JP2008210949A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high conversion efficiency photoelectric conversion capable of suppressing separation of an interface between an insulating layer and a crystalline semiconductor particle and efficiently incorporating light reaching the lower side of the crystalline semiconductor particle into the crystalline semiconductor particle. To get the equipment.
SOLUTION: A photoelectric conversion device includes a plurality of spherical first-conductivity-type crystal semiconductor particles 2 each having a second-conductivity-type semiconductor portion 3 formed on a surface layer on a conductive substrate 1 and bonded to each other. 2 is a photoelectric conversion device in which an insulating layer 4 is formed on a conductive substrate 1 between two, and a light-transmitting conductive layer 5 is formed on the semiconductor portion 3 and the insulating layer 4. A step 2a in which the diameter of the crystalline semiconductor particles 2 changes stepwise is formed over the entire periphery in the vicinity of the upper side of the joint 2b with the conductive substrate 1 on the surface, and the radius in the vertical cross section below the step 2a. The insulating layer 4 covers from the boundary 2c with the junction 2b on the surface of the crystalline semiconductor particle 2 to the upper side of the step 2a.
[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.

  FIG. 2 shows an example of a conventional solar cell, particularly a photoelectric conversion device using crystalline semiconductor particles. In this photoelectric conversion device, a large number of crystalline semiconductor particles 12 such as crystalline silicon particles are bonded to a conductive substrate 11 made of aluminum or the like at intervals. An insulating layer 14 made of polyimide or the like is provided on the conductive substrate 11 between the crystalline semiconductor particles 12. In the photoelectric conversion device using such crystal semiconductor particles 12, the crystal semiconductor particles 12 are spherical.

  In FIG. 2, reference numeral 13 denotes a second conductivity type (for example, n-type) semiconductor portion formed on the surface layer of the first conductivity type (for example, p-type) crystalline semiconductor particle 12. Reference numeral 15 denotes a translucent conductor layer made of ITO or the like formed on the crystalline semiconductor particles 12 and the insulating layer 14.

In such a photoelectric conversion device, the outside of the crystalline semiconductor particles 12 is generally sealed with a transparent resin or glass to produce a photoelectric conversion module. As the resin, a thermoplastic resin is used, and a method of crimping the resin to the photoelectric conversion device while heating the photoelectric conversion device and the resin is performed.
JP 2005-159168 A

  As described above, when heat treatment for manufacturing a photoelectric conversion module is performed, separation may occur between the insulating layer 14 and the crystalline semiconductor particles 12. This is because when the photoelectric conversion module is assembled, a downward force is applied to the insulating layer 14 and a stress is generated at the interface between the insulating layer 14 and the crystalline semiconductor particles 12.

  That is, in the photoelectric conversion device having the configuration shown in FIG. 2, the stress of the insulating layer 14 is caused by the above stress because the contact angle of the contact portion 14a with the spherical surface of the crystalline semiconductor particle 12 of the insulating layer 14 is close to a right angle. It is thought that this is because the contact portion 14a is easily peeled off.

  As shown in FIG. 2, a recess 12a is formed on the entire lower end of the crystal semiconductor particle 12, and the corner between the recess 12a and the spherical surface of the crystal semiconductor particle 12 is formed in an acute angle. Yes. This is caused by removing the lower end portion of the semiconductor portion 13 by an etching method or the like in order to prevent the second conductivity type semiconductor portion 13 from coming into contact with the first conductivity type conductive substrate 11. When there is a recess 12a having sharp corners, when the liquid insulating layer 14 made of polyimide or the like is applied between the crystalline semiconductor particles 12, the contact portion 14a of the liquid insulating layer 14 is located above the recess 12a. Since it cannot smoothly crawl up on the spherical surface of the crystalline semiconductor particles 12, the contact angle of the contact portion 14a with the spherical surface of the crystalline semiconductor particles 12 is close to a right angle.

  In addition, since the recess 12a has a small depth and size, the effect of dispersing the stress by the interface with the insulating layer 14 inside the recess 12a is small. Therefore, the stress is concentrated on the contact portion 14a between the spherical surface of the crystalline semiconductor particle 12 and the insulating layer 14, and peeling occurs in the contact portion 14a.

  When delamination occurs between the insulating layer 14 and the crystalline semiconductor particles 12, the transparent conductive layer 15 formed on the insulating layer 14 and the crystalline semiconductor particles 12 is broken, thereby increasing the internal resistance and increasing the photoelectrical property. There has been a problem that the photoelectric conversion efficiency (hereinafter, also referred to as conversion efficiency) of the conversion device is lowered.

  Further, since the surface of the crystal semiconductor particle 12 is almost spherical, the incident light that has entered from above the photoelectric conversion device and reached the lower side of the crystal semiconductor particle 12 is reflected several times on the surface of the crystal semiconductor particle 12. It tends to go out of the photoelectric conversion device. For this reason, the ratio that incident light is taken into the crystalline semiconductor particles 12 is lowered, and there is a problem that the conversion efficiency of the photoelectric conversion device is lowered.

  Accordingly, the present invention has been completed in view of the above-described problems in the prior art, and an object thereof is to suppress separation of the interface between the insulating layer and the crystalline semiconductor particles, and It is to obtain a photoelectric conversion device with high conversion efficiency that can efficiently take light that has reached the side into crystalline semiconductor particles.

  In the photoelectric conversion device of the present invention, a plurality of spherical first-conductivity-type crystal semiconductor particles each having a second-conductivity-type semiconductor portion formed on a surface layer are joined on a conductive substrate, A photoelectric conversion device in which an insulating layer is formed on a conductive substrate, and a light-transmitting conductive layer is formed on the semiconductor portion and the insulating layer, wherein the crystalline semiconductor particle has the conductive property on the surface thereof. A step in which the diameter of the crystalline semiconductor particles changes stepwise is formed over the entire circumference in the vicinity of the upper side of the joint with the substrate, and the radius in the vertical cross section below the step is small, and the insulation The layer is characterized by covering from the boundary with the junction on the surface of the crystalline semiconductor particle to the upper side of the step.

  The photoelectric conversion device of the present invention is preferably characterized in that a radial depth of the step is 0.1 to 30% of a diameter of the crystalline semiconductor particle.

  The photoelectric conversion device of the present invention is preferably characterized in that the vertical cross-sectional shape of the corner of the deepest part of the step is an arc.

  In the photoelectric conversion device of the present invention, it is preferable that the radius of curvature in the longitudinal section of the corner of the step is 0.8 to 2 times the depth of the step.

  In addition, the photoelectric conversion device of the present invention is preferably characterized in that the angle of the crystalline semiconductor particles of the insulating layer in contact with the surface of the semiconductor portion is an acute angle.

  In the photoelectric conversion device of the present invention, a large number of spherical first-conductivity-type crystal semiconductor particles each having a second-conductivity-type semiconductor portion formed on a surface layer are joined on a conductive substrate, and the conductivity between the crystal-semiconductor particles is determined. A photoelectric conversion device in which an insulating layer is formed on a substrate, and a light-transmitting conductive layer is formed on the semiconductor portion and the insulating layer, wherein the crystalline semiconductor particles are bonded to the conductive substrate on the surface. A step in which the diameter of the crystalline semiconductor particles changes stepwise is formed over the entire circumference in the vicinity of the upper side, and the radius in the vertical cross section on the lower side from the step is reduced. The insulating layer is formed on the surface of the crystalline semiconductor particles. Since it covers from the boundary with the junction to the upper side of the step, when stress is applied to the interface between the insulating layer and the crystalline semiconductor particles, the stress is dispersed at the interface inside the step, and the insulating layer and the crystalline semiconductor No delamination between particles

  In addition, as shown in FIG. 4, the crystal semiconductor particles have a lower radius on the lower side of the step, so that a large amount of light (L1) incident on the lower side of the crystal semiconductor particle is confined to the lower side of the step. Since repeated reflections are repeated, a large amount is taken into the crystalline semiconductor particles. As a result, a photoelectric conversion device with high conversion efficiency can be obtained.

  In the photoelectric conversion device of the present invention, preferably, the stepwise radial depth is 0.1 to 30% of the diameter of the crystalline semiconductor particles, so that the bonding strength between the crystalline semiconductor particles and the conductive substrate is ensured. The crystalline semiconductor particles do not fall off from the conductive substrate, and therefore it is possible to prevent the conversion efficiency of the photoelectric conversion device from being lowered.

  In the photoelectric conversion device of the present invention, preferably, the vertical cross-sectional shape of the deepest corner of the step is an arc, so that more light traveling inside the step is reflected and taken in the crystal semiconductor particle side. Therefore, a photoelectric conversion device with high conversion efficiency can be obtained.

  In the photoelectric conversion device of the present invention, preferably, the radius of curvature in the longitudinal section of the corner of the step is 0.8 to 2 times the depth of the step, so that more light travels inside the step. The effect of being reflected and taken into the semiconductor particle side is further improved. Therefore, a photoelectric conversion device with higher conversion efficiency can be obtained.

  In the photoelectric conversion device of the present invention, preferably, the insulating layer has an acute angle with the surface of the semiconductor portion of the crystalline semiconductor particle, so that the contact portion of the insulating layer extends along the surface of the semiconductor portion of the crystalline semiconductor particle. Therefore, when a stress is applied to the contact portion of the insulating layer with the semiconductor portion of the crystalline semiconductor particle during the manufacture of the photoelectric conversion module, the insulating portion contact portion is easily separated from the surface of the semiconductor portion of the crystalline semiconductor particle. Will not peel off.

  Further, as shown in FIG. 4, the light (L2) incident on the contact portion of the insulating layer with the semiconductor portion of the crystalline semiconductor particle is refracted below the step of the crystalline semiconductor particle and proceeds to the inside of the step. A large amount of the crystalline semiconductor particles are trapped inside the step and taken in, so that a photoelectric conversion device with high 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, 2a is a step of the crystalline semiconductor particle 2, and 3 is a semiconductor portion constituting a granular photoelectric converter (hereinafter also referred to as a semiconductor layer). 4) is an insulating layer, 4a is a contact portion of the insulating layer 4 with the spherical surface of the crystalline semiconductor particles 2, and 5 is a translucent conductor layer.

  In the photoelectric conversion device of the present invention, a large number of spherical first-conductivity-type crystal semiconductor particles 2 each having a second-conductivity-type semiconductor portion 3 formed on the surface layer are joined on a conductive substrate 1, so that A photoelectric conversion device in which an insulating layer 4 is formed on a conductive substrate 1 and a light-transmitting conductive layer 5 is formed on the semiconductor portion 3 and the insulating layer 4. A step 2a in which the diameter (radius) of the crystalline semiconductor particles 2 changes stepwise is formed over the entire periphery in the vicinity of the upper side of the joint portion 2b with the conductive substrate 1 on the surface, and a longitudinal section below the step 2a. The insulating layer 4 is configured to cover from the boundary 2c with the junction 2b on the surface of the crystalline semiconductor particle 2 to the upper side of the step 2a.

  With the above configuration, when stress is applied to the interface between the insulating layer 4 and the crystalline semiconductor particles 2, the stress is dispersed at the interface inside the step 2 a, and peeling occurs between the insulating layer 4 and the crystalline semiconductor particles 2. Absent. In addition, as shown in FIG. 4, since the crystal semiconductor particle 2 has a lower radius on the lower side of the step 2a, the light (L1) incident on the lower side of the crystal semiconductor particle 2 is below the step 2a. Since it is confined and repeatedly reflected many times, it is taken in a large amount by the crystalline semiconductor particles 2. As a result, a photoelectric conversion device with high conversion efficiency can be obtained. In FIG. 4, L1 represents incident light incident on the spherical surface of the crystalline semiconductor particle 2 from above vertically, and L2 incident on the contact portion 4a of the insulating layer 4 with the spherical surface of the crystalline semiconductor particle 2 from above vertically. Indicates incident light.

  The step 2a formed on the surface of the crystalline semiconductor particle 2 is formed in a step shape in the almost radial direction of the crystalline semiconductor particle 2, but is formed so that the radius is completely reduced along the radial direction. It does not need to be, and it is sufficient if it is formed substantially along the radial direction. In addition, the step 2a may be a corner whose innermost portion is a substantially right-angled corner in the longitudinal section, or a corner having a curvilinear corner such as an arc in the longitudinal section. .

  The insulating layer 4 covers from the boundary 2c with the junction 2b on the surface of the crystalline semiconductor particle 2 to the upper side of the step 2a, but it is preferable to cover the upper side of the step 2a with a length of 5 to 200 μm. . When the thickness is less than 5 μm, peeling easily occurs between the insulating layer 4 and the crystalline semiconductor particles 2, and when the thickness exceeds 200 μm, the light is reflected on the surface of the insulating layer 4 and the light does not reach the inside of the crystalline semiconductor particles 2. .

  The conductive substrate 1 may be made of a metal such as aluminum, ceramics having a conductive layer, or the like, for example, aluminum, aluminum alloy, iron, stainless steel, nickel alloy, alumina ceramic, or the like. When the material of the conductive substrate 1 is an insulator, a conductive layer can be formed on the substrate made of the material by vapor deposition, sputtering, plating, or the like.

  A large number (several thousand to 100,000) of the first conductive type crystalline semiconductor particles 2 are arranged on the conductive substrate 1 at intervals. For example, if the first conductivity type is p-type in Si as a main component, the crystalline semiconductor particle 2 may be an element such as B, Al, or Ga as a p-type impurity, or the first conductivity type may be n-type. For example, 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 spacing between the adjacent crystalline semiconductor particles 2 is preferably wider in order to reduce the amount of the crystalline semiconductor particles 2 used, but more preferably wider than the radius of the crystalline semiconductor particles 2. The number of the crystalline semiconductor particles 2 is about ½ or less compared to the case where the crystalline semiconductor particles 2 are arranged in a close-packed manner.

  Further, by making the surface of the crystalline semiconductor particles 2 rough, reflection on the surface of the crystalline semiconductor particles 2 can be reduced. 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 using an RIE (Reactive Ion Etching) apparatus or the like. good.

  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 the 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 wafer cutting portion. The advantage of reducing the amount of semiconductor used 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. Accordingly, the diameter of the crystalline semiconductor particles 2 is more preferably 0.2 to 0.4 mm in relation to the amount of silicon used.

  The depth in the radial direction of the step 2 a formed on the crystalline semiconductor particle 2 is preferably 0.1 to 30% of the diameter of the crystalline semiconductor particle 2. As a result, the bonding strength between the crystalline semiconductor particles 2 and the conductive substrate 1 is ensured, and the crystalline semiconductor particles 2 are not dropped from the conductive substrate 1, thus preventing the conversion efficiency of the photoelectric conversion device from being lowered. it can.

  When the depth in the radial direction of the step 2 a is less than 0.1% (0.2 μm to 0.8 μm) of the diameter of the crystalline semiconductor particle 2, the bonding strength between the crystalline semiconductor particle 2 and the conductive substrate 1 is ensured. However, since the effect of confining incident light inside the step 2a hardly occurs, the effect of improving the conversion efficiency becomes extremely small. In addition, since the effect of dispersing the stress inside the step 2 a is reduced, the insulating layer 4 is easily peeled off from the crystalline semiconductor particles 2.

  When the depth in the radial direction of the step 2a exceeds 30% (60 μm to 240 μm) of the diameter of the crystalline semiconductor particle 2, the bonding strength between the crystalline semiconductor particle 2 and the conductive substrate 1 decreases, and the crystalline semiconductor particle 2 becomes conductive. It becomes easy to drop off from the substrate 1.

  The step 2a is formed on the entire surface of the surface of the crystalline semiconductor particle 2 in the vicinity of the upper side of the joint portion 2b with the conductive substrate 1. The height of the step 2a (the length in the vertical direction) is It is good that it is about 10 μm to 150 μm from the boundary 2 c of the two joint portions 2 b. If it is less than 10 μm, the semiconductor part 3 and the conductive substrate 1 are likely to be short-circuited. When the thickness exceeds 150 μm, the confinement effect of the light (L1) incident on the lower side of the crystalline semiconductor particles 2 becomes small.

  The vertical cross-sectional shape of the deepest corner of the step 2a is preferably an arc. In this case, more light that has traveled to the inside of the step 2a is reflected and taken into the crystalline semiconductor particle 2 side, so that a photoelectric conversion device with high conversion efficiency can be obtained.

  In this case, the radius of curvature in the longitudinal section of the corner of the step 2a is preferably 0.8 to 2 times the depth of the step 2a. With this configuration, the effect that more light traveling to the inside of the step 2a is reflected and taken into the crystalline semiconductor particle 2 side is further improved. When the radius of curvature in the longitudinal section of the corner of the step 2a is less than 0.8 times the depth of the step 2a and more than twice the depth, the light capture effect is reduced, and conversion efficiency is likely to decrease. Become.

  The corner between the step 2a and the spherical surface of the crystalline semiconductor particle 2 is preferably obtuse. In this case, when a liquid resin or the like serving as the insulating layer 4 is applied between the crystalline semiconductor particles 2, the liquid resin or the like smoothly crawls up from the step 2a to the spherical surface of the semiconductor portion 3 of the crystalline semiconductor particle 2 above. The contact angle of the contact portion 4a of the insulating layer 4 with respect to the spherical surface of the semiconductor portion 3 of the crystalline semiconductor particle 2 tends to be an acute angle.

  It is preferable that the angle of the insulating layer 4 in contact with the semiconductor portion 3 of the crystalline semiconductor particle 2 is an acute angle. From this, since the contact part 4a of the insulating layer 4 becomes a shape along the surface of the semiconductor part 3 of the crystalline semiconductor particle 2, the contact with the semiconductor part 3 of the crystalline semiconductor particle 2 of the insulating layer 4 when the photoelectric conversion module is manufactured. When stress is applied to the contact portion 4 a, the contact portion 4 a of the insulating layer 4 is not easily peeled off from the surface of the semiconductor portion 3 of the crystalline semiconductor particle 2.

  In addition, as shown in FIG. 4, the light (L2) incident on the contact portion 4a of the insulating layer 4 with the semiconductor portion 3 of the crystalline semiconductor particle 2 is refracted below the step 2a of the crystalline semiconductor particle 2 and is stepped. Since it progresses to the inside of 2a, it will be confined inside the level | step difference 2a and will be taken in more by the crystalline semiconductor particle 2, and a photoelectric conversion apparatus with high conversion efficiency can be obtained.

  The angle of the contact portion 4a having an acute angle is preferably 60 ° or less. When it exceeds 60 °, the effect that the contact portion 4a is not easily peeled off from the surface of the semiconductor portion 3 of the crystalline semiconductor particle 2 becomes extremely small.

  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 disposed.

  Next, after arranging a large number (several 1000 to 100,000) of crystalline semiconductor particles 2 at intervals, aluminum is applied to the conductive substrate 1 by applying a constant load from above with a pressing plate or the like. Heat to a eutectic temperature (577 ° C.) or higher with silicon forming the crystalline semiconductor particles 2. As a result, a eutectic layer (eutectic portion) of the conductive substrate 1 and the crystalline semiconductor particles 2 is formed, and the conductive substrate 1 and the crystalline semiconductor particles 2 are bonded via the eutectic layer.

  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.

  Note that the method of bonding the crystalline semiconductor particles 2 to the conductive substrate 1 is not limited to the above method, and the conductive substrate 1 made of aluminum and the crystalline semiconductor particles 2 made of silicon are brought into contact with each other, so that the aluminum and silicon can be bonded together. A method of forming a eutectic layer (alloy layer) of aluminum and silicon by heating to a crystal temperature (577 ° C.) or higher and bonding the conductive substrate 1 and the crystalline semiconductor particles 2 through the eutectic layer. If it is.

  The semiconductor portion 3 of the second conductivity type is made of, for example, Si. For example, in the vapor phase of the silane compound, the gas of the phosphorus compound for exhibiting the n-type when the second conductivity type is the n-type is formed by the 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 portion 3 may be any of crystalline, amorphous, or a mixture of crystalline and amorphous, but considering the high light transmittance, crystalline or crystalline and amorphous It is good to have a mixture of

  Further, the semiconductor portion 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. For example, when the crystalline semiconductor particle 2 is p-type, the surface of the crystalline semiconductor particle 2 is 0.5 by inserting the crystalline semiconductor particle 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 part 3 can be formed with a thickness of ˜5 μm.

The concentration of the trace element for imparting the second conductivity type in the semiconductor unit 3 is, for example, about 1 × 10 ¹⁶ to 1 × 10 ²¹ atoms / cm ³ . Furthermore, the semiconductor part 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.

  In order to form the step 2a on the surface of the crystalline semiconductor particle 2, for example, the following method is used. First, an acid resistant or alkaline resistant resist is attached to the upper side of the surface of the crystalline semiconductor particles 2. The resist is solidified by standing at room temperature or baking at about 200 ° C.

  Next, the surface of the crystalline semiconductor particles 2 not covered with the resist is etched away by immersing the crystalline semiconductor particles 2 in a hydrofluoric acid, a mixed solution of hydrofluoric acid, or an aqueous caustic soda solution. At this time, by removing a part of the semiconductor portion 3 on the surface of the crystalline semiconductor particle 2 by etching, a step 2a is formed and pn separation is also performed.

  Next, an oxide film is formed on the surface of the crystalline semiconductor particles 2 by oxidizing the entire photoelectric conversion device. Thereby, the disappearance of carriers due to surface recombination in the crystalline semiconductor particles 2 is prevented, and the conversion efficiency of the photoelectric conversion element (having one crystal semiconductor particle 2 as a unit of photoelectric conversion) is improved. As an oxidation method, all methods for oxidizing the crystalline semiconductor particles 2 made of silicon can be applied. For example, a steam oxidation method, an oxidation method in dry oxygen, an electrolytic anodization method, a vapor phase anodization method, or the like can be applied.

  The thickness of the oxide film is preferably about 50 to 300 mm. If the thickness is less than 50 mm, the above-described effect cannot be obtained. If the thickness exceeds 300 mm, the oxide film forming process takes a long time, and the productivity is lowered.

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

  The insulating layer 4 is formed as follows. An insulating material paste, solution, sheet, or the like is applied or disposed on the crystalline semiconductor particles 2 and heated at a temperature of 577 ° C. or lower, which is the eutectic temperature of aluminum and silicon. As a result, the gap between the crystalline semiconductor particles 2 is filled and fired, solidified or thermally cured to form the insulating layer 4. In this case, when the heating temperature exceeds 577 ° C., the alloy layer of aluminum and silicon starts to melt, so that the bonding between the conductive substrate 1 and the crystalline semiconductor particles 2 becomes unstable, and in some cases, the crystalline semiconductor particles 2 Becomes 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.

On the semiconductor layer 3 and the insulating layer 4, the translucent conductor layer 5 that also serves as the other electrode is formed with respect to the conductive substrate 1 that is one electrode. 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 appropriately selected.

  The translucent conductor layer 5 is preferably formed along the surface of the semiconductor part 3 and 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.

  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 0.3 mm as the crystalline semiconductor particles 2, phosphorous (P) is thermally diffused in the surface layer of each of a large number (10,000) of crystalline silicon particles, thereby producing crystals. A pn junction was formed with the outer portion of the silicon particle as the n-type semiconductor portion 3.

  Next, an aluminum-silicon eutectic paste was applied to each portion where the crystalline silicon particles on the main surface of the conductive substrate 1 made of aluminum were disposed and baked to form an aluminum-silicon hypereutectic layer.

  Next, crystalline silicon particles are respectively disposed on these aluminum-silicon hypereutectic layers and heated at a temperature of 577 ° C. or higher (630 ° C.), which is the eutectic temperature of aluminum and silicon, for about 10 minutes. Crystalline silicon particles were bonded onto the conductive substrate 1 at intervals.

  Next, the resist was transferred by a printing method above the position of the step 2a on the surface of the crystalline silicon particles, and baked in an oven at 160 ° C. for 10 minutes to solidify the resist.

  Next, after the crystalline silicon particles were immersed in a mixed solution of hydrofluoric acid and nitric acid to form the step 2a, the crystalline silicon particles were immersed in alcohol to remove the resist. The depth of the formed step 2a in the radial direction is 5% (15 μm) of the diameter (0.3 mm) of the crystalline silicon particles, and the vertical cross-sectional shape of the step 2a has a radius of curvature in the radial direction of the step 2a. The arc shape was 1.0 times (15 μm) of (15 μm).

  Next, the crystalline silicon particles were oxidized in an oxygen atmosphere at 570 ° C. for 5 hours.

  Next, liquid polyimide was dropped between the crystalline silicon particles and applied, and the polyimide was cured by heat drying to form an insulating layer 4 having a thickness of 30 μm. The angle of the contact portion 4a between the crystalline silicon particles of the insulating layer 4 and the spherical surface of the semiconductor portion 3 was 30 °.

  Next, the surface of the semiconductor part 3 of crystalline silicon particles was washed, and an ITO film as a translucent conductor layer 5 was formed on the crystalline silicon particles and the insulating layer 4 to a thickness of 80 nm by a sputtering method.

  Then, the linear finger electrode containing silver was formed on the translucent conductor layer 5, and it was set as the extraction electrode. Further, as shown in FIG. 3, a transparent resin layer 6 was formed so as to cover the crystalline silicon particles 2 and the conductive substrate 1 to produce a photoelectric conversion module.

(Comparative example)
As shown in FIG. 2, a photoelectric conversion device using crystalline silicon particles having a recess 12a formed at the lower end was produced. The recess 12a was formed when PN separation for separating the electrical contact between the semiconductor portion 13 and the conductive substrate 11 was performed. In the PN separation, the upper side of the crystal silicon particles where the semiconductor portion 13 is bonded to the conductive substrate 11 is etched with hydrofluoric acid over the entire circumference, thereby forming a recess 12a having an acute corner at the lower end of the crystal silicon particles. did. Thereafter, the surface layer portion of the semiconductor portion 13 on the surface layer of the crystalline silicon particles was oxidized by a thermal oxidation method. As a result, PN separation was performed. A photoelectric conversion device was produced in the same manner as in the above example except for the formation of the recess 12a.

  In this photoelectric conversion device, the depth of the concave portion 12a was 20 μm, and the height (length in the vertical direction) of the concave portion 12a was 5 μm. The angle of the contact portion 14a between the crystalline silicon particles of the insulating layer 14 and the spherical surface of the semiconductor portion 13 was about 90 °.

  Thereafter, a transparent resin layer was formed so as to cover the crystalline silicon particles and the conductive substrate 11 to produce a photoelectric conversion module.

  The photoelectric conversion device of the example of the present invention was compared with the photoelectric conversion device of the comparative example. In the example and the comparative example, the photoelectric conversion efficiency was almost the same in the state of the photoelectric conversion device, but in the state of the photoelectric conversion module, the photoelectric conversion efficiency of the photoelectric conversion device of the example was 9.5%, compared The photoelectric conversion efficiency of the example photoelectric conversion device was 8.6%, and the photoelectric conversion efficiency of the example was increased by 10%.

  This is because in the photoelectric conversion device of the comparative example, peeling occurs between the insulating layer 14 and some of the crystalline silicon particles, and the transparent portion formed on the insulating layer 14 and the crystalline silicon particles in the peeling generation portion. It is considered that the photoconductive layer 15 is broken, and as a result, the internal resistance increases and the fill factor (FF) decreases.

  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 one example of embodiment about the photoelectric conversion apparatus of this invention. It is sectional drawing of one example of the conventional photoelectric conversion apparatus. It is sectional drawing at the time of using the photoelectric conversion apparatus of this invention of FIG. 1 as a photoelectric conversion module. It is sectional drawing for demonstrating a mode that incident light is taken in into a crystalline semiconductor particle about the photoelectric conversion apparatus of this invention of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conductive substrate 2 ... Crystalline semiconductor particle 2a ... Level difference 2b ... Joint part 2c ... Boundary 3 ... Semiconductor part 4 ... Insulating layer 4a ... Contact part 5 ..Translucent conductor layer 6 ... Transparent resin layer

Claims (5)

  A large number of spherical first-conductivity-type crystal semiconductor particles having a second-conductivity-type semiconductor portion formed on a surface layer are joined on a conductive substrate, and an insulating layer is formed on the conductive substrate between the crystal-semiconductor particles. A photoelectric conversion device formed and having a light-transmitting conductor layer formed on the semiconductor portion and the insulating layer, wherein the crystalline semiconductor particles are in the vicinity of the upper side of the junction with the conductive substrate on the surface A step in which the diameter of the crystalline semiconductor particles changes stepwise is formed over the entire circumference, and a radius in a vertical cross section below the step is small, and the insulating layer is formed of the crystalline semiconductor particles. A photoelectric conversion device that covers from the boundary with the joint on the surface to the upper side of the step.   2. The photoelectric conversion device according to claim 1, wherein a depth of the step in a radial direction is 0.1 to 30% of a diameter of the crystalline semiconductor particle.   The photoelectric conversion device according to claim 1, wherein a vertical cross-sectional shape of a corner portion of the deepest portion of the step is an arc shape.   4. The photoelectric conversion device according to claim 3, wherein a radius of curvature in a longitudinal section of the corner of the step is 0.8 to 2 times a depth of the step.   5. The photoelectric conversion device according to claim 1, wherein the insulating layer has an acute angle with the surface of the semiconductor portion of the crystalline semiconductor particle.

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