JP2006156874A - Photoelectric conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable photoelectric conversion device using crystalline semiconductor particles manufactured at low cost. <P>SOLUTION: In the photoelectric conversion device, large number of crystalline semiconductor particles 4 in one conduction type are disposed on one main surface of a conductive substrate 1 in a way that they are bonded to the substrate 1 at lower portions with insulating materials 3 being interposed between adjacent particles, and exposed from the insulating materials 3 at upper portions. The crystalline semiconductor particles 4 have semiconductor portions 3 in the other conduction type and translucent conductor layers 6 formed thereon. In the crystalline semiconductor particles 4, a boundary surface between a bonded portion to the conductive substrate 1 and the remainder is approximately parallel to the one main surface of the conductive substrate 1, or the central portion of the boundary surface is positioned at a conductive substrate 1 side with respect to an outer circumferential portion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Conventionally, a solar cell with high photoelectric conversion efficiency using a crystalline silicon wafer as a photoelectric conversion device has been put into practical use. This crystalline silicon wafer is manufactured by cutting out a large crystalline silicon ingot having good crystallinity, low impurities, and no uneven distribution. However, large crystalline silicon ingots take a long time to produce and are therefore less productive, which makes them expensive. Therefore, the emergence of highly efficient next-generation solar cells that do not require large crystalline silicon ingots is strongly desired. It is rare.

As a photoelectric conversion device that does not require a large crystalline silicon ingot, a photoelectric conversion device using crystalline silicon particles has been proposed. For example, a large number of crystalline silicon particles are disposed on a conductive substrate made of aluminum or a conductive substrate having an aluminum layer formed on the surface, and aluminum is formed on the conductive substrate surface or the interface between the aluminum layer and the crystalline silicon particles. The thing of the structure which formed the junction part which consists of an alloy layer with silicon | silicone is disclosed (for example, refer patent document 1).
JP 2002-43602 A

  However, in the above-described conventional technology, an alloy layer is formed by crystal silicon particles and an aluminum layer, and both are joined. However, silicon (Si) of crystal silicon particles and aluminum forming a conductive substrate, Due to the difference in thermal expansion with the aluminum-silicon alloy layer, if reliability evaluation such as temperature cycle is performed, there is a problem that cracks are generated at the boundary surface of the joint, and as a result, the photoelectric conversion efficiency is deteriorated.

  Therefore, the present invention has been completed in view of the above problems, and an object of the present invention is to provide a highly reliable photoelectric conversion device using crystal semiconductor particles that can be manufactured at low cost.

  In the photoelectric conversion device of the present invention, on one main surface of the conductive substrate, a large number of one-conductivity-type crystal semiconductor particles each provided with a semiconductor portion of the other conductivity type on the surface, the lower part is bonded to the conductive substrate, In a photoelectric conversion device in which an insulating material is interposed between adjacent ones and an upper part is exposed from the insulating material, and the transparent semiconductor layer is provided on the crystalline semiconductor particles, the crystalline semiconductor particles are The boundary surface between the junction with the conductive substrate and the remaining portion is substantially parallel to one main surface of the conductive substrate, or the central portion of the boundary surface is closer to the conductive substrate than the outer peripheral portion. It is located.

  According to the photoelectric conversion device of the present invention, on one main surface of the conductive substrate, a large number of one-conductivity-type crystal semiconductor particles provided on the surface with the other-conductivity-type semiconductor portion, and the lower portion are bonded to the conductive substrate, In a photoelectric conversion device in which an insulating material is interposed between adjacent ones and an upper portion is exposed from an insulating material, and the transparent semiconductor layer is provided on the crystalline semiconductor particles, the crystalline semiconductor particles are electrically conductive. The boundary surface between the joint portion with the conductive substrate and the remaining portion is substantially parallel to one main surface of the conductive substrate, or the central portion of the boundary surface is located closer to the conductive substrate than the outer peripheral portion. In addition, it is possible to provide a highly reliable photoelectric conversion device in which the occurrence of cracks generated at the boundary surface in the reliability evaluation such as the temperature cycle is suppressed and the photoelectric conversion efficiency is less deteriorated in long-term actual use.

  The photoelectric conversion device of the present invention will be described in detail below based on the drawings.

  FIG. 1 is a cross-sectional view showing an example of an embodiment of a photoelectric conversion device of the present invention, where 1 is a conductive substrate, 2 is a component of a conductive substrate 1 and a component of crystalline semiconductor particles 4 is formed. An alloy layer, 3 is an insulating material, 4 is one conductive crystal semiconductor particle, 5 is the other conductive semiconductor portion, and 6 is a translucent conductor layer. The alloy layer 2 is an alloy layer formed by heating and melting the contact portion between the conductive substrate 1 and the one-conductivity type crystalline semiconductor particle 4, and can be said to constitute a part of the conductive substrate 1.

  The conductive substrate 1 is made of a conductive metal, and for example, aluminum or a composite material having an aluminum layer on the surface can be used. The base substrate of the composite material may be any metal having a melting point equal to or higher than that of aluminum. For example, iron (Fe), nickel (Ni), stainless steel (SUS), Fe—Ni alloy, Fe—Ni—Co An alloy having a low thermal expansion coefficient mainly composed of an alloy or the like is used. The thickness of the surface aluminum layer in the composite material is preferably 0.01 mm (10 μm) or more in view of the amount of aluminum necessary for uniformly melting and bonding the crystalline semiconductor particles 4 onto the conductive substrate 1.

  Further, when the conductive substrate 1 is made of a composite material, a part of the main surface opposite to the side where the crystalline semiconductor particles 4 are disposed or for the purpose of suppressing warpage of the conductive substrate 1 caused by a thermal load or the like It is also possible to provide an aluminum layer (not shown) on the entire surface.

  Moreover, it is preferable that the thickness of the electroconductive board | substrate 1 is 0.1-2 mm. When the thickness is less than 0.1 mm, the thickness of the conductive substrate 1 becomes thin. Therefore, when the crystalline semiconductor particles 4 are welded to the conductive substrate 1, the conductive substrate 1 is likely to be warped, and the photoelectric conversion efficiency is improved. descend. Moreover, since the weight of the electroconductive board | substrate 1 itself will increase when it exceeds 2 mm, the weight reduction of a photoelectric conversion apparatus becomes difficult.

The insulating material 3 is made of an insulating material for separating the positive electrode and the negative electrode. For example, glass containing silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), lead oxide (PbO), boron oxide (B ₂ O ₃ ), zinc oxide (ZnO), etc., heat resistant resin material, heat resistance A mixture of a functional resin material and an inorganic filler, an organic-inorganic composite material containing silicon, a mixture of an organic-inorganic composite material containing silicon and an inorganic filler, and the like. The insulating material 3 is formed in layers on the surface of the alloy layer 2 so as to be interposed between the crystalline semiconductor particles 4, and the preferred thickness varies depending on the insulation resistance of the insulating material 3, but the insulating material 3 is made of a heat resistant resin. In this case, it is preferably 0.001 mm (1 μm) or more.

  The crystalline semiconductor particles 4 are boron (B), aluminum (Al), gallium (Ga), etc. exhibiting p-type in silicon (Si), or phosphorus (P), arsenic (As), etc. exhibiting n-type as trace elements. It is included. The grain size of the crystalline semiconductor particles 4 is preferably 0.1 to 0.6 mm. If the grain size exceeds 0.6 mm, the amount of silicon (Si) used in a conventional crystal plate type photoelectric conversion element remains the same, and the advantage of using the crystalline semiconductor particles 4 is small. Become. On the other hand, if it is smaller than 0.1 mm, the loss of light energy due to light transmission or the like increases, and the photoelectric conversion efficiency tends to decrease. Further, the shape of the crystalline semiconductor particles 4 may be various shapes such as a spherical shape, a spheroid shape, a polygonal solid shape, and a corner portion of the polygonal solid shape that is a curved surface.

  On the other hand, the conductive-type semiconductor portion 5 is made of, for example, silicon (Si), and is formed by a thermal diffusion method, a vapor phase growth method, or the like, for example, a vapor phase of a phosphorus compound that exhibits n-type in a vapor phase of a silane compound, or a p-type. It is formed by introducing a small amount of the gas phase of the boron compound to be exhibited. The thickness is preferably 10 nm or more, and the film quality may be crystalline, amorphous, or a mixture of crystalline and amorphous.

  Furthermore, it is preferable that the other conductivity type semiconductor portion 5 is formed along the surface shape of the one conductivity type crystalline semiconductor particle 4. Accordingly, the one-conductivity-type crystalline semiconductor particle 4 has a convex curved surface, so that the area of the pn junction formed between the crystalline semiconductor particle 4 and the semiconductor portion 5 can be increased. Electrons generated by photoelectric conversion inside the crystalline semiconductor particles 4 can be efficiently collected.

  The crystal semiconductor particles 4 contain a small amount of n-type phosphorus (P), arsenic (As), etc. or p-type boron (B), aluminum (Al), gallium (Ga), etc. on the surface thereof. In the case where a layer having a certain region is used, this layered region may be used as the other conductivity type semiconductor portion 5, and the translucent conductor layer 6 may be directly formed on the semiconductor portion 5.

The translucent conductor layer 6 is formed by a sputtering method, a vapor deposition method, a coating baking method, or the like, and one or more selected from SnO ₂ , In ₂ O ₃ , ITO, ZnO, TiO _{2, and the} like. Or a layer made of one or more metals selected from Ti, Pt, Au and the like. The translucent bioconductive layer 6 transmits a part of incident light at a portion where the crystalline semiconductor particles 4 are not present, is reflected by the lower conductive substrate 1 and is irradiated to the crystalline semiconductor particles 4, thereby producing a photoelectric conversion device. It becomes possible to efficiently irradiate the crystal semiconductor particles 4 with the light energy irradiated to the whole.

A protective layer (not shown) may be formed on the translucent conductor layer 6. As such a protective layer, a light-transmitting and dielectric material is preferably used. For example, silicon oxide, cesium oxide (Cs ₂ O), aluminum oxide (Al ₂ O ₃ ), silicon nitride ( Si ₃ N ₄ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), yttrium oxide (Y ₂ O ₃ ), etc., in a single composition or multiple compositions, in combination of a single layer or multiple layers, What is necessary is just to form by CVD method, PVD method, etc. Since this protective film is disposed on the light incident surface, it needs to be translucent, and it needs to be a dielectric material to prevent leakage of current obtained by photoelectric conversion. Furthermore, the protective layer can be expected to function as an antireflection film by optimizing the thickness.

  In addition, in order to reduce the series resistance value, a pattern electrode (not shown) made up of finger electrodes and bus bars at regular intervals is provided on the other conductive type semiconductor portion 5 or the translucent conductor layer 6 to increase the photoelectric conversion efficiency. It is also possible to improve.

  In the present invention, on one main surface of the conductive substrate 1, there are a large number of one-conductive type crystalline semiconductor particles 4, the lower part is bonded to the conductive substrate 1, and the insulating material 3 is interposed between adjacent ones. In the photoelectric conversion device in which the upper portion is arranged to be exposed from the insulating material 3 and the other semiconductor type 3 and the translucent conductor layer 6 are provided on the crystalline semiconductor particles 4, the crystalline semiconductor particles 4 are electrically conductive. The boundary surface between the joint portion with the substrate 1 and the remaining portion thereof is substantially parallel to one main surface of the conductive substrate 1, or the central portion of the boundary surface is located closer to the conductive substrate side 1 than the outer peripheral portion. . With this configuration, it is possible to obtain a highly reliable photoelectric conversion device that suppresses the occurrence and progress of cracks generated at the boundary surface in reliability evaluation such as temperature cycle, and has little deterioration in photoelectric conversion efficiency in long-term actual use. it can.

  As described above, the crystalline semiconductor particles 4 are such that the boundary surface between the joint portion with the conductive substrate 1 and the remaining portion is substantially parallel to one main surface of the conductive substrate 1, or the central portion of the boundary surface is the outer periphery. The configuration (also referred to as configuration A) that is located on the side of the conductive substrate 1 relative to the portion heats the crystalline semiconductor particles 4 to the conductive substrate 1 to a temperature equal to or higher than the eutectic point of those components (for example, aluminum and silicon). Thus, it can be realized by a manufacturing method in which a pressure is applied so that the crystalline semiconductor particles 4 sink into the viscous eutectic alloy.

For example, the above-described configuration A can be achieved by applying a pressure of about 0.002 to 1 N / cm ^{2 to} about 700 crystalline semiconductor particles 4 from above. When the pressure is less than 0.002 N / cm ² , it is difficult to push the crystalline semiconductor particles 4 into the eutectic part. If it exceeds 1 N / cm ² , the crystalline semiconductor particles 4 are damaged, or the eutectic part is pushed too much and the eutectic metal is easily pushed out from the lower part of the crystalline semiconductor particles 4.

  When bonding is performed only by eutectic formation without applying pressure, the progress of the eutectic in the natural oxide film formed on the surface of the crystalline semiconductor particles 4 is slower than the progress of the eutectic inside the crystalline semiconductor particles 4. As shown in FIG. 3, the outer peripheral portion is located on the conductive substrate 1 side with respect to the central portion of the boundary surface.

  In the present invention, the outer peripheral portion located on the conductive substrate 1 side as shown in FIG. 3 is pushed into the eutectic by pressurizing the crystalline silicon particles 4 to the conductive substrate 1 side during the formation of the eutectic at the joint. Thus, eutectic formation at the outer peripheral portion is promoted. As a result, the boundary surface is substantially parallel to one main surface of the conductive substrate 1 as shown in FIGS. 2A to 2E, or the central portion of the boundary surface is closer to the conductive substrate 1 than the outer peripheral portion. It can be set as the structure located in.

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

A solar cell using crystalline silicon particles as the photoelectric conversion device shown in FIG. 1 will be described. First, after the surface of crystalline silicon particles having an average particle diameter of 400 μm as crystalline semiconductor particles to which a small amount of boron (B) is added as a p-type dopant is washed, thermal diffusion is performed in a POCl ₃ atmosphere at 850 ° C. for 30 minutes. Then, an n-type silicon layer was formed as the semiconductor portion 5 of the other conductivity type on the surface of the crystalline silicon particles. At this time, an n-type silicon layer was formed only in a necessary portion by covering a portion where boron was not diffused with silicon oxide.

  Next, a single layer of crystalline silicon particles having an n-type silicon layer formed thereon is densely disposed on the conductive substrate 1 made of aluminum, and diffusion bonding conditions such as a bonding temperature, a bonding time, a heating rate, and a cooling rate. Various samples were changed, and samples in which the conductive substrate 1 and the crystalline silicon particles were diffusion bonded were produced.

  Next, polyimide was selected as the insulator material of the insulating substance 3, and the insulating substance 3 was formed so as to cover the surface of the conductive substrate 1 between the crystalline silicon particles. Next, the translucent conductor layer 6 made of ITO was formed on the conductive substrate 1 with a thickness of 100 nm to produce a photoelectric conversion device.

  Table 1 shows the results of conducting initial photoelectric conversion characteristics, reliability evaluation, and cross-sectional observation of this photoelectric conversion device, and confirming the presence or absence of crack propagation and the boundary surface shape. As for reliability, a temperature cycle test was performed 500 cycles with a temperature of −40 ° C. to 90 ° C. for 6 hours as one cycle, and the reduction rate of photoelectric conversion efficiency before and after the reliability evaluation was evaluated.

In Table 1, Sample 1 is an example in which a pressure of 0.07 N / cm ² is applied to 700 crystalline silicon particles and bonded to the conductive substrate 1, and Sample 2 is 700 crystalline silicon particles. Pressure is 0.06 N / cm ² for sample 3, sample N is 0.05 N / cm ² for 700 crystalline silicon particles, and sample 4 is 0.04 N / cm ² for 700 crystalline silicon particles sample 5 is an example of adding 700 of a pressure of 0.03 N / cm ² relative to the crystal silicon grain, sample 6 for 700 of the crystalline silicon grains pressure 0.02 N / cm ^2.

Samples 7 and 8 are examples in which no pressure is applied to the crystalline silicon particles during bonding to the conductive substrate 1.

  From Table 1, the boundary surface between the alloy layer (bonding portion) formed by heat-welding the conductive substrate 1 and the crystalline silicon particles and the remainder of the crystalline silicon particles is substantially parallel to one main surface of the conductive substrate 1. In some cases, or because the central portion of the boundary surface is located closer to the conductive substrate side 1 than the outer peripheral portion, crack progress after reliability evaluation was not confirmed, and the photoelectric conversion efficiency deterioration rate was also reduced.

  The present invention is not limited to the above-described embodiments and examples, and various modifications may be made without departing from the scope of the present invention.

It is sectional drawing which shows an example of embodiment about the photoelectric conversion apparatus of this invention. (A)-(e) is sectional drawing which shows the various examples of the interface of the junction part of the crystalline semiconductor particle in the photoelectric conversion apparatus of this invention. It is sectional drawing which shows the shape of the interface of the junction part of the crystal semiconductor particle of the photoelectric conversion apparatus in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conductive board | substrate 2 ... Alloy layer 3 ... Insulating substance 4 ... One-conductivity type crystalline semiconductor particle 5 ... Other conductive-type semiconductor part 6 ... Translucent conductor layer

Claims (1)

A large number of one-conductivity-type crystalline semiconductor particles each having a semiconductor portion of the other conductivity type provided on the surface on one main surface of the conductive substrate, and the lower part is bonded to the conductive substrate and insulated between adjacent ones In the photoelectric conversion device in which a substance is interposed and an upper portion is exposed from the insulating substance, and the crystal semiconductor particles are provided with a light-transmitting conductive layer, the crystal semiconductor particles are bonded to the conductive substrate. The boundary surface between the portion and the remaining portion is substantially parallel to one main surface of the conductive substrate, or the central portion of the boundary surface is located closer to the conductive substrate than the outer peripheral portion. Photoelectric conversion device.

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