Photoelectric conversion element

Abstract

The present invention pertains to a heterojunction-type photoelectric conversion element (10) characterized by comprising a photoelectric conversion layer (14) in which a semiconductor layer (14A) and a metal nanoparticle layer (14B) are bonded, wherein the metal nanoparticle layer (14B) is such that a plurality of metal nanoparticles (P) are disposed so that the metal nanoparticles (P) are separated from each other and the separation distance between the metal nanoparticles (P) adjacent to each other is equal to or less than the distance over which electron movement is possible.

Description

photoelectric conversion element

[0001] The present invention relates to a photoelectric conversion element using metal nanoparticles. This application claims priority to Japanese Patent Application No. 2024-030461, filed February 29, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, solar cells have been widely used due to the progress of decarbonization. Conventionally, solar cells are classified structurally into silicon-based solar cells using silicon crystals, compound-based solar cells using inorganic compounds such as GaAs, and organic solar cells using organic dyes and organic semiconductors. Of these, compound-based solar cells and organic solar cells are considered to be heterojunction solar cells in which different materials are joined together as a photoelectric conversion layer.

[0003] On the other hand, solar cells (photoelectric conversion elements) are known that are structurally similar to organic solar cells but use metal nanoparticles (for example, metal particles with an average particle diameter in the range of 1 nm or more and 100 nm or less, hereinafter referred to as metal nanoparticles) as a photoelectric conversion layer.

[0004] For example, Patent Document 1 discloses a photoelectric conversion element having metal bodies arranged in island-like isolation along the interface between the electron transport layer and the hole transport layer. In this type of photoelectric conversion element, metal nanoparticles are used as the metal bodies. Because the particle size of these metal nanoparticles is smaller than the wavelength of light, irradiation with visible light or the like creates a pseudo-state in which an AC electric field of several hundred THz is applied, resulting in resonance at a specific wavelength (localized surface plasmon resonance: LSPR). The collective resonance and movement of electrons in these metal nanoparticles creates a secondary electric field around them, providing an assisting function that helps improve photoelectric conversion efficiency.

[0005] It is also known that electrons resonating due to LSPR enter a high-energy state (hot electrons), although only for a femtosecond timescale before energy dissipation occurs due to collisions with protons, and this state can be used to cause charge separation (plasmon-induced charge separation: PICS). Because the resonating frequency (wavelength) of nanoparticles can be changed depending on their size and shape, they have potential as optical antennas and power generation elements that can respond to various wavelengths.

[0006] In Patent Document 1, since a power generation mechanism is provided that generates PICS by LSPR and extracts electric charge, LSPR must be initiated as a trigger for the series of mechanisms. That is, to prevent electron movement (tunneling) between adjacent metal nanoparticles, the metal nanoparticles are arranged in an island-like fashion with a distance sufficient to prevent tunneling.

[0007] Japanese Patent Publication No. 2016-162890

[0008] However, in the photoelectric conversion element disclosed in Patent Document 1, the metal nanoparticles are intended to generate electricity over a wide range of wavelengths using PICS, and the mechanism for this is based on LSPR. The metal nanoparticles exhibit various colors depending on the absorption band due to LSPR, and are transparent when the absorption band is in the infrared range. This makes it possible to fabricate multicolored or transparent photoelectric conversion elements, but there is a problem in that it is not possible to fabricate photoelectric conversion elements with a metallic appearance.

[0009] The aspects of the present invention have been made in consideration of the above circumstances, and aim to provide a photoelectric conversion element that has a metallic appearance and is capable of photoelectric conversion by using a laminated film of metal nanoparticles as a photoelectric conversion layer.

[0010] In order to solve the above problems, the present invention employs the following configuration: A photoelectric conversion element according to one embodiment of the present invention is a heterojunction photoelectric conversion element having a photoelectric conversion layer in which a semiconductor layer and a metal nanoparticle layer are joined together, wherein the metal nanoparticle layer is characterized in that the metal nanoparticles are arranged such that the metal nanoparticles are spaced apart from one another and the distance between adjacent metal nanoparticles is equal to or less than the distance that allows electrons to move.

[0011] According to an aspect of the present invention, a metal nanoparticle laminated film can be used as a photoelectric conversion layer to achieve both a metallic appearance and photoelectric conversion, thereby realizing a photoelectric conversion element that can be applied to parts, devices, decorative items, etc. that have a metallic appearance and are not applicable to any existing photoelectric conversion element.

[0012] FIG. 1 is a schematic cross-sectional view showing a photoelectric conversion element according to one embodiment of the present invention. FIG. 2 is an electron microscope photograph showing a metal nanoparticle layer using silver nanoparticles. FIG. 3 is an explanatory diagram showing the preparation of a sample of an example. FIG. 4 is a graph showing the measurement results of spectral sensitivity of Inventive Example 1. FIG. 5 is a graph showing the measurement results of spectral sensitivity of Comparative Example 1. FIG. 6 is a graph showing the measurement results of spectral sensitivity of Comparative Example 2. FIG. 7 is a graph showing the measurement results of spectral sensitivity of Comparative Example 3.

[0013] Traditionally, basic and applied research on metal nanoparticles has been premised on interest in LSPR, which can confine light in nanoscale regions and be used as a trigger for enhancement or energy conversion. Therefore, research has not considered the transfer and movement of electrons due to tunneling between nanoparticles, and has relied on simulations using the finite-difference time-domain method (FDTD), which only considers the behavior inside individual nanoparticles. While it is known that electron spillover (hereinafter referred to as spillout) occurs, to a small extent, research has focused on samples in which sufficient interparticle distance is maintained using dispersants (ligands) to allow for this to be ignored and to avoid discrepancies with simulations.

[0014] Meanwhile, a detailed investigation of the behavior of a laminated film of silver nanoparticles, a type of metal nanoparticle, in which the interparticle distance is sufficiently close (approximately 2 nm or less) due to the selection of a dispersant, revealed a phenomenon that cannot be explained by LSPR and can only be explained by assuming that electrons pass between the nanoparticles and "behave as if they were free electrons." In other words, the researchers discovered that, rather than simply spilling out, electrons behaved as if they had formed a new band between the particles.

[0015] These results explain why metal nanoparticle laminated films have a metallic appearance even though the nanoparticles are spaced apart. Because they are not continuous thin films, they do not require vacuums such as sputtering or vapor deposition, nor do they require chemical reactions on the target, such as the silver mirror reaction. This makes them a means of easily achieving a metallic appearance using simple methods such as coating.

[0016] On the other hand, it is known that metal nanoparticles can undergo PICS and be used for photoelectric conversion. The inventors have discovered that when metal nanoparticles are randomly scattered, a photoelectric conversion element with a metallic appearance can be realized by combining a configuration in which electrons can tunnel between multiple metal nanoparticles, allowing them to move freely between the metal nanoparticles, with the photoelectric conversion properties of PICS. Furthermore, when metal nanoparticles are regularly arranged, the phenomenon closely resembles the phenomenon predicted and confirmed by intermediate band theory in quantum dot superlattice photoelectric conversion elements, and thus a photoelectric conversion element with a metallic appearance can be realized. Based on the above, a thin film capable of photoelectric conversion while having a metallic appearance can be obtained by a simple coating method.

[0017] A photoelectric conversion element according to one embodiment of the present invention will be described below. Note that the embodiment described below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality.

[0018] In this embodiment, visible light refers to light with a wavelength in the range of 380 to 750 nm. Infrared light refers to light with a wavelength in the range of 850 to 1600 nm. In addition, in this embodiment, nanoparticles refer to particles with an average particle size of nano-order, specifically, 1 nm or more and less than 200 nm.

[0019] 1 is a schematic cross-sectional view showing a photoelectric conversion element according to one embodiment of the present invention. The photoelectric conversion element 10 of this embodiment is composed of a substrate 11 and a first electrode layer 12, a photoelectric conversion layer 14, and a second electrode layer 15, which are stacked in this order on one surface of the substrate 11.

[0020] The substrate 11 is made of a light-transmitting transparent plate that can transmit at least sunlight, such as a glass plate or a transparent resin plate. The glass plate may be made of quartz, sodium carbonate, calcium carbonate, or the like. The transparent resin plate may be made of polymethyl methacrylate, polycarbonate, acrylic urethane, or the like. It is preferable that such a substrate 11 has a transmittance of 90% or more for sunlight (wavelengths of approximately 1 nm to 2500 nm).

[0021] The first electrode layer 12 is made of a light-transmitting transparent electrode material that can transmit at least sunlight. Examples of the transparent electrode material include indium tin oxide, zinc oxide, tin oxide, titanium oxide, graphene, polyaniline, etc. In this embodiment, indium tin oxide (ITO) is used as the first electrode layer 12.

[0022] The photoelectric conversion layer 14 of this embodiment is composed of a laminate in which an n-type semiconductor layer (semiconductor layer) 14A and a metal nanoparticle layer 14B are bonded together. The n-type semiconductor layer 14A is composed of a material that has an n-type semiconductor type. The constituent material of the n-type semiconductor layer 14A is metal alkoxide (M(OR) ｎ Examples of the metal alkoxide include titanium alkoxide and zirconium alkoxide.

[0023] Among these, examples of titanium alkoxides include titanium i-propoxide, titanium n-butoxide, titanium 2-ethylhexoxide, titanium tert-butoxide, titanium stearyl alkoxide, etc. In this embodiment, a titanium alkoxide dissolved in chlorobenzene (CB) as a solvent was used as the n-type semiconductor layer 14A.

[0024] It has been found that the surface roughness (smoothness) of the n-type semiconductor layer 14A has a significant effect on the arrangement of the metal nanoparticles P that make up the metal nanoparticle layer 14B. That is, if the surface of the n-type semiconductor layer 14A is not smooth, the arrangement of the metal nanoparticles P in the joined metal nanoparticle layer 14B becomes disordered, hindering the transport of electrons (carriers) from the metal nanoparticles P. This increases the likelihood of electron recombination, hindering photoelectric conversion and reducing photoelectric conversion efficiency.

[0025] Disturbances in the surface roughness of the n-type semiconductor layer 14A occur when titanium dioxide is produced by hydrolysis of titanium alkoxide due to moisture in the air. It is known that the shorter the chain of an alkoxide, the faster it decomposes, and that decomposition occurs in the order of tertiary, secondary, and primary. Therefore, titanium alkoxides with long-chain primary alcohols are the most suitable. Titanium n-butoxide polymers are particularly suitable because they are low-decomposable and viscous, and act as a primer after application, forming a smooth surface.

[0026] In this embodiment, the semiconductor layer is an n-type semiconductor layer 14A, but the semiconductor type of the semiconductor layer is not limited to n-type. For example, the semiconductor layer may be a p-type semiconductor layer, an i-type semiconductor layer, or the like.

[0027] The metal nanoparticle layer 14B is composed of a plurality of metal nanoparticles P. The metal nanoparticle layer 14B is a layer that functions as a p-type semiconductor layer that forms a pn junction with the n-type semiconductor layer 14A. The metal nanoparticles P that compose the metal nanoparticle layer 14B are preferably made of either silver (Ag) or indium (In). In this embodiment, silver nanoparticles are used as the metal nanoparticles P.

[0028] When the metal nanoparticles P constituting the metal nanoparticle layer 14B are silver nanoparticles, the shape of each silver nanoparticle is preferably spherical, discoid, rod-like, or rectangular. Furthermore, it is preferable that the shapes of multiple silver nanoparticles are uniform. When indium nanoparticles are used as the metal nanoparticles P, it is preferable that the individual indium nanoparticles have irregular shapes that are not uniform from one another.

[0029] The plurality of metal nanoparticles P constituting the metal nanoparticle layer 14B are arranged so that the individual metal nanoparticles P are spaced apart from one another and the distance between adjacent metal nanoparticles P is equal to or less than the distance that allows electrons to move. That is, in this embodiment, the silver nanoparticles are arranged so that they are spaced apart without contacting one another and the distance between the silver nanoparticles is within a range that allows electron tunneling effect to be exerted.

[0030] In this embodiment, the distance between the silver nanoparticles (metal nanoparticles P) arranged at a distance from each other is 2 nm or less. This distance allows free electrons to pass between the silver nanoparticles and behave freely (tunneling effect). This prevents the free electrons from moving to adjacent silver nanoparticles before an individual silver nanoparticle generates LSPR, preventing resonance from occurring at an individual silver nanoparticle.

[0031] Furthermore, by setting the distance between the silver nanoparticles within a range that allows the tunneling effect to be exhibited, for example, 2 nm or less, the photoelectric conversion layer 14 can be made to have a metallic luster (metallic appearance). This allows the photoelectric conversion element 10 to be placed on a decorative surface that requires a metallic luster.

[0032] On the other hand, when silver nanoparticles are individually dispersed near the boundary with the n-type semiconductor layer 14A, it is expected that the tunneling of electrons and LSPR compete with each other. It is expected that this LSPR triggers PICS, resulting in charge injection.

[0033] On the other hand, when silver nanoparticles are densely aligned near the boundary with the n-type semiconductor layer 14A, a transition to the intermediate band and charge injection from there occur, so that the free electrons in the intermediate band give the material a metallic appearance, while the injection from that band allows photoelectric conversion.

[0034] 2 shows an electron microscope photograph of a metal nanoparticle layer using silver nanoparticles as an example of the metal nanoparticle layer 14B of this embodiment. It can be seen from Fig. 2 that multiple silver nanoparticles are formed spaced apart without contact with each other, and that the separation distance is maintained at about 2 nm, which is sufficient to generate the tunneling effect.

[0035] In this way, the metal nanoparticle layer 14B of this embodiment functions as a p-type semiconductor layer that forms a pn junction with the n-type semiconductor layer 14A, as electrons move freely between multiple metal nanoparticles P due to the tunneling effect, and photoelectric conversion can be performed in the photoelectric conversion layer 14, for example, by absorbing sunlight.

[0036] The metal nanoparticle layer 14B of this embodiment is formed by laminating, for example, three or more layers of single-layer metal nanoparticle films in which metal nanoparticles P are arranged in a plane. This allows electrons to move freely in three dimensions in both the plane direction and the thickness direction of the metal nanoparticle layer 14B, thereby improving the photoelectric conversion efficiency.

[0037] The thickness of the metal nanoparticle layer 14B may be, for example, 50 nm to 300 nm, preferably 150 nm to 200 nm. When the thickness of the metal nanoparticle layer 14B is in the range of 150 nm to 200 nm, the photoelectric conversion layer 14 can efficiently perform photoelectric conversion.

[0038] It is also preferable that the metal nanoparticles P constituting the metal nanoparticle layer 14B are spaced apart without contacting adjacent metal nanoparticles P, and that the separation distance is maintained to an extent that allows the tunneling effect to be exerted, so that a spacing material is further applied to the surface of each metal nanoparticle P.

[0039] Furthermore, the metal nanoparticle layer 14B may further contain a resin made of a polymer dispersant in addition to the metal nanoparticles P. The content of the metal nanoparticles P contained in the metal nanoparticle layer 14B is preferably 50 to 90% in terms of volume filling rate (%). The remainder may be the resin (polymer dispersant).

[0040] By setting the metal nanoparticle P content in the range of 50 to 90%, adjacent metal nanoparticles P are spaced apart without contacting each other, and the distance between the metal nanoparticles P can be maintained to a degree that allows the tunneling effect to be exhibited. If the metal nanoparticle P content is less than 50%, the distance between the metal nanoparticles P becomes too large, which may prevent the electron tunneling effect from being maintained and reduce the degree of freedom of electron movement. There is also a concern that metallic luster may not be obtained. On the other hand, if the metal nanoparticle P content exceeds 90%, the metal nanoparticles P may come into contact with each other, which may prevent the distance between the metal nanoparticles P from being maintained.

[0041] The polymer dispersant preferably has a styrene-maleic anhydride resin structure in which a portion of the maleic anhydride has been modified with a polyalkylene glycol having a terminal hydroxyl group or a polyalkylene glycol having a terminal amino group. The polyalkylene glycol preferably has a molar ratio of polyethylene glycol chains to polypropylene glycol chains of 6 / 4 to 8 / 1 and a molecular weight of 500 to 3000. By using a polymer dispersant with such a configuration, the metal nanoparticles P can be stably dispersed within the metal nanoparticle layer 14B.

[0042] The polymer dispersant preferably has an acid value of 150 or less, which makes it possible to suppress oxidation of the metal nanoparticles P.

[0043] The second electrode layer 15 is made of a conductive polymer, such as PEDOT / PSS (Poly3,4-EthyleneDiOxyThiophene / Poly4-StyreneSulfonate). By using PEDOT / PSS as the second electrode layer 15, it can function as both a carrier transport layer and an electrode layer. Note that such PEDOT / PSS may be used as a carrier transport layer, and the second electrode layer 15 made of silver or the like may be provided on top of it.

[0044] According to the photoelectric conversion element 10 of this embodiment configured as described above, the metal nanoparticle layer 14B constituting the photoelectric conversion layer 14 is configured such that the individual metal nanoparticles P are spaced apart from one another and the distance between adjacent metal nanoparticles P is equal to or less than the distance that allows electrons to move. This allows electrons to move freely between the multiple metal nanoparticles P due to the tunneling effect, and the metal nanoparticle layer 14B can be used as a photoelectric conversion layer (power generation layer). This allows for a photoelectric conversion element 10 that is capable of photoelectric conversion and has a metallic luster.

[0045] Next, an example of a method for manufacturing the metal nanoparticle layer constituting the photoelectric conversion element of the present embodiment will be described. As an example of a method for manufacturing the metal nanoparticle layer, it is possible to manufacture the metal nanoparticle layer by forming a single laminated film on a substrate, rather than by alternately laminating multiple thin films with different refractive indices as in the conventional method.

[0046] That is, the method comprises a preparation step of preparing a coating solution, and a coating film formation step of spraying the coating solution onto the surface of a substrate and then drying the coating solution. Below, each step will be described when silver nanoparticles are used as the metal nanoparticles.

[0047] In the preparation step, at least one silver compound selected from silver oxide and silver carbonate and a polymer dispersant are dispersed in an alcohol solvent, and then ultrasonic waves are applied to reduce and disperse the silver compound, thereby preparing a coating liquid.

[0048] The polymer dispersant may be one of those described above. Polymer dispersants having a styrene-maleic acid copolymer structure and polymer dispersants in which part of the maleic anhydride has been modified with a hydroxyl-terminated polyalkylene glycol or an amino-terminated polyalkylene glycol are already commercially available. Examples of styrene-maleic acid copolymers used as base resins include SMA (registered trademark) Base Resin 1000, 2000, and 3000, SMA Ester Resin 1440 and 2625 (all manufactured by Cray Valley USA, LLC), and Arastar 700 (manufactured by Arakawa Chemical). These base resins with an SMA structure have high acid values ​​of 175 to 500. Disperbyk 190 and 2015 (non-volatile content 40%, acid value 10, manufactured by BYK Corporation) have a styrene-maleic anhydride resin structure in which part of the maleic anhydride is modified with a polyalkylene glycol or the like having a terminal hydroxyl group, and the acid value of the non-volatile content in both products is 25.

[0049] As described above, commercially available polymer dispersants vary in acid value from those with high to those with low acid values, but the acid value is fixed at a predetermined value. Therefore, by using SMA Base Resin 1000, a polymer dispersant with a styrene-maleic acid copolymer structure, and modifying part of the maleic anhydride in the styrene-maleic acid copolymer structure with a hydroxyl-terminated polyalkylene glycol or an amino-terminated polyalkylene glycol, the acid value can be adjusted to 150 or less.

[0050] The alcohol solvent is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, and 1-methoxy-2-propanol.

[0051] The at least one silver compound selected from silver oxide and silver carbonate is not particularly limited as long as it is in powder form.

[0052] The amount of polymer dispersant added to the silver compound is 2 to 25% by mass in terms of the mass ratio of the nonvolatile content, and the concentration of the silver compound in the alcohol solution is 5 to 40% by mass.

[0053] When silver oxide or silver carbonate is added to an alcoholic solvent containing a polymeric dispersant, a heterogeneous alcoholic solution is obtained in which the silver oxide or silver carbonate is dispersed in a solid-liquid two-phase state. When this alcoholic solution is irradiated with ultrasound, bubbles (cavitation) are generated in the solution. The generation and collapse of these cavitations creates a high-temperature local reaction field in the solution, aiding in the generation of radicals, which in turn promotes a sonochemical reaction. In other words, a decomposition-reduction reaction occurs in the silver oxide or silver carbonate, producing metallic silver without the need for a separate reducing agent, which precipitates in the form of silver nanoparticles. Examples of the reaction formula are shown in Equations (1) and (2) below.

[0054] Ag ２ O → 2Ag + O ２ ↑ ... (1) Ag ２ CO ３ → 2Ag + 1 / 2O ２ ↑ + CO ２ ↑ ... (2)

[0055] As shown in the above reaction formula, oxygen (in the case of silver oxide) or oxygen and carbon dioxide (in the case of silver carbonate) are generated as by-products, but these are volatile, and the alcohol solvent is also volatile, and both substances are non-corrosive. Therefore, by performing the coating film formation process, it is possible to easily produce a visible-infrared separation membrane consisting of silver nanoparticles and a polymer dispersant.

[0056] Next, in the coating film forming step, the coating liquid obtained in the preparation step is applied to the surface of the substrate by, for example, spraying, and then drying. The drying may be performed, for example, in an atmosphere of 5 to 80°C.

[0057] A general sprayer may be used as a means for spraying the coating liquid. There are no particular limitations on the spray conditions, but examples of such conditions include adjusting the needle so that the coating liquid discharge rate is 30 to 60 mL / min and setting the atomization pressure to 0.2 to 0.3 MPa.

[0058] In the coating film formation process, a form in which the coating liquid is applied to the surface of the substrate by atomizing (spraying) has been described, but this embodiment is not limited to this, and various liquid application methods such as screen printing and spin coating may also be used.

[0059] The metal nanoparticle layer constituting the photoelectric conversion element of this embodiment can be manufactured through the above-described steps. By this manufacturing method, a metal nanoparticle layer can be obtained in which a plurality of metal nanoparticles are arranged so that the individual metal nanoparticles are spaced apart from each other and the distance between adjacent metal nanoparticles is equal to or less than the distance that allows electrons to move.

[0060] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims.

[0061] The method for forming a photoelectric conversion element according to the present invention will be described in detail below using various experimental examples. However, the various experimental examples shown below are examples for embodying the technical concept of the present invention, and are not intended to limit the present invention to those shown in these experimental examples. The present invention can equally be applied to other embodiments included in the scope of the claims. The following explanation is of operations common to each example.

[0062] [Etching of ITO substrate] Etching is performed to insulate the center of the ITO-deposited glass. In preparation for etching, masking tape is applied to both sides, leaving the center as a guide (see Figure 3(a)). When applying the masking tape, use a tester or similar tool to check that it is on the surface where ITO is deposited.

[0063] Once the masking is complete, the exposed glass area is immersed in hydrochloric acid and left to etch. Once etching is complete, the ITO-coated glass is removed, thoroughly washed with water, and the masking tape is removed. Finally, a tester or similar tool is used to check that the etched area is insulated.

[0064] [Method for preparing titanium alkoxide solution] Put a few drops of titanium alkoxide into a screw cap and measure the weight. Place a stirrer in the screw cap and place it on a magnetic stirrer to stir. Using the above procedure, prepare the respective titanium alkoxide solutions.

[0065] [Coating PEDOT-PSS electrodes] The element is placed on a screen printer and a stainless steel metal mask with a rectangular hole is pressed against it. A thin layer of PEDOT-PSS is applied to the mask to electrically connect the power generation layer to the ITO part on the opposite side.

[0066] (Example of the present invention) Polymer-type titanium butoxide (manufactured by Aldrich Corporation, product number 510718, hereinafter referred to as TiOBu) was weighed into a screw tube, followed by dropwise addition of chlorobenzene (hereinafter referred to as CB), followed by stirring to prepare a TiOBu / CB solution.

[0067] Next, the above-mentioned etched ITO substrate was set on a spin coater, and the above-mentioned TiOBu / CB solution was evenly dropped onto it, followed by high-speed spin coating. After spin coating, the substrate was wiped off, leaving about 1 / 4 of the top right corner. After wiping, the substrate was left as is. After leaving the substrate, it was heated on a heated hot plate and dried. Note that since TiOBu solidifies when heated and dried, wiping with CB was performed before drying.

[0068] Next, the ITO substrate coated with TiOBu was set on the spin coater again, and the silver nanoparticle dispersion was evenly dropped onto the substrate, followed by spin coating at a low speed for a short period of time. The substrate was then left as it was until the thinner, which was the solvent contained in the silver nanoparticle dispersion, evaporated, giving the substrate a metallic appearance.

[0069] The substrate was then removed from the spin coater and wiped again, leaving approximately the top right quarter of the substrate. This time, the TiOBu coating was left completely covered (see Figure 3(b)). After that, the substrate was again heated and dried on a heated hot plate to completely volatilize the thinner, which was the solvent contained in the silver nanoparticle dispersion.

[0070] A PEDOT-PSS electrode is applied to the power generation layer obtained by the above process using a screen printer (see Figure 3(c)). After the electrode is applied, it is left as is and then heated and dried on a heated hot plate. After drying, cellophane tape is attached to the upper half of the element to protect the entire power generation layer, and two ITO parts at the bottom are thinly soldered to form electrodes (see Figure 3(d)). The spectral sensitivity of the element of the present invention created using the above procedure was measured.

[0071] (Comparative Example 1: Conditions where PEDOT-PSS is not penetrated) TiOBu was weighed into a screw tube. Then, CB was added dropwise and stirred to prepare a TiOBu / CB solution. Next, the above-mentioned etched ITO substrate was prepared, and this ITO substrate was set on a spin coater. The above-mentioned TiOBu / CB solution was added dropwise evenly and spin-coated at high speed. After spin-coating, wiping was performed, leaving about one-quarter of the top right. After wiping, the substrate was heated and dried on a heated hot plate. Note that, because TiOBu solidifies when heated and dried, wiping with CB was performed before drying.

[0072] Next, the ITO substrate coated with TiOBu was set on the spin coater again, and the silver nanoparticle dispersion was evenly dropped onto the substrate, followed by spin coating at a low speed for a short period of time. The substrate was then left as it was until the thinner, which was the solvent contained in the silver nanoparticle dispersion, evaporated, giving the substrate a metallic appearance.

[0073] The substrate was then removed from the spin coater and wiped again, leaving approximately the top right quarter. Thereafter, the substrate was again heated and dried on a heated hot plate to completely volatilize the thinner, which was the solvent contained in the silver nanoparticle dispersion.

[0074] A PEDOT-PSS electrode is applied to the power generation layer obtained by the above process using a screen printer (see Figure 3(c)). After the electrode is applied, it is dried by heating on a heated hot plate. After drying, cellophane tape is attached to the upper half of the element to protect the entire power generation layer, and two ITO parts at the bottom are thinly soldered to form electrodes (see Figure 3(d)). The spectral sensitivity of the element of Comparative Example 1 created by the above procedure was measured.

[0075] Comparative Example 2: Example in which spin coating conditions were changed Titanium isopropoxide (hereinafter referred to as TiOX) was weighed and placed in a screw tube, followed by dropwise addition of CB and stirring to prepare a TiOX / CB solution.

[0076] Next, the above-mentioned etched ITO substrate was prepared and set on a spin coater, and the above-mentioned TiOX / CB solution was evenly dropped onto it to perform spin coating. After spin coating, the substrate was wiped off, leaving about 1 / 4 of the top right corner. After wiping, the substrate was heated and dried on a heated hot plate. Note that since the TiOX solidifies when heated and dried, wiping with CB was performed before drying.

[0077] Next, the ITO substrate coated with TiOX was set again on the spin coater, and the silver nanoparticle dispersion was evenly dropped onto it, spin-coating it at high speed for three coats.Then, the thinner, which was the solvent contained in the silver nanoparticle dispersion, was evaporated, resulting in a metallic appearance.

[0078] The substrate was then removed from the spin coater and wiped again, leaving approximately the top right quarter. Thereafter, the substrate was again heated and dried on a heated hot plate to completely volatilize the thinner, which was the solvent contained in the silver nanoparticle dispersion.

[0079] A PEDOT-PSS electrode is applied to the power generation layer obtained by the above process using a screen printer (see Figure 3(c)). After the electrode is applied, it is heated and dried on a heated hot plate. After drying, cellophane tape is attached to the upper half of the element to protect the entire power generation layer, and two ITO parts at the bottom are thinly soldered to form electrodes (see Figure 3(d)). The spectral sensitivity of the element of Comparative Example 2 created by the above procedure was measured.

[0080] Comparative Example 3: Example of changing spin coating conditions and thick coating of titanium alkoxide TiOX was weighed into a screw tube, and then CB was added dropwise and stirred to prepare a TiOX / CB solution.

[0081] Next, the above-mentioned etched ITO substrate was prepared and set on a spin coater. The above-mentioned TiOX / CB solution was evenly dropped onto the substrate, and spin-coated at high speed, with three coats. After spin-coating, the substrate was wiped off, leaving about 1 / 4 of the top right corner. After wiping, the substrate was dried by heating on a heated hot plate. Note that, since TiOX solidifies when heated and dried, wiping with CB was performed before drying.

[0082] Next, the ITO substrate coated with TiOX was set again on the spin coater, and the silver nanoparticle dispersion was evenly dropped onto it, spin-coating it at high speed for three coats.Then, the thinner, which was the solvent contained in the silver nanoparticle dispersion, was evaporated, resulting in a metallic appearance.

[0083] The substrate was then removed from the spin coater and wiped again, leaving approximately the top right quarter. Thereafter, the substrate was again heated and dried on a heated hot plate to completely volatilize the thinner, which was the solvent contained in the silver nanoparticle dispersion.

[0084] A PEDOT-PSS electrode is applied to the power generation layer obtained by the above process using a screen printer (see Figure 3(c)). After the electrode is applied, it is heated and dried on a heated hot plate. After drying, cellophane tape is attached to the upper half of the element to protect the entire power generation layer, and two ITO parts at the bottom are thinly soldered to form electrodes (see Figure 3(d)). The spectral sensitivity of the element of Comparative Example 3 created by the above procedure was measured.

[0085] [Measurement of Spectral Sensitivity] The spectral sensitivities of the elements (samples) of the invention examples and comparative examples 1 to 3 were measured using a spectral sensitivity measurement device (CEP-2000RS, manufactured by Bunkoukeiki Co., Ltd.). The measurement mode was external quantum yield, irradiation energy 2.5 mW cm ２ The spectral sensitivity was measured in 10 nm increments, with a 5-time average, a bias voltage of 5 V, and a measurement range of 300 nm to 1000 nm. The measurement results of the spectral sensitivity of the inventive example are shown in graphs in Figure 4, and the measurement results of the spectral sensitivity of comparative examples 1 to 3 are shown in graphs in Figures 5 to 7, respectively.

[0086] According to the results shown in FIGS. 5 to 7, it was confirmed that the inventive example had higher spectral sensitivity in the wavelength range of around 300 nm to 500 nm and better photoelectric conversion efficiency in the visible light range compared to comparative examples 1 to 3.

[0087] According to the photoelectric conversion element of the present invention, by using a metal nanoparticle layer as a photoelectric conversion layer (power generation layer), it is possible to realize a photoelectric conversion element that has metallic luster and is capable of photoelectric conversion. Such a photoelectric conversion element can be applied to parts, devices, ornaments, etc. with a metallic appearance that cannot be applied to conventional solar cells, and can impart the ability to generate electricity to parts, devices, ornaments, etc. with a metallic appearance while maintaining their conventional appearance. Therefore, it has industrial applicability.

[0088] 10...photoelectric conversion element, 11...substrate, 12...first electrode layer, 13...electron transport layer, 14...photoelectric conversion layer 14, 14A...n-type semiconductor layer, 14B...metal nanoparticle layer, P...metal nanoparticles.

Claims

1. A heterojunction photoelectric conversion element having a photoelectric conversion layer in which a semiconductor layer and a metal nanoparticle layer are joined together, wherein the metal nanoparticle layer is configured so that the metal nanoparticles are spaced apart from one another and the distance between adjacent metal nanoparticles is equal to or less than the distance that allows electrons to move.

2. The photoelectric conversion element according to claim 1, characterized in that the metal nanoparticle layer is made of a laminated film in which a plurality of silver nanoparticle films, each having a plurality of silver nanoparticles arranged therein, are laminated.

3. The photoelectric conversion element according to claim 1 or 2, wherein the semiconductor layer is an n-type semiconductor layer.

4. The photoelectric conversion element according to claim 3, wherein the n-type semiconductor layer contains a metal alkoxide compound.

5. The photoelectric conversion element according to claim 4, wherein the metal alkoxide compound is a titanium alkoxide compound.

6. The photoelectric conversion element according to claim 1 or 2, characterized in that a spacing material is further applied to the surface of the metal nanoparticles to maintain the spacing distance between adjacent metal nanoparticles.

7. The photoelectric conversion element according to claim 1 or 2, characterized in that the metal nanoparticle layer has a metallic luster.

8. The photoelectric conversion element according to claim 1 or 2, characterized in that the metal nanoparticle layer has a function as a carrier transport layer.

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