JP2008010531A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion device that can be manufactured at a low cost by reducing the amount of semiconductor used, and that has a light reflecting member having a concave mirror-shaped light reflection surface. Providing products with high light contribution (light utilization efficiency).
SOLUTION: A photoelectric conversion device includes a plurality of spherical first-conductivity-type crystalline semiconductor particles 2 each having a second-conductivity-type semiconductor portion 3 formed on a surface layer on a conductive substrate 1 spaced apart from each other. An insulating layer 4 is formed on the conductive substrate 1 between the crystalline semiconductor particles 2 and the current collecting layer is formed on the insulating layer 4 so as to conduct to the translucent conductor layer 5. A light reflecting member 7 having a concave mirror-shaped light reflecting surface for condensing the crystal semiconductor particles 2 and having an opening for exposing the upper portion of the crystal semiconductor particles 2 is installed at the lower end of the light reflecting surface. The size of the opening is smaller than the diameter of the crystalline semiconductor particle 2.
[Selection] Figure 1

Description

  The present invention relates to a photoelectric conversion device used for photovoltaic power generation and the like, and particularly to a photoelectric conversion device using crystalline semiconductor particles such as crystalline silicon particles.

  As a conventional concentrating solar cell, a photoelectric conversion element using a small-sized crystalline semiconductor flat plate obtained by cutting a crystalline semiconductor flat plate such as a crystalline silicon flat plate is manufactured, and the photoelectric conversion elements are arranged at intervals. A configuration in which a condensing lens is provided on each photoelectric conversion element has been proposed (see, for example, Patent Document 1).

  Moreover, the conventional photoelectric conversion apparatus using a crystalline semiconductor particle is disclosed by patent document 2, This photoelectric conversion apparatus forms an opening in the 1st aluminum foil, and the opening is on the p-type central core. A silicon sphere having an n-type outer shell is inserted, the n-type outer shell on the back side of the silicon sphere is removed, and an insulating layer is formed on the surface of the silicon sphere from which the first aluminum foil and the n-type outer shell have been removed. After removing the insulating layer at the top of the back side of the sphere, a silicon lens and a second aluminum foil are joined via a metal joint, and a spherical lens is formed for condensing on the silicon sphere. .

  In this photoelectric conversion device, a gap is generated between the silicon spheres, resulting in a photoelectric conversion loss. Therefore, in order to draw light energy incident on the gap between the silicon spheres into the silicon sphere adjacent to the gap, a spherical lens is formed on the silicon sphere in parallel with the curved surface.

In addition, a configuration has been proposed in which light is reflected and condensed on a silicon sphere by forming a substrate as disclosed in Patent Document 3 on a concave mirror.
JP-A-8-330619 U.S. Pat. No. 5,417,782 JP 2002-164554 A

  However, in the photoelectric conversion device disclosed in Patent Document 1, it is necessary to cut a crystalline semiconductor flat plate such as a crystalline silicon flat plate to produce a small-area photoelectric conversion element and connect the photoelectric conversion elements with tabs or the like. However, there is a problem that the number of manufacturing steps increases and the manufacturing becomes complicated. In addition, the photoelectric conversion device formed using such a crystalline semiconductor flat plate has a problem that the amount of semiconductor used increases and the weight increases.

  The photoelectric conversion device disclosed in Patent Document 2 uses a spherical lens formed in parallel with the curved surface of a silicon sphere, and the spherical lens is used to reduce the dependency of photoelectric conversion efficiency on the incident angle of light. When trying to do so, the distance between the silicon spheres can only be increased to about 1/10 of the diameter. As a result, the amount of silicon used in the photoelectric conversion device is not reduced, which is disadvantageous for weight reduction and cost reduction.

  The photoelectric conversion device disclosed in Patent Document 3 is formed by deforming a substrate into a concave shape, but it is difficult to maintain the shape of the substrate, and the adjacent boundary of the concave surface is not formed at an acute angle because of the manufacturing method. The reflection of light cannot be ignored, and photoelectric conversion loss occurs.

  Accordingly, the present invention has been completed in view of the above-described problems in the prior art, and an object thereof is to provide a photoelectric conversion device that can be manufactured at a low cost by reducing the amount of semiconductor used, Even if the distance between the crystal semiconductor particles is increased to 1/10 or more of the diameter of the crystal semiconductor particles, the dependence of the photoelectric conversion efficiency on the incident angle of light can be reduced, and the concave shape (reflection type) can be obtained without bending the substrate. The shape of the photoelectric conversion device can be formed. Another object of the present invention is to provide a photoelectric conversion device using a light reflecting member having a concave mirror-shaped light reflecting surface, which has a high light contribution ratio (light utilization efficiency) to photoelectric conversion.

  The photoelectric conversion device of the present invention is a spherical first conductive type crystal in which a second conductive type semiconductor part is formed on the surface of a conductive substrate and a translucent conductive layer is formed on the semiconductor part. A large number of semiconductor particles are joined to each other with a space therebetween, an insulating layer is formed on the conductive substrate between the crystalline semiconductor particles, and a current collector that is electrically connected to the translucent conductor layer on the insulating layer A photoelectric conversion device in which a layer is formed, having a concave mirror-shaped light reflecting surface for condensing the crystalline semiconductor particles on the current collecting layer, and having the crystalline semiconductor particles at a lower end portion of the light reflecting surface. A light reflecting member having an opening for exposing an upper portion is provided, and the size of the opening is smaller than the diameter of the crystalline semiconductor particles.

  In the photoelectric conversion device of the present invention, preferably, the light reflecting member is made of a resin in which a light reflecting layer made of a metal film is formed on the light reflecting surface, and the hardness of the resin is lower than the hardness of the crystalline semiconductor particles. It is characterized by that.

  According to the photoelectric conversion device of the present invention, a spherical first conductivity type in which a second conductive type semiconductor portion is formed on the surface layer and a translucent conductive layer is formed on the semiconductor portion on the conductive substrate. A large number of crystal semiconductor particles are bonded to each other with an interval between them, an insulating layer is formed on the conductive substrate between the crystal semiconductor particles, and a current collecting layer is formed on the insulating layer that is electrically connected to the translucent conductor layer. In the photoelectric conversion device, a concave mirror-shaped light reflecting surface for condensing the crystalline semiconductor particles is formed on the current collecting layer, and an opening exposing the upper portion of the crystalline semiconductor particles is formed at the lower end of the light reflecting surface Since the size of the opening is smaller than the diameter of the crystalline semiconductor particles, the light is sufficiently supplied to the crystalline semiconductor particles even if the area occupied by the crystalline semiconductor particles on the conductive substrate is small. Can be collected in It is possible to reduce the amount of conductor, lighter, a photoelectric conversion device which is low cost can be manufactured.

  Further, since it is not necessary to deform the conductive substrate or the electrode plate in order to form the concave mirror shape, the insulating layer is not destroyed. Therefore, a highly reliable photoelectric conversion device can be manufactured.

  Further, since the light reflecting member can be formed by a resin molding method or the like, for example, various shapes of the light reflecting member can be formed at once with a large area using a mold.

  Furthermore, since the collected light is incident on the upper part of the crystal semiconductor particle, the light incident on the crystal semiconductor particle passes through the crystal semiconductor particle for a long distance, and contributes to the photocurrent in the crystal semiconductor particle. A lot. When the light incident on the crystalline semiconductor particles reaches the conductive substrate, it is sufficiently absorbed and attenuated by the crystalline semiconductor particles, so that the light reflection formed on the surface of the conductive substrate made of aluminum or the like Loss due to absorption in an aluminum-silicon eutectic part having a low rate can be reduced. Therefore, light can be effectively absorbed by the crystalline semiconductor particles, so that the photocurrent can be increased.

  In the photoelectric conversion device of the present invention, preferably, the light reflecting member is made of a resin in which a light reflecting layer made of a metal film is formed on the light reflecting surface, and the hardness of the resin is lower than the hardness of the crystalline semiconductor particles. Even if the reflecting member directly contacts the crystalline semiconductor particles, the light reflecting member can be disposed so as not to damage the crystalline semiconductor particles, and a highly reliable photoelectric conversion device module can be configured.

  That is, since the light reflecting member comes into contact with the crystalline semiconductor particles made of silicon or the like, if the semiconductor portion on the surface of the crystalline semiconductor particles is damaged, the pn junction is destroyed and a leakage current is generated. As a result, the photoelectric conversion efficiency is reduced. Therefore, in the present invention, since the light reflecting member is softer than the crystalline semiconductor particles, the surface of the crystalline semiconductor particles is hardly damaged, and good photoelectric conversion efficiency can be obtained.

  An example of an embodiment of the photoelectric conversion device of the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating an example of an embodiment of a photoelectric conversion device according to the present invention. In FIG. 1, 1 is a conductive substrate, 2 is a crystalline semiconductor particle constituting a granular photoelectric converter, 3 is a semiconductor portion constituting the granular photoelectric converter (hereinafter also referred to as a semiconductor layer), 4 is an insulating layer, 5 is A translucent conductor layer, 6 is a eutectic layer of, for example, aluminum, which forms the conductive substrate 1, and silicon, for example, which forms the crystalline semiconductor particles 2, 7 is a light reflecting member, 8 is a light reflecting layer on the surface of the light reflecting member 7, Reference numeral 9 denotes insulating particles as insulating spacers, and 10 denotes an electrode plate as a current collecting layer. Further, the electrode plate 10 is covered with the translucent conductor layer 5. Therefore, the current collecting layer is composed of the electrode plate 10 and the translucent conductor layer 5.

  The photoelectric conversion device of the present invention has a spherical first conductive structure in which a second conductive type semiconductor portion 3 is formed on the surface of a conductive substrate 1 and a translucent conductor layer 5 is formed on the semiconductor portion 3. A large number of crystal semiconductor particles 2 of a type are bonded to each other with an interval therebetween, and an insulating layer 4 is formed on the conductive substrate 1 between the crystal semiconductor particles 2, and the translucent conductor layer 5 is formed on the insulating layer 4. A collector layer having a concave mirror-shaped light reflecting surface for condensing the crystalline semiconductor particles 2 on the current collecting layer, and a crystal semiconductor at a lower end portion of the light reflecting surface. A light reflecting member 7 in which an opening exposing the upper part of the particle 2 is provided, and the size of the opening is smaller than the diameter of the crystalline semiconductor particle 2.

  With the above structure, the amount of semiconductor used can be reduced, and a photoelectric conversion device that is reduced in weight and cost can be manufactured.

  Further, since it is not necessary to deform the conductive substrate 1 and the electrode plate 10 in order to form a concave mirror shape, the insulating layer 4 is not destroyed. Therefore, a highly reliable photoelectric conversion device can be manufactured.

  Further, since the light reflecting member 7 can be formed by a resin molding method or the like, for example, the light reflecting member 7 having various shapes can be formed at a stretch with a large area using a mold.

  Further, since the condensed light is incident on the upper part of the crystal semiconductor particle 2, the light incident on the crystal semiconductor particle 2 passes through the crystal semiconductor particle 2 for a long distance and contributes to the photocurrent in the crystal semiconductor particle 2. Generates many electrons and holes. When the light incident on the crystalline semiconductor particles 2 reaches the conductive substrate 1, the light is sufficiently absorbed and attenuated by the crystalline semiconductor particles 2, so that it is formed on the surface of the conductive substrate 1 made of aluminum or the like. Loss due to absorption in the aluminum-silicon eutectic part having a low light reflectance can be reduced. Accordingly, the light can be effectively absorbed by the crystalline semiconductor particles 2, so that the photocurrent can be increased.

  The conductive substrate 1 of the present invention itself may be made of aluminum, or a conductive layer made of aluminum or the like may be provided on an insulating substrate. The conductive substrate 1 may be made of aluminum, a metal having a melting point higher than that of aluminum, ceramics having a conductive layer, and the like, for example, aluminum, aluminum alloy, iron, stainless steel, nickel alloy, alumina ceramics, etc. Used. When the material of the conductive substrate 1 is other than aluminum, a conductive layer made of aluminum can be formed on a substrate made of the material.

  A large number of first-conductivity-type crystalline semiconductor particles 2 are arranged on the conductive substrate 1 at intervals. For example, if the first conductivity type is p-type, the crystalline semiconductor particles 2 are elements such as B, Al, and Ga as p-type impurities if the first conductivity type is p-type, or if the first conductivity type is n-type. A trace amount of elements such as P and As as n-type impurities is contained.

  In the following embodiments, the case where the conductive substrate 1 is made of aluminum and the crystalline semiconductor particles 2 are made of silicon will be described.

  The shape of the crystalline semiconductor particles 2 is preferably a spherical shape having a convex curved surface that can reduce the dependency of the light beam angle of incident light. The spacing between the adjacent crystalline semiconductor particles 2 is preferably wide in order to reduce the amount of the crystalline semiconductor particles 2 used. More preferably, the spacing is larger than the radius of the crystalline semiconductor particles 2, and the crystalline semiconductor The number of crystalline semiconductor particles 2 is about ½ or less compared to the case where the particles 2 are arranged in a close-packed manner.

  Moreover, the reflectance on the surface of the crystalline semiconductor particle 2 can be reduced by making the surface of the crystalline semiconductor particle 2 rough. In order to form this rough surface, the surface of the crystalline semiconductor particles 2 may be etched in an alkaline solution, or the surface of the crystalline semiconductor particles 2 may be finely processed with an RIE (Reactive Ion Etching) apparatus or the like.

  The diameter of the crystalline semiconductor particles 2 is preferably 0.2 to 0.8 mm. When the thickness exceeds 0.8 mm, the amount of silicon used in the photoelectric conversion device using a small crystalline silicon flat plate cut out from the crystalline silicon flat plate (wafer) is the same as the amount of silicon used including the cutting portion of the wafer. The advantage of reducing the amount of use is lost. Moreover, when smaller than 0.2 mm, the problem that it becomes difficult to assemble the crystalline semiconductor particle 2 to the conductive substrate 1 occurs. Therefore, the diameter of the crystalline semiconductor particles 2 is more preferably 0.2 to 0.6 mm in relation to the amount of silicon used.

  The photoelectric conversion device of the present invention is manufactured, for example, as follows. On the conductive substrate 1, a hypereutectic aluminum-silicon eutectic paste containing a large amount of boron is applied to at least a portion where the crystalline semiconductor particles 2 are arranged, and a large number (several 1000 to 100,000) is applied. After the crystalline semiconductor particles 2 are arranged at a distance from each other, a constant load is applied from above by a pressing plate or the like to eutectic temperature (577) between aluminum forming the conductive substrate 1 and silicon forming the crystalline semiconductor particles 2. The eutectic layer (eutectic portion) 6 of the conductive substrate 1 and the crystalline semiconductor particles 2 is formed by heating to a temperature higher than or equal to (° C.), and the conductive substrate 1 and the crystalline semiconductor particles 2 are bonded via the alloy layer 6. Join. Furthermore, a silicon layer containing a large amount of boron is precipitated from the hypereutectic layer (hypereutectic part) formed by heating the aluminum-silicon eutectic paste, and this is converted into a p + layer. ) You can get an effect.

The insulating layer 4 is made of an insulating material for separating the positive electrode and the negative electrode. For example, SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , CaO, MgO, P ₂ O ₅ , Li ₂ O, SnO, ZnO, Low-temperature firing glass (glass frit) material containing a material such as BaO or TiO ₂ as an optional component, a glass composition in which a filler composed of one or more of the above materials is combined, an organic type such as a polyimide resin or a silicone resin Made of insulating material.

  The spherical insulating particles 12 that are insulating spacers are made of an insulating material such as glass, ceramics, or resin, and the size (diameter) is preferably 4 to 20 μm. By dispersing the insulating particles 12 in the insulating layer 4, the electrode plate 10 disposed on the insulating layer 4 and the conductive substrate 1 are provided so as not to contact each other.

  The insulating layer 4 including the insulating particles 12 is formed as follows. By applying a paste, solution, sheet or liquid of an insulating material containing the insulating particles 12 from above the crystalline semiconductor particles 2 and heating at a temperature not higher than 577 ° C. which is the eutectic temperature of aluminum and silicon, the crystalline semiconductor particles The insulating layer 4 is formed by filling the gap between the two and baking solidifying or thermosetting. In this case, when the heating temperature exceeds 577 ° C., the alloy layer 6 of aluminum and silicon starts to melt, so that the bonding between the conductive substrate 1 and the crystalline semiconductor particles 2 becomes unstable. 2 is detached from the conductive substrate 1 and the generated current cannot be taken out. In addition, after the insulating layer 4 is formed, the surface of the crystalline semiconductor particles 2 is cleaned with a cleaning solution containing hydrofluoric acid.

  The semiconductor layer 3 of the second conductivity type is made of, for example, Si, and a gas of a phosphorus compound for exhibiting an n-type when the second conductivity type is an n-type, for example, in a gas phase of a silane compound by a vapor deposition method or the like. When the phase or the second conductivity type is p-type, a small amount of a gas phase of a boron compound for exhibiting p-type is introduced. The film quality of the semiconductor layer 3 may be crystalline, amorphous, or a mixture of crystalline and amorphous, but considering light transmittance, crystalline or a mixture of crystalline and amorphous What to do is good.

  Further, the semiconductor layer 3 may be formed on the surface portion (surface layer portion) of the crystalline semiconductor particle 2 by, for example, a thermal diffusion method before the crystalline semiconductor particle 2 is bonded to the conductive substrate 1. When the crystalline semiconductor particles 2 are, for example, p-type, the surface of the crystalline semiconductor particles 2 is 1 μm thick by inserting the crystalline semiconductor particles 2 into a quartz tube at a temperature of 900 ° C. for 30 minutes using phosphorus oxychloride as a diffusing agent. The n-type semiconductor layer 3 may be formed. At this time, in order to electrically separate the semiconductor layer 3 and the eutectic layer 6, the surface other than the lower end portion of the semiconductor layer 3 except for the vicinity of the eutectic layer 6 is covered with an acid resistant resist or the like, and an uncoated portion ( The lower end portion of the semiconductor layer 3 is removed by removing the lower end portion of the semiconductor layer 3 with an etching solution.

The concentration of the trace element for imparting the second conductivity type in the semiconductor layer 3 is, for example, about 1 × 10 ¹⁶ to 1 × 10 ²¹ atoms / cm ³ . Furthermore, the semiconductor layer 3 is preferably formed along a convex curved surface of the surface of the crystalline semiconductor particle 2. By being formed along the surface of the convex curved surface of the crystalline semiconductor particle 2, the area of the pn junction can be increased and carriers generated inside the crystalline semiconductor particle 2 can be efficiently collected. Become.

  A translucent conductor layer 5 also serving as the other electrode is formed on the semiconductor layer 3 and the insulating layer 4. An electrode plate 10 is formed on the insulating layer 4, and the translucent conductor layer 5 is formed so as to cover the electrode plate 10. In the example of FIG. 1, the electrode plate 10 and the translucent conductor layer 5 constitute a current collecting layer. Note that the conductive substrate 1 performs the function of one of the electrodes.

The translucent conductive layer 5 is composed of one or more oxide-based films selected from SnO ₂ , In ₂ O ₃ , ITO, ZnO, TiO _2, etc., and is formed by sputtering, vapor phase epitaxy, or coating. It is formed by a firing method or the like. The translucent conductor layer 5 can also provide an effect as an antireflection film if the thickness is selected.

  The translucent conductor layer 5 is preferably formed along the surfaces of the crystalline semiconductor particles 2 and the semiconductor layer 3 and is formed along the convex curved surfaces of the crystalline semiconductor particles 2 and the semiconductor layer 3. In this case, the area of the pn junction can be increased widely, and carriers generated inside the crystalline semiconductor particles 2 can be collected efficiently.

  Further, a protective layer (not shown) may be formed on the semiconductor layer 3 or the translucent conductor layer 5. Such a protective layer preferably has a characteristic of a transparent dielectric, such as silicon oxide, cesium oxide, aluminum oxide, silicon nitride, titanium oxide, tantalum oxide, yttrium oxide, etc. It is formed by combining a single layer or a plurality of layers with a single composition or a plurality of compositions. Since this protective layer is on the light incident side, it needs to be transparent, and it should be an insulator in order to prevent current leakage between the semiconductor layer 3 or the translucent conductor layer 5 and the outside. is necessary. In addition, if the thickness of a protective layer is optimized, the function as an antireflection layer can also be provided.

  In order to reduce the series resistance value between the translucent conductor layer 5 and the external terminal, an electrode plate 10 is preferably provided as a collecting electrode on the insulating layer 4 between the adjacent crystalline semiconductor particles 2. Thereby, the photocurrent generated by the crystalline semiconductor particles 2 can be efficiently taken out from the photoelectric conversion device with reduced resistance loss. That is, the electrode plate 10 functions as a low resistance conductor. Further, the flatness and mechanical strength of the part on which the light reflecting member 7 is placed by the electrode plate 10 are improved, and the light reflecting member 7 can be installed with high reliability. The electrode plate 10 may be formed on the translucent conductor layer 5.

  The electrode plate 10 is preferably made of a metal plate in which an opening for exposing the upper portion of the crystalline semiconductor particles 2 is formed. For example, Al, Cu, Ni, Cr, Ag and alloys thereof have high reflectivity. It is suitable in terms of being obtained. The thickness of the electrode plate 10 is preferably 20 to 200 μm in order to maintain low resistance and mechanical strength. The use of the electrode plate 10 is preferable in that it also serves as a support member that firmly supports the light reflecting member 7 installed thereon.

  In addition, instead of the electrode plate 10, a pattern electrode composed of finger electrodes (not shown) with a constant interval is provided on the translucent conductor layer 5 as a collector electrode, and is electrically connected to the translucent conductor layer 5. May be.

  By avoiding the crystalline semiconductor particle 2 and providing the electrode plate 10 or the finger electrode, it is possible to eliminate the formation of a shadow area directly by the electrode plate 10 or the finger electrode. Furthermore, the electrode plate 10 and the finger electrode can be covered by the light reflecting member 7, and the appearance and aesthetics can be improved. A bus bar electrode (not shown) may be further formed as a collecting electrode.

  Then, the light reflecting member 7 is formed on the electrode plate 10 that also serves as the other electrode between the crystal semiconductor particles 2 and the translucent conductor layer 5. As shown in FIG. 1, the light reflecting member 7 has a concave mirror shape centered on the crystalline semiconductor particles 2, and the boundary between the concave mirror shapes preferably forms an acute convex portion. As in the photoelectric conversion device using the substrate deformed into the concave shape of Patent Document 3, when the boundary portion between the concave shapes is wide, the boundary portion is a wide flat surface. Therefore, there is a problem that the light is reflected upward as it is. In the case of the light reflecting member 7 of the present invention, since the boundary portion forms an acute angle, there is no light reflected upward at the boundary portion, and the light incident on the photoelectric conversion device is effectively used as the crystalline semiconductor particle 2. The light can be condensed.

  In the present invention, the size of the opening of the light reflecting member 7 in which the light condensed by the light reflecting member 7 enters the crystal semiconductor particles 2 (for example, the diameter if the opening is circular) is the diameter of the crystal semiconductor particles 2. Smaller than. Therefore, the incident part of light becomes the upper part of the crystal semiconductor particle 2, and the light incident on the crystal semiconductor particle 2 passes through a long distance in the crystal semiconductor particle 2 corresponding to approximately the diameter of the crystal semiconductor particle 2, and eutectic layer Therefore, most of the light is absorbed by the crystalline semiconductor particles 2 in the middle of reaching the eutectic layer 6 and can contribute to photovoltaic power generation effectively. That is, since the light collected by the light reflecting member 7 is incident on the upper part of the crystal semiconductor particle 2, the light incident on the crystal semiconductor particle 2 passes through the crystal semiconductor particle 2 for a long distance, Many electrons and holes that contribute to the photocurrent are generated. When the light incident on the crystalline semiconductor particles 2 reaches the conductive substrate 1, the light is sufficiently absorbed and attenuated by the crystalline semiconductor particles 2, so that it is formed on the surface of the conductive substrate 1 made of aluminum or the like. Loss due to absorption in the aluminum-silicon eutectic layer 6 having a low light reflectance can be reduced. Accordingly, the light can be effectively absorbed by the crystalline semiconductor particles 2, so that the photocurrent can be increased.

  On the other hand, when the light reflecting member 7 is formed so that the upper and lower portions of the crystalline semiconductor particles 2 are exposed, the light incident from the lower surface of the crystalline semiconductor particles 2 reaches the eutectic layer 6 at a short distance. The crystal semiconductor particles 2 are not sufficiently absorbed. The light that has not been absorbed is reflected by the eutectic layer 6, but the reflectance at the surface of the eutectic layer 6 is low and is absorbed by the eutectic layer 6, resulting in light loss. For this reason, the generated photocurrent is reduced and the photoelectric conversion efficiency is lowered. The present invention has been made on the basis of such knowledge, and by limiting the light incident portion to the upper part of the crystalline semiconductor particles 2, light loss is prevented and photoelectric conversion efficiency is improved. be able to.

The size of the opening of the light reflecting member 7 is 0.4 ≦ R ₁ / R ₂ <1 when the diameter of the circular opening is R ₁ and the diameter of the crystalline semiconductor particle 2 is R _2. It is preferable. When R ₁ / R ₂ <0.4, the condensing region by light reflection is limited to a small size, and the condensing rate at the time of light incidence from an oblique direction is lowered. When R ₁ / R ₂ ≧ 1, light enters the gap between the opening and the crystalline semiconductor particle 2, so that the effective utilization rate of light is reduced.

  The shape of the opening of the light reflecting member 7 may be various shapes such as a circle, an ellipse, a triangle, a quadrangle, and a pentagon or more polygon.

  The size of the maximum opening at the upper end of the concave mirror of the light reflecting member 7 is about 1.3 to 3 of the diameter of the crystalline semiconductor particles 2 in the case of a circle, and the shape of the maximum opening is a circle. Various shapes such as an ellipse, a triangle, a quadrangle, and a pentagon or more polygon can be used.

  The shape of the inner surface of the concave mirror of the light reflecting member 7 can be a shape suitable for condensing, such as a spherical surface or a spheroid surface.

  The concave mirror-shaped light reflecting member 7 is formed of, for example, a resin such as polycarbonate, acrylic resin, fluorine resin, olefin resin, metal, or other material capable of maintaining the shape. A concave mirror shape is formed by these materials, and an opening is provided at the bottom of the concave mirror shape so that the upper portion of the crystalline semiconductor particle 2 enters and is exposed, and a light reflecting layer 8 is provided on the inner surface of the concave mirror shape. There is a light reflecting surface.

  Since this light reflecting member 7 comes into contact with the crystalline semiconductor particles 2 made of silicon, if the semiconductor layer 3 is damaged, the pn junction is destroyed and a leak current is generated, and the photoelectric conversion efficiency is reduced. Result. Therefore, the light reflecting member 7 is made of a resin in which a light reflecting layer made of a metal film is formed on the light reflecting surface, and the hardness of the resin is preferably lower than the hardness of the crystalline semiconductor particles. Thereby, since the light reflection member 7 is softer than the crystal semiconductor particle 2, the surface of the crystal semiconductor particle 2 is hard to be damaged, and favorable photoelectric conversion efficiency can be obtained.

  Furthermore, the position accuracy of the crystalline semiconductor particles 2 bonded on the conductive substrate 1 is not good, and the position of the crystalline semiconductor particles 2 may deviate from a predetermined position. In this case, the resin constituting the light reflecting member 7 is If it is hard, the light reflecting member 7 that has been displaced and the surrounding light reflecting member 7 will be lifted up, making it impossible to obtain desirable light collecting characteristics. Therefore, even if a positional deviation occurs in the light reflecting member 7 by using a soft material (for example, epoxy resin, Teflon (registered trademark) resin, polycarbonate resin, etc.) that easily deforms the resin constituting the light reflecting member 7. The surrounding light reflecting member 7 does not float, and the light reflectivity and light condensing property can be improved. Even if the conductive substrate 1, the electrode plate 10, the insulating layer 4, etc. are uneven, the light reflecting member 7 can be disposed so as to follow them.

  The light reflecting member 7 is made of a mold having a large number of concave mirror-shaped negative shapes (complementary shapes) on the molding surface, and is molded with resin, metal, or other material capable of maintaining the shape. The light reflecting layer 8 on the surface of the light reflecting member 7 is made of Ag, Al, Au, Cu, Pt, Zn, Ni, Cr or the like by a method such as vacuum deposition, sputtering, electroless plating, or electrolytic plating. It is made of a metal having a high reflectance. Then, the light reflecting member 7 is placed on the current collecting layer on the insulating layer 4 so that the upper part of the crystalline semiconductor particles 2 is exposed from the opening of the light reflecting member 7 and bonded as it is, or the light reflecting member 7. A transparent filler, a transparent protective material, etc. are laminated on top and sealed with a vacuum heating device or the like.

  In the photoelectric conversion device of Patent Document 3, the light reflection surface is formed of an aluminum foil that also serves as an electrode plate. In the photoelectric conversion device of the present invention, the light reflection surface is a metal formed on the surface of a resin substrate. By forming with a film, a higher reflectance can be obtained. This is because the reflectance of the surface of the metal thin film formed by the vacuum deposition method is higher than the reflectance of the surface of a bulk member such as an aluminum foil.

  In addition, in the method of manufacturing a photoelectric conversion device of Patent Document 3, crystal semiconductor particles are inserted into the openings of individual aluminum foils. For example, the operation of arranging 100,000 individual crystal semiconductor particles is extremely difficult. This is a laborious operation, and it is practically difficult to manufacture and operate a solar cell that should supply energy at a low cost. On the other hand, in the photoelectric conversion device of the present invention, a large number of crystal semiconductor particles 2 are collectively arranged at predetermined positions on the conductive substrate 1 and bonded using a jig or the like. In addition, since the light reflecting member 7 molded at once with the mold can be collectively installed on the large number of crystal semiconductor particles 2, the photoelectric conversion device can be manufactured easily and stably.

  According to an optical simulation, the light collection rate by the light reflecting member 7 can be 2 to 30 times that when the light reflecting member 7 is not provided. The higher the light collection rate, the higher the photoelectric current generated in the crystalline semiconductor particles 2 and the higher the open-circuit voltage, so that higher photoelectric conversion efficiency can be obtained. However, on the other hand, the crystalline semiconductor particles 2 become high temperature due to the heat generated by condensing, and the output of photocurrent is reduced, so that the photoelectric conversion efficiency is improved by condensing and the photoelectric conversion by heat generation. The light collection rate is determined so as to balance the reduction in efficiency. In the photoelectric conversion device of the present invention, since the crystalline semiconductor particles 2 are directly bonded onto the conductive substrate 1, the heat generated in the crystalline semiconductor particles 2 is easily dissipated to the conductive substrate 1, and the temperature The rise is suppressed. Further, since the diameter of the crystalline semiconductor particles 2 is 1 mm or less (100 to 400 μm), the heat distribution of the conductive substrate 1 becomes nearly uniform, and the temperature rise of the crystalline semiconductor particles 2 can be reduced. Therefore, water cooling or the like of the conductive substrate 1 is unnecessary, and the system is stable and has few failures.

  Note that a photoelectric conversion device in which one photoelectric conversion element (a photoelectric conversion unit having one crystal semiconductor particle 2) having the above-described configuration is provided or a plurality of photoelectric conversion elements are connected (connected in series, parallel, or series-parallel) can do. Furthermore, one photoelectric conversion device is provided, or a photoelectric conversion module in which a plurality of photoelectric conversion devices are connected (connected in series, parallel, or series-parallel) is used as the power generation means, and the generated power is directly supplied from the power generation means to the DC load. May be. In addition, after the power generation means converts the generated power into appropriate AC power via power conversion means such as an inverter, it is possible to supply this generated power to an AC load such as a commercial power system or various electric devices. It is good also as a simple electric power generating apparatus. Furthermore, it is also possible to use such a power generation device as a photovoltaic power generation device such as a solar power generation system in various modes by installing it on the roof or wall surface of a building with good sunlight.

  Examples of the photoelectric conversion device of the present invention will be described below.

  A photoelectric conversion device having the configuration of FIG. 1 was produced as follows. By using p-type crystalline silicon particles having a diameter of about 0.3 mm as the crystalline semiconductor particles 2, phosphorus (P) is thermally diffused on the surface layer of a large number (about 10,000) of crystalline silicon particles. A pn junction was formed with the outer portion of the silicon particle as an n-type semiconductor portion (n + layer) 3.

  Next, an aluminum-silicon eutectic paste is applied to each portion where the crystalline silicon particles on the main surface of the conductive substrate 1 made of aluminum are disposed and fired to form an aluminum-silicon hypereutectic layer. On the aluminum-silicon hypereutectic layer, a large number of crystalline silicon particles are arranged at an interval of about 3 times its diameter, and the eutectic temperature of aluminum and silicon is 577 ° C. or higher (630 ° C.). Then, a large number of crystalline silicon particles were bonded onto the conductive substrate 1 by heating for about 10 minutes.

  Next, the entire periphery of the lower end portion of the crystalline silicon particles is etched to remove the n-type semiconductor portion, pn separation is performed, and then an electrode plate is interposed between a number of crystalline silicon particles on the conductive substrate 1. A copper plate having a thickness of 50 μm as 10 was placed on the insulating layer 4 made of polyimide. This copper plate is a plate-like body having a large number of openings so that each crystalline silicon particle is exposed.

  Next, the surface of the semiconductor part of the crystalline silicon particles was washed, and an ITO film as a light-transmitting conductive layer 5 was formed with a thickness of 80 nm on the insulating layer 4, the electrode plate 10 and the crystalline silicon particles by a sputtering method. .

  Next, the light reflecting member 7 was produced as follows. Using a mold formed on the molding surface so that a large number of longitudinal half-spheroids having a maximum width 2.5 times the diameter of the crystalline silicon particles are arranged, the crystalline silicon is formed on the polycarbonate film by a vacuum molding method. A number of concave mirror shapes having 200 μm diameter openings smaller than the particle diameter of 300 μm were formed, and the light reflecting member 7 was produced.

  Contrary to the upper concave portion forming the concave mirror of the light reflecting member 7, the concave portion is also formed in the lower portion that does not contribute to light collection. This was formed by sandwiching a polycarbonate film between the mold described above and a mold for forming a recess at the bottom, and heating and melting to mold. There is a deviation in the positional accuracy of the bonded crystalline silicon particles, and in order to absorb this deviation, it is necessary to make the opening of the light reflecting member 7 larger than the crystalline semiconductor particles 2. The light reflecting member 7 smoothly entered between the crystalline silicon particles, and the light reflecting member 7 could be pressed above the electrode plate 10.

  Next, an Al film having a thickness of 0.2 μm as the light reflecting layer 8 was formed on the inner surface of the concave mirror of the light reflecting member 7 by vacuum vapor deposition.

  Then, the light reflecting member 7 is epoxyd on the current collecting layer (the electrode plate 10 and the translucent conductor layer 5) on the conductive substrate 1 so that the upper part of each crystalline silicon particle protrudes from the opening of the light reflecting member 7. A photoelectric conversion device was manufactured by adhering with a resin.

(Comparative example)
A point in which a large number of crystalline silicon particles are densely arranged on the main surface of the conductive substrate 1, and a thermosetting Ag paste on the translucent conductor layer 5 on the insulating layer 4 instead of the electrode plate 10 as a collecting electrode. A photoelectric conversion device was produced in the same manner as in the above example except that a finger electrode formed by applying and curing with heat was formed and the light reflecting member 7 was not used.

  When the photoelectric conversion device of the present invention was compared with the photoelectric conversion device of the comparative example, the amount of crystalline silicon particles used in the photoelectric conversion device of the comparative example was about nine times that of the photoelectric conversion device of the example. Moreover, the photoelectric conversion efficiency of the photoelectric conversion device of the example was 1.1 times that of the photoelectric conversion device of the comparative example.

  This is because the short circuit current is almost the same between the example and the comparative example, but the open circuit voltage of the example is higher than the open circuit voltage of the comparative example, and the photoelectric conversion device of the present invention greatly reduces the semiconductor raw material. It was confirmed that the photoelectric conversion efficiency could be improved.

  In addition, this invention is not limited to said embodiment and Example, It cannot be overemphasized that a various change can be performed within the range which does not deviate from the summary of this invention.

It is sectional drawing which shows the example of embodiment about the photoelectric conversion apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conductive substrate 2 ... Crystalline semiconductor particle 3 ... Semiconductor part (semiconductor layer)
4 ... Insulating layer 5 ... Translucent conductor layer 6 ... Aluminum-silicon eutectic layer 7 ... Light reflecting member 8 ... Light reflecting layer 9 ... Insulating particle 10 ... Electrode plate

Claims (2)

  On a conductive substrate, a plurality of spherical first conductive type crystalline semiconductor particles in which a second conductive type semiconductor portion is formed on the surface layer and a transparent conductive layer is formed on the semiconductor portion are spaced apart from each other. Photoelectric conversion in which an insulating layer is formed on the conductive substrate between the crystalline semiconductor particles, and a current collecting layer is formed on the insulating layer and is electrically connected to the translucent conductor layer. The device has a concave mirror-shaped light reflecting surface for condensing the crystalline semiconductor particles on the current collecting layer, and an opening for exposing an upper portion of the crystalline semiconductor particles is formed at a lower end portion of the light reflecting surface. The photoelectric conversion device is characterized in that a light reflecting member is provided and the size of the opening is smaller than the diameter of the crystalline semiconductor particles. The said light reflection member consists of resin in which the light reflection layer which consists of a metal film was formed in the said light reflection surface, The hardness of the said resin is lower than the hardness of the said crystalline semiconductor particle, The said Claim 1 characterized by the above-mentioned. Photoelectric conversion device.

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