Photoelectric conversion element

Abstract

To improve photoelectric conversion efficiency in multi-junction photoelectric conversion elements.SOLUTION: A photoelectric conversion element has a first resonator mirror layer, a second resonator mirror layer, and a multi-junction optical absorption layer provided between the first and second resonator mirror layers, and the position of each tunnel junction layer in the multi-junction optical absorption layer is determined based on the position of the standing wave nodes generated in the multi-junction optical absorption layer when a single wavelength of light is incident on the first resonator mirror layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to photoelectric conversion technology. [Background technology]

[0002] As one of the wireless power supply technologies, for example, an optical wireless power supply technology is known, as disclosed in Non-Patent Document 2. In the optical wireless power supply technology, a beam (monochromatic light) output from a laser is incident on a photoelectric conversion element, which converts the light into electricity.

[0003] In the above-described optical wireless power supply using a laser, it is desired to improve the efficiency of photoelectric conversion in the photoelectric conversion element.

[0004] As a method for increasing the efficiency of photoelectric conversion elements, a multi-junction structure is known in which light absorbing layers are stacked in multiple stages to obtain a higher voltage than that of a single layer (Non-Patent Document 1). In the multi-junction structure, a low-resistance tunnel junction layer (hereinafter, TJ layer: Tunnel Junction) with low current loss is used between two light absorbing layers. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Hidefumi Akiyama, "Diagnosis and design of multi-junction solar cells and evaluation of absolute luminescence value and luminescence quantum efficiency", Applied Physics, Vol. 84, No. 4 (2015), https: / / www.jstage.jst.go.jp / article / oubutsu / 84 / 4 / 84_319 / _pdf / -char / ja, retrieved on June 2, 2023 [Non-Patent Document 2] Tomoyuki Miyamoto, "Optical wireless power transfer realized by optical beams" (2021), https: / / www.jsap.or.jp / columns / gx / e1-8, retrieved June 2, 2023 Summary of the Invention [Problem to be solved by the invention]

[0006] When a photoelectric conversion element has multiple junctions, it is necessary to use a highly doped material for the TJ layer described above in order to reduce current loss.

[0007] However, when the incident light passes through the inside of the photoelectric conversion element (i.e., when photoelectric conversion takes place), some of the light is absorbed due to the high concentration doping in the TJ layer, resulting in losses, which in turn reduces the photoelectric conversion efficiency.

[0008] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a technique for improving the photoelectric conversion efficiency in a multi-junction photoelectric conversion element. [Means for solving the problem]

[0009] According to the disclosed technique, a first cavity mirror layer, A second cavity mirror layer; a multi-junction type light absorbing layer provided between the first resonator mirror layer and the second resonator mirror layer; The position of each tunnel junction layer in the multi-junction type light absorption layer is determined based on the position of a node of a standing wave generated in the multi-junction type light absorption layer when light of a single wavelength is incident on the first resonator mirror layer. A photoelectric conversion element is provided. Effect of the Invention

[0010] According to the disclosed technique, a technique for improving the photoelectric conversion efficiency in a multi-junction photoelectric conversion element is provided. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing an example of the configuration of a photoelectric conversion element 100 according to an embodiment of the present invention. [Diagram 2] 2A to 2C are diagrams illustrating multiple reflections in a photoelectric conversion element 100 according to an embodiment of the present invention. [Diagram 3]2 is a diagram showing the state of light distribution inside the photoelectric conversion element 100. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment. In this embodiment, a photoelectric conversion element is targeted for optical wireless power supply using a laser that is a single-wavelength light.

[0013] (Overview of the Technology Relating to the Embodiments) In this embodiment, in order to solve the problem of a decrease in photoelectric conversion efficiency in a multi-junction photoelectric conversion element, a multi-junction light absorbing layer in the photoelectric conversion element is operated as a resonator, that is, a resonator structure is introduced into the photoelectric conversion element.

[0014] In optical wireless power supply using a laser, light of a single wavelength is incident, so the light is confined inside the photoelectric conversion element by the resonator structure, and standing waves are generated inside the photoelectric conversion element due to multiple reflections.

[0015] Standing waves have nodes where the optical amplitude (optical intensity) becomes small. By designing the thickness and number of each optical absorption layer so that the TJ layer of the multi-junction optical absorption layer is located at the node of the standing wave, it is possible to obtain the benefit of low electrical resistance provided by the TJ layer while reducing the disadvantage of optical absorption, thereby achieving higher conversion efficiency.

[0016] An example of the configuration of the photoelectric conversion element according to this embodiment will be described in detail below.

[0017] (Example of photoelectric conversion element configuration) Fig. 1 shows a configuration example of a photoelectric conversion element 100 according to the present embodiment. Fig. 1 shows a cross section of the photoelectric conversion element 100 cut along a plane perpendicular to a plane on which light (monochromatic light, light of a single wavelength) is incident in the photoelectric conversion element 100.

[0018] 1, the photoelectric conversion element 100 has a resonator mirror layer 10, a multi-junction light absorption layer 20, and a resonator mirror layer 30. The side on which light is incident is the positive pole, and the opposite side is the negative pole.

[0019] The cavity mirror layer 10 includes a high refractive index layer 11 and a low refractive index layer 12. The cavity mirror layer 30 includes a low refractive index layer 31, a high refractive index layer 32, and a low refractive index layer 33.

[0020] The resonator mirror layer 10 and the resonator mirror layer 30 can generate a standing wave in the multi-junction type light absorbing layer 20 .

[0021] The multi-junction light absorbing layer 20 has a pair of a P layer and an N layer as a light absorbing layer, and also has a TJ layer. Each light absorbing layer absorbs light energy and converts it into electrical energy. A plurality of light absorbing layers are provided. Each TJ layer is sandwiched between two light absorbing layers, and these light absorbing layers are connected in series. Four TJ layers 21 to 24 are shown in FIG. 1. The positive and negative electrodes are electrodes for extracting current.

[0022] The generation of standing waves is shown in Fig. 2. As shown in Fig. 2, light is multiple-reflected between the boundary between the resonator mirror layer 10 and the light absorption layer and between the boundary between the resonator mirror layer 30 and the light absorption layer, causing optical resonance, resulting in the generation of standing waves.

[0023] 1, five light absorbing layers are provided in the photoelectric conversion element 100, but the number of light absorbing layers being five is merely an example. The number of light absorbing layers is not limited to five.

[0024] (Regarding the location of the TJ layer) Next, a configuration for obtaining the effect of increasing the photoelectric conversion efficiency in the photoelectric conversion element 100 will be described.

[0025] The portion enclosed by the dotted line in Fig. 2 is shown in Fig. 3. Fig. 3 shows the state of light distribution inside the photoelectric conversion element 100.

[0026] In a photoelectric conversion element for monochromatic light, the wavelength of the incident light is assumed in advance. The photoelectric conversion element 100 according to the present embodiment employs a resonator structure and operates as a resonator.

[0027] As a condition for the photoelectric conversion element 100 to operate as a resonator, if the distance between the reflecting surfaces of the two resonator mirror layers (=resonator length) is L, the wavelength of the input light is λ, and the refractive index of the light absorption layer in the resonator is n, the following relationship must be established when each TJ layer is sufficiently thinner than the light absorption layer or the refractive index of each TJ layer is equivalent to the refractive index of the light absorption layer. In this embodiment, it is assumed that each TJ layer is sufficiently thinner than the light absorption layer or the refractive index of each TJ layer is equivalent to the refractive index of the light absorption layer.

[0028] 2nL=mλ (m: an integer equal to or greater than 1) When monochromatic light is incident on the resonator (photoelectric conversion element 100), a light amplitude intensity distribution is generated in the multi-stage light absorption layer 20 due to standing waves that depend on the wavelength of the incident light and the refractive index of the light absorption layer.

[0029] In the photoelectric conversion element 100 of this embodiment, the thickness of each light absorbing layer and the number of layers of the absorbing layers are determined so that the position of the TJ layer with large absorption loss coincides with the node of the optical amplitude intensity (node ​​of the standing wave) during the resonator operation, which makes it possible to minimize the loss in each TJ layer.

[0030] That is, in the resonator structure, a node of the optical electric field (node ​​of the standing wave) occurs in the light absorption layer when monochromatic light is incident, as shown in Fig. 3. By designing the photoelectric conversion element 100 so that the position of the TJ layer overlaps with the node of the optical electric field, it is possible to minimize the loss.

[0031] More specifically, within the resonator, nodes in the optical amplitude intensity are generated at depths of λ / 2n from the boundary between the resonator mirror layer 10 on the incident side and the absorption layer. Therefore, the photoelectric conversion element 100 has the thickness of each light absorption layer and the number of light absorption layers so that the depth of the TJ layer is λm / 2n (m: integer). This provides the effect of increasing the photoelectric conversion efficiency.

[0032] 3, when light of wavelength a is used, one optical absorption layer exists between a certain node and the next node. In other words, when light of wavelength a is used, TJ layers exist at positions m=1, 2, 3, and 4 in a / 2n.

[0033] When light of wavelength b is used, one absorption layer exists between a node and the node after the node. In other words, when light of wavelength b is used, TJ layers exist at positions bm / 2n, where m = 2, 4, 6, and 8.

[0034] (Effects of the embodiment) As described above, in the technology according to the present embodiment, a resonator structure is introduced into a photoelectric conversion element for monochromatic light, and the thickness of the internal light absorption layer is optimized in accordance with the wavelength of the incident monochromatic light and the refractive index of the absorption layer. This makes it possible to reduce light absorption caused by the introduction of a TJ layer in multiple junctions while obtaining the effect of improving the photoelectric conversion efficiency by using multiple junctions.

[0035] In other words, the light absorption that occurs due to the multi-junction structure formed by the introduction of the TJ layer can be reduced, and the photoelectric conversion efficiency can be made higher than that of conventional multi-junction photoelectric conversion elements.

[0036] The following supplementary notes are further disclosed regarding the above embodiment.

[0037] <Additional Notes> (Additional note 1) A first cavity mirror layer; A second cavity mirror layer; a multi-junction type light absorbing layer provided between the first resonator mirror layer and the second resonator mirror layer; The position of each tunnel junction layer in the multi-junction type light absorption layer is determined based on the position of a node of a standing wave generated in the multi-junction type light absorption layer when light of a single wavelength is incident on the first resonator mirror layer. Photoelectric conversion element. (Additional note 2) 2. The photoelectric conversion element according to claim 1, wherein a tunnel junction layer in the multi-junction light absorbing layer is present at a node position of the standing wave. (Additional note 3) When the wavelength of the light is λ, the refractive index of the light absorption layer constituting the multi-junction type light absorption layer is n, and m is an integer, and each tunnel junction layer is sufficiently thinner than the light absorption layer, or the refractive index of each tunnel junction layer is equivalent to the refractive index of the light absorption layer, the thickness of each light absorption layer is determined so that the depth of each tunnel junction layer is λm / 2n based on the boundary between the first resonator mirror layer and the multi-junction type light absorption layer. 3. The photoelectric conversion element according to claim 1 or 2.

[0038] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0039] 100 Photoelectric conversion element 10, 20 Resonator mirror layer 20 Multi-junction light absorbing layer 11, 32 High refractive index layer 12, 31, 33 Low refractive index layer 21~24 TJ layer

Claims

1. A first cavity mirror layer; A second cavity mirror layer; a multi-junction type light absorbing layer provided between the first resonator mirror layer and the second resonator mirror layer; The position of each tunnel junction layer in the multi-junction type light absorption layer is determined based on the position of a node of a standing wave generated in the multi-junction type light absorption layer when light of a single wavelength is incident on the first resonator mirror layer. Photoelectric conversion element.

2. The photoelectric conversion element according to claim 1 , wherein a tunnel junction layer in the multi-junction type light absorbing layer is present at a node position of the standing wave.

3. When the wavelength of the light is λ, the refractive index of the light absorption layer constituting the multi-junction type light absorption layer is n, and m is an integer, and each tunnel junction layer is sufficiently thinner than the light absorption layer, or the refractive index of each tunnel junction layer is equivalent to the refractive index of the light absorption layer, the thickness of each light absorption layer is determined so that the depth of each tunnel junction layer is λm / 2n based on the boundary between the first resonator mirror layer and the multi-junction type light absorption layer. The photoelectric conversion element according to claim 1 or 2.

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