DYE-SENSITIZED SOLAR CELL AND METHOD FOR FABRICATING THE SAME
A dye-sensitized solar cell and method for fabricating the same are provided. The dye-sensitized solar cell includes a photo electrode including a first electrode and a Zn-doped TiO2 porous layer disposed on the first electrode, wherein the Zn-doped TiO2 porous layer absorbs a dye. A second electrode is disposed opposite to the photo electrode, wherein the Zn-doped TiO2 porous layer is disposed between the first and second electrodes. An electrolyte is disposed between the photo electrode and the second electrode.
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This application claims priority of Taiwan Patent Application No. 098141672, filed on Dec. 7, 2009, the entirety of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a dye-sensitized solar cell and a method for fabricating the same, and in particular, to a photo electrode of a dye-sensitized solar cell and a method for fabricating the same.
2. Description of the Related Art
Solar energy is a promising alternative energy source. Developments in solar energy technology are driven by the fact that solar energy is continuous and sustainable. Also, solar energy is environmentally friendly.
Generation of solar energy requires solar cells. Simplistically, electricity is generated by circuitry, generated by illumination of a material to generate electrons and holes. For example, a dye-sensitized solar cell (DSSC) is formed by sintering a semiconductor type metal oxide such as TiO2 on a conductive substrate. A dye is then absorbed by a surface of the semiconductor type metal oxide to form a photo-anode. An electrolyte between the photo-anode and a cathode aids in electrical conduction. Currently, technological development of DSSCs is popular due to its high photo-induced electron transfer efficiency and low costs. However, for a DSSC applied in a portable power supply, electron loss resulting in decreased photo-induced electron transfer efficiency is a problem when the DSSC is under a low light intensity environment.
Meanwhile, conventionally used semiconductor photocatalytic materials, may comprise TiO2, ZnO, SnO2 or CdS. Of the materials, TiO2 is a popular material due to its high oxidation-reduction ability, high chemical stability and the fact that it is non-poisonous. The conventional metal ion-doped photocatalytic materials are mainly applied to improve photocatalytic activity by trapping oxides to increase the absorption of light.
Thus, a novel dye-sensitized solar cell and a method for fabricating the same are desired with minimum electron loss under a low light intensity environment, resulting in increased photo-induced electron transfer efficiency.
BRIEF SUMMARY OF INVENTIONA dye-sensitized solar cell and a method for fabricating the same are provided. An exemplary embodiment of a dye-sensitized solar cell comprises a photo electrode comprising a first electrode and a Zn-doped TiO2 porous layer disposed on the first electrode, wherein the Zn-doped TiO2 porous layer absorbs a dye. A second electrode is disposed opposite to the photo electrode, wherein the Zn-doped TiO2 porous layer is disposed between the first and second electrodes. An electrolyte is disposed between the photo electrode and the second electrode.
An exemplary embodiment of a method for fabricating a dye-sensitized solar cell comprises: (a) mixing a TiO2 powder, a Zn-containing compound and an alkaline aqueous solution to form a mixture and performing a thermal process on the mixture to form a Zn-doped TiO2 powder; (b) mixing a binder solution with the Zn-doped TiO2 powder to form a paste; (c) coating the paste on a first electrode, and the paste is sintered to form a Zn-doped TiO2 porous layer, wherein the Zn-doped TiO2 porous layer and the first electrode construct a photo electrode; (d) disposing a second electrode opposite to the photo electrode after a dye is absorbed by the Zn-doped TiO2 porous layer; and (e) disposing an electrolyte between the photo electrode and the second electrode.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
Table. 1 shows flat band voltage and donor density comparisons between the conventional photo electrode formed by undoped TiO2 and various exemplary embodiments of photo electrode formed by a Zn-doped TiO2 porous layer of the invention.
The following description is of a mode for carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. Wherever possible, the same reference numbers are used in the drawings and the descriptions to refer the same or like parts.
The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto and is only limited by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual dimensions to practice of the invention.
One exemplary embodiment of the invention provides a dye-sensitized solar cell, wherein a photo electrode of the dye-sensitized solar cell comprises a Zn-doped TiO2 porous layer having a continuous electron transport path, thereby minimizing electron loss and increasing photoelectric conversion efficiency; especially in low light intensity environments.
When operating one exemplary embodiment of the DSSC 500 of the invention, the outside light is transmitted through the first electrode 200 into the Zn-doped TiO2 porous layer 204 of the DSSC 500, and the Zn-doped TiO2 porous layer 204 converts light energy from the light into electrical energy.
In one embodiment, a method for fabricating the DSSC 500 may comprise disposing the Zn-doped TiO2 porous layer 204 between the first electrode 200 and the opposing second electrode 202. Next, an electrolyte 206 is disposed between the photo electrode 201 and the second electrode 202 using an injection or coating process. A method for fabricating the Zn-doped TiO2 porous layer 204 may comprise steps as below.
Step (a): A TiO2 powder, a Zn-containing compound and an alkaline aqueous solution are disposed in an autoclave and mixed to form a mixture. In one embodiment, the TiO2 powder may comprise a commercial TiO2 photocatalytic (Degussa P25). The Zn-containing compound may comprise Zn-containing inorganic metal salts or organic Zn-containing compounds, for example, Zn(NO3)2·6H2O or Zn(CH3COO)2·xH2O. The alkaline aqueous solution may comprise a sodium hydroxidean aqueous solution (NaOH), wherein the alkaline aqueous solution has a normality of between about 5 to 15 N, preferably about 10 N.
Step (b): Performing a first thermal process on the mixture. In one embodiment, the first thermal process may comprise a hydrothermal synthesis process, wherein the first thermal process may have a process time of between about 20 and 40 hours, preferably about 20 hours. The first thermal process may have a process temperature of between about 110° C. and 140° C., preferably about 130° C. After performing the first thermal process, a flaky mixture is formed.
Step (c): A washing process is performed on the mixture using an acidic aqueous solution to neutralize the alkaline aqueous solution until the pH value of the mixture reaches about 1.5 to 4. During this time, a Zn-doped TiO2 multiple layer nano tube is formed. In one embodiment, the acidic aqueous solution may comprise an aqueous solution of nitric acid (HNO3) or hydrogen chloride (HCl), wherein the acidic aqueous solution has a normality of between about 0.02 and 0.2N, preferably about 0.1N.
Step (d): A second thermal process is performed on the mixture to recrystallize the mixture, thereby more Zn atoms are doped in the TiO2. After performing the second thermal process, Zn-doped TiO2 powder is formed. In one embodiment, the second thermal process may comprise a hydrothermal synthesis process, wherein the first thermal process may have a process time of between about 10 and 20 hours, preferably about 12 hours. The second thermal process may have a process temperature, which is higher than the first thermal process, of between about 180° C. and 250° C., preferably about 240° C.
Step (e): A binder solution is mixed with the Zn-doped TiO2 powder to form a paste. In one embodiment, a solvent of the binder solution may comprise H2O, an alcohol of C1-4, terpineol or carbitol. The binder of the binder solution may comprise sodium carboxymethyl cellulose, carboxymethyl cellulose (CMC), polyethylene glycol (PEG), ethyl cellulose (EC) or arcylic resin. In an embodiment of the binder solution formed by the H2O solvent and the PEG binder, the Zn-doped TiO2 powder may have a weight percentage of between about 30 wt % and 50 wt %, preferably about 40 wt %.
Step (f): The paste is coated on a first electrode 200 using a blade coating or screen printing process and then the paste is performed a sintering process to form a Zn-doped TiO2 porous layer 204, wherein the Zn-doped TiO2 porous layer 204 and the first electrode 200 construct a photo electrode 201.
Step (g): A second electrode 202 is disposed opposite to the photo electrode 201, so that the Zn-doped TiO2 porous layer 204 is disposed between the first and second electrodes 200 and 202 with absorbing a dye.
Additionally, Zn-doped TiO2 may be used in photocatalytic materials. In the fabrication process, Zn ion can be oxidized to form ZnO or be introduced into the TiO2 crystal lattice, thereby changing the material composition of TiO2. Therefore, Zn-doped TiO2 photocatalytic performance under visible light may be changed. Zn-doped TiO2 used in photocatalytic materials, however, has a purpose that is different from one exemplary embodiment of a photo electrode formed by a Zn-doped TiO2 porous layer of the invention. The Zn-doped TiO2 photocatalytic materials may be used to provide oxide traps, thereby increasing absorption of light to improve photocatalytic activity. One exemplary embodiment of a Zn-doped TiO2 photo-anode is used to provide an electron transport path with rapid transport velocity. Meanwhile, the fabricating method of one exemplary embodiment of a Zn-doped TiO2 photo-anode is different from the Zn-doped TiO2 photocatalytic.
From
One exemplary embodiment provides a dye-sensitized solar cell and a method for fabricating the same, wherein a photo electrode of the dye-sensitized solar cell is formed by a Zn-doped TiO2 porous layer represented by Ti(1-x)ZnxO2, wherein 0<x≦0.007. One exemplary embodiment of a photo electrode formed by a Zn-doped TiO2 porous layer has high Fermi energy EFn, thereby causing a more curved energy band CB curve. The number of unoccupied state traps of the photo electrode formed by the Zn-doped TiO2 porous layer is reduced when compared to conventional photo electrode formed by undoped TiO2. Therefore, one exemplary embodiment of the photo electrode formed by the Zn-doped TiO2 porous layer can provide a more continuous electron transport path. Therefore, electron transportation may be increased, so that the dye-sensitized solar cell still has high photoelectric conversion efficiency and a high output current; especially in low light intensity environments.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Claims
1. A dye-sensitized solar cell, comprising:
- a photo electrode comprising a first electrode and a Zn-doped TiO2 porous layer disposed on the first electrode, wherein the Zn-doped TiO2 porous layer absorbs a dye;
- a second electrode disposed opposite to the photo electrode, wherein the Zn-doped TiO2 porous layer is disposed between the first and second electrodes; and
- an electrolyte disposed between the photo electrode and the second electrode.
2. The dye-sensitized solar cell as claimed in claim 1, wherein the Zn-doped TiO2 porous layer is represented by Ti(1-x)ZnxO2, wherein 0<x≦0.007.
3. The dye-sensitized solar cell as claimed in claim 1, wherein the first electrode is a transparent electrode.
4. The dye-sensitized solar cell as claimed in claim 1, wherein the second electrode comprises Pt, conductive polymer, carbon or composite materials.
5. A method for fabricating a dye-sensitized solar cell, comprising:
- (a) mixing a TiO2 powder, a Zn-containing compound and an alkaline aqueous solution to form a mixture and performing a thermal process on the mixture to form a Zn-doped TiO2 powder;
- (b) mixing a binder solution with the Zn-doped TiO2 powder to form a paste;
- (c) coating the paste on a first electrode, and the paste is performed a sintering process to form a Zn-doped TiO2 porous layer, wherein the Zn-doped TiO2 porous layer and the first electrode construct a photo electrode;
- (d) disposing a second electrode opposite to the photo electrode after a dye is absorbed by the Zn-doped TiO2 porous layer; and
- (e) disposing an electrolyte between the photo electrode and the second electrode.
6. The method for fabricating a dye-sensitized solar cell as claimed in claim 5, wherein the thermal process further comprising:
- (a) performing a first thermal process on the mixture;
- (b) performing a washing process on the mixture using an acidic aqueous solution; and
- (c) performing a second thermal process on the mixture.
7. The method for fabricating a dye-sensitized solar cell as claimed in claim 5, wherein the Zn-containing compound comprises Zn-containing inorganic metal salts or organic Zn-containing compounds.
8. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the first thermal process and the second thermal process comprise a hydrothermal synthesis process.
9. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the first thermal process has a process time of between about 20 to 40 hours.
10. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the first thermal process has a process temperature of between about 110° C. and 140° C.
11. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the second thermal process has a process time of between about 10 and 20 hours.
12. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the second thermal process has a process temperature of between about 180° C. and 250° C.
13. The method for fabricating a dye-sensitized solar cell as claimed in claim 5, wherein the alkaline aqueous solution is a sodium hydroxide aqueous solution.
14. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the acidic aqueous solution is a nitric acid or hydrogen chloride aqueous solution.
15. The method for fabricating a dye-sensitized solar cell as claimed in claim 6, wherein the mixture after performing the washing process reaches a pH value of between about 1.5 and 4.
16. The method for fabricating a dye-sensitized solar cell as claimed in claim 5, wherein the Zn-doped TiO2 porous layer is represented by Ti(1-x)ZnxO2, wherein 0<x≦0.007.
17. The method for fabricating a dye-sensitized solar cell as claimed in claim 5, wherein a solvent of the binder solution comprises H2O, an alcohol of C1-4, terpineol or carbitol, and a binder of the binder solution comprises sodium carboxymethyl cellulose, carboxymethyl cellulose (CMC), polyethylene glycol (PEG), ethyl cellulose (EC) or arcylic resin.
Type: Application
Filed: Aug 17, 2010
Publication Date: Jun 9, 2011
Applicant: INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE (Hsinchu)
Inventors: Ming-De Lu (Miaoli County), Yung-Liang Tung (Hualien County), Kai-Ping Wang (Tainan City), Hsisheng Teng (Tainan City), Po-Tsung Hsiao (Taoyuan County)
Application Number: 12/858,324
International Classification: H01L 31/0288 (20060101); H01L 31/18 (20060101);