Method for manufacturing photoelectrochemical device including single-crystal titanium dioxide protective layer and photoelectrochemical device manufactured thereby

Abstract

The present invention relates to: a method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer; and a photoelectrochemical device manufactured thereby, in which, by bonding single-crystal titanium dioxide to the surface of a semiconductor material to form the protective layer, the distance between atoms can be reduced and the thickness can be increased, thereby preventing the semiconductor material from being exposed to an electrolyte, thus improving the stability and lifetime of the photoelectrochemical device.

Description

Method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer and a photoelectrochemical device manufactured thereby

[0001] The present invention relates to a method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer and a photoelectrochemical device manufactured thereby.

[0002] Photoelectrochemical water electrolysis devices integrate light-absorbing semiconductor materials and electrochemical water electrolysis catalysts into a single device to produce hydrogen and oxygen. They operate by directly transferring electrons and holes generated in the semiconductor materials to the water electrolysis catalyst, rather than relying on an external power grid. Compared to technologies that produce hydrogen by connecting separate solar cells and water electrolyzers, photoelectrochemical water electrolysis device technology offers advantages in that it simplifies the structure of the device and system, eliminating unnecessary components and thereby increasing efficiency and reducing costs. Therefore, research is ongoing to develop more efficient and practical photoelectrochemical water electrolysis devices.

[0003] Electrolytes interact closely with photoelectrochemical devices to drive photoelectrochemical reactions. Within photoelectrochemical devices, electrolytes provide ionic conductivity and facilitate charge transfer. This plays a key role in promoting and controlling charge transfer and reaction rates. Typically, photoelectrochemical devices consist of an anode and a cathode, and the electrolyte provides ionic conductivity between the anode and cathode, forming a path for charge transfer. Ions move within the electrolyte, participating in photoelectrochemical reactions or acting as charge relays, thus significantly impacting the performance and stability of photoelectrochemical devices. However, exposure of semiconductor materials within photoelectrochemical devices to acidic or alkaline electrolytes containing dissolved electrolytes can lead to various problems. For example, the electrolyte interacts with the semiconductor material, causing corrosion or oxidation, damaging the surface of the semiconductor device and significantly reducing the stability and lifespan of the photoelectrochemical device.

[0004] To solve the problems caused by exposure to acidic or alkaline electrolytes, a transparent, conductive, chemically stable, and fluid-impermeable protective layer can be formed on the surface of a semiconductor material to increase chemical stability. Conventional methods for forming protective layers for photoelectrochemical devices have mainly been studied by depositing a thin film of organic, amorphous, or polycrystalline metal oxide on the surface of a semiconductor material to a thickness of several nanometers to several hundred nanometers (Korean Patent No. 2309628). However, this is not sufficient to form a thickness to completely block electrolyte leakage. Furthermore, since the distance between atoms is longer than in a single crystal structure, electrolyte leakage occurs through microscopic gaps in the metal oxide thin film protective layer. Therefore, since it is not possible to completely prevent corrosion of semiconductor materials, development and research into more effective protective layers for photoelectrochemical devices are necessary.

[0005] Accordingly, the inventors of the present invention have made efforts to develop an effective photoelectrochemical device protective layer, and have developed a method to form a protective layer by bonding a single crystal of titanium dioxide to the surface of a semiconductor material, thereby preventing molecules and ions (H + , OH - The present invention was completed by manufacturing a photoelectrochemical device that introduces a protective layer capable of tightly and densely blocking the penetration of electrolytes such as electrolytes (e.g., H2O, etc.) without gaps.

[0006] The present invention aims to solve the above-mentioned problems and other problems related thereto.

[0007] An exemplary object of the present invention is to provide a method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer, which improves stability and lifespan by preventing exposure of a semiconductor material to an electrolyte.

[0008] Another exemplary object of the present invention is to provide a photoelectrochemical device manufactured by the above manufacturing method.

[0009] The technical problem to be achieved according to the technical idea of ​​the invention disclosed in this specification is not limited to the problem to solve the above-mentioned problem, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0010] This is explained in detail as follows. Meanwhile, each description and embodiment disclosed in this application can also be applied to each other description and embodiment. In other words, all combinations of the various elements disclosed in this application fall within the scope of this application. Furthermore, the scope of this application is not limited by the specific descriptions described below.

[0011] As one aspect for achieving the above object, the present invention provides a method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer, comprising the following steps.

[0012] (a) a step of heat treating single crystal titanium dioxide;

[0013] (b) a step of depositing an electrochemical catalyst on one surface of the heat-treated single crystal titanium dioxide and forming an electrode on the other surface;

[0014] (c) forming a semiconductor material on a substrate and forming an electrode on the semiconductor material; and

[0015] (d) A step of forming a stack by applying an adhesive between the electrode formed on one side of the single crystal titanium dioxide in step (b) and the electrode formed on the semiconductor material in step (c).

[0016] In the present invention, the heat treatment in step (a) can be performed at 500°C to 900°C in a hydrogen atmosphere or vacuum.

[0017] In the present invention, a step of applying infrared rays and pressure may be further included after the step of forming a stack by applying the adhesive of step (d).

[0018] In the present invention, the pressure may be 5 bar to 10 bar.

[0019] In the present invention, the adhesive of step (d) can be manufactured by including the following steps.

[0020] (i) a step of heating paraffin to 60°C to 100°C; and

[0021] (ii) A step of adding conductive particles to the heated paraffin.

[0022] In the present invention, the conductive particles may be carbon compound or polymer particles.

[0023] In the present invention, the carbon compound may be at least one selected from the group consisting of graphite, graphene, carbon nanotubes, and carbon nanofibers.

[0024] In the present invention, the polymer particles may be at least one selected from the group consisting of polystyrene (PS), polymethyl methacrylate (PMMA), polystyrene / divinylbenzene (PS / DVB), polyamide, poly(butyl methacrylate) (PBMA), and combinations thereof.

[0025] As another aspect for achieving the above object, the present invention provides a photoelectrochemical device including a single-crystal titanium dioxide protective layer manufactured according to the above manufacturing method.

[0026] In the present invention, the thickness of the single crystal titanium dioxide protective layer may be 100 μm to 1,000 μm.

[0027] The method for manufacturing a photoelectrochemical device including a single crystal titanium dioxide protective layer of the present invention is different from a method of depositing a titanium dioxide protective layer in an amorphous or polycrystalline structure with a thickness of several nm to several hundred nm using vacuum equipment, etc., by bonding single crystal titanium dioxide with a thickness of 100 μm to 1000 μm to the surface of a semiconductor material to form a protective layer, thereby reducing the distance between atoms and forming a thick layer, thereby enabling molecules and ions (H + , OH - , H2O, etc.) can be tightly and tightly blocked against the permeation of electrolytes.

[0028] Meanwhile, the scope of the present invention is not limited by the effects described above.

[0029] FIG. 1 is a schematic diagram of a device for applying infrared heat (IR lamp) and pressure to a stack of a 'titanium dioxide single crystal-semiconductor material (halide perovskite thin film)' according to one embodiment of the present invention.

[0030] Figure 2 is a schematic diagram of a photoelectrochemical device protective layer formed using single-crystal titanium dioxide.

[0031] Figure 3 is a schematic diagram of a device that controls the electrical potential of an ITO electrode on the back of a halide perovskite thin film using a potentiostat.

[0032] Figure 4 shows the results of confirming the photovoltage and photocurrent of a device without a protective layer (comparative group 1) and a device protected with a 100 nm thick amorphous titanium dioxide thin film (comparative group 2).

[0033] Figure 5 shows the results of checking the appearance before and after a performance evaluation experiment of a device without a protective layer (comparative group 1) and a device protected with a 100 nm thick amorphous titanium dioxide thin film (comparative group 2).

[0034] Figure 6 shows the results of confirming the photovoltage and photocurrent of a photoelectrochemical device according to one embodiment of the present invention.

[0035] Figure 7 is a drawing showing the appearance of a photoelectrochemical device before and after a stability evaluation experiment according to one embodiment of the present invention.

[0036] Figure 8 shows the results of a stability evaluation experiment of a photoelectrochemical device according to one embodiment of the present invention.

[0037] The present invention is specifically described as follows.

[0038] Meanwhile, each description and embodiment disclosed in this application can also be applied to each other description and embodiment. In other words, all combinations of the various elements disclosed in this application fall within the scope of this application. Furthermore, the scope of this application is not limited by the specific descriptions described below.

[0039] In the present invention, when it is said that a member is located “on” another member, this includes not only a case where a member is in contact with another member, but also a case where another member exists between the two members.

[0040] In the present invention, when a part is said to “include” a certain component, this does not mean that other components are excluded, but rather that other components can be further included, unless otherwise specifically stated. The terms “about,” “substantially,” etc. used in the present invention are used in a meaning close to or at the numerical value when manufacturing and material tolerances inherent to the mentioned meaning are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure, which mentions exact or absolute values ​​to aid understanding of the present invention. The terms “step of doing ~” or “step of ~” used in the present invention do not mean “step for ~.”

[0041] In the present invention, the term “combination(s) thereof” included in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including one or more selected from the group consisting of the components.

[0042] As one aspect for achieving the above object, one example of the present invention provides a method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer, comprising the following steps.

[0043] (a) a step of heat treating single crystal titanium dioxide;

[0044] (b) a step of depositing an electrochemical catalyst on one surface of the heat-treated single crystal titanium dioxide and forming an electrode on the other surface;

[0045] (c) forming a semiconductor material on a substrate and forming an electrode on the semiconductor material; and

[0046] (d) A step of forming a stack by applying an adhesive between the electrode formed on one side of the single crystal titanium dioxide in step (b) and the electrode formed on the semiconductor material in step (c).

[0047] The term "titanium dioxide (TiO2)" of the present invention refers to a compound composed of titanium and oxygen atoms, which generally functions as a photocatalyst. The most common form is the rutile structure, in which titanium and oxygen atoms are arranged alternately with relatively short interatomic distances of approximately 0.18 nm to 0.20 nm. Titanium dioxide possesses photoelectrochemical properties and photocatalytic properties, allowing it to absorb light of a specific wavelength to generate charges and form active oxygen, thereby promoting chemical reactions. Accordingly, it is widely used in various fields such as solar cells, photocatalysts, and sensors.

[0048] In the present invention, the manufacturing method is different from the conventional method of depositing titanium dioxide with an amorphous or polycrystalline crystal structure on a semiconductor material, and by applying single crystal titanium dioxide, the distance between atoms is short, so that molecules and ions (H) constituting the electrolyte + , OH - , H2O, etc.) can be more effectively prevented from penetrating.

[0049] In one embodiment of the present invention, the single crystal titanium dioxide may be used in a wafer form, but is not limited thereto.

[0050] In one embodiment of the present invention, the electrochemical catalyst may be at least one selected from the group consisting of platinum (Pt), nickel (Ni), rhodium (Rh), iridium (Ir), gold (Au), and cobalt (Co).

[0051] For example, the electrochemical catalyst may be platinum. By applying platinum as a catalyst, hydrogen can be generated with high efficiency in a photoelectrochemical device.

[0052] In one embodiment of the present invention, the semiconductor material may be a material that absorbs light.

[0053] As a specific example, the semiconductor material may be selected from the group consisting of a halide or chalcogenide series.

[0054] In one embodiment of the present invention, the semiconductor material may be a halide perovskite.

[0055] The term "halide perovskite" of the present invention has a structure of the form ABX3, where A represents an organic cation, B represents a metal cation (Pb, Sn, etc.), and X represents a halide ion (Cl, Br, I, etc.). The structural stability of perovskite is mainly determined by the halide ion (X), and the halide ion is generally large in size and has strong polarity, so it tends to interact with moisture. When moisture interacts with perovskite, the water molecule binds to the halide ion (X) and changes the position of the halide ion. Therefore, the structural deformation occurs, the interaction between ions is weakened, or some ions escape, which not only affects the electrical characteristics of the perovskite device, but can also cause long-term stability problems. To improve this, various research and development are being conducted, such as protective coating of perovskite devices, manufacturing and use in a sealed environment, and introduction of stabilizing agents.

[0056] In one embodiment of the present invention, the halide perovskite may be selected from the group consisting of, but is not limited to, an organic cation such as methylammonium (MA) or formamine (FA), a metal cation such as lead thiocyanate (Pb), and a halide ion of lead monoxide (PbI2), lead monoxide (PbCl2), or mercury monoxide (HgCl2).

[0057] In one embodiment of the present invention, the electrode may be, but is not limited to, indium tin oxide (ITO), fluorine doped tin oxide, or aluminum doped zinc oxide.

[0058] In one embodiment of the present invention, the single crystal titanium dioxide has conductivity, and the conductivity can be imparted by one method selected from the group consisting of thermal treatment, doping, oxygen treatment, layering, and nanostructure control.

[0059] In one embodiment of the present invention, the heat treatment may be performed at 300°C or higher, 400°C or higher, 500°C or higher, 600°C or higher, or 700°C or higher under a hydrogen atmosphere or in a vacuum.

[0060] In one embodiment of the present invention, the heat treatment may be performed at 1000°C or less, 900°C or less, 800°C or less, or 700°C or less under a hydrogen atmosphere or in a vacuum.

[0061] Preferably, the heat treatment can be performed at 500°C to 900°C under a hydrogen atmosphere or in vacuum.

[0062] If the above heat treatment is performed outside the above temperature range, the single crystal titanium dioxide may not be reduced, resulting in an increase in electrical resistance.

[0063] In one embodiment of the present invention, a step of applying infrared rays and pressure may be further included after applying the adhesive of step (d).

[0064] In one embodiment of the present invention, the infrared ray can be applied using a light bulb-shaped lighting device (IR lamp) that emits light in the infrared region.

[0065] In one embodiment of the present invention, the pressure may be 1 bar or more, 2 bar or more, 3 bar or more, 4 bar or more, or 5 bar or more.

[0066] In one embodiment of the present invention, the pressure may be 15 bar or less, 14 bar or less, 13 bar or less, 12 bar or less, 11 bar or less, or 10 bar or less.

[0067] Preferably, the pressure may be 5 bar to 10 bar.

[0068] If the above pressure exceeds the appropriate range, it may cause mechanical damage to the sample, and if it is lower than the appropriate range, the gap between the electrodes may widen, preventing the two electrodes from being electrically connected through the conductive particles.

[0069] At this time, the above bar is 1 square meter (m 2 ) is the pressure corresponding to a force of 100,000 Newtons (N), which is equivalent to 1 bar = 100,000 pa = 0.1 mpa.

[0070] In the present invention, the adhesive of step (d) can be manufactured by including the following steps.

[0071] (i) a step of heating paraffin to 60°C to 100°C; and

[0072] (ii) A step of adding conductive particles to the heated paraffin.

[0073] In one embodiment of the present invention, the conductive particles may be carbon compound and / or polymer particles.

[0074] As a specific example, the carbon compound may be at least one selected from the group consisting of graphite, graphene, carbon nanotubes, and carbon nanofibers.

[0075] As a specific example, the polymer particles may be one or more selected from the group consisting of polystyrene (PS), polymethyl methacrylate (PMMA), polystyrene / divinylbenzene (PS / DVB), polyamide, poly(butyl methacrylate) (PBMA), and combinations thereof.

[0076] In one embodiment, the polymer particles may be coated with a metal such as gold, silver, platinum, or copper. More specifically, the polymer particles may be silver-coated particles having a diameter of 40 μm or less.

[0077] In one embodiment of the present invention, the adhesive may be a conductive transparent material, and may be in a form in which the conductive particles are combined with a transparent polymer, but is not limited thereto.

[0078] As another aspect for achieving the above object, one example of the present invention provides a photoelectrochemical device including a single-crystal titanium dioxide protective layer manufactured by the above manufacturing method.

[0079] In one embodiment of the present invention, the thickness of the single crystal titanium dioxide protective layer may be 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, or 100 μm or more.

[0080] In one embodiment of the present invention, the thickness of the single crystal titanium dioxide protective layer may be 1,500 μm or less, 1,400 μm or less, 1,300 μm or less, 1,200 μm or less, 1,100 μm or less, or 1,000 μm.

[0081] Preferably, the thickness of the single crystal titanium dioxide protective layer may be 100 μm to 1,000 μm.

[0082] As described above, when a single crystal titanium dioxide protective layer is adhered to the surface of a semiconductor material with a thickness of 100 μm to 1000 μm, the permeation of the electrolyte can be prevented more effectively.

[0083] The term "stack" in the present invention refers to a limitedly accessible array structure. The stack structure is used in devices in which each layer is composed of different materials and each layer operates based on a different operating principle. The stack structure can improve the overall performance by combining the characteristics of various devices, and can be used, for example, to describe a structure in which various layers are laminated to perform the function of converting an optical signal into an electrical signal in an optoelectrochemical device, or conversely, converting an electrical signal into an optical signal, but is not limited thereto.

[0084]

[0085] Hereinafter, the present invention will be described in more detail through the following examples. However, these examples are intended to exemplify the present invention and the scope of the present invention is not limited to these examples.

[0086]

[0087] Example 1: Fabrication of a photoelectrochemical device protected by single-crystal titanium dioxide

[0088] A single crystal of titanium dioxide (Rutile, 1 cm X 1 cm) with a thickness of 100 μm to 1000 μm was heat-treated at a temperature of approximately 700°C in a hydrogen atmosphere or vacuum to increase its conductivity. Platinum (Pt) was deposited on one surface of the titanium dioxide as an electrochemical catalyst, and indium tin oxide (ITO) was deposited on the opposite surface as an electrode for electrical connection.

[0089] A halide perovskite thin film was used as a semiconductor material to absorb light. The halide perovskite thin film was formed on an ITO substrate, and an ITO electrode was formed on the halide perovskite thin film for electrical connection.

[0090] A solid conductive transparent adhesive was prepared to ensure a seamless interface between an ITO electrode formed on a titanium dioxide single crystal and an ITO electrode formed on a halide perovskite thin film. The solid conductive transparent adhesive was prepared by dispersing conductive particles (graphite powder of 20 μm or less or silver-coated PMMA particles of 40 μm or less) in melted paraffin heated to 60 to 100 °C, and then solidifying the conductive particles by lowering the temperature. The amount of conductive particles was adjusted to 0.5 to 2 wt % based on the weight of paraffin.

[0091] 15 mg / cm at the interface between the ITO electrode formed on the single crystal titanium dioxide and the ITO electrode formed on the halide perovskite film. 2 20 mg / cm 2 The conductive transparent adhesive was positioned. The stack was placed in a device (see Fig. 1) for applying heat and pressure to the 'titanium dioxide single crystal-halide perovskite thin film' stack. Infrared heat (IR lamp) penetrating the single crystal titanium dioxide was applied to melt the paraffin contained in the conductive transparent adhesive and make it liquid. Pressurized gas of about 5 to 10 bar was injected to expand the transparent polymer (PFA) film attached to the device, thereby applying uniform pressure through the part in contact with the stack. At this time, sufficient pressure should be applied so that the conductive particles inside the conductive transparent adhesive can contact the two ITO electrodes and form an electrical connection. While maintaining the pressure of the pressurized gas, the infrared heat was turned off to solidify the paraffin contained in the conductive transparent adhesive. The pressurized gas was discharged, and the 'titanium dioxide single crystal-halide perovskite thin film' stack was removed from the device to complete bonding (see Fig. 2).

[0092]

[0093] Example 2: Performance and stability evaluation of a photoelectrochemical device with a single-crystal titanium dioxide protective layer formed thereon.

[0094] For the photoelectrochemical device manufactured in Example 1, a performance evaluation experiment was conducted by controlling the electrical potential of the ITO electrode on the back of the semiconductor material using a potentiostat and measuring the current value flowing according to the voltage generated in the semiconductor material. At this time, a stability evaluation experiment was additionally conducted based on the time for which the photocurrent lasted (see Fig. 3). As a comparison group for the photoelectrochemical device formed with a single-crystal titanium dioxide protective layer, i) a device without a protective layer (comparison group 1) and ii) a device formed with a 100 nm thick amorphous titanium dioxide thin film protective layer (comparison group 2) were prepared. A reference electrode (Ag / AgCl) was used to confirm the potential value vs. RHE, and halide perovskite was used as a semiconductor material and platinum (Pt) was used as an electrochemical catalyst.

[0095] The device without a protective layer had a low photovoltage due to corrosion of the semiconductor material before the experiment, and during the experiment, the photovoltage and photocurrent values ​​of both Comparative Groups 1 and 2 rapidly decreased within a few minutes, confirming that the device performance was not working properly (see Fig. 4). In addition, the corrosion of the semiconductor material in Comparative Groups 1 and 2 could be observed visually, as evidenced by the change in the color of the halide perovskite from brown before the experiment to yellow after the experiment (see Fig. 5). In contrast, the photoelectrochemical device protected by the titanium dioxide single crystal manufactured in Example 1 measured constant photovoltage and photocurrent values ​​(see Fig. 6), and there was no change in appearance due to corrosion (see Fig. 7). In addition, the photocurrent value continued for more than 24 hours and operated stably (see Fig. 8). Therefore, it was confirmed that a protective layer was formed by the titanium dioxide single crystal to prevent the electrolyte from penetrating into the semiconductor material, indicating that the semiconductor material was densely and tightly protected.

[0096] The above description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0097] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer, comprising the following steps: (a) a step of heat treating single crystal titanium dioxide; (b) a step of depositing an electrochemical catalyst on one surface of the heat-treated single crystal titanium dioxide and forming an electrode on the other surface; (c) forming a semiconductor material on a substrate and forming an electrode on the semiconductor material; and (d) A step of forming a stack by applying an adhesive between the electrode formed on one side of the single crystal titanium dioxide in step (b) and the electrode formed on the semiconductor material in step (c).

2. In paragraph 1, The heat treatment of step (a) is performed at 500°C to 900°C under a hydrogen atmosphere or in vacuum. A method for manufacturing a photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

3. In paragraph 1, After the step of forming a stack by applying the adhesive of the above step (d), further comprising the step of applying infrared rays and pressure, A method for manufacturing a photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

4. In the third paragraph, The above pressure is 5 bar to 10 bar, A method for manufacturing a photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

5. In paragraph 1, A method for manufacturing a photoelectrochemical device including a single-crystal titanium dioxide protective layer, wherein the adhesive of step (d) is manufactured by including the following steps: (i) a step of heating paraffin to 60°C to 100°C; and (ii) A step of adding conductive particles to the heated paraffin.

6. In paragraph 5, The above conductive particles are carbon compound or polymer particles. A method for manufacturing a photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

7. In paragraph 6, The above carbon compound is at least one selected from the group consisting of graphite, graphene, carbon nanotubes and carbon nanofibers. A method for manufacturing a photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

8. In paragraph 6, The polymer particles are at least one selected from the group consisting of polystyrene (PS), polymethyl methacrylate (PMMA), polystyrene / divinylbenzene (PS / DVB), polyamide, poly(butyl methacrylate) (PBMA), and combinations thereof. A method for manufacturing a photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

9. A photoelectrochemical device comprising a single-crystal titanium dioxide protective layer manufactured by the manufacturing method of paragraph 1.

10. In paragraph 9, The thickness of the single crystal titanium dioxide protective layer is 100 μm to 1,000 μm, A photoelectrochemical device comprising a single-crystal titanium dioxide protective layer.

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