Dye-sensitized solar cell

Abstract

To provide a dye-sensitized solar cell including an ITO electrode with a resistance value comparable to an FTO electrode even after sintering processes.SOLUTION: A dye-sensitized solar cell includes an electrode, an electron transport layer, a light absorption layer, a counter electrode, a catalyst layer, an electrolytic solution, and a sealing material. The electrode is formed on a first substrate. The electron transport layer is formed on the electrode. The light absorption layer is formed on the electron transport layer and includes an electron capturing agent and a dye. The counter electrode is formed on a second substrate disposed facing the first substrate. The catalyst layer is formed on the counter electrode. The electrolytic solution fills a space between the light absorption layer and the catalyst layer. The sealing material is held between the first substrate and the second substrate and seals the electrode, the electron transport layer, the light absorption layer, the counter electrode, the catalyst layer, and the electrolytic solution. The electrode is an ITO electrode having a film thickness of 230 nm or more and 330 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to dye-sensitized solar cells. [Background technology]

[0002] Solar cells are expected to be used as power sources for IoT (Internet of Things) devices and as energy harvesting elements. Solar cells are broadly divided into silicon-based solar cells, compound-based solar cells, and organic solar cells. Among the organic solar cells, dye-sensitized solar cells (DSC) are well known. Dye-sensitized solar cells generate electricity through an oxidation-reduction reaction using a dye to absorb light and an electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2009 / 157175 Summary of the Invention [Problem to be solved by the invention]

[0004] Transparent conductive oxide films (TCO) are often used for the electrodes of dye-sensitized solar cells. Known transparent conductive oxide films include indium tin oxide (ITO) and fluorine-doped tin oxide (FTO). FTO is often used as the electrode for dye-sensitized solar cells. This is because the light absorption layer of dye-sensitized solar cells is formed through a process in which the TiO2 applied to the transparent conductive film is sintered in air at 500-600°C. The resistance of FTO remains almost unchanged before and after the sintering process, whereas the resistance of ITO increases due to the incorporation of oxygen during the sintering process. This increase in resistance leads to a decrease in output.

[0005] In the case of FTO, electrode formation by etching is difficult, so electrodes are generally formed by laser processing. Laser processing tends to be costly. In contrast, electrode formation by etching is not difficult in the case of ITO. To reduce the cost of electrode formation, there is a demand for dye-sensitized solar cells with ITO electrodes that have resistance values ​​comparable to FTO electrodes even after the sintering process.

[0006] The present disclosure provides a dye-sensitized solar cell having an ITO electrode that has a resistance comparable to that of an FTO electrode even after a sintering process. [Means for solving the problem]

[0007] One embodiment of the dye-sensitized solar cell includes an electrode, an electron transport layer, a light absorbing layer, a counter electrode, a catalyst layer, an electrolyte, and a sealant. The electrode is formed on a first substrate. The electron transport layer is formed on the electrode. The light absorbing layer is formed on the electron transport layer and contains an electron collector and a dye. The counter electrode is formed on a second substrate disposed opposite the first substrate. The catalyst layer is formed on the counter electrode. The electrolyte is filled between the light absorbing layer and the catalyst layer. The sealant is interposed between the first substrate and the second substrate and seals the electrode, electron transport layer, light absorbing layer, counter electrode, catalyst layer, and electrolyte. The electrode is an ITO electrode with a film thickness of 230 nm or more and 330 nm or less. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a dye-sensitized solar cell having an ITO electrode that has a resistance value comparable to that of an FTO electrode even after a sintering process. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a dye-sensitized solar cell according to an embodiment. [Figure 2] FIG. 2 is a diagram for explaining the principle of power generation in a dye-sensitized solar cell. [Figure 3] FIG. 3 shows the transmittance of electrodes prepared under various conditions. [Figure 4] FIG. 4 is a graph showing the relationship between the ITO film thickness and the transmittance based on the results of FIG. [Figure 5] FIG. 5 is a diagram showing the sheet resistance of electrodes fabricated under various conditions. [Figure 6] FIG. 6 is a diagram showing the relationship between the electrode film thickness and the series resistance. [Figure 7] FIG. 7 is a graph showing the relationship between the ITO film thickness and the sheet resistance based on the results of FIG. [Figure 8] FIG. 8 is a diagram showing the characteristics of dye-sensitized solar cells using electrodes 13 fabricated under various conditions. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a dye-sensitized solar cell according to an embodiment. As shown in FIG. 1, the dye-sensitized solar cell 1 has a first substrate 11 and a second substrate 12. The first substrate 11 is a transparent substrate such as a glass substrate. The second substrate 12 is disposed so as to face the first substrate 11. Like the first substrate 11, the second substrate 12 is also a transparent substrate such as a glass substrate. For example, the first substrate 11 and the second substrate 12 may be glass substrates with a thickness of 0.4 mm to 0.7 mm.

[0011] An electrode 13 is formed on the first substrate 11 serving as an anode substrate. The electrode 13 is made of indium tin oxide (ITO) serving as a transparent conductive oxide film (TCO). The electrode 13 is used as an anode electrode.

[0012] A counter electrode 14 is formed on the second substrate 12, which serves as a cathode substrate, at a position facing the electrode 13. The counter electrode 14 is formed of indium tin oxide (ITO) as a transparent conductive oxide film (TCO), similar to the electrode 13. The counter electrode 14 is used as a cathode electrode.

[0013] An electron transport layer 15 is formed on the electrode 13. The electron transport layer 15 is made of titanium oxide (TiOx The electron transport layer 15 is made of a metal oxide film of TCO, which has a higher resistance than metal. The electron transport layer 15 can be provided to suppress loss due to the electrode 13 made of TCO, which has a higher resistance than metal. Furthermore, the formation of the electron transport layer 15 improves the adhesion of the light absorption layer 16, which is further formed on the electron transport layer 15.

[0014] A light absorbing layer 16 is formed on the electron transport layer 15. The light absorbing layer 16 is a porous semiconductor layer formed by adsorbing a dye to an electron collector. The electron collector is, for example, an aggregate of minute oxide semiconductor particles, such as titanium oxide (TiO2). The dye is, for example, a ruthenium (Ru) dye (RU) (such as N719 dye). The electron collector is not limited to titanium oxide, but may be, for example, zinc oxide, tin oxide, tungsten oxide, niobium oxide, indium oxide, or a composite thereof. Furthermore, the dye is not limited to N719 dye. For example, N3 dye, Black Dye, or the like may be used as a ruthenium-based dye.

[0015] A catalyst layer 17 is formed on the counter electrode 14. The catalyst layer 17 is, for example, a platinum layer.

[0016] An electrolyte solution 18 is filled between the light absorption layer 16 and the catalyst layer 17. Examples of solvents that can be used for the electrolyte solution 18 include acetonitrile, methoxyacetonitrile, and ethylene carbonate. Examples of solutes that can be used for the electrolyte solution 18 include iodine (I2), 1,2-dimethyl-3-n-propylimidazolium iodide (DMPImI), lithium iodide (LiI), and 4-tert-butylpyridine (TBP).

[0017] A sealant 19 is formed between the electron transport layer 15 and the catalyst layer 17 at the outermost periphery of the dye-sensitized solar cell 1. The sealant 19 bonds the first substrate 11 and the second substrate 12 together and prevents the electrolyte solution 18 from leaking out. In other words, the electrolyte solution 18 is sealed by the first substrate 11, the second substrate 12, and the sealant 19. The sealant 19 is, for example, a resin.

[0018] 2 is a diagram for explaining the power generation principle of the dye-sensitized solar cell 1. In the following example, the electron collector is titanium oxide (TiO), the dye is a ruthenium (Ru) dye, and the electrolyte 18 is an iodine (I) electrolyte.

[0019] First, when light is incident on the dye-sensitized solar cell, the light is absorbed by the dye 16a formed on the substrate. The dye 16a is excited by absorbing the light. The reaction formula is shown, for example, in the following formula (1). Ru → Ru + +e - (1)

[0020] Electrons (e - ) are injected into the electron collector 16b, which is made of, for example, porous titanium oxide (TiO2). The electrons injected into the electron collector 16b move to the electrode 13, which is the anode electrode.

[0021] On the other hand, electrons (e - The dye 16a that has lost the iodide ion (I - ) in the electrolyte 18. - ) is an electron (e - ) to dye 16a, triiodide ions (I3 - ) The reaction formula is shown in the following formulas (2) and (3). Ru+e - →Ru (2) 3I - →I3 - +2e - (3)

[0022] The triiodide ion (I3 - ) is transferred from the counter electrode 14, which is the cathode electrode, to the electrons (e -) is received. At this time, a potential difference occurs between the counter electrode 14 and the electrode 13. If a load is connected between the counter electrode 14 and the electrode 13, the electrons that have moved to the electrode 13 will move through the load to the counter electrode 14. Then, the electrons that have reached the counter electrode 14 will be converted into triiodide ions (I3 - ) is absorbed by the triiodide ion (I3 - ) is the iodide ion (I - ) The reaction formula is shown in the following formula (4), for example. I3 - +2e - →3I - (4)

[0023] The above redox reaction is repeated to generate electricity in the dye-sensitized solar cell unit. For this redox reaction to occur, the energy level of the excited dye 16a must be higher than that of the electron collector 16b, and the energy level of the ground dye 16a must be lower than that of the electrolyte 18.

[0024] Fig. 3 is a diagram showing the transmittance of the electrode 13 produced under various conditions. The horizontal axis of Fig. 3 represents wavelength. The vertical axis of Fig. 3 represents transmittance and IPCE (Incident-Photon-to-Current Conversion Efficiency: Quantum Conversion Efficiency, which corresponds to the spectral sensitivity characteristics of a dye-sensitized solar cell).

[0025] Furthermore, "plain glass" in FIG. 3 indicates the transmittance of only the glass substrate. In other words, plain glass is the transmittance of only the first substrate 11 on which no electrode 13 is formed. The glass substrate is a 0.7 mm thick glass substrate. As shown in FIG. 3, the transmittance of plain glass in the wavelength range of 400 nm to 700 nm is constant at approximately 92%.

[0026] "FTO Glass 1000nm·500℃*1hr" in Figure 3 shows the transmittance of a glass substrate on which an FTO electrode with a thickness of 1000nm is formed. This glass substrate has undergone a sintering process at 500℃ for 1 hour, which is equivalent to the sintering process for the light absorption layer 16.

[0027] "ITO glass 130nm·450℃*1hr" in Figure 3 shows the transmittance of a glass substrate on which an ITO electrode with a film thickness of 130nm is formed. This glass substrate has undergone a sintering process at 450℃ for 1 hour, which corresponds to the sintering process for the light absorption layer 16.

[0028] "ITO glass 280nm·500℃*1hr" in Figure 3 shows the transmittance of a glass substrate on which an ITO electrode with a film thickness of 280nm is formed. This glass substrate has undergone a sintering process at 500℃ for 1 hour, which is equivalent to the sintering process for the light absorption layer 16.

[0029] "ITO glass 500nm·500℃*1hr" in Figure 3 shows the transmittance of a glass substrate on which an ITO electrode with a thickness of 500nm is formed. This glass substrate has undergone a sintering process at 500℃ for 1 hour, which is equivalent to the sintering process for the light absorption layer 16.

[0030] "IPCE (Ru diameter dye)" in Figure 3 indicates the IPCE of the Ru dye. As shown in Figure 3, the IPCE of the Ru dye is high in the wavelength range of 420 nm to 620 nm. Therefore, if the electrode 13 can transmit a large amount of light in this wavelength range, the quantum conversion efficiency of the light-absorbing layer 16 can be increased. In Figure 3, the ITO electrode with a thickness of 130 nm, and the ITO electrodes with thicknesses of 280 nm and 500 nm have a wavelength range of higher transmittance than the FTO electrode with a thickness of 1000 nm in the wavelength range of 420 nm to 620 nm. In particular, the ITO electrode with a thickness of 130 nm and the ITO electrode with a thickness of 280 nm have a wavelength range of higher transmittance than the FTO electrode with a thickness of 1000 nm in a wide wavelength range of 420 nm to 620 nm. As shown in Figure 3, the ITO electrode has a thickness that is more advantageous in terms of transmittance than the FTO electrode for the IPCE of the Ru-based dye.

[0031] Figure 4 shows the relationship between the ITO electrode thickness and the transmittance (C light source equivalent) in the 400-700 mm band, based on the results of Figure 3. Hereinafter, the thickness of the ITO electrode will be referred to as the ITO film thickness. As shown in Figure 4, the overall trend is that the transmittance decreases as the ITO film thickness increases. On the other hand, the transmittance peaks at ITO film thicknesses of approximately 130 nm, 280 nm, and 430 nm.

[0032] Figure 5 shows the sheet resistance of electrodes 13 fabricated under various conditions. Figure 5 shows the sheet resistance of a 1000 nm-thick single-layer FTO electrode, a 50 nm-thick single-layer ITO electrode, a 130 nm-thick single-layer ITO electrode, a 280 nm-thick single-layer ITO electrode, and a 500 nm-thick single-layer ITO electrode. The sheet resistances for each electrode are shown before and after the sintering process. The "initial" values ​​for the 1000 nm-thick single-layer FTO electrode, the 50 nm-thick single-layer ITO electrode, the 130 nm-thick single-layer ITO electrode, the 280 nm-thick single-layer ITO electrode, and the 500 nm-thick single-layer ITO electrode indicate the sheet resistance before the sintering process. The sheet resistance after each sintering process is shown for the 1000nm thick single-layer FTO electrode at "500℃*1hr", the 50nm thick single-layer ITO electrode at "450℃*1hr", the 130nm thick single-layer ITO electrode at "500℃*1hr", the 280nm thick single-layer ITO electrode at "500℃*1hr", and the 500nm thick single-layer ITO electrode at "500℃*1hr".

[0033] As shown in Figure 5, the sheet resistance of the FTO electrode remains almost unchanged before and after the sintering process. In contrast, the sheet resistance of the ITO electrode increases after the sintering process. The increase in the sheet resistance of the ITO electrode after the sintering process decreases as the film thickness increases. In Figure 5, when the ITO film thickness increases from 50 nm to 130 nm, the sheet resistance of the ITO electrode after the sintering process decreases sharply from 92.7 Ω / sq to 30.4 Ω / sq.

[0034] FIG. 6 is a diagram showing the relationship between electrode film thickness and series resistance Rs. Series resistance Rs is one of the indicators of the performance of a dye-sensitized solar cell, and corresponds to the sum of the internal resistances of the electrode, light-absorbing layer, and electrolyte of the dye-sensitized solar cell. Here, in FIG. 6, the series resistance Rs is shown as a ratio when the series resistance Rs of an ITO film thickness of 500 nm is set to 1. The electrode in FIG. 6 has an ITO electrode as electrode 13 and a TiO x It is a laminate of layers. Generally, the lower the series resistance Rs, the higher the performance of the dye-sensitized solar cell. As shown in Figure 5, there is a tendency for a negative correlation between ITO film thickness and sheet resistance, and as shown in Figure 6, there is also a tendency for a negative correlation between ITO film thickness and the series resistance of the cell characteristics. The series resistance Rs of an ITO electrode with a film thickness of 500 nm is approximately the same as the series resistance Rs of an FTO electrode with a film thickness of 1000 nm.

[0035] Figure 7 shows the relationship between ITO film thickness and sheet resistance based on the results of Figure 5. Here, the sheet resistance in Figure 7 is the value after the sintering process. As shown in Figure 7, the sheet resistance decreases as the ITO film thickness increases. In other words, Figure 7 also shows that increasing the ITO film thickness suppresses the increase in sheet resistance after the sintering process.

[0036] As described above, when considering using an ITO electrode as an electrode for a dye-sensitized solar cell, a smaller film thickness is better in terms of transmittance, while a larger film thickness is better in terms of increasing sheet resistance after the sintering process. Therefore, by specifying the range of ITO film thickness that provides good transmittance and resistance, it is possible to improve the processability of the electrode while obtaining good output characteristics.

[0037] Figure 8 shows the characteristics of dye-sensitized solar cells using electrode 13 fabricated under various conditions. Figure 8 shows the characteristics of dye-sensitized solar cells, including short-circuit current density, open-circuit voltage, maximum power output, maximum power operating voltage, and maximum power operating current. The short-circuit current density is the current density when the voltage is zero on the IV characteristic curve of the dye-sensitized solar cell. The open-circuit voltage is the voltage when the current is zero on the IV characteristic curve of the dye-sensitized solar cell. The maximum power output is the output at the point where the product of the current and voltage is maximum on the IV characteristic curve of the dye-sensitized solar cell. The maximum power output operating voltage is the voltage at maximum power output. The maximum power output operating current is the current at maximum power output. Each characteristic shown in Figure 8 is expressed as a ratio, with the value when an FTO electrode is used as electrode 13 being set to 1.

[0038] As shown in Figure 8, when comparing ITO thicknesses of 130 nm and 280 nm, the short-circuit current density and open-circuit voltage increase as the film thickness increases from 130 nm to 280 nm. This is thought to be because the series resistance Rs decreases as the ITO film thickness increases, as shown in Figure 6. Furthermore, the increase in short-circuit current density and open-circuit voltage also increases the maximum output.

[0039] On the other hand, as shown in Figure 8, when comparing an ITO film thickness of 280 nm with that of 500 nm, the short-circuit current density and open-circuit voltage decrease as the ITO film thickness increases from 280 nm to 500 nm. This is thought to be because, as shown in Figure 6, the series resistance Rs decreases with an increase in ITO film thickness, but as shown in Figure 4, the transmittance of the Ru-based dye relative to the IPCE also decreases with an increase in ITO film thickness. Furthermore, the decrease in short-circuit current density and open-circuit voltage also decreases the maximum output. Note that, as shown in Figure 4, the transmittance peaks when the ITO film thickness is 430 nm. Therefore, it is thought that the maximum output also increases when the ITO film thickness is 430 nm.

[0040] In comparison with FTO electrodes, the short-circuit current density and open-circuit voltage of the 280-nm and 500-nm ITO electrodes are both higher than those of the FTO electrodes. Therefore, the maximum output power of the 280-nm and 500-nm ITO electrodes is also higher than that of the FTO electrodes. The 280-nm ITO electrode has a sheet resistance of approximately 16.1 Ω / sq and a high transmittance for the Ru-based dye IPCE, achieving a maximum output power comparable to that of the FTO electrode. Similarly, the 500-nm ITO electrode has a sheet resistance of 10.5 Ω / sq, achieving a maximum output power comparable to that of the FTO electrode. Furthermore, a sheet resistance of 30 Ω / sq or less achieves a maximum output power roughly equivalent to that of the FTO electrode. As shown in Figure 7, an ITO electrode with a thickness of approximately 230 nm achieves a sheet resistance of 30 Ω / sq or less.

[0041] Furthermore, as shown in Figure 8, when an ITO electrode is used as electrode 13, it is believed that the maximum output peak occurs between film thicknesses of 280 nm and 430 nm. However, increasing the electrode thickness increases the electrode's weight, making the substrate more susceptible to warping. In experiments conducted by the applicant, it was confirmed that, for a 0.7 mm thick glass substrate, substrate warping is more likely to occur when the ITO film thickness exceeds 370 nm.

[0042] Taking the above into consideration, in this embodiment, the electrode 13 is formed with a film thickness in the range of 230 nm to 330 nm, preferably 280 nm, which suppresses an increase in resistance after the sintering process for forming the light absorbing layer 16 and allows for a maximum output equivalent to that obtained when an FTO electrode is used.

[0043] Typically, the anode substrate and the cathode substrate are fabricated separately. That is, the counter electrode 14 does not undergo a sintering process. Therefore, the thickness of the counter electrode 14 does not need to be 230 nm to 330 nm. For example, the thickness of the counter electrode 14 may be increased as long as it does not cause warping of the second substrate 12.

[0044] As described above, according to this embodiment, an ITO electrode with a film thickness in the range of 230 nm to 330 nm is used as the anode electrode on which the light absorption layer is formed. This maintains high transmittance for the Ru-based dye with respect to IPCE, while also suppressing increases in resistance and warpage of the substrate after the sintering process. Therefore, a dye-sensitized solar cell with the same maximum output as one using an FTO electrode can be obtained. Furthermore, since an ITO electrode can be used as the electrode, it is also easy to process.

[0045] The present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in appropriate combinations, in which case the combined effects can be obtained. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by combining selected elements from the disclosed elements. For example, if the problem can be solved and the desired effect can be obtained even if some elements are deleted from all elements shown in the embodiments, the configuration from which these elements are deleted can be extracted as an invention. [Explanation of symbols]

[0046] 1 dye-sensitized solar cell, 11 first substrate, 12 second substrate, 13 electrode, 14 counter electrode, 15 electron transport layer, 16 light absorption layer, 17 catalyst layer, 18 electrolyte, 19 encapsulant.

Claims

1. an electrode formed on the first substrate; an electron transport layer formed on the electrode; a light absorbing layer formed on the electron transport layer and including an electron collector and a dye; a counter electrode formed on a second substrate disposed opposite the first substrate; a catalyst layer formed on the counter electrode; an electrolyte solution filled between the light absorbing layer and the catalyst layer; a sealant interposed between the first substrate and the second substrate, which seals the electrode, the electron transport layer, the light absorbing layer, the counter electrode, the catalyst layer, and the electrolyte solution; Equipped with The electrode is an ITO electrode having a film thickness of 230 nm or more and 330 nm or less. Dye-sensitized solar cells.

2. The sheet resistance of the electrode is 30 Ω / sq or less. The dye-sensitized solar cell according to claim 1 .

3. The dye is a ruthenium-based dye. The dye-sensitized solar cell according to claim 1 .

4. the electrode has a film thickness corresponding to a peak of transmittance of the ruthenium-based dye with respect to IPCE; The dye-sensitized solar cell according to claim 3 .

5. The first substrate is a glass substrate having a thickness of 0.4 mm to 0.7 mm. The dye-sensitized solar cell according to claim 1 .

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