JP2018143025A - Heat radiation photovoltaic generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiation photovoltaic generator having high output density and high generation efficiency.SOLUTION: A heat radiation photovoltaic generator comprises: a heat radiation body 12; a photoelectric conversion element 11 which is arranged apart from the heat radiation body 12 and comprises semiconductor layers 1111, 1112, 1121 and 1122; and an intermediate member 13 which is brought into contact with the photoelectric conversion element 11, is arranged apart from the heat radiation body 12 by a distance of 1/3 or less of a band gap wavelength being a wavelength corresponding to minimum band gap energy in bandgap energies of a semiconductor constituting respective semiconductor layers between the heat radiation body 12 and the photoelectric conversion element 11, and is formed of a material in which a real part of a dielectric constant has a positive value on light of wavelength 0.5 to 1000 μm and through which at least light of a part of the wavelength in a wavelength range which is photoelectrically converted in the photoelectric conversion element 11 passes. Since near-field light can be used as the heat radiation body 12 and the intermediate member 13 are near, output density is high, and power generation efficiency is high since light of the long wavelength, which does not contribute to power generation in the photoelectric conversion element 11, can be prevented from passing on a surface of the semiconductor layer of the photoelectric conversion element 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermal radiation light power generation apparatus that generates electric power by photoelectrically converting thermal radiation generated by heating an object. In this specification, “thermal radiation light” includes electromagnetic waves other than visible light and infrared rays.

  In general, when an object is heated, thermal radiation light having a spectrum corresponding to the material constituting the object and the temperature of the object is emitted. Electric power can be generated by irradiating the photoelectric conversion element with this heat radiation light. By using this principle, for example, in a power generator using a thermal power plant or an engine, power generation is performed by heat radiation generated by heat generated without contributing to power generation, so that the energy use efficiency can be increased. Moreover, as long as there is a heat source, electric power can be obtained without preparing a separate power source. For example, in an exhaust gas sensor for analyzing components in engine exhaust gas using infrared rays, power generation is performed by heat radiation generated by engine waste heat, and the exhaust gas sensor can be operated without preparing a separate power source. Electric power can be obtained.

  The thermal radiation power generation device is composed of a heat radiator that emits heat radiation light by heating and a photoelectric conversion element that converts the heat radiation light into electricity. In order to protect the photoelectric conversion element, the two are in direct contact with each other. It is not possible to make a gap between them. When the heat radiator is heated, heat radiation light is emitted from the whole including the inside, but the heat radiation light generated inside is emitted from the surface of the heat radiator to the outside. Some remain in the heat radiating body due to total reflection at the surface. However, even the light staying in the heat radiating body in this way is leached slightly outside the surface (for example, within a range of less than 1 μm from the surface). Such light is called near-field light. If near-field light can also be taken into the photoelectric conversion element, the output density of power generation can be increased. Therefore, in the thermal radiation light power generation device described in Patent Document 1, the distance between the thermal radiator and the semiconductor layer constituting the photoelectric conversion element (the size of the gap) is determined by the near-field light generated near the surface of the thermal radiator. It is configured to be sufficiently small (for example, nano-order, that is, less than 1 μm) so as to propagate to the semiconductor layer.

JP 2008-300626 Gazette

  In the semiconductor layer doped with carriers of the photoelectric conversion element, there is a wavelength at which the real part of the dielectric constant has a negative value in a region where the wavelength is longer than the wavelength range contributing to power generation. This is because the light in the semiconductor can move so as to cancel the electric field of the light because the wavelength of the light is long, that is, the frequency is small and the electric field changes slowly. In addition, in compound semiconductors composed of two or more types of atoms, the real part of the dielectric constant is negative in the region where the wavelength is longer than the wavelength range that contributes to power generation, even when the lattice vibration couples with light. The resulting wavelength is generated. Such long-wavelength light cannot propagate in the semiconductor layer due to the cancellation of the electric field, but only the light that is localized near the surface of the semiconductor layer and travels in a direction parallel to the surface is propagated. can do. Even if a part of the light generated by the thermal radiation light source propagates to the semiconductor layer as near-field light in the thermal radiation light-power generating device described in Patent Document 1, it is thus near the surface of the semiconductor layer. Long-wavelength light propagating in a direction parallel thereto is consumed as heat without contributing to power generation, and is not used effectively. Hereinafter, light that is localized near the surface of the semiconductor layer and propagates in a direction parallel to the surface is referred to as a surface wave.

  The problem to be solved by the present invention is that a near-wavelength light having a wavelength contributing to power generation propagates from a heat radiator to a semiconductor layer of a photoelectric conversion element while a long-wavelength surface wave not contributing to power generation propagates. It is possible to provide a thermal radiation power generation device that can be prevented and thereby has both high power density and high power generation efficiency.

The thermal radiation power generation device according to the present invention, which has been made to solve the above problems,
a) a heat radiator;
b) a photoelectric conversion element having one or more semiconductor layers disposed apart from the heat radiator;
c) Between the thermal radiator and the photoelectric conversion element, a wavelength corresponding to a band gap energy of a semiconductor constituting the one semiconductor layer, or each semiconductor layer of the plurality of layers is in contact with the photoelectric conversion element Dielectric constant for light with a wavelength of 0.5 to 1000 μm arranged at a distance of 1/3 or less of the bandgap wavelength, which is the wavelength corresponding to the smallest of the semiconductor bandgap energy And an intermediate member made of a material that transmits light of at least a part of wavelengths within a wavelength range that is photoelectrically converted by the photoelectric conversion element.

  According to the thermal radiation light-emitting power generation device according to the present invention, the intermediate member is disposed away from the heat radiator by a sufficiently short distance of 1/3 or less of the band gap wavelength, and the material of the intermediate member is photoelectric. In order to transmit light of at least a part of the wavelength within the wavelength range that is photoelectrically converted (contributes to power generation) in the conversion element, the light of the wavelength including the near-field light passes through the intermediate member from the thermal radiator and the photoelectric conversion element And photoelectrically converted to generate electricity. Therefore, the thermal radiation light power generation device according to the present invention has a high output density.

  On the other hand, since the real part of the dielectric constant of the material of the intermediate member has a positive value with respect to light having a wavelength in the wavelength range of 0.5 to 1000 μm, the intermediate member facing the heat radiator within the above wavelength range Surface waves do not occur on the surface. Further, since the surface wave does not propagate inside the intermediate member, the surface wave is not induced on the surface of the semiconductor layer of the photoelectric conversion element by the heat radiation generated from the heat radiator. Therefore, in all wavelengths of 0.5 to 1000 μm obtained practically by the heat radiator, long wavelength light that does not contribute to power generation is prevented from being consumed as heat by the intermediate member or the photoelectric conversion element as a surface wave. be able to. Thereby, the thermal radiation light power generation device according to the present invention has high power generation efficiency.

  Some photoelectric conversion elements have one semiconductor layer and a metal layer, and others have a plurality of semiconductor layers. As described above, the band gap wavelength is defined by the wavelength corresponding to the band gap energy of the semiconductor constituting the semiconductor layer when the semiconductor layer is a single layer, and when there are a plurality of semiconductor layers, It is defined by a wavelength corresponding to the minimum band gap energy of the semiconductor constituting the semiconductor layer. The band gap wavelength corresponds to the maximum value of the wavelength range in which photoelectric conversion is performed in the photoelectric conversion element.

  The distance between the thermal radiator and the intermediate member is a configuration in which the thermal radiator and the photoelectric conversion element are separated from each other without arranging an intermediate member (this is the configuration of the thermal radiation photovoltaic power generation device according to the present invention). In this case, it is desirable that the photoelectric conversion element has a thickness of 0.2 μm or less where energy loss caused by absorption of surface waves becomes significant. This requirement is such that the thermal radiation generator and the intermediate member in the thermal radiation generator according to the present invention are brought close to the distance where the decrease in power generation efficiency becomes remarkable due to absorption of surface waves in the conventional thermal radiation generator, Since the intermediate member hardly absorbs the surface wave, it means that the effect of improving the efficiency of the thermal radiation light power generation apparatus according to the present invention with respect to the conventional heat radiation light power generation apparatus becomes remarkable.

  For the same reason, the distance between the thermal radiator and the intermediate member is generated by the thermal radiator in a configuration in which the thermal radiator and the photoelectric conversion element are spaced apart without arranging the intermediate member. It is shorter than the distance between the thermal radiator and the photoelectric conversion element when the ratio of the loss of energy caused by the photoelectric conversion element absorbing surface waves in the total energy of the heat radiation light is 10%. desirable. The total energy of the heat radiation generated by the heat radiator and the magnitude of the energy loss caused by the photoelectric conversion element absorbing the surface wave can be obtained by numerical calculation.

  Since the energy of the heat radiation light that can be transmitted to the photoelectric conversion element by the intermediate member via the near-field light is proportional to the square of the refractive index, the material of the intermediate member is photoelectrically converted in the photoelectric conversion element. It is desirable that the refractive index be high within the wavelength range, for example, 3 or more. A temperature that has such a high refractive index and has a positive real part of the dielectric constant with respect to light having a wavelength of 5 to 1000 μm as described above, and is generally used in a thermal radiation power generator. As a material that transmits infrared light having a wavelength of 1.1 to 2.5 μm that mainly contributes to power generation in heat radiation generated from a heat radiator of 1000 to 2000K, intrinsic semiconductor (that is, no carrier added) Si is cited. It is done.

  The thermal radiator preferably has a photonic crystal structure that amplifies light having a wavelength that is transmitted by the intermediate member. The photonic crystal structure is a structure in which a periodic refractive index distribution is formed. Among various lights having different wavelengths, light having a specific wavelength corresponding to this period is selectively amplified by interference. Has characteristics. When the heat radiator has such a photonic crystal structure, it is possible to amplify light having a wavelength that passes through the intermediate member and contributes to power generation by the photoelectric conversion element, thereby further increasing output density and power generation efficiency. can do. In addition, the heat radiating body having a photonic crystal structure is irradiated with sunlight to heat the heat radiating body, and light emitted from the heat radiating body and having a wavelength contributing to power generation is amplified. The photoelectric conversion efficiency can be made higher by performing photoelectric conversion by irradiating the solar cell than when performing photoelectric conversion by directly irradiating the photoelectric conversion element with sunlight. The photonic crystal structure has, for example, a periodic arrangement of members made of a semiconductor or the like, or a plate-like base material made of a semiconductor or the like that has a region having a refractive index different from that of the base material (a different refractive index region). It can form by providing. In the different refractive index region, a hole can be typically used, but a member different from the base material embedded in the hole may be used.

  According to the present invention, it is possible to prevent the propagation of near-wavelength light that does not contribute to power generation while propagating near-field light having a wavelength that contributes to power generation from the heat radiator to the semiconductor layer of the photoelectric conversion element. It is possible to obtain a thermal radiation light power generation device having both high output density and power generation efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the principal part of one Embodiment of the thermal radiation light power generator which concerns on this invention. The perspective view from the opposite side of the surface which opposes a photoelectric conversion element which shows the structure of a part of thermal radiation body in the thermal radiation light-power generation apparatus of this embodiment. The graph which shows the difference in the value of the real part of the dielectric constant by the difference in wavelength about n-InP which is an example of the material of a semiconductor layer, and Si which is not added the carrier which is an example of the material of an intermediate member. In the case of using an InGaAs / InP photoelectric conversion element, it has an intermediate member having a thickness of 10 μm, and the distance between the intermediate member and the heat radiator is sufficiently long to exceed (a) 0.01 μm (Example 1) and (b) 100 μm. In the case of (Comparative Example 1), there is no intermediate member, and the distance between the first n-type semiconductor layer and the heat radiator is (c) 0.01 μm (Comparative Example 2) and (b) a sufficiently long distance exceeding 100 μm (Comparison The graph which shows the result of having calculated | required the spectrum of the heat radiation light which reaches | attains a photoelectric conversion element from a heat radiator about the case of Example 3). In the case of using an InGaAs / InP photoelectric conversion element, the intensity of thermal radiation that contributes to power generation and the loss of thermal radiation that contributes to power generation when (a) has an intermediate member with a thickness of 10 μm and (b) has no intermediate member. The graph which shows the result of having calculated | required the value which integrated | accumulated about all the wavelengths by calculation. In the case of using an InGaAs / InP photoelectric conversion element, power generation out of the heat radiation emitted from the heat radiator when the thickness t of the intermediate member is 0.1 μm, 1 μm, 10 μm and 100 μm, and when there is no intermediate member, respectively. The graph which shows the result of having calculated | required the ratio of the intensity | strength (electric power generation contribution rate) of what contributes to several distance d or d 'by calculation. When an InGaAs / InP photoelectric conversion element is used, the amount of electrons added to the first n-type semiconductor layer is (a) 1 × 10 ¹⁹ cm ⁻³ , (b) 1 × 10 ¹⁸ cm ⁻³ , and (c) 1 × The graph which shows the result of having calculated | required the electric power generation contribution rate with and without the case where the intermediate member of 10 micrometers in thickness is in the case of 10 ^{< 17} > cm ^<-3 >. In the case of using a GaSb photoelectric conversion element, the intensity of thermal radiation that contributes to power generation and the loss of thermal radiation that contributes to power generation are reduced when (a) the intermediate member has a thickness of 10 μm and (b) there is no intermediate member. The graph which shows the result of having calculated | required the value integrated about the wavelength by calculation. In the case of using a GaSb photoelectric conversion element, the results of calculating the power generation contribution ratio with and without an intermediate member having a thickness of 10 μm are shown. Schematic which shows an example of the whole structure of the thermal radiation light power generator which concerns on this invention. The perspective view which shows the other example of the photonic crystal structure in a heat radiator. The schematic block diagram of the principal part which shows the example which is a modification of the thermal radiation light-power generation apparatus which concerns on this invention, and a heat radiator does not have a photonic crystal structure.

  1 to 12, an embodiment of a thermal radiation light power generation device according to the present invention will be described. FIG. 1 is a schematic diagram illustrating the configuration of a thermal radiation light power generation apparatus 10 according to the present embodiment. The thermal radiation light power generation apparatus 10 includes a photoelectric conversion element 11, a heat radiator 12, and an intermediate member (intermediate substrate) 13.

The photoelectric conversion element 11 includes a first n-type semiconductor layer 1111, a second n-type semiconductor layer 1112, a second p-type semiconductor layer 1122, and a first p-type semiconductor layer 1121 formed of a plurality of semiconductor layers stacked in this order. Have For example, n-InP, n-InGaAs, p-InGaAs, and p-InP can be used as materials for these four semiconductor layers in the order described above. Hereinafter, a photoelectric conversion element using these four semiconductor layers is referred to as an “InGaAs / InP photoelectric conversion element”. In an InGaAs / InP photoelectric conversion element, photoelectric conversion occurs due to light within a wavelength range of 1.68 μm or less. Alternatively, n.sup. ⁺ -GaSb, n-GaSb, p-GaSb, and p.sup. ⁺ -GaSb can be used in the order described above for the material of these four semiconductor layers. Hereinafter, a photoelectric conversion element using these four semiconductor layers is referred to as a “GaSb photoelectric conversion element”. Here, n ⁺ -GaSb indicates that the amount of added electrons is larger than that of n-GaSb, and p ⁺ -GaSb indicates that the amount of added holes is larger than that of p-GaSb. In the GaSb photoelectric conversion element, photoelectric conversion occurs due to light in the wavelength range of 1.77 μm or less.

  A first electrode 1131 is connected to the first n-type semiconductor layer 1111, and a second electrode 1132 is connected to the first p-type semiconductor layer 1121.

The heat radiator 12 is made of Si to which no carrier is added (hereinafter, referred to as “non-added Si”), and faces the first n-type semiconductor layer 1111 of the photoelectric conversion element 11 to the first n-type semiconductor layer 1111. A plate-like portion 121 arranged in parallel and a photonic crystal portion 122 provided on the surface of the back side of the plate-like portion 121 (opposite the surface facing the first n-type semiconductor layer 1111) are provided. As shown in FIG. 2, the photonic crystal portion 122 is formed by arranging a number of rod members 1221, which are rod-shaped members made of Si, in parallel with a period (interval) a on the surface on the back side of the plate-like portion 121. It is configured. The heat radiator 12 receives heat from an external heat source to emit heat radiation light, and selectively amplifies light having a wavelength corresponding to the period a in the photonic crystal part 122. The wavelength of the light amplified here refers to the wavelength in the photonic crystal part 122 and is a value obtained by dividing the wavelength λ ₀ in vacuum by the effective refractive index n _eff of the photonic crystal part 122. The effective refractive index n _eff is a refractive index in consideration of the ratio of the electric field intensity of light distributed in the photonic crystal part 122 and the filling rate of the rod member 1221 with respect to the entire photonic crystal part 122. A specific example of the period a will be described later together with the configuration of the intermediate member 13.

  The intermediate member 13 is a plate-like member made of additive-free Si, and between the first n-type semiconductor layer 1111 of the photoelectric conversion element 11 and the plate-like portion 121 of the heat radiator 12, the first n-type semiconductor layer 1111 and The heat radiator 12 is arranged in parallel. The intermediate member 13 is in contact with the first n-type semiconductor layer 1111 of the photoelectric conversion element 11, but is separated from the plate-like portion 121 of the thermal radiator 12 by a predetermined distance d. The distance d is set to 1/3 or less of the band gap wavelength corresponding to the minimum value among the band gap energies of the semiconductors constituting the four semiconductor layers of the photoelectric conversion element 11. This distance d corresponds to a distance in which near-field light due to thermal radiation whose wavelength is in a range contributing to power generation in the photoelectric conversion element 11 can propagate to an object facing the thermal radiator. For example, in the InGaAs / InP photoelectric conversion element, the band gap wavelength is 1.68 μm, and the distance d is 0.560 μm or less. In the GaSb photoelectric conversion element, the band gap wavelength is 1.77 μm, and the distance d is 0.590 μm or less.

  As shown in FIG. 3, additive-free Si, which is the material of the intermediate member 13 in the present embodiment, has a positive value of the real part of the dielectric constant at all wavelengths of 0.5 to 1000 μm. This means that surface waves do not propagate on the surface of the intermediate member 13. Further, the additive-free Si transmits light having a wavelength in the range of 1.1 to 1.7 μm. This wavelength range is included in the wavelength range in which photoelectric conversion is performed in the photoelectric conversion element for any example of the InGaAs / InP photoelectric conversion element and the GaSb photoelectric conversion element. Accordingly, light having a wavelength in the range of 1.1 to 1.7 μm that is emitted by thermal radiation in the thermal radiator 12 can pass through the intermediate member 13 and reach the photoelectric conversion element 11. It is photoelectrically converted. The period of the rod member 1221 is adjusted so that the wavelength of the light amplified in the photonic crystal part 122 of the thermal radiator 12 matches the wavelength within the wavelength range that is transmitted through the intermediate member 13 and photoelectrically converted by the photoelectric conversion element 11. Set a.

  Operation | movement of the thermal radiation light power generation apparatus 10 of this embodiment is demonstrated. The heat radiator 12 is heated by an external heat source. Thereby, the heat radiator 12 produces | generates the heat radiation light which has a spectrum corresponding to heating temperature. Of the heat radiation light, light having a wavelength corresponding to the period a of the rod member 1221 provided in the photonic crystal portion 122 is amplified. Therefore, the spectrum of the heat radiation light emitted from the heat radiator 12 is enhanced in intensity at the wavelength corresponding to the period a. Of the heat radiation light emitted from the heat radiator 12, light having a wavelength that passes through the intermediate member 13 including the wavelength corresponding to the period a reaches the photoelectric conversion element 11 and is subjected to photoelectric conversion. The amplification of the intensity of light having a wavelength corresponding to the period a in this way contributes to increasing the output density and efficiency of photoelectric conversion.

  Further, near-field light that is not emitted out of the heat radiator 12 as it is is leached on the surface of the plate-like portion 121 of the heat radiator 12. Among these, the near-field light having a wavelength that leaches out on the surface facing the intermediate member 13 and passes through the intermediate member 13 is only a short distance of 1/3 or less of the band gap wavelength between the heat radiator 12 and the intermediate member 13. Since it is not spaced apart, it can propagate from the heat radiator 12 to the intermediate member 13, thereby reaching the photoelectric conversion element 11 and being subjected to photoelectric conversion. In this respect, the thermal radiation power generation apparatus 10 has a high output density of photoelectric conversion.

  On the other hand, since the intermediate member 13 is made of additive-free Si, surface waves are not generated on the surface of the intermediate member 13 at all wavelengths of 0.5 to 1000 μm. Therefore, among the heat radiation light generated by the heat radiator 12, light having a wavelength longer than the band gap wavelength that does not contribute to power generation in the photoelectric conversion element 11 propagates from the heat radiator 12 to the intermediate member 13 as a surface wave. Can be prevented. The first n-type semiconductor layer 1111 of the photoelectric conversion element 11 is made of a material in which surface waves can exist on the surface. However, since the surface waves do not propagate in the intermediate member 13, the surface is generated by heat radiation generated from the heat radiator. Surface waves are not induced in Therefore, such long-wavelength light stays in the heat radiator 12 and is absorbed by the heat radiator 12 as heat. A part of the heat absorbed by the heat radiating body 12 thus passes through the intermediate member 13 by heat radiation and becomes a wavelength that can be subjected to photoelectric conversion by the photoelectric conversion element 11, so that the efficiency of photoelectric conversion is increased.

  As described above, the thermal radiation light power generation apparatus 10 of the present embodiment increases both the output density and efficiency of photoelectric conversion due to three factors. In particular, the improvement in the efficiency of photoelectric conversion due to the fact that long-wavelength surface waves do not propagate to the surface of the intermediate member 13 is a remarkable effect that is not found in conventional thermal radiation light power generation devices.

Hereinafter, the result of having performed simulation in a more specific example is shown. First, an InGaAs / InP photoelectric conversion element was simulated under the following condition 1.
First n-type semiconductor layer 1111: made of n-InP, thickness 0.1 μm, electron addition density 2 × 10 ¹⁸ cm ⁻¹ .
Second n-type semiconductor layer 1112: made of n-InGaAs, thickness 0.3 μm, electron addition density 1 × 10 ¹⁸ cm ⁻¹ .
Second p-type semiconductor layer 1122: made of p-InGaAs, thickness 2.0 μm, hole addition density 1 × 10 ¹⁷ cm ⁻¹ .
First p-type semiconductor layer 1121: made of p-InP, thickness 0.1 μm, hole addition density 2 × 10 ¹⁸ cm ⁻¹ .
Plate-like part 121: made of additive-free Si, thickness 1.5 μm.
Photonic crystal part 122: made of additive-free Si, thickness 0.5 μm, period a 0.4 μm, rod member 1221 width 0.28 μm.
Heating temperature of the heat radiator 12: 1400K.
Intermediate member 13: made of additive-free Si, thickness t varies from simulation to simulation.
Distance d: Different for each simulation.

  In the case where the thickness t of the intermediate member 13 is 10 μm and the distance d is a sufficiently long distance (Comparative Example 1) exceeding (a) 0.01 μm (Example 1) and (b) 100 μm in Condition 1, thermal radiation The spectrum of heat radiation reaching the photoelectric conversion element 11 from the body 12 was obtained by calculation. Further, the photoelectric conversion element 11 and the heat radiator 12 have the same configuration as described above, and when the intermediate member 13 is not provided, the distance (d ′) between the plate-like portion 121 and the first n-type semiconductor layer 1111 is ( The same calculation was performed for c) 0.01 μm (Comparative Example 2) and (d) a sufficiently long distance exceeding 100 μm (Comparative Example 3).

  The result of this calculation is shown in FIG. FIG. 4 shows the intensity of thermal radiation light that contributes to power generation in the photoelectric conversion element 11, the intensity (transmission loss) of thermal radiation light that passes through each semiconductor layer of the photoelectric conversion element 11 without contributing to power generation, The intensity of surface waves on the surface of the member 13 (Example 1 and Comparative Example 1) or the first n-type semiconductor layer 1111 (Comparative Examples 2 and 3) is shown. In addition, the spectrum of black body radiation at 1400K is shown in each figure.

  In Example 1, thermal radiation light that contributes to power generation has reached the photoelectric conversion element 11 with an intensity greater than 1400K blackbody radiation in a wavelength region equal to or less than the band gap wavelength. On the other hand, in both Comparative Examples 1 and 3, the intensity of the thermal radiation that contributes to power generation is smaller than the intensity of the black body radiation of 1400K in the wavelength region below the band gap wavelength. This is because in Example 1, the distance d between the heat radiator 12 and the intermediate member 13 is sufficiently short, 0.01 μm, which is 1/3 or less of the band gap wavelength, so that black body radiation is outside the heat radiator 12. While the near-field light that is not emitted is introduced into the photoelectric conversion element 11 through the intermediate member 13, the distance d or d ′ is sufficiently long exceeding 100 μm in Comparative Examples 1 and 3, so that the near-field light is photoelectrically converted. This is because it is not introduced into the element 11. In Comparative Example 2, it is considered that the intensity of the heat radiation light contributing to power generation has the same intensity as that of Example 1, and the near-field light is introduced into the photoelectric conversion element 11. However, Comparative Example 2 has the following problem.

  In Comparative Example 2, absorption loss due to surface waves occurs in a wavelength range exceeding 10 μm which does not contribute to power generation, whereas in Example 1, no absorption loss due to surface waves is observed. In the first embodiment, an intermediate member 13 made of additive-free Si having a positive real part of dielectric constant at all wavelengths of 0.5 to 1000 μm is provided between the photoelectric conversion element 11 and the thermal radiator 12 in the first embodiment. This is because the generation of surface waves is prevented.

  As described above, in Example 1, by introducing near-field light into the photoelectric conversion element 11, it is possible to increase the power density and suppress the absorption loss due to the surface wave, thereby increasing the power generation efficiency. .

Next, for the case where the intermediate member 13 having a thickness t of 10 μm is provided, a value obtained by integrating the intensities of the heat radiation light contributing to power generation and the heat radiation light causing loss for all wavelengths is calculated for a plurality of examples having different distances d. FIG. 5 (a) shows the result obtained in the above. Similarly, FIG. 5B shows the result of the same calculation performed for a plurality of examples having different distances d ′ when the intermediate member 13 is not provided. From FIG. 5 (a), the integrated value of the total intensity of the heat radiation generated from the heat radiator corresponds to 1/3 of the band gap wavelength (denoted as “λ _gap / 3” in the figure). When the distance d is longer than the length, it hardly changes, whereas when the distance d is shorter than λ _gap / 3, it increases as the distance d becomes shorter. This means that near-field light can be introduced into the photoelectric conversion element 11 through the intermediate member 13 by shortening the distance d to be shorter than 1/3 of the band gap wavelength.

  5A and 5B, when the distance d or d ′ is smaller than 0.2 μm, the case where there is no intermediate member 13 is larger in the photoelectric conversion element 11 than when the intermediate member 13 is provided. It can be seen that the absorption loss in the first n-type semiconductor layer 1111 closest to the heat radiator 12 is high. This is because when there is no intermediate member 13, a loss occurs due to propagation of a long-wave surface wave on the surface of the first n-type semiconductor layer 1111, whereas when the intermediate member 13 is provided, such a loss occurs. This is because it does not occur. Further, the range where the distance d is smaller than 0.2 μm is that the absorption loss of the first n-type semiconductor layer 1111 in the absence of the intermediate member 13 (FIG. 5B) is the overall intensity of the heat radiation light generated from the heat radiator. This also corresponds to a range of 10% or more of the integrated value, and it can be seen that the loss ratio can be reduced by inserting the intermediate member 13.

  FIG. 6 shows the proportion of the intensity of the heat radiation emitted from the thermal radiator 12 that contributes to power generation (power generation contribution ratio) when the thickness t of the intermediate member 13 is 0.1 μm, 1 μm, 10 μm, and 100 μm. Shows the result of calculation for a plurality of distances d. The figure also shows the result of performing the same calculation for a plurality of distances d ′ when there is no intermediate member 13. When the case where the intermediate member 13 is present is compared with the case where the distance d is the same as the distance d ′, the intermediate member 13 is in the region where the distance d is 0.2 μm or less regardless of the thickness of the intermediate member 13. The difference in the power generation contribution rate from the case of no 13 is significant. Further, in the region where the distance d is 0.2 μm or less, the power generation contribution rate is slightly higher when the thickness of the intermediate member 13 is 1 μm and 10 μm than when the thickness is 0.1 μm and 100 μm. This is because, as the thickness t decreases, the ratio of long-wavelength light directly coupled from the heat radiator 12 to the surface wave generated on the surface of the photoelectric conversion element 11 beyond the intermediate member 13 increases. Since the ratio of light absorption in the intermediate member 13 increases as t increases, the power generation contribution ratio increases when the thickness t is 1 μm and 10 μm. It is thought that it has become.

FIG. 7 shows that the addition amount of electrons in the first n-type semiconductor layer 1111 is (a) 1 × 10 ¹⁹ cm ⁻³ , (b) 1 × 10 ¹⁸ cm ⁻³ , and (c) 1 × 10 ¹⁷ cm ⁻³ . The result of having calculated | required the electric power generation contribution rate with and without the case where the intermediate member 13 with a thickness of 10 μm is present is shown. In (a) with the largest amount of added electrons, the power generation contribution rate is slightly lower than in (b) and (c) when the distance d is reduced. This is because loss due to light absorption increases in the first n-type semiconductor layer 1111 due to an increase in electrons. In other respects, there is almost no influence due to the difference in the amount of electrons added to the first n-type semiconductor layer 1111. In any case, when the distance d is smaller than 0.2 μm, the intermediate member 13 is not present. The power generation contribution rate is significantly higher than that.

Next, the calculation similar to FIG.5 and FIG.6 was performed about the following conditions 2 about the GaSb photoelectric conversion element.
First n-type semiconductor layer 1111: made of n-GaSb, thickness 0.05 μm, electron addition density 2 × 10 ¹⁸ cm ⁻¹ .
Second n-type semiconductor layer 1112: made of n-GaSb, thickness 0.3 μm, electron addition density 1 × 10 ¹⁸ cm ⁻¹ .
Second p-type semiconductor layer 1122: made of p-GaSb, thickness 2.0 μm, hole addition density 1 × 10 ¹⁷ cm ⁻¹ .
First p-type semiconductor layer 1121: made of p-GaSb, thickness 0.05 μm, hole addition density 2 × 10 ¹⁸ cm ⁻¹ .
Plate-like part 121: made of additive-free Si, thickness 1.5 μm.
Photonic crystal part 122: made of additive-free Si, thickness 0.5 μm, period a 0.4 μm, rod member 1221 width 0.28 μm.
Heating temperature of the heat radiator 12: 1400K.
Intermediate member 13: made of additive-free Si, thickness 10 μm.
Distance d: Multiple values.

  As shown in FIG. 8, in the condition 2 as well as in the case of the condition 1, the shorter the distance d is within the range where the distance d is shorter than 1/3 of the band gap wavelength, the more the heat radiation light contributing to power generation becomes. Strength increases. Further, in the range where the distance d or d ′ is smaller than 0.2 μm, the first n-type closest to the heat radiator 12 in the photoelectric conversion element 11 when the intermediate member 13 is not provided is more than when the intermediate member 13 is provided. The absorption loss in the semiconductor layer 1111 is high.

  Further, as shown in FIG. 9, in the condition 2 as well as in the case of the condition 1, the difference in the power generation contribution ratio between the case where the intermediate member 13 is present and the case where the intermediate member 13 is not present in the range where the distance d or d ′ is smaller than 0.2 μm. Becomes prominent.

In FIG. 10, an example of the whole structure of the thermal radiation light-emitting power generator of this invention containing components other than the photoelectric conversion element 11, the heat radiator 12, and the intermediate member 13 is shown. In this example, a support base (support substrate) 14 that supports the heat radiator 12 is used. A plurality of cavities 141 are provided on the surface of the support base 14 facing the heat radiator 12 from the surface into the support base 14, and a columnar portion 142 is formed between the nearest cavities 141. Yes. The heat radiator 12 is in contact with the support base 14 only at the columnar portion 142. With such a configuration, it is possible to reduce the heat conduction loss in the support base 14 as compared with the case where the heat radiator 12 is supported by the support base without the cavity 141, and also the heat radiation due to the thermal expansion of the support base 14. The deformation of the photovoltaic device can be suppressed. As the cavity 141, one provided with a plurality of grooves in parallel or one provided with a plurality of holes arranged two-dimensionally can be used. In the case where sunlight is used as the heat source, SiO ₂ is preferably used as the material of the support base 14 because it transmits sunlight and can easily form the cavity 141 and the columnar portion 142 by wet etching. Can be used.

  A spacer 15 is provided on the edge of the upper surface of the support base 14 (outside the region where the cavity 141 is provided), and the intermediate member 13 is placed on the spacer 15. The distance d between the heat radiator 12 and the intermediate member 13 can be set by the thickness of the spacer 15.

The present invention is not limited to the above embodiment.
For example, in each of the embodiments described above, the photoelectric conversion element has two layers each composed of an n-type semiconductor and two layers composed of a p-type semiconductor. However, these are one layer each, or three layers or more. Also good. Alternatively, a photoelectric conversion element using a Schottky junction and having a structure in which a single semiconductor layer made of an n-type or p-type semiconductor and a metal layer are joined may be used. The material of each semiconductor layer of the photoelectric conversion element is not limited to the above example, and any semiconductor material of a photoelectric conversion layer used in a normal photoelectric conversion element (solar cell) can be applied. The material of the heat radiator 12 is not limited to the above. Furthermore, the material of the intermediate member 13 is not limited to the above, and the real part of the dielectric constant has a positive value with respect to light having a wavelength of 0.5 to 1000 μm, and light having a wavelength equal to or less than the band gap wavelength (that is, Any material that transmits light having a wavelength that contributes to power generation by the photoelectric conversion element may be used.

  The photonic crystal structure of the heat radiator is not limited to the above example. For example, a plurality of holes 1221A are periodically and two-dimensionally formed in a plate-like base material 1222A shown in FIG. A member provided with a member having a refractive index different from that of the base material 1222A instead of the hole 1221A can be used. Alternatively, as shown in FIG. 11B, a two-dimensional arrangement of columnar members 1221B may be used as the photonic crystal structure. Furthermore, as shown in FIG. 11 (c), a rod member 1221C may be used as a photonic crystal structure by combining the rod members 1221C in a three-dimensional pattern. In the above example, only part of the heat radiator 12 is the photonic crystal portion 122, but a photonic crystal structure may be formed on the entire heat radiator.

  In the thermal radiation light-emitting power generation device of the present invention, it is not essential that the thermal radiator has a photonic crystal structure, and as shown in FIG. 12, the thermal radiator 12A does not have a photonic crystal structure. May be. In the thermal radiation power generation device 10A having such a configuration, the output density can be increased by being able to photoelectrically convert near-field light within the wavelength range that transmits the intermediate substrate, and the wavelength is longer than the band gap wavelength. Can be prevented from propagating from the heat radiator 12A to the intermediate member 13 as surface waves, so that the efficiency of photoelectric conversion is increased.

DESCRIPTION OF SYMBOLS 10, 10A ... Thermal radiation light generator 11 ... Photoelectric conversion element 110 ... Photoelectric conversion part 1111 ... 1st n-type semiconductor layer 1112 ... 2n-type semiconductor layer 1121 ... 1st p-type semiconductor layer 1122 ... 2nd p-type semiconductor layer 1131 ... 1st 1 electrode 1132 ... 2nd electrode 12, 12A ... thermal radiator 121 ... plate-like part 122 ... photonic crystal part 1221, 1221C ... rod member 1221A ... hole 1221B ... columnar member 1222A ... base material 13 ... intermediate member 14 ... support Base 141 ... Cavity 142 ... Columnar portion 15 ... Spacer

Claims (6)

a) a heat radiator;
b) a photoelectric conversion element having one or more semiconductor layers disposed apart from the heat radiator;
c) Between the thermal radiator and the photoelectric conversion element, a wavelength corresponding to a band gap energy of a semiconductor constituting the one semiconductor layer, or each semiconductor layer of the plurality of layers is in contact with the photoelectric conversion element Dielectric constant for light with a wavelength of 0.5 to 1000 μm arranged at a distance of 1/3 or less of the bandgap wavelength, which is the wavelength corresponding to the smallest of the semiconductor bandgap energy And an intermediate member made of a material that transmits light of at least a part of the wavelength within a wavelength range that is photoelectrically converted in the photoelectric conversion element. Power generation device.   The thermal radiation power generation device according to claim 1, wherein a distance between the thermal radiator and the intermediate member is 0.2 μm or less.   In the configuration in which the thermal radiator and the photoelectric conversion element are arranged apart from each other without disposing the intermediate member, the distance between the thermal radiator and the intermediate member is the amount of thermal radiation generated by the thermal radiator. Claims characterized by being shorter than the distance between the thermal radiator and the photoelectric conversion element when the ratio of the loss of energy caused by the photoelectric conversion element absorbing surface waves in the total energy is 10%. Item 3. The thermal radiation light power generation device according to Item 1 or 2.   The thermal radiation power generator according to any one of claims 1 to 3, wherein a refractive index of a material of the intermediate member is 3 or more within a wavelength range in which photoelectric conversion is performed in the photoelectric conversion element.   The thermal radiation generator according to claim 1, wherein the thermal radiator has a photonic crystal structure that amplifies light having a wavelength transmitted by the intermediate member.   The thermal radiation generator according to any one of claims 1 to 5, wherein the thermal radiator is placed on the columnar portion of a support base having a plurality of columnar portions formed on a surface thereof.

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