JP2017059578A - Solar battery and solar battery manufacturing method - Google Patents

Abstract

PURPOSE: To decrease an amount of silver to be used or eliminate its use, and to reduce an amount of lead (lead glass) to be used or eliminate its use, in a solar battery and a solar battery manufacturing method.CONSTITUTION: A solar battery comprises: an area formed on a substrate, which produces a high electron concentration when irradiated with light or the like; an insulating film formed over the area, which allows light or the like to travel therethrough; and a bus electrode for extracting electrons from an electron extraction port formed in the insulating film. In the solar battery, conductive paste is mixed with conductive glass as glass frit of 100% by weight ratio to form the bus electrode, and the resultant mixture is baked to form the bus electrode. The solar battery is characterized in that conductive glass is used as the conductive paste.SELECTED DRAWING: Figure 1

Description

  The present invention creates a region that generates a high electron concentration when light or the like is irradiated on a substrate, and forms an insulating film that transmits light or the like on the region, and then emits electrons from an electron outlet formed in the insulating film. The present invention relates to a solar cell having a bus electrode for taking out and a method for manufacturing the solar cell.

  Conventionally, solar cells, which are one of the uses of renewable energy, have been developed based on semiconductor technology, which is the leading role in the 20th century. It is an important development at the global level that affects the survival of humankind. The challenge of the development is progressing while facing not only the efficiency of converting sunlight into electric energy but also the problem of reduction in manufacturing costs and pollution-free. In efforts to achieve these, it is particularly important to reduce or eliminate the amount of silver (Ag) and lead (Pb) used in the electrodes.

  In general, as shown in a plan view of FIG. 10A and a cross-sectional view of FIG. 10B, a solar cell has an N-type / P-type silicon substrate 43 that converts solar energy into electric energy, a silicon substrate, and the like. 43 prevents the reflection of the surface of the silicon nitride film 45, which is an insulating thin film, the finger electrode 42 that extracts the electrons generated in the silicon substrate 43, the bus bar electrode 41 that collects the electrons extracted by the finger electrode 42, and the bus bar electrode 41 It consists of each element of the lead electrode 47 for taking out the electrons to the outside.

  Of these, silver and lead (lead glass) are used for the bus bar electrode (bus electrode) 41 and the finger electrode 42, and the amount of silver used is eliminated or reduced, and the use of lead (lead glass). It has been desired to reduce or eliminate the amount, to make it low cost and no pollution.

  Among the components of the conventional solar cell of FIG. 10 described above, silver and lead (lead glass as a binder) are used for the finger electrode 42 and the like, and the amount of silver used is eliminated or reduced, and There was a problem of reducing or eliminating the amount of lead (lead glass) used, reducing the manufacturing cost of the solar cell, and making it pollution-free.

  The inventors of the present invention experimentally created bus electrodes and the like using NTA glass 100%, which will be described later, in the paste, and the same characteristics as when the bus electrodes and the like were created using the above-described conventional silver paste or excellent characteristics. It has been found that it is possible to create a solar cell having the following (described later).

  Based on these findings, the present invention eliminates or reduces the amount of silver used, and reduces or eliminates the amount of lead (lead glass) used, such as a bus electrode (bus bar electrode) that is a component of a solar cell. The paste is made of vanadate glass (hereinafter referred to as conductive NTA glass, “NTA” is registered trademark No. 5009023) and fired to reduce the amount of silver and lead (lead glass) used. It can be eliminated or reduced.

  Therefore, the present invention creates a region that generates a high electron concentration when light or the like is irradiated on a substrate, and forms an insulating film that transmits light or the like on the region, and an electron outlet formed in the insulating film. In a solar cell having a bus electrode for taking out electrons from the conductive electrode, the bus electrode is formed by baking conductive glass as a glass frit at a weight ratio of 100% to form a bus electrode. Glass is used.

  At this time, the conductive glass is changed to 100% by weight, and the conductive glass is made from 100% to 71% by weight, and the rest is made of silver.

  The conductive glass is vanadate glass containing at least vanadium or vanadium and barium.

  Moreover, the time of the process which mixes and heats conductive glass is made into 1 second or more within 1 minute at the longest.

  The conductive glass is Pb free.

  In addition, when the finger electrode is baked, the finger electrode has one end in the high electron concentration region, and the other end forms a portion that is the same as the height of the upper surface of the bus electrode or a portion protruding through the upper surface of the bus electrode. Yes.

  A lead electrode is provided on the bus electrode formed by firing.

  In addition, the lead electrode is formed by ultrasonic soldering on the fired bus electrode and bonded to the bus electrode, finger electrode, and other parts that are in contact with the lead electrode, so as to improve the adhesive strength of the lead electrode I have to.

  In the present invention, as described above, conductive NTA glass 100%, further up to about 71% (further content can be reduced) is used instead of the conventional silver paste, and is fired. The amount of silver used in the silver paste can be eliminated or reduced, and the amount of lead (lead glass) used can be reduced or eliminated. These have the following characteristics.

  First, NTA glass (registered trademark No. 5009023, Patent No. 5333976), which is a conductive vanadate glass, is used to form a bus bar electrode (bus electrode) of a solar cell. It was used in place of the silver paste to eliminate or reduce the amount of Ag used, and further to reduce or eliminate the amount of lead (lead glass) used.

  Secondly, the efficiency of converting solar energy into electronic energy is almost the same or slightly higher by using about 100% to 71% of NTA glass as a bus bar electrode (bus electrode). A high electrode formation exhibiting the effect as a bus bar electrode was obtained as an experimental result in the initial stage (see FIG. 9). This is because NTA glass is (1) conductive, and (2) the NTA glass is used so that the finger electrode has the same height as the upper surface of the bus bar electrode (bus electrode) or the portion protruding through the upper surface. These portions are joined by ultrasonic soldering of the lead electrode, and as a result, the high electron concentration region and the lead electrode are directly connected by finger electrodes, and other factors (for example, “third” described below) This is considered to be caused by

  Third, unlike the prior art, the finger electrode and the bus bar electrode are formed using a paste containing glass frit that is different. Conventionally, it has been necessary to generate a phenomenon called firing in the formation of finger electrodes. This is a finger electrode that breaks through the insulating layer of the silicon nitride film formed on the surface layer of the silicon substrate by the action of component molecules in the glass frit used as a sintering aid for silver, for example, lead molecules in lead glass. As a result, the electrons generated on the silicon substrate were efficiently collected. However, the firing phenomenon is not necessary for the formation of the bus bar electrode. Conventionally, the bus bar electrode was also sintered using lead glass containing lead component as a sintering aid, but although the structure is different, an electrical conduction path between the bus bar electrode and the silicon substrate is formed to reduce the conversion efficiency. It was a thing. By using NTA glass that does not cause the firing phenomenon as the sintering aid used for forming the bus bar electrode, reduction in conversion efficiency could be eliminated.

  Fourth, there is a problem of high cost (raw material cost) of solar cells due to the use of silver powder material. The problem of material procurement has also emerged due to excessive demand for silver materials. The industry has been able to produce solar cells without reducing the conversion efficiency even if the content ratio of NTA glass, which is a conductive glass, is greatly increased to 100% to 71% and the amount of silver is reduced accordingly. I think it will have a big impact on

  Fifth, it was possible to eliminate the use of lead glass that was used to form the conventional bus bar electrode, that is, lead-free. This makes it possible to eliminate the environmental problems of lead pollution.

  FIG. 1 shows a structural diagram of one embodiment of the present invention (process completion drawing: sectional view).

  In FIG. 1, a silicon substrate 11 is a known semiconductor silicon substrate.

  The high electron concentration region (diffusion doping layer) 12 is a known region (layer) in which a desired p-type / n-type layer is formed on the silicon substrate 11 by diffusion doping or the like. This is a region where electrons are generated (power generation) in the silicon substrate 11 when light is incident and the electrons are accumulated. Here, the accumulated electrons are taken out upward by an electron outlet (finger electrode (silver)) 14 (see the effect of the invention).

  The insulating film (silicon nitride film) 13 is a known film that allows sunlight to pass (transmits) and electrically insulates the bus bar electrode 15 from the high electron concentration region 14.

  The electron take-out port (finger electrode (silver)) 14 is a port (finger electrode) that takes out electrons accumulated in the high electron concentration region 12 through a hole formed in the insulating film 13. In the present invention, as shown in the figure, when the bus bar electrode 15 is baked with NTA glass 100% (or about 71%), the finger electrode 14 is the same as the height of the upper surface of the bus bar electrode 15 or It is possible to form (fire) a portion that penetrates and protrudes to the upper surface, and allows electrons in the high electron concentration region 12 to directly flow into the lead wire 17 through the finger electrodes 14 (directly take out electrons). Become. That is, the high electron concentration region 12, the finger electrode 14, the bus bar electrode 15, and the route 1 of the lead wire 17 (conventional route 1), and the high electron concentration region 12, the finger electrode 14, and the route 2 of the lead wire 17 (in the present invention). Electrons (current) in the high electron concentration region 12 can be extracted to the outside through the lead wire 17 through two routes including the added route 2). As a result, the high electron concentration region 12 and the lead wire 17 It is possible to make the resistance value between the two very small, thereby reducing the loss and consequently improving the efficiency of the solar cell.

  A bus bar electrode (electrode 1 (NTA glass 100%)) 15 is an electrode for electrically connecting a plurality of electron outlets (finger bar electrodes) 14, and an electrode to be used to eliminate or reduce the amount of Ag used (See the effect of the invention).

  The back electrode (electrode 2 (aluminum)) 16 is a known electrode formed on the lower surface of the silicon substrate 11.

  The lead wire (solder formation) 17 takes out electrons (current I) electrically connected to the plurality of bus bar electrodes 15 to the outside, and in the present invention, the finger electrode 14 has the same height as the upper surface of the bus bar electrode 15. It is a lead wire that takes out the electrons (current) to the outside by ultrasonic soldering the lead wire to the portion or the protruding portion.

  Under the structure shown in FIG. 1, when sunlight is irradiated from the top to the bottom, the sunlight passes through the portion without the lead wire 17 and the electron outlet 14 and the insulating film 13 and enters the silicon substrate 11. To generate electrons. Thereafter, the electrons accumulated in the high electron concentration region 12 pass through the electron take-out port (finger electrode) 14, the bus bar electrode 15, the route 1 of the lead wire 17, and the electron take-out port (finger electrode) 14 and the route 2 of the lead wire 17. It is taken out via both paths. At this time, as will be described later with reference to FIGS. 2 to 9, the bus bar electrode 15 is mixed with NTA glass (conductive glass) 100% to 71% (more or less, see FIG. 9) as a glass frit in the paste. It is possible to eliminate or reduce the amount of Ag used. Details will be sequentially described below.

  FIG. 2 is a flowchart for explaining the operation of the present invention, and FIGS.

  In FIG. 2, a silicon substrate is prepared in S1.

  In S2, cleaning is performed. These S1 and S2 cleanly clean the surface (surface on which the high electron concentration region 12 is formed) of the silicon substrate 11 prepared in S1, as shown in FIG.

  S3 is diffusion doped. As shown in FIG. 3B, this involves performing known diffusion doping on the silicon substrate 11 cleaned in FIG. 3A to form a high electron concentration region 12.

  In S4, an antireflection film (silicon nitride film) is formed. As shown in FIG. 3 (c), the high electron concentration region 12 of FIG. 3 (b) is formed, and an antireflection film (sunlight is passed through and surface reflection is made as much as possible. For example, a silicon nitride film is formed by a known method as the reduced film.

  S5 screen-prints the finger electrodes. As shown in FIG. 3 (d), the pattern of the finger electrode 14 to be formed is screen-printed on the silicon nitride film 13 shown in FIG. 3 (c). As the printing material, for example, silver mixed with lead glass as a frit is used.

  In S6, the finger electrode is fired and fired through. This is because the finger electrode 14 pattern (mixed with silver and lead glass frit) screen-printed in FIG. 3D is fired, and as shown in FIG. The finger electrode 14 in which silver (conductivity) is formed is formed through fire-through.

  S7 screen-prints the bus bar electrode (electrode 1). As shown in FIG. 4 (f), the pattern of the bus bar electrode 15 to be formed is screen-printed on the finger electrode 14 shown in FIG. 3 (e). For the printing material, for example, NTA gas (100%) is used as a frit.

  In S8, the bus bar electrode is fired. This is because the bus bar electrode 15 pattern (NTA glass (100%) frit) screen-printed in (f) of FIG. 3 is fired (fired within 1 minute at most, 1-3 seconds or longer). As shown in FIG. 4G, the bus bar electrode 15 is formed in the uppermost layer, and the finger electrode 14 is the same height as the upper surface of the bus bar electrode 15 formed in the uppermost layer, which is a feature of the present invention. Or a portion that has been penetrated.

  Note that S5 and S7 may be printed and both may be fired simultaneously.

  S9 forms a back electrode (electrode 2). For example, as shown in FIG. 4H, an aluminum electrode is formed on the lower side (back surface) of the silicon substrate 11, for example.

  S10 solders the lead wire. As shown in FIG. 4 (i), when the lead wires for electrically connecting the bus bar electrodes in FIG. 4 (g) are formed by soldering, for example, by ultrasonic soldering, they are electrically connected. High electron concentration region 12, finger electrode 14, bus bar electrode 16, path 1 of lead wire 17 (conventional path 1) and high electron concentration region 12, finger electrode 14, lead wire 17 path 2 (added in the present invention) In both the paths 2) and 2), the electrons (current) in the high electron concentration region 12 can be taken out via the lead wire 17, and the resistance between the high electron concentration region 12 and the lead wire 17 can be extracted. The value can be made very small to reduce loss and improve solar cell efficiency. That is, in the path 2 added in the present invention, one end of the finger electrode 14 is in the high electron concentration region 12, and the other end is a portion that is the same height as the top surface of the bus bar electrode 15 made of NTA glass 100% or a portion that penetrates. Since the lead wire is directly joined to this portion (direct joining by ultrasonic soldering), the path 2 of the high electron concentration region 12, the finger electrode 14, and the lead wire 17 is formed. The route 1 is a conventional route.

  Through the above steps, a solar cell can be formed on the silicon substrate.

  FIG. 5 is a detailed explanatory view (firing of the bus bar electrode) of the present invention.

  5A schematically shows an example in which the bus bar electrode is baked with 100% silver and 0% NTA (weight ratio), and FIG. 5B shows the bus bar electrode with 50% silver and NTA 50% weight ratio. FIG. 5C schematically shows an example in which the bus bar electrode is fired at 100% NTA (weight ratio). The firing time was set to 1 to 3 seconds or longer within 1 minute at the longest.

  In a prototype experiment of a solar cell formed to have substantially the same structure as shown in FIGS. 5A, 5B, and 5C, the following experimental results are obtained. It was.

Conversion efficiency of solar cells
Fig. 5 (a) Ag 100%, NTA 0% Average 17.0%
Fig. 5 (b) Ag 50%, NTA 50% Average about 17.0%
Fig. 5 (c) Ag 0%, NTA 100% Average 17.2%
As a result of the prototype experiment, the conversion efficiency when solar cells are formed is almost the same at an average of about 17.0% in FIG. 5 (a) and FIG. 5 (b) as materials for printing the bus bar electrode pattern. The result was obtained. Further, in FIG. 5C, the average conversion efficiency was about 17.2%. It can be seen from the initial experimental results that all of (a) to (c) in FIG. 5 are within the same conversion efficiency range, or that NTA 100% in FIG. 5 (c) has a slightly higher conversion efficiency. NTA glass is composed of vanadium, barium, and iron. In particular, iron is strongly bonded internally and stays in the interior, and its bonding property is extremely small even when mixed with other materials. (See Japanese Patent No. 5333976 and the like), and it is presumed to be due to the improvement of the path between the high electron concentration region of the present invention and the lead wire (path 1 and path 2 are in parallel).

  6 and 7 are explanatory diagrams (bus bar electrodes) of the present invention.

  6 (a) and 6 (b) are NTA 50% and Ag 50%, FIG. 6 (a) shows an overall plan view, and FIG. 6 (b) shows an enlarged view. . FIG. 7 (c) shows NTA 100% Ag 0%, and FIG. 7 (c) shows an enlarged view.

  6 (a) and 6 (b), the bus bar electrode 15 is a long bar-shaped electrode as shown in the overall plan view of FIG. 6 (a), and this is enlarged by an optical microscope. Then, a structure as shown in FIG. 6B was observed.

  In FIG. 6 (b), the bus bar electrode 15 was uniformly dispersed when fired with conventional Ag and lead glass frit, but it was fired with the Ag and NTA glass frit of the present invention (longer). In the case of firing within 1 minute for 1 to 3 seconds or more, it has been found that Ag is collected and formed in the central portion of the bus bar electrode 15 as shown in FIG. Therefore, as explained in the column of the effect of the invention, when NTA glass is mixed with Ag and fired for a short time (at least 1 minute, firing for 1 to 3 seconds or more), Ag collects in the central portion and becomes conductive. NTA glass is improved by reducing the Ag ratio due to comprehensive actions such as improved (conventionally improved Ag compared to the case where Ag was dispersed uniformly in the past) and NTA glass itself also has conductivity. As described above, the conversion efficiency when manufactured as a solar cell was about 16.9% even in the experiment.

  The firing temperature is 500 ° C. to 900 ° C., but it is necessary to determine the optimum temperature by experiment when it is produced as a solar cell. If it is too low or too high, the structure as shown in FIG. 6B cannot be obtained, and it is necessary to determine by experiment.

  In FIG. 7C, the bus bar electrode 15 is a bar-shaped electrode having a wide lateral width at the center portion shown in the figure, and shows an example of an enlarged photograph of 100% NTA according to the present invention.

  The bus bar electrode 15 in FIG. 7C has a portion in which the finger electrode 14 having a narrow width in the vertical direction protrudes through the bus bar electrode 15 and slightly protrudes upward, and the periphery of the protruding portion is the original finger. It turns out that it is thicker than the width of the electrode 14. Then, ultrasonic soldering is performed on the bus bar electrode 15 as shown in FIG. 8 to be described later in detail with a width that is the same as the width of the bus bar electrode 15, slightly smaller or slightly larger. High in both paths 1 (path 1 of photoelectron concentration region 12, finger electrode 14, bus bar electrode 15, lead wire 17) and path 2 (path 2 of photoelectron concentration region 12, finger electrode 14, lead wire 17) described above. The concentration electron region and the lead wire are conductively connected to reduce the loss of electrons (current) and can be efficiently extracted to the outside. The conversion efficiency is substantially the same as (a) and (b) of FIG. Alternatively, a slightly high conversion efficiency (about 17.2%) was obtained.

  The firing temperature is approximately 500 ° C. to 900 ° C., which is almost the same as in FIGS. 6A and 6B, but it is necessary to determine the optimum temperature by experiment when it is fabricated as a solar cell. If it is too low or too high, the structure as shown in FIG. 7C cannot be obtained, and it is necessary to determine by experiment.

  FIG. 8 shows an explanatory diagram (ultrasonic soldering) of the present invention. This is the case of NTA 100% in FIG. 7C described above (in the same manner, it may be applied to FIGS. 6A and 6B).

  FIG. 8A shows a state after the finger electrode 14 is fired.

  FIG. 8B shows a conventional soldering of a slightly larger (or the same or smaller) lead wire 17 shown by a dotted line on the bus bar electrode 15 of FIG. 8A. An example of In this conventional example, since normal soldering is performed, the portion (Ag) where the finger electrode 14 protrudes and the lead wire 17 are soldered together, but the portion where the finger electrode 14 does not protrude (portion of NTA 100%) The lead wire 17 is not sufficiently soldered and the mechanical strength is not sufficient. On the other hand, when ultrasonic soldering of FIG. 8C described later was performed, soldering was performed and the mechanical strength was greatly improved.

  In FIG. 8C, a slightly larger lead wire 17 indicated by a dotted line is ultrasonically soldered on the bus bar electrode 15 in FIG. 8A (the bus bar electrode 15 in FIG. 7C). The example of this invention is shown. In this example of the present invention, since the soldering is performed by ultrasonic soldering, the portion (Ag) from which the finger electrode 14 protrudes and the lead wire 17 are soldered together, and further, the portion without the finger electrode 14 (portion of NTA 100%) The lead wire 17 is also soldered to significantly improve the mechanical strength, and the conductivity of the path 2 (the high electron concentration region 12, the finger electrode 14, the bus bar electrode 15, the path 2 of the lead wire 17) described above is improved. did.

FIG. 9 shows a measurement example (efficiency) of the present invention. FIG. 9 shows an example of good measurement when the NTA is changed from 100% to 70% for the bus bar electrode 15 described above. The horizontal axis in FIG. 9 indicates the sample number, and the vertical axis indicates the efficiency. (%). sample,
・ NTA 100% Ag 0%
・ NTA 90% Ag 10%
・ NTA 80% Ag 20%
・ NTA 70% Ag 30%
These were used to make solar cells, and each measurement result (efficiency) was as shown. In addition, since it is an initial experiment, there are considerable variations in the measurement results as shown in the figure, but they are within the range of 16.9 to 17.5, and the bus bar electrode 15 is created with NTA 100% (that is, Even when a solar cell is manufactured without using Ag), it is found that the efficiency is comparable or slightly higher than that of NTA 70% (or 80%, 90%) and can be used even with NTA 100%. (The inventors found this fact).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It is an operation | movement explanatory flowchart of this invention. It is detailed process explanatory drawing (the 1) of this invention. It is detailed process explanatory drawing (the 2) of this invention. It is detailed explanatory drawing (baking of a bus-bar electrode) of this invention. It is explanatory drawing (bus-bar electrode) of this invention. It is explanatory drawing (bus-bar electrode) of this invention. It is explanatory drawing (ultrasonic soldering) of this invention. It is a measurement example (efficiency) of the present invention. It is explanatory drawing of a prior art.

11: Silicon substrate 12: High electron concentration region (diffusion doping)
13: Insulating film (silicon nitride film)
14: Electron outlet (finger electrode)
15: Bus bar electrode 16: Back electrode 17: Lead wire

Claims (12)

A region that generates a high electron concentration when light or the like is irradiated on the substrate is formed, and an insulating film that transmits light or the like is formed on the region, and electrons are taken out from an electron outlet formed in the insulating film. In a solar cell having a bus electrode,
In order to form the bus electrode, the conductive electrode is baked at a weight ratio of 100% as a glass frit to the conductive paste to form the bus electrode, and the conductive glass is used as the conductive paste. battery.   2. The solar cell according to claim 1, wherein the conductive glass is replaced with a weight ratio of 100%, the conductive glass is made from 100% to 70% or more, and the remainder is silver.   3. The solar cell according to claim 1, wherein the conductive glass is vanadate glass containing at least vanadium or vanadium and barium.   4. The solar cell according to claim 1, wherein a time of the step of mixing and baking the conductive glass is within 1 minute at most and 1 second or longer.   The solar cell according to any one of claims 1 to 4, wherein the conductive glass is Pb-free.   When the finger electrode (electron outlet) is fired, the finger electrode has one end in the high electron concentration region, and the other end is the same as the height of the upper surface of the bus electrode or a portion protruding through the upper surface The solar cell according to claim 1, wherein the solar cell is formed.   The solar cell according to any one of claims 1 to 6, wherein the lead electrode is provided on the fired bus electrode.   A lead electrode was formed by ultrasonic soldering on the fired bus electrode, and joined to the bus electrode, finger electrode, and other parts with which the lead electrode is in contact, thereby improving the adhesive strength of the lead electrode The solar cell according to claim 1, wherein: A region that generates a high electron concentration when light or the like is irradiated on the substrate is formed, and an insulating film that transmits light or the like is formed on the region, and electrons are taken out from an electron outlet formed in the insulating film. In a method for manufacturing a solar cell having a bus electrode,
In order to form the bus electrode, the method includes a step of baking the conductive glass as a glass frit on the conductive paste at a weight ratio of 100% to form the bus electrode, and using the conductive glass as the conductive paste. A method for manufacturing a solar cell.   The method for manufacturing a solar cell according to claim 1, wherein the conductive glass is replaced with a weight ratio of 100%, the conductive glass is made from 100% to 70% or more, and silver is mixed as a balance.   The method for manufacturing a solar cell according to claim 9, wherein the conductive glass is vanadium glass containing at least vanadium or vanadium and barium.   The method for producing a solar cell according to any one of claims 9 to 11, wherein a time of the step of mixing and baking the conductive glass is 1 minute or less within 1 minute at the longest. .