Flexible photo-anode of dye-sensitized solar cell and manufacturing method thereof

A flexible photo-anode of dye-sensitized solar cell and a manufacturing method thereof are provided. The method includes steps of: coating zinc oxide nanoparticles on a flexible substrate to form a seed layer; immersing the flexible substrate into a first reaction solution; heating the seed layer to form a zinc oxide nanowire array; cooling the flexible substrate to the room temperature, immersing it into the second reaction solution, and stirring the second reaction solution, so that the zinc oxide nanowire array forms a cactus-like structure. Thus, the sintering and embossing processes can be prevented.

FIELD OF THE INVENTION

The present invention relates to a flexible photo-anode of a dye-sensitized solar cell and a manufacturing method for the flexible photo-anode of a dye-sensitized solar cell, and more particularly to form a zinc oxide nanowire array with a cactus-like structure by a chemical bath deposition method at room temperature.

BACKGROUND OF THE INVENTION

Nano-scale thin film solar cell of the third generation is called dye sensitized solar cell (DSSC), wherein the solar cell has advantages of low material cost, easy processing and simple equipment. The solar cell comprises a substrate and a photo-anode formed on the substrate, the photo-anode comprises a titanium dioxide layer and dyes absorbed in the titanium dioxide layer for absorbing UV light to convert into electric energy by titanium dioxide layer and simultaneously absorbing the visible light to improve energy output efficiency by the dyes. In the traditional technologies, a titanium dioxide film is formed by micron-scale wet coating method, electrophoresis method, screen printing method or blade coating method, and then the titanium dioxide film is sintered to form the titanium dioxide layer.

However, the above-mentioned methods still have the following problems, the production equipment for the micron-scale wet coating method or the electrophoresis method is high cost; the screen printing method and the blade coating method coated are carried out by mechanical compression, so that the titanium oxide layer is not firmly attached on the substrate; after sintering, the quality of the structure of the titanium dioxide layer is affected, the solar cell thus can not be applied to the flexible substrate. Furthermore the titanium dioxide layer must absorb the dyes by being immersed into a dye solution at least eight hours, and the time of the process is relatively long.

Therefore it is necessary to provide a flexible photo-anode of a dye-sensitized solar cell and a manufacturing method for the flexible photo-anode of a dye-sensitized solar cell, so as to form a zinc oxide nanowire array with a cactus-like structure by a chemical bath deposition method at room temperature to avoid the sintering and mechanical compression.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a flexible photo-anode of a dye-sensitized solar cell, which is used to form a zinc oxide nanowire array with a cactus-like structure by a chemical bath deposition method at room temperature to avoid the sintering and mechanical compression.

A secondary object of the present invention is to provide a manufacturing method for the flexible photo-anode of a dye-sensitized solar cell, which is used to form a zinc oxide nanowire array with a cactus-like structure by a chemical bath deposition method at room temperature to simplify the manufacturing process, reduce the cost and improve the application of the flexible product.

The technical solution of the present invention is to provide a manufacturing method for a flexible photo-anode of a dye-sensitized solar cell, comprising steps of: (a) preparing a plurality of zinc oxide nanoparticles; (b) coating the zinc oxide nanoparticles on a flexible substrate as a seed layer; (c) immersing the flexible substrate into a first reaction solution, the first reaction solution comprising zinc acetate and hexamethylenetetramine; (d) heating the first reaction solution to 90-100° C., so as to form a zinc oxide nanowire array on the seed layer; and (e) taking out the flexible substrate from the first reaction solution, cooling the flexible substrate to the room temperature, immersing the flexible substrate into a second reaction solution followed by a stirring operation, so that a plurality of spurs are extended from each of nanowires of the zinc oxide nanowire array to form a cactus-like structure, wherein the second reaction solution comprises zinc ions and alkali.

In one embodiment of the present invention, the stirring operation is to stir the second reaction solution 2 to 10 minutes at a rotation speed of 300 to 1500 rpm.

In one embodiment of the present invention, the particle sizes of the zinc oxide nanoparticles are 5 to 10 nm.

In one embodiment of the present invention, the zinc acetate in the first reaction solution has a molar concentration from 0.01 to 0.03 mole/L.

In one embodiment of the present invention, the hexamethylenetetramine in the first reaction solution has a molar concentration from 0.01 to 0.03 mole/L.

In one embodiment of the present invention, the zinc ions in the second reaction solution are selected from zinc nitrate, zinc acetate, zinc chloride or zinc sulfate.

In one embodiment of the present invention, the alkali in the second reaction solution is sodium hydroxide or potassium hydroxide.

In one embodiment of the present invention, the zinc ions in the second reaction solution have a molar concentration from 0.4 to 0.7 mole/L, the alkali in the second reaction solution has a molar concentration from 3 to 5 mole/L.

In one embodiment of the present invention, after the step (e), the method further comprises a step of: (f) coating a plurality of zinc oxide nanoparticles on the zinc oxide nanowire array as a light scattering layer, and immersing the flexible substrate into the second reaction solution followed by a stirring operation.

To achieve the above object, the present invention provides a flexible photo-anode of a dye-sensitized solar cell which comprises a flexible substrate; a zinc oxide nanowire array formed on the flexible substrate; and a light scattering layer formed on the zinc oxide nanowire array, wherein each of nanowires of the zinc oxide nanowire array has a cactus-like structure and a plurality of spurs are extended from each of the nanowires.

In one embodiment of the present invention, the flexible substrate is a transparent nonmetallic substrate.

In one embodiment of the present invention, the thickness of the zinc oxide nanowire array is 3 to 12 μm.

In one embodiment of the present invention, the light scattering layer comprises a plurality of zinc oxide nanoparticles.

As described above, forming a zinc oxide nanowire array with the cactus-like structure by chemical bath deposition method at room temperature, the titanium oxide layer is replaced, so as to avoid the sintering and mechanical compression in the process, and to simplify the manufacturing process, reduce the cost and improve the application of the flexible product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings. Furthermore, directional terms described by the present invention, such as upper, lower, front, back, left, right, inner, outer, side, longitudinal/vertical, transverse/horizontal, and etc., are only directions by referring to the accompanying drawings, and thus the used directional terms are used to describe and understand the present invention, but the present invention is not limited thereto.

Referring now toFIGS. 1-4, a manufacturing method for a flexible photo-anode of a dye-sensitized solar cell according to an embodiment of the present invention is illustrated and comprises steps of: (S1) forming a seed layer3on the flexible substrate2; (S2) immersing the flexible substrate2by a chemical bath deposition method; (S3) immersing the flexible substrate2by a first chemical bath deposition method; and (S4) immersing the flexible substrate2by a second chemical bath deposition method. The present invention will be discussed in more detail hereinafter.

Referring now toFIG. 1, the step (S1) of the manufacturing method for a flexible photo-anode of a dye-sensitized solar cell according to the embodiment of the present invention is firstly to form a seed layer3on the flexible substrate2. As shown, a plurality of zinc oxide nanoparticles31are prepared in advance, wherein the particle diameter of the zinc oxide nanoparticles are 5 to 10 nm, the zinc oxide nanoparticles31are coated on the flexible substrate2by sputtering or spin coating, so as to be a ZnO seed layer3.

Referring now toFIG. 2, the step (S2) is then to immerse the flexible substrate2into a first reaction solution (not-shown) by a chemical bath deposition method, wherein the first reaction solution comprises zinc acetate and hexamethylenetetramine, the zinc acetate in the first reaction solution has a molar concentration from 0.01 to 0.03 mole/L, the hexamethylenetetramine in the first reaction solution has a molar concentration from 0.01 to 0.03 mole/L. Then, the first reaction solution is heat to 90-100° C., so as to form a zinc oxide nanowire array4on the seed layer3.

It should be noted that, the formation of the zinc oxide nanowire array4requires to use the zinc oxide as a precursor, i.e. reacting zinc source with alkali. In the present embodiment, the zinc source in the first reaction solution is zinc nitrate (Zn(NO3)2) or zinc acetate (Zn(CH3COO)2.2H2O), and the alkali in the first reaction solution is hexamethylenetetramine (C6H12N4) or ammonia (NH4OH), wherein the reaction temperature is 80 to 100° C. The precursor of zinc oxide nanowire array4according to the preferred embodiment is zinc acetate and hexamethylenetetramine, wherein the reaction temperature is 95° C.

Referring now toFIG. 3, the step (S3) is then to immerse the flexible substrate2into a second reaction solution (no shown) by a first chemical bath deposition method, followed by taking out the flexible substrate2from the first reaction solution and cooling the flexible substrate2to the room temperature, wherein the second reaction solution comprises zinc ions and alkali, the zinc ions in the second reaction solution has a molar concentration from 0.4 to 0.7 mole/L, the alkali in the second reaction solution has a molar concentration from 3 to 5 mole/L, the zinc ions in the second reaction solution are selected from zinc nitrate (Zn(NO3)2), zinc acetate (Zn(CH3COO)2.2H2O), zinc chloride (ZnCl2) or zinc sulfate (ZnSO4). The alkali in the second reaction solution has a molar concentration from 3 to 5 mole/L, wherein the alkali in the second reaction solution is selected from sodium hydroxide, potassium hydroxide or other alkaline earth metal oxide. Than, followed by a stirring operation, the stirring operation is to stir the second reaction solution 2 to 10 minutes at a rotation speed of 300 to 1500 rpm. In the embodiment, the stirring operation is preferably to stir the second reaction solution 4 minutes at a rotation speed of 700 rpm, so that a plurality of spurs42are extended from each of nanowires41of the zinc oxide nanowire array4to form a cactus-like structure.

Referring now toFIG. 4, the step (S4) is then to coat a plurality of zinc oxide nanoparticles51on the zinc oxide nanowire array4as a light scattering layer5, and to immerse the flexible substrate2into a second reaction solution by a second chemical bath deposition method, followed by a stirring operation, wherein the stirring operation is to stir the second reaction solution 4 minutes at a rotation speed of 700 rpm, so as to improve the attachment between the nanoparticles51and the connection between the nanoparticle51and the zinc oxide nanowire array4.

Referring now toFIGS. 5A and 5B,FIG. 5Ais a crystal picture illustrating a structural top view of the zinc oxide nanowire array4with the one dimensional structure according toFIG. 2, andFIG. 5Bis a crystal picture illustrating a structural top view of the zinc oxide nanowire array4of the cactus-like structure according toFIG. 3. Furthermore,FIG. 6is an experimental data of photovoltaic performances (voltage-current density curve). Referring toFIG. 6, the conductivity of the zinc oxide nanowire array4of the cactus-like structure is better than the conductivity of the zinc oxide nanowire array4of the one dimensional structure.

As described above, the adhesion between the light scattering layer5and the zinc oxide nanowire array4is improved by forming the zinc oxide nanowire array4on the seed layer3, forming a cactus-like structure on each of nanowires41of the zinc oxide nanowire array4by the first chemical bath deposition method and executing the second chemical bath deposition method after coating the light scattering layer5.

The traditional titanium oxide layer can be replaced with the zinc oxide nanowire array4with the cactus-like structure formed by the first chemical bath deposition method, and the zinc oxide nanowire array4with the cactus-like structure can be used as a photo-anode, so as to avoid the sintering and mechanical compression in the process, and to simplify the manufacturing process, reduce the cost and improve the application of the flexible product. Additionally, the adhesion between the nanoparticles51can be improved by the second chemical bath deposition method, so that the mechanical strength and conductivity of the light scattering layer5are improved.

Referring now toFIG. 7, a flexible photo-anode of a dye-sensitized solar cell100according to an embodiment of above method is illustrated and comprises two flexible substrates2,2′, a seed layer3, a zinc oxide nanowire array4, a light scattering layer5and an electrolyte layer6. The flexible substrates2,2′ are transparent nonmetallic substrates, and an interval is formed between the two substrates2,2′, wherein the seed layer3is coated on the flexible substrate2, the zinc oxide nanowire array4is formed on the flexible substrate2, the thickness of the zinc oxide nanowire array4is 3 to 12 μm, the nanowires41of the zinc oxide nanowire array4are extended toward flexible substrate2′ from the seed layer3, each of nanowires41of the zinc oxide nanowire array4is a cactus-like structure and a plurality of spurs are extended from each of the nanowires4, the light scattering layer5comprises a plurality of zinc oxide nanoparticles51, the zinc oxide nanoparticles51are formed on the zinc oxide nanowire array4, and the electrolyte layer6is filled between the flexible substrate2′ and the light scattering layer5.

As described above, the traditional titanium oxide layer can be replaced with the zinc oxide nanowire array4with the cactus-like structure formed by the first chemical bath deposition method, and the zinc oxide nanowire array4with the cactus-like structure can be used as a photo-anode, so as to avoid the sintering and mechanical compression in the process, and to simplify the manufacturing process, reduce the cost and improve the application of the flexible product. Additionally, the adhesion between the nanoparticles51can be improved by forming the zinc oxide nanoparticles51on the zinc oxide nanowire array4, so that the inter-necking and conductivity of the light scattering layer5are improved.