Photoelectric conversion element

The present invention relates to a photoelectric conversion element, and more particularly to a photoelectric conversion element using the effect of enhancing the photoelectric field by localized surface plasmon resonance.

Solar cells have the advantages of low carbon dioxide emissions per amount of power generation and no need for fuel for power generation. Therefore, research on various types of solar cells is being actively pursued. Currently, among the solar cells in practical use, single-junction solar cells using single-crystal silicon or polycrystalline silicon and having a set of pn junctions are the mainstream. However, since the theoretical limit of the photoelectric conversion efficiency of a single-junction solar cell (hereinafter referred to as "theoretical limit efficiency") is only about 30%, a new method for further improving the theoretical limit efficiency is being studied. ..

One of the new methods being studied so far is a solar cell using the quantum structure of a semiconductor. Quantum dots, quantum wells, quantum wires, and the like are known as quantum structures used in this type of solar cell. By using the quantum structure, it is possible to absorb the sunlight spectrum in a band that could not be absorbed by the conventional solar cell. It is thought that it will be possible to improve it to 60% or more.

Several techniques related to such solar cells (including photovoltaic devices and photoelectric conversion elements) or techniques applicable to solar cells have been disclosed so far. For example, Patent Document 1 has a surface illuminated by incident light and an unilluminated surface, and at least one of the illuminated surface and the unilluminated surface is the incident light and a surface on the surface. A surface plasmon-enhanced light generator comprising a first metal electrode having an array of apertures having an aperture property that produces a resonance interaction with plasmons and a second electrode spaced apart from the first metal electrode. Power devices are disclosed. Further, in Patent Document 2, a photoelectric conversion element in which a mixture containing at least a multiphoton absorbing organic material, metal fine particles that generate a localized plasmon enhancing field, and a dispersant is used as at least a part of the constituent elements. Is disclosed. Further, in Patent Document 3, the surface of almost spherical metal particles having an average particle size of 0.1 to 10 μm is coated with a dielectric layer, and one or more of the coated particles are dispersed in a resin. The composite dielectric material is disclosed. Further, Patent Document 4 discloses a method for producing insulating magnetic metal particles and insulating magnetic material. Further, in Patent Document 5, the i-layer, which is a photodetection layer and has a pin structure, contains quantum dots having a three-dimensional quantum confinement action, and the energy band structure of the quantum dots and the barrier layer surrounding them is type II. A solar cell characterized by forming is disclosed.

<p><patcit num="1"><text>JP-A-2002-76410</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2008-122439</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2001-303102</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2008-41961</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 2006-114815</text></patcit></p>

<p> According to the technique disclosed in Patent Document 1, since the resonance interaction with the surface plasmon is used, it is possible to promote light absorption, and as a result, it is also possible to improve the photoelectric conversion efficiency. Is thought to be. However, there is a problem that the effect of promoting light absorption tends to be insufficient in the form of utilizing the resonance interaction with the surface plasmon on the surface as in the technique disclosed in Patent Document 1. On the other hand, according to the technique disclosed in Patent Document 2, since the metal fine particles that generate the localized plasmon enhancing field are three-dimensionally arranged, the light absorption is higher than that of the technique disclosed in Patent Document 1. It is considered that the promoting effect of However, in the technique disclosed in Patent Document 2, metal fine particles are dispersed in the electrolyte. Therefore, it is difficult to uniformly disperse the metal fine particles, and there is a problem that the effect of improving the photoelectric conversion efficiency is easily reduced. It was difficult to solve these problems even if the techniques disclosed in Patent Documents 1 to 5 were combined.</p><p> Therefore, an object of the present invention is to provide a photoelectric conversion element capable of improving the photoelectric conversion efficiency.</p>

<p> In order to solve the above problems, the present invention takes the following means. That is, The present invention<u style="single">The p-layer and the n-layer and the i-layer arranged between the p-layer and the n-layer are provided, and the i-layer is a quantum structure portion and a semiconductor layer arranged around the quantum structure portion. The semiconductor is included in the constituent material of the quantum structure part, and the inside of the quantum structure part</u>And semiconductors<u style="single">layer</u>Inside<u style="single">, The distance between at least a part of the metal nanoparticles arranged inside the semiconductor layer and the quantum structure portion is equal to or less than the diameter of the metal nanoparticles.</u>This is a photoelectric conversion element.</p><p> Here, the "metal nanoparticles" refer to metal particles having a diameter of 100 nm or less, preferably 2 nm or more and 10 nm or less. Examples of the metal constituting the metal nanoparticles include Au, Ag, Pt and the like.</p><p> Also,<u style="single">The "quantum structure part" refers to, for example, quantum dots, quantum wells, quantum wires, and the like.</u></p><p> Also,<u style="single">The "semiconductor layer arranged around the quantum structure portion" means a semiconductor serving as a base material in which the quantum structure portion is embedded when the quantum structure portion is embedded in the semiconductor. On the other hand, when semiconductors that do not form a quantum structure and quantum structures are alternately laminated, the "semiconductor layer arranged around the quantum structure" is between adjacent quantum structures. A laminated semiconductor that does not form a quantum structure.</u></p><p><u style="single">Further, in the present invention, it is preferable that at least a part of the surface of the metal nanoparticles is covered with an insulator.</u></p><p><u style="single">Further, in the present invention, the diameter of the metal nanoparticles arranged in the region where the distance from the light receiving surface is D1 is R1, and the diameter of the metal nanoparticles is arranged in the region where the distance from the light receiving surface is D2, which is farther than D1. When the diameter of the metal nanoparticles is R2, it is preferable that R2&gt; R1.</u></p>

<p><u style="single">In the present invention, metal nanoparticles are arranged in the semiconductor layer arranged inside and around the quantum structure part. By arranging the metal nanoparticles inside or near the quantum structure portion, it is possible to enhance the photoelectric field in the quantum structure portion. Further, by arranging the metal nanoparticles in the semiconductor layer arranged around the quantum structure portion, it becomes possible to enhance the photoelectric field in the semiconductor layer. Therefore, according to the present invention, it is possible to provide a photoelectric conversion element capable of improving the photoelectric conversion efficiency. Further, it is considered that the effect of enhancing the photoelectric field by the localized surface plasmon resonance is exhibited up to a distance similar to the diameter of the metal nanoparticles. Therefore, in the present invention, the distance between at least a part of the metal nanoparticles arranged inside the semiconductor layer and the quantum structure portion is equal to or less than the diameter of the metal nanoparticles, so that not only the semiconductor layer but also the quantum structure It becomes easy to enhance the photoelectric field also in the part. Therefore, it becomes easy to improve the photoelectric conversion efficiency by adopting such a form.</u></p><p> Also<u style="single">, The present invention</u>At least part of the surface of the metal nanoparticles<u style="single">But</u>Must be covered with insulator<u style="single">This makes it possible to reduce the situation in which carriers generated by light irradiation are captured by metal nanoparticles. Therefore, it becomes easy to improve the photoelectric conversion efficiency by adopting such a form.</u></p><p> Also<u style="single">, The present invention</u>In<u style="single">By arranging small metal nanoparticles in a region close to the light receiving surface, it is possible to enhance the short wavelength photoelectric field in a region close to the light receiving surface where short wavelength light is easily absorbed. Become. Further, by arranging large metal nanoparticles in a region far from the light receiving surface, it is possible to enhance the long wavelength photoelectric field in a region far from the light receiving surface where long wavelength light is easily absorbed. It will be possible. Therefore, it becomes easy to improve the photoelectric conversion efficiency by adopting such a form.</u></p>

<figref num="1"><u style="single">It is sectional drawing which shows the morphological example of the solar cell 40.</u></figref>

<u style="single">1 ... nanoparticles, 13 ... antireflection film and transparent conductive film, 14 ... front electrode (second electrode), 15 ... back electrode (first electrode), 31 ... p layer, 32 ... n layers, 40 ... solar cells, 41 ... i layers, 42 ... quantum structures, 42a ... wet layers, 42b ... quantum dots, 43 ... intermediate layers ( Semiconductor layer)</u>

<u style="single">Hereinafter, a case where the present invention is applied to a solar cell will be described with reference to the drawings. The forms shown below are examples of the present invention, and the present invention is not limited to the forms shown below.</u>

<u style="single">FIG. 1 is a cross-sectional view showing a morphological example of the solar cell 40 of the present invention. In order to facilitate the understanding of the present invention, in FIG. 1, the thicknesses of the p layer 31, the n layer 32, and the i layer 41 are shown thickly. Further, in FIG. 1, nanoparticles 1, 1, ... Are shown in a simplified manner.</u>

<u style="single">As shown in FIG. 1, the solar cell 40 includes the p-layer 31 and the n-layer 32, the i-layer 41 (light absorption layer 41) arranged between the p-layer 31 and the n-layer 32, and the n-layer 32. Antireflection film / transparent conductive film 13 disposed on the surface of the surface, a comb-shaped surface electrode 14 disposed on the surface of the antireflection film / transparent conductive film 13, and a back surface disposed on the back surface of the p layer 31. It is equipped with an electrode 15. The i-layer 41 has a quantum structure portion 42 having a wet layer 42a and quantum dots 42b, 42b, ... grown on the wet layer 42a, and a semiconductor having a wider bandgap than the semiconductor constituting the quantum structure portion 42. It is configured by alternately stacking the intermediate layers 43 composed of the above. The intermediate layer 43 includes a region in which the distance from the quantum dots 42b, 42b, ... Is equal to or less than the diameter of the nanoparticles 1, 1, ... (hereinafter referred to as "quantum dot neighborhood region"), and a quantum. Nanoparticles 1, 1, ... In the region where the distance from the dots 42b, 42b, ... exceeds the diameter of the nanoparticles 1, 1, ... (hereinafter referred to as "quantum dot non-nearby region"). Are arranged. Further, in the solar cell 40, nanoparticles 1, 1, ... Are also arranged inside the quantum dots 42b, 42b, .... The nanoparticles 1 have metal nanoparticles and an insulator arranged so as to cover the entire surface of the metal nanoparticles. The p-layer 31 is composed of a p-type semiconductor, and the n-layer 32 is composed of an n-type semiconductor.</u>

<u style="single">When the solar cell 40 is irradiated with light, the light whose reflection is suppressed by the antireflection film / transparent conductive film 13 is incident on the n layer 32, the i layer 41, and the p layer 31. The incident light is absorbed by these layers to generate carriers. In the generated carriers, electrons move to the front electrode 14 and holes move to the back electrode 15 due to the internal electric field formed by the p layer 31 and the n layer 32. In the solar cell 40, when light is incident on the i-layer 41, carriers are generated in the quantum structure portions 42, 42, ..., And the intermediate layers 43, 43, .... The carriers generated in the quantum structure parts 42, 42, ... Pass through the intermediate layers 43, 43, ... by the resonance tunnel, and pass through the quantum structure parts 42, 42, ..., And the surface electrode 14 Or it reaches the back electrode 15. On the other hand, the carriers generated in the intermediate layers 43, 43, ... Drop into the quantum structure parts 42, 42, ..., and the carriers generated in the quantum structure parts 42, 42, ... In the same manner, the front electrode 14 or the back electrode 15 is reached. Here, as described above, the solar cell 40 includes quantum dots 42b, 42b, ... (hereinafter, may be simply referred to as "quantum dots 42b"), and a region near the quantum dots in the intermediate layer 43. Nanoparticles 1, 1, ... Are arranged in the non-near quantum dot region. By arranging nanoparticles 1 on the quantum dots 42b, it is possible to express the effect of localized surface plasmon resonance on the quantum dots 42b, and as a result, it is possible to enhance the photoelectric field on the quantum dots 42b. Become. In addition, by arranging nanoparticles 1, 1, ... In the region near the quantum dots of the intermediate layer 43, the intermediate layer 43 and the quantum dots 42b existing around the nanoparticles 1, 1, ... It becomes possible to exhibit the effect of plasmon resonance on the surface, and as a result, it becomes possible to enhance the photoelectric field in the intermediate layer 43 and the quantum dots 42b. In addition, by arranging nanoparticles 1, 1, ... In the non-quantum dot region of the intermediate layer 43, nanoparticles 1, 1, ... It is possible to exert the effect of localized surface plasmon resonance in the intermediate layer 43 existing around the nanoparticles, and as a result, the photoelectric field is enhanced in the intermediate layer 43 existing around the nanoparticles 1, 1, ... It becomes possible to make it. When the photoelectric field is enhanced by the quantum dots 42b, it becomes easy to generate a plurality of electrons and holes by the quantum dots 42b. When a plurality of electrons and holes are generated in the quantum dots 42b, it becomes easy for the electrons to interact with each other in the quantum dots 42b, and it becomes easy for the holes to interact with each other in the quantum dots 42b. Further, when the photoelectric field is enhanced in the intermediate layer 43 existing around the nanoparticles 1, 1, ..., It becomes easy to generate a plurality of electrons and holes in the intermediate layer 43. Since it is considered that the electrons and holes generated in the intermediate layer 43 reach the front electrode 14 and the back surface electrode 15 via the quantum structure portions 42, 42, ..., a plurality of electrons and positives are generated in the intermediate layer 43. By generating holes, it becomes easy for electrons and holes to interact with each other in the quantum dot 42b. It is possible to reduce the energy loss of electrons by interacting with each other in the quantum dot 42b, and it is possible to reduce the energy loss of holes by interacting with each other in the quantum dot 42b. Become. Therefore, the solar cell 40 capable of improving the photoelectric conversion efficiency by arranging nanoparticles 1, 1, ... In the quantum dot 42b and the quantum dot near region and the quantum dot non-neighborhood region is provided. can do. When the photoelectric field is enhanced in the intermediate layer 43 existing around the intermediate layer 43, it becomes easy to generate a plurality of electrons and holes in the intermediate layer 43. Since it is considered that the electrons and holes generated in the intermediate layer 43 reach the front electrode 14 and the back surface electrode 15 via the quantum structure portions 42, 42, ..., a plurality of electrons and positives are generated in the intermediate layer 43. By generating holes, it becomes easy for electrons and holes to interact with each other in the quantum dot 42b. It is possible to reduce the energy loss of electrons by interacting with each other in the quantum dot 42b, and it is possible to reduce the energy loss of holes by interacting with each other in the quantum dot 42b. Become. Therefore, the solar cell 40 capable of improving the photoelectric conversion efficiency by arranging nanoparticles 1, 1, ... In the quantum dot 42b and the quantum dot near region and the quantum dot non-neighborhood region is provided. can do. When the photoelectric field is enhanced in the intermediate layer 43 existing around the intermediate layer 43, it becomes easy to generate a plurality of electrons and holes in the intermediate layer 43. Since it is considered that the electrons and holes generated in the intermediate layer 43 reach the front electrode 14 and the back surface electrode 15 via the quantum structure portions 42, 42, ..., a plurality of electrons and positives are generated in the intermediate layer 43. By generating holes, it becomes easy for electrons and holes to interact with each other in the quantum dot 42b. It is possible to reduce the energy loss of electrons by interacting with each other in the quantum dot 42b, and it is possible to reduce the energy loss of holes by interacting with each other in the quantum dot 42b. Become. Therefore, the solar cell 40 capable of improving the photoelectric conversion efficiency by arranging nanoparticles 1, 1, ... In the quantum dot 42b and the quantum dot near region and the quantum dot non-neighborhood region is provided. can do.</u>

<u style="single">In the solar cell 40, the constituent material of the antireflection film / transparent conductive film 13 is, for example, MgF.</u>_{<u style="single">2</u>}<u style="single">And TiO</u>_{<u style="single">2</u>}<u style="single">Etc., known materials can be used. The thickness of the antireflection film / transparent conductive film 13 can be, for example, 0.1 μm. Further, as the constituent material of the front electrode 14 and the back electrode 15, known materials such as Ag can be used. The thickness of the front electrode 14 can be, for example, 0.1 to 10 μm, and the thickness of the back electrode 15 can be, for example, 0.1 to 2 μm. Further, as the constituent material of the metal nanoparticles, for example, Au, Ag, Pt and the like can be used. When the metal nanoparticles are composed of Ag, the insulator can be composed of AgO or the like produced by oxidizing Ag. When the metal nanoparticles are composed of Pt, the insulator can be composed of PdO or the like. The diameter of the metal nanoparticles can be, for example, 2 nm or more and 100 nm. For example, when the diameter of the metal nanoparticles is 2 nm, the thickness of the insulator can be 1 nm. Further, the constituent material of the p layer 31 has, for example, a hole density of 1 × 18 cm.</u>^{<u style="single">-3</u>}<u style="single">A known p-type semiconductor such as a Be-doped p-type GaAs can be used. The thickness of the p-layer 31 (thickness in the vertical direction of the paper surface in FIG. 1; hereinafter the same in this paragraph) can be, for example, 5 to 20 nm. In addition, the constituent material of n-layer 32 has, for example, an electron density of 1 × 18 cm.</u>^{<u style="single">-3</u>}<u style="single">A known n-type semiconductor such as an n-type GaAs doped with Si can be used. The thickness of the n-layer 32 can be, for example, 10 to 30 nm. Further, as the constituent material of the intermediate layer 43, for example, GaN As which is not doped with p-type impurities or n-type impurities can be used. The thickness of each of the intermediate layers 43, 43, ... Can be, for example, 40 nm. Further, as the constituent material of the quantum structure portion 42, a semiconductor having a narrower bandgap than the semiconductor constituting the intermediate layer 43, such as InAs which is not doped with p-type impurities or n-type impurities, can be used. The thickness of each of the wet layers 42a, 42a, ... Can be, for example, about 1 to 2 molecules. Further, the heights of the respective quantum dots 42b, 42b, ... (height in the vertical direction of the paper surface in FIG. 1) can be, for example, 3 to 10 nm, and the respective quantum dots 42b, 42b, .. The diameter of. (Quantum dots 42b, 42b, ... maximum length in the left-right direction of the paper surface in FIG. 1) can be, for example, 5 nm to 100 nm. The thickness of the i-layer 41 can be, for example, 300 nm to 2 μm.</u>

<u style="single">An example of a method for manufacturing the solar cell 40 configured as described above will be described below. In order to manufacture the solar cell 40, first, the back surface electrode 15 is formed on the surface of a substrate (not shown) by a known method such as thin film deposition or sputtering. After the back electrode 15 is formed, a p-type semiconductor is deposited on the surface by a chemical vapor deposition (CVD) method or a molecular beam epitaxy (MBE) method. After the p-type semiconductor is deposited in this way, the back electrode 15 on which the p-type semiconductor is deposited is taken out from the CVD device or MBE device, and the core-shell-shaped metal nanoparticles (the surface of Pt is coated with Pd). An aqueous solution in which metal nanoparticles) are dispersed (for example, "Pt / Pd (core / shell) PVP-system", manufactured by Tanaka Kikinzoku Co., Ltd., hereinafter referred to as "metal nanoparticles solution") is prepared by a spin coater. , Apply evenly to the surface of p-type semiconductors. After applying the metal nanoparticles solution, the nanoparticles 1, 1, .. are composed of metal nanoparticles (Pt) whose surface is coated with an insulator (PdO) by evaporating water in a furnace in an oxygen atmosphere. Is arranged on the surface of the p-type semiconductor. After arranging the nanoparticles 1, 1, ... In this way, set the back electrode 15 on which the nanoparticles 1, 1, ... and the p-type semiconductor are arranged on the front surface again in the CVD device or MBE device, and set the nano. The p-type semiconductor is deposited on the surface of particles 1, 1, ... And the p-type semiconductor by the CVD method or the MBE method. After that, by repeating the arrangement of the nanoparticles 1, 1, ... And the deposition of the p-type semiconductor, the p-layer 31 in which the nanoparticles 1, 1, ... Are arranged inside is placed on the back surface electrode. It can be formed on 15 surfaces. After the p-layer 31 is formed in this way, nanoparticles 1, 1, ... Are arranged on the surface of the p-layer 31 by the same method as described above.To. After the nanoparticles 1, 1, ... Are arranged in this way, the semiconductors that are not doped with p-type impurities or n-type impurities by the CVD method or MBE method (the bandgap is larger than that of the semiconductor that should form the intermediate layer 43). The wet layer 42a is formed by depositing a semiconductor) on the surface of the p-layer 31 in which nanoparticles 1, 1, ... Are arranged. Then, by further continuing the deposition of the semiconductor, quantum dots 42b, 42b, ... Are formed by the SK (Stranski-Krastanov) growth mode, and the wet layer 42a and the quantum dots 42b, 42b, ... Are provided. The quantum structure portion 42 is formed on the surface of the p layer 31. By forming the quantum dots 42b, 42b, ... In this form, the quantum dots 42b, 42b, ... It is considered that the nanoparticles 1, 1, ... Can be selectively arranged inside the quantum dots 42b, 42b, .... After the quantum structure portion 42 is formed in this way, nanoparticles 1, 1, ... Are subsequently arranged on the surface of the quantum structure portion 42 by the same method as described above. After the nanoparticles 1, 1, ... were arranged, the nanoparticles 1, 1, ... were arranged on a semiconductor that was not doped with p-type impurities or n-type impurities by the CVD method or MBE method. The intermediate layer 43 is formed by depositing on the surface of the quantum structure portion 42. By forming the intermediate layer 43 on the surface of the quantum structure portion 42 in this way, nanoparticles 1, 1, .. It becomes possible to arrange. After forming the intermediate layer 43 in this way, nanoparticles 1, 1, ... Are subsequently arranged on the surface of the intermediate layer 43 by the same method as described above. After the nanoparticles 1, 1, ... Are arranged in this way, the quantum structure portion 42 is formed on the surface of the intermediate layer 43 in which the nanoparticles 1, 1, ... Are arranged by the same method as described above. After that, nanoparticles 1, 1, ... , The formation of the intermediate layer 43 on the surface of the quantum structure portion 42 in which the nanoparticles 1, 1, ... Are arranged, the arrangement of the nanoparticles 1, 1, ... on the surface of the intermediate layer 43. The i-layer 41 is formed on the surface of the p-layer 31 by sequentially repeating the setting and the formation of the quantum structure portion 42 on the surface of the intermediate layer 43 in which the nanoparticles 1, 1, ... Are arranged. After the i-layer 41 is formed in this way, nanoparticles 1, 1, ... Are arranged inside by the same method as the p-layer 31 forming method except that an n-type semiconductor is used instead of the p-type semiconductor. Layer 32 is formed on the surface of i-layer 41. After the n-layer 32 is formed, the antireflection film / transparent conductive film 13 is subsequently formed on the surface of the n-layer 32 by the CVD method or the MBE method. Then, the solar cell 40 can be manufactured by forming the surface electrode 14 on the surface of the antireflection film / transparent conductive film 13 by a known method such as a vapor deposition or a sputtering method.</u>

<u style="single">In the above description of the solar cell 40, a form in which quantum dots are formed on the n-layer side of the wet layer has been illustrated, but the present invention is not limited to this form. The solar cell (photoelectric conversion element) of the present invention may have a structure in which the p-layer 31 and the n-layer 32 of the solar cell 40 are interchanged.</u>

<u style="single">Further, in the above description of the solar cell 40, a mode in which the p-layer 31 and the n-layer 32 in which nanoparticles 1, 1, ... Are arranged is provided has been exemplified, but the present invention is limited to this mode. It's not something. The solar cell (photoelectric conversion element) of the present invention may be provided with a p-layer and / or an n-layer in which metal nanoparticles are not arranged.</u>

<u style="single">Further, in the above description regarding the present invention, a form in which the size of nanoparticles 1, 1, ... Is changed according to the distance from the light receiving surface is not mentioned, but in the present invention, the distance from the light receiving surface is not mentioned. It is preferable to dispose nanoparticles having a relatively large diameter in a region far from the light receiving surface and to dispose nanoparticles having a relatively small diameter in a region close to the light receiving surface. That is, when light is irradiated from the upper side of the paper surface of the solar cell shown in FIG. 1, the diameter of the nanoparticles arranged on the upper side of the paper surface in the figure is R1, and the diameter of the nanoparticles arranged on the lower side of the paper surface in the figure. When is R2, it is preferable that R1 &lt;R2. On the other hand, when the solar cell is a double-sided light receiving type, it is preferable to dispose nanoparticles having a relatively small diameter in the vicinity of the light receiving surface and to dispose nanoparticles having a larger diameter as the distance from the light receiving surface increases. There is a correlation between the wavelength of the photoelectric field enhanced by localized surface plasmon resonance and the diameter of the metal nanoparticles, and the short wavelength photoelectric field is likely to be enhanced around the metal nanoparticles with a small diameter, and the diameter is large. Long wavelength photoelectric fields are likely to be enhanced around metal nanoparticles. Therefore, by disposing the metal nanoparticles having a relatively small diameter in the region near the light receiving surface where the short wavelength light is easily absorbed, it is possible to form a form in which the short wavelength light is easily absorbed. Further, by arranging metal nanoparticles having a relatively large diameter in a region away from the light receiving surface where long wavelength light is easily absorbed, it is possible to form a form in which long wavelength light is easily absorbed. .. Therefore, from the viewpoint of providing a photoelectric conversion element having a form in which the photoelectric conversion efficiency can be easily improved, metal nanoparticles having a relatively large diameter are arranged in a region far from the light receiving surface, and the metal nanoparticles having a relatively large diameter are arranged from the light receiving surface. It is preferable to dispose metal nanoparticles having a relatively small diameter in the region where the distance is short.</u>

<u style="single">Further, in the above description of the present invention, a form in which nanoparticles 1 composed of metal nanoparticles whose surface is coated with an insulator is disposed has been exemplified, but the present invention is not limited to this form. It is also possible that the metal nanoparticles whose surface is not covered with an insulator are arranged in the semiconductor. However, since the metal nanoparticles are conductive substances, if they are arranged in the semiconductor of the photoelectric conversion element, the carriers generated by light irradiation may be captured by the metal nanoparticles during movement. When the carriers are captured by the metal nanoparticles, the number of carriers reaching the electrode is reduced, so that the effect of improving the photoelectric conversion efficiency may be reduced. Therefore, in the present invention, from the viewpoint of making it easy to improve the photoelectric conversion efficiency, nanoparticles formed by disposing an insulator on at least a part of the surface of the metal nanoparticles are arranged in the semiconductor. It is preferable to provide the nanoparticles, and it is more preferable to dispose the nanoparticles formed by coating the entire surface of the metal nanoparticles with an insulator in the semiconductor.</u>

<u style="single">Further, in the above description of the present invention, a form in which the quantum structure portion is a quantum dot has been illustrated, but the present invention is not limited to this form. The photoelectric conversion element of the present invention can also be in a form in which a quantum well or a quantum wire is used in the quantum structure portion. In the present invention in which quantum wires are used in the quantum structure, for example, a solar cell in which quantum wires are arranged in the light absorption layer so that the axial direction of the quantum wires intersects the current / voltage directions in the light absorption layer is shown in FIG. It can be represented by the same cross section as 1. In the present invention, when a quantum wire is used for the quantum structure portion, the material and structure constituting the quantum wire are not particularly limited, and a known quantum wire such as a carbon nanotube can be used.</u>

<u style="single">Further, although the case where the present invention is applied to a solar cell has been described so far, the photoelectric conversion element of the present invention is not limited to the solar cell. The present invention can also be applied to other photoelectric conversion elements such as photodetector elements.</u>

<u style="single">The photoelectric conversion element of the present invention can be used as a power source for an electric vehicle, a solar power generation system, or the like.</u>