotube. The nanocomposite having the above-mentioned structure can be used to fabricate DSSCs as well as materials for other industry fields and facilitates charge transfer using nanotubes. The nanocomposite also provides increased surface area of nanotubes and, in particular, nanoparticles, thus increasing the amount of dye molecules as well as other general molecules absorbed. The nanocomposite having the above features will now be described in more detail with reference to
More specifically, referring to
The nanotubes 100 and the nanoparticles 110 are nano oxides that may be formed of titanium dioxide (TiO2), tin dioxide (SnO2), zinc oxide (ZnO), or mixtures thereof. In particular, the nanotubes 100 and the nanoparticles 110 may be formed of TiO2.
An outer diameter X2 of the nanotube 100 is greater than 50 nm, preferably, in a range of between 50 and 300 nm. An inner diameter X1 of the nanotube 100 is greater than 50 nm, preferably, in a range of between 50 and 200 nm. The distance between two adjacent nanotubes 100 may be greater than 50 nm. A longitudinal length of the nanotube 100 is in a range of 5 to 100 μm. The diameter of the nanoparticle 110 may be in a range of 2 to 50 nm. While the nanoparticle 110 shown in
When the nanocomposite 120 having the above-mentioned structure is used in a DSSC as described in detail later, the nanotubes 100 having a higher charge transfer rate than the nanoparticles 110 can accelerate movement of electrons. In particular, nanoparticles 110 filling the empty space within the nanotube 100 can significantly increase the amount of dye molecules absorbed to the surface thereof. Thus, the use of the the nanocomposite 120 in a DSSC can significantly improve the energy conversion efficiency.
Referring to
Subsequently, a plurality of nanoparticles to be incorporated into the nanotube are formed with a diameter of less than the inner diameter of the nanotube (step 210). The nanoparticles are synthesized using TiO2, SnO2, ZnO, WO3, or mixture thereof. Each of the plurality of nanoparticles has the same diameter as described above. The plurality of synthesized nanoparticles are dispersed within the nanotube or between adjacent nanotubes using a technique such as electrophoresis, spin coating, or deep coating (step 220).
Based on the foregoing, a nanocomposite and a method of manufacturing the same according to embodiments of the present invention will now be described. In the examples below, it is assumed that nanotubes and nanoparticles are formed of TiO2.
More specifically, after a Ti foil substrate was dipped into a mixture of acetone and alcohol, fine foreign materials and an oxide layer were removed using ultrasonic waves and 0.1% HF solution, respectively. To obtain TiO2 nanotube, a Ti foil sample was dipped into a solution of ethylene glycol containing 0.25% ammonium fluoride (NH4F) and then a voltage of 50 V was applied using platinum (Pt) as a counter electrode to etch the sample by anodization. After performing the etching for about 10 hours, the sample was cleaned with acetone and alcohol to form a TiO2 nanotube.
Subsequently, a TiO2 nanoparticle was synthesized. More specifically, 0.5 mole (M) titanium tetrachloride (TiCl4) aqueous solution was formed at 0° C., followed by hydrolysis of TiCl4 at room temperature for 1 week such that white TiO2 powder was produced. The TiO2 powder sedimented in the aqueous solution was then recovered using a rotary evaporator and redispersed in a distilled water. The resulting TiO2 aqueous solution was evaporated again using the rotary evaporator to synthesize a white TiO2 nanoparticle. The synthesized TiO2 nanoparticles have a diameter of less than an inner diameter of a nanotube or distance between nanotubes into which they will be later incorporated.
After synthesizing the TiO2 nanoparticles, a TiO2 nanotube was submerged in the aqueous solution in which the TiO2 nanopartcles had been dispersed and then a voltage of 10V was applied such that the TiO2 nanopartcles were incorporated into the TiO2 nanotube. Although in the present Example, electrophoresis was performed to incorporate the TiO2 nanopartcles into the TiO2 nanotube, spin coating or deep coating may be used to achieve the same effect. Electrophoresis is preferred over other techniques.
The resulting material with the TiO2 nanopartcles incorporated into the TiO2 nanotube was then heat treated at 500° C. for 30 minutes under an air atmosphere. After the resulting product was dipped into the TiCl4 solution at 70° C., it was heat treated again at 500° C. for 30 minutes under an air atmosphere to complete a nanocomposite having the TiO2 nanopartcles incorporated into the TiO2 nanotube.
More specifically, Ti was sputter-coated on a substrate to a thickness of about 20 μm. The substrate may be a polymer substrate or glass substrate coated with indium titanium oxide (ITO) or fluorine (F)-doped SnO2. As in the Example 1, the coated Ti layer was etched by anodization to form a TiO2 nanotube.
More specifically,
The structure of a DSSC using the nanocomposite and a method of manufacturing the same will now be described in detail with reference to
More specifically, referring to
The first electrode unit 20 includes a first substrate 10 and an overlying nanocomposite layer 125 with dye molecules 115 absorbed thereon. The first substrate 10 may be a conducting substrate such as a Ti foil or a Ti substrate coated with ITO. Alternatively, the first substrate 10 may be a polymer or glass substrate coated with ITO or F-doped SnO2.
The nanocomposite layer 125 acts as an electrode and includes a nanocomposite 120 having a plurality of nanotubes 100 and a plurality of nanoparticles 110 as described above. The plurality of nanoparticles 110 are dispersed within each of the plurality of nanotubes or between the plurality of nanotubes and have a diameter of less than an inner diameter of each nanotube. The ruthenium (Ru)-based dye molecules 115 are chemically absorbed on the nanocomposite 120.
The second electrode unit 40 is disposed under the first electrode unit 20 to face the first electrode unit 20 and includes a second substrate 30 and a Pt electrode layer 32 facing the nanocomposite layer 125 in the first electrode unit 20. The second substrate 30 may be a conducting substrate with a Ti layer formed on a glass or polymer substrate. Either of the first or second substrate 10 or 30 may be a transparent substrate.
An acetonitrile solution containing 0.6 M butylmethylimidazolium, 0.02 M iodine I2), 0.1M Guanidinium thiocyanate, and 0.5M 4-tert-butylpyridine may be used as the electrolytic solution 60 filled between the first and second electrode units 20 and 40.
Next, operation of the DSSC according to an embodiment of the present invention is described.
More specifically, dye molecules attached to the nanocomposite 125 absorbs sunlight using light penetrating through the transparent first substrate 10, to excite electrons from ground state into excited state and create an electron-hole pair. The excited electrons are then injected into a conduction band of the nanocomposite layer 125.
The electrons that have been injected into the nanocomposite layer 125 are transferred to the first conducting substrate 10 in contact with the nanocomposite layer 125 via an interface between particles and then move to the Pt electrode layer 32 in the second electrode unit 40 through an external wire (not shown). The dye molecules oxidized due to electron transfer receive electrons supplied by oxidation (3I−1→I3−+2e−) of iodine (I) ion within the electrolytic solution 60 to undergo reduction. The oxidized iodine ion I3− gains electrons from the second electrode unit 40 and becomes reduced again, thereby completing the operation of the DSSC.
More specifically, referring to
A second electrode with a Pt electrode layer formed on a second substrate is subsequently prepared (step 310). The Pt electrode layer is formed by coating Pt on the second substrate. Thereafter, the first and second electrode units are sealed with a sealing member for connection, followed by injection of an electrolytic solution between the first and second electrode units through the second electrode unit. In this way, a DSSC is fabricated (step 330).
DSSCs including nanocomposites fabricated according to the Example 1 and Example 2 are hereinafter referred to as a “DSSC of Example 1” and a “DSSC of Example 2”, respectively.
More specifically, a DSSC according to the Comparative Example 1 has the same configuration as the DSSC of the Example 1 except that it includes a nanocomposite having only a plurality of TiO2 nanotubes. That is, the nanocomposite in the DSSC according to the Comparative Example 1 does not include TiO2 nanoparticles.
More specifically, a DSSC according to the Comparative Example 2 has the same configuration as the DSSC of the Example 2 except that it includes only a plurality of TiO2 nanoparticles having a thickness of about 10 μm. That is, the nanocomposite in the DSSC according to the Comparative Example 2 does not include TiO2 nanotubes. The first substrate used in the Comparative Example 2 is a glass substrate coated with F-doped SnO2.
Tables 1 and 2 below respectively show comparisons between DSSCs of the Example 1 and the Comparative Example 1 and between DSSCs of the Example 2 and the Comparative Example 2.
More specifically, the following Table 1 shows a comparison between surface areas of nanocomposite in the DSSC of Example 1 and TiO2 nanotube of the Comparative Example 1. As evident from Table 1, the surface area of the nanocomposite is increased by about 20% compared to the surface area of the TiO2 nanotube. This means the area of the dye molecules that can be absorbed in the DSSC of Example 1 is increased about 20% compared to that in the DSSC of Comparative Example 1. Thus, the DSSC of Example 1 can provide improved cell performance over the DSSC of Comparative Example 1.
The following Table 2 shows a comparison between energy conversion efficiency of DSSCs of Examples 1 and 2 and Examples. As evident from Table 2, energy conversion efficiency in the DSSCs of the Examples 1 and 2 is improved by about 20% and 10% compared to those in the DSSC of the Comparative Examples 1 and 2, respectively.
Based on the result of comparisons, the DSSCs of Examples 1 and 2 using nanocomposites including both TiO2 nanotubes and TiO2 nanoparticles as an electrode provide improved cell efficiency over the DSSCs of Comparative Examples 1 and 2 using either TiO2 nanotubes or TiO2 nanoparticles as an electrode. The DSSCs of Examples 1 and 2 according to the present invention deliver improved cell efficiency because of their fast charge transfer exhibited by TiO2 nanotubes and large surface areas exhibited by TiO2 nanoparticles.
More specifically, as indicated by curve (a) on the I-V graph, a DSSC of Example 1 exhibits current density of about 15.5 mA/cm2 and voltage of about 0.78 V. On the other hand, as indicated by curve (b), a DSSC of Comparative Example 2 exhibits current density of about 10.7 mA/cm2 and voltage of about 0.73 V. That is, the DSSC of Example 1 including both TiO2 nanotubes and TiO2 nanoparticles shows better current-voltage characteristics than the DSSC of Comparative Example 1 because of its fast charge transfer exhibited by the TiO2 nanotubes and large surface area exhibited by TiO2 nanoparticles
As described above, a nanocomposite according to the present invention includes a plurality of nanotubes and a plurality of nanoparticles that are dispersed within each nanotube or between adjacent nanotubes and have a diameter of less than an inner diameter of the nanotube. The nanocomposite having the above-mentioned structure facilitates electron movement while providing increased surface area of nanotubes and, in particular, nanoparticles so that the amount of absorbed general molecules can be increased.
When the nanocomposite is used in a DSSC, nanotubes in the nanocomposite can accelerate movement of electrons and nanotubes and nanoparticles (in particular, nanoparticles) can significantly increase the amount of dye molecules. Thus, the use of the nanocomposite in the DSSC can significantly improve the energy conversion efficiency.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2007-0098887 | Oct 2007 | KR | national |
