JP5640952B2 - Organic thin film solar cell - Google Patents

Description

  The present invention relates to an organic thin film solar cell in which a concavo-convex sheet is disposed on a light incident side surface of a power generation element including a power generation layer made of an organic thin film.

  Conventionally, a power generation element 100 having a configuration shown in FIG. 24 is known as a solar cell. This power generation element 100 is formed by laminating a back electrode 101, a power generation layer 102 made of an organic thin film, a transparent electrode 103, and a light-transmitting substrate 104 in this order. In this configuration, when light is incident on the power generation element 100 from the substrate 104 side, the incident light is absorbed by the power generation layer 102 and converted into electric power, and is extracted from the back electrode 101 and the transparent electrode 103.

At this time, as shown in the figure, when considering the light L ₁₁ incident perpendicularly to the power generation element 100 from the outside, the light L ₁₁ is incident on the substrate 104 with almost no deflection on the surface of the substrate 104. Propagate as ₁₂ . A part of the light L ₁₂ is absorbed by the power generation layer 102, but the rest is not absorbed and is reflected as the light L ₁₃ . The light L ₁₃ is separated on the surface of the substrate 104 into light L ₁₄ reflected to the power generation layer 102 side by Fresnel reflection and light L ₁₅ transmitted through the substrate 104. Although the light L ₁₄ is used for power generation and enters the power generation layer 102 (photoelectric conversion in the power generation layer 102), light L ₁₅ is not used for power generation.

If the refractive index of the substrate 104 is about 1.5 like glass, the ratio of the light L ₁₄ to the light L ₁₅ is 4:96 in the case of substantially normal incidence as described above, and the light L ₁₃ Most of them will not be used for power generation.

  Therefore, in order to avoid such a decrease in light utilization efficiency (power generation efficiency), a solar cell 200 having a configuration shown in FIG. 25 is also conventionally known. In this solar cell 200, an uneven sheet 105 having the same refractive index as that of the substrate 104 is installed on the surface of the power generation element 100 in FIG. This configuration is equivalent to a configuration in which an uneven shape is formed on the surface of the substrate 104 without providing the uneven sheet 105.

In this configuration, the light L _{21 that} is vertically incident on the solar cell 200 from the outside is deflected by the uneven sheet 105 and is incident on the substrate 104 as the light L ₂₂ . A part of the deflected light L ₂₂ is absorbed by the power generation layer 102 and converted into electricity, but the rest is not absorbed by the power generation layer 102 and is reflected toward the substrate 104 as light L ₂₃ . In the absence of the concavo-convex sheet 105, most of the light L ₂₃ is transmitted through the substrate 104 and is not used for power generation. However, with the concavo-convex sheet 105, most of the light L ₂₃ is reflected by the concavo-convex surface 105 a of the concavo-convex sheet 105. The light L ₂₄ travels toward the power generation layer 102 side. The light L ₂₄ is absorbed by the second incidence on the power generation layer 102 and used for power generation. The remainder of the light L ₂₃ is refracted by the concave / convex surface 105a of the concave / convex sheet 105 and is emitted to the outside as the light L ₂₅ . Thereafter, most of the light that has entered the power generation layer 102 and has not been absorbed is repeatedly reflected between the power generation layer 102 and the concavo-convex sheet 105, so that most of the light is absorbed by the power generation layer 102.

  Further, for example, in Patent Document 1, the concavo-convex sheet is composed of a plurality of layers, and the refractive index of each layer is gradually reduced from the power generation layer side toward the light incident side (side away from the power generation layer). The light incident on the power generation element is lengthened and the confinement effect of stopping in the power generation element is obtained, so that the power generation efficiency is improved.

Japanese Patent Laying-Open No. 2005-340583 (refer to claim 2, paragraphs [0012] and [0037], FIG. 6 and the like)

  By the way, in general, the power generation layer cannot absorb incident light at one time, and light is incident on the power generation layer more obliquely than when light is incident on the power generation layer vertically. It is known that the amount of light absorption in the power generation layer increases because it propagates in an oblique direction inside. Such a tendency is more remarkable as the thickness of the power generation layer is reduced.

  In this regard, in the configuration of FIG. 25 and the configuration in which the refractive index of the concavo-convex sheet is set as in Patent Document 1, since the effect of deflecting incident light is small, the effect of increasing the amount of absorption in the power generation layer can be enhanced. Can not. In addition, if the refractive index of the light incident side layer of the concavo-convex sheet is the same as or smaller than that of the substrate of the power generation element, incident light is reflected by the power generation layer without being absorbed by the power generation layer for the first time. Even if it reaches the uneven surface, the confinement effect of returning the light to the power generation layer side is small because the reflectance of the reached light on the uneven surface is small. For this reason, the total light utilization efficiency (power generation efficiency) cannot be reliably increased.

  The present invention was made to solve the above problems, and its purpose is to enhance the effect of deflecting incident light with the concavo-convex sheet and enhance the effect of increasing the amount of absorption in the power generation layer, Organic thin-film solar that can increase the light confinement effect by increasing the reflectivity at the uneven surface of the light reflected by the power generation layer and incident on the uneven sheet, and increase the total light utilization efficiency To provide a battery.

  The organic thin-film solar cell of the present invention is a power generation element in which a plurality of layers including a power generation layer made of an organic thin film are stacked, and is installed on a light incident side surface of the power generation element, and a surface opposite to the power generation element It is an organic thin film solar cell provided with the uneven sheet which is an uneven surface, The refractive index of the uneven sheet is higher than the refractive index of the layer located in the most uneven sheet side of the power generating element. .

  According to said structure, compared with the structure whose refractive index of an uneven | corrugated sheet is the same or lower than the refractive index of the layer located in the most uneven | corrugated sheet side (light incident side) of an electricity generating element, an electricity generating element from an uneven | corrugated sheet The incident angle of light incident on the power generation layer can be increased, and the light incident on the power generation layer for the first time can be deflected to an incident angle that is easily absorbed by the power generation layer. As a result, the effect of increasing the amount of absorption of the first incident light in the power generation layer can be enhanced. In particular, when the power generation layer is thin, the effect can be significantly obtained.

  Moreover, even if incident light is not absorbed by the power generation layer for the first time and is reflected there, the ratio of the reflected light to be totally reflected by the concavo-convex surface of the concavo-convex sheet increases, and the light is returned to the power generation layer side. The confinement effect can be enhanced. As a result, the amount of light incident on the power generation layer after the second time can be increased, and the total light use efficiency (power generation efficiency) can be reliably increased.

  In the organic thin-film solar cell of the present invention, the power generation element includes a light-transmitting substrate for supporting the power generation layer as one of the plurality of layers, and the substrate includes the power generation layer. The element may be located closest to the concave-convex sheet, and the refractive index of the concave-convex sheet may be higher than the refractive index of the substrate.

  In this case, the effect of the present invention described above can be obtained in an organic thin-film solar cell having a configuration in which a light-transmitting substrate is positioned on the most uneven sheet side of the power generating element and the uneven sheet is installed on the substrate.

  In the organic thin-film solar cell of the present invention, the power generation element includes a substrate for supporting the power generation layer, and a light transmission that is positioned on the opposite side of the power generation layer from the substrate and protects the power generation layer. Each of the plurality of layers, and the protective layer is located closest to the concavo-convex sheet of the power generating element, and the refractive index of the concavo-convex sheet is The structure may be higher than the refractive index of the protective layer.

  In this case, the effect of the present invention described above can be obtained in the organic thin-film solar cell in which the light-transmitting protective layer is positioned on the most uneven surface side of the power generating element and the uneven sheet is installed on the protective layer. it can.

  In the organic thin-film solar cell of the present invention, the power generation layer has a thickness in which there is an incident angle range in which the amount of absorption of incident light is larger than the amount of absorption at the time of normal incidence. Also good.

  When the light absorption in the power generation layer increases in the oblique incidence than in the normal incidence, a concavo-convex sheet is provided to make the incident light obliquely incident on the power generation element and increase the absorption in the power generation layer. The configuration of the invention is effective. In particular, when the power generation layer is thin, the increase in the amount of absorption in the power generation layer is more significant in the oblique incidence than in the normal incidence, and thus the configuration of the present invention described above is very effective.

  In the organic thin film solar cell of the present invention, it is desirable that an antireflection mechanism for preventing surface reflection of incident light is provided on the uneven surface of the uneven sheet.

  When the refractive index of the concavo-convex sheet is increased, there is a concern that the light use efficiency (power generation efficiency) is reduced due to surface reflection when light enters the concavo-convex sheet from the outside. By providing an antireflection mechanism on the concavo-convex surface of the concavo-convex sheet, light loss due to surface reflection (Fresnel loss) can be reduced and light utilization efficiency can be increased.

  In the organic thin-film solar cell of the present invention, the antireflection mechanism may be an antireflection film composed of a dielectric multilayer film coated on the surface of the uneven surface. Moreover, the organic thin-film solar cell of this invention WHEREIN: The said reflection preventing mechanism may be comprised with the reflection preventing structure which roughened the surface of the said uneven surface.

  With such an antireflection film or antireflection structure, it is possible to reliably reduce the Fresnel loss on the concavo-convex surface and to improve the light utilization efficiency.

  In the organic thin-film solar cell of the present invention, the concavo-convex surface of the concavo-convex sheet is formed by two-dimensionally arranging unit structures that are convex on the side opposite to the power generation element or concave on the power generation element side. The unit structure may have any shape of a hemisphere including an elliptical hemisphere, a cone, a quadrangular pyramid, a truncated cone, and a truncated pyramid. Further, in the organic thin film solar cell of the present invention, the uneven surface of the uneven sheet is formed by arranging in parallel a unit structure that is convex on the side opposite to the power generating element or concave on the power generating element side. The unit structure may be in the form of a prism or a cylindrical lens.

  Regardless of the shape of the concavo-convex surface of the concavo-convex sheet, depending on the setting of the height of the concavo-convex surface, the light incident from the outside is largely deflected by the concavo-convex surface and incident obliquely on the power generation layer and absorbed. The effect of increasing the amount can be enhanced.

  By setting the refractive index of the concavo-convex sheet as in the present invention, the incident angle of light incident on the power generation element from the concavo-convex sheet is increased, and the amount of absorption of light incident on the power generation layer in the first time is increased. Can be increased. In addition, the light that is reflected by the power generation layer without being absorbed by the power generation layer for the first time is returned to the power generation layer side by total reflection on the concave and convex surface of the concave and convex sheet, and the light that is incident on the power generation layer after the second time. The amount of absorption can be increased. As a result, the total light use efficiency can be reliably increased.

It is explanatory drawing which shows the schematic structure of the solar cell which concerns on embodiment of this invention. It is explanatory drawing which shows the detail of the optical path when light injects into the uneven | corrugated sheet | seat with which the said solar cell is provided substantially perpendicularly from the outside. It is sectional drawing which shows the structural example of the said uneven | corrugated sheet. It is a top view of the said uneven | corrugated sheet. It is explanatory drawing which shows the degree of the deflection | deviation of the light inside the said uneven | corrugated sheet | seat when light injects into the uneven | corrugated sheet of a reference example substantially perpendicularly. It is explanatory drawing which shows the degree of the deflection | deviation of the light inside the said uneven | corrugated sheet | seat when light injects into the uneven | corrugated sheet | seat of the said embodiment substantially perpendicularly. It is explanatory drawing which shows the degree of deflection | deviation of the light in the said uneven | corrugated sheet and the said board | substrate when the uneven | corrugated sheet | seat of FIG. 6 is installed on a board | substrate, and light injects into the said uneven | corrugated sheet substantially perpendicularly. It is a graph which shows the incident angle dependence of the light absorption amount in the electric power generation layer of the said solar cell. It is explanatory drawing which shows the optical path of the light reflected without being absorbed in the electric power generation layer in the uneven | corrugated sheet | seat of a reference example. It is explanatory drawing which shows the optical path of the light reflected without being absorbed in the electric power generation layer in the uneven | corrugated sheet | seat of the said embodiment. It is a graph which shows the relationship between the refractive index of the said uneven | corrugated sheet | seat, and the reflectance in the uneven | corrugated surface of the light which injected from the board | substrate side. It is sectional drawing of the uneven | corrugated sheet | seat which provided the antireflection film in the uneven | corrugated surface as an antireflection mechanism. It is sectional drawing of the uneven | corrugated sheet | seat which provided the antireflection structure in the uneven surface as an antireflection mechanism. (A) is sectional drawing which shows the other structure of the uneven | corrugated sheet of the said embodiment, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). (A) is sectional drawing which shows other structure of the said uneven | corrugated sheet, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). (A) is sectional drawing which shows other structure of the said uneven | corrugated sheet, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). (A) is sectional drawing which shows other structure of the said uneven | corrugated sheet, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). (A) is sectional drawing which shows other structure of the said uneven | corrugated sheet, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). (A) is sectional drawing which shows other structure of the said uneven | corrugated sheet, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). (A) is sectional drawing which shows other structure of the said uneven | corrugated sheet, (b) is a top view of the uneven | corrugated sheet | seat of the same figure (a). It is explanatory drawing which shows the relative ratio for every incident angle of the light which injects into the said uneven | corrugated sheet | seat perpendicularly | vertically, and injects into the electric power generation layer, when the uneven | corrugated surface of an uneven | corrugated sheet is hemispherical shape. It is explanatory drawing which shows the relative ratio for every incident angle of the light which injects into the said uneven | corrugated sheet | seat perpendicularly | vertically, and injects into an electric power generation layer, when the uneven | corrugated surface of an uneven | corrugated sheet is cone shape. It is explanatory drawing which shows the other structure of the said solar cell. It is explanatory drawing which shows the schematic structure of the electric power generation element as a conventional solar cell. It is explanatory drawing which shows the other structure of the conventional solar cell.

  An embodiment of the present invention will be described below with reference to the drawings.

(About organic thin film solar cells)
FIG. 1 is an explanatory diagram showing a schematic configuration of an organic thin film solar cell (hereinafter simply referred to as a solar cell) 1 of the present embodiment. The solar cell 1 of the present embodiment includes a power generation element 2 and an uneven sheet 3. The concavo-convex sheet 3 is installed on the light incident side surface of the power generation element 2, and the surface opposite to the power generation element 2 is a concavo-convex concavo-convex surface 3 a. In addition, the detail of the uneven | corrugated sheet | seat 3 is mentioned later.

  The power generating element 2 is configured by laminating a plurality of layers. Specifically, the power generation element 2 is configured by laminating a back electrode 11, a power generation layer 12, a transparent electrode 13, and a substrate 14 in this order. The back electrode 11, the power generation layer 12, the transparent electrode 13, and the substrate 14 constitute independent layers, and the power generation element 2 is constituted by these plural layers.

  The power generation layer 12 is a photoelectric conversion layer that receives light and converts it into electric power (electricity). In the present embodiment, the power generation layer 12 is composed of an organic thin film. More specifically, the power generation layer 12 is configured by stacking a P layer, an I layer, and an N layer in this order. The P layer is composed of a p-type organic semiconductor material, the I layer is composed of a mixed layer of a p-type organic semiconductor material and an n-type organic semiconductor material, and the N layer is composed of an n-type organic semiconductor material. . In the p-type organic semiconductor material, holes contribute to electric conduction, and in the n-type organic semiconductor material, electrons contribute to electric conduction. For example, P3HT (poly-3-hexylthiophene) can be used as the p-type organic semiconductor material, and PCBM (6,6-phenyl-C61-butyric acid methyl ester) can be used as the n-type organic semiconductor material, for example. Can be used.

  When light is incident on the power generation layer 12, excitons (electrons and holes) are generated, and electrons are collected on the N layer side and holes are collected on the P layer side, so that a potential difference is generated between the back electrode 11 and the transparent electrode 13. Therefore, a current corresponding to the potential difference can be taken out through the back electrode 11 and the transparent electrode 13.

  The back electrode 11 and the transparent electrode 13 are electrodes for taking out the electric power generated in the power generation layer 12, and one corresponds to the positive electrode and the other corresponds to the negative electrode. The back electrode 11 is made of, for example, aluminum, and the transparent electrode 13 is made of, for example, ITO (Indium Tin Oxide). The substrate 14 is a light transmissive transparent substrate for supporting the power generation layer 12 and is made of, for example, glass. In the present embodiment, the substrate 14 is located closest to the light incident side in the power generation element 2, that is, closest to the uneven sheet 3.

In the above configuration, light (sunlight) L ₁ incident from the outside substantially perpendicular to the solar cell 1 is deflected by the uneven sheet 3 and enters the substrate 14 as light L ₂ . The light L ₂ passes through the transparent electrode 13 and enters the power generation layer 12. A part of the light L ₂ is absorbed by the power generation layer 12 and converted into electricity, but the remaining light is not completely absorbed by the power generation layer 12. It is reflected toward the substrate 14 side as L _3. Of the light L _2, light transmitted through the power generation layer 12 is returned to the power generation layer 12 side is reflected by the back surface electrode 11, reuse is achieved.

In the absence of the uneven sheet 3, most of the light L ₃ passes through the substrate 14 and is not used for power generation. However, since the uneven sheet 3 is present, most of the light L ₃ is reflected by the uneven surface 3 a of the uneven sheet 3. The light L ₄ travels toward the power generation layer 12 side. The light L ₄ is absorbed by the second incidence on the power generation layer 12 and used for power generation. Thereafter, the light that has entered the power generation layer 12 and has not been completely absorbed can be mostly absorbed by the power generation layer 12 by being repeatedly reflected between the power generation layer 12 and the uneven sheet 3 (uneven surface 3a). The

(About uneven sheet)
Next, details of the uneven sheet 3 will be described. In the present embodiment, the refractive index of the concavo-convex sheet 3 is set to be higher than the refractive index of the layer located closest to the concavo-convex sheet 3 of the power generation element 2. That is, as in the present embodiment, when the layer located closest to the concave-convex sheet 3 of the power generating element 2 is the substrate 14, the refractive index of the glass constituting the substrate 14 is 1.52, for example. Is made of a material having a refractive index larger than 1.52. As a material constituting such an uneven sheet 3, for example, polycarbonate (PC; refractive index 1.59) and epoxy resin (refractive index; 1.55 to 1.61) can be used. Further, as the concavo-convex sheet 3, a resin having a high refractive index (refractive index: 1.8) (for example, an organic-inorganic mixed material containing inorganic (TiO ₂ or the like) fine particles having a high refractive index) can be used.

FIG. 2 shows the details of the optical path when the light L ₁ is incident on the concavo-convex sheet 3 from the outside substantially perpendicularly. Since the refractive index of the concavo-convex sheet 3 is larger than the refractive index of the substrate 14, the light incident on the interface with the substrate 14 from the concavo-convex sheet 3 side in the light L ₂ and the light L ₄ , Refracts according to the law of The light L ₅ represents passes through the uneven surface 3a of the uneven sheet 3 among the light L _3, which represents the light that is not used for power generation.

According to the configuration of the present embodiment, compared with the conventional configuration of FIG. 25 and the configuration of Patent Document 1, (1) the deflection angle when substantially perpendicular incident light is incident on the concavo-convex sheet 3 (the deflection angle of the light L ₂ ). ) Is large, and (2) the ratio of light L ₃ that cannot be absorbed by the power generation layer 12 is reflected again by the uneven surface 3 a and reused as light L ₄ (light is incident on the power generation layer 12 a second time). The amount of light absorbed can be increased), and higher light utilization efficiency than before can be realized. Hereinafter, the above points (1) and (2) will be described in more detail.

(About increasing the deflection angle)
FIG. 3 is a cross-sectional view showing a configuration example of the concavo-convex sheet 3, and is a cross-sectional view when the concavo-convex surface 3a is formed by two-dimensionally arranging an elliptical hemisphere. The elliptical hemisphere refers to a shape obtained by cutting a solid obtained by rotating an ellipse with a major axis or a minor axis as a rotation axis along a plane perpendicular to the major axis or the minor axis. When the height from the bottom of the elliptical hemisphere is h (cm) and the period (pitch) in the arrangement direction is d (cm), the aspect ratio a is defined as a = h / d. One of the height h and the period d of the elliptical hemisphere corresponds to half the length of the major axis (or minor axis) of the ellipse, and the other corresponds to the length of the minor axis (or major axis) of the ellipse. . When a = 0.5, the elliptical hemisphere has a perfect hemispherical shape (a hemispherical shape with a perfect cross section).

  If the height h is considered as a height corresponding to the height difference between the convex portion and the concave portion of the uneven surface 3a, and the period d is considered as a repetition period of the convex portion or the concave portion of the uneven surface 3a, The aspect ratio definition described above can be used regardless of the shape of the surface 3a described later.

FIG. 4 is a plan view of the uneven sheet 3. In FIG. 4, when the uneven portion 3a ₁ is the uneven portion 3a _{1 and} the flat portion other than the uneven portion 3a ₁ is 3a ₂ , the ratio S occupied by the flat portion 3a ₂ in the uneven surface 3a is the ratio S of the uneven portion 3a ₁ . The area is represented by S = (S2 / (S1 + S2)), where S1 (cm ² ) and the area of the planar portion 3a ₂ is S2 (cm ² ). For example, as shown in FIG. 4, when the respective elliptical hemispheres are two-dimensionally arranged so that the outer circumferences (circular in plan view) of the elliptical hemispheres are in contact with each other, S is about 0.09 (9%).

FIG. 5 is a reference example and is an explanatory diagram showing the degree of light deflection inside the concavo-convex sheet 3 ′ when light is incident substantially perpendicularly on the concavo-convex sheet 3 ′ having the same refractive index as the substrate 14. . 5, the refractive index of the concave-convex sheet 3 'and n1, a deflection angle at which the incident light is deflected by refraction at the ellipse hemisphere and theta _1. As shown in FIG. 5, the deflection angle θ ₁ is maximized when light is incident on a portion where the incident angle with respect to the elliptical uneven surface 3 b is approximately 90 °. In other words, the maximum value of the deflection angle θ ₁ is from Snell's law:
1 · sin (90 °) = n1 · sin (90 ° −θ ₁ )
It is a value that satisfies Thus, for example, when n1 = 1.5, the maximum value of the deflection angle theta ₁ is about 48 °.

  That is, when the uneven surface 3b is formed by two-dimensionally arranging an elliptical hemisphere as shown in FIG. 5, light incident on the uneven sheet 3 ′ substantially perpendicularly is 0 to 48 ° by the uneven sheet 3 ′. The angle is deflected (the deflection angle varies depending on the incident position with respect to the uneven surface).

FIG. 6 is an explanatory diagram showing the degree of light deflection inside the concavo-convex sheet 3 when light is incident substantially perpendicularly on the concavo-convex sheet 3 having a refractive index larger than that of the substrate 14 as in the present embodiment. . 6, the refractive index of the concave-convex sheet 3 and n2, the deflection angle at which the incident light is deflected by refraction at the ellipse hemisphere and theta _2. As shown in FIG. 6, the deflection angle θ ₂ is maximized when light is incident on a portion where the incident angle with respect to the elliptical uneven surface 3a is approximately 90 °. In other words, the maximum value of the deflection angle θ ₂ is from Snell's law:
1 · sin (90 °) = n2 · sin (90 ° −θ ₂ )
It is a value that satisfies Thus, for example, when n2 = 1.8, the maximum value of the deflection angle theta ₂ is about 56 °.

  That is, in the case of n1 <n2, θ1 <θ2, and if the refractive index of the uneven sheet 3 is high, incident light can be largely deflected. When the uneven surface 3a is a cone, a quadrangular pyramid, or a prism shape, the substantially perpendicular incident light is deflected at one angle within a range of 0 to 56 ° (the deflection angle is concentrated at one angle). However, this point will be described later.

FIG. 7 shows the degree of light deflection inside the concavo-convex sheet 3 and the substrate 14 when the concavo-convex sheet 3 of FIG. 6 is installed on the substrate 14 and light is incident on the concavo-convex sheet 3 substantially perpendicularly. It is explanatory drawing. 7, the refractive index of the concave-convex sheet 3 and n2 (= 1.8), the deflection angle at which the incident light is deflected by refraction at the ellipse hemisphere and theta _2, the refractive index of the substrate 14 n1 (= 1. 5), and the deflection angle of light in the substrate 14 is θ ₃ . The maximum value of the deflection angle θ ₂ is the same as in the case of FIG. 6 (about 56 °), and from Snell's law,
n2 · sin θ ₂ = n1 · sin θ ₃
Holds. From this equation, the maximum value of the deflection angle θ ₃ within the substrate 14 is about 84 °. That is, since the refractive index n1 of the substrate 14 is lower than the refractive index of the concave-convex sheet 3, the maximum value of the deflection angle theta ₃ of in the substrate 14 is larger than the maximum value of the deflection angle theta _2.

Although not shown, when the refractive index of the substrate 14 is higher than the refractive index of the concave-convex sheet 3, contrary to the above, the maximum value of the deflection angle theta ₃ of in the substrate 14, the deflection angle theta ₂ It is clear from Snell's law that it is smaller than the maximum value.

  From the above, it can be said that the incident light can be largely deflected in the substrate 14 by disposing the uneven sheet 3 having a refractive index higher than that of the substrate 14 on the substrate 14. Thereby, the amount of light absorption in the power generation layer 12 can be increased, and the effect can be enhanced as compared with the conventional case. Here, the effect of increasing the light absorption amount of the power generation layer 12 becomes higher as the power generation layer 12 is thinner. Hereinafter, the relationship between the thickness of the power generation layer 12 and the amount of absorption will be described.

FIG. 8 is a graph showing the incident angle dependence of the amount of light absorption in the power generation layer 12 when the power generation layer 12 is thin (for example, layer thickness 100 nm) and thick (for example, layer thickness 300 nm). In FIG. 8, the short-circuit current density Jsc (mA / cm ² ) on the vertical axis is a short-circuit current generated per unit area of the solar cell (a state in which the positive and negative electrodes of the solar cell are connected by a conductive wire and are short-circuited) Current). The amount of light absorption in the power generation layer 12 and the short-circuit current density Jsc are in a correspondence relationship. When the amount of absorption in the power generation layer 12 increases, the short-circuit current density Jsc also increases.

  From FIG. 8, when the power generation layer 12 is made sufficiently thick, the power generation layer 12 absorbs the maximum amount without depending on the internal angle, but the power generation layer 12 is thin and cannot absorb light at one time. In this case, if the light is incident on the power generation layer 12 at an angle, the amount of absorption increases because light propagates in the power generation layer 12 in an oblique direction. When the power generation layer 12 is thin, the short-circuit current density Jsc (absorption amount) becomes maximum when the incident angle is about 60 °, which is about 1.3 times as large as that of the normal incidence (incident angle 0 °).

  Here, as shown in FIG. 5, in the configuration using the concavo-convex sheet 3 ′ having the same refractive index (for example, 1.5) as that of the substrate 14, the light is deflected by about 48 ° at the maximum as described above. Cannot be deflected to 60 ° (the angle at which the absorption amount becomes maximum when the power generation layer 12 is thin) by one deflection. For this reason, when the power generation layer 12 is thin, the amount of absorption in the power generation layer 12 cannot be increased.

  However, as shown in FIG. 7, by setting the refractive index of the concavo-convex sheet 3 to 1.8 and higher than the refractive index (1.5) of the substrate, the deflection angle in the substrate 14 is set to 0 ° to 84 °, which includes a deflection angle of 60 ° at which the absorption is maximized. Therefore, by devising the shape design (for example, aspect ratio) of the concavo-convex sheet 3 and deflecting a large amount of light so that the incident angle with respect to the power generation layer 12 is about 60 °, It becomes possible to increase the amount of absorption of incident light.

  When the power generation layer 12 is thick, the degree of increase in the amount of absorption due to the oblique incidence on the power generation layer 12 is smaller than that in the case where the power generation layer 12 is thin as shown in FIG. Will continue to increase. Therefore, if the thickness of the power generation layer 12 is such that there is an incident angle range in which the amount of absorption of incident light once is greater than the amount of absorption when it is perpendicularly incident (incidence angle 0 °). The concavo-convex sheet 3 having a high refractive index can increase the amount of absorption in the power generation layer 12 by deflecting the incident light at an angle such that the amount of absorption in the power generation layer 12 is larger than that in normal incidence. It can be said.

(About an increase in the amount of absorption of light incident on the power generation layer 12 after the second time)
FIG. 9 is an explanatory diagram showing the optical path of the light L ₃ reflected without being absorbed by the power generation layer 12 inside the concavo-convex sheet 3 ′ having a refractive index of 1.5. The light L ₃ is incident on the concavo-convex surface 3 b of the concavo-convex sheet 3 ′, and is divided into light L _{5 that} is refracted and transmitted by Snell's law and light L ₄ that is reflected by the structure of the concavo-convex surface 3 b.

On the other hand, FIG. 10 is an explanatory view showing the optical path of the light L ₃ reflected without being absorbed by the power generation layer 12 inside the concavo-convex sheet 3 having a refractive index of 1.8. The light L ₃ is incident on the concavo-convex surface 3 a of the concavo-convex sheet 3, and is divided into light L _{5 that} is refracted and transmitted according to Snell's law and light L ₄ that is reflected by the structure of the concavo-convex surface 3 a. At this time, since the refractive index of the concave-convex sheet 3 is high and 1.8, of the light L ₃ incident on the uneven surfaces 3a, satisfies the total reflection condition light in uneven surface 3a is increased. Light repeatedly totally reflected in the convex shape of the uneven surface 3a ultimately becomes light L ₄ back to the substrate 14 and the power generation layer 12 side.

Here, in the concavo-convex sheet 3 having the concavo-convex surface 3a, the ratio of the light incident on the concavo-convex surface 3a from the substrate 14 side (reflectance R) is a function of the refractive index n of the concavo-convex sheet 3 (R = 1-1). / N ² ) was found by numerical calculation or the like. That is, FIG. 11 shows the relationship between the refractive index n of the concavo-convex sheet 3 and the reflectance R at the concavo-convex surface 3a of light incident from the substrate 14 side. Although there are some numerical differences depending on the concavo-convex shape of the concavo-convex sheet 3 (elliptical hemisphere, cone, quadrangular pyramid), the reflectance R tends to increase as the refractive index n increases in each structure. In addition, the relationship between the refractive index n and the reflectance R is asymptotic to a function of R = 1−1 / n ² , and the higher the refractive index n of the concavo-convex sheet 3, the higher the reflectance R becomes. It was found that the light incident on layer 12 for the second time increased.

(Summary)
As described above, in the solar cell 1, the refractive index of the concavo-convex sheet 3 is higher than the refractive index of the layer (substrate 14 in the above example) located closest to the concavo-convex sheet 3 of the power generation element 2. The incident angle of the light incident on the power generation layer 12 can be increased, and the light incident on the power generation layer 12 at the first time has an incident angle with a large amount of absorption in the power generation layer 12 (incidence angle at which the power generation layer 12 is easily absorbed). Can be deflected. Thereby, the effect of increasing the absorption amount of the light incident on the power generation layer 12 at the first time can be enhanced. In particular, when the power generation layer 12 is thin, the amount of absorption in the power generation layer 12 is significantly increased in the oblique incidence than in the normal incidence, and thus the above-described effect is further enhanced.

  Further, since the refractive index of the concavo-convex sheet 3 is high, even if incident light is reflected by the power generation layer 12 without being absorbed by the power generation layer 12 for the first time, the reflected light is totally reflected by the concavo-convex surface 3 a of the concavo-convex sheet 3. Since the ratio (reflectance R) to increase increases, the confinement effect which returns the said light to the electric power generation layer 12 side can be heightened. As a result, the amount of light incident on the power generation layer 12 after the second time can be increased, and the total light use efficiency (power generation efficiency) can be reliably increased.

  Note that the higher the refractive index n, the higher the reflectance R due to the relationship between the refractive index n and the reflectance R of the concavo-convex sheet 3 shown in FIG. The higher the value, the larger

  Further, in the power generation element 2, in the configuration in which the substrate 14 is located closest to the concave and convex sheet 3, the refractive index of the concave and convex sheet 3 is higher than the refractive index of the substrate 14, so in the solar cell 1 having such a configuration, The effect mentioned above can be acquired.

  Further, as shown in FIG. 8, the power generation layer 12 has such a thickness that there is an incident angle range in which the amount of absorption of incident light once is larger than the amount of absorption at the time of vertical incidence. Therefore, in order to increase the amount of absorption in the power generation layer 12, the configuration of the present embodiment in which the uneven sheet 3 having a high refractive index is provided and the incident light is obliquely incident on the power generation element 2 is very effective. .

(Supplement)
Increasing the height h of the uneven surface 3a of the uneven sheet 3 can increase the incident angle of light incident on the power generation layer 12 through the uneven surface 3a. Therefore, by adjusting the height of the concavo-convex surface 3 a together with the adjustment of the refractive index of the concavo-convex sheet 3, the deflection angle can be efficiently adjusted to the incident angle with a large amount of absorption in the power generation layer 12. Can do.

  Further, for example, depending on the refractive index of the concavo-convex sheet 3, the angle that can be deflected once by the concavo-convex sheet 3 may not reach the incident angle (for example, 60 °) at which the amount of absorption at the power generation layer 12 is large. is there. Even in such a case, by adjusting the height of the concavo-convex surface 3a, the deflection angle can be changed to an incident angle with a large amount of absorption in the power generation layer 12 without replacing with the concavo-convex sheet 3 having a higher refractive index. Can be matched.

(Antireflection mechanism)
The advantages of making the refractive index of the concavo-convex sheet 3 higher than that of the substrate 14 are as described above. However, if the refractive index of the concavo-convex sheet 3 is increased, surface reflection when light enters the concavo-convex sheet 3 from the outside (Fresnel reflection). Loss (decrease in light utilization efficiency). Therefore, as shown in FIGS. 12 and 13, it is desirable to provide an antireflection mechanism 20 for preventing the surface reflection of incident light on the uneven surface 3 a of the uneven sheet 3.

  FIG. 12 is a cross-sectional view of the concavo-convex sheet 3 when the antireflection mechanism 20 is configured by the antireflection film 21, and FIG. 13 is a cross section of the concavo-convex sheet 3 when the antireflection film 20 is configured by the antireflection structure 22. FIG. The antireflection film 21 is a dielectric multilayer film coated on the surface of the uneven surface 3a. The antireflection structure 22 is a structure in which the surface of the uneven surface 3a is further roughened into an uneven shape. Such an antireflection structure 22 is formed on the uneven surface 3a if the unevenness formed on the surface of the uneven surface 3a faces in one direction (for example, a direction perpendicular to the interface between the uneven sheet 3 and the substrate 14). It can be realized by devising the shape of the mold used sometimes.

  Thus, by providing the anti-reflection mechanism 20 on the uneven surface 3 a of the uneven sheet 3, light loss (Fresnel loss) due to surface reflection at the uneven surface 3 a is reduced, and incident on the power generation layer 12. The amount of light and the amount of absorption can be increased, and the light utilization efficiency (power generation efficiency) can be increased.

  In addition, by configuring the antireflection mechanism 20 with the antireflection film 21 or the antireflection structure 22, it is possible to reliably reduce the Fresnel loss on the uneven surface 3a and to reliably increase the light utilization efficiency.

  In particular, in the case of photovoltaic power generation, it is necessary to enhance the antireflection effect in a very wide wavelength region and incident angle. In the antireflection film 21, in order to enhance the antireflection effect in a wide wavelength region, a film configuration (material) , The number of layers, etc.) becomes complicated. In this regard, in the antireflection structure 22, the formation pitch and the height difference of the concave portions or the convex portions constituting the antireflection structure 22 are determined according to the use wavelength, that is, the wavelength range of light that is photoelectrically converted by the power generation layer 12 (for example, 400 nm to 400 nm). 700 nm) (for example, a pitch of 200 nm or less, a height difference of 200 nm or more and less than 400 nm), an effect of reducing the Fresnel loss can be obtained even when the wavelength range of incident light is wide and the incident angle range is wide. Can do. Therefore, it is desirable to use the antireflection structure 22 as the antireflection mechanism 20.

(Example)
Next, regarding the relationship between the thickness of the power generation layer 12 of the solar cell 1, the presence or absence of the uneven sheet 3, the refractive index of the uneven sheet 3, the presence or absence of the antireflection structure 22, and the short-circuit current density generated in the power generation layer 12 This will be described as Examples 1 to 4. Moreover, Comparative Examples 1-3 are also shown for the comparison with Examples 1-4. In addition, all the uneven | corrugated surface 3a of the uneven | corrugated sheet | seat 3 shall be formed by the two-dimensional arrangement | positioning of the elliptical hemisphere. Moreover, the refractive index of the board | substrate 14 with which the uneven | corrugated sheet | seat 3 is installed was 1.52.

  Comparative Examples 1 and 2 and Examples 1 and 2 show the results when the thickness of the power generation layer 12 is as thin as 100 nm. On the other hand, Comparative Example 3 and Examples 3 and 4 show the results when the thickness of the power generation layer 12 is relatively thick at 300 nm. From these comparative examples and examples, whether the power generation layer 12 is thick or thin, the short-circuit current density is increased by providing the concavo-convex sheet 3 having a refractive index higher than that of the substrate (refractive index; 1.52). It was found that the short-circuit current density is further increased by providing the antireflection structure 22.

(Regarding variations in uneven surface shape)
14-20 shows the variation of the shape of the uneven surface 3a of the uneven sheet 3, (a) shows sectional drawing of the uneven sheet 3, (b) is the plane of the uneven sheet 3 The figure is shown. The shape of the concavo-convex surface 3a of the concavo-convex sheet 3 is not limited to that formed by a two-dimensional arrangement of elliptical hemispheres.

  That is, as shown in FIGS. 14A and 14B, the uneven surface 3a may be formed by two-dimensionally arranging a hemisphere having a perfect cross section. Moreover, as shown to Fig.15 (a) (b), the uneven surface 3a may be formed by arrange | positioning a cone two-dimensionally. Moreover, as shown to Fig.16 (a) (b), the uneven surface 3a may be formed by arrange | positioning a quadrangular pyramid two-dimensionally. Moreover, as shown to Fig.17 (a) (b), the uneven surface 3a may be formed by arrange | positioning a truncated cone two-dimensionally. Moreover, as shown to Fig.18 (a) (b), the uneven surface 3a may be formed by arrange | positioning a square pyramid two-dimensionally. Further, as shown in FIGS. 19A and 19B, the uneven surface 3a may be formed by providing in parallel prisms extending in one direction (for example, triangular prisms having a triangular cross section). Further, as shown in FIGS. 20A and 20B, the uneven surface 3a may be formed by providing in parallel a cylindrical lens extending in one direction.

  In any of the above-described configurations, by appropriately setting the height of the uneven surface 3a (the difference in height between the concave portion and the convex portion), the light incident from the outside is largely deflected by the uneven surface 3a to generate power. It is possible to increase the effect of increasing the amount of absorption in the power generation layer 12 by entering the layer 12 obliquely. Also,

  FIG. 21 shows a relative ratio (light distribution) for each incident angle of light that is perpendicularly incident on the uneven sheet 3 and incident on the power generation layer 12 when the uneven surface 3a is hemispherical. Yes. Here, as the above-described hemispherical shape, both a hemisphere having a perfect cross section and a hemisphere having an elliptic cross section are shown.

  When the uneven surface 3a has a hemispherical shape, the direction of refraction differs depending on the incident position of the incident light with respect to the uneven surface 3a. Therefore, as shown in FIG. 21, the incident angle of the light incident on the power generation layer 12 can be distributed. it can. Thereby, light can be incident on the power generation layer 12 in a wide incident angle range, and the amount of absorption in the power generation layer 12 can be increased.

  FIG. 22 shows a relative ratio (light distribution distribution) for each incident angle of light that is perpendicularly incident on the uneven sheet 3 and incident on the power generation layer 12 when the uneven surface 3a has a conical shape. Yes. As shown in FIG. 22, when the uneven surface 3a is formed as a cone, the incident angle of the light with respect to the power generation layer 12 is concentrated at almost one angle. That is, incident light can be concentrated and deflected in one direction by refraction at the concavo-convex surface 3a. Moreover, by changing the aspect ratio a (= h / d) of the concavo-convex surface 3a, the concentrated incident angle can be changed. Thereby, in addition to the adjustment of the refractive index of the concavo-convex sheet 3 described above, by setting the aspect ratio a of the concavo-convex surface 3a so as to match the incident angle at which the power generation layer 12 absorbs a large amount, It is possible to increase the light absorption efficiency.

  Such an effect can be obtained in the same manner even when the uneven surface 3a is formed by a conical system other than a cone (for example, a quadrangular pyramid) or by a parallel arrangement of prisms.

Note that in FIG. 21 and FIG. 22, the high proportion of the incident angle of 0 ° is due to the uneven surface 3a has a flat portion (corresponding to the flat portion 3a ₂ of FIG. 4). In other words, when the uneven surface 3a is formed by two-dimensionally arranging hemispheres and cones, a flat portion can be formed between the adjacent hemispheres and cones, no matter how densely they are arranged. When light enters the plane portion perpendicularly, the light is not deflected by the plane portion and enters the power generation layer 12 perpendicularly (with an incident angle of 0 °). For this reason, in FIGS. 21 and 22, the ratio at an incident angle of 0 ° is high.

  In addition, in the above, the shape of the uneven surface 3a is a hemispherical convex shape (an elliptical hemispherical convex shape, a perfect circular hemispherical convex shape), a conical convex shape, a quadrangular pyramid convex shape, a truncated cone convex shape, a quadrangular pyramid convex shape, a prism convex shape. The case where the shape is a cylindrical convex shape has been described, but the concave and convex shape opposite to the above, that is, a hemispherical concave shape (an elliptical hemispherical concave shape, a perfect circular hemispherical concave shape), a conical concave shape, a quadrangular pyramidal concave shape, a truncated cone Even in the concave shape, the truncated pyramid shape, the prism concave shape, and the cylindrical concave shape, the same tendency as in the convex shape is exhibited.

  Therefore, in summary of the above, the concavo-convex surface 3a of the concavo-convex sheet 3 is formed by two-dimensionally arranging unit structures that are convex on the opposite side of the power generation element 2 or concave on the power generation element 2 side. Thus, it can be said that the unit structure may have any shape of a hemisphere including an elliptical hemisphere, a cone, a quadrangular pyramid, a truncated cone, and a truncated pyramid. Further, the uneven surface 3a of the uneven sheet 3 is formed by arranging in parallel a unit structure that is convex on the opposite side of the power generation element 2 or concave on the power generation element 2 side. Or it can be said that the shape of a cylindrical lens may be sufficient.

  In addition, it is desirable that the area of the flat portion of the uneven surface 3a, that is, the area of the surface parallel to the substrate 14 in the uneven surface 3a is small. This is because the smaller the area of the flat portion, the lower the ratio of perpendicular incident light to the photovoltaic layer 12, the higher the deflection effect of the uneven surface 3a as a whole, and the better the power generation efficiency.

(About other configurations of solar cells)
FIG. 23 is an explanatory diagram showing another configuration of the solar cell 1. The power generation element 2 of the solar cell 1 may have the following configuration. That is, the power generation element 2 may be configured by laminating the back electrode 11, the power generation layer 12, the transparent electrode 13, and the protective layer 15 in this order on the substrate 14. And the uneven | corrugated sheet | seat 3 may be installed on the protective layer 15. FIG.

  That is, in this solar cell 1, the protective layer 15 is located on the side opposite to the substrate 14 with respect to the power generation layer 12 and on the most uneven sheet 3 side of the power generation element 2. The protective layer 15 is a light-transmitting laminate layer for protecting the power generation layer 12, and is made of, for example, EVA resin (Ethylene-Vinyl Acetate) or ETFE resin (Ethylene tetrafluoroethylene).

  In addition, the board | substrate 14 may be comprised with the flexible board | substrate which has flexibility other than a glass substrate. Moreover, the back surface electrode 11 may be comprised with the transparent electrode which uses ITO etc. as a material.

When the power generation element 2 is configured as described above, the refractive index of the uneven sheet 3 only needs to be set higher than the refractive index of the protective layer 15 positioned closest to the uneven sheet 3 of the power generation element 2. For example, when the protective layer 15 is composed of the above-mentioned ETFE (refractive index; 1.42) or EVA (refractive index; 1.482), the concavo-convex sheet 3 is, for example, PC (refractive index 1.59). And epoxy resin (refractive index; 1.55 to 1.61) can be used, as well as resin having a high refractive index (refractive index; 1.8) (for example, inorganic (TiO ₂ or the like) fine particles having a high refractive index). It is also possible to use an organic-inorganic mixed material).

  As described above, the refractive index of the concavo-convex sheet 3 is also protected in the solar cell 1 in which the protective layer 15 is positioned closest to the concavo-convex sheet 3 of the power generating element 2 and the concavo-convex sheet 3 is installed on the protective layer 15. By setting the refractive index higher than that of the layer 15, the effect of the present embodiment described above can be obtained. That is, the effect of increasing the amount of light incident on the power generation layer 12 for the first time by increasing the deflection angle of the incident light by the uneven sheet 3 can be enhanced. Moreover, the reflectance of the uneven surface 3a of the light incident on the power generation layer 12 and reflected there can be increased, so that the light confinement effect can be enhanced, and the light incident on the power generation layer 12 after the second time can be increased. By increasing the amount of absorption, the total light utilization efficiency can be reliably increased.

  The present invention is applicable to organic thin film solar cells.

1 Solar cell (organic thin-film solar cell)
DESCRIPTION OF SYMBOLS 2 Power generation element 3 Uneven surface 3a Uneven surface 12 Power generation layer 14 Substrate 15 Protective layer 20 Antireflection mechanism 21 Antireflection film 22 Antireflection structure

Claims (10)

A power generation element in which a plurality of layers including a power generation layer made of an organic thin film are stacked;
An organic thin-film solar cell that is provided on a light incident side surface of the power generation element, and an uneven sheet whose surface opposite to the power generation element is an uneven surface,
The refractive index of the concavo-convex sheet is approximately perpendicular to the concavo-convex sheet and is within the range of the deflection angle of light deflected inside the layer closest to the concavo-convex sheet of the power generation element. The organic thin-film solar cell is set to be higher than the refractive index of the layer located closest to the concave-convex sheet of the power generation element so that the deflection angle at which the one-time absorption amount is maximum is included . A power generation element in which a plurality of layers including a power generation layer made of an organic thin film are stacked;
An organic thin-film solar cell that is provided on a light incident side surface of the power generation element, and an uneven sheet whose surface opposite to the power generation element is an uneven surface,
The refractive index of the uneven sheet is set higher than the refractive index of the layer located closest to the uneven sheet side of the power generation element,
The amount of absorption at one time in the power generation layer is the maximum within the range of the deflection angle of light that is incident substantially perpendicularly to the concave-convex sheet and is deflected inside the layer located closest to the concave-convex sheet of the power generation element. In addition to setting the refractive index of the concavo-convex sheet, the height of the concavo-convex surface is set so as to include a deflection angle. The power generation element includes a light-transmitting substrate for supporting the power generation layer as one of the plurality of layers,
The substrate is located on the most uneven sheet side of the power generating element,
The organic thin-film solar cell according to claim 1 or 2, wherein a refractive index of the uneven sheet is higher than a refractive index of the substrate. The power generation element includes a substrate for supporting the power generation layer, and a light-transmitting protective layer that is located on the opposite side of the power generation layer from the substrate and protects the power generation layer. Including as one of a plurality of layers,
The protective layer is located on the most uneven sheet side of the power generation element,
  The organic thin film solar cell according to claim 1 or 2, wherein the refractive index of the uneven sheet is higher than the refractive index of the protective layer. The power generation layer has a thickness in which there is an incident angle range in which an absorption amount of incident light is larger than an absorption amount at the time of normal incidence. 4. The organic thin film solar cell according to any one of 4 above. The organic thin film solar cell according to any one of claims 1 to 5, wherein an antireflection mechanism for preventing surface reflection of incident light is provided on the uneven surface of the uneven sheet. The organic thin film solar cell according to claim 6, wherein the antireflection mechanism is an antireflection film made of a dielectric multilayer film coated on a surface of the uneven surface. The organic thin film solar cell according to claim 6, wherein the antireflection mechanism includes an antireflection structure in which a surface of the uneven surface is roughened. The concavo-convex surface of the concavo-convex sheet is formed by two-dimensionally arranging unit structures that are convex on the side opposite to the power generation element or concave on the power generation element side,
  The organic thin-film solar cell according to any one of claims 1 to 8, wherein the unit structure has any one of a hemisphere including an elliptical hemisphere, a cone, a quadrangular pyramid, a truncated cone, and a quadrangular pyramid. The concavo-convex surface of the concavo-convex sheet is formed by arranging in parallel unit structures that are convex on the side opposite to the power generation element or concave on the power generation element side,
The organic thin-film solar cell according to claim 1, wherein the unit structure is in the shape of a prism or a cylindrical lens.

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