Description

METHOD OF FORMING POROUS LAYER, DYE-SENSITIZED SOLAR CELL USING THE SAME, AND METHOD OF FABRICATING THE DYE-SENSITIZED SOLAR CELL

Technical Field

[1] The present invention disclosed herein relates to a method of forming a porous layer, dye-sensitized solar cell using the same, and a method of fabricating the dye- sensitized solar cell.

[2] The present invention has been derived from research undertaken as a part of the information technology (IT) development business by the Ministry of Information and Communication and Institute for Information Technology Advancement of the Republic of Korea [Project management No.: 2006-S-006-02, Project title: component module for ubiquitous terminal] . Background Art

[3] A solar cell is a photovoltaic energy conversion system that converts light energy radiated from the sun to electrical energy. Silicon solar cells widely used today employ a p-n junction diode formed within silicon for photovoltaic energy conversion.

[4] However, to prevent premature recombination of electrons and holes, silicon must have a high degree of purity and a low incidence of defects. Since this technical requirement precipitates an increase in material cost, silicon solar cells have a high fabrication cost per watt.

[5] Moreover, because photons, which have an energy level greater than a bandgap, contribute to generation of more current, silicon used for silicon solar cells is doped with dopant to have a bandgap as low as possible. However, due to the lowered bandgap, electrons excited by blue light or ultraviolet light become overly energized, and are consumed to generate heat rather than electrical current.

[6] Also, a p-type layer must be sufficiently thick to increase photon capturing probability; however, because the p-type layer increases the probability of excited electrons recombining with holes before they can reach a p-n junction, a silicon solar cell has low efficiency ranging from about 7% to about 15%.

[7] In 1991, Michael Gratzel, Mohammad K. Nazeeruddin, and Brian O'Regan disclosed a Dye-sensitized Solar Cell (DSC), based on the photosynthesis reaction principle, and known as the "Gratzel cell" in U.S. Pat. No. 5,350,644.

[8] A dye-sensitized solar cell based on the Gratzel model is a photoelectrochemical system that employs a dye material and a transition metal oxide layer instead of a p-n junction diode for photovoltaic energy conversion. Specifically, a dye-sensitized solar

cell includes a semiconductor electrode with the dye material and a transition metal oxide, a counter electrode coated with platinum or carbon, and an electrolyte between the electrodes.

[9] Because the material used in such a dye-sensitized solar cell is inexpensive and the fabrication method is simple, fabrication costs are lower than those of silicon solar cells. Furthermore, because a dye-sensitized solar cell has an energy conversion efficiency similar to that of a silicon solar cell, it has a lower fabrication cost per output watt than a silicon solar cell. In particular, in the aftermath of extensive research conducted recently on materials, dye- sensitized solar cells are projected to be capable of satisfying various industrial requirements such as improved energy conversion efficiency and reduced fabrication costs.

[10] Meantime, the electrolyte of the dye-sensitized solar cell based on the Gratzel model is encapsulated between the semiconductor electrode and the counter electrode by a predetermined encapsulating element. The breakage of the encapsulated element causes the leakage of the electrolyte, thereby reducing the lifespan thereof and causing environmental pollution. Thus, a technology for preventing the leakage of the electrolyte is needed to commercially use the dye- sensitized solar cell. To satisfy this technical need, dye-sensitized solar cells including a gel type electrolyte or a solid type electrolyte are recently suggested. However, it has been reported that the gel type or the solid type electrolyte is inferior to a liquid type electrolyte in performance. Disclosure of Invention

Technical Problem

[11] The present invention provides a method of forming a porous layer that can stably retain a liquid.

[12] The present invention provides a method of fabricating a dye- sensitized solar cell that can prevent the leakage of a liquid type electrolyte.

[13] The present invention provides a dye-sensitized solar cell that can prevent the leakage of a liquid type electrolyte. Technical Solution

[14] Embodiments of the present invention provide methods of forming a porous layer, including: preparing a high molecular compound; dissolving the high molecular compound in a solvent to prepare a source solution; and evaporating the solvent from the source solution to form a high molecular layer, wherein the evaporating of the solvent is performed when a humidity of air in contact with the source solution is under control such that the high molecular layer has a porous structure.

[15] In some embodiments, the high molecular compound includes one of a poly vinylidene fluoride polymer and a copolymer thereof. The solvent includes one of

acetone and N-methylpyrrolidone (NMP).

[16] In other embodiments, the preparing of the source solution includes dissolving the high molecular compound in the solvent in a range of about 1 weight % to about 5 weight %. The evaporating of the solvent is performed under a humidity condition of air contacting the source solution in a range of about 30 % to about 70 %.

[17] In still other embodiments, the high molecular layer is formed to include pores that continuously penetrate therethrough and a volume ratio of the pores to the high molecular layer ranges from about 30 % to about 80%.

[18] In other embodiments of the present invention, dye-sensitized solar cells include: an upper electrode structure disposed on a lower electrode structure; a semiconductor electrode layer in contact with the lower electrode structure and disposed between the lower electrode structure and the upper electrode structure; a porous high molecular layer disposed between the semiconductor electrode layer and the upper electrode structure and define pores; and an electrolyte filling the pores of the porous high molecular layer.

[19] In some embodiments, the porous high molecular layer is a high molecular compound including one of a poly vinylidene fluoride polymer and a copolymer thereof. Each of the pores has a width ranging from about 10 nm to about 100 mm. The porous high molecular layer has a thickness ranging from about 5 mm to about 50 mm.

[20] In other embodiments, the pores are formed to continuously penetrate through the porous high molecular layer between the semiconductor electrode layer and the upper electrode structure such that the semiconductor electrode layer is electrically connected to the upper electrode structure through the electrolyte. A volume ratio of the pores to the porous high molecular layer ranges from about 30 % to about 80%.

[21] In still other embodiments of the present invention, methods of fabricating a dye- sensitized solar cell, include: forming a semiconductor electrode layer on a lower electrode structure; forming a dye layer on a surface of the semiconductor electrode layer; forming a porous high molecular layer on a resultant structure including the dye layer, the porous high molecular layer defining pores; forming an upper electrode structure on the porous high molecular layer; and injecting an electrolyte into the pores of the porous high molecular layer.

[22] In some embodiments, each of the pores has a size ranging from about 10 nm to about 100 mm and is formed to continuously penetrate through the porous high molecular layer, and a volume ratio of the pores to the porous high molecular layer ranges from about 30 % to about 80%.

[23] In other embodiments, the forming of the porous high molecular layer includes: coating a source solution on the semiconductor electrode layer including the dye layer, the source solution including a high molecular compound and a solvent mixed therein;

and evaporating the solvent, wherein the high molecular compound includes one of a poly vinylidene fluoride polymer and a copolymer thereof. An amount of the high molecular compound, which is dissolved in the solvent, ranges from about 1 weight % to about 5 weight %. The solvent includes one of acetone and N-methylpyrrolidone (NMP). The evaporating of the solvent is performed under a humidity condition of air contacting the source solution in a range of about 30 % to about 70 %.

Advantageous Effects

[24] According to the present invention, a source solution including a high molecular compound is dried under a controlled humidity condition. Here, a resultant high molecular layer has a porous structure or a porous luffa sponge structure that can provide an excellent capillary phenomenon. Because of the excellent capillary phenomenon, the porous high molecular layer of the present invention is advantageous to prevent the leakage of a liquid material, as seen from test results.

[25] As a result, according to the present invention, a liquid electrolyte is retained in the porous high molecular layer of a dye-sensitized solar cell, thereby preventing environmental pollution caused by the leakage of the liquid electrolyte and improving the lifespan of the dye-sensitized solar cell.

[26] Furthermore, it can be seen from the test results that the dye-sensitized solar cell including the porous high molecular layer of the present invention prevents the deterioration of its electric performance. That is, according to the present invention, although the liquid electrolyte is retained in the porous high molecular layer, the dye- sensitized solar cell does not deteriorate in its performance. Brief Description of the Drawings

[27] The accompanying figures are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the figures:

[28] FIG. 1 is a cross-sectional view illustrating a dye-sensitized solar cell according to an embodiment of the present invention;

[29] FIG. 2 is a flowchart illustrating a method of forming a porous high molecular layer according to the present invention;

[30] FIGS. 3 and 4 are electron microscope images illustrating a porous high molecular layers according to the present invention;

[31] FIG. 5 is a flowchart illustrating a method of fabricating a dye-sensitized solar cell according to an embodiment of the present invention;

[32] FIG. 6 is a cross-sectional view illustrating a method of fabricating a dye-sensitized solar cell according to an embodiment of the present invention; and

[33] FIG. 7 is a graph illustrating an electrical characteristic of a dye-sensitized solar cell according to the present invention. Mode for the Invention

[34] Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as 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 scope of the present invention to those skilled in the art. Also, reference numerals illustrated in the order of description is not limited to the order. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout.

[35] It will also be understood that when a layer is referred to as being on another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present.

[36] FIG. 1 is a cross-sectional view illustrating a dye-sensitized solar cell 100 according to an embodiment of the present invention.

[37] Referring to FIG. 1, the dye-sensitized solar cell 100 according to the present embodiment includes a lower electrode structure 10, an upper electrode structure 50, and a semiconductor electrode layer 20 in contact with the lower electrode structure 10 and disposed between the lower electrode structure 10 and the upper electrode structure 50.

[38] The lower electrode structure 10 includes a lower substrate 12 and a lower electrode layer 14 coated on a surface of the lower substrate 12, and the upper electrode structure 50 includes an upper substrate 52 and an upper electrode layer 54 coated on a surface of the upper substrate 52. Here, the lower electrode layer 14 of the lower electrode structure 10 and the upper electrode layer 54 of the upper electrode structure 50 are disposed facing one another.

[39] According to an embodiment of the present invention, the lower substrate 12 and the upper substrate 52 may be formed of glass. According to another embodiment of the present invention, the lower substrate 12 and the upper substrate 52 may be formed of a flexible material. For example, at least one of the lower substrate 12 and the upper substrate 52 may include at least one of metal materials such as stainless steel and aluminum. Furthermore, when the lower substrate 12 is formed of a metal material, an insulating film or a semiconductor film may be further provided between the lower substrate 12 and the lower electrode layer 14. Likewise, when the upper substrate 12 is formed of a metal material, an insulating film or a semiconductor film may be further provided between the upper substrate 52 and the upper electrode layer 54. While the

lower substrate 12 is formed of a metal material, the upper substrate 52 may be formed of a light-transmitting high molecular material. Likewise, while the upper substrate 52 is formed of a metal material, the lower substrate 12 may be formed of a light- transmitting high molecular material.

[40] The lower electrode layer 14 and the upper electrode layer 54 may be formed of a transparent conductive material. For example, the lower electrode layer 14 may be formed of at least one of Indium Tin Oxide (ITO), SnO ₂ , SnO ₂ :F (FTO), ZnO, and carbon nanotubes, and the upper electrode layer 54 may be formed of the same material as the lower electrode layer 14, for example, at least one of ITO, SnO ₂ , FTO, ZnO, and carbon nanotubes.

[41] The semiconductor electrode layer 20 may be formed of one of various metal oxides including a transition metal oxide. For example, the semiconductor electrode layer 20 may be one of titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), and zinc oxide (ZnO).

[42] According to an embodiment of the present invention, the semiconductor electrode layer 20 may be a titanium oxide layer having a thickness ranging from about 5 mm to about 30 mm. When light, which has an energy level greater than a bandgap, is radiated on the titanium oxide layer, electrons in the titanium oxide layer are transferred to a conduction band, and holes are formed in a valence band. These electrons and holes are involved in an oxidation reaction or a reduction reaction, or recombine with each other to generate heat. Specifically, an oxidizing agent such as oxygen is reduced by electrons of the conduction band, and a reducing agent is oxidized by holes of the valence band. In particular, the holes generate hydroxyl radicals by oxidizing water molecules or ions adsorbed onto the surface of the titanium oxide layer. The hydroxyl radical is an extremely reactive radical that dissolves a nondegradable organic material by oxidizing it.

[43] A dye layer including dye molecules is formed on the surface of the semiconductor electrode layer 20. When sunlight is radiated on the dye layer, excited electrons are injected into the conduction band of the semiconductor electrode layer 20, and then transferred to the lower electrode layer 14. For this, the dye layer may be a ruthenium complex. For example, the dye material may be N719 (Ru(dcbpy)2(NCS)2 containing 2 protons). However, although not illustrated herein, at least one of various well- known dye materials may be applicable to a dye-sensitized solar cell of the present invention. For example, dye material such as N712, Z907, Z910, and K19 may be used for a dye- sensitized solar cell according to the present invention.

[44] According to an embodiment of the present invention, the semiconductor electrode layer 20 may be formed of particles formed of nano-crystalline titanium oxide (nc TiO ₂ ). Here, while the nc TiO ₂ particles are each separately formed, in order to transfer

excited electrons to the lower electrode layer 14, they are each formed to physically contact at least oneadjacent nc TiO ₂ particle. The dye molecules in the dye layer are adsorbed onto the surface of the nc TiO ₂ particles that may have a diameter ranging from about 3 nm to about 30 nm.

[45] According to the present invention, a porous high molecular layer 30 having pores is disposed between the upper electrode 54 and the semiconductor electrode layer 20. The pores of the porous high molecular layer 30 are filled with an electrolyte (not shown).

[46] According to an embodiment of the present invention, the porous high molecular layer 30 may be at least one of high molecular compounds including a poly (vinylidene fluoride) polymer or its copolymer. The upper electrode layer 54 is electrically connected to the semiconductor electrode layer 20 through the electrolyte such that the dye-sensitized solar cell 100 of the present invention continually generate electric current. Each of the pores has a size ranging from about 10 nm to about 100 mm and is configured to continuously penetrate through the porous high molecular layer 30 to electrically connect the upper electrode 54 to the semiconductor electrode layer 20.

[47] According to an embodiment of the present invention, a volume ratio of the pores to the porous high molecular layer 30 may be in a range from about 30 % to about 80%, and the porous high molecular layer 30 may have a thickness ranging from about 5 mm to about 50 mm (each of the pores may have a thickness greater than that of the porous high molecular layer 30 because the porous high molecular layer 30 has a thin thickness relative to its width). However, it is obvious to those skilled in the art that the volume ratio and the thickness of the porous high molecular layer 30 may vary. When the volume ratio of the pores to the porous high molecular layer 30 is in a range from about 30 % to about 80%, the porous high molecular layer 30 may have a porous luff a sponge structure to improve a capillary phenomenon, as illustrated in FIG. 3. Thus, the porous high molecular layer 30 configured to improve a capillary phenomenon prevents the electrolyte of the dye- sensitized solar cell 100 from leaking.

[48] The electrolyte may be a redox iodide electrolyte. According to an embodiment of the present invention, the electrolyte may be an acetonitrile electrolyte with 0.6 M butylmethylimidazolium, 0.02 M 12, 0.1 M guanidinium thiocyanate, and 0.5 M 4-tert-butylpyridine. However, one of various electrolytes not exemplarily mentioned above may be used in the electrolyte according to the present invention. For example, the electrolyte may include alkylimidazolium iodides or tetra-alkyl ammoniumiodides, and surface additives including tert-butylpyridin (TBP), benzimidazole (BI), and N- Methylbenzimidazole (NMBI). Acetonitrile, propionitrile, or a mixed liquid of valer- onitrile and acetonitrile is used as a solvent.

[49] Furthermore, a catalyst layer 56, which accelerates a process of reducing triiodide of

the electrolyte to iodide, may be further formed on the upper electrode layer 54. The catalyst layer 56 may be a platinum (Pt) layer formed on the upper electrode layer 54 at a volume ranging from about 5 μg/cm2 to about 10 μg/cm2.

[50] The excited electrons transferred through the semiconductor electrode layer 20 to the lower electrode layer 14 are transferred through the upper electrode layer 54 and the electrolyte to the dye molecules. Thus, the dye-sensitized solar cell continually generates electrical current through the electron circulation system. For this circulation system of electrons, the upper electrode layer 54 and the lower electrode layer 14 may be connected through a predetermined interconnection structure 60, and a load 62 consuming energy from the electrons may be provided to the interconnection structure 60.

[51] FIG. 2 is a flowchart illustrating a method of forming a porous high molecular layer according to the present invention.

[52] Referring to FIG. 2, in operation Sl, a source material 201 and a solvent 202 are mixed to be a source solution 203 that is used to form the porous high molecular layer.

[53] According to an embodiment of the present invention, the source material 201 may be a high molecular compound including a poly (vinylidene fluoride) polymer or its copolymer. The solvent 202 may be acetone or N-methylpyrrolidone (NMP). According to the present invention, the amount of the source material 201, which is dissolved in the source solution 203, may be in a range from about 1 weight % to about 5 weight %.

[54] Next, in operation S2, the source solution 203 is dried to form the porous high molecular layer formed of the source material 201. According to the present invention, the process of drying the source solution 203 may be performed when a humidity of air in contact with the source solution 203 ranges from about 30 % to about 70 %. According to an embodiment of the present invention, the process of drying the source solution 203 may be performed when the humidity ranges from about 40 % to about 60 %.

[55] FIGS. 3 and 4 are electron microscope images illustrating porous high molecular layers according to the present invention. Specifically, referring to FIGS. 3 and 4, samples were formed using the same method (that is, the method of forming a porous high molecular layer, illustrated in FIG. 2) except that source solutions are dried under different humidity conditions, respectively. The sample of FIG. 3 is formed under a humidity condition of 40 %, and the sample of FIG. 4 is formed under a humidity condition of 15 %.

[56] Referring to FIGS. 3 and 4, while the porous high molecular layer formed under the humidity condition of 40 % has a porous luffa sponge structure having a number of pores, the porous high molecular layer formed under the humidity condition of 15 %

has few pores.

[57] Test results shown in Table 1 below, illustrate relations between the humidity conditions of operation S2 and abilities of the porous high molecular layers to retain an electrolyte. Hereinafter, the ability to retain the electrolyte will be referred to as electrolyte retainability for convenience in description. Sample 1 of Table 1 was formed using the method of forming the sample of FIG. 3. Sample 2 of Table 1 was formed using the method of forming the sample of FIG. 4. That is, the samples 1 and 2 were formed using the same method except that a source solution of the sample 1 and a source solution of the sample 2 were dried under the humidity conditions of 40 % and 15 %, respectively. Sample 3 of Table 1 was a layer having a typical porous structure.

[58] A process for obtaining the test results will now be described. An electrolyte was injected in the same amount into the samples 1, 2 and 3 (formed in a bottom of different containers with each other, respectively). The containers were then turned upside down to observe whether the electrolytes flowed down. Referring to Table 1, it can be observed that the electrolyte of the sample 1 did not flow down but the electrolyte of the samples 2 and 3 flowed down. From the test result, it can be observed that the sample 1 is superior in electrolyte retainability to the samples 2 and 3. Also, from a difference between the morphologies of the layers illustrated in FIGS. 3 and 4, it can be appreciated that a difference in electrolyte retainabiltiy between the samples 1 and 2 depends upon whether the samples 1 and 2 have a porous structure capable of providing a capillary phenomenon.

[59] Table 1 [Table 1] [Table ]

[60] Thus, it can be seen that a humidity condition suitable for forming the porous high molecular layer is in a range including the humidity condition of 40 % used by the present inventors. An upper limit and a lower limit of the humidity condition may be determined through an additional test that may be easily performed by those skilled in the art.

[61] FIG. 5 is a flowchart illustrating a method of fabricating a dye-sensitized solar cell according to an embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating the method of fabricating the dye-sensitized solar cell according to the embodiment of FIG. 5.

[62] Referring to FIGS. 5 and 6, a lower electrode structure 10 is prepared in operation

SlO. The lower electrode structure 10 includes a lower substrate 12 and a lower electrode layer 14 coated on one side of the lower substrate 12. The lower electrode layer 14 may be at least one of ITO, SnO ₂ , FTO, ZnO, and carbon nanotubes.

[63] According to the present invention, the lower substrate 12 may be formed of glass or a flexible material. As described above, the flexible material may include at least one of metal materials such as stainless steel and aluminum.

[64] Next, a semiconductor electrode layer 20 is formed on the lower electrode structure

10 in operation S20. The semiconductor electrode layer 20 may be one of metal oxides that include a transition metal oxide. For example, the semiconductor electrode layer 20 may be one of titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), niobium oxide (Nb ₂ O ₅ ), and zinc oxide (ZnO).

[65] According to an embodiment of the present invention, the semiconductor electrode layer 20 may be formed of titanium oxide particles having a size ranging from about 3 nm to about 30 nm, and may be coated at a thickness ranging from about 5mm to about 30mm on the lower electrode structure 10. For example, the process of forming the semiconductor electrode layer 20 may include coating a viscous colloid having nano particles TiO ₂ on the lower electrode structure 10, followed by performing a predetermined heat treatingoperation to leave only the titanium oxide particles on the lower electrode structure 10.

[66] Specifically, preparing of the viscous colloid having nano particles TiO ₂ may include preparing a liquid colloid TiO ₂ , evaporating a solvent from the liquid colloid TiO ₂ , and adding at least one of polyethylenglycol and polyethyleneoxide to a solution including the nano particles TiO ₂ .

[67] The liquid colloid TiO ₂ may be obtained by hydrothermal synthesis using titanium isopropoxide and acetic acid in an autoclave that is set to about 220 ⁰ C. The evaporation of the solvent is performed until the TiO ₂ has the content ranging from about 10 % to about 15 % by weight, through which the nano particles TiO ₂ forming the semiconductor electrode layer 20 are formed in the liquid colloid TiO ₂ . The solution including the nano particles TiO ₂ has viscosity because polyethylenglycol and polyethyleneoxide are added thereto. The added polyethylenglycol and polyethyleneoxide are removed through the heat treating operation such that the nano particles TiO ₂ are left on the lower electrode structure 10. The heat treating operation may be performed at a temperature ranging from about 450 ⁰ C to about 550 ⁰ C.

[68] Next, a dye layer including dye material molecules is formed on the surface of the semiconductor electrode layer 20 in operation S30. The process of forming the dye layer includes immersing the lower electrode structure 10 with the semiconductor electrode layer 20 formed in an alcohol solution including dye for about 24 hours.

Then, after the lower electrode structure 10 with the semiconductor electrode layer 20 is taken out of the alcohol solution, the lower electrode structure 10 may be cleaned using alcohol.

[69] The dye may include a ruthenium complex. For example, the dye may be N719

(Ru(dcbpy)2(NCS)2 containing 2 protons). However, at least one of various dye materials not exemplarily described herein may be used for a dye-sensitized solar cell of the present invention. For example, widely-known dyes such as N712, Z907, Z910, and K19 may be used for a dye-sensitized solar cell of the present invention.

[70] In operation S40, the porous high molecular layer 30 is formed on a resultant structure including the dye layer. For example, the porous high molecular layer 30 may be formed using the method illustrated in FIG. 2. Specifically, the process of forming of the porous high molecular layer 30 may include immersing the resultant structure in the source solution 203 (refer to FIG. 2) including a poly (vinylidene fluoride) polymer or its copolymer for a short time (e.g., one second), and drying a resultant structure under a humidity condition ranging from about 40 % to about 60 % (refer to FIG. 5).

[71] Next, in operation S50, referring back to FIG. 1, the upper electrode structure 50 is attached to the porous high molecular layer 30. The upper electrode structure 50 includes the upper substrate 52 and the upper electrode layer 54 coated on the surface of the upper substrate 52. The upper substrate 52 may be formed of glass or a flexible material. As described above, the flexible material may include at least one of metal materials such as stainless steel and aluminum. The upper electrode layer 54 may be at least one of ITO, SnO ₂ , FTO, ZnO, and carbon nanotubes. Furthermore, the catalyst layer 56 may be further formed on the upper electrode layer 54. According to an embodiment of the present invention, the catalyst layer 56 may be a platinum layer coated on the upper electrode layer 54 at a thickness ranging from about 5 μg/cm2 to about 10 μg/cm2.

[72] The upper electrode structure 50 is attached so that the catalyst layer 56 and the upper electrode layer 54 face the porous high molecular layer 30 or the semiconductor electrode layer 20. This attaching process, after a high molecular layer 40 is formed between the lower electrode structure 10 and the upper electrode structure 50, may include compressing the lower and upper substrates 12 and 52 at a temperature ranging from about 100 ⁰ C to about 140 ⁰ C under a pressure ranging from about 1 atm to about 3 atm. Here, the high molecular layer 40 may employ the product called SURL YN™ manufactured by the company, Dupont.

[73] Next, in operation S60, the electrolyte is injected between the lower and upper substrates 12 and 52 through a predetermined injection hole (not shown). The electrolyte may be a redox iodide electrolyte. According to an embodiment of the present invention, the electrolyte may be acetonitrile including 0.6M butylmethylim-

idazolium, 0.02 M 12, 0.1 M guanidinium thiocyanate, 0.5 M 4-tert-butylpyridine. However, one of various other electrolytes not exemplarily described may be used for a dye- sensitized solar cell of the present invention. For example, the electrolyte may further include alkylimidazolium iodides or tetra-alkyl ammoniumiodides, surface additives including tert-butylpyridin (TBP), benzimidazole (BI), and N- Methylbenzimidazole (NMBI). Acetonitrile, propionitrile, or a mixed liquid of valer- onitrile and acetonitrile is used as a solvent.

[74] FIG. 7 is a graph illustrating an electrical characteristic of a dye-sensitized solar cell according to the present invention.

[75] A test is performed to compare a related art dye-sensitized solar cell with the dye- sensitized solar cell of the present invention. While the dye-sensitized solar cell of the present invention included the porous high molecular layer 30 (refer to FIG. 1) formed under a humidity condition of 40 %, the related art dye-sensitized solar cell did not include the porous high molecular layer 30. The dye-sensitized solar cells had the same structure except for the porous high molecular layer 30.

[76] Photovoltages and photocurrents of the dye-sensitized solar cells were measured, and a xenon lamp, Oriel, 91193 is used as a light source. A solar condition of the xenon lamp was calibrated using a standard solar cell.

[77] Referring to FIG. 7, the dye-sensitized solar cells had almost the same I - V characteristic.

[78] Test results shown in Table 2 below, illustrate photovoltaic energy conversion efficiencies of dye-sensitized solar cells of the present invention. Samples 1 and 4 were the dye- sensitized solar cell of the present invention and the related art dye-sensitized solar cell of FIG. 7, respectively. Sample 2 was a dye-sensitized solar cell including a high molecular layer formed under a humidity condition of 15 %, and sample 3 was a dye-sensitized solar cell including a typical porous layer.

[79] Referring to Table 2, the samples 1 and 4 had the same photovoltaic energy conversion efficiency of 8%, the sample 2 had a photovoltaic energy conversion efficiency of 2.3 %, and the sample 3 had a photovoltaic energy conversion efficiency of 7.8 %. The photo-conversion efficiencies of the samples 2 and 3 are less than those of the samples 1 and 4.

[80] Table 2

[Table 2] [Table ]

[81] As described above, the dye-sensitized solar cell including the gel type electrolyte or the solid type electrolyte, which is used to prevent the leakage of the electrolyte was deteriorated. However, the dye- sensitized solar cell including the porous high molecular layer of the present invention prevents the deterioration of its electric performance, as seen from the test results of Table 2 and FIG. 7.

[82] [83] [84]