Photoelectric conversion element, optical sensor, power generation device, and photoelectric conversion method

Abstract

[Problem] To provide a new photoelectric conversion element in which scattering of carriers caused by light incident on a photoelectric conversion part is reduced, even at a high temperature equal to or higher than room temperature, and a current generated by movement of the carriers can be efficiently extracted from the photoelectric conversion part.　[Solution] This photoelectric conversion element comprises: a photoelectric conversion part made of an organic nonlinear optical material and having no p-n junction; and first and second electrodes provided to the photoelectric conversion part and arranged with a space therebetween. The photoelectric conversion part is polarized in a direction aligned with the first and second electrodes and has a structure in which space inversion symmetry is broken.

Description

Photoelectric conversion element, optical sensor, power generation device, and photoelectric conversion method

[0001] The present invention relates to a technique for causing majority carriers (electrons or holes) to move in a photoelectric conversion section when light is incident on the photoelectric conversion section, and extracting a current resulting from this movement from an electrode provided in the photoelectric conversion section.

[0002] Conventionally, a typical photoelectric conversion unit includes an n-type semiconductor and a p-type semiconductor. An internal electric field is generated in the photoelectric conversion unit due to the p-n junction between the n-type and p-type semiconductors. When light is incident on this photoelectric conversion unit, electrons jump from the valence band to the conduction band, generating electron-hole pairs. These electrons and holes move to the n-type side and p-type side, respectively, due to the internal electric field, and are separated. This allows current to be extracted from the photoelectric conversion unit. Such a photoelectric conversion element is described, for example, in Patent Document 1.

[0003] However, carriers (electrons or holes) generated by light incident on such a photoelectric conversion unit having a p-n junction are scattered by impurities, defects, lattice vibrations, etc. in the photoelectric conversion unit, and since the movement of the carriers is accompanied by scattering, the energy of the carriers is dissipated, and there is a limit to the efficiency of extracting current.

[0004] Therefore, Patent Document 2 proposes a technique for reducing scattering of carriers generated by light incident on a photoelectric conversion section, and for efficiently extracting current resulting from the movement of the carriers from the photoelectric conversion section.

[0005] JP 2015-130464 A Patent No. 6978775 A

[0006] However, the polar materials described in Patent Document 2 are substances that become ferroelectric when cooled to or below their Curie temperature, and therefore, depending on the substance, photoelectric conversion cannot be performed near room temperature, and current must be extracted while the device is cooled, which poses practical problems. Therefore, there is a need for new photoelectric conversion elements. An object of the present disclosure is to provide a new photoelectric conversion element.

[0007] As a result of intensive research, the present inventors have found that using an organic nonlinear optical material in the photoelectric conversion section can function as a photoelectric conversion element. It was previously believed that no shift current would be generated from crystals of organic substances. However, by using an organic nonlinear optical material in the photoelectric conversion section, the photoelectric conversion section is polarized in the same direction between the electrodes over a wide temperature range below the melting point of the organic nonlinear optical material, and the photoelectric conversion section has a structure in which spatial symmetry is broken, thereby generating a shift current. This disclosure may include the following inventions.

[0008] [1] A photoelectric conversion element comprising: a photoelectric conversion section made of an organic nonlinear optical material and having no p-n junction; and first and second electrodes provided on the photoelectric conversion section and arranged at a distance from each other, wherein the photoelectric conversion section is polarized in the same direction between the first and second electrodes and has a structure in which spatial inversion symmetry is broken. [2] The photoelectric conversion element according to [1], wherein the organic nonlinear optical material has a second-order electric susceptibility of 100 pm / V or more. [3] The photoelectric conversion element according to [1] or [2], wherein the organic nonlinear optical material is a single crystal made of an ionic crystal. [4] The photoelectric conversion element according to any of [1] to [3], wherein the organic nonlinear optical material includes a compound of chemical formula (A). (In formula (A), R １ is an alkyl group, and R ２ is an alkyl group or a benzyl group, and R ３is an alkyl group or a halogen atom, and n is an integer of 1 to 5. [5] The photoelectric conversion element according to any one of [1] to [4], wherein the metal material of the first electrode is the same as the metal material of the second electrode. [6] The photoelectric conversion element according to any one of [1] to [5], wherein the first and second electrodes are arranged at an interval in the polarization direction of the photoelectric conversion unit. [7] An optical sensor comprising the photoelectric conversion element according to any one of [1] to [6], which detects light incident on the photoelectric conversion unit by current extracted from the first and second electrodes. [8] A power generation device comprising the photoelectric conversion element according to any one of [1] to [6], which supplies electric power extracted from the first and second electrodes to a storage battery or a load. [9] A photoelectric conversion method using a photoelectric conversion element comprising a photoelectric conversion unit made of an organic nonlinear optical material and first and second electrodes provided on the photoelectric conversion unit and arranged at a distance from each other, the method comprising: a light incidence step of irradiating light onto the photoelectric conversion unit; and an extraction step of extracting a current generated in the photoelectric conversion unit from the first and second electrodes, wherein the photoelectric conversion unit does not have a p-n junction and is polarized in the same direction between the first and second electrodes, and the light incidence step is a step in which majority carriers move to one of the first and second electrodes due to the polarization in the photoelectric conversion unit, thereby generating an electromotive force between the first and second electrodes.

[0009] According to the present disclosure, a new photoelectric conversion element can be provided in which, over a wide temperature range from room temperature to the melting point of an organic nonlinear optical material, scattering of carriers generated by light incident on the photoelectric conversion section is minimal, and current resulting from the movement of the carriers can be efficiently extracted from the photoelectric conversion section. In this specification, "room temperature" refers to 300K.

[0010] 1 is a schematic diagram showing the configuration of one embodiment of a photoelectric conversion element; FIG. 2 is an equivalent circuit diagram of one embodiment of a photoelectric conversion element; FIG. 3 is a light irradiation system for measuring shift current; FIG. 4 is a diagram showing the temperature dependence of photocurrent when horizontally and vertically polarized light is incident in Experimental Example 1; FIG. 5 is a diagram showing the incident light intensity dependence of photocurrent at room temperature in Experimental Example 1; FIG. 6 is a diagram showing the temperature dependence of photocurrent when horizontally and vertically polarized light is incident in Experimental Example 2; FIG. 7 is a diagram showing the temperature dependence of photocurrent when horizontally and vertically polarized light is incident in Experimental Example 3; FIG. 8 is a diagram showing the temperature dependence of photocurrent when horizontally and vertically polarized light is incident in Experimental Example 4; FIG. 9 is a diagram showing the temperature dependence of photocurrent when horizontally and vertically polarized light is incident in Experimental Example 5.

[0011] One aspect of the present disclosure is a photoelectric conversion element comprising a photoelectric conversion section made of an organic nonlinear optical material and having no p-n junction, and first and second electrodes provided in the photoelectric conversion section and arranged at a distance from each other, which will be described below with reference to the drawings. Note that common parts in each drawing are given the same reference numerals, and redundant description will be omitted. The following description does not limit the invention described in the claims.

[0012] 1 is a schematic diagram showing the configuration of one embodiment of a photoelectric conversion element 10. The photoelectric conversion element 10 includes a photoelectric conversion section 1, a first electrode 2, and a second electrode 3.

[0013] The photoelectric conversion section 1 is made of an organic nonlinear optical material. An organic nonlinear optical material is an organic material in which, when irradiated with light, the induced polarization is not proportional to the external electric field. The organic nonlinear optical material used in the photoelectric conversion section 1 is not particularly limited as long as it meets the above definition, but examples thereof include 2-methyl-4-nitroaniline (MNA), 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST), 4-dimethylamino-N-methyl-4-stilbazolium-2,4,6-trimethylbenzenesulfonate (DSTMS), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP1), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP2), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP3), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP4), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP5), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP6), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP6), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP7), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP8), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP9), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP1), 4-dimethylamino-N-benzyl-4-stilbazolium toluenesulfonate (BP1), 4 Examples thereof include amino-N-4-methylbenzyl-4-stilbazolium toluenesulfonate (BP2), 4-dimethylamino-N-2,5-dimethylbenzyl-4-stilbazolium toluenesulfonate (BP3), 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA), 4-dimethylamino-4'-nitrostilbene (DANS), and 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohexyl-2-enylidene)malononitrile (OH-1).

[0014] The organic nonlinear optical material preferably has a second-order electric susceptibility, which indicates the likelihood of electric polarization, of 100 pm / V or more, more preferably 500 pm / V or more, and even more preferably 1000 pm / V or more. Furthermore, the organic nonlinear optical material preferably has a Pockels constant, which indicates the relationship between an applied electric field and a refractive index, of 40 pm / V or more, more preferably 60 pm / V or more, and even more preferably 100 pm / V or more.

[0015] The form of the organic nonlinear optical material is not particularly limited, but is preferably an organic crystalline material, and more preferably an ionic crystal. Furthermore, the crystal is preferably a single crystal. A preferred organic nonlinear optical material is a single crystal made of an ionic crystal such as 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST), 4-dimethylamino-N-methyl-4-stilbazolium-2,4,6-trimethylbenzenesulfonate (DSTMS), 4-dimethylamino-N-4-methylbenzyl-4-stilbazolium toluenesulfonate (BP2), or 4-dimethylamino-N-dimethylbenzyl-4-stilbazolium toluenesulfonate (BP3), because a significant increase in shift current is observed when the temperature is increased.

[0016] The organic nonlinear optical material is preferably a compound represented by the following formula (A).

[0017] In the formula R １ is an alkyl group, preferably an alkyl group having 1 to 8 carbon atoms, more preferably a methyl group, an ethyl group, a propyl group, or a butyl group, and even more preferably a methyl group. ２ is an alkyl group or a benzyl group, and in the case of an alkyl group, an alkyl group having 1 to 8 carbon atoms is preferred, a methyl group, an ethyl group, a propyl group, or a butyl group is more preferred, and a methyl group is even more preferred. In the case of a benzyl group, benzyl or a benzyl group in which the benzene ring is substituted with a methyl group is preferred, and benzyl, 4-methylbenzyl, 2,5-dimethylbenzyl, etc. are even more preferred. ３ is an alkyl group or a halogen element, preferably an alkyl group having 1 to 8 carbon atoms, fluorine, chlorine, bromine, or iodine, more preferably a methyl group, ethyl group, propyl group, or butyl group, and even more preferably a methyl group. Chlorine is preferred as the halogen element. n represents an integer of 1 to 5, preferably 1 or 2, and more preferably 1.

[0018] The organic nonlinear optical material forming the photoelectric conversion section 1 may be a single layer, or may be a laminate of N layers (N is an integer of 1 or more) of laminated thin films. This laminated thin film is formed by laminating, in this order, layers A, B, and C made of different crystalline materials. Each of the layers A, B, and C may be a single crystal.

[0019] The photoelectric conversion section 1 does not have a pn junction. The organic nonlinear optical material that constitutes the photoelectric conversion section 1 is an insulating material. Note that the term "insulating" used here means that the electrical resistance is 10 ８ ~10 １８ This means that the resistance is Ωcm.

[0020] The first electrode 2 and the second electrode 3 are intended to extract to the outside a current resulting from the movement of majority carriers generated in the photoelectric conversion unit 1 in response to the incidence of light on the photoelectric conversion unit 1 (hereinafter also simply referred to as "current generated in the photoelectric conversion unit 1"). A current line 4 (e.g., a conductor) is connected to the first electrode 2 and the second electrode 3. The current generated in the photoelectric conversion unit 1 flows to the current line 4 via the first electrode 2 and the second electrode 3. The first electrode 2 and the second electrode 3 may be connected to each other via the current line 4. In the example of FIG. 1 , a resistor (light bulb) 13 is provided on the current line 4.

[0021] The first electrode 2 and the second electrode 3 are provided in the photoelectric conversion unit 1 and are spaced apart from each other. Here, "spaced apart" means that they are not in physical contact with each other, and it is preferable that the spaced apart is larger than the spot diameter of the irradiated light from the viewpoint of the magnitude of the electromotive force. Hereinafter, the direction in which the first electrode 2 and the second electrode 3 are spaced apart from each other is referred to as the electrode separation direction. The first electrode 2 and the second electrode 3 may be in direct contact with the photoelectric conversion unit 1. In the electrode separation direction, the structure of the photoelectric conversion unit 1 has broken spatial inversion symmetry. Furthermore, the photoelectric conversion unit 1 may be polarized in the electrode separation direction, and it is preferable that the photoelectric conversion unit 1 be polarized in the same direction without being electrically neutralized.

[0022] The first electrode 2 and the second electrode 3 are made of a metal material that does not substantially generate a potential barrier. This potential barrier prevents majority carriers (hereinafter simply referred to as majority carriers) for the photoelectric conversion unit 1 from moving from the first electrode 2 and the second electrode 3 to the photoelectric conversion unit 1. In other words, when the first electrode 2 and the second electrode 3 are joined to the photoelectric conversion unit 1, there is no potential barrier against majority carriers at the interface between each electrode 2 and 3 and the photoelectric conversion unit 1, as viewed from the first electrode 2 and the second electrode 3. The metal material of the first electrode 2 may be the same as or different from the metal material of the second electrode 3.

[0023] There are no particular limitations on the material used for the electrodes, so long as there is no potential barrier due to interaction with the organic nonlinear optical material. Examples include gold, aluminum, silver, platinum, copper, and titanium.

[0024] <Breaking of spatial inversion symmetry> The organic nonlinear optical material is composed of electron-donating groups (donor groups) and electron-accepting groups (acceptor groups). When an electric field is applied to the photoelectric conversion unit 1 in the direction separating the electrodes, the positively charged donor groups are displaced in the direction of application of the electric field, and the negatively charged acceptor groups are displaced in the direction opposite to the direction of application of the electric field. This causes the photoelectric conversion unit 1 to become polarized. In other words, the photoelectric conversion unit 1 is polarized in the direction of application of the electric field, and the spatial inversion symmetry of the structure is broken. The polarization of the photoelectric conversion unit 1 is maintained even after the application of the voltage is stopped. Therefore, the broken spatial inversion symmetry of the structure of the photoelectric conversion unit 1 is maintained even after the application of the voltage is stopped.

[0025] In this way, the molecular structure of the photoelectric conversion unit 1 has broken spatial inversion symmetry, so no matter where a planar mirror perpendicular to the electrode separation direction is placed in the electrode separation direction, the molecular structure reflected in the mirror will not match the original molecular structure corresponding to that molecular structure.

[0026] <Potential Barrier> The potential barrier can be understood by referring to the description in Patent Document 2.

[0027] <Equivalent Circuit> Fig. 2 shows an equivalent circuit of the photoelectric conversion element 10 according to this embodiment. In Fig. 2(A), the first electrode 2 and the second electrode 3 are open, and in Fig. 2(B), the first electrode 2 and the second electrode 3 are connected by a current line 4, and an ammeter 14 is provided on the current line 4.

[0028] When light is incident on the photoelectric conversion unit 1, a current I flows through the photoelectric conversion unit 1 due to the breaking of the spatial inversion symmetry of the structure. ｓｈｉｆｔ 2. In this case, if the first electrode 2 and the second electrode 3 are opened, I ｓｈｉｆｔ is the resistance R ｂｕｌｋ At this time, the voltage (open circuit voltage) between the first electrode 2 and the second electrode 3 is V ＯＣ Let's say. V ＯＣ is expressed by the following equation (1).

[0029] In FIG. 2A, R ｃｏｎｔａｃｔ represents the combined resistance of the contact resistance between the first electrode 2 and the photoelectric conversion unit 1 and the contact resistance between the second electrode 3 and the photoelectric conversion unit 1. The first electrode 2 and the second electrode 3 are connected by a current line 4 from the state shown in FIG. 2(A) to the state shown in FIG. 2(B). In FIG. 2(B), the above-mentioned current I ｓｈｉｆｔ But the resistance R ｂｕｌｋ and the current I flowing through the contact resistance Rcontact to the current line 4. ＳＣ Here, I ＳＣ is expressed by the following equation (2).

[0030] Therefore, R ｂｕｌｋ is R ｃｏｎｔａｃｔ If I is sufficiently large compared to ＳＣ Ga I ｓｈｉｆｔ Equation (2) shows the case where no bias voltage is applied between the first electrode 2 and the second electrode 3. In FIG. 2B, when a bias voltage V ｂ When the current is applied, the current value I measured by the ammeter 14 is ｏｂｓ is expressed by the following equation (3).

[0031] From the above formulas (1), (2), and (3), I ｏｂｓ When becomes zero, the bias voltage V ｂ The magnitude of the open circuit voltage V ＯＣ The symbol R below is ｂｕｌｋ , R ｃｏｎｔａｃｔ , V ＯＣ , I ＳＣ , V ｂ , I ｏｂｓ are the R ｂｕｌｋ , R ｃｏｎｔａｃｔ , V ＯＣ , I ＳＣ , V ｂ , I ｏｂｓ means.

[0032] Experimental Example 1 A description will be given of Experimental Example 1 using the photoelectric conversion element 10 according to the present embodiment. In this Experimental Example 1, the organic nonlinear optical material forming the photoelectric conversion section 1 was 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST) single crystal, and the material forming the first electrode 2 and the second electrode 3 was silver paste.

[0033] As shown in Figure 1, the first electrode 2 and the second electrode 3 were connected by a current line 4, and an ammeter 14 was provided on the current line 4 instead of the resistor 13 shown in Figure 1 (as shown in Figure 2(B)). Next, light was irradiated onto the photoelectric conversion unit 1 using a light irradiation system whose conceptual diagram is shown in Figure 3. Specifically, plasma light from a laser plasma light source 31 (XWS-30, manufactured by ISTEQ) was passed through a monochromator 32, a filter 33, and a polarizer 35 to generate a monochromatic polarized beam. Using a removable camera 36 and focusing with a lens 37, the light was irradiated onto the surface of a sample 38 under a cryostat. Light from the light source 31 was horizontally and vertically polarized and incident at wavelengths of 350 to 1000 nm on the photoelectric conversion unit 1 at room temperature. At this time, the value of the current flowing through the current line 4 between the first electrode 2 and the second electrode 3 in the photoelectric conversion unit 1 was measured with an ammeter 14. The results of the temperature dependence of the photocurrent measured in this manner for horizontally and vertically incident light are shown in Figure 4. The graph in FIG. 4 shows measurements taken in the electrode spacing direction parallel to the polarization direction of the material and in a direction perpendicular to the electrode spacing direction.

[0034] As a result, photocurrent was observed even when the bias voltage was zero. Furthermore, the photocurrent due to incident light clearly exhibited polarization dependence, confirming that it was a shift current. It was also confirmed that the shift current significantly increased with increasing temperature above room temperature. In Figure 4, larger shift currents were measured at temperatures above room temperature of 300 K, 340 K, 380 K, and 420 K. This demonstrates that current can be efficiently generated in the temperature ranges of 300 K or higher, 340 K or higher, 380 K or higher, and 420 K or higher, below the melting point of the organic nonlinear optical material.

[0035] The dependence of photocurrent on light intensity was measured using a 490 nm laser light source. The current value was measured as the laser output was increased from 10 μW to 80 μW. The measurement results are shown in Figure 5. The measured current increased linearly with light intensity within this range. Similar experiments were also performed using a supercontinuum laser instead of a laser plasma light source. The results are shown in Figure 5 (CDL_490).

[0036] Experimental Example 2: Instead of using 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST) as in Experimental Example 1, a 4-dimethylamino-N-methyl-4-stilbazolium-2,4,6-trimethylbenzenesulfonate (DSTMS) single crystal was used to measure the temperature dependence of photocurrent for horizontally and vertically incident light. The results are shown in Figure 6. As a result, photocurrent was observed even when the bias voltage was zero. Furthermore, the photocurrent due to incident light clearly exhibited polarization dependence, confirming that it was a shift current. It was also confirmed that the shift current significantly increased with increasing temperature above room temperature. Note that, in Figure 6, larger shift currents were measured at temperatures above room temperature of 300 K, 340 K, and 380 K, respectively. This demonstrates that current is efficiently generated in the temperature ranges of 300 K or higher, 340 K or higher, and 380 K or higher, below the melting point of the organic nonlinear optical material. A small shift current was also observed at 260 K.

[0037] Experimental Example 3: Instead of using 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST) in Experimental Example 1, a single crystal of 4-dimethylamino-N-dimethylbenzyl-4-stilbazolium toluenesulfonate (BP3) synthesized by the method described in the literature (CrystEngComm, 2011, 13, 444-451) was used to measure the temperature dependence of photocurrent for horizontally and vertically incident light. The results are shown in Figure 7. As a result, photocurrent was observed even when the bias voltage was zero. Furthermore, the photocurrent due to incident light exhibited a clear polarization dependence, confirming that it was a shift current. It was also confirmed that the shift current significantly increased with increasing temperature above room temperature. Note that, in Figure 7, larger shift currents were measured at temperatures above room temperature of 300 K, 340 K, 380 K, and 420 K. Therefore, it can be seen that current is generated efficiently in the temperature ranges below the melting point of the organic nonlinear optical material, namely, above 300 K, above 340 K, above 380 K, and above 420 K. A slight shift current was also observed at 260 K.

[0038] Experimental Example 4 Instead of using 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST) in Experimental Example 1, a 2-methyl-4-nitroaniline (MNA) single crystal was used to measure the temperature dependence of photocurrent for horizontally and vertically incident light. The results are shown in Figure 8. As a result, photocurrent was observed even though the bias voltage was zero. Furthermore, the photocurrent due to incident light had a clear polarization dependence, confirming that it was a shift current. No significant increase in shift current with temperature rise above room temperature was observed.

[0039] Experimental Example 5 Instead of using 4-dimethylamino-N-methyl-4-stilbazolium toluenesulfonate (DAST) in Experimental Example 1, a 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohexyl-2-enylidene)malononitrile (OH-1) single crystal was used to measure the temperature dependence of photocurrent for horizontally and vertically incident light. The results are shown in Figure 9. As a result, photocurrent was observed even though the bias voltage was zero. Furthermore, the photocurrent due to incident light had a clear polarization dependency, confirming that it was a shift current. No significant increase in shift current with temperature rise above room temperature was observed.

[0040] 10A is a schematic diagram of an optical sensor 100 to which the photoelectric conversion element 10 according to this embodiment is applied. The optical sensor 100 detects light incident on the photoelectric conversion unit 1 by a current extracted from the first electrode 2 and the second electrode 3. The optical sensor 100 may include the above-described photoelectric conversion element 10, a current line 4, and a detection unit 101.

[0041] The current line 4 is connected to the first electrode 2 and the second electrode 3. The first electrode 2 and the second electrode 3 may be connected to each other via the current line 4. The current generated in the photoelectric conversion unit 1 is extracted to the current line 4 via the first electrode 2 and the second electrode 3.

[0042] The detection unit 101 detects the current flowing through the current line 4. When the detection unit 101 detects the current, it outputs a detection signal indicating that light has entered the photoelectric conversion unit 1. For example, the detection unit 101 may be configured to output the detection signal when the value of the current flowing through the current line 4 exceeds a threshold value.

[0043] 10(B) is a schematic diagram of a power generating device 200 to which the photoelectric conversion element 10 according to this embodiment is applied. The power generating device 200 supplies power extracted from the first electrode 2 and the second electrode 3 to a storage battery or a load (storage battery 201 in FIG. 10(B)). The power generating device 200 may include the above-described photoelectric conversion element 10, a current line 4, and the storage battery 201 (or the load). Note that the storage battery 201 (or the load) does not have to be a component of the power generating device 200.

[0044] The current line 4 is connected to the first electrode 2 and the second electrode 3. The first electrode 2 and the second electrode 3 may be connected to each other via the current line 4. A current generated in the photoelectric conversion unit 1 when light is incident on the photoelectric conversion unit 1 is extracted to the current line 4 via the first electrode 2 and the second electrode 3. Here, the light incident on the photoelectric conversion unit 1 may be, for example, sunlight or radiant light emitted from a heat source.

[0045] The storage battery 201 receives and stores the power generated by the current generated in the photoelectric conversion unit 1 via the current line 4 .

[0046] When a load is provided instead of the storage battery 201, the power generated by the current generated in the photoelectric conversion unit 1 is supplied to the load via the current line 4. This load may be a device (such as an electric lamp or a driving device) that consumes the supplied power.

[0047] <Photoelectric Conversion Method> Although not shown in a flow chart, the photoelectric conversion method according to this embodiment includes steps S1 and S2. In step S1, the above-described photoelectric conversion element 10 is prepared and installed at a desired position. In step S2, in the photoelectric conversion element 10 prepared in step S1, light is incident on the photoelectric conversion unit 1 at a position between the first electrode 2 and the second electrode 3, and a current generated in the photoelectric conversion unit 1 is extracted from the first electrode 2 and the second electrode 3 to the current line 4. The extracted current flows through the current line 4 to a desired location (for example, the above-described detection unit 101, the storage battery 201, or a load).

[0048] Before performing step S2, the photoelectric conversion unit 1 is polarized in the electrode separation direction to align the polarization direction of the photoelectric conversion unit 1. In this state, step S2 is performed. For example, an electric field is applied to the photoelectric conversion unit 1 in the electrode separation direction to align the polarization direction of the photoelectric conversion unit 1 in the electrode separation direction. In this state, step S2 is performed. However, when performing step S2, the application of the electric field to the photoelectric conversion unit 1 may be stopped.

[0049] <Effects of the embodiment> (1) According to the above-described embodiment, pairs of electrons and holes generated by light incidence on the photoelectric conversion unit 1 are moved in opposite directions due to the broken spatial inversion symmetry of the structure of the organic nonlinear material that forms the photoelectric conversion unit 1. As a result, majority carriers (electrons or holes) in the photoelectric conversion unit 1 move toward one of the first electrode 2 and the second electrode 3.

[0050] (2) On the other hand, no potential barrier is generated that prevents majority carriers from flowing into the photoelectric conversion unit 1 from the other of the first electrode 2 and the second electrode 3. Therefore, as majority carriers in the photoelectric conversion unit 1 move to one of the electrodes 2 or 3 due to the breaking of spatial inversion symmetry, majority carriers flow into the photoelectric conversion unit 1 from the other electrode 2 or 3.

[0051] (3) The currents due to (1) and (2) above have a fundamentally different generation mechanism from the current generated by the p-n junction. Currents with a generation mechanism different from conventional ones have the characteristic of less scattering (see, for example, FIG. 15(A) of Patent Document 2). That is, in conventional photoelectric conversion units having a p-n junction, carriers generated by incident light move while being affected by scattering due to impurities, defects, lattice vibrations, etc., whereas in this embodiment, a current is generated that is not affected by such scattering. In addition, in this embodiment, since there is no potential barrier against majority carriers as described above, the current due to majority carriers generated in the photoelectric conversion element 10 can be efficiently extracted to the outside.

[0052] (4) Since the photoelectric conversion portion 1 does not have a pn junction, it is not necessary to consider constraints related to the pn junction, such as the formation of an appropriate pn junction surface.

[0053] (5) It is possible to generate a current that is independent of temperature by light incident on the photoelectric conversion unit 1 (see, for example, FIG. 9A of Patent Document 2).

[0054] (6) It is possible to obtain an electromotive force (open circuit voltage VOC) that far exceeds the voltage corresponding to the band gap width of the photoelectric conversion unit 1 (see, for example, FIGS. 9(B) and 12(B) of Patent Document 2).

[0055] (7) When photoelectric conversion is performed using a photoelectric conversion unit having a p-n junction as in the past, shot noise occurs due to fluctuations in the number of electrons. In contrast, in the photoelectric conversion method according to the present embodiment described above, current is generated due to the wave nature of electrons, so no shot noise occurs. Therefore, low-noise photoelectric conversion can be achieved.

[0056] (8) In the photoelectric conversion unit 1, current is generated on the time scale of optical transition between bands (usually on the order of femtoseconds), so that when pulsed light is incident on the photoelectric conversion unit 1, photoelectric conversion with a fast response to the pulsed light and low noise is possible. Therefore, for example, an optical sensor 100 with a fast response and low noise can be realized.

[0057] The invention described in this disclosure is not limited to the above-described embodiments, and various modifications may be made within the scope of the technical concept. For example, the above-described effects do not necessarily limit the invention. Furthermore, any of the effects described in this specification or other effects that can be understood from this specification may be achieved.

[0058] [Additional Remarks] The photoelectric conversion element, optical sensor, power generation device, and photoelectric conversion method disclosed herein enable low power consumption, which can contribute to the achievement of Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Create the infrastructure for industry, innovation and resilience."

[0059] REFERENCE SIGNS LIST 1 Photoelectric conversion unit 2 First electrode 3 Second electrode 4 Current line 10 Photoelectric conversion element 13 Resistor 14 Ammeter 24 Current line 25 Ammeter 31 Plasma light source 32 Monochromator 33 Filter 34 Parabolic mirror 35 Polarizer 36 Camera 37 Condenser lens 38 Sample 100 Optical sensor 101 Detector 200 Power generation device 201 Storage battery

Claims

1. A photoelectric conversion element comprising: a photoelectric conversion unit made of an organic nonlinear optical material and having no p-n junction; and first and second electrodes provided on the photoelectric conversion unit and arranged at a distance from each other, wherein the photoelectric conversion unit is polarized in the same direction between the first and second electrodes and has a structure in which spatial inversion symmetry is broken.

2. The photoelectric conversion element according to claim 1, wherein the organic nonlinear optical material has a second-order electric susceptibility of 100 pm / V or more.

3. The photoelectric conversion element according to claim 1, wherein the organic nonlinear optical material is a single crystal made of an ionic crystal.

4. The photoelectric conversion element according to claim 1, wherein the organic nonlinear optical material comprises a compound of chemical formula (A). (In formula (A), R １ is an alkyl group, R ２ is an alkyl group or a benzyl group, and R ３ represents an alkyl group or a halogen atom, and n represents an integer of 1 to 5.

5. The photoelectric conversion element according to claim 1, wherein the metal material of the first electrode is the same as the metal material of the second electrode.

6. The photoelectric conversion element according to claim 1, wherein the first and second electrodes are arranged at an interval in the polarization direction of the photoelectric conversion section.

7. An optical sensor comprising the photoelectric conversion element according to any one of claims 1 to 5, which detects light incident on the photoelectric conversion section by current extracted from the first and second electrodes.

8. A power generation device comprising the photoelectric conversion element according to any one of claims 1 to 5, which supplies electric power extracted from the first and second electrodes to a storage battery or a load.

9. A photoelectric conversion method using a photoelectric conversion element comprising a photoelectric conversion unit made of an organic nonlinear optical material and first and second electrodes disposed at a distance from each other on the photoelectric conversion unit, the method comprising: a light incidence step of irradiating light onto the photoelectric conversion unit; and an extraction step of extracting a current generated in the photoelectric conversion unit from the first and second electrodes, wherein the photoelectric conversion unit does not have a p-n junction and is polarized in the same direction between the first and second electrodes, and the light incidence step is a step in which majority carriers move to one of the first and second electrodes due to the polarization in the photoelectric conversion unit, generating an electromotive force between the first and second electrodes.

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