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

Abstract

A photoelectric conversion element (10) according to one embodiment of the present disclosure has a photoelectric conversion unit (1), wherein: the photoelectric conversion unit (1) has a light-receiving surface (1a); the photoelectric conversion unit (1) contains a ferroelectric semiconductor material; the ferroelectric semiconductor material is polarized in an in-plane direction of the light-receiving surface (1a), thereby breaking the spatial inversion symmetry of the photoelectric conversion unit (1); the ferroelectric semiconductor material contains one or both of a halogenated metal perovskite semiconductor material and a haolgenated perovskite semiconductor material containing formamidinium ions; and radiation light radiated onto the light-receiving surface (1a) is photoelectrically converted, thereby generating a photocurrent that flows in the polarization direction of the ferroelectric semiconductor material.

Description

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

[0001] This disclosure relates to a photoelectric conversion element, a photosensor, a power generation device, and a photoelectric conversion method using the same, and more particularly to a technique for causing the movement of majority carriers (electrons or holes) in the photoelectric conversion section of the photoelectric conversion element by incident light on the photoelectric conversion section, and for extracting the current (photocurrent) resulting from this movement from electrodes provided in the photoelectric conversion section.

[0002] Conventionally, a typical photoelectric conversion unit comprises an n-type semiconductor and a p-type semiconductor. An internal electric field is generated in the photoelectric conversion unit by a 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, creating electron-hole pairs. These electrons and holes move to the n-type and p-type sides, respectively, and separate due to the internal electric field. As a result, an electric current can 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 incidence into a photoelectric conversion unit having such a p-n junction are scattered by impurities, defects, lattice vibrations, etc. in the photoelectric conversion unit. Because carrier movement is accompanied by scattering, the carrier energy is dissipated, and there is a limit to the efficiency of current extraction.

[0004] Therefore, Patent Document 2 proposes a technique to reduce the scattering of carriers generated by the incidence of light into the photoelectric conversion section of a photoelectric conversion element, and to efficiently extract the current caused by the movement of said carriers from the photoelectric conversion section, by constructing the photoelectric conversion section from a material in which spatial inversion symmetry is broken by polarization.

[0005] Japanese Patent Publication No. 2015-130464, Japanese Patent Publication No. 6978775

[0006] However, even with the photoelectric conversion element configuration described in Patent Document 2, there is a desire to improve the photoelectric conversion efficiency from light to photocurrent. Furthermore, the constituent materials of the photoelectric conversion unit described in Patent Document 2 do not exhibit ferroelectricity at or near room temperature. As a result, there are practical problems such as the inability to perform photoelectric conversion over a wide temperature range including room temperature, and the need to extract current while cooling the photoelectric conversion unit.

[0007] The object of this disclosure is to provide a photoelectric conversion element with high photoelectric conversion efficiency, particularly high photoelectric conversion efficiency at room temperature, as well as a photosensor, power generation device, and photoelectric conversion method using the same.

[0008] The inventors of this disclosure have found that, in order to address the above-mentioned problems, it is effective to use a ferroelectric semiconductor material containing either or both a metal halide perovskite semiconductor material and a halide perovskite semiconductor material containing formamidinium ions as a constituent material of the photoelectric conversion unit, and have completed this disclosure. Accordingly, the aspects of this disclosure are as follows.

[0009] [1] A photoelectric conversion element having a photoelectric conversion unit, wherein the photoelectric conversion unit has a light-receiving surface, the photoelectric conversion unit includes a ferroelectric semiconductor material, the ferroelectric semiconductor material is polarized in the in-plane direction of the light-receiving surface, thereby breaking the spatial inversion symmetry of the photoelectric conversion unit, the ferroelectric semiconductor material includes one or both of a metal halide perovskite semiconductor material and a halide perovskite semiconductor material containing formamidinium ions, and a photocurrent flowing in the polarization direction is generated when the irradiated light irradiated onto the light-receiving surface is photoelectrically converted.

[0010] [2] The photoelectric conversion element according to [1], wherein the photoelectric conversion unit has a first electrode and a second electrode, and the first electrode and the second electrode are spaced apart along the polarization direction.

[0011] [3] The photoelectric conversion element according to [2], wherein the first electrode and the second electrode are made of the same metallic material.

[0012] [4] The photoelectric conversion element according to any one of [1] to [3], wherein the ferroelectric semiconductor material exhibits ferroelectricity at least 25°C.

[0013] [5] The photoelectric conversion element according to any one of [1] to [4], wherein the ferroelectric semiconductor material exhibits ferroelectricity in a temperature range of at least 10°C to 40°C.

[0014] [6] The photoelectric conversion element according to any one of [1] to [5], wherein the metal halide perovskite semiconductor material is a compound represented by the following general formula (1).

[0015] ABX ,

[0022] ,

[0021] (1)

[0016] However, in the above general formula (1), A represents at least one monovalent cation selected from the group consisting of Cs ＋ and Rb ＋ B represents at least one divalent cation selected from the group consisting of Ge ２＋ Sn ２＋ and Pb ２＋ X represents at least one halide ion selected from the group consisting of F －１ Cl －１ Br －１ I －１

[0017] [7] The photoelectric conversion element according to [6], wherein in the general formula (I), X contains at least I －１

[0018] P [8] The photoelectric conversion element according to any one of [1] to [7], wherein the ferroelectric semiconductor material is an MBE single crystal film. E

[0019] [9] A photosensor comprising the photoelectric conversion element according to any one of [1] to [8], and detecting irradiated light irradiated to the light receiving surface of the photoelectric conversion unit by the photocurrent generated in the photoelectric conversion unit.

[0020]

[10] A power generation device comprising the photoelectric conversion element according to any one of [1] to [8], and obtaining electric power by the photocurrent generated in the photoelectric conversion unit. <0000!73>

[0021]

[11] A photoelectric conversion method using the photoelectric conversion element according to any one of [1] to [8], comprising a light irradiation step of irradiating light to the light receiving surface of the photoelectric conversion unit, and a photocurrent acquisition step of extracting an external photocurrent generated by the light incident on the photoelectric conversion unit.

[0022]

[12] The photoelectric conversion method according to

[11] , wherein a bias voltage is applied in the polarization direction during the light irradiation step.

[0023] According to this disclosure, the scattering of carriers generated by the incidence of light on the photoelectric conversion section of a photoelectric conversion element is suppressed, and the current generated by the movement of such carriers can be efficiently extracted from the photoelectric conversion section at room temperature. Therefore, according to this disclosure, it is possible to provide a photoelectric conversion element with high photoelectric conversion efficiency, particularly high photoelectric conversion efficiency at room temperature, as well as a photosensor, power generation device, and photoelectric conversion method using the same.

[0024] This is a configuration diagram of a photoelectric conversion element according to one embodiment of the present disclosure. This is an equivalent circuit of a photoelectric conversion element according to one embodiment of the present disclosure, where (A) is an equivalent circuit in which the space between the first electrode and the second electrode is open, and (B) is an equivalent circuit in which the first electrode and the second electrode are connected to an ammeter. This is the light irradiation system for measuring the shift current used in Experimental Example 1. CsGeI synthesized in Synthesis Example 1 ３ This is the XRD measurement result of the black solid. CsGeI film was fabricated by MBE in Synthesis Example 2. ３ This is the XRD measurement result of the MBE thin film. CsGeI synthesized in Synthesis Example 1 ３ This graph shows the dependence of the photocurrent per unit of incident light power on the incident light wavelength at room temperature, as measured in Experimental Example 1 using a black solid. The CsGeI film fabricated by MBE in Synthesis Example 2 is shown here. ３ This graph shows the dependence of the photocurrent per unit of incident light power on the incident photon energy at 20K, as measured in Experimental Example 1 using an MBE thin film. (A) is a schematic diagram of a photosensor using the photoelectric conversion element according to this embodiment, and (B) is a schematic diagram of a power generation device using the photoelectric conversion element according to this embodiment.

[0025] Embodiments of this disclosure will be described with reference to the drawings. Common parts in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted. Furthermore, the following description is not intended to limit the invention as described in the claims. For example, the present invention is not limited to comprising all of the components described below.

[0026] <Photoelectric Conversion Element> Figure 1 is a diagram showing the configuration of a photoelectric conversion element 10 according to one embodiment of the present disclosure. The photoelectric conversion element 10 comprises a photoelectric conversion unit 1, a first electrode 2, and a second electrode 3.

[0027] The photoelectric conversion unit 1 has a light-receiving surface 1a. The photoelectric conversion unit 1 includes a ferroelectric semiconductor material. The photoelectric conversion unit 1 may be composed solely of a ferroelectric semiconductor material. The ferroelectric semiconductor material includes one or both of a metal halide perovskite semiconductor material and a formamidinium ion-containing halide perovskite semiconductor material. The metal halide perovskite semiconductor material is a metal halide that does not contain organic matter and is a ferroelectric semiconductor material having a perovskite crystal structure. The formamidinium ion-containing halide perovskite semiconductor material is a halide that contains formamidinium ions and is a ferroelectric semiconductor material having a perovskite crystal structure. The ferroelectric semiconductor material is polarized in the in-plane direction of the light-receiving surface 1a of the photoelectric conversion unit 1. The ferroelectric semiconductor material may be polarized in one direction along the surface of the light-receiving surface 1a of the photoelectric conversion unit 1. Polarization of the ferroelectric semiconductor material breaks the spatial inversion symmetry of the photoelectric conversion unit 1. The ferroelectric semiconductor material may be a single crystal or a polycrystalline material as long as it is polarized, but a single crystal is more preferable. In Figure 1, the photoelectric conversion unit 1 is polarized from the second electrode 3 toward the first electrode 2, but it may also be polarized from the first electrode 2 toward the second electrode 3. There are no particular restrictions on the size of the light-receiving surface 1a of the photoelectric conversion unit 1. The thickness of the photoelectric conversion unit 1 may be, for example, in the range of 1 nm to 10 mm. The photoelectric conversion unit 1 may also be a thin film with a film thickness in the range of 1 nm to 200 nm.

[0028] As a method for forming the photoelectric conversion unit 1, solution processes such as spin coating, blade coating, inkjet printing, and spray coating, gas phase methods such as thermal deposition and chemical vapor deposition (CVD), temperature gradient methods and solution growth methods, crystal growth control methods such as annealing in air / nitrogen / vacuum, and molecular beam epitaxy (MBE) can be used. MBE is preferred as the method for forming the photoelectric conversion unit 1. That is, the photoelectric conversion unit 1 (ferroelectric semiconductor material) is preferably an MBE single crystal film formed by MBE.

[0029] The first electrode 2 and the second electrode 3 are for extracting the photocurrent (hereinafter simply referred to as "photocurrent generated in the photoelectric conversion unit 1") generated by the movement of majority carriers in the photoelectric conversion unit 1 due to the incidence of light on the light-receiving surface 1a of the photoelectric conversion unit 1, to the outside. A current line 4 (for example, a conductor) is connected to the first electrode 2 and the second electrode 3. The photocurrent generated in the photoelectric conversion unit 1 flows through the first electrode 2 and the second electrode 3 to the current line 4. The first electrode 2 and the second electrode 3 may be connected to each other via the current line 4. In the example in Figure 1, a resistor (light bulb) 13 is provided in the current line 4.

[0030] The first electrode 2 and the second electrode 3 are provided in the photoelectric conversion unit 1 and are spaced apart from each other along the polarization direction of the ferroelectric semiconductor material. Hereinafter, the direction in which the first electrode 2 and the second electrode 3 are separated from each other will be 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.

[0031] The first electrode 2 and the second electrode 3 are made of a metallic material that does not substantially create a potential barrier. This potential barrier prevents the majority carriers (hereinafter also 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. That is, when the first electrode 2 and the second electrode 3 are joined to the photoelectric conversion unit 1, there is no potential barrier for majority carriers at the interface between the first electrode 2 and the second electrode 3 and the photoelectric conversion unit 1, as seen from the perspective of the first electrode 2 and the second electrode 3.

[0032] The materials used for the first electrode 2 and the second electrode 3 are not particularly limited, as long as they do not create a potential barrier through interaction with the ferroelectric semiconductor material. Examples include gold, aluminum, silver, platinum, copper, and titanium. The metallic material of the first electrode 2 may be the same as or different from the metallic material of the second electrode 3.

[0033] <Breaking of Spatial Inversion Symmetry> When an electric field is applied to the photoelectric conversion unit 1 in the direction of electrode separation, the ferroelectric semiconductor material contained in the photoelectric conversion unit 1 becomes polarized. That is, the spatial inversion symmetry of the molecular structure of the photoelectric conversion unit 1 is broken because the ferroelectric semiconductor material is polarized in the direction of the applied electric field. Since the ferroelectric semiconductor material of the photoelectric conversion unit 1 exhibits ferroelectricity, the polarization of the ferroelectric semiconductor material is maintained even after the application of the electric field is stopped. Therefore, even after the application of the electric field is stopped, the state in which the spatial inversion symmetry of the molecular structure of the photoelectric conversion unit 1 is broken is maintained.

[0034] Thus, because the molecular structure of the photoelectric conversion unit 1 has broken spatial inversion symmetry, no matter where in the direction of electrode separation a mirror perpendicular to the direction of electrode separation is placed, the molecular structure reflected in the mirror will not match the original molecular structure corresponding to that molecular structure.

[0035] <Specific examples of materials> The metal halide perovskite semiconductor material used as the ferroelectric semiconductor material for the photoelectric conversion unit 1 is ABX, which is represented by the following general formula (1). ３ It is a compound that takes on a specific structure.

[0036] ABX ３ (1)

[0037] However, in the above general formula (1), A is Cs ＋ and Rb ＋ It represents at least one monovalent cation selected from the group consisting of, where B is Ge ２＋ Sn ２＋ and Pb ２＋ X represents at least one divalent cation selected from the group consisting of F －１ , Cl －１ , Br －１ , I －１It represents at least one halide ion selected from the group consisting of the following.

[0038] Metal halide perovskite semiconductor materials do not contain organic matter. Metal halide perovskite semiconductor materials that do not contain organic matter exhibit high ferroelectricity, and the photoelectric conversion unit 1 containing it is prone to breaking of spatial inversion symmetry, resulting in a large photocurrent. In general formula (1), the A site ion is Cs based on the magnitude of the photocurrent. ＋ The following is preferably used. The B site ion is Ge from the viewpoint of exhibiting ferroelectricity at room temperature. ２＋ The following is preferably used. The B site ion is Sn ２＋ and Pb ２＋ One or both of Ge ２＋ It may include and. Sn ２＋ and / or Pb ２＋ By combining these, the moisture resistance of metal halide perovskites is improved. Halide ions are important from the perspective of band gap size. － This is preferably used.

[0039] The formamidinium ion-containing halide perovskite semiconductor material used as the ferroelectric semiconductor material in the photoelectric conversion unit 1 is represented by the following general formula (2): FABX ３ It is a compound that takes on a specific structure.

[0040] FABX ３ (2)

[0041] However, in the above general formula (2), FA is formamide ion (CH(NH ２ ) ２ ＋ ) represents, and B is Ge ２＋ Sn ２＋ and Pb ２＋ X represents at least one divalent cation selected from the group consisting of F －１ , Cl －１ , Br －１ , I －１ It represents at least one halide ion selected from the group consisting of the following.

[0042] Formamidinium ion-containing halide perovskite semiconductor material exhibits high ferroelectricity because it contains formamidinium ions as A-site ions. The photoelectric conversion section 1 containing this material is prone to breaking spatial inversion symmetry, resulting in a large photocurrent. Formamidinium ion-containing halide perovskite semiconductor material FAPbI ３ It is preferable that this be the case.

[0043] In this embodiment, it is preferable that the ferroelectric semiconductor material has ferroelectric properties at room temperature, and that the spatial inversion symmetry of the photoelectric conversion unit 1 is broken by the polarization of the ferroelectric semiconductor material. Room temperature is, for example, 25°C. It is preferable that the ferroelectric semiconductor material has ferroelectric properties at 10°C, at 40°C, and especially at 60°C. It is preferable that the spatial inversion symmetry of the photoelectric conversion unit 1 is broken at 10°C, at 40°C, and especially at 60°C. As a result, the photoelectric conversion element 10 can be suitably used in sensor and power generation applications.

[0044] In this embodiment, the photoelectric conversion unit 1 may contain one or both of the metal halide perovskite semiconductor material and the formamidinium ion-containing halide perovskite semiconductor material, either individually or in combination of multiple types. When multiple types of metal halide perovskite semiconductor materials with different compositions are included, each of the multiple types of metal halide perovskite semiconductor materials may differ in, for example, one or both of the B-site ions and halogen ions. By combining multiple types of metal halide perovskite semiconductor materials, the moisture resistance of the photoelectric conversion unit 1 can be improved or its photosensitivity can be increased. To improve moisture resistance, for example, the B-site ion may be Ge ２＋ In a metal halide perovskite semiconductor material, the B-site ion is Pb ２＋ and / or Sn ２＋A small amount of metal halide perovskite semiconductor material may be added. To enhance photosensitivity, multiple types of metal halide perovskite semiconductor materials with different halogen ions may be combined.

[0045] Alternatively, the ferroelectric semiconductor material forming the photoelectric conversion unit 1 may be a stack of N layers of thin films stacked on top of each other (where N is an integer of 1 or more). This stacked thin film may consist of, for example, layers A, B, and C, each made of a different crystalline material, stacked in that order. By stacking them in this way, the photosensitivity of the photoelectric conversion unit 1 can be increased. Each of the A, B, and C layers may be single crystal or polycrystalline. The stacked thin film may consist of, for example, layers A and B with different polarization directions stacked in that order. The intersection angle between the polarization direction of layer A and the polarization direction of layer B may be 80° or more and 100° or less, preferably 90°. The thickness of layer A may be a thickness that allows light to reach layer B. By doing so, even if the photoelectric conversion unit 1 has polarization angle dependence, its photosensitivity to normal light in nature (unpolarized light) can be increased.

[0046] The ferroelectric semiconductor material and the materials of the first electrode 2 and the second electrode 3 are not limited to the specific examples described above.

[0047] <Equivalent Circuit> Figure 2 shows the equivalent circuit of the photoelectric conversion element 10 according to this embodiment. In Figure 2(A), the first electrode 2 and the second electrode 3 are open, and in Figure 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.

[0048] When light is incident on the photoelectric conversion unit 1, a current I is generated in the photoelectric conversion unit 1 due to the breaking of the spatial inversion symmetry of its structure. ｓｈｉｆｔ Assume that the following occurs as shown in Figure 2. At this time, if the connection between the first electrode 2 and the second electrode 3 is opened, I ｓｈｉｆｔ This is the resistor R in the photoelectric conversion unit 1. ｂｕｌｋ Let V be the voltage between the first electrode 2 and the second electrode 3 (open-circuit voltage). ＯＣ Let's assume that. V ＯＣ This can be expressed by the following equation (1).

[0049]

[0050] In Figure 2(A), R ｃｏｎｔａｃｔ This 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. From the state in Figure 2(A), the first electrode 2 and the second electrode 3 are connected by the current line 4 to reach the state in Figure 2(B). In Figure 2(B), the above-mentioned current I ｓｈｉｆｔ However, resistor R ｂｕｌｋ The current flowing through it and the contact resistance R ｃｏｎｔａｃｔ Current I flows through to current line 4 ＳＣ It is divided into two. Here, I ＳＣ This can be expressed by the following equation (2).

[0051]

[0052] Therefore, R ｂｕｌｋ R ｃｏｎｔａｃｔ If it is sufficiently larger than I ＳＣ I ｓｈｉｆｔ It can be considered to be equal to . Equation (2) shows the case when no bias voltage is applied between the first electrode 2 and the second electrode 3. In Figure 2(B), when a bias voltage Vb is applied between the first electrode 2 and the second electrode 3, the current value I measured by the ammeter 14 is ｏｂｓ This can be expressed by the following equation (3).

[0053]

[0054] From the above equations (1), (2), and (3), I ｏｂｓ The bias voltage V when it becomes zero ｂ The magnitude of the open-circuit voltage V ＯＣ It becomes equal to the size of . The symbol R below ｂｕｌｋ , R ｃｏｎｔａｃｔ , V ＯＣ , I ＳＣ , V ｂ , I ｏｂｓ The R values ​​described above are shown in Figure 2. ｂｕｌｋ , R ｃｏｎｔａｃｔ , V ＯＣ , I ＳＣ , V ｂ , I ｏｂｓ It means...

[0055] [Experimental Example 1] Experimental Example 1 of a photoelectric conversion element 10 according to an embodiment of the present invention will be described. In this experimental example 1, the metal halide perovskite semiconductor material that forms the photoelectric conversion section 1 is CsGeI synthesized in the synthesis example 1 below. ３ The material used to form the first electrode 2 and the second electrode 3 was silver paste. The shift current of the photoelectric conversion element 10 was measured using the light irradiation system shown in Figure 3. The light irradiation system shown in Figure 3 comprises a light source 31, a monochromator 32, an optical filter 33, a parabolic mirror 34, a polarizer 35, a camera 36, ​​and a lens 37. The camera 36 is removable. The light irradiation system converts light (supercontinent laser) generated by the light source 31 into a polarized monochromatic beam by passing it through the monochromator 32, optical filter 33, and polarizer 35, and then uses the camera 36 to focus the beam with the lens 37 and irradiate the surface of the sample 38.

[0056] <Synthesis Example 1> Under argon flow (Ar), 81.6 mL of HI (57 wt% sol.) was added to a 300 mL four-necked flask (reaction vessel), and H was added to the HI. ３ PO ２ (40.8 mL, 51 wt% sol.) was added and stirred with a stirring bar. The reaction vessel was immersed in an ice bath and Ar was gently bubbling for 1 minute to degas it. Then, after raising the temperature of the reaction vessel to room temperature, GeO ２(1.26 g, 12 mmol) was added. Subsequently, the reaction vessel was immersed in an oil bath and heated to an external temperature of 120 °C. The maximum temperature of the internal temperature was 105 °C. As the internal temperature increased, the solution in the reaction vessel changed color from yellow to orange. After reaching an internal temperature of 105 °C and stirring for 30 minutes, it changed to a yellow transparent solution. While maintaining that temperature, CsI (3.12 g, 12 mmol) was quickly added to the yellow transparent solution. Immediately after the addition, the yellow transparent solution changed to a black suspension slurry. After continuing stirring for 5 minutes while maintaining that temperature, heating and stirring were stopped, and it was allowed to cool while maintaining an Ar flow to grow the crystals in the black suspension slurry. A filter-connected tube was connected to the reaction vessel, and the black suspension slurry was filtered while maintaining an Ar atmosphere. The black solid recovered by the filter was washed 5 times with 5 mL of deoxygenated EtOH using a gastight syringe and then dried under reduced pressure at room temperature for 16 hours. Next, the black solid was brought into a glove box while maintaining a reduced pressure state. After restoring the pressure, 6.2 g of black solid was recovered. The recovered black solid was subjected to XRD measurement using an air non-exposed measurement jig. The results are shown in Fig. 4 together with the JCPDS card data of CsGeI ３ It was confirmed from the results of Fig. 4 that the obtained black solid was CsGeI ３ .

[0057] <Synthesis Example 2> CsGeI ３ thin films were formed by molecular beam epitaxy (MBE). That is, CsI and GeI ２ were used as evaporation sources, and using an evaporation cell, the flux amounts of both were adjusted so that they were approximately 1:1, and they were co-evaporated onto a substrate to obtain CsGeI ３ MBE thin films. The film formation rate was set to about 1 nm / min. The substrate temperature during film formation was set to 80 °C. The film thickness was 70 nm. The prepared CsGeI ３ MBE thin films were subjected to XRD measurement. The results are shown in Fig. 5. From the results of Fig. 5, diffraction peaks of the (001) plane, (002) plane, (003) plane, and (004) plane of CsGeI ３ were clearly observed, and the obtained CsGeI ３ MBE thin films were (001)-oriented CsGeI ３It was confirmed that it is a single-crystalline epitaxial thin film.

[0058] <Measurement of photocurrent (shift current)> CsGeI obtained in Synthesis Example 1 ３ For the black solid, the first electrode 2 and the second electrode 3 were provided as shown in FIG. 1, and the first electrode 2 and the second electrode 3 were connected to each other by a current line 4. A galvanometer 14 (see FIG. 2(B)) was provided in the current line 4 instead of the resistor 13 in FIG. 1. The measurement of the photocurrent was performed by irradiating the light-receiving surface 1a of the photoelectric conversion unit 1 of the photoelectric conversion element 10 with a polarized beam of a supercontinuum laser using the light irradiation system shown in FIG. 3. The light irradiated on the light-receiving surface 1a was arranged on the sample surface and focused using a removable camera. At room temperature, light with wavelengths of 400 to 650 nm and 650 to 1000 nm was incident on the light-receiving surface 1a of the photoelectric conversion unit 1 as horizontal polarization (hpol: horizontal polarization) and vertical polarization (vpol: vertical polarization). At that time, in the photoelectric conversion unit 1, the value of the photocurrent flowing through the current line 4 between the first electrode 2 and the second electrode 3 was measured with the galvanometer 14. FIG. 6 shows the wavelength dependence of the incident light of the value obtained by normalizing the photocurrent measured in this way by the incident light power. The measurement of the photocurrent was performed in a room temperature environment.

[0059] CsGeI ３ Instead of the black solid, CsGeI obtained in Synthesis Example 2 ３ The photocurrent was measured in the same manner as above, except that the MBE thin film was used, the light irradiated on the light-receiving surface 1a was unpolarized light, and the measurement was performed in a temperature environment of 20K.FIG. 7 shows the incident photon energy dependence of the value obtained by normalizing the measured photocurrent by the incident light power.

[0060] From the graphs of FIGS.6 and 7, a photocurrent could be observed even though the bias voltage was zero. Also, from the graph of FIG.6, it was confirmed that the photocurrent due to the incident light is a shift current because it has a clear polarization dependence. Also, from the graph of FIG.7, it was confirmed that a photocurrent is generated by irradiation with unpolarized light.

[0061] <Example of Application> Figure 8(A) is a schematic diagram of a light sensor 100 to which the photoelectric conversion element 10 according to an embodiment of the present invention is applied. The light sensor 100 detects the incidence of light on the photoelectric conversion unit 1 by current extracted from the first electrode 2 and the second electrode 3. The light sensor 100 may include the photoelectric conversion element 10 described above, a current line 4, and a detection unit 101.

[0062] 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 taken out to the current line 4 via the first electrode 2 and the second electrode 3.

[0063] The detection unit 101 detects the current flowing through the current line 4. Once the detection unit 101 detects the current, it outputs a detection signal indicating that light has been incident on the photoelectric conversion unit 1. For example, the detection unit 101 may be configured to output a detection signal when the value of the current flowing through the current line 4 exceeds a threshold value.

[0064] Figure 8(B) is a schematic diagram of a power generation device 200 to which the photoelectric conversion element 10 according to an embodiment of the present invention is applied. The power generation 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 Figure 8(B)). The power generation device 200 may include the photoelectric conversion element 10 described above, a current line 4, and a storage battery 201 (or load). Note that the storage battery 201 (or load) does not have to be a component of the power generation device 200.

[0065] 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 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.

[0066] The storage battery 201 receives and stores the power generated by the current in the photoelectric conversion unit 1 via the current line 4.

[0067] If a load is provided instead of the battery 201, the power generated by the current in the photoelectric conversion unit 1 is supplied to the load via the current line 4. This load may be equipment that consumes the supplied power (for example, a light fixture or a drive unit).

[0068] <Photoelectric Conversion Method> The photoelectric conversion method according to an embodiment of the present invention comprises step S1 and step S2. In step S1, the above-described photoelectric conversion element 10 is prepared and installed at a desired position. Step S2 comprises a light irradiation step of irradiating light onto the light-receiving surface 1a of the photoelectric conversion unit 1, and a photocurrent acquisition step of extracting the photocurrent generated by the light incident on the photoelectric conversion unit 1 to the outside. In the light irradiation step, light is incident on the light-receiving surface 1a of the photoelectric conversion unit 1 at a position between the first electrode 2 and the second electrode 3 of the photoelectric conversion element 10 prepared in step S1. In the photocurrent acquisition step, the current generated in the photoelectric conversion unit 1 is extracted from the first electrode 2 and the second electrode 3 into a current line 4. The extracted current flows through the current line 4 into a desired location (for example, the above-described detection unit 101, storage battery 201, or load).

[0069] Before performing step S2, polarize the photoelectric conversion unit 1 in the direction of electrode separation to align the polarization direction of the photoelectric conversion unit 1. Perform step S2 in this state. For example, the polarization direction of the photoelectric conversion unit 1 is aligned in the direction of electrode separation by applying an electric field to the photoelectric conversion unit 1 in the direction of electrode separation. Perform step S2 in this state. However, the application of the electric field to the photoelectric conversion unit 1 may be released when performing step S2. Alternatively, when performing step S2, the application of the electric field may be continued and a bias voltage may be applied in the polarization direction of the photoelectric conversion unit 1.

[0070] <Effects of the Embodiment> (1) According to the embodiment of the present disclosure described above, the electron-hole pairs generated by the incidence of light on the photoelectric conversion unit 1 are moved in opposite directions due to the breaking of spatial inversion symmetry in the structure of the ferroelectric semiconductor material forming the photoelectric conversion unit 1. As a result, the majority carriers (electrons or holes) of the photoelectric conversion unit 1 move towards one of the first electrode 2 and the second electrode 3.

[0071] (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 move to one of the first electrodes 2 or the second electrode 3 in the photoelectric conversion unit 1 due to the breaking of spatial inversion symmetry, majority carriers begin to flow into the photoelectric conversion unit 1 from the other of the second electrode 3 or the first electrode 2.

[0072] (3) The current generated by (1) and (2) above has a fundamentally different generation mechanism from the current generated by the p-n junction. Currents with such a different generation mechanism have the characteristic of less scattering. 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 to this, in this embodiment, as described above, there is no potential barrier for majority carriers, so the current generated by the majority carriers in the photoelectric conversion element 10 can be efficiently extracted to the outside.

[0073] (4) Since the photoelectric conversion unit 1 does not have a p-n junction, it is not necessary to consider constraints related to p-n junctions, such as the formation of a proper p-n junction surface.

[0074] (5) It is possible to generate a current that is independent of temperature by injecting light into the photoelectric conversion unit 1.

[0075] (6) An electromotive force (open-circuit voltage VOC) far exceeding the voltage corresponding to the bandgap width of the photoelectric conversion unit 1 can be obtained.

[0076] (7) When photoelectric conversion is performed using a photoelectric conversion unit having a p-n junction as in the conventional method, shot noise is generated due to fluctuations in the number of electrons. In contrast, in the photoelectric conversion method according to this embodiment described above, current is generated by the wave nature of electrons, so such shot noise is not generated. Therefore, low-noise photoelectric conversion can be achieved.

[0077] (8) In the photoelectric conversion unit 1, the current is generated on the time scale of the optical transition between bands (usually around femtoseconds). Therefore, when pulsed light is incident on the photoelectric conversion unit 1, it becomes possible to perform photoelectric conversion with a fast response to the pulsed light and low noise. Thus, for example, a photosensor 100 with a fast response and low noise can be realized.

[0078] The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical idea of ​​the present invention. For example, the effects described above do not necessarily limit the present invention. Furthermore, the present invention may achieve any of the effects shown herein, or other effects that can be understood from this specification.

[0079] Embodiments of this disclosure are described below.

[0080] [Note 1] A photoelectric conversion element having a photoelectric conversion section, wherein the photoelectric conversion section has a light-receiving surface, the photoelectric conversion section contains a ferroelectric semiconductor material, the spatial inversion symmetry of the photoelectric conversion section is broken by polarization of the ferroelectric semiconductor material in the in-plane direction of the light-receiving surface, the ferroelectric semiconductor material contains one or both of a metal halide perovskite semiconductor material and a formamidinium ion-containing halide perovskite semiconductor material, and a photocurrent flowing in the polarization direction of the ferroelectric semiconductor material is generated when the irradiated light irradiated onto the light-receiving surface is photoelectrically converted.

[0081] [Note 2] The photoelectric conversion unit has a first electrode and a second electrode, and the first electrode and the second electrode are spaced apart along the polarization direction, as described in Note 1. According to the photoelectric conversion unit of Note 2, the photocurrent generated in the photoelectric conversion unit can be stably extracted to the outside via the first electrode and the second electrode.

[0082] [Note 3] The first electrode and the second electrode are photoelectric conversion elements as described in Note 2, wherein the first electrode and the second electrode contain the same metal material. According to the photoelectric conversion element of Note 3, since the first electrode and the second electrode contain the same metal material, the production process can be simplified, and productivity can be improved.

[0083] [Note 4] The ferroelectric semiconductor material is a photoelectric conversion element according to any one of Notes 1 to 3, which exhibits ferroelectricity at least 25°C. The photoelectric conversion element according to Note 4 has a high photoelectric conversion efficiency at room temperature.

[0084] [Note 5] The photoelectric conversion unit is a photoelectric conversion element according to any one of Notes 1 to 4, wherein spatial inversion symmetry is broken at least at 25°C. According to the photoelectric conversion element of Note 5, the photoelectric conversion efficiency at room temperature is increased.

[0085] [Note 6] The ferroelectric semiconductor material is a photoelectric conversion element according to any one of Notes 1 to 5, which exhibits ferroelectricity in a temperature range of at least 10°C to 40°C. According to the photoelectric conversion element of Note 6, the photoelectric conversion efficiency is high over a wide temperature range of 10°C to 40°C.

[0086] [Note 7] The photoelectric conversion unit is a photoelectric conversion element according to any one of Notes 1 to 6, wherein spatial inversion symmetry is broken in a temperature range of at least 10°C to 40°C. According to the photoelectric conversion element of Note 7, the photoelectric conversion efficiency is high in a wide temperature range of 10°C to 40°C.

[0087] [Note 8] The metal halide perovskite semiconductor material is a compound represented by the following general formula (1), as described in any one of Notes 1 to 7. The metal halide perovskite semiconductor material used in the photoelectric conversion element of Note 8 is a compound represented by the following general formula (1), and therefore exhibits higher dielectric properties. Thus, the photoelectric conversion element of Note 8 results in higher photoelectric conversion efficiency.

[0088] ABX ３ (1)

[0089] However, in the above general formula (1), A is Cs ＋ and Rb ＋It represents at least one monovalent cation selected from the group consisting of, where B is Ge ２＋ Sn ２＋ and Pb ２＋ X represents at least one divalent cation selected from the group consisting of F －１ , Cl －１ , Br －１ , I －１ It represents at least one halide ion selected from the group consisting of the following.

[0090] [Note 9] In general formula (1), A is at least Cs ＋ A photoelectric conversion element as described in Appendix 8, including the above. The metal halide perovskite semiconductor material used in the photoelectric conversion element of Appendix 9 is Cs as the A-site ion. ＋ Because it contains [a certain substance], the ferroelectricity at room temperature is improved. Therefore, according to the photoelectric conversion element described in Appendix 9, the photoelectric conversion efficiency at room temperature is increased.

[0091] [Note 10] In general formula (1), B is at least Ge ２＋ A photoelectric conversion element as described in Appendix 8 or 9, including the following. The metal halide perovskite semiconductor material used in the photoelectric conversion element of Appendix 10 is Ge as the B-site ion. ２＋ Because it contains [a certain substance], the ferroelectricity at room temperature is improved. Therefore, according to the photoelectric conversion element described in Appendix 10, the photoelectric conversion efficiency at room temperature is increased.

[0092] [Note 11] In general formula (1), B is Sn ２＋ and Pb ２＋ One or both of Ge ２＋ A photoelectric conversion element as described in Appendix 8 or 9, including the above. The metal halide perovskite semiconductor material used in the photoelectric conversion element of Appendix 11 is Sn as the B-site ion. ２＋ and Pb ２＋ Since it includes one or both of these, moisture resistance is improved. Therefore, according to the photoelectric conversion element in Appendix 11, the photoelectric conversion efficiency is high even in high humidity environments.

[0093] [Note 12] In general formula (1), X is at least I －１A photoelectric conversion element as described in any one of appendices 8 to 11, including the above. The metal halide perovskite semiconductor material used in the photoelectric conversion element of appendice 11 is I as the halogen ion. －１ Because it includes this, the size of the band gap with respect to the irradiated light becomes appropriate. Therefore, the photoelectric conversion element in Appendix 12 generates a larger photocurrent.

[0094] [Note 13] The photoelectric conversion unit includes multiple types of metal halide perovskite semiconductor materials, wherein the multiple types of metal halide perovskite semiconductor materials differ from each other in either or both of their B-site ions and halide ions, as described in any one of Notes 1 to 12. According to the photoelectric conversion element of Note 13, the performance of the photoelectric conversion element as a whole can be improved by the synergistic effect of the properties of the individual metal halide perovskite semiconductor materials. For example, Ge ２＋ A metal halide perovskite semiconductor material containing Pb ２＋ Ya Sn ２＋ By combining it with a metal halide perovskite semiconductor material containing [the specified element], it is possible to improve moisture resistance while maintaining high photoelectric conversion performance.

[0095] [Note 14] The halide perovskite semiconductor material containing formamidinium ions is a compound represented by the following general formula (2), as described in any one of Notes 1 to 7. The formamidinium ion-containing halide perovskite semiconductor material used in the photoelectric conversion element of Note 14 is a compound represented by the following general formula (2), and therefore exhibits higher dielectric properties. Thus, the photoelectric conversion element of Note 14 results in higher photoelectric conversion efficiency.

[0096] FABX ３ (2)

[0097] However, in the above general formula (2), FA is formamide ion (CH(NH ２ ) ２ ＋ ) represents, and B is Ge ２＋ Sn ２＋ and Pb ２＋X represents at least one divalent cation selected from the group consisting of F －１ , Cl －１ , Br －１ , I －１ It represents at least one halide ion selected from the group consisting of the following.

[0098] [Note 15] A photoelectric conversion element according to any one of Notes 1 to 14, wherein the generated photocurrent exhibits dependence on the polarization angle of light. According to the photoelectric conversion element of Note 15, it is possible to provide a photoelectric conversion element in which the spatial inversion symmetry of the photoelectric conversion section is broken.

[0099] [Note 16] A photoelectric conversion element described in any one of Notes 1 to 15, wherein the thickness of the photoelectric conversion section is within the range of 1 nm to 10 mm. According to the photoelectric conversion element in Note 16, since the thickness of the photoelectric conversion section is 1 nm or more, the amount of photocurrent generated is large. Also, since the thickness of the photoelectric conversion section is 10 mm or less, the light received at the light receiving surface easily propagates uniformly to the photoelectric conversion section, resulting in high photoelectric conversion performance.

[0100] [Note 17] The ferroelectric semiconductor material is an MBE single-crystal thin film, as described in any one of Notes 1 to 16. According to the photoelectric conversion element in Note 17, the ferroelectric semiconductor material constituting the photoelectric conversion part is a single-crystal thin film formed of MEB, and because it has high orientation, it has high photoelectric conversion performance.

[0101] [Note 18] A photoelectric element laminate comprising a plurality of photoelectric elements described in any one of Notes 1 to 17, wherein the plurality of photoelectric elements are stacked so that their polarization directions intersect. According to the photoelectric element laminate of Note 18, since the plurality of photoelectric elements are stacked so that their polarization directions intersect, a stable photocurrent can be generated even when the polarization angle of the irradiated light changes.

[0102] [Note 19] The photoelectric element stack described in Note 18, wherein the intersection angle of the polarization directions of each stacked photoelectric element is 80° or more and 100° or less. According to the photoelectric element stack of Note 19, a photocurrent can be generated stably over a wide range of changes in the polarization angle of the irradiated light.

[0103] [Note 20] A light sensor comprising a photoelectric conversion element described in any one of Notes 1 to 17 or a photoelectric conversion element laminate described in Note 18 or 19, which detects the irradiated light shining on the light-receiving surface of the photoelectric conversion unit by the photocurrent generated in the photoelectric conversion unit. According to the light sensor of Note 20, since the above-mentioned photoelectric conversion element or photoelectric conversion element laminate is used as the photoelectric conversion element, the irradiated light can be detected stably.

[0104] [Note 21] A power generation device comprising a photoelectric conversion element described in any one of Notes 1 to 17 or a photoelectric conversion element laminate described in Note 18 or 19, which obtains power from a photocurrent generated in a photoelectric conversion unit. According to the power generation device of Note 21, since the above-mentioned photoelectric conversion element or photoelectric conversion element laminate is used as the photoelectric conversion element, power can be obtained stably.

[0105] [Note 22] A photoelectric conversion method using a photoelectric conversion element described in any one of Notes 1 to 17, comprising: a light irradiation step of irradiating a light receiving surface with light to the photoelectric conversion unit; and a photocurrent acquisition step of extracting the photocurrent generated by the light incident on the photoelectric conversion unit to the outside. According to the photoelectric conversion method of Note 22, since the above-mentioned photoelectric conversion element is used as the photoelectric conversion element, light can be stably converted into photocurrent.

[0106] [Note 23] The photoelectric conversion method described in Note 22, wherein a bias voltage is applied in the polarization direction during the light irradiation step. In the photoelectric conversion method of Note 23, since a bias voltage is applied in the polarization direction during the light irradiation step, the polarization state of the metal halide perovskite semiconductor material stabilizes, and the photoelectric conversion unit stabilizes in a state where spatial inversion symmetry is broken. Therefore, according to the photoelectric conversion method of Note 23, the generated photocurrent becomes larger.

[0107] 1 Photoelectric conversion unit 1a Light receiving surface 2 First electrode 3 Second electrode 4 Current line 10 Photoelectric conversion element 13 Resistor 14 Ammeter 24 Current line 25 Ammeter 100 Light sensor 101 Detection unit 200 Power generation device 201 Storage battery

Claims

1. A photoelectric conversion element having a photoelectric conversion unit, wherein the photoelectric conversion unit has a light-receiving surface, the photoelectric conversion unit comprises a ferroelectric semiconductor material, the spatial inversion symmetry of the photoelectric conversion unit is broken by polarization of the ferroelectric semiconductor material in the in-plane direction of the light-receiving surface, the ferroelectric semiconductor material comprises one or both of a metal halide perovskite semiconductor material and a halide perovskite semiconductor material containing formamidinium ions, and a photocurrent flowing in the polarization direction of the ferroelectric semiconductor material is generated by photoelectric conversion of irradiated light onto the light-receiving surface.

2. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion unit has a first electrode and a second electrode, and the first electrode and the second electrode are spaced apart along the polarization direction.

3. The photoelectric element according to claim 2, wherein the first electrode and the second electrode are made of the same metallic material.

4. The photoelectric conversion element according to claim 1 or 2, wherein the ferroelectric semiconductor material exhibits ferroelectricity at least 25°C.

5. The photoelectric conversion element according to claim 1 or 2, wherein the ferroelectric semiconductor material exhibits ferroelectricity in a temperature range of at least 10°C to 40°C.

6. The photoelectric conversion element according to claim 1 or 2, wherein the metal halide perovskite semiconductor material is a compound represented by the following general formula (1). ABX －１ , －１ , －１ , ２＋ , ２＋ , ２＋ , －１ (1) However, in the above general formula (1), A represents at least one monovalent cation selected from the group consisting of Cs ＋ and Rb ＋ ; B represents at least one divalent cation selected from the group consisting of Ge ２＋ , Sn ２＋ and Pb ２＋ ; and X represents at least one halide ion selected from the group consisting of F s －１ , Cl －１ , Br －１ , I －１ .

7. In the general formula (1) above, X is at least I －１ The photoelectric conversion element according to claim 6, including the above.

8. The photoelectric conversion element according to claim 1, wherein the ferroelectric semiconductor material is an MBE single crystal film.

9. A light sensor comprising a photoelectric conversion element according to claim 1 or 2, which detects the irradiated light irradiated onto the light-receiving surface of the photoelectric conversion unit by the photocurrent generated in the photoelectric conversion unit.

10. A power generation device comprising a photoelectric conversion element according to claim 1 or 2, which obtains power from the photocurrent generated in the photoelectric conversion unit.

11. A photoelectric conversion method using the photoelectric conversion element described in claim 1 or 2, comprising: a light irradiation step of irradiating the photoelectric conversion unit with light onto the light receiving surface; and a photocurrent acquisition step of extracting the photocurrent generated by the light incident on the photoelectric conversion unit to the outside.

12. The photoelectric conversion method according to claim 11, wherein a bias voltage is applied in the polarization direction during the light irradiation step.

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