Photoelectric converter

Abstract

To improve electric power generation efficiency by increasing an absorption quantity of incident light even with a structure which has a columnar inorganic semiconductor formed in an organic semiconductor.SOLUTION: A photoelectric conversion device 1 comprises a photoactive layer 3 which is formed of an organic semiconductor material and receives external light on a top surface to generate an exciton, and an electron transport region 5 which is formed of an inorganic semiconductor material in a columnar shape from the reverse surface to the top surface of the photoactive layer 3, and is provided with a projection part 51 at the top of the electron transport region 5 that the external light received on the top surface of the photoactive layer 3 impinges on.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a photoelectric conversion device. [Background technology]

[0002] Conventionally, a photovoltaic device comprising an organic semiconductor and an inorganic semiconductor has been disclosed in Patent Document 1. In the photovoltaic device disclosed in Patent Document 1, a columnar separation region formed of an inorganic semiconductor was formed within a photoactive region formed of an organic semiconductor. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 042579 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in the conventional photovoltaic devices described above, columnar inorganic semiconductors are formed within the organic semiconductor, so the volume of the organic semiconductor decreases by the volume of the inorganic semiconductor that is formed. Organic semiconductors absorb light, while inorganic semiconductors transmit light, so when the volume of the inorganic semiconductor increases and the volume of the organic semiconductor decreases, the amount of light absorbed decreases, resulting in a problem of reduced power generation efficiency.

[0005] Therefore, the present invention has been proposed in view of the above circumstances, and aims to provide a photoelectric conversion device that can increase the amount of incident light absorbed and improve power generation efficiency, even in a structure in which columnar inorganic semiconductors are formed inside an organic semiconductor. [Means for solving the problem]

[0006] To solve the above-mentioned problems, a photoelectric conversion device according to one aspect of the present invention comprises a photoactive layer formed of an organic semiconductor material that generates excitons, and an electron transport region formed of an inorganic semiconductor material that is columnar in shape from the lower surface to the upper surface of the photoactive layer. Furthermore, a projection is provided at the tip of the electron transport region into which external light is incident. [Effects of the Invention]

[0007] According to the present invention, even in a structure in which columnar inorganic semiconductors are formed within an organic semiconductor, the amount of incident light absorbed can be increased, thereby improving power generation efficiency. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a perspective view showing the structure of a photoelectric conversion device according to the first embodiment. [Figure 2] Figure 2 is a cross-sectional view showing the structure of a photoelectric conversion device according to the first embodiment. [Figure 3] Figure 3 is an enlarged cross-sectional view illustrating the refraction of light incident on the electron transport region of the photoelectric converter according to the first embodiment. [Figure 4] Figure 4 is an enlarged cross-sectional view illustrating the case where light incident on the electron transport region of the photoelectric converter according to the first embodiment undergoes total internal reflection. [Figure 5] Figure 5 is an enlarged cross-sectional view showing the structure of the protrusion of the photoelectric converter according to the second embodiment. [Figure 6] Figure 6 is an enlarged cross-sectional view illustrating the refraction of light incident on the electron transport region of the photoelectric converter according to the second embodiment. [Figure 7] Figure 7 is an enlarged cross-sectional view illustrating the refraction of light incident on a projection of the photoelectric converter according to the second embodiment. [Figure 8] Figure 8 is an enlarged cross-sectional view showing the structure of the electron transport region of the photoelectric conversion device according to the third embodiment. [Figure 9] Figure 9 is a diagram illustrating electron affinity in a photoelectric conversion device according to the third embodiment. [Modes for carrying out the invention]

[0009] [First Embodiment] A first embodiment to which the present invention is applied will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals, and detailed descriptions are omitted.

[0010] [Structure of a photoelectric converter] The structure of the photoelectric converter according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a perspective view showing the structure of the photoelectric converter according to this embodiment, and Figure 2 is a cross-sectional view showing the structure of the photoelectric converter according to this embodiment. The photoelectric converter 1 is a solar cell with a hybrid structure combining an organic semiconductor and an inorganic semiconductor, and as shown in Figures 1 and 2, it comprises a photoactive layer 3 formed of an organic semiconductor material, an electron transport region 5 formed of an inorganic semiconductor material, an anode electrode 7, and a cathode electrode 9.

[0011] The photoactive layer 3 receives light from the outside on its upper surface, and the organic semiconductor material absorbs the light that enters the interior of the layer, generating bound electron-hole pairs called excitons.

[0012] The organic semiconductor materials that form the photoactive layer 3 are P3HT, P3OT, P3DDT, PTAA, MEH-PPV, MDMO-PPV, F8BT, F8T2, POT-co-DOT, p-DTS(FBTTh2)2, DR3TSBDT, Pd(PPh)4, benzoporphyrin, tetrabenzoporphyrin, phthalocyanine, tetracene, anthracene, triphenylene, pyrene, chrysene, tetrafen, perylene, coronene, hexabenzocoronene, PDI, PDIth, and PC. 60 BM, PC 61 BM, PC 70 BM, PC 71 BM, PC 84 BM, BisPC 60It contains at least one selected from BM, PCBB, PCBO, PNTz4T, PNOz4T, ThC60BM, d5-PCBM, SIMEF, PEDOT:PSS, MADN, N719, N3, N907, YD2-o-C8, MK-1, MK-2, TA-St-CA, MR-1, MR-2, MR-3, and derivatives thereof.

[0013] A plurality of electron transport regions 5 are provided inside the photoactive layer 3 and are formed in a columnar shape by extending from the lower surface to the upper surface of the photoactive layer 3, and transport electrons dissociated from excitons. As shown in FIG. 2, the upper end of the electron transport region 5 is not connected to the anode electrode 7 and is covered by the photoactive layer 3. On the other hand, the lower end of the electron transport region 5 is connected to the cathode electrode 9.

[0014] In addition, a protrusion 51 is provided at the tip of the electron transport region 5 where external light received on the upper surface of the photoactive layer 3 is incident. When the electron transport region 5 is a cylinder, the shape of the protrusion 51 is a cone, and when the electron transport region 5 is a quadrangular prism, the shape of the protrusion 51 is a quadrangular pyramid. However, since the protrusion 51 only needs to refract the incident light, it does not need to be limited to the shape of a cone or a quadrangular pyramid, and it may have a protrusion shape. Further, since the protrusion 51 is a part of the electron transport region 5, it is formed of the same inorganic semiconductor material as the electron transport region 5.

[0015] The inorganic semiconductor materials that form the electron transport region 5 are AlN, AlGaN, GaN, InGaN, InN, AlAs, AlGaAs, GaAs, InGaAs, InAs, AlP, AlGaP, GaP, GaAsP, GaAs, AlP, AlAsP, InAlAs, InAs, GaAsSb, GaSb, AlSb, AlGaSb, GaSb, AlSb, AlInSb, InSb, MgS, MgZnS, ZnS, MgS, MgSSe, MgSe The material comprises ZnS, ZnSSe, ZnSe, MgSe, MgZnSe, ZnSe, CuAlS2, CuAlSSe, CuAlSe2, CuAlS2, CuGaAlS2, CuGaS2, CuGaSSe, CuGaSe2, CuInGaS2, CuInS2, CuInSSe, CuInSe2, CuGaSe2, CuInGaSe2, MgSe, MgZnSeTe, and ZnTe, and at least one selected from these derivatives.

[0016] The anode electrode 7 is a transparent electrode formed on the upper surface of the photoactive layer 3 and functions as the positive electrode of the solar cell by outputting holes dissociated from excitons. The cathode electrode 9 is formed on the lower surface of the photoactive layer 3 and is connected to the electron transport region 5, so it functions as the negative electrode of the solar cell by outputting electrons dissociated from excitons.

[0017] In a photoelectric converter 1 with this structure, as shown in Figure 2, when external light is incident on the photoactive layer 3, the organic semiconductor material absorbs the light and generates bound electron-hole pairs called excitons. After this, the excitons reach the boundary between the photoactive layer 3 and the electron transport region 5, where electrons and holes dissociate at the interface between the inorganic semiconductor and the organic semiconductor. The dissociated carriers move through the inorganic semiconductor and the organic semiconductor, respectively, to the anode electrode 7 and the cathode electrode 9, thereby generating electricity. In other words, in the photoelectric converter 1, the organic semiconductor material absorbs light, the interface between the organic semiconductor material and the inorganic semiconductor material performs exciton dissociation to generate free carriers, and the inorganic semiconductor material transports electrons.

[0018] Here, since the natural diffusion distance of excitons generated in organic semiconductor materials is generally short, around tens of nanometers, electron transport regions 5 formed from inorganic semiconductor material are created in a columnar shape at nanoscale intervals to compensate for this short diffusion distance. This increases the probability that excitons generated at any position within the organic semiconductor material will reach the interface between the organic and inorganic semiconductor materials. Furthermore, the area of ​​the interface region between the organic and inorganic semiconductor materials is also increased, improving the exciton dissociation efficiency and, as a result, increasing the amount of electricity generated.

[0019] However, if the tip of the electron transport region 5 is flat as in the conventional case, light incident from directly above the electron transport region 5 will pass through the electron transport region 5 and will not contribute to power generation. In particular, as shown in Figure 1, if the volume of the columnar electron transport region 5 increases, the amount of light that passes through the inorganic semiconductor material increases, making it impossible to increase the amount of power generated.

[0020] Therefore, in the photoelectric converter 1 according to this embodiment, a projection 51 is provided at the tip of the electron transport region 5. By providing the projection 51, light incident from vertically above the electron transport region 5 is refracted when it enters the inclined surface of the projection 51, so that it can enter the photoactive layer 3 from the side of the electron transport region 5. As a result, it becomes possible to absorb the light incident from vertically above the electron transport region 5 with the organic semiconductor material of the photoactive layer 3 and use it for power generation.

[0021] Now, referring to Figure 3, we will explain how light incident from vertically above the electron transport region 5 is refracted when the projection 51 is provided. As shown in Figure 3, when the inclination angle of the slope of the projection 51 is θ, light incident from vertically above the electron transport region 5 is incident on the slope of the projection 51 at an incident angle θ1. In this case, the relationship given by equation (1) holds. Inclination angle θ=incident angle θ1... (1)

[0022] Then, when light incident on the electron transport region 5, it is refracted at a refraction angle θ2 when it is incident on the slope of the protrusion 51 and travels into the electron transport region 5. At this time, when the refractive index of the organic semiconductor material is n1 and the refractive index of the inorganic semiconductor material is n2, the relationship in equation (2) holds. n1·sinθ1= n2·sinθ2··· (2)

[0023] The light that has entered the electron transport region 5 exits from the side of the electron transport region 5 and enters the photoactive layer 3. This allows light incident from directly above the electron transport region 5 to be absorbed by the organic semiconductor material of the photoactive layer 3 and used for power generation. Therefore, by providing a projection 51 at the tip of the electron transport region 5, it becomes possible to use light for power generation that would not have been usable without the projection 51. In Figure 3, the cross-sectional shape of the projection 51 is triangular, but it does not need to be limited to a triangle as long as it refracts the incident light; any protruding shape is acceptable. Also, it does not need to be a single projection; multiple projections may be formed.

[0024] However, if the protrusion 51 is provided, total internal reflection may occur on the side surface of the electron transport region 5, as shown in Figure 4. Therefore, it is necessary to ensure that the total internal reflection condition is not met on the side surface of the electron transport region 5.

[0025] As shown in Figure 4, the angle of incidence to the side of the electron transport region 5 is 90°-θ1+θ2, so the total internal reflection condition is given by equation (3). n2·sin(90°-θ1+θ2)=n1··· (3)

[0026] Therefore, since the inclination angle θ = incidence angle θ1, if the inclination angle θ of the slope of the projection 51 is made larger than θ1 which satisfies equation (3), total internal reflection will not occur. By setting it in this way, the inclination angle θ of the slope of the projection 51 is set to an angle at which light incident from vertically above the electron transport region 5 does not undergo total internal reflection at the side surface of the electron transport region 5 after being refracted by the projection 51. Therefore, light incident from vertically above the electron transport region 5 can be refracted by the projection 51 and reliably incident onto the photoactive layer 3 from the side surface of the electron transport region 5.

[0027] [Effects of the First Embodiment] As described above, the photoelectric converter 1 according to this embodiment comprises a photoactive layer 3 made of an organic semiconductor material that receives external light on its upper surface and generates excitons, and an electron transport region 5 made of an inorganic semiconductor material that is formed in a columnar shape from the lower surface to the upper surface of the photoactive layer 3. A projection 51 is provided at the tip of the electron transport region 5 into which the external light received on the upper surface of the photoactive layer 3 is incident. As a result, even in a structure in which a columnar inorganic semiconductor is formed inside an organic semiconductor, the incident light can be refracted by the projection 51, thereby increasing the amount of incident light absorbed and improving the power generation efficiency.

[0028] In particular, by providing the protrusion 51, light incident from vertically above the electron transport region 5 can be refracted by the protrusion 51 and incident on the photoactive layer 3 from the side of the electron transport region 5. Therefore, light incident from vertically above the electron transport region 5, which would conventionally be transmitted, can be absorbed by the organic semiconductor material of the photoactive layer 3 and used for power generation, thereby increasing the amount of incident light absorbed and improving power generation efficiency.

[0029] Furthermore, in the photoelectric converter 1 according to this embodiment, the inclination angle of the slope of the projection 51 is set to an angle such that light incident from vertically above the electron transport region 5 does not undergo total internal reflection at the side surface of the electron transport region 5 after being refracted by the projection 51. This prevents total internal reflection of the light refracted by the projection 51, thereby increasing the amount of absorbed incident light and further improving power generation efficiency.

[0030] Furthermore, in the photoelectric conversion device 1 according to this embodiment, when the refractive indices of the organic semiconductor material and the inorganic semiconductor material are n1 and n2 respectively, and the incident angle of light incident from vertically above the electron transport region 5 is θ1, the refraction angle is θ2, and the inclination angle is θ, the inclination angle θ is greater than the value that satisfies the following equation. θ = θ1··· (1) n1·sinθ1= n2·sinθ2··· (2) n2·sin(90°-θ1+θ2) = n1··· (3) This prevents total internal reflection of light refracted by the projection 51, thereby increasing the amount of absorbed incident light and further improving power generation efficiency.

[0031] [Second Embodiment] A second embodiment to which the present invention is applied will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals, and detailed descriptions are omitted.

[0032] Figure 5 is a cross-sectional view showing the shape of the electron transport region 5 of the photoelectric converter 1 according to this embodiment. As shown in Figure 5, the difference from the first embodiment is that the inclination angle of the projection 51 is different in the central region and the outer peripheral region. The inclination angle of the central region of the projection 51 increases from the inclination angle of the outer peripheral region of the projection 51 towards the tip. That is, the inclination angle of the outer peripheral region of the projection 51 is constant, but in the central region the inclination angle gradually increases towards the tip. Therefore, the projection 51 of this embodiment has a pointed shape in the center.

[0033] In the first embodiment, the inclination angle of the projection 51 is set so that light incident from vertically above the electron transport region 5 does not undergo total internal reflection. As shown in Figure 6, light L1 incident from vertically above the electron transport region 5 does not undergo total internal reflection. However, if light L2 is incident at a larger angle of incidence than that from vertically above, total internal reflection is possible, as shown in Figure 6.

[0034] Therefore, in this embodiment, in order to prevent total internal reflection of light incident from diagonally above the electron transport region 5, the inclination angle of the central region of the projection 51 is formed to become sharper towards the tip, with the angle increasing towards the tip.

[0035] As a result, as shown in Figure 5, the light L2 incident from diagonally above is directed to the pointed tip of the projection 51. Consequently, as shown in the enlarged cross-sectional view of Figure 7, which is an enlargement of part A in Figure 5, the light L2 incident from diagonally above is refracted or reflected at the tip of the projection 51 and can be directed back into the photoactive layer 3.

[0036] [Effects of the second embodiment] As described in detail above, in the photoelectric conversion device 1 according to this embodiment, the inclination angle of the projection 51 differs between the central region and the outer peripheral region. The inclination angle of the central region of the projection 51 increases from the inclination angle of the outer peripheral region towards the tip. As a result, not only light incident from vertically above the electron transport region 5, but also light incident from diagonally above can be absorbed by the organic semiconductor material of the photoactive layer 3 and used for power generation. This increases the amount of incident light absorbed and further improves the power generation efficiency.

[0037] [Third Embodiment] A third embodiment to which the present invention is applied will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals, and detailed descriptions are omitted.

[0038] Figure 8 is a cross-sectional view showing the shape of the electron transport region 5 of the photoelectric converter 1 according to this embodiment. As shown in Figure 8, the photoelectric converter 1 according to this embodiment differs from the first embodiment in that a coating layer 80 is formed on the side surface of the electron transport region 5. The coating layer 80 is made of a material having a refractive index greater than that of the electron transport region 5.

[0039] By forming the coating layer 80 with a high refractive index on the side surface of the electron transport region 5 in this way, it is possible to reduce the possibility of total reflection on the side surface of the electron transport region 5. Therefore, as shown in FIG. 8, not only the light L1 incident vertically above the electron transport region 5 but also the light L2 incident obliquely upward can be prevented from total reflection on the side surface of the electron transport region 5. In FIG. 8, the case where the coating layer 80 is formed on the side surface of the electron transport region 5 of the first embodiment is illustrated, but it is also possible to form the coating layer 80 on the side surface of the electron transport region 5 of the second embodiment.

[0040] Further, the coating layer 80 has an electron affinity close to that of the electron transport region 5. If the electron affinity of the electron transport region 5 and the electron affinity of the coating layer 80 are different, when excitons generated in the photoactive layer 3 reach the interface between the photoactive layer 3 and the coating layer 80, electrons may not be dissociated.

[0041] However, as shown in FIG. 9, when the electron affinity B1 of the electron transport region 5 and the electron affinity B2 of the coating layer 80 are substantially equal, when the bound exciton 94 of the electron 90 and the hole 92 reaches the interface between the photoactive layer 3 and the coating layer 80, the electron 90 can be easily dissociated. Therefore, even if the coating layer 80 is formed on the side surface of the electron transport region 5, power generation can be performed in the same manner as when the coating layer 80 is not formed.

[0042] Specific materials for forming such a coating layer 80 include Al x Ga 1-x N, Al x In 1-x N, Al x Ga 1-x There are polycrystals such as As. By adjusting the value of x of such crystals, the electron affinity can be adjusted so that the electron affinity of the coating layer 80 is within a predetermined range of the electron affinity of the electron transport region 5.

[0043] [Effect of the Third Embodiment] As described in detail above, in the photoelectric converter 1 according to this embodiment, a coating layer 80 is formed on the side surface of the electron transport region 5, and the coating layer 80 is made of a material having a refractive index greater than that of the electron transport region 5. This reduces the possibility of total internal reflection at the side surface of the electron transport region 5, so that not only light incident from vertically above the electron transport region 5, but also light incident from diagonally above can be absorbed by the organic semiconductor material of the photoactive layer 3 and used for power generation. Therefore, the amount of absorbed incident light can be increased, and the power generation efficiency can be further improved.

[0044] The embodiments described above are merely examples of the present invention. Therefore, the present invention is not limited to the embodiments described above, and various modifications are possible in forms other than those described above, as long as they do not depart from the technical spirit of the present invention, depending on the design and other factors. [Explanation of symbols]

[0045] 1. Photoelectric converter 3 Photoactive layer 5 Electron transport area 7 Anode electrode 9 Cathode electrode 51 Protrusion 80 Coating layer 90 electron 92 holes 94 excitons

Claims

1. A photoactive layer formed from an organic semiconductor material that receives external light on its upper surface and generates excitons, It comprises an electron transport region formed of an inorganic semiconductor material, which is formed in a columnar shape from the lower surface to the upper surface of the photoactive layer, A projection is provided at the tip of the electron transport region into which external light received on the upper surface of the photoactive layer is incident. The photoelectric converter is configured such that the inclination angle of the slope of the projection is set to an angle at which light incident from vertically above the electron transport region does not undergo total internal reflection at the side surface of the electron transport region after being refracted by the projection.

2. When the refractive index of the organic semiconductor material is n1, the refractive index of the inorganic semiconductor material is n2, the angle of incidence of light incident on the protrusion from vertically above the electron transport region is θ1, the angle of refraction of light incident on the protrusion from vertically above the electron transport region is θ2, and the inclination angle is θ, The aforementioned inclination angle θ is, θ = θ1 ... (1) n1・sinθ1 = n2・sinθ2 ・・・ (2) n2・sin(90°−θ1+θ2) = n1... (3) A photoelectric conversion device according to claim 1, which is greater than the value satisfying the requirement.

3. The photoelectric conversion device according to claim 1 or 2, wherein the projection has different inclination angles in its central region and outer peripheral region, and the inclination angle of the central region increases from the inclination angle of the outer peripheral region towards the tip.

4. The photoelectric conversion device according to claim 1 or 2, wherein a coating layer is formed on the side surface of the electron transport region, and the coating layer is made of a material having a refractive index greater than that of the electron transport region.

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